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The nonignorable grid impedance is one of the characteristics of a weak grid. Meanwhile, the filter inductance also fluctuates with temperature or aging factors. The resonant frequency offset of an LCL filter will be caused by the change in power grid impedance and filter inductance. To this end, a strong adaptability control based on dual-division-summation (D-D-Σ) control is proposed in this article, which considers both the accuracy of grid-connected current tracking and resonance suppression under the variation of grid impedance and filter inductance. A full inductance parameter identification method based on an extended Kalman filter for simultaneously estimating filter inductance and grid impedance is proposed without remote voltage sampling. An enumeration method of the Routh array with less calculation is proposed. The algebraic relationship between control parameters and total inductance parameters is obtained by the Routh criterion. A gain correction method to realize strong adaptive control is proposed to deal with the variation of grid impedance and filter inductance. The experimental results prove the feasibility of D-D-Σ control in a three-phase LCL-type grid-connected inverter under the variation of grid impedance and filter inductance. [ABSTRACT FROM AUTHOR]

The battery charging technology is a rapidly developing area in the electric vehicle (EV) industry. The nonavailability of charging stations, longer battery charging times, and range-anxiety are main concerns for EV users. A fast, light, and efficient on-board charger is the need of the hour. Integrated battery chargers (IBC) are a viable solution since it uses the driving circuit (motor and inverter) already present in the EV for charging the battery. IBC using split-phase machine and three-legged inverter is an interesting topology. It has the advantage of using the existing three-phase machine and three-legged inverter. Also, this topology generates zero instantaneous torque while charging the battery. Due to motor winding reconfiguration during charging, even when the grid supply is balanced, the grid currents were found to be highly unbalanced. In this article, a mathematical model of the IBC using a split-phase machine in stationary and rotating reference frame is developed and presented for the first time. Mathematical proof for zero instantaneous torque production while charging the battery is presented. The effects of mutual inductance, Ldq along with Ld and Lq, are presented in the rotating reference frame model of the IBC. This is found to make the system unbalanced, and the grid currents represented the in rotating reference frame are found to contain second harmonic components along with the expected dc terms. Using the mathematical model, new feedforward terms have been developed, and used in the control loop with proportional integral controller (PI) and proportional resonant controllers to mitigate grid current harmonics. Exhaustive simulation and experimental results are included for the proposed system. [ABSTRACT FROM AUTHOR]

This article presents a control approach for HVdc interconnections that provides damping of frequency oscillations in asynchronous ac grids by introducing a virtual friction for coupling their inertial dynamics. The HVdc interconnection is modeled by using the concept of common and differential power flow, allowing for independent control of the dc voltage and the net power transfer between HVdc terminals, respectively. The proposed controller introduces a damping effect in the differential power flow, which is equivalent to a mechanical friction between the generators connected to the ac grids at the two terminals. This virtual friction-based damping can effectively attenuate poorly damped frequency oscillations that can be observed, where the HVdc interconnection is interfaced to either of the ac grids without relying on fast communication between the converter terminals. The impact of the proposed control technique on the stability and damping of two interconnected power systems is first analyzed by using a simplified model. Then, the sensitivity to the frequency and damping of the oscillation modes appearing in the ac grid frequencies, as well as the effect of the dc line resistance on the oscillation damping are evaluated. Finally, the control system performance is experimentally validated on a scaled laboratory setup. [ABSTRACT FROM AUTHOR]

Humans cannot feel the contact (or touching) force when it is too weak and falls in a specific range. For instance, if it is between several dozens and hundreds of milligram force, then humans may not be able to distinguish whether the object has come in contact with their skin or not. The minimum contact force that the human can feel is called the light touch threshold (LTT). This paper presents a novel apparatus to measure the LTT, which is referred to as an active von Frey (AVF) in this paper. To the best of the authors’ knowledge, an LTT measurement device with a precise weak force range is proposed for the first time in this paper. It is possible for the AVF to provide the touching force range from 1 to 400 [mgf]. In order to provide a precise touching force for individual subjects, D’Arsonval movement is chosen as an actuator to rotate the touching AVF pin. Both an electric current applied to the D’Arsonval movement and a rotational angle of the AVF pin are utilized to calculate the touching force by the electromechanical statics. As outcomes of this paper, we found out that the LTTs are very different from individual to individual and they are approximately proportional to the vibration perception thresholds with the results of 13 participants. It is expected that the AVF for LTT measurement can be utilized to design or control the personalized haptic device and, furthermore, to research the human nervous system diseases. [ABSTRACT FROM AUTHOR]

This paper presents a topology for a three-phase generation system for an isolated unbalanced load fed by a doubly fed induction generator with a neutral wire to include single-phase loads. The challenges of unbalanced loads connected to the system are presented along with a proposal for mitigating current imbalance by employing a four-leg rectifier. The proposed compensation method is based on the sequence decomposition analysis, and thus, it is based on previous works that use current control in double synchronous reference frames. Nevertheless, a conceptual analysis is presented that vindicates the use of resonant controllers in the stationary $abc$ frame. [ABSTRACT FROM PUBLISHER]

Power oscillation and current quality are the important performance targets for the grid-connected inverter under unbalanced grid faults. First, the inherent reason for the current harmonic and power oscillation of the inverter is discussed with a quantitative analysis. Second, a new control strategy is proposed to achieve the coordinate control of power and current quality without the need for a phase-locked loop (PLL) or voltage/current positive/negative sequence extraction calculation. Finally, the experimental tests are conducted under unbalanced grid faults, and the results verify the effectiveness of the propose method. [ABSTRACT FROM AUTHOR]

In this paper, various types of discontinuous space vector pulse-width modulation techniques for a three-leg voltage source inverter supplying balanced two-phase loads are proposed. The main objectives of the paper are to analyze switching loss characteristics associated with semiconductor devices and to reduce output current ripple by dealing with various types of zero space vector time in each switching sequence. Capabilities of reductions in switching losses and current ripple for both balanced and unbalanced output phase voltages at high modulation index and load power factor angle of 30° lagging are focused. The validity of the proposed techniques is verified by simulation and experimental results in terms of voltage spectrum, current waveforms, reductions in switching losses, and output current ripple at high modulation index when compared to a continuous space vector pulse-width modulation technique. [ABSTRACT FROM AUTHOR]

This paper presents modeling and triple-loop control for a high-efficiency three-phase balanced inverter for using in grid-connected two-stage microinverter applications. An average signal model based on a synchronous rotation frame for a three-phase four-wire inverter has been developed. The inner current loop consists of a variable frequency bidirectional current mode (VFBCM) controller which regulates output filter inductor current thereby achieving ZVS, improved system response, and reduced grid current THD. Active damping of the LCL output filter using filter inductor current feedback is discussed along with small signal modeling of the proposed control method. Since the dc-link capacitor plays a critical role in two-stage microinverter applications, a dc-link controller is implemented outside of the two current control loops to keep the bus voltage constant. Finally, based on a two-stage 400-W prototype, simulation and experimental results are presented to verify the validity of the theoretical analysis, the effectiveness and feasibility of the proposed VFBCM control strategy. [ABSTRACT FROM AUTHOR]

Impedance-source networks cover the entire spectrum of electric power conversion applications (dc-dc, dc-ac, ac-dc, ac-ac) controlled and modulated by different modulation strategies to generate the desired dc or ac voltage and current at the output. A comprehensive review of various impedance-source-network-based power converters has been covered in a previous paper and main topologies were discussed from an application point of view. Now Part II provides a comprehensive review of the most popular control and modulation strategies for impedance-source network-based power converters/inverters. These methods are compared in terms of theoretical complexity and performance, when applied to the respective switching topologies. Further, this paper provides as a guide and quick reference for researchers and practicing engineers in deciding which control and modulation method to consider for an application in a given topology at a certain power level, switching frequency and demanded dynamic response. [ABSTRACT FROM AUTHOR]

Single-phase ac/dc or dc/ac systems are inherently subject to the harmonic disturbance that is caused by the well-known double-line frequency ripple power. This issue can be eased through the installation of bulky electrolytic capacitors in the dc link. Unfortunately, such passive filtering approach may inevitably lead to low power density and limited system lifetime. An alternative approach is to use active power decoupling so that the ripple power can be diverted into other energy storage devices to gain an improved system performance. Nevertheless, all existing active methods have to introduce extra energy storage elements, either inductors or film capacitors in the system to store the ripple power, and this again leads to increased component costs. In view of this, this paper presents a symmetrical half-bridge circuit which utilizes the dc-link capacitors to absorb the ripple power, and the only additional components are a pair of switches and a small filtering inductor. A design example is presented and the proposed circuit concept is also verified with simulation and experimental results. It shows that at least ten times capacitance reduction can be achieved with the proposed active power decoupling method, and both the input current and output voltage of the converter can be well regulated even when very small dc-link capacitors are employed. [ABSTRACT FROM AUTHOR]

To control the switching dynamics of an optically triggered hybrid device, a photonic-control mechanism is outlined. The optically triggered hybrid device comprises a power MOSFET, as the main power semiconductor device (PSD), and a pair of GaAs-based optically triggered power transistors (OTPTs), serving as the driver for the power MOSFET . The switching-transition controller modulates the turn-off transition of the power MOSFET by modulating the optical intensity of the OTPTs. The independent and unified $dv/dt$ and $di/dt$ control of the PSD is achieved using a single control circuit which also predicts the onset of transition between the $di/dt$ and the $dv/dt$ regions of control. Experimental control results validating the OTPT-based dynamical modulation of the turn-off characteristic of the power MOSFET are provided. In this study, the power MOSFET is chosen to be a SiC mosfet . However, the proposed photonic-control mechanism can be extended to Si power MOSFETS as well. [ABSTRACT FROM AUTHOR]

An on-chip compensated wide output range boost converter with fixed-frequency adaptive off-time current-mode control is presented. The small signal characteristic of the boost converter with current-mode control is reviewed, and an adaptive current sensing technique is proposed to reduce the variation of phase margin at different output voltages. On-chip compensation is achieved with a Type II compensator. Adaptive off-time control is adopted for its fast response and no need for slope compensation, while its disadvantage of varying switching frequency is eliminated by the proposed off-time generator. The IC controller was fabricated in a 0.5 μm 2P3M BCD 40 V process. Measurement results confirm that an output range of 5.5 V ~ 36 V with an input voltage of 5 V is achieved. The switching frequency is fixed at 1 MHz with a variation of ±1%. The measured peak efficiency and maximum output power are 92.9% and 8.6 W, respectively. For a load step of 200 mA using a 3.3-μH inductor and a 20-μF output capacitor, overshoot and undershoot of the load transient responses are smaller than 1% of the output voltage. [ABSTRACT FROM AUTHOR]

A cooperative control paradigm is used to establish a distributed secondary/primary control framework for dc microgrids. The conventional secondary control, that adjusts the voltage set point for the local droop mechanism, is replaced by a voltage regulator and a current regulator. A noise-resilient voltage observer is introduced that uses neighbors' data to estimate the average voltage across the microgrid. The voltage regulator processes this estimation and generates a voltage correction term to adjust the local voltage set point. This adjustment maintains the microgrid voltage level as desired by the tertiary control. The current regulator compares the local per-unit current of each converter with the neighbors' and, accordingly, provides a second voltage correction term to synchronize per-unit currents and, thus, provide proportional load sharing. The proposed controller precisely handles the transmission line impedances. The controller on each converter communicates with only its neighbor converters on a communication graph. The graph is a sparse network of communication links spanned across the microgrid to facilitate data exchange. The global dynamic model of the microgrid is derived, and design guidelines are provided to tune the system's dynamic response. A low-voltage dc microgrid prototype is set up, where the controller performance, noise resiliency, link-failure resiliency, and the plug-and-play capability features are successfully verified. [ABSTRACT FROM AUTHOR]

A high-efficiency boost dc-dc converter with adaptive peak-inductor-current (APIC) control method is proposed. Besides, a novel two-step startup procedure is also proposed and applied on the boost converter. The proposed integrated boost converter was fabricated by using a 0.18-μm 1P6M mixed-signal process with a die area of 0.96 mm × 0.75 mm, and it is meant to be used with low-power, low-voltage green energy sources and batteries, such as fuel cells, solar cells, and nickel-metal hydride batteries. Hence, the power efficiency, minimal startup voltage, and minimal input voltage are the most important design considerations. The output voltage of the proposed converter is set to 1.8V, and the measured power efficiency is up to 90.6%, occurring when the input voltage is 1.3 V, the output voltage is 1.8 V, and the load current is 50 mA. According to the measured results, the proposed converter can start up successfully with a 0.43-V input voltage. Then, the input voltage can be further lowered to 0.22 V after startup. Moreover, both the efficiency and the output voltage ripple are improved with the proposed APIC method. Furthermore, a two-step startup procedure, which does not require any extra startup assist circuit, is proposed. [ABSTRACT FROM AUTHOR]

In this paper, the experimental validation of a predictive current control strategy for a four-leg indirect matrix converter is presented. The four-leg indirect matrix converter can supply energy to an unbalanced three-phase load while providing a path for the zero sequence load. The predictive current control technique is based on the optimal selection among the valid switching states of the converter by evaluating a cost function, resulting in a simple approach without the necessity for modulators. Furthermore, zero dc-link current commutation is achieved by synchronizing the state changes in the input stage with the application of a zero-voltage space vector in the inverter stage. Simulation results are presented and the strategy is experimentally validated using a laboratory prototype. [ABSTRACT FROM AUTHOR]

Four power stages for voltage regulator module (VRM) are adopted to provide high current driving capability and low output ripple in cloud computing. Thus, the time-shift current balance (TSCB) technique is proposed to achieve high performance power supply for servers. In addition, the power request, which includes the number of active phases and voltage identification, is acknowledged by servers for high driving capability during high throughput and high efficiency during standby mode. Furthermore, to equally distribute the current in each phase, the proposed TSCB technique in either voltage-mode or peak current-mode control improves the current balance performance and solves the stability problem. In the scale-down clouding computing prototype, the efficiency can be kept higher than 90% over a wide load current range of 2 A. In addition, the performance and operating frequency of the servers in stable operation are not limited by the VRM with the TSCB technique. [ABSTRACT FROM AUTHOR]

Rigorous analysis and design of the current control loop in voltage source converters (VSCs) requires an accurate modeling. The loop behavior can be significantly influenced by the VSC working conditions. To consider such effect, converter losses should be included in the model, which can be done by means of an equivalent series resistance. This paper proposes a method to identify the VSC equivalent loss resistance for the proper tuning of the current control loop. It is based on analysis of the closed-loop transient response provided by a synchronous proportional-integral current controller, according to the internal model principle. The method gives a set of loss resistance values linked to working conditions, which can be used to improve the tuning of the current controllers, either by online adaptation of the controller gains or by open-loop adaptive adjustment of them according to prestored data. The developed identification procedure is tested in the laboratory at different specifications of power level and switching frequency. [ABSTRACT FROM AUTHOR]

An approach to eliminate mutual flux effect on rotor position estimation of switched reluctance motor drives at rotating shaft conditions without a prior knowledge of mutual flux is proposed in this paper. Neglecting the magnetic saturation, the operation of conventional self-inductance estimation using phase current slope difference method can be classified into three modes: Mode I, II, and III. At positive-current-slope and negative-current-slope sampling point of one phase, the sign of current slope of the other phase changes in Mode I and II, but does not change in Mode III. Theoretically, based on characteristics of a 2.3 kW, 6000 rpm, three-phase 12/8 SRM, mutual flux introduces a maximum ±7% self-inductance estimation error in Mode I and II, while, in Mode III, mutual flux effect does not exist. Therefore, in order to ensure that self-inductance estimation is working in Mode III exclusively, two methods are proposed: variable-hysteresis-band current control for the incoming phase and variable-sampling self-inductance estimation for the outgoing phase. Compared with the conventional method which neglects mutual flux effect, the proposed position estimation method demonstrates an improvement in position estimation accuracy by 2°. The simulations and experiments with the studied motor validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The performance of direct model predictive control (MPC) with reference tracking and long prediction horizons is evaluated through simulations, using the current control problem of a variable speed drive system with a voltage source inverter as an illustrative example. A modified sphere decoding algorithm is used to efficiently solve the optimization problem underlying MPC for long horizons. For a horizon of five and a three-level inverter, for example, the computational burden is reduced by four orders of magnitude, compared to the standard exhaustive search approach. This paper illustrates the performance gains that are achievable by using prediction horizons larger than one. Specifically, for long prediction horizons and a low switching frequency, the total harmonic distortion of the current is significantly lower than for space vector modulation, making direct MPC with long horizons an attractive and computationally viable control scheme. [ABSTRACT FROM AUTHOR]

This paper presents a transformerless static synchronous compensator (STATCOM) system based on multilevel H-bridge converter with star configuration. This proposed control methods devote themselves not only to the current loop control but also to the dc capacitor voltage control. With regards to the current loop control, a nonlinear controller based on the passivity-based control (PBC) theory is used in this cascaded structure STATCOM for the first time. As to the dc capacitor voltage control, overall voltage control is realized by adopting a proportional resonant controller. Clustered balancing control is obtained by using an active disturbances rejection controller. Individual balancing control is achieved by shifting the modulation wave vertically which can be easily implemented in a field-programmable gate array. Two actual H-bridge cascaded STATCOMs rated at 10 kV 2 MVA are constructed and a series of verification tests are executed. The experimental results prove that H-bridge cascaded STATCOM with the proposed control methods has excellent dynamic performance and strong robustness. The dc capacitor voltage can be maintained at the given value effectively. [ABSTRACT FROM AUTHOR]

This paper proposes a new modulated carrier control method for an interleaved continuous conduction mode (CCM) power factor correction (PFC) boost converter. The proposed method allows precise sinusoidal line current shaping for a PFC boost converter operating in CCM. This is accomplished by simply comparing modulated carrier signal with switch current, such that inner current loop compensation design and rectified line voltage sensing are not required. The proposed control method greatly simplifies current sensing and control circuitry of multiphase converters since average current control is available by just sensing the switch current for each module. This also enables simple current balancing between parallel converters by employing modulated carrier signals with same amplitude. The principle of the control method is presented. The performance of the proposed control method is experimentally verified on a 600-W PFC converter. The measured power factor remains above 94.9% down to 20% of a full load for 110-Vrms and 220-Vrms line voltages. The line current harmonics also meet the IEC61000-3-2 Class D standard. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) inverters without the isolation transformer become more attractive due to higher efficiency and lower weight. However, it may have dc offset current problem and is critical to the power system. In this paper, a novel control strategy of suppressing dc current injection to the grid for PV inverters is investigated. It is based on the idea of accurately sensing the dc offset voltage of PV inverter output. Since dc component of the inverter output can be eliminated, dc injection to the grid can be effectively suppressed. Finally, the control scheme is verified by the experiment. [ABSTRACT FROM AUTHOR]

The sinusoidal-wave and square-wave driving modes have been commonly used in permanent-magnet synchronous motor (PMSM) drives for household refrigerator compressors. In general, the sinusoidal-wave drive performs better in some aspects such as torque ripples, a starting performance, and a flux-weakening capability than the square-wave drive. The square-wave drive, however, has the advantage of higher efficiency at low-output-power conditions because of its relatively lower switching loss than the sinusoidal-wave drive. To selectively utilize the benefits of both driving modes, a seamless transition control between the two driving modes is proposed in this paper. Considering that the overall control structure of the sensorless PMSM drive is quite different according to the driving mode, initialization strategies, necessary for a smooth transition, for the pulse-width modulator of the inverter, speed and current controller, and sensorless position/speed estimator are presented. With the proposed method, a dual-mode operation of the sensorless PMSM drive can be achieved without stopping the compressor. The dynamic performance of the proposed transition scheme is tested using simulations and verified by experiments. Experimental result shows that the efficiency of a refrigerator increases up to 2 [%] using the dual-mode operation in comparison with the sinusoidal-wave only drive. [ABSTRACT FROM AUTHOR]

This paper presents implementation of distribution static compensator (DSTATCOM) using kernel incremental metalearning algorithm (KIMEL) control algorithm. It demonstrates the functions of DSTATCOM such as reactive power compensation, harmonics elimination, and load balancing under linear and nonlinear loads with its self-supporting dc-bus voltage. The proposed control algorithm based on KIMEL is applied for extraction of fundamental active and reactive power components of load currents that are required for estimation of reference supply currents. These reference supply currents are used for gating pulses generation using indirect current control principle. A DSTATCOM with features of self-supporting dc bus (capacitor) is developed using DSP (dSPACE-1104), and the response of proposed control algorithm is studied under various operating conditions and found satisfactory. [ABSTRACT FROM AUTHOR]

The universal integrated synchronization and control (UISC) is proposed to operate a single-phase dc/ac converter in both grid-connected (GC) and stand-alone (SA) modes and offer seamless transition between these modes without any reconfiguration of control structure. As a matter of fact, the UISC does not need to use an islanding detection algorithm in the conventional sense. In GC mode, the UISC controls the real and reactive powers independently. In SA mode, it provides voltage and frequency support. The UISC is not based on direct current control or direct output voltage control. It adjusts the internal converter voltage through a nonlinear mechanism that amounts to the control of the current in GC mode and the voltage in SA mode. The UISC does not require a separate synchronization unit such as a phase-locked loop (PLL). In principle, the UISC is analogous to the combined governor and automatic voltage regulator controls in a synchronous machine (SM). In this sense, it may be considered among the converters that mimic the SMs such as the synchronverter. The proposed UISC is arguably the most unified method that can address different modes of operation of a converter within a microgrid environment without control switching actions. This paper presents the derivations, stability analysis, and numerical results to illustrate the performance of the proposed controller in a single phase situation. A mathematical analysis on the analogies and differences between the UISC and some similar methods is also presented. [ABSTRACT FROM AUTHOR]

A pulse-width modulation modulator for a noninverting bidirectional buck-boost converter is analyzed and a corresponding average-mode current controller design is revealed. The main feature of the modulator is the ability to create switching sequences for both converter legs without requiring any information regarding either operation mode or the direction of power flow. The modulator receives a control signal generated by the current controller, and a triangular carrier and generates driving signals with two different duty cycles, allowing tight control of the inductor current throughout the entire operating range. The underlying circuitry is thus relatively simple; moreover, the proposed method greatly simplifies the outer loop controller design. The revealed findings are supported by simulations and experiments. [ABSTRACT FROM AUTHOR]

Historically, cascaded H-bridge, capacitor-clamped, and neutral point-clamped topologies have been used for medium- to high-voltage applications but the modular multilevel converter (M2LC) is becoming a popular alternative. However, in comparison to other topologies, control of the load current, which is inherently coupled with circulating currents, is more difficult in the M2LC topology. This paper proposes a modified M2LC topology that allows for decoupled control of circulating currents from the load current. Each arm of the modified topology comprises a plurality of half-bridge modules and one full-bridge module. The full-bridge module minimizes harmonic currents within the converter without affecting the load current. A state-space model, which is generalized per arm with an N number of half-bridge modules and one full-bridge module, is presented to accurately predict the behavior of the proposed topology. Theoretical as well as experimental results of a single-phase three-level 800-VA prototype converter are presented with a discussion to demonstrate the viability of both the proposed mathematical model and modified topology. A comparative investigation with respect to a conventional topology reveals that the proposed topology offers superior performance. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose the primary-side peak current measurement strategy (PCMS) for the high-precision constant output current converter. The primary-side regulator (PSR) is widely used for low-cost and low-power light-emitted diode (LED) lighting application with universal input voltage range. However, the conventional PSR suffers from the drawback of current inaccuracy so that the LED may be damaged easily. Therefore, the PCMS method for PSR to achieve high-precision constant output current control is proposed. In this paper, the real causes of the output current inaccuracy by using PSR are discussed. The mathematical expression of the output current measurement error is derived. Then, the operation principle of the proposed PCMS is presented. Hardware experimental measurements are presented to verify the performance of the proposed PCMS. The measured data show that by using the PSR with the proposed PCMS, the LED output current error can be limited within ±2% under different operation conditions. [ABSTRACT FROM AUTHOR]

This paper presents a merged-two-stage circuit topology suitable for either wide-range dc input voltage or ac line voltage at low-to-moderate power levels (e.g., up to 30 W). This two-stage topology is based on a soft-charged switched-capacitor preregulator/transformation stage and a high-frequency magnetic regulator stage. Soft charging of the switched capacitor circuit, zero voltage switching of the high-frequency regulator circuit, and time-based indirect current control are used to maintain high efficiency, high power density, and high power factor. The proposed architecture is applied to an LED driver circuit, and two implementations are demonstrated: a wide input voltage range dc-dc converter and a line interfaced ac-dc converter. The dc-dc converter shows 88%-96% efficiency at 30-W power across 25-200-V input voltage range, and the ac-dc converter achieves 88% efficiency with 0.93 power factor at 8.4-W average power. Contributions of this paper include: 1) demonstrating the value of a merged two-stage architecture to provide substantial design benefits in high-input voltage, low-power step down conversion applications, including both wide-range-input dc-dc and line-input ac-dc systems; 2) introduction of a multimode soft-charged SC stage for the merged architecture that enables compression of an 8:1 input voltage range into a 2:1 intermediate range, along with its implementation, loss considerations, and driving methods; and 3) merging of this topology with an resonant transition discontinuous-mode inverted buck stage and pseudocurrent control to enable step-down power conversion (e.g., for LED lighting) operating at greatly increased frequencies and reduced magnetics size than with more conventional approaches. [ABSTRACT FROM AUTHOR]

This paper presents a single-phase to three-phase power conversion system with parallel rectifier and series inverter to cope with single-phase to three-phase asymmetry. Such converter guarantees both reduction in the input current processed by rectifier circuit and reduction of the output voltage processed by the inverter circuit. It is worth mentioning that, in spite of proposing a topology with features not yet observed on the technical literature, this paper presents a comprehensive model of the proposed converter, modulation strategy, and a general comparison with the conventional configuration. Simulated and experimental results are also presented. [ABSTRACT FROM AUTHOR]

Two-stage single-phase inverters have been widely used as they can achieve voltage matching and galvanic isolation between the input and output. Due to the pulsating output power of the downstream inverter, an ac current at twice the output frequency, which is called second harmonic current (SHC), arises in the input side of the downstream inverter. This SHC will penetrate to the front-end dc-dc converter, leading to reduced conversion efficiency. This paper first analyzes the propagation mechanism of the SHC and load transient response of two-stage single-phase inverters from the viewpoint of output impedance. Then, based on the current mode control and load current feed forward, two control methods to achieve low SHC in the front-end dc-dc converter and fast dynamic performance during load transient are proposed in this paper. Finally, a 2-kW two-stage single-phase inverter prototype has been constructed and tested, and the experimental results are provided to verify the effectiveness of the proposed control methods. [ABSTRACT FROM AUTHOR]

This paper presents a novel modulation and capacitor voltage control method for the modular multilevel converter (MMC) allowing the fixed switching frequency of 50 Hz. In the proposed modulation method, the switching angles are calculated through a new approach with reference to the nearest voltage level control. And then, every four pulse patterns are grouped together for averaging the dc and fundamental ac components in the output voltage of individual submodules. Accordingly, the absorbed power of each submodule could be self-balanced during few line periods simply by periodically swapping the pulse patterns. Moreover, the different power losses or different initial energy states of the submodules may also cause the dc capacitor voltage deviation although the absorbed power is equally distributed. Therefore, a closed-loop-based method of exchanging the leading or falling edges of pulse patterns is developed for dc capacitor voltage control. Simulation results show that the MMC circuit together with the proposed method functions very well in both rectifier and inverter modes. Experimental results on a single-phase MMC-based inverter with four submodules in one arm show the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) is considered as a promising topology for voltage-source converter (VSC) high-voltage, direct current (HVDC) applications. This paper presents a new control strategy for MMC-HVDC under unbalanced grid conditions. First, a new inner loop current control strategy based on nonideal proportional resonant (PR) controllers in stationary αβ frame is designed, which is more concise compared to the existing dual sequence current control scheme. Second, an analytical expression for circulating current is obtained which shows that the circulating currents will be asymmetric under unbalanced grid conditions and can be decomposed into positive-, negative-, and zero-sequence component. In order to suppress all these components, a new circulating current suppressing strategy is analyzed and designed also based on nonideal PR controllers. Application of nonideal PR controllers makes the control system well adapt to the fluctuation of grid frequency. The effectiveness of the proposed control strategy is verified through a simulation case of a 251-level MMC-HVDC transmission system using real-time digital simulator. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is attractive for medium- and high-power applications because of its high modularity, availability, and power quality. In this paper, the current ripple on the dc link of the three-phase MMC derived from the phase-shifted carrier-based pulse-width modulation scheme is analyzed. A control strategy is proposed for the current ripple elimination. Through the regulation of the phase-shifted angles of the carrier waves in the three phases of the MMC, the current ripple on the dc link of the three-phase MMC can be effectively eliminated. Simulations and experimental studies of the MMC were conducted, and the results confirm the effectiveness of the proposed current ripple elimination control. [ABSTRACT FROM AUTHOR]

This paper presents the analysis and control of a multilevel modular converter (MMC)-based HVDC transmission system under three possible single-line-to-ground fault conditions, with special focus on the investigation of their different fault characteristics. Considering positive-, negative-, and zero-sequence components in both arm voltages and currents, the generalized instantaneous power of a phase unit is derived theoretically according to the equivalent circuit model of the MMC under unbalanced conditions. Based on this model, a novel double-line frequency dc-voltage ripple suppression control is proposed. This controller, together with the negative- and zero-sequence current control, could enhance the overall fault-tolerant capability of the HVDC system without additional cost. To further improve the fault-tolerant capability, the operation performance of the HVDC system with and without single-phase switching is discussed and compared in detail. Simulation results from a three-phase MMC-HVDC system generated with MATLAB/Simulink are provided to support the theoretical analysis and proposed control schemes. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (M2LCs) are typically controlled by a hierarchical control scheme, which essentially requires at least two control loops: one to control the load current and another to control circulating currents. This paper presents an M2LC with a single controller, which is based on model predictive direct current control (MPDCC) with long prediction horizons. The proposed MPDCC scheme maintains the load current within tight bounds around sinusoidal references and minimizes capacitor voltage variations and circulating currents. An internal prediction model of the M2LC is used to minimize the number of switching transitions for a given current ripple at steady state while providing a fast current response during transient conditions. A state-space model, which is generalized for an N number of modules per each arm of the M2LC, is also presented to investigate the dynamic behavior of arm currents and capacitor voltages. Simulated performance of the converter, under various operating conditions, is presented in comparison to measured performance of a single-phase, three-level 860-VA M2LC prototype to demonstrate the proposed MPDCC philosophy. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is an upcoming topology for high-power drive applications especially in the medium voltage range. This paper presents the design process of a holistic control system for a MMC to feed variable-speed drives. First, the design of the current control for the independent adjustment of several current components is derived from the analysis of the equivalent circuits. Second, the current and voltage components for balancing the energies in the arms of the MMC are identified systematically by the investigation of the transformed arm power components. These fundamentals lead to the design of the cascaded control structure, which allows the balancing task in the whole operating range of a three-phase machine. The control system ensures a dynamic balancing of the energies in the cells of the MMC at minimum necessary internal currents over the complete frequency range. Simultaneously, all other circulating current components are avoided to minimize current stress and additional voltage pulsations. The performance of the control system is finally validated by measurements on a low-voltage MMC prototype, which feeds a field-oriented controlled induction machine. [ABSTRACT FROM AUTHOR]

In this paper, previously developed stability results for open-loop sum-capacitor-voltage control of modular multilevel converters are extended. To give improved damping, circulating-current feedback is included in the control law. With the output-current control loop and a first-order measurement lag taken into account, global asymptotic stability is proven. Careful consideration of the on-line sum-capacitor-voltage reference computation is given, since this is the most critical part of the control system. [ABSTRACT FROM AUTHOR]

Resonant parts can be used in current controllers to suppress harmonics. However, they may cause destabilization of poorly damped grid and/or input-filter resonances, particularly for a nonnegligible converter time delay. This letter presents a design method whereby destabilization is prevented by making the converter's input admittance passive. [ABSTRACT FROM AUTHOR]

The use of common dc-link parallel three-phase PWM converters without isolating transformers will cause zero-sequence circulating current problem. Previous works have proven that the circulating current is mainly affected by zero vectors employed in each PWM cycle. This paper proposes a novel method to suppress the circulating current. Detailed analysis is presented on the causes of zero-sequence circulating current based on a derived average model. A zero vectors feed-forward control strategy in combination with traditional PI control method is proposed to reject disturbances in zero-axis current system. In addition, a dual current sampling and dual PWM duty ratio update (DSDU) scheme is used to expand the bandwidth of zero-axis current loop. As a result, better circulating current suppression performance can be achieved in different filter inductance and converter output currents condition. Compared with the PI control method, the converters operated in parallel can be switched on and switched off separately with small current impact. Experimental results confirm the performance and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

At a certain level of abstraction, power converters can be represented as linear circuits connected to diodes and controlled electronic switches. The evolutions of the electrical variables are determined by the state-dependent switchings, which complicate the mathematical modeling of controlled power converters. Differently from the complementarity models previously presented in the literature, the model proposed in this paper allows to represent as a linear complementarity system also closed-loop power converters, without requiring the a priori knowledge of the converter modes. A model construction procedure, not dependent on the specific converter topology, is presented. The discretization of the continuous-time model allows to formulate mixed linear complementarity problems for the computation of the control-to-output frequency response and the evolutions of both transient and steady-state currents and voltages. As illustrative examples, Z-source, boost, and buck dc-dc power converters under voltage-mode control and current-mode control operating both in continuous and discontinuous conduction modes are considered. [ABSTRACT FROM AUTHOR]

For direct model predictive control with reference tracking of the converter current, we derive an efficient optimization algorithm that allows us to solve the control problem for very long prediction horizons. This is achieved by adapting sphere decoding principles to the underlying optimization problem. The proposed algorithm requires only few computations and directly provides the optimal switch positions. Since the computational burden of our algorithm is effectively independent of the number of converter output levels, the concept is particularly suitable for multilevel topologies with a large number of voltage levels. Our method is illustrated for the case of a variable speed drive system with a three-level voltage source converter. [ABSTRACT FROM AUTHOR]

This paper addresses the harmonic stability caused by the interactions among the wideband control of power converters and passive components in an ac power-electronics-based power system. The impedance-based analytical approach is employed and expanded to a meshed and balanced three-phase network which is dominated by multiple current- and voltage-controlled inverters with LCL- and LC-filters. A method of deriving the impedance ratios for the different inverters is proposed by means of the nodal admittance matrix. Thus, the contribution of each inverter to the harmonic stability of the power system can be readily predicted through Nyquist diagrams. Time-domain simulations and experimental tests on a three-inverter-based power system are presented. The results validate the effectiveness of the theoretical approach. [ABSTRACT FROM AUTHOR]

A discrete time-domain modeling and analysis for the peak current controlled (PCC) buck light-emitting diode (LED) driver is presented in this paper. The discrete time-domain equation representing the buck LED driver is derived and linearized about the equilibrium state. Also the switching control law, the proportional-integral compensator is used here as an example of the error amplifier, is linearized about the equilibrium state. The linearized buck LED driver and the control law are then combined to arrive at a linearized PCC buck LED driver. The root-locus method is employed to analyze the closed-loop system. The design guidelines and experimental results for the PCC buck LED driver are presented. [ABSTRACT FROM AUTHOR]

Modular dc-dc converters are popular in dc-power systems due to their advantageous characteristics such as fault tolerance, ease of thermal management, reducing voltage/current stress of the components, and modularity. In this paper, the concept of cooperative control in multiagent systems is introduced for modular dc-dc converters. Each constituent converter is represented by a node in a directed communication graph that models the information flow among converters. The proposed cooperative control scheme enjoys structural modularity, plug-and-play capability, fault tolerance against random failures in the converters and/or communication links, and satisfactory dynamic performance. This paper provides a general analytical framework to study modular dc-dc converters with an arbitrary communication graph. Hence, the designer has the freedom to choose among the various types of graphs based on the available communication resources and the desired level of reliability and fault tolerance. The dynamic model of the cooperative multiconverter system is developed and analyzed. Hardware measurements are presented to verify the plug-and-play capability, fault tolerance in both cyber and physical domains, and dynamic performance of the proposed cooperative control scheme. [ABSTRACT FROM AUTHOR]

This paper describes a complete digitally controlled dc-dc buck converter performed by field-programmable gate array (FPGA) circuitry. The voltage and current-mode control is based on a voltage control oscillator (VCO) performed measurements regarding output-voltage and inductor current, respectively. This measurement principle also uses digital-counters (digital-integrators) in order to obtain integral values for the output-voltage and inductor current. In analog current-mode control, the instantaneous inductor current-value-measurement is used for the switching action. When the VCO is used for the inductor current measurement, the integral is measured during the switching-on time set as an observation interval and the switching action occurs based on this measurement. Such a principle enables full digitalization of the voltage- and current-control loop and also the used measurement principle is capable of rejecting the switching disturbances during current and voltage measurements. All the tasks for current and voltage control were implemented within the FPGA. The algorithm was verified by simulation and experimentation at a switching-frequency of 25kHz. [ABSTRACT FROM AUTHOR]

This paper presents a boost five-switch three-phase (BFSTP) topology in brushless dc motor (BLDCM) drives by combining a four-switch three-phase (FSTP) inverter and a boost circuit together. In BLDCM drives, load and speed ranges are greatly restricted when the conventional FSTP inverter is employed, especially in the cases of solar power and battery, where power supply voltage is lower than the rated voltage of motor. Based on the novel topology, a boost three-effective-vector (BTEV) scheme is also presented. With the proposed BTEV scheme, two functions are realized. First, the voltage across the capacitors on the side of dc link is boosted by inserting shoot-through vectors in Modes V and VI, thus widening the speed and load ranges under low power supply voltage. Second, by taking the advantages of two adjusting vectors, possible distortion of currents caused by phase C back-EMF is restrained by employing a three-effective-vector scheme in Modes I and IV. The proposed BFSTP topology has a compact structure and a small size. Moreover, the BTEV current control scheme is easy to implement and needs no complex calculation involved in conventional vector control. The effectiveness of the proposed BFSTP topology and the BTEV scheme is validated through experiment. [ABSTRACT FROM AUTHOR]

This paper reports an uncooled transmitter system using a digital super-mode (DS) distributed Bragg reflector (DBR) tunable laser, which is able to act as an athermal, wavelength agnostic transmitter suitable for wavelength division multiplexed (WDM) passive optical network (PON) applications. An open-loop laser current control algorithm is designed to compensate autonomously for wavelength drift, thus allowing constant operating wavelength to be achieved regardless of ambient temperature. An improved wavelength accuracy of ±3 GHz is achieved when using low bandwidth feedback from the central office using information from a centralized shared wavelength locker. The entire laser start-up, channel selection and subsequent wavelength control is autonomous and has been implemented on micro-controllers and field programmable gate arrays. We demonstrate a three channel WDM-PON system comprising an uncooled packaged DS-DBR laser in the presence of two neighboring interfering channels. Error free transmission over 40 km single mode fiber of 10 Gb/s externally modulated NRZ data, is achieved for each of 48 C-band channels on the 100 GHz ITU grid. Successful athermal operation is demonstrated by sweeping the ambient temperature of the laser from 15 to 70 °C with a maximum wavelength deviation for any channel of no more than 0.1 nm. [ABSTRACT FROM PUBLISHER]

The current-controlled grid-connected inverter with LCL filter is widely used in the distributed generation system (DGS), due to its fast dynamic response and better power quality features. However, with the increase of power injected into the grid, control performances of the inverter will be significantly influenced by the nonideal grid conditions. Specifically, the possible wide variation of the grid impedance challenges the system stability. Meanwhile, background harmonics of the grid can greatly distort the injected current. Therefore, the control of the inverter should be designed with strong stability-robustness and high harmonic-rejection-ability, both of which correlate closely with the inverter output impedance. However, it is difficult to shape the output impedance into the one with a desirable characteristic simply by adjusting the current loop gain. In this paper, an impedance shaping method is proposed with virtual impedances, and the current control loop can be designed independently. The implementation and parameter design of the virtual impedances are studied under the practical considerations. With this proposed method, the grid-connected inverter can work stably over a wide range of the typical inductive-resistive grid impedance and exhibit strong rejection ability of grid-voltage harmonics. Experimental results from a 6-kW single-phase grid-connected inverter confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]