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This paper proposes a high-reliable magnetic design method considering DC-biased magnetization for a Loosely Coupled Inductor (LCI) used in interleaved three-phase boost converters. The interleaved multi-phase boost converters with an LCI are well-known as one of the attractive circuit topologies that can achieve high-power-density of the converters. However, when designing and implementing an LCI in the interleaved converter, DC-biased magnetization in the transformer part of LCI must be taken into account because magnetic saturation of the core may easily occur. This phenomenon is caused by unbalanced inductor average currents in each phase. Inserting air-gaps into magnetic paths of the transformer part of a LCI is considered as one of the solutions to prevent the magnetic saturation. Nonetheless, in this case, the volume and weight of LCI increase, and they become a matter of concern because the characteristics of an LCI goes closer to the characteristics of the independent inductors. Therefore, there is a trade-off between handling the DC-biased magnetization and downsizing the magnetic core. To optimize this trade-off, a novel magnetic design method for LCI is proposed by considering the maximum permissible percentage of unbalanced inductor average currents. This paper focuses on the three-phase coupled inductors used in three-phase interleaved boost converters. The accuracy and the effectiveness of the proposed magnetic design method are discussed from both theoretical and experimental points of view.

Supercapacitor technology has reached a level of maturity as a viable energy storage option available to support a modern electric power system grid; however, its application is still limited because of its energy capacity and the cost of the commercial product. In this paper, we demonstrate transient models of supercapacitor energy storage plants operating in coordination with run-of-the-river (ROR), doubly-fed induction generator hydropower plants (HPP) using a conceptual system control architecture. A detailed transient model of a supercapacitor energy storage device is coupled with the grid via a three-phase inverter/rectifier and bidirectional DC-DC converter. In addition, we use a version of a 14-bus IEEE test case that includes the models of the supercapacitor energy storage device, ROR HPPs, and synchronous condensers that use the rotating synchronous generators of retired coal-powered plants. In this paper, we emphasize the control coordination among the components of the power system. The control actions must be coordinated and prioritized based the capability, response time, the power rating, and the energy content of the components.

This paper presents the design of a digital controller for a 600 W Boundary-Conduction-Mode (BCM) interleaved boost converter used in an ac-dc Power-Factor-Correction (PFC) power supply. The output voltage of a typical boost PFC rectifier contains a 2nd harmonic ripple. Therefore to achieve good power factor, the output voltage compensator must have a low bandwidth, in order to sufficiently attenuate this 2nd harmonic component. As a result, the output voltage can suffer from poor transient response, especially at low input voltage. In this paper, a small-signal model of the output voltage dynamics is derived, where it is shown the open-loop gain of the system decreases with low input voltage. As a result, the output voltage transient response also deteriorates at low levels of input voltage. This can lead to poor voltage transient response for boost PFC converters that are designed to have an operating input line voltage range from 85 to 265 V. Having poor output voltage transient response is undesirable as it can lead to high peak over shoot on the output capacitors, or even worse, lead to an output voltage tracking failure. To correct this behaviour, an adaptive digital voltage compensator is designed to change gain at low input voltage, to ensure the output voltage maintains good transient response. Finally, the derived small-signal analysis, and output voltage compensator performance are experimentally verified on a 600 W interleaved BCM converter.

Buck and buck-boost ac-ac converter topologies with a center-point-clamped circuit configuration have been recently reported in literature. These converter circuits reduce the voltage stress on the bidirectional switches employed in corresponding direct ac-ac converters. This new topological structure enables access to the mid-point of voltage terminals. This paper introduces a family of such ac-ac direct converters which are solid state functional equivalents of ac transformers with a continuously variable transformation ratio. The family of proposed variants include buck, boost, and buck-boost converters. This paper is aimed at presenting the operating principles, design guidelines, dynamic analysis and the results of a comparative study of these converters. Detailed design equations are provided along with typical examples of design of various converters for power conditioning applications. Experimental waveforms obtained with scaled laboratory prototypes presented in the paper verify that proposed converters offer reduced voltage stress on the bi-directional switches when compared to conventional ac-ac direct power converters. They also confirm the applicability of this novel family of direct ac-ac converters called Center-Point-Clamped Switched Mode Power Converters.

The LCL-type grid connected inverter has been widely used as the intelligent power interface between the distributed generation unit and the power grid. To reduce the cost and volume of the filter, it is desirable to design the LCL filter with higher resonance frequency provided that the quality of injected grid current is not compromised. Actually, it is the typical case for the T-type or NPC three-level inverter to design its LCL resonance frequency close to half of the switching frequency. In this case, however, the sideband effect of SPWM modulation can impose a significant impact on the system stability, and the traditional ZOH model is inadequate to describe the dynamic behavior of the digital SPWM modulator. In this paper, by extending the multi-frequency model to AC system, the stability of the grid-connected inverter is examed with the consideration of sideband effect. An interesting discovery in this paper is that the influence of grid voltage on the system stability can be successfully predicted, which provides a useful tool to study the stability of inverter in presence of large grid voltage disturbances. Experimental results from a down-scaled three-phase inverter confirm the effectiveness of stability analysis.

Conventional permanent magnet (PM) machine open-phase fault detection relies on the estimation of current harmonics using existing drive current sensors. Because the magnitudes of current harmonic are proportional to the machine load condition, it is still a challenge to detect a phase fault at light load when fault induced current harmonics are too small to estimate. This paper investigates the phase fault detection specifically for the conditions under low fault harmonic magnitudes. Both fault induced harmonics in dq currents and neutral point (NP) voltage are analyzed to find a suited signal for the phase fault detection. By adding a voltage sensor to measure the NP voltage in a PM machine, a better fault detection performance is achieved because the fault harmonic in NP voltage shows the reduced effect on torque loads and sensor measurement errors. A 50-W PM machine is tested to verify the phase fault detection performance under low fault harmonic magnitudes. This paper includes the experimental evaluation to analyze the detection limitation in terms of load capability based on current and voltage fault signals.

A three-phase three-port rectifier (TPTPR), which is capable of handling an AC port, a low voltage DC port and a high voltage DC port simultaneously, is presented in this paper. To directly transfer power from the AC port to the low voltage DC port within single-stage power conversion, a modified SVPWM strategy based on asymmetric three-level vector space is analyzed and evaluated in this paper. With the TPTPR and modified SVPWM control strategy, the low voltage port with wide voltage range can obtain energy directly from the AC grid. As a result, the power conversion stages are reduced and the power rating of the downstream DC-DC converter can be reduced significantly. The presented topology and its corresponding vector space are both different from those of traditional two-stage rectifier composed of a three-phase three-level rectifier and a cascaded DC-DC converter. A 5kW prototype with fixed high voltage DC port and a variable low voltage DC port is built and tested to verify effectiveness of the presented solution.

Wide Band Gap power semiconductor switching devices offer superior performance compared to an equivalent Si power device. SiC MOSFETs can be competitive when compared to Si IGBTs of the same voltage class, whilst offering greater benefits at high switching frequencies. Operating SiC MOSFETs at high switching frequencies imposes significant challenges, including: Ringing and voltage overshoot issues, making accurate high bandwidth measurements, and the requirement for a high-performance gate drive circuit. This paper presents a prototype low inductance PCB design for a SiC MOSFET switching circuit. In addition, a linear current gate-drive circuit and a high bandwidth on-board measurement system have been developed and the designs for these are presented. The measurement system showed good agreement with the external probe measurements and superior bandwidth. Hard-switching tests with a 900V SiC MOSFET showed that the dV DS /dt becomes largely invariant to changes in load current when using a current source gate drive. The measured dV DS /dt slew rates are compared with the dV DS /dt slew rates estimated from the parameter values given in the SiC MOSFET datasheet, and the two sets of results show good agreement. In this paper, the performance of an optimised circuit is successfully demonstrated and the benefits are discussed.

This paper presents a single-stage isolated softswitching tri-port converter for integrating a renewable resource like solar PV, and energy storage with single-phase AC grid through high-frequency galvanic isolation. The single-stage approach reduces the component count, and the full-range softswitching feature realizes higher efficiencies compared to the state-of-the-art methods. A significant advantage of the proposed topology is the elimination of DC capacitors which are major life limiting components in a PV inverter. The tri-port converter can be designed to connect to single-phase or split-phase AC grids, realizing soft switching across the entire range of operating load levels. This paper presents the concept, principles of operation and control, and verification through simulation and experimental results of the proposed tri-port converter.

This paper presents a DC bus voltage balancing control method for the grid-connected hybrid cascaded converter with renewable energy sources. The proposed control method is based on the power flow management in the hybrid cascaded converter, which is investigated in this paper, and is thus capable of overcoming the unbalanced conditions arising at DC-side or AC-side. Laboratory test results under unbalanced conditions are provided to verify the feasibility of the proposed control method.

A health monitoring method using the saturationregion resistance is proposed in this paper to identify the level of aging associated with power semiconductor switches inside a Boost converter. Power MOSFETs are one of the most age-affected components in power electronic converters, and the on-resistance has been proved to be the most significant aging factor in power MOSFETs. However, the small value of the on-resistance makes it difficult to identify. To solve this problem, the saturation-region resistance is used as the failure precursor parameter for MOSFET health monitoring and the magnitude-frequency gain at low gate drive voltage is used to identify the aging status of MOSFETs. The shift of the saturation-region resistance caused by degradation is demonstrated by power cycle tests in this paper. The proposed method can be implemented by fast Fourier transform (FFT) and no extra measuring point is added. Simulation results are given to verify the effectiveness of the proposed method.

In this paper, a new control method for capacitive link universal power converters is proposed to eliminate the need for measuring the output and input voltages. Capacitive link universal converters are a new class of power converters that offer high power density and reliability, and are capable of transferring power between any type of source and load, dc or ac, with any number of phases, emerges. The high frequency ac link of this type of converters allows electrolytic capacitors to be substituted by small film capacitors. Unlike dc link converters that typically use a bulky three phase low frequency transformer for providing galvanic isolation, in this converter a compact single phase high frequency transformer can be used. A precise closed loop control is needed for operation of this type of converters, and considering the limitations of voltage sensors, analog to digital converters, and processors, the maximum switching frequency is confined. The control method proposed in this paper can address these shortcomings and allows exploiting promising features of the capacitive link universal converters. This control method can be implemented both in analog and digital. Moreover, a simple voltage divider, instead of an isolated voltage sensor, meets the requirement for link voltage measurement, which is the only required measurement. Therefore, using the proposed control method will increase the maximum feasible switching frequency; and, at the same time, dismisses the need for costly voltage sensing at the output and input in a closed loop control. The proposed control method is presented in this paper, and its effectiveness is evaluated through simulations and experimental results.

This paper presents a single-stage soft-switching high-frequency link isolated converter for bidirectional motor drive applications. The ‘minimal’ topology is based on the recently proposed soft-switching solid-state transformer (S4T) with a single current-source power conversion stage. This single stage approach reduces total switch rating, provides sinusoidal input and output voltages, and uses zero-voltage switching (ZVS) to reduce switching losses, dv/dt, common-mode noise issues associated with conventional PWM converter drives. Moreover, a high-frequency transformer is employed for dramatic size and cost reduction compared with drives that use standard line frequency transformers for isolation — a very common practice. The modulation scheme ensuring ZVS for entire load and power factor operating range considering the effect of leakage inductance of the high frequency transformer is presented in this paper. The effectiveness of the presented four-quadrant motor drive converter is verified by both simulation and experimental results.

Deadbeat control (DBC) has been known for decades due to its conceptual simplicity and good performance. Recently finite control set model predictive control (FCS-MPC) is emerging as a powerful strategy for control of power converters. Different from DBC, which uses a modulator such as space vector modulation (SVM), FCS-MPC directly obtained the optimal switching states of power converters by minimizing a cost function. Several improved versions of FCS-MPC have been proposed to improve the steady state performance by introducing two or three vectors during one control period. This paper investigates the inherent relationship between SVM-DBC and multiple-vector FCS-MPC. It is found that with the aim of tracking error minimization, the two kinds of predictive methods can be unified in one frame, where the vector sequence and duration in FCS-MPC can be easily obtained from SVM-DBC. In other words, under some special cases, FCS-MPC and its improved versions can be considered as special cases of SVM-DBC. This is the main contribution of this paper, because DBC and FCS-MPC are previously studied separately. The theoretical study is confirmed by the analysis on state-of-the-art DBC and FCS-MPC and supported by the selected simulation study and experimental tests from a three-phase two-level voltage source PWM rectifier.

Compared with the conventional high voltage DC power supply, the high voltage pulse power supply can significantly improve the dust removal efficiency of electrostatic precipitator and reduce the energy consumption. This paper presents a new type of high voltage pulse electrostatic precipitator power supply topology, the symmetric cascaded structure of the low voltage side which can significantly reduce the voltage stress of switching device, rectifier circuit, clamp circuit and resonant capacitor, thereby significantly reducing the cost. This paper analyzes the steady-state operating principle of the high voltage pulse power supply and the working conditions during flashover while the expressions of the output voltage and current of the transformer primary side are both deduced and verified by simulations. Finally, the experimental verification is carried out by a pulse power supply with a peak voltage of 100kV.

In this paper, a zero-voltage switching DC-AC inverter is designed and realized. The neutral point clamped topology and fix-frequency PWM control are used in the proposed inverter to implement a single-phase DC-AC inverter. Also, an auxiliary inductor and two auxiliary switches are adopted to achieve zero-voltage switching, which can improve the inverter efficiency. In this paper, the proposed DC-AC inverter is introduced, the operational principles and the steady-state are analyzed. In addition, the neutral point clamped architecture and zero-voltage switching mechanism are described in detail. Finally, an experimental prototype with the input voltage of 720Vdc and the output of 220Vac / 2kW is implemented to verify the theoretical analysis. The experimental results show that the highest efficiency is 98.12% and the full load efficiency is 97.49%.

While many advantages can be offered by DC-based integrated power system, it is a challenging task to continuously maintain optimal performance with a dynamic load profile. Coordination between the real-time controllers and system optimizer is not a trivial task in such conditions. Some of the protection schemes provide fault detection and isolation functions, but do not consider system level optimization constraints or power balance after fault isolation. In this paper, a novel methodology is introduced to control and optimally reconfigure a DC power system automatically detecting system disturbances. The proposed method includes autonomous fault detection and coordination of real-time constraint restricted problem formulation to optimize the system performance. A DC-bus distribution system developed for the U.S. Coast Guard's 270-ft Medium Endurance Cutter using Simulink's Simscape toolbox was used in this paper and bidirectional communication between the control and optimization system is implemented using CPLEX/MATLAB API. The simulation result demonstrates a successful performance over the scenarios considered. DC power system, shipboard power, protection, optimization.

This paper proposes a new family of electric motors based on the concept of an airgap-less device with an internal rotor. The internal flux and therefore electromagnetic torque is maximized because the rotor is allowed to touch the stator. The proposed family of motors are competitive in applications where hydraulic motors are prevalent, i.e., low-speed and high-torque requirements. Furthermore, the proposed motors present the following advantages over hydraulic motors: (1) higher efficiency, (2) lower number of energy conversion stages, and (3) converts electrical energy directly to mechanical energy with no extra braking system. The modeling, simulation and experimental validation are presented in this paper as well. A proof-of-concept electric motor with six magnetic poles is built to validate the theoretical assumptions.

Application areas such as electric vehicles, data centers and microgrids increasingly rely on power electronic converters and electric motor drives to control loads. These tightly regulated converters act as Constant Power Loads (CPLs) in the context of the entire system. The negative incremental impedance of a CPL causes inherent instability which may lead to a grid collapse. This paper reviews the operating principles of the Smart Resistor concept wherein a bi-directional current compensation circuit and energy storage are attached at the point-of-load to stabilize the system. This decentralized control allows the equivalent load to behave as a linear resistor, which is inherently stable during either voltage or power perturbations. These adaptive resistors can work with smart sources to realize ultimate smart power networks. This paper then details the full control strategy needed to realize the concept. Smart Resistor voltage and current trajectory control principles are analyzed and validated using a hardware test setup. Energy management strategies are discussed and verified in simulation to ensure uninterrupted operation.

In this paper, a resonant switched-capacitor dc-dc converter is proposed for data center application. The proposed converter possesses features such as high efficiency, high power density and light-weight. Zero current switching (ZCS) can be achieved with the resonant operation, which allows the converter operating under high efficiency. Proper switching device selection and in-depth power loss analysis on different devices have been performed to support better design of the proposed converter. Simulation results are provided in this paper to validate operation principle of the proposed converter. A GaN based prototype with nominal 450W, 54V input and 9V output has been built to verify the theoretical analysis. The maximum power rating of the designed prototype is 600W. Power density of the prototype reaches 750W/in3. When the prototype operating at 253kHz, it achieves 98.55% peak efficiency.

To avoid the stability problem of grid connected inverter caused by the conventional phase locked loop (PLL), the direct power control of voltage source inverter in virtual synchronous reference frame without PLL is investigated considering grid voltage disturbance in the paper. Based on the small signal analysis methods, comparison between conventional PLL and no PLL is made. It can be found that the control scheme based on virtual synchronous reference introduces a virtual phase angle which is counterpart to the angle achieved by PLL. However, this virtual phase angle is directly proportional to the voltage perturbation of point of common coupling (PCC). Since PCC voltage is not stiff in the weak grid, the PCC voltage disturbance may result in instability of grid connected inverter system based on the control scheme without PLL. Therefore, this paper proposes an improved control strategy by adding two low pass filters to improve the operation performance of inverter when PCC voltage is disturbed. Simulation results show that proposed scheme can achieve the stable operation of grid connected inverter under the voltage disturbance.

Linear Electric Submersible Pump is a new industrial solution in artificial lift applications. Linear motors are placed downhole to drive the reciprocating pump directly. This system is intended to overcome some of the sucker rod pump limitations. The new configuration will allow implementation in deviated and off-shore oil wells. Integrated Drive-Motor technology shows many promising advantages. In this paper, a modified configuration for Linear Electric Submersible Pumps used in an Integrated Drive-Motor system is presented. In this system, the rectifier is placed on the surface while the inverter is integrated with the motor downhole. The reciprocating pump is required to run reliably at optimal conditions since any fault may result in several days of shut down time and a huge loss in production. This paper proposes a new fault monitoring system for the Linear Electric Submersible Pumps. The proposed system is constructed using a model based load force observer. Experimental results verified the effectiveness of the proposed method.

This paper investigates an economic and highly efficient power converter topology and its modulation scheme for 60kW buck-type rectifier system. The target system consists of three-phase three-switch buck-type rectifier topology. A new Carrier Based PWM scheme along with its simple implementation using logic gates is introduced. This PWM scheme replaces the diode rectifier equivalent switching state with an active switching state producing the effectively same current flowing path as a reference command of converter input current. As a result, the distortion of input current during the polarity reversal of capacitor line voltage can be mitigated. In this paper, the characteristics of the PWM methods are analyzed and compared based on two criteria such as the capacitor voltages and grid currents distortion. The proposed modulation technique is also confirmed through simulation and HILS verification.

This paper presents a technique to balance inductor currents of parallel-operated unipolar-PWM inverters. Firstly, the problem of unbalanced currents in parallel-operated unipolar-PWM inverters is defined and analyzed in the paper. Secondly, a technique to eliminate unbalanced currents is proposed. The proposed technique only requires one more current sensor in an inverter module rather than changing converter topology or modulation method, which makes it possible to apply unipolar-PWM inverters in parallel-operation while keeping the advantages of high power efficiency and small output chokes. Performance of the proposed current balancing method is experimentally verified. Experimental results show a good agreement to the analytical study.

A method for in situ high-bandwidth junction temperature estimation of insulated-gate bipolar transistors is introduced in this paper. The method is based on the acquisition of the gate voltage plateau during turn- on . It can be related to the junction temperature at any known device current, that can be effectively approximated using existing phase current measurements. This allows fast overtemperature protection of the power device or even active thermal cycle reduction via thermal control. This paper discusses, first, the physical mechanisms leading to the temperature sensitivity of the gate voltage plateau. Second, a rigorous sensitivity analysis of the gate voltage plateau is conducted. It allows to determine the maximal estimation error and provides information about the suitability of this method for various devices and applications. Finally, a sensing circuitry is presented, which allows accurate gate voltage plateau sensing every switching period as well as an easy integration into the gate driver. The performance of the proposed method is experimentally demonstrated with the sensing circuitry on a double pulse test bench over a wide operation range.

This paper introduces a single-phase matrix converter (SPMC) excited rotary transformer system to replace the slip rings of traditional wound field synchronous machine (WFSM). Compared to an inverter excited rotary transformer system, the matrix converter is compact due to the absence of a bulky DC Link capacitor. In this paper, the proposed SPMC uses a new constant volts per Hz modulation method that generates a medium frequency voltage waveform to reduce the size and loss of a rotary transformer. The new modulation method maintains the flux in the rotary transformer over each switching cycle to be a nearly constant value so that the loss and the size of the rotary transformer are minimized. A new commutation strategy is also developed by the authors to ensure safe commutation of the converter switches. Simulation results for the proposed excitation system are discussed and verified by hardware prototypes of the matrix converter with two different types of topologies.

The resonance problems may arise among multi-connected LCL-filtered inverters and make the system instable. The recently proposed GSPWM can reduce the filter order without reducing other performance in large-scale application, which has potential to avoid the resonance. But GSPWM will introduce specific phase delay to PWM sequences and it may influence the response character in different grid conditions. These issues have effect on the application of GSPWM and have not been analyzed before. So this paper investigates the stability performance of multi-connected L-filtered inverters with considering the influence of GSPWM in different grid condition. Firstly, this paper briefly introduces the basic principle of GSPWM and the principle of reducing the filter order. Then, this paper analyzes the stability performance of GSPWM in normal operation and fault operation with different grid conditions. And the conclusion indicates that multi-connected L-filtered inverters with GSPWM can get better stability performance in different grid condition when the quantity of inverters is large. Finally, simulation and experimental results are proposed to verify the stability performance of multi-connected L-filtered with GSPWM.

This paper presents a multilevel modular step-down DC-DC switched-capacitor converter that utilizes soft switching resonant operation. Previous versions of traditional multilevel modular switched-capacitor dc-dc converters (MMSCC) have a low switching device voltage rating. Moreover, capacitor voltage stress increases proportionally as the voltage conversion ratio increments. Significant advantage of proposed converter in this paper is high voltage conversion ratio with capacitor voltage stress always being only two times of the low side voltage. Additionally, the proposed circuit (SWRMC) shares all of the advantages from the (MMSCC) type converters such as soft switching, low voltage device rating, bidirectional operation, high conversion ratio, extremely high or low environment temperature operation, basic control algorithm and modular structure. In comparison with the magnetic core based converter the converter proposed in this paper is found to be superior due to the simple structure, soft switching, low conduction loss and 97% or higher efficiency.

This paper presents a high performance 12 kW motor drive system for an aerospace application. In order to achieve higher power density and reliability, the system uses a PMSM motor, SiC MOSFET inverter, high performance PWM control, and liquid cooling with phase change material. A power density of 33 KW/KG was achieved for the power inverter and control electronics excluding the cooling loop, and an overall power density of 0.75 kW/kg motor and drive system. An efficiency of 98% for the power inverter and 91% for the motor and drive system was achieved. Test results up to 10 kW are presented in the paper. The paper also presents challenges in the implementation of the inverters using SiC devices.

This paper proposes modulation and control strategy for a single-phase to three-phase (1p-3p) indirect matrix converter (IMC) drives. The 1p-3p IMC is composed of a singlephase current source rectifier (1p-CSR) and a three-phase voltage source inverter (3p-VSI). The 3p-VSI is operated with modulation strategy similar to that of a common inverter. The 1p-CSR must be operated with a restriction where a closed loop of that must be guaranteed consistently because the 1p-3p IMC does not have DC-link energy storage elements such as inductors and capacitors. Therefore, the 1p-CSR is necessary to additional methods regarding a circuit, modulation strategy, and control strategy. In this paper, the modulation and control strategy for the 1p-3p IMC drives with additional filter capacitor are proposed. The effectiveness of the proposed modulation and control strategy is verified by simulation results.

The second-harmonic circulating current in the phase legs of modular multilevel converter (MMC) leads to additional power losses. Existing circulating current suppressing strategies are realized by injecting the second-harmonic component in arm voltage reference. This paper presents a modified circulating current suppressing strategy including two controllers with a fixed-band submodule (SM) state transition principle. The proposed strategy is different from traditional methods, and especially suitable for MMC with nearest level control (NLC). Operating as hysteresis control, the peak values of circulating current can be approximately limited within the fixed-band. A detailed analysis in this paper for traditional circulating current suppressing controllers (TCCSC) and the proposed controller1 demonstrates that the peak-to-peak (p-p) value of the controlled circulating current for the former is greater than the latter, mainly due to the operation characteristic of MMC in the case of NLC. Moreover, the proposed controllers are simpler to be implemented with very fast dynamic performance. Simulation results proved effectiveness of the proposed control strategy.

High-voltage and high-current power converters are essential in numerous applications, including shipboard power systems and industrial motor drives. Most of the existing topologies are based on dc-link converters, and use dc-dc or dc-ac power cells to realize a multilevel power converter. Therefore, they require a large number of capacitors with high capacitances. This paper proposes a new modular three-phase ac-ac converter, the power cells of which are formed by a new class of three-phase ac-ac converters. In the proposed modular converter, the input and output terminals of the power cells can be connected in series or in parallel. This paper studies the Input-Series Output-Parallel (ISOP) structure. The proposed modular converter requires a small number of power cells, and consequently a small number of capacitors. Moreover, the capacitance of each capacitor in a power cell is very small. This eliminates the need for electrolytic capacitors, which have high failure rates. This paper presents the principles of the operation of the proposed modular converter. The proposed ISOP modular configuration is evaluated in this paper, and the results verify its promising features for the high power applications.

Harmonic power can be shared by controlling the equivalent harmonic impedance of distributed generation (DG) units in islanded microgrids. This paper firstly reviews several methods for controlling the equivalent harmonic impedance of DGs and adopts the method based on resistive active power filter (R-APF). Then, a droop relationship between the equivalent harmonic impedance of DGs and their remaining power capacities (Z DG_h_eq -S DG_remaining droop relationship) is put forward. And it is combined with the R-APF based control method to form the control scheme for DGs in islanded microgrids. With this control scheme, harmonic power is shared according to the remaining power capacities of DGs. Unlike many existing control schemes for harmonic power sharing, the control scheme proposed in this paper is insensitive to line impedance variations and does not need communication systems. Finally, the effectiveness of the proposed control scheme is verified by simulation results.

The virtual inertia J in single-phase synchronverter (SPSV) can be designed specifically to improve system stability. However, J also relates to active power loop (APL) and reactive power loop (RPL) time constants, which restricts the flexibility of control parameters choice and increases the complexity of parameter design process. This paper proposes a method to increase SPSV overall inertia without increasing virtual inertia J, based on the delayed character of hold filter. The SPSV small signal analysis of this paper explains that hold filter will influence the frequency to respond when load accessing or shedding. Furthermore, this paper reveals the inertia increasing feature contributed by the hold filter in single-phase synchronverter (SPSV). Both simulation and experimental results verified the inertia character embedded in hold filter.

This paper presents a novel hybrid adaptive droop controller to simultaneously regulate both the AC-side and DC-side parameters for power electronic converters in single-phase Microgrids. The main contribution of this paper is to integrate the AC-side and DC-side controllers. Unlike previously presented control schemes, where the DC-bus is considered as an infinite bus or constant voltage bus, the proposed control method incorporates the dynamics of the DC-side while regulating voltage and frequency at the AC-side. Designing the control scheme in single-phase is challenging due to the existence of double-frequency ripples in DC-bus voltage and converter output active/reactive power signals. In order to improve the transient performance of the proposed controller, two adaptive estimators have been used to estimate the real-time values of DC-bus voltage and output active/reactive power signals without the need to add low-pass filters. This controller can provide a tightly regulated voltage required for critical loads in MGs while improving the transient response in both DC and AC side. Simulation and experimental results in a single-phase islanded Microgrid show the superior performance of the proposed control scheme in regulating the desired parameters in AC and DC side in comparison with the conventional droop-based controllers.

In this paper a power-hardware-in-the-loop (PHIL) based machine emulator is developed. The main utility of this PHIL based machine emulation system is in testing the driving inverter and controller of an electric drive system. This paper presents an inductive filter to interface the PHIL emulator and the driving inverter, simplifying the control of the proposed machine emulator, significantly. A detailed analysis of the machine emulator control to accurately emulate the machine model behavior is also presented. Furthermore, the machine emulator discussed in this paper, uses finite element analyses (FEA) based machine models, which allows emulation of the machine's geometric and magnetic characteristics, thus greatly improving the emulation accuracy. Real-time simulations are presented to validate the proposed machine emulator control and functioning, followed by experimental validation of the results with a surface-mounted permanent magnet synchronous motor (PMSM) coupled to a DC dynamometer. Experimental results are also presented in this paper to verify the machine emulator control with transients and bidirectional power flow capability.

Single stage power factor corrected (SSPFC) AC-DC converters are attractive in particular applications because they are less expensive than conventional two-stage converters. One of the main drawbacks of SSPFC converters, however, is that their intermediate DC bus voltage varies considerably when used in universal voltage range applications. A new method for reducing the DC bus voltage variation for universal voltage applications and increase the light-load DC bus voltage is proposed in the paper. In this paper, the method is introduced and discussed in detail, the modes of operation of a SSPFC converter implemented with the proposed method are explained, general design guides are given, and experimental results from a prototype converter are presented.

This paper presents a novel control method that enables operation of Modular Multilevel Converters under non-sinusoidal AC supply conditions based on frequency domain decomposition of supply voltages. The proposed control method enables to inject or draw near sinusoidal grid currents even during the presence of harmonic distortions in the supply voltages without the use of additional hardware filters. The paper also presents a modified feedback approach for circulating current suppressing controller which minimizes circulating current while maintaining sub-module capacitor voltage dc level to the desired value and also minimizes dc bus current ripples. Simulation results show the effectiveness of the proposed control structure under supply harmonic distortions.

This paper proposes a modular multilevel converter (MMC) topology, designed particularly for load balancing in 50 Hz railway applications. The asymmetrical character of the traction load requires higher device rating for a Double-star or Delta-connected MMC compared to a symmetrical static compensator. This is due to the symmetrizing components to rebalance the capacitor voltages in the submodules. In this paper a reduced chain-link MMC topology, consisting of a two phase-leg converter, is proposed in order to avoid overrating the semiconductors in the main current path. In addition, the main circuit is equipped with dc-dc dual half-bridge (DHB) converters that connect the submodule capacitors of the two legs. The DHBs are operating as “Power Channels,” enabling energy exchange to restore the power imbalance among the capacitors. Simulation results show that the proposed converter is capable of achieving load balancing under any operating conditions, while the balance of the capacitor voltage is ensured.

This paper proposes a novel input-series output-parallel (ISOP) current-fed modular dual-active-bridge (CF-MDAB) dc-dc converter for medium-voltage dc (MVDC) system application. The proposed converter exhibits favorite features of DAB converter such as galvanic isolation, soft-switching condition and small passive components. Compared to ISOP DAB converter, the proposed topology has direct dc current controllability, thus can achieve dc circuit breaking and fault ride-through operation. The operating principle is described, and the corresponding control system is developed to realize the power flow and balancing control. A case study of 500 kW, 20 kHz ISOP CF-MDAB is simulated for validation and downscaled experimental results will be given in full paper.

There is an increasing need to model large networks of inverter-based distributed generation due to the limits of existing simulation tools. A deliberate enforcement of intra-feeder coherency between adjacent droop-controlled inverters is a worthwhile objective, as phase angle coherency will allow for a deliberate partitioning of fast and slow dynamics within the network. This partitioning, in turn, results in simpler and more tractable reduced-order network dynamics that are easier to model. This paper presents the adaptation of the generalized eigenvalue perturbation approach to the identification of coherent groups within grid-forming, droop-controlled inverter networks. For many networks, a rigorously-derived condition of coherency can be difficult to achieve, given the expected range of L-C-L filter and grid-tie impedances. To remedy this limitation, this paper investigates the use of multi-loop voltage regulation and virtual impedance to enforce the conditions that allow for coherency, and thereby more rigorously justify the use of simple nonlinear aggregate inverter models to accurately model large sections of the inverter network.

This paper proposes a novel field excitation scheme employing 4-leg converter in Machine-side Converter (MSC) of Wound Rotor Synchronous Generator (WRSG) wind turbines. The conventional thyristor rectifier and brush/slip-ring contact for supplying the field excitation is replaced by the rotating transformer and diode rectifier in the field winding side. 4th-leg power converter of MSC provides ac voltage of medium frequency to the primary side of rotating transformer in order to reduce the size of rotating transformer. This paper also proposes a control and switching modulation scheme to regulate the field current by varying the amplitude of ac voltage at 4th-leg power converter. Generation of ac voltage of 960 Hz and the regulation of field flux has been verified through the simulation. The proposed field excitation scheme can reduce the physical size and maintenance cost of WRSG wind turbines.

This paper proposes a single-phase AC converter with an active power decoupling circuit operated in DCM (discontinuous current mode) for PV (photovoltaic) systems. The proposed converter consists of an H-bridge single-phase AC converter and a boost converter, and a compensation circuit employed with a small capacitor for the power ripple. In many active power decoupling topologies that have been studied, an additional magnetic component for the voltage control of the buffer capacitor is required. This worsens the power density and the converter efficiency. In the proposed converter, the boost inductor is utilized for both the boost operation and the active power decoupling operation by using DCM. In this paper, by harmonic analysis, the effectiveness of the active power decoupling method is evaluated. As a calculating result, the maximum power density of the proposed converter is 1.26 times higher than that of the passive topology. Especially, the boost inductor volume can be reduced by 42.7% applying by DCM. The fundamental operation is confirmed by a 1-kW prototype. From experimental results, a second-order harmonics on the input current is reduced by 90.2% with the proposed active power decoupling method. In addition, the maximum efficiency of 96.0% is achieved at the output power of 600 W.

This paper proposes an efficient ramp rate control scheme for capacity firming of an integrated Photovoltaic (PV) power system with battery energy storage. This scheme addresses one of the main limitations of PV systems, namely intermittency, making available energy to be non-dispatchable to the grid and cannot be forecasted on a day ahead basis. The paper also proposes a novel state of charge controller which monitors the energy storage State-Of-Charge and adjusts the battery charge and discharge rates so that in the event of a steep variation in the PV power, it doesn't over charge or deep discharges and continues to be available for the next cycle. The combined ramp rate and state of charge control achieves a smooth dispatchable PV profile, keeps the system loss at a minimum, while improving the system reliability and performance by preserving battery life. The controller can be implemented without affecting the normal PV system control and operation. The proposed firming concept has been theoretically explained and simulation results verifies the expected theoretical performance.

In this paper, the stability study of a multiple offshore parallel long-cable-connected inverters (MOPLI) systemhs has been presented. It is shown that, since this MOPLI system is consisted of a large number of different inverters and long cables, its stability assessment actually faces big challengs. In addition, though there are lots of existing impedance-based stability criteria about prallel inverters, most of them are based on two assumptions: all the inverters are the same and the impacts of the cables can be ignored. However, the above two assumptions are not established in the real MOPLI system. In order to solve this problem, this paper first rederive the models of the inverters and long cables one by one. Based on the rederived models, a general and concise three-step impedance-based stability criterion has been proposed for the MOPLI system. The proposed criterion is not only simple and practicable, but also fully takes account of the inverters difference and the impacts of the cables. Finally, the effectiveness of the proposed criterion has been validated by a 4.9 kW MOPLI system, which is composed of 3 totoally different inverters & non-negligible cables.

This paper proposes a high efficient soft-switching multiple-input positive buck-boost converter. Multiple-input converters (MIC) use usually forward-conducting-bidirectional-blocking (FCBB) switches to control their input voltages and currents. However, these FCBB switches may decrease the overall system efficiency because of their switching losses. This paper applied a soft-switching method into multiple-input (MI) positive buck-boost converter's switches in order to design a high efficient MIC. Based on the hardware experiment result, the proposed converter showed that its power conversion efficiency was 95.25%.

This paper highlights the power limited nature of the Distributed Generation inverter and demonstrates the practical way to integrate them into the microgrid. Since the energy source of Distributed Generation inverters is power limited in nature, they constrain the operation of inverters to which they are coupled. If the power demanded from these inverters is beyond their capability, their DC-link voltage decreases and they are isolated from microgrid. This can have a catastrophic impact on the reliability of the entire system. In this paper, a virtual resistance based DC-link voltage regulation technique is developed to provide power limit management of the Distributed Generation inverter. This will allow Distributed Generation inverters to source their available power even when the power demand is higher than their capacity or hardware ratings. This technique has been modeled and implemented on 200 Watt single phase PV inverter. Experimental results are presented to compare the operation of the inverter with and without virtual resistance based DC Link voltage regulation.

This paper proposes a new current controller with modified decoupling and anti-windup schemes for a permanent magnet synchronous motor (PMSM) drive. In designing the controller, an improved voltage model, which is different from existing models in that it reflects all the nonlinear characteristics of the motor, is considered. In an actual PMSM, unintentional distortion occurs in inductance and flux due to magnetic saturation and structural asymmetry. In this paper, the effects of such distortion on voltage ripple are analyzed and the effect of voltage distortion on current control is analyzed in detail. Based on the voltage model, a decoupling controller is developed to effectively separate the d-q current regulators. The controller produces compensation voltages using the current error of the other axis. In addition, an anti-windup controller is designed that takes into account not only the integrator output in PI controllers but also the integrator output in decoupling controllers. The proposed current controller aimed at compensating all nonlinearities of PMSM enables high-performance operation of the motor. The feasibility of the proposed current control scheme is verified by experimental results.

This paper focuses on the relevant content of the MVDC-connected photovoltaic system based on the modular cascaded structure. This paper proposes a new topology for the DC grid-connected photovoltaic system with a novel capacitor voltage balancing control strategy, including the module input power ratio feed forward and module capacitor voltage closed-loop control. The proposed control strategy is independent from the realization of the photovoltaic maximum power point tracking function of the first stage. The operation principles of the proposed converter are analyzed and verified by the simulation and experimental results.

A reliable modular dc-dc converter that is well-suited to the MVDC grid applications is proposed in this paper. This converter benefits from zero current turn-off and soft turn-on switching; hence, it can use naturally commutated switches such as silicon-controlled rectifiers (SCR). SCRs offer numerous advantages over other types of switches, among them are simple control, long lifetime, low losses, low cost, and availability at both high voltage and high current ratings; therefore, use of SCRs in the proposed converter is expected to improve its attributes. The behavior of each power module in the proposed modular converter is similar to that of a Quasi-Square-Wave Cuk converter. Each power module is designed and controlled such that it employs a very small film capacitor for transferring the power from the input to the output. This feature eliminates the need for electrolytic capacitors that have high failure rates. Furthermore, each power module can be configured as an isolated converter, using an integrated high frequency transformer. Another advantage of the proposed converter is the possibility of having bidirectional flow of power. The input and output terminals of the power modules can be connected in series or in parallel. In this paper, an input-parallel output-series (IPOS) modular configuration is considered to increase the voltage blocking capability at the output. Design and analysis of the proposed modular converter are discussed in this paper. Moreover, its performance is evaluated through simulations and experiments.