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In the electrical engineering field, there are two types of system which can potentially generate resonance under excitation, one is the electrical system with inductor and capacitor, the other is the mechanical system with spring-mass characteristic. A lot of research on active damping control algorithms for grid-connected inverters with LCL filter and inverter-driven machine with multirotating masses have been demonstrated. However, research works for these two systems were carried out independently and there is a lack of systematic comparison for modelling and control between these two systems. This article will unify the mathematical models and active damping control algorithms for these two systems. It is found that the mathematical models and control structures are fundamentally the same. The existing or future potential active damping control algorithms used in electrical system can be applied in mechanical system and vice versa to avoid reinventing the wheel. Parameter sensitivity analysis for controller and feedback gains was performed for electrical systems in the discrete z-domain. For mechanical systems, it is found that a substantial electromagnetic torque overshoot was introduced when applying the active damping control and it was analyzed quantitatively with various damping coefficients to guide the inverter design. Finally, experimental tests were done to verify the findings. [ABSTRACT FROM AUTHOR]

To achieve an individual and continuous power distribution for multireceiver wireless power transfer (WPT) systems, a novel multifrequency modulation method has been proposed. In the proposed method, a look-up table and delta-sigma modulation scheme are introduced to generate a mixed-frequency driving voltage pulse by synthesizing it from the given voltage pulses. The components of synthesized driving voltage pulse have continuously and individually varying amplitudes of multiple specific frequencies. With the proposed modulation method, only a standard full-bridge inverter is employed in the transmitting side to achieve power distribution among receivers, leading to a simple configuration of the transmitting source. Moreover, the proposed method has a small calculation burden and can be easily extended to the system with more receivers. When compared with the existing multifrequency modulation method, a lower switching frequency is obtained in the proposed method. Finally, the effectiveness of the proposed modulation method is verified theoretically and experimentally. [ABSTRACT FROM AUTHOR]

This article proposes a circulating current and second harmonic current (SHC) suppression method by introducing virtual impedance into the circulating current and output current feedback control loops of the dc solid-state transformer (DCSST). The virtual impedance is employed to adjust impedance in the circulating current feedback control loop to decrease the circulating current when the transmission efficiency of each dual active bridge is different. And a SHC suppression method, which introduces the virtual impedance containing a bandpass filter, is adopted to reduce the SHC and improve the dynamic performance of the DCSST. Moreover, a relatively independent modular control method, which is conducive to the modular expansion of the DCSST, is proposed. Compared with traditional DCSST control methods, the proposed method can simultaneously realize the output current sharing and effectively reduce the SHC with modular control. Finally, a DCSST prototype is built and the results of the experiment verify the validity and effectiveness of the proposed control strategy and solutions. [ABSTRACT FROM AUTHOR]

The droop control is an advantageous approach for stand-alone supply systems consisting of multiple batteries, allowing among various inverters without intercommunication. The droop coefficients of batteries always vary with their state-of-charge (SoC) and charge/discharge mode, resulting in small-signal instability. Nevertheless, the existing impedance-based approaches can only assess the droop coefficients stability point, but not the stability region. Therefore, this article proposes a droop coefficients stability region analysis approach. First, the charge/discharge SoC-based droop controlled battery, the P&Q controlled distributed generator and the constant power load are separately discussed. Meanwhile, the state matrix and return-ratio matrix are established, respectively. Furthermore, the novel forbidden region criterion based on the return-ratio matrix is constructed, which reduces conservatism compared with norm-based impedance criteria and partial forbidden region criteria. Such a forbidden region criterion is first switched to the Hurwitz identification problem regarding the equivalent return-ratio matrix. Combined the state matrix and the equivalent return-ratio matrix, the generalized incidence matrix is constructed to simultaneously identify subsystem stability and interactive stability. Based on the generalized incidence matrix, an adaptive step search strategy is proposed to obtain the droop coefficients coordinated stability region. Finally, the simulation and experimental results illustrate the validity of the proposed method. [ABSTRACT FROM AUTHOR]

The high penetration of renewable energy sources always leads to the fluctuation of the droop coefficients which are designed in inverse proportion to their rated capacity, and power electronics devices are prone to static instability. Although the impedance-based approaches have been widely studied to deal with this problem, the stability-oriented droop coefficients region identification due to the fluctuation of renewable energy sources is not provided. Thus, this article proposes an impedance-based approach to assess the droop coefficients stability region in the power system consisting of numerous distributed generators (DGs). First, the modified phase margin and opposing argument (MPMOA) forbidden criterion is constituted to acquire the complementary space of the droop coefficients stability region. The MPMOA forbidden criterion is first transformed into the condition that the generalized return-ratio matrix is Hurwitz through mirror, rotation, and translation mapping. In comparison with the previous simplified stability criteria, the conservatism of the proposed criterion is reduced a lot. Thereafter, the droop coefficients stability region is directly calculated by the generalized return-ratio matrix and guardian map theory. Eventually, the simulation and experimental results are provided to validate the conservatism and effectiveness of the impedance-based stability region identification approach. Therein, the simulation results illustrate that the proposed droop coefficients stability operation criterion has lower conservatism than these of the previous simplified stability criteria. Furthermore, the simulation and experimental results illustrate that the proposed stability-oriented droop coefficients region identification approach can provide an effective parameter stability region. [ABSTRACT FROM AUTHOR]

The penetration level of photovoltaic (PV) keeps increasing in modern distribution networks, which leads to various severe voltage limits violation problems. This article aims to aggregate and utilize the PV inverters for voltage regulation by a fully distributed two-level Volt/VAr control (VVC) scheme. In the lower-level VVC (real-time scale), the rooftop PV inverters are aggregated via consensus algorithms and then governed by droop controllers in medium-voltage networks. The droop controller adjusts the reactive power output of each PV aggregator in real-time from its dispatched value depending on the bus voltage variations. In the upper-level VVC (15-min timescale), the reactive power of PV aggregators is dispatched for power loss minimization, where control signals are set as base values for PV aggregators. This problem is formulated as second-order cone programming and solved by the alternating direction method of multipliers. The simulation results demonstrate the effectiveness of the proposed method in both short-term and long-term scenarios with different system scales. [ABSTRACT FROM AUTHOR]

This paper introduces a compensation strategy to deal with both current and voltage measurement errors in the three-phase pulsewidth modulated rectifier system. The dc offset and scaling errors in the voltage and current measurements cause the injection of undesired dc and unbalanced currents into the three-phase input current and subsequently lead to voltage ripple at the dc output voltage. This paper proposes a compensation scheme for current measurement error where the dc offset and scaling errors in the current measurement are estimated from the characteristic of the dc output voltage ripple combining with simple band-pass and low-pass filters. Meanwhile, an advanced current controller designed with a proportional integral plus two resonant controllers tuned at the fundamental grid frequency $({{\omega _s}})$ and $2{\omega _s}$ in the synchronous (d–q) reference frame is suggested to reject the impact of the dc offset and scaling errors in the voltage measurement. The proposed compensation method is developed without the need of extra hardware circuit, sensor, or precise information of system parameters so that it can be considered as more cost-effective and robust solution. The effectiveness of the proposed solution is verified by experimental results. [ABSTRACT FROM AUTHOR]

The dc offset and scaling errors in the voltage measurements cause the injection of undesired dc and harmonic currents into the three-phase output currents of the grid-connected inverter. This study proposes an enhanced current control scheme to eliminate the dc and harmonic currents caused by voltage distortion and voltage measurement error in three-phase grid-connected inverters. The proposed current controller is designed in the synchronous (d-q ) reference frame and composed of a proportional resonant (PR) controller and a repetitive controller (RC). The role of the RC is to regulate the grid current follow the reference value as well as compensate all 6\rmn\omega {\rm{s}} and (6\rmn\pm 2)\omega{\rm{s}}\,(n= 1,\,2,\,3,\ldots) harmonic components caused by distorted grid voltage and scaling errors. Meanwhile, the PR controller helps to compensate the dc current generated by dc offset measurement errors to guarantee that the three-phase grid currents are balanced and sinusoidal with extremely low dc component. Since the RC employed in the proposed current controller reduces to time delay by four times compared to the conventional RC, the proposed control system ensures good steady-state performance of the grid current without deteriorating its fast dynamic response. The effectiveness of the suggested solution is verified by various experimental tests. [ABSTRACT FROM AUTHOR]

This study proposes an advanced current control strategy for three-phase grid-connected inverters to reject the impact of the dc offsets and scaling errors in the grid voltage measurement on the grid current performance. The proposed current controller designed in the synchronous (d-q) reference frame is developed with a proportional integral (PI) plus three vector PI controllers. The PI controller regulates the fundamental current to follow its reference, meanwhile, three vector PI controllers tuned at the fundamental grid frequency ( \omega _s), 2\omega _s, 6\omega _s are employed to eliminate the dc, unbalance, harmonic components in the grid current. As a result, the three-phase grid currents are controlled to be balanced, sinusoidal, and extremely low dc component despite the presence of the dc offset and scaling errors in the grid voltage measurement and distorted grid voltage conditions. The main advantage of the proposed control scheme is that it is developed without the need of additional hardware circuit, dc extraction, and harmonic detection scheme so that it can be integrated into the existing grid-connected inverter system without extra cost. The effectiveness of the suggested solution is verified by experimental results under various grid voltage conditions and the grid voltage measurement errors. [ABSTRACT FROM PUBLISHER]

Repetitive control strategies have been commonly applied in pulse-width-modulated (PWM) voltage source inverters (VSIs) for many industrial applications. This paper presents a repetitive controller for voltage harmonic mitigation of VSI-based islanded microgrids. The phase delay in the overall control system, e.g., the delay caused by the digital duty cycle calculation, PWM generation, and repetitive controller, has to be compensated by elaborately designed phase lead filters in order to prevent control performance deterioration and system instability. Nevertheless, quantificational analysis and practical design of the time advance unit in such filters are hardly found in existing literature works. In view of this, this paper proposes an explicit analysis of the phase lead filters and a novel design method of the time advance unit in repetitive controllers to ensure system stability. Moreover, with the help of the proposed method, the overall system stability margin is predictable and improved controller performance is achieved as well. The proposed method is implemented experimentally to show the accurate stability margin calculation as well as the excellent steady state and dynamic performances of the repetitive control scheme. [ABSTRACT FROM PUBLISHER]

This brief presents an inverter-based low-noise single-ended to differential continuous-time variable gain amplifier (VGA) for 2–6-MHz second harmonic cardiac ultrasound imaging probes. The proposed VGA is based on a transimpedance amplifier and composed of resistive arrays and three equal inverters to form the resistive feedback loop. The inverters operate in the class C mode by being biased in the subthreshold region to improve both the power and noise performances of the VGA. The 6-bit thermometer resistive arrays can control the gain range from −1 to 21 dB for a 2-D piezoelectric transducer (PZT) model, and for a 50- \Omega source resistor, the gain range is from 20 to 26 dB. The second harmonic distortion (HD2) is lower than −55 dB in most cases due to the single-ended to differential conversion, and the equivalent input referred noise is 7 \text{nV}/\sqrt{\text{Hz}} at 5 MHz with the maximum gain. The VGA is fabricated in 65-nm CMOS technology and has the power consumption of 54 \mu\text{W}$ at a supply voltage of 0.5 V. The die size of the VGA is 154\ \mu\text{m} \times 102\ \mu\text{m}. [ABSTRACT FROM PUBLISHER]

This paper presents a probabilistic approach in the modeling of stand-alone microgrids to predict their operational adequacy performance considering uncertainty of energy storage system (ESS), photovoltaic system (PVS) and conventional generator (CG). Instead of using the daily or hourly time step, operating period a minutely time step is considered to incorporate the effect of fast ramp up/down of system components on microgrid operating adequacy through expected energy not supplied (EENS) and expected energy not used (EENU), due to load and resource variations. A time varying state of charge (SOC) model is proposed to determine power output of an ESS in reliability modeling. The reliability of a PVS is modeled in detail based on the total cross-tied configuration (TCTC) of photovoltaic (PV) cells and arrays. The proposed technique and indices will be useful for system planners to select the type and size of microgrid systems that contain alternative energy sources and storage. [ABSTRACT FROM PUBLISHER]

Droop schemes have traditionally been applied to the control of parallel synchronous generators in power systems. It has subsequently been brought over to the control of distributed generators (DGs) in microgrids with the same retained objective of proportional power sharing based on ratings. This objective might, however, not suit microgrids well since DGs are usually of different types, unlike synchronous generators. Other factors like cost, efficiency, and emission penalty of each DG at different loading must be considered since they contribute directly to the total generation cost (TGC) of the microgrid. To reduce this TGC without relying on fast communication links, an autonomous droop scheme is proposed here, whose resulting power sharing is decided by the individual DG generation costs. Comparing it with the traditional scheme, the proposed scheme retains its simplicity and it is hence more likely to be accepted by the industry. The reduction in TGC has been verified by experiment. [ABSTRACT FROM PUBLISHER]

This paper proposes a multiple-input versatile matrix converter (VMC) for integrating hybrid ac/dc energy resources and storages to the power grid. The VMC is developed from the traditional indirect matrix converter but operates in the reverse-boost mode rather than in the forward-buck mode. The reverse-boost mode is more relevant here since most renewable sources and energy storages have lower voltages than the grid. The eventual VMC developed uses an alternative nine-switch converter, rather than usual six-switch voltage-source converter, for providing six input terminals in total. One three-phase ac source and three dc sources, or other source combinations, can therefore be connected to the VMC. Powers from these sources are channeled to the three-phase utility grid through the VMC's current-source inverter. Their proper dispatches are guaranteed by the proposed control and modulation schemes, which also help maintain near-sinusoidal input and output current waveforms. Mathematical proofs, simulation, and experimental results have shown that the VMC can indeed operate as intended. [ABSTRACT FROM PUBLISHER]

Indirect matrix converter (IMC) is an alternative for ac/ac energy conversion, usually operated with a voltage stepped-down gain of only 0.866. For applications like distribution generation where voltage-boost functionality is required, the traditional style of operating the IMC is therefore not appropriate. Like most power converters, the operation of the IMC can surely be reversed to produce a boosted gain, but so far its relevant control principles have not been discussed. These challenges are now addressed in this paper with distributed generation suggested as a potential application. Simulation and experimental results for validating various performance aspects of the proposed control schemes can be found in a later section of this paper. [ABSTRACT FROM AUTHOR]

This paper presents a novel matrix converter with one ac input and two ac outputs. The presented topology is based on the traditional indirect matrix converter, but with its rear-end six-switch inverter replaced by a compact nine-switch inverter. With only three extra switches added, the proposed converter can produce two sets of three-phase ac outputs, whose amplitudes, frequencies, and phases can appropriately be regulated. Features such as sinusoidal input and outputs, unity input power factor and minimum commutation count are all retained by the proposed topology, despite having an additional output. Its modulation is realized by the computationally less intensive carrier-based method, whose unique carrier requirements can easily be managed within a programmable logic device. Mathematical proof for validating sinusoidal input and outputs achieved by this modulation technique is also discussed, before being verified in simulation and experimentally, together with other findings. [ABSTRACT FROM AUTHOR]