Zhikang Shuai

Combined System for Harmonic Suppression and Reactive Power Compensation

In this paper, a combined system of static Var compensator (SVC) and active power filter (APF) was proposed. The system has the function of power factor correction, voltage stability, and harmonic suppression. The SVC, which consists of delta-connected thyristor-controlled reactor (TCR) and Y-connected passive power filter (PPF), is mainly for voltage stability and power factor correction. The small rating APF is used to filter harmonics generated by the nonlinear load and the TCR in the SVC and to suppress possible resonance between the grid and the PPFs. The configuration and principle of the combined system were discussed first, and then, the control method of the combined system was presented. An optimal nonlinear proportional-integral control was proposed to improve the dynamic response and decrease the steady-state error of the SVC. Harmonic detection with precompensation method and improved generalized integrator control were proposed to improve the performance of APF. The new combined system is compared to classical SVC. It is implemented in a 200-kVA prototype in the laboratory. Simulation and experimental results show that the proposed combined configuration can effectively stabilize system voltage, correct power factor, and suppress harmonic currents.

Fuzzy-PI-Based Direct-Output-Voltage Control Strategy for the STATCOM Used in Utility Distribution Systems

In this paper, the control strategy for the static synchronous compensator (STATCOM) used in utility distribution systems is investigated, and a novel fuzzy-PI-based direct-output-voltage (DOV) control strategy is presented. Based on power balancing principle and feedforward decoupling control, this novel DOV control strategy cannot only reduce the active and reactive current control loops of a conventional double-loop control strategy but also achieve the decoupling control to regulate dc-link voltage and maintain the voltages at the point of common coupling (PCC). In order to effectively improve the immunity capability of this novel DOV control strategy to the uncertainties in system parameters, two fuzzy PI controllers are separately employed to maintain the voltages at the PCC and to simultaneously regulate dc-link voltage. The validity and effectiveness of this novel control strategy for the STATCOM used in utility distribution systems have been verified by simulation results, and a scaled physical prototype rated at plusmn300 kVAr is also developed to test the STATCOM system.

Development of Hybrid Active Power Filter Based on the Adaptive Fuzzy Dividing Frequency-Control Method

This paper deals with a hybrid active power filter with injection circuit (IHAPF). It shows great promise in reducing harmonics and improving the power factor with a relatively low capacity active power filter. This paper concluded that the stability of the IHAPF based on detection supply current is superior to that of others. To minimize the capacity of IHAPF, an adaptive fuzzy dividing frequency-control method is proposed by analyzing the bode diagram, which consists of two control units: a generalized integrator control unit and fuzzy adjustor unit. The generalized integrator is used for dividing frequency integral control, while fuzzy arithmetic is used for adjusting proportional-integral coefficients timely. And the control method is generally useful and applicable to any other active filters. Compared to other IHAPF control methods, the adaptive fuzzy dividing frequency control shows the advantages of shorter response time and higher control precision. It is implemented in an IHAPF with a 100-kVA APF installed in a copper mill in Northern China. The simulation and experimental results show that the new control method is not only easy to be calculated and implemented, but also very effective in reducing harmonics.

Power Electronic Hybrid System for Load Balancing Compensation and Frequency-Selective Harmonic Suppression

The proposed power electronic hybrid system which consists of a thyristor-controlled reactor (TCR) and a resonant-impedance-type hybrid active power filter (RITHAPF) is used for compensating reactive power and harmonic current. From the point of the nature of load balancing compensation, the calculation of balancing controlled susceptance based on voltage vector transformation is proposed for the TCR to exactly compensate negative-sequence current caused by asymmetrical loads in industrial field. Because the impedance of a filter inductor, a matching transformer, and passive power filters according to the harmonic current is inductive, the phase of the RITHAPF compensating current through them would be shifted. A π-aimed Smith predictor is established based on the fact that there is a π delay between the compensating current and the sum of harmonic currents of loads and the TCR. In terms of the proposed predictor and generalized integrators, a frequency-selective predictive current controller is designed for perfectly eliminating the impact of phase shift on the RITHAPF filtering performance. The simulation and industrial application results validate the theoretical analysis.

Design Considerations for Maintaining DC-Side Voltage of Hybrid Active Power Filter With Injection Circuit

Hybrid active power filter with injection circuit (IHAPF) shows great promise in reducing harmonics and improving power factor with a relatively low capacity active power filter, but suffers from DC-side voltage instability that inadvertently impacts the compensation performance and safety of the IHAPF. In this paper, two new methods are proposed to overcome this major technical challenge with a hysteretic control and energy release circuit, and a controllable pulsewidth modulation (PWM) rectifier. Modeling, theoretical analysis, and experimental results have verified that both methods can stabilize DC-side voltage within a certain range. A prototype IHAPF system was built incorporating the PWM rectifier DC voltage control scheme, and installed in a 220 kV substation in Southern China. It demonstrated significant improvement in harmonics reduction and power factor. The DC voltage stability issue was also resolved with the new design.

Railway Static Power Conditioners for High-speed Train Traction Power Supply Systems Using Three-phase V/V Transformers

In order to eliminate the negative-sequence and harmonic currents in the high-speed train traction systems with three-phase V/V transformers, a compensation strategy based on the railway static power conditioners (RPC) is proposed in this paper. An RPC contains two converters that are connected back to back by sharing the same dc link. In this paper, the structure and principle to compensate negative-sequence currents for the RPC with a three-phase V/V transformer are explained, and a strategy to provide the compensation references for negative-sequence and harmonic currents is proposed. Also, a method to separate active current, reactive current, and harmonic current references from the total negative-sequence and harmonic current references is given. Moreover, a controller is proposed to maintain the dc-link voltage and to compensate the negative-sequence and harmonic currents. Simulation and experimental results are provided to demonstrate that the proposed strategy is very effective.

An Improved Reactive Current Detection and Power Control Method for Single-Phase Photovoltaic Grid-Connected DG System

In the single-phase photovoltaic (PV) grid-connected distributed generation (DG) system located at the end of the feeder, it is necessary to provide quickly active and reactive power to the local loads. In this paper, an improved reactive current detection and power control method are proposed to realize active power control and reactive power compensation. To detect quickly the loads reactive current, a fast reactive current detection method using the derivative and ip-iq algorithm is presented, and it can overcome the long delay in a conventional phase-shift method. In the inner current loop, the quasi-proportional-resonant (QPR) control method with grid voltage feed-forward is presented to control accurately the grid current with zero steady error, and to reduce the current distortion due to the frequency offset and distortion of the grid voltage. The inner loop stability is analyzed, and the proper parameters are selected. In the outer loop, proportional-integrator (PI) controller is applied to stabilize the dc-link voltage, and power feed-forward is introduced to speed up system response. Simulation and experimental results verified the validity of the proposed control method.

Study on a Novel Hybrid Active Power Filter Applied to a High-Voltage Grid

A novel hybrid active power filter (HAPF) applied to a high-voltage grid is proposed. The passive filter of this topology can be used for reactive power compensation as well as for harmonic mitigation caused by the nonlinear load. The active power filter, which is shunted to a fundamental resonance circuit, is connected in series with a matching transformer, thus forming the injection-type hybrid active power filter. Because of this advantage, it is effective to be used in the high-voltage distribution grid. The basic principle of this topology is introduced particularly. Then, the steady compensation characteristic and the resonance-damping characteristic of this system are analyzed in detail. The principle about the designing method of HAPF is proposed. A HAPF prototype with the proposed designing method was built, and installed in a copper plan in Southern China. Experimental and application results prove that the proposed HAPF is good in harmonics elimination, reactive power compensation, and reliability.

A self-powered ultra-fast DC solid state circuit breaker using a normally-on SiC JFET

This paper introduces a new self-powered solid state circuit breaker (SSCB) concept using a normally-on SiC JFET as the main static switch and a fast-starting isolated DC/DC converter as the protection driver. The new SSCB detects short circuit faults by sensing its drain-source voltage rise, and draws power from the fault condition to turn and hold off the SiC JFET. The new two-terminal SSCB can be directly placed in a circuit branch without requiring any external power supply or additional wiring. A unique low power isolated DC/DC converter is designed and optimized to provide a fast reaction to a short circuit event. The SSCB prototypes have experimentally demonstrated a fault current interruption capability up to 180 amperes at a DC bus voltage of 400 volts within 0.8 microseconds. DC circuit protection applications provide a unique market opportunity for wide bandgap power semiconductor devices outside the conventional focus on power electronic converter applications.

Series and Parallel Resonance Problem of Wideband Frequency Harmonic and Its Elimination Strategy

The extensive use of pulse width modulation control technology in smart grid will lead to prominent enlargement of high-frequency harmonics. The effects of the distributed capacitances of transmission line and transformer that are neglected previously will be very obvious. The performance of the traditional harmonic eliminating method for wideband harmonic is limited, which will lead to huge challenge to the analysis, evaluation, and elimination of harmonics as well as series and parallel resonance problem. In this paper, to accurately describe the influence of wideband harmonic on smart grid, the multiterminal analysis model of harmonic degradation in smart grid is established, especially the distributed capacitances of the transmission line and the transformer are considered. Then, a novel topology of hybrid active power filter (HAPF) for resonance damping and multitype harmonic eliminating is proposed. The resonance damping model of the new topology is established; analysis results indicate that the proposed HAPF has a good harmonic resonance damping characteristic. Both simulation and experimental results have validated the validity of the theoretical analysis in this paper.