Li Yaohua

Capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters

High-power applications of cascaded multilevel inverter to active power filters (APF) is hindered by the problem of keeping capacitor voltage balance while retaining good filtering performances. This paper proposes a novel capacitor voltage balance control technique with closed-loop harmonic compensation for the cascaded multilevel inverter used in high- power APF. The proposed control method not only maintains capacitor voltage balance but also has good filtering performances, which suits for APF based on five-level and more level cascaded inverters. The steady state and dynamic experiment waveforms obtained from a prototype APF using cascaded multilevel inverter are presented to verify the validity and effectiveness of the proposed control methods.

A closed-loop selective harmonic compensation with capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters

This paper proposes a closed-loop selective harmonic compensation with capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters (APF). Firstly, the sum of each phase capacitor voltage is built through absorbing the fundamental active power current from the power system. Further, the capacitor voltage regulation method is presented to balance the voltages of flying capacitor of each cascaded cell in the same phase. Secondly, the selective compensation currents are injected into the power system to provide high power quality at the point of common coupling of a power system. Finally, a prototype APF, rated at 40 kVA based on cascaded multilevel inverter is described and the proposed method is implemented with a digital signal processors (DSP) control system. The steady state and dynamic experimental waveforms show that good filtering characteristics and fast responses of the APF are achieved and the each capacitor voltage is also controlled and balanced by using the proposed control methods, which can also be used in high-power applications of more than five-level cascaded inverter for active power filters.

Optimal parameters for filter using improved genetic algorithms

The objective of this paper is to propose a new approach for designing the passive filter system by using improved genetic algorithms (IGA). The new approach combined serial single-tuned filters with high-pass filter. The model can be used in two situations: (1) filter system just suppress harmonic current. (2) filter system suppress harmonic current and provide reactive power compensation at the same time. Through applying IGA to solve these kinds of complex discontinuous optimization problems, designer can quickly find appropriate parameter values to meet the desired power quality requirement, which minimize the total investment cost. A practical optimal algorithm based on IGA for selecting filter capacity values to achieve lowest investment of the filter system is obtained. Calculation results for a practical system show that the proposed method is valuable and powerful.

A Novel Combined System Using Cascaded Active Power Filter and Static Var Compensator for High-Power Applications

As a compromise between economy and good performance, this paper adopts the combined system using cascaded active power filter (APF) and static var compensator(SVC) to compensate reactive power and harmonic currents simultaneously for high-power applications. The SVC is constructed by fixed capacitor (FC) and thyristor controlled reactor (TCR), and the APF is constructed by a cascaded multi-level voltage source converter and its filter reactor. SVCacts as a classic reactive power compensator for load balancing and power factor correction, and APF is used to compensate the harmonic current. Firstly, the circuit topology and the principle of the combined system are introduced in detail. Then filtering characteristics using the novel control method are analyzed. Furthermore, the steady state and dynamic waveforms show that good performance and system stability of the combined system are achieved.

Investigation on the switching property of IGCT used in large power voltage source inverter

The integrated gate commutated thyristors (IGCTs) have the features of high current, high voltage, high reliability, compact structure and low loss. They have been widely used in large power voltage source inverter systems now, and they have extensive application prospect. In the paper, the performance of IGCT and diode is introduced. With the function models of IGCT and diode, the switching property of IGCT used in large power voltage source inverter is investigated. And part of the simulation results are verified with experiment results. During the turn-on process of IGCT, over current through it will appears for the reverse recovery of the fly-wheel diode. During the turn-off process of IGCT, over voltage over it will appear for the existence of the stray inductance and the clamp inductance. The property of the snubber diode and the parameters of the circuit will also influence the turn-off process of the IGCT. In order to ensure the performance reliability, the parameters of the diode and the circuit should be carefully chosen.

Investigation on the Space Vector PWM for Large Power Three-Level DC-Link Voltage Source Inverter Equipped with IGCTs

In high performance AC drive systems, the large power three-level voltage source inverters equipped with IGCTs are widely used now and have promising future. In this paper, the principle of space vector PWM (SVPWM) for three-level inverter is introduced. Some problems of SVPWM for three-level inverter are discussed. Based on the system simulation, a high power three-level inverter equipped with IGCTs is designed. The working performance of the inverter is verified with system experiment. The experiment results show that the inverter has excellent performance

Investigation on the 30MVA IGCT-based voltage source converter

The high power AC-DC-AC converters are widely used in various industrial fields. The integrated gate commutated thyristor (IGCT) is applied in medium and high voltage converter on a large scale due to its excellent characteristics. In this paper the investigation on the 30MVA IGCT-based high power voltage source converter is presented. The 30MVA converter is composed of two 15MVA IGCT-based five-level converters and the outputs of the two converters are in parallel connection. Each phase of the 15MVA five-level converter is composed of two IGCT-based three-level neutral point clamped (NPC) legs in an H-bridge form. The detailed topology design of the 30MVA large power converter is introduced in this paper. The modularization design is adopted in the converter to reduce its size and improve its power density. The power module of IGCT-based three-level NPC leg has been developed. The switching characteristics of IGCT are investigated and the influences of snubber circuit are simulated. The experiment of turn off process of IGCT is carried out. One type of carrier-based modified in-phase disposition (IPD) modulation scheme is researched and simulated.

The development of IGCT-based large capacity three-level dual-PWM converter

In media and high voltage large capacity converter systems the Integrated Gate Commutated Thyristor (IGCT) take the place of Gate Turn Off Thyristor (GTO) duo to its outstanding performance. And IGCT-based large capacity three-level converters are widely used in industrial motor-driving field. In this paper the development of a set of IGCT-based large capacity three-level dual-PWM converter is introduced. The converter includes PWM rectifier, DC capacitors, PWM inverter. The topology of the converter is given. The close-loop control strategy and SVPWM algorithm of PWM rectifier is presented in this paper. The control strategy and algorithm of the PWM inverter is also presented. The experiments were performed and the results show that the converter reaches the design requirement and has excellent performance.

A High-efficiency Cascade Multilevel Class-D Amplifier with Sliding Mode Control

The article presents a new switch-mode power amplifier based on a cascade multilevel topology. The amplifier adopts phase-shifted PWM technology and enjoys a switching frequency, which is 2N times of that of a single unit. It has a small total output voltage ripple and only requires a small filter to suppress the switching frequency harmonics. The article lays emphasis on the design of the sliding mode control and deducts the parameters, and then develops a 2 kW cascade multilevel Class-D power amplifier adopting sliding mode control. The research results show that this kind of amplifier significantly increases the system bandwidth, provides the system with fast following performance and stability, high efficiency, and low THD value of output signals, no matter the system is under resistive load or bridge rectifier load.The article presents a new switch-mode power amplifier based on a cascade multilevel topology. The amplifier adopts phase-shifted PWM technology and enjoys a switching frequency, which is 2N times of that of a single unit. It has a small total output voltage ripple and only requires a small filter to suppress the switching frequency harmonics. The article lays emphasis on the design of the sliding mode control and deducts the parameters, and then develops a 2 kW cascade multilevel Class-D power amplifier adopting sliding mode control. The research results show that this kind of amplifier significantly increases the system bandwidth, provides the system with fast following performance and stability, high efficiency, and low THD value of output signals, no matter the system is under resistive load or bridge rectifier load.

Control methods of hybrid active power filters reduced rating of its converter

This paper presents three control methods for a hybrid active power filter (HAPF), which is reduced the rating of active converter. Main circuit topology and their principles of the HAPF were discussed in detail. The single-phase equivalent circuits in harmonic domain of the HAPF are also given. Experiment waveforms were gotten from a laboratory prototype, rated at 10 kVA. Experiment results prove the active converter rating accounts for only 4.42% of the HAPF rating while the total harmonic distortion of the source current is reduced to 4.25% from 26.95% with the combined control method, which is better than the other control methods.