Yunping Zou

Cascade multilevel inverter with phase-shift SPWM and its application in STATCOM

A cascade multilevel voltage-source inverter with separate dc sources is proposed for static synchronous compensation (STATCOM). It can solve the size-and-weight problems of conventional transformer-based multipulse inverters and the component-counts problems of multilevel diode-clamp and flying-capacitor inverter. Phase-shift sinusoidal pulse width modulation (PS-SPWM) technique is employed to control the switching devices of each voltage-source inverter, as a result, the devices operate at a higher equivalent carrier frequency. In conclusion, the inverter has such advantages as: 1) reducing power loss because of transform-less design; 2) generating almost sinusoidal waveform voltage with high equivalent carrier frequency; 3) eliminating transformers of multipulse inverters used in the conventional STATCOM; 4) dynamic response fast; and 5) direct connection to power distribution system without any transformer. This paper focuses on feasibility and control schemes of the cascade multi-level inverter. Simulation of a three-phase 5-level inverter with reactive power regulation using MATLAB-Simulink power system blockset is carried out. The analytical and simulated results show the feasibility and superiority of the proposed inverter for static synchronous compensation.

Modeling and Control of Neutral-point Voltage Balancing Problem in Three-level NPC PWM Inverters

This paper explores the mathematic model and control method of neutral-point voltage balancing problem in three-level NPC inverter. A comprehensive mathematic model of three-level inverter is established. Then, based on the space vector PWM strategy, a simple neutral-point voltage balancing control method, which depends on the direction information detection of each phase leg current and neutral-point voltage ripple, is proposed in this paper. According to the direction information, the control method selects appropriate switching states sequences to drive three-level NPC inverter. As a result, the neutral-point imbalance is restrained in a small bound, while the switching loss and the dv/dt of output voltage will not increase. The experimental results verify the correctness and feasibility of the proposed control scheme

Current characteristic of high voltage capacitor charging power supply using a series resonant topology

Pulse power supply applications usually require short and intense bursts of energy that may be derived by rapidly discharging an energy storage capacitor. Series resonant topology is used in capacitor charging power supply because of its approximate constant current characteristic from zero volts to maximum voltage. But the series resonant topology with open-loop control is not accurate constant current charging characteristic because the DC bus voltage is variable and the transformer is not ideal. Furthermore, the high voltage rectifier diodes are also not ideal. This paper presents the current characteristic of series resonant power supply with ideal and actual components, respectively. And moreover, some valuable figures given in this paper can be used during the course of designing and debugging.

Research on AC electronic load based on back to back single-phase PWM rectifiers

This paper presents a kind of AC electronic load for testing AC power source with energy recycling capability. The proposed structure is based on back to back single-phase PWM rectifiers of the voltage-source type. The operation principle of the model is described in detail to research the power matching problem and DC bus harmonic phenomenon. To achieve power balance and good performance, an independent control strategy for the two PWM rectifiers is proposed. In addition, a novel control technique of compensating second-harmonic voltage of dc bus is put forward. The research is proved to be effective in power recovery by the prototype experiments.

A new diode-clamp cascade multilevel converter

Cascade and diode-clamp voltage source converter have become increasingly popular in recent years due to their practicability. This paper will present a new diode-clamp cascade multilevel converter that is derived from these two topologies. The new concept of the novel diode-clamp cascade converter is based on the connection of multiple three-level diode-clamp converter modules. The multilevel waveform is synthesized by adding of each converter output voltage. Subharmonic PWM method is employed in the new topology. The proposed converter is also verified by computer simulation using Saber. Simulation results are also presented in this paper. Conclusion is made in the final part.

A simple neutral-point voltage balancing control method for three-level NPC PWM VSI inverters

Based on the space vector PWM (SVPWM) strategy, this paper mainly focuses on the control method of neutral-point voltage balancing problem in three-level NPC PWM VSI inverter. A comprehensive mathematic model of three-level inverter is set up. Then, a simple neutral-point voltage balancing control method, which only requires the direction information detection of each phase legs current and neutral-point voltage ripple, is proposed in this paper. According to the information, the control method selects the appropriate SVPWM switching states sequences to drive three-level NPC inverter. The scheme is easy to implement. As a result, the neutral-point voltage imbalance is limited without increasing the switching loss and the dv/dt of output voltage. The experimental results verify the correctness and feasibility of the proposed control scheme

A STATCOM based on cascade multilevel inverter with phase-shift SPWM

Static synchronous compensation (STATCOM) is a flexible ac transmission system (FACTS) device, which can be used to generate reactive power in long distance ac power transmission. The conventional STATCOM consists of several voltage-source inverters connected together through zigzag arrangement transformers, which arouse some problems, such as expensive, producing much loss, difficult to control and unreliable. This paper proposes another STATCOM, named a cascade multilevel inverter with phase-shift sinusoidal pulse width modulation (PS-SPWM) technique, which eliminates the bulky transformer and can respond much faster. The PS-SPWM switching scheme is employed to operate the switches of this inverter, which can: 1) reduce power loss because of transformless design; 2) expand the power capacity easily; 3) generate almost sinusoidal waveform voltage with high equivalent carrier frequency; and 4) make possible direct connection to power distribution system without any transformer. This paper focuses on feasibility and control schemes of the cascade multilevel inverter. Simulation of a three-phase 5-level inverter with reactive power regulation using MATLAB-Simulink power system blockset is carried out. The analytical and simulated results show the feasibility and superiority of the proposed inverter for static synchronous compensation.

Spectral Analysis of Novel Hybrid Modulated Asymmetric 5-level Inverter

In this paper, a novel asymmetric 5-level inverter is studied which is composed of a half-bridge diode-clamp inverter and a conventional half-bridge inverter connected to a common split-capacitor power supply. Analysis of a modulation technique for the inverter, which incorporates square-wave synthesis in conjunction with the PWM subharmonic method, is illustrated. According to the proposed control technique, new configuration permits faster devices and higher voltage devices operating together. In order to estimate spectra accurately, the mathematic models of the modulation process with three carrier dispositions will be built, at the same time rigorous analytic solution of spectra is derived from an extension of Bennets method. We illustrate and sum up spectral feature of output waveform covering all operation conditions. On purpose to verify the proposed approach, a single-phase 5-level asymmetric inverter is constructed and experimental results are provided

Research on an Improved Adaptive Algorithm Applied To Active Power Filters

For the moment, there have been a number of harmonic current detecting methods for active power filters (APF), including the filtration approach by fixed frequency filters, the composition method of the imaginary and the real power based on the instantaneous reactive power theory, adaptive noise canceling method, wavelet technology, and so on. Especially for the adaptive harmonic measuring, since its unique advantages of well bandwidth behaving, simple algorithm, automatically tracking grid frequency and robustness to circuit parameter variation, it has received significant attention in recent years. The paper provides an improved adaptive algorithm of detecting harmonic currents. It adopts a new variable step size least mean square (LMS) method allowing more flexible control of misadjustment and convergence time without the need to compromise one for the other. Moreover, the algorithm can effectively adjust the step size while maintaining the immunity against harmonic current disturbance. Meanwhile the additional calculation is very little, so the algorithm presented is easy to implement. The simulation results illustrate that the performance of the proposed approach is satisfactory

An Evaluation of Spectral Characteristic of Novel Hybrid Asymmetric Modulated 9-level Inverter

This paper proposed a novel hybrid asymmetric 9-level inverter in which an asymmetric 5-level inverter and an H-bridge inverter with equal DC bus voltage are series connected. A hybrid asymmetric modulation technique for the novel inverter is illustrated. In terms of the control technique adopted, the new configuration permits faster devices and higher voltage devices operating in synergism. In the case of three carrier dispositions, the mathematic models of the modulation process are built. The rigorous analytic solution is derived from an extension of Bennets method, which benefits the evaluation of spectra accurately. We summarize spectral characteristics of output waveforms involving all operation conditions. Experiment is carried out to validate the feasibility of the proposed approach