Three-phase Voltage-source PWM Converter Research Articles

Influence of Neutral-Point Voltage Deviation of PWM Converter on Insulation Monitoring in Medium-Voltage Networks

Insulation monitoring is crucial to personal safety and equipment operation in the power distribution system. Recently, with the rapid development of distributed generators, the three-phase voltage-source PWM converter (VSC) is widely used as the bidirectional interface between the dc microgrids and the distribution networks. This paper presents the relationship between the response of insulation monitoring device (IMD) and the neutral-point voltage deviation (NPVD) of VSC, by analyzing the disturbances of the switching function and the dc-side insulation balancing. Then, a method of detecting the NPVD for grid-connected VSC is proposed, based on the dc signal injection and the Duffing oscillator. Furthermore, the proposed method takes the mean and spectrum of the neutral-point voltage as the primal characteristics. Thus, the dc signal injection is adopted to detect the mean of the neutral-point voltage, and the Duffing oscillator is adopted to determine the frequency disturbance of the neutral-point voltage, respectively. The test result confirms the existence of the neutral-point voltage deviation and verifies the availability of the proposed method. Hence, the proposed method could be used to improve the response of IMD.

Study of a control strategy for grid side converter in doubly- fed wind power system

The grid side converter is an important part of the excitation system of doubly-fed asynchronous generator used in wind power system. As a three-phase voltage source PWM converter, it can not only transfer slip power in the form of active power, but also adjust the reactive power of the grid. This paper proposed a control approach for improving its performance. In this control approach, the dc voltage is regulated by a sliding mode variable structure control scheme and current by a variable structure controller based on the input output linearization. The theoretical bases of the sliding mode variable structure control were introduced, and the stability proof was presented. Switching function of the system has been deduced, sliding mode voltage controller model has been established, and the output of the outer voltage loop is the instruction of the inner current loop. Affine nonlinear model of two input two output equations on d-q axis for current has been established its meeting conditions of exact linearization were proved. In order to improve the anti-jamming capability of the system, a variable structure control was added in the current controller, the control law was deduced. The dual-loop control with sliding mode control in outer voltage loop and linearization variable structure control in inner current loop was proposed. Simulation results demonstrate the effectiveness of the proposed control strategy even during the dc reference voltage and system load variation.

An active-passive capacitor-commutated converter for HVDC systems with a three-phase voltage-source PWM converter

This paper introduces a new approach to the capacitor-commutated converters (CCCs) for HVDC systems. A small-rated three-phase voltage-source PWM converter is connected between a series commutation capacitor and thyristor converter through matching transformers. The PWM converter acts as auxiliary commutation-capacitor for the thyristor converter while the series passive capacitor acts as the main commutation capacitor. The capacitance, which is the sum of the small-rated active and series passive capacitors, is variable, so that stable commutation is obtained. In CCCs, commutation failure occurs when the AC bus voltage is recovered whereas the proposed combined commutation-capacitor can achieve successful commutation for both rapidly decreasing and increasing AC bus voltages. The basic principle of the proposed active–passive capacitor-commutated converter is discussed in detail. Then, constant margin angle control with a constant firing angle of the thyristor converter is proposed using a function generator block. Digital simulation demonstrates the novelty and effectiveness of the proposed active–passive capacitor-commutated converter. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 66–75, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20030

An Active-Passive Capacitor-Commutated Converter for HVDC Systems with a Three-Phase Voltage-Source PWM Converter

This paper introduces a new approach to the capacitor-commutated converters (CCCs) for HVDC systems. A small-rated three-phase voltage-source PWM converter is connected between a series commutation capacitor and thyristor converter through matching transformers. The PWM converter acts as auxiliary commutation-capacitor for the thyristor converter while the series passive capacitor acts as the main commutation capacitor. The capacitance, which is the sum of the small-rated active and series passive capacitors, is variable, so that stable commutation is obtained. In CCCs commutation failure occurs when the ac bus voltage is recovered whereas the proposed combined commutation-capacitor can achieve successful commutation for both rapidly decreasing and increasing ac bus voltages. The basic principle of the proposed active-passive capacitor commutated converter is discussed in detail. Then, constant margin-angle control with a constant firing angle of the thyristor converter is proposed using a function generator block. Digital simulation demonstrates the novelty and effectiveness of the proposed active-passive capacitor commutated converter.