A New Strategy to Control Reactive Power of a PMS Wind Generator with Matrix Converter

A New Strategy to Control Reactive Power of a PMS Wind Generator with Matrix Converter
Authors:C. JAYA KRISHNA, K. MEENENDRANATH REDDY, G. VENKATA SURESH BABU

Abstract: In this paper, a new strategy is proposed to increase the maximum achievable grid-side reactive power of a matrix converter-fed PMS wind generator. Unlike conventional back-to-back converters in which a huge dc-link capacitor makes the control of the generator and grid-side converters nearly independent, a matrix converter control the generator and grid-side quantities simultaneously. Matrix converter is a direct AC-AC converter topology that is able to directly convert energy from an AC source to an AC load without the need of a bulky and limited lifetime energy storage element. Due to the significant advantages offered by matrix converter, such as adjustable power factor, capability of regeneration and high quality sinusoidal input/output waveforms, matrix converter has been one of the AC–AC topologies that receive extensive research attention for being an alternative to replace traditional AC-DC-AC converters in the variable voltage and variable frequency AC drive applications. Different methods for controlling a matrix converter input reactive power is investigated. It is shown that in some modulation methods, the grid-side reactive current is made from the reactive part of the generator-side current. In other modulation techniques the grid side reactive current is made from the active part of the generator-side current. In the proposed method, which is based on a generalized SVD (singular valued decomposition) modulation method, the grid side reactive current is made from both active and reactive parts of the generator-side current. In existing strategies, a decrease in generator speed and output active and reactive power will decrease the grid-side reactive power capability. A new control structure is proposed which uses the free capacity of the generator reactive power to increase the maximum achievable grid-side reactive power. Simulation results for a case study show an increase in the grid-side reactive power at all wind speeds if the proposed method is employed. 

Keywords: Permanent Magnet Synchronous Generator (PMSG), Matrix Converter, Reactive Power Control, Singular Value Decomposition (SVD) Modulation, Space Vector Modulation (SVM).

 INTRODUCTION

         In an integrated power system, efficient management of active and reactive power flows is very important. Quality of power supply is judged from the frequency and voltage of the power supply made available to the consumers. While frequency is the measure of balance between power generated (power available) and MW demand impinged on the system, the voltage is indicative of reactive power flows. In a power system, the ac generators and EHV and UHV transmission lines generate reactive power. Industrial installations whether small or large as also the irrigation pump motors, water supply systems draw substantial reactive power from the power grid. The generators have limited defined capability to generate reactive power- this is more so in respect of large size generating units of 210 MW/500 MW capacity. Generation of higher reactive power correspondingly reduces availability of useful power from the generators. During light load conditions, there is excess reactive power available in the system since the transmission lines continue to generate the reactive power...

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