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Publication Title | Matrix Converter for Reducing Harmonics in Micro- Turbine Generation System

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Matrix Converter for Reducing Harmonics in Micro- Turbine Generation System

Francisco Jurado, Manuel Ortega and Antonio Cano

Department of Electrical Engineering

University of Jaén

Linares (Jaén), Spain

fjurado@ujaen.es, maortega@ujaen.es, and acano@ujaen.es.

Abstract— This paper evaluates the performance of a micro- turbine generation system which is interfaced to a utility system through a matrix converter. The micro-turbine generation unit is composed of a high-speed gas turbine and a permanent-magnet synchronous generator. The performance of the system, based on time-domain simulation in the MATLAB package, shows that the matrix converter is a viable alternative to the conventional converter system as the interface unit of a micro-turbine generation system. In this paper a new switching strategy and a control approach for the matrix converter is introduced. The proposed switching strategy provides symmetrical input/output waveforms.

Keywords —Gas turbines; matrix converter; predictive control I. INTRODUCTION

A micro-turbine generator (MTG) unit is a high-speed rotating machine with the output power of up to a few hundreds of kW, and the output frequency up to several kHz [1]. Therefore, it is interfaced through a power electronic converter to the load system. The converter offers control of frequency as well as control of the output voltage and power flow. In a conventional manner the AC–DC–AC conversion system is took for the MTG unit [2-3].

Recently, matrix converters have experienced significant attention as a competitor to the commonly used pulsewidth- modulated voltage-source inverter (PWM-VSI). Compared to the PWM-VSI with diode rectification stage at the input, the matrix converter offers sinusoidal input and output waveforms, bidirectional power flow, controllable input power factor, and a more compact design [4].

From another point of view, the matrix converter can only

be linearly modulated to an output voltage equal to 0.866

This work was supported in part by the Ministry of Education and Science of Spain through grant DPI2006-04225.

times the input voltage [5]. In addition, the filter design is complex and a decoupling between input and output distortions is to some extent reduced [6]. Concerning the converter efficiency, at low switching frequencies, the VSI are the most efficient, while at higher switching frequencies, the matrix converter becomes superior [7] .

The salient feature of the matrix converter is to maintain the distortion and harmonic levels at both ac sides within acceptable limits, at the switching frequency of 1 kHz. If instead a PWM-based switching strategy is used, a switching frequency of 20 kHz is required to achieve a comparable matrix converter performance. This switching frequency, not only results in significantly higher switching losses, it also requires a more complicate and larger cooling system.

Model predictive control (MPC) is a control strategy that uses a model of the system to predict the response over a future interval, called the costing or prediction horizon [8]. Future control inputs are determined through minimizing a customized criterion, e.g. deviation from a desired set-point, over a piece of this future interval, the control horizon. The main profit of MPC is its constraint handling capacity. Unlike most other control strategies, constraints on inputs and outputs can be incorporated into the MPC optimization. Another benefit of MPC is its ability to foresee to future events as soon as they enter the prediction horizon. At last, MPC is an essentially multivariable control strategy, implying that control loops do not need to be decoupled, because all interactions between multiple inputs and outputs are described by the model.

For micro-turbine control, this means that physical

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