Understanding the modelling and analysis of a shunt active power filter using MATLAB/Simulink

International Journal of Electrical Engineering Education, Jul 2006 by Bayindir, K Çagatay, Ermis, Muammer

Abstract This paper deals with the modelling and analysis of a shunt active power filter by the use of a MATLAB/Simulink program. The modelling approach adopted in the paper is graphical in nature, as opposed to mathematical models embedded in code using a high-level computer language. The model is presented clearly and in a detailed manner, targetted especially at postgraduate students. The performance of the active power filter is illustrated by considering a 400 kV A, six-pulse, fully controlled bridge rectifier supplied from a typical distribution system via a rectifier transformer.

Keywords active power filter; MATLAB/Simulink

(ProQuest Information and Learning: ... denotes formulae omitted.)

In typical distribution systems the proliferation of diode and thyristor rectifiers has resulted in serious utility interface issues as well as power quality degradation such as supply current and voltage harmonics, reactive power, flicker and resonance problems in industrial applications. Voltage distortion due to current harmonics is becoming a major problem for the utilities at distribution levels. Utilities more frequently encounter harmonic related problems, such as higher transformer and line losses, reactive power and resonance problems, required derating of distribution equipment, harmonic interactions between customers or between the utility and load, reduced system stability and reduced safe operating margins.1 This has led to the proposal of more stringent requirements regarding power quality; standards such as IEEE-519 reflect these preoccupations.2

Passive filters are being used widely for harmonic elimination. However, they may create system resonances, need to be significantly overrated to account for possible harmonic absorption from the power system, must be coordinated with reactive power requirements of the loads and need a separate filter for each harmonic frequency to be cancelled.

The concept of using active power filters to mitigate harmonic problems and to compensate reactive power was proposed more than two decades ago.3 Since then the theories and applications of active power filters have become more popular and have attracted great attention. Without the drawbacks of passive harmonic filters, the active power filter appears to be a viable solution for reactive power compensation as well as for eliminating harmonic currents.

In this paper modelling and analysis of a shunt active power filter by the use of a MATLAB/Simulink program is presented. The modelling approach adopted in the paper is graphical in nature, as opposed to mathematical models embedded in code using a high-level computer language as in Ref. 4. Modelling of shunt active power filters with simulation programs is presented in many studies.5-7 However, the models are not presented in detail and only results are emphasised. In this paper the model is presented clearly and in a detailed manner so that the reader can easily understand and use the model for her further studies. Performance of the modelled shunt active power filter is illustrated by considering a 400kV A, six-pulse, fully controlled bridge rectifier supplied from a typical distribution system via a rectifier transformer. Characteristic values for rectifier load and power system parameters are taken which are typical for industry.

For modelling, SIMULINK provides a graphical user interface for building models as block diagrams. Models are hierarchical, so models can be built using top-down and bottom-up approaches. The system can be viewed at a high level and it is possible to go down through the levels to see the increasing levels of model detail. This approach provides an insight into how a model is organised and how its parts interact.

MATLAB/Simulink model for active power filter system simulation

Active power filter configuration

The active power filter uses power electronic switching to generate harmonic currents that cancel the harmonic currents from a load. The active power filter configuration investigated in this study is based on a voltage source inverter that interfaces to the system through an interface reactor. In this configuration, the filter is connected in parallel with the load being compensated. Therefore the configuration is often referred to as a shunt (parallel) active power filter. The approach is based on the principle of injecting harmonic current into the a.c. system, of the same amplitude and reverse phase to that of the load current harmonics.

Figure 1 illustrates the concept of the harmonic current cancellation so that the current being supplied from the source is sinusoidal.

Figure 2 shows the MATLAB/Simulink model of the active power filter system. As seen from the figure, the model consists of the following main parts:

* Main customer bus;

* Voltage source inverter;

* Interface reactor;

* Reference current generator;

* Firing pulse generator;

* 400kV A nonlinear load;

* Measurement and feedback components.

Voltage source inverter

The voltage source inverter used in the active power filter makes the harmonic control possible. This inverter uses a d.c. capacitor as the supply and can switch at a high frequency to generate a signal which will cancel the harmonics from the nonlinear load.