13-06-2013, 04:21 PM
ACTIVE POWER FILTER FOR HARMONIC SUPPRESSION
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Abstract
In this paper, a novel active power filter is proposed and implemented by using a voltage-source power converter with a series connected inductor and capacitor set. The power converter is controlled to generate a compensating voltage that is converted into a compensating current via the series connected inductor and capacitor set. The compensating current flows into the power feeder in order to suppress the harmonic currents generated by nonlinear loads. The salient advantages of the proposed active Power filter are lower voltage rating of dc capacitor and power switching devices, smaller filter inductor, smaller dimension, light weight, better filter performance and low electromagnetic interference (EMI). A three-phase 100 k VA active power filter is developed to demonstrate the performance of the proposed method. The results show that the proposed active power filter has the expected performance.
INTRODUCTION
The power electronic related facilities may generate a large amount of harmonic current due to the nonlinear input characteristic. The harmonic current may pollute the power system causing problems such as transformer overheating, rotary machine vibration, voltage quality degradation, destruction of electric power components, and alfunctining of medical facilities .In order to solve the problem of harmonic pollution effectively, many harmonic limitation standards.
SYSTEM CONFIGURATION AND OPERATION PRINCIPLE
The system configuration of the proposed active power filter is shown in Fig. 2.
It consists of a series connected inductor and capacitor set, a power converter and a high frequency ripple filter. The voltage-mode control is used to control the power converter. The power converter generates a compensating voltage that is converted into a compensating current flowing through the series connected inductor and capacitor set, and the compensating current flows into the power feeder in order to filter harmonic currents generated by nonlinear loads. The configuration of the proposed active power filter is similar to that of the hybrid power filter in the first view. However, the function and dimension of the passive elements (L-C) are not the same. In the proposed method, the inductor of the series connected inductor and capacitor set is very small, and it is used to filter the switching ripple of the power converter. The capacitor in the series connected inductor and capacitor set is used to supply a fixed reactive power. However, the passive elements (L-C) in the hybrid power filter are used to tune the dominant harmonic component of the load current. The inductance in the hybrid power filter is larger than that used in the proposed active power filter, then, the dimension and weight of the inductor used in the hybrid power filter are also larger than that used in the proposed active power filter. The high frequency ripple filter is configured by a set of capacitors and resistor, and it uses to further filter out the switching ripple of the power converter.
CONTROL THEORY
Conventionally, the active power filter was controlled by the current-mode. However, it is hard to be implemented under low filter inductance due to the high switching ripple, and it may generate multiple crossing during a carrier period of pulse-width modulator. The phenomenon of multiple crossing will result in more than one switching operation during a carrier period. In the proposed active power filter, the voltage-mode control is used.
EXPERIMENTAL RESULTS
For demonstrating the performance of the proposed active power filter, a three-phase 100KVA prototype is developed. The major parameters of the prototype are shown in Table I. The utility power is supplied by a three-phase three-wire utility system with 380 V and 60 Hz. A comparison of the proposed active power filter and the conventional parallel active power filter is shown in Table II. Since the inductance of series connected inductor and capacitor set is only 58 H, a ferrite core can be used to reduce the power Loss, weight and volume. Hence, the volume and weight of the proposed active power filter is evidently smaller than that of the conventional parallel active power filter. In addition, the hardware cost is also reduced significantly.
CONCLUSION
Recently, many power electronic application technologies have been used to replace the role of conventional passive elements in the distribution power system for solving the problems of power quality. The active power filter is used to solve the harmonic problems in the industrial power system, and this becomes popular gradually. However, the wide use of the active power filter is still limited due to the high cost and the power rating of power electronics. In this paper, a novel active power filter is proposed. The proposed active power filter has the advantages of lower voltage rating for dc capacitor and power switching devices.