Unintentional series and/or parallel resonances, due to the tuned passive filter and the line inductance, may result in severe harmonic distortion in the industrial power system. This paper presents a hybrid active filter to suppress harmonic resonance and to reduce harmonic distortion. The proposed hybrid filter is operated as variable harmonic conductance according to the voltage total harmonic distortion; therefore, harmonic distortion can be reduced to an acceptable level in response to load change or parameter variation of the power system. Since the hybrid filter is composed of a seventh-tuned passive filter and an active filter in series connection, both dc voltage and kVA rating of the active filter are dramatically decreased compared with the pure shunt active filter. In real application, this feature is very attractive since the active power filter with fully power electronics is very expensive. A reasonable tradeoff between filtering performances and cost is to use the hybrid active filter. Design consideration are presented, and experimental results are provided to validate effectiveness of the proposed method. Furthermore, this paper discusses filtering performances on line impedance, line resistance, voltage unbalance, and capacitive filters.

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Hybrid Active Filter With Variable Conductance for Harmonic Resonance Suppression in Industrial Power Systems

Active power filters (APFs) have been developed to solve the problems of harmonic suppression and reactive power compensation simultaneously, In this paper, a three-phase four-wire power filter comprising a three-phase three-wire APF and a Zig-Zag transformer is developed. A hardware prototype is implemented and tested to verify the performance of the proposed power filter under various ideal and non-ideal power conditions. Experimental results show that this three-phase four-wire power filter has the desired performance under limited zero sequence utility voltage.

A Three-Phase Four-Wire Power Filter Comprising a Three-Phase Three-Wire Active Power Filter and a Zig–Zag Transformer

Neutral current compensation in three-phase, four-wire systems: A review

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 kVA 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.

A novel active power filter for harmonic suppression

Power System Capacitors

This paper investigates the harmonic amplification problems in a plastics plant and the appropriate mitigation methods. Four single-tuned filters (LC filters) were installed to eliminate the harmonic currents from three 6-pulse rectifiers. However, after the capacitance reduction of some filter capacitors, the driving point impedance at the frequency of 8th order harmonic increased severely and the harmonic current of this order was amplified. There were many failures of the power filter capacitors. Field measurements and computer simulations are used to verify the disturbance problems. Finally, two high-pass damped filters are recommended to replace the original single-tuned filters. The amplification problems at some even-order harmonics can be avoided.

Investigation and mitigation of harmonic amplification problems caused by single-tuned filters

This paper presents the applications of regression models to predict the future growth trend of total harmonic distortions (THD) of 40 power transformers from field measurement data. The prediction values are important and can be used for transformer planning. Those transformers which feed different types of customers reveal different harmonic characteristics. While the linear regression model is suitable for harmonic voltage distortion, the nonlinear exponential regression model is better for current. All transformers' harmonic voltage distortions follow with harmonic current distortions, that is, feeder loads are harmonic sources. The prediction harmonic values of regression analysis are lower than that from the method of average spread rate.

Shih-Song Yen

Papers

Investigation and mitigation of harmonic amplification problems caused by single-tuned filters

Application of regression models to predict harmonic voltage and current growth trend from measurement data at secondary substations