A New Three Phase Hybrid Passive Filter to Dampen Resonances and Compensate Harmonics and Reactive Power for Any Type of Load under Distorted Source Conditions

This paper proposes a new three phase hybrid passive filter (HPF) for compensating voltage and current harmonics type of load, and power factor. The proposed filter is not sensitive to source impedance variations, eliminate the chances of series and parallel resonance and eliminates large variation of power factor and terminal voltage caused by varying loads under stiff and distorted source conditions. Besides these, the topology also helps fast settling of transients and blocking of harmonics. The investigations are carried out to validate the performance of proposed HPF with detuned resonance, for effective and efficient operation under varying loads and source conditions. The topology of HPF is chosen to shift the resonance frequency of the resulting system below 80 Hz where no excitation is expected. The frequency response shows excellent damping characteristic for load harmonic current above 80 Hz, The simulation results show that the proposed passive filter can simultaneously compensate effectively all harmonics and reactive power for a variety of nonlinear loads.

I. Introduction

Harmonics contamination, due to the increasing use of nonlinear loads, has become a serious problem in power systems for a long time. Nonlinear loads are characterized into two types of harmonic sources-current source nonlinear loads and voltage-source nonlinear loads, such as phase-controlled thyristor rectifiers having a sufficient dc inductance, and diode rectifiers with smoothing dc capacitors [3], [6]. These two types of harmonic sources have completely distinctive, dual properties and characteristics. Based on their properties and characteristics, the current-source nonlinear loads and voltage-source nonlinear loads have their own suitable filter configurations, respectively. Harmonic compensation has been suggested through passive filters, active filters and hybrid filters [6]–[9], [10]–[12]. By far amongst these, the passive filters have still remained popular because of their reliability, ruggedness, high efficiency low cost and less maintenance as compared to active or hybrid power filters [3], [5]. Various topologies of passive filters have been proposed in the literature having different compensation characteristics and applications. Indeed, the shunt (parallel) passive filter (PPF) is effective for compensating such current-source nonlinear loads. However, it has been shown that the shunt passive filter is not effective for compensating such voltage-source type of nonlinear loads [2]. Instead, a series passive filter (SPF) should be used to compensate for voltage-source nonlinear loads. The principle of the PPF is to provide a low-impedance shunt branch to the load's harmonic current, thus reducing harmonic current flowing into the source. Besides harmonic compensation, PPF can also provide limited reactive power compensation and voltage regulation. These filters suffer from inherent problem of getting into series and parallel resonance with power system components, what amplifies the current at resonant frequency thus cause distortion in the voltage at point of common coupling (PCC), posing dysfunction of relays and can alter protection system [1]. The capacitance of the filter enlarges the DC voltage ripples and AC peak current of the rectifier [3]. Moreover, at light load conditions the shunt passive filters also cause problems of voltage regulation [5]. On the other hand SPF found to be suitable for voltage fed type of harmonic producing loads; it blocks the flow of current harmonics towards source side by providing high impedance path at specific harmonic frequencies. Since the harmonic compensation is virtually independent of line impedance, the series filters effectively block the harmonic flow into the source. The application of these filters also reduces the current ripple on the DC side [7]. The SPF suffers heavily from poor power factor throughout its range of operation and poor voltage regulation at point of common coupling (PCC) [4]. Besides, due to finite inductive reactance and resistance of the coil, there exists a finite small voltage drop across them both at fundamental frequencies and large drop at harmonic frequencies.