【正文】 on of inductive and capacitive reactance. This resonance point is limited in magnitude only by the amount of resistance in the circuit, and is often many times the value of the inductive impedance at that frequency. The more capacitance added to the circuit, the lower the frequency at which this resonance point occurs. This highimpedance point, coupled with the operation of harmonicproducing loads, can result in much higher levels of voltage distortion than the circuit without capacitors. That’s why it is so important to closely evaluate the addition of power factor correction capacitors on a power circuit serving harmonic loads. The example estimate below shows the distortion estimate associated with the same 103 ampere, 23% THD load shown earlier, except that the impedance at the 7th harmonic is assumed to be ten times its nonPFC value (a resonance point at or near 420 Hz). Note that this change results in nearly a tenfold increase in voltage distortion. Harmonics and Power Factor – Displacement and Total As discussed, harmonic distortion and power factor correction are seldom considered as separate topics. This is due to the dramatic effect on system impedance at harmonic frequencies that can result from the addition of conventional power factor correction capacitors. The relationship, unfortunately, does not end there. Due to their nonlinear nature, the presence of harmonic loads can sometimes fool the power engineer into considering unnecessary power factor correction in the first place! Power Factor of a PWM Drive – An Extreme Example? The pulsewidthmodulated (PWM) variablefrequency drive (VFD) produces a characteristic current waveform when energized from a sinusoidal voltage source. Thisthreephase device produces a voltage and current waveform for one phase that resembles the following graphic: If the power parameters (real, reactive, and apparent) associated with this PWM device are measured with a truerms meter, the typical values would show a relationship of real (kW) to apparent power (kVA) of approximately . The engineer might conclude from this knowledge that the power factor of the device is poor, and that a circuit containing many of these PWM drives (not unmon) would require power factor correction capacitors. Unfortunately, this line of reasoning is incorrect and can lead to disastrous results. While the kW/kVA relationship indicated above is accurate, is not the power factor of the device. At least, it is not the plete picture of the power factor. Further measurements would reveal that the displacement angle between voltage and current for this device is 0. That is, the current and voltage are in phase with each other. Or, more accurately, the fundamental (60Hz) ponent of voltage and the fundamental (60Hz) ponent of current are in phase, as shown below. Since harmonic loads like PWM drives are able to consume power in a nonlinear fashion。無功功率補償畢業(yè)論文中英文資料外文翻譯文獻(xiàn) HARMONIC DISTORTION AND REACTIVE POWER COMPENSATION IN SINGLE PHASE POWER SYSTEMS USING ORTHOGONAL TRANSFORMATION TECHNIQUE W. Hosny(1)and B. Dobrucky(2) (1) University of East London, England (2) University of Zilina, Slovak Republic ABSTRACT This paper reports a novel strategy for analysing a single phase power system feeding a nonlinear load. This strategy is based on a new theory to transform the traditional single phase power system into an equivalent twoaxis orthogonal system. This system is based on plementing the single phase system with a fictitious second phase so that both of the two phases generate an orthogonal power system. This would yield a power system which is analogous to the three phase power system but with the phase shift between successive phases equal to л/2 instead of 2л/3. Application of this novel approach makes it possible to use the plex or Gauss domain analytical method in a similar way to the well known method of instantaneous reactive power for three phase power system instigated by Akagi et al in 1983. Thus, for the fictitious twoaxis phase power system, the concept of instantaneous active and reactive power could be instigated. Moreover, the concept of instantaneous power factor could be defined. The novel strategy of power system analysis outlined in this paper is applied to a single phase power system feeding a nonlinear load in conjunction with an active power filter. The latter serves the purpose of pensating for either of the instantaneous reactive power or the harmonic current distortion in the single phase power system under investigation or for pensating of both. Experimental results demonstrated the effectiveness of the novel single phase power system analysis reported in this paper. Keywords: single phase power systems, orthogonal transformation technique, harmonic distortion and reactive power pensation 1 INTRODUCTION In this section the orthogonal transformation technique applied to a single phase power system instigated by Akagi et al, reference [1], is described. By adopting this technique expressions for the reference currents used in an active power filter for the pensation of harmonic distortion or reactive power or both, are derived. Consider a single phase power system which is defined by its input voltage and input current as follows: vRe(t) = V Cos ωt (1) iRe(t) = I Cos (ωt – Ф) Where V and I respectively are the peak values of the voltage and current, ω is the angular frequency of the power supply and Ф is the phase shift between voltage and current. The power system described by Eq.(1