International Renewable Energy Congress November 5-7, 2010 – Sousse, Tunisia
THREE-PHASE PFC RECTIFIER USING A SWITCHING CURRENT INJECTION DEVICE FOR VEHICLE POWER TRAIN APPLICATIONS A. TOUMI1, M. GHARIANI2, I. BEN SALAH3, and R. NEJI4 1
Laboratoire d’Electronique et des Technologies de l’Information e-mail:
[email protected] 2 Association d’Ingénierie ElectroMécanique e-mail:
[email protected] 3 Association d’Ingénierie ElectroMécanique e-mail:
[email protected] 4 Laboratoire d’Electronique et des Technologies de l’Information e-mail:
[email protected]
Abstract -This paper presents PFC (Power Factor Correction) rectifier using harmonic injection with a switching current in the injection device. In this method, a periodic current is injected in the control circuit to vary the duty cycle of the rectifier switch within a line cycle so that the third-order harmonic of the input current is reduced to meet the total harmonic distortion (THD) requirement. The third harmonic current is generated by a tuned LC circuit and three switches are used for the injection device. As a result, the circuit gives a total input harmonic current distortion of 4.2% at a load of approximately 7.7kW. Simulations results (Matlab–Simulink) are used to highlight the effectiveness of this design method. Keywords - Boost converter, discontinuous conduction mode, harmonic injection, power factor correction, three-phase rectifier 1. Introduction In most of power electronics applications, diode rectifiers are commonly used. The rectifiers are nonlinear devices; therefore they generate harmonic currents into the AC power source and cause various problems. The nonlinear operation of the diode rectifiers causes highly distorted input current. The non-sinusoidal shape of the input current drawn by the rectifiers causes a number of problems in the sensitive electronic equipment and in the power distribution network. The distorted input current flowing through the system produces distorted voltages at the input of the common coupling. Thus, the increased harmonic currents result in increasing volt-ampere ratings of the utility equipment, such as
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generators, transmission lines and transformers. In addition to the inefficient use of electric energy, the discontinuous conduction of the bridge rectifier results in a high total harmonic distortion (THD) in the input lines and can lead to malfunctioning of the sensitive electronic equipment. Several methods of power factor correction were proposed [1,5]. Amongst the three-phase ac-to-dc rectifiers, boost type topologies are frequently used because of continuous input currents and high output voltages. Basically, two topologies are most popular: a six-switch full-bridge boost rectifier and a single switch boost rectifier. The first one uses six switches to achieve sinusoidal input current control and to share the output power, resulting in features, which include continuous input current, excellent power factor and low switch current rating. However, this circuit is very complicated in power stage and control, making it too expensive for medium power level (5-10kW) applications. The second one uses six diodes and one switch to control input currents and output power as depicted in figure. 1[3]. Since these rectifiers have a single switch and perform input current wave-shaping naturally, without a need for a complex control circuitry, they are very suitable for the low cost power three-phase ac-dc applications. In addition, they can achieve extremely high efficiencies because the reverse-recovery-related losses of the boost diode are eliminated. In this paper, we present a PFC rectifier using harmonic injection with a switching current in the injection device. It is a cost effective and economical solution to mitigate harmonics generated by power electronic equipment. It consists on the use of three single-phase power factor corrected rectifiers in cascade. The main advantage of this configuration is that a well-known single-phase power factor
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correction (PFC) technique can be used in threephase applications required for high power processing application such as EV.
current i1 (Figure 3). Then the three-phase diode bridge rectifier suffers from relatively high total harmonic distortion (THD) of the input currents; about 29,11% (Figure 4) for the presented circuit in figure 2. We can reduce this distortion using the third harmonic current injection method. The next paragraph represents the general schema of a third harmonic current injection.
Figure 1. Boost-star three-phase single switch PFC. Figure 3. Source current i1.
2. The Three-Phase Rectifier A three-phase full bridge rectifier as shown in figure 2 consists of six diodes. Three of them rectify the positive wave and the last three ones rectify the negative wave.
Figure 4. FFT of the input currents without injection. 2.1. Third harmonic current injection Figure 2. Three-Phase rectifier. The rectifier is supplied by unbalanced undistorted three phase voltage source specified by:
2 v p Vm sin 0t ( p 1) , p 1,2,3 (1) 3 The positive output signal equal to the maximum of input source and described by the equation below: v max( v1 , v2 , v3 ) (2) While the negative output signal equal to the minimum of input source: v min(v1 , v2 , v3 ) (3) Since one phase voltage cannot be the highest and the lowest at the same time for the given set of phase voltages, two of the phases are connected to the load while one phase is unconnected in each point in time. This results in an input current equal to zero in the time interval when the phase voltage is neither maximal nor minimal. The gaps in the phase currents are the main reason for introducing the current injection methods. Moreover three-phase diode bridge rectifier suffers from relatively high total harmonic distortion (THD) in the input currents that can be reduced using the injection method. Carried out simulation results show a discontinuity in source
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The general scheme of harmonic injection method is presented in figure 5. In comparison to the diode bridge rectifier shown in figure 2, with the circuit shown in figure 5 two units was added: a current injection network and a current injection device. The current injection network: it produce an injected
i
i
current ; the frequency of is three time the frequency of the source. In this paper the frequency of current injection is 150 Hz. In the other hand,
i
current injection device divides into three parts; every part will be injected to each of the input source phase.
Figure 5. General scheme of harmonic injection method.
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2.2. Current injection network Various method of the current injection network was presented in bibliography [1,2,4]. The figure 6 represents the current injection network used in this paper. It use two inductances with two capacitors tuned to resonant frequency of 150Hz, the resistance limits the injected current.
iX1 in the first voltage line. By using the injection approach the total harmonic distortion (TDH) is improved. Figure 8.c and figure 8.d show the threephase current, before and after injection. The line current becomes approximately sine wave. The source current present a 4,3% distortion after current injection (Figure 8.e). Figure 8.f and figure 8.g show respectively the DC output current and the DC output voltage. They are the same comparing with the results found in “1”.
(a) Injected current
i
Figure 6. Current injection network. 2.3. Switching current Injection device The switching current injection device is represented in figure 7. It consists of three switches commanded by a logic control. Every switch is turned on when the specified phase are unconnected to the diode bridge; therefore the current in each phase doesn’t present a discontinuity after injection.
(b) Injected current iX1
(c) Line current before injection (iS1) Figure 7. Switching current injection device. 3. Simulation results The block diagram of the control circuit for the converter is shown in figure 5. A three-phase bridge rectifier followed by band-pass filter is used to generate the sixth-order harmonic and a multiplier is used to modify the amplitude of the sixth-order harmonic by the modulation index. The converter has been tested with the following parameters: Input: 3×110V/50Hz, Output: 250V/ 7.7kW Switching frequency: 45kHz Modulation index m: 4.6 Control band width: 200Hz Input inductor: 50µH Output capacitor: 220µF Simulation (MATLAB SIMULINK) results are shown in figure 8. Figure8.a shows the injected current in the switching device
i
(d) Line current after injection (i1)
(e) FFT of the input currents after injection
; and figure 8.b shows the injected current
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[8]
P. Pejovic and Z. Janda, “Optimal Current Programming in Three-Phase High-Power-Factor Rectifier Based on Two Boost Converters”, IEEE Transactions On Power Electronics, Vol. 13, No. 6, November 1998.
(f) DC output current
(g) DC output voltage Figure 8. Simulation results of the presented rectifier. 4. Conclusion In this study, a low cost harmonic injection method for three-phase discontinuous conduction current rectifiers is implemented. The paper presents a PFC rectifier using a switching current in the injection device. By using the injection approach the third order harmonic is reduced, the total harmonic distortion (THD) is improved. The circuit gives a THD of 4.2% at a load of approximately 7.7kW. 5. References [1] J.I. Itoh and I. Ashida, “A Novel Three-Phase PFC rectifier using a harmonic current injection method”, IEEE Transactions On Power Electronics, Vol. 23, No. 2, March 2008. [2] M. Rastogi, R. Naik, and N. Mohan, “Optimization of a novel DC-link current modulated interface with three-phase utility systems to minimize line current harmonics”, IEEE PESC’92, 1992, Vol. 1, pp. 162– 167. [3] S.M. Bashi, N. Mariun, S.B. Noor and H.S. Athab, “Three-Phase single switch power factor correction circuit with harmonic reduction”, Journal of Applied Sciences : 80-84, 2005, ISSN 1607-8926. [4] P. Pejovic, “Two Three-Phase high power factor rectifiers that apply the third harmonic current injection and passive resistance emulation”, IEEE Transactions On Power Electronics, Vol. 15, No. 6, November 2000. [5] S.Chattopadhyay and V. Ramanarayanan, “Digital implementation of a line current shaping algorithm for three-phase high power factor boost rectifier without input voltage sensing”, IEEE APEC, 2001, pp. 592598. [6] P. Pejovic and Z. Janda, “An Analysis of Three-Phase Low-Harmonic Rectifiers Applying the ThirdHarmonic Current Injection”, IEEE Transactions On Power Electronics, Vol. 14, No. 3, May 1999 [7] P. Pejovic and Z. Janda, “Three-Phase Rectifiers that Apply Optimal Current Injection”, IEEE Transactions On Aerospace And Electronic Systems, Vol. 38, No. 1, January 2002.
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