International Conference on Intelligent Systems Research and Mechatronics Engineering (ISRME 2015)

Transcription

1 International Conference on Intelligent Systems Research and Mechatronics Engineering (ISRME 2015) An Improved Control Strategy for Fll-controlled Single-phase H Bridge Rectifier Qi Sheng-long 1, a, X Cheng-cheng 2, b, Zhang Chang-ha 1,b Jiang Chen 1, b 1 School of Energy Science and Engineering, University of Electronic Science and Technology of China, Chengd, , China 2 Electronic Experiment Center, Chengd University of Information Technology, Cheng D , China a qsl_estc@126.com, b chenjiang_2014@163.com Keywords: Single-phase Rectifier; PLL; PR Controller; Power Factor; Voltage Ripple Abstract. In this paper, an improved single-phase H bridge rectifier controller with high power factor, and low DC ripple is presented. After introdction the working principle and electrical circit topology of single-phase rectifier with the H bridge, the design method of its essential parts of controller, phase locked loop (PLL) and proportional resonant (PR) control strategy, is discssed. These two parts play important role to achieve extremely high power factor and low DC ripple. And via Matlab/Simlink simlation, this conclsion is showed. At the last part of this paper, the physical experiment was carried ot on a 10kV rectifier and the reslt proved the effectiveness of the presented controller. Introdction Direct crrent (DC) devices are widely sed in or daily life and indstrial applications. Bt ntil now, the already sed power grid only spplies electrical energy in the form of alternative crrent (AC). Ths rectifiers which have the fnction to convert AC power to DC power are becoming an essential link between the AC power grid and DC energy consming devices. There are many ways to realize this conversion. Maybe the simplest one is non-controlled rectifier bridge which is jst directly constitted by several electrical diodes [1]. Althogh DC power is spplied bt its power factor and power qality seems too low to satisfy the electrical energy integration reqirements of power grid [2]. Althogh some effective soltions were proposed, jst like PFC in [3], bt generally speaking fll-controlled rectifiers perform mch better on the aspects of a higher power factor and less DC ripple. At the same time, with advanced digital controller technology, it s also easier to reglate flexibly magnitde of the DC voltage with a fast speed. This benefits the operation of DC energy consming devices. Bt it s a pity that most crrent researches focs on the three-phase sitations and less attentions is paid on single-phase rectifier [4]. In this paper, an improved controller for single-phase rectifier was presented. Firstly the typical topology of single-phase rectifier is introdced. Then the PLL and PR control strategy are discssed. Thirdly with simlation method, the proposed method is proved by Simlink. The last part of this paper, a physical experiment of 10kW rectifier is showed and effectiveness of control strategy is proved. Fll-controlled Single-phase H Bridge Rectifier The typical topology of fll-controlled single-phase H bridge rectifier is shown in Fig.1. L s is indctance on the AC inpt side and is sed to filter ot harmonics and store energy temporarily. R s is impedance of the filter indctor. S i (i = 1,2,3,4) represent IGBT and VD i (i = 1,2,3,4) mean parallel connected freewheeling diodes. Filter capacitor C at the otpt side will benefit to redce voltage ripple and accelerate transient process. Load Z connected after the C. It shold be noted that this fll-controlled single-phase bridge rectifier works in a way jst the The athors - Pblished by Atlantis Press 996

2 same as a BOOST circit. S i alternately trn on and off, ths the energy stored in indctor is discharged and then charged again. Thereby the otpt voltage is pmped times higher than s [5]. Phase Locked Loop Fig.1. The typical topology of single-phase H bridge rectifier In order to make the phase of inpt AC crrent absoltely keep the same as the AC voltage, which means high power factor obtained, the high precision phase measrement method is very important. One method is called phase locked loop (PLL) which widely sed in three-phase system. Assming that there lie three-phase symmetrical signals, and phase angle difference between each other is±2π/3 and phase a is taken as the reference, ths three signals are expressed as follows: 2 2 a Umcos t; b Umcos t ; c Umcos t (1) 3 3 Throgh dq transformation, the three phase voltage a, b and c cold be converted to d and q, which are the d-axis component and q-axis component respectively. This can be explained by formla: a a a 1 1/2 1/2 d cos sin 2 M b = b b M1 M 2 q sin cos 3 0 3/2 3/2 (2) c c c M represents the matrix sed to transform and θ * is the otpt angle of PLL. Make θ=ωt can obtain the following reslts: U cos ; U sin (3) d m q m From the above eqation can be seen that when the phase is completely locked, ie when θ*=θ, then d =U m and q =0. The PLL controller can be designed as Fig.2 shows. The core idea is to control the q vale eqals to 0 and then the otpt angle θ * is the phase of a, b, c. Fig.2. PLL for three-phase Bt for single-phase rectifier, it fails to se above PLL to track the voltage phase becase there only one phase inpt signal. In [6], a method is proposed via constrcting two virtal orthogonal signals and then sing the matrix M 1 to calclate d and q. However orthogonal transformation method wold filter ot the information beyond 314rad/s (if the fndamental anglar velocity is 314rad/s). Therefore, when the inpt voltage has serios harmonic polltion, then the power factor wold not be very high. Actally if constrct symmetrical three-phase signals by shifting the phase of the original signal (similar to the relation between a, b and c ), the controller mentioned above is still valid. And in this way, the information of harmonic voltage is remained. 997

3 Proportional Resonant Controller Proportional resonant (PR) controller has better performance than PI controller when tracking a AC signal. Typical PR controller transfer fnction is: 2K R s Gc s KP (4) 2 2 s Where K P is the proportional coefficient; K R is the resonant coefficient; ω represents the resonance anglar freqency which is eqal to the anglar freqency of the controlled variable. Taking K P =1, K R =25, ω=314rad/s, the Bode diagram of the typical PR controller is drawn in Fig.3 (a). However, it s not easy to make the typical PR controller stable becase of its seriosly narrow bandwidth in natre. In order to alleviate this limitation, a revised PR controller is shown as [7]: 2KR cs Gc s KP (5) 2 2 s 2 cs Taking ω c =10rad/s and other parameters keeping nchanged, the Bode diagram of eqation (5) is shown in Fig. 3. Compare Fig.3 (a) and (b), and find that at resonant freqency ω=314rad/s they both achieves its maximm gain, bt nearby the resonant freqency, the magnitde gain of the revised PR controller performs less sensitive than the former. This will benefit its operating stably. Control Strategy Fig.3. The Bode diagram of the typical PR controller and revised PR controller The Fig.4 is a control framework of a single-phase rectifier. The controller mainly consists of three parts: the PI controller which is sed to control the DC voltage, the PR controller which is sed to control power factor, the PLL which is to track the phase of the inpt voltage. Fig.4. Control strategy of single-phase rectifier U d * is reference of the DC voltage and U d is its corresponding real-time measred vale. I d * is reference signal of inpt AC crrent and i s is its real-time measred vale. I d is the amplitde of I d * and the phase of I d * cold be spplied by PLL. After PR controller filtering and amplifying fnction, 998

4 the difference between I d * and I d generates the modlate wave U r which is sed to control switching of IGBT and realize the energy conversion. Simlation reslts In order to prove effectiveness of the above control strategy, bild simlation model in MATLAB with respect to Fig.1. Make L s =5mH [8], R s =0.1Ω, C=3300F, U d =700V and Z is a 49 ohms, which is a pre resistor. The simlation reslts are as follows: i P Q sinθ* Fig.5. The simlation reslts When the system state became stable, the voltage of the DC side stabilized at arond 700V and the voltage ripple was abot 15V as Fig.5(a) show. On the AC side, the phase of the crrent and voltage is the same absoltely. Hence the power factor is enogh high (as Fig.5(b) show). From Fig.5(c), similar conclsion was made becase active power was nearly abot 10kW and the reactive power was close to 0 var. So in this way, design object to obtain high power factor and less DC ripple is realized. Fig.5(d) is sed to prove tracking phase ability of the PLL. Freqency of inpt AC signal is 50Hz with 45 degree initial phase. It s can be seen that within 0.01 seconds, the crve of the PLL otpt is sccessflly overlapped the inpt signal. This proves the PLL mentioned in Fig.2 has satisfied tracking speed and accracy. Experimental reslts A 10kW prototype was made sing the DSP TMS320F28335 which is widely sed in electronic control. The control program rnning inside the DSP chip was written according to the Fig.4. The hardware is designed referring to the Fig.1. The Fig.6(a) shows that after the initial oscillation and ramp increase (manally adjst to avoid the voltage and power overshoot), the DC voltage stabilizes eventally at 700V. As Fig.6(b) show, voltage ripple of the DC bs is abot 5V when spplies power to a 10kW load. On the AC side the waveform of crrent and voltage is nearly overlapped as Fig.6(c) shows. The power factor is abot 97.5%. Ud (10V/div) (a) (b) (c) Fig.6. The experimental reslts 999

5 Conclsion This paper discssed an improved design method of fll-controlled single-phase H bridge rectifier with high power factor and less DC ripple. PLL and PR controller plays extremely important roles in rectifier operating. Simlation reslts with MATLAB and physical experiment proved the effectiveness of proposed method. References [1] Wang Zhao-an, Hang-jn. Power Electronic Technology [M]. Beijing: China Machine Press, [2] Li Jin-jn, Wang Zhao-an. Harmonic analysis of LC-filtered single phase bridge rectifiers [J]. Power Electronic Technology, [3] Lang Yn-ping. Investigation on Boost-PFC Pereglators and Their Control Strategies [D]. Zhejiang: Zhejiang University, [4] X Jin-bang. Research of Three Phase Voltage Sorce PWM Rectifier Control Technology [D]. Hbei: Hazhong University of Science & Technology, [5] Chen Xin-ming, Lv Hong-shi, Li Go-ha. Analysis and simlation stdy on single-phase H-bridge rectifier/inverter [J]. Electric Drive Atomation, (5) 1-7. [6] W Chn-ha, X F-qiang, Zho Di-qing. F Li. Digital implementation of signal phase PLL [J]. Electric Drive, (6) [7] R. Teodoresc, F. Blaabjerg, M. Liserre, etc. Proportional resonant controllers and filters for grid-connected voltage-sorce converters. IEE Proceedings on Electric Power Applications, (5) [8] Zhang Xing, Yang Xiao-zhi, Li Zheng-zhi. Zhang Chong-wei. Design of indctance for AC line of single phase voltage sorce PWM rectifier [J]. Jornal of HeFei University of Technology, (1)