Bi-polarity phase-shifted controlled voltage mode AC/AC converters with high frequency ac link*

Transcription

1 Bi-polarity phase-shifted controlled voltage mode AC/AC converters with high frequency ac link* Daolian Chen and Lei Li College of Automation Engineering, Nanjing University of Aeronautics & Astronautics Nanjing, Jiangsu, P. R. China Abstract- A circuit topology family of the voltage mode ACIAC converters with high frequency ac link are proposed. The kind of circuit topologies are constituted of input cycloconverter, high frequency transformer, and output cycloconverter. The bipolarity phase-shifted control strategy and steady principles are deeply investigated. The output characteristics of the converters are given. By using commutation overlap of the output cycloconverter and the polarity selection of the input voltage and the output filtering inductance current, the leakage inductance energy and the output filtering inductance current are naturally commutated, and the surge voltage and the surge current of the cycloconverters are overcome. The converters have the advantages such as simple topology, two-stage power conversions(lfac/hfac/lfac), bi-directional power flow, high frequency electrical isolation, good line current waveform and output voltage waveform, and strong load adapting function. The converters lay key technical foundation on new-type regulated sinusoidal ac power supplies and electronic transformers. The correction and advancement of the converters are well verified by simulation and principle test. technical foundation on new-type regulated sinusoidal ac power supplies and electronic transformers. The steady principles are deeply investigated and the output characteristics curve is obtained. Simulation and principle test are provided to verify the correction and advancement of the converters. 11. CIRCUITOPOLOGY FAMILY AND CONTROL STRATEGY A. Circuit Configuration And Circuit Topology Family As shown in Fig.l(a), the circuit configuration of the proposed converters is constituted of input cycloconverter, high frequency transformer and output cycloconverter. The cycloconverters are made of four-quadrant power switches. Fig. l(b)-(i) show the circuit topology family. I. INTRODUCTION The high frequency link DC/DC converters, the high frequency link AC/DC converters (switching mode rectifiers), and the high-frequency link DC/AC inverters[ 11 have been deeply investigated and well known. However, the research on AC/AC converters are mainly limited to the thyristor phase-controlled cycloconverters[2] and the matrix converters[3] without electrical isolation. So far, only a push-pull full-wave mode AC/AC converter with high frequency electrical isolation was presented[4]. In [4], the simple operational principle and test results are given, but surge voltage and surge current of the cycloconverters are not investigated, and the push pull-full wave mode AC/AC converter is only suit for low input voltage and low output voltage. This paper proposes and deeply investigates a family of the bi-polarity phase-shifted controlled voltage mode AC/AC converters with high frequency ac link, which are based on forward converters. The converters lay key (b) single-forward mode This paper is supported by National Nature Science Foundation of China( ), Nature Science Foundation of Jiangsu Province of China(BK99121), and Aviation Basic Science Foundation of China(02F52027) /03/$ IEEE 677

2 I (c) interleaved-forward mode I. 57 (h) full bridge-full wave mode (i) full bridge-full bridge mode Fig.1. Circuit configuration and circuit topologies family B. Bi-polarity Phase-shified Control Strategv Taking the full bridge-111 wave mode circuit topology shown in Fig.2 as an example, the bi-polarity phase-shifted control strategy is deeply investigated. '5 L,......, 1 ' (e) push pull-full bridge mode._..._._..._... 1 (g) half bridge-full bridge mode Fig.2. Example of the full bridge-full wave mode converter where U,: the input voltage; y: the output voltage; T: the high frequency transformer; un,: the primary voltage of T; UN+N3: the secondary voltages of T; uosh: the voltage stress of uab: the voltage across the output L,C, filter; ili: the input current; i,: the primary current of T; i2,i3: the secondary current of T; i,r: the output filtering inductance current; Li,Ci: the input filters; Ldl,La,Ld3: the leakage inductances of T; It: the loads. Fig.3(a) shows a control block diagram of the control strategy. The principle waveforms are shown in Fig.3@). It should be stated Fig.3@) shows a case that the polarity of ui is the same as that of il, In Fig. 3@),& is the dead-time and t, is the commutation overlap period. 678

3 during to, and the surge voltage of the output cycloconverters is overcome; 2) the surge current of the output cycloconverters during to is overcome by using the polarity selection of ilf; 3) the energy of Ldl and the feedback energy from the loads are naturally released by using the polarity selection of U; STEADY PRINCIPLE AND OUTPUT CHARACTERISTICS A. Steady Principle The switching state circuits during one switching period T, are shown in Fig.4. In order to simplify the analysis, it is assumed that the converter operates steadily in continuous current mode (CCM), and to are ignored, and NZ=N3. Li Li (a) SI(S~'), &:on; S2[SzI), S4: off principle waveforms Fig.3. Principle of the bi-polarity phase-shifted control strategy When the polarity of U, and ilf is positive (the analysis is applied to the case that the polarity of them is negative), S1,(Sl,')and SZa(SZa'), S3, and S4, are altematively driven with nearly 50% duty ratio signals. The period DTJ2 in which both S3, and SI, (S4, and S2,) keep on during one switching period T, is described as follows: DTJ2=Ts( )/(2*180") (1) where D: duty ratio(d=o-1); 8 : phase difference between S3, and Sla(S4, and Sz,) ( 8 =0-180'). As 8 and DTJ2 vary sinusoidally and the voltage uab is bi-polarity SPWM voltage, the control strategy is called bipolarity phase-shifted control strategy. By adjusting 8 and DT,/2, the output voltage U, can be adjusted and kept stable when the input voltage ui or the load varies. By using commutation overlap of the output cycloconverter and the polarity selection of the input voltage and the output filtering inductance current, the bi-polarity phase-shifted control strategy has following advantages: 1) the energy of La, La and ilf are naturally commutated V U (b) SZ(&'), I cit S3: on; SI(SI'), Sq : off N3 y q R L l a o 679

4 where r is the equivalent resistance including the equivalent resistance of the transformer, the on resistance of the power switches and the parasitic resistance of the filtering inductance and so on. I (a) Sl(S,'), S3: on or S2(S2'), S4: S2(Sz1), Sn: on or S,(S,'), Fig.5. Two equivalent circuits in steady state and CCM mode B, Output Characteristics S4: on As the switching frequency F, is sufficiently higher than both the cut-off frequency of the LfCf filter and the modulation frequency (the frequency of ui and U, in the ACJAC converters), the state-space averaging method can be used to establish the equations of ilt U, and ui. The state equation of the equivalent circuit shown in fig.5(a) is: U,N2 (20-1) U,= N, Similarly using the state-space averaging method, output characteristic in ideal state (A) and critically continuous current mode is: Io=4IommD(I-D) (6) Output characteristic in ideal state (r-0) and discrete current mode (DCM) is: -_ U0-4D2-10 JI", - U; 40' +I, II,,, NI In (6) and (7), Lis the load current, and I, N2 (7) is the maximum value of I,. From (4.b), (S), (6) and (7), normalized output characteristics are derived as shown in Fig.6. In Fig.6, curve A is determined by (6). The solid line and the dashed line in the right of curve A are determined by (5) and (4.b) respectively. From the dashed line, the statement is that with I, increasing, U, decreases. The curve in the left of curve A is determined by (7). From it, output characteristic of DCM is related not only with D, but also with I, D= 1 Io Iomax The state equation of the equivalent circuit shown in Fig.S(b) is: (3.4 Fig.6. Normalized output Characteristics Iv. SIMULATION AND PRINCIPLE TEST By averaging equation (2) and (3) and letting dilddt=o, dujdt=o, then the steady-state value ILf and U, during one T, are: U;(2D-1)N2 1 IL,= Nl RL + r U;(20-1)N2 1 U,= N, l-!-rlrl Equation (4.b) describes output characteristic of the converter in actual state and CCM. From (4), output characteristic in ideal state (1-0) and CCM is: The designed example: the full bridge-full wave mode circuit topology, bi-polarity phase-shifted control strategy, the input voltage Ui= V(5OHz)AC, the output voltage UO=220V(50Hz)AC, the normalized capability S=3kVA, the switching frequency FS=5OkHz, the turn ratio of the transformer N1:N2:N3=14:18:1 8, the input filtering inductance Li=l OuH, the input filtering capacitance Ci=SOuF, the output filtering inductance LeO.SmH, the output filtering capacitance C~20uF, the dead-time h=oaus, the commutation overlap period t.,=0.4us. Fig.7 shows simulation waveforms of the ACIAC converter in steady state under the condition of different 680

5 input voltages and different loads. As shown in Fig.7(a), the transformer operates at high frequency and the voltage U- is bi-polarity SPWM voltage. The waveform of U, is good and the waveform of il, is well sinusoidal. show that the converter has powerful adaptation to different loads and perfect capability of stabilizing voltage. Simulation results agree well with theoretical analyses , , ~ ~ l I.._.. I m 5s =* 15.r zar Zmr 0.I 0 "0 d LLf.,O (d) U,=242V and normalized capacitive load Fig.7. Simulation waveforms of the 3kVA voltage mode AC/AC converter Fig.8 shows principle test waveforms of the AC/AC converter. From Fig.8, the converter has good output waveforms. The transformer operates at high frequency and the voltage uab is bi-polarity SPWM voltage. Principle test results agree well with theoretical analyses. honzontal: Smddiv; vertical: 100V/div(Ch 1) SNdiv(Ch2) (a) output voltage and output filtering inductance current horizontal: Smddiv; vertical: 10 V/div (b) amplified error voltage U, 68 1

6 I. ~...,...,.... ~... ~..... _...,.. q (4)The steady principles and the output characteristics of this kind of AC/AC converters are given. (5)Both simulation and principle test verify the correction and advancement of the AC/AC converters well. REFERENCES honzontal: 5ms/div; vertical: 100V/div (c) voltaee across the Dnmarv windine of the transformer [l]daolian Chen, Yahong Xiong, Research on Aviation Static Inverter with duty cycle extended high frequency pulse dc link, Trans. of China electrotechnical society, Vo1.16, No.5, pp.35-39,2001. [Z]B.R.Pelley, Thyristor phase-controlled converters and cycloconverters, New York Willey, [3]Charles L.Neft, Colin DSchauder, Theory and design of a 30-hp matrix converter. IEEE Trans. On IA, Vo1.28, No.3, pp , [4]Koosuke Harada, Fumimasa Anan, Kiyomi Yamasaki, Intelligent transformer, IEEE PESC 96, pp ,1996. horizontal: 2mddiv; vertical: loov/div (d) voltage across the output filter uab Fig.8. Principle test waveforms V. CONCLUSION From the discussion presented in this paper, the following conclusions are obtained. (1) A new concept of the voltage mode AC/AC converters with high frequency ac link is proposed. The circuit configuration of the AC/AC converters is constituted of input cycloconverter, high frequency transformer and output cycloconverter. The circuit topology family includes eight circuit topologies, such as single forward mode, interleaved forward mode, push pull-full wave mode, push pull-full bridge mode, half bridge-full wave mode, half bridge-full bridge mode, full bridge-full wave mode, and full bridge-full bridge mode. (2)This kind of AC/AC converters have the advantages such as simple topology, two-stage power conversions, bidirectional power flow, high frequency electrical isolation, good line current waveform and output voltage waveform, and strong regulated voltage ability and load ability. (3)The surge voltage and the surge current of the cycloconverters are overcome by using the bi-polarity phaseshifted control strategy with commutation overlap of the output cycloconverter, the polarity selection of the input voltage and the output filtering inductance current. 682