外文原文Principle, Modeling and Control of DC-DCConvertors for EVZHAN G Cheng-ning , SUN Feng-chun , ZHAN G Wang (School of Vehic le and Transportation Engineering , Beijing Institute of Technology , Beijing 100081)Abstract :DC-DC convertors can convert the EV’s high-voltage DC power supply into the lowvoltage DC power supply. In order to design an excellent convertor one must be guided by theory of automatic control. The principle and the method of design, modeling and control for DC-DC convertors of EV are introduced. The method of the system-response to a unit step-function input and the frequency-response method are applied to researching the convertor’s mat- hematics model and control characteristic. Experiments show that the designed DC-DC convertor’s output voltage precision is high , the antijamming ability is strong and the adjustable performance is fast and smooth.Key words: EV ; DC-DC convertors ; automatic control ; mathematics model ; Bode drawingCLC number : U 469-72 Document code : A Generally there are two power supplies in EV. One is the DC high-voltage power supply that is used by high power devices such as traction motors and air conditioners etc. The other is the DClow-voltage power supply that is usually used in some control circuitand low-voltage electrical devices such as the inst- rument and lighting. It s rating voltage is 24 V or 12 V. The low-voltage power supply can be gained from the high-voltage power supply by aDC-DC conver-tor.In this paper, the main performance of the designed convertor is that the input voltage range is from DC 250 V to DC 450 V , the output voltage is DC 24 V , the maximum output current is DC 20 A , and the output precision is 1 %.1 Principle of the Convertor1.1 The Block Diagram of the DC-DC ConvertorThe block diagram of the DC-DC convertor is showed in Fig. 1. The battery series provide the DC high-voltage input U s. Thelow-voltage output of the con-vertor is U o. The setting value U i of the convertor is equal to or is in proportion to the demanded output voltage U o. The convertor is a closed-loop negative feedback-system with voltage feedback.1.2 Power Switch CircuitThe power switch circuit with semi-bridge mode is showed in Fig. 2. L1 and C1 constitute an input filter to avoid high-frequencyimpulses flowing bac- kwards. Capacitors C2and C3 constitute the partial-voltage circuit while resist-ances R1 and R2do so. IGBT1 and IGBT2 are semiconductor switch devices. C6 is a separation DC capacitor. T1 is a transformer that reduces the voltage. L2 and C7 constitute an output filter. RL is the load resistance. When the PWM signalsin the reverse semi-waves are inputted onto IGBT1 and IGBT2’s control poles , the corresponding DC voltage can be yielded from the convertor.Fig. 2 Principle circuit of power switch with semi-bridge mode 1.3 Control CircuitThe chip SG3525 is used in the PWM control circuit showed in Fig. 3. V cc is the power voltage applied to the chip, it is 12.0 V. A base-voltage of 5.1 V is yielded on pin16 of the chip that is partially used as parameter voltage input U i. The chip includes asawtooth-wave generator. R t and C t are the external resis-tance and capacity that determine the sawtooth-wave’s frequency.Pin2 of the chip is a positive-phase input port. Voltage input U i is putted to the port, here U i =2. 5 V. Pin1 of the chip is the negative-phase input port where the feedback voltage is inputted.Pin9 of the chip is the output end of the inside amplifier of the chip. The proper resistance and capacitor are connected between the pin1 andpin9 to realize compensation of the DC-DC convertor.C8 is the integral capacitor. The integral compensator is adopted as the system-compensation of the system. The PWM impulses are yielded from pin11 and pin14 of the chip. When the PWM control circuit operates normally, U i on the pin2 and U b on the pin1 should be balanced. When U b is not equal to U i , the PWM width can be automatically adjusted by the PWM control circuit to make U b equal to U i. By this way we can control the output voltage of the convertor.Fig. 3 The connection circuit for the PWM control chip SG3525 1.4 Drive CircuitThe drive circuit of IGBT usually adopts a pulse-transformer or an opto-coupler to isolate the power circuit from the control circuit. An individual power supply is needed if an opto-coupler is used, which increases the complexity of the system. So the isolation-circuit adopt s a pulse-transformer showed in Fig. 4. Transistors BG1 and BG2 in Fig. 4 compose a complementation power amplification circuit. T2 is the pulse-transformer that isolates the power circuit from the control circuit. R5 and C8 compose the acceleration circuit. The diode D6eliminates negative impulses. The diode D7 and transistor BG3 compose the rapid discharge circuit of the distributing capacitor at the control pole of IGBT.Fig. 4 Principle circuit for IGBT drive2Modeling and Control2.1 ModelingThe DC-DC convertor is a voltage negative feedback-system. Aiming to obtain the better dynamic and static characteristic we must model and analyse it in theory. According to Ref. [ 1 ] ,DC-DC convertors are the approximate second-order systems. In order to obtain accurate parameters , the method of the system-response to a unit step-function input is adopted in this paper.2.1.1 Measuring the Open-Loop System’s Response to a Unit Step-Function InputThe block diagram for measuring is shown in Fig. 5. The concrete method is described as follows : ①The voltage feedback signal is cut off ; ②The setting value of the chip SG3525 adopts themiddling value U i0 to make the width of an impulse be about 0.5 T ;③U i0 is superimposed with d U i that is composed by positive and negative rectangle wave impulses. The amplitude of d U i is taken to be equal to 0.2U i0. It should make d U o be easy to be observed to select the rectangle wave frequency , adopting f 1 = 400 Hz ; ④The output waveform of U o ( = U o 0 + d U o ) is shown in Fig. 6. As shown in Fig. 6 when f 1 = 400 Hz , period T = 2.5 ms (5 grills) , the time for the maximum voltage value is about 0.2 grills. d U o’s stable voltage amplitude is - grills. Peak overshoot is 1 grill. Every grill in the vertical direction represents 5 V. By this way the data of system-response to a unit step-function input can be obtained as follows :peak time t p = 0.1 ms ; peak overshoot σp = 1/ 2 = 50 %;output and input’s incremental ratio K0 = d U o/ d U i = 10/ 1 = 10.Fig.5 The measuring block diagram of the open-loop systemFig. 6 The system-response to a unit step-function inpu t2.1.2Determining the Open-Loop Transfer FunctionAccording to Ref s. [2,3 ] , we have the damping ratio ξ, undamped natural frequency ωn and transfer function of controlled object G p ( s) as follows :In order to ensure that when the output voltage U o =24 V the feedback voltage to pin1 of the SG3525 is 2.5 V to balance the input voltage U i = 2.5 V, we take the feedback and measuring factor asK b = U b/ U o = -15/ -4 = 01104.( 4 )2.2Design of the PID Regulator2.2.1The Principle Scheme and Transfer Function of the PID RegulatorTo resist the disturbance of the power supply voltage and load current to the DC-DC convertor so as to improve control precision , an integral compensator is adopted. The principle scheme of the integral compensator is shown in Fig. 7.Fig. 7 The principle scheme of the integral compensatorIt s transfer function isG c ( s) = K i/ s = 1/ ( RCs).( 5 )In Fig. 7 and Eq. (5), R = 10 kΩ, C = 0.1μF , K i = 1/ ( RC) = 1/ (10 ×103 ×011 ×10 - 6)= 1 000.2.2.2The Bode Drawing of the System Open-Loop Transfer FunctionThe system open-loop transfer function is the product of the controlled object’s , feedback and measuring circuit’s and integral compensator’s transfer functions. We haveG( s) = G c ( s) G p ( s) G b ( s) =The system Bode drawing is shown in Fig. 8 from Eq. (6). The curves ①and ④are respectively the logarithmic gain-frequency characteristic ,logarithmic phase-frequency characteristic of controlled object G p ( s). The curves ②and ⑤are respectively the logarithmic gain-frequency characteristic , logarithmicphase-frequency characteristic of the feedback and measuring circuit joint the integral compensator. The curves ③and ⑥are respectively the logarithmic gain-frequency characteristic and logarithmic phase-frequency characteristic of the compensatedopen-loop system. By Fig. 8 we know that the system is I-model system. When the input doesn’t change , there isn’t steady-state error. It s original phase-margin frequency ωc = 1 016 rad/ s , phase margin γ= 89.21°, so the adjustable performance of the system is fast and smooth.Fig. 8 The Bode drawing of the system open2loop transfer function 3 The Result and Conclusion of ExperimentWhen the load resistance R L = 1.2Ω, the experiment data of U s , I s , U o , I o , η(ηis efficiency of the convertor) are shown in Tab. 1. When the load resistance R L = 2.4Ω, the experiment data ofU s , I s , U o , I o , ηare shown in Tab.2.4 Conclusions①Because the integral compensator is adopted , the output voltage U o of the convertor has quite high precision even if the input power voltage and the load changes.②The width of the impulses is adjusted automatically in the convertor to realize constant output voltage value. With the increase of the input voltage the width of the impulses turn narrow , the convertor’s efficiency drops. In the process of designing a DC-DC convertor, we must diminish the adjustable range of the impulse width and make the impulse width wider when the convertor operates.③The reasonable value of the resistance and capacitor in the feedback circuit must be selected so that the feedback-system has enough gain margin and phase margin that can guarantee thecontrol-system to be adjusted smoothly.References:[1 ] Cai Xuansan , Gong Shaowen. High-frequency electronics (in Chinese) [ M].Beijing : Science Press , 1994. 232 - 246.[2] Zhang Wang , Wang Shiliu. Automatic control principle (in Chinese)[M]. Beijing: Beijing Institute of Technology Publishing House , 1994. 71 - 72.[3 ] D’Azzo J J. Linear control system analysis and design [M]. San Francisco: McGraw-Hill Book Company,1981. 83 - 92.电动汽车DC-DC电源转换器的原理、建模和控制张承宁, 孙逢春, 张旺(北京理工大学车辆与交通工程学院, 北京100081)摘要：为了设计出在电动汽车上把高压直流电源变换成低压直流电源的高品质DC-DC 变换器,采用自动控制理论进行指导. 介绍电动汽车DC-DC 变换器原理和设计,建模与控制方法. 应用阶跃响应法、频率法研究其数学模型和控制特性,并且进行分析和计算. 实验结果表明,用这种方法所研制的电动汽车DC-DC 变换器输出电压精度高,抗干扰能力强,调节特性快速、平稳.关键词：电动汽车; DC-DC 变换器; 自动控制; 数学模型; Bode 图中图分类号U 469172 文献标识码A通常有两种电源电动汽车。