外文原文
Principle, Modeling and Control of DC-DC
Convertors for EV
ZHAN 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 drawing
CLC number : U 469-72 Document code : A Generally there are two power supplies in EV. One is the D
C high-voltage power supply that is used by high power devices such as traction motors and air conditioners etc. The other is the DC
low-voltage power supply that is usually used in some control circuit
and 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 a
DC-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 Convertor
1.1 The Block Diagram of the DC-DC Convertor
The block diagram of the DC-DC convertor is showed in Fig. 1. The battery series provide the DC high-voltage input U s. The中文翻译英文转换器
low-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 Circuit
The power switch circuit with semi-bridge mode is showed in Fig. 2. L1 and C1 constitute an input filter to avoid high-frequency
impulses 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 signals
in 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 Circuit
The 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 a
sawtooth-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 and
pin9 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 Circuit
The 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 D6
eliminates 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 drive
2Modeling and Control
2.1 Modeling
The 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 Input
The 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 the

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