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Energy-saving AC drive system in electric vehicle application

Print View , by: iSee ,Total views: 46 ,Word Count: 2254 ,Date: Wed, 26 Aug 2009 Time: 10:03 PM

In electric car, the batteries and electric drive systems are two critical, and their level of technology to a large extent determines the main performance of electric vehicles. Unlike most industrial and home electric drive systems, electric vehicle, whether it is the manner in which the supply of electricity, the energy is limited, so to meet the particularity of electric vehicles, the new electric drive system in the motor and power conversion installations should meet the following basic requirements: ① high efficiency; ② small size and light weight; ③ high starting torque multiplier; ④ good speed performance and controllability; ⑤ reliability must be high, life must be as long as possible, Low maintenance or even no maintenance; ⑥ reduce noise and reduce vibration and improve comfort.

At present, China Electric Vehicle DC motor drive system is still driven mainly commonly used from the battery to the power converter and then to drive the motor-way energy transfer method, which there is much to be desired. In particular, although the DC motor has a simple structure, good controllability, speed range is wide, a larger starting torque multiplier, the control circuit is relatively simple and low cost advantages, but its disadvantages also not be ignored. Brush DC motor due to the existence of mechanical components for the brushes or commutator, it is easily lead to sparks, noise and vibration serious, prominent problem of electromagnetic interference, and the brush or commutator maintenance more difficult, short life, In addition, the motor size is very large, resulting in a waste of limited space; brushless DC motor brush motor while overcoming some of the flaws, but it is difficult for the rotor position detection, machine price is high, price is relatively low. And then from a system efficiency point of view, since the majority of systems use a one-way power transmission, making the vehicles braking deceleration or downhill slide when a lot of wasted energy. In addition, the brushes, commutator such as mechanical shock, friction, also caused reduced efficiency of the system. Therefore, this paper, the above problems, combined with the basic requirements for electric drive system is proposed a new type of ZCZVS Boost DC-DC bidirectional converter and inverter combination to drive the squirrel cage induction motor energy-saving AC drive electric vehicles .

System design requirements and overall design

The system mainly as electric motorcycles and other light electric vehicles driven devices, the basic technical parameters are as follows: Input voltage DC 36V; DC converter output voltage Vo of DC 150V; drive motor capacity of not more than 300W; to achieve deceleration, brake Energy can be feedback function; to achieve acceleration and deceleration adjustable soft-start function; with overcurrent, overvoltage, undervoltage protection features.

Energy-saving AC drive system for electric vehicles basic components shown in Figure 1, which includes the battery V5, ZCZVS step-up DC-DC converters, three-phase bridge inverter circuit, AC induction motor and the corresponding control, detection unit. High-frequency inductance L and the electronic switches Su pose a step-up DC-DC converters, the grounds of S1 ~ S6 composition VVVF inverter to provide input voltage, capacitance Csu the buffer capacitor, anti-parallel diodes in the energy feedback Dsu mode under the freewheeling; Sd for the energy feedback control switch used to control the flow of energy and size of the buffer capacitor capacitance Csd, anti-parallel diodes Dsd can run in electric mode for freewheeling. When a vehicle is sliding downhill braking deceleration or when the AC motor will definitely greater than the back-end inverter rated input voltage in the power generation state, then the detection unit moves, it had blockaded the boost circuit of electronic switches Su, at the same time open the energy feedback switch Sd, the system energy is fed back to the supply side. Three-phase bridge inverter circuit working in VVVF mode, when the vehicle needs to be carried out according to accelerate and decelerate regulation, just the speed of adjustment in a given instruction, the change in frequency control circuit controls the speed of adjustment can be realized. In addition, in order to squirrel cage induction motors for driving motor, from the structure to overcome the shortcomings of the DC motor, reduced maintenance, increased overall system capacity and speed, has greatly improved the reliability and efficiency.

Energy-saving AC drive system in electric vehicle application

Figure 1 Energy-saving AC drive electric vehicles

The main unit of Circuit Design

A switch control circuit Su

Upon request, the control chip must have a soft start, overcurrent, undervoltage protection function, the system selected Motorola Inc. UC3842A, it is a complete feedback voltage comparator, error amplification, over-current protection, under voltage protection function current track-type PWM control IC.

Su switch control circuit shown in Figure 2. Its operating characteristics are: ① the maximum supply voltage Vcc = 30V, a 36V internal regulator tubes can effectively prevent the damage caused by high-pressure fleeing into; ② under-voltage lockout turn-on voltage threshold is 16V, off voltage of 10V, 6V start to close the margin to be effective in preventing the threshold voltage of the circuit generated when working near the oscillation; ③ comes with a stable 5V reference voltage from the pin 8 output for external use, the output current of 20mA; ④ Output HIGH to 13.5V (Vcc = 15V, output current 200mA pm), low level of 1.5V (when the input current of 200mA); ⑤ high, low rise, fall time of 100ns, current sampling signal (from pin 3 input) is greater than 1V, the PWM latch to flip the output pin 6 immediately dropped to low from high, therefore, to change the size of the current sampling resistor, you can change the over-current protection threshold of action . ⑥ current tracking characteristics: Figure 2 mid-stream off switch Su current increases, the sampling resistor R21 on the sample voltage increases, the signal into the corresponding 3-pin UC3842A larger, this time through the regulation of the internal circuitry 3842A regulation, Pin 6 output pulse duty cycle of the corresponding smaller, makes the DC-DC converter output voltage is reduced, the current flowing through the corresponding Su is also on the smaller, play-current protection.

Energy-saving AC drive system in electric vehicle application

Figure 2 switch control circuits Su

2 switch control circuit Sd

In the energy feedback, the switch Sd is in working condition, in order to ensure adequate feedback system energy, while avoiding the switch Sd a long time to bear a large feedback currents, using 555 constitute a frequency of 20kHz the "multi-harmonic oscillator + high-frequency pulse transformer "to drive Sd.

Figure 3 for the "multi-harmonic oscillator + frequency pulse transformer," consisting of drive circuit, of which 555 constituted by the multi-harmonic oscillator operating frequency f = 1.43 / (R18 +2 R22) / C19. In the circuit, the detection and interlock circuit controls the 555 Manifold pin 4. When the pin 4 is high, the detection circuit detects that the system should enter the energy feedback state, began to Sd multivibrator output switching pulse; when the pin 4 is low, the system is running under the electric, multi-harmonic Sd not to switch the oscillator output pulse.

Energy-saving AC drive system in electric vehicle application

Figure 3 switch control circuit Sd

3 Detection and Interlock Circuit

In this system, detection and interlock circuit is exceptionally important role. First of all, it detects the DC-DC converter output voltage of the size, to determine whether a circuit mode of transfer of energy from the electric running back the state or the state into electrical energy feedback from the running state; Second, it need to test and to judge the results of the corresponding switch to control electric operation and energy feedback switch drive circuit. Figure 4 for the detection and interlock circuit, which works as follows: First, according to DC-DC converters work properly when the size of the output voltage, set the comparator reference voltage pin 2 and the resistor divider to detect the DC - DC converter output voltage. When the system is going downhill deceleration or braking, the electric motor in the power generation state, then the machine-side back-EMF is greater than the DC-DC converter output voltage, which is detected by comparison of resistive voltage divider is greater than a given reference voltage, making the comparator flip, pin 1 the output is high, forcing the transistor Q1 turns on and will switch gate signals Su pull-down to low; In addition, the same as provided to the UC3842A divider Pin 2's voltage exceeds the reference voltage within a chip the size of it immediately off UC3842A outward pulse output. Both very safe way blocked switch Su. At the same time, comparison of high pin a pin into the multivibrator 4, opening a multi-harmonic oscillator circuit, so that the whole system into the energy feedback state.

Energy-saving AC drive system in electric vehicle application

Figure 4 Detection and Interlock Control Circuit

4 Main circuit Intelligent Power Module IPM

In this system, three-phase inverter circuit has a very important role, not only for the squirrel-cage induction motor to provide power supply voltage, but also the motor frequency control. In the past, the inverter circuit mainly uses six separate IGBT modules to build, the need for each IGBT module to provide a driving circuit, overheat protection circuit, overcurrent protection circuit, they want to and the main circuit overvoltage, short circuit protection circuit and IGBT modules to match, making the design of variable frequency inverter circuit has a very difficult. However, with the Intelligent Power Module (IPM) the emergence of this situation has been a huge change, especially in recent years, IPM are being gradually replaced by ordinary IGBT modules.

IPM module is based on IGBT chips as the main body, the chip and the gate drive, control, and overcurrent, overvoltage, overheating, short circuit, undervoltage lockout protection and fault detection and other integrated circuits in one high-performance high-power devices, has a compact structure, smaller, stable performance, reliable, affordable and so on. Therefore, the combination of electric vehicle drive the basic requirements, the system select the Mitsubishi company PS21255-E of IPM modules for inverter circuit.

In PS21255-E module, the bridge arm 3 of the drain pipe at the same point, that point through a small current sense resistor connected to the system ground can be directly used systematically as a reference point of the +15 V power supply to drive control, but the bridge arm 3 of the drain pipe is not in place, through an external circuit, the next bridge arm tube turn, the next bridge arm of the +15 V drive power at the same time to an external capacitor charging, disconnect the moment arm bridge , capacitance at both ends to keep +15 V voltage drop, and its low potential coincided with the end of the bridge arm IGBT drain pipe connected to, and therefore realized the bridge arm IGBT gate voltage than the drain pipe a high bootstrap function, it is to achieve a good drive on the bridge arm tubes.

5 system, acceleration and deceleration

Energy-saving AC drive system in electric vehicle application

Figure 5 acceleration and deceleration control logic flow chart

The system uses SA866AE/AM chip VMON and IMON two pins for acceleration and deceleration control, control flow in Figure 5. ① If the VMON valid (ie VMON ≥ 0.5VDD), then the acceleration and deceleration command is invalid, the condition has the highest priority, which helps prevent excessive deceleration of renewable energy through the power tube which led to over-voltage. Usually VMON <0.5VDD when the acceleration and deceleration can be adjusted. ② If the IMON effective, regardless of UP, DOWN at what state, the instantaneous frequency will be reduced to a pre-set deceleration frequency level, if the instantaneous frequency down to 0, IMON ≥ VDD, then the PWM pulse output cut-off, this time can not be operation of any acceleration and deceleration. The conditions of lower priority than VMON, it can lead to over-current to prevent overheating in high speed switch is damaged. ③ When these both fail, algorithms will combine the output of the comparator logic, DIR pin control, and counter signals, together with the speed control to draw final.

6 SA866AE/AM with the EEPROM parameter settings

SA866AE/AM three-wire serial interface with 256-bit or 1024 bits serial EEPROM connection, such as the 93C06 or 93C46. All the parameters are stored in EEPROM, the serial interface automatically reset after the download. The system parameters to be used 93LC46 storage, and SA866AE/AM interface shown in Figure 6.

Energy-saving AC drive system in electric vehicle application

Figure 6 SA866AE/AM and EEPROM Structure

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