Design of Vehicle Inverter Power Supply Circuit Based on 87C196MH

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Overview:
The use of subways and high-speed trains brings convenience to people as well as major hidden dangers. Because its window door needs to be in a closed state. If the train stays in the tunnel due to a power failure, the air conditioning and exhaust equipment will stop running, which will seriously affect the safety of passengers. There is an urgent need to invert a battery DC 110 V voltage into a three-phase 230 V/50 Hz AC power supply to power the locomotive power equipment to ensure passenger safety.

1 System structure This design cleverly utilizes the power correction circuit of the Boost structure of the high power factor PWM control chip L4981A to realize the design of the DC boost converter. A design scheme of inverter power supply with 87C19MH as the control core and IPM as the switching device is proposed. The block diagram of the inverter power system is shown in Figure 1. The two-stage structure is adopted. The first stage is a DC/DC converter, the second stage is a DC/AC inverter, and the DC/DC converter converts the 110 V DC voltage into 400. V DC voltage, DC/AC inverter inverts this DC voltage into an AC voltage with an effective value of 230 V and a frequency of 50 Hz to drive the load [1-2]. The system has protection functions such as input over-voltage, output over-current, phase loss, load short-circuit and over-temperature.

2 DC / DC circuit design The first stage of the inverter power supply is DC / DC boost circuit design, using Boost type APFC control, the topology of the boost circuit is shown in Figure 2.

Boost APFC boost control circuit design application integrated control chip L4981A, through the sampling resistor Rs (RS102, RS101) through the 8, 9 two-pin acquisition system input current; DC input voltage (VCCP +) after the current limiting resistor R17, added 4 feet, as the tracking signal to control the input current; the effective value of the input voltage is sent to the multiplier through the 7-pin to adjust the constant total input power; the output voltage (VOUT) is via R27, R28, W3 (adjustable potentiometer) and After R32 is divided, 14 pins are applied to the input of the error amplifier inside the chip. The above four signals are used as reference values ​​for the internal circuit control mode of the L4981A chip, and the double closed loop adjustment is realized by the voltage control loop and the current control loop inside the chip structure. After the collected output voltage signal is compared with the internal reference voltage of the L4981A chip, the error signal is sent to the multiplier through PI adjustment to adjust the output voltage to a stable value. The current error signal is adjusted to generate the PWM pulse signal output. The output end of the L4981A (20 feet) turns the PWM control IGBT tube on and off, and sets the PWM switching frequency through the timing resistor and capacitor of the external oscillator. The output capacitor Ca is filtered to achieve a DC output. The boosted output voltage VOUT is divided by R29, R30, R31 and W4 (adjustable potentiometer) and added to pin 3. When the voltage of this pin is greater than 5.1 V, that is, VOUT exceeds 410 V, L4981A will be realized. Overvoltage protection, the output will be forced to ground to force the power switch tube [3-4].
The input current is applied to pin 2 via R22 to achieve peak current limiting. At the same time, the voltage divider is used to set the undervoltage lock-up turn-on and turn-off threshold of the chip, and the undervoltage lockout control terminal controls whether the undervoltage is undervoltage. When the voltage of pin 15 is lower than 10 V (Q3 is turned on), undervoltage lockout is realized; when the voltage of pin l5 is higher than 15.5 V (Q3 is disconnected), it will start normally, so that the power supply voltage has hysteresis function. The soft start time of the L4981A circuit is determined by the capacitance value of E3.

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