The control loop is composed of a control power source, a pulse width modulation circuit, a drive circuit, a protection circuit, and the like.
1) The control power supply adopts switching power supply and outputs 15V and 20V DC power supplies. Among them, 15V supplies power to the pulse width modulation circuit of the control part. This way the power supply is not suspended; 20V supplies power to the control part of the drive circuit and the cooling fan. This way is suspended and must be well isolated from the line voltage and cannot be grounded. The switching power supply is only provided for the control circuit. It is not allowed to connect the illumination lamp and the horn on the locomotive. 2) The pulse width modulation circuit is used to generate the pulse signal, and the pulse width can be changed by changing the resistance value of the RW through the speed control handle. The pulse width can be adjusted within the range of 10%~90%, so that the average value of the motor terminal voltage is continuously adjusted within the range of 10%~90%; 3) the driving circuit is used to amplify the pulse signal and drive the IGBT to work; 4) protection The circuit mainly has soft start protection, current limit protection, desaturation protection, over voltage and under voltage protection, and temperature protection. (1) Soft start protection is used to prevent the starting current from being too large to damage the motor. The motor current is sensed by Hall sensor H and sent to the protection circuit to control the pulse width modulation current. If the motor current is too large at startup, the protection circuit controls the pulse width modulation circuit to reduce the pulse width, thereby reducing the voltage and current of the motor. As the speed of the locomotive increases, the current gradually decreases, and the pulse width may gradually increase. In the speed regulation state, no matter how fast the speed control handle is applied, the pulse width will slowly increase beyond the specified value to ensure smooth starting and uniform speed regulation, and achieve soft start; (2) If the motor current instantaneously exceeds the specified value, the current limit The protection circuit turns the pulse width modulator off and then soft-starts itself. This process may occur repeatedly, knowing that the current reaches the specified value; (3) for special reasons, such as motor short circuit, freewheeling diode breakdown, etc., so that the IGBT current is too large, the IGBT is working in saturation state, the desaturation protection circuit will make The drive circuit and pulse width modulator are quickly turned off and the whole machine stops working. If this is the case, you must turn off the power and look for the cause. The fault is not eliminated and cannot be restarted to avoid damage to the IGBT tube. (4) When the line voltage is higher than the specified value or the output voltage of the switching power supply is low, the pulse width modulator will be turned off; (5) If the fan is damaged and the series and parallel are connected The absorption circuit is damaged, so that the temperature of the IGBT heat sink is higher than a certain value (the machine is 75 °C), the temperature relay contact KT is disconnected, the RW is cut off, the pulse width modulation circuit is turned off, and the whole machine stops working.
