Electric bicycles are generally powered by lead-acid batteries. They are available in 24V, 36V and 48V specifications, but the electric vehicle's lighting, audio, burglar alarm, mileage speed display, motor controller generally only needs 12V DC voltage, the article introduces one The step-down DC-DC switching power supply based on the chip TL494PWM technology stabilizes the output voltage through closed-loop control, and the system has over-current protection and phase compensation design to make the system work stably.
Electric bicycles are generally powered by lead-acid batteries. They are available in 24V, 36V and 48V specifications, but electric vehicle lighting, audio, burglar alarms, mileage speed display, motor controllers generally only need 12V DC voltage.
The electric vehicle controller is the core control device used to control the start, run, advance and retreat, speed, stop and other electronic devices of the electric vehicle. It is like the brain of an electric vehicle and an important part of an electric vehicle. Electric vehicles currently include electric bicycles, electric two-wheeled motorcycles, electric tricycles, electric three-wheeled motorcycles, electric four-wheeled vehicles, battery vehicles, etc. Electric vehicle controllers also have different performance and characteristics due to different models. .
In the face of exhaust pollution and exhaustion of diesel locomotives, electric vehicles are now gradually entering people's lives. The world's major automobile manufacturers are vigorously developing electric vehicle control technology, and have launched electric vehicles at the recent auto show. The motor controller is the most critical part of the electric vehicle control system, and its development has a profound impact on the popularity and promotion of electric vehicles. The mainstream electric vehicle controller is now mainly composed of power electronics, in which the motor controller directly acts as the heart.
The principle of electric motor controllerIn this paper, the electric vehicle adopts the excitation DC brush motor, and the power battery adopts 6-section lead-acid batteries in series. The rated voltage of each battery is 6V, and the total rated output voltage is 36V. The rated voltage of the shunt DC motor is 36V, the rated power is 3kW, the output rated torque is 10.84Nm, the rated speed is 2600r/min, the excitation current is 10A, and the maximum load current is 110A.
In the design scheme of the controller, the armature control part adopts a two-quadrant DC chopper PWM system, and the excitation control part adopts a bipolar reversible DC chopper PWM system. The controller uses TL494 chip, which has the advantages of simple structure, reliable function, low price and good stability. The TL494 has a built-in 5V ± 5% reference power supply, two error amplifiers, a PWM generation comparator, and an adjustable dead time control.
Two-quadrant DC chopper PWM systemThe schematic diagram of the two-quadrant DC chopper is shown in Figure 1. The half-bridge structure is used. The current Ia flowing through the motor can be positive or negative. The switch S2 only works during braking. The system can work in two quadrants. Although the control scheme can only make the motor work in the first and second quadrants, it has the energy feedback braking function, and the control is convenient, and fewer electronic components are used, which is beneficial to reducing the volume of the controller and the system is reliable. High sex, low cost of the program
The schematic diagram of the bipolar reversible DC chopper is shown in Figure 2. This DC chopper can operate the motor in four quadrants, that is, the armature voltage Va and the current Ia can be either positive or negative.
The control scheme can make the motor run in four quadrants, the circuit and control are not complicated, the micro-vibration current when the motor stops, can eliminate the dead zone of static friction; at low speed, the driving pulse of each power switch tube is still wide, which is beneficial to ensure Reliable conduction of the power switch tube. The current passing through the excitation circuit of the DC motor is not large, and the excitation circuit does not need to be switched frequently. It only needs to work in the first and third quadrants.
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