Motor controllers for electric vehicles have developed so fast in recent years that it is unimaginable that the operation is becoming more and more “fool”, and the Display is more and more complicated. For example, the speed control of electric vehicles has been developed to “cruise lock”; in terms of driving, some have both electric performance and power assist functions. By stepping on the pedals, assist can be performed or the amount of assist can be determined. This issue of this issue begins to tell you the knowledge of the controller, so that you have a more comprehensive understanding of the controller.
1. Electric vehicle controller and protection function
(1) Introduction to the controller
Briefly speaking, the controller is composed of peripheral devices and the main chip (or single-chip microcomputer). Peripheral devices are some functional devices, such as execution, sampling, etc. They are resistors, sensors, bridge switch circuits, and devices that assist single-chip microcomputers or application-specific integrated circuits to complete the control process; single-chip microcomputers are also called microcontrollers. A memory, a decoder with a signal language conversion, a sawtooth wave generator and a pulse width modulation function circuit, and the power tube of the switching circuit can be turned on or off, and the conduction time of the power tube can be controlled by a square wave to control the motor speed. The drive circuit, input and output ports, etc. are integrated together to form a computer chip. This is the smart controller for electric bikes. It is a high-tech product in the form of a “fool”.
The design quality and characteristics of the controller, the function of the microprocessor used, the circuit of the power switch device and the layout of peripheral devices, etc., are directly related to the performance and operating status of the vehicle, and also affect the performance and efficiency of the controller itself. Controllers of different quality, used in the same vehicle and equipped with the same set of batteries in the same charge and discharge state, sometimes show great differences in driving ability.
(2) The type of controller
At present, the controller circuit principle used by electric bicycles is basically the same or similar.
Most of the brushed and brushless DC motors of electric vehicles use the PWM control method of pulse width modulation for speed regulation, but the difference in the selection of driving circuits, integrated circuits, switching circuit power transistors and some related functions. Differences in components and circuits make up the difference in controller performance. The controller is divided into two types in structure, we call it separate type and integral type.
1. Separation The so-called separation refers to the separation of the main body of the controller and the Display part (Figure 4-22, Figure 4-23). The latter is installed on the handlebar, and the main body of the controller is hidden in the body box or the electric box, and is not exposed outside. In this way, the connection distance between the controller, the power supply and the motor is shortened, and the appearance of the vehicle body is simple.
2. One-piece control part and display part are integrated into one, and they are housed in a delicate special plastic box. The box is installed in the middle of the handlebar, and the panel of the box has a number of small holes with a diameter of 4~5mm, and a transparent waterproof membrane is applied outside. There are light-emitting diodes at the corresponding positions in the holes to indicate vehicle speed, power supply and remaining battery power.
(3) Protection function of the controller
The protection function is the protection measures taken by the circuit according to the feedback signal when the commutation power tube in the controller and the power supply are not over-discharged, and when the motor is running, the damage that may be caused by a certain fault or misoperation occurs. . The basic protection functions and extended functions of electric bicycles are as follows:
1. Brake power off The two caliper brake handlebars on the electric bicycle handlebar are equipped with contact switches. When braking, the switch is pushed to close or open, and the original switch state is changed. This change forms a signal and transmits it to the control circuit, and the circuit issues an instruction according to the preset program to immediately cut off the base drive current, so that the power is cut off and the power supply is stopped. Therefore, both the power tube itself and the motor are protected, and the waste of power supply is also prevented.
2. Under-voltage protection This refers to the voltage of the power supply. In the final stage of discharge, under the load state, the power supply voltage is close to the “discharge termination voltage”, and the controller panel (or the instrument display panel) will indicate that the power is insufficient, attracting the attention of the rider and planning their own trip. When the power supply voltage has reached the end of discharge, the voltage sampling resistor will feed the shunt information into the comparator, and the protection circuit will issue an instruction according to the preset program to cut off the current to protect the Electronic device and power supply.
3. Overcurrent protection Excessive current may cause damage to a series of components of the motor and circuit, or even burn it, which should be absolutely avoided. In the control circuit, the protection function of this overcurrent must be provided, and the current will be cut off after a certain delay when the overcurrent occurs.
4. Overload protection Overload protection and overcurrent protection are the same, overload overload will inevitably cause current overload. The load capacity of electric bicycles is specially indicated on the manual, but some cyclists either do not pay attention to this, or deliberately overload with the mentality of trying it out. If there is no such protection function, it will not necessarily cause damage in any link, but the switch power tube will bear the brunt. As long as one power tube of the brushless controller is burned, the motor will become powerless after it becomes a two-phase power supply. Immediately, you can feel the abnormal pulsation; if you continue to ride, the second and third power tubes will be burned. If the two-phase power tube does not work, the motor will stop running, and the brushed motor will lose its control function. Therefore, overcurrent caused by overload is dangerous. However, as long as there is overcurrent protection, the circuit will automatically cut off the power supply after the load exceeds the limit, and a series of consequences caused by overloading can be avoided.
5. Under-speed protection still belongs to the category of over-current protection. It is set for the brushless control system that does not have the 0-speed starting function.
6. Speed limit protection is a unique design control program for power-assisted electric bicycles. When the vehicle speed exceeds a certain predetermined value, the circuit stops power supply and does not assist. For electric electric bicycles, the vehicle speed is uniformly specified as 20km/h. When the vehicle motor is designed, the rated speed has been set, and the control circuit has also been set. Electric bicycles can only run at a speed not exceeding this speed.
The location of the controller does not affect performance, it depends on the designer’s intent.
But there are a few principles:
(1) When operating operations allow;
(2) When the overall arrangement allows;
(3) When the line layout is required;
(4) When required by supporting facilities