Electric motor controller
Release time：2018-3-6 9:36:02 Number of clicks：424
Motor controller, as one of the core components of electric vehicle, is the decisive factor of the automobile power performance. It get the demand of the vehicle from the vehicle controller, electric energy from the power battery pack, after the modulation inverter itself, needs of current and voltage control motor, provided to the motor, make the motor speed and torque of meet the requirements of the vehicle.
The position and function of motor controller in electric vehicle.
From the outside, the general motor controller has at least two high - voltage interfaces. A pair of input interfaces for connecting the power battery pack high voltage interface; The other pair is the high voltage output interface, connected to the motor, providing control power.
At least one low-pressure connector, all communications, sensors, low-voltage power supply and so on will be introduced through this low pressure connector, connected to the vehicle controller and power battery management system.
The diagram below is a typical electrical diagram of a pure electric vehicle, where the blue line is the low-voltage communication line and the red line is the high voltage power line. The second one on the right is the motor controller. The parts that have strong electric connection with the motor controller are the motor and the power battery pack; The motor controller is connected to the vehicle's CAN bus, which CAN communicate with the vehicle controller, digital dashboard, power battery management system, exchange data and receive instructions.
1.2 working process
1.2.1 instructions and responses.
Motor controller, the trigger signal of the speed control instruction, from the command of the vehicle controller. Vehicle controller reflect driver's intentions on the one hand, on the other hand, from safety and vehicle electrical system running status, the assessment on the driver's response is reasonable, and finally executed or discount. The driver's intent is expressed through the accelerator pedal and brake pedal and passed to the vehicle controller.
The vehicle controller gives specific instructions to the motor controller, which is related to the power system in the following categories: acceleration, deceleration, braking, parking. The response of the motor controller is to change the power current, voltage, frequency and other parameters, so that the operation state of the motor meets the needs of the vehicle controller.
The motor controller itself is a set of closed-loop control system, which adjusts the target parameters to check whether the controlled function value reaches the expected value. If it does not match, feedback to the controller and adjust the target parameters again. After repeated closed-loop feedback, high accuracy control is achieved.
The vehicle speed sensor, controller to collect various electrical components important state parameters, such as temperature, voltage, judge the vehicle's comprehensive, is in line with the drivers of demand, at the same time not interfere with the health of the whole system. This process is the closed-loop control of the vehicle level.
1.2.3 improvement direction.
On the one hand, a good control strategy will have an important influence on the control accuracy and response speed, so it is an important field for r&d personnel to invest energy.
On the other hand, with the improvement of the operation capability of each part, the driving experience of electric cars will become more and more "freewheeling".
Basic composition of motor controller.
Motor controller system composition, central control module, power module, drive control module, various sensors.
2.1 central control module.
Including PWM wave generation circuit, reset circuit, sensor signal processing circuit, interactive circuit. The central control module, externally, gets the instruction and status information of other parts on the vehicle through external interface. Internally, the translated instruction is passed to the inverter driver circuit, and the control effect is detected.
2.2 power module
The theme of the motor controller is an inverter, which controls the current voltage of the motor. Frequently selected power devices are MOSFET, GTO, IGBT, etc.
2.3 drive control module.
The instructions of the central control module are converted into the pass-through instruction of the thyristor in the inverter, and as a protective device, it has the monitoring and protection function of overpressure and overcurrent.
2.4 the sensor
The sensor used in the system includes current sensor, voltage sensor, temperature sensor, motor shaft Angle position sensor, etc., which can be added or reduced according to the design requirements.
What should a good motor controller look like?
3.1 characteristics of good motor controller.
The different working principle of the motor directly influences the complexity and precision of the regulation process.
According to control from easy to difficult arrangement, dc brushless motor, permanent magnet synchronous motor, switched reluctance motor, asynchronous motor.
Electronically controlled easily, both the size of the hardware system design, high and low in cost, and also includes the software algorithm of high and low control precision and in order to achieve the accuracy of the strategies and methods used in the stand or fall of robustness.
It is expected that the hardware structure is simple, the software algorithm is simple, the control precision is high, the system stability good control system.
3.2 the motor controller has the national standard.
Electric motor and controller standards, existing national standards:
GB /T 18488.1 -- 2015 "electric motor and its controller part 1: technical conditions";
GB /T 18488.2-2015 "electric motor and its controller part 2: test method".
In the standard, specific requirements are proposed for safety and environmental resistance, such as the insulation resistance performance of various parts and various environmental resistance. And the technical parameter of the motor, as the verification project, as long as the manufacturer's own declaration can be.
Main circuit selection of motor controller.
4.1 selection basis
Motor controller as a specific functions of inverter, using the pressure regulating frequency modulation technology in the power electronic technology, it will be stored in the dc power battery, made into the rectangular wave control motor or are XuanBo alternating current (ac), change of output power of voltage, current amplitude and frequency, and then change the motor speed, torque, and achieve the goal of control of the vehicle speed and acceleration.
Power electronic circuit design, according to different speed regulation needs, to make the complex degree of different, cost also different design.
For example, for dc motor control. If the single tube chopper circuit is adopted, it can only be regulated in one direction and the current cannot be commuted. In the case of dual-tube chopper circuit, energy feedback can be realized, but the dc motor can not be commuted. If H bridge type chopper circuit is adopted, it can be regulated by dc motor and energy feedback, and the excitation current can be reversed.
But the three choices above, one is more complex than the other, and one is more expensive than the other. Designers need to choose between performance and cost, the most expensive is not necessarily the best, the most suitable is good.
5 thermal design
5.1 source of heat
The power module is the main heat source of the whole controller. The MOSFET or IGBT used is the heating element.
The heating of SCR mainly comes from the following parts: conduction loss, switching loss, leakage current and drive loss, and the first two are the big ones.
5.1.1 conduction loss.
Thyristor can be triggered, normal flow state, its own internal resistance generation loss. It is proportional to the time of the flow, the square of the current and the internal resistance.
5.1.2 switching loss.
The opening and closing of silicon controlled silicon is very short, but there is a continuous time. The current and voltage on the device are not transmitted outward, but work on itself. The heat is directly proportional to the voltage of the device, and is proportional to the half of the maximum current in the process of opening and closing, which is directly proportional to the opening and closing time, and is directly proportional to the frequency.
5.1.3 leakage current loss.
When the SCR is off, there is still a small current passing through, and its dissipated energy is called leakage current loss. But this part of the loss is extremely small, generally do hot design, can be ignored.
5.1.4 drive loss.
Thyristor controlled circuit, which provides triggering and maintenance voltage, belongs to the secondary control circuit, and is compared with the strong electric circuit, and there is an order of magnitude difference.
5.2 basic design process of radiator.
5.2.1 determine the heat conduction path.
Introduce a concept first, thermal resistance, the heat transfer between media and media, to the difficulty of the unit is ° C/W. The size of the thermal resistance can affect the heat transfer path and the delivery speed.
Take the above illustration as an example, the heat from the core to the shell, from the shell to the environment is a propagation path; From the core to the shell, from the shell to the radiator is another path. To calculate thermal resistance, the specific path is required.
5.2.2 draw the equivalent heat map.
According to the path planned in the model, the thermal resistance is abstracted, as the resistance is considered, and the equivalent thermal resistance diagram is drawn.
According to the maximum thermal power allowed by the system, the former divided by the latter can obtain the overall thermal resistance of the system.
Find the power thyristor parameter table in the inverter, find the pipe core to the shell, the shell to the environment, the shell to the heat resistance of the radiator. Finally, the heat resistance of the heat transfer path can be reduced by the total thermal resistance, and the heat resistance of the radiator and the environment can be obtained.
5.2.3 radiator selection.
Select the main basis of radiator, except the structure form of radiator, the main parameter is its thermal resistance. Through the previous calculation, the heat resistance of the radiator needed is deduced, and the final selection of heat resistance of the radiator must be less than this calculation value. Theoretically, the system will not overheat. Of course, the system needs a certain amount of residual, can give the radiator thermal resistance to a discount after the selection of radiator standards.
5.3 components layout points.
The controlled silicon in parallel is best placed on the same radiator, so that the temperature of the parallel device is consistent and the grid resistance is consistent. In parallel, the control silicon is too large, and the device with the smallest internal resistance is easy to burn because the current is too large.
6. Manufacturer of motor controller.
At present, the leading technology of motor controller is still in the hands of foreign manufacturers.
Bosch group, continental group, Japan Toyota, nissan, Hitachi, all have their own representative products. The motor controller has been developed in the direction of integration. The highest power density has been increased to 60 kW/L. New power electronic devices such as SiC have been applied in new products.
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