At present, most of the discussion on the key components of electric vehicles mainly focuses on the discussion of power batteries, but there are few discussions on the electronic control of motors. The reason is that on the one hand, regarding the development of power battery technology, new technologies and new hot spots appear from time to time, and it is easy to attract the attention of the media and readers. In terms of motor electronic control, new technologies and new hotspots are rare. Second, in the field of motor electronic control, especially in the field of electronic control, domestic suppliers are still at a relatively preliminary stage, and the products developed cannot reach the international level. Leading level, which also greatly limits the concern of consumers for motor electronic control technology. In view of the limited space, the author only makes a brief introduction to the basic knowledge of motor electronic control, I hope to help everyone.
Motor technology analysis
The so-called motor, as its name suggests, is a kind of power component that converts electrical energy and mechanical energy into each other. When electrical energy is converted into mechanical energy, the electric motor exhibits the operating characteristics of the electric motor; when electrical energy is converted into mechanical energy, the electric motor exhibits the operating characteristics of the electric generator. Most electric vehicles in the state of brake braking, mechanical energy will be converted into electrical energy, through the generator to feed back the battery.
The motor is mainly composed of rotor, stator winding, speed sensor, housing, cooling and other components. In the field of new energy vehicles, permanent magnet synchronous motors are widely used. The so-called permanent magnet refers to the addition of permanent magnets when manufacturing the rotor of the motor, so that the performance of the motor is further improved. The so-called synchronization means that the rotational speed of the rotor is always consistent with the current frequency of the stator winding. Therefore, by controlling the input current frequency of the stator winding of the motor, the vehicle speed of the electric vehicle will eventually be controlled. How to adjust the current frequency is the problem to be solved in the electronic control part.
Compared with other types of motors, the biggest advantage of permanent magnet synchronous motors is that they have higher power density and torque density. To put it bluntly, compared with other types of motors, permanent magnet synchronous motors are of the same mass and volume. It can provide maximum power output and acceleration for new energy vehicles. This is also the reason why the permanent magnet synchronous motor is the first choice for the majority of auto manufacturers in the new energy auto industry, which has extremely high requirements on space and self-weight.
In addition to permanent magnet synchronous motors, asynchronous motors have also received extensive attention due to the use of Tesla. Compared to synchronous motors, the rotational speed of the rotor of the motor is always less than the rotational speed of the rotating magnetic field (generated by the stator winding current). Therefore, the rotor appears to be "inconsistent" with the current frequency of the stator winding, which is why it is called an asynchronous motor.
Compared with permanent magnet synchronous motors, asynchronous motors have the advantages of low cost and simple process; of course, the disadvantage is that their power density and torque density are lower than those of permanent magnet synchronous motors. Why does Tesla ModelS use asynchronous motors instead of permanent magnet synchronous motors? In addition to the main reason for controlling costs, it is also important that larger ModelS bodies have enough space to place relatively large asynchronous motors. factor.
In addition to synchronous and asynchronous motors, hub motors are also a hot spot for new energy automotive applications. The biggest feature of the hub motor is that the vehicle's power unit, transmission and brakes are integrated into the hub. Compared with the traditional power unit, the advantages of the hub motor are obvious. Due to the large number of transmission components, the vehicle structure is relatively simple. Of course, in the synchronous control of the motor, the wading seal, etc., there are still many problems in the hub motor. solve.
Electronic control technology analysis
The electronic control unit is equivalent to the ECU of a conventional automobile, and is the main execution unit for controlling the high-voltage components on the electric vehicle. In addition to motor control, the control of related components such as the car charger, DC-DC unit, etc., is also realized by the electronic control unit.
The core of the electronic control unit is the control of the drive motor. The power unit provider - the power battery provides direct current, and the drive motor requires three alternating current. Therefore, what the electronic control unit is to achieve is a process called inverter in power electronics technology, that is, converting the direct current of the power battery end into the alternating current of the input side of the motor.
In order to realize the inverter process, the electronic control unit needs DC bus capacitors, IGBT and other components to work together. After the current is output from the power battery terminal, the DC bus capacitor is first used to eliminate the harmonic component. After that, by controlling the switch of the IGBT and the cooperation of other control units, the DC power is finally inverted into AC power, and finally used as a power motor. Input Current. As described above, by controlling the frequency of the three input currents of the power motor and the feedback value of the speed sensor and the temperature sensor on the power motor, the electronic control unit finally realizes the control of the motor.
In addition to the control of the motor, the electronic control unit is also the main control mechanism of the components such as the car charger and the DC-DC unit. Charging is just the opposite of motor control. It is necessary to convert the AC power provided by the grid into the DC power of the power battery, which is called the rectification process in power electronics. The DC-DC unit is a process of charging a 12V battery through a power battery. The electronic control unit needs to convert the high voltage of the power battery end into a low voltage end of the 12V battery to finally realize charging for the new energy vehicle.
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