The conventional design of the main drive motor controller includes power circuit design, thermal design, structural design, drive circuit design, control circuit design, motor control algorithm design, vehicle application software design, etc. Among them, power device drive technology, thermal management technology and high-efficiency high-precision control technology are the key technologies to achieve high reliability, high power density and high efficiency.
Power Device Drive Technology Drive circuits for driving, controlling and protecting power semiconductor devices are the core components for the realization of weak power control and strong power, which is of great significance to the operating efficiency, reliability and electromagnetic compatibility of motor controllers. As shown in Figures 1, the slope, spikes, etc. of voltage and current change waveforms during IGBT turn-on and shutdown are affected by the drive circuit, which affects the performance of module loss, safety and electromagnetic interference.
The drive circuit should meet the following requirements: 1) The driving power supply must be stable and reliable, and the isolated power supply is generally used in high-power drives for vehicles. 2) The drive circuit should provide the electrical isolation between the control circuit and the power circuit, generally using optical isolation, magnetic isolation or capacitive isolation. 3) The drive circuit should make the power semiconductor device work in the ideal switching state, shorten the switching time and reduce the switching loss under the condition of ensuring safety. 4) The drive circuit should have the function of power semiconductor device protection and fault output.
5) The driving circuit should have good electromagnetic compatibility and temperature stability.
The following pictures show an example of a drive circuit. After the PWM signal from the control unit is fed into the drive chip and electrically isolated, it is fed into the output amplification circuit via an intermediate transmission circuit and connected to the IGBT gate by the gate drive resistance. To prevent overcurrent and short-circuit failures, protective circuits such as saturated voltage drop detection and Miller clamps are also available.
The characteristics of power semiconductor devices themselves determine that their key indicators such as efficiency, reliability and electromagnetic compatibility cannot be combined. In addition, the non-linear variation of power semiconductor device parameters with temperature, load and so on also makes the design of the drive circuit more difficult. Therefore, the design of the drive circuit needs to combine the characteristics of the device itself, precise control of the turn-on and shutdown process, so that the power semiconductor device is driven at the optimum balance of efficiency, reliability and electromagnetic compatibility.
2. Thermal Management Technology The power of the drive motor system of the car ranges from ten kilowatts to several hundred dry watts, and its main heating component is the power semiconductor device, which needs to be cooled efficiently. In addition, capacitors, power bus and other components of the design also need to consider the management of the problem, so the need from the entire controller level for thermal management design, generally can be designed from three aspects.
1. Prevent thermal damage For the maximum power of the hair hold
Semiconductor devices are designed with an efficient cooling system to avoid overheating of modules. Cooling methods are air-cooled and water-cooled, currently mainly water-cooled. Figures 5-49 show a profile diagram of a single-sided indirect cooling IGBT module. The cooling of power semiconductor components is by means of the module's internal insulation lining and thermal substrate, through the diffuser cooling. Therefore, it is important to reduce the heat sun and improve the radiator capacity. Direct cooling IGBT shown in Figures 5-50a can effectively reduce thermal resistance, while double-sided cooling IGBT shown in Figure 5-50b can reduce thermal resistance by about half. Different cooling schemes supporting the radiator structure is very different, the internal structure layout of the motor controller also has a certain shadow ah, need to be comprehensively considered in the design.
2. Avoid
over-designing the IGBT module with a defined maximum allowable junction temperature (Tjmax is generally 150 degrees C in the switching state and 175 degrees C in the non-switching state), and the thermal design needs to control the module junction temperature below this temperature, but it cannot leave too much room.
3. Further optimization of the thermal management system In addition to unified planning of the temperature zone division and structure of the motor controller, it can also be combined with motor control strategies (e.g., by reducing the switching frequency or power to reduce heat generation appropriately), to achieve efficient thermal management of the motor controller.
4. High-efficiency and high-precision control technology
4.1Electric vehicles require high torque control accuracy, while ensuring the highest possible efficiency in the entire operating range.
4.2. Efficient control
Before the most efficient working point is obtained through comprehensive scanning, the controller's loss can be reduced through the optimization of the controller hardware and software level, thus improving the controller efficiency. Improving voltage utilization through modulation strategy can reduce phase current and thus the on loss of the power module of the motor controller, and the switching loss of the power module can be reduced by reducing the switching frequency and optimizing the process of driving circuit lift-off." The maximum efficiency of the vehicle motor controller can generally be more than 98%, Toyota Prius using two-way DC / DC converter to increase bus voltage, over-modulation strategy and a series of measures, so that the controller maximum efficiency of 99%, as shown in the following picture.
5.Performance evaluation of the main drive motor controller Obviously, it is difficult to evaluate the motor controller, often the controller and motor as a system to evaluate. The evaluation method of the drive motor and its controller, national standard GB / T 1848812015 gives comprehensive and detailed regulations.
There is also a more commonly used evaluation indicator for motor controllers, kW/L, which is the ratio of the maximum output power of the motor controller to its volume. Motor controllers with higher power density tend to represent higher design levels under other conditions with similar performance indicators. At present, the power density of domestic mass-produced passenger car motor controller can reach 15 to 20kW/L, the advanced level of foreign countries can reach 20kW/L or more, and the motor controller of Sic device can reach 40kW/L or more.
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