1. Basic Applications of Motor Controllers
1.1 Motor controller integration form
Integration methods include:
Single main drive controller, auxiliary three-in-one controller (integrated: EHPS controller + ACM controller + DC-DC), auxiliary five-in-one controller (integrated: EHPS controller + ACM controller + DC-DC + PDU + dual-source EPS controller), passenger vehicle controller (integrated: main drive + DC-DC), logistics vehicle three-in-one controller (integrated: main drive + DC-DC + PDU), logistics vehicle five-in-one controller (integrated: main drive + EHPS controller + ACM controller + DC-DC + PDU).
1.2 Basic Principles of Motor Controllers
Basic functions of a motor controller: Drives the motor by modulating the output sine wave through an inverter bridge. An all-in-one controller includes...
Power distribution circuits: provide power to various parts of the integrated controller, such as TM contactors, fuses, power supply for electric air conditioning circuits, power supply for electric defrosting circuits, etc.
IGBT drive circuit: Receives control signals, drives IGBTs and provides status feedback, providing voltage isolation and protection;
Auxiliary power supply: provides power to the control circuit and provides isolated power to the drive circuit;
DSP circuit: Receives vehicle control commands and provides feedback information, detects motor system sensor information, and transmits motor control signals according to the commands;
Structure and heat dissipation system: Provides heat dissipation for the motor controller, provides controller installation support, and provides controller safety protection.
Motor controller thermal design
The actual operating environment of the vehicle is complex and the working conditions are relatively harsh, which places high demands on thermal design.
Simulation experiments need to be multi-layered:
System-level simulation (primarily focusing on the thermal design rationality of the controller system, including the internal ambient temperature simulation; system-level simulation includes module-level models)
Module-level simulation (key component model capacitor, bronze medal simulation, using density and heat flux density to simulate capacitor temperature).
Single-board level simulation (simulating the ambient temperature of the single-board and the heat dissipation of key components on the single-board, the purpose of which is to accurately measure the heat dissipation of a key component on the single-board, such as a key resistor on the single-board. If single-board simulation is performed in advance, more accurate design can be carried out more quickly)
Chip-level simulation (IGBT, main power module simulation; IGBT is the core of the module controller, and how to maximize the IGBT's capabilities depends on the accuracy of the IGBT chip-level simulation).
The test must meet high precision requirements: multiple rounds of testing and closed-loop simulation must be conducted, with a heat sink deviation of ±3℃.
Simulation of complex operating conditions: simulation of typical operating conditions under rated and overload conditions, simulation of special operating conditions under stall conditions, and determination of the controller's maximum capacity under periodic and nonlinear loads.
2. Efficiency Optimization Technology for Electrical Control Systems
A 1% improvement in the efficiency of the electronic control system has significant advantages in terms of vehicle economy and weight. Efficiency optimization technologies include dynamic carrier frequency adjustment, DPWM waveform generation technology, overmodulation technology, and wide-area high-efficiency HSM motor.
2.1 Carrier frequency dynamic adjustment technology
The main source of loss in the electrical control system is the inverter, with 70% of the inverter losses coming from the switching section.
To reduce switching losses, dynamic carrier frequency adjustment technology was studied. Simulation experiments revealed that adjusting the switching frequency can improve controller efficiency by up to 2%. Using dynamic carrier frequency technology, especially at low speeds where carrier frequency requirements are less stringent, can effectively reduce controller losses and improve efficiency. Preliminary estimates suggest an improvement of approximately 1.5 kilometers per 100 kilometers . However, the carrier frequency cannot be adjusted indefinitely; overall vehicle noise and motor control needs must also be considered.
2.2 Application of DPWM Waveform Generation Technology
The application of discontinuous waveform technology, using DPWM technology reduces the number of switching operations by 1/3 compared to COWM technology, which can significantly reduce the number of switching operations and achieve the goal of reducing switching losses.
When the modulation ratio M > 0.816 , the harmonics under CPWM and DPWM modulation are approximately the same. In this region, DPWM technology can be used to reduce device losses.
2.3 Application of overmodulation technology
Controller losses include switching losses and conduction losses. Conduction losses are highly dependent on the output current; for a given output power, a decrease in output current necessitates a corresponding increase in output voltage.
By adding overmodulation, the output power and output torque in the weak magnetic region can be effectively improved, the output voltage can be increased by 4%, the peak power can be increased by about 4%, and the overall vehicle's power performance at high speed can be improved.
By adding overmodulation, the current will be significantly reduced when outputting the same power, which can reduce system heat generation, improve the overload capacity of the controller, and improve the overall vehicle power performance.
By adding overmodulation, the fundamental voltage can be effectively increased. Compared with no overmodulation, this can effectively improve motor efficiency and significantly reduce motor current (0~8%). Improved efficiency can effectively extend the driving range.
2.4 Wide-area high-efficiency HSM motor
In addition to improvements in electronic control efficiency, this also includes improvements in motor efficiency.
HSM (Hybrid Synchronous Motor) motors, compared to IPM (Integrated Power Motor) motors, offer a balance between low-speed and high-speed efficiency. HSMs exhibit a particularly significant efficiency advantage in the medium-to-high speed constant power operating range. Tests have shown that HSMs are more efficient than conventional IPM motors in both low-speed and high-speed ranges; overall, using HSM technology can improve motor efficiency.
In the operating conditions of buses and group vehicles, when comparing IPM and HSM motors, the HSM motor has the advantage.
The comprehensive energy efficiency optimization technology, which considers the overall vehicle operating conditions, achieves targeted efficiency optimization by adjusting the proportion of each loss component in the motor. Combined with specific vehicle model and road condition information, it customizes and develops motors with higher overall energy efficiency, thereby improving driving range.
3. Junction temperature protection technology for electronic control system modules
We conducted numerous thermal simulations to determine the controller's maximum capability. However, the maximum capability may not be sufficient to protect the motor controller, as real-world operating conditions are quite complex.
3.1 . Practical Significance of IGBT Junction Temperature Estimation
Junction temperature is an important condition for determining whether an IGBT is operating safely, and the operating junction temperature of an IGBT limits the maximum output capacity of the controller.
Overheating damage to IGBTs has serious consequences due to a variety of factors, including design flaws, complex operating conditions, high vibration, temperature shock, and aging of the silicone grease. Indirect protection of IGBT junction temperature based on the NTC (Non-Temperature Control Center) has limitations. Under extreme conditions such as stalled operation, heat distribution is highly uneven, a temperature difference exists between the IGBT and the NTC, and the relationship between the NTC and junction temperature is not well-defined, requiring prior experimental exploration. Furthermore, the slow response time of the NTC cannot accurately and promptly reflect junction temperature fluctuations, easily leading to IGBT overheating damage. Therefore, the traditional method of using NTC for indirect IGBT junction temperature protection has limitations.
Using NTC alone for protection is very dangerous in harsh working conditions.
3.2 . IGBT Junction Temperature Estimation Based on NTC
Based on operating parameters such as voltage, current, and frequency, accurate thermal simulations are performed to extract heat flow parameters, calculate and correct them, and predict the IGBT junction temperature in advance. After testing, simulation, and cross-validation with the software model, the final junction temperature estimation error is within ±3℃.
3.3 . IGBT Junction Temperature Estimation Based on Temperature Sampling Diode
The temperature sampling diode is directly integrated in the middle of the IGBT. Compared with traditional modules, it can directly collect the wafer junction temperature (approximately), which improves the module capability, can obtain the junction temperature fluctuation of the wafer, improves reliability, and ensures lifespan. The disadvantage is that directly collecting the wafer junction temperature raises safety issues related to high and low voltage.
The module has 6 junction temperature sampling channels, which increases the cost of the module and external circuits. Currently, the temperature of one IGBT junction and the temperature of a single diode are used. Through loss calculation and heat flow parameter calculation, the temperatures of the other IGBTs are derived.
Using single-channel diode temperature sampling, and employing advanced loss calculation and heat flow parameter calculation methods, along with cross-verification through testing, simulation, and software models, the junction temperature estimation error can be within 3℃ in steady state and within 10℃ in transient state.
3.4 Temperature protection strategy based on junction temperature estimation
Advantages:
The junction temperature monitoring is more direct, resulting in better acceleration performance of the entire vehicle;
Real-time monitoring of junction temperature ensures that the controller can perform at its maximum capacity under stall conditions while preventing overheating and damage, thus enhancing the overall vehicle safety.
Under normal vehicle operating conditions, the current capability of the IGBT is maximized, resulting in stronger vehicle power.
The controller can conduct more advanced algorithm research based on actual operating conditions, such as real-time calculation of IGBT life damage, to improve the reliability of the whole vehicle.
Protective measures:
Set a junction temperature limit. When the junction temperature is at risk, implement a strategy of reducing the load frequency or torque. Once the risk is eliminated, the frequency or torque data will recover.
4. Development Trends of Motor Controller Technology
4.1 High security
Torque safety is achieved through SBC+MCU monitoring architecture, high-voltage backup power supply, safety-related driver chips, comprehensive diagnosis of IGBT faults, independent safety shutdown path, independent ADC channel resolver signal decoding, two high-voltage sampling circuits of different types, and three-phase current Hall sensors of different types.
4.2 High EMC level
Current second-generation products may achieve Class 3 or Class 4 EMC performance, but future EMC requirements will need to reach Class 5, necessitating miniaturization and lower costs. Our core breakthrough in EMC innovation lies in achieving high-level EMC requirements with superior filtering solutions and lower-cost EMC devices. For example, to achieve Class 5 EMC performance, the volume percentage should be less than 5%, and the cost less than 50 RMB.
The research and development content includes: EMC solutions for "electric control + motor" systems, EMC characteristic research and solutions for core components, and EMC simulation platform for "electric control + motor" systems.
4.3 High pressure
Primarily targeting passenger vehicles, the current voltage is generally around 300-400V, but it is likely to develop towards higher voltages in the future. Super-fast charging and increased power requirements are the inherent driving forces behind the shift towards higher voltages in electric vehicles. For example, increasing the charging voltage from 400V to 800V could halve the charging time. This improvement is essential for the future widespread adoption of electric vehicles. Higher voltage is a development trend, and correspondingly, inverter design will evolve from 650V IGBT designs towards higher voltages of 750V and 1200V IGBTs.
4.4 High power density
From a packaging perspective, traditional easy-to-use modules are trending towards square, ultra-thin shapes, and ultimately, bare DBC/chip forms. The overall size is shrinking as packaging becomes more compact, potentially reaching 1/10 of the size of modules from 2013 by 2018 or in the future.
From a chip perspective, the trend is towards higher efficiency and higher operating junction temperatures. For example, the E3 chip has an operating junction temperature of 150°C, the EDT2 chip's junction temperature can be increased to 175°C, and the SiC (silicon carbide) chip's junction temperature can exceed 175°C. If the power loss of the E2 chip is 1, the power losses of the latter two are 0.8 and 0.3 to 0.5 , respectively. Using SiC devices can significantly reduce switching losses, improve system efficiency, reduce dead time, and enhance system output capability. Considering the overall battery pack and controller, the total cost decreases by 5%, and considering the entire vehicle, the driving range increases by 10%. Using SiC devices improves overall efficiency.
With the development of components and packaging technology, cost predictions will gradually decrease.
From a product perspective, the controller supplied to Haima can achieve a power density of 18kW/L, the second passenger vehicle controller can achieve a power density of 26kW/L, the latest passenger vehicle controller currently under development can achieve 35kW/L, and in the future, using SiC materials, the power density is expected to reach 45kW/L.
4.5 . Device integration and customization
Functional safety, highly integrated :
Functional safety, higher clock speed:
Driver isolation IC: Functionally safe, highly integrated.
Model capacitors have become highly customized, with even EMC (Electronic Control Unit) components integrated into them. For example, the Y capacitor for controller EMC is often added on a separate circuit board, and the future trend is towards integration. This applies to the motor controller itself, and future systems are also moving towards integration.
