If the HIL tests for an electric drive system have to include the power stages, testing at signal level is not enough. Testing at electrical power level is essential. One way is to operate a real drive motor on a test bench. Another is to simulate the electric motor at the electrical power level. This involves simulating the electrical behavior of a real motor by mapping the real terminal voltages and currents and feeding them to the ECU. Compared with a mechanical drive test bench, a purely electrical test bench of this kind is easier and safer to operate. Tests can be run at a very early stage, even if the real drive motor is not available yet. Moreover, it is also possible to simulate different motor types. Unlike mechanical test benches, these simulators have no restrictions on dynamic processes.
The new electronic load emulator covers voltages of more than 800 V and power outputs of up to 100 kW. Thus, it is suitable for the HIL simulation of today’s and future electrical drive systems.
The electronic load emulator emulates the variable, active parts of the voltages uEMK induced in the motor coils, while the inductive behavior of the motor coils is represented by equivalent substitute inductivities LMotor. The induced voltages uEMK are calculated in real time by an electric motor model and implemented by the electronic load simulator.
The load emulator uses inverters from the ServoOne series by LTi. The electric motor model for computing the induced voltages is implemented on a dSPACE real-time system by means of Simulink®. The model components that can be simulated include the drivetrain. Various sensor and actuator simulations are added to the real-time system for this, according to project-specific requirements. A hybrid ECU requires at least one appropriate simulation of an engine speed sensor (such as a resolver).
The concept of the electronic load emulator can be used for simulating all types of motors. The physical properties of each motor, such as motor inductivity, torque generation and power consumption, are represented very realistically. For variable inductivities (such as in an interior permanent magnet (IPM) motor, or with saturation effects), mean values have to be used in the load emulator due to the constant substitute inductivities. Nevertheless, it is possible to represent the torque and power correctly. Any desired hybrid and electrical vehicle configurations can be simulated by using different electric motor models in conjunction with variable drivetrain models (such as the Automotive Simulation Models). The concept is also suitable for various industrial HIL applications.