## 3 Materials and Methods
### Test Bench Setup
#### 3.2.1 Electric Machine Test Bench
###### Abstract  
The following describes the subsystems' functionalities.  
1. _Active front-end, battery simulator, and load machine inverter_ This subsystem represents the interface of the test bench to the grid. The battery simulator rectifies and converts the grid voltage to a variable DC link voltage in a first DC link with the aid of the active front-end subsystem. The voltage is then variably reduced from this first high-voltage DC link to a second DC link with the aid of a buck converter subsystem. Characteristic curves can also be stored in the buck converter so that the voltage can be adjusted depending on the operating point. Battery behavior can thus be simulated. See [52] for a more detailed description of the battery simulator. The inverter for the test bench's load machine is also supplied from the first intermediate circuit of higher voltage. A real-time control system and various internal measurement devices with limit value monitoring and emergency shutdown are used to control the subsystems listed.  
2. Load machine The test bench's load machine is statically connected to the machine bed, and various test specimens can be mounted via a fixture. The shafts of the two machines are connected with the EK6 elastomer coupling from R+W Servomax. This permits the assembly and operation of a wide range of different electrical machines on the test bench. A torque measuring shaft (Manner Sensortelemetrie, type 500 N m) and a speed measuring device are also be permanently installed.  
3. Automotive AC inverter and machine This inverter has semiconductors from the automotive sector. The subsystem is supplied by the battery simulator and operates the device under test. For the research, a prototype hybrid machine of an OEM was mounted on the test bench as the DUT.  
4. Superimposed real-time system test bench control unit The control and regulation of all subsystems and thus of the entire test bench was carried out by the TCU at 10 kHz. This real-time system (dSpace MicroLabBox) connects the interface to a host PC and thus allows for user communication. The measurement data of all sensors also converge in this real-time system and can be recorded at 2-10 kHz and viewed centrally.  
5. Temperature control system The DUT temperature can be controlled separately by a temperature control device. The performance data are listed in Table 3. Furthermore, the test bench can be extended  
\begin{table}
\begin{tabular}{c c c} \hline
**Component** & **Parameter** & **Value** \\ \hline Active front-end and battery simulator & Max. DC voltage & 900 V \\  & Max. DCDC current & 900 A \\  & Max. power & 250 kW \\ \hline AC inverter & Max. DC voltage & 800 V \\  & Rms AC current & 500 A \\  & Max. power & 250 kW \\ \hline Load machine & Max. power & 215 kW \\  & Max. speed & 15,000 min\({}^{-1}\) \\  & Max. torque & 540 N m \\ \hline Device under test & Peak power & 85 kW \\  & Continuous power & 40 kW \\  & Max. speed & 6500 min\({}^{-1}\) \\ \hline \end{tabular}
\end{table}
Table 2: EM test bench system parameters.  
by adding more temperature control devices for the components exposed to a variable temperature in the vehicle. The temperature control devices control the component temperature by modifying the temperature and the volume flow, as dictated by the superimposed real-time system.  
Due to the decreasing temperature difference between the cooling medium and the primary cooling circuit during cooling, the time required for temperature control to lower temperatures is very high. This is irrelevant for normal vehicle operation, but must nevertheless be considered, in particular when tempering to an initial temperature at the start of the test run.