# A Survey on Mission-Profile-Based Stress Testing of Electric Motor Drives
## 4 Reliability and Lifespan Improvement Methods for EMD Components
### Active Thermal Control  
Temperature related stress has the greatest impact on the overall degradation of EMD components, especially power modules in frequency converters. The complexity of mission profiles demands the development of new techniques to control temperature within normal operating limits. As a result, active thermal control (ATC) has gained popularity due to its significant reduction of thermal stress on EMD power modules. Several related review papers on ATC methods are presented in [88; 89; 90; 91; 92; 93; 94; 95; 96]. ATC procedures reduce the thermal stress of components by controlling electrical parameters to regulate junction temperature and reduce temperature cycling of the power module [88]. According to [88], the ATC techniques can be categorized into the following:  
* Enhancing the overload capacity of power modules; \begin{table}
\begin{tabular}{c c c c c} \hline
**Reference** & **Mission Profile** & **Target Component** & **Indicator** & **MTTF** \\ \hline
[70] & Mechanical and vibration profiles & Bearings & Degradation of bearings and mechanical stress & - \\ \hline
[71] & Voltage sags (types A, B, and C) & Induction motor & Insulation, current, mechanical stress & - \\ \hline
[75] & Multiple stress factors (test chamber) & VSI & Degradation of IGBTs and diodes & 1011, 1029, 1463 h \\ \hline
[76] & Environmental stress factors & Frequency converter & Broken IGBT, FET short-circuit & 3000 h \\ \hline
[77] & FTP-75 driving cycle & IGBT modules (VSI) & Junction temperature cycling & 760 h \\ \hline
[78] & FTP-72 driving cycle & IGBT modules (VSI), diodes, capacitors & Junction and absolute temperature profile & 4.11 years \\ \hline
[79] & Speed and torque profiles and real-time DC data & IGBT modules (VSI) & Junction temperature profile & 16.3 years \\ \hline
[80] & WLTP test cycle & IGBT modules (VSI) & Temperature profile & - \\ \hline
[81] & Solar irradiance and thermal profile & PV inverter & Parasitic capacitance and junction temperature & 4.2, 6.7, 8.5 years \\ \hline
[82] & Thermal profiles & VSI & Fault occurrence & - \\ \hline
[83] & Artemis cycle profile & VSI & Current and thermal stress & - \\ \hline
[84] & Wind speed profile & VSI & Junction temperature profile & 39.5 years \\ \hline
[85] & High and low-frequency profiles & MOSFET (VSI) & Degradation of MOSFET parameters & - \\ \hline
[87] & Different PWM methods & IGBT (VSI) & Thermal stress and energy losses & - \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._* Controlling switching and conduction losses;
* Improvement of the modulation process;
* Balancing the thermal stress of parallel semiconductor devices;
* Thermal stress control at the system level. Scientific papers dealing with ATC typically utilize only one of these techniques. Thus, there is a lack of comprehensive ATC methods for reducing thermal stress at multiple levels. Figure 7 illustrates a flowchart of ATC methods designed for thermal stress management at the system level in multimodular power converter drives. The fundamental concept of power routing involves distributing the load power among multiple modules in multimodular power converter drives to achieve thermal balance and improve system reliability. In [97], an ATC method for modular power converters in a multiphase PMSM system is proposed. Depending on the operating mode, one converter may be overloaded, leading to higher temperatures and longer thermal cycles. To reduce thermal stress, excess power is redistributed to other converters. ATC uses a temperature controller to calculate power distribution coefficients based on reference and measured values, which determine the reference power for each converter. An increase in THDU, power losses, and operational costs, along with potential stability issues, are the main drawbacks of implementing the ATC strategy in system operation. The authors in [98] reduce the junction temperature and thermal cycling stress of converters in electric cars. The proposed method utilizes the control of switching frequency and current.