# Design and Verification of Multiphase Multilevel Traction Inverter
## 2 Materials and Methods
### Hardware Design Procedure
This board is created on a 4-layer PCB with the exact dimensions as the driver board, thus 123 \(\times\) 49 mm. It mainly consists of a 26-pin Insulation Displacement Connector (IDC). The Ready and Fault indication LED was also populated to indicate different driver stages. This PCB is located above the driver PCB. The finalized PCB model can be seen in Figure 5.
* _Distribution BUS-BAR PCB:_ A distribution board must be designed to connect all power modules to the input power supply properly. The PCB is designed as a 4-layer PCB with 6 oz copper layers to handle the converter power output. It connects the input power supply, smoothing DC-BUS capacitors and power modules. The final dimensions are 308 \(\times\) 310 mm. Figure 6 shows the prototype of the board that was manufactured. The novelty of this design of this power distribution PCB enables easy manufacturing of the laminated bus bar, which lower overall cost of the inverter build. * _Control board design stage:_ A powerful Digital Signal Processor (DSP) must be selected to control this type of converter properly. In this prototype, the dual-core TMS320F28379D (Dallas, TX, USA) was used. The control board has populated all the necessary circuits for proper inverter operation. In the top right corner, all power supplies are populated. The 12 V power supply powers the board, and on-board power supplies generate the following rails:
* +15 V for resolver driver
* +15 V / -15 V for current sensors
* Isolated 5 V for CAN drivers
\t* 3.3 V for DSP
\t* 1.2 V for DSP Core The board has 6 IDC connectors, distributing all necessary signals to the power module drivers. The board also contains high-voltage measurement of the DC BUS, to monitor voltage properly. Additionally, the resolver and encoder interfaces are populated to monitor the motor position. The designed control board can be seen in Figure 7. The Phase A-F markings show positions of the connectors for the driver board. Figure 5: Interconnect PCB connecting driver and control board. The final block diagram in Figure 8 shows the composition and construction of the prototype of the TNPC inverter. Figure 1:0 Power BUS-BAR Laminated PCB. Figure 1:1 Control PCB of the 6-phase TNPC. The designed boards are assembled to create a 6-phase TNPC inverter with a rated power output of 100 kW. The power modules will be mounted on a liquid-cooled plate. The modules comprise a driver board and an interconnection board, interconnected by a BUS PCB transferring the power. A control board at the top monitors system parameters and manages the power modules. Six HALL current sensors monitor the output current, whose reading goes back to the analog section for feedback and regulation to the control board. The 3D model of the final prototype is shown in Figures 9-11. Figure 1:2 Block diagram of designed inverter prototype. Figure 1:3 3D model of the prototype left side view. The design is targeted to the laboratory environment and testing and is not greatly optimized for operation in vehicle. The reliability of inverters in traction applications is greatly influenced by the vibration and fluctuating temperatures of an environmental source. Vibration causes mechanical stress that can result in solder joint fatigue, degraded insulation, and weakened connections between power modules. Temperature fluctuations induce thermal cycling, further accelerating component aging, which degrades the lifetime of the power electronics. Inverter designs, therefore, must consider these stresses carefully with a view to long-term reliability through robust mechanical and thermal management strategies. Design is focusing on the relatively easy access to test points for during inverter operation. The presented sample was designed to have high power density. This design brings some interesting challenges and trade-offs. Higher power density often leads to decreasing efficiency of the converter due to the smaller components and more heat generation. Additionally, this brings some other challenges in the cooling design.