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Direct bypass to DC-DC boost converter in traction inverter increases converter's capability and efficiency significantly by providing a lower loss path for power flow between the battery and DC-link terminal. A bypass using diode is an excellent solution to achieve this capability at low cost and system complexity. Bypass diode operates in the linear operating region (DC Q-point) when the battery discharges through the bypass diode to drive the electric motors. Therefore, thermal stress on the DC-link capacitor is shared between the input and DC-link capacitors through the bypass diode. On the other hand, inverters introduce voltage oscillation in the DC-link terminal which results in unwanted energy oscillation through the bypass diode during battery charging. Both of these phenomena have been explained in details.

Power modules play a key role in traction inverters for vehicle electrification applications. The harsh automotive operating environment is a big challenge for power modules. The paper highlights the challenges for power modules usage in electrified vehicles (xEVs), and proposes a design verification procedure for such application in order to ensure the reliable operation under all conditions. First, power modules operate in all climate zones and are exposed to a wide ambient temperature range underhood from -40°C to 105°C. A typical automotive power module should therefore withstand a junction temperature from -40°C to up to 175°C without exceeding its safe operating area (SOA), e.g. avalanche breakdown voltage, maximum current, and thermal limit. Second, an inductive induced high voltage spike could be generated during the power semiconductor fast switching at high voltage and high current conditions.

A hybrid electric vehicle (HEV) can utilize the electromechanical path to optimize the ICE operation and implement the regenerative brake, the fuel economy of a vehicle therefore gets improved significantly. Bi-directional Boost converter is usually used in an electric drive system to boost the high voltage (HV) battery voltage to a higher dc-link voltage. The main advantages for a system with Boost converter is that the traction inverter is de-coupled from battery voltage variations causing it to be over-sized. When designing this Boost converter, the switching frequency is a key parameter for the converter design. Higher switching frequency will lead to higher switching loss of power device (IGBT +diode), moreover, it has significant impact on inductor ripple current, HV battery ripple current and input capacitor current. Therefore, the switching frequency is one of the most important parameters for the design and selection of both active and passive components.

Electric vehicles (EV) and hybrid electric vehicles (HEV) require high torque/acceleration ability and wide speed range. To meet both of them, the traction machines usually have to be oversized, which results in high volume and weight, high cost, and low efficiency. In practical application, high speed motors combining with gear box provide the expected torque and speed capability. If pole-changing machines are employed to achieve wide torque and speed ranges, gear box and motor size can be reduced in EVs/HEVs. This paper presents a pole-phase modulation motor drive which changes both of poles and phases simultaneously, as a result that the motor extends its torque/speed capability in a flexible way. Simulation results verify the principle and control method for this kind of motor drives.

Boost converter is widely applied to hybrid electric vehicles (HEV). Typical control methods employ two proportional-integral (PI) regulators to fulfill DC bus voltage closed-loop control and inductor current closed-loop control, respectively. They have intrinsic performance limitations: 1) slow dynamic response of DC bus voltage regulation; 2) high overshoot voltage during transient state; 3) it is difficult to design four gains best fit all operational conditions. This paper proposes a model prediction based boost converter control method for HEV applications. The proposed control method employs model based instantaneous power prediction and dynamic optimization in real time by minimizing a defined cost function to overcome above issues. First of all, the issues of typical control methods are analyzed. Then, the proposed control method is presented in detail, followed by simulation verification and comparison with PI based control method.

Variable Voltage Converter (VVC) is adopted in Power-Split structure of hybrid electric vehicles (HEVs) to optimize the Electric-Drive (e-Drive) system performance. With the wider availability of Silicon Carbide (SiC) power semiconductor for automotive applications, there are new opportunities to further optimize and improve performance of VVC, e.g. lower power loss, smaller size, and lighter weight, comparing to use traditional Silicon (Si) IGBT and diode. In this paper, a SiC based VVC is designed, prototyped, and evaluated. In order to maximize the benefits of SiC power devices in VVC application, each key component is carefully designed and selected, including SiC power module, power capacitor, and power inductor. The characterization and evaluation results demonstrate the benefits of advanced SiC devices in VVC design optimization, and such benefits quantified in this paper.

Insulated Gate Bipolar Transistors (IGBT) are widely used for the vehicle traction inverter. Switching characteristics of these devices contribute to the inverter total loss and inverter efficiency is affected by the energy loss during each switching event. Traditional gate driver circuits are usually designed to meet the worst-case scenario and result is high switching loss of the IGBTs. Gate driver turn on and turn off resistances are selected accordingly for the worst-case scenario and their purpose is to protect the device from overshoot voltage that can cause the avalanche breakdown of the device. The gate charge and discharge circuit is usually composed of one or two resistors and the loss during turn-on and turn-off time is not optimized for all of the vehicle-operating conditions. Since microprocessor (μP) monitors the dc-bus voltage, output current and torque command, it can also determine if the device switching speed needs to be changed under different operating conditions.

The IGBTs are dominantly used in traction inverters for automotive applications. Because the Si-based device technology is being pushed to its theoretical performance limit in such applications during recent years, the gate driver design is playing a more prominent role to further improve the traction inverter loss performance. The conventional gate driver design in traction inverter application needs to consider worst case scenarios which adversely limit the semiconductor devices' switching speed in its most frequent operation regions. Specifically, when selecting the gate resistors, the IGBT peak surge voltage induced by fast di/dt and stray inductance must be limited below the device rated voltage rating under any conditions. The worst cases considered include both highest dc bus voltage and maximum load current. However, the traction inverter operates mainly in low current regions and at bus voltage much lower than the worst case voltage.