High-efficiency main drive inverter solutions increase the adoption of electric vehicles

Global environmental regulations are driving automakers to design electric powertrain systems with smaller size and weight and the highest power efficiency. One of the challenges in designing an electric powertrain is that the battery provides DC power, while the main drive motor requires AC power. The main drive inverter is a key part of the electric powertrain, responsible for converting the DC voltage of the high-voltage battery (350-800 VDC) into an AC voltage of three-phase AC sinusoidal current, which in turn rotates the electric induction motor and drives the vehicle forward. The performance of this module affects the overall energy efficiency of the vehicle, including acceleration and driving range. ON Semiconductor provides energy-efficient, stable and reliable main drive inverter solutions and advanced packaging technologies with cost-competitive advantages, including discrete solutions, isolated gate drivers and innovative VE-Trac series modules and wide bandgap (WBG) solutions to help increase the mileage of electric vehicles, thereby increasing the adoption rate of electric vehicles.  

Main drive inverter solution topology

As shown in Figure 1, the topology includes four main functional blocks: three-phase inverter stage, isolated power supply, signal processing and regulation, and communication bus. 

Figure 1: Main drive inverter solution topology

3-phase inverter stage

The main components of the 3-phase inverter stage are the high-side and low-side switches in the half-bridge switches in each phase of the inverter and the corresponding high isolation voltage gate drivers, which turn on and off those switches to generate 3-phase AC sinusoidal waveforms to operate the induction motor. The variable frequency drive control algorithm configured by the microprocessor manages the high-side and low-side switch control of each inverter phase.

Main drive inverters typically use high voltage battery systems of 400 V (HVL1) or 800 V (HVL2), the latter becoming increasingly popular in the latest designs. These systems require the maximum operating voltage of the power semiconductor devices to be in the range of 600 V to 750 V, or 900 V to 1200 V, corresponding to HVL1 or HVL2, respectively. The power inverter is required to handle large amounts of power at current levels in the range of 400 A to 1000 A per phase. To this end, some manufacturers connect discrete packaged devices in parallel, while most use power integrated modules (PIMs). ON Semiconductor offers discrete IGBTs, silicon carbide (SiC) MOSFETs and the innovative VE-Trac series of PIMs, as well as bare chips of IGBTs and fast recovery diodes to build the main drive inverter phases. All of these solutions can be interfaced with high voltage gate drivers.

In addition to providing galvanic isolation for isolating high-voltage systems from low-voltage systems, ON Semiconductor's high-voltage gate driver technology also has a key feature, the desaturation (DESAT) detection feature, which prevents the "breakdown" effect under IGBT short-circuit conditions. In addition, it also has a Miller clamp function to prevent one of the switches from accidentally turning on. And for enhanced protection, it also has a fault indication function to notify the system of faults and enable inputs.

ON Semiconductor's AECQ-101 certified discrete IGBT devices have excellent thermal and electrical performance. Because the IGBT has extremely low VCE(sat) and gate charge, conduction and switching losses are minimized, resulting in energy-efficient operation. ON Semiconductor's IGBTs are co-packaged with fast reverse recovery diodes and built using competitive field-stop trench technology, which uses a fine cell pitch design to create high power density devices and has stable resistance to dynamic latch-up conditions. Depending on the power requirements of the motor, multiple IGBTs can be connected in parallel on the corresponding high-side and low-side switches on each half-bridge of the inverter.

ON Semiconductor's VE-Trac family of PIMs, offering best-in-class electrical and thermal performance, supports two main drive inverter design platforms: VE-Trac™ Dual and VE-Trac™ Direct.

VE-Trac Dual combines dual-sided cooling (DSC) half-bridge modules that stack and scale in a compact footprint, providing a small footprint platform solution for applications from 80 kW to 300 kW. The first device in the platform is the NVG800A75L4DSC, which is rated at 750 V and 800 A, doubling the capacity of existing competing devices. Efficient dual-sided cooling ensures market-leading thermal performance, and the absence of any wire bonds in the module doubles its rated life. The NVG800A75L4DSC is an AQG-324 qualified module with embedded smart IGBTs, integrated over-current and over-temperature protection, and faster protection response time, providing a more robust overall solution. ON Semiconductor will release additional devices in the VE-Trac Dual platform with higher voltage and various current level options in the coming months to address a variety of emerging applications.

Figure 2: VE-Trac Dual PIM

The VE-Trac Direct platform offers best-in-class performance and benefits, including excellent thermal performance with direct cooling. The first device in the platform is the NVH820S75L4SPB, which meets AQG-324 certification. The device uses a six-pack architecture package and has been widely recognized and adopted by automotive OEMs and system suppliers. This will support multi-source supply and minimize layout changes. With multiple power levels available, the VE-Trac Direct platform will provide simple and fast power adjustments for different automotive platforms and applications.

Both the VE-Trac Dual and VE-Trac Direct platforms are capable of continuous operation at junction temperatures up to 175ºC, enabling higher power to be delivered within the compact footprint of a modular solution.

For 800V battery electric vehicle systems, 1200V, 20mΩ, 80mΩ SiC MOSFETs in D2PAK-7L and TO-247 packages can be inserted into the high-side and low-side switches on each half-bridge of the three inverters. SiC MOSFETs offer superior switching performance and higher reliability than silicon, with low on-resistance and compact chip size, ensuring low capacitance and gate charge. These features bring system advantages, including high energy efficiency, fast operating frequency, higher power density, lower electromagnetic interference (EMI), and the convenience of reduced footprint.

ON Semiconductor offers diodes and IGBT die optimized for main drive inverter applications, capable of continuous operation at 175°C, with lower VCE(sat) and forward voltage (VF), and enhanced reliability and robustness.

Signal Processing and Conditioning

The main function of the analog measurement and signal conditioning module is to process the current and temperature detection signals from the inverter and the current and motor position detection signals from the induction motor. An isolated power supply constructed using a resonant and flyback controller can provide power to the microcontroller, signal conditioning, and analog measurement circuits. ON Semiconductor provides AECQ-compliant logic components, comparators, operational amplifiers, and current sensing amplifiers to build signal processing circuits that interface with the microcontroller analog-to-digital converter unit to form a closed-loop system.

Communication Bus

ON Semiconductor provides transceivers based on CAN, CAN-FD, LIN, Flexray and system basis chips (SBC) to ensure reliable and stable in-vehicle communications at data rates exceeding 1 Mbps to meet the requirements of modern in-vehicle networks. In addition, ON Semiconductor also provides AECQ-101 certified communication bus protection devices with a maximum junction temperature of 175°C to protect vehicle communication lines from electrostatic discharge (ESD) and other harmful transient voltage events. These devices provide bidirectional protection for each data line, providing system designers with a cost-effective option to improve system reliability and meet stringent EMI requirements.

Evaluation Kit

To facilitate designers to evaluate the performance of VE-Trac Dual modules and VE-Trac Direct power modules respectively in the early stages of developing main drive inverters, ON Semiconductor provides the VE-Trac Dual evaluation kit NVG800A75L4DSC-EVK and VE-Trac Direct evaluation kit NVH820S75L4SPB-EVK, which can be used as a double pulse test to measure key switching parameters or as a 3-phase inverter for motor control with a power of up to 150 kW.

The VE-Trac Dual Evaluation Kit contains three VE-Trac Dual power modules mounted on a double-sided cooling heatsink, with a 6-channel gate driver board, DC link capacitors and external Hall effect current sensing feedback for motor control, without a pulse width modulation (PWM) controller. Its features include:

• Integrated 800A, 750V 4th Generation Field Stop (FS4) IGBT/Diode Chipset

• Automotive grade isolated high current, high efficiency IGBT gate driver with built-in electrical isolation NCV57000/1

• On-chip current sensing in power modules enables faster and simpler over-current protection (OCP)

• Integrates on-chip temperature sensing in the power module, enabling faster, closer to true Tvj Over-Temperature Protection (OTP)

• Custom designed double-sided heat sink provides low pressure drop and excellent thermal performance

• Custom film DC link capacitors rated to 500 VDC, 500 uF

Figure 3: VE-Trac Dual evaluation kit

The VE-Trac Direct Evaluation Kit contains a VE-Trac Direct power module mounted in a cooling jacket with a 6-channel gate driver board, DC bus capacitors, and no PWM controller or external current sensors. Features include:

• Integrated 820 A, 750 V FS4 IGBT/diode chipset and direct cooling features

• Automotive grade isolated high current, high efficiency IGBT gate driver with built-in electrical isolation NCV57000/1

• Film DC Link Capacitors, Rated to 500VDC, 500 uF