A traction inverter generally requires a low-voltage bias supply that connects to a low-voltage source such as a 12-V battery. TI offers several products to fulfill that function.
First, the UCC14240-Q1 isolated DC-DC converter module delivers 1.5 W of output power and provides ±1.3% output voltage regulation. The UCC25800-Q1 inductor-inductor-capacitor resonant converter features ultra-low EMI emissions, and the SN6507-Q1 high-frequency push-pull transformer driver comes equipped with integrated MOSFETs. Finally, the LM2518x-Q1 family of primary-side-regulated (PSR) flyback converters has integrated power switches that can operate over a 4.5- to 42-V input voltage range.
A traction inverter may also require a high-voltage bias supply to establish a redundant power source for powering up safety-relevant circuits. TI presents several reference designs for this function. One, the TIDA-01505 automotive flyback reference design, generates a 15-V, 4-A output from a 40-V to 1-kV input. And the company’s PMP22817 reference design describes a bias supply that provides the high isolation necessary for 800-V DC applications.
Safety considerations also require that traction inverters include a DC-link active-discharge function. This function must discharge the DC-link capacitor at vehicle key-off or during an emergency. The subsystem implementing this function must meet ASIL D as well as operate independently of the MCU in the event of MCU failure.
Several products from TI can be used to implement this function, including the TPSI3050-Q1 reinforced isolated switch driver. It has an integrated 10-V gate supply that drives the discharge power switches with no need for a secondary bias supply.
Sensible Sensors
Inverters also need several sensors, including rotor position sensors to provide feedback to the speed and torque control loops. Although inductive position-sensing technology is making inroads, these sensors have traditionally been variable-reluctance resolvers, whose primary windings require an excitation voltage generated through excitation amplifiers such as TI’s ALM2403-Q1 or TAS5431-Q1.
A position-sensor interface IC takes the resolver differential sine and cosine output signals and applies them to the MCU for processing. TI’s TIDA-01527 reference design describes a discrete resolver front-end that provides ±0.1-degree accuracy.
In addition, traction inverters require isolated sensors for voltage and current measurements such as DC-link voltages and motor phase currents. TI’s AMC1311B-Q1 and AMC1351-Q1 isolated amplifiers and AMC1305-Q1 isolated modulators help to achieve high accuracy, high bandwidth, low latency, and low temperature drift for such applications. The products offer both basic and reinforced levels of isolation and include a silicon-dioxide capacitive isolation barrier to support a high level of magnetic-field immunity.
Variable Gate-Drive Strength
In traction inverters, varying the gate-drive current controls the slew rate of the SiC power switches. Fast switching generally implies higher efficiency, but the accompanying high slew rates can cause voltage overshoots. The TI UCC5880-Q1 gate driver with real-time variable gate-drive strength helps optimize efficiency while minimizing overshoot to keep the powertrain cool and running.
For a fully charged battery, the UCC5880-Q1 applies weak gate-drive strength to reduce voltage overshoot and improve the SiC switches’ reliability. As the battery discharges, the device applies strong gate-drive strength to reduce SiC switching losses and significantly increase efficiency. The efficiency gain can be significant—real-world drive-log speed and acceleration data show the increased powertrain efficiency can add miles of driving range per battery charge.
Inverter Reference Design
To help you get started on a traction-inverter project, Texas Instruments and Wolfspeed developed the TIDM-02014 800-V, 300-kW SiC-based traction-inverter system reference design. The design demonstrates how a TI UCC5880-Q1 high-performance isolated gate driver with real-time variable gate-drive strength drives a Wolfspeed SiC power module, minimizing voltage overshoot and optimizing efficiency (Fig. 3).
