Most three-phase inverters use insulated gate bipolar transistors (IGBTs) in applications like variable-frequency drives, uninterruptible power supplies, solar inverters and other similar inverter applications. Each phase of a three-phase inverter uses a high- and low-side IGBT to apply an alternating positive and negative voltage to the motor coils. Pulse-width modulation (PWM) to the motor controls the output voltage.
The three-phase inverter also uses six isolated gate drivers to drive the IGBTs. Apart from the IGBTs and isolated gate drivers, three-phase inverters include DC bus voltage sensing, inverter current sensing and IGBT protection like over temperature, overload and ground fault.
Cost and performance are challenging trade-offs in many end applications like heating, ventilation and air conditioning (HVAC), solar pumps and appliances.
So what are the best ways to save bill of materials (BOM) cost without compromising system performance? Here are some tactics:
TI’s newly released UCC21520 is a reinforced isolated dual channel gate driver. With best in class propagation delay of 19ns (typical), programmable dead time and wide voltage ranges make it really suitable for such inverter applications.
Apart from the IGBTs, the IGBT gate drivers and current sensing play a major role in determining the cost and performance of the three-phase inverter stage. Consider the following tactics save BOM in current sensing circuit:
AMC1301 is TI’s newly released precision reinforced isolated amplifier. It is optimized for direct connection to shunt resistors and supports accurate current control. The high linearity and low temperature drift of offset and gain errors of the AMC1301 results in system-level power savings and lower torque ripple. With 3µs delay and detection feature of missing high-side supply makes is suitable for motor drives applications.
The new TI Designs Reference Design for Reinforced Isolation 3-Phase Inverter with Current, Voltage and Temp Protection (TIDA-00366) provides a reference solution for a three-phase inverter rated up to 10kW. Figure 1 is a high-level block diagram.
Figure 1: High-level block diagram of TIDA-00366
The design includes the UCC21520 reinforced isolated dual-IGBT gate driver, AMC1301 reinforced isolated amplifier and TMS320F28027 MCU. A lower system cost is possible by using the AMC1301 to measure motor current (interfaced with the MCU’s internal ADC), with a bootstrap power supply for the IGBT gate drivers. The inverter is designed to have protection against overload, short circuit, ground fault, DC bus undervoltage and overvoltage, and IGBT module over temperature.
What techniques do you use for saving the BOM? Tell us.
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