Product definition, design and verification of Pukong Technology’s 11kW ultra-high power density inverter

As my country steadily advances the green and low-carbon energy transformation and continues to promote the optimization and upgrading of the industrial structure, under the guidance of the "double carbon" goal (carbon peak and carbon neutrality), the transmission composed of a variable frequency drive (VFD) and a motor The energy efficiency index of the system (Power Drive System, PDS) has become particularly important. Therefore, the design of inverter products using a new generation of power devices IGBT7 and new high-energy-efficiency control software can bring significant energy-saving benefits and performance improvements to industry applications, and better adapt to the requirements of new international energy efficiency standards for inverter products such as IEC61800-9.

This article will introduce a new generation of ultra-high power density 11kW heavy-duty general-purpose inverter developed based on Infineon TRENCHSTOP™ IGBT7 series EasyPIM™ 2B 1200V 50A module FP50R12W2T7_B11. The inverter has small size, high power density, and a full load efficiency of up to 98.1 %, can be adapted to IE3/4 and above high-energy-efficiency three-phase asynchronous motors and high-speed synchronous motors, supports a variety of bus communications, and has Wi-Fi IoT cloud connection capabilities and other features. At the same time, this design has a built-in EMC filter that can meet the requirements of IEC61800-3 C3. Especially suitable for high-efficiency, high-performance fans, pumps, compressor drives and other applications.

Overall dimensions: 220mm high * 115mm wide * 180mm deep. Due to the high efficiency and low loss characteristics of the IGBT7 device, the size of the radiator is effectively reduced, allowing this design to reduce the size of the 11kW inverter to the size of the traditional 7.5kW inverter. level, far ahead of similar products on the market, see the table below:

• Output rated power P ld =11kW

• Output rated current I ld =23A (ambient temperature 45°C, can withstand 150% overload for 1 minute every 10 minutes)

• Efficiency>98%

The 11kW design of this design has the same appearance as the mainstream 7.5kW product in the market.

IGBT is the core component that realizes frequency conversion and voltage conversion in the frequency converter. This design uses Infineon's EasyPIM™2B module FP50R12W2T7_B11. This module uses the latest generation IGBT7 technology. Compared with the traditional IGBT4, IGBT7 uses an MPT micro Trench technology and thinner wafers, through careful design of cell structure and spacing, improve parasitic capacitance parameters, reduce conduction losses, and provide better dv/dt controllability.

This chip defined for motor drives has obvious advantages in specific inverter design:

High power density, reducing the 50A module from Econo2 package size to Easy 2B size, reducing the board area occupied by 43.7%

Since inverters are used in practical applications, there are usually short-term overload conditions. When short-term overload occurs, the actual junction temperature of the IGBT will further increase (such as the protruding part of the blue curve). Compared with the traditional IGBT4, IGBT7 will overload. The maximum junction temperature is increased to 175°C, and the overload and non-overload junction temperature design limits are considered separately, so that the module capacity can be used more fully.

The resistance value of the IGBT turn-on resistor R on is selected as 11.2ohm, and the measured dv/dt=4.57kV/us meets the motor insulation requirements.

The hardware overcurrent point is 64A, and the protection action delay time is 6us<8us, which meets the short circuit time requirements of IGBT7.

The frequency converter even meets the EMC requirements of C2-5m.

i.Conduction limits and testing

ii. Radiation limits and testing

Under the load condition of the permanent magnet synchronous machine, the output is 19.5A and the output power is 11.3kW. The overall efficiency of the machine can reach 98.1%.

The inverter ran stably for 1 hour under the above working conditions, and the measured temperature rise data of the IGBT module were as follows:

Calculate the IGBT module loss under the above working conditions as follows:

According to the thermal resistance data, it is estimated that the IGBT junction temperature is about 73°C. If converted according to the ambient temperature of 45°C, the IGBT junction temperature in this working condition is about 100°C, and the design margin is sufficient.

The inverter is small in size and high in power. How to quickly dissipate heat is a major difficulty in system design. Comparing various layout schemes, the layout scheme in the figure below has small wind resistance and a large air volume flowing through the radiator. It can The heat of the module is quickly dissipated. The bus capacitors are separated from the radiator by plastic parts, and a certain amount of air flows through the surface of the bus capacitors, which reduces the ambient temperature around the bus capacitors and increases the life of the capacitors.

This design uses Infineon's 1ED3121MU12H driver IC. The on-resistance and off-resistance of the chip can be configured separately. It has a peak drive current of up to 5.5A, which is enough to drive the IGBT of the module; the driver IC has a common mode of up to 200kV/us. The suppression ratio can reduce the IGBT switching interference transmitted to the control side; the electrical gap >8mm between the primary and secondary sides of the chip itself meets the creepage distance requirements; it can directly receive the 3.3V PWM signal of the MCU, compared with the built-in hardware of the MCU The protection PWM shutdown function is perfectly matched, simplifying system design.