Application of Ansoft software in power inverter system of vehicle power integration

Faced with the highly competitive hybrid and electric vehicle (HEV/EV) market, power integration R&D engineers are challenging themselves to achieve higher system efficiency, stability and reliability. The power inverter is crucial in the power integration system and is usually composed of 6 4×6-inch packaged IGBT modules. These IGBT modules output AC power to the motor by quickly switching hundreds of amperes of current on and off, controlling electronic systems and other systems. The switching frequency of IGBT ranges from tens of kHz to hundreds of kHz, and the turn-on rise time and turn-off fall time are 50~100ns.

High switching speeds make IGBTs ideal for power inverter systems, but they also bring two major electromagnetic problems: conducted radiation (through current-carrying structures) is usually below 30MHz, which can cause power integrity problems or cause energy reflection waves that are potentially harmful to the inverter and motor; radiated electromagnetic fields (through air) are usually above 30MHz and may affect other electronic systems on the vehicle.

In order to comply with government and international vehicle electromagnetic radiation standards, the above two types of interference issues must be fully considered in the design. Therefore, the responsible engineer must design the electromagnetic compatibility and electromagnetic interference of the basic structural components of the system.

To complete the EMC and EMI design of power inverter systems, engineers must first address the underlying physical factors that determine EMC and EMI, and then complete the design with the help of circuits and systems. This simulation-driven approach helps to deal with other electromagnetic issues that must be considered, including current quality, power consumption, and overall system efficiency.

These calculations, typically performed using linear circuit elements and simplified circuit solvers, require a number of crude approximations and overly simplified assumptions. Skipping the simulation of these critical underlying physics mechanisms will result in incorrect simulation results, and hardware prototyping—and multiple redesign iterations—may be required before performance requirements are met.

In most cases, these testing cycles are not performed until late in the design process, which can significantly increase costs and lead to missed market opportunities. Being able to predict electromagnetic effects early in the development process, before the power inverter is manufactured, is not possible without simulation of multi-physics problems.

The Ansoft software package provides full-frequency domain multi-physics problem analysis tools for studying the electromagnetic performance of devices such as IGBTs. Ansoft software specializes in electromagnetic field simulation, and can also simulate circuits and systems. Ansoft tools that can be used for power inverter development include:

HFSS: A finite element based full-wave solver for extracting parasitic parameters and displaying 3D electromagnetic fields.

Simplorer: A multi-domain circuit and system simulator that can easily integrate multi-physics domain simulation components such as electrical, thermal, mechanical, magnetic and fluid.

Q3D Extractor: A quasi-static electromagnetic field solver that can be used to compute frequency-dependent resistors, inductors, capacitors, and conductance parameters in current-carrying structures.

To accurately describe the performance of switching devices such as IGBTs, engineers usually start with a parameterized wizard that imports IGBT performance curves and table data from performance sheets provided by suppliers. The data processing program automatically extracts the required parameters (approximately 140) to generate a semiconductor circuit model for the IGBT, eliminating the need for manual work.

The power converter design layout can then be imported directly from the CAD software or layout design tool into the Q3D Extractor tool. Q3D Extractor calculates the frequency-dependent resistance, partial inductance and capacitance of the conductive paths from the design layout.

Engineers use this tool to generate equivalent circuit models for system simulation in Simplorer. Once the model is built, it can be combined with the semiconductor circuit model to form an electrical integrity model of the IGBT. The electrical integrity model can be used for conducted radiation analysis of power supplies, control systems, and loads.

The results of this simulation can be used by HFSS to examine radiated emissions, a type of radiation that is of particular concern given the frequency domain harmonics caused by fast switching time sequences. To determine this effect, Simplorer's results can be used as input to the HFSS full-wave electromagnetic solver. Engineers can then gain a comprehensive understanding of its radiated electromagnetic fields and can calculate the electromagnetic field strength at any given point in space and determine whether the inverter package meets relevant standards.

In this way, engineers can use the tools provided by Ansoft to design the electromagnetic compatibility and electromagnetic interference of the inverter system, and trace its electromagnetic performance to the inverter layout design. Thus, the design parameters are changed and a series of simulation results are obtained until the conducted radiation and radiated electromagnetic emission levels are within acceptable limits.

The value of this approach is that once the model is complete, the design can be modified by changing a few key parameters, which allows engineers to study various parameter options and explore a wide range of what-if analyses. This approach can provide a fully optimized design that meets performance requirements before any hardware is built. Compared to the prototype processing-prototype testing model, the multi-physics simulation method can save time and money and enable companies to compete in the market with better designed products.