Facing the highly competitive hybrid vehicle and electric vehicle (HEV / EV) market, power integration R & D engineers are challenging higher system efficiency, stability and reliability. Power inverters are essential in power integrated systems and are usually composed of six 4 "x 6" IGBT modules. These IGBT modules output AC power to the motor by quickly switching the on and off of hundreds of amperes of current to control electronic systems and other systems. The switching frequency of IGBT is from tens of kHz to hundreds of kHz, and the turn-on rise time and turn-off fall time can reach 50 ~ 100ns.
The high switching speed makes IGBT very suitable for power inverter systems but it also brings two major electromagnetic problems: Conducted radiation (through current-carrying structure) is usually below 30MHz, which may cause power integrity problems or cause reverse Transformers and motors have potentially hazardous energy reflection waves; the radiated electromagnetic field (through air) is usually higher than 30MHz, which may affect other electronic systems on the vehicle.
In order to comply with government and international vehicle electromagnetic emission standards, the above two types of interference 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. In order to complete the electromagnetic compatibility and electromagnetic interference design of the power inverter system, engineers must first solve those potential physical factors that determine electromagnetic compatibility and electromagnetic interference, and then complete the design with the help of circuits and systems. This simulation-driven approach is conducive to dealing with other electromagnetic issues that must be considered, including current quality, power consumption, and overall system efficiency.
Linear circuit components and simplified circuit solvers are often used for these calculations, requiring a large number of rough approximations and oversimplified assumptions. Skip the simulation of these crucial basic physical mechanisms, the simulation results will no longer be correct, and hardware prototype testing may be required before the performance requirements are met-multiple iterations of redesign. In most cases, these test cycles will not be carried out until later in the design process, then the cost will increase significantly and miss market opportunities. If the influence of electromagnetics can be predicted before the power inverter is manufactured and early in the development, simulation without multi-physics problems is impossible.
The Ansoft software package provides a full-frequency domain multiphysics problem analysis tool for the electromagnetic performance research of devices such as IGBT. Ansoft software's specialty is electromagnetic field simulation, and it can also simulate circuits and systems. Ansoft tools that can be used for power inverter development include:
Simplorer: A multi-domain circuit and system simulator that can easily integrate electrical, thermal, mechanical, magnetic and fluid simulation components in multiple physical domains.
Q3D Extractor: A quasi-static electromagnetic field solver that can be used to calculate the conductance parameters of frequency-variable resistance, inductance, capacitance, and current-carrying structures.
HFSS: A full-wave solver based on finite elements, which can be used to extract parasitic parameters and display three-dimensional electromagnetic fields.
In order to accurately describe the performance of IGBT and other switching devices, engineers usually start with a parameterized wizard, which can be used to import IGBT performance curves and table data from the performance sheet provided by the supplier. The data processing program will automatically extract the required parameters (about 140) to generate the semiconductor circuit model of IGBT, without manual completion.
Then, the design layout of the power converter can be directly imported into Q3D Extractor tool from CAD software or layout design tool. Q3D Extractor calculates the frequency-dependent resistance, partial inductance and capacitance of the conductive path from the design layout. Then, engineers use this tool to generate equivalent circuit models for system simulation in Simplolor. Once the model is built, it can be combined with the semiconductor circuit model to form the 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 verify radiated emissions—a type of radiation that is of particular interest considering the harmonics in the frequency domain caused by fast on and off time series. To determine this effect, Simplorer's results can be used as input to the HFSS full-wave electromagnetic solver. Then, the engineer can fully understand the radiated electromagnetic field, and can calculate the electromagnetic field strength at any given point in the space, and determine whether the inverter package meets the 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 the source of the electromagnetic performance to the layout design of the inverter. As a result, parameter changes are made to the design and a series of simulation results are obtained until the levels of conducted radiation and radiated electromagnetic emissions are within acceptable limits. The value of this method is that once the model is completed, the design can be modified by changing several key parameters, which allows engineers to study various parameter schemes and do hypothesis analysis and exploration in a wide range. This method can provide a design result that satisfies the performance requirements and is completely optimized before requiring the slightest hardware manufacturing. Compared with prototyping-prototyping test mode, the multi-physics simulation method can save time and money, and enable the company to participate in market competition with better designed products.
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