Introduction
In the world of power electronics, electromagnetic interference (EMI) and electromagnetic compatibility (EMC) concerns can make or break a design. Switched-mode power converters, while efficient and compact, are common sources of electromagnetic noise that can wreak havoc on nearby components and systems. As designs grow more complex and regulatory requirements more stringent, engineers need powerful simulation tools to predict and mitigate these issues before physical prototyping.
Ansys HFSS and SIwave are two industry-leading full-wave simulation platforms which provide engineers with unprecedented insight into the electromagnetic behavior of their designs. These tools can help identify potential EMI sources, understand coupling mechanisms, and implement effective mitigation strategies, all within a virtual environment that saves time and resources.
In this post, we'll explore how these powerful EM simulation tools can be used in conjunction with Ansys Circuit to address EMI/EMC challenges in switched-mode power converters and similar power electronics designs. Whether you're dealing with a complex multi-phase converter or electric vehicle powertrain inverter, the correct simulation approach can help ensure that your product meets regulatory standards and performs reliably in its intended environment.
Ansys SIwave
SIwave is a specialized hybrid solver for efficient signal integrity, power integrity, and EMI/EMC simulation of PCB and package designs. Its robust capabilities enable engineers to perform comprehensive analyses including extracting S-parameters from PCB layouts, identifying layout-based resonances which may cause radiated emissions, evaluating susceptibility of a PCB to incident sources, and simulating near fields and far fields. SIwave includes automated SI/PI/EMI design rule checks for an entire PCB layout which can help engineers quickly identify potential problem areas and implement effective solutions early in the design cycle.
Figure 1: Ansys SIwave capabilities for SI/PI/EMI simulation of PCBs
Figure 2: SIwave can predict near fields and far fields for a PCB layout and signal sources to identify EMI issues and confirm compliance with EMC standards.
Ansys HFSS
HFSS is an industry-leading 3D electromagnetic field solver with comprehensive capabilities for EMI/EMC simulation. It offers a library of 3D components and templates specifically designed for EMC applications, including antennas, connectors, current transformers, human body models, and shielding structures. Engineers can leverage efficient hybrid solvers or mesh fusion to simulate multi-scale problems typical in EMI/EMC scenarios.
Using HFSS, engineers can create a virtual test bench environment that replicates standard EMC test setups, allowing them to evaluate designs against common standards like CISPR 22, FCC Part 15, and IEC 61000 before physical testing. This capability, coupled with specific training modules tailored for EMC applications, enables even those new to electromagnetic simulation to develop expertise quickly and apply best practices to their designs.
Figure 3: HFSS enables a wide range of EMI/EMC simulations including immunity, emissions, and human safety.
Figure 4: Example radiated emissions at 1 meter from a device under test from the HFSS model and corresponding anechoic chamber measurement (courtesy of GEMCO/UFSC).
Ansys Circuit
Ansys Circuit provides a fully-featured capability for frequency-domain and time-domain circuit simulation. A key feature is the seamless integration with Ansys EM solvers, enabling dynamic links between the schematic and the field solutions. This linkage provides a robust solution to analyze the electromagnetic behavior of complex circuits and systems. Using the Push Excitations feature, the required excitation information from the circuit simulation is transferred to enable insightful field visualizations in HFSS and SIwave, with automatic setup of the frequency, amplitude, and phase of the source signals.
Ansys Circuit can be used with the integrated results from the EM solvers to efficiently design switched-mode power converters. The transient circuit solver can incorporate SPICE models of active components such as MOSFETs and diodes and models of passive components such as inductors and capacitors which incorporate frequency-dependent effects, make it a powerful platform for simulating the dynamic behavior of switching circuits. Including realistic circuit component models is particularly important for accurately capturing the behavior of high-frequency switching systems.
Additionally, Ansys Circuit includes a comprehensive component library including common components such as Line Impedance Stabilization Networks (LISNs) for conducted emissions analysis, making it a versatile tool for EMI/EMC analysis and compliance testing. Engineers can quickly build virtual test setups that mirror physical compliance testing environments using pre-validated models that incorporate realistic parasitic effects.
Figure 5 shows an example EM/circuit co-simulation model for a traction inverter in an electric vehicle powertrain system. A traction inverter converts DC voltage from the vehicle's battery to AC voltage for the electric motor. The circuit model includes detailed SPICE models for the three half-bridge SiC power modules. The circuit also includes the battery, LISN, inverter controller, motor load circuit, and dynamic link to an HFSS model of the physical layout of the system. The results include the current waveforms delivered to the motor, the conducted emissions spectrum at the LISN output port, and the magnetic field in the vehicle at the 20 kHz switching frequency.
Figure 5: Ansys Circuit model of electric vehicle traction inverter system with dynamically-linked HFSS model.
Workflow for Multi-Phase Buck Converter
A workflow to simulate the conducted and radiated emissions from a four-phase buck converter is shown in Figure 6. This device is a DC-DC step-down converter with four interleaved phases operating in parallel to supply current to the load. Each phase consists of its own switching elements (MOSFETs), inductor, and control circuitry, and the phases are synchronized with a phase shift. A multi-phase buck converter offers significant advantages over a single-phase converter in terms of efficiency, thermal management, ripple reduction, and transient response, making it the preferred choice for high-current applications. This example converts a 12 V input voltage to below 1 V to supply a SMT component drawing 10 Amps.
The workflow begins by importing the PCB layout into SIwave. SIwave can import common ECAD formats including ODB++, IPC-2581, and EDB. The ports are assigned to the signal nets and a frequency sweep simulation is performed to extract the S-parameters of the PCB layout.
The SIwave model is then dynamically linked into a Circuit schematic, and the active and passive components are added to complete the circuit model. The circuit model includes a CISPR16 LISN to obtain the conducted emissions of the power converter. A time-domain (transient) simulation is performed to obtain the output voltage and current. The time-domain results are automatically transformed to the frequency domain to show the conducted emissions spectrum. The conducted emissions can be compared to permissible limits for the device and mitigation techniques such as filters can be used to obtain compliance.
The Circuit results are then linked back to SIwave to provide realistic excitations for PCB near field and radiated field simulation. This automatically creates the source files for the complex spectral data necessary to compute the field levels emitted by the PCB. The near fields can be plotted on any specified surface around the PCB, and the radiated emissions can be plotted at distances such as 1 meter or 3 meters away from the PCB.
It is often desired to evaluate the effects of an enclosure or housing on the emissions from a PCB. This can be readily performed by linking the near field solution from SIwave into HFSS. The near field link automatically creates the excitation, solution setup, and frequency sweep for the HFSS model. The effects of the enclosure on the EMI/EMC performance can be investigated in HFSS, and the EM field distribution can be examined at desired frequencies to understand how to mitigate any issues.
Figure 6: Example workflow to simulate conducted and radiated emissions for a multi-phase buck converter.
Summary
Industry-leading electronics simulation tools from Ansys enable design engineers to address EMI/EMC challenges and reduce the risk of product delays and compliance failures. Integrated electromagnetic and circuit workflows can predict conducted and radiated emissions from electronic systems such as the switched-mode power converter shown here. The coupling between solvers allows the design performance to be analyzed from both the circuit and field perspectives.
HFSS and SIwave provide detailed simulation of the fields and interactions within the physical layout of the system. This allows engineers to identify and mitigate potential issues such as crosstalk, radiation, and coupling at the component and board level. The integration with advanced circuit solvers includes bi-directional transfer of information and co-simulation of circuit and electromagnetic behavior. By leveraging these best-in-class capabilities, engineers can deal with EMI/EMC issues early in the design process to reduce the risk of costly design iterations and ensure successful development of reliable and compliant products.
Please watch the video below to view the presentation from OzenCon 2025 on this topic!