What is the best simulation software for power electronics?

POWER ELECTRONICS SIMULATORS

What is the best simulation software for power electronics?

Modern power electronics systems typically involve sophisticated designs while being critical to the reliability and safety of their target environments. Due to their internal components’ complex interactions and behaviors, simulation is often the only way to predict their performance.*

This article looks at the different types of power electronics simulators that are currently available.

(Source: Tommyview – stock.adobe.com)

Your power electronics system contributes critically to your product’s success; it must reliably deliver the correct voltages, currents, and waveforms to the points of load without causing or being susceptible to electrical noise. It also carries significant safety requirements, especially if it operates at high voltages and currents.

Thermal management is a further concern in any power electronics system as components can reach extremely high temperatures very quickly. Additionally, noise in switching regulators can induce unintended switching in low level downstream digital components, especially when these regulators run at high current.

However, modern power electronic systems exhibit a strong interaction between voltage sources, loads, power semiconductors, and control circuits. This element interaction is complex due to the nonlinear behavior of the power semiconductors and the different magnitudes of the circuit’s time constants. Due to this complexity, simulation is almost the only way to study the behavior of power-electronic systems prior to prototyping.

Many electronics simulators are available on the market, so which is the best for power electronics projects? Or, since it would be unreasonable to expect anyone package to be best in every respect, a more useful question is: How do I identify the optimal choice for my project?

The answer to this is influenced by the following factors:

• Many simulators are intended for all types of electronic circuits, of which power electronics is just one subset.

• Conversely, more specialized packages are available. These are typically for higher-level systems, such as power electronics designs for automobiles, or for complete wind farms or photovoltaic (PV) installations.

• So the first step could be to identify one or more candidates for your project, based on how well their specifications align with your project type.

• Confidence in this choice will be considerably enhanced by any available insight into how well it performs in practice.

This article addresses these issues. Firstly, we look at the key tests that a power electronics simulation should run. Then, we summarize some popular (and some less well-known) packages currently available, showing their major features for initial comparison. Next, are some survey results showing how users rated these packages against one another, together with comments about their experiences with them. These extend to some findings from a research team that assessed four examples from these commercially available simulation packages.

What to examine in a power electronics simulation

Cadence PCB Solutions, who supply the PSPICE simulator, advise that the answer to this question depends on the type of system you are building. Different regulators and other power systems require different designs and different simulations to ensure components are selected properly. In general, you need to simulate the following aspects of any power electronics system:

• Average output voltage/current vs. input voltage/current. The power transfer characteristics of your design can be determined by comparing the input and output voltages/currents in the system.

• Linearity. Power electronics systems will have some range over which the output and input are related by a linear function. This should be simulated for different loads as you need to examine the smallest load (i.e., largest current) that can be connected to the system.

• Ripple. Power Factor Correction (PFC) circuits, switching regulators, rectifiers, and other circuits will not produce a flat DC output. There will be some ripple on the output when switching or rectifying elements are present in the circuit. Ripple is normally quantified as a percentage of the average output voltage/current.

• Buck or boost functionality. Switching DC-DC converters and PFC circuits have different topologies that provide buck (step-down) or boost (step-up) functionality. You will need to verify that the output changes with changes in duty cycle according to the standard formulas for your converter topology.

Popular simulation packages

PSIM
PSIM from Powersim Inc is a modular package specifically designed for power electronics and motor drives. Target systems range from complex motor drives to fully realized hybrid electric vehicle (HEV) systems. A wide choice of modules means that systems can be configured exactly to users’ requirements, without unnecessary functionality or complexity. PSIM’s modules integrate with other popular platforms, such as TI kits, JMAG, Modelsim, and Simulink.

PSCAD
PSCAD allows you to build, simulate, and model your power systems while including electromagnetic transients simulation. Its library of systems modules ranges from simple passive elements and control functions to electric machines and other complex devices. Applications include wind, solar, and distributed generation, protection and relays, and equipment failure analysis.

MATLAB Simulink
MATLAB is a programming platform designed specifically for engineers and scientists. It is used for analyzing data, developing algorithms, and creating models and applications. MATLAB and Simulink can be used together to combine textual and graphical programming to design your system in a simulation environment.
You can use MATLAB to create input data sets to drive simulation and run thousands of simulations in parallel. Then you can analyze and visualize the data in MATLAB. Simulink for Power Electronics Control Design helps you to design and implement digital control for motors, power converters, and battery systems.

ORCAD and PSPICE
Both packages are available from Cadence. OrCAD PCB design solutions offer fully integrated front-end design, analog/mixed signal simulation, signal integrity analysis, and place-and-route technologies.
PSPICE provides a complete circuit simulation and verification solution. It includes accurate analog and mixed-signal simulations supported by a wide range of board level models. PSPICE can be used together with MATLAB Simulink for analysis and visualization of data for multi-domain simulations of dynamic electromechanical systems.

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PLECS
PLECS tools from Plexim can be applied to many disciplines of power electronics engineering. Conceived with a top-down approach in mind, PLECS facilitates the modeling and simulation of complete systems, including power sources, power converters, and loads.
Included with PLECS is a comprehensive component library, which covers the electrical, as well as the magnetic, thermal, and mechanical aspects of power conversion systems and their controls. Power electronics circuits are captured with a schematic editor in a way that is familiar and intuitive for electrical engineers. Typical power electronics components such as semiconductors, inductors, and capacitors are placed on the circuit diagram and connected by drawing wires.

SPICE
SPICE, developed in the University of California, Berkeley in 1973, was the progenitor of many later commercial versions, including LTspice (Freeware from Analog Devices) and PSPICE from Cadence, which is still in use. There are also many open-source and academic continuations available.
SPICE (“Simulation Program with Integrated Circuit Emphasis”) is a general-purpose, open-source analog electronic circuit simulator. It is a program used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior.

LTspice
Analog Devices’ LTspice is a high-performance SPICE simulation software, schematic capture, and waveform viewer with enhancements and models for easing the simulation of analog circuits. Included in the download of LTspice are macro models for a majority of Analog Devices switching regulators and amplifiers, as well as a library of devices for general circuit simulation.
Enhancements to SPICE have made simulating switching regulators extremely fast compared to normal SPICE simulators, allowing you to view waveforms for most switching regulators in just a few minutes.

NL5 Circuit Simulator
NL5 is an analog electronic circuit simulator working with ideal and piecewise-linear components.
The NL5 Circuit Simulator package includes NL5 DLL, a standard Windows Dynamic-Linked Library (DLL). It performs transient simulation of circuits created by NL5 Circuit Simulator. NL5 DLL can be used as an analog simulator, which is started and controlled from other applications and tools (MATLAB, Python, custom C/C++ code), and as an analog co-simulation tool working with digital simulation tools, for example SystemVerilog simulators (through DPI interface).

COMSOL Multiphysics
You can use the COMSOL Multiphysics simulation platform and the suite of add-on products from SolidWorks to model any combination of structural mechanics, heat transfer, electromagnetics, acoustics, fluid flow, chemical reaction phenomena, etc. The software lets you simulate any physics-based system that can be described with partial differential equations (PDEs).
The LiveLink for SOLIDWORKS add-on product smoothly integrates your COMSOL Multiphysics simulations and SOLIDWORKS software designs, all within the SOLIDWORKS software modeling environment.

SaberEXP
SaberEXP from Synopsis is a piecewise linear platform for designing, modeling, and simulating physical systems, enabling full-system virtual prototyping for applications in analog/power electronics, electronic power generation/conversion/distribution, and system/wiring/harness design and mechatronics. It offers a scalable implementation solution with fast convergence.

Users’ ratings

Table 1: Ranked listing of popular simulation packages.

(Source: Nigel Charig)

Two forums (Quora and ResearchGate) asked for users’ views on the best software for simulation of power electronics. Table 1 below lists the main packages that were mentioned in responses across both sites, ranked by the number of favorable comments received.

Note that this is not a scientific survey; the numbers are too small for statistical accuracy, and a ‘favorable comment’ could be anything from a slightly positive mention to a strong endorsement. However, with these limitations in mind, it offers an indication of users’ views of the simulation packages on offer.

The user experience – key takeaways

In reviewing the responses to the two surveys, some trends and a few strong comments became apparent. These are summarized below to show how the packages compare with one another in users’ eyes, as far as is possible with the limited number of users in the sample.

• PSCAD is valued for power electronics with high voltage and power.

• ORCAD has a wide semi-real component library, which is useful for later hardware implementations – although components can sometimes be hard to locate.

• MATLAB Simulink is quick, easy, and reliable but may generate small errors after hardware implementation. These errors can be neglected for most circuits.

• MATLAB is better for power electronics, compared with PSPICE or ORCAD for electronic circuits only.

• Simulink is valuable due to its ability to implement control strategies and mathematical models.

• SABER modeling uses components that are then available to purchase for real systems. It returns more accurate results than Simulink.

• PLECS is based on Simulink, but is easy to use and offers a good Octave and scripting interface.

• COMSOL is good for electromagnetic or heat transfer simulation.

• Conventional SPICE-based simulators attempt to perform accurate simulation using real models of nonlinear components. By contrast, NL5 uses simpler, ‘ideal’ components for clear and predictable behavior, together with piecewise linear (PWL) representation. The NL5 website provides a detailed explanation of this approach and its advantages.

• LTspice is popular, partly because it is free. Additionally, it is good for low level circuitry simulation, with detailed models for the devices of interest (MOSFETs, diodes, op-amps, etc.). It also handles switching power supplies. LTspice is particularly useful if you are using Linear Technology ICs. Additionally, Analog Devices has been adding models for Analog Device parts since purchasing Linear Technology in 2016.

• PSIM is straightforward to use in both design and simulation if you want to simulate a converter with few switches and a simple control strategy. PSIM also has good solver. Simulink, especially with MATLAB, becomes a better, easier to use choice for simulating converters with six or more switches. However, PSIM can also be used with MATLAB and Simulink. A published white paper that compares PSIM with MATLAB/Simulink is available for download. For ideal power converters, use PSIM. For non-ideal types, use PSPICE. For power electronics control techniques, use MATLAB/Simulink. PSIM is also valued for DC to DC converters and PV applications.

An investigation of power electronics simulation tools

A team from Universidad Técnica Federico Santa María assessed four different types of commercial simulation programs designed to simulate power electronic systems on a single-phase boost rectifier circuit:

• 1. Equation solver: MATLAB: Simulink Version 5.3.0

• 2. Circuit-equation solver: MATLAB: Power System Blockset Version 1.1

• 3. General circuit solver: PSpice (Microsim 8)

• 4. Power-electronics-specific circuit solver: Simplorer 4.2

Simulation of a single-phase boost power-factor connector was performed to compare the four programs. The circuit has several features that are commonly found in modern power electronics:

• A fast current-control loop that can be implemented with a Bang-Bang controller or a proportional-integrative (PI) controller plus pulse-width-modulation (PWM) modulator.

• A slow DC voltage-control loop.

• Use of fast-switching power semiconductors.

The purpose of the boost rectifier is to generate a controlled DC output voltage and a sinusoidal input current.
Results: The team found MATLAB-Simulink to be clearly the fastest simulator. Although Simulink and PSB use the same simulation environment, they show the largest execution time difference. However, with MATLAB-Simulink the execution time does not allow for the initial setup time required to obtain the equations and corresponding block-diagram representation.

The MATLAB environment is well known for its very powerful control tools. Simplorer can use these tools through the Sim2Sim module to extend its control library. This capability lets Simplorer implement the standard controllers used in power electronics. Finally, PSpice’s control features are limited and are more difficult to implement, making PSpice a poor simulation alternative. MATLAB-Simulink is the most difficult to use, while Simplorer is the simplest.

Accordingly, the team concluded that a power-electronics-specific circuit simulator offers the most convenience. This type of program simulates the power and control parts of the circuit very well. In addition, these types of simulators have low execution times, are numerically robust, and are user friendly.

*This article looks at the various types of simulators currently available.

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