While computer aided design tools have found wide adoption by practicing engineers, control testing has been lagging.
Most of the control system type testing is still done manually, in the lab, using small scale or large full scale power hardware, which can significantly prolong the time it takes to bring new power electronics products to market.
So why do practicing engineers use power hardware to test their control systems in the first place?
One good reason is that until recently there was no satisfactory alternative. Once the real time software is loaded to the DSP and the FPGA starts generating PWM pulses with nanosecond resolution, there is little else what can be done other than hooking it up to their inverters and slowly increasing the voltage, hoping that this time they won’t hear a loud BANG.
Luckily, things are improving and powerful, commercially available controller hardware-in-the-loop (C-HIL) test equipment are becoming available. VDC Research Group, a technology market research company, predicted in their report “The Global Market for Hardware-in-the-Loop Testing Solutions” that the adoption of commercial C-HIL solutions for power electronics will depend on the speed at which new C-HIL solutions will be able to replace the in-house developed test rigs industries have been building over the decades.
What is Hardware-in-the-Loop?
Hardware-in-the-loop means that there is something physical connected to the real-time simulation. This can be a piece of the power hardware or a piece of the controller hardware. HIL simulation with power hardware is often referred to as Power Hardware-in-the-Loop (P-HIL). In the case of HIL simulation where controller hardware is connected to the real-time simulation, it is called Controller Hardware-in-the-Loop (C-HIL).
Only recently, in large part thanks to the advances in FPGA technology, commercial C-HIL test systems with extremely small simulation time step and latency became feasible, and finally in 2009 the world’s fastest real-time digital simulator platform with 1 µs sampling time and latency became commercially available.
What is the difference between simulation and real-time simulation?
Real-time simulation progresses at the same rate as the actual time passes (the time you can observe on your wrist watch or your smart phone). The simulation time step can be anything, even minutes, so long as the simulation time corresponds to real time. This is in stark contrast to computer simulation that can be slower or faster than the real time.
What is this “C-HIL” and where did it come from?
C-HIL test method is the test procedure where the performance of the physical control system hardware, firmware and software is tested against a mathematical model, simulated in real-time on the C-HIL platform. This approach has been used for decades in automotive and aerospace industries as the method of choice when testing sophisticated control systems. By connecting controllers to the virtual plant model, simulated in real-time, they were able to test operating conditions that are difficult and/or impractical to test in the lab in addition to being time consuming and unjustifiably expensive.
Let us now look closer into some important benefits and trade-offs of C-HIL and the two related, yet distinctly different approaches: Software-in-the-Loop (SIL) and Power Hardware-in-the-Loop (P-HIL) methods of testing control systems.