HIL SIMULATION Power HIL for grid applications

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Hardware-in-the-loop simulation is limited to low-voltage and low-current signals. Power Hardware-in-the-loop or simply PHiL is an extension of HIL simulation of high-power devices. In power electronics, PHiL is a useful technology to save time and cost for power engineering teams. This article describes PHiL for power electronics grid use cases.

Power hardware-in-the-loop is a simulation in which a virtual power interface is created between digital simulation and DUTs (Devices Under Test). Effective power interfaces use complex algorithms. DUTs can be power semiconductors, supplies, inverters, converters, drivers, machines, batteries, chargers, and many more devices.

These power components or devices are integrated into a simulated environment called RTS (Real Time Simulator) with the help of an appropriate voltage or current power amplifier. The power amplifier amplifies low voltage and current signals between RTS and DUTs.

In addition to power amplifiers, sensing hardware tracks important physical parameters like voltages, currents, impedance, power, temperature, pressure, and many other important characteristics to virtually predict the system’s functionality. In closed-loop PHiL simulation, this data is fed back from the output to the input.

A PHiL simulation enables predicting a system’s functionality in advance. It deals with real-time high-voltage high-current signals for DUTs (Devices Under Test). Simply put, PHiL determines the response of a high-power device to virtual realistic stimuli.

PHiL for grid

Achieving low carbon emissions and the ever-increasing depletion of non-renewable resources is giving rise to the integration of renewable technologies in vehicles and residential and commercial settings.

PHiL is an appropriate testing method to evaluate the functionality of the grid. This section discusses how PHiL testing for a low-voltage grid is an appropriate method.

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Choice of power amplifier

PHiL integrates power electronic DUTs with an RTS for the electrical grid using power amplifiers. The choice of linear and power amplifiers alters the output of the test. There are two types of power amplifiers- linear or switching power amplifiers.

Linear power amplifiers: Power amplifiers like class A, class B, class AB, and class C amplifiers are examples of linear amplifiers. Choosing linear power amplifiers to integrate RTS and DUTs offers faster results but compromises on stability.

Switching power amplifiers: Switching power amplifiers like class D and class E amplifiers might be a slower approach but have an inbuilt ability to minimize harmonics to enhance the stability of the system.

Interface algorithm

These RTSs run fast in micro or milliseconds. Choosing an interface algorithm is critical to ensure the success of the power interface between RTS and DUTs. A wrong choice could give rise to unnecessary delays, harmonics, and noise.

One of the most critical factors to consider for grid stability is the impedance ratio. Impedance matching is a term that describes effective signal or power transmission from source to load. In grid applications, DUTs, especially inverters, can have non-linear impedance ratios. It gives rise to unstable operations in commercial settings.

Feedback signal filtering

A technique called FSF (Feedback Signal Filtering) is applied to the feedback signal that connects DUTs with RTS. This technique improves stability by introducing first-order low-pass filters. The addition of LPFs in the PHiL setup eliminates the high-frequency components induced by non-linear loads.

Compensator network

LPFs damp rapid fluctuations in the PHiL system. However, passive low-pass filters tend to induce phase delays that reduce the power factor. Ideally, the power factor should be as high as possible. A compensator network using linear inverters deals with the power factor reduction tendencies of the LPFs.

Advantages of using PHiL for grid applications

Enterprises and manufacturers implement PHiL to test power electronic components and devices for applications like PVs, renewables, wind farms, industrial plants, etc.

Advance estimation

Power engineers can test various types of power equipment virtually with real-world power conditions, delays, and computer networks, without wasting components. As a result, customers can make uninterrupted use of renewable technologies.

Avoid commercial failure

The only drawback of renewable energy systems is their fluctuating nature due to weather and many other factors. Hence, renewable systems should be tested in advance to avoid failure and delay before commercial deployment.

High safety

PHiL can test all harder-to-induce “what if” use cases in power electronics. It is safe to use on the system level and tends to run high-fidelity tests. As all power electronic environments generate loads of heat, PHiL simulation can “virtually” predict a system’s performance in dangerous use cases.

Cut-down on expenses

Real-world power electronic tests are costly due to the safety and maintenance of high-power environments. Whereas PHiL has a lower implementation cost due to RTS, DUTs, and power and sensing hardware. In such cases, power engineering teams can save testing, and maintenance costs by a huge margin.

References

• www.mdpi.com

• www.opal-rt.com/power-hardware-in-the-loop

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