RT Box Performance Test

Simulation Model

This modular multilevel converter (MMC) model is used to compare the real-time performance of the RT Box 1, 2 and 3. The MMC is particularly useful for such benchmarking as it allows:

• easy scaling of the number of cells in the converter and
• splitting the system into different parts to run them on a single or multiple cores. This can be done with the new Task Frames available in PLECS 4.4.

The MMC has a configurable number of sub-cells per arm that all contain a full-bridge, a DC capacitor and a non-ideal DC voltage input. Given a number of cells (N) per arm, the total number of switching devices in this converter is 24 x N. Due to the different number of digital inputs the

• RT Box 1 and 2 with 32 digital I/Os are able to simulate up to 5 cells, whereas
• the RT Box 3 is able to simulate up to 10 cells per arm.

The model is open-loop controlled with the switching signals generated by another RT Box.

Performance Metric

The performance metric for evaluating the different RT Box targets is the average execution time per core. For the RT Box 1 and the single core operation of the RT Box 2 and 3, this means only one core is calculating the complete MMC plant model. In the case of the RT Box 2/3's multicore operation, total average execution time is calculated from the average execution time of each of the three available simulation cores.

Results

Using the described model, different simulations are performed:

• Single Core: For each RT Box target, a simulation of the plant system is performed on one single CPU core.
• Multi Core: For the RT Box 2 and 3 the simulation of the plant can also be split onto the three available CPU cores.

  Core 1: Grid and phase inductance/resistance

  Core 2: All high side sub-cells

  Core 3: All low side sub-cells

In both cases only the RT Box 3 allows simulation of up to 10 sub-cells per arm, as it has 64 digital inputs vs. 32 on the RT Box 1/2. There is a clear performance gain with the RT Box 2/3’s 1.5 GHz processor over the 1 GHz processor in the RT Box 1. Another significant performance gain is achieved by running the plant model on different simulation cores of the RT Box 2 and 3.