Multi-rate control on PLECS with ACG SDK

This document provides instructions on how to configure multirate control for imperix controllers using PLECS with the ACG SDK. It allows executing part of the control algorithm at a slower rate, without violating real-time constraints. This is typically useful for running supervisory logic, slow outer control loops, energy management, or MPPT algorithms.

This page gives only PLECS-specific configuration instructions. For general multi-rate control on imperix controller, please refer to PN265. For Simulink-specific instructions, please refer to PN145.

Single-tasking and multitasking configurations

Imperix users can choose between single-tasking and multitasking approaches to execute their multi-rate control algorithms. Single-tasking runs all execution rates sequentially within a single, monolithic control task, whereas multitasking utilizes priority-based task scheduling with preemption, as detailed in PN265.

By default, PLECS is configured in single-tasking mode. To enable multitasking, the Tasking mode should be set to multi-tasking in the Scheduling tab of the Coder Options dialog.

Base rate and sub-rates configuration

In PLECS, the base rate, which corresponds to the CPU interrupt rate of the controller, is defined in the Config block via the CLK0 frequency and the optional postscaler parameters, as explained in PN137.

Sub-rate tasks are configured in the Scheduling tab of the Coder Options, as shown below. Because sub-rate tasks must have a sample time that is an integer multiple of the base rate, it is recommended to define their sample time explicitly (as shown in the example below) to prevent configuration errors.

Now that the sub-rate task is defined in the Coder Options, it can be assigned in the model using a Task Frame, as shown below. All components enclosed within the frame will be executed inside the selected task. The illustrative example below shows a Task Frame surrounding a subsystem that assigns its execution to Task 1, which was configured earlier to run 5 times slower than the base rate.

Application example

An example of use is presented in Maximum Power Point Tracking (MPPT) (TN117). It shows how one part of the control (in the MPPT task below) can be executed at a slower rate than the main control code.