Real-Time Implementation of Long-Horizon Direct Model Predictive Control on an Embedded System

Eyke Liegmann,Ralph Kennel,Petros Karamanakos

doi:10.1109/ojia.2021.3133477

Abstract

This paper deals with the real-time implementation of a long-horizon finite control set model predictive control (FCS-MPC) algorithm on an embedded system. The targeted application is a medium-voltage drive system which means that operation at a very low switching frequency is needed so that the switching power losses are kept relatively low. However, a small sampling interval is required to achieve a fine granularity of switching, and thus ensure superior system performance. This renders the real-time implementation of the controller challenging. To facilitate this, a high level synthesis (HLS) tool, which synthesizes C <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</monospace> code into VHDL, is employed to enable a higher level of abstraction and faster prototype development of the real-time solver of the long-horizon FCS-MPC problem, namely the sphere decoder. Experimental results based on a small-scale prototype, consisting of a three-level neutral point clamped (NPC) inverter and an induction machine, confirm that the algorithm can be executed in real time within the targeted control period of 25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s.

Highlights

T HE main control methods for drive systems are the field oriented control (FOC) [1], and direct torque control (DTC) [2]
A block diagram of the experimental setup is provided in Fig. 9, while the rated parameters as well as those of the drive system are listed in Tables II and III, respectively
The load machine operates in constant-speed mode, while both inverters share the same dc-link voltage, so that only the losses are supplied by the power supplies

Summary

Introduction

T HE main control methods for drive systems are the field oriented control (FOC) [1], and direct torque control (DTC) [2]. The former employs linear controllers to generate the modulating signal which is subsequently fed into an explicit modulator stage. Due to the linear control principle, decoupling of the d- and q-axes is not fully achieved during transients, a phenomenon which becomes even more prominent as the switching frequency decreases. DTC can achieve excellent dynamic performance owing to its direct control principle, i.e., a dedicated modulator does not exist, but rather the switching signals are directly applied to the power converter. High current distortions can be produced at steady-state operation since the current is indirectly controlled by keeping the electromagnetic torque and flux magnitude within given bounds

Methods

Results

Conclusion