Ralph Kennel

Predictive Control in Power Electronics and Drives

Predictive control is a very wide class of controllers that have found rather recent application in the control of power converters. Research on this topic has been increased in the last years due to the possibilities of todays microprocessors used for the control. This paper presents the application of different predictive control methods to power electronics and drives. A simple classification of the most important types of predictive control is introduced, and each one of them is explained including some application examples. Predictive control presents several advantages that make it suitable for the control of power converters and drives. The different control schemes and applications presented in this paper illustrate the effectiveness and flexibility of predictive control.

Sensorless speed and position control of synchronous machines using alternating carrier injection

High frequency carrier injection is a promising approach solving high performance sensorless drive demands. Position control at low and zero speed is only possible using anisotropic effects considered in high-frequency models. The usually open loop carrier signal injection is impacted by nonlinear inverter properties like the dead-time effect. This paper discusses the influence of the dead time effect on the carrier signal excitation comparing alternating and revolving injection principles. To overcome disturbing effects an alternating injection procedure is proposed using a predefined injection angle. The approach reduces the effects of the inverter distortion voltages. As a result it is possible to track even small saliencies typical for surface mounted permanent magnet synchronous machines. For processing the high frequency current for position estimation, there is no additional hardware necessary within a standard drives with field oriented control. The paper presents theoretical analysis and experimental results.

High-Performance Control Strategies for Electrical Drives: An Experimental Assessment

This paper presents a comparative study between field-oriented control (FOC) and Predictive Torque Control (PTC) applied to induction machines. Both strategies are implemented on the same experimental bench and similar tests are performed. Furthermore, they were previously adjusted to get an equivalent switching frequency at a specific operation point, achieving the fairest possible comparison at steady state. Experimental results verify that PTC can achieve results similar to FOC, possibly even improving performance in transient conditions.

Sensorless position control of permanent magnet synchronous machines without limitation at zero speed

Sensorless position control of surface mounted permanent magnet synchronous machines (SMPMSM) still is a challenge. High performance position control at low and zero speed is only possible using anisotropic effects being considered not in the fundamental-frequency machine models, but in extended high-frequency models. This paper presents a new high-frequency injection method estimating the rotor position, which overcomes the small signal to noise ratio inherent to methods of this type published so far. This enables to track even small saliencies typical for SMPM synchronous machines. A small high-frequency voltage signal is injected into the rotor d-axis with no influence on the torque producing q-current. The demodulation of the responding high-frequency current signal is independent on machine parameters. Therefore the proposed method is independent on machine parameters and simply adaptable to different machines. As only the high frequency current has to be processed for position estimation, there is no additional hardware necessary besides that for standard drives with field oriented control.

Generalized predictive control (GPC)-ready for use in drive applications?

A usual argument against GPC is its demand for processing power. In industry, however, this is not a serious argument if better control performance can be reached. As the development of new processors with increased performance takes place rather rapidly, the lag of processing power never was a long-term issue to prevent new algorithms from being introduced. This paper presents a practical realization of generalized predictive control (GPC) for field oriented control of induction machines. The results are compared with conventional PI-control. Considering the strong real time conditions of drive applications, implementation aspects according to the great calculation effort in case of GPC are discussed to contribute to closing the gap between theory and practice.

An Improved FCS–MPC Algorithm for an Induction Motor With an Imposed Optimized Weighting Factor

In this paper, an improved finite control set-model predictive control (FCS-MPC) with an optimized weighting factor is presented. The main goal of this paper is reducing the torque ripples when the FCS-MPC is implemented by means of the two-level inverter. For this purpose, the weighting factor is calculated via an optimization method. The optimization is based on dividing the control interval into two parts: active time for applying the active voltage vectors and zero time for applying the zero voltage. With this technique, the torque ripple is calculated as a function of weighting factor and it is optimized. The method is validated by simulations and experiments, using two-level inverter, at two speed regions (nominal speed and low speed). The results are compared with conventional FCS-MPC.

Using Full Order and Reduced Order Observers for Robust Sensorless Predictive Torque Control of Induction Motors

In this paper, two kinds of observer-based sensorless predictive torque control methods are proposed. The predictive method is based on examining feasible voltage vectors (VVs) in a prescribed cost function. The VV that minimizes the cost function is selected. A novel robust prediction model is presented. The prediction model includes sliding mode feedbacks. The feedback gains are assigned by the H-inf method. Two kinds of observers are applied for flux and speed estimation, i.e., sliding mode full order observer and reduced order observer. In order to verify the proposed method, simulation and experimental results are presented in wide speed range. A comparison of the two methods is performed based on the results.

Finite-Control-Set Model Predictive Torque Control With a Deadbeat Solution for PMSM Drives

This paper proposes a control strategy of finite-control-set model predictive torque control (FCS-MPTC) with a deadbeat (DB) solution for permanent-magnet synchronous motor drives. By using a DB solution, the process of selection of the best switching vector is optimized. The predicted DB voltage sector consisting of the desired voltage vector (VV) avoids the complete enumeration for testing all feasible VVs, which relieves the big calculation effort of the traditional FCS-MPTC method. The proposed system is experimentally carried out both in the steady state and in the transient state.

Anisotropy Comparison of Reluctance and PM Synchronous Machines for Position Sensorless Control Using HF Carrier Injection

Position sensorless control of reluctance and permanent magnet synchronous machines at zero and low speed is possible using HF voltage injection and proper demodulation. The so-called saliency position, which is tracked by the HF sensorless scheme, is different from the actual rotor position: the difference contains both offset and rotor-position-varying components, which may be explained by carefully considering the HF behavior of the machine and the effect that fundamental excitation and rotor position have upon it. This paper gives insight into the HF behavior of synchronous machines and serves as a practical guide for implementation of stable and robust position estimation at zero and low speed.

Cascade-Free Predictive Speed Control for Electrical Drives

This paper presents the design of a predictive speed controller for electrical drives. The control scheme does not have a cascaded structure; instead, it uses a single optimization algorithm to generate the control action to be applied at the next sampling instant. The control is based on the optimization of a cost function, which is designed using the insight given by the solution of the minimum-time control problem for a simplified system, namely, the double integrator, which is a reasonable model of the machine dynamic behavior. The experimental results obtained with a permanent-magnet synchronous motor and an induction machine, fed by a two-level three-phase inverter, confirm that this approach reaches a very good dynamic performance without a high computational effort.