Ulrich Ammann

Predictive Current Control of a Voltage Source Inverter

This paper presents a predictive current control method and its application to a voltage source inverter. The method uses a discrete-time model of the system to predict the future value of the load current for all possible voltage vectors generated by the inverter. The voltage vector which minimizes a quality function is selected. The quality function used in this work evaluates the current error at the next sampling time. The performance of the proposed predictive control method is compared with hysteresis and pulsewidth modulation control. The results show that the predictive method controls very effectively the load current and performs very well compared with the classical solutions

Model Predictive Control—A Simple and Powerful Method to Control Power Converters

This paper presents a detailed description of finite control set model predictive control (FCS-MPC) applied to power converters. Several key aspects related to this methodology are, in depth, presented and compared with traditional power converter control techniques, such as linear controllers with pulsewidth-modulation-based methods. The basic concepts, operating principles, control diagrams, and results are used to provide a comparison between the different control strategies. The analysis is performed on a traditional three-phase voltage source inverter, used as a simple and comprehensive reference frame. However, additional topologies and power systems are addressed to highlight differences, potentialities, and challenges of FCS-MPC. Among the conclusions are the feasibility and great potential of FCS-MPC due to present-day signal-processing capabilities, particularly for power systems with a reduced number of switching states and more complex operating principles, such as matrix converters. In addition, the possibility to address different or additional control objectives easily in a single cost function enables a simple, flexible, and improved performance controller for power-conversion systems.

Predictive Control of a Three-Phase Neutral-Point-Clamped Inverter

A new predictive strategy for current control of a three-phase neutral-point-clamped inverter is presented. The algorithm is based on a model of the system. From that model, the behavior of the system is predicted for each possible switching state of the inverter. The state that minimizes a given quality function is selected to be applied during the next sampling interval. Several compositions of are proposed, including terms dedicated to achieve reference tracking, balance in the dc link, and reduction of the switching frequency. In comparison to an established control method, the strategy presents a remarkable performance. The proposed method achieves comparable reference tracking with lower switching frequency per semiconductor and similar transient behavior. The main advantage of the method is that it does not require any kind of linear controller or modulation technique, achieving a different approach to control a power converter.

New time-discrete modulation scheme for matrix converters

While the known modulation strategies for matrix converters are based on pulsewidth modulation (PWM)-or vector modulation-this paper presents a novel time-discrete modulation method based on real-time prediction calculation to select the switching states. The decision about which switching state is to be set for the following sampling period is made by the use of a predictive quality function. Using this approach, unity displacement factor is seen at the supply side with minimum line current distortion while the load currents follow their reference values with good accuracy. The quality function is derived from a mathematical model of the matrix converter and the controlled system. Measurements taken on a model plant, consisting of a matrix converter and a standard induction machine with a rated output power of 11 kW, show that the matrix converter, equipped with the control method presented here, offers advantages over systems with conventional frequency converters, especially in terms of the input current distortion.

Predictive Current Control of an Induction Machine Fed by a Matrix Converter With Reactive Power Control

A different approach to perform the control of an induction machine fed by a matrix converter (MC) is presented in this paper. The proposed technique is based on predictive control and effectively controls input and output variables to the power converter, as expected from an MC. The method allows the use of all valid switching states, including rotating vectors that are not considered in most control techniques, as space vector modulation or direct torque control for induction machines fed by MCs. Experimental results show the excellent performance of the proposed approach, with low-distortion input currents, adjustable power factor, sinusoidal output currents with smooth frequency transitions, and good speed control in motoring and regeneration conditions, even working under an unbalanced power supply. The implementation and comprehension of the method should be considered simple compared to other control strategies with similar features. The high computational effort required should not be a problem considering recent progresses in digital signal processors-and even less in years to come.

Predictive Torque Control of an Induction Machine Fed by a Matrix Converter With Reactive Input Power Control

This paper presents a new control method for a matrix-converter-based induction machine drive. A discrete model of the converter, motor, and input filter is used to predict the behavior of torque, flux, and input power to the drive. The switching state that optimizes the value of a quality function, used as the evaluation criterion, is selected and applied during the next discrete-time interval. Experimental results confirm that the proposed strategy gives high-quality control of the torque, flux, and power factor with a fast dynamic control response. The key implementation issues are analyzed in depth to give an overview of the realization aspects of the proposed algorithm.

Predictive Approach to Increase Efficiency and Reduce Switching Losses on Matrix Converters

The matrix converter stands as an alternative in power conversion. It has no energy storage devices, performing the energy conversion by directly connecting input with output phases through bidirectional switches based on power semiconductors, allowing high-frequency operation. For this reason, it is known as the all-silicon power converter, featuring reduced size and weight. Forced commutations of the high number of semiconductors cause switching losses that reduce the efficiency of the system and imply the use of large heat sinks. This paper presents a novel method to reduce switching losses based on predictive control. The idea is to predict switching losses for every valid switching state of the converter, if applied during the next sampling time, and then, select the optimum state based on an evaluation criterion. The proposed strategy was experimentally tested on an 18-kVA matrix converter driving an 11-kW induction machine, reducing energy losses and increasing efficiency up to 3% compared to the basic strategy. As a consequence, the converter misuses less energy and requires smaller heat sinks.

Predictive Strategy to Control Common-Mode Voltage in Loads Fed by Matrix Converters

Common-mode voltages (CMVs) cause overvoltage stress to the winding insulation and bearings deterioration, reducing the lifetime of electric machines. This paper presents a predictive strategy that effectively mitigates CMVs from matrix converters (MCs), without affecting its functionality and allowing the use of rotating vectors. The method was experimentally tested on an MC feeding an induction machine, mitigating CMVs in 70% and reducing abrupt changes. The reduction is achieved with no tradeoff on the performance of the drive until reaching 40%, point where further reduction comes with an increase on the total harmonic distortion of line side currents. The designer can adjust the method in order to protect the AC machine, extending its lifetime and reducing negative effects of CMVs, and still comply with the standard for connection to the grid due to the flexibility allowed by the proposed strategy.

New modulation strategy for a matrix converter with a very small mains filter

While known modulation strategies for matrix converters are based on PWM or vector-modulation, this paper presents a novel time-discrete modulation method by which the switching state of the matrix converter is changed only at equidistant points in time. The decision about which switching state is to be set for the following sampling period, is made by use of a quality function. Using this approach, the switching state is selected in such a way as unity displacement factor is seen at the supply side whilst the load currents follow their reference values with good accuracy. The quality function mentioned above is determined via a mathematical model of the matrix converter and the controlled system. The one switching state that induces the optimum value of the quality function is selected for the next sampling interval. Measurements taken on a model plant, consisting of a matrix converter and a standard induction machine with a rated output power of 11 kW show that the matrix converter, equipped with the control method presented here, offers some advantages over systems with conventional frequency converters.

Cost Function-Based Predictive Control for Power Converters

This paper presents a cost function-based predictive control strategy and its application to the control of power converters and drives. Discrete-time models of the system are used to predict the behavior of the controlled variables for all the possible switching states of the converter. A cost function defines the desired behavior of the system. The switching state that minimizes this function is selected and applied during the next sampling period. Different variables of the system can be controlled by defining an appropriate cost function, depending on the objective of each specific application