The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

Adaptive reference model predictive control for power electronics

An adaptive reference model predictive control (ARMPC) approach is proposed as an alternative means of controlling power converters in response to the issue of steady-state residual errors presented in power converters under the conventional model predictive control (MPC). Differing from other methods of eliminating steady-state errors of MPC based control, such as MPC with integrator, the proposed ARMPC is designed to track the so-called virtual references instead of the actual references. Subsequently, additional tuning is not required for different operating conditions. In this paper, ARMPC is applied to a single-phase full-bridge voltage source inverter (VSI). It is experimentally validated that ARMPC exhibits strength in substantially eliminating the residual errors in environment of model mismatch, load change, and input voltage change, which would otherwise be present under MPC control. Moreover, it is experimentally demonstrated that the proposed ARMPC shows a consistent erasion of steady-state errors, while the MPC with integrator performs inconsistently for different cases of model mismatch after a fixed tuning of the weighting factor

An area-time efficient FPGA-implementation of online finite-set model based predictive controllers for flying capacitor inverters

Recently there has been an increase in the use of model-based predictive control (MBPC) for power-electronic converters. Especially for flying-capacitor multilevel converters (FCC) this offers an interesting possibility to simultaneously control output current and the capacitor voltages. The computational burden however is very high and often restrictive for a good implementation. In this paper a time and resource efficient design methodology is presented for the FPGA implementation of FCC MBPC. The control is fully implemented in programmable digital logic. Due to a parallel processing for the three converter phases and a fully pipelined calculation of the prediction stage an area-time efficient implementation is realized. Furthermore, this is achieved by using a high-level design tool. The implementation aspects for 3, 4 and 5-level FC inverters are discussed, with a focus on the 4-level case

A predictive control with flying capacitor balancing of a multicell active power filter

Unlike traditional inverters, multicell inverters have the following advantages: lower switching frequency, high number of output levels, and less voltage constraints on the insulated-gate bipolar transistors. Significant performances are provided with this structure which is constituted with flying capacitors. This paper deals with a predictive and direct control applied to the multicell inverter for an original application of this converter: a three-phase active filter. To take advantage of the capabilities of the multicell converter in terms of redundant control states, a voltage control method of flying capacitor is added, based on the use of a switching table. Flying capacitor voltages are kept on a fixed interval, and precise voltage sensors are not necessary. The association of predictive control and voltage balancing increases considerably the bandwidth of the active filter

FPGA implementation of online finite-set model based predictive control for power electronics

Recently there has been an increase in the use of model based predictive control (MBPC) for power-electronic converters. MBPC allows fast and accurate control of multiple controlled variables for hybrid systems such as a power electronic converter and its load. The computational burden for this control scheme however is very high and often restrictive for a good implementation. This means that a suitable technology and design approach should be used. In this paper the implementation of finite-set MBPC (FS-MBPC) in field-programmable gate arrays (FPGAs) is discussed. The control is fully implemented in programmable digital logic by using a high-level design tool. This allows to obtain very good performances (both in control quality, speed and hardware utilization) and have a flexible, modular control configuration. The feasibility and performance of the FPGA implementation of FS-MBPC is discussed in this paper for a 4-level flying-capacitor converter (FCC). This is an interesting application as FS-MBPC allows the simultaneous control of the output current and the capacitor voltages, yet the high number of possible switch states results in a high computational load. The good performance is obtained by exploiting the FPGA’s strong points: parallelism and pipe-lining. In the application discussed in this paper the parallel processing for the three converter phases and a fully pipelined calculation of the prediction stage allow to realize an area-time efficient implementation

Innovative Predictive Current Control for Synchronous Reluctance Machines

In recent decades, the use of power converters has become very popular in the field of electric drives. Several control techniques have been proposed for power converters and every year, the ongoing research and the always more powerful microprocessors, lead to new high performance solutions. Despite this, since the output of the worldwide research often results in complex and hardly applicable solutions, other well-established techniques, such as linear and hysteresis control with pulsewidth modulation, are still the main choice in a great number of industrial applications. The reasons of their leadership can be found considering the characteristics of these methods: on one side simplicity of comprehension and implementation and, on the other, sufficiently good performance and robustness. Due to these relevant features, despite there is still extensive room for improvements, it is not painless to propose solutions that can be attractive for people working in industry to compete with, and possibly to replace, traditional methods. Desirably, a control algorithm for electric drives has to be simple and easily understandable. Besides, it has to be suitable for real-time applications. Robustness and reliability, beyond that performance, have to be guaranteed since the nature of the different applications, e.g. home appliances and automotive. In this perspective, Predictive Control could represent a candidate to introduce improvements and gains in the aforementioned industrial applications. Predictive control is a wide class of controllers that uses the model of the system for the prediction of the future behavior of the controlled variables. This information is used by the regulator in order to obtain the optimal actuation, according to a predefined optimization criterion represented by a cost function. This control techique is based on concepts that are extremely simple and intuitive and besides, depending on the type of predictive control, the implementation can also be simple. In parcticular, Finite Control Set allows considering the discrete nature of the power converter and results in an extremely simple implementation. Beyond simplicity, other advantages can be recognized. First, with predictive control it is possible to avoid the cascaded structure obtaining a very fast transient response. Besides, nonlinearities can be included in the model avoiding the need of linearizing the model for a given operating point and improving the operation of the system for all conditions. Finally, it is possible to include limitations of the variables when designing the regulator. The aim of this thesis is to study Predictive Control applied to the current control of synchronous reluctance machines, analysing and addressing some open research topics regarding this kind of control. In particular, two main aspects are studied, namely the need of a precise knowledge of the machine model and the possibility to drive a synchronous reluctance machine along the Maximum Torque per Ampere, the Flux Weakening and the Maximum Torque per Voltage operations. The performance are strictly related to the accuracy of the model used for the prediction. In case of parameters mismatch or variation, rather than other model inadequacies, the prediction could be affected causing a worsening of the overall behaviour of the drive. The first part of this work is commited to study this aspect, analysing the effects of mismatches and variations focusing in particular on the detrimental effects of iron saturation. A novel model-free solution is presented to overcome the limitations given by an inadequate model. This method allows achieving good reference tracking and limited current ripple in every working condition. Besides, it presents great advantages in terms of simplicity: no additional hardware and no complicated calculations are required. The design is effortless since there are no gains, thresholds and so on, that have to be tuned. This technique could be used to develop an universal drive, meaning that completely different machines could be controlled with exactely the same algorithm, without self commissioning or identification procedures. Thanks to the aforementioned features, this techique could allow the spread of predictive control in industrial applications. In order to fully exploit the characteristics of the drive while assuring the lowest power losses in every working condition, a proper control algorithm has to be used. In the second part of this work, a predictive regulator able to track the most suitable trajectory depending on the machine operation is presented. In particular, the Maximum Torque per Ampere, the Flux Weakening and the Maximum Torque per Voltage trajectories are considered. The proposal is a combination of predictive control and hysteresis control, since its aim is to keep the current error within a certain hysteresis band, and it allows combining the benefits of the two control techniques. This study is carried out considering Predictive Current Control for Synchronous Reluctance machines. This kind of machine has been considered since it is of great interest due to the fact that it features high power density, superior reliability, high efficiency and it is cost effective due to the absence of permanent magnets and circuits in the rotor. Besides, since its significant iron saturation, its control represents a challenge (in particular) for predictive control schemes and for this reason it is a perfect case study

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386