Power converters systems aimed at renewable energy applications have become a common option for sustainable electricity and distributed generation, since their performance has improved, and prices have steadily been reduced in the last years. However, there are still several drawbacks that hinder their widespread installation, such as the simultaneous minimization of cost and volume, efficiency maximization, size reduction, etc. Quite often, accomplishing these goals requires dealing with complicated optimization problems, which are difficult to solve by classical methods. Metaheuristic techniques provide a viable alternative to solve complex intricate optimization problems, such as those encountered in the development of power electronics converters. This paper presents a comprehensive coverage of metaheuristic methodologies applied in the area of power converters. The review includes a classification of the methodologies and main objective functions in each paper surveyed. An aim for this paper is to highlight the importance of the optimization tools, and the many benefits they provide to tackle the challenges encountered in the design, operation, and control of power converters.

Metaheuristic Optimization Methods Applied to Power Converters: A Review

The wind turbine generator system requires a power conditioning circuit called power converter that is capable of adjusting the generator frequency and voltage to the grid. Several types of converter topologies have been developed in the last decades; each of them has some advantages and disadvantages. Mainly two converter topologies are currently used in the commercial wind turbine generator systems. Most of the proposed converters require line filters and transformers to improve the power quality and step-up the voltage level, respectively. These heavy and bulky components significantly increase the tower construction, and turbine installation and maintenance costs. Recent advances in power semiconductors and magnetic materials have led to the development of new structure of converters, which would be a possible solution to reducing the size, weight, and cost of power converters. In this chapter, a comprehensive study of power converter technologies, current research and development is conducted.

Power converters for wind turbines: Current and future development

In This paper a generalized formulation for selective harmonic elimination for cascade and Modular multilevel converters is considered. Modular multilevel converter is a new type converter that is similar to cascade multilevel converters. This converter consists of several sub-modules. In this formulation the amount of DC sources are considered as variables with certain constraints. Therefore the degree of freedom is increased in comparison with conventional method and low order harmonic elimination and THD minimization is achieved by optimum selection of switching angles and amount of DC sources. For the solution of this problem a method based on harmony search approach is used because this method has high rate of convergence, precision and simplicity compared to other optimization methods. Simulation results show the effectiveness of this method.

A generalized optimization in cascade and Modular multi-level inverters by harmony search method

Multilevel inverters have been drawing growing attention in the recent years especially in the distributed energy resources area due to the fact that several batteries, fuel cells, solar cell, wind and micro turbines can be connected through multilevel inverter to feed a load or the ac grid. Multilevel inverter becomes an alternative in the area of high- power medium-voltage energy control. Therefore, Harmonic Reduction in multi level inverters are considered very important task. For eliminating the harmonics lot of researchers have suggested modifications in the circuit topology and optimal selection of firing angle using conventional and nonconventional optimization algorithms. This paper presents a review application by different optimization techniques for harmonic reduction in multilevel inverters.

A Review on Mitigation of Harmonics in Cascaded H- Bridge Multilevel Inverter using optimization Techniques

Among all control methods for induction motor drives, Direct Torque Control (DTC) seems to be particularly interesting being independent of machine rotor parameters and requiring no speed or position sensors. The DTC scheme is characterized by the absence of PI regulators, coordinate transformations, current regulators and PWM signals generators. In spite of its simplicity, DTC allows a good torque control in steady state and transient operating conditions to be obtained. This paper is aimed to analyze DTC principles, the strategies and the problems related to its implementation and the possible improvements using Space Vector Pulse Width Modulation (SVPWM). In SVPWM for each sampling period the switching instants of different space vectors are determined to reduce torque ripple. The time durations of two adjacent voltage space vectors and the corresponding zerovoltage space vectors are determined in this method depending on maximum and average switching frequency, allowable for the switching devices in the three phase inverter. Simulation studies have been carried out for different operating conditions of the drive system. The results have been presented and compared with those of the conventional method.

http://dspace.nitrkl.ac.in:8080/dspace/bitstream/2080/725/1/bcbabu2008.pdf

High Performance Direct Torque Controlled Induction Motor Drive for Adjustable Speed Drive Applications

In this paper, the operation principle of the Z-source inverter is analyzed in detail. According to the characteristics of allowed short-shrougt zero state in the Z-source inverter, SPWM control method of the Z-source inverter is obtained by inserting fixed short-shrougt zero state into zero state of SPWM. It is simple and easily implemented in practice. However, in inductive load condition the output voltage and current of Z-source inverter have serious distortion and affect the inverting quality. The cause of this distortion is analyzed in detail and an improved SPWM control method is proposed, which can better solve the output voltage and current distortion problem of the Z-source inverter under the condition of inductive load. Matlab simulation results verify that the improved SPWM control method not only eliminates distortion caused by inductive load, but also decreases the switch times and quantities in each cycle. Therefore, it decreases the THD of AC output effectively and improves the efficiency of the inverter, and its theoretical analysis is verified to be effective.

An Improved Control Method for Inductive Load of Z-Source Inverter

This paper presents a stochastic Newton method to compute the switching angles in multilevel converters so as to produce the required fundamental voltage while at the same time not generate higher order harmonics. For Newton method, a good initial guess which should be very close to exact solution patterns is necessary, so using stochastic techniques gives a new way to find possible initial values, such as the beginning process of particle swarm optimization (PSO). This synthetic method is called stochastic Newton method (SNM), which is applied to multilevel inverters with any number of levels. All sets of solutions are found for eleven and nineteen levels converters to show the simplicity, effectiveness, and easy implementation of SNM.

Elimination of Harmonics in Multilevel Converters Using Stochastic Newton Method

Selected harmonic eliminated pulse width modulation technique applicable to the five-level voltage-source inverter is studied in details in this paper, which includes the foundation of selected harmonic elimination nonlinear equations and the chosen for initial switching angles. A method for producing initial angles of the nonlinear equations by using SPWM control is adopted, which may get a high convergence speed of the nonlinear equations. According to the switching angles obtained by solving the nonlinear equations numerically, the five-level inverter is simulated with MATLAB and the harmonic elimination effect using SHEPWM Technique is compared with that using traditional SPWM Technique. Simulation results proved the advantages of SHEPWM Technique.

Jianze Wang

Papers

An Improved Control Method for Inductive Load of Z-Source Inverter

Elimination of Harmonics in Multilevel Converters Using Stochastic Newton Method

Research on Solutions to Selective Harmonic Eliminated PWM Switching Angles for Novel Five-level Inverter