Modulated predictive control for indirect matrix converter

Finite State Model Predictive Control (MPC) has been recently applied to several converter topologies as it can provide many advantages over other MPC techniques. The advantages of MPC include fast dynamics, multi-target control capability and relatively easy implementation on digital control platforms. However, its inherent variable switching frequency and lower steady state waveform quality, with respect to standard control which includes an appropriate modulation technique, represent a limitation to its applicability. Modulated Model Predictive Control (M2PC) combines all the advantages of MPC with the fixed switching frequency characteristic of PWM algorithms. The work presented in this paper focuses on the Indirect Matrix Converter (IMC), where the tight coupling between rectifier stage and inverter stage has to be taken into account in the M2PC design. This paper proposes an M2PC solution, suitable for IMC, with a switching pattern which emulates the desired waveform quality features of Space Vector Modulation (SVM) for matrix converters. The switching sequences of the rectifier stage and inverter stage are rearranged in order to always achieve zero-current switching on the rectifier stage, thus simplifying the current commutation strategy

Mitigation of DC Current Injection in Transformerless Grid-Connected Inverters

PhD ThesisWith a large number of small-scale PV plants being connected to the utility grid, there is increasing interest in the use of transformerless systems for grid-connected inverter photovoltaic applications. Compared to transformer-coupled solutions, transformerless systems offer a typical efficiency increase of 1-2%, reduced system size and weight, and reductions in cost. However, the removal of the transformer has technical implications. In addition to the loss of galvanic isolation, DC current injection into the grid is a potential risk. Whilst desirable, the complete mitigation of DC current injection via conventional current control methods is known to be particularly challenging, and there are remaining implementation issues in previous studies. For this reason, this thesis aims to minimize DC current injection in grid-connected transformerless PV inverter systems. The first part of the thesis reviews the technical challenges and implementation issues in published DC measurement techniques and suppression methods. Given mathematical models, the performance of conventional current controllers in terms of DC and harmonics mitigation is analyzed and further confirmed in simulations and experiments under different operating conditions. As a result, the second part of the thesis introduces two DC suppression methods, a DC voltage mitigation approach and a DC link current sensing technique. The former method uses a combination of a passive attenuation circuit and a software filter stage to extract the DC voltage component, which allows for further digital control and DC component mitigation at the inverter output. It is proven to be a simple and highly effective solution, applicable for any grid-connected PV inverter systems. The DC link sensing study then investigates a control-based solution in which the dc injection is firstly accurately determined via extraction of the line frequency component from the DC link current and then mitigated with a closed loop. With an output current reconstruction process, this technique provides robust current control and effective DC suppression based on DC link current measurement, eliminating the need for the conventional output current sensor. Results from rated simulation models and a laboratory grid-connected inverter system are presented to demonstrate the accurate and robust performance of the proposed techniques. This thesis makes a positive contribution in the area of power quality control in grid-connected inverters, specifically mitigating the impact of DC injection into the grid which has influences on the network operating conditions and the design and manufacture of the PV power converter itsel

Nove metode strujnog upravljanja pretvaračima energetske elektronike

n this dissertation, the analysis, development and experimental verification of new current mode control methods of power electronics converters is performed, in order to obtain improved performances compared to other relevant current mode control methods. New proposed current mode control methods have been developed by modification and improvement of the conventional dual current mode control (DCMC) method, which besides its excellent features, such as constant switching frequency, simple implementation and stability for the entire range of duty cycle, has a main drawback, and that is a current error – a difference between the average and reference inductor current. Two ways for eliminating the current error of DCMC method are proposed in this dissertation: using an adaptive current bandwidth, which is equal to the measured instantaneous peak-to-peak ripple of the inductor current, resulting in a new adaptive dual current mode control (ADCMC) method; inserting an inner current-loop compensator (application of I2 concept) in the DCMC structure, which leads to a new I2 DCMC method. By using the I2 concept on ADCMC, a new I2 ADCMC method is also derived. After mathematical analysis and modelling, the operation of the proposed current mode control methods, applied on three basic DCDC converters: buck, boost and non-inverting buck-boost converter, was tested with simulations in Matlab/Simulink. Afterwards, development and realization of the experimental platform (multipurpose converter’s prototype, control and measurement electronic module), which is used for experimental verification of the proposed control methods on different types of converters, were performed. The obtained simulation and experimental results confirmed the excellent performances of the proposed current mode control methods: equality between the average and reference inductor current, stability for whole range of duty cycle, excellent dynamics of the current loop, robustness to the input voltage and load disturbances of converters, etc. Thanks to these qualities, the proposed control methods can be applied to practically all types of converters. Some new ideas for further improvements of the proposed control methods and for their implementation in specific applications of existing and some future converters topologies are also presented in this dissertation