When paralleling multiple inverters that are capable of operating as an island, the inverters typically employ the droop control scheme. Traditional droop control enables the decentralized regulation of the local voltage and frequency of the microgrid by the inverters. The droop method also enables the inverters to share the real and reactive power required by the loads. This paper focuses on some of the limitations of parallel islanded single phase inverters using droop control. Algorithms with the aim to address the following limitations in islanded operation were proposed: reactive power sharing and reduction of the voltage harmonic distortion at the point of common coupling (PCC). Experimental results were then presented to show the suitability of the proposed algorithms in achieving reactive power sharing and in improving the voltage harmonic distortion at the PCC.

Microgrids are an effective way to increase the penetration of distributed generation into the grid. They are capable of operating either in grid-connected or in islanded mode, thereby increasing the supply reliability for the end user. This paper focuses on achieving seamless transitions from islanded to grid-connected and vice versa for a single phase microgrid made up from voltage controlled voltage source inverters (VC-VSIs) and current controlled voltage source inverters (CC-VSIs) working together in both modes of operation. The primary control structures for the VC-VSIs and CC-VSIs is considered together with the secondary control loops that are used to synchronize the microgrid as a single unit to the grid. Simulation results are given that show the seamless transitions between the two modes without any disconnection times for the CC-VSIs and VC-VSIs connected to the microgrid.

Optimization of the islanded and grid-connected operation of microgrids is important to achieve a high degree of reliability. In this paper, the authors consider the effect of current harmonics in single phase microgrids during both modes of operation. A detailed analysis of the effect of the output impedance of the considered primary control loops on the harmonic output of the considered voltage source inverters is initially carried out. A virtual admittance loop is proposed to attenuate the current harmonic output in grid-connected operation that is generated due to the grid voltage distortion present at the point of common coupling (PCC) and due to local non-linear loads. This paper also considers the harmonic current sharing and resulting voltage harmonics at the PCC during islanded operation of the microgrid. A capacitive virtual impedance loop was implemented to improve the harmonic current sharing and attenuate the voltage harmonics at the PCC. Experimental results are given to validate the operation of the proposed algorithms.

Recently there has been considerable interest in the use of matrix converter technology for motor drive applications, with particular interest being shown by Siemens, Rockwell and Yaskawa. An introduction to matrix converter technology is given and the suitability and design of matrix converters for industrial applications is reviewed. The potential advantages of matrix converter technology are examined and the factors that have so far prevented commercial exploitation Of the circuit are discussed. The remaining technical challenges are defined and the work in progress to meet these challenges are highlighted.

This paper is concerned with the process of current commutation in matrix converters. The mechanisms involved in the commutation process are described and practical waveforms are presented. A novel commutation strategy is described that uses gate drive level intelligence in the form of a field-programmable gate array. Current direction is determined using device voltages and, therefore, the measurement problems associated with all other commutation methods are overcome. Practical results from an 18-kW matrix converter induction motor drive are presented.

Matrix converters are becoming a real alternative to traditional topologies for many ac-ac power conversion applications. One of the less well-known advantages is the potential for reduced waveform distortion that arise from device characteristics and commutation delays. This paper describes the origin of distortion effects for a matrix converter with current sign-based commutation and gives a novel approach to the method that can, in principle, eliminate the distorting effects to give a power converter having excellent linear behavior. The effectiveness of compensation techniques are illustrated for both an open-loop matrix converter driving a passive load and a matrix converter as part of a vector-controlled drive.