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Here, a finite-control-set sliding-mode control (FCS-SMC) method is proposed for single-phase three-level T-type inverter-based transformerless dynamic voltage restorers (TDVRs). The inherent advantages of SMC (fast dynamic response and high robustness) are combined with FCS concept to increase the effectiveness of the method in achieving the desired control objectives. First, the use of FCS eliminates the modulator requirement, which reduces the design complexity in the practical implementation. Second, an effective method based on charging/discharging conditions of DC capacitors is proposed for balancing capacitor voltages using relevant switching state rather than combining DC voltage error with the inductor current error through a suitable weighting factor in forming the cost function. Therefore, the weighting factor necessity in the control algorithm is eliminated. Finally, the steady-state error in the compensation voltage is eliminated by the proportional-resonant (PR) controller. The studied T-type inverter-based TDVR topology offers an alternative solution to the existing DVR topologies. Experimental results are carried out to demonstrate the effectiveness of the proposed FCS-SMC method in maintaining the load voltage at the desired level despite the voltage sags, swells, and distortions occurring in the grid voltage.

The pulse-width amplitude modulation (PWAM) method was proposed for the single-phase quasi-Z-source inverter (qZSI)-based photovoltaic (PV) power system to reduce quasi-Z-source (qZS) impedance values while improving efficiency. The method modified sinusoidal pulse-width modulation (SPWM) of the qZSI by combining pulse-amplitude modulation (PAM) and a varied dc-link voltage envelope was produced. The SPWM worked at low dc-link voltage, lowering voltage stress and avoiding shoot-through switching. The PAM worked at the varied dc-link voltage, reducing the number of switching events. As a result, the power dissipation decreased compared to working at the constant dc-link voltage. This study further investigates the PWAM-based single-phase qZS PV inverter system. An improved topology with control strategy is proposed for its grid-connected and standalone operation. Design method of impedance parameters is detailed. The performance in boost and buck operation is discussed when the single-phase qZSI using SPWM and PWAM. Simulation and experimental results verify outstanding features of the PWAM for single-phase qZSI, and the proposed approach for dual-mode operation of the PWAM-based single-phase qZS PV power system.

This study presents a high-efficient maximum power point tracking (MPPT) of photovoltaic (PV) systems by means of model-predictive control (MPC) techniques that is applied to a high-gain DC-DC converter. The high variability and stochastic nature of solar energy requires that the MPPT control continuously adjust the power converter operating point in order to track the changing maximum power point; a concept well known in the literature. The main contribution of this study is a model-predictive-based controller with a fixed step that is combined with the traditional incremental conductance (INC) method. This technique improves the speed at which the controller can track rapid changes in solar insolation and results in an increase in the overall efficiency of the PV system. The controller speeds up convergence since MPC predicts error before the switching signal is applied to the high-gain multilevel DC-DC converter and thus is able to choose the next switch event to minimise error between the commanded and actual converter operation. Comparing the proposed technique to the conventional INC method shows substantial improvement in MPPT effectiveness and PV system performance. The performance of the proposed MPC-MPPT is analysed and validated experimentally.

This study presents a decoupled active and reactive power control technique, for a single-phase grid-tied inverter, using model predictive control (MPC). The proposed technique does not use conventional phase-locked loop, pulse-width modulation nor a synchronisation transform, which makes the control algorithm well suited for an all-digital implementation. The proposed controller minimises the number of switching state transitions required to control the grid-side current while simultaneously constraining the harmonics distortions and protecting the inverter from overcurrent condition. In this study, the switching frequency is reduced by using a look-up table to minimise the number of switching state transitions, which helps lowering down the switching losses. The proposed technique uses an adaptive weight factor which gives more priority to commanded power tracking during transient, and minimises the tracking error and switching frequency in steady state while constraining the harmonics distortion. This method improves the tracking performance as well as reduces the switching losses by minimising the switching frequency compared to the MPC with fixed weight factor and conventional decoupled power control. Thus, the outcome of proposed controller is a constraint multi-objective optimisation between the switching frequency reduction and grid-side current harmonics in terms of cost function with weighting factor.

This study presents fuzzy-proportional-integral (PI)-based sensorless frequency and voltage control strategy for doubly fed induction generator connected to a dc microgrid system. A significant reduction of the costs can be achieved by this topology because only a single dc/ac converter and a diode rectifier are required instead of the traditional back-to-back converter topology. To improve the performance of the rotor current controller, a fuzzy PI-based control algorithm is used. Furthermore, a simple sensorless control technique based on the detection of the stator frequency is employed to detect the rotor position. The sensorless control technique can operate without the knowledge of the machine parameters. The main aim of this study is to keep the stator frequency as well as the dc bus voltage at the desired value under different load and wind speed conditions without using position sensor. Simulation and experimental studies were performed to verify the dynamic and steady-state performances of the proposed control strategy The results show that the proposed strategy not only has an excellent steady state and dynamic performance, but also it is robust against the variation of system parameters such as wind speed and load.

This study presents a novel sensorless model predictive control (MPC) strategy of a wind-driven doubly fed induction generator (DFIG) connected to a dc microgrid. In this configuration, the stator is directly connected to the dc microgrid through a diode rectifier, and the rotor is fed by only a voltage source converter (VSC). This connection structure brings considerable benefits such as simple control scheme and reduced power converter cost. In order to obtain sensorless operation, a simple and effective sensorless position detection technique has been proposed. It is based on the detection of the stator frequency, and it is designed to operate without any machine parameters. Thus, the proposed sensorless method offers as a model-free solution. In addition, the MPC strategy has been used as a current controller to overcome the weaknesses of the inner control loop and to consider the discrete-time operation of the VSC. The proposed control system is robust against machine parameters, speed, and load variations. To verify the dynamic and steady-state performances of the proposed sensorless MPC scheme under various speed and load conditions, experimental studies are performed with 6.4 kW DFIG. Experimental results aim to show that the proposed sensorless MPC strategy works properly at steady state and in transient.

This paper discusses the space vector pulse width modulation (SVPWM) scheme for an eleven-phase two-level voltage source inverter (VSI), aimed at producing a sinusoidal output voltage waveform. Generalised space vector theory is used to realise the SVPWM. As per the general inverter switching theory, there are 211 = 2048 switching states that yield 2046 active voltage space vectors and one zero voltage vector, which results with two switching states. Out of the total of 2046 active voltage vectors, the most suitable set comprising 110 active voltage vectors is identified and is utilised in the implementation of the SVPWM. The sinusoidal voltage is obtained by controlling the duty cycles of the applied voltage space vectors in such a way that the non-zero reference voltage in the first (d-q) plane is achieved, while simultaneously zeroing the average voltage in the other four (x-y) planes in accordance with the zero references. The theoretical results are verified by experimentation using a passive resistive-inductive load. Finally, experimentally obtained THD values of the phase voltage and current for the eleven-phase SVPWM are compared with the corresponding values obtained using SVPWM for other odd phase numbers.\ud \ud Keywords: Eleven-phase system, Multi-phase drives, Space vector PWM, Voltage source inverter

The quasi-Z-source inverter (qZSI) with battery can balance the stochastic fluctuations of PV power injected to the grid/load, but there is no literature to disclose its modelling and controller design in detail. This study proposed a dynamic small-signal model of qZSI with battery and a control strategy for photovoltaic (PV) power generation system. The built model discloses the dynamic relationship of PV panel voltage, battery current, quasi-Z-source inductor currents and capacitor voltages. The proposed control method achieves the grid-tie operation with unity power factor, PV panel's maximum power point tracking and battery management. The novel space vector modulation for the qZSI divides the total shoot-through time interval into six equal parts per control cycle to be combined into the six switching moments, and lower inductor current ripple and higher inverter efficiency are performed. The experimental and simulation results verify the theoretical analysis and proposed control methods.

A phase-shifted pulse-width-amplitude modulation (PS-PWAM) is proposed for a quasi-Z-source cascade multilevel inverter (qZS-CMI)-based photovoltaic power system. The switching actions of each power device of the qZS-CMI in the PS-PWAM technique are greatly reduced when compared with that in the phase-shifted sinewave pulsewidth modulation, so the qZS-CMI's power loss is reduced when using the PS-PWAM. The PS-PWAM principle and the qZS-CMI's loss analysis are presented. The simulation and experimental results verify the proposed PS-PWAM and the resultant efficiency improvement.

There are three existing space-vector modulation (SVM) methods for three-phase Z-source/quasi-Z-source inverter (ZSI/qZSI), and a new one can be extended from the existing SVMs. These four SVMs are never compared and evaluated in terms of their performances. This study conducts the theoretical analysis and experimental evaluations of four SVMs. The switching control patterns, the available shoot-through duty ratio, the boost capability, the maximum voltage stress across the switch, inductor current ripple, total average switch device power, ac output current's harmonic and efficiency are fully addressed in the theoretical and experimental comparisons. A three-phase qZSI prototype is built to carry out the experimental evaluation. The valuable suggestions are summarised in the conclusion.