A new approach is proposed here to control the two-level three-phase grid side converter. The proposed control strategy is an extended state observer (ESO)-based adaptive control, consists of two cascaded control loops. The adaptive-multi-input multi-output controller is employed in the inner control loop, which is used to regulate the active and reactive component of the grid currents. The outer-loop consists of an adaptive controller augmented with an ESO to regulate the DC bus voltage. The goal of the proposed control strategy is to maintain a unity power factor while keeping the DC bus voltage constant under a sudden change in load demand at DC side, i.e. change in the resistive load connected across the DC bus. The proposed adaptive controller in the inner control loop does not require any information about the parameters associated with the grid filter (L-filter), and hence, it is found to be more robust towards parametric variations. The ESO-based adaptive controller is compared with the classical proportional–integral control in real-time, and the comparison indicates that the proposed controller not only accomplishes a nearly flawless tracking performance but also delivers a complete robust performance against resistive load variation across the DC bus.

This study presents a multi-fault tolerant strategy for a cascaded H-bridge (CHB) based static synchronous compensator (STATCOM) with star configuration. A new method for post-fault operation of CHB-STATCOM is proposed, where after switch failures, the full-bridge (FB) submodules are used as two different types of half-bridge submodules named as positive half-bridge (P-HB) and negative half-bridge (N-HB). Using a modified level shift pulse-width modulation technique, a combination of FB, P-HB and N-HB submodules is employed in three legs of the converter to generate the maximum attainable ac side voltage in post-fault condition. In order to restore the nominal capacity of CHB-STATCOM, the capacitor voltage of submodules is increased based on the type and number of switch failures. Furthermore, by utilising a voltage balancing strategy, the voltages of submodules’ capacitors are kept balanced and regulated at the desired value in post-fault condition. The feasibility and effectiveness of the proposed strategy is validated on a scaled-down 9-level CHB-STATCOM laboratory prototype.

The integration of the distributed generation to the unbalanced loads or the grid requires a three-phase four-wire inverter. The three-phase four-wire inverter could be of three-leg or four-leg topology. However, both the topologies have their drawbacks. The three-leg inverter topology with a split capacitor suffers from poor DC link voltage regulation and poor DC link voltage utilisation. The four-leg inverter topology suffers from poor electromagnetic compatibility. To solve these problems, the split link inverters with active balancing capabilities are studied by many researchers. The split link inverter with an active balancing inverter requires a constant DC link voltage and has less flexibility regarding the variation of the DC link voltage. In this study, a new converter topology is proposed, which provides the controllable DC link voltage to split link inverter with active balancing capability and also reduces the voltage stress to semiconductor switches to half DC link voltage. The detailed description of the proposed converter topology, design of the controller, and control hardware-in-the-loop verification are presented in this study.

This study presents a novel solid-state transformer (SST) with four ports that can connect the medium-voltage (MV) DC bus, the MV AC bus, the low-voltage (LV) DC bus, and the LV AC bus, respectively. This SST is suitable for application in the hybrid AC/DC power grid that functions as an energy router between AC and DC systems. Furthermore, the SST submodule is enhanced with two types of dual-half bridge converters, namely DHSM1 or DHSM2, depending on if an additional active switch is used to block the possible short circuit. Thanks to the designed structure of the proposed SST that combines DHSM1 and DHSM2 as the front-end stage, it achieves reduced hardware complexity with the remaining capability to handle the DC short-circuit fault that may occur at the medium- or high-level voltage DC grid. In addition, an optimised overall control strategy that can reduce the measurement demand and control complexity is proposed, with the possible power flow path inside the SST fully analysed. Simulation and experimental results validate the feasibility of the proposed SST and the effectiveness of the overall control scheme with the DC fault handle capability.

In this study, a new approach based on adaptive dynamic programming (ADP) is proposed to control permanent magnet synchronous motors (PMSMs). The objective of this study is to control the torque and consequently the speed of a PMSM when an unknown load torque is applied to it. The proposed controller achieves a fast transient response, low ripples and small steady-state error. The control algorithm uses two neural networks, called critic and actor. The former is utilised to evaluate the cost and the latter is used to generate control signals. The training is done once offline and the calculated optimal weights of actor network are used in online control to achieve fast and accurate torque control of PMSMs. This algorithm is compared with field oriented control (FOC) and direct torque control based on space vector modulation. Simulations and experimental results show that the proposed algorithm provides desirable results under both accurate and uncertain modelled dynamics. Although the performance of FOC method is comparable with ADP under nominal conditions, the torque and speed response of ADP is better than FOC under realistic scenarios, that is, when parameter uncertainties exist.