Active damping (AD) is a popular approach to suppress the resonance in LCL filtered grid-connected inverter (GCI) owing to lossless damping and efficient system design. In capacitor voltage (CV) damping methods, a differential compensator is essentially needed in feedback path where the damping effectiveness depends on emulated derivative characteristics of the compensator. Such capacitor voltage feedback compensation (CVFC) methods face design limitation at the critical resonance frequency and may require additional delay reduction to ensure stability. In this paper, an alternative parallel feedforward compensation (PFC) method is proposed to synthesize an almost strictly positive real (ASPR) plant and achieved damping with modified stability characteristics. A second-order bandpass section (BPS) employed as a compensator in damping loop based on the proposed control scheme. The main features of the proposed method are effective damping without critical resonance frequency damping limit, extended stable damping region, improved control performance and good robustness under filter parameters and grid inductance variation conditions. The simulation and experimental results are presented to verify the effectiveness of the proposed method.

Improvements in control of renewable energy-based microgrids are a growing area of interest. A hierarchical control structure is popularly implemented to regulate key parameters such as power sharing between generation sources, system frequency and node voltages. A distributed control infrastructure is realized by means of a communication network that spans the micro-distribution grid. Measured and estimated values, as well as corrective signals are transmitted across this network to effect required system regulation. However, intermittent latencies and failures of component communication links may result in power imbalances between generation sources, deviations in node voltages and system frequency. This paper proposes a hierarchical control structure to regulate the operation of an islanded AC microgrid experiencing communication link failures. The proposed strategy aims to virtually sub-divide the microgrid into controllable “islands”. Thereafter, active power sharing, frequency and voltage restoration is achieved by competing converter systems through multi-agent consensus. The effectiveness of the proposed methodology has been verified through stability analyses using system wide mathematical small signal models and case study simulations in MATLAB, Simpower systems.

Communication-based distributed secondary control is extensively used in DC microgrids. Compared to centralized control, it can provide better voltage regulation and load sharing in microgrids. A conventional secondary control technique that converges the system to a common operating point is improved by using the control methodology to detect the communication link failure and stabilize the system operation during communication islanding. Recently, more robust control schemes have been proposed to improve resilience, but communication islanding has not been addressed at the secondary level control for which the system requires additional tertiary control. However, link failure is a possibility in the microgrid, so this paper proposes a control scheme at the secondary level to detect communication islanding. Communication islanding may lead the system to unpredictable behavior, which may cause the system to become unstable and may further lead to a cascading failure. The proposed control scheme sustains the stability and operation of a DC microgrid. Voltage and current observer works in a parallel manner with the proposed secondary control to achieve a correction term for global operating points. The proposed control scheme has been verified through analysis and simulation.

Recently, wireless power transfer (WPT) systems with active receivers have been proposed for conduction loss reduction, bidirectional power transfer and efficiency improvement. However, the synchronization of WPT systems is complex in nature with the selection of high operating frequencies. Without proper synchronization, power oscillations appear and the system can become unstable. In this paper, a detailed analysis of different WPT systems is presented and the essence of the synchronization technique is derived as being composed of two functions: independent frequency locking and reference phase calibration. The voltage across the receiver-side compensation capacitor is divided and utilized for frequency locking, whereas the reference phase calibration is realized through software code. The proposed method is effective and easy to implement, with a lower overall cost due to its simplicity. The technique can work effectively at high frequency and withstand large variations of operating frequency, load and mutual inductance. In addition, it can address the synchronization problem of multiple active receiver WPT systems with and without cross coupling among the receiving coils. Theoretical analysis and experimental results validate the proposed technique.

The cross-coupling effect between the induction coils of a multiple-receiver wireless power transfer (MRWPT) system severely weakens its overall performance. In this paper, a time-sharing control strategy for MRWPT systems is proposed to reduce the cross-coupling between receiver coils. An active-bridge rectifier is introduced to the receivers to replace the uncontrollable rectifier to achieve synchronization of the time-sharing control. The synchronization signal generated by an active-bridge rectifier can be directly used to realize the synchronization of time-sharing control and hence saved the traditional zero-crossing point detection circuits for time-sharing circuits. Moreover, the proposed time-sharing system has the advantages of both operating under a resistance-matching condition and providing target output voltage for each receiver. Furthermore, a voltage control strategy was developed to provide both high efficiency and a target output voltage for each receiver. Finally, the simulation and experimental results show that the time-sharing MRWPT system reduced the cross-coupling effect between the receiver coils, and the voltage control strategy provided both a high efficiency and a target output voltage for each receiver.

Self-governed micro power networks are a promising solution for meeting the energy needs of isolated communities not having access to regular transmission networks. The control of such isolated networks requires regulation and “fair” sharing of several power generation and storage resources as well as efficient peer-to-peer coordination between power converters operating in the network. The regulation of key parameters as voltage, frequency and power sharing is to be ensured for the system to operate optimally. This paper proposes a new, de-centralized, and hierarchical control approach for power inverters in isolated micro networks with multi-layered controls, each addressing the regulation of key system parameters. The proposed scheme uses distributed quasi-averaging estimators at each participating node to achieve resilience towards disturbances caused by delayed transmission of measurement and control signals in the data acquisition and information exchange layer. Detailed system models are developed using MATLAB and Sim-power systems to test the effectiveness of the proposed scheme under varying control and network scenarios. The results of these studies are presented as pole zero evolutions, stability margins and case study wise simulations. The studies carried out verify the validity of the proposed control strategy for micro-distribution networks.