This paper proposes a robust control strategy for the synchronization of parallel connected single-phase inverters through sliding mode-controlled harmonic oscillators. Synchronization is achieved through two non-linear sliding surfaces and, in finite time (less than 2 AC cycles), invariant to initial conditions and parameter perturbations. High-quality synchronization and robustness to uncertainties enable the inverters to operate in grid-forming mode too. The proposed control strategy generates perfect sinusoidal response at the output of inverters, i.e., lower levels of total harmonic distortion (THD) are achieved, which helps in maintaining the power quality of the electrical grid. The analytical results are validated by simulation case studies.

For the implementation of distributed cooperative control of the dc microgrid (DCMG), dependency on the communication layer is inevitable. Consequently, the DCMG, a typical cyber-physical system, is susceptible to cyber-attacks, which can hinder the achievement of overall control objectives, and the system may even get destabilized. To detect and mitigate cyber-attacks on actuators as well as sensors, a resilient mechanism is proposed in this article. First, the detection mechanism is proposed using a finite-state machine model-based technique that exploits a dynamic function. This function keeps investigating the actual and estimated values of actuator and sensor signals to authenticate the attack detection. Second, mitigation of attacks is carried out using a robust sliding-mode functional observer (SMFO). The signal of the compromised node is replaced by the SMFO estimated value in the event of an attack detection. The SMFO-based proposed technique is insensitive to measurement noise and parametric variations. The proposed approach is validated by simulation as well as experimental studies on a prototype of a 4-node DCMG.

Introducing distributed communication and control in DC microgrids significantly improves the overall performance of the system. However, these developments also raise the possibility of malicious attacks. Denial-of-service (DoS) attacks and false data injection (FDI) attacks are the most common cyber-attacks. DoS attacks disrupt data availability, and FDI attacks tamper with data integrity, which is perilous for the DC microgrid system. These attacks have the potential to create a detrimental effect on the DC microgrid's sensors, actuators, and communication channels. The combination of DoS and FDI attacks on the actuator signal can have a severe impact, endangering the secure functioning of DC microgrid and potentially destabilizing the entire system. To address these concerns, this chapter introduces an attack detection and mitigation method for mixed FDI and DoS attacks. This detection mechanism uses a state-machine-based technique with a dynamic signature function. The dynamic function constantly compares the actual signal of the actuator with its estimated signal. A Linear Unknown Input Functional Observer (LUIFO) can mitigate mixed attacks and provide an estimated actuator signal to the signature function. This detection and mitigation method ascertain the security and stable functioning of the DC microgrid system. The MATLAB simulation results on four distributed generators-based DC microgrid demonstrate the performance of the methods.

The dc–ac conversion in microgrids leads to second-order oscillations in the dc side voltages and source currents. These oscillations are mitigated using either active or passive filters. Active filters are preferred, as they mitigate oscillations with lesser component size than passive filters. The active filters are regulated to absorb the harmonic ripples at the ripple frequency, and do not provide any voltage support during dc bus voltage fluctuations due to load changes. In this article, a robust integral sliding mode control (RISMC) is proposed to regulate bidirectional converter (BDC)-based dc active filters to facilitate voltage conditioning along with reduction of second-order harmonics which are caused due to dc–ac conversions. The proposed RISMC enhances capability of the BDC active filters to provide dc bus voltage conditioning in case of transience during load variations and uncertain voltage fluctuations. The proposed control consists of a nominal dual-loop PI control which regulates the voltage of the storage capacitor of BDC and a nonlinear integral sliding mode control which regulates dc bus voltage. The proposed control mitigates voltage and current ripples hence preventing them to propagate toward the sources while providing additional voltage support functionality. The proposed control is verified through simulations and experimentation.

Unlike VSIs, the single-stage inverters (SSIs) from the family of Z-converters are capable of boosting input dc to a desired ac voltage. The Z-network of these converters consists of a symmetric X-shaped network or a combination of inductors and capacitors. The basic Z-source converter (ZSC), connected in X-shaped fashion is modeled as a fourth-order system. This can be further modeled as a second-order system to reduce the sensor count but this may lead to an unstable system if there is an asymmetry in network parameters. Also, the source current of SSIs contains second-order ripple current (SRC) component, which oscillates at twice the supply frequency and has detrimental effects on sources. To alleviate the above problems, a parametric uncertainty compensation and ripple mitigation (PUCRM) control methodology is proposed. PUCRM control can be used to maintain stability and achieve desired performance during parametric uncertainties in the dc–dc stage and to reduce SRC propagating to the sources while feeding ac loads. PUCRM consists of a nominal dual-loop PI controller, which regulates the SSIs to achieve desired performance and a nonlinear integral sliding mode component that mitigates the uncertainties and ripple component. The proposed method is verified using simulation and experimentation.