In the operation of battery energy storage systems (BESSs) based on the cascaded H-bridge (CHB) converters, it is desirable to balance the state of charge (SoC) among the submodules (SMs) within each phase arm. However, there are constraints on the active power distribution among the SMs that intend to balance the SoC. For instance, each SM in a practical system is designed with a specific power rating and can be damaged if it is exceeded. Therefore, a novel rule-based method is proposed in this article to achieve a fast SoC balancing, while respecting the power constraints of the SMs. The proposed method is general and readily applicable to hybrid BESSs, where the SMs are integrated with heterogeneous energy storage. Experimental results are obtained to verify the effectiveness of the proposed algorithm and to compare its performance with respect to existing methods.

The dc solid-state transformer (dcSST) plays a vital role in interconnecting diverse dc sources and loads in dc microgrids. However, output voltage regulation and submodule power balance control have always been two essential control challenges of the dcSST. To address these challenges, this article proposes a multiagent soft actor-critic-based active disturbance rejection control (MASAC-ADRC) method. The ADRC method is used for uncertainty estimation and compensation in modular dcSST. Specifically, the controller gains of the ADRC method are optimized adaptively by the MASAC method, thus enhancing the adaptability to changing conditions from the environment. Compared with the existing controller gain optimization methods, the proposed method does not rely on predetermined datasets. Instead, it provides a tailored strategy, employing a neural network to map optimal ADRC parameters from the measured states. Through the incorporation of diverse environmental scenarios, encompassing variant input voltage and output power, the MASAC-ADRC method achieves superior dynamic performance. Experimental validation underscores the efficacy of the proposed algorithm, showcasing its superiority over alternative approaches. The proposed method yields enhancements exceeding 50% in dynamic performance metrics such as overshoot, settling time, and mean square error when compared with existing methods.

The cascaded H-bridge (CHB) low-capacitance static compensator (LC-StatCom) has a limited operating range in the inductive region compared to a conventional StatCom due to the inherent large oscillations on the capacitor voltages. This limitation constitutes a great drawback of CHB LC-StatComs. This article presents an effective hardware-free solution to overcome this drawback. The proposed solution is based on the injection of an optimal third-harmonic circulating current to suitably shape the capacitor voltages aiming at avoiding overmodulation. Considering all the effects of the third-harmonic circulating current, the article proposes a reference design that guarantees a prescribed safe operating voltage limit, thus increasing the operational range of the LC-StatCom. The proposed approach takes into account the inherent induced oscillation on the capacitor voltages. This approach has been verified by simulation and experimentally with a laboratory prototype, corroborating the excellent performance that agrees with the theoretical analysis.

Solar photovoltaic (PV) power generation inherently fluctuates due to erratic weather conditions. Although an energy storage system (ESS) can effectively mitigate these fluctuations, conventional methods require a large ESS capacity to control both increasing and decreasing rates of PV power change. This article explores an opportunity to reduce the required ESS capacity in PV power smoothing applications by delegating the power smoothing during positive irradiance transients to a flexible power point tracking algorithm. Therefore, the ESS only needs to regulate the power ramp rate during negative irradiance transients and it no longer requires the reserved capacity for positive transients. After discharging the ESS, the proposed control fully restores it without violating the allowed ramp rate. The efficacy of the proposed power ramp rate control under rapid irradiance transients is demonstrated experimentally using a laboratory-scale setup. In addition, based on simulated case studies using a specific real-field one-day irradiance profile, the proposed control allows around $64\%$ reduction in the required ESS capacity compared to the conventional ESS-based control.