This paper proposes a deep reinforcement learning (DRL)-aided strategy for intelligently managing state-of-health (SoH) and state-of-charge (SoC) imbalances in a group of battery energy storage systems (BESSs) with varying SoH levels. The proposed method prioritizes SoH balancing during normal operation. However, when one or more BESSs approach full charge or discharge, it shifts priority to SoC balancing, as the aggregated system’s total power capability decreases unnecessarily if any BESS reaches its limits prematurely. A DRL agent is trained to determine when and how to switch between SoH and SoC balancing modes. Unlike state-of-the-art energy management methods for BESSs, whose performance heavily depends on predefined control parameters, the proposed strategy provides a more adaptive and robust solution.

A physics-informed deep transfer reinforcement learning (PIDTRL) strategy is proposed for enabling advanced control and modulation of a dc solid state transformer (DCSST) in a dc microgrid. The strategy involves three stages: (i) Centralized training of deep reinforcement learning agents to balance power and reduce current stress in the DCSST; (ii) effective knowledge transfer from a Source-simulation system to a Target-experimental system using minimal experimental data; and (iii) deployment of multiple agents for online control in the DCSST. The proposed method adaptively determines optimal modulation variables (duty cycles and phase shifts) in stochastic and uncertain environments without requiring accurate model information. Experimental results validate the effectiveness of the proposed PIDTRL algorithm.

Advanced reserve power point tracking (RPPT) algorithms are becoming popular and are expected to replace the conventional maximum power point tracking (MPPT) and flexible power point tracking (FPPT) algorithms. RPPT enables power reserve availability while injecting flexible power into the grid. Hence, it combines the MPPT and FPPT functionalities simultaneously. However, due to inherent continuous sweeping across the PV curve, RPPT suffers from high dc-link voltage fluctuations. For this reason, this paper extends the RPPT concept from the single-string photovoltaic (PV) system to the multi-string PV system. Specifically, a two-string PV system is proposed, where two PV strings that are interleaved at the dc-link. This approach offers advantages over using a single PV string of the same capacity, notably by reducing the ripple in the dc-link voltage caused by RPPT. The effectiveness of this proposed algorithm in the interleaved PV system is demonstrated through simulation results under varying grid frequency and irradiance conditions.

Cascaded H-bridge (CHB) static compensator (Stat-Com) enhances stability of the electricity power grid, which is becoming ever increasingly vulnerable as a consequence of replacing fossil fuel-based synchronous generators by intermitten renewable sources. A CHB StatCom needs large dc capacitors in the submodules to operate, which is a major drawback that hinders a widespread use of this technology. In order to overcome this drawback, the low-capacitance StatCom (LC-StatCom) technology was developed. Other than reducing the capacitors size, improvement in power quality and reduced losses were listed as further advantages of the LC-StatCom. On the other hand, control challenges and reduced stable operating range are the main challenges of this technology. This study aims to provide a better understanding of the prospects and challenges of the LC-StatCom technology as compared to the conventional$C$HB StatComs.

Intermittent changes in irradiance caused by passing clouds inevitably lead to fluctuations in photovoltaic (PV) power generation. To ensure the stability of a power grid with integrated solar PV generation, a battery energy storage system (BESS) is an intrinsic solution to effectively process the PV power before transmitting it into the grid. Alternatively, a PV software-based ramp rate (RR) control can be applied to mitigate the PV power fluctuations without any BESS, which is known to be cost-effective. The contribution of this paper is to compare various BESS-based and cost-effective software-based RR control strategies operating with real-time measured information, and analyze their effectiveness in regulating the PV power fluctuations. Furthermore, this paper studies the BESS utilization behavior among hardware-based control strategies, and also provides insights into which strategy is more appropriate for specific applications. The investigations are carried out through simulation case studies with a real-field one-day fluctuated irradiance profile.

This paper presents a novel zero-sequence voltage injection method for discontinuous modulation (DM) in star-connected cascaded H-bridge (CHB) static compensators (Stat-Coms). Conventional DM methods in CHB StatComs suffer from control interactions during unbalanced grid conditions. This paper proposes a DM that eliminates this control interaction by inserting a clamping transition within a third of the fundamental period. The transition instant is decided by comparing a duty cycle, which is calculated to mitigate the fundamental-frequency in the zero-sequence voltage for discontinuous operation, with a triangular carrier signal with a frequency of three times the fundamental. The clamping intervals under the proposed DM are affected by the phase-shift of this carrier. Specifically, the paper analyses the effects on the harmonic content of the proposed zero-sequence voltage, switching loss, twice-fundamental-frequency capacitor voltage ripple, and current total harmonic distortion, for different phase-shift angles of the DM carrier signal. Besides, the feasibility of the proposed DM in dealing with a grid voltage sag is also discussed.

In a modular multilevel converter (MMC) based battery energy storage system (BESS), a fault tolerant design ensures uninterrupted operation of the MMC when a given number of submodules (SMs) have faulty batteries or no batteries. This paper quantitatively investigates the fault tolerance improvement in MMC-based BESSs with different numbers of redundant SMs, which is commonly practiced to improve the fault tolerance in modular converter topologies. Simulation results are obtained to verify the proposed analysis. The presented analysis provides guidelines for designers to choose an appropriate number of redundant SMs to achieve a desired fault tolerance.

This paper proposes a horizon-one constrained model predictive control (MPC) with integral action for dc-dc H-bridge converters. An integral-action MPC law is analytically derived. The proposed controller takes into account the bilinear dynamics of the converter both in the control law derivation and constraints modeling. In addition, the proposed cost function does not presume the knowledge of the equilibrium point. In this paper, a three-level H-bridge converter for regulation purposes is considered to illustrate the proposed approach, though it is applicable to other dc-dc converter topologies as well. The paper compares the performance of the proposed analytical MPC law and the solution provided by an iterative optimisation algorithm. Simulation results are provided to verify the theoretical predictions, that is, the control law rejects constant disturbances while satisfying the designed constraints.

In this paper, a cascaded H-bridge low capacitance StatCom with modular capacitors is proposed. The low capacitance StatCom benefits from having large capacitor voltage ripple to reduce losses and improve harmonic performance. The proposed LC-StatCom can operate with large capacitor voltage ripple even in light loading conditions by keeping redundant capacitor modules in standby mode when the current is low. Effectiveness of the proposed system is confirmed using a simulated 8.5-MVA StatCom system.

This paper proposes a multi-input linear time-variant control law based on the incremental passivity theory for cascaded H-bridge (CHB) low-capacitance static compensators (LC-StatComs). The proposed control law guarantees global asymptotic stability of the system and controls the capacitor voltages and inductor current without assuming fast dynamics in the current and slow dynamics in voltages. This is particularly important for LC-StatCom applications as the control of the inductor current and capacitor voltages are inherently coupled due to the reduced capacitance. After introducing the incremental model of the converter, a passivity-based control that ensures the global stability is derived. Simulation results on a seven-level 1-kVA CHB LC-StatCom are shown to corroborate its excellent performance in steady-state and during transients.