Rupesh G. Wandhare

This study investigates the stability of a voltage source converter (VSC) employed in fast-charging station for an electric vehicle (EV) connected to weak grid conditions utilizing a hybrid energy source. The digital control delay induces instability challenges in VSCs equipped with LCL filters. This phenomenon transpires when the resonance frequency descends below the critical frequency ($f_{s}/6$) as a result of grid impedance variations in a weak grid. An RC-damped LCL filter is designed for VSC to attenuate high-frequency instability. A direct power synchronization (DPS) technique is utilized to enhance low-frequency stability in comparison to PLL synchronization methods. To augment the efficacy of DPS, a frequency adaptive double third-order generalized integrator (FA-DTOGI) filter is incorporated into the system. The EV charging converter, with bidirectional power capabilities, and a photovoltaic (PV) system are connected at the DC link. The VSC outer power loop controller regulates the DC link to maintain a set reference, ensuring consistent operation of the EV charging station despite variations in photovoltaic power output. The proposed control method is validated through simulation studies and laboratory experiments, addressing scenarios such as unbalanced voltages, variations in PV and EV power, and both V2G and G2V operations.

This paper describes a robust dual-loop PI-based control technique used in a DC Microgrid. The proposed technique is implemented on a DC-DC half-bridge boost converter as a hybrid constant switching frequency PWM Sliding Mode Control (SMC) technique. The hybrid SMC includes a linear sliding manifold (SM)-based Double-Integral SMC (DI-SMC) technique combined with non-linear non-singular Extended-Order Fixed-Time Terminal SMC (EOFT+DI-SMC). The dual-loop control structure includes an outer output voltage control loop and an inner average inductor current control loop. The proposed EOFT+DI-SMC technique is based on a modified equivalent control law derived by considering a specific orientation of a sliding curve given by the intersection of SM and its orthogonal manifold (OM) for faster response and reduced chattering. The EOFT principle is used to modify an equivalent control law derived using the sliding curve principle, to enable disturbance rejection with minimal dependency on an observer. Further, feed-forward gains of the control loop are tuned in real time adaptively using the existence condition of SMC considering state boundary value conditions and small signal stability analysis. The novel EOFT+DI-SMC principle is proved mathematically in terms of the equivalent control law, Lyapunov stability analysis, and fixed-time convergence. The proposed control technique is simulated using MATLAB/Simulink tool. An experimental prototype of a half-bridge converter is developed and tested to validate the proposed technique.

The proportional-integral-based double-integral sliding mode control suffers from linearization issues, restricted eigenvector-based state trajectory placement, and reduced robustness. To address these issues, this article describes a reduced-order dual-loop adaptive feed-forward double-integral back-stepping sliding mode control technique for a dc–dc converter used in dc microgrids. The proposed technique enables an observerless mitigation of unmodeled uncertainties using an adaptive feed-forward compensation. An ultimate compensatory feed-forward term is introduced to circumvent overall unmodeled converter uncertainties. The compensatory term also ensures a chattering-free faster reaching condition, that is selected based on a nonlinear pseudo sliding manifold (PSM). PSM is a non-singular extended-order fixed-time convergent manifold. The proposed technique uses double-integral back-stepping method to derive the control signal and PSM to mitigate the uncertainties. ADC and sensor uncertainties are corrected using a higher-order generalized polynomial weighted least squares convex optimization. To further support the compensation action, feed-forward constants of the proposed control loop are tuned online using a hybrid controller design approach considering loop shaping analysis, boundary conditions of parameter variations and small-signal closed-loop stability analysis. Experimental verification of the proposed control technique is carried out along with simulation analysis to ascertain the proposed technique against different test conditions, and comparisons are drawn with conventional techniques.

Voltage source converters show considerable potential in integrating renewable energy sources with the power grid. The stability of LCL-type grid-connected converters is significantly affected by internal resonances within filters. The digital control delay can lead to instability with proportional capacitor current feedback-based active damping. This instability emerges when the resonance frequency nears the critical frequency (fs/6) owing to fluctuations in grid impedance, in weak grid. To address this limitation, a hybrid damping comprising grid current feedback with a damping resistor is proposed to mitigate the effect of digital control delay. A feed-forward PCC voltage compensation is proposed without additional sensor requirements to enhance the phase margin. The proposed hybrid damping compensates for the digital control delay, extending the critical frequency region to the Nyquist frequency (fs/2). The proposed design of PCC voltage feed-forward enhances the phase margin and strengthens the robustness against grid impedance variation. An Open Loop Synchronization (OLS) is implemented to mitigate the instability raised due to PLL-based synchronization (Low Frequency Instability). The hybrid damping and PCC voltage feedforward controller are designed using a graphical approach. The proposed control achieves a stable operation even when the Short Circuit Ratio is significantly low ( $\leq 2$ ). An admittance-based stability analysis is performed followed by a closed-loop pole trajectory. To validate the proposed method and controller design, comprehensive simulation studies on a 100 kVA system and laboratory experiments on a 15 kVA prototype are conducted. The proposed methodology is tested for unbalanced voltage conditions and with an outer power loop control.

The dynamic interaction between an LCL filter-based voltage source converter and a weak grid leads to instability. A capacitor-current feedback active-damping technique, with additional sensors, is commonly employed to address high-frequency instability problems. High bandwidth PLL, can expand non-passive regions in low-frequency zones. Grid-current feedback-based active damping is proposed and employed in an Open Loop Synchronization (OLS) based current control for grid-connected converters to overcome instability and oscillation problems. The high-frequency non-passive region is made passive via the active damper with a wider phase margin to enhance stability in weak grids. This paper provides a passivity-based damper design along with the analysis and design of the OLS control. The system’s rigidity against variations in the grid impedance is demonstrated using an admittance-based stability analysis. The proposed control provides stable operation even at a very low short circuit ratio (SCR≤ 2). The proposed procedure can be exercised in both single-phase and three-phase systems. Simulation studies and laboratory experiments are conducted to verify the proposal and controller design.

In this paper, a new control strategy is designed and evaluated for a Hybrid DC power supply that provides regulated DC bus voltage, and the fast transient response against load variation and source variations. The proposed DC bus is powered by a Solar photovoltaic source and supported with a battery and ultracapacitor storage. The averaged model is developed for the system under study and established its control strategy. The same model is used to determine compensator parameters used in various loops of the control strategy. After serving each transient, the perturb value of ultracapacitor voltage is brought back to nominal value using the proposed control strategy to prepare it for the future transient. Bi-directional converter associated with ultracapacitor is regulating DC bus voltage against load and source variations. The battery is providing a prolonged backup for the entire system. Analytically derived compensators for feedback and feedforward loops are verified by simulation results.

This paper optimizes the operation of Brushless DC motor (BLDC) operated solar water pumping system. The proposed system is assisted with single phase supply to ensure the system operation in the high efficiency zone which is governed by the pump. In conventional systems consisting of either AC supply or PV leads to low reliable and inconsistent operation of the motor for water pumping applications. The proposed system consists of Power Factor Correction (PFC) converter for grid input, DC-DC converter as MPPT channel for PV, and three phase inverter to control BLDC type motor-pump set. The entire system is equipped with the control strategy which has multiple modes of operation based on availability of sources. The modelling of all the power converters and their compensator design are provided in this paper. Performance of the system is investigated using developed test-bed with water-pump, tank, power conditioning unit, solar PV simulator, and grid supply. The control strategy and overall system efficiency is verified by simulation and experimental results.

In this paper, a non-isolated dc-dc converter is proposed to provide a high voltage gain with a low inductance requirement. The circuit can be generalized for multiple stages to realize the desired DC output voltage from a low DC voltage source. In the proposed topology, the capacitors and inductors are charged/magnetized in parallel and discharged/demagnetized in series during switched on and off period respectively to obtain a high step-up voltage gain. The proposed power circuit is suitable for many applications based on renewable energy and energy storage where the desired DC-link voltage requirement can be as high as 560V (three-phase inverter input), and input voltage can be as low as 48V (a string of four batteries or fuel cell). A detailed analysis of the steady-state operation of the power converter is provided in this paper to obtain the voltage gain of the converter. The circuit design is simulated in MATLAB Simulink to verify the results of the analysis of this converter. Further, the design guidelines are provided for the generalized form of the converter to achieve desired steady-state input-output gain.