José Carlos Ugaz Peña

This paper presents the validation of a voltage balancing converter for a bipolar DC microgrid designed to ensure reliable operation in both grid-connected and islanded modes. This microgrid includes unipolar constant power loads (CPL), a unipolar Battery Energy Storage System (BESS), and local PV generation. The BESS converter employs a V–I droop strategy using only inductor current feedback, reducing sensing requirements while maintaining plug-and-play capability and ensuring smooth transitions between connected and islanded modes. In such a microgrid, the voltage balancing converter regulates the differential voltages under severe unbalanced load conditions and during transients caused by changes in unipolar loads and sources. The experimental results validate the voltage balancing strategy across various scenarios in a small-scale prototype. The results show tight voltage regulation under unbalanced conditions, and smooth transitions during load transients and unintentional islanding, even if there is no dc voltage source in one of the poles of the bipolar dc bus. For both conditions, the imbalance between the unipolar voltages is less than 0.5% of the total bipolar voltage.

This work presents a self-synchronizing control technique for single-phase grid-connected converters. Commonly, these controls use a PLL that synchronizes through measurements of the grid voltage. The proposed method generates a synchronous reference frame by processing a single-phase current signal combined with a quadrature component produced via a quarter-cycle delay. This approach enables the adaptation of selfsynchronizing current control, initially designed for three-phase systems, to single-phase applications. The control strategy uses fewer sensors to ensure simultaneous DC-link voltage regulation and AC current tracking. Only two measurements are needed: the AC current and the DC-link voltage. The proposed control strategy is implemented in the microcontroller TMS320F28335 and validated by real-time simulation in the Hardware-in-theloop platform Typhoon HIL 604. The simulations demonstrate that the control is stable and capable of maintaining DC voltage control and synchronization even under abnormal operating conditions.

Microgrids play an important role in modern power systems, integrating distributed energy resources (DER) that enhance resilience through advanced control capabilities. Managing frequency, voltage, and power dynamics in microgrids under varying conditions, however, poses significant challenges. This paper proposes an adaptive, data-driven secondary control framework for real-time tuning of hierarchical controllers in both islanded and grid-connected modes. The approach employs a multiple-input multiple-output (MIMO) Virtual Reference Feedback Tuning (VRFT) method with a novel lowmemory formulation optimized for digital signal processor (DSP) implementation. Integrated with a performance detector, it enables automated controller retuning during open-and closedloop operations, ensuring robust reference tracking and dynamic performance under disturbances. Hardware-in-the-loop (HIL) simulations, incorporating significant communication delays, validate the framework’s effectiveness. The results highlight the proposed method’s practical applicability, offering a scalable solution for microgrid management in real-world conditions.

This work presents a droop-based control strategy for a dc nanogrid designed to operate under the Net Zero Energy (NZE) concept, enabling seamless transitions between grid-connected and islanded modes. The nanogrid integrates photovoltaic (PV) generation, a fast electric vehicle charging station (EVSE), and a battery energy storage system (BESS) into a $700~$V dc bus interfacing with the ac grid via a bidirectional three-phase AC-DC converter. An isolated DC-DC converter establishes a secondary $48~$V dc bus for powering dc loads. An energy management system (EMS) defines an optimal day-ahead power dispatch for the BESS to meet NZE objectives. At the primary control level, a modified power-to-voltage droop strategy ensures accurate power tracking and parallel operation with the AC-DC converter. This approach enables continuous voltage regulation of the main bus under instantaneous power imbalances caused by schedule deviations or operational mode transitions. Additionally, the proposed strategy eliminates the need for secondary control or high-bandwidth communication. The system is validated through hardware-in-the-loop (HIL) simulations using the Typhoon HIL 604 platform, with the control strategy implemented on a DSP. Real-time simulation results confirm stable performance under various operating conditions, including transitions between modes.

This paper examines high-frequency disturbances in interconnected converters within dc microgrids, focusing on the effects of electromagnetic interference (EMI) filters and long interconnection cables. Understanding these phenomena is essential for systems with multiple power converters as it facilitates the identification and mitigation of voltage and current oscillations. The study investigates the beating effect in dc microgrids, providing an analytical derivation of the oscillation amplitudes at the beat frequency. It also explores how interactions between long cables inductive impedance and EMI filter capacitors can influence the system performance, distinguishing it from previous works. The study examines a dc microgrid consisting of two connected cascaded buck converters. Two scenarios are analyzed: one considers no filters between the two converters, while the other includes a low-pass filter (LPF), an EMI filter, and a cable feeder between them. The proposed theoretical models are validated using a 2 kW experimental prototype comprising two interconnected buck converters. In addition, the paper presents various strategies to mitigate the beating effect in dc microgrids, discussing their effectiveness and the associated implementation challenges.

The massive integration of renewable energies into the grid using fast-response converters without inertia generates issues such as inertia reduction, temporary voltage violations, and power quality reduction. The system inertia reduction is a critical problem that could lead to grid frequency exceeding the acceptable range, resulting in undesirable load-shedding or even large-scale blackouts. To overcome these issues, the use of electric vehicle bidirectional chargers (EVBCs) implementing functionalities such as distributed virtual inertia (VI), long-term frequency support, voltage support by reactive power, and harmonics compensation, has been proposed as a possible solution. This article proposes a novel control strategy to manage a hybrid energy storage system (HESS) composed of dc-link capacitors and battery, through an isolated two-stage ac–dc converter (composed of a dual active bridge resonant type dc–dc converter cascaded to a voltage source inverter), intended for off-board EVBCs. The HESS management allows decoupling of the active power dynamic response since dc-link capacitors supply the fast dynamic response for VI support whereas the battery supplies the slower dynamic response for long-term frequency support, respectively. Hence, the VI support does not affect the battery lifetime. Simulations and experimental results are presented for a 2.5 kW prototype to validate VI, frequency-voltage support along with harmonics compensation.

Ocean waves contain the highest energy density among renewable energy sources. However, harnessing the energy from ocean waves represents a challenge because wave energy converters (WECs) must be designed to have great survivability and efficiency. The power production challenge of any WEC depends on the power take-off (PTO) system efficiency. Maximum power point tracking (MPPT) algorithms have been widely applied in renewable energy from photovoltaic and wind sources, and have subsequently been adapted to wave energy converters (WECs). Energy extraction is optimized by applying MPPT, resulting in an increase in efficiency. This study aims to address the analysis of the influence of the perturb and observe MPPT in the electrical power performance of a WEC composed of a point absorber, a hinged arm and a direct mechanical drive PTO system. The PTO is characterized by a pulley system, a counterweight, one-way bearings, a gearbox, a flywheel and an electric generator; in the present study it is considered to be a cylindrical point absorber. The linear theory and the viscous damping effect are applied to analyze the hydrodynamic behavior of the point absorber. Regarding the two generators considered in the present study, the contribution of MPPT is greater for the low power generator; the high values of the capture width ratio (CWR) occur at low values of period and wave height, showing the maximum value in the high-power generator.

The utilization of voltage source inverters with LCL filters is extended in Distributed Energy System. In these applications, the system is controlled as a current source, however, it can also be controlled as a voltage source. Hence, this configuration is suitable for microgrids environment, where the capability to operate in grid connected and islanded modes is required. This paper proposes a strategy to control a three phase voltage source inverter (VSI) with LCL filter with in both operation modes, achieving specific control goals in each mode and smooth transitions between them, even in front of disturbances and variation on system parameters, imposing High Power Quality indices of operation. The proposed strategy is based on a two control loops scheme. Each loop provides a component of the control input (duty cycles) by means of a state-feedback controller. In order to track sinusoidal references with minimum error and to suppress low order harmonics, state vector is expanded to include the states of a resonant controller. Controllers are designed by means of Linear Matrix Inequalities based on discrete time state-space representations of each operation mode, considering uncertainty due to grid impedance. Experimental results of a 4 kW prototype are presented in order to verify the validity of the proposed strategy.