Search Results (325)

Determining charge and discharge behavior is essential for optimizing charging strategies and evaluating balancing algorithms in battery energy storage systems and electric vehicles. Conventionally, a sequence of circuit simulations or tedious hardware tests is required to evaluate the performance of the balancing algorithm. To mitigate these problems, this paper proposes a variable capacitor model that can be easily built from the incremental capacity curve. This model provides a direct and insightful R-C time constant method for the charge/discharge time calculation. After validating the model accuracy by experimental results based on the cylindrical lithium-ion cell test, a switched-capacitor active balancing and a passive cell balancing circuit are implemented to further verify the effectiveness of the proposed model in calculating the cell balancing time within 2% error. Full article

For Modular Multilevel DC-Link T-Type Converter (MMDTC)-based STATCOMs, under identical operating conditions, the submodule (SM) capacitor voltage ripple is inversely proportional to its capacitance value. A configuration with a lower capacitance will inevitably result in significant capacitor voltage ripples. During the PWM modulation process, these ripples can lead to distortions in the output voltage waveform. To address this issue, this paper proposes an innovative carrier reconfiguration method that not only compensates for the output voltage pulse deviation caused by SM capacitor voltage ripples but also achieves effective balancing of the SM capacitor voltages. Finally, the validity and performance of the proposed carrier reconfiguration method are verified through both simulations and experimental results. Full article

For the high-voltage AC port of power electronic transformer (HVAC-PET) with three-phase independent DC buses on the low-voltage side, a decoupling control strategy, concerning the influence of grid voltage imbalance, three-phase active-load imbalance, and high-order harmonic distortion, is proposed in this paper to simultaneously realize the functions of active power control, reactive power compensation, and active power filtering. In the outer power control loop, according to the distribution rule of decoupled average active power components in three phases, stability control for the sum of cluster average active power flows is realized by injecting positive-sequence active current, so as to control the average cluster voltage (i.e., the average of all the DC-link capacitor voltages), and by injecting negative-sequence current, the cluster average active power flows can be controlled individually to balance the three cluster voltages (i.e., the average of the DC-link capacitor voltages in each cluster). The negative-sequence reactive power component is considered to realize the reactive power compensation. In the inner current control loop, the fundamental and high-order harmonic components are uniformly controlled in the positive-sequence dq frame using the PI + VPIs (vector proportional integral) controller, and the harmonic filtering function is realized while the fundamental positive-sequence current is adjusted. Experiments performed on the 380 V/50 kVA laboratory HVAC-PET verify the effectiveness of the proposed control strategy. Full article

As the penetration of intermittent renewable energy sources continues to increase, ensuring reliable power system and frequency stability is of importance. Battery energy storage systems (BESSs) have emerged as an important solution to mitigate these challenges by providing essential grid support services. In this context, a state-of-charge (SOC)-frequency control strategy for grid-forming BESSs is proposed to enhance their role in stabilizing grid frequency and improving overall system performance. In the system, the DC-link capacitor is regulated to maintain the angular frequency through a matching control scheme, emulating the characteristics of the rotor dynamics of a synchronous generator (SG). Thereby, the active power control is implemented in the control of the DC/DC converter to further regulate the grid frequency. More specifically, the relationship between the active power and the frequency is established through the SOC of the battery. In addition, owing to the inevitable presence of differential operators in the control loop, a high-gain observer (HGO) is employed, and the corresponding parameter design of the proposed method is elaborated. The proposed strategy simultaneously achieves frequency regulation and implicit energy management by autonomously balancing power output with available battery capacity, demonstrating a novel dual benefit for sustainable grid operation. To verify the effectiveness of the proposed control strategy, a 0.5-Hz frequency change and a 10% power change are carried out through simulations and also on a hardware-in-the-loop (HIL) platform. Full article

Considering the lightweight requirement of modular multilevel converter (MMC), the implementation of arm multiplexing significantly improves submodule utilization and achieves remarkable lightweight performance. However, the challenges of overvoltage and energy imbalance during pole-to-ground fault still exist. To address these issues, this paper proposes a hybrid half-wave alternating MMC (HHA-MMC) and presents its fault ride-through strategy. First, a transient equivalent model based on topology and operation principles is established to analyze fault characteristics. Depending on the arm’s alternative multiplexing feature, the half-wave shift non-blocking fault ride-through strategy is proposed to eliminate system overvoltage and fault current. Furthermore, to eliminate energy imbalance caused by asymmetric operation during non-blocking transients, dual-modulation energy balancing control based on the third-harmonic current and the phase-shifted angle is introduced. This strategy ensures capacitor voltage balance while maintaining 50% rated power transmission during the fault period. Finally, simulations and experiments demonstrate that the lightweight HHA-MMC successfully accomplishes non-blocking pole-to-ground fault ride-through with balanced arm energy distribution, effectively enhancing power supply reliability. Full article

Dual Maximum Power Point Tracking (MPPT) inverters are essential in residential and small commercial solar power systems, optimizing power extraction from two independent solar panel arrays to enhance efficiency and energy harvesting. On the other hand, the Three-Level T-Type Voltage Source Inverter (3L T-Type VSI) is known for its reduced switching losses, improved harmonic distortion, and reduced part count in comparison to other three-level topologies. In this paper, a novel architecture is proposed to integrate the dual MPPT structure directly to each DC-side split capacitor of the 3L T-Type VSI, taking advantage of the intrinsic characteristics of the inverter’s topology. Further performance enhancement is achieved by integrating a classical MPPT strategy to the control framework to make it feasible for a real-case grid integration. The combination of these methods ensures faster and stable tracking under dynamic irradiance conditions. Considering that strategies dedicated to balancing the DC-link capacitor’s voltage slightly affect the AC-side current waveform, an enhanced sliding mode control (SMC) strategy tailored for dual MPPT and 3L T-Type VSI is deployed, combining the simplicity of conventional PI controllers used in the independent MPPT-based DC-DC converters with the superior robustness and dynamic performance of SMC. Real-time results obtained using the OPAL-RT Hardware-in-the-Loop platform validated the performance of the proposed control strategy under realistic test scenarios. The current THD was maintained below 4.8% even under highly distorted grid conditions, and the controller achieved a steady state within approximately 15 ms following perturbations in the DC-link voltage, sudden irradiance variations, and voltage sags and swells. Additionally, the power factor remained unitary, enhancing power transfer from the renewable source to the grid. The proposed system was able to achieve efficient power extraction while maintaining high power quality (PQ) standards for the output, positioning it as a practical and flexible solution for advanced solar PV systems. Full article

Recent advancements in photovoltaic (PV) and battery technologies, combined with improvements in power electronic converters, have accelerated the adoption of rooftop PV systems and electric vehicles (EVs) in distribution networks, while these technologies offer economic and environmental benefits and support the transition to sustainable energy systems, they also introduce operational challenges, including voltage fluctuations, increased system losses, and voltage regulation issues under high penetration levels. Traditional Voltage and Var Control (VVC) strategies, which rely on substation on-load tap changers, voltage regulators, and shunt capacitors, are insufficient to fully manage these challenges. This study proposes a novel Voltage, Var, and Watt Control (VVWC) framework that coordinates the operation of PV and EV resources, conventional devices, and demand responsive loads. A mixed-integer nonlinear multi-objective optimization model is developed, applying a Chebyshev goal programming approach to balance objectives that include minimizing PV curtailment, reducing system losses, flattening voltage profile, and minimizing demand not met. Unserved demand has, in particular, been modeled while incorporating the concepts of distributional and recognition energy justice. The proposed method is validated using a modified version of the IEEE 123-bus test distribution system. The results indicate that the proposed framework allows for high levels of PV and EV integration in the grid, while ensuring that EV demand is met and PV curtailment is negligible. This demonstrates an equitable access to energy, while maximizing renewable energy usage. Full article

This paper introduces a high-conversion ratio multiphase nonisolated converter built from generic LC cells. The unique architecture that hinges on a generic capacitor inductor switching module enables the high modularity of the topology, providing a quick extension of the converter design in an interleaved configuration for lower ripple and higher current output. The generic module comprises the basic power components of a nonisolated DC–DC converter, where the unique interaction between the capacitor and the inductor results in a soft charging operation, which curbs the losses of the converter, and contributes to a higher efficiency. Additional features of the new converter include a significantly extended effective duty ratio, and a lower voltage stress on the switches, a very high output current, and architecture-inherent output current sharing that balances the loading between the phases. In addition, a power extension using a paralleling and interleaving approach is presented to provide higher output current capabilities. Simulation and experimental results of a modular interleaved three-phase prototype demonstrate an excellent proof of concept and agree well with the theoretical analyzes developed in this study. Full article

This study examines the impact of midpoint voltage fluctuations on the performance of multilevel converters and proposes an advanced control strategy to reduce the required DC bus capacitance while maintaining system stability. The research demonstrates that active voltage imbalance control in active neutral-point-clamped (ANPC) topologies allows for stable operation with significantly reduced capacitor values. A hybrid control approach, combining fuzzy logic control and third-harmonic injection PWM (THIPWM), is developed to enhance voltage balancing, and modulation techniques are systematically optimized. Both simulation and experimental analyses confirm the efficacy of the proposed method, which achieves superior voltage regulation compared to conventional PI-based control schemes. Specifically, experimental results show a reduction in peak-to-peak DC-link voltage fluctuation from 116 V to just 4 V, and the phase current THD is reduced from 3.6% to 0.8%. The results indicate a substantial reduction in voltage fluctuations, contributing to a total harmonic distortion (THD) as low as 0.8%. Furthermore, the proposed strategy facilitates an approximate 26-fold decrease in DC bus capacitor size without compromising system stability. The reduction in capacitance not only lowers the overall system costs and hardware complexity but also improves reliability. The inverter was tested at a rated power of 62.5 kW using 0.3 mF capacitors instead of the theoretically required 7.8 mF. This work advances power electronics by presenting an efficient voltage balancing methodology, offering a cost-effective and robust solution for multilevel converter applications. The findings are validated through comprehensive simulations and experimental tests, ensuring practical applicability. Full article

Inductor parameter variations often affect the control performance of digital current mode (CM)-controlled buck converters as their high performance relies on accurate converter modeling. However, recent studies have shown that reliably monitoring inductance with current sensors and high-frequency sampling greatly increases the overall cost of this process. To address this issue, an online inductance monitoring method without a current sensor is proposed in this study. First, an inductance calculation model is derived by applying the dynamic characteristics of a buck converter with inductor volt-second and capacitor charge balance principles. The model’s accuracy is guaranteed by considering inductor current switching ripple characteristics. Nevertheless, output capacitor equivalent series resistance (ESR) can degrade the accuracy of the proposed calculation model. Thus, to enhance the tolerance of the inductance calculation model to capacitor ESR, the ESR effect on inductance monitoring is investigated. With the proposed capacitor ESR estimation method, inductance monitoring achieves reliable accuracy, even for a buck converter with high capacitor ESR. The effectiveness of the proposed method is verified by simulations and experiments on a buck converter with digital sensorless current mode (SCM) control. Full article

Unlike diesel generators or energy storage systems, photovoltaic (PV) arrays lack inherent rotational inertia and have output limitations due to their operational environmental dependencies. These characteristics restrict their suitability as primary power system backbone components. This study proposes a grid-forming (GF) control strategy for PV inverters in low voltage grid (LVG) using a model predictive control (MPC) approach. The proposed method introduces a novel predictive model accounting for capacitor dynamics to precisely regulate both AC-side output voltage and DC-side voltage. Furthermore, in this paper, P-V droop control replaces the traditional frequency regulation, achieving the real-time balance of DC/AC power and seamless sharing of multiple photovoltaic power sources. By integrating a modified cost function, the controller can flexibly switch between maximum power point tracking (MPPT) mode and power reserve mode according to varying output demands. The proposed strategy can provide advanced frequency stability, MPPT accuracy, and fast dynamic response under rapidly changing solar irradiance and load conditions. Simulation and experimental tests are carried out to validate the effectiveness of the proposed strategy. Full article

As renewable energy sources are integrated into power grids on a large scale, modular multilevel converter-high voltage direct current (MMC-HVDC) systems face two significant challenges: traditional PI (proportional integral) controllers have limited dynamic regulation capabilities due to their fixed parameters, while improved PI controllers encounter implementation difficulties stemming from the complexity of their control strategies. This article proposes a dual-agent adaptive control framework based on the twin delayed deep deterministic policy gradient (TD3) algorithm. This framework facilitates the dynamic adjustment of PI parameters for both voltage and current dual-loop control and capacitor voltage balancing, utilizing a collaboratively optimized agent architecture without reliance on complex control logic or precise mathematical models. Simulation results demonstrate that, compared with fixed-parameter PI controllers, the proposed method significantly reduces DC voltage regulation time while achieving precise dynamic balance control of capacitor voltage and effective suppression of circulating current, thereby notably enhancing system stability and dynamic response characteristics. This approach offers new solutions for dynamic optimization control in MMC-HVDC systems. Full article

The modular multilevel matrix converter (M3C) can perform AC/AC conversion directly. However, M3C operation often requires a pre-charging process, which can be challenging due to the need for fast pre-charging with low inrush current. To address the issue, a closed-loop fast pre-charging strategy is proposed that utilizes an improved nearest level modulation (NLM) based on a quick-sorting algorithm for M3C. By improving the current limiting resistor and the number of Sub-Modules (SMs) inserted into the NLM, we achieve a reduction in inrush current when connected to the grid, and unlock the control algorithm, respectively. This paper presents the relationship between the current-limiting resistor, the pre-charging current, and the pre-charging time. Reactive power compensation is applied on the AC grid during the pre-charging process to ensure stability. Furthermore, the balanced control of capacitor voltage is employed to achieve synchronized and coordinated growth of capacitor voltages in SMs using a quick-sorting algorithm based on NLM. The simulation and experimental results demonstrate the effectiveness of this approach, making it suitable for M3C with a high number of SMs. Full article

This paper presents a Maxwell–Wien bridge for use in the calibration of standard inductances with values between 100 µH and 10 H and frequencies from 20 Hz to 20 kHz. The inductances are measured by comparison with a variable standard capacitor, in parallel association with a variable standard resistor, on the bridge modified by a Wagner balance. The variable standards are calibrated after the bridge balance. The other resistors in the bridge are standard resistors, pre-calibrated in AC using an automatic Wheatstone bridge and in DC after the bridge has been balanced using a comparison bridge with standard resistors traceable to the quantum Hall effect standards. PXI modules are used to supply the bridge with two voltages controllable in amplitude and phase. Design details and the uncertainty budget are discussed. For an inductance of 100 mH characterized by an internal resistance of 83 Ω, the expanded uncertainties are less than 6 µH on the inductance and 20 mΩ on the internal resistance. For inductances from 100 µH to 10 H, the relative uncertainties are less than 0.02% of the inductance and 0.2% of the internal resistance from 20 Hz to 20 kHz. Full article

This article presents an efficient non-isolated DC-DC hybrid converter for direct large-ratio step-down applications such as data centers. The converter topology employs a three-level-assisted Dickson switched capacitor network and interleaved dual inductors, significantly mitigating voltage swings at the switching nodes. As a result, the conduction duration of rectifying switches is substantially extended. This configuration is suitable for both odd- and even-order converters, achieving self-balancing of the flying capacitor voltages and inductor currents. To address uneven interleaved inductor currents, a duty-cycle-matching-based current distribution method is proposed to ensure equal current sharing and facilitate loss transfer between inductors. Additionally, an intrinsic charge-ratio-based method for capacitance optimization is introduced to achieve quasi-complete soft charging of the flying capacitors. This method eliminates surge currents during reconfiguration of the capacitor network, reduces losses, and enhances the capacitor utilization. Operating at 300 kHz, the prototype achieves high-ratio voltage conversion from 48 V to 0.5–2.0 V, with a maximum output current of 30 A. It attains a peak efficiency of 91.96% and a power density of 944.88 W/in³. Quasi-complete soft charging of the flying capacitors results in an approximate 2.94% improvement in the conversion efficiency. Full article