Search Results (13)

In the scenario where renewable energy sources (RESs) are connected to the power system (PS) through a flexible high-voltage direct current (HVDC) transmission system, their output becomes highly intermittent and volatile due to meteorological factors like wind direction and speed. This variability poses significant challenges to the real-time power balance and control of the PS. To address the uncertainties in system operation and the challenges of RES consumption, this paper proposes an artificial intelligence (AI) algorithm-driven collaborative optimization strategy for virtual power plants (VPPs) considering RESs transmitted by flexible HVDC. Firstly, a self-attention mechanism and multiple gated structures are integrated into a long short-term memory (LSTM) deep learning model. This enhancement improves the model’s ability to capture multi-timescale characteristics of RESs, increasing forecasting accuracy and robustness. Based on these forecasts, a total cost optimization model for VPP operation is developed, which includes high penalty costs for wind and solar curtailment. By embedding economic constraints that prioritize RESs usage, the model can reduce waste caused by traditional cost-driven scheduling. Additionally, to solve the high-dimensional nonlinear optimization problem in VPP scheduling, an improved population-based incremental learning (PBIL) algorithm is introduced. It incorporates an elite retention strategy and an adaptive mutation operator to boost global search efficiency and convergence speed. Simulations based on an VPP incorporating typical offshore wind and solar RESs transmitted via flexible HVDC demonstrate that the improved LSTM reduces MAPE by 7.14% for wind and 4.27% for PV compared to classical LSTM, and the proposed method achieves the lowest curtailment rates (wind 10.74%, PV 10.23%) and total cost (43,752 RMB), outperforming GA, PSO, and GW by 10–18% in cost reduction. Simulation results show that the proposed strategy enhances RESs consumption while maintaining system economy under flexible HVDC transmission. This work offers theoretical and practical insights for optimizing PS with high RES penetration and supports the low-carbon transition of new-type PS. Full article

The high-frequency modulation method (HFM) for a switched capacitor (SC) inverter often leads to high switching loss since it increases switching frequency. In order to reduce the switching frequency and switching loss in the HFM for SC inverter, this paper proposes a novel hybrid modulation strategy as well as a corresponding demo switched capacitor topology. The hybrid strategy limits the number of high-frequency switches, thus reducing the switching loss significantly. Meanwhile, the demo topology maintains the merits of current switched capacitor inverter such as low switch count, quadruple voltage-boosting ability and self-balancing capacity. The principle of the hybrid modulation method and the circuit configuration of the inverter are analyzed in detail. And comparisons are introduced to demonstrate the advantages of the proposed modulation method and topology. Finally, experimental results have proved the feasibility of the proposed inverter. Full article

Three-level neutral-point clamped (NPC) inverters are widely used in the new energy power generation, motor drive, and many other occasions. However, the neutral-point voltage imbalance of an NPC inverter will affect the output of the inverter system, and the control of the neutral point voltage has become a popular research topic. In this paper, a compensation-voltage-injection-based neutral-point voltage balancing method is proposed. During the switching cycle, the average value model of the neutral-point current under different voltage vectors is applied to calculate the value of the compensation voltage that needs to be injected. The self-balance of the neutral-point voltage based on a switching cycle is realized, and the influence of modulation ratio and power factor on equalization ability is discussed. A MATLAB/Simulink simulation model and a small power prototype are established to verify the effectiveness of the method, and the simulation and experimental results show that the proposed method can effectively suppress the neutral-point voltage fluctuation in a wide range of modulation ratios and power factors. Full article

In this study, a new switched-capacitor-based seven-level inverter topology with a photovoltaic system is presented. The proposed topology requires a smaller number of devices and has the ability to self-balance the voltage across the capacitor. The proposed topology configuration is simple and has the ability to extend to higher levels of voltage. This multilevel inverter topology is suitable for low- and medium-voltage applications with photovoltaic (PV) system integration. To improve the PV system efficiency as an input of a DC–DC boost converter, a Fuzzy logic-based maximum power point controller technique is used. A PV system with a DC–DC boost converter integrates with the proposed seven-level inverter topology. The anti-predatory particle swarm optimization (APSO) technique is used to solve the non-linear transduction equations of the seven-level PV switched-capacitor-based multilevel inverter (7L−PV−SCMLI) topology. The proposed APSO is described to minimize the harmonics in the multilevel inverter (MLIs), which is a complex optimization problem involving a non-linear transcendental equation. Furthermore, APSO can be applied in order to solve non-linear transcendental equations for all symmetrical and asymmetrical MLIs that have equal and non-equal DC sources. The APSO-based selected harmonic elimination (SHE) technique obtained the best switching angle value, and the optimized obtained switching angles reduced the total harmonic distortion (THD) of 7L−PV−SCMLI. Full article

This article proposes a single-stage, seven-level (7L), switched-capacitor-based grid-connected inverter architecture with a common ground feature. This topology has the ability to boost the output voltage up to three times the input voltage. The proposed topology can diminish the leakage current in grid-connected photovoltaic (GC-PV) applications, and its capacitor voltages are self-balanced without any additional control strategies. The different operating modes are described in detail with their related mathematical expressions. The design of passive components and a detailed power loss analysis are presented. The merits of the proposed structure are demonstrated using a detailed comparative assessment. The grid-connected operation of the proposed inverter structure is simulated in the MATLAB/Simulink environment, and the results are presented. The laboratory prototype of 935 W is built and analyzed to validate the performance of the proposed structure. Full article

An 11-level switched-capacitor multilevel inverter (SCMLI) with 2.5 times boosting feature is presented in this paper. It can produce an 11-level output voltage waveform by utilizing 14 switches, 3 capacitors, 2 diodes, and 1 DC source. Only nine driver circuits are needed as the topology has three pairs of complementary switches and two bidirectional switches. It has inherent capacitor self-balancing property as the capacitors are connected across the DC voltage source during several states within a fundamental cycle to charge the capacitors to the input voltage. A detailed comparison shows the effectiveness of the proposed topology in terms of the number of switches, number of capacitors, number of sources, total standing voltage (TSV), efficiency, and boosting ability with the state-of-art recently proposed circuits. Subsequently, the performance of the proposed SCMLI is validated experimentally utilizing the nearest level control (NLC), a fundamental frequency-based switching technique. Full article

A large number of modular multilevel converters (MMC) are connected to HVDC transmission systems nowadays. This paper aims at the short-circuit fault in the DC line of the HVDC transmission system and the problem of capacitor voltage imbalance in MMC, proposing a new type of MMC sub-module, which has both the DC fault self-clearing ability and the capacitor voltage self-balancing ability. This sub-module combines the topology of half bridge and full bridge. It uses the reverse capacitor voltage to forcibly turn off the conducting diode to block the fault current loop. At the same time, the two capacitances charge and discharge states are consistent by utilizing the operating mode of the sub-module. It is possible to directly achieve a self-balancing capacitor voltage without complex balancing voltage control. The MATLAB/Simulink simulation verifies the effectiveness of the DC fault blocking capability and capacitor voltage balance capability of the proposed sub-module. Full article

This article presents an innovative self-reconfigurable battery (SRB) architecture, which is able to generate directly at its output any waveform signals. Thanks to that specific characteristic of the proposed system, it is even possible to dispense with any AC charger. Although the individual ability of each cell in the battery pack to perform an efficient active cell balancing has been already studied in the literature, the system presented in this article is the first of its kind. This article describes a real prototype of a high frequency SRB of 128 cells and demonstrates that it can be charged without any dedicated charger directly on the electrical grid, by generating a sinusoidal waveform voltage, while perfectly balancing the cells in real time. Full article

This paper aims to present a novel switched-capacitor multi-level inverter. The presented structure generates a staircase near sinusoidal AC voltage by using a single DC source and a few capacitors to step-up the input voltage. The nearest level control (NLC) strategy is used to control the operation of the converter. These switching states are designed in a way that they always ensure the self-voltage balancing of the capacitors. Low switching frequency, simple control, and inherent bipolar output are some of the advantages of the presented inverter. Compared to other existing topologies, the structure requires fewer circuit elements. Bi-directional power flow ability of the proposed topology, facilitates the operation of the circuit under wide range of load behaviors which makes it applicable in most industries. Besides, a 13-level laboratory prototype is implemented to realize and affirm the efficacy of the MATLAB Simulink model under different load conditions. The simulation and experimental results accredit the appropriate performance of the converter. Finally, a theoretical efficiency of 92.73% is reached. Full article

In the contactless unregulated power converter application with high output current, optimizing coil structures and using synchronous rectification are important for achieving high efficiency. This paper proposes a separated planar structure of coils to achieve the design goals and gives its equivalent circuit model. On the power transmitting pad, double coils are used to enhance the ability of the output power levels. In order to implement full-wave synchronous rectification (FWSR), the power receiving pad also adopts double coils. The power coils on both sides have similar structures to obtain a balance-induced voltage in each half of the switching period, and the principles of the optimal turn ratio in coils are discussed. Meanwhile, four typical self-driven coil structures are compared and analyzed. The effect of the coupling coefficient and load currents on the loss of the duty cycle is discussed. To satisfy the requirements of output voltage, the rules for selecting the minimum ferrite core are summarized. A 120 W unregulated intermediate bus converter is built. The whole system achieves 90.7% efficiency under all loading ranges, and the maximum efficiency of the system is 94.5% at a 3.5A load current. Full article

A new structure of switched capacitor multilevel inverter (SCMLI) capable of voltage boosting and with self-balancing ability is introduced in this article. This advantage is the result of a step by step rise of capacitor voltages in each module, supplied by just one DC voltage source. The proposed topology generates a sinusoidal output waveform with a magnitude several times greater than the input one. Higher output staircase AC voltage is obtained by applying a nearest level control (NLC) modulation technique. The most significant features of this configuration can be mentioned as: fewer semiconductor devices, remarkably low total harmonic distortion (THD), desirable operating under high/low frequency, high efficiency, inherent bipolar voltage production, easy circuit expansion, ease of control and size reduction of the circuit thanks to utilizing neither bulky transformer nor inductor. Moreover, the proposed SCMLI is comprehensively surveyed through theoretical investigation and a comparison of its effectiveness to recent topologies. Eventually, the operating principle of a 25-level prototype of the suggested SCMLI is validated by simulation in the MATLAB SIMULINK environment and experimental results. Full article

The article comments on claims made by Rêgo et al. about the sensor they developed to determine soil water content and its salinity via the admittance measurement of electrodes embedded in the soil. Their sensor is not based on a self-balanced bridge, as stated, but on a more common technique relying on Ohm’s law. A bridge is a zero method of measurement which can provide direct voltages proportional to soil permittivity and conductivity with a high resolution. Thanks to modern electronics the method can be adapted for fast and continuous monitoring in a remote site. Because of this confusion about the different measurement techniques among available admittance or capacitance sensors, we give a succinct review of them and indicate how they compare to the two techniques under discussion. We also question the ability of Rêgo et al.’s current sensor to determine both soil water content and salinity due first to instrument biases and then to the soil complexity as a dielectric medium. In particular, the choice of sensor frequencies is crucial in the two steps. In addition, the procedure to determine and account for temperature influences on readings is not presented clearly enough. It is important to distinguish between the effect resulting from electronics sensitivity, and those that are soil-specific. The comment does not invalidate the design of the sensor, but indicates points, especially parasitic contributions, which must be dealt with to avoid major errors. Full article

Recently, the use of DC microgrid distribution system has become more attractive than traditional AC systems due to their energy efficiency and ability to easily integrate with renewable energy sources and batteries. This paper proposes a 500 V DC microgrid which consists of a 20 kWp photovoltaic panel, batteries, and DC loads. A hierarchical control strategy to ensure balance power of the DC microgrid and the maintenance of common DC bus voltage is presented. The capability of exchanging power energy of the microgrid with the power system of neighborhood buildings is also considered. Typical operation modes are simulated in the Matlab/simulink environment to confirm the good performance of the controllers and the efficiency of appropriately controlling the charge–discharge of the battery system. This research is expected to bring benefits to the design and operation of the system, such as reducing the capacity of batteries, increasing the self-supply of buildings, and decreasing the electricity demand from the AC grid. Full article