The Hybrid DC/DC converter is proposed to be used in the condition of bidirectional asymmetric power flow between DC buses. Firstly, this paper analyzes the switching mode of the Hybrid DC/DC converter under Extended Phase Shift (EPS) Control. Then, this paper calculates the converter losses and models the losses of the power and magnetic devices based on soft-switching characterization. The losses of those are not only by their material characteristics, but also closely related to the phase shift ratio. Based on the loss model and transmission power model of the converter, the power optimization allocation control strategy is proposed with the goal of efficiency optimization. Finally, the optimization method is verified through simulation analysis.

The virtual oscillator control (VOC) strategy, as a grid-forming controller, demonstrates substantial potential for application in weak grid scenarios. However, research on voltage support strategies for VOC during grid sag faults remains limited. This paper establishes an Andronov-Hopf VOC (AH-VOC) system with voltage-current dual-loop control, then systematically analyzes the principles of inverter-based voltage support at the point of common coupling (PCC) during grid sag faults. The relationship between voltage support effectiveness, grid impedance ratio, and system short-circuit ratio (SCR) is thoroughly investigated. Specifically for AHVOC, an optimal power distribution strategy and a modified voltage reference scheme are proposed to achieve precise power regulation and optimal voltage support under grid sag fault conditions. The effectiveness of the proposed control strategies is validated through MATLAB/Simulink simulations.

As the core equipment of DC power system interconnection and energy transmission, the improvement of DC solid state transformers’ performances has an extremely important impact on the development and application of DC power system. In this paper, a Partial-Power-Processing (PPP) LLC-DAB DC/DC converter with a bridge arm reusing rectifier is proposed for DC microgrids. The proposed converter topology can not only decrease the switching devices’ quantity, but also increase the control freedom of the converter and improve the light load efficiency. The operation principles, soft switching characteristics and power loss analysis of the designed converter are carried out. Finally, the feasibility of the proposed topology and the correctness of the theoretical analysis were verified by simulation results.

High efficiency is a primary goal for photovoltaic (PV) inverters. Optimization procedures followed by PV inverter designers result in static circuit designs, with respective efficiency curves that exhibit their maxima in a narrow range of PV array voltage and power. Nevertheless, the individual PV array characteristics, the solar irradiance and ambient temperature conditions with their daily and seasonal variations, as well as possible partial shading of the PV array, normally shift the operating point of PV inverters away from their maximum-efficiency range. This paper proposes a dynamic self-reconfiguration method for transformerless Buck-Boost PV inverters. The proposed method involves extending the PV inverter’s power circuit with appropriately selected components and reconfiguring its structure and switching frequency in real-time, so that its efficiency is maximized under any operating conditions. The experimental results obtained using a reconfigurable Buck-Boost PV inverter prototype demonstrate that by applying the proposed technique, the PV inverter’s energy efficiency can be increased by 1.5%.

In this paper, a novel LLC-asymmetric half-bridge flyback converter (AHB) that can realize a wide range of voltage gains is proposed. This type of topology utilizes the idea of topology morphing to realize the mode transition between LLC mode and AHB mode by adding a switch. The sharing of the same set of resonant tank parameters for both LLC and AHB can be realized by suitable resonant tank parameter design, which allows this topology to use the AHB mode at low voltage gains and the full-bridge LLC mode (FBLLC) and half-bridge LLC (HBLLC) modes at higher voltage gains, and each topology operates in its more suitable operating range. The design considerations, design ideas of this topology are discussed in this paper. Finally, the performance and realizability of the proposed topology are confirmed by simulation results.

This paper proposes a novel single-stage single-phase transformerless topology based on a buck-boost converter for grid-connected photovoltaic (PV) inverters. The proposed inverter has a wide input voltage range, low total harmonic distortion of current, and effective suppression of common-mode leakage current. The single-input structure ensures that it does not suffer from energy imbalance problems. The new inverter utilizes dead beat control and refines the method of controlling the inverter when the input energy is insufficient. The simulation results verify that the proposed grid-connected PV inverter maintains high grid-connected power quality both during normal operation under conventional conditions and when operating under discontinuous conduction mode (DCM) during energy insufficiency. The simulation models the operating mode of the inverter under abnormal environments, such as load changes and grid voltage transients, which proves that the proposed inverter under dead beat control has a better dynamic performance.

This paper presents the design of an output-series active-clamp flyback high-voltage power supply. By utilizing an output-series connection, the voltage stress on rectifying diodes is reduced. Active-clamp technique is adopted to address issues such as reduced efficiency and high voltage stress on the main switch, which are caused by increased leakage inductance in the transformer due to insulation requirements of high-voltage outputs. The operational principles and design considerations of the converter are introduced, with particular attention given to the transformer's electric field distribution. A prototype is built to validate the feasibility of the system design.

As the search for sustainable, environmentally friendly energy sources continues, DC devices such as new energy-electric vehicles and energy-saving LED lights have been actively promoted. Consequently, the necessity for the DC microgrid in grid system development will become increasingly apparent, and the research on three-terminal output converters is increasing. Besides, double-frequency ripple power is an inherent problem in single-phase power electronic systems. This paper proposes a three-terminal output AC/DC converter with automatic power decoupling and common ground for the DC microgrid as a solution to the issues above. The equivalent circuit has been subjected to a detailed analysis to elucidate its underlying operating principles. Due to the structure of the common ground, the common mode leakage current can be eliminated in this converter. In addition, the implementation of automatic power decoupling enables the replacement of electrolytic capacitors with film capacitors, leading to higher power density and longer lifespan. Furthermore, the employed deadbeat control has a fast dynamic response capability. Finally, the simulation results are presented to verify the theoretical analysis and the performance of this converter.

This article presents a novel transformer-less single-stage buck-boost inverter (SSBBI) utilizing coupled inductors and its dual-mode time-sharing control method. The leakage current can be completely suppressed by connecting the neutral of the electrolytic capacitors to the common ground of the power grid. Besides, only one MOSFET operates at high-frequency in Buck and Boost mode. As a result, in theory, high conversion efficiency can be guaranteed for the proposed inverter. Moreover, compared with conventional Aalborg inverters, the number of switches, diodes, and inductors is further reduced to reduce cost and increase power density. In addition, the operating principle based on equivalent circuits and the control strategy of the proposed inverter are given in this article. As a proof of concept, the simulation results based on PSIM of the proposed SSBBI with different input voltages and output powers and a 110 V power grid are provided.

Virtual oscillator control (VOC) is a grid-forming controller designed for microgrids, where inverters are regulated to mimic the dynamics of weakly nonlinear oscillators. VOC operates in the time domain and offers a faster transient response compared to the virtual synchronous generator. However, conventional VOC implementations often result in reduced power system inertia, which poses a risk to frequency stability due to the lack of inertia. The inertial response is introduced into VOC by integrating the swing equation of a synchronous generator to represent virtual inertia and damping. Unlike real synchronous generators, the parameters of the swing equation can be adjusted in real time to support frequency stability. By employing varying levels of virtual inertia and damping during frequency deviation and recovery, improvements of 10.4% in frequency nadir and 4.9% in the rate of change of frequency are achieved compared to fixed inertia setups. Simulation results confirm the effectiveness of the proposed approach.

In DC microgrid, the uncontrollable DC link short-circuit current seriously shortens the life of the electrolytic capacitors in conventional AC/DC converters. To solve the issue, a new AC/DC converter with controllable DC link short-circuit current is proposed. Simulation results have verified the performance of the proposed converter.

In order to mitigate the negative effect of multi-frequency ripple power, a non-isolated micro-inverter with active power decoupling has been proposed in recent years, which shows some potential advantages, in terms of low cost, fewer switches, high efficiency, and a brief system control strategy. However, it has two independent PV panel input dc sources, which may be asymmetrical in realistic PV systems, resulting in a decrease in the power generation capacity of the whole system. To address this problem, an improved non-isolated micro-inverter topology with active power decoupling is proposed in this paper. Similar to the conventional micro-inverter, it can effectively suppress the common-mode leakage current. Different from the conventional micro-inverter topology, it uses a single PV panel input dc source and achieves positive and negative half-line cycle equivalent dc sources through two split-bus capacitors. The simulation has validated the effectiveness of the proposed non-isolated micro-inverter.

This article proposes a new type of flux modulation linear permanent magnet (FMLPM) generator with dual-sided modular primary and consequent-pole structure to fulfil the low-cost and large-scale deployment requirements of wave energy converter. The key parameters of the generator are optimized using finite element analysis and the Taguchi method to maximize the performance of the designed generator. By comparing with traditional FMLPM, it is demonstrated that the proposed generator has advantages in terms of cost and performance and is more suitable for large-scale deployment of wave energy converter.

Due to the advantages of low cost and high-reliability, the bidirectional asymmetric power flow (BAPF) DC/DC converters are regarded as the competitive DC/DC candidate for power electronics transformers (PETs) in low-penetration renewable energy systems. For this converter, this paper researches the active operation mode and analyzes the circulating current caused by the parallel connection of two full bridges on the low-voltage (LV) side. Based on that, the circulating current suppression method based on extended-phase-shift (EPS) modulation is proposed in the BAFP converters. The simulation results clearly verify the correctness of theoretical analysis and the effectiveness of the proposed method.

As the core equipment for interconnection and energy transmission of DC power systems with different voltage levels, the improvement of DC transformers' performances has an extremely important impact on the development and application of DC power system. Given the asymmetric characteristics of DCTs' power flow in low-penetration renewable energy networks, a hybrid isolated DC-DC converter with bidirectional asymmetric power flow is proposed. The proposed converter topology can not only satisfy the power flow requirements, but also reduce the number of active power semiconductor devices, decrease the system cost and improve the converter capability. For the proposed converter, the power transfer modes are studied, the operating principles of the converter in different modes are analyzed. Finally, the feasibility of the proposed topology and the correctness of the theoretical analysis are verified by simulation results.

In low-penetration-renewable-energy DC distribution networks, the bidirectional power flows in power electronic transformers are asymmetric. Based on the above power transmission characteristics of power electronic transformers, this article proposes an isolated DC/DC converter topology. The proposed topology not only meets with the power transmission requirements, but also reduces the active device quota and system cost, increases the number of power paths and improves the power density. The operating principles, soft switching characteristics, return power characteristics and device stress of the proposed converter topology are analyzed in detail. The feasibility of the proposed topology is verified by simulation results.

In grid-connected inverter systems, the three-phase asymmetric LCL (A-LCL) filter has outstanding characteristics of simple structure, almost the smallest total inductance, and the strong resistance to the adverse effects of parameter shifts. Nevertheless, the order of this kind of power filter is high, and the control model is complicated due to its asymmetric structure. In this paper, a simplified modeling method, which effectively reduces the system order is proposed, without affecting the control performance. Then, the Kalman filter estimation (KF-estimation) is adopted to reconstruct the PCC voltage. A 380 V/50 Hz/6 kW three-phase laboratory setup has been developed to verify the correctness and effectiveness of the proposed control strategy.

In distribution networks integrated distributed generation, the forward and reverse power of power electronic transformers may be unequal. For this regard, this paper proposes a bidirectional asymmetric-power-flow isolated DC/DC (BAI-DC/DC) converter topology, which not only meets the requirements of bidirectional asymmetric power transmission, but also reduces the active device rating and increases the number of power paths, which can decrease system cost and improve system reliability. Simulation and preliminary experimental results verify the feasibility of the proposed topology.

In recent years, the deadbeat-control-based MPC algorithm (DBC-MPC) has been widely studied because it can effectively reduce the number of candidate vectors. However, for the LCL-type grid-connected inverter, when calculating the reference value of the inverter output voltage, the control algorithm only addresses the influence of the current tracking error on the reference value of the output voltage of the inverter, and ignores the influence of the filter capacitor voltage, resulting in poor control performance. Therefore, in this paper an improved DBC-MPC is proposed for the LCL-type grid-connected inverter, where both effects of current and voltage tracking errors on the control performance are fully considered. Compared with the traditional DBC-MPC algorithm, the control performance of the system is greatly improved, while still effectively reducing the number of candidate voltage vectors. Finally, a three-phase simulation model is built to verify the control performance of the proposed algorithm.

This paper investigates the design of passivity-based control for LCL-filtered grid-connected inverter based on the port-controlled Hamiltonian with dissipation (PCHD) model. The interconnection matrix is changed from the original antisymmetric matrix to the upper triangular matrix with zero corner elements, which simplifies the design process. What’s more, to enhance the stability of the system, the combination of classic control theory and modern control theory is proposed to design the damping parameters of the controller. The main idea is to ensure the inverter output impedance is passive. The relationship between the controller parameters and the external interaction stability is compared. The simulation results are carried out to validate the effectiveness and robustness of the proposed approach.

The power supply system design of a marine data buoy system is a challenge. Due to cost reasons, it is difficult for marine buoys to obtain electricity directly from the power grid. At present, marine buoys use solar energy, wind energy or wave energy to supply power to sensors. Among them, the employment of wave energy and solar energy has broad application prospects due to the complementary power production of these sources. This paper presents a new wave energy conversion (WEC) device for a marine buoy, which is composed of a floating body and a power generation device. In addition, a three-dimensional finite element simulation model of the buoy movement is established, and the simulation is carried out using hydrodynamic software. On the basis of simulation, experiments are carried out on a 50 kg core power generation unit to estimate the power generation performance of the proposed WEC device.

This paper presents an IGBT open-circuit fault diagnosis method based on Kalman filter model and reconfiguration algorithm for H6 grid-tied inverter. This method can detect open-circuit fault by only sampling the inductor current through Kalman filter model. Then, through the reconfiguration algorithm, the H6 grid-tied inverter is reconfigured as a Boost-type converter to identify the faulty IGBT device. The Kalman filter model can also predict the grid voltage provided to the control loop, thus saving the ac voltage sensor for the system. This method does not require extra sensors and diagnostic circuits, so it can be easily embedded in the DC/AC inverter system.

In grid-tied DC/AC inverter applications, the equivalent grid impedance often varies widely, which may limit the bandwidth of the inverter control system. This paper introduces a new method to perform the online estimation of the equivalent grid impedance with a Kalman filter by observing the grid voltage and grid current, as well as the voltage at the point of common coupling (PCC). With the estimated grid impedance, a high control bandwidth can be achieved for the grid-tied inverter through online regulation of the proportional coefficient of a current controller. A MATLAB/Simulink model of a grid-tied single-phase inverter has been setup to demonstrate the effectiveness of the proposed method. The simulation results show that the online estimated impedance is accurate enough and the inverter system can continuously maintain a high bandwidth, even under weak grid operating conditions.

Virtual oscillator control (VOC) has been proposed for Microgrids, since compared to the droop control method, VOC has a faster transient response. However, the output voltage of the conventional VOC always contains the third-harmonic. Thus, in the grid-connected mode, the third-harmonic voltage causes the generation of significant third-harmonic current which is injected into the power grid. In this paper, by analyzing the nonlinear oscillator and simplifying the nonlinear current source in the oscillator, a novel VOC for three-phase DC/AC inverter is proposed, where the third-harmonic of the oscillator output voltage can be successfully eliminated, whether in the islanded or grid-connected mode of operation. In addition, compared with the traditional VOC, the dynamic response of the proposed VOC-based inverter can be significantly improved, especially in the islanded mode. Experimental device designed on the DSPACE DS1202 is developed to verify the feasibility of the proposed strategy.

The Passivity-Based Control (PBC) has been adopted in LCL-filtered grid-tied inverter (GTI). However, the conventional PBC method depends much on accurate mathematical model, where zero steady-state error can't be realized when the accurate model parameters are not available or parameters drift occur. Furthermore, due to the utilizing of three state variables in the conventional PBC controller for LCL-filtered GTI, twelve sensors (voltage and current) must be used in a three phase system, which increase the costs and the failure rate of hardware. In order to handle the problems, a novel state observer based modified PBC (SOMPBC) controller for LCL-filtered GTI is proposed in this paper. Six sensors can be saved by the state observer and zero steady-state error can be easily realized by two modified control methods, where an integral regulator is insert into the conventional PBC controller with two different ways. Simulation platform is built in MATLAB/Simulink and a 3-kW experimental device is carried out with DS1202 to verify the correctness and effectiveness of proposed control method.

Magnetic lead screw (MLS) owns many merits for wave energy generation system applications. However, to resist the huge, instantaneous impact of the waves, the radius of the mover and rotor of the MLS should be large to obtain sufficient stiffness. And the length of the mover needs to match the height of the wave to transfer as much power as possible. Therefore, a great many of permanent magnets (PMs) will be consumed when size of the traditional MLS is huge, and the maximum thrust force would be much greater than the wave excitation force. This will lead to the waste of PMs and poor starting performance. Also, the ideal spiral PMs are quite difficult to manufacture. Therefore, in this paper, a novel type single-helix MLS, which adopt single spiral PMs on the surface of the rotor and translator, is proposed to save PM consumption on the premise of meeting the demand of wave power generation system. The new structure provides a new choice for the application of magnetic screw in wave power system. The performance and the design features of the proposed novel MLS is analyzed through the three-dimensional finite-element method and compared with the traditional MLS and reluctance-based MLS. In addition, a simple spiral PM installation method based on discretized PMs for the proposed MLS is also proposed in this paper.

As a promising new transmission device, the magnetic lead screw (MLS) is considered to have a huge potential for wave energy conversion (WEC). The wave power generation device which using MLS can well transfer low-speed linear motion into high-speed rotation and offer much higher force density than that using traditional linear permanent magnet generator. The MLS has the advantages of inherent overload capability, high force density, no mechanical friction, and low maintenance. Therefore, in this paper, a wave power generation system consists of MLS and a permanent magnet synchronous generator (PMSG) is proposed. And a linear motor is used to simulate the sea wave. To verity the system, the prototype is manufactured and tested in the laboratory. In addition, the MLS performance is evaluated by using the finite- element analysis (FEA).

In this paper, the single-stage Maximum Power Point Tracking (MPPT) control strategy for the Aalborg photovoltaic inverter is presented. Aalborg inverter has many advantages, such as high efficiency, wide range of input voltage, minimum voltage drop of the filtering inductors, etc. Nevertheless, it is essentially a “half-bridge” inverter with two input sources, where one source works in MPPT mode, the other is out of control. If without the reasonable parameter design and the proper control, the bus-voltage of this inverter may change greatly, resulting in the serious power oscillation around maximum power point and the reduction of the energy utilization of PV array. In this paper, the MPPT algorithm of two independent PV arrays is proposed, and then the relation between ripple ratio and dc-link capacitance is analyzed. An 110V/50Hz prototype has been constructed. Simulations and experiments show that the proposed control strategy has good steady-state and dynamic performances.