The real-time monitoring of the grid-connected renewable energy generations is of great significance to the operation and control of active distribution systems (ADS). Considering the detailed photovoltaic (PV) system model and ambient influencing factors, this paper develops a state estimation framework for the ADS with integrated PV power plants. Firstly, suitable models of PV arrays and power converters for steady-state state estimation are developed. Based on these models, the state variables of a PV generation system are selected, and the measurement equations are derived. Finally, combined with the state estimation model of distribution networks, a framework for state estimation and bad data processing of an ADS with PV power plants is presented. A parameter estimation approach for PV power plants based on multiple measurement scans is also developed in order to address the practical situation of unknown model parameters. Simulation results show that the proposed framework can effectively capture the operating state of the distribution network and PV power plants. In addition, it enhances the estimation accuracy and bad data processing capability compared to conventional state estimation frameworks.

State Estimation for Situational Awareness of Active Distribution System With Photovoltaic Power Plants

Since the solar panels and fuel cells have low output voltage, which need to be converted to the 400 V or higher dc bus voltage in the renewable energy power generation systems, where, the high gain dc–dc converter plays a key role. Furthermore, with the requirement of the converter in low cost and high efficiency, the soft-switching interleaved boost-type converters based on switched-capacitor and voltage multiplier cell as the high gain dc–dc converters have been widely applied. However, the above-mentioned soft-switching interleaved boost-type converters in literature have resonant spikes on the switches or there are coupled inductors, which will cause the high cost due to the large stresses of the switches or low efficiency due to the high core losses of the coupled inductors. To solve the above-mentioned problems, a modified interleaved capacitor clamped (MICC) dc–dc converter with non-resonant soft-switching (NRSS) is proposed, in which only an auxiliary inductor operating in discontinuous conduction mode with few μH is used to achieve the zero-current-switching for all switches and diodes. Furthermore, the operating principle of the proposed converter is given, the interleaved boost structure is used as the front stage of the proposed converter to reduce the input current ripple and lighten the current stress on all switches and magnetic components, the MICC structure with NRSS as the output stage is proposed as a voltage multiplier module to achieve the high voltage gain. Then, the circuit parameter design for this converter is presented. Finally, a 400 W experimental prototype is built to verify the correctness and the effectiveness of the proposed topology. 

A Modified Interleaved Capacitor Clamped DC–DC Converter With Non-Resonant Soft Switching

Since the solar panels and fuel cells have low output voltage, which need to be converted to the 400 V or higher dc bus voltage in the renewable energy power generation systems, where, the high gain dc–dc converter plays a key role. Furthermore, with the requirement of the converter in low cost and high efficiency, the soft-switching interleaved boost-type converters based on switched-capacitor and voltage multiplier cell as the high gain dc–dc converters have been widely applied. However, the above-mentioned soft-switching interleaved boost-type converters in literature have resonant spikes on the switches or there are coupled inductors, which will cause the high cost due to the large stresses of the switches or low efficiency due to the high core losses of the coupled inductors. To solve the above-mentioned problems, a modified interleaved capacitor clamped (MICC) dc–dc converter with non-resonant soft-switching (NRSS) is proposed, in which only an auxiliary inductor operating in discontinuous conduction mode with few μH is used to achieve the zero-current-switching for all switches and diodes. Furthermore, the operating principle of the proposed converter is given, the interleaved boost structure is used as the front stage of the proposed converter to reduce the input current ripple and lighten the current stress on all switches and magnetic components, the MICC structure with NRSS as the output stage is proposed as a voltage multiplier module to achieve the high voltage gain. Then, the circuit parameter design for this converter is presented. Finally, a 400 W experimental prototype is built to verify the correctness and the effectiveness of the proposed topology.

This article proposes an analysis and controller design of a bidirectional bridgeless single-stage DC&#x002F;AC converter with high frequency-link and low part count. Dual phase-shift control is proposed to control and modulate the AC power and to minimize the Root Mean Square (RMS) of the transformer current. Furthermore, the phase shift angle is chosen to assure wide range of ZVS turn-on of all the switching devices. The proposed controller has a reduced THD at the output AC current without zero-crossing spikes. A continuous-time average model, that well predicts both transient and steady-state relations between the high-frequency AC link and the DC side, is needed to simplify the controller design. Since complex discrete-time models were used in previous literatures, simple and powerful continuous-time tools were not used to design the closed-loop system. In this paper, a novel continuous-time Generalized Average Model (GAM) is proposed. The derived model precisely predicts the high-frequency state variables of the converter, including a simple formula for the transformer current RMS value. The formula is used to minimize the transformer current to reduce the losses. Moreover, the transient analysis and the closed-loop control design are presented. A prototype circuit is tested to verify the performance of the proposed control scheme with the proposed isolated single-stage DC&#x002F;AC converter. 

Single-Stage Isolated DC/AC Converter With Continuous Dynamic Model and Controller Design

This study introduces a new topology for a single-phase photovoltaic (PV) grid connection. This suggested topology comprises two cascaded stages linked by a high-frequency transformer. In the first stage, a new buck–boost inverter with one energy storage is implemented. The buck–boost inverter can convert the PV module's output voltage to a high-frequency square wave (HFSWV) and can enhance maximum power point tracking (MPPT) even under large PV voltage variations. The high-frequency transformer gives galvanic isolation for the system, which decreases the leakage current and improves the system power quality. The second stage of the topology involves using a rectifier-inverter system to interface the produced HFSWV to the utility grid. The proposed system uses high switching frequency which increases the power density, reduces the grid filter size, and increases the system reliability. Buck–boost DC/AC inversion, MPPT and low grid current injection are implemented. The working principles of the proposed topology have been investigated, and the theoretical and experimental results are developed and analyzed. 

Two-stage grid-connected inverter topology with high frequency link transformer for solar PV systems

This article proposes a novel single-stage isolated cascade photovoltaic (PV) inverter topology based on a multibus dc collection. The PV power plant can be divided into many arrays, each of which supplies power to three cascaded isolated inverter units through a dc bus. This isolated inverter unit is composed of cascade isolated bridge cells (I-BCs) connected in input-parallel output-series (IPOS). Compared with a conventional two-stage isolated cascade PV converter, the proposed PV topology can totally eliminate the individual dc-link capacitors at the high-voltage (HV) side, which leads to extremely reduced system volume and eliminated the voltage-balancing control between the dc-link capacitors. This article, first, describes the basic principle and the carrier phase shift pulse-width modulation (CPS-PWM) applied to this topology and, then, analyzes the power balance constraints between the cascade three-phase units for the PV grid-connected system. Finally, the effectiveness of the novel topology is verified by the simulation and experimental results.

Novel High-Frequency Isolated Cascade PV Inverter Topology Based on Multibus DC Collection

This paper proposes an isolated medium-voltage AC grid-connected PV power generation system structure based on DC bus collection with high-frequency link concept. The proposed system structure consists of centralized photovoltaic power plant, inverter unit based on isolated bridge converter (I-BC), and capacitor at the junction of dc bus. PV plant is divided into many arrays, each PV array is connected in parallel with each phase inverter unit. Inverter unit is composed of two I-BC. Compare with conventional two-stage PV inverter, I-BC can totally eliminate the individual DC-link capacitors at the highvoltage side, which leads to extremely reduced system volume and voltage-balancing control between individual capacitors. Second harmonic power oscillations seen in typical system structure can also be eliminated or reduced through use of the proposed system. This paper presents the analysis and operation of the proposed PV system structure with experimental results on a scaled-down laboratory.

High-Frequency Isolated Medium-Voltage AC Grid-connected PV Power Generation System Structure based on DC Bus Collection

The invention discloses an energy router. The energy router is a three-phase structure. Each phase is composed of an upper bridge arm and a lower bridge arm connected in series by a reactor. Each of the upper and lower bridge arms is formed by connecting the input ends of a plurality of isolating modular converters in series and connecting the output ends of the plurality of isolating modular converters in parallel. The energy router has a basic voltage port at a low-voltage DC side, a basic voltage port at a high-voltage DC side, and a basic voltage port at a high-voltage AC side, and can realize energy interaction between the ports. The energy router is located in a micro grid, and connects the micro grid and a public grid. The energy router includes a new energy power generation deviceand an energy storage device. The energy router, in an island mode, has an LVDC-HVDC, HVAC mode, a HVDC-LVDC, HVAC mode, and a HVAC-LVDC, HVDC mode. By constructing a system model and determining a control variable, a dual-loop decoupling control strategy based on V/f control is provided. The energy router has the advantages of improving the operating stability and energy utilization efficiency ofthe system by acquiring the electrical quantity of each port in the energy router in real time and using the constant-frequency and constant-voltage double-loop control strategy.

Energy router and island control strategy based on the same

The invention discloses an intelligent reclosing system for a submarine cable-overhead hybrid line, comprising all-fiber current transformers and submarine cable local differential protection devices.The all-fiber current transformers are respectively installed at the two ends of a submarine cable to sense the current at the two ends of the submarine cable. The submarine cable local differentialprotection devices collect, calculate and process the differential current of the submarine cable line to judge whether the fault point is located in the submarine cable. If the submarine cable localdifferential protection devices judge that the fault point is located in the submarine cable through calculation, a reclosing locking signal is sent to the related protection devices in transformer substations on the two sides. The advantage is that separate differential protections for the submarine cable line are constructed in submarine cable terminal stations to judge the internal fault of thesubmarine cable line, and if the fault is judged to be inside the submarine cable line, a reclosing locking signal is sent to the related protection devices in the transformer substations on the twosides of the submarine cable-overhead hybrid line to achieve the function of reclosing locking and prevent the protections from reclosing to the fault of the submarine cable.

Intelligent reclosing system for submarine cable-overhead hybrid line

This paper introduces an isolated modular multilevel converter (I-MMC) structure which can transport the energy power from LVDC to HVDC and HVAC with single-stage, and the arm balance control strategy. The paper also analyzes the reason of leading to the unbalance in arm, establish the relevant model, and propose the unbalance control strategy of the arm. Finally, the method is verified by simulation and experiment.

Arm Balance Control Scheme of Novel Isolated Modular Multilevel Converter (I-MMC)

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