A shunt active power filter (SAPF) is coupled with load admittance in weak grid conditions, which poses a challenge to stability analysis. In this article, the admittance model of the SAPF is developed, which reveals the coupling mechanism between SAPF and load concisely and accurately. On top of that, the stability region of the system is investigated. The passivity region of the load admittance to guarantee the system stability is first explored. However, the passivity region has a very narrowband at a specific frequency, which makes it difficult to achieve. The stability region is then studied and it turns out to be an extension of the passivity region, and especially the narrowband is expanded. Therefore, the stability region is much easier to meet. The stability-oriented design is then summarized in a flowchart. In the end, the effectiveness of the newly defined stability region is verified by experimental results.

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In this paper, a coupled-inductor-based LCC resonant converter with the primary-parallel-secondary-series (PPSS) configuration is proposed to achieve output-voltage sharing ability for HV generator applications. The PPSS configuration of the LCC resonant converter with the voltage multipliers is introduced to achieve high output-voltage and increase the output-power level. However, the variations of the magnetizing inductance, leakage inductance, and winding capacitance of the HV transformer and voltage multiplier impact on the output-voltage sharing performance. Subsequently, the resonant inductors in the primary side of the conventional LCC resonant converters with the PPSS configuration are coupled to achieve the output-voltage sharing without any additional circuits and control efforts. Furthermore, an analytical equivalent circuit model considering the magnetizing inductor of the HV transformer is derived to analyze the output-voltage sharing ability. Moreover, the design method for the coupled inductors considering the output-voltage sharing performance affected by the leakage inductance of the coupled inductors is presented. Finally, the output-voltage sharing performance of the proposed coupled-inductor-based LCC resonant converter with the PPSS configuration is validated by the experimental results of a 50-V input, 5-kV output 100-W prototype. The prototype experimental results show that the unbalance voltage degree decreases from 67.7% to 8.5% with the utilization of the coupled inductor.

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Nowadays Shunt Active Power Filter (SAPF) system still suffers from stability issue which heavily detect its performance. In this paper, an improved system level model is proposed to investigate the coupling effect that will cause the system level instability. This model describes the coupling effect with an additional output admittance and shows system stability more directly. In order to investigate the correctness of the proposed method, a grid including the SAPF and a non-linear load is modelled with both conventional approach and proposed modeling method. Simulations are carried out with the same parameters. Results show that the instability of the grid current observed in the simulation results is not reflected in the stability analysis based on the conventional model. On the other hand, the stability analysis with the new model matches the simulation results very well. Also, further verification is made by a frequency-sweep result, which proves the accuracy of proposed model.@en

Constant power loads combined with low inertia form a major challenge for future distribution grids. This paper presents a state-space representation to model dc distribution systems. Two methods are discussed to analyze the (small-signal) stability of these dc distribution systems; an algebraic method and a Brayton-Moser method. The system models and the methods for stability analysis were verified using an experimental dc microgrid set-up. Furthermore, it was found that the instability of dc distribution systems can be classified into two categories: equilibrium instability and oscillatory instability.

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To tackle the challenges of future distribution systems, dc is being reconsidered. However, broad adoption of dc distribution systems requires additional research into the modeling, stability, protection and control of these systems. Previous research presents modeling methods that only consider monopolar configurations and do not take mutual couplings into account. Therefore, this paper presents a state-space method that can be applied to any dc distribution system, regardless of configuration and mutual couplings. Moreover, it shows how the state-space matrices can be derived in a programmatic manner. Furthermore, the models are validated using an experimental dc microgrid set-up. Due to the mathematical nature, the presented modeling method can be applied easily, and the stability and control can be analyzed algebraically.

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In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series-parallel (LCC) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor (RC) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers.

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The state-of-the-art architectures of high frequency high voltage (HFHV) generators are surveyed and classified according to their applications to achieve compact size, high energy efficiency and high power density. HFHV generation architectures and derivation methodology are concluded systematically based on the level of distributedness of the main sub-components. The characteristics for each HFHV generation architecture are described in details. Comparative qualitative evaluation of HV generation architectures are performed considering different output voltage and output power ratings in various industrial applications. The HV generation architecture with distributed HV transformer and distributed multiplier overall outperforms compared with other HV generation architectures. The recommendations for the HV generation architecture selections would be provided to identify the promising architectures for different output voltage and power applications with optimal performance finally.

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Power packaging technology plays an important role to achieve high performance for high voltage (HV) generator. The HV generator packaging techniques are systematically classified according to different component level packaging and system assembly technology. Both component level packaging and system assembly technology are included in the review and their advantages and disadvantages are discussed. Planar air-core multi-layer printed circuit board (PCB) winding transformer is introduced for HV generator with planar structure. A 450kHz switching frequency HV generator prototype with 310W output power and 1kV output voltage is built in lab. The high frequency HV generator prototype can achieve 1.09kW/L power density at rated 1kV output voltage and 310W full power. The litz wire air-core HV transformer prototype is built to compare the efficiency, thermal performance and size with planar air-core HV transformer. The planar PCB air-core transformer enables high voltage generation circuit system compact planar packaging. The litz wire air-core HV transformer behaves higher efficiency and thermal performance with low high frequency AC winding loss.

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This paper introduces the unified equivalent circuit model for modular high voltage(HV) power generation architectures. The HV generation architectures are introduced considering the modularity of key HV components such as transformers or rectifier circuits firstly. An equivalent resister and capacitor circuit network is adopted to model the HV transformer and multi-stage voltage multiplier circuit for HV generation architectures to simplifies the analysis, design and optimization for HV generation architectures. The expressions of equivalent resister and capacitor network in modular HV generation architectures are deduced. Based on the proposed equivalent circuit model, a 400kHz switching frequency 500W 20kV output HV generator prototype based on modular HV architecture is built to validate the equivalent circuit model. The experimental results of HV generator prototype are given finally.

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This paper introduces the high voltage generation architectures derivation methodology and comparative evaluation of high voltage power generation architectures based on the key performance items such as efficiency, power density, high voltage pulse speed, high voltage pulse ripple, HV insulation and scalability for different output voltage and output power ratings. Based on comparative evaluation of high voltage generation architectures with single inverter configuration, high voltage generation architecture with single inverter, multiple high voltage transformers and multiple stage voltage multiplication circuits overall outperforms other high voltage generation architectures based on architecture performance comparative analysis and evaluation at 100kV/10kW output rating as case study.

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