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"Inverters"
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Overview on Grid-Forming Inverter Control Methods
In this paper, different control approaches for grid-forming inverters are discussed and compared with the grid-forming properties of synchronous machines. Grid-forming inverters are able to operate AC grids with or without rotating machines. In the past, they have been successfully deployed in inverter dominated island grids or in uninterruptable power supply (UPS) systems. It is expected that with increasing shares of inverter-based electrical power generation, grid-forming inverters will also become relevant for interconnected power systems. In contrast to conventional current-controlled inverters, grid-forming inverters do not immediately follow the grid voltage. They form voltage phasors that have an inertial behavior. In consequence, they can inherently deliver momentary reserve and increase power grid resilience.
Journal Article
Stability Analysis of Power Systems with High Penetration of State-of-the-Art Inverter Technologies
With the increasing level of inverter-based resources (IBRs) in modern power systems, this paper presents a small-signal stability analysis for power systems comprising synchronous generators (SGs) and IBRs. Four types of inverter controls are considered: two grid-following (GFL) controls, with or without grid support functions; droop-based grid-forming (GFM) controls; and virtual oscillator control-based GFM. We also analyze the impact of STATCOM and synchronous condensers on system stability to assess their role in the energy mix transition. With the small-signal dynamic behavior of the major technologies modeled, this paper provides stringent stability assessments using the IEEE 39-bus benchmark system modified to simulate future power systems. The exhaustive test cases allow for (a) assessing the impacts of different types and controls of generation and supplementary grid assets, as well as system inertia and line impedance on grid stability, and (b) elucidating pathways for the stabilization of IBR-dominated power systems. The analysis also indicates that future power systems can be stabilized with only a fraction of the total generation as voltage sources without SGs or significant system inertia if they are well distributed. This study provides insights into future power system operations with a high level of IBRs that can also be used for planning and operation studies.
Journal Article
A Comprehensive Review of dc/ac Single-Phase Differential-Mode Inverters for Low-Power Applications
Switched-mode power supplies (SMPSs) are single-switch, two-state, dc/dc power electronic converters and can be generally classified into buck, boost, and buck–boost converters according to voltage transfer functions. There are more than 33 SMPSs with different characteristics in terms of their current and voltage ripples, voltage and current stresses, and their being voltage/current sourced. Although they are usually employed in the dc/dc mode, these SMPSs can be connected differentially to operate as single- and three-phase dc/ac inverters; hence, they are used in low-power applications. The resultant inverters will behave differently according to the topologies that they are descendant from. Several publications have presented differential-mode single-phase inverters (DMSIs) for low-power applications, focusing on their suitability for renewable energy systems. These proposals have mainly focused on boost and buck–boost configurations, with less focus on the buck inverter topologies. Also, several possible configurations for other DMSIs have not yet been proposed or discussed. This paper proposes a comprehensive review of the different possible configurations of the DMSIs, illustrating a systematic method by which to generate and explore them. The paper will mainly categorize the DMSIs in terms of their voltage transfer function and will then discuss the topologies, presenting the main advantages and disadvantages of each one.
Journal Article
Radio-magnetotelluric transmitter in full-bridge resonance inverter
Radio-magnetotelluric (RMT) is a widely used method for shallow subsurface electromagnetic exploration, employing magnetic sources (coils) for signal transmission. A common challenge is the low frequency and unstable current of the instrumentation. To address this, a full-bridge resonant inverter circuit is designed for signal transmission.
Journal Article
Design of LCL type filter based on single-phase grid-connected inverter
The grid-connected inverter adopts an LCL output filter, which has advantages such as low switching frequency and low output current harmonics. Compared with traditional L-type or LC-type filters, it has significant advantages. This article investigates a dual closed-loop current control strategy for LCL filters that are prone to output oscillations. By analyzing the dual closed-loop current control strategy selected in this article, a comparative analysis, calculation, and value selection of the advantages and disadvantages of the L-type, LC-type, and LCL filters are conducted. Finally, the values of each parameter of the filter are determined, and the single-phase grid-connected inverter designed is simulated on the MATLAB/SIMULINK simulation platform to demonstrate the feasibility of the selected control strategy. The established single-phase grid-connected inverter can smoothly achieve grid-connected operation and meet the required requirements.
Journal Article
SVM strategy and analysis of a three-phase quasi-Z-source inverter with high voltage transmission ratio
Herein, we propose a novel three-phase quasi-Z-source inverter with a high voltage transmission ratio to address challenges such as high switching loss and sizeable magnetic components in the basic quasi-Z-source inverter. The proposed circuit topology, control strategy, and related analysis are presented. The circuit topology of the inverter comprises a quasi-Z-source network with an integrated magnetic inductor, an active clamp circuit, a three-phase inverter bridge, and an output
LC
filter, all of which are connected in series. An improved 12-sector space vector modulation scheme is proposed based on the root-mean-square value of the voltage and the instantaneous value of the current. Furthermore, analyses of the inverter voltage transmission ratio, resonant process, and parametric design guidelines for integrated magnetic inductor and zero-voltage switching conditions are presented. Experimental results on a 1-kVA prototype inverter demonstrate that the proposed inverter exhibits a higher transmission ratio and efficiency than existing inverters; thus, the proposed inverter would have broad prospects in low-voltage DC-AC applications.
Journal Article
A Switched Quasi-Z-Source Inverter with Continuous Input Currents
Impedance source converters as single-stage power conversion alternatives can boost and regulate the output voltages of renewable energy sources. Nevertheless, they, also known as Z-source inverters (ZSIs), still suffer from limited voltage gains and higher stresses across the components. To tackle such issues, extra diodes, passive components, and active switches can be utilized in the basic ZSIs. In this paper, a modified switched-quasi-Z-source inverter (S-qZSI) is proposed, which features continuous input currents and high boosting capability to boost output voltage by minor modifications of a prior-art topology. Furthermore, the voltage stress of the active switches is reduced, which contributes to a lower cost. The operation principles are discussed comprehensively. The performance of the proposed ZSI in terms of conversion ratio, voltage gain, and stresses on the power switches and capacitors is benchmarked with selected ZSIs. Finally, simulations and experimental tests substantiate the theoretical analysis and superior performance.
Journal Article
An improved resonant DC link inverter with a simple structure
To further streamline the architecture of the resonant DC link inverter, this article shows an improved resonant DC link inverter with straightforward architecture. There is no oscillating capacitor on the main tubes. Part of the resonant current during resonance is detached from the main tubes. The soft-switching action of all the tubes of this topology can be effectuated by using a set of resonant cavities, and its topology is simple. It has main tubes for ZVS movement and auxiliary tubes for ZCS movement. Also, the circuit has a controllable zero voltage notch duration. The article will elaborate on the operating scheme of the circuit. Eventually, the simulation outcomes are given to validate the effectiveness of the circuit.
Journal Article
An improved soft-switching inverter to eliminate pre-charge current
To address the current stress problem brought on by the auxiliary resonant pole inverter’s pre-charge state, this paper gives an improved auxiliary circuit based on the original inverter. The improved circuit avoids a pre-charge state by adding auxiliary capacitors to form a resonant branch. In contrast to the original inverter, this inverter lowers the current stress on both the auxiliary and primary switches by resolving the pre-charge state’s current stress issue. As a result, the inverter’s losses are decreased, which raises the system’s efficiency. The working principle of this inverter is given in the paper. After a comparison and analysis of the inverter’s pre-charge state, an experiment is used to confirm the device’s viability.
Journal Article