Piecewise Linear Electrical Circuit Simulation Research Articles

Advanced Current-Limiting and Power-Sharing Control in a PV-Based Grid-Forming Inverter Under Unbalanced Grid Conditions

Grid-forming (GF) inverter technology is a novel and evolving concept for systems with high penetration of renewables. The integration of these grid-independent units with the existing conventional generators and gradually replacing them should contribute to stabilizing the power grid. Several control strategies are proposed in order to design GF inverters to emulate the kinetic energy and the self-synchronization features of synchronous machines with robust control on voltage and frequency to deal with the dynamic issues of the grid. In this article, a photovoltaic (PV)-based GF inverter with a modified virtual synchronous machine control in parallel with a battery supported inverter with an enhanced droop control is considered to operate under non-ideal grid voltage conditions and in the isolated mode of operation. The control methodology encloses a PV synchronous generator, along with the nonlinear feedback linearization current-limiting control with voltage ride-through capabilities. They enable the GF PV inverter and the grid-following battery inverter to provide active and reactive power to the load during unbalanced grid conditions seamlessly. A hardware cosimulation environment in Simulink using the software tool of Piecewise Linear Electrical Circuit Simulation (PLECS) and System Generator from Xilinx is applied to evaluate the operation of the controller and verify its flexibility and effectiveness in different case studies.

Flying‐start and continuous operation of a permanent‐magnet wind generator based on discontinuous currents, discrete second‐order sliding‐mode observer and phase‐locked loop

In wind energy conversion systems of type 4, the critical operating point in permanent-magnet generators (PMGs) is the moment of switching on the generator-side converter (GSC). The induced back-electromotive force (EMF) acting on PMG terminals can cause inrush currents if the synchronisation between PMG and GSC is not done well. The main condition for achieving a satisfying synchronisation is to know the rotor angle, rotating speed and induced back EMF before the GSC is switched on. This synchronisation together with the switching on of the GSC is called the flying start of a PMG. In this study, a novel sensorless PMG flying-start method is proposed to ensure good synchronisation. The flying-start method is based on an extended flux PMG model in a rotating reference frame with a discrete second-order sliding-mode observer and a phase-locked loop controller during the discontinuous operating mode. This is based on discontinuous currents, which are induced because of the PMG rotation caused by wind energy. The proposed method ensures the operation of PMGs in the continuous operating mode as well. The effectiveness of the proposed method is verified on saturable models of low- and high-power surface and interior PMGs through simulations in Simulink and Piecewise Linear Electrical Circuit Simulation (PLECS).

Numerical Methods for Event-Detection State Vector Simulation of Switched-Mode Power Supplies

This article presents a new method for the state vector simulation of switched-mode power supplies using decomposed matrices. With this method, switching instances are updated reliably from previously computed values, providing a highly efficient means for event-detection state vector simulation. The method is demonstrated on a 23rd-order state-space piecewise linear model of a boost converter with and without control feedback, resulting in up to $1000\times $ speedup of the simulation, relative to the same circuit simulated in LTspice or Piecewise Linear Electrical Circuit Simulation for Simulink (PLECS).

Thermal analysis and reliability evaluation of cascaded H‐bridge MLPVI for grid‐connected applications

Nowadays, great progress has been made in the development of multilevel inverters (MLIs) in grid-connected photovoltaic (PV) energy systems, because of the advantages such as reduced voltage stress on the power semiconductor switches and having higher efficiency. Since the multilevel PV inverter (MLPVI) has been a critical part within the failures of a PV energy system, so it becomes important to predict the lifetime of the components and the MLPVI system. In this paper, a five-level modular cascaded H-bridge MLI is analyzed based on grid-connected application for PV energy system, and an independent dc-link voltage controller for each H-bridge is implemented by taking the reference value generated from the maximum power point tracking algorithm of each PV module. The loss and thermal distributions of the different power devices in the MLPVI system are investigated and illustrated for various pulse-width modulation (PWM) controllers. The junction temperature and power losses of the components in the MLPVI are simulated by MATLAB/Simulink and Piecewise Linear Electrical Circuit Simulation (PLECS) blockset, which validate the theoretical analysis. The reliability of the MLPVI is evaluated using parts stress method. It shows that the MLPVI has a good reliability when phase shift PWM control technique is used.

Comparison of Four Different Types of Ferromagnetic Materials for Fault Current Limiter Applications

A comparison of neodymium, samarium-cobalt, aluminum-nickel-cobalt, and laminated steel is presented for use in fault current limiter applications. The ferromagnetic material properties are modeled using the Preisach method of hysteresis. The nonlinear inductance of each magnetic core is calculated and displayed. Only the material properties are changed during each consecutive simulation and are subjected to distribution system parameters to assess their fault current limitation applicability. Finite-element analysis is performed on the casing and coils of the mechanical design structure of the new hybrid fault current limiter. A new fault current limiter topology is presented and simulated in Piecewise Linear Electrical Circuit Simulation. The simulated results show the effect of different materials on the current limiter's performance. Conclusions are made that neodymium is the most suitable ferromagnetic material (of the materials tested) for fault current limiter applications.

Quantitative Power Quality and Characteristic Analysis of Multilevel Pulsewidth-Modulation Methods for Three-Level Neutral-Point-Clamped Medium-Voltage Industrial Drives

The inherent low switching frequency in medium-voltage alternating-current industrial drives presents power-quality and filter-design challenges. In this paper, four multilevel pulsewidth-modulation methods; phase disposition (PD), switching-loss minimization (SLM), and selective harmonic elimination (SHE) up to the 17th and 29th harmonics, respectively, are considered. The characteristics of long-cable effects on common-mode voltage (CMV) and differential-mode voltage (DMV), inverter losses and efficiency, induction machine voltage, and current harmonics are analyzed. Very little has been published in these quantitative comparisons. It is shown that the SHE method has reduced CMV as compared with the PD and SLM algorithms. Elimination of up to the 29th harmonic achieves the best harmonic performance without needing an output filter, at the expense that the losses are higher with a lower efficiency. Analytical and simulation results using the Piecewise Linear Electrical Circuit Simulation for the power-electronic circuits and MATLAB/Simulink for control systems are experimentally verified with a 1000-hp 4160-V neutral-point-clamped adjustable-speed-drive system that includes a 24-pulse front-end voltage source converter.

A Three-Phase Unity Power Factor Single-Stage AC–DC Converter Based on an Interleaved Flyback Topology

This paper presents the design and implementation of a three-phase unity-power-factor single-stage ac-dc converter based on an interleaved flyback topology. The primary market target of the converter is within the telecommunications industry where it supplies high-quality dc power to the telecom loads and performs high-capacity battery charging while providing zero harmonic emission and unity power factor to the utility grid. The main design objective is to produce the lowest cost within a small-size system. The study includes mathematical analysis and simulation steps where the optimum number of cells to be interleaved and the associated phase shifts among the cells are determined while the emphasis being on the design of a perfectly coupled flyback transformer. Design of a transformer with the lowest leakage inductance and selection of components providing the lowest parasitic effects are critical for obtaining high efficiency and good performance. After the design is verified through simulation studies that uses Simulink and piecewise linear electrical circuit simulation model (PLECS) of the converter, a full-scale prototype is implemented to evaluate the performance of the design. In conclusion, experimental results demonstrate that converter works successfully and meets the commercialization expectations.