Piecewise Linear Electrical Circuit Simulation Research Articles

Model-Based Thermal Stress and Lifetime Estimation of DFIG Wind Power Converter

Turbine systems equipped with doubly fed induction generation (DFIG) are becoming increasingly vital in wind power generation, with the reliability of the devices serving as a pillar in the industrial sector. Thermal stress and lifetime assessment are fundamental indicators in this regard. This paper primarily addresses the thermal stress and lifespan of power semiconductor devices utilized in a DFIG grid-side converter (GSC) and rotor-side converter (RSC). PLECS (Piecewise Linear Electrical Circuit Simulation) is employed to validate the electrical and thermal stress of the power devices. Additionally, Ansys Icepak, a finite element analysis (FEA) software, is utilized to confirm temperature fluctuations under various operations. The power consumption and junction temperature of the power devices in the GSC and RSC of a 2 MW DFIG are compared. It is evident that the most stressed power semiconductor is the IGBT for the GSC with a temperature swing of 3.4 °C, while the diode in the RSC is the most stressed with a temperature swing of 10.1 °C. This paper also presents a lifetime model to estimate the lifespan of the power device based on the annual wind profile. By considering the annual mission profile, we observe that the lifetime of the back-to-back power converter is limited by the diode of the RSC, whose B10 lifetime is calculated at 15 years.

Analysis and assessment of electrical and thermal performance of five‐phase voltage source inverter under different modulation strategies: Comparative study under balanced and unbalanced load

SummaryThis paper compares four modulation strategies applied to five‐phase voltage source inverters (5PH‐VSI). The modulation strategies under investigation are sine wave pulse width modulation (S‐PWM), fifth‐harmonic injection PWM (FH‐PWM), space vector‐PWM using two large vectors (2V‐SVPWM), and space vector‐PWM using two medium and two large vectors (4V‐SVPWM). The study utilizes simulations to analyze the results based on four performance criteria: low‐order harmonics (LOH), maximum modulation index (MMI), common mode voltage (CMV), and total harmonic distortion (THD) under balanced and unbalanced load. To validate the simulation results for these criteria, an experimental test‐bench is employed, which includes a 5PH‐VSI feeding an R‐L load, and controlled by a low‐cost STM32F4‐DISCOVERY microcontroller board. Additionally, a mathematical approach is used to calculate the total thermal losses (TTL) then simulations are performed using Piecewise Linear Electrical Circuit Simulation (PLECS) software to assess the modulation schemes based on additional thermal performance criteria: conduction losses (CL), switching losses (SL), TTL, the efficiency, and the maximum permissible heat sink thermal resistance (MPHTR) at the steady‐state regime. The results indicate that the 4V‐SVPWM method demonstrates superior efficiency in terms of THD. Furthermore, it showcases the lowest TTL at high switching frequencies, allowing for the best efficiency and minimizing MPHRT, therefore providing the largest margin for the heat sink thermal resistance design. On the other hand, the 2V‐SVPWM offers the highest MMI, but this comes at the cost of high TTL and some LOHs appearing. In addition, it exhibits the highest CMV for unbalanced load. S‐PWM and FH‐PWM offer the advantage of simpler implementation.

Modelling for Multiport Converter-based Hybrid Power supply for Renewable Energy Source Application

This research work deals with the design, modeling and technical evaluation of multiport modular converter based hybrid Power supply using solar PV for small village. The village’s maximum power demand is 50kvA, consisting of demands of twenty (20) households. The first converter in the proposed multiport system is a high frequency isolated DC-DC converter fed with HVDC link yielding an output voltage of 700vDC. The isolated DC-DC converter uses a medium frequency transformer with primary and secondary side converters in input-series output-parallel (ISOP) configuration. Also, the output of first converter is connected to a solar PV and battery system through a buck-boost converter. The second converter in the system is solar PV fed three phase modular inverter designed to have output AC line voltage of 0.415 kV. The three phase inverter is based on modular multilevel converter (MMC) with interleaved modulation techniques. A silicon carbide power MOSFETs, with model numbers CPM3-10000-0270(CREE) and SD11703 (Solitron) are used as a building blocks for isolated DC-DC converter. On the other hand, SiC -MOSFET with part number SCT3017AL (RHOM) is used as basic building block for modular inverter. A solar PV module with open circuit voltage of 85V and maximum power rating of 415W is used to feed the inverter. Different scenarios such as changes in load and changes in solar irradiance are used for critically evaluating the performances of the system under question. The output voltage THD, current distortions, changes in the converter output voltage, current magnitude and converter efficiency are used for performance evaluation of the system under consideration. Simulink/ PLECS (Piecewise Linear Electrical Circuit Simulation) combo simulation platform is used to model and simulate the system in question. Simulation results showed that the proposed multiport converter system can be a viable alternative to low frequency distribution transformer.
 Keywords: Multiport converter, MMC, DC-DC converter, Hybrid power Supply, Solar PV.

Self-aligned hybrid carrier-based PWM for modular multilevel converters

The self-aligned hybrid carrier-based pulse-width modulation (PWM) for modular multilevel converters (MMC) based on decentralized control is proposed in this paper. It is based on parallel cells in a submodule (SM) using self-aligned hybrid carrier-based PWM, which combines the concept of level-shifted carrier-based PWM (LSC-PWM) and phase-shifted carrier-based PWM (PSC-PWM) methods. By implementing a decentralized control system digitally, hybrid carriers align themselves. Each SM interacts with the other SMs and each parallel cell in an SM communicates with the other cells to generate hybrid carriers. The proposed control strategy makes advantage of the redundancy idea by adding or removing a cell in the case of cell malfunction and system reconfiguration. A current balancing method is incorporated into the decentralized control system to ensure current balance among parallel cells in an SM. The simulation results illustrate the effectiveness of the presented control method in piecewise linear electrical circuit simulation (PLECS) software.

Design and Implementation of Three-Phase Smart Inverter of the Photovoltaic Power Generation Systems

The main purpose of this paper is to conduct design and implementation on three-phase smart inverters of the grid-connected photovoltaic system, which contains maximum power point tracking (MPPT) and smart inverter with real power and reactive power regulation for the photovoltaic module arrays (PVMA). Firstly, the piecewise linear electrical circuit simulation (PLECS) power electronic real-time control system was applied to construct the simulation and actual test environment for the three-phase mains parallel photovoltaic system, where the KC200GT photovoltaic module was used to form a 1600 W system for conducting the simulation. For enabling the PVMA to output the maximum power in terms of both insolation and ambient temperature, where the perturbation and observation (P&O) method was used for MPPT. Then, the voltage-power control technology was added to the grid-connected photovoltaic inverter. When the grid voltage p.u. value is between 1.0 and 1.03, the smart inverter starts voltage-power regulation, reducing the real power output to 1440 W, and absorbing the system’s reactive power to 774 VAr. The power factor of the grid system end is controlled to 0.9 (lagging), and the grid voltage is reduced to norminal value 220 V. If the grid voltage p.u. value is between 0.97 and 1.0, the smart inverter starts voltage-power regulation, controlling the output real power to 1440 W and the reactive power to the system to 774 VAr, so that the power factor of the system end is controlled to 0.9 (leading), and the grid voltage is increased to norminal value 220 V. Finally, the results from the simulation and actual test were used to demostrate the effectiveness of the regulation performance of the smart inverter.

Evaluation of insulated gate bipolar transistor valve converter based unified power flow controller reliability and efficiency

The effectiveness and reliability of the unified power flow controller (UPFC) are determined by the insulated gate bipolar transistor (IGBT) valve. Thermal losses, conduction losses, and switching losses in the IGBT valve all affect the efficiency of UPFC. The failure rate of the converter valves is influenced by junction temperature, which has an impact on the converter's reliability. Piecewise linear electrical circuit simulation (PLECS) was used to simulate two IGBT valve-based converter legs working at 12000 Hz, part number GT30F123. By reference to the switching characteristics produced by PLECS, switching losses, conduction losses, and thermal losses are analyzed. Simulation results are corroborated with analytical measurements. The chance of achieving 100%, 50%, and 0% functioning modes are among the reliability indices that are analyzed. The chance of achieving a hundred percent, fifty percent, or zero percent functioning mode is assessed. The frequency of achieving the state probability and mean time to failures (MTTF) are obtained from probabilities using the Markov model. The thermal losses, failure rate, and lifetime of the UPFC are all quantified to give a complete picture of the UPFC's performance.

Decentralized Energy Management and Voltage Regulation in Islanded DC Microgrids

Battery energy storage systems (BESSs) are essential units in islanded dc microgrids (MGs) with tangible penetration of distributed renewable energy sources. These units play a crucial role in energy management and preferably should be controlled in a decentralized manner. In this regard, the conventional droop control is a well-known technique to implement a decentralized control for load sharing in the presence of various-sized distributed generator (DG) units and variable state-of-charge (SoC) level of BESS units. This method provides plug-and-play (PnP) feature for DG units; however, load sharing accuracy is poor, and voltage is unregulated. This article proposes a novel control system for energy management in islanded dc MGs while providing regulated voltage and highly accurate load sharing simultaneously in a decentralized way. The method uses the SoC level of BESS units in a modified droop control technique. A superimposed ac voltage on the nominal dc voltage of the network is used by the control system, bearing a frequency representing the network's load state. This frequency defines the operation mode of BESS units. Conducting simulation studies using piecewise linear electrical circuit simulation (PLECS) validates the effectiveness of the proposed control system. The experimental results confirm the viability and feasibility of the proposed control system.

A new transformerless quadratic buck–boost converter with high‐voltage gain ratio and continuous input/output current port

A new transformerless quadratic buck–boost converter with a common ground and a high-voltage gain ratio of D/(1−D)2 is proposed in this study. The output and input currents of the proposed structure are continuous due to the presence of inductive filters in the output and input ports. The continuity of the output current simultaneously reduces the voltage ripple and also the capacitor stress at the output port. With the proposed quadratic structure, a lower total switching device power and a higher voltage gain ratio are attained at the same duty cycle. Due to the advantages of the proposed structure, it can be widely used with renewable energy. The presented model is investigated in terms of steady-state analysis, continuous conduction mode, small-signal modelling, and efficiency with parasitic resistance effects. To validate the performance of the proposed converter, experiments are conducted in the laboratory to claim the theoretical waveforms obtained from the piecewise linear electrical circuit simulation (PLECS) simulation.

A Push–Pull Series Connected Modular Multilevel Converter for HVdc Applications

This article introduces a push–pull series connected (PPSC) ac–dc converter intended for high-voltage direct current applications. The proposed topology requires fewer submodules compared to a standard modular multilevel converter (MMC) to withstand the same dc voltage. Each converter phase unit is connected to its corresponding phase on the ac side via a center-tapped single-phase transformer which also provides the galvanic isolation needed in most applications. The required arm inductance can be merged into the transformer leakage inductance avoiding the need for additional inductors. In this article, both the design and operation of the converter are discussed in detail. Furthermore, a comparison of the PPSC and MMC in terms of energy storage requirements and efficiency is presented. The converter concept and the control strategy proposed is validated by computer simulations using the piecewise linear electrical circuit simulation (PLECS) simulation package as well as through experiments on a small-scale, 300-V, 2-kW laboratory prototype.

An IDA-PBC Design with Integral Action for Output Voltage Regulation in an Interleaved Boost Converter for DC Microgrid Applications

This paper describes the output voltage regulation control for an interleaved connected to a direct current (DC) microgrid considering bidirectional current flows. The proposed controller is based on an interconnection and damping passivity-based control (IDA-PBC) approach with integral action that regulates the output voltage profile at its assigned reference. This approach designs a control law via nonlinear feedback that ensures asymptotic stability in a closed-loop in the sense of Lyapunov. Moreover, the IDA-PBC design adds an integral gain to eliminate the possible tracking errors in steady-state conditions. Numerical simulations in the Piecewise Linear Electrical Circuit Simulation (PLECS) package for MATLAB/Simulink demonstrate that the effectiveness of the proposed controller is assessed and compared with a conventional proportional-integral controller under different scenarios considering strong variations in the current injected/absorbed by the DC microgrid.

Small-signal analysis of a single-stage bridgeless boost half-bridge AC/DC converter with bidirectional switch

A small-signal analysis of a single-stage bridgeless boost half-bridge alternating current/direct current (AC/DC) Converter with bidirectional switches is performed using circuit averaging method. The comprehensive approach to develop the small signal model from the steady state analysis is discussed. The small-signal model is then simulated with MATLAB Simulink. The small-signal model is verified through the comparison of the bode-plot obtained from MATLAB Simulink and the simulated large signal model in piecewise linear electrical circuit simulation (PLECS). The mathematical model obtain from the small-signal analysis is then used to determine the proportional gain K_p and integral gain K_i. In addition, the switch large-signal model is developed by considering the current and voltage waveforms during load transients and steady-state conditions.

Local Measurement-Based Protection Coordination System for a Standalone DC Microgrid

A reliable protection coordination system between the power electronic converters and solid-state device-based fast protection unit in a standalone dc microgrid supplied by a wave energy converter (WEC) and an energy storage unit is presented. A system model with solid-state circuit breakers is developed in Piecewise Linear Electrical Circuit Simulation (PLECS) to analyze the steady-state operation as well as faulted conditions. The effect of both resistive and constant power loads on a current-limited bus controlling converter behavior during an overload event is analyzed theoretically. Also, the variation in the WEC power output and its effect on bus voltage during overload are investigated. The analysis has led to a novel dual current-voltage feedback-based protection coordination system. The method does not require any communication between the solid-state circuit breakers and converters and eliminates the need for adaptive updating of the overcurrent threshold with varying renewable generation output. Bus capacitor discharge during a short-circuit is analyzed theoretically as well to formulate an instantaneous trip threshold selection utilizing device gate driver functionality. The proposed protection coordination system ensures rapid fault isolation and continued power delivery to the healthy segments. An SiC-based bidirectional, solid-state dc circuit breaker prototype is designed and fabricated, which has been used to implement the proposed protection method with a 380-V dc bus-based system.

A New High-Gain DC-DC Converter with Continuous Input Current for DC Microgrid Applications

The growth of renewable energy in the last two decades has led to the development of new power electronic converters. The DC microgrid can operate in standalone mode, or it can be grid-connected. A DC microgrid consists of various distributed generation (DG) units like solar PV arrays, fuel cells, ultracapacitors, and microturbines. The DC-DC converter plays an important role in boosting the output voltage in DC microgrids. DC-DC converters are needed to boost the output voltage so that a common voltage from different sources is available at the DC link. A conventional boost converter (CBC) suffers from the problem of limited voltage gain, and the stress across the switch is usually equal to the output voltage. The output from DG sources is low and requires high-gain boost converters to enhance the output voltage. In this paper, a new high-gain DC-DC converter with quadratic voltage gain and reduced voltage stress across switching devices was proposed. The proposed converter was an improvement over the CBC and quadratic boost converter (QBC). The converter utilized only two switched inductors, two capacitors, and two switches to achieve the gain. The converter was compared with other recently developed topologies in terms of stress, the number of passive components, and voltage stress across switching devices. The loss analysis also was done using the Piecewise Linear Electrical Circuit Simulation (PLCES). The experimental and theoretical analyses closely agreed with each other.

Three-Phase Multilevel Inverter Using Selective Harmonic Elimination with Marine Predator Algorithm

In this paper, the marine predator algorithm (MPA) is proposed for solving transcendental nonlinear equations in a selective harmonic elimination technique using a multilevel inverter (MLI). It proved its suitability and supremacy over the other selective harmonic (SHE) techniques used in recent research as it has good precision, high probability of convergence, and improving quality of output voltage. The optimum values of switching angles from MPA are applied to control a three-phase 11-level MLI using cascaded H-bridge (CHB) topology to control the fundamental component and cancel the low order harmonics for all values of modulation index from 0 to 1. Analytical and simulation results demonstrate the robustness and consistency of the technique through the MATLAB simulation platform. The results obtained from simulation show that the MPA algorithm is more efficient and accurate than other algorithms such as teaching-learning-based optimization (TLBO), flower pollination algorithm (FPA), and hybrid particle swarm optimization with gray wolf optimization (PSOGWO). A prototype for a three-phase seven-level cascaded H-bridge inverter (7L-MLI-CHB) experimental setup is carried out. The output of this experimental test validated and supported the results obtained from the simulation analysis. The model of power loss of three-phase 7L-MLI-CHB using the silicon metal-oxide-semiconductor field-effect transistor (MOSFET) is obtained according to the modulation technique. Conduction and switching losses are calculated based on the experimental manufacturer data from the Si-MOSFET using the thermal model of Piecewise Linear Electrical Circuit Simulation (PLECS). Losses and output power are measured at different modulation index values based on the MPA algorithm. Finally, a design of heatsink volume is presented for this design at different temperatures.

Control Configurations for Reactive Power Compensation at the Secondary Side of the Low Voltage Substation by Using Hybrid Transformer

The high penetration of new device technologies, such as Electric Vehicles (EV), and Distributed Generation (DG) in Distribution Networks (DNs) has risen new consumption requirements. In this context, it becomes crucial to implement a flexible, functional and fast responsive management of the voltage level and Reactive Power (RP) in the DN. The latest improvements in the Solid State Switches (SSS) field demonstrate they can be used as a Power Electronic (PE) converter. In particular, they have been shown to be capable of operating synchronously with transformers, making the Hybrid Distribution Transformer (HT) concept a potential and cost-effective solution to various DN control issues. In this paper, a HT-based approach consisting of augmenting the conventional Low Voltage (LV) transformer with a fractionally rated PE converter for regulating and controlling the RP in the last mile of the DN is proposed. In this way, it is expected to meet the demand of the future DN from an efficiency, controllability and volume perspective. The proposed approach is implemented using a back-to-back converter. In addition, a power transfer control topology is used to implement the proposed control of the RP injection that controls the voltage level at the Direct Current (DC) link. The proposed approach has been demonstrated in different load scenarios using the Piecewise Linear Electrical Circuit Simulation (PLECS) tool. The simulation results show that the proposed approach can compensate the loads with their need from RP instead of feeding them from the transmission grid at the primary side of the Distribution Transformer (DT). In this way, the proposed approach is able to decrease the transferred amount of RP in the transmission lines.

Hybrid resonant three‐level ZCS converter suitable for photovoltaic power MVDC distribution network

This study presents a hybrid resonant three-level (TL) zero-current-switching (ZCS) converter for distributed photovoltaic power applications accessing medium-voltage DC (MVDC) distribution network. The main constituents of the converter is a neutral point clamped TL circuit, an auxiliary circuit along with two transformers and six switches. The ZCS condition of the TL circuit is reached by operating the auxiliary circuit utilising pulse width modulation technique. It delivers the majority of the power and the switching loss is remarkably reduced. A section on the influence of the turn's ratio of the auxiliary transformer on the current is also presented. The piecewise linear electrical circuit simulation simulation results validate the designed parameter principles. For the sake of comparison, an experimental prototype is developed of 300–1500 V/1500 W to validate the performance of the proposed converter.

Accurate Computation of IGBT Junction Temperature in PLECS

In the article, a new method to improve the accuracy of the insulated-gate bipolar transistor (IGBT) junction temperature computations in the piecewise linear electrical circuit simulation (PLECS) software is proposed and described in detail. This method allows computing the IGBT junction temperature using a nonlinear compact thermal model of this device in PLECS. In the method, a nonlinear compact thermal model of the IGBT is used, which considers the dependence of thermal resistance on the junction temperature. The usefulness of the method is experimentally verified, and it is confirmed that it increases the accuracy of the computations and shortens their time. The differences between the measured and computed characteristics are discussed. The application of the developed method for computations resulted in a significant reduction of their error to only a few percent. The developed method can be applied in the system-level simulations of the power electronics converters.

Thermal Mapping of Power Semiconductors in H-Bridge Circuit

In this paper, a universal H-bridge circuit is used as a loading emulator to investigate the loss and thermal models of the power semiconductor. Based on its operation principle and modulation method, the dominating factors’ (e.g., power factor, loading current, fundamental frequency, and switching frequency) impact on the thermal stress of power semiconductors is considerably evaluated. The junction temperature in terms of the mean value and its swing is verified by using Piecewise Linear Electrical Circuit Simulation (PLECS) simulation and experimental setup. It helps to allocate the loading condition in order to obtain the desired thermal stress.

Analysis and Demonstration of a Dynamic ZVS Angle Control Using a Tuning Capacitor in a Wireless Power Transfer System

In this article, a dynamic zero-voltage switching (ZVS) angle control scheme on the wireless power transfer (WPT) system inverter is proposed by implementing a tuning capacitor. High-frequency (HF) and high-power WPT systems are desired in battery charging applications to reduce the battery charging time. Consequently, the power semiconductor devices are subjected to increased voltage, current, and thermal stresses. In this article, the switching losses in the primary-side inverter of a WPT system are suppressed by realizing the ZVS operation during the battery charging process. A dual-loop control strategy is proposed, which involves traditional phase shift control between the inverter phase legs to maintain constant-current (CC)/constant-voltage (CV) at the output and a tuning capacitor to dynamically tune the ZVS angle. The dynamic tuning of the ZVS angle ensures a minimum reactive power requirement from the input source and, therefore, helps to improve the overall efficiency of the system. Closed-loop simulations of the proposed control strategy are carried out using the piecewise linear electrical circuit simulation (PLECS) simulation software. The proposed control strategy is verified on a 10-W WPT prototype by performing the open-loop experimental validations. The maximum efficiency of the proposed control strategy is found to be ~ 87 % during the CC/CV charging modes. The improvement of ~ 10 % in the dc-dc efficiency is achieved with the proposed ZVS control strategy.

Optimization and Control of a Z-Source, Ultrafast Mechanically Switched, High-Efficiency DC Circuit Breaker

A novel design of the Z-source circuit breaker topology is presented to minimize on -state losses of the protection device. An ultrafast mechanical switch is proposed to commutate the fault current and improve the controllability of the circuit breaker. Replacing the power thyristor in the Z-source circuit breaker and integrating an advanced control scheme reduces energy losses with a low-resistance mechanical contactor. The proposed design facilitates bidirectional current flow, enhances control capability for distributed energy resources, and improves ride-through capabilities during load transients. Z-source circuit breakers utilize an impedance network to create a forced current zero crossing in the event of a fault, allowing the inline thyristor to isolate the fault from the source through reverse bias. However, full load current flows through the thyristor, resulting in high loss and heat generation. The concept is validated, and a proper control scheme is developed for this circuit breaker through an analytical estimation model of the system dynamics during a fault. Simulation and modeling are performed in power systems computer aided design (PSCAD) and piecewise linear electrical circuit simulation (PLECS). Finally, an experimental laboratory prototype is tested to validate the analytical and simulation models and certify the control logic.