Line-commutated Inverter Research Articles

Average-Value Modeling of Line-Commutated Inverter Systems With Commutation Failure

Line-commutated converters are extensively used as the interface between ac grids and classic HVDC systems. At the inverter side, commutation failure of switches is one of the most common faults that can pose threats to the system operation. Practical and reliable study of such phenomena relies on accurate and efficient converter models for simulations. Recently, a parametric average-value model (PAVM) has been presented for ac–dc rectifiers, which considers the internal faults of the converter. In this paper, the PAVM methodology is extended to the dc–ac inverter systems, including the commutation failure of switches. The proposed PAVM also augments an automatic fault detection technique to determine the faulty switches. Using comprehensive simulation studies, the developed model is verified to accurately predict the commutation failure of switches and reconstruct the waveforms consistent with the detailed switching models of inverters while being computationally more efficient. The proposed PAVM is envisioned to be an efficient and accurate asset for simulation of HVDC systems and inevitable when faults of switches need to be considered.

Reactive power control of grid-connected photovoltaic micro-inverter based on third-harmonic injection

<span lang="EN-US">This paper presents four interleaved flyback DC-DC converters. Each flyback converter contains a separate maximum power point tracker (MPPT). The MPP tracker is used to collect the maximum power value from photovoltaic panel by using (P&O) algorithm with an output of reference current. In latest years, the active third-harmonic injection circuit have received much interest, this technique contributed to getting a better quality of injection current into the utility grid and control the reactive power. For converting direct current to three-phase sinusoidal currents, a line-commutated current source inverter type (CSI) with filter is used. The developed micro-inverter of (1000 W) offers an expanded range of reactive power control with balanced three-phase output power and good efficiency 95.07%. The effectiveness of the suggested system is clarified through the MATLAB program simulation. The system proposed in this paper has proven its effectiveness in obtaining reactive power control, nearly sinusoidal three-phase output currents and it is compared with the traditional PV micro-inverter system. The comparison shows that the PV micro-inverter is best in more specification than the traditional PV system such as efficiency and total harmonic distortion (THD) and the system losses.</span>

MPPT Controller Based on Fuzzy Logic for Photovoltaic Systems using Line-Commutated Inverter and Sepic Converter

A controller for maximum power point tracking (MPPT) based on fuzzy logic was developed to connect the solar panels and three phase grid through an inverter. MPPT controller traces the maximum power and then feeds this power to the three phase grid irrespective of the changes in solar irradiations. The input and output variables for the fuzzy logic controller were selected in order to vary the inverter firing angle to track the maximum power from the solar panels. The proposed system using fuzzy logic controller was built using MATLAB Simulink /Power System Block (PSB) set. A DSP controller has been embedded with program for firing of the thyristors used in the inverter with appropriate pulses. Hardware of the entire system was fabricated in the laboratory and the outputs from the PV array of 90 volts, 11 amperes are exhibited. Both the hardware and simulation outputs have been compared which are in close agreement to validate the suggested system.

Experimental Investigations of the Self-Controlled Synchronous Motor Connected to a Three-Phase Line Commutated SCR Inverter

<p>This paper concerns the experimental investigations of the three-phase line commutated SCR inverter fed synchronous motor. The fabricated system consists of a line-commuted inverter, a three-phase synchronous motor with the excitation winding connected in series to the inverter input, a terminal voltage sensor and a gate-pulse generating circuit. The firing pulses for SCRs of the inverter are generated by the microprocessor in proper sequence with the help of synchronizing signal derived from the terminal voltages of the synchronous machine. The steady state performance characteristics are obtained experimentally using the fabricated system. The experimental results show that a three-phase synchronous motor supplied by a line commutated inverter with the excitation winding connected in series to the dc link provide excellent characteristics of the conventional dc series motor.</p><p> </p>

Fuzzy logic controller vs. PI controller for MPPT of three-phase grid-connected PV system considering different irradiation conditions

In this paper, a comparison between fuzzy logic controller (FLC) and conventional proportional-integral controller (PIC) is presented for a connected PV array system to utility grid via a three-phase line-commutated inverter. The main objective of the controller is providing maximum power for utility grid in different solar radiation conditions. The simulink model of the studied schemes is built using MATLAB/PSB for generating firing pulses of the thyristors in the inverter by applying PIC and FLC methods separately. Three different radiation conditions are examined on both controller which are constant solar radiation, step solar radiation and a combination of step and ramp scheme. According to simulations, FLC dominates PIC for all radiation types and in many important aspects. Some of these aspects could be named as, extracting power from PV array, providing active power for grid, shape of output current of inverter, shape of grid current waveform and total harmonic distortion (THD) of these currents.

Sinusoidal current injection based on a line-commutated inverter for single-phase grid-connected renewable energy sources

Sinusoidal current injection based on a line-commutated inverter for single-phase grid-connected renewable energy sources

Power Electronic Interface with Maximum Power Point Tracking Using Line-commutated Inverter for Grid-connected Permanent Magnet Synchronous Generator

—This article presents a simple grid interactive system that extracts maximum power from a wind-driven permanent magnet synchronous generator using an integrated cascade boost converter and a three-phase line-commutated inverter. The firing angle of the line-commutated inverter is held constant at an appropriate value that provides a constant DC-link voltage, and only DC-link current is sensed for maximum power point tracking. For wide wind variation, maximum power from the permanent magnet synchronous generator is achieved using a simple load current (DC-link current) perturb and observe maximum power point tracking technique. This is obtained by varying the duty ratio of the integrated cascade boost converter with an adaptive incremental step that varies the load on the permanent magnet synchronous generator in accordance with changing wind. Experiments have been conducted on a 3-phase, 750-W, 500-rpm laboratory size permanent magnet synchronous generator. The operation and analysis of the proposed topology with a fixed firing angle for a line-commutated inverter is presented. The results obtained from MATLAB (The MathWorks, Natick, Massachusetts, USA) simulation are verified with experimental results, and a close correlation has been found, proving the efficacy of the system.

A Current-Forced Line-Commutated Inverter for Single-Phase Grid-Connected Photovoltaic Generation Systems

A simple power electronic interface based on the line-commutated inverter (LCI) has been developed in order to inject sinusoidal current to the grid for single-phase grid-connected pho ...

Hybrid power electronic controller for combined operation of constant power and maximum power point tracking for single‐phase grid‐tied photovoltaic systems

This study presents a hybrid technique that offers constant power operation for single-phase grid-tied photovoltaic (PV) systems while performing maximum power point tracking function. A boost converter and a line commutated inverter (LCI) have been used for interfacing PV array with utility grid. Fixed firing angle of the LCI keeps the dc-link voltage constant and the boost converter extracts maximum power from the solar PV array by simply adjusting the duty ratio of the boost converter. A low-capacity battery bank connected at the dc link is used to deliver constant power to grid. Harmonic filter is eliminated as the system inherently delivers quality supply with reduced current harmonics. PIC microcontrollers have been programmed for generating pulses to the inverter and the boost converter. The system has been simulated in MATLAB/Simulink and the simulation results are presented. The parameters of a PV panel rated for 100 W, 21.5 V and 6.83 A have been used for the simulation. Experiments have been conducted on the 21.5 V, 6.83 A PV panel for obtaining a constant power of 80 W with varying irradiation and the results correlate with the simulation study.

Simple power electronic controller for photovoltaic fed grid‐tied systems using line commutated inverter with fixed firing angle

A power electronic interface with maximum power point tracking (MPPT) for grid connected photovoltaic (PV) systems using an integrated cascade boost converter (ICBC) and line commutated inverter (LCI) has been proposed. The variable dc voltage of the PV array is fed as input to the ICBC and the output voltage of the ICBC is maintained constant with the firing angle of the LCI being fixed at an appropriate value greater than 90°. The interesting feature of this scheme is that, it is not mandatory that the constant dc-link voltage should be more than the peak value of the grid voltage. As the array voltage is now boosted and fixed at the dc link, any variation in the PV output power is reflected in the variation of the dc-link current and hence only one parameter (the dc-link current) sensing is required for the MPPT. Furthermore, the proposed controller has made it possible to dispense with the step up transformer between the LCI and the utility grid. The complete scheme has been constructed and experiments have been conducted on an 84 V, 10 A PV array feeding power to a three-phase 230 V utility grid and the experimental results are compared with the MATLAB simulation results. The steady-state analysis of the overall system and the experimental results confirm the validity of the proposed controller and the efficacy of the analysis.

Power electronic configuration for the operation of PV system in combined grid‐connected and stand‐alone modes

A simple photovoltaic (PV) system capable of operating in both grid-connected mode and stand-alone mode using multilevel boost converter (MBC) and line commutated inverter (LCI) has been developed for extracting the maximum power and feeding it to a single phase utility grid and stand-alone system simultaneously. Theoretical analysis of the proposed system is done and the duty ratio of the MBC is estimated for extracting maximum power from PV array. For a fixed firing angle of LCI, the proposed system is able to track the maximum power with the determined duty ratio which remains the same for all irradiations. This is the major advantage of the proposed system which eliminates the use of a separate maximum power point tracking (MPPT) controller. Experiments have been conducted on a 80 V, 9.4 A PV array feeding a 110 V single phase grid and a 230 V, 100 W DC motor. The MBC extracts maximum power from the PV array and feeds the major portion of power to the single phase utility grid via LCI and the remaining power to separately excited DC motor. It was found that the theoretical analysis, simulation and experimental results closely correlate with each other and proves the effectiveness of the proposed configuration.

Investigations of an improved PV system topology using multilevel boost converter and line commutated inverter with solutions to grid issues

A photovoltaic (PV) system using multilevel boost converter (MBC) and line commutated inverter (LCI), operating in both grid-connected mode and stand-alone mode has been analysed. This proposed system extracts and feeds the maximum power to a single phase utility grid and stand-alone system simultaneously. The duty ratio of the MBC is estimated from the theoretical analysis of the proposed system, for extracting maximum power from PV array. The proposed system tracks the maximum power with the determined duty ratio which remains the same for all irradiations, for a fixed firing angle of LCI. The flexibility of supplying required proportion of extracted power to grid and stand-alone load and the elimination of a separate MPPT controller are the major benefits of the proposed system under normal grid conditions. In addition to it, the grid issues like voltage swell, blackout and brownout are considered and necessary remedial measures have been taken in the proposed system. Based on the issues, either the firing angle of LCI is adjusted or LCI is disconnected and replaced by a battery. Simulation studies have been carried out and the dynamic response of the system is observed. A laboratory prototype is built and experimental investigations have also been carried out. The theoretical analysis, simulation and experimental results are found to be closely associating with each other proving the efficacy of the proposed configuration.

Enhancement of Commutation Reliability of an HVDC Inverter by Means of an Inductive Filtering Method

A new filter-commutated inverter (FCI) is proposed in this paper to enhance the commutation reliability of the HVDC systems applied in the high-voltage fields. The topology of the FCI is established based on an inductive filtering method, which mainly consists of a new converter transformer, fully tuned (FT) branches, inverter bridges, and a related control system. Unlike the traditional line-commutated inverter (LCI), the equivalent commutating impedance of the FCI includes not only the transformer leakage impedance but also the total impedance of the FT branches. The mathematical model is established to express such equivalent commutating impedance. Based on this, the commutation performance of the FCI is investigated in detail by comparing with LCI. Besides, the commutation reliability is evaluated under different operating conditions (e.g., normal operation, balanced, and unbalanced faults). Both the simulation and the experimental results validate the theoretical analysis, and indicate that the FCI with the use of the inductive filtering method can greatly increase the commutation margin of the HVDC systems, enhance the commutation reliability of the inverter, and prevent the occurrence of commutation failures.

Analysis and control of wind-driven self-excited induction generators connected to the grid through power converters

The analysis of the wind-driven self-excited induction generators (SEIGs) connected to the grid through power converters has been developed in this paper. For this analysis, a method of representing the grid power as equivalent load resistance in the steady-state equivalent circuit of SEIG has been formulated. The technique of genetic algorithm (GA) has been adopted for making the analysis of the proposed system simple and straightforward. The control of SEIG is attempted by connecting an uncontrolled diode bridge rectifier (DBR) and a line commutated inverter (LCI) between the generator terminals and three-phase utility grid. A simple control technique for maximum power point tracking (MPPT) in wind energy conversion systems (WECS), in which the firing angle of the LCI alone needs to be controlled by sensing the rotor speed of the generator has been proposed. The effectiveness of the proposed method of MPPT and method of analysis of this wind-driven SEIG-converter system connected to the grid through power converters has been demonstrated by experiments and simulation. These experimental and simulated results confirm the usefulness and successful working of the proposed system and its analysis.

Grid-Tied Photovoltaic Array Using Power Electronic Converters with Fuzzy Logic Controller for Maximum Power Point Tracking

A simple closed-loop power electronic controller for grid-connected photovoltaic (PV) system using interleaved dual boost (IDB) converter and line commutated inverter (LCI) has been developed for feeding the maximum power to single-phase utility grid. A proportional-integral controller designed using operational amplifier adjusts the duty cycle of the IDB converter to provide the required constant DC voltage to the inverter under varying conditions of PV array. If the PV array output is directly connected to the utility grid through an inverter, a step-up transformer would be required between the inverter and the grid supply. Alternatively the array voltage is to be increased to match with the grid voltage. The introduction of DC-DC converter between PV array and LCI not only eliminates the need for step-up transformer between LCI and the utility grid, but also adds flexibility in the maximum power point tracking algorithm. The fuzzy logic controller, which is designed to vary the firing angle of the inverter to track the maximum power, has been implemented using National Instruments DAQ USB 6009 device and MATLAB tool boxes. The proposed scheme is modelled using MATLAB/PSB and interfaced in real-time for generating the firing pulses to the thyristors in the inverter. The comparison of results obtained from simulation with that of experimental investigation validates the proposed scheme.

Simulation and Analysis of a Multilevel Converter Topology for Solar PV Based Grid Connected Inverter

There has been a noticeable increase in use of Solar PV based systems for power generation, given its renewable nature. A solar PV based grid tie inverters are used for dc-ac conversion. The conventional line commutated ac-to-dc inverters have square-shaped line current which contains higher-order harmonics. The line current with the high harmonic contents generates EMI and moreover it causes more heating of the core of distribution/power transformers. Alternatively, PWM based inverters using MOSFET/IGBT switches are also used for the same purpose. However, apart from higher switching losses, the power handling capability and reliability of these devices are quite low in comparison to thyristors/SCR. Nevertheless, the conventional thyristor based forced commutated inverters are not suitable for PWM applications due to the problems of commutation circuits. A pure sinusoidal line current or waveform with low har- monic contents is the most desirable. In the present work, a multilevel line commutated inverter topology has been proposed and analyzed which improves the wave shape and hence reduces the total harmonic distortion (THD) of the line current in a grid tie line commutated inverter. The scheme has successfully been implemented and tested. Moreover, the performance of the proposed topology is far better than the conventional line-commutated inverter. It reduces THD, losses, switching stress and EMI.

Fuzzy logic controller with MPPT using line-commutated inverter for three-phase grid-connected photovoltaic systems

A fuzzy logic controller has been developed for interfacing PV array with utility grid through a three-phase line-commutated inverter for the first time. The controller tracks and feeds maximum power to the utility grid. The linguistic variables have been selected appropriately to modulate the firing angle of the inverter for tracking the maximum power. The simulink model of the proposed scheme employing fuzzy logic controller has been built using MATLAB/PSB. A PIC microcontroller has been programmed for generation of firing pulses to the thyristors in the inverter. Experimental setup of the proposed scheme has been built and the results obtained on a PV array of 54 V, 12 A rating are presented. The comparison of experimental and simulation results shows very close agreement between the two thus validating the controller proposed.

Soft-switched current-source inverter for single-phaseutility interfaces

A novel soft-switched current-source inverter for single-phase utility interfaces is presented. To provide the soft-switching capability under the pulsewidth modulation for a single-phase line-commutated thyristor inverter, an auxiliary resonant switch to bypass the current on the DC side is connected across the DC input of a thyristor inverter.

Fault analysis of the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system

AbstractFault analyses are performed for the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system through a line‐commutated inverter. The behavior of the interconnecting system is first examined for the case of single misfiring of one thyristor in the inverter. In this case, the load current increases because the inverter system is short‐circuited. Following the theory of inverter commutation, the load current decreases to the rated value and the MHD generator is restored to the rated condition. Next, the cases of a single‐line ground fault and of a three‐phase short circuit fault are investigated. The line voltage decreases and thus the load currents increase after the fault. This increase of load currents destroys the design‐point flow of the MHD generator. Phase‐control angle control of the inverters is required in order to restore the rated operation of the MHD generator. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 29–36, 2001

Fault analysis of Ar–Cs segmented-loading disk magnetohydrodynamics generator connected to electric power system

The authors study numerically an interconnecting system between the segmented-loading Ar–Cs closed cycle disk magnetohydrodynamics (MHD) generator and an infinite bus through the line-commutated inverter system and double-circuit power transmission line when faults occur at the inverter system and the power transmission line. Simulation results at the inverter fault condition show that misfiring of the inverter at not only the downstream but also the upstream results in a large disturbance at the downstream in various quantities of the generator. The firing angle control is very important to recover the operating condition of the MHD generator. Simulation results at the power line fault condition show that the inverters become out of operation, and ionization instability of the plasma is induced in the MHD generator when the fault occurs. When the fault is removed, the MHD generator can be recovered by means of the firing angle control of the inverters.