Single Voltage Source Inverter Research Articles

Review on Close Loop Control of Novel Transformer Less Inverter Topology for Single Phase Grid Converter

The continuous urge for improvement in our standard of living has increased the consumption of electrical energy by leaps and bounds. This hike in energy consumption, draining of fossil fuels and degrading global environment has led to invention of green power generation systems. Thus, the global demand for renewable resources has led to flourishing of photovoltaic (PV) market. The enabling technology in the PV systems is the inverter, which could be either: 1) with transformer isolated or 2) without transformer non-isolated (transformer-less inverter). Recently, single phase transformerless voltage source inverters (VSI) have been extensively used for distributed photovoltaic grid tied systems. The objective of this paper is to review a few notable topologies and propose a new topology for transformer-less photovoltaic inverter. The analysis and design of the proposed topology is verified by simulating it on PSIM. Furthermore, the simulation results are validated by testing a proof-of-concept laboratory hardware prototype rated at 250 W. Keywords— Photovoltaic (PV) systems, transformer-less, single phase inverter

Utility Interactive Renewable Microgrid with Backup Power Functionality

This paper deals with three-phase wind-solar-photovoltaic microgrid (WPV-MG), which is capable of performing in grid-tied and island modes of operation under steady state and in DSTATCOM (Distribution Static Compensator) mode, utility-interactive and disconnecting modes under dynamic state. This microgrid (MG) uses a single VSI (Voltage Source Inverter) with reduced power converters and switches. At the DC bus of VSI, a battery bank is used to provide load leveling either at less renewable generation or at light loads. The control of VSI is also able to maintain power balance among various units and provides PQ (Power Quality) improvement in the MG under local nonlinear loads. During no renewable power generation, it works as a DSTATCOM to improve PQ and provides power factor correction and reduces voltage harmonics in PCC (Common Coupling Point) under local linear/nonlinear loads. During abnormal grid conditions, it provides power backup to local consumers under island operation. For this three-phase WPV-MG, a laboratory prototype is developed and its performance under different operations is validated through test results.

Performance evaluation of isolated three-phase voltage source inverter with LC filter adopting different MPC methods under various types of load

As the variety of loads in microgrids continues to grow rapidly, the drawbacks of using conventional voltage and current double closed-loop PI control are becoming increasingly intolerable. These disadvantages include poor static tracking of the output and the need for complicated tuning of optimal PI control parameters. Model predictive control (MPC) is widely studied in recent years and gradually applied to the inverter as a modern control strategy. Currently, the research on MPC mainly focuses on reducing the computational burden of algorithms and improving computing skills. In this paper, the control theory of continuous-control-set model predictive control (CCS-MPC), optimal switching vector model predictive control (OSV-MPC), quasi-sliding mode model predictive control (QS-MPC) and optimal switching sequence model predictive control (OSS-MPC) are elaborated. Also, the disadvantages of adopting conventional voltage and current double closed-loop PI control on microgrids are clarified. Moreover, aiming at evaluating the influence of connecting and/or removing the common loads, such as electric vehicles to the microgrid on the output performance of microgrids in practical engineering applications, single three-phase voltage source inverter with LC filter system with two-phase pure resistance load, three-phase diode rectifier bridge nonlinear load, constant power load and constant current source load applying four different MPC methods, are simulated. The simulation results show that under different types of load, system with nonlinear load applying OSV-MPC method has the biggest value of total harmonic distortion (THD) of the output voltage and the biggest steady state root mean square (RMS) tracking error of the output voltage, which are 1.33% and 2.1 V, respectively. The performances of the output voltage of the system adopting MPC are generally improved compared to the system using conventional voltage and current double close-loop PI control. Regarding the output voltage performance of a system under load step change, a system using the OSS-MPC method with a nonlinear load exhibits the smallest overshoot of the output voltage and the smallest root mean square value of the tracking error (RMSE) between the output voltage and the reference value within 20ms after the load step change. Specifically, the overshoot and RMSE are 2.804 V and 0.810 V, respectively. The simulation results provide valuable guidance for selecting the appropriate model predictive control strategy for microgrid integrating complex loads, such as electric vehicles in practical applications.

A Power Control Scheme for a Wind Turbine/Fuel Cell Hybrid Power System with DFIG-DC Link Topology

This study discusses the performance of the power control strategy for a Wind Turbine/Fuel Cell Hybrid System with a Doubly Fed Induction Generator (DFIG)-Direct Current (DC) link configuration. To overcome high cost and the complex structure of the previous study, a new DFIG-DC link configuration is proposed that uses a single Voltage Source Inverter (VSI) and a diode rectifier to connect the stator and rotor to the DC-link, respectively. Also, the DFIG-DC system is modeled and a Stator Field-Oriented Control (SFOC) is adopted to control the VSI to extract the maximum power generated by the wind turbine. The model and the control of the DC-DC boost converter used to connect the hydrogen fuel cell to the DC-link are established. To achieve better performance of the proposed DFIG-DC system, the power control strategy has been tested by using the dSpace DS1104 processor board and the experimental results show the performance of the control strategy in terms of parameters regulation under a different scenario.

Design Voltage Controller of Bipolar SPWM Voltage Source Inverter

This paper presents single phased VSI (Voltage Source Inverter) type bipolar SPWM. The main purpose of this system is generating a constant sinusoidal output waveform without affected by load (resistive) demand. Its concept is to get reference voltage from PI control and compare it with modulated triangular carrier for controlling inverter’s switches. The system is also represented by a LCL output filter. The LCL filter is employed to reduce the high frequency harmonic components in current waveform due to PWM switching and to reduce the output current THD. Simulation result and analysis are bravely presented to verify the effectiveness of proposed approach.

Second-Order Rotating Sliding Mode Control With Composite Reaching Law for Two Level Single Phase Voltage Source Inverters

In the recent past, the integration of distributed generation via power electronic interface like voltage source inverter (VSI) allows attaining the desired voltage quality by adopting appropriate control law. This paper presents sliding mode control (SMC) with composite reaching law technique for regulating output voltage under variable load conditions for single phase VSI. Inherent properties of SMC like robustness are achieved usually at the cost of chattering along the sliding surface. To handle this trade-off, optimal sliding surface selection mechanism is applied with adoptive reaching law based on state variables magnitude to set the value of control gain. The novelty of the proposed technique is related to composite reaching law that overcomes constraints associated with SMC. The proposed reaching law is a combination of exponential, power, and difference function. The intelligent mix of these functions makes the suggested reaching law more effective in achieving a high-speed convergence rate of system states and significant chattering reduction. Moreover, the sliding surface is chosen using a time-varying slope based on error variables. Comparative study of SMC with cosine exponential reaching law (Cos-ERL) results, fractional power rate reaching law (FPRRL) and proposed composite reaching law with rotating sliding surface(C-RL-RSS) applied on single phase voltage source inverter under variable load conditions validates the effectiveness of the proposed C-RL-RSS based SMC. It is revealed that the proposed C-RL-RSS based SMC is proficient in achieving very low %THD in the output voltage along with reduced chattering and minimum tracking time.

Independent Fuzzy Logic Control of Two Five-phase Linear Induction Motors Supplied from a Single Voltage Source Inverter

Background and Objectives: The principal aim of this paper is to show an independent vector control of two five-phase Linear Induction Motors (LIMs) that are supplied from a single VSI. Methods: The LIMs are running at the same speed but with different load conditions. This concept can be especially beneficial in long trains with distributed power. To achieve excellent control characteristics and to reduce the undesirable tension forces between the train mechanical couplers, Fuzzy Logic Controllers (FLCs) have been utilized.Results: As a result, the fault occurrence of the train control systems decreases, and the system reliability increases. The results prove the electrical independence in control of a five-phase two-LIM drive supplied with a single VSI. Furthermore, in the presence of the train mechanical couplers and connections, the application of FLC offers excellent control characteristics and reduces the undesirable tension forces. Furthermore, to obtain a more worthwhile validation of the theoretical results, an experimental set up has been constructed and results have also been presented.Conclusion: According to the results, the undesirable tension forces imposed on train couplers are reduced. Consequently, it leads to higher system efficiency, lower deterioration of the train couplers and connections, greater system reliability, and higher passenger safety and comfort.

Novel Self-Excited Brush-Less Wound Field Vernier Machine Topology

To realize the brush-less operation for wound field vernier machines (WFVMs), a novel self-excited topology is proposed in this paper which involves a four-pole main armature winding and a two-pole excitation winding connected in series using an uncontrolled rectifier. Upon supplying current from a single current-controlled voltage source inverter (VSI), this procedure results in four-pole and two-pole magnetomotive force (MMF) components in the airgap. The four-pole MMF produces the main stator field while the two-pole MMF component develops a sub-harmonic field in the airgap. The rotor is altered to house a forty-four-pole rotor field and two-pole harmonic windings. The two-pole harmonic field is employed to induce a current in the harmonic winding, which is rectified by means of a full-bridge diode rectifier to energize the rotor field winding and realize brush-less operation for WFVM. Two-dimensional finite element analysis (2-D FEA) is implemented in JMAG-Designer to confirm the operation of the proposed WFVM topology and attain the electromagnetic performance for a four-pole, twenty-four-slot outer-rotor vernier machine.

Direct Torque Control of Two Series Connected Six-Three phases Motor Fed by Single Six Phases VSI Based on Optimum Vectors Selection

In this paper, a direct torque control (DTC) is developed for a two series connected six-phase & three-phase motor drive (IMs) with sinusoidal distributed windings and fed by single six-phase voltage source inverter (VSI). Direct torque control also considered as a variable structure control strategy with simplicity, fast response and tolerance to motor parameter variations; it provides direct control of stator flux and torque by optimally selecting the inverter states in each sampling period. In case of multi-phase system drive, the increased number of voltages vectors offers greater flexibility in optimizing the selection of the inverter states. The technique elaborated in this work based direct torque control allows independently control of the system fed by single inverter. The effectiveness and capability of the proposed method are shown by computer simulation.

Non-independent speed control for dual-PMSM drives fed by a single three-leg VSI

<span>The objective of this article is to analyze the performances of Non-Independent Speed Control of Dual-PMSM (Permanent Magnet Synchronize Motor) Drives by a single Three-Leg Voltage Source Inverter (VSI) using control of Mean and Differential Torque technique. In general, there are two types of control strategies for Dual-Motor drives. One is Master-Slave technique and another one is Mean Control technique. For mean control technique, this study chooses mean and differential approach for the motors parameters and averaging the voltage space vector. The advantages of Dual-Motor drives fed by a single inverter topology are, it can reduce size and cost compared to the Dual-motor drives fed by individual inverter, either in industrial or in traction applications. However, by using a single three-phase inverter, the topology only restricted for the same operating conditions which are at the same speed, same parameters and same direction. The dual-motors are dependent (non-independent) on the other motor. It is can only be tested on different load operation. The analysis is focuses on speed and load variation for Dual-PMSM drives considering the forward and reverse operations of the motor. This simulation model is modelled using MATLAB-Simulink.</span>

Circulating Current Suppression in Parallel Interleaved 2L VSIs Using Modified CM Offset Based Method During Inductors Mismatch Condition

Parallel interleaved two-level voltage source inverters (VSIs) could be analyzed as a single multilevel VSI and hence, a significance reduction in the grid side voltage and current ripple could be achieved. However, the parallel interleaved VSIs have a major issue of circulating current. The circulating current is mainly composed of two frequency components: high frequency component and low frequency component. The high frequency component is generated due to the instantaneous difference in the common-mode (CM) voltages of the VSIs. While due to inductance value mismatch in the ac side line frequency inductors, a low frequency circulating current also flows in the system. This low frequency component needs to be controlled as it could saturate the CM, coupled, or interphase inductors used for limiting the high frequency component of circulating current. In this article, an analysis is carried out for circulating current during the inductors mismatch condition. A CM offset signal is also proposed to limit the flow of low frequency component of the circulating current. The proposed CM offset is derived in terms of existing CM offset signals, and hence any existing pulsewidth modulation technique could be implemented using the proposed method. Simulation and experimental results show the improvement in the circulating current using the proposed modified offset.

Constrained LQR Control of Dual Induction Motor Single Inverter Drive

Control of dual induction motor fed by a single voltage source inverter is a challenging task especially during unbalanced load conditions on each motor. Such drive configurations are common, for example, in traction. Conventional control algorithms solve the control of each motor in a separate control loop and the overall control action is designed as a weighted contribution of each control loop. In such a case, the control performance strongly relies on the specific design of weighting coefficients, which should be state dependent and time varying value in majority of cases. In this contribution, we formulate the control problem as an optimization task and investigate the use of state-dependent Riccati equation and predictive control concepts. We show that it is sufficient to consider a simple linear quadratic regulator (LQR) with rule-based predictive controller for current limitation. The proposed control algorithm naturally weights contribution of tracking error of each drive. Moreover, due to high level of symmetry in the system, only two parameters are tuned manually. Experimental testing is used to validate the control algorithm on a laboratory prototype of dual induction motor drive with a rated power of 2 × 4.5 kW.

An Improved Finite Control Set-MPC-Based Power Sharing Control Strategy for Islanded AC Microgrids

Hierarchical linear control scheme is widely used in ac microgrids. However, its transient response is slow and parameter tuning is time-consuming. Finite Control Set-Model Predictive Control (FCS-MPC) strategy has desired dynamic performance. Nevertheless, it requires an additional sensor to measure the inductor current. This article aims to mitigate these problems by introducing an improved FCS-MPC strategy for paralleled Voltage Source Inverters (VSIs). A capacitor current estimator is employed to reduce the extra current sensor in each VSI. The proposed control scheme consists of two loops: voltage reference generation loop and voltage tracking loop. The voltage reference generation loop achieves accurate load power sharing using virtual impedance-based droop control. Thus, communication is unnecessary among parallel VSIs. The voltage tracking loop utilizes a modified FCS-MPC block with capacitor current estimator to regulate the VSI output voltage. In order to verify the concept of the proposed control strategy, an ac microgrid consisting of two paralleled VSIs is implemented in dSPACE DS1202 hardware-in-the-loop platform. Then a single VSI hardware prototype is implemented and tested experimentally. The proposed method has the merits of good extensibility, low system cost and compact structure. Its steady-state performance is competitive with hierarchical linear control, while the transient response is significantly improved.

Design and Implementation of Fuzzy Logic based Single Phase Inverter using FPGA Controller

The single phase inverter provides continuous AC power supplies without any interrupt .The idea is to serve sinusoidal AC output whose voltage and frequency can be controlled by PWM pulse. The main theme of this concept is to present a new construction of an FPGA based control techniques for inverter. In this proposed system, a PI controller is used to the single phase PWM voltage source inverter. It minimizes periodic distraction resulted from linear load. Simulation provides the results, with reduced harmonics distortion of the output voltage .and innovative technique for including a fuzzy logic controller through a usual sampled pulse-width modulator is reported. The FLC is used to decrease the harmonic distortion and to offer better standard regulation. Simulations are carried out in ALTERA-Quartus II 8.0 software in addition by means of Matlab/Simulink and the results are presented for various control techniques. FPGA controller is preferred for the real time realization of the switching approach, for the most part owing to its larger computation speed which is able to guarantee the precision of the PWM pulse is developed. At the concluding stage the FPGA is used as a PWM generator in order to apply the appropriate signals for inverter switches

Independent Speed Control of Two Parallel Connected Split-Phase IM With a Common DC Link and Inverter

A novel pulsewidth modulation (PWM) scheme for the decoupled and coordinated control of two parallel connected split-phase induction machines is discussed in this paper for the first time. Both the motors are operated from a single six-phase voltage source inverter which acts as a power source, and two switched capacitor-fed auxiliary inverters to limit the flow of nontorque producing currents in each motor. Both the motors can be operated at its full rated power with low switching frequency, and decoupled control for full power range can be achieved with the proposed topology. This is possible because the individual machines do not carry the load/harmonic currents of other machine (unlike the conventional series or parallel connected systems). The converters can be modulated using sine-triangle PWM or space vector pulsewidth modulation (SVPWM). Furthermore, two different schemes of SVPWM techniques are proposed and compared in this paper. Exhaustive experimental results for all the modulation schemes are provided for steady state and transient operating conditions including start-up to validate the proposed topology and modulation schemes.

Model predictive control of a dual induction motor drive fed by a single voltage source inverter

In dual induction motor control applications, averaging of controlled variables, mean circuit models, or master/slave strategies are used, which lead to unbalanced and unstable operation of the overall drive system. An improved finite control set predictive torque control (FCS-PTC) method is proposed for the parallel operation of two induction motors. The optimization cost function of the controller is shown to meet multiple objectives simultaneously, eliminating the use of averaging techniques and without leading to unbalanced conditions. The simulation results are compared with direct torque control (DTC) for dual induction motors. As compared to DTC, model predictive control shows low torque and flux ripple, 5{\%} lower current THD, improved current balancing between the motors, and negligible effect of parameter mismatch.

Open-End Winding Induction Machine Fed by a Dual-Output Indirect Matrix Converter

Open-ended winding induction machines fed from standard two-level voltage source inverters (VSIs) provide an attractive arrangement for ac drives. An alternative approach is to use a dual-output indirect matrix converter (IMC). It is well known that the IMC provides fully bidirectional power flow operation, with small input size filter requirements. While a standard IMC consists of an ac–dc matrix converter (MC) input stage followed by a single VSI output stage, it is possible to replicate the VSI to produce multiple outputs. In this paper, an open-end winding induction machine fed by an IMC with two output stages is presented. The IMC modulation strategy aims to reduce the common-mode voltage (CMV), while compensating any zero-sequence voltage fed to the machine. The system is modeled using a PSIM and MATLAB/Simulink platform. Experimental results demonstrating the viability of the method are presented using a 7.5-kW prototype.

A New Topology for a Single Phase Multilevel Voltage Source Inverter with Reduced Number of Components

Multilevel inverters have gained much attention for its operation involving applications ranging values of high power rating. This paper proposes a switching topology for asymmetric multilevel inverter utilizing less number of power electronics components. When the number of the output level increases, it requires more switching states and eventually the number of switching components. The increased number of switches results in higher switching losses which may lead to power loss, and reduction of efficiency of the overall conversion system. The salient feature of this proposed topology is that the module can be used as a sub multiple level structure and can be extended for any number of level with minimal increase in the switching components.

Direct torque control of induction motors fed by a single frequency converter

Direct torque control of an induction motor is established by survey of operation regimes of traction electric drives to thoroughly satisfy the requirements for a traction electric drive. The advantages and shortcomings of three-level voltage source inverters in locomotive traction electric drives are highlighted in relation to two-level ones. A mathematical model of a multimotor system fed by a single frequency converter based on direct torque control is developed. It is shown that the variables of an induction motor can be represented as the sum of its average value and deviation from it. The equations for stator flux linkage and torque of an induction motor have been developed for a two-motor system fed by a single voltage source inverter. The topology and principles of operation of direct torque control of induction motors with a three-level voltage source inverter are described. The simplified structure and mathematical model of the mechanical part of a traction drive using basic and axle suspension are considered. The results of simulation carried out by Matlab are shown.

Study on Series Control Method for Dual Three-Phase PMSM based on Space Vector Pulse Width Modulation

Decoupling control of two-motor dual three-phase permanent-magnet synchronous motor (PMSM) series-connected system can be realized by using proper phase transposition rules with a single supply from a six-phase voltage source inverter (VSI), which solved the control problem of two motors in series. Since the traditional two-vector SVPWM strategy, which is commonly used in three-phase system, exists 5 th and 7 th harmonics in x-y plane, making it hard to realize decoupling control of two-motor dual three-phase PMSM series-connected system. Meanwhile, the DC bus voltage utilization of carrier-based PWM strategy is lower. Thus one method, which adopted a TBTSB-SVPWM strategy with two modulators, was proposed in this paper. It ensures the inverter output voltage only contains two kinds of fundamental components required by the two seriesconnected motors with a single VSI, making it possible to realize decoupling control of two-motor dual three-phase PMSM series-connected system. Simulation results indicate that there is no influence on the other motor while the speed/load of any one motor changed, achieving the decoupling control of series-connected system, and the feasibility and validness of the proposed approach are verified.