Output Current Of Inverter Research Articles

Synchronization control of single-phase full bridge photovoltaic grid-connected inverter

In this paper, the single-phase full bridge photovoltaic (PV) grid-connected inverter is introduced. Based on the working principle and circuit theory, the corresponding dimensionless mathematical model with 8-dimensions piecewise smooth state equation is established. An improved unidirectional correlation method for synchronizing the inverter to the utility grid is proposed. Analysis shows that the presented control scheme is effective and can synchronize the output current of PV inverter with the phase and frequency of utility grid by selecting appropriate correlation factor, disregarding the dynamics behavior of inverter.

Predictive Current Control Methods With Reduced Current Errors and Ripples for Single-Phase Voltage Source Inverters

This paper proposes two model predictive current control (MPCC) methods utilizing two output voltages with variable application durations in one sampling period to control the output currents of single-phase voltage source inverters (VSIs). In the proposed methods, the application durations of the two voltages, as well as the selection of two output voltages used in the future sampling period, are determined by an optimization process to minimize current error inside the future sampling period and to eliminate current error at the end of the future sampling instant. By utilizing the two voltages with variable durations, the two proposed MPCC methods can reduce steady-state current errors and decrease output current ripples without increasing the sampling frequency in comparison with the conventional MPCC method, despite only three distinctive output voltages being allowed in the single-phase VSI. The two proposed methods along with the conventional MPCC method are compared in terms of current errors and total harmonic distortion. The effectiveness of the two proposed methods for the single-phase VSIs is verified with both simulation and experimental results.

Criteria-Based Modulation for Multilevel Inverters

Pulse width modulation schemes are aimed at adjusting the fundamental component while reducing the harmonic content of an inverter output voltage or current. This paper addresses the topic of optimal inverter operation in reference to a given objective function. The objective function could embody either a single performance criterion, such as voltage or current total harmonic distortion (THD), or a weighted sum of multiple criteria. The proposed method ensures primacy of the chosen solution while imposing no restriction over its modulation index. In particular, operating the inverter by the chosen solution would result in performances superior to any other modulation scheme commutating in an equal number of switching angles per fundamental cycle. The proposed method allows for the consideration of practical inverter constraints and prevents the possibility of impractical switching sequence. A detailed investigation of the method is given, accompanied by two practical cases minimizing, respectively, phase-voltage THD and line-current THD of a three-level inverter. Selected simulation and experimental results are presented to validate the theoretical part.

Fuzzy PI controlled inverter for grid interactive renewable energy systems

In this study, a fuzzy-PI controlled grid interactive inverter has been designed and implemented. The proportional and integral gains of the PI controller are decided and tuned by the fuzzy logic controller (FLC) according to required operation point of the system. Thus, adaptive nature of the FLC and robust structure of the PI controller are synthesised. Eventually, an adaptive PI controller which can adopt changes because of different operation conditions, grid disturbances and natural effects with fast transient response is obtained. Simulation studies are validated with experimental results. Both simulation and experimental results show that proposed system has fast dynamic response and tracks reference current with a low overshot and short settling time. In addition, the waveform of the inverter output current is sinusoidal and also the current is in same phase and frequency with the line voltage. Furthermore, the total harmonic distortion level of the inverter current meets the international standards. In addition, the proposed inverter system is compared with conventional PI controlled grid interactive inverter with various proportional and integral gains.

Performance analysis of a low-cost current-source 1-ph grid-connected PV inverter

This paper investigates the design and performance of a 150 W single-phase current-source grid-connected inverter topology that is based on a PV array and DC link inductor acting as a constant-current source. The inverter is implemented using a single boost switch, an H-bridge inverter, and a CL output filter. The inverter output current is simply controlled using the boost switch and open-loop or feedforward control. The dark I-V configuration is used to simulate two series PV modules. Comprehensive test results are obtained to validate the computer simulation results. Furthermore, the proposed inverter's ability to deliver a sinusoidal current to the grid while meeting the appropriate standards, i.e. total harmonic distortion and power factor requirements, is also examined for various modulation index values and irradiances.

Harmonic Characteristic Analysis of Five-Phase Space Vector PWM

Pulse modulation width (PWM) of multi-phase inverter is the key technologies of ships electrical propulsion. In this paper, theories and realization of space vector PWM (SVPWM) for five-phase inverter is analyzed. The proposed SVPWM adopts two adjacent large voltage vectors to composite the reference voltage vector and this method have advantages of easy to realize. Theoretical waveform and harmonics of five-phase inverter output voltages under the proposed control method are deduced. The analysis shows that there are very large third harmonics in the inverter output voltages and currents. The total harmonic distortion (THD) is large also, and changes small with the modulation index. Simulation and experiments certify the conclusions.

Two‐loop power‐flow control of grid‐connected microgrid based on equivalent‐input‐disturbance approach

This study employed the equivalent‐input‐disturbance (EID) approach to devise a two‐loop power‐flow control system that controls the output current of an inverter so as to regulate the flow of active and reactive power between a distributed generation unit and a utility grid. It actively eliminates disturbances that degrade the power quality of a microgrid. The pq theory and an all‐pass filter are employed to generate an instantaneous reference current for the control system based on the prescribed active and reactive power of a utility grid terminal. The inner loop consists of a disturbance compensator and a state observer. The disturbance compensator uses information acquired from the state observer to estimate disturbances, such as drops and harmonics in the grid voltage, and compensates for them by incorporating the equivalent input disturbance into the control law. The outer loop consists of a resonance‐based internal model and a state‐feedback controller, which enables the output current of inverter to track the instantaneous reference current. The small‐gain theorem ensures the stability of the system. The system improves the power quality and guarantees that the flow of active and reactive power from the grid and inverter has low harmonic distortion. Simulations demonstrated the effectiveness of the system. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Phase-shifted Discontinuous Pulse-Width Modulation Methods for Multi-level Inverters Operated in Over-modulation Range

This article presents combinations of the generic phase-shifted pulse-width modulation method with conventional discontinuous pulse-width modulation methods operated in the over-modulation range. The treated discontinuous methods are the third harmonic injection, Depenbrock's DPWM1, and Ogasawara's DPWM2. The significant advantage of the present approach over the conventional phase disposition pulse-width modulation method is the equal power flow between the H-bridges and the improved distribution of the switching operations number between them. Furthermore, they provide improved linearity in the over-modulation range. The proposed pulse-width modulation methods are analyzed by extensive simulation results. Several aspects, such as the total harmonic distortion factor of the inverter output currents and voltages, harmonic content, frequency spectrum distribution, and switchings number, are studied.

A Systematic Method for Designing a PR Controller and Active Damping of the LCL Filter for Single-Phase Grid-Connected PV Inverters

The Proportional Resonant (PR) current controller provides gains at a certain frequency (resonant frequency) and eliminates steady state errors. Therefore, the PR controller can be successfully applied to single grid-connected PV inverter current control. On the contrary, a PI controller has steady-state errors and limited disturbance rejection capability. Compared with the L- and LC filters, the LCL filter has excellent harmonic suppression capability, but the inherent resonant peak of the LCL filter may introduce instability in the whole system. Therefore, damping must be introduced to improve the control of the system. Considering the controller and the LCL filter active damping as a whole system makes the controller design method more complex. In fact, their frequency responses may affect each other. The traditional trial-and-error procedure is too time-consuming and the design process is inefficient. This paper provides a detailed analysis of the frequency response influence between the PR controller and the LCL filter regarded as a whole system. In addition, the paper presents a systematic method for designing controller parameters and the capacitor current feedback coefficient factor of LCL filter active-damping. The new method relies on meeting the stable margins of the system. Moreover, the paper also clarifies the impact of the grid on the inverter output current. Numerical simulation and a 3 kW laboratory setup assessed the feasibility and effectiveness of the proposed method.

Neutral point voltage balancing of five-level inverter fed by twelve-pulse rectifier

The paper presents 5-level, neutral point clamped, H-bridge inverter fed by 12-pulse rectifier. Two configurations of rectifier and inverter neutral point connection are studied: the first configuration with disconnected neutral points and the second configuration with connected neutral points. Furthermore, novel neutral point voltage balancing methods suitable for the presented configurations are proposed. Extensive simulation results of the proposed configurations with the neutral point voltage balancing methods are presented. The simulation results deal with aspects such as total harmonic distortion (THD) Factor of the inverter output currents, and voltages, grid current, harmonic content, frequency spectrum distribution. The results confirm the effectiveness of the proposed methods. The voltage balancing methods are compared and their advantages and disadvantages are explained.

Compensation Strategy to Eliminate the Effect of Current Measurement Offsets in Grid-Connected Inverters

For the digital control of systems such as grid-connected inverters, measuring inverter output currents accurately is essential. However, current measurement offsets are inevitably generated by current measurement paths and cause DC current components in real inverter output currents. Real inverter output currents with DC components cause the DC-link capacitor voltage to oscillate at the frequency of a utility voltage. For these reasons, current measurement offsets deteriorate the overall system performance. A compensation strategy to eliminate the effect of current measurement offsets in grid-connected inverters is proposed in this study. The validity of the proposed compensation strategy is verified through simulations and experiments. Results show that the proposed compensation strategy improves the performance of grid-connected inverters.

Power Control System Design in Induction Heating with Resonant Voltage Inverter

This paper is concerned with the design of the power control system for a single-phase voltage source inverter feeding a parallel resonant induction heating load. The control of the inverter output current, meaning the active component of the current through the induction coil when the control frequency is equal or slightly exceeds the resonant frequency, is achieved by a Proportional-Integral- Derivative controller tuned in accordance with the Modulus Optimum criterion in Kessler variant. The response of the current loop for different work pipes and set currents has been tested by simulation under the Matlab-Simulink environment and illustrates a very good behavior of the control system. 

Power control for grid connected applications based on the phase shifting of the inverter output voltage with respect to the grid voltage

In photovoltaic (PV) systems connected to the grid, the main goal is to control the power that the inverter injects into the grid. According to the grid demands, injected power does not only include the control of the active power, but also the control of the injected reactive power. This paper presents, a digital control strategy based on the phase shifting of the inverter output voltage with respect to the grid voltage, in order to control the power factor with a minimum number of Digital Sinusoidal Pulse Width Modulation (DSPWM) patterns and for a wide range of the inverter output current. This proposed method has been described, simulated and validated by experimental results.The proposed control strategy requires few hardware and computational resources. As a result, the inverter implementation is simple, and it becomes an attractive solution for low power grid connected applications.

A Practical Judge Model to Simulate Lithium-Ion Battery Material Discharge Voltage Threshold

The output current of the current-source inverter (CSI) can be very steady. It is applied in the circumstance when precise current is needed. But the output characteristic of CSI depends on not only its performance but also the batterys nature. This paper presented a practical judge model which can simulate the batterys output threshold. In a simulation system, the amplitude of inverting current can be a very large value provided the loop impedance is small enough and the output current can remain steady. But in actual operation CSI has its out put limitation. When the given current is big, the output current will be unsteady. It is very risky because it might cause short circuit between both sides power. The output characteristic of CSI is studied from the mechanism when the control block generate the trigger impulse. The reason why the output values differ greatly between simulation and test is discussed. The simulation used a method by adopting a concussion judgment module to detect the CSIs output state. The reference currents the amplitude information and phase information is separated. The proportion between reactive component and active component is concerned to regulate CSIs output current. Simulations and tests proved the correctness and feasibility of the method.

Novel Multilevel Hybrid Cascaded Inverter for High Power Motion Control Systems

The paper presents an analysis of a novel multilevel inverter that can be used in the power modules of motion control systems for soft starting and speed control of high power medium voltage synchronous and induction motors. The inverter is constructed from hybrid cascaded H-bridge cells. The advantages of the proposed inverter upon standard topologies are significant reduction of electrical components and as a result, smaller size and weight. The proposed approach can be extended to any desired number of voltage levels. Extensive simulation results validate the practicability of the proposed inverter. Several aspects, such as Total Harmonic Distortion Factor of the inverter output currents and voltages, harmonic content, and frequency spectrum distribution are studied.

A New Topology of Five-Level Neutral Point Clamped Inverter for Motion Control Systems

The paper presents a new topology of 5-level neutral point clamped inverter that can be used for speed and torque control of synchronous and induction motors. The proposed topology has only two bi-directional and four standard IGBT switches per phase. The significant advantages of the proposed inverter are simpler control and lower number of switches than in the standard 5-level inverters. Extensive simulation results validate the practicability of the proposed inverter. Several aspects as Total Harmonic Distortion Factor of the inverter output currents, and voltages, harmonic content, and frequency spectrum distribution are studied.

The Design of Wind Power Converter Based on LCL Filter

As to the output current of grid inverter in high-power wind power generation system contains large current harmonic, the solution is to introduce the LCL filter to replace the typical inductance filter in grid inverter, which brings instability to the system, thus the control strategy is to use the grid inverter current indirect control combined with the grid voltage feed forward compensation. A 15KW wind power simulation platform is constructed. The experimental results show that the grid converter can run stably, and also have a better dynamic and static performance.

Analysis of the Deadbeat Control Algorithm for Photovoltaic Grid Connected Inverter Output Current

Photovoltaic grid connected inverter is the core interface device in the photovoltaic power generation system to grid. The power quality of photovoltaic power generation system is affect by the waveform of output sinusoidal AC current directly. In this paper, current deadbeat control algorithm and a two-stage photovoltaic grid-connected inverter control strategy are proposed by analyzing the derivation of a photovoltaic grid-connected inverter. According to the grid connected Photovoltaic system features, a set of three-phase Photovoltaic grid connected inverter is designed, which rated power is 15 kW. The deadbeat control algorithm is introduced, based on the analysis of photovoltaic grid connected inverter topology, grid connected voltage, current, power, and the current waveform distortion rate. The deadbeat control algorithm is effective to control the three phase inverter output current through the system simulation and analysis.

Five-Level Inverter for Renewable Power Generation System

In this paper, a five-level inverter is developed and applied for injecting the real power of the renewable power into the grid to reduce the switching power loss, harmonic distortion, and electromagnetic interference caused by the switching operation of power electronic devices. Two dc capacitors, a dual-buck converter, a full-bridge inverter, and a filter configure the five-level inverter. The input of the dual-buck converter is two dc capacitor voltage sources. The dual-buck converter converts two dc capacitor voltage sources to a dc output voltage with three levels and balances these two dc capacitor voltages. The output voltage of the dual-buck converter supplies to the full-bridge inverter. The power electronic switches of the full-bridge inverter are switched in low frequency synchronous with the utility voltage to convert the output voltage of the dual-buck converter to a five-level ac voltage. The output current of the five-level inverter is controlled to generate a sinusoidal current in phase with the utility voltage to inject into the grid. A hardware prototype is developed to verify the performance of the developed renewable power generation system. The experimental results show that the developed renewable power generation system reaches the expected performance.

A Current Decoupling Parallel Control Strategy of Single-Phase Inverter With Voltage and Current Dual Closed-Loop Feedback

The output characteristics of a single-phase inverter with voltage and current dual closed-loop feedback control are analyzed, and the equivalent circuit model of a parallel single-phase inverter system is introduced. By taking both resistance and inductance components of the equivalent output impedance into consideration, a current decoupling control strategy of the parallel inverter system is then proposed. Furthermore, by constructing a three-phase balanced current according to the output current of the single-phase inverter, an active and reactive current decomposition method is presented to decompose the output current of the single-phase inverter into active and reactive currents according to the instantaneous reactive power theory. The block diagram of the active and reactive current decomposition method is given, and current decomposition simulation results are shown to verify the analysis results. The prototype is developed, and the control of two parallel-connected 2-kVA inverters is realized. The experimental results show its feasibility and effectiveness.