Inverter Control System Research Articles

Integrated Control System for Three-level Inverters based on Artificial Neural Network

In the actual operation of power grid, inverter is the access of source and power grid, and is an important control link affecting power quality. The three-level inverter has very strong nonlinearity, and the loading of nonlinear load produces large harmonic, which seriously affects the transmission quality. The artificial neural network has good fault tolerance and adaptive ability when dealing with the nonlinear system. Based on the artificial neural network algorithm, the three-level inverter control system is designed and simulated. The results show that the neural network control can deal with the nonlinear and uncertainty of the three level inverter control system. With constant voltage and constant frequency, the fluctuation of the output voltage and frequency is within controllable range. The three-level inverter controlled by artificial neural network shows smaller fluctuation and faster adjustment speed. The steady-state error of artificial neural network control is smaller than that under the control of PID. The use of artificial neural network control can greatly improve the dynamic and static capacity of the inverter system.

UDE-Based Current Control Strategy forLCCL-Type Grid-Tied Inverters

LCL filter is usually used as an interface between inverters and the grid. However, due to the characteristics of LCL filter and system uncertainties, it is complex to design a controller with proper parameters. In this paper, with LCCL filter, the order of the inverter control system can be reduced from third order to first order, and an uncertainty and disturbance estimator based control strategy for grid-tied inverters with LCCL filter is proposed. Specifically, the proposed control strategy consists of differential feedforward, proportional–integral controller, and grid voltage feedforward. Moreover, with one-sampling computation plus half-sampling pulse width modulation delays considered, a simple and clear tuning algorithm for the proposed control strategy is presented. Finally, the inverter system with the proposed control strategy is investigated, and the effectiveness is supported by the tuning and comparative experiments with a 2-kW inverter.

Three phase voltage source inverters with grid connected industrial application

The grid-connected issue is one of the major problems in the field of Power Electronics. In this paper, the Three Phase Voltage Source Inverter (VSI) is controlled by a Space Vector Pulse Width Modulation (SVPWM) Technique. SVPWM control technique and Park transformation, the managed inverter control system to convert input DC power into AC power, stabilize the output voltage and current, and feeds the excess power to the utility grid can be achieved by controllers. Usually, the grid source contains higher level of harmonics. To analyze the harmonics, nonlinear load is connected externally in the point of common coupling. The main aim of this paper is to modeling, simulation and experimental study of the three-phase grid connected inverter. By using the control algorithm, the grid sides Total Harmonics Distortion (THD) are controlled to the 1.54% for 800V DC as per the IEEE standard. The stimulation results such as AC output voltage and current, inverter system power flow, and grid disturbances detection signals, proves the effectiveness of the developed control algorithm. The control algorithms to makes the for this inverter outputs is pure sinusoidal.

A Novelty Half-bridge Inverter Control System Design and Control Regulation

A novelty method of pulse frequency power modulation and pulse width power modulation strategy are proposed for solving the problem of the skin effect of the load in the inductance heating mainly. A series half-bridge and inductance surface hardening is described. In the paper, established modeling for a series of half-bridge inverter circuit. An inductance heating system circuit is built through Simulink software to verify the feasibility of the complex power adjustment rules. After the circuit testing, results show that the composite power adjustment strategy can effectively achieved the control of constant power output and the load frequency tracking. Our strategy can improve the ability of adaptability and the overall performance with a certain feasibility and effectiveness.

A New Feed-forward Compensation Inverter Control Strategy

With the development of new energy research, photovoltaic inverter is widely used in solar photovoltaic power generation system. In this paper, a new static feedforward compensation control strategy for current loop is proposed for the shortcomings of the single-phase PV inverter in the use of the typical Ⅰ-type system in the double closed-loop control system. Through the improved Park transformation, the equivalent model of the single-phase inverter is obtained. The control equation of the current is obtained by the method of feed-forward decoupling control in the equivalent inverter model. For the interference signal in the current control equation, The static feed-forward compensation control method eliminates the interference signal present in the inner loop of the current. Through this control method, the current loop in ensuring the performance of good follow at the same time effectively improve the current loop anti-jamming performance. At the same time, current loop control and voltage outer loop control using PI control, the formation of double closed-loop control system. The simulation results show that the anti - jamming performance of the double closed-loop inverter control system with static feed-forward compensation is better, the output waveform distortion rate of the inverter is low, and the PV inverter is stable in the presence of disturbance.

Principles for construction the compensators of reactive power with voltage stabilization for transformer substations

Based on the booster transformer and the transistor converter with a DC link, a system is proposed for fast and accurate unloading the electric network from reactive power with simultaneous stabilization of voltage among consumers. The system contains a discrete stage of reactive power compensation and adjustable part. The adjustable part includes series and parallel reactive power compensators. The series compensator consists of a booster transformer, a voltage inverter and is designed to be switched on to the high voltage of the transformer substations. The parallel compensator consists of a rectifier with an input choke and is connected to the low voltage of the substation. The rectifier and inverter are connected by a DC link with an LC filter. The rectifier regulates the output voltage and the phase of the sinusoidal input current. The inverter regulates the magnitude and phase of the voltage on the control winding of the booster transformer. The rectifier and inverter control systems are synchronized with the network and with pulse width modulation.

A Current Limiting Strategy to Improve Fault Ride-Through of Inverter Interfaced Autonomous Microgrids

With high penetration of distributed energy resources, fault management strategy is of great importance for the distribution network operation. The objective of this paper is to propose a current and voltage limiting strategy to enhance fault ride-through (FRT) capability of inverter-based islanded microgrids (MGs) in which the effects of inverter control system and inverter topology (four/three-wire) are considered. A three-phase voltage-sourced inverter with multi-loop control system implemented in synchronous, stationary, and natural reference frames is employed in this paper for both four- and three-wire configurations. The proposed strategy provides high voltage and current quality during overcurrent conditions, which is necessary for sensitive loads. Several time-domain simulation studies are conducted to investigate the FRT capability of the proposed strategy against both asymmetrical and symmetrical faults. Moreover, the proposed method is tested on the CIGRE benchmark MG to demonstrate the effectiveness of the proposed limiting strategy.

Modeling and design of a multivariable control system for multi-paralleled grid-connected inverters with LCL filter

The quality of injected current in multi-paralleled grid-connected inverters is a matter of concern. The current controlled grid-connected inverters with LCL filter are widely used in the distributed generation (DG) systems due to their fast dynamic response and better power features. However, designing a reliable control system for grid-connected inverters with LCL filter is complicated. Firstly, overcoming to system resonances due to LCL filters is a challenging task, intrinsically. This could become worse as number of paralleled grid-connected inverters increased. In order to deal with resonances in the system, damping methods such as passive or active damping is necessary. Secondly and perhaps more importantly, paralleled grid-connected inverters in a microgrid are coupled due to grid impedance. Generally, the coupling effect is not taken into account when designing the control systems. In consequence, depending on the grid impedance and the number of paralleled inverters, the inverters installed in a microgrid do not behave as expected. In other words, with a proper control system, a single inverter is stable in grid-connected system, but goes toward instability with parallel connection of other inverters. Therefore, consideration of coupling effect in the multi-paralleled grid-connected inverters is vital. Designing control systems for multi-paralleled grid-connected inverters becomes much more difficult when the inverters have different characteristics such as LCL filters and rated powers. In this paper, the inverters with different characteristics in a microgrid are modeled as a multivariable system. The comprehensive analysis is carried out and the coupling effect is described. Also, the control system design for multi-paralleled grid-connected inverters with LCL filter is clarified and a dual-loop active damping control with capacitor current feedback is designed. Finally, the proposed multivariable control system for a microgrid with three-paralleled grid-connected inverters with LCL filter is validated by simulation.

Study of a Current Control Strategy Based on Multisampling for High-Power Grid-Connected Inverters With an LCL filter

The high-power grid-connected inverters with LCL filters have been widely used. Current control plays a key role in the grid-connected inverter control system. To cope with the inherent resonance of the LCL filter, active damping (AD) methods are usually employed. However, the AD performance is impaired by control delays which are introduced in the digital control implementation process. Besides, the lag phase due to control delays limits the system bandwidth and stability margin. The effects of control delays are more noteworthy in the high-power grid-connected inverter due to its low switching frequency. This paper investigates the current control strategy based on multisampling for the high-power grid-connected inverter with the LCL filter. First, the multisampled AD scheme is studied, which can reduce control delays effectively and improve AD performance. Besides, the multisampled control without additional damping whether passive or active is researched. Through the inverter-side current feedback, the system can realize single-current-loop control based on multisampling. Thus, the control system is simplified and it can be stable, and achieve better dynamic performance. Finally, experimental results show that the proposed control schemes are effective.

Transient processes in welding inverters and their influence on the stability of welding current

Inverter converters used for dc-arc electric welding have been manufactured by many foreign and domestic companies and showed good results for decades. Until recently, ac welding was carried out only at an industrial frequency of 50 Hz. Earlier, we suggested carrying out arc welding at an increased frequency within the range of 25–75 kHz, proving it to be efficient taking into account welding physical processes. Results of investigations of “slow” electrical processes in a high-frequency inverter for ac welding at different stages of the welding cycle are given in this article. In particular, the transition processes in the inverter are studied in detail taking into account a whole variety of factors. We conducted a complex of investigations concerning the study of the character and duration of the transient processes in an alternative sign welding inverter with increased frequency, as well as the level of influence of the transition coefficient and time constant of the inverter-control system on these processes. The influence of design and parasitic data of the scheme on the nature of the “fast” and “slow” transient processes and changes in the parameters of the electric arc (loading) and parameters of the actuating signals were assessed. All this allowed determining the effect on the stability of the welding current and, therefore, on the welding quality.

Experimental Validation of Improved Control Strategy of Grid-interactive Power Converter for Wind Power System

In this paper grid-voltage oriented control of grid-side converter for wind power system is presented, which aims to optimize the performance of utility grid during transient conditions. To realize this objective, a digitally controlled inverter system is implemented which provides independent control of active and reactive power delivered to the grid under sudden change in reactive load. Initially, the proposed grid-voltage oriented control scheme is analyzed in order to manage the power flows into the grid followed by the mathematical modelling of grid-side converter. And then, a closed-loop control structure of the grid-side converter is implemented using a conventional proportional integral (PI) controller with space vector pulse width modulation (SVPWM) current controller. In order to analyze the results of the proposed study, in this paper, the complete system is modelled and simulated in the MATLAB/Simulink environment and the numerical results are discussed. The experimental results, obtained using DSP TMS320F2812 processor, confirm the high performance of the proposed control system in terms of good sinusoidal grid current, low harmonic content and fast dynamic response.

Design of Speed Control System for PMSM Based on Three-Level Structure

三相永磁同步电机在节约电能方面具有非常广阔的前景，它具有结构简单、体积小、效率高、易于散热和维护简单等优点。相比传统的两电平逆变器，三电平逆变器具有很多优点：单管耐压低、开关损耗降低、谐波含量小等，因此将三电平技术应用到永磁同步电机调速系统中，具有重要的理论意义和实用价值。本文主要研究了基于三电平中点箝位型(NPC)逆变器的永磁同步电机(PMSM)调速系统。电机采用转子磁场定向的矢量控制。为了达到控制目的，在三电平逆变器控制系统中引入了零序电压注入法。这种方法很好地控制了中点电压的平衡，以期降低逆变器输出电压谐波含量，改善电机定子电流波形，这将减小电机转矩脉动，改善电机控制性能。本文介绍了永磁同步电机的数学模型和矢量控制方法，阐述了中点箝位型三电平逆变器的拓扑结构和换流模式，分析了中点电位平衡算法和调制策略，最后通过实验验证了系统的可靠性和稳定性。 The three-phase PMSM has a very broad prospect in saving electrical energy. It has the characte-ristics of simple structure, small volume, high efficiency and good heat radiation. Compared with conventional two-level inverters, three-level inverter has a series of advantages such as low vol-tage-proof for single transistor, low switching loss and low harmonic content, etc. Therefore, it is of great theoretical significance and practical value to apply the three-level inverter to the speed regulating system of permanent magnet synchronous motor (PMSM). In this paper, the speed regulating system of permanent magnet synchronous motor on the basis of three level neutral point clamped (NPC) inverter is studied. Rotor flux oriented vector control method is applied on the motor. In order to implement the control process, zero sequence voltage injection method is introduced in the proposed three-level inverter control system. With this method, the balance of the neutral point voltage can be well achieved to reduce the harmonic content of the output voltage of the inverter and improve the stator current waveform, which will further minimize the motor torque ripple, and improve motor control performance. The mathematical model and vector control method of PMSM are introduced in this paper, both the topology and commutation mode of three-level inverter with neutral point clamping mode are described, and the neutral point potential balance algorithm and modulation strategy are also analyzed. Finally, the experiment verified the reliability and stability of the system.

Development of Propulsion Inverter Control System for High-Speed Maglev based on Long Stator Linear Synchronous Motor

In the case of a long-stator linear drive, unlike rotative drives for which speed or position sensors are a single unit attached to the shaft, these sensors extend along the guideway. The position signals transmitted from a maglev vehicle cannot meet the need of the real-time propulsion control in the on-ground inverter power substations. In this paper the design of the propulsion inverter control system with a position estimator for driving a long-stator synchronous motor in a high-speed maglev train is proposed. The experiments have been carried out at the 150 m long guideway at the O-song test track. To investigate the performance of the position estimator, the propulsion control system with, and without, the position estimator are compared. The result confirms that the proposed strategy can meet the dynamic property needs of the propulsion inverter control system for driving long-stator linear synchronous motors.

Measuring the real parameters of single-phase voltage source inverters for UPS systems

ABSTRACTThe design of a voltage source inverter (VSI) control system requires knowledge about its continuous or discrete model. The output filter inductance and the equivalent serial resistance, which is partly the result of power losses in the core, have values at the operating point that are significantly different from the assigned nominal values, particularly for iron-powder cores. Measurements using standard laboratory equipment are not sufficient because it is impossible to get the voltage and current of the operating point. So the best solution is to measure the Bode plots of the inverter control function at the operating point, to estimate the results of the measurements using the proper analytic function and to calculate the real values of the inverter parameters. Knowledge about the equivalent serial resistance enables the estimation of the inverter power losses. Two approaches to measurements are shown – one that does not require any additional equipment and the other that uses a specialised system to automatically measure the Bode plots. The advantages and disadvantages of both approaches are presented. These measurements enable the validation of the coil core magnetic material by taking into account the power losses. The applications of the measurements in the control design are shown.

A Hidden Block in a Grid Connected Active Front End System: Modelling, Control and Stability Analysis

An LCL filter utilized in an active front end (AFE) converter can generate significant resonance, which can affect quality and stability of the system. Thus, a proper active or passive damping technique and/or a suitable controller is required to be designed for the converter. The duty cycle constraint—though inevitable in practical inverter systems—is often ignored in most of the existing literature. The effects of measurement noise on filter control system performance must be considered and evaluated under different conditions. Finally, almost all inverter control systems are implemented digitally using microcontrollers. Consequently, the effects of sampling on control system stability and performance should be evaluated as well. Thus, this paper presents stability analysis of an AFE converter-based filter design with a complete practical system configuration, including saturation and sampling blocks and measurement noises. Mathematical analysis and simulations have been carried out to validate the proposed method.

Simulation and Experimental Validation of Multicarrier PWM Techniques for Three-phase Five-Level Cascaded H-bridge with FPGA Controller

The FPGA represents a valid solution for the design of control systems for inverters adopted in many fields of power electronics because of its high flexibility of use. This paper presents an overview and an experimental validation of the MC SPWM techniques for a three-phase, five-level, cascaded H-Bridge inverter with FPGA controller-based. Several control algorithms are implemented by means of the VHDL programming language and the output voltage waveforms obtained from the main PWM techniques are compared in terms of THD%. Simulation and experimental results are analyzed, compared and discussed.

Моделирование самообучающейся системы управления инвертором преобразователя частоты для подавления высших гармоник

Simulation of a three-phase frequency converter based on three single-phase full-bridge voltage inverters with a sine-wave output filter is considered. A new self-learning control system for the converter’s inverters is proposed. The previously developed inverter control system uses the discrete Fourier transform (DFT) to suppress the output voltage higher harmonic components. Individual regulators are used to control each harmonic component (including the fundamental and higher-order ones). The DFT algorithm produces signals proportional to the amplitudes of the fundamental and a number of higher-order harmonic components, which are applied to the regulators as feedbacks. The main drawback of the existing system is that it poses rather high demand to the microcontroller computation capacities. The newly proposed system is based on the self-learning principle and uses a periodic integrator (a P-integrator) as the output voltage regulator. The P-integrator is represented in discrete form by an array of discrete integrators, each of which operates only in the 1/64 part of the fundamental harmonic component cycle. The new control system's software code is much smaller in size and contains a fewer number of “slow” arithmetic operations, due to which it is easier to implement and less demanding with respect to computation resources. The control system analysis results demonstrate its good performance in terms of suppressing higher harmonic components: the output voltage total harmonic distortion factor does not exceed 5% for the cases of operation on linear and nonlinear loads. The article describes the modernized control system structure and its implementation in MATLAB Simulink software package. Advantages of the self-learning algorithm as compared with the algorithm based on the discrete Fourier transform are demonstrated. The simulation results confirm the applicability of the new control method. The algorithm is implemented in the C language in the MATLAB S-function block and is suitable for being implemented in real-time control systems based on dedicated microcontrollers without the need of significantly modifying the software code.

Capacitor Current Feedback-Based Active Resonance Damping Strategies for Digitally-Controlled Inductive-Capacitive-Inductive-Filtered Grid-Connected Inverters

Inductive-capacitive-inductive (LCL)-type line filters are widely used in grid-connected voltage source inverters (VSIs), since they can provide substantially improved attenuation of switching harmonics in currents injected into the grid with lower cost, weight and power losses than their L-type counterparts. However, the inclusion of third order LCL network complicates the current control design regarding the system stability issues because of an inherent resonance peak which appears in the open-loop transfer function of the inverter control system near the control stability boundary. To avoid passive (resistive) resonance damping solutions, due to their additional power losses, active damping (AD) techniques are often applied with proper control algorithms in order to damp the LCL filter resonance and stabilize the system. Among these techniques, the capacitor current feedback (CCF) AD has attracted considerable attention due to its effective damping performance and simple implementation. This paper thus presents a state-of-the-art review of resonance and stability characteristics of CCF-based AD approaches for a digitally-controlled LCL filter-based grid-connected inverter taking into account the effect of computation and pulse width modulation (PWM) delays along with a detailed analysis on proper design and implementation.

Nonlinear dynamics control in single-phase inverter with sinusoidal pulse-width modulation

A variant of technical implementation of the control system of a single-phase voltage inverter with sinusoidal pulse-width modulation, based on target-oriented control, which ensures the desired nonlinear dynamic properties of the system, is proposed. The control system under discussion solves the problem of providing a sinusoidal output voltage of the inverter when changing its parameters in a wide range, accompanied by bifurcations. This eliminates unwanted dynamic modes without parametric synthesis of the system. The target-oriented control for managing the dynamics of nonlinear systems with sinusoidal pulse-width modulation is used for the first time and gives a number of advantages compared to other known methods.

Research and development of conversion of direct current voltage to the quasi-sinusoidal voltage with pulse-width modulation

Practically all widely used variable-frequency alternating-current electric drives with autonomous voltage inverters (AVIs) use pulse-width modulation (PWM) according to one of the following techniques: sinusoidal, space-vector, and relay. Fulfilling the relay PWM requires an analog–digital converter (ADC) with high resolution and sample rate. Vector PWM has a nonsinusoidal output voltage that causes additional losses in the motor. The main problem of a symmetrical (centered) sinusoidal PWM is underuse of a dc link. For a long time, the vector PWM method was taken to be most promising one due to the absence of this defect. In practice, this technique is applied in areas without a strong voltage criterion, for which reason it has limited use. Moreover, due to another significant problem, which is the “dead” time on the sector borders at the vector PWM, different modified methods for constructing the sinusoidal PWM have become widespread, especially in modern asynchronous motor control systems, with the development of digital microprocessor systems. To determine the quality of different types of PWMs, a complex model of an electric drive, incorporating an inverter control system that implements different algorithms of constructing the discrete PWM signals is developed. The model and the electric circuit are constructed in LabVIEW and NI Multisim, respectively. The obtained simulation data can be used to select the optimal method of controlling the AVI. The analysis that has been conducted allows one to select an optimal PFWM control strategy in terms of research results concerning electric power quality and mechanical properties.