Repetitive current control of an interleaved grid-connected inverter

Active power filters (APFs) with repetitive control (RC) could compensate for the harmonics. However, there are some problems in IGBT-380V-APFs with RC, such as the adaptability of grid frequency varying because of the non-integer value of RC parameters. SiC-MOSFETs that could reach high switching frequency provide a new way to increase the compensation accuracy and the frequency adaptability for 380V/APFs. In this paper, a novel frequency adaptive fast repetitive control (FAF-RC) for APF with SiC-MOSFET inverter to achieve optimal performance in variable frequency girds through changing RC order N was proposed. Taking the advantage of the high switching and sampling frequency of SiC-APF, the control method proposed with low computational complexity could compensate the harmonics more accurately with less software debugging. The control method with 50kHz switching and sampling frequency is described, designed, and verified experimentally in a two-level APF prototype made up of SiC-MOSFETs. The results obtained that 380V/75A-SiC-APFs with the control method proposed and volume of 37L (that 66% of IGBT-APFs) have a high compensation accuracy (THD<5%) with the grid frequency variations.

Active power filters (APFs) with repetitive control (RC) could compensate for the harmonics. However, there are some problems in IGBT-380V-APFs with RC, such as the adaptability of grid frequency varying because of the noninteger value of RC parameters. SiC- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s that could reach high switching frequency provide a new way to increase the compensation accuracy and the frequency adaptability for 380V/APFs. In this article, a novel frequency adaptive fast repetitive control (FAFRC) for APF with SiC- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> inverter to achieve optimal performance in variable frequency girds through changing RC order <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> was proposed. Taking the advantage of the high switching and sampling frequency of SiC-APF, the control method proposed could compensate for the harmonics more accurately with an integer RC order <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> . The control method with 50 kHz switching and the sampling frequency is described, designed, and verified experimentally in a two-level 380V/75A APF prototype made up of SiC- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s, which volume is 37L that 66% of IGBT-APFs. The results obtained that 380V/75A-SiC-APFs with the control method proposed have a high compensation accuracy (THD<5%) with the grid frequency variations.

This paper describes a comprehensive analysis of a three-phase two-level silicon carbide (SiC) MOSFET V2G inverter including the LCL filter design. The efficiency is compared between the SiC MOSFET and Si IGBT. Using a SiC device enables the inverter to operate at high switching frequency and this leads to improved efficiency up to 99.05% at 10 kHz and 97.71% at 100 kHz switching frequency. The output LCL filter is also designed based on a specific switching frequency and the filter value is most significantly reduced at the highest switching frequency. The SiC inverter and LCL filter is simulated using LTSpice and MATLAB Simulink.

The paper proposes the design method of output filter and repetitive controller of inverter in stand-alone PV system. The design of filter considers the impact of filter on the inverter main circuit in order to increase the stability of the inverter. For the serious waveform distortion when the inverter runs independently with non-liner load, the circuit introduces repetitive control and presents a new parameter design method of repetitive controller. The simulation results prove that the design method is correct and feasible.

This paper proposes a frequency separation type current control system for a grid-connected single-phase five-level inverter. The proposed control system realizes high tracking performance and high disturbance suppression performance. To obtain high tracking performance to the sinusoidal reference signal, a repetitive controller is applied to the current controller. The current controller with a repetitive controller is capable of tracking to fundamental frequency, without the steady-state error. The disturbance observer using a notch filter (notch type disturbance observer) is used to obtain the high disturbance suppression performance. Using the notch type disturbance observer, the frequency components except for the fundamental frequency are suppressed. The proposed control system is configured by combining the current controller with a repetitive controller and a PI controller, and adding a notch type disturbance observer. Numerical simulation results and experimental results confirm that the proposed control system effectively reduces the output current distortion. The THD of the output current is reduced by 15.5 % when using the proposed control system.

In this paper, a new grid current control strategy based on internal model control and repetitive control is designed. The performance characteristic and operation principle are analyzed according to the basic principle of internal model control and the dynamic mathematical model of three-phase photovoltaic grid-connected inverters. Because the harmonic current caused by the dead-time effect and the periodic disturbance of the grid can not be eliminated by internal model control, a composite control strategy with internal model control and repetitive control is proposed in the paper. Internal model control can simplify the controller’s parameters and ensure the dynamic quality of the system. Repetitive control is able to restrain the dead-time effect and the periodic disturbance of the grid. It can also reduce the total harmonic distortion of the grid-connected current. The simulation results show that the proposed control strategy has good dynamic and steady-state performance and can restrain the periodic disturbance as well.KeywordsThree-phase grid-connected invertersInternal model controlRepetitive controlDead-time effect

In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve better efficiency. The design method introduces capacitor-current-feedback active damping into the H∞ controller design process by proposing an equivalent controlled plant. Additionally, based on the discrete model of the controlled plant with variable computation delay, the algebraic expression of the stable region for the feedback coefficient and the computation delay is obtained to avoid system instability caused by the digital control delay. Finally, the stability criterion is proposed to evaluate the stability of the discrete control system with the H∞ repetitive current control scheme. The theoretical analysis and experimental results prove that the control scheme presented in this paper not only can reject the harmonics of output currents, but is robust under the variation of the grid-impedance.

The photovoltaic grid-connected inverter is the most important device of photovoltaic generation which is a widely adopted application of solar energy. Its control strategy determines the working status and performance of the photovoltaic generation system. Repetitive control strategy of the photovoltaic grid-connected inverter is analyzed in this paper. The method based on repetitive control and pole assignment is also presented to solve the one-cycle-lag disadvantage of repetitive control, and the simulation model in Matlab/Simulink is established. The simulation results show that the dynamic performance of grid-connected inverter is improved and the waveform deviation rate is reduced effectively with the help of pole assignment.

—In this article, an improved deadbeat control algorithm suitable for digital signal processor-based circuit implementation is proposed. The control algorithm allows the derivation of a nearly sine wave output current with a fixed switching frequency of a current-controlled voltage source inverter. Two low-pass output filters configurations are considered in this study: a simple inductance filter and an LCL-filter. By taking advantage of prior knowledge of the state variables’ shape, the improved deadbeat control algorithm is based on a simple prediction model to derive the expected duty cycle needed to switch on and off the power switches. The control study of the grid-connected inverter with L and LCL output filters has been considered using a co-simulation approach with (Powersim Inc., Rockville, Maryland, USA) and MATLAB software (The MathWorks, Natick, Massachusetts, USA). The obtained results show the improvement of both shape quality and tracking accuracy of the output current quantified by low ripple content and a nearly unity power factor.

In order to improve the quality of the power injected into the grid, a deadbeat (DB) control strategy based on weighted average current with plug-in repetitive control (RC) scheme is proposed for a grid-connected inverter with LCL filter. Firstly, we calculate weighted average current of input and output current of the LCL filter, and use this variable to simplify the control strategy. Therefore, the equivalent model of the LCL filter is reduced from the third-order to the first-order. Secondly, DB controller is designed in discrete-time based on this simplified model. In order to suppress the harmonics of fed-in grid current, the RC is proposed to plug-in with the DB controller in parallel by providing the required harmonic elimination of the periodic signals. In the proposed combined control, the deadbeat control can track a given signal with fast dynamic response, and the RC can make the steady state error converge to zero gradually. The simulation and experimental results have demonstrated the effectiveness and advantages of the proposed method.

The hysteresis current controllers (HCC) for grid-connected inverter (GCI) system is a well-known controller for its robustness, fast reference tracking, better dynamics, and easier implementation compared to other controllers. This article proposes a modified double-band HCC (MDBHCC) for single-phase GCI system with LCL -filter. The proposed algorithm implements an unipolar symmetrical pulse width modulation (PWM) strategy for reducing inverter switching losses through a sequential logic, with an adaptive clock. It improves the variation in switching frequency and limits the maximum switching frequency of HCC while enhancing the total harmonic distortion (THD) of the injected current into the grid. In order to alleviate power quality problems, two such MDBHCC schemes, i.e., MDBHCC1 and MDBHCC2, are implemented. Where MDBHCC2 operates at the higher switching frequency with lesser % THD and MDBHCC1 operates at lower switching frequency. Simulation and experimental results are presented with a significant decrease in switching frequency and an improvement in grid current harmonics at both steady-state and dynamic conditions.

Transformerless grid-connected inverters, due to their advantages in high efficiency, small volume and light weight, gain more research and interest in recent years. Due to the asymmetrical driving signal in pulse-width-modulation (PWM) caused by time-delay, zero-drift of the current sensors and imparities of the power transistors, etc. Output of the grid current contains dc component. As a result, power quality of the grid is degraded. In this paper, a dc component suppression scheme with recursive integral PI controller are introduced, according to the change tendency of tracking error, the coefficients of PI controller are regulated by BP neural network in real time, and the global optimization requirements are met. Sliding-Window-Double-Iteration-Method (SWDIM) is utilized for fast dc current extraction. Simulation results from a 2-kW three-phase grid-connected inverter confirm the effectiveness of the proposed scheme.

This paper describes how to design the output filter of a pulsewidth-modulation inverter used in an uninterruptible power supply. Several constraints apply to this design: physical limitations of all material and components, output waveform quality, losses, cost, etc. All models used in the design process are described: semiconductor, inductor and capacitor losses, cost, total harmonic distortion, short-circuit behavior, etc. Input parameters are control law, switching frequency, inductor design parameters (number of turns and magnetic circuit), and capacitor values. Based on these design models, optimization is carried out, and cost-losses tradeoff curves are deduced. Two power levels (30 and 300 kVA) are taken as design example, with the same models, in order to show the robustness of the method.

The efficiency of linear power amplifiers can be improved by modulating its supply voltage according to the peak value of the signal that is being amplified in a technique usually known as envelope tracking. High bandwidth dc/dc converters called envelope amplifiers (EAs) are used to carry out the supply modulation in an efficient manner. In the case of linear RF power amplifiers, the bandwidth requirements over the EA strongly depend on the signal being amplified: in modern telecommunication applications it can range from several hundred kilohhertzs to a few tens of megahertz. The path to achieve such bandwidths usually goes through increased switching frequencies and/or reduced ratio of switching frequency to converter bandwidth. However, these may lead to lower converter efficiency and increased distortion, making the design of EAs a challenging task. This paper addresses the analysis and design of the output filter for Buck converters operating as EA. The output filter must provide enough attenuation at the switching frequency and harmonics to guarantee a desired level of distortion while enabling tracking of wide-bandwidth envelope signals with high converter efficiency. This paper focuses on the use of high-order filters (up to sixth-order Bessel-Thomson, Butterworth, and Legendre-Papoulis filters) in a buck dc/dc converter working as an EA. The filters are analytically described and characterized, and a design procedure that takes into account the major design constraints is proposed, allowing the selection of the appropriate filter for a given application. The proposed analysis and design method are supported by simulation results, as well as by experiments obtained using a 1 MHz buck converter operating as an EA.

Low back pain is one of the most common pains that people experience in their lives. This pain is mainly associated with the weakness of back muscles that increases the risk of spine damage. Proper exercise can increase muscle strength and improve spine stability and protect it against damages. A new exercise device intended for back muscles is developed here based on biomechanical, rehabilitation and engineering requirements. A novel mechanism has been designed and fabricated such that the flexion/extension and lateral bending tests and trains can be conducted in sitting/standing positions with a single actuation and monitoring system all in one device, enhancing functionality and reducing costs. The muscles torque is monitored via a mechanism composed of two single-point load cells. An electrical motor with closed loop control is used to provide the required constant speed (in the isokinetic operation mode). The parameters in the dynamic model of the electrical motor are estimated through system identification. Two controllers (including a PI and a repetitive controller) are designed and implemented. Both controllers demonstrated good tracking and disturbance rejection in the steady state performance. The test results associated with the isokinetic and isometric operation modes obtained in the training of an adult subject are also presented and discussed.