A General Parallel Structure Repetitive Control Scheme for Multiphase DC–AC PWM Converters

Two optimized control schemes of shunt active power filter (SAPF) in balanced three-phase three-wire system are proposed in this paper, including a fast fractional-order repetitive control (RC) strategy and a computation reduced harmonic detecting method. The improved RC is implemented in the synchronous reference frame (SRF) and based on the fractional-delayed-filter. Compared with the conventional RC (CRC), the proposed strategy can reduce the repetitive period from one fundamental cycle to one-sixth of the fundamental cycle, which results in the faster dynamic response. The fractional-delayed-filter, as the delay part of the proposed improved RC strategy, is used to achieve the high tracking accuracy of reference signals for control systems with different sampling rates. This paper also proposes a harmonic detecting method in the SRF based on the sliding Discrete Fourier transform (SDFT) with reduced computational burden, catering for selective harmonic elimination. Simulations and experiments show the validity of the proposed solutions.

In this paper, a parallel structure repetitive control scheme is proposed for three-phase PWM inverters to compensate 6k ± 1th order harmonics. This new control scheme divides conventional repetitive control into two branches in parallel structure. By this design, it avoids using filters in series, thus achieving higher gains for targeted harmonic groups than other 6k±1 repetitive controllers. Besides, the proposed control scheme reduces the number of delay units required to one third of that in conventional repetitive control schemes, thereby offering faster convergence rate and better transient performance. Stability and convergence of this approach are proved mathematically. Experimental results are provided to show the effectiveness of the proposed control scheme.

The differential current in Modular Multilevel Converters (MMCs) is inherently subjected to even order harmonics, which are mainly caused by the voltage mismatch between phase legs and dc bus. This issue may exist in both single-phase and multi-phase MMC systems and can be eased by repetitive control based active harmonic suppression methods, which regulate the circulating current through legitimate adjustment of the voltage applied on the arm inductance. Nevertheless, conventional repetitive controllers have relatively slow dynamic response because of the presence of one fundamental period delay, and all the sampled errors in the past one cycle have to be stored for closed-loop control. This paper presents an improved even-harmonic repetitive control scheme that requires less data memory with faster dynamic response. The steady state performance can also be enhanced if system disturbances e.g. frequency deviation are considered. In order to verify its practicality and effectiveness, PLECS simulation and experimental results are presented to show the excellent dynamic response and disturbance rejection of the proposed even-harmonic elimination scheme.

A number of soft-switching pulse-width-modulated (PWM) converter techniques have been proposed, aimed at combining the desirable features of both the conventional PWM and resonant converters while avoiding their respective limitations. In this paper, three classes of zero-voltage soft-switching PWM converters (namely the zero-voltage switched (ZVS) quasi-square-wave converters, ZVS-PWM converters, and zero-voltage-transition PWM converters) and two classes of zero-current soft-switching PWM converters (namely the zero-current-switched PWM converters and zero-current-transition PWM converters) are reviewed; their merits and limitations are assessed. Experimental results of several prototype of converters are presented to illustrate each class of converter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper present the power factor improvement technique in the midpoint converter-based switched reluctance motor (SRM) drive using an AC-DC three level pulse width modulation (PWM) converter. A conventional SRM drive produces very high level of harmonics content and poor power factor at AC mains. The proposed converter with midpoint converter fed SRM drive improves the power factor at AC mains with low current harmonics. The SRM drive with converter is modelled and its performance is simulated in MATLAB/Simulink environment.

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.

Photovoltaic (PV) systems with integrated energy storage units traditionally have been complex and required multiple DC-DC converters. In this paper, a novel multiport isolated LLC resonant converter and a modified maximum power point tracking (MMPPT) control method are introduced to reduce complexity. The proposed topology is designed to operate under a wide input voltage range and contains an integrated bidirectional pulse width modulation (PWM) converter and a LLC resonant converter. Frequency modulation control is implemented for regulating the output voltage of the whole system while the PWM converter is controlled by the MMPPT which generates the battery current reference and PI controller. MATLAB/Simulink was used to demonstrate the feasibility of the topology.

In magnetically suspended rotor (MSR) systems, harmonic current mainly originates from rotor mass imbalance and sensor runout, which can generate multifrequency vibration. Repetitive control (RC) is an effective method to eliminate periodic disturbance from a control system. Conventional RC (CRC) method requires the exact knowledge of the period of the periodic signal. However, in some applications, the period may fluctuate or may not be available with sufficient accuracy, in which case the performance of the CRC severely decays. Besides, the transient response of the CRC is relatively slow. In response to these issues, a second-order RC that incorporates dual mode structure scheme is presented in this paper. By introducing Lagrange-interpolation-based fractional delay filters, the current suppression accuracy gets enhanced in fractional cases. The stability criterion with rigorous proof for the proposed scheme is addressed. The sensitivity to period-time of the proposed scheme is analyzed as well, from the aspect of sensitivity transfer function. Simulation and experimental validations are performed on an MSR to show the effectiveness of the proposed approach.

Repetitive control (RC) presents an attractive solution to achieve low steady-state tracking error and total harmonic distortion for periodic signals. For the conventional RC (CRC), it requires the ratio of the reference signal period to the fixed sampling period to be an integer. Therefore, the reference signal with a variable frequency or a fractional period ratio will lead to severe performance degradation. Although existing hardware variable sampling (VS) rate methods enable the CRC to be frequency adaptive, the VS frequency will also influence the overall system stability, and they need that the CPU has the VS frequency ability. In this paper, a flexible and easy-to-implement method, virtual VS (VVS), is proposed to enable the RC to be frequency adaptive. The proposed VVS method that creates a virtual delay unit to approximate each VS delay achieves a flexible VS as similar to the hardware-based VS but it does not influence the overall system sampling frequency and stability. Experimental results of a single-phase dc/ac converter system are presented to demonstrate the effectiveness of the proposed VVS-RC.

In recent years, wind turbines have been growing in size and became more lightweight and thus more flexible. Spatial variation in the wind speed results in asymmetrical blade loads, which include a periodic component increasing with growing wind turbine size. Asymmetrical blade loads can be reduced by individual blade pitch control in general and repetitive control can reduce especially the periodical parts of the loads. We investigate, how a repetitive control based individual blade pitch controller as extension to an existing collective pitch controller can reduce periodical loads resulting from unsteady non-uniform wind conditions under consideration of variable rotor speeds. As plant, we use a simulation model of a 3 MW wind turbine, developed by W2E Wind to Energy GmbH, and control it with a model predictive collective pitch controller. This controller is extended with the proposed repetitive individual pitch control scheme. This study shows, that the presented repetitive controller reduces especially the tower yaw moments by up to 65% and higher harmonics of the blade root moments by up to 30% at the cost of increased pitch activity. Hence, for the use of this controller one has to balance the load reduction of blades and tower with increased loads of the pitch actuators.

This paper presents a novel synchronous-frame repetitive controller for three-phase UPS inverters. Distinguished from conventional repetitive control techniques, the proposed synchronous-frame approach minimizes the repetitive control time delay to one-sixth of the fundamental period such that the dynamic response is significantly improved. In order to overcome the harmonic distortions under severe load conditions (e.g., unbalanced and nonlinear), in this paper, three synchronous rotating frames are deliberately selected, in each of which the repetitive controller is incorporated. Resultantly, the (6n ±1)th harmonics as well as the triplen harmonics are compensated. Moreover, a high-performance fourth-order linear phase infinite-impulse-response filter is applied to further enhance the accuracy of steady-state tracking. The proposed controller is programmed on the 16-bit fixed-point digital signal processor (TI TMS320LF2407) and eliminates high-resolution current sensors for cost effectiveness. Simulations and experimental tests have been carried out based on an 18-kW three-phase UPS system. Low total harmonic distortion (<;0025;) has been achieved under heavily distorted nonlinear load and unbalanced load. Fast dynamic response has been demonstrated during step load transients.

A bidirecitonal dual active converter with the power factor control capability is proposed for low-power on-board battery charger application. The source side half-bridge acts as a pulse-width modulation (PWM) converter that maintains the unity power factor. The battery side half-bridge converter acts as a dual active bridge (DAB) together shares the same DC link voltage with the PWM converter. Asymmetric duty cycle technique in which turn-on and -off time duration of primary switches in DAB converter are changed to control the charges of two capacitors is employed to eliminate imbalance voltage phenomenon. Thus, the input current can shape in phase with the voltage source and promising high efficiency of PWM converter. Simulation and experimental results are included to verify theoretical analysis.

TDA 16888 is designed for off-line switched mode power supplies (SMPS) with optional universal input and power factor correction, for example, for PCs, monitors, CTVs and industrial applications. Combi-IC TDA 16888 includes the pulse width modulated (PWM) control for a SMPS and the control for the preconverter to improve the power factor and to reduce the harmonics of the AC input current. Both sections are internally synchronized on the same operating frequency. The preferred topology of the PFC-preconverter is boost, but flyback is also possible. The PWM section can be designed as a forward or as a flyback converter. Maximum duty cycle of the PFC is about 95%, in order to achieve minimal line current gaps. Maximum duty cycle of the PWM is limited to 50% to prevent transformer saturation. In normal operation the PFC section operates with dual loop control. A first control loop controls the shape of the line current by average current control enabling either continuous or discontinuous operation mode. The second loop controls the DC bus voltage. There is a third control loop available that enables the PFC section as an auxiliary power supply even during disabling the PWM section. In this paper the PFC preconverter, PWM converter, PFC and PWM gate drive, and oscillator and synchronisation are described.

Dear Editor, This letter presents an improved repetitive controller (IRC) that uses a complex-coefficient filter to enhance the tracking performance of a system for periodic signals. Compared with the low-pass filter used in the conventional repetitive controller (CRC), the complex-coefficient filter causes less change in the phase and amplitude of a signal at the frequencies of the periodic signal, especially at the fundamental frequency, when the two filters have the same cutoff-frequency. Thus, the IRC-based control system has better tracking performance than the CRC-based control system. Simulation results of a rotational control system demonstrate the superiority of the IRC.

The harmonic current in active magnetic bearing (AMB) system usually results from rotor unbalance and sensor runout. It not only causes considerable harmonic vibration, but also brings about the power saturation and the instability of AMB system especially for the high-speed rotor. Therefore, a novel parallel finite dimension repetitive controller (PFDRC) is proposed to restrain the harmonic current in this paper. Compared with the conventional repetitive controller (RC), PFDRC only introduces the limited imaginary poles, so that the problem that the infinite imaginary poles of RC endanger the stability and instantaneous characteristic of the closed-loop system is solved. In order to realize the harmonic current suppression, the power amplifier system is taken as the controlled object, and the proposed PFDRC is parallel with the original equivalent main controller. Then the root reclus method is adopted to design the parameters and to analyze the closed-loop system stability. Based on the phase-frequency characteristic of the system function, the compensators are introduced to improve the system stability margin. Meanwhile, the low-pass property of power amplifier system is sufficiently taken into consideration in the parameters design. Finally, the simulations and experiments are implemented to validate the effectiveness of the proposed PFDRC, and the results demonstrate that the harmonic current is dramatically restrained by the proposed method.