Virtual Variable Sampling Repetitive Control of Single-Phase DC/AC PWM Converters

In active heave compensation, in order to realize the smooth control of the heave compensation platform, it is necessary to use the ship motion measurement system to accurately obtain the ship displacement signal, invert the ship displacement signal, and then control the expansion and contraction of the electric cylinder so that the compensation platform remains horizontal. The ship displacement measurement system generally adopts the second integral of the acceleration sensor to obtain the ship displacement signal. During the acquisition process of the ship displacement signal, the quadratic integration process of the acceleration, and the communication process of the output control command, there is a processing lag which makes the error accumulate, resulting in a delay in the measurement of the ship motion. In order to collect the ship motion more accurately and control the heave compensation platform more precisely, this paper proposes a ship motion prediction method based on a variable step-variable sampling frequency characteristic LSTM (Long Short-Term Memory) neural network. First, we use the autocorrelation function algorithm to calculate the inherent delay of the lag in the process of signal acquisition by the measurement system. Secondly, the LSTM neural network is used to predict the inherent delay step of the lagging ship displacement signal. During the prediction process, it is found that the difference in the sampling frequency of the displacement signal will lead to a change in the step of the inherent delay—experiment in the laboratory to verify. By controlling the motion platform to simulate the motion of the ship and using the ship motion measurement system and the laser sensor system to measure the displacement signal of the motion platform synchronously, it is verified that the ship motion measurement system does have an inherent delay. Thirdly, on a sailing ship, ship displacement signals are collected by setting multiple sets of ship motion measurement systems. Finally, multiple sets of sampling frequency and multiple steps are set, and the ship motion is predicted based on the variable step-variable sampling frequency LSTM neural network. It is verified that the prediction accuracy is related to the sampling frequency of the signal collector and the prediction step of the LSTM neural network, which improves the prediction accuracy of the model and the timeliness of ship motion acquisition.

On the design of variable sample size and sampling intervals [formula omitted] charts under non-normality

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.

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.

The tracking/rejection of periodic signals constitutes a wide field of research in the control theory and applications area and Repetitive Control has proven to be an efficient way to face this topic; however, in some applications the period of the signal to be tracked/rejected changes in time or is uncertain, which causes and important performance degradation in the standard repetitive controller. This thesis presents some contributions to the open topic of repetitive control working under varying frequency conditions. These contributions can be organized as follows: One approach that overcomes the problem of working under time varying frequency conditions is the adaptation of the controller sampling period, nevertheless, the system framework changes from Linear Time Invariant to Linear Time-Varying and the closed-loop stability can be compromised. This work presents two different methodologies aimed at analysing the system stability under these conditions. The first one uses a Linear Matrix Inequality (LMI) gridding approach which provides necessary conditions to accomplish a sufficient condition for the closed-loop Bounded Input Bounded Output stability of the system. The second one applies robust control techniques in order to analyse the stability and yields sufficient stability conditions. Both methodologies yield a frequency variation interval for which the system stability can be assured. Although several approaches exist for the stability analysis of general time-varying sampling period controllers few of them allow an integrated controller design which assures closed-loop stability under such conditions. In this thesis two design methodologies are presented, which assure stability of the repetitive control system working under varying sampling period for a given frequency variation interval: a mu-synthesis technique and a pre-compensation strategy. On a second branch, High Order Repetitive Control (HORC) is mainly used to improve the repetitive control performance robustness under disturbance/reference signals with varying or uncertain frequency. Unlike standard repetitive control, the HORC involves a weighted sum of several signal periods. With a proper selection of the associated weights, this high order function offers a characteristic frequency response in which the high gain peaks located at harmonic frequencies are extended to a wider region around the harmonics. Furthermore, the use of an odd-harmonic internal model will make the system more appropriate for applications where signals have only odd-harmonic components, as in power electronics systems. Thus an Odd-harmonic High Order Repetitive Controller suitable for applications involving odd-harmonic type signals with varying/uncertain frequency is presented. The open loop stability of internal models used in HORC and the one presented here is analysed. Additionally, as a consequence of this analysis, an Anti-Windup (AW) scheme for repetitive control is proposed. This AW proposal is based on the idea of having a small steady state tracking error and fast recovery once the system goes out of saturation. The experimental validation of these proposals has been performed in two different applications: the Roto-magnet plant and the active power filter application. The Roto-magnet plant is an experimental didactic plant used as a tool for analysing and understanding the nature of the periodic disturbances, as well as to study the different control techniques used to tackle this problem. This plant has been adopted as experimental test bench for rotational machines. On the other hand, shunt active power filters have been widely used as a way to overcome power quality problems caused by nonlinear and reactive loads. These power electronics devices are designed with the goal of obtaining a power factor close to 1 and achieving current harmonics and reactive power compensation.

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 repetitive control technique is widely adopted in ac systems, because of its excellent steady‐state tracking performance and low total harmonic distortion. The repetitive control method with one‐sixth of the system fundamental period T0 as the delay time has been proposed to achieve fast transient response. In this study, an improved control scheme based on the T0/6 repetitive control is proposed for three‐phase grid‐connected inverters. The proposed scheme adopts T0/6 as the delay time in the positive‐rotating and negative‐rotating synchronous reference frames to suppress the 6n ± 1 harmonics. Meanwhile, the proportional‐integral regulator and the plug‐in repetitive controller are combined to reinforce the system performance. A new auxiliary function based on the linear interpolation is proposed to maintain the ideal repetitive control performance when one‐sixth of the ratio of the sampling frequency to the grid fundamental frequency is non‐integer. The effectiveness of the proposed scheme on improving the T0/6 repetitive control is confirmed by simulation and experimental results finally.

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.

The seasonal cycle of parthenogenetic and gamogenetic reproduction modes of the marine cladoceran Pleopis polyphemoides was studied in a shallow semi-enclosed Parnu Bay, the NE Baltic Sea. Population development of P polyphemoides was found to be very seasonal with a strong dominance of parthenogenetic females. The gamogenetic reproduction mode occurred almost throughout the whole reproductive season being the most intense during the population abundance peak. The change from parthenogenetic to gamogenetic reproduction was found to be neither influenced by water temperature, salinity nor Chl a concentration. Parthenogenetic fecundity was inversely correlated with water temperature and exhibited a positive relationship with total female body size, but showed no relationship with population density. In general, parthenogenetic females were larger just before or during the population peak. While the population development of P polyphemoides in spring seemed to be associated with temperature, the drastic decline during the summer was a result of changes in the biotic conditions (predation) rather than in the abiotic environment. Significant fine-scale spatio-temporal variability in the population development and several vital rates of P polyphemoides observed in the current study calls for caution when interpreting cladoceran multi-annual abundance dynamics from time series obtained with variable and/or low sampling frequencies.

This paper presents a general parallel structure repetitive control (PSRC) scheme for multiphase dc-ac pulse-width modulation (PWM) converters to cancel output total harmonic distortion more efficiently. With parallel structure, categorized harmonic frequency internal models are connected in parallel. Each categorized internal model has its own independent control gain and PSRC can optimize the total convergence rate by tuning the control gains independently according to the harmonic distribution. Compared with a multiresonant controller, PSRC has more compact structure and yields much less computation burden. Compared with conventional repetitive control (CRC), PSRC can achieve a much faster dynamic response without any loss of tracking accuracy or any added data memory. Moreover, PSRC is a general parallel structure RC for housing various existing RC, such as CRC, odd-harmonic RC, and dual-mode-structure RC. Experimental results of the PSRC-controlled three-phase dc-ac PWM converters show the validity and advantages of the proposed PSRC 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.

SummaryIn this paper, a simple approximate phase cancellation repetitive controller is proposed for a constant‐voltage constant‐frequency pulse‐width modulation inverter. The compensator is a linear combination of linear phase compensators, which can better fit the inverse of a plant model phase curve compared with the conventional linear phase compensator. Repetitive controllers with the proposed phase compensator can improve pulse‐width modulation inverter system's stability, tracking accuracy, and error convergence rate. An optimization method is applied to design the parameters of the proposed phase compensation repetitive controller. Analysis and design of the proposed repetitive controller are presented. Furthermore, simulations and experiments are provided to demonstrate the advantages of the approximate phase cancellation repetitive controller design.

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.

The problem of designing output error controllers to track periodic reference signals for a class of uncertain linear time-delay systems subject to periodic disturbances is addressed. A repetitive controller, which is a type of output error controller, is developed for these systems and a sufficient condition for stability of the closed-loop system is derived by applying the Lyapunov–Krasovskii functional and linear matrix inequalities (LMIs). In order to relax the stability condition, the theory of the modified repetitive control (RC) system is extended to the systems represented by irrational transfer functions. Based on the extended theory of the modified RC system, a modified repetitive controller, another type of output error controller, is developed for these systems and sufficient conditions for stability of the closed-loop system are derived in terms of a frequency-domain criterion and LMI. Numerical simulations are presented to demonstrate the effectiveness of the proposed controllers.

In the paper, a digital repetitive control scheme is proposed for the single-phase inverters to achieve the high-quality sinusoidal output voltages and the minimum total harmonics distortion. In the proposed control scheme, the repetitive controller is plugged into the stable state feedback controlled single-phase inverter system. The repetitive controller is designed to eliminate the periodic disturbance and track the periodic or dc reference signal with zero tracking error. The design method of the controller is described systematically, besides the stability of system is analysed. Simulation results illustrate the availability of the proposed scheme.