A Simple DC Imbalance Rejection Technique for UPS Inverters

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.

Repetitive control is one control algorithm based on the Internal Model Principle (Francis & Wonham, 1976) and has been widely implemented in various applications. A repetitive control based system has been shown to work well for tracking periodic reference commands or for rejecting periodic disturbances. Although the idea has been verified as early as 1981 (Inoue et al., 1981), a rigorous analysis and synthesis of repetitive controllers for continuous-time systems was not proposed until 1989, by Hara et al. (Hara et al., 1988). Tomizuka et al. (Tomizuka et al., 1989) addressed the analysis and synthesis of discrete-time repetitive controller, considering the fact that digital implementation of a repetitive controller is simpler and more straightforward. Since then, repetitive control has gained popularity in applications where periodic disturbances rejection or repetitive tracking are required, see (Wang et al., 2009; Cuiyan et al., 2004) and the references therein. These include controls of disk drive servo (Tomizuka et al., 1989; Guo, 1997; Moon et al., 1998), hydraulic closed-loop servo for material testing (Srinivasan & Shaw, 1993), vibration suppression (Hillerstrom, 1996), rejection of load disturbances in steel casting process (Manayathara et al., 1996), servo control for a positioning table (Yamada et al., 1999), X-Y table (Tung et al., 1993), noncircular turning process (Alter & Tsao, 1994), motor speed ripple reduction (Godler et al., 1995; Rodriguez et al., 2000), and eccentricity compensation (Garimella & Srinivasan, 1996). In literatures, repetitive controllers are synthesized and operate in time domain, which is in accordance with the fact that models or differential equations of physical systems are mostly derived using time as the independent variable. One of the key steps for designing a repetitive controller is to determine the period, or equivalently, the number of delay taps (q−1, q is the one step advance operator). This can usually be done by analyzing the periodic tracking or disturbance signal using techniques such as fast Fourier transform (FFT). To ensure effectiveness of the design, an underlying assumption is that the frequency constitutions of the periodic tracking or disturbance signal do not vary with respect to time, which corresponds to a stationary or time-invariant frequency spectrum of the signal. This assumption can be satisfied when the design objective is to track a prespecified periodic trajectory. However, it might be violated for disturbance rejection problems where the frequency constitutions of the disturbance are time-varying. For a motion system with rotary components such as gear-train, the disturbances due to gear

High performance sensorless AC drives require the exact knowledge of the motor phase voltages in the whole speed range. The use of voltage sensors may be eschewed if the reference voltage signals, generated by the control algorithm, can be used instead. To this aim, an accurate compensation of most of inverter non-idealities is stringent. This paper presents a novel technique for the cancellation of inverter non-idealities, based on repetitive control. The main advantage is that the compensation automatically includes the IGBT parasitic effects during current zero-crossing, whose exact knowledge is one of the major problems in most of the standard dead-time cancellation techniques. Despite its elaborated theoretical background, the method requires few computational resources and it is easy to implement. Mathematical developments, design hints and an extensive batch of successful experimental tests are included in the paper.

In this work, we develop novel control algorithms suitable for the smart shock absorber (SSA) component of the intelligent vehicle and bridge system (IVBS). The SSA control serves two IVBS purposes: 1) working as the vehicle suspension to increase driver comfort and controllability when the vehicle is on the pavement, and 2) reducing the vibration of highway bridges and thus prolonging bridge life. We propose and discuss in this paper algorithms targeted at the first purpose. Based on the application of active noise control techniques to an active suspension system, we introduce the clipped active noise control (clipped ANC) algorithm. The main advantage of this algorithm is that because it is adaptive, it can effectively balance the comfort and controllability. A simplified control algorithm based on the clipped ANC is also proposed to reduce the implementation cost. The simplified algorithm has no requirements for system modeling, so it substantially reduces the implementation cost. The effectiveness of our proposed algorithm is indicated by analyses, simulations and laboratory testing.

An improved control algorithm of repetitive controller based on virtual resistance was proposed to solve the problem of the slow dynamic response and the high total harmonic distortion (THD). The proportional-integral controller (PI controller) can not only adjust rapidly but also eliminate residual error effectively and the repetitive controller can eliminate periodic interference signal effectively. The double loop control combined with PI control and repetitive control. The controller has been used to control the inverter in grid-connected section which can improve the regulating speed and system stability. It can also achieve fairly good control effect under the circumstances of mutations of voltage and load. By designing the parameters of the controller, THD of the grid-connected current is lower than 0.61%. The simulation result shows that the algorithm is correct and feasible.

Effects of Non-Periodic Disturbances on Repetitive Control Systems

A quasi-continuous-time approach to the design of a digital PID control for DC/AC inverters with LC filter that use semiconductor switches producing PWM output voltage is presented. It is shown that an appropriately chosen continuous-time model of the digital controller with the PWM converter behaves like the actual discrete-time system, which allows for a simple controller design. SIMULINK models are used to validate this approach for a nonlinear rectifier load. The outcomes are compared with a real inverter experiment.

A method which fully controls current and speed of the permanent magnet AC servomotor in the discrete time domain with high dynamic performance and wide bandwidth is discussed. The current controller, which controls motor current in the stationary d-q coordinates, consists of a nonlinear feedback controller compensating back EMF, a phase lead compensator, and a PI controller with gains varying according to motor speed. The final output of the current control algorithm is pulsewidth modulated through comparison with a digital triangular carrier signal to produce a PWM waveform. To obtain accurate estimation of motor speed, a speed observer is utilized in the speed control loop. Furthermore, a repetitive controller is applied in order to compensate errors in the position transducer. To investigate the control performance, the full digital servo control algorithm is applied to a SCARA robot with four degrees of freedom through execution on the control system based on the one-chip microprocessor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper presents an approach for kinematic compensation of the laser shaping process which is capable of achieving improved dimensional accuracy for non‐circular profiles. In this approach, a plug‐in repetitive controller is added into the existing position servo loop to improve tracking of the desired sinusoidal trajectory and subsequently reduce tracking errors. The effect of tracking errors on different dimensional error modes in the non‐circular shaping process is identified. Simulation models are developed for testing the performance of the repetitive controller in shaping various non‐circular profiles with different operating parameters such as oscillating amplitudes and sampling time. Simulation results show that better tracking performance can be obtained with the addition of the repetitive controller. Experimental results include fabrication of single‐harmonic‐term profiles such as triangular, square, hexagonal and octagonal profiles and multiple‐harmonic‐term profiles such as diamond‐shaped profiles in polymethyl methacrylate with both control algorithms. The non‐circular profiles are measured through optical CMM to determine the dimensional accuracy in edge straightness, angularity, parallelism and feature size.

When the fundamental frequency is shifting, it's hard for traditional repetitive controller to work at the resonant frequencies. In this paper, a novel self-adaptive repetitive controller is proposed to suppress the current harmonics. This controller can adjust the sampling times in the grid cycles based on a special self-adaptive control algorithm. Mathematical analysis, simulations and physical experiments have validated the effectiveness of the self-adaptive repetitive controller.

Repetitive control is useful if periodic disturbances act on a control system. Perfect (asymptotic) disturbance rejection is achieved if the period-time is exactly known. The improved disturbance rejection at the periodic frequency and its harmonics is achieved at the expense of a degraded system sensitivity at intermediate frequencies. A convex optimization problem is defined for the design of high-order repetitive controllers, where a trade-off can be made between robustness for changes in the period-time and for reduction of the error spectrum in-between the harmonic frequencies. The high order repetitive control algorithms are successfully applied in experiments with the tracking control of a CD-player system.

A high-precision additive manufacturing (AM) process, powder bed fusion (PBF) has enabled unmatched agile manufacturing of a wide range of products from engine components to medical implants. While finite element modeling and closed-loop control have been identified key for predicting and engineering part qualities in PBF, existing results in each realm are developed in opposite computational architectures wildly different in time scale. This paper builds a first-instance closed-loop simulation framework by integrating high-fidelity finite element modeling with feedback controls originally developed for general mechatronics systems. By utilizing the output signals (e.g., melt pool width) retrieved from the finite element model (FEM) to update directly the control signals (e.g., laser power) sent to the model, the proposed closed-loop framework enables testing the limits of advanced controls in PBF and surveying the parameter space fully to generate more predictable part qualities. Along the course of formulating the framework, we verify the FEM by comparing its results with experimental and analytical solutions and then use the FEM to understand the melt-pool evolution induced by the in- and cross-layer thermomechanical interactions. From there, we build a repetitive control (RC) algorithm to attenuate variations of the melt pool width.

In a continuing effort to determine the feasibility of applying optimal control to building structures, a comprehensive experimental study was carried out using a standardized structural model under base excitation produced by the Earthquake Simulator at SUNY/Buffalo. Based upon computer simulations and experimental results, this paper presents a comparison of effectiveness of several optimal control algorithms using instantaneous optimal criteria, including time delay compensation. All investigations were done under similar conditions to permit a systematic evaluation of efficiency. Comparisons were also made between analytical and experimental results and between instantaneous control algorithms and classical closedloop linear feedback. Conclusions drawn regarding relative merits of the control algorithms considered under varying conditions are presented herein.

As the trend towards the decentralization of grids continues, new typologies such as microgrids have gained popularity in recent years. Microgrids offer greater reliability as they can operate both connected to the main grid and in islanded mode. However, the transition to island mode can be even more challenging when a microgrid has a high penetration of intermittent sources like Doubly-Fed Induction Generators (DFIGs). In this context, designing new controller algorithms is essential to improve frequency support in microgrids with DFIGs. Therefore, this paper proposes a novel Filtered Repetitive Model Predictive Control (FR-MPC) applied to the frequency support in a microgrid. The control structure is applied to the Grid Side Converter (GSC) of a DFIG, while the DC bus voltage is supplied by a Battery Energy Storage System (BESS). The FR-MPC prediction model uses a state-space model with an embedded repetitive action, which has the capacity to mitigate harmonics of the microgrid. However, the inclusion of the repetitive loop degrades the closed-loop robustness. To overcome this limitation, the prediction model features a robustness low pass filter. repetitive loop. Furthermore, this paper presents an analysis of the frequency response and pole map of the key components of the controller: the ZP-FIR, the repetitive loop, and the control law. Finally, simulation results demonstrate that the proposed controller outperforms both the pure Repetitive MPC (R-MPC) and the Generalized Predictive Control (GPC) in terms of performance.

A new control scheme for a single phase shunt Active Power Filter (APF) is proposed in this paper. The goal is the introduction of a new reference generator along with a repetitive current control scheme. The proposed reference generator uses a filter based on a sinusoidal signal integrator and the instantaneous reactive power theory to compute the APF reference current. The proposed scheme can be easily adapted to work in a distributed generation system, injecting active power into the grid. The whole control algorithm has been implemented on the dSPACE DS1103 development system controlling a single phase APF prototype to demonstrate the feasibility of the proposed solution.