Spatial Repetitive Controller Research Articles

Tracking control for a position-dependent periodic signal in a variable-speed rotational system

This paper concerns the problem of tracking a position-related periodic signal for an uncertain nonlinear rotational system. Applying the additive-state-decomposition (ASD) technique decomposes the original uncertain nonlinear system into two subsystems: A primary linear time-invariant system that performs spatial repetitive control, and a secondary nonlinear system that ensures robust stability of the whole system with respect to unknown nonlinear dynamics and exogenous disturbances. This method has four features: (i) The ASD technique provides an effective way to deal with the coupling between the spatial periodicity and other factors (temporal and state-dependent uncertainties and disturbances) in a rotational system. This technique ensures satisfactory tracking and disturbance rejection performance; (ii) A real-time digital implementation of a spatial repetitive controller enables repetitive control with an exact period in the position. This ensures the synchronous execution of repetitive control in the position domain and robust stability in the time domain; (iii) The method of accurate phase compensation in a spatial repetitive controller leads to a significant improvement in steady-state tracking performance; and (iv) An extended-state observer precisely estimates the overall effect of disturbances. Integrating a disturbance estimate into a control input effectively compensates for disturbances. Stability criteria and design algorithms are presented in detail. Finally, experiments of a rotational speed-control system demonstrate the effectiveness of this method.

Capacitor Voltage Ripple Suppression in a Modular Multilevel Converter Using Frequency-Adaptive Spatial Repetitive-Based Circulating Current Controller

In this article, a new circulating current control architecture is proposed to suppress the submodule capacitor voltage ripple in a modular multilevel converter (MMC). The proposed cascaded control architecture uses the spatial repetitive controller (SRC) in both the outer voltage loop and the inner current loop, and can effectively suppress the second harmonic component of the submodule capacitor voltage ripple even under variable line frequency conditions. The dual SRC-based circulating current controller injects a second harmonic component into the circulating current to suppress the submodule capacitor voltage ripple. The SRC, which is a frequency-adaptive periodic digital controller, incorporates a phase sampling technique to achieve dynamic change in the sampling frequency, can adaptively tune its gain characteristics according to operating line frequency of the MMC. Unlike the existing techniques, the proposed controller uses the submodule capacitor voltage information for circulating current harmonic reference generation and, hence, does not require additional sensing of the output current. Detailed mathematical analysis and architecture of the proposed controller are presented in this article. A 400-V, 1-kW MMC laboratory prototype is developed and experimental results demonstrating the performance of the proposed circulating current control architecture for variable frequency and load conditions are also presented.

A New Control Architecture With Spatial Comb Filter and Spatial Repetitive Controller for Circulating Current Harmonics Elimination in a Droop-Regulated Modular Multilevel Converter for Wind Farm Application

Circulating current control is one of the critical issues in modular multilevel converters (MMCs). When a frequency-droop-regulated MMC is used to integrate an offshore wind farm into an high-voltage dc transmission system, the variation in its operating ac line frequency induces a change in circulating current harmonic frequencies. Hence, the conventional circulating current controllers, such as proportional-resonant or repetitive controller, which are tuned to a specific frequency, fail to alleviate the circulating current harmonics. In this paper, a new control architecture comprising of a spatial comb filter (SCF) and a spatial repetitive controller (SRC) is proposed to effectively attenuate the even-order harmonics in the circulating current independent of the operating ac line frequency of the MMC. The proposed controller incorporates the phase sampling technique to achieve the dynamic change in the sampling frequency, which is the key to strong periodic disturbance rejection capability of the SCF and SRC even under variable frequency operation. A system level simulation model has been developed on PLECS simulation software to demonstrate the performance of the proposed control architecture. In addition, a scaled-down laboratory prototype of a 1-kW, 400-V, five-level single-phase MMC is developed and the experimental results are presented to substantiate the performance of the proposed control scheme.

Robust Discrete-Time Spatial Repetitive Controller

This brief proposes a novel discrete-time realization of the spatial repetitive controller topology, an internal model principle-based regulator, which deals with the exogenous position-dependent periodic signals. A simple procedure is proposed in order to estimate the time-varying delay required to implement this spatial controller, resulting in a single recursive equation. A robust synthesis methodology based on a convex optimization problem constrained by linear matrix inequalities is also presented in order to guarantee the closed-loop system stability and performance in the presence of uncertain plant dynamics. The proposed design and implementation methods are validated on a direct current motor subject to angle-dependent disturbances.

A Spatial Repetitive Controller Applied to an Aeroelastic Model for Wind Turbines

A Spatial Repetitive Controller Applied to an Aeroelastic Model for Wind Turbines

Application of Four-Switch-Based Three-Phase Grid-Connected Inverter to Connect Renewable Energy Source to a Generalized Unbalanced Microgrid System

In this paper, a four-power-semiconductor-switch-based three-phase inverter is proposed for renewable energy source integration to a generalized microgrid system. The proposed topology <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$b \hbox{-}4$</tex></formula> of three-phase inverter is investigated to make the commercial microgrid system to be cost effective and hardware optimized. A simple sine-pulse-width-modulation-based (SPWM) control strategy is proposed for the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$b\hbox{-}4$</tex></formula> inverter topology instead of the traditional complex four-switch-based space vector techniques. The overall control structure is implemented using the Lyapunov function-based nonlinear controller to track the inverter current directly in the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$a {-} b {-} c$</tex></formula> frame so that a specific amount of active and reactive grid power flow to the grid can be controlled in a decoupled manner along with low total harmonic distortion of grid currents in the presence of nonlinear load at the point of common coupling (PCC). A novel technique of using the spatial repetitive controller (SRC) is also proposed to eliminate the effect of midpoint voltage fluctuation of the dc link even in the case of asymmetrically split dc-link capacitors without any extra voltage or current sensors unlike conventional methods. Detailed experimental results are provided to show the efficacy of the proposed hardware system for grid-connected applications in the microgrid.

A Plug and Play Operational Approach for Implementation of an Autonomous-Micro-Grid System

In this paper, a plug and play type autonomous-micro-grid system formation is proposed. Multiple distributed generating sources and loads interaction is considered pertaining to the stability of the micro-grid. The proposed method enables communication-less operation of each of the elements of the micro-grid system. It is also considered that the sources are of different power capacity as can be seen in a typical autonomous micro-grid system. Spatial Repetitive Controller (SRC) is proposed to control each of the distributed generating sources in a decentralized manner to stabilize the overall micro-grid system. The proposed system considers sudden change in load as well as other distributed generators conditions like a true plug and play operation. A novel signature frequency voltage injection method is proposed to identify the presence of special distributed generator and operation of backup distributed generators. The implemented control architecture also ensures stability of the micro-grid fundamental frequency even in the case of dynamic conditions unlike the traditional droop-control method. A detailed experimental study is carried out and the experimental results presented show the efficacy of the proposed system.

Single-Phase Inverter Control Techniques for Interfacing Renewable Energy Sources With Microgrid—Part I: Parallel-Connected Inverter Topology With Active and Reactive Power Flow Control Along With Grid Current Shaping

In this paper, a novel current control technique is proposed to control both active and reactive power flow from a renewable energy source feeding a microgrid system through a single-phase parallel-connected inverter. The parallel-connected inverter ensures active and reactive power flow from the grid with low-current total harmonic distortion even in the presence of nonlinear load. A p-q theory-based approach is used to find the reference current of the parallel-connected converter to ensure desired operating conditions at the grid terminal. The proposed current controller is simple to implement and gives superior performance over the conventional current controllers, such as rotating frame proportional-integral controller or stationary frame proportional resonant controller. The stability of the proposed controller is ensured by direct Lyapunov method. A new technique based on the spatial repetitive controller is also proposed to improve the performance of the current controller by estimating the grid and other periodic disturbances. Detailed experimental results are presented to show the efficacy of the proposed current control scheme along with the proposed nonlinear controller to control the active and reactive power flow in a single-phase microgrid under different operating conditions.

Single-Phase Inverter-Control Techniques for Interfacing Renewable Energy Sources With Microgrid—Part II: Series-Connected Inverter Topology to Mitigate Voltage-Related Problems Along With Active Power Flow Control

In this paper (Part II), a control strategy for a single-phase series-connected inverter with the microgrid is proposed to interface ac loads not only to regulate the load voltage under voltage disturbances, but also to control the load power drawn from the microgrid. The inverter compensating voltage works in such a way that, irrespective of any type of disturbances in the microgrid voltage (such as sag, swell, or harmonic distortions), the load voltage is maintained at its rated voltage level with low total harmonic distortion (THD) in voltage. The proposed control strategy also facilitates a specific amount of active power flow (from renewable energy source) to the load irrespective of the microgrid voltage condition. The rest of the load power is supplied by the microgrid. To facilitate this control strategy, a spatial repetitive controller (SRC) is proposed and implemented in microgrid phase ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\theta$</tex> </formula> ) domain to make the controller independent of the microgrid frequency. The proposed controller ensures dynamic stability of the system even if there is a sudden change in the microgrid frequency. Detailed experimental results are presented to show the efficacy of the proposed series inverter system along with the controller under different operating conditions.