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In this paper a current-limiting droop control of grid-tied inverters that introduces virtual inertia and operates without a phase locked loop unit is proposed. The proposed controller inherits a self-synchronization function and can guarantee tight bounds for the inverter frequency. In addition, using nonlinear Lyapunov theory, it is analytically proven that the inverter current never violates a...
This paper presents some results concerning the cancellation of a periodic disturbance acting on a time-invariant linear stable, possibly non-minimum phase, plant. In particular it shows that a fractional-order repetitive controller can be designed under the hypothesis that the frequency response of the plant, in the range starting from the fundamental frequency of the disturbance signal to infinity,...
This paper addresses the optimal current control of grid-connected converters with uncertain parameters. The grid is modeled as a voltage source, affected by harmonics, in series with an uncertain inductance. As a main contribution, the comparison of ℋ2 state feedback strategies based on linear matrix inequalities is carried out. It is shown by means of examples that a suboptimal strategy can lead...
This paper presents a Linear Quadratic Regulator (LQR) based bumpless transfer controller for achieving seamless transition between the grid connected and the islanded modes of operation in microgrids. During the grid connected mode, the inverter based Distributed Generators (DGs) operate in current controlled mode where they supply a constant active and reactive power. During the islanded mode, the...
The problem of disturbance rejection roughly appears in control systems, active noise, and vibration control. This paper presents an algorithm to cancel sinusoidal disturbances with uncertain frequency acting on unknown plant. This algorithm consists of a second order generalized integrator frequency locked-loop (SOGI-FLL) and an adaptive mechanism for estimation of plant's frequency response. Then...
In the paper a problem of the control vibrations of the smart aluminum plate with SFSF (Supported-Free-Supported-Free) boundary conditions is considered. In order to obtain effectively control system the plate is equipped in two piezo-patch actuators and two piezo-patch sensors oriented in two perpendicular directions X and Y, respectively. Such locations and orientations of the piezo-elements allow...
This paper is concerned with the problem of the robust sampled-data H∞ control for an offshore steel jacket platform subject to the self-excited wave force and the external disturbance. First, by using the input delay method, the corresponding closed-loop system with the sampling measurements is transformed into a continuous-time system. Then, based on a Lyapunov functional, the H∞ performance is...
In this paper is proposed a method to improve the tracking performance of repetitive controllers in Uninterruptible Power Supplies (UPS). The main idea is to simultaneously compensate the gain reduction and frequency shift caused by the introduction of a low-pass filter in series with the delay element. Also, an optimization problem based on LMI constraints is presented to determine controller gains...
In this paper, we propose an event-driven output feedback control strategy for a class of nonlinear systems subject to disturbances. Different from the time-driven control, the event-driven control can be regarded as a more reactive approach where the control actions are taken only when an event is triggered, thus the event-driven control has a better balance between the control performance and other...
In this paper, a repetitive controller (RC) is proposed for flyback inverter operating in continuous conduction mode, which has simple structure, low cost, and high efficiency. Conventional controller results in poor control performance due to the effect of the right-half-plane zero in CCM operation. To achieve the fast dynamical response, the repetitive controller is developed and applied to flyback...
We propose a two-degree-of-freedom washout control structure for tracking of sinusoidal references in lightly damped structures subject to sensor drift and measurement noise. An algorithm is derived, assigning stable parameter intervals to a second-order washout damping compensator for a resonant plant with a single dominant mode. Simulation results demonstrate quality drift and noise rejection performance...
We explore two different frequency control strategies to ensure stability of power networks and achieve economic dispatch between generators and controllable loads. We first show the global asymptotic stability of a completely decentralized frequency integral control. Then we design a distributed averaging-based integral (DAI) control which operates by local frequency sensing and neighborhood communication...
Although periodicity simplifies design and analysis in control theory, it results in a conservative usage of resources (because the control signal is computed and updated at the same rate regardless whether is really required or not). The event-triggered paradigm is proposed as a solution to reduce the control updates (and, consequently, the resource utilization) for similar final performance. An...
An electromechanical device has been developed as a hand-held ultrasonic scanning probe. The device is composed of an oscillating probe where the ultrasound transducer is mounted, part of which is flexible so the probe can oscillate when energized. Electric current is supplied to two electromagnetic coils acting on two permanent magnets mounted on both sides of the probe. Two control schemes, a PID...
In this paper, we propose a new ℋ2 controller reduction method using the Riccati equations and the block balanced truncation. To maintain the closed-loop properties such as stability and ℋ2-norm performance, we employ the Riccati equations for controller reduction. A low-order controller is obtained by block balancing the solutions of the Riccati equations which include a full order controller. A...
Algorithm of adaptive PID-controller for plant with unknown coefficients in the presence of unknown-but-bounded disturbance is derived. It makes use of a sufficient small test signal. Adaptation process consists of intervals on which a plant and closed-loop system are identified on the base of finite-frequency identification technique. The plant coefficients estimates are used for controller redesign...
Shunt active power filters are proved as useful elements to correct the distorted currents caused by nonlinear loads in power distribution systems. This work presents an all digital approach, based on the repetitive control technique, for their control. The design is performed for the particular case of singlephase shunt active filter with a full-bridge boost topology. Several simulation results are...
In this paper, a linear robust controller is proposed for systems comprising a hysteresis operator preceding a linear stable system. The hysteresis operator is modeled with piecewise linear characteristics with uncertainties, and a nominal inverse operator is included to mitigate the hysteresis effect. An H∞ control design is proposed to handle the remaining uncertainties in a two-degree-of freedom...
In this paper, the solution to controller reduction problem for systems with a feedback controller via a double-sided frequency weighted model reduction technique is considered. A new method with a fast algorithm for finding low order controllers is proposed. This algorithm is based on new frequency weights derived using closed-loop system approximation criterion. The formulas of frequency weights...
This paper proposes a new technique for frequency shaping of the closed-loop system. The technique does not involve any weighting function for shaping, which is often used in the conventional H∞ control theory, but selects a desirable analytic function from a set of H∞ suboptimal solutions with a bounded degree. The Nevanlinna-Pick interpolation theory with a degree bound plays a central role in deriving...
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