Search Results (6)

To enhance frequency and active power control performance, this research proposes a decentralized robust optimal tuning approach for power grid frequency regulation support using energy storage systems (ESSs) as the primary source of grid-forming (GFM) converters. The proposed approach employs the robust Kharitonov theory to find a family of stabilizing sets of a proportional-integral (PI)-based supplementary controller, which is used in the outer control layer of the GFM control system. A family of stabilizing parameter sets is found in the presence of system uncertainties and disturbances that are common in power grid operation. Then, using a developed Bayesian optimization algorithm, an optimal set of parameters is determined among the mentioned family member sets. The proposed sophisticated combination of a robust control theorem and an optimization algorithm provides a promising solution for the robust and optimal tuning of control system parameters in ESS-based GFM converters. The efficacy of the proposed method is demonstrated via simulation and laboratory real-time experiment results for a given detailed case study. Full article

Large dimensional systems are complicated and very tough to control. The effective solution is to reduce the large dimension of the systems to a lower dimension. This paper aims to reduce the dimension of a higher-order fractional commensurate interval system to a low-order fractional commensurate interval system by using evolutionary techniques. Kharitonov’s theorem and artificial bee colony optimization technique are used to determine the interval numerator and denominator polynomials for the simplified models. The algorithm is very modest and generates a stable reduced dimensional commensurate fractional interval model preserving the properties of the original system. The efficiency of the suggested strategy is illustrated with a numerical example. Full article

The conversion of the electrical energy into the mechanical is usually realized by a motor, power electronics and cascade control. The relative stability ($\Theta$-stability), i.e., the displacement of its eigenvalues of this system is analyzed for a drive with a BLDC motor. The influence of changing the basic parameters of the motor and power supply system on the drive operation is considered. 4th order closed-loop transfer-function of the cascade control is presented, where boundaries of the transfer-function coefficients are used. The cascade system which uncertainty of the resistance, inductance, flux and gain parameters is analyzed. Theoretical calculations for the cascade control, simulations and laboratory tests are included in the article. Full article

This paper presents a novel direct form to design a digital robust control using RST structure (i.e., name given because of the R, S and T polynomials computed) based on convex optimization such as Chebyshev sphere; this approach was applied to a DC-DC Buck converter. This methodology takes into account parametric uncertainties and a Chebyshev sphere constraint in order to ensure robust performance and stability of the system in the discrete domain. For this purpose, a mathematical model for the DC-DC Buck converter is presented when considering uncertainties in electrical variables, such as load resistance, inductance, capacitance, and source voltage variation, also to obtain the discrete model of the system by using the bilinear transformation. The proposed methodology is compared with two other approaches designed in a discrete domain: the classical pole placement and the robust methodology based on the Kharitonov theorem. Wide-ranging experiments are performed in order to evaluate the behavior of the control methodologies when the system is subject to parametric variations of the load resistance and voltage setpoint variation. The results show that the proposed methodology outperforms the other approaches in 90% of the tests and ensures robust stability and robust performance when the system is subjected to a parametric uncertainties family. Full article

Wind energy has recently become one of the most prominent technologies among electrical energy generation systems. As a result, wind-based renewable energy generation systems are incessantly growing, and wind turbines of different characteristics are being installed in many locations around the world. One drawback associated with different characteristics of the wind turbines is that controllers have to be designed individually for each of them. Additionally, stable performance of the wind turbines needs to be ensured in the whole range of their operating conditions. Nowadays, there are many causes for uncertainties in the actual performance of a horizontal axis wind turbine, such as variations in the characteristics of the wind turbine, fabrication tolerances of its elements or non-linearities related to different operating-points. Hence, in order to respond to these uncertainties and ensure the stability of the wind turbine, robust control and stability theories have been gaining importance during recent years. Nevertheless, the use of robust stability analyses with complex wind turbine models still needs to be faced and remarkably improved. In this paper, a stability analysis of the pitch system control of a horizontal axis wind turbine based on the Kharitonov robust stability method is proposed. The objective was to assess the robust stability of a pitch controller in response to uncertainties arising from varying operating conditions of the National Renewable Energies Laboratory (NREL) 5 MW class IIA wind turbine. According to the results, the proposed method could satisfactorily respond to limited variations in the characteristics of the model, but could lack accuracy in cases of bigger variations or employment of high order complex mathematical models. Full article

The rapid switching action of power metal-oxide-semiconductor field-effect transistor (MOSFET) causes high-level electromagnetic interference (EMI) in power converters. The switching transient waveform modification method realized by closed-loop gate drive has been recognized as an effective high-frequency EMI reduction approach. However, feedback control of power MOSFET in the saturation region would introduce stability problems. This paper presents a sufficient condition-based stability analysis of all the operating points during turn-off using Kharitonov’s theorem. Firstly, a small-signal MOSFET model during turn-off was used to derive the closed-loop system transfer function. The nonlinear capacitances and the rest constant parameters of the small-signal model were determined based on the device characteristics and the expected outcome of the drain-source voltage. Then we split the turn-off switching transient into several subintervals, during which the system characteristic equation became an interval polynomial due to the nonlinear capacitances. Finally, Kharitonov’s theorem was applied in each subinterval to evaluate the stability, thereby achieving the overall system stability analysis during turn-off. Experiments were conducted to investigate the system’s stability and the results confirmed the validity of the proposed analysis. This work presents an implementable design guideline for the applied switching transient waveform modification of power converters via closed-loop gate drive. Full article