A consistent framework for robust linear quadratic regulators (LQRs) control of power converters is presented. Systems with conventional LQR controllers present good stability properties and are optimal with respect to a certain performance index. However, LQR control does not assure robust stability when the system is highly uncertain. In this paper, a convex model of converter dynamics is obtained taking into account uncertainty of parameters. In addition, the LQR control for switching converters is reviewed. In order to apply the LQR control in the uncertain converter case, we propose to optimize the performance index by using linear matrix inequalities (LMIs). As a consequence, a new robust control method for dc-dc converters is derived. This LMI-LQR control is compared with classical LQR control when designing a boost regulator. Performance of both cases is discussed for load and line perturbations, working at nominal and non nominal conditions. Finally, the correctness of the proposed approach is verified with experimental prototypes.

/pdf/robust-lqr-control-for-pwm-converters-an-lmi-approach-3uteo6nxha.pdf

Robust LQR Control for PWM Converters: An LMI Approach

Distributed generation (DG) is one of the key components of the emerging microgrid concept that enables renewable energy integration in a distribution network. In DG unit operation, inverters play a vital role in interfacing energy sources with the grid utility. An effective interfacing can successfully be accomplished by operating inverters with effective control techniques. This paper reviews and categorises different control methods (voltage and primary) for improving microgrid power quality, stability and power sharing approaches. In addition, the specific characteristics of microgrids are summarised to distinguish from distribution network control. Moreover, various control approaches including inner-loop controls and primary controls are compared according to their relative advantages and disadvantages. Finally, future research trends for microgrid control are discussed pointing out the research opportunities. This review paper will be a good basis for researchers working in microgrids and for industry to implement the ongoing research improvement in real systems.

Overview of AC Microgrid Controls with Inverter-Interfaced Generations

Conventional direct torque control (DTC) is one of the excellent control strategies available to control the torque of the induction machine (IM). However, the low switching frequency of the DTC causes high ripples in the flux and torque that leads to an acoustic noise which degrades the control performances, especially at low speeds. Many direct torque control techniques were appeared to remedy these problems by focusing specifically on the torque and flux. In this paper, a state of the art review of various modern techniques for improving the performance of DTC control is presented. The objective is to make a critical analysis of these methods in terms of ripples reduction, tracking speed, switching loss, algorithm complexity and parameter sensitivity. Further, it is envisaged that the information presented in this review paper will be a valuable gathering of information for academic and industrial researchers.

/pdf/modern-improvement-techniques-of-direct-torque-control-for-1jvcunrxig.pdf

Modern improvement techniques of direct torque control for induction motor drives - a review

https://onlinelibrary.wiley.com/doi/pdf/10.1002/2050-7038.12822

A comprehensive review on control techniques for stability improvement in microgrids

This paper highlights the controller of a bidirectional converter to interface an ultracapacitor as storage device to renewable energy systems. Ultracapacitors are typically used in renewable energy systems to improve the system's reliability and energy conversion efficiency. The controller of the converter system has been designed and simulated based on the integration of both Current Mode Control and Linear Quadratic Regulator methods. The controller performance is tested under different modes of operating conditions in bidirectional converter using MATLAB/Simulink simulation package. The simulation results show that a good DC bus voltage regulation is achieved in the tested conditions. In addition to that, the controller ensures smooth transition between the buck and boost modes of the bidirectional converter operation.

Control of a bidirectional converter to interface ultracapacitor with renewable energy sources

Averaging techniques have been widely applied to model PWM power electronic converters The averaged models obtained by using this technique are very useful for the simulation of the systems as well as for the design of controllers In this work, some general considerations about linear-quadratic regulators (LQR) are made Then, an LQR is designed and applied to the particular case of a DC-DC buck converter Some simulation and experimental results show very good performance of the system under start-up and transient events

A Linear-Quadratic Regulator with Integral Action Applied to PWM DC-DC Converters

This paper presents a novel controller based on Direct Torque Control (DTC) strategy. This controller is designed to be applied in the control of Induction Motors (IM) fed with a three-level Voltage Source Inverter (VSI). This type of inverter has several advantages over the standard two-level VSI, such as a greater number of levels in the output voltage waveforms, lower dV/dt, less harmonic distortion in voltage and current waveforms and lower switching frequencies. In the new controller, torque and stator flux errors are used together with the stator flux angular frequency to generate a reference voltage vector. Experimental results of the novel system are presented and compared with those obtained for Classical DTC system employing a two-level VSI. The new controller is shown to reduce the ripple in the torque and flux responses. Lower current distortion and switching frequency of the semiconductor devices are also obtained in the new system presented.

/pdf/new-dtc-control-scheme-for-induction-motors-fed-with-a-three-1d15afkbvu.pdf

New DTC Control Scheme for Induction Motors fed with a Three-level Inverter

In this paper a new scheme based on direct torque control strategy is presented. The new controller is used to control an induction motor fed with a three-level inverter. The new control scheme avoids the use of the classical hysteresis block and the look-up table. Instead, the torque and stator flux errors are used together with the motor speed to generate a reference voltage that can be synthesized using different techniques afterwards. Experimental results show some improvement regarding the reduction of torque ripple, stationary mean torque error, THD in stator currents and switching frequency when compared to the classical DTC scheme.

New DTC control scheme for the induction motor fed with a three-level inverter

An adaptive model applied to PWM DC-DC converters is presented in this paper. Parasitic resistors have been considered in the converter. The coefficients of the state-space matrices, which depend on the parameters of the circuit, are calculated on-line. In the proposed method, the state vector variables should be sampled in real time. Then, the coefficients of state-space matrices are estimated by means of a simple matrix calculation. The values of the components of the averaged circuit can also be calculated from the matrix coefficients. Therefore, the changes in the values of the parameters of the circuit are quickly updated in the averaged model. As a result, robust control strategies can be implemented by using these models. In this paper, the method is applied to a buck-boost converter. Some simulation results are included in this work to validate the procedure. The estimated matrices coefficients match very well the expected values.

Adaptive Model Applied to PWM DC-DC Converters Using Averaging Techniques

Design of a sliding mode controller based on local averaged technique and applied to the buck converter

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