Design Of Proportional Resonant Controllers Research Articles

A Novel Design of PR Controller With Antiwindup Scheme for Single-Phase Interconnected PV Systems

This article presents the design methodology of an alternative approach for implementing proportional-resonant (PR) controller for single-phase grid-tied inverter. The developed PR controller is designed to regulate the grid current with the aim of controlling either the dc-link voltage or the active/reactive power injected into the grid. The control design is based on combining a state feedback controller with a disturbance observer. It turns out that the composite controller can be expressed as a PR controller plus an antiwindup scheme. The latter is required by the resonant portion of the PR controller to attenuate the effect of the control input saturation during transients. On the other hand, when the voltage harmonics are taken into account in the observer design, the composite controller reduces to multiple resonant controllers with an antiwindup scheme. The performance of the existing PR controller was investigated under control saturation to highlight the poor transient performances associated with modulating signal limitation. Experimental tests have been conducted to verify the the performance of the proposed controller. The obtained results demonstrated good transient performances compared with the existing PR controller, particularly during control saturation. Furthermore, performance results under voltage harmonics showed that the proposed controller can achieve accurate control of the current with low total harmonic distortion values.

Power Quality Enhancement Using Dynamic Voltage Restorer (DVR)-Based Predictive Space Vector Transformation (PSVT) With Proportional Resonant (PR)-Controller

In the power distribution system, the Power Quality (PQ) is disturbed by the voltage sag and swells. The Dynamic Voltage Restorer (DVR) is used to enhance various PQ problems like voltage sag, swells, and Harmonics. The previous Intrinsic Space Vector Transformation (ISVT) control techniques with DVR system, to compensate the power quality issue. It produced a steady-state error, low efficiency, and high THD. The SMES based DVR has provided excellent results in overcoming these issues. The energy is stored by DVR through a storage element, which takes alternate energy from a Solar PV cell. The Maximum Power Point Tracking (MPPT) based P&O algorithm is implemented to equalize the solar power. The Voltage Source Inverter (VSI) generates the reactive power, which has to be compensated with the help of Pulse Width Modulation (PWM) and the feedback control loop are essential to enhance the injection of reactive power to the line. Due to this reason, a proposed Predictive Space Vector Transformation (PSVT) control-based DVR is implemented. It analyzes the variation of power on the distribution side and generates the proper feedback control to the inverter systems. In the instant of voltage injection to the line with the help of DVR, the phase angle mismatch happens which is not synchronized reactive power to the grid. Due to the non-synchronization of reactive power, more harmonic distortion is generated. A Proportional Resonant (PR) controller is introduced, which is Proportional Resonant (PR) current controller. The current injected by the inverter into the grid in phase with the grid voltage maintain constant with unity power factor. The PR controller design is cascaded with a harmonic compensator to mitigate low order odd harmonic components present in the output current of VSI and minimize the total harmonic distortion (THD). The performance of the proposed is evaluated using MATLAB 2017b software.

Improving performance of LVRT capability in single-phase grid-tied PV inverters by a model-predictive controller

New interconnection standards for Photovoltaic systems are going to be mandatory in some countries. Such that the next generation of PV should support a full range of operation mode like in a power plant and also support Low-Voltage Ride-Through (LVRT) capability during voltage sag fault. Since the voltage sag period is short, a fast dynamic performance along with a soft behavior of the controller is the most important issue in the LVRT duration. Recently, some methods like Proportional Resonant (PR) controllers, have been presented to control the single phase PV systems in LVRT mode. However, these methods have had uncertainties in respect their contribution in LVRT mode. In PR controllers, a fast dynamic response can be obtained by tuning the gains of PR controllers for a high bandwidth, but typically the phase margin is decreased. Therefore, the design of PR controllers needs a tradeoff between dynamic response and stability. To fill in this gap, this paper presents a fast and robust current controller based on a Model-Predictive Control (MPC) for single-phase PV inverters in other to deal with the LVRT operation. In order to confirm the effectiveness of the proposed controller, results of the proposed controller are compared with the classical PR controller. They are also implemented in a 1 kW single-phase transformerless HERIC (Highly Efficient and Reliable Inverter Concept) inverter.

Modeling and control of a cascaded multilevel converter‐based electronic power transformer

Control strategy of a cascaded multilevel converter based electrical power transformer (EPT) in a distribution system with capabilities of low voltage ride‐through and unbalanced load current management is investigated in this study. The mathematical model and decoupled control schemes of the system, including a high‐voltage side control scheme, an isolation‐stage control scheme, and a low‐voltage side control scheme, are presented in detail. A dual current control scheme is introduced to control both positive and negative sequence currents for enhancing the low voltage ride‐through capability of the high‐voltage side cascaded H‐bridge converter. Positive, negative, and zero‐sequence voltages are controlled for the low voltage side three‐phase four‐wire converter in the decoupled control scheme, respectively, for unbalanced load current management. A proportional resonant controller (PRC) is utilized to control the zero‐sequence voltage, while the root locus method is applied in the PRC design. Three‐dimensional space vector pulse width modulation (PWM) switching strategy is then used for the low voltage side converter. Simulation studies were conducted with MATLAB/Simulink to validate the coordinated control strategy. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Proportional-Resonant Current Controllers Design Based on Desired Transient Performance

Stationary reference frame proportional-resonant (PR) controllers have recently became a viable alternative to rotation reference frame proportional-integrative compensators in ac applications because of their ability of achieving zero steady-state error without the need for computational-intensive reference frame transformations. While extensive efforts have been put into performance comparison of the two control schemes, design of PR controllers according to desired closed-loop time-domain transient performance was barely investigated. This letter proposes a method for deriving PR controller structure and coefficients according to desired transient behavior of ac signal amplitude, applied to typical power converter current loop. The method is based on the fact that if ac signal envelope is perceived as dc signal, its transient behavior may be easily shaped utilizing well-known approaches employed in dc systems loop shaping while keeping zero phase tracking error at all times. On the other hand, while desired transient performance is easily achieved, the relation between crossover frequency and transient processes time constant is not as straightforward as in dc systems. The validity of the presented theoretical analysis is evaluated by simulations.

Harmonic Suppression and Performance Improvement for a Small-scale Grid-tied Wind Turbine Using Proportional–Resonant Controllers

Small-scale wind turbines installed at the end of a distribution feeder are beneficial in reducing fossil fuel use as well as power transmission loss. However, wind turbines are inherently noisy due to the electro-mechanical oscillation attributed to the harmonic distortion. To eliminate the low-order harmonic distortion and refine the power quality without purchasing additional equipment, two control loops with power factor correction and selective harmonic compensation capabilities are proposed for the inverters tapped at the wind turbine generator side and the grid side. The capacity used for selective harmonic compensation is removable with escalating wind power in the case of the over-loading condition. A proportional–resonant controller with the advantages of easy implementation and high immunity to disturbance was adopted for the inverters to achieve quick and tight regulation in current response. An algebraic algorithm based on the pole-zero cancellation technique is proposed to simplify the proportional–resonant controller design and can be used in fundamental and harmonic current control for the stator-side and grid-side inverters. The proposed strategy was assessed and validated experimentally using a 1.5kW vertical axis wind turbine (VAWT)-driven permanent magnet synchronous generator (PMSG) under various wind speeds.

Analysis and Design of Resonant Current Controllers for Voltage-Source Converters by Means of Nyquist Diagrams and Sensitivity Function

The following two types of resonant controllers are mainly employed to obtain high performance in voltage-source converters: 1) proportional + resonant (PR) and 2) vector proportional + integral (VPI). The analysis and design of PR controllers is usually performed by Bode diagrams and phase-margin criterion. However, this approach presents some limitations when resonant frequencies are higher than the crossover frequency defined by the proportional gain. This condition occurs in selective harmonic control and applications with high reference frequency with respect to the switching frequency, e.g., high-power converters with a low switching frequency. In such cases, additional 0-dB crossings (phase margins) appear; therefore, the usual methods for simple systems are no longer valid. In addition, VPI controllers always present multiple 0-dB crossings in their frequency response. In this paper, the proximity to the instability of PR and VPI controllers is evaluated and optimized through Nyquist diagrams. A systematic method is proposed to obtain the highest stability and avoidance of closed-loop anomalous peaks: it is achieved by the minimization of the inverse of the Nyquist trajectory distance to the critical point, i.e., the sensitivity function. Finally, several experimental tests, including an active power filter that operates at a low switching frequency and compensates harmonics up to the Nyquist frequency, validate the theoretical approach.