Suzan Eren

Composite Nonlinear Feedback Control and Stability Analysis of a Grid-Connected Voltage Source Inverter With

In this paper, the stability analysis of a grid-connected voltage source inverter with an LCL filter is presented. The Poincaré map is used to analyze the stability of the system from a geometric point of view and provides a better understanding of the system performance. In addition, a composite nonlinear feedback (CNF) control is proposed in order to improve the transient and steady-state performance of the control system. Simulation and experimental analysis verify the validity of the analysis and also show the superiority of the CNF-based controller compared to the conventional proportional-resonant controller during transients and steady-state operation.

LCL

This paper presents a very fast dc-bus voltage controller for a single-phase grid-connected voltage-source inverter (VSI) with an LCL output filter used in renewable energy applications. In single-phase grid-connected inverters, the design of the dc-bus voltage control scheme is very challenging due to the presence of a second harmonic ripple across the dc-bus voltage. The proposed dc-bus voltage control scheme is able to address the difficulties introduced by the second-harmonic ripple. The dc-bus voltage controller is based on an adaptive droop control technique, which is able to provide a very fast transient response for the closed-loop system and ensures the optimal operation of the VSI during steady-state conditions. Also, the simple structure of the controller makes it very practical for grid-connected VSIs used in renewable energy power conditioning systems. Theoretical analysis and experimental results demonstrate the superior performance of the proposed control approach compared to conventional dc-bus voltage control schemes.

Filter

This paper presents a novel control approach for a current-driven full-bridge dc/dc converter, which is able to significantly improve the converter performance over a very wide range of operating conditions. The proposed control approach is based on the self-sustained oscillating control (SSOC) scheme, in order to adaptively change the phase shift and the switching frequency of the converter for different operating points. In this control technique, the timing signal is produced based on the transformer primary current, which is a feedback to the control system to determine the switching instants of the power MOSFETs. Therefore, the control system automatically tunes the control variables for different operating conditions. The comprehensive mathematical analysis of the proposed SSOC scheme is presented in detail. The mathematical analysis is based on the geometric viewpoint of the control system, which provides a very good insight into designing the control system. Experimental results provided from a 3 kW prototype confirm the feasibility of the proposed scheme and prove the superiority of the performance compared to the conventional phase-shift control approach.

An Adaptive Droop DC-Bus Voltage Controller for a Grid-Connected Voltage Source Inverter With LCL Filter

This paper presents a new active/reactive power closed-loop control system for a hybrid renewable energy generation system used for single-phase residential/commercial applications. The proposed active/reactive control method includes a hybrid estimator, which is able to quickly and accurately estimate the active/reactive power values. The proposed control system enables the hybrid renewable energy generation system to be able to perform real-time grid interconnection services such as active voltage regulation, active power control, and fault ride-through. Simulation and experimental results demonstrate the superior performance of the proposed closed-loop control system.

Self-Sustained Oscillating Control Technique for Current-Driven Full-Bridge DC/DC Converter

This paper introduces a new control method to track the maximum power point for a Wind Energy Conversion System (WECS). This WECS is based on a permanent magnet synchronous generator (PMSG) fed by a matrix converter. Since the mechanical power generated by the wind turbine is a function of its shaft speed at a given wind velocity, the proposed controller provides the desired voltage at the output of the matrix converter so as to control the generator speed. This controller is based on the nonlinear adaptive backstepping approach which is well suited for this system. This method is able to effectively accommodate the effects of system uncertainties. Theoretical discussions and performance analysis verify the feasibility and performance of the proposed approach.

A Hybrid Estimator for Active/Reactive Power Control of Single-Phase Distributed Generation Systems With Energy Storage

This paper presents a modified three-phase phase locked loop, consisting of a multi-block adaptive notch filter (ANF) integrated into a conventional three-phase synchronous reference frame phase-locked loop (SRFPLL). The addition of the ANF to the system allows it to become frequency adaptive. Also, since the ANF consists of multiple blocks which are in parallel with one another, the system is able to remove multiple input signal distortions. Thus, the proposed system is able to eliminate the double frequency ripple that is normally caused in the conventional three-phase SRFPLL by input unbalance, as well as harmonic errors, despite the presence of frequency variations in the input signal. The proposed system is compared to a conventional three-phase SRFPLL, as well as a three-phase SRFPLL with a simple notch filter, and the advantages of the proposed system are discussed.

Maximum power point tracking of a Wind Energy Conversion System using adaptive nonlinear approach

This paper presents a novel series-parallel current-driven (SPCD) full-bridge dc/dc converter, which is able to process and deliver power efficiently over a wide range of load variations. In order to guarantee reliable operation of high-frequency dc/dc converters, the converter should be able to sustain soft switching for a wide range of operating conditions. The SPCD full-bridge converter, proposed in this paper, is able to offer soft switching for the input power semiconductors and smooth commutations for the output diodes. Also, the particular structure of the proposed converter eliminates the need for extra auxiliary circuits to provide reactive current for soft switching at light loads. The proposed topology can fully eliminate voltage spikes across the output diodes by providing smooth and lossless commutations for the output diodes. Thus, the proposed converter can be an efficient and reliable solution for variety of applications with a high switching frequency and a high output voltage. The SPCD full-bridge converter has the ability to integrate all magnetic components into an integrated transformer in order to achieve a high power density. The integrated transformer is thoroughly analyzed using ANSYS high-frequency structure simulator. Simulation and experimental results confirm the superior performance of the proposed SPCD full-bridge dc/dc converter.

Enhancing the three-phase synchronous reference frame PLL to remove unbalance and harmonic errors

This paper presents a new control method to track the maximum power point for a Wind Energy Conversion System (WECS). This WECS is based on a permanent magnet synchronous generator (PMSG) fed by a matrix converter. Since the mechanical power generated by the wind turbine is a function of its shaft speed at a given wind velocity, the proposed controller provides the desired voltage at the output of the matrix converter so as to control the generator speed. This controller is based on the nonlinear adaptive backstepping approach which is well suited for this system. This method is able to effectively accommodate the effects of system uncertainties. Theoretical analysis and simulation results verify the feasibility and performance of the proposed approach.

A Series–Parallel Current-Driven Full-Bridge DC/DC Converter

This paper presents an advanced current controller for grid-connected bidirectional ac/dc converters used for energy storage systems (ESSs). The proposed control scheme is designed to incorporate both the time-domain and frequency-domain dynamics to achieve superior transient and steady-state performance. The advanced current controller can overcome the various challenges faced by the conventional current controllers used in this application, which lead to sluggish transients and steady-state errors when tracking the sinusoidal reference for the grid current. Combining the time-domain dynamics with the frequency-domain dynamics creates a more intelligent controller compared to existing methods, which only consider the dynamics of one domain. The proposed controller is able to eliminate steady-state error by adaptively changing the controller coefficients in the frequency domain according to the current error. In the time domain, the control scheme minimizes the derivative of a defined energy function in order to optimize the transient performance. Simulation and experimental results obtained from a 3.3-kW grid-connected ac/dc converter demonstrate its superior performance.

Adaptive nonlinear maximum power point tracker for a WECS based on permanent magnet synchronous generator fed by a matrix converter

This paper presents a control scheme for a grid-connected three-phase voltage source inverter with an LCL filter, which is suited for renewable energy applications. The proposed method has the following properties: fast tracking, optimized dynamics, grid disturbance rejection, and active resonance damping. The controller is based on an augmented linear quadratic regulation (LQR) scheme, which is optimized based on a weighted cost function. The LQR controller is augmented to include two complex conjugate poles at the grid frequency for sinusoidal voltage disturbance rejection upon connection to the grid. Furthermore, this control scheme actively damps the resonance introduced into the closed-loop system through the third-order LCL filter. Finally, the current reference is found by calculating the instantaneous power, which allows for faster power tracking compared to using the technique of measuring average power. Results verify the validity of the proposed control scheme.