Control Of Three-phase Grid-connected Inverter Research Articles

A Generic Multicell Network Control for Three-Phase Grid-Connected Inverters

The inherent resonance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filters threatens the inverter stability seriously. Moreover, the strong <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dq$</tex-math></inline-formula> -axis cross-coupling of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered grid-connected inverters in a synchronous frame goes against the independent regulation of active ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$P$</tex-math></inline-formula> ) and reactive ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> ) power that is required in various applications. Besides, the imbalance and harmonics of the grid voltage will deteriorate the injected grid current, so the disturbance suppression performance of grid-connected inverters is important. Furthermore, excellent steady-state and dynamic performance is essential for grid-connected inverters. To solve the above four issues simultaneously, a complex-domain model of grid-connected inverters is established, and a generic multicell network control (GMNC) structure is proposed in this article. Based on the proposed GMNC structure, a number of control schemes are obtained, and the quantitative relationship between inverter performance and control parameters can be given directly and precisely for each scheme. Therefore, it is convenient and simple for engineers to select proper control schemes depending on the practical conditions and to design all the control parameters for an expected steady-state, dynamic, and antidisturbance performance without the resonance and the coupling issues. Finally, the effectiveness of the proposed control is verified by the experiments.

Adaptive, Optimal, Virtual Synchronous Generator Control of Three-Phase Grid-Connected Inverters Under Different Grid Conditions—An Adaptive Dynamic Programming Approach

This article proposes an adaptive, optimal, data-driven control approach based on reinforcement learning and adaptive dynamic programming to the three-phase grid-connected inverter employed in virtual synchronous generators (VSGs). This article takes into account unknown system dynamics and different grid conditions, including balanced/unbalanced grids, voltage drop/sag, and weak grids. The proposed method is based on value iteration, which does not rely on an initial admissible control policy for learning. Considering the premise that the VSG control should stabilize the closed-loop dynamics, the VSG outputs are optimally regulated through the adaptive, optimal control strategy proposed in this article. Comparative simulations and experimental results validate the proposed method's effectiveness and reveal its practicality and implementation.

Current-Limiting Virtual Synchronous Control and Stability Analysis Considering DC-Link Dynamics Under Normal and Faulty Grid Conditions

An improved nonlinear virtual synchronous control for three-phase grid-connected inverters, that can maintain a reliable operation under both normal and faulty grid conditions, i.e. balanced grid voltage sags, is proposed. The proposed controller can ensure a desired RMS current limitation at all times, provide virtual inertia and damping via the DC-link voltage and AC system frequency coupling, and realize the desired real and reactive power regulation without requiring accurate knowledge of the system parameters. Opposed to the conventional methods that use saturated PI controllers with or without anti-windup techniques to limit the reference value of the inverter current, the proposed controller includes a nonlinear bounded integrator, which limits the actual value (instead of the reference) of the inverter RMS current and leads to a fast system recovery even after significant grid voltage sags. The closed-loop stability of entire system is rigorously proven using nonlinear singular perturbation theory. Moreover, analytic conditions for the controller parameter selection to guarantee the stability of entire inverter system with the DC-link dynamics are provided. To prove the effectiveness of proposed controller and its superior performance compared to the traditional approaches, extensive Matlab/Simulink-based simulations are performed, followed by Typhoon-HIL hardware-in-the loop implementation using a TI microcontroller.

The Reactive Power Support Strategy based on Dual-loop Control for Three-phase Grid-connected Inverter

Renewable energy sources (RESs) generally connected with electric power system via power electronic interface. This paper presents a reactive power and voltage (Q/V) control strategy of three-phase photovoltaic (PV) system to offering reactive power based on the typical dual-loop control topology. It is worth mentioning that control strategy can support reactive power when a low voltage fault occurs in AC bus without additional compensation device. With the help of the decoupling control, the PV array can generate active power as much as possible in variable external solar radiation conditions. The voltage of PV arrays is adopted as the objective, which on account of the easy availability and controllability of voltage, to control output active power. Besides, accurately modeling process from a PV cell to PV array is described in the beginning to acquire the P-V and V-I characteristics of PV arrays, which promote the designment of Q/V control.

Pseudo-Derivative-Feedback Current Control for Three-Phase Grid-Connected Inverters With &lt;italic&gt;LCL &lt;/italic&gt; Filters

Pseudo-derivative-feedback (PDF) control is, for the first time, applied to the current control of three-phase grid-connected inverters with LCL filters, which significantly improves the transient response of the system to a step change in the reference input through the elimination of overshoot and oscillation. Two PDF controllers with different terms in the inner feedback path are developed for an inverter current feedback system and a grid current feedback system, respectively. For the inverter current feedback system, a simple PDF controller with a proportional term is used. The influence of the controller parameters on the transient performance is discussed in detail. Compared with a PI controller, the PDF controller is able to eliminate the transient overshoot and oscillation easily, while maintaining a fast response. For the gird current feedback system, a PDF controller with a proportional term and a second-order derivative is developed. The implementation and design of the PDF controller are presented. Active damping is achieved with only the feedback from the grid current, and at the same time, the system transient response is improved. Both theoretical analysis and experimental results verify the advantages of the PDF control over PI control methods.

Research on Dual-Loop Control of Three-Phase Grid-Connected Inverter with LCL Filter Based on PCI Control

Research on Dual-Loop Control of Three-Phase Grid-Connected Inverter with LCL Filter Based on PCI Control

An Adaptive Robust Predictive Current Control for Three-Phase Grid-Connected Inverters

This paper presents an adaptive robust predictive current control (RPCC) for grid-connected three-phase inverters that exhibit zero steady-state current error. The error correction is achieved by means of an adaptive strategy that works in parallel with the deadbeat algorithm, therefore preserving the typical fast response of the predictive law. The resulting control adapts to any particular <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> or <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$LCL$</tex></formula> filter by estimation of the resistive part of the filter. As a variety of the RPCC class of control, it offers the best tradeoff between robustness and speed.

Quasi Resonant Direct Power Control of Three-Phase Grid-Connected Inverters in Distributed Generation Systems

The paper proposes a quasi resonant direct power control algorithm for three-phase grid-connected inverters without grid voltage sensors in distributed generation systems. According to the active and reactive power references, grid virtual flux and the inverter output current references are calculated. In order to accurately and fast track the output current references, the quasi proportional resonant (QPR) controller is used. The theoretical principle of this method is discussed. The steady-state and dynamic experimental results of quasi resonant direct power control that can illustrate the operation and performance of the presented control strategy are displayed. It is shown that the control system exhibits several advantages, such as constant switching frequency, sinusoidal grid currents and good dynamic response. Experimental results are provided to demonstrate the effectiveness of the proposed control strategy.

A Synchronous Reference Frame Robust Predictive Current Control for Three-Phase Grid-Connected Inverters

This paper presents a new predictive current control for three-phase grid-connected inverters in the synchronous reference frame. The control combines a deadbeat control law with a diagonal Luenberger observer to estimate the future value of the grid currents. It provides a decoupled control of the active and reactive power and offers robustness against the computational delay inherent in the digital implementation and against filter and grid-impedance uncertainties. This control exhibits a very fast current response while widely improving the gain and phase margins of the traditional predictive controllers.

A Robust Predictive Current Control for Three-Phase Grid-Connected Inverters

This paper presents a new predictive control algorithm for grid-connected current-controlled inverters. The control combines a two-sample deadbeat control law with a Luenberger observer to estimate the future value of the grid currents. The resulting control offers robustness against the computational delay inherent in the digital implementation and considerably enhances the gain and phase margins of the previous predictive controls while maintaining the high-speed response typical of the deadbeat controllers.