An adaptive phase‐locked loop‐less control strategy for LCL‐filtered grid‐connected inverter under complex grid conditions

Abstract

The phase-locked loop, as a method to extract grid voltage phase angle, is commonly used for grid-connected inverter to synchronize the injected grid current with the grid. However, the phase-locked loop will also bring some problems. The current loop controller, the phase-locked loop, and the grid impedance are coupled together under the weak grid. Then, the phase angle of the inverter output impedance will be reduced, causing the system to be unstable. Moreover, the output phase angle of the phase-locked loop participates in the coordinate transformation under the unbalanced grid voltage condition, which degrades the quality of the injected grid current generated by the inverter with high harmonic content. Therefore, a vector current control strategy without phase-locked loop derived from direct power control is used in this paper. An adaptive linear Kalman filter algorithm is also applied to observe the voltage information and avoid the harmonic problems caused by power calculation. Finally, simulations and experiments are conducted to verify that the proposed method is effective, and the results are consistent with the theoretical analysis. K E Y W O R D Sgrid-connected inverter, Kalman filter, phase-locked loop, unbalanced grid voltage, weak grid | INTRODUCTIONDistributed generation systems, such as photovoltaic or wind energy, use power converter as an interface to the grid, so the performance of distributed power grid-connected converter directly affects the system reliability. 1,2 Aiming to achieve safe and efficient operation of grid connection, the synchronization of injected current with the voltage of the common coupling point (PCC) is one of the most important issues. 3 Especially, in the event of grid voltage distortion or imbalance, it is necessary to design a reliable synchronous algorithm with fast response and small error.At present, in order to synchronize grid-connected current with the grid voltage phase angle, the phase-locked loop (PLL) is commonly used. 4,5 However, PLL can also have some adverse effects on the system. Under the influence of PI controllers of PLLs connected to weak grids, phase information of the output will be disturbed by small signals disrupting the phase information. Due to this, the grid-connected inverter's coordinate system does not coincide with its

Advanced adaptive algorithm controlled single‐phase DSTATCOM operation during weak grid conditions

“…Adaptive neural network (ADALINE) control offers a better training procedure but suffers from the linear separability constraint of the perceptron. However, the hardware implementation of ADALINE requires a microcontroller with parallel processing 5–26 …”

“…Shunt-connected inverters as a DSTATCOM with appropriately tuned control at the distribution end are essential in controlling and supporting weak grid conditions, that is, voltage sag/swell, DC bus stability, and power quality issues. 8,10 Various control algorithms belonging to the time domain, frequency domain, and advanced adaptive controls have been discussed in the literature for performing multifunctional operations. 11,12 Conventional time domain controls, that is, synchronous reference frame (SRF) and power balance theory (PBT), have been extensively used for the reference current generation.…”

Distributed damping reshaping control with constraints on dual stabilities for grid‐connected inverter in high penetration grid

“…15 In addition, for facing the new form of the weak grid, some novel control methods are designed to ensure the stable operation of the GCI. To avoid the influence of the asymmetric phase-locked loop on harmonic resonance and improve the power quality of the output current under complex grid conditions, an adaptive phase-locked loop-less control strategy based on the Kalman filter is adopted in Huang et al 16 Considering various grid strengths, the model predictive control with adaptive cost function and the sliding model controller with Kalman filter estimation are proposed to enhance the performance of the inverter. 17,18 From the view of impedance matching, several schemes have been proposed to reshape the grid-source impedance and improve the damping in the region of negative impedance.…”

“…11,15 Based on the advanced control theory, some novel control methods, such as model predictive control and sliding model control, are proposed in previous papers. [16][17][18] These methods are complex, and the generalizability and reliability in engineering applications need to be discussed. On the basis of the conventional current control loop, the revised control scheme with grid voltage feed-forward or current feedback in previous papers [23][24][25][26][27][28][29] can effectively suppress harmonic resonance.…”

“…Considering the new constraints, the redesign of the control parameters can improve the GCI's performance, but the design procedure is complex 11,15 . Based on the advanced control theory, some novel control methods, such as model predictive control and sliding model control, are proposed in previous papers 16–18 . These methods are complex, and the generalizability and reliability in engineering applications need to be discussed.…”