An active control method for grid-connected inverter system impedance based on phase angle margin compensation
A technology of phase angle margin and active control, which is applied to the AC network to reduce harmonics/ripples, harmonic reduction devices, etc., can solve problems such as grid-connected system instability, achieve strong real-time performance, and suppress harmonic resonance , high accuracy effect
Active Publication Date: 2016-04-20
NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
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However, in the actual power grid, due to the influence of parameters such as transmission cables, the grid impedance is not zero, so the grid impedance and converter impedance will produce an intersection point in the frequency domain
If the grid impedance is too large, or the control parameter design of the converter is unreasonable, it may cause specific sub-harmonic oscillation (near the frequency of the impedance intersection point) due to too small phase angle margin, which will eventually lead to instability of the grid-connected system
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[0026] Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:
[0027] figure 1 It is a block diagram of single-phase LCL grid-connected inverter system under weak grid conditions. The single-phase LCL grid-connected inverter includes a DC source 1 , an inverter bridge 2 , an LCL filter 3 , a public grid 4 considering grid impedance, and a controller 5 . Among them, the inverter bridge 2 is composed of the switching tube Q 1 ~Q 4 Composition; LCL filter 3 is composed of filter inductor L 1 , L 2 and filter capacitor C f Composed; the public grid 4 consists of an ideal voltage source u g and grid impedance R g and L g Equivalent in series.
[0028] figure 2 Simplified control block diagram for the inverter after adding voltage feed-forward compensation. It can be seen from the figure that the impedance active method proposed by the present invention adopts the output voltage u of the feed-forward ...
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The invention relates to a phase angle margin compensation-based system impedance active control method of a grid-connected inverter. Because the changing impedance exists in a power grid, a dynamic interaction influence exists between the grid-connected inverter and the power grid and thus the grid-connected current waveform quality is influenced, so that the weakening of the impedance interaction influence is crucial to improvement of the grid-connected current quality. According to the invention, the impedance active control method is characterized in that real-time grid impedance information is obtained in real time and thus a phase angle margin at an inverter output impedance amplitude-frequency curve intersection point frequency is solved; a voltage feedforward control method is employed and a phase angle margin of the inverter impedance at the impedance intersection point frequency is compensated in real time; operation is carried out on a voltage feedforward link output and a current ring PI result so as to obtain an SPWM control signal. According to the invention, because the active impedance control method with the phase angle margin compensation function is used, the harmonic resonance generated by the dynamic interaction influence between the inverter and the power grid near the impedance intersection point frequency can be effectively suppressed, so that the rid-connected current waveform quality of the inverter is improved and the grid-connected stability is enhanced.
Description
technical field [0001] The invention relates to a method for actively controlling the impedance of a grid-connected inverter system based on phase angle margin compensation, which belongs to the inverter control technology in the power conversion technology. Background technique [0002] Almost all renewable energy is connected to the AC grid through grid-connected inverters. A dynamic interconnection system is formed between the grid-connected inverters and the grid. However, there may be some Unexpected dynamic interaction effects. [0003] For an ideal grid-connected system, the grid impedance is infinitesimal and the grid voltage harmonics are not considered. At this time, the output current of the system is mainly determined by the output current of the converter, and there is no harmonic oscillation in the grid-connected system. However, in the actual power grid, due to the influence of parameters such as transmission cables, the grid impedance is not zero, so the gri...
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IPC IPC(8): H02J3/01
CPCY02E40/40
Inventor 陈新张旸陈杰陈姝慧吴佳王赟程
Owner NANJING UNIV OF AERONAUTICS & ASTRONAUTICS