Method for improving phase-locked loop for inverter and inspection method thereof

Abstract

The invention discloses a method for improving a phase-locked loop with the enhancement of damping characteristic of an inverter control system and an inspection method thereof. Two cascaded single-phase phase-locked loops are included, and the method comprises the steps that: pre-stage and post-stage single-phase phase-locked loops collect three-phase voltage signals ega, egb, and egc of a powergrid, and the three-phase voltage signals are converted into two-phase voltage signals egd and egq, e'gd, and e'gq by using Clark transformation and Park transformation; the pre-stage single-phase phase-locked loop is subjected to coordinate transformation to obtain a difference value between egq and a reference value 0 to be a reference value input of e'gq of the post-stage single-phase phase-locked loop; and the accurate phase locking of the grid voltage is achieved by a loop filter and a voltage controlled oscillator through reference value correction, and a phase angle of a voltage signalobtained by the post stage is taken as an output phase angle of the improved phase locked loop. According to the method, the resonance of the inverter system can be suppressed.

Description

technical field [0001] The invention relates to the field of inverter control systems, in particular to an improvement method of a phase-locked loop for enhancing the damping characteristics of an inverter control system and a testing method thereof. Background technique [0002] Grid-connected inverters are the most commonly used interface between the grid and distributed generation systems. With the wide application of non-linear loads, low-order harmonics often appear at the interface between the inverter and the grid, and the appearance of these harmonics will cause the output current of the inverter to contain certain harmonic currents, seriously It affects the output power quality of the distributed generation system. In addition, with the increase in the number of inverters connected to the grid, due to the existence of grid impedance, there is coupling between the output currents of each inverter, which easily causes system resonance and seriously restricts the deve...

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Problems solved by technology

With the wide application of non-linear loads, low-order harmonics often appear at the interface between the inverter and the grid, and the appearance of these harmonics will cause the output current of the inverter to contain certain harmonic currents, seriously Affecting the output power quality of the distributed generation system

In addition, with the increase in the number of inverters connected to the grid, due to the existence of grid impedance, there is coupling between the output currents of each inverter, which can easily cause system resonance and seriously restrict the development of distributed generation.

[0003] The phase-locked loop is an important link in the inverter control system. The traditional phase-locked loop, taking SPLL as an example, mainly consists of a phase detector, a loop filter and a voltage-controlled oscillator. Although it can accurately control the grid voltage Phase-locked, but in the face of grid voltage containing harmonics, the traditional phase-locked loop presents an obvious disadvantage, that is, grid voltage harmonics enter the control system of the inverter through the phase-locked loop, causing the entire control system to be at a harmonic frequency The damping characteristics are weakened, which can easily cause system resonance

At present, to deal with the problem of grid-connected resonance of inverters, two methods are mainly adopted: active damping and passive damping. Although passive damping is simple, it increases the loss of the system, while active damping is mainly through changing the inverter The main method is to introduce the grid voltage feed-forward, capacitor current feed-forward, etc., although it can play a certain degree of damping effect, but these methods are limited by the introduction of the grid voltage by the traditional phase-locked loop. The influence of harmonics weakens the effect of active damping and fails to achieve the ideal active damping effect

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