VSG control method under grid voltage symmetrical drop fault

Abstract

The invention discloses a VSG control method under a grid voltage symmetrical drop fault, which includes the following steps: S1, grid voltage information at a tie line is collected and transmitted to a local controller of a VSG in a micro grid; S2, active and reactive power reference instructions and a voltage reference instruction are calculated when a grid voltage symmetrical drop fault is detected; S3, a grid-connection small signal cable at the operation point of the fault is established, control parameters satisfying given dynamic performance and stability performance indexes are calculated, active power and voltage rated values are synchronously switched to the active power and voltage reference instructions, and the control parameters are switched; S4, the local collector collects local voltage and current information and establishes a voltage loop control model, a fault current limiting control model and a current loop control model; and S5, when the fault is detected to be eliminated, smooth transition from a fault state to a normal state is realized by adjusting the phase angle. Smooth and fast transition of the VSG from a fault operation state to a normal operation state after recovery of grid voltage can be realized.

Description

[0001] Field [0002] The invention belongs to the technical field of grid-connected control of new energy power generation, and in particular relates to a VSG control method under a grid voltage symmetrical drop fault. Background technique [0003] Distributed generation (distributed generation, DG), as a power generation technology that can efficiently utilize new energy, has received extensive attention. However, most distributed power sources are connected to the grid through power electronic conversion devices, which lack the damping and inertia similar to traditional synchronous machines, and some distributed power sources, such as wind power and photovoltaics, have random and fluctuating power generation, making it difficult to participate in the system voltage. And frequency regulation, as the penetration rate of distributed power increases, it will pose a threat to the safe and stable operation of the system. In this context, VSG control technology has been extensive...

AI Technical Summary

Problems solved by technology

[0005] At present, the research on VSG low voltage ride through control can be divided into two types: non-control mode switching type and control mode switching type: for non-control mode switching type, there are literatures that multiply the measured value of the grid voltage by a variable gain. , with the VSG power outer ring voltage reference command and line impedance calculation to obtain the VSG output current reference command, combined with the current limiter, to avoid the grid voltage drop and cause the calculated VSG output current reference value to be too large, so as to limit the fault transient and The output current of VSG during the steady state; there is a literature using a dynamic voltage feed-forward compensation method, by quickly detecting the peak current and calculating the voltage compensation amount to feed forward compensation to the output voltage of the VSG, so as to limit the peak current output by the VSG at the moment of failure , but none of them theoretically analyzed the transient response of VSG current and power during voltage sag, and did not pay attention to the control of VSG providing active and reactive power support to the grid during faults; The combined method of current limiting and current limiting is used to limit the steady-state fault current and transient impact current of the VSG during the fault period, but the virtual impedance will change the output impedance of the VSG, thereby affecting the output dynamics and steady-state of the VSG under normal operation. characteristics; for the control mode switching type, there are literatures that switch the control of the VSG output voltage to the control of the VSG output current before and after the grid voltage drops, which involves the switching of two control loops. Due to the reference of voltage control and current control There are differences in phase angles and control loops, and there will be complex seamless switching control problems. The control structure is more complicated and difficult to implement in engineering; some literature proposes to use balanced current control when the VSG is in normal operation, and switch to VSG after the grid voltage drops. Traditional low-voltage ride-through control, the control object is the output current of VSG, although it does not involve the switching of the control object, but because it controls the output current of VSG, it may affect the voltage support provided by the VSG during normal operation and fault operation. Ability; Some studies have proposed to lock the given voltage and frequency reference value of the VSG power outer loop at the moment of a fault. During the fault, the voltage controller adopts proportional control, and its output is limited by the amplitude limiter. The output current is limited by an additional current The compensation link adjusts the current reference value of the inner loop to realize the control of VSG output active power and reactive power during the fault period. This method blocks the frequency inertia link of the VSG power outer loop during the fault period, which will affect the VSG’s effect on the power grid during the fault period. Inertial frequency support ability, secondly, its dynamic performance is not good in the transient process of fault occurrence and elimination

[0006] After the grid voltage drops, due to the inertia of the VSG itself, the amplitude and phase angle of its output voltage remain unchanged in a short period of time, and there will be a short-term output peak current, which will cause the action of the protection and turn the VSG from In a grid with a high penetration rate of distributed power, the removal of a large number of distributed power from the grid will also lead to an excessive active and reactive power deficit, threatening the stability and reliability of the entire system; if The small peak current is not enough to trigger the protection action, and the VSG achieves stability again after a period of transient adjustment process through its own adjustment function, but because the primary frequency modulation and primary voltage regulation characteristics of the VSG itself are set under normal conditions , there are certain limitations. Under different levels of voltage drop scenarios, it cannot provide the expected active and reactive power support, which is not conducive to the safe and stable operation of the VSG and the parallel grid during the fault period; for the current common VSG low-voltage ride-through control , it mostly uses the control of VSG output current during the fault period, and it is difficult to provide voltage and frequency support for the power grid during the fault period; and after the fault is eliminated, the current VSG low-voltage ride-through control strategy pays less attention to achieving its rapid and stable return to normal operation control

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