CN-121395317-B - Virtual impedance and power reference cooperative adjustment method and system for grid-connected converter

CN121395317BCN 121395317 BCN121395317 BCN 121395317BCN-121395317-B

Abstract

The invention discloses a method and a system for collaborative adjustment of virtual impedance and power reference of a grid-connected converter, which relate to the technical field of power control, wherein a virtual synchronous generator system introduces virtual impedance to increase the equivalent output impedance of an inverter, and monitors the internal voltage reference of the inverter generated by a virtual synchronous generator algorithm in real time; the method comprises the steps of measuring a local voltage at a public coupling point in real time, monitoring the local voltage measured at the public coupling point in real time, solving the accurate amplitude of virtual impedance in real time based on the vector difference between an internal voltage reference and the local voltage and combining the maximum current limit value of a power electronic device, determining the functional relation between an active power reference value and reactive power based on the accurate amplitude of virtual impedance, and monitoring the reactive power measured at the public coupling point in real time, and adjusting the active power reference value according to the functional relation so as to keep a stable balance point. Virtual impedance is dynamically calculated to accurately limit current, active power reference is adaptively adjusted according to real-time reactive response, and maximized power grid support and safe and stable operation of the converter are achieved.

Inventors

ZHANG ZHENBIN
LIU JIAWEI
LI ZHEN
ZHANG CHENGBO
HU CUNGANG
YIN ZHONGGANG
LIU YIQI
WANG YINGQI
ZHU XINYU

Assignees

山东大学

Dates

Publication Date: 20260508
Application Date: 20251224

Claims (9)

1. A method for collaborative adjustment of virtual impedance and power reference of a grid-tied converter, wherein a virtual synchronous generator system introduces virtual impedance to increase inverter equivalent output impedance, comprising: monitoring an internal voltage reference of the inverter generated by a virtual synchronous generator algorithm in real time; monitoring the local voltage measured at the point of common coupling in real time; Based on the vector difference between the internal voltage reference and the local voltage, combining the maximum current limit value of the power electronic device, and solving the accurate amplitude value of the virtual impedance in real time; The virtual synchronous generator system predicts the local voltage output at the next moment based on the local voltage at the current moment, and is expressed as follows: Wherein, the 、 Respectively is The dq-axis component of the time PCC voltage, 、 Respectively represent The dq-axis component of the time-of-day pcc voltage, A control period of the system is indicated, Representing the capacitance of the LC filter, 、 Respectively represent The dq-axis component of the time-of-day pcc current, Representing the rated angular frequency of the converter; and determining a functional relation between the active power reference value and the reactive power based on the accurate amplitude of the virtual impedance, monitoring the reactive power measured at the public coupling point in real time, and adjusting the active power reference value according to the functional relation so as to keep a stable balance point.
2. The method of cooperative adjustment of virtual impedance and power reference of a grid-tied converter as recited in claim 1, wherein the virtual impedance magnitude is expressed as: Wherein, the Representing the virtual impedance of the device and, Representing the resistance-to-inductance ratio of the virtual impedance, Representing a voltage amplitude reference, Representation of The local voltage at the moment in time is, 、 Representing the virtual reactance and the virtual resistance respectively, Representing the maximum current limit.
3. A method of collaborative adjustment of virtual impedance and power reference for a grid-tied current transformer as set forth in claim 1 wherein the impedance angle of the virtual impedance is also adaptively adjusted.
4. A method of collaborative adjustment of virtual impedance and power reference of a grid-tied current transformer as claimed in claim 3, wherein the impedance angle is expressed as: Wherein, the Representing a function of the resistance to inductance ratio over time, The duration of the fault is indicated and, Indicating the duration of the rush current suppression phase, The time constant is represented by a time constant, And The minimum and maximum values of the impedance angle of the virtual impedance are represented, respectively.
5. The method of claim 1, further providing a cooperative active power adjustment strategy, wherein the locally measured reactive power output is used as a real-time indicator of fault severity, and when the reactive power increases, the system adaptively adjusts the active power reference value according to a preset functional relationship.
6. The method of cooperative adjustment of virtual impedance and power reference of a grid-tied converter as recited in claim 5, wherein the active power reference value is expressed as: Wherein, the Indicating the value of the active power reference, Representing the power adjustment factor and, Representing the calculated reactive power measured at the point of common coupling, Representing the magnitude of the output voltage of the current transformer, Representing the virtual reactance of the reactor and, Representing the virtual reactance.
7. A grid-tied converter virtual impedance and power reference co-regulation system, wherein a virtual synchronous generator system introduces virtual impedance to increase inverter equivalent output impedance, comprising: a voltage reference acquisition module configured to monitor in real time an internal voltage reference of the inverter generated by a virtual synchronous generator algorithm; a local voltage acquisition module configured to monitor in real time a local voltage measured at the point of common coupling; a dynamic virtual impedance solving module configured to solve for an accurate magnitude of the virtual impedance in real time based on a vector difference of the internal voltage reference and the local voltage in combination with a maximum current limit of the power electronics; The virtual synchronous generator system predicts the local voltage output at the next moment based on the local voltage at the current moment, and is expressed as follows: Wherein, the 、 Respectively is The dq-axis component of the time PCC voltage, 、 Respectively represent The dq-axis component of the time-of-day pcc voltage, A control period of the system is indicated, Representing the capacitance of the LC filter, 、 Respectively represent The dq-axis component of the time-of-day pcc current, Representing the rated angular frequency of the converter; and the cooperative active power adjustment module is configured to determine a functional relation between an active power reference value and reactive power based on the accurate amplitude of the virtual impedance, monitor the reactive power measured at the public coupling point in real time, and adjust the active power reference value according to the functional relation so as to maintain a stable balance point.
8. A computer readable storage medium having stored thereon a computer program, which when executed by a processor performs the steps of a method for collaborative adjustment of virtual impedance and power reference of a grid formed converter according to any of claims 1-6.
9. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor implements the steps of a method for collaborative adjustment of virtual impedance and power reference of a grid formed converter according to any of claims 1-6 when the program is executed.

Description

Virtual impedance and power reference cooperative adjustment method and system for grid-connected converter Technical Field The invention relates to the technical field of power control, in particular to a method and a system for collaborative adjustment of virtual impedance and power reference of a grid-connected converter. Background The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art. The grid-constructed converter can actively provide inertia support for the system by simulating the rotor motion characteristic of the synchronous generator, can still keep high stability under the condition of weak power grid, and is a key technology for supporting high-proportion new energy grid connection and enhancing the toughness of the power grid. However, due to the low overcurrent capability of the power electronics, the grid-tied current transformer must be equipped with current limiting strategies to prevent overload and thermal damage from occurring. In the existing scheme, although the direct current limiting method can quickly inhibit fault current, the current transformer can be converted into a current source mode from a voltage source mode, so that the stability margin is reduced and even out of control. Conventional virtual impedance current limiting suppresses current by increasing equivalent output impedance while maintaining the voltage source characteristics of the device, suffers from low bandwidth and poor accuracy, or relies on difficult to obtain and unreliable grid-side information. In addition, the application of virtual impedance can limit the maximum power transmission capacity of the converter, so that a stable balance point can disappear, transient instability of the inverter can occur, and the stability of a grid-connected system is threatened. Therefore, the virtual impedance influence needs to be comprehensively considered, and the active power reference value needs to be dynamically adjusted to avoid power unbalance. In summary, the existing virtual impedance method has defects, the traditional current limiting method has poor precision, so that the capacity of the converter is not fully utilized, and the existing improvement method depends on remote power grid information which is difficult to acquire in real time, so that the reliability and response speed of the system are affected. Meanwhile, most of the existing power adjustment strategies fail to comprehensively consider the limitation of virtual impedance on the maximum power transmission capacity, so that transient instability risks are caused. Disclosure of Invention In order to overcome the defects in the prior art, the invention provides a cooperative adjustment method and a system for virtual impedance and power reference of a grid-structured converter, which dynamically adjusts virtual impedance according to the difference value between the output reference voltage of a virtual synchronous generator (Virtual Synchronous Generators, VSG) and the voltage of a Point of Common Coupling (PCC) during power grid faults so as to precisely limit the output current to a maximum allowable value during the faults, and adaptively adjusts the active power reference value according to the current limiting state so as to ensure stable operation of the system, thereby exerting the power grid supporting capability of an inverter to the maximum extent. To achieve the above object, one or more embodiments of the present invention provide the following technical solutions: In a first aspect, the present invention provides a method for collaborative adjustment of virtual impedance and power reference of a grid-tied converter, the virtual synchronous generator system introducing virtual impedance to increase the equivalent output impedance of the inverter, comprising: monitoring an internal voltage reference of the inverter generated by a virtual synchronous generator algorithm in real time; monitoring the local voltage measured at the point of common coupling in real time; Based on the vector difference between the internal voltage reference and the local voltage, combining the maximum current limit value of the power electronic device, and solving the accurate amplitude value of the virtual impedance in real time; and determining a functional relation between the active power reference value and the reactive power based on the accurate amplitude of the virtual impedance, monitoring the reactive power measured at the public coupling point in real time, and adjusting the active power reference value according to the functional relation so as to keep a stable balance point. According to a further technical scheme, the virtual synchronous generator system predicts the local voltage output at the next moment based on the local voltage at the current moment, and the local voltage is expressed as: Wherein, the 、Respectively isThe dq-axis component of the ti