US-20260128589-A1 - DIRECT CURRENT VOLTAGE CONTROL METHOD AND SYSTEM FOR ENHANCING TRANSIENT STABILITY OF GRID-CONNECTED CONVERTER

US20260128589A1US 20260128589 A1US20260128589 A1US 20260128589A1US-20260128589-A1

Abstract

A direct current (DC) voltage control method for enhancing transient stability of a grid-connected converter includes the steps of: processing a control signal of a synchronization control loop by a DC-link transient energy correction module (DC-TECM) when either a power angle limit violation-based fault diagnosis module (PAV-FDM) or a voltage limit violation-based fault diagnosis module (VLV-FDM) determines that a voltage sag or phase jump fault has occurred, and subjecting a DC voltage reference value to temporary storage of unbalanced power and inertia correction; comparing a voltage value of a DC-link capacitor with the DC voltage reference value, and obtaining a DC voltage control output reference value through a steady-state DC voltage control module; obtaining a synchronization control signal and an internal electromotive force reference value; and generating converter driving signals. In the present disclosure, the transient stability issues of the grid-connected converter under grid faults can be effectively addressed.

Inventors

Zhixiang ZOU
Chenhang XU
Xinlei Liu
Zheng Wang

Assignees

SOUTHEAST UNIVERSITY

Dates

Publication Date: 20260507
Application Date: 20250925
Priority Date: 20241106

Claims (9)

1 . A direct current (DC) control method for enhancing transient stability of a grid-connected converter, comprising the steps of: processing a control signal of a synchronization control loop by a DC-link transient energy correction module (DC-TECM) when either a power angle limit violation-based fault diagnosis module (PAV-FDM) or a voltage limit violation-based fault diagnosis module (VLV-FDM) determines that a voltage sag or phase jump fault has occurred, and subjecting a DC voltage reference value to temporary storage of unbalanced power and inertia correction, acquiring a voltage value of a DC-link capacitor, comparing the voltage value with the DC voltage reference value, and obtaining a DC voltage control output reference value through a steady-state DC voltage control module, acquiring output data of a converter at a point of common coupling (PCC), and obtaining a synchronization control signal based on the synchronization control loop, obtaining an internal electromotive force reference value through an internal electromotive force control loop based on the synchronization control signal, and generating converter driving signals based on the internal electromotive force reference value, wherein the subjecting a DC voltage reference value to temporary storage of unbalanced power and inertia correction comprises the steps of: acquiring an angular frequency ω of a converter output voltage, filtering a difference between the angular frequency ω and a rated value ω n by a notch filter to remove power frequency disturbance, and amplifying the difference by a damping-voltage mapping coefficient k D−V to obtain a DC voltage elevation increment ΔV Pu for temporary storage of transient unbalanced power; acquiring an angular frequency change rate {dot over (ω)} of the converter output voltage, filtering the angular frequency change rate {dot over (ω)} through a low-pass filter (LPF) to remove high-frequency oscillation, and amplifying the angular frequency change rate by an inertia-voltage mapping coefficient k J−V to obtain a DC voltage elevation increment ΔV J for inertia correction of the converter; and multiplying a sum ΔV dc of the DC voltage elevation increments for the temporary storage of transient unbalanced power and of the inertia correction of the converter with a fault detection signal S F , superimposing the multiplied value to the DC voltage reference value V dc_ref , and regulating the DC voltage.
2 . The method according to claim 1 , wherein the inertia-voltage mapping coefficient is designed by setting an inertia correction amount ΔJ of swing characteristics of the converter, and the inertia-voltage mapping coefficient is calculated by the following formula: k J−V =Δ J /k pdc , where k pdc is a proportional coefficient in steady-state DC voltage control; and the damping-voltage mapping coefficient is designed by setting a damping correction amount ΔD of swing characteristics of the converter, and the damping-voltage mapping coefficient is calculated by the following formula: k D−V =(ΔD+k idc ·k J−V )/k pdc , where k idc is an integral coefficient in steady-state DC voltage control.
3 . The method according to claim 1 , wherein the converter is a grid-forming converter (GFM); and the acquiring an angular frequency ω of a converter output voltage comprises the steps of: acquiring an output PCC voltage u PCC and an output PCC current i PCC of the converter to obtain an active power; obtaining the angular frequency ω of the GFM output voltage through active power-phase synchronization control loop based on a difference between the active power and an active power reference value; or the converter is a grid-following converter (GFL); and the acquiring an angular frequency 0 of a converter output voltage comprises the steps of: acquiring an output PCC voltage u PCC of the converter; and obtaining the angular frequency ω of the GFL output voltage through a phase-locked loop based on the output PCC voltage u PCC .
4 . The method according to claim 1 , wherein determining that a grid voltage sag or phase jump fault has occurred comprises the steps of: considering, when it is determined that the converter has at least one of the following issues: power angle limit violation (PAV) or voltage limit violation (VLV), that the grid voltage sag or phase jump fault occurs, the fault detection signal S F being set to 1, otherwise, the fault detection signal S F being set to 0.
5 . The method according to claim 4 , wherein determining whether the converter triggers PAV comprises the steps of: acquiring a current power angle δ of the grid-connected converter and an initial point δ 0 of the power angle under stable operation conditions, and calculating a difference between the two; and comparing an absolute value of the difference with a power angle threshold value δ th , and determining that the converter triggers PAV if the absolute value exceeds the power angle threshold value δ th .
6 . The method according to claim 4 , wherein determining whether the converter triggers VLV comprises the steps of: acquiring a difference between a voltage amplitude V of the grid-connected converter and a rated voltage amplitude value V n ; and comparing an absolute value of the difference with a voltage threshold value V th , and determining that the converter triggers VLV if the absolute value exceeds the preset voltage threshold value V th .
7 . The method according to claim 1 , wherein the converter is a GFM; and the acquiring a voltage value V dc of a DC-link capacitor, comparing the voltage value with the DC voltage reference value V dc_ref , and obtaining a DC voltage control output reference value comprise the steps of: acquiring the voltage value V dc of the DC-link capacitor, and comparing the voltage value with the DC voltage reference value V dc_ref to generate an active power reference value P ref as a DC voltage control reference value; the acquiring output data of a converter at a PCC, and generating a synchronization control signal based on the synchronization control loop comprise the steps of: acquiring an output PCC voltage u PCC and an output PCC current i PCC of the converter to obtain an active power P e and a reactive power Q e ; and obtaining a phase reference value θ of the output voltage of the converter based on a difference between the active power P e and the active power reference value P ref ; obtaining a reference value V of an output voltage amplitude of the converter according to a difference between the reactive power Q e and a reactive power reference value Q ref ; and the synchronization control signal comprising the phase reference value θ and an amplitude reference value V; and the obtaining an internal electromotive force reference value through an internal electromotive force control loop based on the synchronization control signal comprises the steps of: applying coordinate transformation to the amplitude reference value V using the phase reference value θ to obtain an output voltage reference value of the converter output voltage in a synchronous reference frame; and comparing the output PCC voltage u PCC of the converter with the output voltage reference value in the synchronous reference frame, and obtaining the internal electromotive force reference value based on a difference between the two values.
8 . The method according to claim 1 , wherein the converter is a GFL; and the acquiring a voltage value of a DC-link capacitor, comparing the voltage value with the DC voltage reference value V dc_ref , and obtaining a DC voltage control output reference value comprise the steps of: acquiring the voltage value V dc of the DC-link capacitor, and comparing the voltage value with the DC voltage reference value V dc_ref to generate an active current reference value I d_ref as the DC voltage control output reference value; the acquiring output data of a converter at a PCC, and generating a synchronization control signal based on the synchronization control loop comprise the steps of: acquiring an output PCC voltage u PCC of the converter; and obtaining the angular frequency a of the output PCC voltage u PCC using a phase locked loop, and integrating the angular frequency to obtain a voltage phase θ as a synchronization control signal; and the obtaining an internal electromotive force reference value through an internal electromotive force control loop based on the synchronization control signal comprises the steps of: acquiring an output PCC current i PCC of the converter, and applying coordinate transformation to the current i PCC using the voltage phase θ to obtain an active current I d and a reactive current I q of converter output; comparing the active current I d of the converter with a preset active current reference value I d_ref to obtain a first difference value; and comparing the reactive current I q of the converter output with a preset reactive current reference value I q_ref to obtain a second difference value; and obtaining an internal electromotive force reference value using the first and second difference values.
9 . A DC voltage control system for enhancing transient stability of a grid-connected converter, comprising: a PAV-FDM, configured to determine that a voltage sag or phase jump fault occurs in a grid, a VLV-FDM, configured to determine that a voltage sag or phase jump fault occurs in the grid, a DC-TECM, configured to process a control signal of a synchronization control loop by the DC-TECM when either the PAV-FDM or the VLV-FDM determines that a voltage sag or phase jump fault has occurred, and subject a DC voltage reference value to temporary storage of unbalanced power and inertia correction, a steady-state DC voltage control module, configured to acquire a voltage value of a DC-link capacitor, and obtain a DC voltage control output reference value by comparing the voltage value with the DC voltage reference value, a synchronization module, configured to acquire output data of a converter at a PCC, and obtain a synchronization control signal based on the synchronization control loop, an internal electromotive force control module, configured to obtain an internal electromotive force reference value through an internal electromotive force control loop based on the synchronization control signal, and a pulse width modulation module, configured to generate a converter driving signal according to the internal electromotive force reference value, wherein the subjection of a DC voltage reference value to temporary storage of unbalanced power and inertia correction comprises: acquisition of an angular frequency ω of a converter output voltage, filtering of a difference between the angular frequency ω and a rated value ω n by a notch filter to remove power frequency disturbance, and amplification of the difference by a damping-voltage mapping coefficient k D−V to obtain a DC voltage elevation increment ΔV Pu for temporary storage of transient unbalanced power; acquisition of an angular frequency change rate {dot over (ω)} of the converter output voltage, filtering of the angular frequency change rate {dot over (ω)} through an LPF to remove high-frequency oscillation, and amplification of the angular frequency change rate by an inertia-voltage mapping coefficient k J−V to obtain a DC voltage elevation increment ΔV J for inertia correction of the converter; and multiplication of a sum ΔV dc of the DC voltage elevation increments for temporary storage of transient unbalanced power and of the inertia correction of the converter with a fault detection signal S F , superimposition of the multiplied value to the DC voltage reference value V dc_ref , and regulation of the DC voltage.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of PCT/CN2025/077604, filed on Feb. 17, 2025 and claims priority of Chinese Patent Application No. 202411573516.5, filed on Nov. 6, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure belongs to the technical field of power system application, and in particular to a direct current (DC) voltage control method and system for enhancing transient stability of a grid-connected converter. BACKGROUND Faced with the challenges of fossil energy depletion and climate and environmental conditions, all countries around the world have implemented various strategies to improve energy structures. These strategies include enhancing energy utilization and vigorously developing clean and renewable energy, all with the aim of ensuring a sustainable energy supply and fostering harmonious economic and social development. The 19th National Congress of the Communist Party of China placed a strong emphasis on ecological civilization construction, urging efforts to promote green, circular and low-carbon development. China has committed to working collaboratively with the international community to actively address climate change. Controlling greenhouse gas emissions and achieving green and low-carbon development are also crucial for China to transform its development mode, overcoming resource and environmental constraints, and enhance its international competitiveness. With the rapid development of renewable energy power generation technology, renewable energy sources including photovoltaic and wind power are integrated into the same alternating current (AC) power grid through power electronic devices. This integration has resulted in the formation of a multi-source renewable energy feeding system. The grid connection through grid-connected converters has significantly changed the dynamic characteristics of modern power grids, thereby posing challenges to the security and stability of the grid. When the voltage sags and phase jump faults occur in the power grid, the DC-side power of the grid-connected converter may exceed the AC-side output power, creating an unbalanced power condition during the transient process, which can finally lead to the risk of transient power angle instability. SUMMARY An objective of the present disclosure is to provide a DC voltage control method and system for enhancing transient stability of a grid-connected converter, which can effectively solve the stability issue of the grid-connected converter when a transient grid fault occurs. To achieve the above objective, the present disclosure adopts the following solutions. A DC voltage control method for enhancing transient stability of a grid-connected converter includes the steps of: processing a control signal of a synchronization control loop by a DC-link transient energy correction module (DC-TECM) when either a power angle limit violation-based fault diagnosis module (PAV-FDM) or a voltage limit violation-based fault diagnosis module (VLV-FDM) determines that a voltage sag or phase jump fault has occurred, and subjecting a DC voltage reference value to temporary storage of unbalanced power and inertia correction;acquiring a voltage value of a DC-link capacitor, comparing the voltage value with the DC voltage reference value, and obtaining a DC voltage control output reference value through a steady-state DC voltage control module;acquiring output data of a converter at a point of common coupling (PCC), and obtaining a synchronization control signal based on the synchronization control loop;obtaining an internal electromotive force reference value through an internal electromotive force control loop based on the synchronization control signal; andgenerating converter driving signals based on the internal electromotive force reference value. The subjecting a DC voltage reference value to temporary storage of unbalanced power and inertia correction includes the steps of: acquiring an angular frequency ω of a converter output voltage, filtering a difference between the angular frequency ω and a rated value ωn by a notch filter to remove power frequency disturbance, and amplifying the difference by a damping-voltage mapping coefficient kD−V to obtain a DC voltage elevation increment ΔVPu for temporary storage of transient unbalanced power;acquiring an angular frequency change rate {dot over (ω)} of the converter output voltage, filtering the angular frequency change rate {dot over (ω)} through a low-pass filter (LPF) to remove high-frequency oscillation, and amplifying the angular frequency change rate by an inertia-voltage mapping coefficient kJ−V to obtain a DC voltage elevation increment ΔVJ for inertia correction of the converter; andmultiplying a sum ΔVdc of the DC voltage elevation increments for the temporary storage of transient unbalanced power and of the inertia correction of the converter with a fault detection s