DC control method and system for improving transient stability of grid-connected converter

Abstract

Disclosed in the present invention are a DC control method and system for improving transient stability of a grid-connected converter. The method comprises: when either a power-angle over-limit-based fault determination module or a voltage over-limit-based fault determination module determines that a voltage sag or phase jump fault has occurred in a power grid, a DC port transient energy correction module processes an angular velocity control signal of a synchronous control loop, and increases a DC voltage reference value for temporary storage of unbalanced power and inertia correction; a voltage value of a DC port capacitor is compared with the DC voltage reference value, and is processed by a steady-state DC voltage control module to obtain a DC voltage control reference value; output data of a converter at a point of common coupling is acquired, and a synchronization control signal is obtained from the synchronization control loop; and on the basis of the synchronization control signal, an internal potential reference value is obtained from an internal potential control loop, and then a converter driving signal is generated. The present invention can effectively solve the problem of stability of grid-connected converters during transient faults in the power grid.

Description

DC control methods and systems for improving the transient stability of grid-connected converters Technical Field

[0001] This invention belongs to the field of power system application technology, specifically relating to a DC control method and system for improving the transient stability of grid-connected converters. Background Technology

[0002] Faced with the dual pressures of fossil fuel depletion and climate change, countries worldwide have adopted measures to improve energy efficiency and vigorously develop clean and renewable energy sources to improve their energy structures, aiming to achieve sustainable energy supply and harmonious economic and social development. my country's 19th National Congress placed ecological civilization construction in a prominent position, requiring a strong focus on promoting green, circular, and low-carbon development, and working with the international community to actively address climate change. Controlling greenhouse gas emissions and achieving green and low-carbon development are also inherent requirements for my country to transform its development model, overcome resource and environmental constraints, and enhance its international competitiveness.

[0003] With the vigorous development of new energy power generation technologies, photovoltaic, wind power, and other new energy sources are connected to the same AC power grid through power electronic equipment. These new energy sources and the AC power grid together constitute a multi-new energy feed-in system. The grid connection of new energy sources through converters significantly changes the dynamic characteristics of modern power grids, posing challenges to the safety and stability of the grid. When voltage dips and phase jump faults occur in the grid, the DC-side power of the grid-connected converter will overflow the AC-side output power. The unbalanced power during the transient process poses a risk of transient power angle instability. Summary of the Invention

[0004] The purpose of this invention is to provide a DC control method and system for improving the transient stability of grid-connected converters, which can effectively solve the stability problem of grid-connected converters when transient faults occur in the power grid.

[0005] To achieve the above objectives, the solution of the present invention is:

[0006] A DC control method for improving the transient stability of grid-connected converters includes,

[0007] When either the fault judgment module based on power angle over-limit or the fault judgment module based on voltage over-limit determines that a voltage drop or phase jump fault has occurred in the power grid, the control signal of the synchronization control link will be processed by the DC port transient energy correction module to raise the DC voltage reference value for temporary unbalanced power and for inertia correction.

[0008] The voltage value of the DC port capacitor is obtained, compared with the DC voltage reference value, and processed by the steady-state DC voltage control module to obtain the DC voltage control reference value;

[0009] Obtain the output data of the converter at the common coupling point, and obtain the synchronization control signal according to the synchronization control link;

[0010] Based on the aforementioned synchronization control signal, an internal potential reference value is obtained according to the internal potential control loop.

[0011] The converter drive signal is generated based on the internal potential reference value.

[0012] This includes raising the DC voltage reference value to address temporary power imbalance and to correct inertia, including:

[0013] Obtain the angular velocity ω of the converter output voltage, and compare the angular velocity ω with the rated value ω. n The difference is filtered out by a notch filter to remove power frequency disturbances, and then processed by the damping-voltage mapping coefficient k. D-V Amplification yields the DC voltage rise ΔV for temporarily storing transient unbalanced power. Pu ;

[0014] Obtain the rate of change of the angular velocity of the converter output voltage rate of change of angular velocity High-frequency oscillations are filtered out by a low-pass filter, and the inertia-voltage mapping coefficient k is applied. J-V Amplification yields the DC voltage rise ΔV for converter inertia correction. J ;

[0015] The sum of the DC voltage rise ΔV for temporary unbalanced power storage and converter inertia correction is calculated. dc With fault detection signal S F Multiply and sum to the DC voltage reference value V dc_ref This allows for correction.

[0016] The design method for the inertia-voltage mapping coefficient is as follows: The inertia correction ΔJ of the converter's oscillation characteristics is determined, and the inertia-voltage mapping coefficient is calculated using the following formula: k J-V =ΔJ / k pdc , where k pdc This is the proportional coefficient in steady-state DC voltage control;

[0017] The design method for the damping-voltage mapping coefficient is as follows: Determine the damping correction ΔD for the converter's oscillation characteristics; the damping-voltage mapping coefficient is then calculated using the following formula: k D-V =(ΔD+k) idc ·k J-V ) / k pdc , where k idc This is the integral coefficient in steady-state DC voltage control.

[0018] The converter is a grid-type converter; the angular velocity ω of the converter output voltage is obtained, including...

[0019] Obtain the output voltage u of the converter at the point of common coupling. PCC and current i PCC Thus, the active power is obtained;

[0020] Based on the difference between the active power and the active power reference value, the angular velocity ω of the converter output voltage is obtained through active-phase synchronization control; or,

[0021] The converter is a grid-connected converter; the angular velocity ω of the converter output voltage is obtained, including,

[0022] Obtain the output voltage u of the converter at the point of common coupling. PCC ;

[0023] For the output voltage u PCC A phase-locked loop (PLL) process is performed to obtain the angular velocity ω of the converter output voltage.

[0024] Among these, determining whether a voltage dip or phase jump fault has occurred in the power grid includes,

[0025] When the converter experiences at least one of the following: power angle over-limit or voltage over-limit, it is considered that a voltage dip or phase jump fault has occurred in the power grid, and the fault detection signal S... F The output is 1; otherwise, the fault detection signal S is 1. F The output is 0.

[0026] Among these, determining whether the converter has exceeded its power angle limit includes,

[0027] Obtain the current power angle δ of the grid-connected converter and its initial power angle δ0 under stable operating conditions, and calculate the difference between the two.

[0028] The absolute value of the difference is compared with the power angle threshold δ. th If the absolute value exceeds the power angle threshold δ, then... th If so, it is determined that the converter has exceeded the power angle limit.

[0029] The determination of a voltage over-limit fault in the converter includes...

[0030] Obtain the voltage amplitude V of the grid-connected converter and its rated value V. n The difference;

[0031] The absolute value of the difference is compared with the voltage stability threshold V. th A comparison is made, and if the absolute value exceeds the voltage stability threshold V... th If so, it is determined that the converter has exceeded the voltage limit.

[0032] The converter is a grid-type converter; the voltage value V of the DC port capacitor is obtained. dc , and the DC voltage reference value V dc_ref By comparison, the DC voltage control reference value is obtained, including:

[0033] Obtain the voltage value V of the DC port capacitor. dc , and the DC voltage reference value V dc_ref After comparison, an active power reference value P is generated. ref , as a reference value for DC voltage control;

[0034] Obtain the converter's output data at the point of common coupling, and obtain the synchronization control signal based on the synchronization control loop, including:

[0035] Obtain the output voltage u of the converter at the point of common coupling. PCC and current i PCC The active power P is obtained. e and reactive power Q e ;

[0036] According to the active power P e With active power reference value P ref The difference is used to obtain the converter output voltage phase reference value θ; based on the reactive power Q e With reactive power reference value Q ref The difference is used to obtain the converter output voltage amplitude reference value V; the synchronization control signal includes a phase reference value θ and an amplitude reference value V;

[0037] Based on the aforementioned synchronization control signal, an internal potential reference value is obtained according to the internal potential control loop, including:

[0038] The amplitude reference value V is transformed using the phase reference value θ to obtain the output voltage reference value of the converter output voltage in the synchronous coordinate system.

[0039] The output voltage u of the converter at the point of common coupling PCC The internal potential reference value is obtained by comparing it with the output voltage reference value in the synchronous coordinate system and the difference between the two.

[0040] The converter is a grid-connected converter; the voltage value of the DC port capacitor is obtained, and compared with the DC voltage reference value V. dc_ref By comparison, the DC voltage control reference value is obtained, including:

[0041] Obtain the voltage value V of the DC port capacitor. dc , and the DC voltage reference value V dc_ref After comparison, an active current reference value I is generated. d_ref , as a reference value for DC voltage control;

[0042] Obtain the converter's output data at the point of common coupling, and obtain the synchronization control signal based on the synchronization control loop, including:

[0043] Obtain the output voltage u of the converter at the point of common coupling. PCC ;

[0044] For the output voltage u PCC A phase-locked loop is performed to obtain the angular velocity ω of the converter output voltage. Integrating this velocity yields the voltage phase θ, which serves as the synchronization control signal.

[0045] Based on the aforementioned synchronization control signal, an internal potential reference value is obtained according to the internal potential control loop, including:

[0046] Obtain the output current i of the converter at the point of common coupling. PCC , to the current i PCC Using the voltage phase θ, a coordinate transformation is performed to obtain the converter output active current I. d and reactive current I q ;

[0047] The converter output active current and active current reference value I are compared. d_ref The difference is compared to obtain the first difference; the reactive current output by the converter is compared with the preset reactive current reference value I. q_ref By comparing the results, a second difference is obtained;

[0048] The internal potential reference value is obtained based on the first difference and the second difference.

[0049] A DC control system for improving the transient stability of grid-connected converters includes,

[0050] The fault judgment module based on power angle over-limit is configured to judge whether the power grid has a voltage drop or phase jump fault.

[0051] The fault detection module based on voltage over-limit is configured to detect voltage drop or phase jump faults in the power grid.

[0052] The DC port transient energy correction module is configured to process the control signal of the synchronization control link through the DC port transient energy correction module when either the fault judgment module based on power angle over-limit or the fault judgment module based on voltage over-limit determines that a voltage drop or phase jump fault has occurred in the power grid, and to perform a boosting of the DC voltage reference value for temporary unbalanced power and a boosting for inertia correction.

[0053] The steady-state DC voltage control module is configured to acquire the voltage value of the DC port capacitor, compare it with the DC voltage reference value, and obtain a DC voltage control reference value.

[0054] The synchronization module is configured to acquire the output data of the converter at the common coupling point and obtain the synchronization control signal according to the synchronization control link.

[0055] The internal potential control module is configured to obtain an internal potential reference value based on the synchronization control signal and the internal potential control loop; and,

[0056] The pulse width modulation module is configured to generate a converter drive signal based on the internal potential reference value.

[0057] By adopting the above scheme, this invention addresses the transient stability problem faced by new energy fields with grid-connected converters under grid fault conditions. It detects grid faults in real time based on the power angle and voltage amplitude of the grid-connected converter's synchronization module. When a fault is detected, the damping correction module and inertia correction module are activated to achieve instantaneous storage of unbalanced energy at the DC port of the grid-connected converter during transient processes, thus avoiding transient instability and DC voltage exceeding limits. This invention does not affect the control structure and performance of the original grid-connected converter synchronization strategy; it only requires adding a DC port compensation stage to the original control system, making implementation convenient. This improves the transient stability of the grid-connected converter without altering its operating characteristics.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows: The control structure of the present invention is simple and the parameters are easy to adjust. It does not affect the reference power of the converter under normal grid operation, does not require mode switching between normal grid operation and fault state, and can adaptively control the DC port of the grid-connected converter to temporarily store unbalanced energy at the moment of transient grid fault, providing real-time transient stability support for the grid-connected converter. In the case of grid transient fault, it can shorten the transient process of the system, enabling the system to recover to a stable operating state in a short time, and reducing the overshoot of DC capacitor voltage, thus mitigating the risk of overvoltage at the DC port. It only uses the power angle and its derivative, voltage amplitude in the synchronous module of the grid-connected converter as feedback quantities, and does not depend on time-varying system information such as voltage drop degree and line impedance, thus avoiding the deviation of DC port temporary energy storage caused by communication delay, improving the speed of transient stability support, and reducing the complexity and implementation difficulty of the control strategy. Attached Figure Description

[0059] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 is a typical system structure and control block diagram of the grid-connected converter in an embodiment of the present invention;

[0061] Figure 2 is a control block diagram of a grid-connected converter with DC port control introduced in an embodiment of the present invention;

[0062] Figure 3 is a block diagram of a typical synchronous control loop of a grid-connected converter in an embodiment of the present invention;

[0063] Among them, (a) is the active power droop synchronization control module, (b) is the virtual synchro machine control module, (c) is the reactive power droop synchronization control module, and (d) is the phase-locked loop synchronization control module.

[0064] Figure 4 is a schematic diagram of the control effect of the present invention;

[0065] Wherein, (a) represents the DC voltage and its reference value using conventional DC voltage control, (b) represents the DC voltage and its reference value using the present invention, (c) represents the actual value and reference value of the output active power using conventional DC voltage control, (d) represents the actual value and reference value of the output active power using the present invention, (e) represents the converter output power angle (converter phase minus grid phase) using conventional DC voltage control, and (f) represents the converter output power angle (converter phase minus grid phase) using the present invention.

[0066] In the picture:

[0067] 1. Power grid; 2. Filtering equipment; 3. Grid-type converter;

[0068] 4. DC port; 4-1. DC port capacitor;

[0069] 5. DC voltage control module; 5-1. Steady-state DC voltage control module;

[0070] 5-2 Fault diagnosis module; 5-2-1 Fault diagnosis module based on power angle exceeding limit; 5-2-2 Fault diagnosis module based on voltage exceeding limit;

[0071] 5-3 DC port transient energy correction module; 5-3-1 Transient power temporary storage module; 5-3-2 Inertia correction module; 5-3-3 Reference voltage superimposed module;

[0072] 6. Synchronization Module; 6-1-1-1. Active Power Droop Synchronization Control Module; 6-1-1-2. Virtual Synchronizer Control Module; 6-1-2. Reactive Power Droop Synchronization Control Module; 6-2. Phase-Locked Loop Synchronization Control Module;

[0073] 7. Internal potential control module; 8. Pulse width modulation module. Detailed Implementation

[0074] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0075] The grid-connected converter to which this invention applies can be referred to Figure 1, including a grid-type converter 3, which has a DC port 4 on its DC side, and a DC port capacitor 4-1 connected in parallel to the DC port 4, wherein P dc V represents the active power input to the DC-side front-end stage. dc This represents the voltage of the DC-side capacitor; the AC side of the grid-type converter 3 is connected to the infinite power grid 1 through a filter device 2, wherein the filter device 2 includes a capacitor L. f and voltage C f The connection point after the filter device becomes a common coupling point, u PCC and i PCC These represent the voltage and current at the common coupling point, respectively; the infinite power grid 1 is composed of the grid-side impedance Z. g and ideal voltage source V g e jθg Characterization.

[0076] This invention provides a DC control method for improving the transient stability of grid-connected converters, comprising the following steps:

[0077] Step 1: When either the fault judgment module based on power angle exceeding the limit or the fault judgment module based on voltage exceeding the limit determines that a voltage drop or phase jump fault has occurred in the power grid, the control signal of the synchronization control link is processed by the DC port transient energy correction module to raise the DC voltage reference value for temporary unbalanced power and for inertia correction.

[0078] Step 2: Obtain the voltage value of the DC port capacitor, compare it with the DC voltage reference value, and obtain the DC voltage control reference value through the steady-state DC voltage control module;

[0079] Step 3: Obtain the output data of the converter at the common coupling point, and obtain the synchronization control signal according to the synchronization control link;

[0080] Step 4: Based on the synchronization control signal, obtain the internal potential reference value according to the internal potential control loop;

[0081] Step 5: Generate a converter drive signal based on the internal potential reference value;

[0082] Steps 2-5 are the conventional control flow of existing grid-connected converters. The improvement of this invention is that, without affecting the existing control strategy, a DC port compensation link is added to control the DC port of the grid-connected converter to temporarily store unbalanced energy at the moment when a transient fault occurs in the power grid, so as to provide real-time transient stability support for the grid-connected converter and improve the speed of transient stability support.

[0083] In step 1, the DC voltage reference value is increased to address both temporary unbalanced power and inertia correction, including:

[0084] Obtain the angular velocity ω of the converter output voltage, and compare the angular velocity ω with the rated value ω. n The difference is filtered out by a notch filter to remove power frequency disturbances, and then processed by the damping-voltage mapping coefficient k. D-V Amplification yields the DC voltage rise ΔV for temporarily storing transient unbalanced power. Pu ;

[0085] Obtain the rate of change of the angular velocity of the converter output voltage rate of change of angular velocity High-frequency oscillations are filtered out by a low-pass filter, and the inertia-voltage mapping coefficient k is applied. J-V Amplification yields the DC voltage rise ΔV for converter inertia correction. J ;

[0086] The sum of the DC voltage rise ΔV for temporary unbalanced power storage and converter inertia correction is calculated. dc With fault detection signal S F Superimposed on the DC voltage reference value V dc_ref This allows for correction.

[0087] The design method for the inertia-voltage mapping coefficient is as follows: The inertia correction ΔJ of the converter's oscillation characteristics is determined, and the inertia-voltage mapping coefficient is calculated using the following formula: k J-V =ΔJ / k pdc , where k pdc This is the proportional coefficient in steady-state DC voltage control;

[0088] The design method for the damping-voltage mapping coefficient is as follows: Determine the damping correction ΔD for the converter's oscillation characteristics; the damping-voltage mapping coefficient is then calculated using the following formula: k D-V =(ΔD+k) idc ·k J-V ) / k pdc , where k idc This is the integral coefficient in steady-state DC voltage control.

[0089] The converter is a grid-type converter; the angular velocity ω of the converter output voltage is obtained, including...

[0090] Obtain the output voltage u of the converter at the point of common coupling. PCC and current i PCC Thus, the active power is obtained;

[0091] Based on the difference between the active power and the active power reference value, the angular velocity ω of the converter output voltage is obtained through active-phase synchronization control; or,

[0092] The converter is a grid-connected converter; the angular velocity ω of the converter output voltage is obtained, including,

[0093] Obtain the output voltage u of the converter at the point of common coupling. PCC ;

[0094] For the output voltage u PCC A phase-locked loop (PLL) process is performed to obtain the angular velocity ω of the converter output voltage.

[0095] In step 1, determining whether a voltage drop or phase jump fault has occurred in the power grid includes,

[0096] When the converter experiences at least one of the following: power angle over-limit or voltage over-limit, it is considered that a voltage dip or phase jump fault has occurred in the power grid, and the fault detection signal S... F The output is 1; otherwise, the fault detection signal S is 1. F The output is 0.

[0097] Among these, determining whether the converter has exceeded its power angle limit includes,

[0098] Obtain the current power angle δ of the grid-connected converter and its initial power angle δ0 under stable operating conditions, and calculate the difference between the two.

[0099] The absolute value of the difference is compared with the power angle threshold δ. th If the absolute value exceeds the power angle threshold δ, then... th If so, it is determined that the converter has exceeded the power angle limit.

[0100] The determination of a voltage over-limit fault in the converter includes...

[0101] Obtain the voltage amplitude V of the grid-connected converter and its rated value V. n The difference;

[0102] The absolute value of the difference is compared with the voltage stability threshold V. th A comparison is made, and if the absolute value exceeds the voltage stability threshold V... th If so, it is determined that the converter has exceeded the voltage limit.

[0103] Among them, the active power-phase synchronization control can adopt a variety of schemes, such as droop control scheme, virtual synchronizing machine control scheme, etc., and is not limited to this embodiment;

[0104] Among them, the droop control scheme refers to applying the difference between active power and the active power reference value through an active-frequency droop coefficient K. p The angular velocity ω is obtained by magnification;

[0105] Among them, the virtual synchronous machine control scheme refers to using the difference between active power and the active power reference value through the inertia coefficient J. p With damping coefficient D p The angular velocity ω is obtained by simulating the frequency response of the synchronous machine.

[0106] The converter is a grid-type converter; step 2 specifically includes...

[0107] Obtain the voltage value V of the DC port capacitor. dc , and the DC voltage reference value V dc_ref After comparison, an active power reference value P is generated. ref , as a reference value for DC voltage control;

[0108] The specific content of step 3 includes:

[0109] Obtain the output voltage u of the converter at the point of common coupling. PCC and current i PCC The active power P is obtained. e and reactive power Q e ;

[0110] According to the active power P e With active power reference value P ref The difference is used to obtain the converter output voltage phase reference value θ; based on the reactive power Q e With reactive power reference value Q ref The difference is used to obtain the converter output voltage amplitude reference value V; the synchronization control signal includes a phase reference value θ and an amplitude reference value V;

[0111] The specific content of step 4 includes,

[0112] The amplitude reference value V is transformed using the phase reference value θ to obtain the output voltage reference value of the converter output voltage in the synchronous coordinate system.

[0113] The output voltage u of the converter at the point of common coupling PCC The internal potential reference value is obtained by comparing it with the output voltage reference value in the synchronous coordinate system and the difference between the two.

[0114] The converter is a grid-connected converter; step 2 specifically includes...

[0115] Obtain the voltage value V of the DC port capacitor. dc , and the DC voltage reference value V dc_ref After comparison, an active current reference value I is generated. d_ref , as a reference value for DC voltage control;

[0116] The specific content of step 3 includes:

[0117] Obtain the output voltage u of the converter at the point of common coupling. PCC ;

[0118] For the output voltage u PCC A phase-locked loop is performed to obtain the angular velocity ω of the converter output voltage. Integrating this velocity yields the voltage phase θ, which serves as the synchronization control signal.

[0119] The specific content of step 4 includes,

[0120] Obtain the output current i of the converter at the point of common coupling. PCC , to the current i PCC Using the voltage phase θ for coordinate transformation, the converter output active current I is obtained. d and reactive current I q ;

[0121] The converter output active current and active current reference value I are compared. d_ref The difference is compared to obtain the first difference; the reactive current output by the converter is compared with the preset reactive current reference value I. q_ref By comparing the values, a second difference is obtained;

[0122] The internal potential reference value is obtained based on the first difference and the second difference.

[0123] As shown in Figures 1 and 2, this embodiment of the invention also provides a DC control system for improving the transient stability of grid-connected converters, comprising:

[0124] DC voltage control module 5 is used to receive the voltage value V of the DC port capacitor. dc , and the DC voltage reference value V dc_ref After comparison, an active power or active current reference value is generated, and the active power reference value P is... ref Or active current reference value I d_ref Input to synchronization module 6;

[0125] The DC voltage control module 5 includes: a steady-state DC voltage control module 5-1, a fault judgment module 5-2, and a DC port transient energy correction module 5-3;

[0126] The steady-state DC voltage control module 5-1 receives the voltage value V of the DC port capacitor of the converter. dc , compared with the preset DC voltage reference value V dc_ref After differential input DC voltage, dual-channel zero steady-state error regulator output converter AC side active power reference value P ref Or active current reference value I d_ref .

[0127] The fault judgment module 5-2 consists of a fault judgment module 5-2-1 based on power angle exceeding the limit and a fault judgment module 5-2-2 based on voltage exceeding the limit. The fault judgment module 5-2-1 based on power angle exceeding the limit calculates the difference between the power angle δ calculated by the grid-connected converter synchronization module and its initial point δ0 under stable operating conditions. After absolute transformation, this difference is compared with the power angle threshold δ. th The voltage amplitude V of the grid-connected converter is compared with its rated value V. If the voltage exceeds the threshold, the system is considered to have failed. The fault judgment module 5-2-2 based on voltage over-limit calculates the voltage amplitude V of the grid-connected converter and its rated value V. n The difference, after being absoluteized, is compared with the voltage stability threshold. If it exceeds the threshold V... th If this occurs, it is considered a system fault. For grid-connected converters, the output voltage reference value V of the reactive power droop control module in the synchronization module is used. o_ref Perform fault diagnosis; for grid-connected converters, use the d-axis voltage amplitude V in the coordinate transformation module. PCC_d Perform fault diagnosis.

[0128] The fault judgment module 5-2-1 based on power angle over-limit and the fault judgment module 5-2-2 based on voltage over-limit operate in parallel. If the detection result of either module is a fault occurrence, the system is considered to have a fault.

[0129] The DC port transient energy correction module 5-3 consists of a transient power storage loop 5-3-1, an inertia correction loop 5-3-2, and a reference voltage superimposed circuit 5-3-3; the transient power storage loop 5-3-1 receives the angular velocity ω from the synchronization module 6 and its rated value ω. n The difference is processed through a damping-voltage mapping stage to obtain the damping correction amount for the oscillation characteristics of the grid-connected converter. This temporarily stores the unbalanced power of the AC port at the DC port of the converter, effectively increasing the unbalanced energy consumed by the damping effect during the transient process. The damping amplification factor of the damping-voltage mapping stage can be set according to the required damping enhancement target, such as 1.5 or 2. The inertia correction module 5-3-2 receives the rate of change of angular velocity from the synchronization module 6. After low-pass filtering, the inertia correction value for the grid-connected converter's oscillation characteristics is obtained through an inertia-voltage mapping stage. This accelerates the transient process of the grid-connected converter and reduces the voltage rise at the DC port. The inertia amplification factor of the inertia-voltage mapping stage can be set according to the desired inertia enhancement target. The reference voltage superimposed circuit 5-3-3 sums the damping correction value and the inertia correction value (ΔV). dc ) 2 With fault detection signal S F The DC voltage reference value V under steady-state conditions dc_ref The DC voltage reference value for AC / DC power balance under grid fault conditions is obtained by superimposing the values.

[0130] Synchronization module 6 is used to synchronize the output voltage u of the grid-connected converter at the point of common coupling. PCC and current i PCC Calculate the amplitude and phase of the converter output voltage or current, and input the amplitude V and phase θ of the converter output voltage or current to the internal potential control module 7.

[0131] For grid-connected converters, a power calculation module is used to calculate the active and reactive power output of the converter; a grid-connected power synchronization module is used to calculate the phase of the converter output voltage based on the active power value and active power reference value, and to calculate the amplitude of the converter output voltage based on the reactive power value and reactive power reference value. The amplitude and phase of the converter output voltage are then input to the output internal potential control module. For grid-connected converters, a grid-connected voltage synchronization module is used to calculate the voltage phase and amplitude on the grid side based on the converter's common coupling point voltage, and then outputs this information to the internal potential control module 7.

[0132] For the aforementioned grid-type power synchronization module, the active power synchronization module includes droop control, virtual synchronizing machine control, and matching control; as shown in Figure 3, the active power droop synchronization control module 6-1-1-1 synchronizes the active power P... e With active power reference value P ref The difference is processed by the active-frequency droop coefficient K. p The angular velocity ω is obtained by amplification; the virtual synchronous machine control module 6-1-1-2 converts the active power P e With active power reference value P ref The difference is obtained through the inertia coefficient J p With damping coefficient D p The angular velocity ω is obtained by simulating the frequency response of the synchronous machine. The reactive power droop synchronization control module 6-1-2 uses droop control, receiving the reactive power Q output from the AC side of the converter. e Its reference value Q ref The offset, via the reactive droop coefficient K qAdjust the reference value V for generating the output voltage amplitude o_ref .

[0133] For the voltage synchronization module with the grid converter, the voltage u at the common coupling point of the grid converter will be... PCC Input the phase-locked loop synchronization control module 6-2 to perform an abc / dq coordinate transformation, converting the q-axis component U of the voltage passing through the common coupling point. PCC_q Perform proportional-integral processing to calculate the phase of the grid-side voltage, based on the d-axis component U of the voltage at the point of common coupling. PCC_d Calculate the magnitude of the voltage on the grid side.

[0134] The internal potential control module 7 is used to compare the phase and amplitude of the converter output voltage or current with the actual value to generate an internal potential reference value, and input the internal potential reference value into the pulse width modulation module 8.

[0135] For grid-type converters, the internal potential control module 7 consists of a voltage control module and a current control module. The voltage control module compares the converter output voltage reference value with the actual value to generate a current reference value, and inputs the current reference value into the current control module. The current control module compares the current reference value with the actual value to generate an internal potential reference value, and inputs the voltage reference value before the filter equipment into the pulse width modulation module. For grid-connected converters, the common coupling point current is transformed into abc / dq coordinates and compared with the dq axis current reference value to generate the internal potential reference value E. ref ;

[0136] Pulse width modulation module 8 is used to generate converter drive signals based on internal potential reference values.

[0137] The specific principle of this invention is as follows:

[0138] Under normal grid operation, the power angle and voltage in the converter synchronization module 6 are within the threshold. The fault detection module detects that no fault has occurred in the grid, and the fault detection signal output is zero. The output of the DC port transient energy correction module 5-3 is set to zero. The DC port of the grid-connected converter operates according to the preset DC voltage reference value. The DC voltage control module does not affect the normal operation and dynamic characteristics of the grid-connected converter.

[0139] When a voltage dip or phase jump fault occurs in the grid, the active power output of the grid-connected converter changes abruptly at the moment of the fault. A significant power difference arises between the active power output on the AC side of the converter and the reference active power value, causing the power angle of synchronization module 6 to rise rapidly. The q-axis voltage of the grid-connected converter also rises rapidly at the moment of the fault, causing the power angle of synchronization module 6 to rise rapidly. At this time, the power angle difference received by the fault detection module 5-2-1 based on power angle sag exceeds a threshold, indicating a fault has occurred. Since the power angle characteristic is a direct factor leading to transient instability, the fault detection module based on power angle sag can achieve accurate detection of grid faults. When the grid voltage dips... When a fault or phase jump fault occurs, the reactive power output of the grid-connected converter changes abruptly at the moment of the fault. A large power difference arises between the reactive power output measured by the AC side of the converter and the reactive power reference value, causing the voltage amplitude of the synchronization module 6 to rise rapidly. When a voltage drop fault or phase jump fault occurs in the grid, the d-axis voltage in the synchronization link 6 of the grid-connected converter changes abruptly at the moment of the fault. At this time, the difference received by the voltage sag-based fault detection module 5-2-2 exceeds the threshold, and it is judged that a fault has occurred. Due to the fast response characteristics of the reactive power synchronization module / coordinate transformation module, the voltage sag-based fault detection module can realize the rapid and timely detection of grid faults.

[0140] When any fault detection module detects a fault, the fault detection signal outputs 1, and the DC port transient energy correction module 5-3 starts working. The transient power storage loop 5-3-1 receives the difference between the angular velocity in the synchronization module 6 and its rated value, and after damping-voltage mapping, obtains the DC voltage rise for transient power storage. The inertia correction module 5-3-2 receives the rate of change of angular velocity in the synchronization module 6, performs low-pass filtering, and after inertia-voltage mapping, obtains the DC voltage rise for inertia correction. The sum of the DC voltage rise for transient power storage and the DC voltage rise for inertia correction is multiplied by the fault detection signal. After passing through the reference voltage superimposed module 5-3-3, the DC voltage reference value under transient fault conditions is raised, changing the dynamic characteristics of the DC port, enabling the DC port to transiently store and compensate for the converter power difference. The converter unbalanced power reduced by the DC port reduces the power angle overshoot, avoiding the potential risk of converter transient power angle instability, and simultaneously limiting and protecting the DC voltage.

[0141] Figure 4 (left and right) illustrates the effects of traditional DC control and improved DC control, respectively. It demonstrates that the DC control method proposed in this invention enables the grid-connected converter to maintain synchronization with the grid under transient faults, avoiding the risk of transient instability. The control method, which does not require mode switching, does not affect the converter's operating point in steady state and can trigger control instantaneously upon fault occurrence, avoiding the instability risk caused by communication delays. This control method accelerates the converter's transient process, shortens the overshoot of the DC capacitor voltage, and avoids the risk of overvoltage at the DC port.

[0142] Based on the same inventive concept, this invention also provides a computer device, comprising: one or more processors, and a memory for storing one or more computer programs; the programs include program instructions, and the processor executes the program instructions stored in the memory. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, used to implement one or more instructions, specifically for loading and executing one or more instructions stored in a computer storage medium to implement the above-described method.

[0143] It should be further explained that, based on the same inventive concept, the present invention also provides a computer storage medium storing a computer program, which, when executed by a processor, performs the above-described method. This storage medium can be any combination of one or more computer-readable media. The computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of computer-readable storage media (a non-exhaustive list) include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In the present invention, the computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0144] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0145] The foregoing has shown and described the basic principles, main features, and advantages of this disclosure. Those skilled in the art should understand that this disclosure is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this disclosure. Various changes and modifications can be made to this disclosure without departing from its spirit and scope, and all such changes and modifications fall within the scope of this disclosure as claimed.

Claims

1. A DC control method for improving the transient stability of grid-connected converters, characterized in that: include, When either the fault judgment module based on power angle over-limit or the fault judgment module based on voltage over-limit determines that a voltage drop or phase jump fault has occurred in the power grid, the angular velocity control signal of the synchronization control link is processed by the DC port transient energy correction module to raise the DC voltage reference value for temporary unbalanced power and for inertia correction. The voltage value of the DC port capacitor is obtained, compared with the DC voltage reference value, and processed by the steady-state DC voltage control module to obtain the DC voltage control reference value; Obtain the output data of the converter at the common coupling point, and obtain the synchronization control signal according to the synchronization control link; Based on the aforementioned synchronization control signal, an internal potential reference value is obtained according to the internal potential control loop. The converter drive signal is generated based on the internal potential reference value.

2. The method as described in claim 1, characterized in that: The DC voltage reference value is increased to accommodate temporary unbalanced power and to correct inertia, including: Obtain the angular velocity ω of the converter output voltage, and compare the angular velocity ω with the rated value ω. n The difference is filtered out by a notch filter to remove power frequency disturbances, and then processed by the damping-voltage mapping coefficient k. D-V Amplification yields the DC voltage rise ΔV for temporarily storing transient unbalanced power. Pu ; Obtain the rate of change of the angular velocity of the converter output voltage rate of change of angular velocity High-frequency oscillations are filtered out by a low-pass filter, and the inertia-voltage mapping coefficient k is applied. J-V Amplification yields the DC voltage rise ΔV for converter inertia correction. J ; The sum of the DC voltage rise ΔV for temporary unbalanced power storage and converter inertia correction is calculated. dc With fault detection signal S F Multiply and sum to the DC voltage reference value V dc_ref This allows for correction.

3. The method as described in claim 2, characterized in that: The design method for the inertia-voltage mapping coefficient is as follows: The inertia correction ΔJ for the converter's oscillation characteristics is determined, and the inertia-voltage mapping coefficient is calculated using the following formula: k J-V =ΔJ / k pdc , where k pdc This refers to the proportional coefficient in steady-state DC voltage control. The design method for the damping-voltage mapping coefficient is as follows: Determine the damping correction ΔD for the converter's oscillation characteristics; the damping-voltage mapping coefficient is then calculated using the following formula: k D-V =(ΔD+k) idc ·k J-V ) / k pdc , where k idc This is the integral coefficient in steady-state DC voltage control.

4. The method as described in claim 2, characterized in that: The converter is a grid-type converter; the angular velocity ω of the converter output voltage is obtained, including... Obtain the output voltage u of the converter at the point of common coupling. PCC and current i PCC Thus, the active power is obtained; Based on the difference between the active power and the active power reference value, the angular velocity ω of the converter output voltage is obtained through active-phase synchronization control. or, The converter is a grid-connected converter; To obtain the angular velocity ω of the converter output voltage, including, Obtain the output voltage u of the converter at the point of common coupling. PCC ; For the output voltage u PCC A phase-locked loop (PLL) process is performed to obtain the angular velocity ω of the converter output voltage.

5. The method as described in claim 1, characterized in that: Determining whether a voltage dip or phase jump fault has occurred in the power grid includes: When the converter experiences at least one of the following: power angle over-limit or voltage over-limit, it is considered that a voltage dip or phase jump fault has occurred in the power grid, and the fault detection signal S... F The output is 1; otherwise, the fault detection signal S is 1. F The output is 0.

6. The method as described in claim 5, characterized in that: Determining if the converter has exceeded its power angle limit includes: Obtain the current power angle δ of the grid-connected converter and its initial power angle δ0 under stable operating conditions, and calculate the difference between the two. The absolute value of the difference is compared with the power angle threshold δ. th If the absolute value exceeds the power angle threshold δ, a comparison is made. th If so, it is determined that the converter has exceeded the power angle limit.

7. The method as described in claim 5, characterized in that: Determining if a converter experiences a voltage over-limit event includes: Obtain the voltage amplitude V of the grid-connected converter and its rated value V. n The difference; The absolute value of the difference is compared with the voltage stability threshold V. th A comparison is made; if the absolute value exceeds the voltage stability threshold V... th If so, it is determined that the converter has exceeded the voltage limit.

8. The method as described in claim 1, characterized in that: The converter is a grid-type converter; the voltage value V of the DC port capacitor is obtained. dc , and the DC voltage reference value V dc_ref By comparison, the DC voltage control reference value is obtained, including: Obtain the voltage value V of the DC port capacitor. dc , and the DC voltage reference value V dc_ref After comparison, an active power reference value P is generated. ref , as a reference value for DC voltage control; Obtain the converter's output data at the point of common coupling, and obtain the synchronization control signal based on the synchronization control loop, including: Obtain the output voltage u of the converter at the point of common coupling. PCC and current i PCC The active power P is obtained. e and reactive power Q e ; According to the active power P e With active power reference value P ref The difference is used to obtain the converter output voltage phase reference value θ; based on the reactive power Q e With reactive power reference value Q ref The difference is used to obtain the converter output voltage amplitude reference value V; the synchronization control signal includes a phase reference value θ and an amplitude reference value V; Based on the aforementioned synchronization control signal, an internal potential reference value is obtained according to the internal potential control loop, including: The amplitude reference value V is transformed using the phase reference value θ to obtain the output voltage reference value of the converter output voltage in the synchronous coordinate system. The output voltage u of the converter at the point of common coupling PCC The internal potential reference value is obtained by comparing it with the output voltage reference value in the synchronous coordinate system and the difference between the two.

9. The method as described in claim 1, characterized in that: The converter is a grid-connected converter; the voltage value of the DC port capacitor is obtained, and compared with the DC voltage reference value V. dc_ref By comparison, the DC voltage control reference value is obtained, including: Obtain the voltage value V of the DC port capacitor. dc , and the DC voltage reference value V dc_ref After comparison, an active current reference value I is generated. d_ref , as a reference value for DC voltage control; Obtain the converter's output data at the point of common coupling, and obtain the synchronization control signal based on the synchronization control loop, including: Obtain the output voltage u of the converter at the point of common coupling. PCC ; For the output voltage u PCC A phase-locked loop is performed to obtain the angular velocity ω of the converter output voltage. Integrating this velocity yields the voltage phase θ, which serves as the synchronization control signal. Based on the aforementioned synchronization control signal, an internal potential reference value is obtained according to the internal potential control loop. include, Obtain the output current i of the converter at the point of common coupling. PCC , to the current i PCC Using the voltage phase θ for coordinate transformation, the converter output active current I is obtained. d and reactive current I q ; The converter output active current and active current reference value I are compared. d_ref Compare the results to obtain the first difference; The reactive current output by the converter is compared with the preset reactive current reference value I. q_ref By comparing the results, a second difference is obtained; The internal potential reference value is obtained based on the first difference and the second difference.

10. A DC control system for improving the transient stability of grid-connected converters, characterized in that: include, The fault judgment module based on power angle over-limit is configured to judge whether the power grid has a voltage drop or phase jump fault. The fault detection module based on voltage over-limit is configured to detect voltage drop or phase jump faults in the power grid. The DC port transient energy correction module is configured to process the control signal of the synchronization control link through the DC port transient energy correction module when either the fault judgment module based on power angle over-limit or the fault judgment module based on voltage over-limit determines that a voltage drop or phase jump fault has occurred in the power grid, thereby increasing the DC voltage reference value for temporary unbalanced power and for inertia correction. The steady-state DC voltage control module is configured to acquire the voltage value of the DC port capacitor, compare it with the DC voltage reference value, and obtain a DC voltage control reference value. The synchronization module is configured to acquire the output data of the converter at the common coupling point and obtain the synchronization control signal according to the synchronization control link. The internal potential control module is configured to obtain an internal potential reference value based on the synchronization control signal and the internal potential control link. as well as, The pulse width modulation module is configured to generate a converter drive signal based on the internal potential reference value.

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