Direct-current side voltage reference value setting method and apparatus, storage medium, and device

Abstract

The present invention discloses a direct-current side voltage reference value setting method and apparatus, a storage medium, and a device. During low-voltage ride-through, direct-current side operation characteristics under different power grid voltage drop conditions are carefully considered. On the basis of different power grid voltage drop conditions, a corresponding strategy is executed to reduce a direct-current voltage reference value, so that a high modulation factor can be maintained during an entire low-voltage ride-through process, switching loss of a grid-forming converter can be reduced, and output waveform quality can be improved. During high-voltage ride-through, because constant-voltage control is adopted, the grid-forming converter may lose balance points. Therefore, according to differences in power grid voltage rise amplitude, the present invention divides a direct-current side reference value setting algorithm into three conditions, and provides an algorithm for maintaining a minimum active current required to stabilize a bus voltage of the direct-current side, so as to ensure that direct-current voltage remains controllable during the entire ride-through process.

Description

A DC side voltage reference value setting method, device, storage medium and equipment Technical Field

[0001] The present invention relates to a method, device, storage medium and equipment for setting a DC side voltage reference value, and belongs to the field of control and protection. Background Art

[0002] In recent years, with the integration of a high proportion of power electronic equipment and a high proportion of renewable energy into the power grid, the power system has gradually developed in the direction of low inertia and weak damping. Power electronic converters have gradually become dominant, and in terms of control, they show the characteristics of multi-level control synergy. Compared with traditional power grids, high-proportion renewable energy power systems involve wider time scale dynamics, which requires them to respond to disturbances within a wide frequency domain. Unlike traditional power grids, high-proportion renewable energy power systems are mainly supported by grid-type converters for voltage and frequency. At the same time, grid-type converters must have a certain fault ride-through capability to ensure the reliable operation of the power system. Current grid-type converters need to achieve stable operation on the DC side, which is a prerequisite for the new energy power system to complete fault ride-through.

[0003] Current grid-type converters typically employ constant voltage control on the DC side during fault ride-through. This approach is broadly divided into two types: For two-stage new energy systems, this involves incorporating DC-side constant voltage control into the chopper circuit or rectifier; for single-stage new energy systems, this approach incorporates DC-side control by improving the grid-type converter control strategy, thereby achieving constant control of the DC bus during fault ride-through.

[0004] However, when the grid-type converter performs high and low voltage ride-through, the use of constant voltage control on the DC side will inevitably sacrifice the quality of the system output waveform. Similarly, for the high voltage ride-through of the grid-type converter, maintaining a constant DC side voltage may cause the grid-type converter to lose its balance point, further causing new energy to be disconnected from the grid.

[0005] Summary of the Invention

[0006] The present invention provides a method, device, storage medium and equipment for setting a DC side voltage reference value, which solve the problems disclosed in the background technology.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A method for setting a DC side voltage reference value, comprising:

[0009] Performing low voltage ride-through in response to a fault ride-through signal of the grid-type converter, and calculating a DC side voltage reference value of the grid-type converter during the low voltage ride-through according to a grid voltage drop during the low voltage ride-through;

[0010] In response to the fault ride-through signal of the grid-type converter, a high-voltage ride-through is performed. According to the grid voltage rise amplitude during the high-voltage ride-through, the minimum active current of the grid-type converter required to maintain the stability of the DC-side bus voltage of the grid-type converter is considered, and the DC-side voltage reference value of the grid-type converter during the high-voltage ride-through is calculated.

[0011] The grid voltage drop conditions include single-phase grid voltage drop, two-phase grid voltage drop and three-phase symmetrical grid voltage drop;

[0012] According to the grid voltage drop, the DC side voltage reference value of the grid-connected converter during low voltage ride-through is calculated, including:

[0013] If the grid voltage drops in a single phase, the DC side voltage reference value of the grid-connected converter during low voltage ride-through is the DC side voltage of the grid-connected converter during steady-state operation.

[0014] If the grid voltage drops in two phases, the DC side voltage reference value of the grid-connected converter during low voltage ride-through is calculated based on the maximum difference between any two phase voltages.

[0015] If the three-phase grid voltage drops symmetrically and the voltage drop ratio calculated based on the three-phase voltage is not less than the threshold, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated based on the voltage drop ratio and the DC side voltage of the grid-type converter during steady-state operation;

[0016] If the three-phase grid voltage drops symmetrically and the voltage drop ratio calculated based on the three-phase voltage is less than the threshold, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated based on the threshold and the DC side voltage of the grid-type converter during steady-state operation.

[0017] According to the maximum difference between any two phase voltages, the DC side voltage reference value of the grid-connected converter during low voltage ride-through is calculated using the formula:

[0018] Where U dc_ref is the DC side voltage reference value of the grid-type converter, V1 and V2 are the two-phase voltage peaks with the largest difference.

[0019] According to the voltage drop ratio and the DC side voltage of the grid-type converter during steady-state operation, the DC side voltage reference value of the grid-type converter is calculated. The formula is: U dc_ref =J*U dc0

[0020] Where U dc_ref is the DC side voltage reference value of the grid-type converter, U dc0 is the DC side voltage of the grid-type converter during steady-state operation, is the voltage drop ratio, V a 、V b 、V cis the three-phase voltage, and V0 is the PCC point voltage of the grid-type converter during rated operation.

[0021] According to the threshold value and the DC side voltage of the grid-type converter during steady-state operation, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated as follows: U dc_ref =A*U dc0

[0022] Where U dc_ref is the DC side voltage reference value of the grid-type converter, U dc0 is the DC side voltage of the grid-type converter during steady-state operation, and A is the threshold.

[0023] In response to a fault ride-through signal of the grid-type converter, a high voltage ride-through is performed. Based on the grid voltage rise amplitude during the high voltage ride-through, the minimum active current of the grid-type converter required to maintain the DC-side bus voltage stability of the grid-type converter is considered, and a DC-side voltage reference value of the grid-type converter during the high voltage ride-through is calculated, including:

[0024] If during the process of grid voltage rising|V g |<U dc / m-ω g L g I max , or U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 <i od1max The reference value of the DC side voltage of the grid-type converter during high-voltage ride-through is the DC side voltage of the grid-type converter during steady-state operation; where V g is the grid voltage, U dc is the DC bus voltage of the grid-type converter, m is the modulation coefficient, ω g is the grid angular frequency, L g is the equivalent inductance of the power grid, I max is the upper limit of the current of the grid-type converter, i dc1 =2i L U dc / (3V gd ) is the minimum active current of the grid converter required to maintain the DC bus voltage stability of the grid converter, i L The current injected into the grid-type converter for the new energy power generation system, V gd is the d-axis component of the grid voltage, i od1max The maximum active current that the grid-type converter can output;

[0025] If the grid voltage rises during the process of U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 ≥i od1max , or |V g |>U dc / m+ω g L g I max , use a fixed step size to adjust the DC side voltage of the grid-type converter until the adjusted DC side voltage of the grid-type converter is not less than U dcmax or i dc1 ≤i od1max , according to the adjusted DC side voltage of the grid-type converter, calculate the DC side voltage reference value of the grid-type converter during high voltage ride-through; where U dcmax is the maximum voltage on the DC side of the grid-type converter.

[0026] If U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 ≥i od1max The initial DC side voltage of the grid-type converter is the DC side voltage of the grid-type converter during steady-state operation. The fixed step size is

[0027] If |V g |>U dc / m+ω g L g I max , the initial DC side voltage U of the grid-connected converter dc_base =m(V gd -ω g L g I max ), the fixed step size is

[0028] A DC side voltage reference value setting device, comprising:

[0029] A first response module performs low voltage ride-through in response to a fault ride-through signal of the grid-type converter, and calculates a DC side voltage reference value of the grid-type converter during the low voltage ride-through according to a voltage drop of the grid during the low voltage ride-through;

[0030] The second response module performs high-voltage ride-through in response to the fault ride-through signal of the grid-type converter. According to the voltage rise amplitude of the grid during the high-voltage ride-through, the minimum active current of the grid-type converter required to maintain the stability of the DC-side bus voltage of the grid-type converter is considered to calculate the DC-side voltage reference value of the grid-type converter during the high-voltage ride-through.

[0031] A computer-readable storage medium stores one or more programs, wherein the one or more programs include instructions. When the instructions are executed by a computing device, the computing device executes a method for setting a DC link voltage reference value.

[0032] A computer device includes one or more processors and one or more memories, wherein one or more programs are stored in the one or more memories and are configured to be executed by the one or more processors, wherein the one or more programs include instructions for executing a method for setting a DC link voltage reference value.

[0033] The beneficial effects achieved by the present invention are as follows: for the case of low voltage crossing, the present invention calculates the DC side voltage reference value of the grid-type converter during low voltage crossing according to the grid voltage drop situation, and then executes a corresponding strategy to reduce the DC voltage reference value, which can maintain a high modulation factor during the entire low voltage crossing process, reduce the switching loss of the grid-type converter, and improve the output waveform quality; for the case of high voltage crossing, according to the different grid voltage rise amplitudes, consider the minimum active current of the grid-type converter required to maintain the stability of the DC side bus voltage, and calculate the DC side voltage reference value of the grid-type converter during high voltage crossing, which can ensure that the DC side voltage is always controllable during the entire high voltage crossing process, thereby ensuring that the grid-type converter always has a stable operating point during the fault crossing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a flow chart of a method for setting a DC side voltage reference value;

[0035] Figure 2 is a grid-connected control system for a grid-connected converter;

[0036] FIG3 is a flow chart showing the calculation of the DC side voltage reference value of the grid-type converter during low voltage ride-through;

[0037] FIG4 is a flow chart showing the calculation of the DC side voltage reference value of the grid-type converter during the high voltage ride-through;

[0038] FIG5 is a flow chart showing a fixed step size adjustment of the DC side voltage of a grid-type converter;

[0039] FIG6 is a complete flow chart of the calculation of the DC side voltage reference value of the grid-type converter. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0041] As shown in FIG1 , a method for setting a DC side voltage reference value includes the following steps:

[0042] Step 1: performing low voltage ride-through in response to a fault ride-through signal of the grid-type converter, and calculating a DC side voltage reference value of the grid-type converter during the low voltage ride-through according to the grid voltage drop during the low voltage ride-through;

[0043] Step 2: Perform high-voltage ride-through in response to the fault ride-through signal of the grid-type converter. According to the grid voltage rise amplitude during the high-voltage ride-through, the minimum active current of the grid-type converter required to maintain the DC side bus voltage stability of the grid-type converter is considered to calculate the DC side voltage reference value of the grid-type converter during the high-voltage ride-through.

[0044] The above method aims at the case of low voltage ride through. According to the grid voltage drop, the DC side voltage reference value of the grid-type converter during low voltage ride through can be calculated, and then the corresponding strategy can be executed to reduce the DC voltage reference value. A high modulation factor can be maintained during the entire low voltage ride through process, the switching loss of the grid-type converter can be reduced, and the output waveform quality can be improved. For the case of high voltage ride through, according to the different grid voltage rise amplitudes, the minimum active current of the grid-type converter required to maintain the stability of the DC side bus voltage is considered, and the DC side voltage reference value of the grid-type converter during high voltage ride through is calculated. This can ensure that the DC side voltage is always controllable during the entire high voltage ride through process, thereby ensuring that the grid-type converter always has a stable operating point during the fault ride through process.

[0045] This method is quite versatile and can be used to set the DC-side voltage reference value of a grid-connected converter. It can also be used in boost circuit control of a two-stage photovoltaic system for DC-side fault ride-through control, with parameter transfer achieved via inter-controller communication. Furthermore, this method can also be applied to two-stage direct-drive wind turbine systems. Simply by integrating the DC-side reference value setting method into the rectifier's DC-side control strategy, this optimizes waveform output quality while providing a reliable DC operating point for grid-side converter fault ride-through.

[0046] The DC-reference value setting method proposed in the present invention is applicable to any grid-type control strategy. Here, the grid-type control shown in Figure 2 is taken as an example to reflect the importance of DC-side reference value setting in the fault ride-through process of the grid-type converter, that is, the frequency and phase angle of the AC output are generated by the dynamic characteristics of the system DC voltage. The part framed by "DC-reference" in the figure adopts the above-mentioned setting method. The system limits the current through virtual impedance and adjusts the dq axis current through the fault ride-through module to meet the reactive power requirements during system fault ride-through; the power-frequency loop control rate is: ω=ω0+G DVC ·(V dc -V dcref ) θ=∫ωdt

[0047] Where ω is the output angular frequency of the grid-connected converter, ω0 is the grid synchronization angular velocity, V dc is the DC side voltage of the grid-type converter, V dcref is the DC side voltage reference value of the grid-type converter; θ is the angular position of the rotating frame dq0 in the Park and anti-Park transformation of the grid-type converter; G DVC is the DC voltage controller, which is implemented using PI control and is defined as:

[0048] Among them, K pdc is the P parameter of the DC voltage controller, K idc is the I parameter of the DC voltage controller.

[0049] When the grid-type converter fault ride-through signal performs low voltage ride-through, firstly, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated according to the grid voltage drop during low voltage ride-through.

[0050] As shown in Figure 3, when a single-phase drop in the grid voltage is detected, the output performance cannot be improved by reducing the DC link voltage because the modulation index remains unchanged at this time. That is, if a single-phase drop in the grid voltage occurs, the reference value of the DC side voltage of the grid-type converter during low voltage ride-through is the DC side voltage of the grid-type converter during steady-state operation.

[0051] When a two-phase voltage drop is detected in the grid, the DC side voltage reference value of the grid-connected converter during low voltage ride-through can be calculated based on the maximum difference between any two phase voltages. For example, when the voltage drops of phases A and C are the same and the voltage of phase B remains unchanged, the minimum DC voltage cannot be less than 0.866 times the maximum difference between the voltages of phases A and B. Assume that the voltages of phases A and B are expressed as:

[0052] Where V1 and V2 are the peak values ​​of the two-phase voltages with the largest difference, that is, the peak values ​​of the output phase voltages of phase A and phase B, ω g is the grid angular frequency, then:

[0053] at this time,

[0054] Where U dc_ref It is the DC side voltage reference value of the grid-connected converter during low voltage ride-through.

[0055] When a three-phase symmetrical drop in the grid voltage is detected, in order to keep the modulation constant, the voltage drop ratio can be set to:

[0056] Where J is the voltage drop ratio, V0 is the PCC point voltage of the grid-type converter at rated operation, V a 、V b 、V c It is a three-phase voltage obtained by sampling. In order to prevent the high-frequency components in the sampled values ​​from causing fluctuations in the DC side reference value, a first-order low-pass filter must be connected before measurement. Its parameters can be designed according to the maximum DC side voltage ripple required by the grid-type converter. The reference value of the filter cutoff frequency is 400 rad / s.

[0057] When J is not less than the threshold, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated based on the voltage drop ratio and the DC side voltage of the grid-type converter during steady-state operation. The formula can be expressed as: U dc_ref =J*U dc0

[0058] Where U dc0 is the DC side voltage of the grid-type converter during steady-state operation;

[0059] When J is less than the threshold, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated based on the threshold and the DC side voltage of the grid-type converter during steady-state operation. The formula can be expressed as: U dc_ref =A*U dc0

[0060] Where A is the threshold value. To prevent the PV grid-connected converter from crossing zero voltage when J=0, the minimum allowable value of J is set to 0.2, that is, A is 0.2.

[0061] According to the dynamic change characteristics of the grid-type converter during low voltage ride-through, the above method can give corresponding DC side reference values ​​according to the symmetrical and asymmetrical voltage drops during low voltage ride-through. In order to prevent the DC side reference value from dropping to zero during zero voltage ride-through of the photovoltaic grid-type converter, the above method sets a minimum DC side voltage drop ratio. While considering various grid voltage drop conditions, it can maintain a high modulation factor, reduce high-frequency harmonics, and improve the output waveform quality.

[0062] When the fault ride-through signal of the grid-type converter performs high-voltage ride-through, maintaining the original reference value on the DC side will cause the system to overmodulate and may also cause the grid-type converter to have no operating point. Therefore, the DC side reference value of the grid-type converter during high-voltage ride-through must be controlled.

[0063] For the system shown in Figure 2, the following two limitations should be noted:

[0064] Where, I max It is the upper limit of the current of the grid-type converter, which is generally set to the rated current I rated 1.5 times of i odq is the output current of the grid-type converter in the dq coordinate system, v odq is the output voltage of the grid-type converter in the dq coordinate system, U dc is the DC bus voltage of the grid-type converter, and m is the modulation coefficient.

[0065] According to the grid voltage rise during high voltage ride through, I rms 、V rms 、V g The relationship between the three mainly includes the following three situations, as shown in Figure 4:

[0066] When |V g |<U dc / m-ω g L g I max Obviously, the output voltage at this time is within the range that the grid-type converter can provide, that is, the DC side voltage reference value of the grid-type converter during high-voltage ride-through is the DC side voltage of the grid-type converter during steady-state operation.

[0067] When U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max , at this time, there must be at least one stable operating point in the grid-type converter, satisfying the following relationship:

[0068] Where V gd is the d-axis component of the grid voltage, i od1 and i oq1 are the active and reactive currents output by the grid-connected converter at this operating point, ω g is the grid angular frequency, L g is the equivalent inductance of the power grid, I maxIt is the upper limit of the current of the grid-type converter, which is generally set to the rated current I rated 1.5 times;

[0069] Solving the above formula, we can get i od1 and i oq1 Obviously, as the grid voltage gradually increases, i oq1 It must also be gradually increased, so the maximum active current i that the grid-type converter can output is od1max will decrease when i oq1 ≥0, obviously at this time i od1max =I max , when i oq1 When <0, the following relationship exists:

[0070] Assume that the active current of the grid-type converter (grid-type converter) required to maintain the stability of the DC bus of the grid-type converter is i dc1 : i dc1 =2i L U dc / (3V gd )

[0071] Where i L The current injected into the grid-type converter for the new energy power generation system; obviously, i od1max Must be greater than i dc1 , that is, when U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 <i od1max The DC side voltage reference value of the grid-type converter is the DC side voltage of the grid-type converter when it is in steady state operation. dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 ≥i od1max , see Figure 5, use a fixed step size to adjust the DC side voltage of the grid-type converter until the adjusted DC side voltage of the grid-type converter is not less than U dcmax or i dc1 ≤i od1max, according to the adjusted DC side voltage of the grid-type converter, calculate the DC side voltage reference value of the grid-type converter during high voltage ride through.

[0072] The specific process in Figure 5 is as follows:

[0073] 1) Assume that the initial DC side voltage of the grid-connected converter is U dc_base , fixed step size ΔU dc ;

[0074] 2) If U dc_base +ΔU dc <U dcmax , then go to 3), otherwise U dc_ref =U dc_base Among them, U dcmax is the maximum voltage on the DC side of the grid-type converter;

[0075] 3) U′ dc_ref =U dc_base +ΔU dc ;

[0076] 4) If U′ dc_ref <U dcmax , go to 5), otherwise U dc_ref =U′ dc_ref -ΔU dc ;

[0077] 5) If i od1max <i dc1 , go to 6), otherwise U dc_ref =U′ dc_ref ;

[0078] 6) U dc_base =U′ dc_ref , go to 3).

[0079] in U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max When the initial DC side voltage of the grid-type converter is the DC side voltage of the grid-type converter in steady-state operation, that is, U dc_base =U dc0 , fixed step size Where m is the modulation coefficient, which is 1 for SPWM modulation and 1 for SVPWM modulation. k is the adjustment step size, which determines the accuracy of the algorithm in Figure 5. The recommended value is 0.1.

[0080] When |Vg |>U dc / m+ω g L g I max In this case, the grid-type converter is uncontrollable and the output voltage has exceeded the operating range of the grid-type converter. The DC side reference must be controlled in the same way as in Figure 5. The only difference is that the initial grid-type converter DC side voltage U dc_base =m(V gd -ω g L g I max ), fixed step size

[0081] Based on the dynamic characteristics of grid-type converters during high-voltage ride-through, the above method divides the DC-side reference value setting algorithm into three cases according to the magnitude of the grid-side voltage rise. At the same time, it takes into account the minimum active current required to maintain the DC-side bus voltage, ensuring that the DC link voltage is always controllable. In addition, the above method can significantly improve the transient impact of sudden grid-side voltage rise on the grid-type converter, thereby avoiding the serious problem of DC-side overvoltage or overcurrent caused by the grid-type converter losing control during high-voltage ride-through.

[0082] Before running the above method, the parameters will be designed and implemented according to the following steps, as shown in Figure 6:

[0083] S1) obtaining startup parameters;

[0084] The maximum DC side voltage of the grid-type converter (U dcmax ), the PCC point voltage, grid angular frequency, grid inductance, grid converter rated current, DC voltage of grid converter during steady-state operation, grid converter switching frequency, etc. of the grid converter during rated operation; obtain the d-axis component of the grid-side voltage during rated operation of the system by measurement or calculation; obtain the minimum active current i of the grid converter required to maintain the DC bus by calculation. dc1 .

[0085] S2) testing the three-phase voltage sensor;

[0086] The system operates in open loop, and by lowering the single-phase / two-phase / three-phase grid-side voltage, it is checked whether the DC-side controller can receive accurate and stable three-phase voltage RMS signals at the PCC.

[0087] S3) Low voltage ride through DC side reference value output test;

[0088] Start the grid-type converter within the steady-state operating voltage range and appropriately lower the single-phase / two-phase / three-phase grid voltage to test whether the DC control of the grid-type converter can issue DC reference value instructions according to the corresponding mode. After a certain period of time, clear the fault voltage and test whether the reference value on the output DC side has been restored.

[0089] S4) High voltage ride through DC side reference value output test;

[0090] Appropriately increase the grid side voltage amplitude to meet U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max and situation |V g |>U dc / m+ω g L g I max , detect whether the DC side voltage satisfies the formula and regulatory relationship.

[0091] Based on the same technical solution, the present invention also discloses a virtual device of the above method, i.e., software, a DC side voltage reference value setting device, comprising:

[0092] A first response module performs low voltage ride-through in response to a fault ride-through signal of the grid-type converter, and calculates a DC side voltage reference value of the grid-type converter during the low voltage ride-through according to a voltage drop of the grid during the low voltage ride-through;

[0093] The second response module performs high-voltage ride-through in response to the fault ride-through signal of the grid-type converter, calculates the DC side voltage reference value of the grid-type converter based on the grid voltage rise amplitude during high-voltage ride-through and the minimum active current of the grid-type converter required to maintain the DC side bus voltage stability of the grid-type converter.

[0094] The data processing procedures and methods of the above modules are consistent and will not be described again here.

[0095] Based on the same technical solution, the present invention also discloses a computer-readable storage medium, which stores one or more programs, and the one or more programs include instructions. When the instructions are executed by a computing device, the computing device executes a method for setting a DC side voltage reference value.

[0096] Based on the same technical solution, the present invention also discloses a computer device, including one or more processors and one or more memories, one or more programs stored in the one or more memories and configured to be executed by the one or more processors, and the one or more programs include instructions for executing a DC side voltage reference value setting method.

[0097] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0098] The present invention is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0099] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0100] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0101] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A method for setting a DC side voltage reference value, characterized in that: include: In response to the grid-type converter fault ride-through signal, low voltage ride-through is performed, and according to the grid voltage drop during the low voltage ride-through, a DC side voltage reference value of the grid-type converter during the low voltage ride-through is calculated; In response to the fault ride-through signal of the grid-type converter, high-voltage ride-through is performed. According to the voltage rise amplitude of the power grid during the high-voltage ride-through, the minimum active current of the grid-type converter required to maintain the stability of the DC side bus voltage of the grid-type converter is calculated, and the DC side voltage reference value of the grid-type converter during the high-voltage ride-through is calculated.

2. The DC link voltage reference value setting method according to claim 1, characterized in that: The grid voltage drop conditions include single-phase grid voltage drop, two-phase grid voltage drop and three-phase symmetrical grid voltage drop; According to the grid voltage drop, the DC side voltage reference value of the grid-connected converter is calculated during low voltage ride-through, including: If the grid voltage drops in a single phase, the reference value of the DC side voltage of the grid-forming converter during low voltage ride-through is the DC side voltage of the grid-forming converter during steady-state operation; If the two-phase voltage of the grid drops, the DC side voltage reference value of the grid-connected converter during low voltage ride-through is calculated based on the maximum difference between any two-phase voltages; If the three-phase grid voltage drops symmetrically, and the voltage drop ratio calculated based on the three-phase voltage is not less than the threshold, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated based on the voltage drop ratio and the DC side voltage of the grid-type converter during steady-state operation; If the three-phase grid voltage drops symmetrically and the voltage drop ratio calculated based on the three-phase voltage is less than the threshold, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated based on the threshold and the DC side voltage of the grid-type converter during steady-state operation.

3. The DC link voltage reference value setting method according to claim 2, characterized in that: According to the maximum difference between any two phase voltages, the DC side voltage reference value of the grid-connected converter during low voltage ride-through is calculated using the formula: Where U dc_ref is the DC side voltage reference value of the grid-type converter, V1 and V2 are the two-phase voltage peaks with the largest difference.

4. The DC link voltage reference value setting method according to claim 2, characterized in that: According to the voltage drop ratio and the DC side voltage of the grid-type converter during steady-state operation, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated. The formula is: U dc_ref =J*U dc0 Where U dc_ref is the DC side voltage reference value of the grid-connected converter, U dc0 is the DC side voltage of the grid-connected converter during steady-state operation, is the voltage drop ratio, V a 、V b 、V c is the three-phase voltage, and V0 is the PCC point voltage when the grid-type converter is in rated operation.

5. The DC link voltage reference value setting method according to claim 2, characterized in that: According to the threshold value and the DC side voltage of the grid-type converter during steady-state operation, the DC side voltage reference value of the grid-type converter during low voltage ride-through is calculated. The formula is: U dc_ref =A*U dc0 Where U dc_ref is the DC side voltage reference value of the grid-connected converter, U dc0 is the DC side voltage of the grid-connected converter during steady-state operation, and A is the threshold value.

6. The DC link voltage reference value setting method according to claim 1, characterized in that: In response to the fault ride-through signal of the grid-type converter, high voltage ride-through is performed. According to the voltage rise amplitude of the power grid during the high voltage ride-through, the minimum active current of the grid-type converter required to maintain the DC side bus voltage stability of the grid-type converter is considered, and the DC side voltage reference value of the grid-type converter during the high voltage ride-through is calculated, including: If during the process of grid voltage rising|V g |<U dc / m-ω g L g I max , or U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 <i od1max , the reference value of the DC side voltage of the grid-type converter during high-voltage ride-through is the DC side voltage of the grid-type converter during steady-state operation; where V g is the grid voltage, U dc is the DC bus voltage of the grid-type converter, m is the modulation coefficient, ω g is the grid angular frequency, L g is the equivalent inductance of the power grid, I max is the upper limit of the current of the grid-connected converter, i dc1 =2i L U dc / (3V gd ) is the minimum active current of the grid-type converter required to maintain the DC bus voltage stability of the grid-type converter, i L The current injected into the grid-connected converter for the renewable energy power generation system, V gd is the d-axis component of the grid voltage, i od1max is the maximum active current that the grid-type converter can output; If the grid voltage rises during the process of U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 ≥i od1max , or |V g |>U dc / m+ω g L g I max , use a fixed step size to adjust the DC side voltage of the grid-type converter until the adjusted DC side voltage of the grid-type converter is not less than U dcmax or dc1 ≤i od1max , according to the adjusted DC side voltage of the grid-type converter, calculate the DC side voltage reference value of the grid-type converter during high voltage ride-through; where U dcmax is the maximum voltage on the DC side of the grid-connected converter.

7. The DC link voltage reference value setting method according to claim 6, characterized in that: If U dc / m-ω g L g I max ≤|V g |≤U dc / m+ω g L g I max And i dc1 ≥i od1max , the initial DC side voltage of the grid-type converter is the DC side voltage of the grid-type converter when it is in steady-state operation. At this time, the fixed step size is If |V g |>U dc / m+ω g L g I max , the initial grid-connected converter DC side voltage U dc_base =m(V gd -ω g L g I max ), the fixed step size is 8. A DC side voltage reference value setting device, characterized in that: include: The first response module performs low voltage ride-through in response to the fault ride-through signal of the grid-type converter, and calculates a DC side voltage reference value of the grid-type converter during the low voltage ride-through according to the grid voltage drop during the low voltage ride-through; The second response module performs high-voltage ride-through in response to the fault ride-through signal of the grid-type converter. According to the voltage rise amplitude of the power grid during the high-voltage ride-through, the minimum active current of the grid-type converter required to maintain the bus voltage stability on the DC side of the grid-type converter is considered to calculate the DC side voltage reference value of the grid-type converter during the high-voltage ride-through.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores one or more programs, wherein the one or more programs include instructions, and when the instructions are executed by a computing device, the computing device executes any one of the methods of claims 1 to 7.

10. A computer device, characterized in that: include: One or more processors and one or more memories, one or more programs are stored in the one or more memories and are configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the methods described in claims 1 to 7.

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