Direct current transmission control system and method for new energy island transmission, medium and equipment

Abstract

The invention provides a DC power transmission control system, method, medium and equipment for new energy island transmission, and a transmitting end island AC power grid. The DC power transmission control system comprises a new energy station, a rectifier and an inverter which are connected in sequence, and a rectifier control module connected with the rectifier and the inverter; the alternating current side of the inverter is connected with an external equivalent alternating current network; when a new energy station sends out power transmission, a rectifier control module adds frequency control for a rectifier based on a current instruction value, a rectifier frequency value and a rectifier current value in an inverter, and generates a rectifier trigger angle; and the rectifier controls the current constantly output by the direct current side of the rectifier to the inverter based on the rectifier trigger angle, and then the current is transmitted to the equivalent alternating current network by the inverter, so that stable transmission of the new energy station is realized. The rectifier control module adds frequency control to the rectifier in combination with related parameters of an inverter and the rectifier in the system, so that the current value of the direct current side of the rectifier is kept constant, and sending-end island alternating current power grid oscillation cannot be caused.

Description

Technical Field

[0001] This application belongs to the field of power electronic transmission control technology, specifically relating to a DC transmission control system, method, medium, and equipment for new energy islanded transmission. Background Technology

[0002] Line commutated converter-based high voltage direct current (LCC-HVDC) transmission, also known as conventional direct current transmission, has been widely used in long-distance, high-capacity power transmission and other applications, offering advantages such as long transmission distance, high transmission power, and low cost.

[0003] The "Shagohuang" region possesses abundant wind and solar energy resources. Due to the lack of traditional synchronous generators in the AC grid of this region, the sending-end renewable energy bases need to be connected to the DC transmission system in an islanded manner. Large-scale renewable energy base islanded DC transmission systems primarily transmit power in one direction, making the bidirectional power transmission capability of DC transmission converters unnecessary. Conventional DC transmission has significant advantages in terms of capacity, cost, and land occupation.

[0004] In existing technologies, for scenarios involving isolated transmission of new energy, the reduced system inertia can easily lead to oscillations in the transmitting-end isolated AC power grid, resulting in decreased reliability. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, in a first aspect, this application proposes a DC power transmission control system for renewable energy islanding, comprising: a sending-end islanded AC power grid; the sending-end islanded AC power grid includes a renewable energy power station, a rectifier and an inverter connected in sequence, and a rectifier control module connected to the rectifier and the inverter; the AC side of the inverter is connected to an external equivalent AC network; When the new energy power station transmits power, the rectifier control module, based on the inverter's internal current command value, rectifier frequency value, and rectifier current value, adds frequency control to the rectifier, generates a rectifier firing angle, and sends it to the rectifier. Based on the rectifier firing angle, the rectifier controls its own DC side to output a constant current to the inverter, which then transmits the current to the equivalent AC network, thus achieving stable power transmission from the new energy power station.

[0006] Preferably, the rectifier control module is specifically used for: When the new energy power station transmits power, the current command value inside the inverter, as well as the rectifier frequency value and rectifier current value are collected; based on the current command value, the rectifier frequency value, and the set additional frequency reference value, the rectifier control current command value is obtained; based on the rectifier current value and the rectifier control current command value, additional frequency control is applied to the rectifier, the rectifier firing angle is generated and sent to the rectifier.

[0007] Preferably, the rectifier control module includes: a first linear filter unit, a second linear filter unit, and a proportional-integral (PI) controller connected to each other; the first linear filter unit is connected to the rectifier and the inverter, the second linear filter unit is connected to the rectifier, and the PI controller is connected to the rectifier; When the new energy power station transmits power, the first linear filter unit collects the current command value and rectifier frequency value inside the inverter. Based on the current command value inside the inverter, the rectifier frequency value, and a set additional frequency reference value, it obtains the rectifier control current command value and sends it to the PI controller. The second linear filter unit collects the rectifier current value and sends it to the PI controller. The PI controller, based on the rectifier current value and the rectifier control current command value, adds frequency control to the rectifier, generates the rectifier firing angle, and sends it to the rectifier.

[0008] Preferably, the first linear filtering unit is specifically used for: When the new energy power station transmits power, the rectifier frequency value is divided by a set additional frequency reference value, then the negative number is taken and 1 is added to obtain the frequency change rate; the frequency change rate is filtered to obtain the filtered frequency change rate; an additional current value is generated based on the filtered frequency change rate; the sum of the current command value inside the inverter and the additional current value is used as the rectifier control current command value and sent to the PI controller.

[0009] Preferably, the PI controller is specifically used for: When the new energy power station sends out power, the difference between the rectifier control current command value and the rectifier current value is calculated to obtain the current deviation; based on the current deviation, the rectifier firing angle is generated and sent to the rectifier.

[0010] Preferably, the additional current value satisfies the following formula:

[0011] In the above formula, Indicates the additional current value. This represents the preset frequency droop coefficient. This indicates the rectifier frequency value. This indicates the set additional frequency reference value. This represents the preset scaling factor. This represents the integral coefficient during filtering. This represents the integral operator used in filtering.

[0012] Preferably, the first linear filtering unit is specifically used for: Divide the filtered frequency change rate by a preset frequency droop coefficient to obtain the adjusted frequency change rate; generate an additional current value based on the adjusted frequency change rate.

[0013] Preferably, the first linear filtering unit is specifically used for: The adjusted frequency change rate is limited to obtain a limited frequency change rate; an additional current value is generated based on the limited frequency change rate.

[0014] Preferably, the new energy power station includes: a new energy wind power station and a new energy photovoltaic power station; the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are connected to the AC side of the rectifier; When the new energy power station sends out power, the current output from the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are collected and sent to the AC side of the rectifier.

[0015] Preferably, the sending-end islanded AC grid further includes: a first grid-side converter and a second grid-side converter; the wind turbine power station of the new energy wind power station is connected to the first grid-side converter; the photovoltaic power station of the new energy photovoltaic power station is connected to the second grid-side converter; then the first grid-side converter and the second grid-side converter are combined and connected to the AC side of the rectifier; When the new energy power station transmits power, the first grid-side converter controls the stability of the voltage and frequency of the current transmitted by the wind turbine power station of the new energy wind power station during its transmission process; the second grid-side converter controls the stability of the voltage and frequency of the current transmitted by the photovoltaic power station of the new energy photovoltaic power station during its transmission process. Both the first grid-side converter and the second grid-side converter are grid-type converters.

[0016] Secondly, this application also proposes a DC transmission control method for renewable energy islanded power transmission, including: When a new energy power station in the sending-end islanded AC grid of the DC transmission control system transmits power, the rectifier control module in the sending-end islanded AC grid uses the current command value inside the inverter in the sending-end islanded AC grid, the rectifier frequency value and the rectifier current value in the sending-end islanded AC grid to add frequency control to the rectifier and generate the rectifier firing angle. The rectifier controls its DC side to output a constant current to the inverter based on the rectifier firing angle, and then the inverter transmits the current to an external equivalent AC network connected to the AC side of the inverter, thereby realizing the stable power transmission of the new energy power station.

[0017] Preferably, when a new energy power station in a remote islanded AC grid at the sending end of a DC transmission control system transmits power, the rectifier control module in the remote islanded AC grid uses the current command value inside the inverter in the remote islanded AC grid, the rectifier frequency value, and the rectifier current value in the remote islanded AC grid to add frequency control to the rectifier and generate the rectifier firing angle, including: When a new energy power plant in a remote islanded AC grid at the sending end of a DC transmission control system transmits power, the rectifier control module in the remote islanded AC grid collects the current command value inside the inverter, as well as the rectifier frequency and current values. Based on the current command value, the rectifier frequency value, and a set additional frequency reference value, a rectifier control current command value is obtained. Based on the rectifier current value and the rectifier control current command value, additional frequency control is applied to the rectifier to generate the rectifier firing angle.

[0018] Preferably, the rectifier control module includes: a first linear filter unit, a second linear filter unit, and a proportional-integral (PI) controller connected to each other; the first linear filter unit is connected to the rectifier and the inverter, the second linear filter unit is connected to the rectifier, and the PI controller is connected to the rectifier; When a new energy power station in a remote islanded AC grid at the sending end of a DC transmission control system transmits power, the rectifier control module in the remote islanded AC grid utilizes the current command value inside the inverter in the remote islanded AC grid, the rectifier frequency value, and the rectifier current value in the remote islanded AC grid to add frequency control to the rectifier and generate the rectifier firing angle, including: When the new energy power station sends out power, the first linear filter unit is used to collect the current command value and rectifier frequency value inside the inverter. Based on the current command value inside the inverter, the rectifier frequency value and the set additional frequency reference value, the rectifier control current command value is obtained. The rectifier current value is collected using the second linear filter unit; Using the PI controller, based on the rectifier current value and the rectifier control current command value, frequency control is added to the rectifier to generate the rectifier firing angle.

[0019] Preferably, when the new energy power station transmits power, the first linear filter unit is used to collect the current command value and rectifier frequency value inside the inverter, and based on the current command value inside the inverter, the rectifier frequency value, and a set additional frequency reference value, the rectifier control current command value is obtained, including: When the new energy power station sends out power, the first linear filter unit is used to divide the rectifier frequency value by the set additional frequency reference value, then take the negative number and add 1 as the frequency change rate. The frequency change rate is filtered to obtain the filtered frequency change rate. Based on the rate of change of the filter frequency, an additional current value is generated; the sum of the current command value inside the inverter and the additional current value is used as the rectifier control current command value.

[0020] Preferably, the step of using the PI controller to add frequency control to the rectifier based on the rectifier current value and the rectifier control current command value, and generating the rectifier firing angle, includes: When the new energy power station sends out power, the difference between the rectifier control current command value and the rectifier current value is obtained to obtain the current deviation; The rectifier firing angle is generated based on the current deviation.

[0021] Preferably, the additional current value satisfies the following formula:

[0022] In the above formula, Indicates the additional current value. This represents the preset frequency droop coefficient. This indicates the rectifier frequency value. This indicates the set additional frequency reference value. This represents the preset scaling factor. This represents the integral coefficient during filtering. This represents the integral operator used in filtering.

[0023] Preferably, generating the additional current value based on the filter frequency change rate includes: Divide the rate of change of the filtered frequency by a preset frequency droop coefficient to obtain the adjusted rate of change of the frequency. An additional current value is generated based on the adjusted rate of frequency change.

[0024] Preferably, generating the additional current value based on the adjusted rate of frequency change includes: The adjusted frequency change rate is limited to obtain a limited frequency change rate; an additional current value is generated based on the limited frequency change rate.

[0025] Preferably, the new energy power station includes: a new energy wind power station and a new energy photovoltaic power station; the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are connected to the AC side of the rectifier; When the new energy power station sends out power, the current output from the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are collected and sent to the AC side of the rectifier.

[0026] Preferably, the sending-end islanded AC grid further includes: a first grid-side converter and a second grid-side converter; the wind turbine power station of the new energy wind power station is connected to the first grid-side converter; the photovoltaic power station of the new energy photovoltaic power station is connected to the second grid-side converter; then the first grid-side converter and the second grid-side converter are combined and connected to the AC side of the rectifier; When the new energy power station transmits power, the first grid-side converter is used to control the stability of the voltage and frequency of the current transmitted by the wind turbine power station of the new energy wind power station during its own transmission process; the second grid-side converter is used to control the stability of the voltage and frequency of the current transmitted by the photovoltaic power station of the new energy photovoltaic power station during its own transmission process. Both the first grid-side converter and the second grid-side converter are grid-type converters.

[0027] Thirdly, this application also proposes an electronic device, comprising: at least one processor and a memory; the memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, the DC power transmission control method for sending new energy islands is implemented.

[0028] Fourthly, this application also proposes a readable storage medium having an executable program stored thereon, which, when executed, implements the aforementioned DC power transmission control method for sending power from a new energy island.

[0029] Compared with the closest prior art, the beneficial effects of this application are as follows: This invention discloses a DC power transmission control system and method for transmitting power from an isolated renewable energy source, comprising: a sending-end isolated AC grid; the sending-end isolated AC grid includes a renewable energy power plant, a rectifier, and an inverter connected in sequence, and a rectifier control module connected to the rectifier and the inverter; the AC side of the inverter is connected to an external equivalent AC grid; when the renewable energy power plant transmits power, the rectifier control module, based on the inverter's internal current command value, rectifier frequency value, and rectifier current value, adds frequency control to the rectifier, generates a rectifier firing angle, and sends it to the rectifier; based on the rectifier firing angle, the rectifier controls its own DC side to output a constant current to the inverter, which then transmits the current to the equivalent AC grid, thereby achieving stable power transmission from the renewable energy power plant. The rectifier control module combines the relevant parameters of the inverter and rectifier in the system with the set additional frequency reference value to add frequency control to the rectifier, so that the current value on the DC side of the rectifier remains constant, realizing the stable power transmission of the new energy power station. Therefore, the system inertia is stable and will not cause the transmitting end islanded AC grid oscillation, resulting in high reliability. Attached Figure Description

[0030] Figure 1 An architecture diagram of a DC power transmission control system for a new energy islanded power transmission provided in this application; Figure 2 A partial schematic diagram of the rectifier control module of a DC power transmission control system for new energy islanding provided in this application; Figure 3 A schematic diagram of the rectifier control module of a DC power transmission control system for new energy islanding provided in this application; Figure 4 A schematic diagram of the first linear filter unit of a DC power transmission control system for new energy islanding provided in this application; Figure 5 A detailed architecture diagram of a DC power transmission control system for new energy islanded power transmission provided in this application; Figure 6 An architecture diagram of a specific use case of a DC power transmission control system for isolated new energy transmission provided in this application; Figure 7 Transient characteristic waveform diagram of a specific use case of a DC power transmission control system for a new energy islanded power transmission provided in this application; Figure 8 A comparison of simulation results of the DC transmission control system for a new energy island provided in this application with the addition of additional control and the conventional DC transmission end without additional control is shown in the figure. Figure 9A comparison of simulation results of the DC receiving end with the addition of additional control and without additional control in a specific use case of a DC power transmission control system for a new energy island provided in this application; Figure 10 A flowchart of a DC power transmission control method for new energy islanded power transmission provided in this application; Figure 11 A schematic diagram of the operation of an electronic device provided in this application. Detailed Implementation

[0031] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1: like Figure 1 As shown, this application proposes a DC power transmission control system for renewable energy islanding, comprising: a sending-end islanded AC power grid; the sending-end islanded AC power grid includes a renewable energy power station, a rectifier and an inverter connected in sequence, and a rectifier control module connected to the rectifier and the inverter; the AC side of the inverter is connected to an external equivalent AC network; When the new energy power station transmits power, the rectifier control module, based on the inverter's internal current command value, rectifier frequency value, and rectifier current value, adds frequency control to the rectifier, generates a rectifier firing angle, and sends it to the rectifier. Based on the rectifier firing angle, the rectifier controls its own DC side to output a constant current to the inverter, which then transmits the current to the equivalent AC network, thus achieving stable power transmission from the new energy power station.

[0033] As described above, the DC transmission control system is responsible for transmitting power and is typically required to operate according to a certain power command. The usual direct control mode involves a constant rectifier current and a constant inverter voltage. Since there are no synchronous generators in the DC transmission control system, its inertia drops to zero. Therefore, the stability of the DC transmission control system is mainly achieved by rapidly controlling and adjusting the system's voltage and frequency to achieve power balance and active / reactive power balance. To effectively improve the stability and fault ride-through capability of the DC transmission control system, based on the constant current control at the sending end, an additional frequency control module is used to control the rectifier, adding frequency droop control. This reflects frequency changes through changes in DC current throughout the entire DC transmission control system, ultimately achieving active power balance and frequency control in the islanded AC grid at the sending end.

[0034] Furthermore, the rectifier control module is specifically used for: When the new energy power station transmits power, the current command value inside the inverter, as well as the rectifier frequency value and rectifier current value are collected; based on the current command value, the rectifier frequency value, and the set additional frequency reference value, the rectifier control current command value is obtained; based on the rectifier current value and the rectifier control current command value, additional frequency control is applied to the rectifier, the rectifier firing angle is generated and sent to the rectifier.

[0035] Furthermore, the rectifier control module includes: a first linear filter unit, a second linear filter unit, and a proportional-integral (PI) controller connected to each other; the first linear filter unit is connected to the rectifier and the inverter, the second linear filter unit is connected to the rectifier, and the PI controller is connected to the rectifier; When the new energy power station transmits power, the first linear filter unit collects the current command value and rectifier frequency value inside the inverter. Based on the current command value inside the inverter, the rectifier frequency value, and a set additional frequency reference value, it obtains the rectifier control current command value and sends it to the PI controller. The second linear filter unit collects the rectifier current value and sends it to the PI controller. The PI controller, based on the rectifier current value and the rectifier control current command value, adds frequency control to the rectifier, generates the rectifier firing angle, and sends it to the rectifier.

[0036] Furthermore, the first linear filtering unit is specifically used for: When the new energy power station transmits power, the rectifier frequency value is divided by a set additional frequency reference value, then the negative number is taken and 1 is added to obtain the frequency change rate; the frequency change rate is filtered to obtain the filtered frequency change rate; an additional current value is generated based on the filtered frequency change rate; the sum of the current command value inside the inverter and the additional current value is used as the rectifier control current command value and sent to the PI controller.

[0037] Furthermore, the PI controller is specifically used for: When the new energy power station sends out power, the difference between the rectifier control current command value and the rectifier current value is calculated to obtain the current deviation; based on the current deviation, the rectifier firing angle is generated and sent to the rectifier.

[0038] like Figure 2 As shown, the rectifier control module has rectifier current values. and the current command value inside the inverter Two inputs, output is the rectifier firing angle The rectifier control module generates the rectifier firing angle and controls the DC side of the rectifier to maintain a constant current value. The rectifier current value is filtered by the first linear filter unit to remove ripple, yielding the DC current value. This DC current value is then subtracted from the rectifier control current command value to calculate the current deviation ε. When generating the rectifier firing angle, the change in current deviation Δε is directly proportional to the change in inverter angle Δβ. When a current difference is detected, an increase in the change in current deviation Δε leads to an increase in inverter angle β, thereby adjusting the rectifier firing angle. Decrease ( Since β = 180°, the rectifier firing angle can be generated based on the current deviation. The input of the PI controller eliminates static errors through the first and second linear filter units, the derivative control improves dynamic characteristics, and the maximum output of β is set to 3.054, or 175°, to limit the rectifier firing angle. The minimum angle is 5°, which is the output rectifier firing angle, enabling constant current control and minimum rectifier firing angle control. Figure 2 In this diagram, + indicates input, - indicates subtraction, G represents gain, T represents time constant, and G / 1+sT is the filtering stage. Indicates 180°. Indicates the additional current value. For the limiting stage, and These represent the maximum and minimum values ​​of the amplitude limit, respectively.

[0039] Furthermore, such as Figure 3-4 As shown, N / D represents input N divided by input D, and the additional current value satisfies the following formula:

[0040] In the above formula, Indicates the additional current value. This represents the preset frequency droop coefficient. This indicates the rectifier frequency value. This indicates the set additional frequency reference value. This represents the preset scaling factor. This represents the integral coefficient during filtering. This represents the integral operator used in filtering.

[0041] Furthermore, the first linear filtering unit is specifically used for: Divide the filtered frequency change rate by a preset frequency droop coefficient to obtain the adjusted frequency change rate; generate an additional current value based on the adjusted frequency change rate.

[0042] Furthermore, the first linear filtering unit is specifically used for: The adjusted frequency change rate is limited to obtain a limited frequency change rate; an additional current value is generated based on the limited frequency change rate.

[0043] Furthermore, such as Figure 5 As shown, the new energy power station includes: a new energy wind power station and a new energy photovoltaic power station; the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are connected to the AC side of the rectifier; When the new energy power station sends out power, the current output from the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are collected and sent to the AC side of the rectifier.

[0044] Furthermore, the sending-end islanded AC grid also includes: a first grid-side converter and a second grid-side converter; the wind turbine power station of the new energy wind power station is connected to the first grid-side converter; the photovoltaic power station of the new energy photovoltaic power station is connected to the second grid-side converter; then the first grid-side converter and the second grid-side converter are combined and connected to the AC side of the rectifier; When the new energy power station transmits power, the first grid-side converter controls the stability of the voltage and frequency of the current transmitted by the wind turbine power station of the new energy wind power station during its transmission process; the second grid-side converter controls the stability of the voltage and frequency of the current transmitted by the photovoltaic power station of the new energy photovoltaic power station during its transmission process. Both the first grid-side converter and the second grid-side converter are grid-type converters.

[0045] Conventional DC transmission is generally used in power systems with synchronous generators or synchronous condensers, where the short-circuit capacity ratio (SCR) at the grid connection point is required to be no less than 2.0. From the perspective of the nature of conventional DC transmission operation, it requires the system to provide a stable commutation voltage and frequency, which has traditionally been provided by the synchronous generators within the system. However, in the islanded conventional DC transmission system of this invention, this can be achieved by using grid-forming control (GFM) of the first and second grid-side converters to simulate the voltage source and frequency regulation characteristics of the synchronous generators. In the sending-end islanded AC grid, a portion of the first and second grid-side converters need to adopt grid-forming control to jointly support the voltage and frequency of the sending-end islanded AC grid, thereby achieving stable synchronous operation of the entire transmission system.

[0046] Furthermore, the sending-end islanded AC grid also includes a generator-side converter; the generator-side converter is connected between the wind turbine power station of the new energy wind farm and the first grid-side converter.

[0047] Furthermore, the sending-end islanded AC grid also includes a DC converter; the DC converter is connected between the photovoltaic power station of the new energy photovoltaic power plant and the second grid-side converter.

[0048] The wind turbine power station of the new energy wind power plant is connected to the turbine-side converter, which is connected to the first grid-side converter via a DC line. The photovoltaic power station of the new energy photovoltaic power plant is connected to the DC converter, which is connected to the second grid-side converter via a DC line. The first grid-side converter and the second grid-side converter are connected via an AC line and then connected to the AC side of the rectifier via a high-voltage bus. The DC side of the rectifier is connected to the DC side of the inverter via a DC transmission line. The AC side of the inverter is connected to the equivalent AC grid, thus realizing the transmission of power from the sending end of the new energy power plant (new energy wind power plant + new energy photovoltaic power plant) to the receiving end of the equivalent AC grid.

[0049] The DC transmission control system for renewable energy islanding of this invention is primarily designed to improve grid stability in the event of system failures, especially when the system inertia is as low as zero. This invention adds frequency control to the conventional DC transmission system control at the renewable energy plant at the sending end. The frequency signal is added to the current command value inside the inverter, thereby reflecting frequency changes through changes in DC current throughout the entire sending-end islanded AC grid. This achieves active power balance and frequency control in the sending-end islanded AC grid. The method of this invention enables the use of conventional DC transmission for large-scale, long-distance transmission of renewable energy from islanded areas.

[0050] To further illustrate the system of the present invention, a specific use case is proposed as follows: like Figure 6 As shown, a model of a conventional DC transmission system for a new energy wind farm and a new energy photovoltaic power station is constructed. The model includes a new energy wind farm (active power output P2), a new energy photovoltaic power station (active power output P1), and a conventional DC transmission system. This system enables the power from both the wind farm and the photovoltaic power station to be transmitted via conventional DC transmission, with an input power of P3, where P3 = P1 + P2 - losses. Because the entire system has no inertia support, it forms a zero-inertia system. Based on this model, the DC transmission control system proposed in this invention is verified.

[0051] Because the first and second grid-side converters in the DC transmission control system for renewable energy islands need to adopt a grid-based control method to jointly support the voltage and frequency of the sending-end island AC grid, in order to achieve stable and synchronous operation of the first and second grid-side converters. In this example, the renewable energy photovoltaic power station adopts grid-based control; the renewable energy wind power station adopts grid-following control with fast AC bus voltage control and frequency active power droop control. Conventional DC transmission systems use... Figures 2-4 Additional frequency control.

[0052] against Figure 6 The model assumes that two typical faults, Condition 1 and Condition 2, occur simultaneously in the system. Condition 1: A three-phase metallic transient ground fault occurs for 100 milliseconds at 3 seconds on the 345kV high-voltage bus at the rectifier sending end of the conventional DC transmission system. Condition 2: A three-phase metallic transient ground fault occurs for 100 milliseconds at 6 seconds on the 230kV high-voltage bus at the receiving end of the conventional DC transmission system. Simulations are performed for Conditions 1 and 2, and the specific simulation results are compared to... Figure 7-9 As shown, Figure 7 The left side shows the simulation results of a zero-inertia system with additional control, and the right side shows the simulation results of a zero-inertia system without additional control. Figure 7 The transient characteristics appearing from 0 to 1 second represent the startup process of the PSCAD (Power System Computer-Aided Design Simulation Startup Process) simulation. The left and right sides, from top to bottom, show the voltage changes of the three high-voltage buses in the zero-inertia system from 0 to 1 second, the active power changes of the three high-voltage buses in the zero-inertia system from 0 to 1 second, the reactive power changes of the three high-voltage buses in the zero-inertia system from 0 to 1 second, the capacity changes of the three high-voltage buses in the zero-inertia system from 0 to 1 second, and the system frequency changes from 0 to 1 second. Figure 8 The top figure shows the simulation results of the conventional DC sending end with additional control, while the bottom figure shows the simulation results of the conventional DC sending end without additional control. Here, AC Voltage is the instantaneous AC voltage at the sending end, AC Volts (RMS) is the effective value of the AC voltage at the sending end, DC Volts is the instantaneous value of the DC voltage at the sending end, and DC Current is the instantaneous value of the DC current at the sending end. Figure 9 The upper figure shows the simulation results of a conventional DC receiving end with additional control, while the lower figure shows the simulation results of a conventional DC receiving end without additional control. In the figures, AC Voltage is the instantaneous AC voltage at the receiving end, AC Volts (RMS) is the effective value of the AC voltage at the receiving end, DC Volts is the instantaneous value of the DC voltage at the receiving end, and DC Current is the instantaneous value of the DC current at the receiving end.

[0053] Depend on Figures 7-9The simulation results clearly show that under the two typical fault disturbances, Condition 1 and Condition 2, the conventional DC system without additional control cannot recover to a stable state. However, the conventional DC transmission system with additional frequency control added to the conventional DC sending end can recover quickly and remain stable, demonstrating reliable fault ride-through capability.

[0054] The control method of the DC transmission control system for new energy islanding of the present invention can adopt grid-type control for the first grid-side converter and the second grid-side converter, thereby adding an additional frequency active power droop control at the sending end of the DC transmission control system. This can effectively improve the stability of the grid for large-scale new energy islanding. In the event of a system failure, the entire system can recover quickly and remain stable, with reliable fault ride-through capability.

[0055] Furthermore, in existing technologies, for isolated wind farms without conventional AC power supply, support can be provided through grid control of renewable energy units or energy storage. Determining the appropriate grid control method for renewable energy units or energy storage, how to define the control functions of conventional DC transmission, and how to upgrade and improve the control of traditional conventional DC transmission systems are effective ways to enhance the stability of large-scale renewable energy isolated power grids. This application, targeting large-scale renewable energy isolated power grid transmission scenarios, adds frequency control to the typical basic control of conventional DC transmission systems, achieving rapid system recovery under fault conditions, maintaining system stability, and possessing reliable fault ride-through capability. This represents an effective way to improve the stability of large-scale renewable energy isolated power grids.

[0056] Example 2: like Figure 10 As shown, the present invention also provides a DC transmission control method for power transmission from a renewable energy island, which may include: Step 1: When a new energy power station in the sending-end islanded AC grid of the DC transmission control system transmits power, the rectifier control module in the sending-end islanded AC grid uses the current command value inside the inverter in the sending-end islanded AC grid, the rectifier frequency value and the rectifier current value in the sending-end islanded AC grid to add frequency control to the rectifier and generate the rectifier firing angle. Step 2: The rectifier controls its own DC side to output a constant current to the inverter based on the rectifier firing angle, and then the inverter transmits the current to the external equivalent AC network connected to the AC side of the inverter, so as to realize the stable power transmission of the new energy power station.

[0057] Further, in step 1 above, when the new energy power station in the sending-end islanded AC grid of the DC transmission control system transmits power, the rectifier control module in the sending-end islanded AC grid uses the current command value inside the inverter in the sending-end islanded AC grid, the rectifier frequency value in the sending-end islanded AC grid, and the rectifier current value to add frequency control to the rectifier and generate the rectifier firing angle, including: When a new energy power plant in a remote islanded AC grid at the sending end of a DC transmission control system transmits power, the rectifier control module in the remote islanded AC grid collects the current command value inside the inverter, as well as the rectifier frequency and current values. Based on the current command value, the rectifier frequency value, and a set additional frequency reference value, a rectifier control current command value is obtained. Based on the rectifier current value and the rectifier control current command value, additional frequency control is applied to the rectifier to generate the rectifier firing angle.

[0058] Furthermore, the rectifier control module includes: a first linear filter unit, a second linear filter unit, and a proportional-integral (PI) controller connected to each other; the first linear filter unit is connected to the rectifier and the inverter, the second linear filter unit is connected to the rectifier, and the PI controller is connected to the rectifier; In step 1 above, when a new energy power station in the sending-end islanded AC grid of the DC transmission control system transmits power, the rectifier control module in the sending-end islanded AC grid uses the current command value inside the inverter in the sending-end islanded AC grid, the rectifier frequency value in the sending-end islanded AC grid, and the rectifier current value to add frequency control to the rectifier and generate the rectifier firing angle. Specifically, this may include: Step 1.1: When the new energy power station sends out power, the first linear filter unit is used to collect the current command value and rectifier frequency value inside the inverter. Based on the current command value inside the inverter, the rectifier frequency value and the set additional frequency reference value, the rectifier control current command value is obtained. Step 1.2: Use the second linear filter unit to collect the rectifier current value; Step 1.3: Using the PI controller, based on the rectifier current value and the rectifier control current command value, add frequency control to the rectifier to generate the rectifier firing angle.

[0059] Further, in step 1.1 above, when the new energy power station transmits power, the first linear filter unit is used to collect the current command value inside the inverter and the rectifier frequency value. Based on the current command value inside the inverter, the rectifier frequency value, and the set additional frequency reference value, the rectifier control current command value is obtained, which may include: Step 1.1.1: When the new energy power station sends out power, the first linear filter unit is used to divide the rectifier frequency value by the set additional frequency reference value, then the negative number is taken and 1 is added as the frequency change rate. Step 1.1.2: Filter the frequency change rate to obtain the filtered frequency change rate; Step 1.1.3: Generate an additional current value based on the filter frequency change rate; use the sum of the current command value inside the inverter and the additional current value as the rectifier control current command value.

[0060] Further, in step 1.3 above, the step of using the PI controller to add frequency control to the rectifier based on the rectifier current value and the rectifier control current command value, and generating the rectifier firing angle, may include: Step 1.3.1: When the new energy power station sends out power, the difference between the rectifier control current command value and the rectifier current value is calculated to obtain the current deviation; Step 1.3.2: Generate the rectifier firing angle based on the current deviation.

[0061] Furthermore, the additional current value satisfies the following formula:

[0062] In the above formula, Indicates the additional current value. This represents the preset frequency droop coefficient. This indicates the rectifier frequency value. This indicates the set additional frequency reference value. This represents the preset scaling factor. This represents the integral coefficient during filtering. This represents the integral operator used in filtering.

[0063] Further, in step 1.1.3 above, generating the additional current value based on the rate of change of the filter frequency includes: Step 1.1.3.1: Divide the rate of change of the filtered frequency by the preset frequency droop coefficient to obtain the adjusted rate of change of the frequency; Step 1.1.3.2: Generate an additional current value based on the adjusted frequency change rate.

[0064] Further, in step 1.1.3.2 above, generating the additional current value based on the adjusted frequency change rate includes: The adjusted frequency change rate is limited to obtain a limited frequency change rate; an additional current value is generated based on the limited frequency change rate.

[0065] Furthermore, the new energy power station includes: a new energy wind power station and a new energy photovoltaic power station; the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are connected to the AC side of the rectifier; When the new energy power station sends out power, the current output from the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are collected and sent to the AC side of the rectifier.

[0066] Furthermore, the sending-end islanded AC grid also includes: a first grid-side converter and a second grid-side converter; the wind turbine power station of the new energy wind power station is connected to the first grid-side converter; the photovoltaic power station of the new energy photovoltaic power station is connected to the second grid-side converter; then the first grid-side converter and the second grid-side converter are combined and connected to the AC side of the rectifier; When the new energy power station transmits power, the first grid-side converter is used to control the stability of the voltage and frequency of the current transmitted by the wind turbine power station of the new energy wind power station during its own transmission process; the second grid-side converter is used to control the stability of the voltage and frequency of the current transmitted by the photovoltaic power station of the new energy photovoltaic power station during its own transmission process. Both the first grid-side converter and the second grid-side converter are grid-type converters.

[0067] Furthermore, the sending-end islanded AC grid also includes a generator-side converter; the generator-side converter is connected between the wind turbine power station of the new energy wind farm and the first grid-side converter.

[0068] Furthermore, the sending-end islanded AC grid also includes a DC converter; the DC converter is connected between the photovoltaic power station of the new energy photovoltaic power plant and the second grid-side converter.

[0069] Example 3: like Figure 11As shown, the present invention also provides an electronic device, which may be a computer device, a microcontroller device, a smart mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, processor, and transceiver component are connected via a bus; the memory can be used to store executable programs, and an exemplary executable program may include instructions; the processor is used to execute the instructions stored in the memory. The memory can also be used to store data, which can be accessed and / or modified when instructions are executed.

[0070] The processor may be a Central Processing Unit (CPU), or it may be 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 core and control core of the terminal, and it is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the storage medium to realize the corresponding method flow or corresponding function, so as to realize the steps of the DC power transmission control method for new energy island power transmission in the above embodiments.

[0071] Example 4: Based on the same inventive concept, this invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory). This readable storage medium is a memory device within an electronic device used to store programs and data. It is understood that the storage medium here can include both built-in storage media within the electronic device and extended storage media supported by the electronic device. The storage medium provides storage space, which stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more executable programs (including program code). It should be noted that the storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. Loading and executing one or more instructions stored in the storage medium by the processor can implement the steps of the DC power transmission control method for renewable energy islanding described in the above embodiments.

[0072] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0073] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0074] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0075] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit its protection scope. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this application, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the application, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims pending approval.

Claims

1. A DC power transmission control system for isolated new energy transmission, comprising: Sending-end islanded AC grid; characterized in that the sending-end islanded AC grid includes a new energy power station, a rectifier and an inverter connected in sequence, and a rectifier control module connected to the rectifier and the inverter; the AC side of the inverter is connected to an external equivalent AC grid; When the new energy power station transmits power, the rectifier control module, based on the inverter's internal current command value, rectifier frequency value, and rectifier current value, adds frequency control to the rectifier, generates a rectifier firing angle, and sends it to the rectifier. Based on the rectifier firing angle, the rectifier controls its own DC side to output a constant current to the inverter, which then transmits the current to the equivalent AC network, thus achieving stable power transmission from the new energy power station.

2. The system according to claim 1, characterized in that, The rectifier control module is specifically used for: When the new energy power station transmits power, the current command value inside the inverter, as well as the rectifier frequency value and rectifier current value are collected; based on the current command value, the rectifier frequency value, and the set additional frequency reference value, the rectifier control current command value is obtained; based on the rectifier current value and the rectifier control current command value, additional frequency control is applied to the rectifier, the rectifier firing angle is generated and sent to the rectifier.

3. The system according to claim 2, characterized in that, The rectifier control module includes: a first linear filter unit, a second linear filter unit, and a proportional-integral (PI) controller connected to each other; the first linear filter unit is connected to the rectifier and the inverter, the second linear filter unit is connected to the rectifier, and the PI controller is connected to the rectifier; When the new energy power station transmits power, the first linear filter unit collects the current command value and rectifier frequency value inside the inverter. Based on the current command value inside the inverter, the rectifier frequency value, and a set additional frequency reference value, it obtains the rectifier control current command value and sends it to the PI controller. The second linear filter unit collects the rectifier current value and sends it to the PI controller. The PI controller, based on the rectifier current value and the rectifier control current command value, adds frequency control to the rectifier, generates the rectifier firing angle, and sends it to the rectifier.

4. The system according to claim 3, characterized in that, The first linear filtering unit is specifically used for: When the new energy power station transmits power, the rectifier frequency value is divided by a set additional frequency reference value, then the negative number is taken and 1 is added to obtain the frequency change rate; the frequency change rate is filtered to obtain the filtered frequency change rate; an additional current value is generated based on the filtered frequency change rate; the sum of the current command value inside the inverter and the additional current value is used as the rectifier control current command value and sent to the PI controller.

5. The system according to claim 3, characterized in that, The PI controller is specifically used for: When the new energy power station sends out power, the difference between the rectifier control current command value and the rectifier current value is calculated to obtain the current deviation; based on the current deviation, the rectifier firing angle is generated and sent to the rectifier.

6. The system according to claim 4, characterized in that, The additional current value satisfies the following formula: In the above formula, Indicates the additional current value. This represents the preset frequency droop coefficient. This indicates the rectifier frequency value. This indicates the set additional frequency reference value. This represents the preset scaling factor. This represents the integral coefficient during filtering. This represents the integral operator used in filtering.

7. The system according to claim 6, characterized in that, The first linear filtering unit is specifically used for: Divide the filtered frequency change rate by a preset frequency droop coefficient to obtain the adjusted frequency change rate; generate an additional current value based on the adjusted frequency change rate.

8. The system according to claim 7, characterized in that, The first linear filtering unit is specifically used for: The adjusted frequency change rate is limited to obtain a limited frequency change rate; an additional current value is generated based on the limited frequency change rate.

9. The system according to any one of claims 1-8, characterized in that, The new energy power station includes: a new energy wind power station and a new energy photovoltaic power station; the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are connected to the AC side of the rectifier; When the new energy power station sends out power, the current output from the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are collected and sent to the AC side of the rectifier.

10. The system according to claim 9, characterized in that, The sending-end islanded AC power grid further includes: a first grid-side converter and a second grid-side converter; the wind turbine power station of the new energy wind power station is connected to the first grid-side converter; the photovoltaic power station of the new energy photovoltaic power station is connected to the second grid-side converter; then the first grid-side converter and the second grid-side converter are combined and connected to the AC side of the rectifier; When the new energy power station transmits power, the first grid-side converter controls the stability of the voltage and frequency of the current transmitted by the wind turbine power station of the new energy wind power station during its transmission process; the second grid-side converter controls the stability of the voltage and frequency of the current transmitted by the photovoltaic power station of the new energy photovoltaic power station during its transmission process. Both the first grid-side converter and the second grid-side converter are grid-type converters.

11. A method for controlling DC power transmission from a renewable energy island, characterized in that, include: When a new energy power station in the sending-end islanded AC grid of the DC transmission control system transmits power, the rectifier control module in the sending-end islanded AC grid uses the current command value inside the inverter in the sending-end islanded AC grid, the rectifier frequency value and the rectifier current value in the sending-end islanded AC grid to add frequency control to the rectifier and generate the rectifier firing angle. The rectifier controls its DC side to output a constant current to the inverter based on the rectifier firing angle, and then the inverter transmits the current to an external equivalent AC network connected to the AC side of the inverter, so as to realize the stable power transmission of the new energy power station. The DC power transmission control system is the DC power transmission control system according to any one of claims 1-10.

12. The method according to claim 11, characterized in that, When a new energy power station in a remote islanded AC grid at the sending end of a DC transmission control system transmits power, the rectifier control module in the remote islanded AC grid utilizes the current command value inside the inverter in the remote islanded AC grid, the rectifier frequency value, and the rectifier current value in the remote islanded AC grid to add frequency control to the rectifier and generate the rectifier firing angle, including: When a new energy power station in the sending-end islanded AC grid of the DC transmission control system transmits power, the rectifier control module in the sending-end islanded AC grid is used to collect the current command value inside the inverter in the sending-end islanded AC grid, as well as the frequency value and current value of the rectifier in the sending-end islanded AC grid. Based on the current command value, the rectifier frequency value, and the set additional frequency reference value, the rectifier control current command value is obtained. Based on the rectifier current value and the rectifier control current command value, frequency control is added to the rectifier to generate the rectifier firing angle.

13. The method according to claim 12, characterized in that, The rectifier control module includes: a first linear filter unit, a second linear filter unit, and a proportional-integral (PI) controller connected to each other; the first linear filter unit is connected to the rectifier and the inverter, the second linear filter unit is connected to the rectifier, and the PI controller is connected to the rectifier; When a new energy power station in a remote islanded AC grid at the sending end of a DC transmission control system transmits power, the rectifier control module in the remote islanded AC grid utilizes the current command value inside the inverter in the remote islanded AC grid, the rectifier frequency value, and the rectifier current value in the remote islanded AC grid to add frequency control to the rectifier and generate the rectifier firing angle, including: When the new energy power station sends out power, the first linear filter unit is used to collect the current command value and rectifier frequency value inside the inverter. Based on the current command value inside the inverter, the rectifier frequency value and the set additional frequency reference value, the rectifier control current command value is obtained. The rectifier current value is collected using the second linear filter unit; Using the PI controller, based on the rectifier current value and the rectifier control current command value, frequency control is added to the rectifier to generate the rectifier firing angle.

14. The method according to claim 13, characterized in that, When the new energy power station transmits power, the first linear filter unit is used to collect the current command value and rectifier frequency value inside the inverter. Based on the current command value inside the inverter, the rectifier frequency value, and a set additional frequency reference value, the rectifier control current command value is obtained, including: When the new energy power station sends out power, the first linear filter unit is used to divide the rectifier frequency value by the set additional frequency reference value, then take the negative number and add 1 as the frequency change rate. The frequency change rate is filtered to obtain the filtered frequency change rate. Based on the rate of change of the filter frequency, an additional current value is generated; the sum of the current command value inside the inverter and the additional current value is used as the rectifier control current command value.

15. The method according to claim 13, characterized in that, The step of using the PI controller to add frequency control to the rectifier based on the rectifier current value and the rectifier control current command value, and generating the rectifier firing angle, includes: When the new energy power station sends out power, the difference between the rectifier control current command value and the rectifier current value is obtained to obtain the current deviation; The rectifier firing angle is generated based on the current deviation.

16. The method according to claim 14, characterized in that, The additional current value satisfies the following formula: In the above formula, Indicates the additional current value. This represents the preset frequency droop coefficient. This indicates the rectifier frequency value. This indicates the set additional frequency reference value. This represents the preset scaling factor. This represents the integral coefficient during filtering. This represents the integral operator used in filtering.

17. The method according to claim 16, characterized in that, The step of generating an additional current value based on the rate of change of the filter frequency includes: Divide the filtered frequency change rate by a preset frequency droop coefficient to obtain the adjusted frequency change rate; generate an additional current value based on the adjusted frequency change rate.

18. The method according to claim 17, characterized in that, The generation of the additional current value based on the adjusted frequency change rate includes: The adjusted frequency change rate is limited to obtain a limited frequency change rate; an additional current value is generated based on the limited frequency change rate.

19. The method according to any one of claims 11-18, characterized in that, The new energy power station includes: a new energy wind power station and a new energy photovoltaic power station; the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are connected to the AC side of the rectifier; When the new energy power station sends out power, the current output from the wind turbine power station of the new energy wind power station and the photovoltaic power station of the new energy photovoltaic power station are collected and sent to the AC side of the rectifier.

20. The method according to claim 19, characterized in that, The sending-end islanded AC power grid further includes: a first grid-side converter and a second grid-side converter; the wind turbine power station of the new energy wind power station is connected to the first grid-side converter; the photovoltaic power station of the new energy photovoltaic power station is connected to the second grid-side converter; then the first grid-side converter and the second grid-side converter are combined and connected to the AC side of the rectifier; When the new energy power station transmits power, the first grid-side converter is used to control the stability of the voltage and frequency of the current transmitted by the wind turbine power station of the new energy wind power station during its own transmission process; the second grid-side converter is used to control the stability of the voltage and frequency of the current transmitted by the photovoltaic power station of the new energy photovoltaic power station during its own transmission process. Both the first grid-side converter and the second grid-side converter are grid-type converters.

21. An electronic device, characterized in that, include: At least one processor and memory; The memory and processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, a DC power transmission control method for sending new energy to isolated power sources as described in any one of claims 11 to 20 is implemented.

22. A readable storage medium, characterized in that, It contains an execution program, which, when executed, implements a DC power transmission control method for new energy island power transmission as described in any one of claims 11 to 20.

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