Programmable Grid-Connected Test System and Method for Large-Capacity Wind Turbines to Improve Coverage

Abstract

A programmable grid-connected testing system and method for large-capacity wind turbines with improved coverage is disclosed. The system includes two sets of back-to-back MMC unit test power supplies and an integrated controller. The integrated controller simultaneously controls both sets of MMC back-to-back unit test power supplies. The station-level control logic, pole-level control logic, and valve-level control logic of the two sets of MMC back-to-back unit test power supplies are all integrated on the CPU board within the integrated controller. No communication link is provided between the station-level control logic and the pole-level control logic on the CPU board, but a gigabit Ethernet communication link is provided between the pole-level control logic and the valve-level control logic. The method includes grid-connected steady-state operation testing and AC voltage fault ride-through testing of the wind turbines. This invention significantly reduces communication latency by using an integrated controller, avoiding problems such as asynchronous commands and inaccurate modulation signals in test control. By reducing the number of test power supply control links, it achieves parallel testing of large-capacity wind turbines based on command synchronization and accurate modulation.

Description

Technical Field

[0001] This invention belongs to the field of wind turbine grid connection testing technology, and more specifically, relates to a programmable grid connection testing system and method for large-capacity wind turbines with improved coverage. Background Technology

[0002] In 2019, my country added 25.74 GW of grid-connected wind power capacity, bringing the cumulative grid-connected capacity to 210.05 GW. Of this, onshore wind power accounted for 23.76 GW and offshore wind power for 1.98 GW. The cumulative grid-connected capacity of onshore wind power reached 0.204 TW, while that of offshore wind power reached 5.93 GW, making offshore wind power a crucial new energy source for the country. With the increasing utilization rate of offshore wind energy resources and the decreasing investment cost per kilowatt of turbine units, the trend towards larger offshore wind turbine units is evident.

[0003] Flexible DC transmission (VSC-HVDC) technology, with its advantages such as no commutation failures, ability to supply power to isolated grids, and ability to provide reactive power support to the system, has broad application prospects in areas such as offshore wind power transmission and isolated renewable energy transmission. The Zhangbei Flexible DC project, based on a modular multilevel converter (MMC), is the world's first truly grid-connected flexible DC project. The Zhangbei Flexible DC project is a typical example of renewable energy transmission via an isolated MMC grid, with the flexible DC converter station connected to the isolated grid acting as a balancing station to provide stable grid-connected voltage for renewable energy.

[0004] With the increasing application of wind power generation, more challenges have been brought to the stability of power grid operation. To address this, the power grid has introduced testing requirements for voltage deviation, three-phase voltage imbalance, harmonics / interharmonics, voltage flicker, frequency deviation, and low-voltage fault ride-through. Existing testing methods and systems, for wind turbines with ever-increasing capacity, present challenges due to the diverse test items and higher testing requirements, increasing the complexity of the test power supply control. When using two sets of MMC back-to-back unit test power supplies to test wind turbines, each set's controller includes: a station-level control box, an electrode layer control box, and a valve layer control box. These three control boxes are connected via a communication loop. Furthermore, the controllers of the two sets of MMC back-to-back unit test power supplies also need to be connected via a communication loop. This leads to problems such as asynchronous commands and inaccurate modulation signals in the test control. Moreover, the various test items are relatively dispersed, requiring manual switching of test items, which reduces the efficiency of wind turbine testing. More importantly, existing testing systems and methods cannot meet the requirements of grid-connected AC voltage fault ride-through testing under the condition of wind turbines transmitting power via flexible direct current. Existing tests have low coverage of fault simulation and cannot meet the comprehensive requirements of grid-connected AC voltage fault ride-through testing. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a programmable grid-connected testing system and method for large-capacity wind turbines with improved coverage. It integrates the station-level control logic, pole-level control logic, and valve-level control logic of two MMC back-to-back unit test power controllers into a single CPU board. For a single MMC back-to-back unit test power controller, no communication loop is required between the three control logics. For two MMC back-to-back unit test power controllers, using an integrated controller eliminates the communication loop between the two controllers, significantly shortening communication latency and avoiding problems such as asynchronous commands and inaccurate modulation signals in test control. By reducing the test power control links, large-capacity wind turbine parallel testing is achieved based on command synchronization and precise modulation. Programmable operation facilitates the switching of test functions, improving wind turbine testing efficiency. A three-in-one high-coverage AC voltage fault ride-through testing method integrating fault simulation equipment, flexible direct transmission equipment, and wind turbine equipment is proposed.

[0006] The present invention adopts the following technical solution.

[0007] This invention proposes a programmable grid-connected test system for large-capacity wind turbines to improve coverage. The grid-connected test system includes two sets of MMC back-to-back unit test power supplies and a wind turbine. The first set of MMC back-to-back unit test power supplies includes: a first station-level control logic, a first pole layer control logic, and a first valve layer control logic. The second set of MMC back-to-back unit test power supplies includes: a second station-level control logic, a second pole layer control logic, and a second valve layer control logic.

[0008] The grid-connected test system includes an integrated controller, which is used to simultaneously control two sets of MMC back-to-back unit test power supplies.

[0009] The integrated controller includes a CPU board; the first-station control logic, the first-level control logic, the first-valve-level control logic, the second-station control logic, the second-level control logic, and the second-valve-level control logic are all integrated on the CPU board; among them...

[0010] On the CPU board, no communication link is set between the first station-level control logic and the first pole-level control logic, no communication link is set between the second station-level control logic and the second pole-level control logic, a gigabit Ethernet communication link is set between the first pole-level control logic and the first valve-level control logic, and a gigabit Ethernet communication link is set between the second pole-level control logic and the second valve-level control logic.

[0011] The integrated controller controls any MMC back-to-back unit test power supply, including station-level control, pole-level control, and valve-level control. Station-level control includes: sequential control logic, target value issuance, and unlocking / locking. Pole-level control includes: phase-locked loop, coordinate transformation, outer loop control, AC voltage fault ride-through, inner loop control, circulating current suppression, and modulation wave generation. Valve-level control includes: sorting of submodule capacitor voltages.

[0012] Both sets of MMC back-to-back unit test power supplies adopt AC adjustable voltage source control mode. When the two sets of MMC back-to-back unit test power supplies are running in parallel, the integrated controller simultaneously sends the AC adjustable voltage source modulation wave to the two sets of MMC back-to-back unit test power supplies.

[0013] In another aspect, this invention proposes a programmable grid-connected testing method for large-capacity wind turbines with improved coverage, which is implemented using a programmable grid-connected testing system for large-capacity wind turbines with improved coverage.

[0014] The testing methods include: wind turbine grid-connected steady-state operation test and AC voltage fault ride-through test.

[0015] The steady-state operation test of wind turbine grid connection includes:

[0016] Step A1: During normal operation, the two sets of MMC back-to-back unit test power supplies are connected to the same AC bus with the wind turbine. The active power generated by the wind turbine is fed into the power grid through the two sets of MMC back-to-back unit test power supplies. The two sets of MMC back-to-back unit test power supplies are controlled by an integrated controller. Both sets of MMC back-to-back unit test power supplies are controlled by an AC adjustable voltage source and operate in parallel.

[0017] Step A2: After the two sets of MMC back-to-back unit test power supplies and the wind turbine are running stably, when the AC voltage fault ride-through response enable plates of the two sets of MMC back-to-back unit test power supplies are both in the off state, the wind turbine grid connection test is carried out by setting different parameters; among them, the wind turbine grid connection test includes: fundamental wave test, harmonic test, interharmonic wave test and voltage flicker test.

[0018] Step A3: Obtain the instantaneous values ​​of the fundamental wave, harmonics, interharmonics, and voltage flicker through the grid connection test of the wind turbine.

[0019] In step A2, the fundamental frequency test includes:

[0020] Step A2.1.1: Adjust the positive sequence voltage amplitude in 1% steps to perform voltage deviation testing;

[0021] Step A2.1.2: Adjust the output frequency of the given AC voltage in 0.1Hz / s increments to perform a frequency deviation test;

[0022] Step A2.1.3, the low voltage fault ride-through test includes the low voltage fault ride-through test for three-phase symmetrical faults and the low voltage fault ride-through test for three-phase asymmetrical faults; wherein, the low voltage fault ride-through test for three-phase symmetrical faults is simulated by the duration of positive sequence voltage amplitude, and the low voltage fault ride-through test for three-phase asymmetrical faults is simulated by the duration of single-phase voltage amplitude.

[0023] Step A2.1.4: Maintain the positive sequence voltage amplitude at 1 p.u. and adjust the negative sequence voltage amplitude in steps of 0.1% of the unbalance to perform a three-phase voltage unbalance test;

[0024] Step A2.1.5: Perform inverse coordinate transformation on the sequence components obtained in steps A2.1.1 to A2.1.4 to output the instantaneous value of the fundamental wave test.

[0025] In step A2, during each harmonic test, the frequency and amplitude of a certain harmonic are set, while the amplitudes of all other harmonics are 0; the sequence components obtained from the test are subjected to inverse coordinate transformation to output the instantaneous values ​​of the harmonic test.

[0026] In step A2, during each interharmonic test, the frequency and amplitude of a certain interharmonic are set, while the amplitudes of all other interharmonics are 0; the sequence components obtained from the test are subjected to inverse coordinate transformation to output the instantaneous values ​​of the interharmonic test.

[0027] In step A2, during the voltage flicker test, the positive sequence voltage is maintained at 1 p.u., and the amplitude of the 0.1 Hz harmonic component is adjusted according to the flicker step size of 0.2. The sequence component obtained from the test is subjected to coordinate inverse transformation to output the instantaneous value of voltage flicker.

[0028] With one MMC back-to-back unit test power supply's AC voltage fault ride-through enable plate in the enabled state and the other MMC back-to-back unit test power supply's AC voltage fault ride-through enable plate in the deactivated state, a modulated wave is used to perform AC voltage fault ride-through testing of the wind turbine via flexible DC transmission; including:

[0029] Step B1: Select one set of MMC back-to-back unit test power supply as the fault simulation device, and deactivate the AC voltage fault ride-through response enable plate of the MMC back-to-back unit test power supply.

[0030] Step B2: Select another set of MMC back-to-back unit test power supply as the fan power output device, and put the AC voltage fault ride-through response enable plate of the MMC back-to-back unit test power supply into operation.

[0031] In step B3 and step 4.1, the MMC back-to-back unit test power supply simulates a fault drop at the bus to generate symmetrical and asymmetrical AC voltages.

[0032] In step B4, the other set of MMC back-to-back unit test power supply and fan, as described in step 4.2, both enter the low voltage fault ride-through logic after detecting an AC voltage fault.

[0033] Low-voltage fault ride-through logic includes active power priority logic and reactive power priority logic.

[0034] The beneficial effects of this invention are that, compared with the prior art, the test method and system proposed in this invention can meet the grid connection test requirements of large-capacity wind turbine units, and integrate multiple functions such as voltage deviation test, three-phase voltage imbalance test, harmonic test, interharmonic test, voltage flicker test, frequency deviation test, low voltage fault ride-through test, and AC voltage fault ride-through response into one system, and achieve the corresponding test functions by setting different parameters.

[0035] The beneficial effects of this invention include:

[0036] 1. This invention addresses the actual operating conditions of increasingly larger single-unit wind turbine capacity by reducing the test power supply control links and realizing parallel testing of large-capacity wind turbines based on command synchronization and precise modulation.

[0037] 2. This invention facilitates the switching of test functions through programmable operation, thereby improving the efficiency of wind turbine testing;

[0038] 3. This invention also considers the grid-connected AC voltage fault ride-through test requirements under the condition of wind turbines being transmitted via flexible direct power supply, optimizes the fault simulation settings of the test power supply, and proposes a three-in-one high-coverage AC voltage fault ride-through test method integrating fault simulation equipment, flexible direct power supply equipment, and wind turbine equipment.

[0039] 4. This invention integrates the control logic, which was originally located in three chassis, onto a single CPU board in one chassis. Furthermore, it integrates the DSP and FPGA chips on the CPU board. Except for the valve layer control, which has a gigabit Ethernet communication link, all other functions are on the same chip, eliminating communication links and greatly reducing control link latency. Previously, station-level control and pole-level control communicated via fiber optic 100Mbps Ethernet, while pole-level control and valve layer control communicated via fiber optic point-to-point using the 60044-8FT3 protocol. However, in this invention, with the control logic integrated onto the CPU board, the gigabit Ethernet used for valve layer control is faster than the FT3 communication method.

[0040] 5. Command synchronization and precise modulation refer to the function of the AC adjustable voltage source. When two sets of equipment are controlled by an AC adjustable voltage source, they exhibit AC voltage source characteristics. Considering the circulating current problem between the two sets of equipment, the voltage sources generally do not operate in parallel. If parallel operation of the two sets of equipment is required, it is necessary to ensure that the modulation waves of the two sets of equipment are highly consistent, so that the generated circulating current is within a controllable range. To ensure the high consistency of the modulation waves of the two sets of equipment, this invention uses the same controller to send the AC adjustable voltage source modulation waves to both sets of equipment, which greatly avoids the amplitude and phase angle differences caused by the two controllers generating their own AC adjustable voltage source modulation waves. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of the programmable grid-connected test system for large-capacity wind turbines with improved coverage in an embodiment of the present invention;

[0042] Figure 1 The annotations in the accompanying drawings are explained as follows:

[0043] 1- First set of MMC back-to-back unit test power supply; 2- Second set of MMC back-to-back unit test power supply; 3- Wind turbine; 4- Integrated controller; 5- CPU board;

[0044] Figure 2 This is a logical schematic diagram of the wind turbine grid connection test item function in an embodiment of the present invention;

[0045] Figure 2 The annotations in the accompanying drawings are explained as follows:

[0046] Ua_ref, Ub_ref, Uc_ref - Three-phase AC voltage amplitude;

[0047] Freq_ref - The output frequency of the given AC voltage;

[0048] Vdq_ref_P - Positive sequence voltage amplitude; Vdq_ref_N - Negative sequence voltage amplitude. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0050] In response to the testing requirements of the power grid, including voltage deviation, three-phase voltage imbalance, harmonics / interharmonics, voltage flicker, frequency deviation, and low-voltage fault ride-through, this invention discloses a programmable grid-connected testing system and method for large-capacity wind turbines with improved coverage.

[0051] The grid-connected testing system includes a first set of MMC back-to-back unit test power supply 1, a second set of MMC back-to-back unit test power supply 2, and a wind turbine 3. The first set of MMC back-to-back unit test power supply 1 includes: a first station-level control logic, a first pole layer control logic, and a first valve layer control logic; the second set of MMC back-to-back unit test power supply 2 includes: a second station-level control logic, a second pole layer control logic, and a second valve layer control logic.

[0052] The grid-connected testing system includes an integrated controller 4, which is used to simultaneously control the first set of MMC back-to-back unit test power supply 1 and the second set of MMC back-to-back unit test power supply 2.

[0053] The integrated controller 4 includes a CPU board 5; the first station-level control logic, the first pole-level control logic, the first valve-level control logic, the second station-level control logic, the second pole-level control logic, and the second valve-level control logic are all integrated on the CPU board 5; among them...

[0054] On CPU board 5, no communication link is set between the first station-level control logic and the first pole layer control logic, no communication link is set between the second station-level control logic and the second pole layer control logic, a gigabit Ethernet communication link is set between the first pole layer control logic and the first valve layer control logic, and a gigabit Ethernet communication link is set between the second pole layer control logic and the second valve layer control logic.

[0055] In this embodiment of the invention, the control logic, originally housed in three separate chassis, is integrated onto a single CPU board within a single chassis. Furthermore, the DSP and FPGA chips on the CPU board are also integrated. Except for the valve layer control, which involves a gigabit Ethernet communication link, all other functions are on the same chip, eliminating communication links and significantly reducing control link latency. Previously, station-level control and pole-level control communicated via fiber optic 100Mbps Ethernet, while pole-level control and valve layer control communicated via fiber optic point-to-point using the 60044-8FT3 protocol. However, in this invention, with the control logic integrated onto the CPU board, the gigabit Ethernet used for valve layer control is faster than the FT3 communication method. By simplifying the controller and control board, communication links are reduced, shortening the overall control link latency.

[0056] The integrated controller controls any MMC back-to-back unit test power supply, including station-level control, pole-level control, and valve-level control. Station-level control includes: sequential control logic, target value issuance, and unlocking / locking. Pole-level control includes: phase-locked loop, coordinate transformation, outer loop control, AC voltage fault ride-through, inner loop control, circulating current suppression, and modulation wave generation. Valve-level control includes: sorting of submodule capacitor voltages.

[0057] Both sets of MMC back-to-back unit test power supplies adopt AC adjustable voltage source control mode. When the two sets of MMC back-to-back unit test power supplies are running in parallel, the integrated controller simultaneously sends the AC adjustable voltage source modulation wave to the two sets of MMC back-to-back unit test power supplies.

[0058] Command synchronization and precise modulation refer to the function of AC adjustable voltage sources. When two sets of equipment are controlled by an AC adjustable voltage source, they exhibit AC voltage source characteristics. Considering the circulating current problem between the two sets of equipment, the voltage sources generally do not operate in parallel. If parallel operation of the two sets of equipment is required, it is necessary to ensure that the modulation waves of the two sets of equipment are highly consistent, so that the generated circulating current is within a controllable range. To ensure the high consistency of the modulation waves of the two sets of equipment, this invention uses the same controller to send the AC adjustable voltage source modulation waves to both sets of equipment, which greatly avoids the amplitude and phase angle differences caused by the two controllers generating their own AC adjustable voltage source modulation waves.

[0059] In another aspect, this invention proposes a programmable grid-connected testing method for large-capacity wind turbines with improved coverage, which is implemented using a programmable grid-connected testing system for large-capacity wind turbines with improved coverage.

[0060] The testing methods include: wind turbine grid-connected steady-state operation test and AC voltage fault ride-through test.

[0061] This invention integrates multiple functions, including voltage deviation testing, three-phase voltage imbalance testing, harmonic testing, interharmonic testing, voltage flicker testing, frequency deviation testing, low-voltage fault ride-through testing, and AC voltage fault ride-through response, into a single unit. Different parameters are set to achieve the corresponding testing functions. This programmable operation facilitates switching between testing functions and improves wind turbine testing efficiency.

[0062] Combined with appendix Figure 2 In detail, voltage deviation testing, three-phase voltage imbalance testing, frequency deviation testing, and low-voltage fault ride-through testing can all be achieved by modifying the logic for generating the fundamental instantaneous value. Harmonic testing, interharmonic testing, voltage flicker testing, and AC voltage fault ride-through response are also included in the appendix. Figure 2 The text indicates the interrelationship of their respective functions.

[0063] The steady-state operation test of wind turbine grid connection includes:

[0064] Step A1: During normal operation, the two sets of MMC back-to-back unit test power supplies are connected to the same AC bus to the wind turbine. The active power generated by the wind turbine is fed into the power grid through the two sets of MMC back-to-back unit test power supplies. The two sets of MMC back-to-back unit test power supplies are controlled by an integrated controller. Both sets of MMC back-to-back unit test power supplies are controlled by an AC adjustable voltage source and operate in parallel.

[0065] Step A2: After the two sets of MMC back-to-back unit test power supplies and the wind turbine are running stably, when the AC voltage fault ride-through response enable plates of the two sets of MMC back-to-back unit test power supplies are both in the off state, the wind turbine grid connection test is carried out by setting different parameters; among them, the wind turbine grid connection test includes: fundamental wave test, harmonic test, interharmonic wave test and voltage flicker test.

[0066] In step A2, the appendix Figure 2 The fundamental instantaneous value in the measurement is the fundamental wave test, which includes:

[0067] Step A2.1.1: Adjust the positive sequence voltage amplitude Vdq_ref_P in 1% steps to perform voltage deviation testing. It is worth noting that those skilled in the art can adjust the positive sequence voltage amplitude in different steps to perform voltage deviation testing according to the test accuracy requirements and actual working conditions. This embodiment is a non-limiting preferred choice.

[0068] Step A2.1.2: Adjust the given AC voltage output frequency Freq_ref in 0.1Hz / s increments to perform frequency deviation testing. It is worth noting that those skilled in the art can adjust the given AC voltage output frequency in different increments according to the test accuracy requirements and actual operating conditions to perform frequency deviation testing. This embodiment is a non-limiting but preferred option.

[0069] Step A2.1.3, the low-voltage fault ride-through test includes a low-voltage fault ride-through test for a three-phase symmetrical fault and a low-voltage fault ride-through test for a three-phase asymmetrical fault. Specifically, the low-voltage fault ride-through test for a three-phase symmetrical fault is simulated using the duration of the positive-sequence voltage amplitude Vdq_ref_P, while the low-voltage fault ride-through test for a three-phase asymmetrical fault is simulated using the duration of a single-phase voltage amplitude. The single-phase voltage amplitude is any one of the phase voltages Ua_ref, Ub_ref, and Uc_ref.

[0070] In step A2.1.4, the positive sequence voltage amplitude Vdq_ref_P is kept at 1 p.u. and the negative sequence voltage amplitude Vdq_ref_N is adjusted in steps of 0.1% of the unbalance to perform a three-phase voltage unbalance test. It is worth noting that those skilled in the art can adjust the negative sequence voltage amplitude in different steps according to the test accuracy requirements and actual operating conditions to perform a three-phase voltage unbalance test. This embodiment is a non-limiting but preferred option.

[0071] Step A2.1.5: Perform inverse coordinate transformation on the sequence components obtained in steps A2.1.1 to A2.1.4 to output the instantaneous value of the fundamental wave test.

[0072] In step A2, during each harmonic test, the frequency and amplitude of a certain harmonic are set, while the amplitudes of all other harmonics are 0. The obtained sequence components are then subjected to an inverse coordinate transformation to output the instantaneous harmonic test values, corresponding to the attached... Figure 2 Instantaneous value of middle harmonic.

[0073] In step A2, during each interharmonic test, the frequency and amplitude of a certain interharmonic are set, while the amplitudes of all other interharmonics are 0. The obtained sequence components are then subjected to an inverse coordinate transformation to output the instantaneous values ​​of the interharmonic tests, corresponding to the attached... Figure 2 Instantaneous value of intermediate harmonic.

[0074] In step A2, during the voltage flicker test, the positive sequence voltage is maintained at 1 p.u., and the amplitude of the 0.1 Hz harmonic component is adjusted according to a flicker step size of 0.2. The obtained sequence component undergoes an inverse coordinate transformation to output the instantaneous voltage flicker value, corresponding to the attached... Figure 2 The instantaneous value of the flicker; it is worth noting that those skilled in the art can adjust the amplitude of the harmonic components according to different flicker step sizes to perform voltage flicker testing based on the test accuracy requirements and actual operating conditions. This embodiment is a non-limiting but preferred option.

[0075] Step A3: Obtain the instantaneous values ​​of the fundamental wave, harmonics, interharmonics, and voltage flicker through the grid connection test of the wind turbine.

[0076] With one MMC back-to-back unit test power supply's AC voltage fault ride-through enable plate in the enabled state and the other MMC back-to-back unit test power supply's AC voltage fault ride-through enable plate in the deactivated state, a modulated wave is used to perform AC voltage fault ride-through testing of the wind turbine via flexible DC transmission; including:

[0077] Step B1: Select one set of MMC back-to-back unit test power supply as the fault simulation device, and deactivate the AC voltage fault ride-through response enable plate of the MMC back-to-back unit test power supply.

[0078] Step B2: Select another set of MMC back-to-back unit test power supply as the fan power output device, and put the AC voltage fault ride-through response enable plate of the MMC back-to-back unit test power supply into operation.

[0079] In step B3 and step 4.1, the MMC back-to-back unit test power supply simulates a fault drop at the bus to generate symmetrical and asymmetrical AC voltages.

[0080] In step B4, the other set of MMC back-to-back unit test power supply and fan, as described in step 4.2, both enter the low voltage fault ride-through logic after detecting an AC voltage fault.

[0081] Low-voltage fault ride-through logic includes active power priority logic and reactive power priority logic.

[0082] The AC voltage fault ride-through response function simulates the AC voltage fault ride-through function of flexible DC transmission when wind power is transmitted via flexible DC. This function detects the degree of AC voltage amplitude drop to achieve low-voltage fault ride-through. The AC voltage fault ride-through response enables the voltage control panel to switch on and off, with corresponding settings as per the attached function. Figure 2 AC fault ride-through response enable pressure plate.

[0083] In this embodiment, the final modulation wave of the test system is the sum of the instantaneous values ​​of the fundamental wave test, harmonic test, interharmonic test, and voltage flicker, combined with the output of the AC voltage fault ride-through response function selected by the AC voltage fault ride-through response enable plate. This integrates multiple functions into one, allowing for the implementation of corresponding test functions by setting different parameters. This programmable operation facilitates the switching of test functions and improves the efficiency of wind turbine testing.

[0084] This testing method is mainly used for wind power transmission via flexible DC. The fault ride-through logic of the test power supply has active power priority and reactive power priority options, and is compatible with the fault ride-through strategies of different flexible DC equipment manufacturers.

[0085] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0086] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0087] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0088] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0089] Various aspects of this disclosure are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It should 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-readable program instructions.

[0090] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0091] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0092] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A programmable grid-connected test system for large-capacity wind turbines with improved coverage, wherein the grid-connected test system includes two sets of MMC back-to-back unit test power supplies and wind turbines, wherein, The first set of MMC back-to-back unit test power supplies includes: first station-level control logic, first pole layer control logic, and first valve layer control logic; the second set of MMC back-to-back unit test power supplies includes: second station-level control logic, second pole layer control logic, and second valve layer control logic; characterized in that... The grid-connected test system includes an integrated controller, which is used to simultaneously control two sets of MMC back-to-back unit test power supplies. The integrated controller includes a CPU board; the first-station control logic, the first-level control logic, the first-valve-level control logic, the second-station control logic, the second-level control logic, and the second-valve-level control logic are all integrated on the CPU board; among them... On the CPU board, no communication link is set between the first station-level control logic and the first pole-level control logic, no communication link is set between the second station-level control logic and the second pole-level control logic, a gigabit Ethernet communication link is set between the first pole-level control logic and the first valve-level control logic, and a gigabit Ethernet communication link is set between the second pole-level control logic and the second valve-level control logic.

2. The programmable grid-connected test system for large-capacity wind turbines with improved coverage as described in claim 1, characterized in that, The integrated controller controls any MMC back-to-back unit test power supply, including station-level control, pole-level control, and valve-level control. Station-level control includes: sequential control logic, target value issuance, and unlocking / locking. Pole-level control includes: phase-locked loop, coordinate transformation, outer loop control, AC voltage fault ride-through, inner loop control, circulating current suppression, and modulation wave generation. Valve-level control includes: sorting of submodule capacitor voltages.

3. The programmable grid-connected test system for large-capacity wind turbines with improved coverage as described in claim 1, characterized in that, Both sets of MMC back-to-back unit test power supplies adopt AC adjustable voltage source control mode. When the two sets of MMC back-to-back unit test power supplies are running in parallel, the integrated controller simultaneously sends the AC adjustable voltage source modulation wave to the two sets of MMC back-to-back unit test power supplies.

4. A programmable grid-connected testing method for large-capacity wind turbines with improved coverage, implemented using the programmable grid-connected testing system for large-capacity wind turbines with improved coverage as described in any one of claims 1 to 3, characterized in that... The testing methods include: wind turbine grid-connected steady-state operation test and AC voltage fault ride-through test; wherein, the wind turbine grid-connected steady-state operation test includes: Step A1: During normal operation, the two sets of MMC back-to-back unit test power supplies are connected to the same AC bus with the wind turbine. The active power generated by the wind turbine is fed into the power grid through the two sets of MMC back-to-back unit test power supplies. The two sets of MMC back-to-back unit test power supplies are controlled by an integrated controller. Both sets of MMC back-to-back unit test power supplies are controlled by an AC adjustable voltage source and operate in parallel. Step A2: After the two sets of MMC back-to-back unit test power supplies and the wind turbine are running stably, when the AC voltage fault ride-through response enable plates of the two sets of MMC back-to-back unit test power supplies are both in the off state, the wind turbine grid connection test is carried out by setting different parameters; among them, the wind turbine grid connection test includes: fundamental wave test, harmonic test, interharmonic wave test and voltage flicker test. Step A3: Obtain the instantaneous values ​​of the fundamental wave, harmonics, interharmonics, and voltage flicker through the grid connection test of the wind turbine.

5. The programmable grid-connected testing method for large-capacity wind turbines with improved coverage according to claim 4, characterized in that, With one MMC back-to-back unit test power supply's AC voltage fault ride-through enable plate in the enabled state and the other MMC back-to-back unit test power supply's AC voltage fault ride-through enable plate in the deactivated state, a modulated wave is used to perform AC voltage fault ride-through testing of the wind turbine via flexible DC transmission; including: Step B1: Select one set of MMC back-to-back unit test power supply as the fault simulation device, and deactivate the AC voltage fault ride-through response enable plate of the MMC back-to-back unit test power supply. Step B2: Select another set of MMC back-to-back unit test power supply as the fan power output device, and put the AC voltage fault ride-through response enable plate of the MMC back-to-back unit test power supply into operation. In step B3 and step 4.1, the MMC back-to-back unit test power supply simulates a fault drop at the bus to generate symmetrical and asymmetrical AC voltages. In step B4, the other set of MMC back-to-back unit test power supply and fan, as described in step 4.2, both enter the low voltage fault ride-through logic after detecting an AC voltage fault.

6. The programmable grid-connected testing method for large-capacity wind turbines with improved coverage according to claim 4, characterized in that, In step A2, the fundamental frequency test includes: Step A2.1.1: Adjust the positive sequence voltage amplitude in 1% steps to perform voltage deviation testing; Step A2.1.2: Adjust the output frequency of the given AC voltage in 0.1Hz / s increments to perform a frequency deviation test; Step A2.1.3, the low voltage fault ride-through test includes the low voltage fault ride-through test for three-phase symmetrical faults and the low voltage fault ride-through test for three-phase asymmetrical faults; wherein, the low voltage fault ride-through test for three-phase symmetrical faults is simulated by the duration of positive sequence voltage amplitude, and the low voltage fault ride-through test for three-phase asymmetrical faults is simulated by the duration of single-phase voltage amplitude. Step A2.1.4: Maintain the positive sequence voltage amplitude at 1 p.u. and adjust the negative sequence voltage amplitude in steps of 0.1% of the unbalance to perform a three-phase voltage unbalance test; Step A2.1.5: Perform inverse coordinate transformation on the sequence components obtained in steps A2.1.1 to A2.1.4 to output the instantaneous value of the fundamental wave test.

7. The programmable grid-connected testing method for large-capacity wind turbines with improved coverage according to claim 4, characterized in that, In step A2, during each harmonic test, the frequency and amplitude of a certain harmonic are set, while the amplitudes of all other harmonics are 0; the sequence components obtained from the test are subjected to inverse coordinate transformation to output the instantaneous values ​​of the harmonic test.

8. The programmable grid-connected testing method for large-capacity wind turbines with improved coverage according to claim 4, characterized in that, In step A2, during each interharmonic test, the frequency and amplitude of a certain interharmonic are set, while the amplitudes of all other interharmonics are 0; the sequence components obtained from the test are subjected to inverse coordinate transformation to output the instantaneous values ​​of the interharmonic test.

9. The programmable grid-connected testing method for large-capacity wind turbines with improved coverage according to claim 4, characterized in that, In step A2, during the voltage flicker test, the positive sequence voltage is maintained at 1 p.u., and the amplitude of the 0.1 Hz harmonic component is adjusted according to the flicker step size of 0.

2. The sequence component obtained from the test is subjected to coordinate inverse transformation to output the instantaneous value of voltage flicker.

10. The programmable grid-connected testing method for large-capacity wind turbines with improved coverage according to claim 5, characterized in that, Low-voltage fault ride-through logic includes active power priority logic and reactive power priority logic.

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