Control method and system capable of providing frequency support for flexible interconnected power distribution network

Abstract

Disclosed in the present invention are a control method and system capable of providing frequency support for a flexible interconnected power distribution network. The method comprises: using a permanent-magnet direct-drive wind turbine connected to a flexible interconnected power distribution network to provide frequency support, measuring a direct-current voltage of a grid-side converter of the wind turbine, calculating a per-unit value and the phase of the direct-current voltage, and calculating the amplitude of a modulation voltage; generating a trigger pulse signal; monitoring the rotation speed of a wind turbine rotor and the rotor position angle of a synchronous generator, and acquiring a per-unit value of optimal power; calculating an active power reference value; on the basis of active power control and current control, outputting a d-axis component and a q-axis component of a modulation voltage of a generator-side converter, and by means of rotating coordinate transformation, generating a three-phase modulation voltage in a stationary coordinate system; and generating a trigger pulse signal by means of a pulse width modulation stage. The present invention enables wind turbines to provide quick response for power distribution networks in a frequency support stage, and prevent rotation speed stalling and suppress secondary frequency drop in a rotation speed recovery stage, thereby improving the support capability of the wind turbines for power grids.

Description

A control method and system capable of providing frequency support for a flexible interconnected power distribution network TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible interconnected power distribution networks, in particular to a control method and system capable of providing frequency support for a flexible interconnected power distribution network. BACKGROUND

[0002] With the continuous advancement of China's "double carbon" goal, green and low-carbon transformation has become the basic orientation of China's energy development. Wind power and photovoltaic power generation equipment based on power electronic interfaces replace traditional synchronous machines and are connected to the power distribution network in large quantities, which has a great impact on the safe and stable operation of the power distribution network. Flexible interconnected devices such as intelligent soft switches can be used to connect different power distribution networks to form a flexible interconnected power distribution network and achieve power flow control, as shown in FIG. 1. However, new energy generation equipment is difficult to actively respond to system frequency changes and presents a nearly zero inertia characteristic, which reduces the inertia of the flexible interconnected power distribution network and easily induces protection actions such as flexible interconnected power distribution network low-frequency load shedding and high-frequency generator tripping, leading to large-area power outages and even operation instability of the flexible interconnected power distribution network; in addition, wind turbines have poor frequency anomaly tolerance and are prone to large-area disconnection in extreme cases, leading to cascading accidents.

[0003] The frequency response process of a wind turbine can be divided into two stages: a frequency support stage and a speed recovery stage. Wind turbines usually operate in maximum power tracking mode, and their participation in frequency support is achieved by releasing their rotor kinetic energy to provide additional energy support. In the frequency support stage, wind turbines change active output by using various additional frequency response strategies to respond to system frequency changes, and after the active support ends, the wind turbine returns to maximum power tracking. If the transition between the frequency support and speed recovery processes is not smooth, the power shortage caused by the reduction of wind turbine active output will cause the system frequency to drop again. Therefore, for wind turbines connected to a flexible interconnected power distribution network, how to develop a control system that can provide frequency support and suppress frequency secondary drop is a problem that needs to be solved.

[0004] SUMMARY

[0005] In view of the above problems, the present application is proposed.

[0006] Therefore, the technical problem solved by the present application is how to solve the problem of lack of frequency support for a flexible interconnected power distribution network by a wind turbine, and a control system capable of providing frequency support for a flexible interconnected power distribution network is proposed to enhance the frequency stability of the flexible interconnected power distribution network and suppress the secondary drop of frequency during the speed recovery process of the wind turbine.

[0007] To solve the above technical problems, the present invention provides the following technical solutions: a control method for providing frequency support for a flexible interconnected distribution network, comprising: utilizing a permanent magnet direct-drive wind turbine generator system connected to the flexible interconnected distribution network to provide frequency support; measuring the DC voltage of the grid-side converter of the permanent magnet direct-drive wind turbine generator system in a control loop of the grid-side converter; calculating the per-unit value and phase of the DC voltage; and calculating the amplitude of the grid-side modulation voltage;

[0008] generating a trigger pulse signal for a grid-side converter by combining the phase of the DC voltage and the amplitude of the grid-side modulation voltage;

[0009] In the control loop of the generator-side converter, the wind rotor speed and the synchronous generator rotor position angle are detected, the generator-side current is converted, and the per-unit value of the optimal power is obtained;

[0010] Calculating an active power reference value through the per-unit value of the optimal power;

[0011] After combining the active power control link and the current control link, the d-axis component and the q-axis component of the modulated voltage of the output side converter are converted into a three-phase modulated voltage in the stationary coordinate system through the rotating coordinate transformation;

[0012] The three-phase modulated voltage generates a trigger pulse signal for the machine-side converter through a pulse width modulation link.

[0013] As a preferred embodiment of the control method for providing frequency support for a flexible interconnected distribution network according to the present invention, wherein: the calculated per-unit value and phase of the DC voltage include the DC voltage u of the grid-side converter dc Divide by the rated value of DC voltage u dcn Get the per-unit value of DC voltage After the gain is ω n The output of the integrator is phase θ, where ω n is the rated angular frequency of the grid;

[0014] The calculation of the amplitude of the grid-side modulation voltage includes the reference value Q of the grid-side converter output reactive power. gere and feedback value Q g The difference is passed through a PI regulator and then superimposed with the initial amplitude of the grid-side modulation voltage U t0 Get the amplitude of the grid-side modulation voltage U t .

[0015] As a preferred solution of the control method for providing frequency support for the flexible interconnected distribution network described in the present invention, wherein: the combination of the phase of the DC voltage and the amplitude of the grid-side modulation voltage includes: combining the phase θ with the amplitude U t integrated into a modulated signal;

[0016] The trigger pulse signal of the grid-side converter is generated by generating a sine waveform reference signal synchronized with the grid frequency based on the integrated modulation signal, and generating a high-frequency triangular wave carrier signal with a frequency higher than the reference signal for pulse width modulation.

[0017] The PWM signal is generated by comparing the reference signal with the carrier signal, generating a high level when the amplitude of the reference signal is higher than the carrier signal, and generating a low level otherwise.

[0018] The amplitude and phase information of the reference signal is encoded into the pulse width of the PWM signal to control the output voltage shape and size of the grid-side converter.

[0019] The generated PWM signal is used to directly drive the switching elements of the grid-side converter to generate the trigger pulse signal Sgabc of the grid-side converter.

[0020] As a preferred scheme of the control method for providing frequency support for a flexible interconnected distribution network, the optimal power reference includes detecting the wind turbine speed ω t and the rotor position angle θr of the synchronous generator in the control loop of the machine-side converter.

[0021] The three-phase alternating current isabc of the machine-side converter is converted to the current i sd , i sq in the dq coordinate system through rotational coordinate conversion, and the phase for rotational coordinate conversion is θr.

[0022] The wind turbine speed is divided by the rated value of the wind turbine speed ω tn to obtain the wind turbine speed reference The optimal power reference is obtained through the maximum power tracking control module

[0023] The calculation of the active power reference value includes, The output of the gating control module is the flag bit Flag.

[0024] Flag enters the control port Ctrl of the controlled switch S1, and the constant 20 is input as the position 1 of the controlled switch S1, and the control coefficient K P is input as the position 2 of the controlled switch S1.

[0025] The digital 1 is subtracted from the DC voltage reference , and then multiplied by the output of the controlled switch S1 to obtain the active power reference value of the machine-side converter .

[0026] The three-phase modulation voltage converted to the stationary coordinate system by the rotation coordinate conversion comprises, After entering the active power control link, the d-axis component of the machine-side converter modulation voltage output after entering the current control link q-axis component The three-phase modulation voltage in the stationary coordinate system is generated by the rotation coordinate conversion

[0027] As a preferred scheme of the control method for providing frequency support for a flexible interconnected power distribution network, the gating control module adopts the following control structure,

[0028] The input of the gating control module is the per-unit value of the wind turbine speed and the rated value of the wind turbine speed The difference is obtained by subtraction determine whether it is less than 0.015 p.u.;

[0029] If the value of the flag bit F1 is 1; if the value of the flag bit F1 is 0;

[0030] The rate of change of the per-unit value of the wind turbine speed is calculated determine whether it is less than 0.01 p.u.;

[0031] If the value of the flag bit F2 is 1; if the value of the flag bit F2 is 0;

[0032] The flag bits F1 and F2 are subjected to Boolean logic operation to generate a flag bit Flag, which is the output of the gating control module.

[0033] The Boolean logic operation is that when F1=1 and F2=1, Flag is 1, and when all other conditions occur, Flag is 0.

[0034] The output, input and control port Ctrl of the controlled switch S1 satisfy the following relationship:

[0035] When the value of the control port Ctrl is 0, the output of the controlled switch S1 is the input of position 1.

[0036] When the value of the control port Ctrl is 1, the output of the controlled switch S1 is the input of position 2.

[0037] As a preferred scheme of the control method for providing frequency support for a flexible interconnected power distribution network, the control coefficient KP The expression is:

[0038] Wherein, k is the frequency modulation coefficient, b is the speed recovery adjustment factor, t represents the actual variable, t swc is the time when the controlled switch S1 is switched from position 1 to position 2, t off is the control coefficient K P The time is reduced.

[0039] As a preferred scheme of the control method for providing frequency support to the flexible interconnected power distribution network, wherein: the frequency modulation coefficient k satisfies the following relationship:

[0040] Wherein, is the synchronous generator speed standard value when the wind turbine is stably running, is the minimum speed standard value of the wind turbine during the frequency support process;

[0041] The t off is set according to the following relationship:

[0042] The speed recovery adjustment factor b is set according to the following relationship:

[0043] A control system for providing frequency support to a flexible interconnected power distribution network, characterized by comprising,

[0044] A DC voltage monitoring and processing module: in the control loop of the grid-side converter, the DC voltage of the permanent magnet direct drive wind turbine grid-side converter is measured, and the standard value and phase of the DC voltage are calculated, and the amplitude of the grid-side modulation voltage is calculated;

[0045] A grid-side PWM trigger signal generation module: combined with the phase of the DC voltage and the amplitude of the grid-side modulation voltage, the trigger pulse signal of the grid-side converter is generated;

[0046] A wind wheel dynamic monitoring and optimal power calculation module: in the control loop of the machine-side converter, the speed of the wind wheel and the rotor position angle of the synchronous generator are detected, the machine-side current is converted, and the standard value of the optimal power is obtained;

[0047] An active power reference value calculation module: the active power reference value is calculated through the standard value of the optimal power;

[0048] A machine-side modulation voltage output module: after combining the active power control link and the current control link, the d-axis component and the q-axis component of the machine-side converter modulation voltage are output, and the three-phase modulation voltage in the stationary coordinate system is obtained through the rotation coordinate transformation;

[0049] Machine side PWM trigger signal generation module: the three-phase modulation voltage passes through a pulse width modulation link to generate a trigger pulse signal of the machine side converter.

[0050] The application has the following advantages: the wind turbine has the operation characteristic of actively supporting the flexible interconnected power distribution network, the droop control about the DC voltage is introduced to the active reference value of the machine side converter, the method of adjusting the droop coefficient according to the wind wheel speed in real time is proposed, the wind turbine can provide fast frequency support for the flexible interconnected power distribution network in the frequency support stage, and the speed stall of the wind turbine can be effectively avoided and the secondary drop of the frequency of the flexible interconnected power distribution network in the speed recovery process of the wind turbine can be inhibited. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0052] Fig. 1 is a whole flow chart of the control method for providing the frequency support for the flexible interconnected power distribution network provided by the first embodiment of the application;

[0053] Fig. 2 is a control system block diagram of the control method for providing the frequency support for the flexible interconnected power distribution network provided by the first embodiment of the application;

[0054] Fig. 3 is a simulation waveform diagram of the wind turbine using the maximum power tracking control in the flexible interconnected power distribution network provided by the second embodiment of the application;

[0055] Fig. 4 is a simulation waveform diagram of the wind turbine using the constant droop coefficient in the flexible interconnected power distribution network provided by the second embodiment of the application;

[0056] Fig. 5 is a simulation waveform diagram of the wind turbine using the control architecture of the application in the flexible interconnected power distribution network provided by the second embodiment of the application. DETAILED DESCRIPTION

[0057] In order to make the above-mentioned purpose, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor should be within the protection scope of the application.

[0058] Embodiment 1

[0059] 1 and 2 , an embodiment of the present invention provides a control method for providing frequency support for a flexible interconnected distribution network, including:

[0060] S1: Using a permanent magnet direct-drive wind turbine connected to a flexible interconnected distribution network to provide frequency support, the DC voltage of the grid-side converter of the permanent magnet direct-drive wind turbine is measured in the control loop of the grid-side converter, and the per-unit value and phase of the DC voltage are calculated, as well as the amplitude of the grid-side modulation voltage.

[0061] DC voltage u of the grid-side converter dc Divide by the rated value of DC voltage u dcn Get the per-unit value of DC voltage After the gain is ω n The output of the integrator is phase θ, where ω n is the rated angular frequency of the grid.

[0062] The calculation of the amplitude of the grid-side modulation voltage includes the reference value of the grid-side converter output reactive power Q gere and feedback value Q g The difference is passed through a PI regulator and then superimposed with the initial amplitude of the grid-side modulation voltage U t0 Get the amplitude of the grid-side modulation voltage U t .

[0063] It should be noted that the measurement of DC voltage in the grid-side converter control loop of permanent magnet direct-drive wind turbines first requires measuring the converter's DC voltage u dc This measurement is fundamental to the entire control strategy, as the DC voltage level directly affects the power level that the converter can deliver to the grid. By measuring the DC voltage u dc Divide by the rated value of DC voltage u dcn To calculate:

[0064] The purpose of this step is to standardize the voltage value so that it can be compared and controlled with other system parameters or standard values. The DC voltage standard value obtained by phase calculation is After a gain of ω n After the integrator, the output is phase θ, where ω n Represents the rated angular frequency of the grid. The purpose of this process is to adjust the output phase according to the change of DC voltage to maintain synchronization with the grid. Calculation of the grid-side modulation voltage amplitude The grid-side modulation voltage amplitude U t The calculation involves the reference value Q of the grid-side converter output reactive power gere and feedback value Q gThe difference is processed by a proportional-integral (PI) regulator and added to the initial amplitude U t0 Superposition: U t = PI (Q gere - Q g ) + U t0

[0065] Here, the role of the PI regulator is to adjust the reactive power output to maintain grid stability and effective operation of the wind turbine. The amplitude U t of the grid-side modulation voltage directly affects the power supply of the converter to the grid.

[0066] S2: Based on the phase of the DC voltage and the amplitude of the grid-side modulation voltage, generate the trigger pulse signal of the grid-side converter.

[0067] Integrate the phase θ and amplitude U t into a modulation signal.

[0068] Generating the trigger pulse signal of the grid-side converter includes generating a sinusoidal waveform reference signal synchronized with the grid frequency based on the integrated modulation signal, and generating a high-frequency triangular wave carrier signal with a frequency higher than the reference signal for pulse width modulation.

[0069] By comparing the reference signal with the carrier signal, when the amplitude of the reference signal is higher than that of the carrier signal, a high level is generated, and vice versa, a low level is generated, to generate the PWM signal.

[0070] The amplitude and phase information of the reference signal are encoded into the pulse width of the PWM signal to control the shape and size of the output voltage of the grid-side converter.

[0071] The generated PWM signal is used to directly drive the switching elements of the grid-side converter to generate the trigger pulse signal Sgabc of the grid-side converter.

[0072] It should be noted that the system integrates the measured DC voltage phase θ and the amplitude U t of the grid-side modulation voltage into a modulation signal. This modulation signal integrates the voltage conditions on the DC side and the reflection of the demand for grid power output, laying the foundation for generating a modulation signal synchronized with the grid frequency.

[0073] Reference signal: Based on the integrated modulation signal, the system generates a sinusoidal waveform reference signal synchronized with the grid frequency. The amplitude and phase of this reference signal are determined by the integrated modulation signal to ensure that the output of the grid-side converter is consistent with the requirements of the grid.

[0074] Carrier signal: a high frequency triangular wave carrier signal is generated simultaneously with the grid frequency synchronous sinusoidal wave reference signal. The high frequency characteristic of the carrier signal enables the final PWM signal to finely control the switching elements over a wide frequency range, thus accurately regulating the output voltage.

[0075] Further, the PWM signal is generated by comparing the reference signal with the carrier signal: when the amplitude of the reference signal is higher than the carrier signal, output high level (ON state); otherwise, when the amplitude of the reference signal is lower than the carrier signal, output low level (OFF state). This process encodes the amplitude and phase information of the reference signal into the pulse width of the PWM signal, allowing the output voltage shape and size of the grid-side converter to be controlled by adjusting the duty cycle of the PWM signal.

[0076] Further, the generated PWM signal is used to directly drive the switching elements (such as IGBTs) of the grid-side converter, generating the trigger pulse signal Sgabc of the grid-side converter. This step is the key link to actually control the converter output to meet the grid requirements. The PWM signal controls the precise switching action of the switching elements, generating the required AC output voltage, thus achieving effective power support for the grid.

[0077] S3: In the control loop of the machine-side converter, the speed of the wind turbine and the rotor position angle of the synchronous generator are detected, the machine-side current is transformed, and the optimal power is obtained.

[0078] In the control loop of the machine-side converter, the speed of the wind turbine ω t and the rotor position angle θr of the synchronous generator are detected.

[0079] The three-phase AC current isabc of the machine-side converter is transformed into the current i sd , i sq in the dq coordinate system through rotation coordinate transformation, and the phase for rotation coordinate transformation is θr.

[0080] The speed of the wind turbine is divided by the rated value of the speed of the wind turbine ω tn to obtain the unit value of the speed of the wind turbine The unit value of the optimal power is obtained through the maximum power tracking control module

[0081] It should be noted that in the control loop of the machine-side converter, the first step is to detect the speed of the wind turbine ω and the rotor position angle θ rReal-time monitoring of these two parameters is essential for understanding the current operating state of the wind turbine and adjusting its output. • Wind rotor speed ω: Directly affects the output power of the generator, and is therefore crucial for optimizing power generation efficiency. • Rotor position angle θ r : Determines the relationship between the motor flux and the current phase, which is necessary for achieving efficient energy conversion and controlling the electromagnetic behavior of the motor. The three-phase AC current i sabc is converted into the dq coordinate system through a rotating coordinate transformation (commonly known as Park's transformation) to obtain the current components i sd and i sq . This step is crucial for achieving efficient energy control, as it allows the control system to handle the direct current (d-axis) and alternating current (q-axis) components separately, simplifying the control strategy.

[0082] The phase θ r of the rotating coordinate transformation provides the angular reference needed to convert the three-phase current into two direct-axis current components.

[0083] The normalized value of the wind rotor speed ω is calculated by dividing the actual wind rotor speed ω by the rated value of the wind rotor speed ω n . This normalized value is used to quantify the position of the wind rotor speed relative to its designed operating point.

[0084] The normalized value of the optimal power P is calculated by the MPPT control module based on the normalized value of the wind rotor speed ω . The purpose of the MPPT control module is to adjust the operating point of the wind turbine so that it always operates at the maximum power output point, which changes with the wind speed.

[0085] S4: Calculate the active power reference value P

[0086] First, the output of the gating control module is a flag Flag.

[0087] Flag enters the control port Ctrl of the controlled switch S1, and the constant 20 is input as the position 1 of the controlled switch S1, and the control coefficient K P is input as the position 2 of the controlled switch S1.

[0088] The difference between the digital 1 and the DC voltage normalized value V is multiplied by the output of the controlled switch S1, and then superimposed to obtain the reference value of the active power output of the machine-side converter P

[0089] The gating control module adopts the following control structure:​

[0090] The input of the gating control module is the unit value of the rotor speed The rated value of the rotor speed The deviation of the rotor speed is obtained by subtraction Judgment Whether it is less than 0.015 p.u.

[0091] If The value of the flag bit F1 is 1; if The value of the flag bit F1 is 0.

[0092] The rate of change of the unit value of the rotor speed is calculated Judgment Whether it is less than 0.01 p.u.

[0093] If The value of the flag bit F2 is 1; if The value of the flag bit F2 is 0.

[0094] The flag bit F1 and the flag bit F2 are subjected to Boolean logic operation to generate the flag bit Flag, which is the output of the gating control module.

[0095] The Boolean logic operation is that when F1=1 and F2=1, Flag is 1, and when all other cases occur, Flag is 0.

[0096] The output of the controlled switch S1, the input and the control port Ctrl satisfy the following relationship:

[0097] When the value of the control port Ctrl is 0, the output of the controlled switch S1 is the input of position 1.

[0098] When the value of the control port Ctrl is 1, the output of the controlled switch S1 is the input of position 2.

[0099] Further, the expression of the control coefficient K P is:

[0100] Wherein, k is the frequency modulation coefficient, b is the speed recovery adjustment factor, t represents the actual variable, t swc is the time when the controlled switch S1 is switched from position 1 to position 2, t off is the time when the control coefficient K P is reduced.

[0101] The frequency modulation coefficient k satisfies the following relationship:

[0102] Wherein, The minimum speed reference value of the wind turbine during the frequency support process, The minimum speed reference value of the wind turbine during the frequency support process,

[0103] It should be noted that the minimum speed reference value of the wind turbine during the frequency support process The minimum speed reference value of the wind turbine during the frequency support process,

[0104] The real-time speed of the wind wheel is detected every 1 millisecond, and the real-time speed of the wind wheel in the last 1 second is detected, and the obtained 1000 data are sent to the memory.

[0105] The data sent to the memory are processed, and the 1000 data are divided into 100 groups, and the average value of 10 data in each group is calculated.

[0106] The minimum average value in the 100 average values is the minimum speed reference value

[0107] t off The minimum speed reference value of the wind turbine during the frequency support process,

[0108] The speed recovery regulation factor b is set according to the following relationship:

[0109] S5: After combining the active power control link and the current control link, the d-axis component and the q-axis component of the machine-side converter modulation voltage are output, and the three-phase modulation voltage in the stationary coordinate system is generated through the rotating coordinate transformation.

[0110] After entering the active power control link and then entering the current control link, the d-axis component of the machine-side converter modulation voltage is output The q-axis component The three-phase modulation voltage in the stationary coordinate system is generated through the rotating coordinate transformation

[0111] Further, the active power reference value is calculated from the previous step (S4) and represents the active power output target that the machine-side converter needs to achieve. First, enter the active power control link, and here the difference between the reference value and the actual output power is calculated through the adjustment strategy (such as a PI controller) to calculate the d-axis voltage component that needs to be adjusted to compensate for the difference and achieve accurate control of active power.

[0112] Subsequently, according to the output of the active power control link and the actual measurement value of the current, the current control link calculates the q-axis voltage component adjustment value to control the reactive power of the machine-side converter, further optimizing system performance. The results of the active power control and current control loops are the d-axis component and the q-axis component of the modulation voltage and After the rotational coordinate transformation (usually an inverse Park transformation), the three-phase modulation voltage in the stationary coordinate system is generated This step converts the voltage components on the d-axis and q-axis back to the traditional three-phase AC voltage form, facilitating the driving of the wind turbine through the machine-side converter and enabling effective interaction with the grid.

[0113] S6: The three-phase modulation voltage undergoes a pulse width modulation (PWM) stage to generate the trigger pulse signal S mabc for the machine-side converter.

[0114] The trigger pulse signal S mabc for the machine-side converter is generated after the pulse width modulation (PWM) stage.

[0115] It should be noted that the three-phase modulation voltage obtained from the previous step (S5) is used as the input to the PWM modulation stage. This three-phase voltage, obtained through rotational coordinate transformation, reflects the voltage waveform and amplitude that the machine-side converter needs to output. In the PWM stage, it is compared with one or more high-frequency carrier signals. The carrier signals are usually fixed-frequency triangular or sawtooth waves. When the modulation voltage is higher than the carrier signal, a high level (ON state) is output; when the modulation voltage is lower than the carrier signal, a low level (OFF state) is output.

[0116] The resulting high-low level sequence from this comparison is the PWM signal, which is used to directly drive the switching elements (such as IGBTs) of the machine-side converter, generating the trigger pulse signal S mabc . By precisely controlling the pulse width (i.e., the duration of each pulse) of the PWM signal, the shape and amplitude of the converter output voltage can be finely adjusted, thereby controlling the operating state of the motor.

[0117] Furthermore, PWM technology minimizes energy loss by operating switching elements only in fully on or fully off states, improving the energy efficiency of the system. By adjusting the pulse width of the PWM signal, the output voltage and current can be very accurately controlled, enabling fine control of the motor and optimizing operating performance. PWM allows the system to flexibly adjust the speed and torque of the motor according to actual needs, adapting to different operating conditions and load requirements.

[0118] The above also includes a control system that can provide frequency support for a flexible interconnected power distribution network, specifically comprising:

[0119] A DC voltage monitoring and processing module: in the control loop of the grid-side converter, the DC voltage of the grid-side converter of the permanent magnet direct drive wind turbine is measured, and the unit value and phase of the DC voltage are calculated, and the amplitude of the grid-side modulation voltage is calculated.

[0120] A grid-side PWM trigger signal generation module: combined with the phase of the DC voltage and the amplitude of the grid-side modulation voltage, the trigger pulse signal of the grid-side converter is generated.

[0121] A wind wheel dynamic monitoring and optimal power calculation module: in the control loop of the machine-side converter, the rotational speed of the wind wheel and the rotor position angle of the synchronous generator are detected, the machine-side current is converted, and the unit value of the optimal power is obtained.

[0122] An active power reference value calculation module: the active power reference value is calculated through the unit value of the optimal power.

[0123] A machine-side modulation voltage output module: after combining the active power control link and the current control link, the d-axis component and the q-axis component of the machine-side converter modulation voltage are output, and the three-phase modulation voltage in the stationary coordinate system is obtained through the rotation coordinate transformation.

[0124] A machine-side PWM trigger signal generation module: the three-phase modulation voltage is generated through the pulse width modulation link to generate the trigger pulse signal of the machine-side converter.

[0125] The computer device can be a server. The computer device includes a processor, a memory, an input / output interface (I / O), and a communication interface. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store the data cluster data of the power monitoring system. The input / output interface of the computer device is used to exchange information between the processor and external devices. The communication interface of the computer device is used to communicate with external terminals through network connection. The computer program is executed by the processor to implement a control method that can provide frequency support for a flexible interconnected power distribution network.

[0126] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when executed, can include the processes of the above-mentioned embodiments. Any reference to memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical storage, high-density embedded non-volatile memory, resistive memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration but not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The database involved in the embodiments provided in the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a block chain, etc., without being limited thereto. The processor involved in the embodiments provided in the present application can be a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., without being limited thereto.

[0127] Embodiment 2

[0128] Referring to FIGS. 3-5, according to an embodiment of the present application, a control method for providing frequency support for a flexible interconnected power distribution network is provided. In order to verify the beneficial effects of the present application, economic benefit calculation and simulation / contrast experiments are used for scientific demonstration.

[0129] Referring to FIG. 3, simulation waveforms of a wind turbine using maximum power tracking control in a flexible interconnected power distribution network are shown, in which the wind speed is 10 m / s, the frequency of the stable operation of the flexible interconnected power distribution network is 50 Hz, and the disturbance is 1.5 MW. After the disturbance of 40 seconds is added to the flexible interconnected power distribution network, the frequency of the flexible interconnected power distribution network drops to 49.79 Hz, the wind turbine rotor speed remains unchanged, and the output power of the wind turbine fluctuates slightly and then recovers.

[0130] Please refer to Figure 4, for the simulation waveform of the wind turbine with constant droop coefficient in the flexible interconnected power distribution network, wherein the constant droop control is introduced on the basis of the maximum power tracking control of the machine side converter, the droop coefficient value is 20, the wind speed is 10 m / s, the frequency of the stable operation of the flexible interconnected power distribution network is 50 Hz, and the disturbance is 1.5 MW. After the disturbance of 40 seconds is added to the flexible interconnected power distribution network, the active power output of the wind turbine increases, and the wind wheel speed of the wind turbine decreases to 0.776 p.u. Compared with the maximum power tracking control, the minimum point of the frequency of the flexible interconnected power distribution network is improved by 0.03 Hz when the constant droop coefficient control strategy is used, and there is a sudden change of the active load of 0.12 p.u. in the speed recovery process, which causes the secondary drop of the frequency of the flexible interconnected power distribution network.

[0131] Please refer to Figure 5, for the simulation waveform of the wind turbine with the control architecture of the application in the flexible interconnected power distribution network, wherein the wind speed is 10 m / s, the frequency of the stable operation of the flexible interconnected power distribution network is 50 Hz, the disturbance is 1.5 MW, the frequency modulation coefficient k is 0.141, and the speed recovery adjustment factor b is 8.38. After the disturbance of 40 seconds is added to the flexible interconnected power distribution network, the active power output of the wind turbine increases, and the wind wheel speed of the wind turbine decreases to 0.776 p.u. Compared with the maximum power tracking control, the minimum point of the frequency of the flexible interconnected power distribution network is improved by 0.03 Hz, and the wind wheel speed of the wind turbine recovers slowly, which effectively weakens the secondary drop of the frequency of the flexible interconnected power distribution network.

[0132] In summary, the control system of the application can make the wind turbine have the operation characteristics of actively supporting the flexible interconnected power distribution network, introduce the droop control about the DC voltage on the active reference value of the machine side converter, and propose the method of adjusting the droop coefficient according to the wind wheel speed in real time, so that the wind turbine can provide fast frequency support for the flexible interconnected power distribution network in the frequency support stage, and the speed stall of the wind turbine can be effectively avoided in the speed recovery stage, and the secondary drop of the frequency of the flexible interconnected power distribution network in the speed recovery process of the wind turbine is inhibited.

[0133] It should be noted that the above embodiments are only used to illustrate the technical solutions of the application rather than limit the application, although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the application, and all should be covered in the scope of the claims of the application.

Claims

1. A control method for providing frequency support to a flexible interconnected power distribution network, characterized by, The method comprises the following steps: A permanent magnet direct drive type wind turbine connected to a flexible interconnected power distribution network provides frequency support. In the control loop of the grid-side converter, the DC voltage of the grid-side converter of the permanent magnet direct drive type wind turbine is measured, and the unit value and phase of the DC voltage are calculated, and the amplitude of the grid-side modulation voltage is calculated; The phase of the DC voltage and the amplitude of the grid-side modulation voltage are combined to generate a trigger pulse signal of the grid-side converter; In the control loop of the machine-side converter, the rotational speed of the wind wheel and the rotor position angle of the synchronous generator are detected, the machine-side current is converted, and the unit value of the optimal power is obtained; The unit value of the optimal power is used to calculate an active power reference value; After combining the active power control link and the current control link, the d-axis component and the q-axis component of the machine-side converter modulation voltage are output, and the three-phase modulation voltage in the stationary coordinate system is obtained through the rotation coordinate transformation; The three-phase modulation voltage passes through a pulse width modulation link to generate a trigger pulse signal of the machine-side converter.

2. The control method of claim 1, wherein: The calculating the unit value and the phase of the direct current voltage comprises dividing the direct current voltage u dc by the rated value u dcn of the direct current voltage n to obtain the unit value of the direct current voltage The output after the integrator with the gain ω n is the phase θ, wherein ω n is the rated angular frequency of the power grid The amplitude of the grid-side modulation voltage includes the reference value Q of the output reactive power of the grid-side converter gere The difference between the feedback value Q g After a PI regulator, the initial amplitude U t0 of the grid-side modulation voltage is obtained.

3. The method of claim 2, wherein the method further comprises: determining a frequency support requirement of the flexible interconnected distribution network; and determining a frequency support capability of the flexible interconnected distribution network. The combining the phase of the direct voltage and the amplitude of the grid-side modulation voltage comprises combining the phase θ with the amplitude U t into one modulation signal; The trigger pulse signal of the grid-side converter comprises generating a sine wave reference signal synchronized with the grid frequency based on the integrated modulation signal, and simultaneously generating a high-frequency triangular wave carrier signal with a frequency higher than the reference signal for pulse width modulation; By comparing the reference signal with the carrier signal, when the amplitude of the reference signal is higher than that of the carrier signal, a high level is generated, and vice versa, to generate a PWM signal; The amplitude and phase information of the reference signal are encoded into the pulse width of the PWM signal to control the shape and size of the output voltage of the grid-side converter; The gating control is performed, and the output is a flag bit Flag; The generated PWM signal is used to directly drive the switching element of the grid-side converter, and a trigger pulse signal S of the grid-side converter is generated gabc .

4. The method of claim 3, wherein the method further comprises: determining a frequency support requirement of the flexible interconnected power distribution network; and determining a frequency support capability of the flexible interconnected power distribution network. The acquisition of the optimal power standard value includes, in the control loop of the machine side converter, detecting the wind wheel rotating speed ω t and the rotor position angle θr of the synchronous generator; The three-phase alternating current isabc of the machine-side converter is subjected to a rotating coordinate transformation to obtain currents i sd , sq , the phase for the rotating coordinate transformation is θr; Wind wheel rotational speed Rated value ω of the wind wheel rotational speed divided by the wind wheel rotational speed tn Obtaining a unit value of the wind wheel rotational speed a maximum power tracking control module obtains a standard value of the optimal power The calculating the active power reference value comprises, for each of the plurality of time intervals, The gating control module adopts the following control structure, Flag enters the control port Ctrl of the controlled switch S1, the constant 20 as the input of the position 1 of the controlled switch S1, the control coefficient K P as the input of the position 2 of the controlled switch S1; Utilizing digital 1 and dc voltage reference Difference, multiplied by the output of the controlled switch S1 and superimposed obtaining a reference value for the active power of the machine-side converter output The three-phase modulation voltage converted to the stationary coordinate system by the rotation coordinate conversion includes, into the active power control loop, and then into the current control loop to output the d-axis component of the machine-side converter modulation voltage q-axis component Generating three-phase modulation voltages in a stationary coordinate system by a rotation coordinate transformation 5. The method of claim 4, wherein the method further comprises: determining a frequency support requirement of the flexible interconnected power distribution network; and determining a frequency support capability of the flexible interconnected power distribution network. whether less than 0.015 p.u.; The input of the gating control module is the unit value of the wind wheel rotating speed with the rated value of the rotational speed of the wind wheel Subtracting gives the deviation of the rotor speed determining If yes, the value of the flag bit F1 is 0; If The value of flag F1 is 1; if whether less than 0.01 p.u.; Computing the rate of change of the rotor speed normalised value determining If yes, the value of the flag bit F2 is 0; If the value of the flag F2 is 1; and if The flag bit F1 and the flag bit F2 are subjected to Boolean logic operation to generate a flag bit Flag, which is the output of the gating control module; The Boolean logic operation is that when F1=1 and F2=1, Flag is 1, and when all other conditions occur, Flag is 0; The output, input and control port Ctrl of the controlled switch S1 satisfy the following relationship: When the value of the control port Ctrl is 0, the output of the controlled switch S1 is the input of position 1; When the value of the control port Ctrl is 1, the output of the controlled switch S1 is the input of position 2. The minimum rotational speed unit value of the wind turbine in the frequency support process; 6. The control method of claim 5, wherein: The control coefficient K P The expression is: where k is the frequency modulation coefficient, b is the speed recovery regulation factor, t represents the actual variable, t swc is the time instant at which the controlled switch S1 is switched from position 1 to position 2, t off is the control coefficient K P is reduced.

7. The method for providing frequency support to a flexible interconnected power distribution network of claim 6, wherein: The frequency modulation coefficient k satisfies the following relationship: wherein to stabilize the synchronous generator speed reference for wind turbine operation, The method comprises the following steps: The t off Adjusting according to the following relationship: The rotational speed recovery regulation factor b is set according to the following relationship:

8. A control system for providing frequency support to a flexible interconnected power distribution network using the method of any one of claims 1 to 7. A DC voltage monitoring and processing module measures the DC voltage of the grid-side converter of the permanent magnet direct drive type wind turbine in the control loop of the grid-side converter, and calculates the unit value and phase of the DC voltage, and calculates the amplitude of the grid-side modulation voltage; A grid-side PWM trigger signal generation module combines the phase of the DC voltage and the amplitude of the grid-side modulation voltage to generate a trigger pulse signal of the grid-side converter; A wind wheel dynamic monitoring and optimal power calculation module detects the rotational speed of the wind wheel and the rotor position angle of the synchronous generator in the control loop of the machine-side converter, converts the machine-side current, and obtains the unit value of the optimal power. ​ An active power reference value calculation module: through the optimal power reference value, an active power reference value is calculated; A machine-side modulation voltage output module: after combining the active power control link and the current control link, a d-axis component and a q-axis component of a machine-side converter modulation voltage are output, and are converted to a three-phase modulation voltage in a stationary coordinate system through a rotating coordinate conversion; A machine-side PWM trigger signal generation module: the three-phase modulation voltage is converted to a trigger pulse signal of the machine-side converter through a pulse width modulation link. 9.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-8 when the computer program is executed by the processor. The processor executes the computer program to implement the steps of the method in any one of claims 1 to 7.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the method in any one of claims 1 to 7.

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