A hybrid mode new energy power transmission system through flexible direct current transmission rapid power control method

Abstract

The application discloses a hybrid mode new energy through flexible direct current sending-out system rapid power control method, and relates to the technical field of new energy through flexible direct current sending-out system and power electronics. The MMC sending end active current instruction of the fusion control is communicated to the MMC sending end by the grid-connected type inverter and is generated through the MMC sending end rapid power calculation formula, and the MMC sending end grid-connected active current instruction is generated by the MMC sending end power compensation calculation formula, so that the MMC sending end active power can be rapidly and stably sent out under a larger communication delay, and the problem that the active power of a new energy large base cannot be rapidly sent out to support the active demand of the receiving end when the grid-connected type equipment exists is solved.

Description

Technical Field

[0001] This invention relates to the fields of new energy transmission via flexible DC systems and power electronics, specifically to a fast power control method for a hybrid-mode new energy transmission via flexible DC systems. Background Technology

[0002] With the continuous construction of large-scale clean energy bases, the stability research of flexible DC transmission systems from these bases has received widespread attention. These bases lack conventional power supply support, thus requiring a large number of reactive power compensation devices and grid-type devices to enhance their voltage and frequency support capabilities. Simultaneously, with the continuous inflow of DC power, the receiving-end system gradually exhibits weak voltage and frequency strength, necessitating a flexible DC system to provide frequency and voltage support. However, the large-scale addition of grid-type devices to these bases leads to a distribution of active power between the grid-type devices and the MMC (Multi-Mechanical Control Center) transmitter when the active power from the new energy source is rapidly transmitted, preventing rapid transmission through the MMC transmitter. Furthermore, when the receiving-end system requires frequency support, the active power transmission speed is limited. Several papers have studied the active power absorption characteristics of grid-connected and network-structured equipment, for example: 1) In the paper "Power-Sharing between Grid-Forming and Grid-Following Inverters" published at the "2021 IEEE 22nd Workshop on Control and Modelling of Power Electronics (COMPEL)" conference in 2021, active power redistribution was achieved by adding control to grid-forming devices to change their active power absorption characteristics. However, this would affect the performance of grid-forming devices and the parameter design would be complex. 2) In the article "Stage-by-Stage Distribution of Disturbance Power in Hybrid Systems of Grid-Connected and Grid-Building Converters" published in the journal "Electric Power Automation Equipment" in 2025, a stage-by-stage control method was proposed to address the differences in the characteristics of active power at different time scales. This method reshapes the active power distribution characteristics between grid-connected and grid-building equipment, but requires adding more additional control to the equipment. However, research is lacking on the issue of grid-type equipment spontaneously absorbing active power and affecting active power transmission in flexible DC transmission systems for new energy sources. As flexible DC transmission continues to feed in, the frequency stability of the receiving-end grid gradually weakens, requiring active support from the frequency regulation equipment at the sending end of the flexible DC dispatching system. Therefore, it is necessary to study a fast active power control method at the sending end using MMC (Multi-Mode Control) to achieve rapid support for the receiving-end grid. Summary of the Invention

[0003] The technical problem this invention aims to solve is the complex parameter design of grid-connected equipment, the gradual weakening of frequency stability in the receiving-end power grid, and the slow active power delivery of the MMC (Multi-mode DC transmission) system. This invention proposes a fast power control method for hybrid-mode renewable energy transmitted via a flexible DC transmission system. This invention transmits the active power step command from the grid-connected renewable energy inverter to the MMC transmitting end, which employs fusion control, through communication. It then achieves rapid active power delivery through fast power and power compensation calculations at the MMC transmitting end, avoiding the slow active power delivery problem caused by the large amount of active power absorbed by grid-connected equipment in large-scale renewable energy bases during the active power ramp-up phase.

[0004] The technical solution of the present invention is as follows.

[0005] A fast power control method for a hybrid-mode renewable energy transmission system via flexible DC transmission is disclosed. The system employing this method includes a renewable energy power plant, an equivalent coupling impedance, and a MMC (Multi-Mechanical Control Unit) transmitter. The renewable energy power plant includes a grid-connected inverter, a grid-connected inverter, and equivalent impedances of branch transmission lines. Two inverters converge at a common coupling point via the equivalent impedances of the branch transmission lines. The renewable energy power plant is connected to the MMC transmitter via the equivalent coupling impedance connected in series at the common coupling point. The steps of the control method are as follows: Step 1, sample the AC side voltage u of the grid-connected inverter. GFLa ,u GFLb ,u GFLc and AC side current i GFLa i GFLb i GFLc And after coordinate transformation, the dq-axis voltage u of the AC side of the grid inverter is obtained. GFLd ,u GFLq And the AC side dq axis current i of the grid-connected inverter GFLd i GFLq When the active power command value P of the grid-connected inverter is detected... refGFL When the power jumps from 0p.u to the step threshold, it will be related to the active power command value P of the grid inverter. refGFL Send to the MMC sender via communication; Given the reactive power command value Q of the grid-connected inverter refGFL The current command value i of the grid-connected inverter is obtained by calculating the current command of the grid-connected inverter. drefGFL i qrefGFL According to the AC side dq axis voltage u of the grid-connected inverter GFLd ,u GFLq , and the AC side dq axis current i of the grid-connected inverter GFLd i GFLq The command value of the dq axis current of the grid-connected inverter i drefGFL i qrefGFLThe dq-axis voltage modulation waveform m of the grid-connected inverter is obtained by using the closed-loop control equation of the AC current loop. GFLd ,m GFLq The three-phase voltage modulation waveform m of the grid inverter is obtained through coordinate transformation. GFLa ,m GFLb ,m GFLc Then, through SPWM modulation, switching signals for the power devices of the grid-connected inverter are generated to control the on and off of the power devices of the grid-connected inverter. Step 2, the MMC sending end receives the active power command value P from the grid-connected inverter. refGFL The active power command P of MMC and grid is obtained according to the fast power calculation formula of MMC sending end. refMMCGFL The active power command P for MMC network construction is obtained based on the MMC sending-end power compensation calculation formula. refMMCGFM ; Sampled MMC AC side voltage u MMCa ,u MMCb ,u MMCc Sample the AC side current i at the MMC sending end MMCa i MMCb i MMCc The MMC grid current i is obtained through the MMC equivalent current calculation equation. MMCGFLa i MMCGFLb i MMCGFLc and MMC network current i MMCGFMa i MMCGFMb i MMCGFMc ; According to the MMC and network active command P refMMCGFL MMC AC side voltage u MMCa ,u MMCb ,u MMCc MMC and grid current i MMCGFLa i MMCGFLb i MMCGFLc， The dq-axis MMC-modulated waveform e is obtained through MMC mesh control. GFLd ,e GFLq Then, through coordinate transformation, the MMC ground-mode modulated wave e is obtained. GFLa ,e GFLb ,e GFLc ; Based on the AC side voltage u of the MMC sending end MMCa ,u MMCb ,u MMCc and MMC network current i MMCGFMa i MMCGFMb i MMCGFMc The dq-axis MMC network modulated wave e is obtained through the MMC network voltage control loop and the MMC network current control loop. GFMd ,eGFMq Then, the MMC network modulation wave e is obtained through coordinate transformation. GFMa ,e GFMb ,e GFMc ; The MMC modulated wave e is obtained by superimposing the two modulated waves according to the MMC network modulation wave superposition calculation formula. MMCa ,e MMCb ,e MMCc Then, the switching signal of the MMC power device is generated by modulation through a circulating current suppressor to control the turn-on and turn-off of the MMC power device.

[0006] Preferably, the step threshold in step 1 is 1.0 pu.

[0007] Preferably, the current command calculation equation for the grid-connected inverter in step 1 is as follows:

[0008]

[0009] The closed-loop control equation for the AC current loop of the grid-connected inverter is as follows:

[0010]

[0011] Among them, K p_CCGFL K is the proportional coefficient of the PI regulator for AC current control of the grid-connected inverter. i_CCGFL s represents the integral coefficient of the PI regulator controlling the AC current of the grid-connected inverter, and s represents the Laplace operator.

[0012] Preferably, the MMC sending-end fast power calculation formula and the MMC sending-end power compensation calculation formula in step 2 are respectively:

[0013]

[0014] Among them, Z eq Z is the equivalent connection impedance value. MMCvir The impedance value is the virtual impedance of the MMC network.

[0015] Preferably, the MMC equivalent current calculation equation in step 2 is:

[0016]

[0017]

[0018]

[0019]

[0020]

[0021] Among them, Y f k is the admittance of the MMC equivalent filter inductor. HYB For a given fusion coefficient, e GFLa’ ,e GFLb’ ,e GFLc’ For the MMC and grid modulation waveform of the previous sampling period, e GFMa’ ,e GFMb’ ,e GFMc’ This is the MMC mesh modulation wave from the previous sampling period.

[0022] Preferably, in step 2, the dq-axis MMC-modulated wave e is obtained through MMC mesh control. GFLd ,e GFLq The control process is as follows: S1, send the AC side voltage u of the MMC terminal. MMCa ,u MMCb ,u MMCc and MMC grid current i MMCGFLa i MMCGFLb i MMCGFLc The grid voltage u at the AC side of the MMC sending end on the dq axis is obtained through coordinate transformation. MMCGFLd ,u MMCGFLq and dq axis MMC and grid current i MMCGFLd i MMCGFLq ; S2, according to the MMC and network active command P refMMCGFL The given MMC and network reactive power command Q refMMCGFL dq axis MMC sending end AC side grid voltage u MMCGFLd ,u MMCGFLq dq axis MMC and grid current i MMCGFLd i MMCGFLq The dq-axis MMC grounding modulated wave e is obtained through the MMC grounding control equations. GFLd ,e GFLq The MMC and network control equations are as follows:

[0023]

[0024] Among them, K p_MMCGFL K is the proportional control coefficient of the PI controller for MMC and grid control. i_MMCGFL s is the integral control coefficient of the MMC-based PI controller, and s is the Laplace operator.

[0025] Preferably, the formula for calculating the superposition of MMC network modulation waves in step 2 is:

[0026]

[0027]

[0028] in, is the given fusion coefficient.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention addresses the problem that when grid-type equipment exists in a large-scale new energy base, the active power absorption by the grid-type equipment causes the MMC sending end to be unable to quickly send out active power. By transmitting the active power command to the MMC sending end using fusion control via communication, and realizing the rapid active power transmission of the MMC through rapid power calculation and power compensation calculation, the requirements for communication delay are low. Even when the communication delay is large, the flexible DC active power can be transmitted quickly and stably. 2. Compared with traditional control, this invention can quickly send out the active power of the new energy base when the flexible DC receiving-end grid needs active power support, thereby improving the active support capability of flexible DC and adapting to scenarios where the strength of the receiving-end grid weakens due to multiple DC feeds. Attached Figure Description

[0030] Figure 1 This is a topology diagram of the hybrid mode new energy system via a flexible DC system used in this embodiment of the invention.

[0031] Figure 2 This is a flowchart illustrating the implementation of the control method of the present invention.

[0032] Figure 3 The waveform diagram shows the active power output from the MMC transmitter when the method of the present invention is used.

[0033] Figure 4 The waveform of active power sent by the MMC transmitter when the method of the present invention is not used is shown.

[0034] Figure 5 The waveform of active power sent by the MMC transmitter when the communication delay is 20ms using the method of this invention is shown. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings.

[0036] The hybrid mode new energy system topology used in this invention is as follows: Figure 1 As shown. By Figure 1As can be seen, the system applying this method includes a new energy power station, an equivalent connection impedance, and an MMC sending end; the new energy power station includes a grid-connected inverter, a grid-connected inverter, and an equivalent impedance of the branch transmission line, and the two inverters converge at a common coupling point after passing through the equivalent impedance of the branch transmission line; the new energy power station is connected to the MMC sending end after being connected in series with the equivalent connection impedance through the common coupling point.

[0037] exist Figure 1 Above, 10 represents a grid-connected inverter, 20 represents a grid-connected inverter, 30 represents the equivalent impedance of the branch transmission line, 40 represents the renewable energy power station, 50 represents the equivalent connection impedance, 60 represents the MMC sending end, and PCC represents the common coupling point. V dc It is a DC voltage.

[0038] In addition, from Figure 1 It can be seen that the equivalent connection impedance consists of the new energy side transformer, the equivalent impedance of the connection line, and the MMC side transformer. Figure 1 In the diagram, T1 is the transformer for the new energy side, and Z... line T1 is the equivalent impedance of the connecting line, and T2 is the transformer on the MMC side.

[0039] In this embodiment, the main circuit parameters of the MMC are: DC voltage V dc The rated voltage is 515.2kV, the rated output line voltage is 290kV / 50Hz, and the rated power is 0.75GW. The inductive component of the equivalent connection impedance between the renewable energy power station and the MMC sending end, referred to the 290kV side, is 209.96mH. The grid-connected inverter in the renewable energy power station generates an additional 0.375GW of active power, and the transformer ratio on the renewable energy side is 600V / 290kV.

[0040] Figure 2 This is a flowchart of the control method of the present invention. Figure 2 As can be seen, the present invention provides a fast power control method for hybrid-mode new energy transmitted through a flexible DC transmission system, the specific steps of which are as follows: Step 1, sample the AC side voltage u of the grid-connected inverter. GFLa ,u GFLb ,u GFLc and AC side current i GFLa i GFLb i GFLc And after coordinate transformation, the dq-axis voltage u of the AC side of the grid inverter is obtained. GFLd ,u GFLq And the AC side dq axis current i of the grid-connected inverter GFLd i GFLq When the active power command value P of the grid-connected inverter is detected... refGFL When the voltage jumps from 0p.u to the step threshold, it will be related to the active power command value P of the grid inverter. refGFL Send to the MMC sender via communication; Given the reactive power command value Q of the grid-connected inverter refGFL The current command value i of the grid-connected inverter is obtained by calculating the current command of the grid-connected inverter. drefGFL i qrefGFL According to the AC side dq axis voltage u of the grid-connected inverter GFLd ,u GFLq , and the AC side dq axis current i of the grid-connected inverter GFLd i GFLq The command value of the dq axis current of the grid-connected inverter i drefGFL i qrefGFL The dq-axis voltage modulation waveform m of the grid-connected inverter is obtained by using the closed-loop control equation of the AC current loop. GFLd ,m GFLq The three-phase voltage modulation waveform m of the grid inverter is obtained through coordinate transformation. GFLa ,m GFLb ,m GFLc Then, through SPWM modulation, switching signals for the power devices of the grid-connected inverter are generated to control the on and off of the power devices of the grid-connected inverter.

[0041] In this embodiment, the step threshold in step 1 is 1.0 pu.

[0042] The equation for calculating the current command of the grid-connected inverter is as follows:

[0043]

[0044] The closed-loop control equation for the AC current loop of the grid-connected inverter is as follows:

[0045]

[0046] Among them, K p_CCGFL K is the proportional coefficient of the PI regulator for AC current control of the grid-connected inverter. i_CCGFL s represents the integral coefficient of the PI regulator controlling the AC current of the grid-connected inverter, and s represents the Laplace operator.

[0047] Step 2, the MMC sending end receives the active power command value P from the grid-connected inverter. refGFL The active power command P of MMC and grid is obtained according to the fast power calculation formula of MMC sending end. refMMCGFL The active power command P for MMC network construction is obtained based on the MMC sending-end power compensation calculation formula. refMMCGFM ; Sampled MMC AC side voltage u MMCa ,u MMCb ,uMMCc Sample the AC side current i at the MMC sending end MMCa i MMCb i MMCc The MMC grid current i is obtained through the MMC equivalent current calculation equation. MMCGFLa i MMCGFLb i MMCGFLc and MMC network current i MMCGFMa i MMCGFMb i MMCGFMc ; According to the MMC and network active command P refMMCGFL MMC AC side voltage u MMCa ,u MMCb ,u MMCc MMC and grid current i MMCGFLa i MMCGFLb i MMCGFLc， The dq-axis MMC-modulated waveform e is obtained through MMC mesh control. GFLd ,e GFLq Then, the MMC ground-mode modulated wave e is obtained through coordinate transformation. GFLa ,e GFLb ,e GFLc ; Based on the AC side voltage u of the MMC sending end MMCa ,u MMCb ,u MMCc and MMC network current i MMCGFMa i MMCGFMb i MMCGFMc The dq-axis MMC network modulated wave e is obtained through the MMC network voltage control loop and the MMC network current control loop. GFMd ,e GFMq Then, the MMC network modulation wave e is obtained through coordinate transformation. GFMa ,e GFMb ,e GFMc ; The MMC modulated wave e is obtained by superimposing the two modulated waves according to the MMC network modulation wave superposition calculation formula. MMCa ,e MMCb ,e MMCc Then, the switching signal of the MMC power device is generated by modulation through a circulating current suppressor to control the turn-on and turn-off of the MMC power device.

[0048] In this embodiment, the MMC sending-end fast power calculation formula and the MMC sending-end power compensation calculation formula described in step 2 are as follows:

[0049]

[0050] Among them, Zeq Z is the equivalent connection impedance value. MMCvir The impedance value is the virtual impedance of the MMC network.

[0051] The equation for calculating the equivalent current of MMC is as follows:

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] Among them, Y f k is the admittance of the MMC equivalent filter inductor. HYB For a given fusion coefficient, e GFLa’ ,e GFLb’ ,e GFLc’ For the MMC and grid modulation waveform of the previous sampling period, e GFMa’ ,e GFMb’ ,e GFMc’ This is the MMC mesh modulation wave from the previous sampling period.

[0058] The dq-axis MMC mesh modulated wave e obtained through MMC mesh control GFLd ,e GFLq The control process is as follows: S1, send the AC side voltage u of the MMC terminal. MMCa ,u MMCb ,u MMCc and MMC grid current i MMCGFLa i MMCGFLb i MMCGFLc The grid voltage u at the AC side of the MMC sending end on the dq axis is obtained through coordinate transformation. MMCGFLd ,u MMCGFLq and dq axis MMC and grid current i MMCGFLd i MMCGFLq ; S2, according to the MMC and network active command P refMMCGFL The given MMC and network reactive power command Q refMMCGFL dq axis MMC sending end AC side grid voltage u MMCGFLd ,u MMCGFLq dq axis MMC and grid current i MMCGFLd i MMCGFLq The dq-axis MMC grounding modulated wave e is obtained through the MMC grounding control equations.GFLd ,e GFLq The MMC and network control equations are as follows:

[0059]

[0060] Among them, K p_MMCGFL K is the proportional control coefficient of the PI controller for MMC and grid control. i_MMCGFL s is the integral control coefficient of the PI controller for MMC and grid control, and s is the Laplace operator.

[0061] The formula for calculating the superposition of MMC network modulated waves is:

[0062]

[0063]

[0064] in, is the given fusion coefficient.

[0065] The coordinate transformation equations in this embodiment are as follows.

[0066] Step 1 describes the AC side dq axis voltage u of the grid-connected inverter. GFLd ,u GFLq And the AC side dq axis current i of the grid-connected inverter GFLd i GFLq The coordinate transformation equation is:

[0067]

[0068]

[0069]

[0070] Step 1 describes the three-phase voltage modulation waveform m of the grid-connected inverter. GFLa ,m GFLb ,m GFLc The coordinate transformation equation is:

[0071]

[0072]

[0073] Where, θ GFL To synchronize with the grid-connected inverter, a digital phase-locked loop is used to synchronize the AC side voltage u of the grid-connected inverter.GFLa ,u GFLb ,u GFLc Phase-locked loop (PLL) is performed to obtain the result.

[0074] Step 2 describes the AC side voltage u of the dq axis MMC sending end. MMCGFLd ,u MMCGFLq and dq axis MMC and grid current i MMCGFLd i MMCGFLq The coordinate transformation equation is:

[0075]

[0076]

[0077]

[0078] Where, θ MMCGFL The phase of the MMC and the grid is obtained by using a digital phase-locked loop to lock the AC side of the q-axis MMC feed terminal with the grid voltage of the previous sampling period.

[0079] Step 2 describes the AC side grid voltage u at the dq axis MMC sending end. MMCGFMd ,u MMCGFMq and dq axis MMC and grid current i MMCGFM d,i MMCGFMq The coordinate transformation equation is:

[0080]

[0081]

[0082]

[0083] θ MMCGFM For the MMC network phase, the calculation equation is as follows:

[0084] Where, k PMMCGFM P is the active power loop factor for the MMC network. refMMCGFM' The active power command for MMC network construction obtained in the previous cycle; P MMCGFM' The active power of the MMC network obtained in the previous cycle is expressed as follows:

[0085] In the formula, The AC side grid voltage of the dq-axis MMC sending end obtained in the previous cycle. This refers to the dq-axis MMC and grid current obtained in the previous cycle.

[0086] In this embodiment, K p_PLLGFL =0.72, K i_PLLGFL =128, Q refGFL =0,K p_CCGFL =0.2, K i_CCGFL =8, Z eq =65.9608Ω, Z MMCvir =22.4267Ω, K p_PLLMMC =4.1755×10 -4 K i_PLLMMC =1.3902×10 -2 Y f =20 / s, where s is the Laplace operator, and K... p_MMCGFL =1.8943×10 -4 K i_MMCGFL =0.0038, k PMMCGFM =4.1867×10 -10 k QMMCGFM =1.3333×10 -10 U0 = 290kV, K pVC_MMCGFM =2.1116×10 -5 K iVC_MMCGFM =8.4465×10 -4 Z MMCvir =22.4267Ω, K pVC_MMCGFM =1.8943×10 -4 K iVC_MMCGFM =0.0038.

[0087] To demonstrate the beneficial effects of the present invention, MATLAB / Simulink simulations were performed on the invention.

[0088] Figure 3 This is a waveform diagram of the active power output from the MMC sending end when using the method of the present invention. Figure 4 The waveform of active power transmitted from the MMC transmitter without using the method of this invention is shown. Figure 3 It can be seen that at 10 seconds, the active power of the new energy power plant and grid-connected inverter jumps by 312.5MW. When using the method of this invention, the MMC sending end can send active power within 500ms, while the power output from the grid-connected inverter is significantly higher than that from the grid-connected inverter. Figure 4 It can be seen that without the method of this invention, due to the absorption effect of the grid-type equipment in the new energy base on active power, it takes several seconds to send out the active power, and only a portion can be sent out. This greatly limits the active power support capability of the receiving end grid.

[0089] Figure 5The image shows the active power waveform transmitted by the MMC transmitter when the communication delay is 20ms using the method of this invention. Even with a large communication delay, the method of this invention can still transmit active power quickly and stably because it does not negatively impact system stability.

Claims

1. A method for rapid power control of a hybrid-mode renewable energy transmission system via flexible DC transmission, wherein the system using this method includes a renewable energy power plant, an equivalent coupling impedance, and an MMC (Multi-Mechanical Control Unit) transmitter; the renewable energy power plant includes a grid-connected inverter, a grid-connected inverter, and equivalent impedances of branch transmission lines, with two inverters converging at a common coupling point after passing through the equivalent impedances of the branch transmission lines; the renewable energy power plant is connected to the MMC transmitter via the equivalent coupling impedance connected in series at the common coupling point; characterized in that... The control method comprises the following steps: Step 1, sample the AC side voltage u of the grid-connected inverter. GFLa ,u GFLb ,u GFLc and AC side current i GFLa i GFLb i GFLc And after coordinate transformation, the dq-axis voltage u of the AC side of the grid inverter is obtained. GFLd ,u GFLq And the AC side dq axis current i of the grid-connected inverter GFLd i GFLq ; When the active power command value P of the grid-connected inverter is detected refGFL When the power jumps from 0p.u to the step threshold, it will be related to the active power command value P of the grid inverter. refGFL Send to the MMC sender via communication; Given the reactive power command value Q of the grid-connected inverter refGFL The current command value i of the grid-connected inverter is obtained by calculating the current command of the grid-connected inverter. drefGFL i qrefGFL According to the AC side dq axis voltage u of the grid-connected inverter GFLd ,u GFLq , and the AC side dq axis current i of the grid-connected inverter GFLd i GFLq The command value of the dq axis current of the grid-connected inverter i drefGFL i qrefGFL The dq-axis voltage modulation waveform m of the grid-connected inverter is obtained by using the closed-loop control equation of the AC current loop. GFLd ,m GFLq The three-phase voltage modulation waveform m of the grid inverter is obtained through coordinate transformation. GFLa ,m GFLb ,m GFLc Then, through SPWM modulation, switching signals for the power devices of the grid-connected inverter are generated to control the on and off of the power devices of the grid-connected inverter. Step 2, the MMC sending end receives the active power command value P from the grid-connected inverter. refGFL The active power command P of MMC and grid is obtained according to the fast power calculation formula of MMC sending end. refMMCGFL The active power command P for MMC network construction is obtained based on the MMC sending-end power compensation calculation formula. refMMCGFM ; Sampled MMC AC side voltage u MMCa ,u MMCb ,u MMCc Sample the AC side current i at the MMC sending end MMCa i MMCb i MMCc The MMC grid current i is obtained through the MMC equivalent current calculation equation. MMCGFLa i MMCGFLb i MMCGFLc and MMC network current i MMCGFMa i MMCGFMb i MMCGFMc ; According to the MMC and network active command P refMMCGFL MMC AC side voltage u MMCa ,u MMCb ,u MMCc MMC and grid current i MMCGFLa i MMCGFLb i MMCGFLc， The dq-axis MMC-modulated waveform e is obtained through MMC mesh control. GFLd ,e GFLq Then, the MMC ground-mode modulated wave e is obtained through coordinate transformation. GFLa ,e GFLb ,e GFLc ; Based on the AC side voltage u of the MMC sending end MMCa ,u MMCb ,u MMCc and MMC network current i MMCGFMa i MMCGFMb i MMCGFMc The dq-axis MMC network modulated wave e is obtained through the MMC network voltage control loop and the MMC network current control loop. GFMd ,e GFMq Then, the MMC network modulation wave e is obtained through coordinate transformation. GFMa ,e GFMb ,e GFMc ; The MMC modulated wave e is obtained by superimposing the two modulated waves according to the MMC network modulation wave superposition calculation formula. MMCa ,e MMCb ,e MMCc Then, the switching signal of the MMC power device is generated by modulation through a circulating current suppressor to control the turn-on and turn-off of the MMC power device.

2. The fast power control method for a hybrid-mode new energy transmission system via flexible DC transmission according to claim 1, characterized in that, The step threshold mentioned in step 1 is 1.0 pu.

3. The fast power control method for a hybrid-mode new energy transmission system via flexible DC transmission according to claim 1, characterized in that, The current command calculation equation for the grid-connected inverter mentioned in step 1 is as follows: The closed-loop control equation for the AC current loop of the grid-connected inverter is as follows: Among them, K p_CCGFL K is the proportional coefficient of the PI regulator for AC current control of the grid-connected inverter. i_CCGFL s represents the integral coefficient of the PI regulator controlling the AC current of the grid-connected inverter, and s represents the Laplace operator.

4. The fast power control method for a hybrid-mode new energy transmission system via flexible DC transmission according to claim 1, characterized in that, The MMC sending-end fast power calculation formula and the MMC sending-end power compensation calculation formula mentioned in step 2 are as follows: Among them, Z eq Z is the equivalent connection impedance value. MMCvir The impedance value is the virtual impedance of the MMC network.

5. The fast power control method for a hybrid-mode new energy transmission system via flexible DC transmission according to claim 1, characterized in that, The MMC equivalent current calculation equation described in step 2 is as follows: Among them, Y f k is the admittance of the MMC equivalent filter inductor. HYB For a given fusion coefficient, e GFLa’ ,e GFLb’ ,e GFLc’ For the MMC and grid modulation waveform of the previous sampling period, e GFMa’ ,e GFMb’ ,e GFMc’ This is the MMC mesh modulation wave from the previous sampling period.

6. The fast power control method for a hybrid-mode new energy transmission system via flexible DC transmission according to claim 1, characterized in that, Step 2 describes obtaining the dq-axis MMC-modulated wave e through MMC mesh control. GFLd ,e GFLq The control process is as follows: S1, send the AC side voltage u of the MMC terminal. MMCa ,u MMCb ,u MMCc and MMC grid current i MMCGFLa i MMCGFLb i MMCGFLc The grid voltage u at the AC side of the MMC sending end on the dq axis is obtained through coordinate transformation. MMCGFLd ,u MMCGFLq and dq axis MMC and grid current i MMCGFLd i MMCGFLq ; S2, according to the MMC and network active command P refMMCGFL The given MMC and network reactive power command Q refMMCGFL dq axis MMC sending end AC side grid voltage u MMCGFLd ,u MMCGFLq dq axis MMC and grid current i MMCGFLd i MMCGFLq The dq-axis MMC grounding modulated wave e is obtained through the MMC grounding control equations. GFLd ,e GFLq The MMC and network control equations are as follows: Among them, K p_MMCGFL K is the proportional control coefficient of the PI controller for MMC and grid control. i_MMCGFL s is the integral control coefficient of the PI controller for MMC and grid control, and s is the Laplace operator.

7. The fast power control method for a hybrid-mode new energy transmission system via flexible DC transmission according to claim 1, characterized in that, The formula for calculating the superposition of MMC network modulation waves in step 2 is as follows: in, is the given fusion coefficient.

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