Active support control method and system for sending new energy through flexible direct current

Abstract

The invention provides an active support control method and system for sending out new energy through flexible direct current, the method is applied to a receiving-end converter station, and the method comprises the steps that the receiving-end converter station adopts a direct-current voltage and alternating-current voltage mixed synchronous control strategy to control direct-current voltage to follow the frequency of a power grid, and the frequency of the power grid is mirrored to the direct-current voltage; the receiving-end converter station adopts capacitor voltage control to obtain a common-mode modulation output quantity of the receiving-end converter station; and the receiving-end converter station generates a modulation signal of the receiving-end converter station based on the common-mode modulation output quantity in combination with an inner loop control strategy and a circulation control strategy. The receiving-end converter station adopts a direct-current voltage and alternating-current voltage hybrid synchronous control strategy, so that the risk of instability in a weak power grid due to adoption of a phase-locked loop is avoided, and the dynamic performance of the system is improved. In addition, a common-mode modulation coefficient is generated through capacitor voltage independent control, and decoupling control over the capacitor voltage and the direct-current voltage is achieved.

Description

Technical Field

[0001] The present invention relates to the fields of power systems, flexible direct current grids and new energy collection, and in particular to an active support control method for sending new energy via flexible direct current. Background Art

[0002] In the future, the proportion of renewable energy in the power system will increase, which will lead to a decrease in the rotational inertia and grid strength of the power system, and pose an increasing threat to the safe and stable operation of the power system. As an important means of transmitting renewable energy, the control strategy of flexible direct current transmission determines the stability of the system under low-inertia weak grids. When flexible direct current is connected to an isolated renewable energy transmission system, traditional voltage and frequency control cannot simulate the inertia of renewable energy to support the receiving grid, and the receiving grid usually uses a phase-locked loop, which is at risk of instability under weak grids. Summary of the invention

[0003] In order to solve the problem that the existing technology cannot realize the inertia simulation of new energy to support the receiving-end power grid, and the receiving-end power grid usually adopts a phase-locked loop and has the risk of instability under weak power grid, the present invention proposes an active support control method for the transmission of new energy through flexible direct current, which is applied to the receiving-end converter station, including:

[0004] The receiving-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage to control the DC voltage to follow the grid frequency and mirror the grid frequency to the DC voltage;

[0005] The receiving-end converter station adopts capacitor voltage control to obtain the common-mode modulation output of the receiving-end converter station, and generates the modulation signal of the receiving-end converter station based on the common-mode modulation output combined with the inner loop control strategy and the circulating current control strategy.

[0006] Preferably, the receiving-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage to control the DC voltage to follow the grid frequency, and mirrors the grid frequency to the DC voltage, including:

[0007] The receiving-end converter station uses the inner loop to control the DC voltage and coordinate with the hybrid synchronization to track the receiving-end grid frequency without static error, thereby controlling the AC q-axis voltage under hybrid synchronization to zero, and then mirroring the grid phase-locked frequency to the DC voltage in proportion.

[0008] Preferably, the receiving-end converter station uses the inner loop to control the DC voltage and coordinate with the hybrid synchronization to track the receiving-end power grid frequency without static error so as to control the AC q-axis voltage under the hybrid synchronization to zero, including:

[0009] The DC voltage reference of the DC voltage control link of the receiving-end converter station adopts the per-unit value of the grid frequency. The change of the DC voltage at the receiving end is consistent with the frequency change of the synchronization link, thereby controlling the AC q-axis voltage under hybrid synchronization to zero.

[0010] Preferably, the receiving end DC voltage variation is consistent with the frequency variation of the synchronization link, thereby controlling the AC q-axis voltage under hybrid synchronization to zero, as shown in the following formula:

[0011]

[0012] Among them, i drefr is the system voltage loop output current reference value, PI dc is the DC voltage PI controller, u dcr is the DC voltage of the receiving converter station, ω r is the frequency per unit value of the receiving AC system, Δu dcr is the change in DC voltage at the receiving end, Δω r is the frequency variation of the synchronization link;

[0013]

[0014] Among them, K uqr is the gain of the first-order inertia link, T uqr is the time constant of the first-order inertial link, s is the Laplace operator, u qr is the q-axis component of the PCC voltage at the receiving converter station in the controller coordinate system, θ g and θ r They are the grid phase at the grid connection point and the phase generated by the converter station, ω g is the AC system frequency.

[0015] Preferably, the common mode modulation output of the receiving end converter station is calculated as follows:

[0016]

[0017] Among them, U mdcr is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr is the change of DC voltage at the receiving converter station.

[0018] Preferably, the modulation signal of the receiving-end converter station includes a modulation reference wave of an upper bridge arm and a modulation reference wave of a lower bridge arm of the receiving-end converter station;

[0019] The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the receiving-end converter station are calculated as follows:

[0020]

[0021]

[0022] In the formula, m kur and m klr are the modulation reference waves of the upper and lower bridge arms of the receiving end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcr It is the common mode modulation output of the receiving converter station.

[0023] On the other hand, the present invention also provides an active support control method for transmitting new energy via flexible direct current, which is applied to a transmitting-end converter station and comprises:

[0024] The sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system;

[0025] The sending-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage, and adjusts the sending-end power grid frequency in combination with the frequency information of the receiving-end AC system;

[0026] The sending-end converter station adopts capacitor voltage control to obtain the common-mode modulation output of the sending-end converter station, and generates the modulation signal of the sending-end converter station based on the common-mode modulation output combined with the inner loop control strategy and the circulating current control strategy.

[0027] Preferably, the sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system, including:

[0028] The DC voltage detected by the sending-end converter station itself is subtracted from the voltage drop determined by the current and line parameters to obtain the DC voltage of the receiving-end converter station estimated by the sending end;

[0029] The DC voltage change at the receiving end estimated by the sending end is obtained by subtracting the per unit value of the DC voltage reference from the DC voltage at the receiving end converter station estimated by the sending end.

[0030] The frequency information of the AC system at the receiving end is determined by the DC voltage variation at the receiving end estimated by the sending end.

[0031] Preferably, the DC voltage change at the receiving end estimated by the sending end is calculated as follows:

[0032]

[0033] Among them, u dcs 、u dcr1 , Δu dcr1 , T dc , L dc , R dc 、i dc is the DC voltage at the sending end, the estimated DC voltage at the receiving end, the estimated DC voltage change at the sending end, the equivalent first-order low-pass filter time constant, the line inductance and resistance, the DC current, and u dcref is the per-unit value of the reference voltage of the receiving converter station, and s is the Laplace operator.

[0034] Preferably, the sending-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage, combined with the frequency information of the receiving-end AC system to adjust the sending-end power grid frequency, including:

[0035] The sending-end converter station adopts an inner-loop network-type constant voltage control, and the steady-state feedback of the q-axis value of the AC voltage in the synchronization link is 0, and the AC side frequency of the sending end is adjusted according to the DC voltage;

[0036] Under the grid-type hybrid synchronous control strategy of DC voltage and AC voltage, the frequency of the AC side at the sending end is consistent with the DC voltage of the receiving end converter station estimated by the sending end, and the estimated DC voltage of the receiving end converter station is consistent with the frequency of the receiving end AC power grid, thereby transmitting the frequency information of the receiving end AC system to the frequency of the sending end converter station.

[0037] Preferably, the sending-end converter station adopts an inner-loop network-type constant voltage control to make the steady-state feedback amount of the AC voltage q-axis value in the synchronization link 0, and adjusts the sending-end AC side frequency according to the DC voltage, as shown in the following formula:

[0038] i qrefs =PI v (u qref -u qs )

[0039] In the formula, i qrefs is the voltage outer loop output of the sending-end converter station, PI v is the voltage outer loop, u qref 、u qs are the q-axis reference value and actual value of the sending-end converter station.

[0040] Preferably, under the hybrid synchronous control strategy of the DC voltage and AC voltage, the frequency of the AC side of the sending end is consistent with the DC voltage of the receiving end converter station estimated by the sending end, and the estimated DC voltage of the receiving end converter station is consistent with the frequency of the receiving end AC power grid, so that the frequency information of the receiving end AC system is transmitted to the frequency of the sending end converter station, as shown in the following formula:

[0041]

[0042] In the formula, θ s is the phase of the sending-end converter station, ω s is the frequency of the sending-end converter station, u dcr1 is the estimated receiving-end DC voltage at the sending-end converter station, u qs , K uqs , T uqs are q-axis AC voltage, q-axis AC voltage feedback gain and time constant respectively, and s is the Laplace operator.

[0043] Preferably, the common-mode modulation output of the sending end is calculated as follows:

[0044]

[0045] Among them, U mdcs is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr1 The estimated DC voltage change at the receiving end is the estimated DC voltage change at the sending end.

[0046] Preferably, the modulation signal of the sending-end converter station includes a modulation reference wave of an upper bridge arm and a modulation reference wave of a lower bridge arm of the sending-end converter station;

[0047] The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the sending-end converter station are calculated as follows:

[0048]

[0049]

[0050] In the formula, m kus and m klsare the modulation reference waves of the upper and lower bridge arms of the sending-end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcs It is the common mode modulation output of the receiving converter station.

[0051] On the other hand, the present invention also provides an active support control system applicable to a new energy source through a flexible direct current transmission system, comprising a sending-end converter station, a receiving-end converter station respectively connected to the sending-end converter station, and a sending-end new energy source;

[0052] The receiving-end converter station is used to control the DC voltage to follow the grid frequency by adopting a hybrid synchronous control strategy of DC voltage and AC voltage, mirroring the grid frequency to the DC voltage, and simultaneously adopting capacitor voltage control to obtain the common-mode modulation output of the receiving-end converter station, and generate a modulation signal of the receiving-end converter station based on the common-mode modulation system combined with the inner loop control strategy and the circulating current control strategy;

[0053] The sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system, and adopts a meshing hybrid synchronous control strategy of DC voltage and AC voltage to convert the DC voltage frequency of the sending-end converter station and thus adjust the sending-end power grid frequency; at the same time, capacitor voltage control is also adopted to obtain the common-mode modulation output of the sending-end converter station, and a modulation signal of the sending-end converter station is generated based on the common-mode modulation output combined with an inner loop control strategy and a circulating current control strategy;

[0054] The sending-end new energy adopts a grid-building or grid-following control strategy to transmit energy through the sending-end converter station and participate in frequency response.

[0055] Preferably, the receiving-end converter station uses the following formula to control the DC voltage to follow the grid frequency:

[0056]

[0057] Among them, Δω r 、u dcr and Δu dcr is the frequency change, DC voltage and DC voltage change of the receiving converter station, u dcref is the per unit value of the reference voltage at the receiving converter station, u qr is the q-axis component of the PCC point voltage in the receiving controller coordinates, K uqr is the gain of the first-order inertia link, T uqr is the time constant of the first-order inertia link, and s is the Laplace operator.

[0058] Preferably, the receiving-end converter station calculates the common-mode modulation output by the following formula:

[0059]

[0060] Among them, U mdcr is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr is the change of DC voltage at the receiving converter station.

[0061] Preferably, the receiving-end converter station calculates the modulation signal of the receiving-end converter station by the following formula, wherein the modulation signal includes: the modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm:

[0062]

[0063]

[0064] In the formula, m kur and m klr are the modulation reference waves of the upper and lower bridge arms of the receiving end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcr It is the common mode modulation output of the receiving converter station.

[0065] Preferably, the sending-end converter station calculates the estimated receiving-end DC voltage change at the sending end by the following formula:

[0066]

[0067] Among them, u dcs 、u dcr1 , Δu dcr1 , T dc , L dc , R dc 、i dc is the DC voltage at the sending end, the estimated DC voltage at the receiving end, the estimated DC voltage change at the sending end, the equivalent first-order low-pass filter time constant, the line inductance and resistance, the DC current, and u dcrefis the per-unit value of the reference voltage of the receiving converter station, and s is the Laplace operator.

[0068] Preferably, the sending-end converter station converts the DC voltage of the sending-end converter station by the following formula, thereby adjusting the sending-end power grid frequency:

[0069] i qrefs =PI v (u qref -u qs )

[0070] In the formula, i qrefs is the voltage outer loop output of the sending-end converter station, PI v is the voltage outer loop, u qref 、u qs are the q-axis reference value and actual value of the sending-end converter station;

[0071] The sending-end AC side frequency in the steady state is consistent with the receiving-end DC voltage estimated by the sending end to perform DC voltage-frequency conversion at the sending-end converter station, as shown in the following formula:

[0072]

[0073] In the formula, θ s is the phase of the sending-end converter station, ω s is the frequency of the sending-end converter station, u dcr1 is the estimated receiving-end DC voltage at the sending-end converter station, u qs , K uqs , T uqs are q-axis AC voltage, q-axis AC voltage feedback gain and time constant respectively, and s is the Laplace operator.

[0074] Preferably, the sending-end converter station calculates the common-mode modulation output of the sending-end converter station by the following formula:

[0075]

[0076] Among them, U mdcs is the common mode modulation output of the sending end converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr1 The estimated DC voltage change at the receiving end is the estimated DC voltage change at the sending end.

[0077] Preferably, the sending-end converter station calculates the modulation signal by the following formula, wherein the modulation signal includes the modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the sending-end converter station;

[0078] The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the sending-end converter station are calculated as follows:

[0079]

[0080]

[0081] In the formula, m kus and m kls are the modulation reference waves of the upper and lower bridge arms of the sending-end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcs It is the common mode modulation output of the receiving converter station.

[0082] In another aspect, the present application further provides a computing device, comprising: one or more processors;

[0083] a processor for executing one or more programs;

[0084] When the one or more programs are executed by the one or more processors, the active support control method for transmitting new energy via flexible direct current as described above is implemented.

[0085] On the other hand, the present application also provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed, it implements the active support control method for transmitting new energy via flexible direct current as described above.

[0086] Compared with the prior art, the present invention has the following beneficial effects:

[0087] The present invention provides an active support control method for the transmission of new energy via flexible direct current. The method is applied to a receiving-end converter station, including: the receiving-end converter station adopts a hybrid synchronous control strategy of direct current voltage and alternating current voltage to control the direct current voltage to follow the grid frequency, and mirror the grid frequency to the direct current voltage; the receiving-end converter station adopts capacitor voltage control to obtain the common-mode modulation output of the receiving-end converter station; the receiving-end converter station generates a modulation signal of the receiving-end converter station based on the common-mode modulation output combined with an inner loop control strategy and a circulating current control strategy. The receiving-end converter station of the present invention adopts a hybrid synchronous control strategy of direct current voltage and alternating current voltage, which avoids the risk of instability in a phase-locked loop under a weak power grid and improves the dynamic performance of the system. In addition, the present invention also adopts independent control of capacitor voltage to generate a common-mode modulation coefficient, thereby realizing decoupling control of capacitor voltage and direct current voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 This is a flow chart of an active support control method for transmitting new energy via flexible direct current according to the present invention applied to a receiving-end converter station;

[0089] Figure 2 A schematic diagram of the basic electrical structure and corresponding electrical quantities of the flexible direct current of the present invention;

[0090] Figure 3 It is a schematic diagram of the island new energy flexible direct current transmission system and the synchronization strategy of the transmitting and receiving ends and the active support control strategy of the present invention;

[0091] Figure 4 (a) is a schematic diagram of system frequency change when the frequency rises to 51 Hz;

[0092] Figure 4 (b) is a schematic diagram of system frequency change when the frequency drops to 49 Hz;

[0093] Figure 4 (c) is a schematic diagram of system frequency change when the frequency drops to 49 Hz when the capacitor voltage regulation of the receiving-end converter station is disabled;

[0094] Figure 5 (a) is a simulation waveform diagram of the new energy power stepping from 800MW to 875MW in 7 seconds under the hybrid synchronous control strategy with DC voltage of the present invention;

[0095] Figure 5 (b) is the simulation waveform of the new energy power stepping from 800MW to 875MW in 7 seconds under the control without DC voltage synchronization;

[0096] Figure 6 (a) The frequency is stepped to 51 Hz, and the same u is added at the sending end. q Synchronous link system dynamic performance diagram;

[0097] Figure 6 (b) The frequency jumps to 51 Hz, and the receiving end synchronization link u q Schematic diagram of system response characteristics when the feedback gain increases to 1;

[0098] Figure 7 The present invention is a flow chart of an active support control method for transmitting new energy via flexible direct current applied to a transmitting end. DETAILED DESCRIPTION

[0099] This patent proposes an improved DC voltage synchronization control strategy for the scenario of new energy islands being transmitted via flexible direct current. This control strategy uses a hybrid synchronization control strategy of DC voltage and AC voltage at both the sending and receiving ends. The receiving end uses an improved hybrid synchronization control strategy without a phase-locked loop and an inner loop DC voltage frequency coupling control to achieve a zero-difference mirror image of the receiving end frequency to the DC voltage. Combined with the capacitor independent control strategy, the first level of frequency support is achieved, and the second level is the capacitor voltage regulation of the sending end converter station and the frequency response of the sending end new energy.

[0100] The sending end adopts an improved hybrid synchronous control strategy, which realizes the voltage-frequency conversion from the DC side to the AC side of the system by controlling the AC voltage of the inner loop q axis to zero and combining the voltage compensation strategy of the sending end. The first level of inertial support of the sending end is realized by combining the independent adjustment of the capacitor voltage. The second level of inertial support of the sending end comes from the frequency response of the new energy at the sending end. This strategy adopts a hybrid synchronous control strategy at the sending and receiving ends, which is highly innovative.

[0101] Embodiment 1:

[0102] An active support control method for renewable energy transmission via flexible direct current is applied to a receiving end converter station, such as Figure 1 As shown, including:

[0103] Step 1: The receiving-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage to control the DC voltage to follow the grid frequency and mirror the grid frequency to the DC voltage;

[0104] Step 2: The receiving-end converter station adopts capacitor voltage control to obtain the common-mode modulation output of the receiving-end converter station, and generates a modulation signal of the receiving-end converter station based on the common-mode modulation output combined with the inner loop control strategy and the circulating current control strategy.

[0105] The receiving converter station that collects the isolated island renewable energy for transmission adopts a hybrid synchronous control strategy of DC voltage and AC voltage. It realizes zero AC q-axis voltage under hybrid synchronization by controlling the DC voltage and the receiving grid frequency through the inner loop, and realizes the proportional mirroring of the grid phase-locked frequency to the DC voltage.

[0106] At the same time, the receiving-end converter station adopts independent regulation of capacitor voltage to achieve independent regulation of capacitor voltage with frequency, which is different from the DC voltage, to achieve the first level of frequency response.

[0107] The second level of frequency response comes from the frequency response of the flexible DC station capacitor at the sending end and the frequency response of the new energy after sensing the DC voltage. The receiving end can combine the current limiting strategy to prevent overcurrent. Finally, compensation modulation is used to generate the modulation signal.

[0108] The receiving end converter station adopts a hybrid synchronization mechanism of DC voltage and AC voltage, which is specifically expressed as follows:

[0109]

[0110] Among them, Δω r 、u dcr and Δu dcr is the frequency change, DC voltage and DC voltage change of the receiving converter station, u dcref is the per unit value of the reference voltage at the receiving converter station, u qr is the q-axis component of the PCC voltage at the receiving converter station in the controller coordinate system, K uqr is the gain of the first-order inertia link, T uqr is the time constant of the first-order inertia link, and s is the Laplace operator.

[0111] The DC voltage reference of the DC voltage control link of the receiving converter station adopts the grid frequency per unit value, and the DC voltage change Δu dcr The frequency change of the synchronization link Δω r Consistent. That is:

[0112]

[0113] Among them, i drefr is the system voltage loop output current reference value, PI dc is the DC voltage PI controller, u dcr is the DC voltage of the receiving converter station, ω r is the frequency per unit value of the receiving AC system, Δu dcr is the change in DC voltage at the receiving end, Δω r is the frequency variation of the synchronization link. Based on this, we can further obtain:

[0114]

[0115] Among them, Δω r is the frequency variation of the synchronization link, Δu dcr K is the change of DC voltage at the receiving converter station, uqr is the gain of the first-order inertia link, T uqris the time constant of the first-order inertial link, s is the Laplace operator, u qr is the q-axis component of the PCC voltage at the receiving converter station in the controller coordinate system, θ g and θ r They are the grid phase at the grid connection point and the phase generated by the converter, ω r is the frequency per unit value of the receiving AC system, ω g is the AC system frequency, and the DC voltage is controlled by PI at the receiving end synchronization link u qr The steady-state value is zero, thus achieving grid phase locking. At this time, u qr As a transient feedback quantity, it is similar to the effect of a phase-locked loop to achieve grid phase locking. The DC voltage and AC voltage in the synchronization link can respectively reflect the dynamics of the new energy side and the AC grid side.

[0116] The common mode control quantity of the receiving converter station adopts the capacitor voltage independent regulation control strategy to achieve the first-level frequency response of the receiving AC system. The specific expression is:

[0117]

[0118] Among them, U mdcr is the common mode modulation output, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral (PI) controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage is the sum of the bridge arm capacitor voltages, where x = a / b / c represents the phase, and k = u / l represents the upper / lower bridge arm. dcr and AC system frequency ω g The standard is consistent, and combined with this control strategy, independent regulation of the capacitor voltage can be achieved as the first level of frequency response.

[0119] The receiving end can adopt a current limiting strategy, which can be a current loop or a q-axis outer loop control with fixed reactive power or AC voltage amplitude.

[0120] The modulation signal of the receiving-end converter station includes a modulation reference wave of an upper bridge arm and a modulation reference wave of a lower bridge arm of the receiving-end converter station;

[0121] The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the receiving-end converter station are calculated as follows:

[0122]

[0123]

[0124] In the formula, m kur and m klr are the modulation reference waves of the upper and lower bridge arms of the receiving end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcr It is the common mode modulation output of the receiving converter station.

[0125] Embodiment 2:

[0126] An active support control method for renewable energy transmission via flexible direct current is applied to a transmission-end converter station, such as Figure 7 As shown, including:

[0127] S1: The sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system;

[0128] S2: The sending-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage, and adjusts the sending-end power grid frequency in combination with the frequency information of the receiving-end AC system;

[0129] S3: The sending-end converter station adopts capacitor voltage control to obtain the common-mode modulation output of the sending-end converter station, and generates a modulation signal of the sending-end converter station based on the common-mode modulation output combined with the inner loop control strategy and the circulating current control strategy.

[0130] The flexible direct current converter station at the sending end that gathers isolated island renewable energy for transmission adopts a hybrid synchronization control strategy of DC voltage and AC voltage. Through the inner loop grid-type constant voltage control, the steady-state feedback of the AC voltage q-axis value in the synchronization link is 0, thereby achieving accurate conversion of DC voltage to the frequency on the sending end AC side.

[0131] In order to obtain the voltage on the DC side of the receiving end, the DC voltage on the receiving end is estimated by combining the DC current, the voltage on the DC side of the sending end and the line parameters to reduce the error caused by the DC line on the frequency image. The first level of frequency response of the sending end converter station is realized by combining the independent adjustment of the capacitor voltage with the DC voltage conversion.

[0132] The second level of frequency response comes from the frequency response of the new energy source at the sending end. The sending end can combine the current limiting strategy to prevent overcurrent. Finally, compensation modulation is used to generate the modulation signal.

[0133] The sending-end converter station adopts a hybrid synchronization control strategy of DC voltage and AC voltage. The specific expression is as follows:

[0134]

[0135] where θ s ,ω s 、u dcr1 、u qs , K uqs , T uqs are the phase, frequency, estimated receiving-end DC voltage, q-axis AC voltage, q-axis AC voltage feedback gain and time constant of the sending-end converter station, and s is the Laplace operator.

[0136] The sending-end converter station adopts inner-loop grid-type constant voltage control to achieve the steady-state feedback of the AC voltage q-axis value in the synchronization link to be 0, thereby achieving accurate conversion of DC voltage to the sending-end AC side frequency. The specific expression is as follows:

[0137] i qrefs =PI v (u qref -u qs )

[0138] Among them, i qrefs is the voltage outer loop output of the sending-end converter station, PI v is the voltage outer loop, u qref 、u qs are the q-axis reference value (0) and the actual value of the sending-end converter station, respectively. In this way, the frequency in the steady state is consistent with the estimated DC voltage at the receiving end, realizing the accurate conversion of the DC voltage frequency at the sending-end converter station, which can be expressed as:

[0139]

[0140] In the formula, θ s is the phase of the sending-end converter station, ω s is the frequency of the sending-end converter station, u dcr1 is the estimated receiving-end DC voltage of the sending-end converter station, and s is the Laplace operator.

[0141] The estimated DC voltage at the sending-end converter station is expressed as follows:

[0142]

[0143] Among them, u dcs 、u dcr1 , Δu dcr1 , T dc , L dc , R dc 、i dcis the DC voltage at the sending end, the DC voltage at the receiving end estimated by the sending end, the DC voltage change at the receiving end estimated by the sending end, the equivalent first-order low-pass filter time constant, line inductance, resistance, and DC current (with the DC current flowing to the receiving end as positive), u dcref It is the per unit value of the reference voltage at the receiving converter station.

[0144] Note that if the line capacitance effect is significant, only the steady-state resistance can be considered as a simplification. At this time, the differential and integral parts of the inductance generated by the sending-end grid frequency can be offset, as shown in the following formula, effectively avoiding numerical oscillation:

[0145]

[0146] In the formula, θ s is the phase of the sending-end converter station, ω s is the frequency of the sending-end converter station, ω r is the frequency per unit value of the receiving AC system, s is the Laplace operator, u dcs is the DC voltage at the sending end, L dc , R dc 、i dc is the line inductance, resistance, and DC current (the current flowing toward the receiving end is positive).

[0147] The sending-end converter station adopts independent capacitor voltage regulation control, and the control strategy is as follows:

[0148]

[0149] Among them, U mdcs is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral (PI) controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and They are the reference value and average value of each bridge arm capacitor voltage respectively is the sum of the bridge arm capacitor voltages, where x = a / b / c represents the phase, and k = u / l represents the upper / lower bridge arm. dcr With ω g The standard is consistent, combined with this control strategy, the independent adjustment of the capacitor voltage can be realized as the first level of frequency response. In this way, the first level of frequency response at the sending end is realized, and the variables involved are consistent with the variables required by the aforementioned patent.

[0150] The second level frequency response of the sending end converter station is the frequency response of the new energy. The two levels of frequency response of the sending end converter station together form the second level frequency response of the receiving end converter station.

[0151] The sending-end converter station can adopt a current limiting strategy, or a current loop and virtual impedance. The sending-end converter station can adopt a q-axis outer loop control with fixed reactive power or AC voltage amplitude. Finally, the modulation signal of the sending-end converter station is generated as:

[0152]

[0153]

[0154] In the formula, m kus and m kls are the modulation reference waves of the upper and lower bridge arms of the sending-end converter station, u c 、u cc They are the voltage reference values ​​generated for differential mode and circulating current control respectively. is the average value of the bridge arm capacitor voltage, U mdcs It is the common mode modulation output of the receiving converter station.

[0155] Embodiment 3:

[0156] The following is a specific simulation model built in PSCAD for the above control strategy. The sending and receiving ends adopt the above-mentioned synchronous control strategy respectively. The new energy adopts the droop control strategy with frequency response. The parameters of the sending and receiving converter stations are shown in Table 1. A total of 160 units of the new energy rated at 5MW are connected to the aggregation model. The specific model configuration diagram is shown in Figure 3 As shown in the figure, the new energy source is upgraded from 0.69kV to 320kV.

[0157] Table 1. Simulation model parameter selection

[0158]

[0159]

[0160] Effects of the present invention: (1) Response under frequency mutation:

[0161] Figure 4 (a) shows the change of system frequency when the frequency increases. Figure 4 (b) shows the condition of frequency decrease. Here we take the rise of 51Hz as an example for analysis. At 7s, the receiving end grid frequency rises to 51Hz. At this time, the power of the receiving end of the system drops rapidly, the capacitor voltage rises rapidly, and the frequency rises to 51Hz (1.02pu) following the system grid frequency. The power at the sending end has a reverse characteristic, first rising and then falling, because the capacitor voltage and DC voltage are regulated independently. The DC voltage rises to 1.02pu, due to D p =4, at this time the capacitor voltage rises to 1.08.

[0162] Likewise, the system response is similar when the frequency drops to 49Hz. Figure 4 (b). In addition, when the independent adjustment of the receiving capacitor voltage is not enabled, Figure 4 As shown in (c), the reverse characteristic of the system becomes almost negligible. At this time, the receiving-end capacitor does not actively participate in the frequency response, and the power rises slowly.

[0163] (2) Response curve under new energy mutation:

[0164] Figure 5 The simulation waveform shows that the new energy jumped from 160 units to 175 units in 7 seconds, and the power increased from 800MW to 875MW. It can be seen that the receiving end adopts a hybrid synchronous control strategy with DC voltage. Figure 5 (a) Compared with the control without DC voltage synchronization Figure 5 (b) (equivalent to a first-order phase-locked loop at the receiving end) is more stable.

[0165] (3) q-axis voltage u q Gain Impact:

[0166] Figure 6 (a) shows that the frequency step is 51Hz, and the same u is added at the sending end q The dynamic performance of the synchronization link system is better Figure 4 (a) shows that the power oscillation disappears. Enabling the q-axis voltage synchronization link at the sending end has an effect on improving stability. In addition, Figure 6 (b) Tested the synchronization link u at the receiving end q When the feedback gain increases to 1, the system response characteristics deteriorate. q The gain can be reduced appropriately, but cannot be 0.

[0167] Figure 2 The basic electrical structure and corresponding electrical quantities of the flexible DC are shown. Each submodule can be a half-bridge or a full-bridge. Taking the half-bridge as an example, it contains two IGBTs and an anti-parallel diode. The submodule capacitance is C SM The DC side passes through the line impedance Z dc Connect to the DC system, the AC side passes through the grid impedance Z g Connect to the AC system. The equivalent resistance and reactance of the bridge arm are R arm With L arm The DC midpoint voltage to ground is v o , DC voltage is denoted as U dc The bridge arm current and circulating current are denoted as i xu ,i xl ,i c (where x = a / b / c represents the phase, and u / l represents the upper / lower bridge arm). The sum of the bridge arm capacitor voltage is The bridge arm modulation coefficient is m xk , the bridge arm voltage is The voltage at the common coupling point PCC is u sk , the grid current is i sk .

[0168] Figure 3 The topology and core control strategy studied in this paper are shown, including the sending-end island system, which can include wind power and photovoltaic island systems. The sending-end converter station (MMCS) is responsible for setting the AC voltage, and the receiving-end converter station (MMCR) is responsible for setting the DC voltage. The DC current is positive when it flows from the sending end to the receiving end.

[0169] Figures 4 to 6 middle is the average value of the bridge arm capacitor voltage, is the bridge arm capacitor voltage and reference value. dc is the DC current flowing from the sending end to the receiving end, u dcs is the voltage of the converter station at the sending end, u dcr DC voltage at the receiving converter station. cdq 、i dq with u dq They are the dq-axis components of circulating current, AC grid current and AC voltage in the control coordinate system.

[0170] Embodiment 4:

[0171] The present application also provides an active support control system applicable to a new energy source through a flexible direct current transmission system, comprising a sending-end converter station, respectively at the sending-end converter station and the sending-end new energy source;

[0172] The receiving-end converter station is used to control the DC voltage to follow the grid frequency by adopting a hybrid synchronous control strategy of DC voltage and AC voltage, mirroring the grid frequency to the DC voltage, and simultaneously adopting capacitor voltage control to obtain the common-mode modulation output of the receiving-end converter station, and generate a modulation signal of the receiving-end converter station based on the common-mode modulation system combined with the inner loop control strategy and the circulating current control strategy;

[0173] The sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system, and adopts a meshing hybrid synchronous control strategy of DC voltage and AC voltage to convert the DC voltage frequency of the sending-end converter station and thus adjust the sending-end power grid frequency; at the same time, capacitor voltage control is also adopted to obtain the common-mode modulation output of the sending-end converter station, and a modulation signal of the sending-end converter station is generated based on the common-mode modulation output combined with an inner loop control strategy and a circulating current control strategy;

[0174] The sending-end new energy adopts a grid-building or grid-following control strategy to transmit energy through the sending-end converter station and participate in frequency response.

[0175] The sending-end renewable energy is connected to the sending-end converter station for energy transmission, and the sending-end converter station is connected to the receiving-end converter station through a DC line, and the receiving-end converter station transmits energy to the receiving-end AC system. The sending-end renewable energy included in the active support control system can adopt a grid-building or grid-following control strategy for frequency response.

[0176] Preferably, the DC voltage and AC voltage mixed synchronous control strategy is as follows:

[0177]

[0178] Among them, Δω r 、u dcr and Δu dcr is the frequency change, DC voltage and DC voltage change of the receiving converter station, u dcref is the per unit value of the reference voltage at the receiving converter station, u qr is the q-axis component of the PCC point voltage in the receiving controller coordinates, K uqr is the gain of the first-order inertia link, T uqr is the time constant of the first-order inertia link, and s is the Laplace operator.

[0179] Preferably, the common mode modulation output of the receiving end converter station is calculated as follows:

[0180]

[0181] Among them, U mdcr is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr is the change of DC voltage at the receiving converter station.

[0182] Preferably, the modulation signal of the receiving-end converter station includes a modulation reference wave of an upper bridge arm and a modulation reference wave of a lower bridge arm of the receiving-end converter station;

[0183] The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the receiving-end converter station are calculated as follows:

[0184]

[0185]

[0186] In the formula, m kur and m klr are the modulation reference waves of the upper and lower bridge arms of the receiving end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcr It is the common mode modulation output of the receiving converter station.

[0187] Preferably, the DC voltage change at the receiving end estimated by the sending end is calculated as follows:

[0188]

[0189] Among them, u dcs 、u dcr1 , Δu dcr1 , T dc , L dc , R dc 、i dc is the DC voltage at the sending end, the estimated DC voltage at the receiving end, the estimated DC voltage change at the sending end, the equivalent first-order low-pass filter time constant, the line inductance and resistance, the DC current, and u dcref is the per-unit value of the reference voltage of the receiving converter station, and s is the Laplace operator.

[0190] Preferably, the grid-type hybrid synchronous control strategy of the DC voltage and the AC voltage is as shown below:

[0191]

[0192] Among them, θ s ,ω s 、u dcr1 、u qs , K uqs , T uqs are the phase, frequency, estimated receiving-end DC voltage, q-axis AC voltage, q-axis AC voltage feedback gain and time constant of the sending-end converter station, and s is the Laplace operator.

[0193] Preferably, the common mode modulation output of the sending-end converter station is calculated as follows:

[0194]

[0195] Among them, U mdcs is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI ucis the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr1 The estimated DC voltage change at the receiving end is the estimated DC voltage change at the sending end.

[0196] Preferably, the modulation signal of the sending-end converter station includes a modulation reference wave of an upper bridge arm and a modulation reference wave of a lower bridge arm of the sending-end converter station;

[0197] The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the sending-end converter station are calculated as follows:

[0198]

[0199]

[0200] In the formula, m kus and m kls are the modulation reference waves of the upper and lower bridge arms of the sending-end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcs It is the common mode modulation output of the receiving converter station.

[0201] In addition, the new energy at the sending end can adopt a control strategy with frequency response, such as grid-building type or grid-following type. If the new energy does not have a frequency response strategy, that is, the sending end does not have a second-level frequency response function, the control strategy can still be provided by flexible direct current with a smaller frequency support capability.

[0202] Embodiment 5:

[0203] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the active support control method for the transmission of new energy through flexible direct current in the above embodiment.

[0204] Embodiment 6:

[0205] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in a computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space that stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of an active support control method for sending new energy through flexible direct current in the above embodiment.

[0206] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0207] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0208] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0209] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0210] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. An active support control method for transmitting new energy via flexible direct current, the method is applied to a receiving-end converter station, characterized in that: include: The receiving-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage to control the DC voltage to follow the grid frequency and mirror the grid frequency to the DC voltage; The receiving-end converter station adopts capacitor voltage control to obtain the common-mode modulation output of the receiving-end converter station, and generates the modulation signal of the receiving-end converter station based on the common-mode modulation output combined with the inner loop control strategy and the circulating current control strategy.

2. The method according to claim 1, characterized in that The receiving-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage to control the DC voltage to follow the grid frequency, and mirrors the grid frequency to the DC voltage, including: The receiving-end converter station uses the inner loop to control the DC voltage and coordinate with the hybrid synchronization to track the receiving-end grid frequency without static error, thereby controlling the AC q-axis voltage under hybrid synchronization to zero, and then mirroring the grid phase-locked frequency to the DC voltage in proportion.

3. The method according to claim 2, characterized in that The receiving-end converter station uses the inner loop to control the DC voltage and coordinate with the hybrid synchronization to track the receiving-end power grid frequency without static error, thereby controlling the AC q-axis voltage under the hybrid synchronization to zero, including: The DC voltage reference of the DC voltage control link of the receiving-end converter station adopts the per-unit value of the grid frequency. The change of the DC voltage at the receiving end is consistent with the frequency change of the synchronization link, thereby controlling the AC q-axis voltage under hybrid synchronization to zero.

4. The method according to claim 3, characterized in that The receiving end DC voltage variation is consistent with the frequency variation of the synchronization link, thereby controlling the AC q-axis voltage under hybrid synchronization to zero, as shown in the following formula: Among them, i drefr is the system voltage loop output current reference value, PI dc is the DC voltage PI controller, u dcr is the DC voltage of the receiving converter station, ω r is the frequency per unit value of the receiving AC system, Δu dcr is the change in DC voltage at the receiving end, Δω r is the frequency variation of the synchronization link; Among them, u dcref K is the per unit value of the reference voltage at the receiving converter station. uqr is the gain of the first-order inertia link, T uqr is the time constant of the first-order inertial link, s is the Laplace operator, u qr is the q-axis component of the PCC voltage at the receiving converter station in the controller coordinate system, θ g and θ r They are the grid phase at the grid connection point and the phase generated by the converter station, ω g is the AC system frequency.

5. The method according to claim 1, characterized in that The common mode modulation output of the receiving converter station is calculated as follows: Among them, U mdcr is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and are the reference value and average value of each bridge arm capacitor voltage respectively, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr is the change of DC voltage at the receiving converter station.

6. The method according to claim 1, characterized in that The modulation signal of the receiving-end converter station includes a modulation reference wave of an upper bridge arm and a modulation reference wave of a lower bridge arm of the receiving-end converter station; The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the receiving-end converter station are calculated as follows: In the formula, m kur and m klr are the modulation reference waves of the upper and lower bridge arms of the receiving end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcr It is the common mode modulation output of the receiving converter station.

7. An active support control method for transmitting new energy via flexible direct current, the method is applied to a transmitting-end converter station, characterized in that: include: The sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system; The sending-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage, and adjusts the sending-end power grid frequency in combination with the frequency information of the receiving-end AC system; The sending-end converter station adopts capacitor voltage control to obtain the common-mode modulation output of the sending-end converter station, and generates the modulation signal of the sending-end converter station based on the common-mode modulation output combined with the inner loop control strategy and the circulating current control strategy.

8. The method according to claim 7, characterized in that The sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system, including: The DC voltage detected by the sending-end converter station itself is subtracted from the voltage drop determined by the current and line parameters to obtain the DC voltage of the receiving-end converter station estimated by the sending end; The DC voltage change at the receiving end estimated by the sending end is obtained by subtracting the per unit value of the DC voltage reference from the DC voltage at the receiving end converter station estimated by the sending end. The frequency information of the AC system at the receiving end is determined by the DC voltage variation at the receiving end estimated by the sending end.

9. The method according to claim 8, characterized in that The estimated DC voltage change at the receiving end is calculated as follows: Among them, u dcs 、u dcr1 , Δu dcr1 , T dc , L dc , R dc 、i dc is the DC voltage at the sending end, the estimated DC voltage at the receiving end, the estimated DC voltage change at the sending end, the equivalent first-order low-pass filter time constant, the line inductance, resistance, and DC current, u dcref is the per-unit value of the reference voltage of the receiving converter station, and s is the Laplace operator.

10. The method according to claim 7, characterized in that The sending-end converter station adopts a hybrid synchronous control strategy of DC voltage and AC voltage, combined with the frequency information of the receiving-end AC system, to adjust the sending-end power grid frequency, including: The sending-end converter station adopts an inner-loop network-type constant voltage control, and the steady-state feedback of the q-axis value of the AC voltage in the synchronization link is 0, and the AC side frequency of the sending end is adjusted according to the DC voltage; Under the grid-type hybrid synchronous control strategy of DC voltage and AC voltage, the frequency of the AC side at the sending end is consistent with the DC voltage of the receiving end converter station estimated by the sending end, and the estimated DC voltage of the receiving end converter station is consistent with the frequency of the receiving end AC power grid, thereby transmitting the frequency information of the receiving end AC system to the frequency of the sending end converter station.

11. The method according to claim 10, characterized in that The sending-end converter station adopts an inner-loop network-type constant voltage control to set the steady-state feedback of the AC voltage q-axis value in the synchronization link to 0, and adjusts the AC side frequency of the sending end according to the DC voltage, as shown in the following formula: i qrefs =PI v (u qref -u qs ) In the formula, i qrefs is the voltage outer loop output of the sending-end converter station, PI v is the voltage outer loop, u qref 、u qs are the q-axis reference value and actual value of the sending-end converter station.

12. The method according to claim 10, characterized in that Under the hybrid synchronous control strategy of the DC voltage and AC voltage, the frequency of the AC side of the sending end is consistent with the DC voltage of the receiving end converter station estimated by the sending end, and the estimated DC voltage of the receiving end converter station is consistent with the frequency of the receiving end AC grid, thereby transmitting the frequency information of the receiving end AC system to the frequency of the sending end converter station, as shown in the following formula: In the formula, θ s is the phase of the sending-end converter station, ω s is the frequency of the sending-end converter station, u dcr1 is the estimated receiving-end DC voltage at the sending-end converter station, u qs , K uqs , T uqs are q-axis AC voltage, q-axis AC voltage feedback gain and time constant respectively, and s is the Laplace operator.

13. The method according to claim 7, characterized in that The common mode modulation output at the sending end is calculated as follows: Among them, U mdcs is the common mode modulation output of the receiving converter station, U dc is the nominal value of DC voltage, PI uc is the capacitor voltage proportional integral controller, s is the Laplace operator, J and D p are the system inertia delay and frequency modulation coefficient, is the deviation of the bridge arm capacitor voltage, and is the reference value and average value of each bridge arm capacitor voltage, is the sum of the bridge arm capacitor voltage, x=a / b / c represents the phase, k=u / l represents the upper / lower bridge arm, Δu dcr1 The estimated DC voltage change at the receiving end is the estimated DC voltage change at the sending end.

14. The method according to claim 7, characterized in that The modulation signal of the sending-end converter station includes a modulation reference wave of an upper bridge arm and a modulation reference wave of a lower bridge arm of the sending-end converter station; The modulation reference wave of the upper bridge arm and the modulation reference wave of the lower bridge arm of the sending-end converter station are calculated as follows: In the formula, m kus and m kls are the modulation reference waves of the upper and lower bridge arms of the sending-end converter station, u c 、u cc The voltage reference generated for differential mode and circulating current control, is the average value of the bridge arm capacitor voltage, U mdcs It is the common mode modulation output of the receiving converter station.

15. An active support control system suitable for a new energy flexible DC transmission system, characterized in that: It includes a sending-end converter station, a receiving-end converter station and a sending-end new energy source respectively connected to the sending-end converter station; The receiving-end converter station is used to control the DC voltage to follow the grid frequency by adopting a hybrid synchronous control strategy of DC voltage and AC voltage, mirroring the grid frequency to the DC voltage, and simultaneously adopting capacitor voltage control to obtain the common-mode modulation output of the receiving-end converter station, and generate a modulation signal of the receiving-end converter station based on the common-mode modulation system combined with the inner loop control strategy and the circulating current control strategy; The sending-end converter station estimates the DC voltage of the receiving-end converter station based on the DC voltage, current and line parameters detected by itself, thereby obtaining the frequency information of the receiving-end AC system, and adopts a meshing hybrid synchronous control strategy of DC voltage and AC voltage to convert the DC voltage frequency of the sending-end converter station and thus adjust the sending-end power grid frequency; at the same time, capacitor voltage control is also adopted to obtain the common-mode modulation output of the sending-end converter station, and a modulation signal of the sending-end converter station is generated based on the common-mode modulation output combined with an inner loop control strategy and a circulating current control strategy; The sending-end new energy adopts a grid-building or grid-following control strategy to transmit energy through the sending-end converter station and participate in frequency response.

16. A computer device, characterized in that: include: one or more processors; The processor is used to store one or more programs; When the one or more programs are executed by the one or more processors, an active support control method for transmitting new energy via flexible direct current as described in any one of claims 1 to 14 is implemented.

17. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, an active support control method for transmitting new energy via flexible direct current as described in any one of claims 1 to 14 is implemented.

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