A method and device for controlling fault ride-through voltage margin of flexible direct current transmission system

Abstract

The present invention provides a method and device for controlling voltage margin during fault ride-through of a flexible direct current transmission system, which determine the change rate of the outer loop current limit value at a fixed direct current voltage end and the change rate of the outer loop current limit value at a fixed frequency control end; determine the limit value of the limit value at the fixed direct current voltage end and the limit value of the limit value at the fixed frequency control end; determine the output value of an inner loop current controller at the fixed direct current voltage end and the output value of the inner loop current controller at the fixed frequency control end, and control the fault ride-through on the alternating current side of the flexible direct current transmission system, thereby greatly reducing fluctuations and shortening the fault recovery time; by dynamically optimizing the control of the flexible direct current transmission system in real time to adapt to the disturbance of a passive alternating current system, the AC transient process can be smoothly passed, and the safe operation of the flexible direct current transmission systems at both ends during the transient fault period of the passive alternating current system and the fault recovery process can be guaranteed, and the direct current control characteristics can be dynamically adjusted according to the fault characteristics to realize AC fault ride-through.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current power transmission, and in particular to a method and device for controlling a fault ride-through voltage margin of a flexible direct current power transmission system. Background Art

[0002] Flexible DC transmission is particularly suitable for application scenarios that connect passive AC systems due to its excellent control characteristics. When one end of the flexible DC transmission system at both ends is connected to a passive network, according to the control principle of the flexible DC transmission system, the active control target of the flexible DC system connected to the passive AC system needs to control the frequency of the passive AC network, so the active control target at the other end is the DC voltage. When a temporary fault occurs in the AC systems at both ends and during the recovery process after the fault, the transient process of the system will have a severe impact on the flexible DC system. If the flexible DC transmission system does not adopt corresponding control measures, it will cause serious overcurrent and overvoltage, which will trigger protection actions, resulting in long-term power transmission interruption and endangering the safe and stable operation of the power grid. For AC system faults with a high probability of occurrence, the flexible DC transmission system should dynamically adjust the corresponding control strategy under the fault state to adapt to the impact of the AC transient process.

[0003] In the prior art, the flexible DC transmission system connected to the passive AC system adopts active dual closed-loop control to realize AC side fault crossing. In the active outer loop controller, the DC voltage reference value (per unit value) or frequency reference value (per unit value) is firstly subtracted from the corresponding DC voltage real-time sampling value (per unit value) or frequency real-time sampling value (per unit value), and then the d-axis reference value of the inner loop current controller is obtained through the PI operation link and the fixed value limiting. The d-axis reference value of the inner loop current controller is then inversely transformed through the inner loop current controller and the dq coordinate system to obtain the final positive sequence modulation wave. However, when a fault occurs in the flexible DC transmission system, under large dynamic conditions, the d-axis reference value of the inner loop current controller obtained by the fixed value limiting strategy will vary greatly. This limiting will hinder the realization of the reference value, thereby lengthening the tracking time of the inner loop current controller for the reference value, resulting in large fluctuations in the flexible DC transmission system and a long fault recovery time. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, such as large fluctuation and long fault recovery time, the present invention provides a method for controlling a fault ride-through voltage margin of a flexible direct current transmission system, comprising:

[0005] Determine the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end respectively based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end;

[0006] Determine the fixed DC voltage end limit value and the fixed frequency control end limit value based on the fixed DC voltage end outer loop current limit value change rate and the fixed frequency control end outer loop current limit value change rate;

[0007] Determine the output value of the inner loop current controller at the fixed DC voltage end based on the fixed DC voltage end amplitude limit, and determine the output value of the inner loop current controller at the fixed frequency control end based on the fixed DC voltage end amplitude limit and the fixed frequency control end amplitude limit;

[0008] The fault ride-through on the AC side of the flexible DC transmission system is controlled based on the output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end.

[0009] The method of respectively determining the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end includes:

[0010] Determine a base value reference value of an outer loop current amplitude limit value at a constant DC voltage end and a base value reference value of an outer loop current amplitude limit value at a constant frequency control end based on an AC bus voltage at a constant DC voltage control end and an AC bus voltage at a constant frequency control end;

[0011] Based on the base value reference value of the outer loop current limit value at the fixed DC voltage end and the base value reference value of the outer loop current limit value at the fixed frequency control end, the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end are determined respectively.

[0012] The method of determining the fixed DC voltage end amplitude limit value and the fixed frequency control end amplitude limit value based on the change rate of the fixed DC voltage end outer loop current amplitude limit value and the change rate of the fixed frequency control end outer loop current amplitude limit value respectively includes:

[0013] The change rate of the current limit value of the outer loop of the fixed DC voltage terminal is processed by the first-order inertia link to obtain the upper limit value of the fixed DC voltage terminal limit value, and the upper limit value of the fixed DC voltage terminal limit value is inverted to obtain the lower limit value of the fixed DC voltage terminal limit value;

[0014] The change rate of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the limit value of the fixed frequency control end, and the upper limit of the limit value of the fixed frequency control end is inverted to obtain the lower limit of the limit value of the fixed frequency control end.

[0015] The output value of the inner loop current controller at the fixed DC voltage end is determined based on the fixed DC voltage end amplitude limit, and the output value of the inner loop current controller at the fixed frequency control end is determined based on the fixed DC voltage end amplitude limit and the fixed frequency control end amplitude limit, including:

[0016] respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system;

[0017] Determine the output value of the inner loop current controller of the fixed DC voltage terminal based on the actual value of the DC voltage and the limit value of the fixed DC voltage terminal;

[0018] The output value of the inner loop current controller of the fixed frequency control terminal is determined based on the actual value of the DC voltage, the actual value of the frequency, the limit value of the fixed DC voltage terminal and the limit value of the fixed frequency control terminal.

[0019] The method of controlling the fault ride-through on the AC side of the flexible DC power transmission system based on the output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end includes:

[0020] The output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end are respectively subjected to the inner loop current control link and the dq coordinate system inverse transformation to obtain a positive sequence modulation wave control signal;

[0021] Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

[0022] The method of respectively determining a base value reference value of an outer loop current amplitude limit value at a constant DC voltage terminal and a base value reference value of an outer loop current amplitude limit value at a constant frequency control terminal based on an AC bus voltage at a constant DC voltage control terminal and an AC bus voltage at a constant frequency control terminal comprises:

[0023] The product of the AC bus voltage at the fixed DC voltage terminal and the fixed DC voltage terminal limit base value amplification coefficient is limited by the upper and lower limits of the fixed DC voltage terminal amplitude base value to obtain a fixed DC voltage terminal outer loop current limit base value reference value;

[0024] The product of the AC bus voltage at the fixed frequency control end and the base amplitude limit amplification coefficient of the fixed frequency control end is limited by the upper and lower limits of the base amplitude limit of the fixed frequency control end to obtain the base amplitude limit reference value of the outer loop current at the fixed frequency control end.

[0025] The method of respectively determining the change rate of the outer loop current amplitude limit value at the fixed DC voltage end and the change rate of the outer loop current amplitude limit value at the fixed frequency control end based on the base value reference value of the outer loop current amplitude limit value at the fixed DC voltage end and the base value reference value of the outer loop current amplitude limit value at the fixed frequency control end comprises:

[0026] The base value reference value of the current limit amplitude of the outer loop of the fixed DC voltage terminal is processed by a first-order inertia link and a derivative operation is performed to obtain a first voltage derivative result; if the voltage derivative result is greater than zero, the positive change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; if the voltage derivative result is less than zero, the negative change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal;

[0027] The base value reference value of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link and a derivative operation is performed to obtain a second voltage derivative result; if the second voltage derivative result is greater than zero, the positive change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end; if the second voltage derivative result is less than zero, the negative change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end.

[0028] The method of determining the output value of the inner loop current controller at the fixed DC voltage end based on the actual DC voltage value and the fixed DC voltage end amplitude limit value includes:

[0029] The difference between the preset DC voltage reference value of the flexible DC transmission system and the actual DC voltage value is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage terminal limit value and the lower limit of the fixed DC voltage terminal limit value to obtain the output value of the fixed DC voltage terminal inner loop current controller.

[0030] The method of determining the output value of the inner loop current controller of the fixed frequency control terminal based on the actual value of the DC voltage, the actual value of the frequency, the fixed DC voltage terminal limit value and the fixed frequency control terminal limit value includes:

[0031] The difference between the preset frequency reference value and the actual frequency value of the flexible DC transmission system is passed through the PI control link, and then the upper limit of the fixed frequency control end limit value and the lower limit of the fixed frequency control end limit value are limited to obtain the upper limit of the fixed high margin DC voltage control outer loop current limit value;

[0032] The product of the preset flexible direct current transmission system direct current voltage reference value and the fixed high margin direct current voltage limit value lower limit coefficient is subtracted from the actual direct current voltage value, and the difference is passed through the PI control link, and then the fixed high margin direct current voltage control outer loop current limit value upper limit and the fixed direct current voltage terminal limit value lower limit are limited to obtain the fixed high margin direct current voltage control outer loop current limit value lower limit;

[0033] The product of the preset flexible DC voltage reference value of the DC transmission system and the upper limit coefficient of the fixed high margin DC voltage limit value is subtracted from the actual DC voltage value, and the difference is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage end limit value and the lower limit of the fixed high margin DC voltage control outer loop current limit value, to obtain the output value of the fixed frequency control end inner loop current controller.

[0034] The present invention also provides a fault ride-through voltage margin control device for a flexible direct current transmission system, comprising:

[0035] A first determination module is used to determine the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end respectively based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end;

[0036] A second determination module is used to determine the fixed DC voltage end amplitude limit value and the fixed frequency control end amplitude limit value based on the change rate of the fixed DC voltage end outer loop current amplitude limit value and the change rate of the fixed frequency control end outer loop current amplitude limit value respectively;

[0037] A third determination module is used to determine the output value of the inner loop current controller of the fixed DC voltage terminal based on the fixed DC voltage terminal amplitude limit value, and determine the output value of the inner loop current controller of the fixed frequency control terminal based on the fixed DC voltage terminal amplitude limit value and the fixed frequency control terminal amplitude limit value;

[0038] The control module is used to control the fault ride-through on the AC side of the flexible DC transmission system based on the output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end.

[0039] The first determining module comprises:

[0040] A reference value determination unit, used to determine a base value reference value of an outer loop current amplitude limit value at a constant DC voltage terminal and a base value reference value of an outer loop current amplitude limit value at a constant frequency control terminal respectively based on an AC bus voltage at a constant DC voltage control terminal and an AC bus voltage at a constant frequency control terminal;

[0041] The change rate determination unit is used to determine the change rate of the fixed DC voltage end outer loop current limit value and the change rate of the fixed frequency control end outer loop current limit value based on the fixed DC voltage end outer loop current limit value base reference value and the fixed frequency control end outer loop current limit value base reference value.

[0042] The second determining module is specifically used for:

[0043] The change rate of the current limit value of the outer loop of the fixed DC voltage terminal is processed by the first-order inertia link to obtain the upper limit value of the fixed DC voltage terminal limit value, and the upper limit value of the fixed DC voltage terminal limit value is inverted to obtain the lower limit value of the fixed DC voltage terminal limit value;

[0044] The change rate of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the limit value of the fixed frequency control end, and the upper limit of the limit value of the fixed frequency control end is inverted to obtain the lower limit of the limit value of the fixed frequency control end.

[0045] The third determination module comprises:

[0046] An acquisition unit, used to respectively acquire an actual value of a DC voltage and an actual value of a frequency of the flexible DC transmission system;

[0047] A first output value determination unit, used to determine an output value of a fixed DC voltage terminal inner loop current controller based on an actual DC voltage value and a fixed DC voltage terminal amplitude limit value;

[0048] The second output value determination unit is used to determine the output value of the inner loop current controller of the fixed frequency control terminal based on the actual value of the DC voltage, the actual value of the frequency, the fixed DC voltage terminal limit value and the fixed frequency control terminal limit value.

[0049] The control module is specifically used for:

[0050] The output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end are respectively subjected to the inner loop current control link and the dq coordinate system inverse transformation to obtain a positive sequence modulation wave control signal;

[0051] Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

[0052] The reference value determination unit is specifically used for:

[0053] The product of the AC bus voltage at the fixed DC voltage terminal and the fixed DC voltage terminal limit base value amplification coefficient is limited by the upper and lower limits of the fixed DC voltage terminal amplitude base value to obtain a fixed DC voltage terminal outer loop current limit base value reference value;

[0054] The product of the AC bus voltage at the fixed frequency control end and the base amplitude limit amplification coefficient of the fixed frequency control end is limited by the upper and lower limits of the base amplitude limit of the fixed frequency control end to obtain the base amplitude limit reference value of the outer loop current at the fixed frequency control end.

[0055] The change rate determination unit is specifically used for:

[0056] The base value reference value of the current limit amplitude of the outer loop of the fixed DC voltage terminal is processed by a first-order inertia link and a derivative operation is performed to obtain a first voltage derivative result; if the voltage derivative result is greater than zero, the positive change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; if the voltage derivative result is less than zero, the negative change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal;

[0057] The base value reference value of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link and a derivative operation is performed to obtain a second voltage derivative result; if the second voltage derivative result is greater than zero, the positive change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end; if the second voltage derivative result is less than zero, the negative change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end.

[0058] The first output value determining unit is specifically used for:

[0059] The difference between the preset DC voltage reference value of the flexible DC transmission system and the actual DC voltage value is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage terminal limit value and the lower limit of the fixed DC voltage terminal limit value to obtain the output value of the fixed DC voltage terminal inner loop current controller.

[0060] The second output value determining unit is specifically used for:

[0061] The difference between the preset frequency reference value and the actual frequency value of the flexible DC transmission system is passed through the PI control link, and then the upper limit of the fixed frequency control end limit value and the lower limit of the fixed frequency control end limit value are limited to obtain the upper limit of the fixed high margin DC voltage control outer loop current limit value;

[0062] The product of the preset flexible direct current transmission system direct current voltage reference value and the fixed high margin direct current voltage limit value lower limit coefficient is subtracted from the actual direct current voltage value, and the difference is passed through the PI control link, and then the fixed high margin direct current voltage control outer loop current limit value upper limit and the fixed direct current voltage terminal limit value lower limit are limited to obtain the fixed high margin direct current voltage control outer loop current limit value lower limit;

[0063] The product of the preset flexible DC voltage reference value of the DC transmission system and the upper limit coefficient of the fixed high margin DC voltage limit value is subtracted from the actual DC voltage value, and the difference is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage end limit value and the lower limit of the fixed high margin DC voltage control outer loop current limit value, to obtain the output value of the fixed frequency control end inner loop current controller.

[0064] The technical solution provided by the present invention has the following beneficial effects:

[0065] In the fault ride-through voltage margin control method of the flexible direct current transmission system provided by the present invention, the change rate of the outer loop current limit value of the fixed direct current voltage end and the change rate of the outer loop current limit value of the fixed frequency control end are determined based on the AC bus voltage of the fixed direct current voltage end and the AC bus voltage of the fixed frequency control end respectively; the limit value of the fixed direct current voltage end and the limit value of the fixed frequency control end are determined based on the change rate of the outer loop current limit value of the fixed direct current voltage end and the change rate of the outer loop current limit value of the fixed frequency control end respectively; the output value of the inner loop current controller of the fixed direct current voltage end is determined based on the limit value of the fixed direct current voltage end, and the output value of the inner loop current controller of the fixed frequency control end is determined based on the limit value of the fixed direct current voltage end and the limit value of the fixed frequency control end; the fault ride-through of the AC side of the flexible direct current transmission system is controlled based on the output value of the inner loop current controller of the fixed direct current voltage end and the output value of the inner loop current controller of the fixed frequency control end, thereby greatly reducing the fluctuation of the flexible direct current transmission system and shortening the fault recovery time;

[0066] The technical solution provided by the present invention is applicable to a flexible DC transmission system at both ends of which is connected to a passive AC system at one end. When a temporary fault occurs in the passive AC system at either end and during the recovery process of the passive AC system after the fault is eliminated, the flexible DC transmission system control is dynamically optimized in real time to adapt to the disturbance of the passive AC system, smoothly pass through the AC transient process, and avoid the flexible DC transmission system from being subjected to severe impact. The safe operation of the flexible DC transmission system at both ends during the transient fault of the passive AC system and the fault recovery process can be guaranteed, and the DC control characteristics can be dynamically adjusted according to the fault characteristics to achieve AC fault riding;

[0067] The technical solution provided by the present invention avoids serious stress over-limit during AC faults, ensures that the system quickly resumes power transmission in a very short time after the fault is eliminated, does not trigger the protection in the converter station, and enables the entire DC transmission system to have the ability to ride through AC side faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is a flow chart of a method for controlling a fault ride-through voltage margin of a flexible direct current transmission system in an embodiment of the present invention;

[0069] Figure 2 1 is a flow chart for determining a base reference value of a current limit value of an outer loop at a given DC voltage terminal according to an embodiment of the present invention;

[0070] Figure 3 1 is a flow chart of determining a base value reference value of a current amplitude limit value of an outer loop of a constant frequency control terminal according to an embodiment of the present invention;

[0071] Figure 4 1 is a flow chart for determining the change rate of the current limit value of the outer loop at a constant DC voltage end in an embodiment of the present invention;

[0072] Figure 5 1 is a flow chart for determining the change rate of the current limit value of the outer loop of the constant frequency control terminal in an embodiment of the present invention;

[0073] Figure 6 is a flow chart of determining a limit value of a fixed DC voltage terminal amplitude limit value in an embodiment of the present invention;

[0074] Figure 7 is a flow chart of determining the limit value of the constant frequency control terminal in an embodiment of the present invention;

[0075] Figure 8 is a flow chart for determining the output value of the inner loop current controller at a constant DC voltage end in an embodiment of the present invention;

[0076] Fig. 9 1 is a flow chart for determining the upper limit of the current amplitude limit value of the outer loop of the fixed height margin DC voltage control in an embodiment of the present invention;

[0077] Fig.101 is a flow chart for determining the lower limit of the current amplitude limit value of the outer loop of the fixed high margin DC voltage control in an embodiment of the present invention;

[0078] Fig.11 is a flow chart for determining the output value of the inner loop current controller of the constant frequency control end in an embodiment of the present invention;

[0079] Fig.12 It is a structural diagram of a fault ride-through voltage margin control device for a flexible direct current transmission system in an embodiment of the present invention. DETAILED DESCRIPTION

[0080] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0081] Example 1

[0082] Embodiment 1 of the present invention provides a method for controlling voltage margin during fault ride-through of a flexible direct current transmission system. In Embodiment 1 of the present invention, one end of the flexible direct current transmission system is connected to a passive alternating current system. When a temporary fault occurs in the passive alternating current system and during the recovery process of the passive alternating current system after the fault is eliminated, the flexible direct current transmission system control is dynamically optimized in real time to adapt to the disturbance of the passive alternating current system, smoothly pass through the AC transient process, and avoid the flexible direct current transmission system from being subjected to severe shock. The safe operation of the flexible direct current transmission systems at both ends can be ensured during the transient fault of the passive alternating current system and the fault recovery process, and the direct current control characteristics can be dynamically adjusted according to the fault characteristics to achieve AC fault ride-through. The specific flow chart of Embodiment 1 of the present invention is shown in the figure below. Figure 1 As shown, the specific process is as follows:

[0083] S101: Determine a change rate of an outer loop current limit value at a constant DC voltage terminal and a change rate of an outer loop current limit value at a constant frequency control terminal based on an AC bus voltage at a constant DC voltage terminal and an AC bus voltage at a constant frequency control terminal, respectively;

[0084] S102: Determine the fixed DC voltage end amplitude limit and the fixed frequency control end amplitude limit based on the change rate of the fixed DC voltage end outer loop current amplitude limit and the change rate of the fixed frequency control end outer loop current amplitude limit;

[0085] S103: determining an output value of an inner loop current controller at a fixed DC voltage end based on a fixed DC voltage end amplitude limit, and determining an output value of an inner loop current controller at a fixed frequency control end based on a fixed DC voltage end amplitude limit and a fixed frequency control end amplitude limit;

[0086] S104: Controlling fault ride-through on the AC side of the flexible DC transmission system based on an output value of an inner loop current controller at a fixed DC voltage end and an output value of an inner loop current controller at a fixed frequency control end.

[0087] Based on the AC bus voltage at the constant DC voltage end and the AC bus voltage at the constant frequency control end, respectively determining the change rate of the outer loop current limit value at the constant DC voltage end and the change rate of the outer loop current limit value at the constant frequency control end, including:

[0088] Determine a base value reference value of an outer loop current amplitude limit value at a constant DC voltage end and a base value reference value of an outer loop current amplitude limit value at a constant frequency control end based on an AC bus voltage at a constant DC voltage control end and an AC bus voltage at a constant frequency control end;

[0089] Based on the base value reference value of the outer loop current limit value at the fixed DC voltage end and the base value reference value of the outer loop current limit value at the fixed frequency control end, the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end are determined respectively.

[0090] Based on the change rate of the outer loop current limit value of the fixed DC voltage end and the change rate of the outer loop current limit value of the fixed frequency control end, the fixed DC voltage end limit value and the fixed frequency control end limit value are determined respectively, including:

[0091] The change rate of the current limit value of the outer loop of the fixed DC voltage terminal is processed by the first-order inertia link to obtain the upper limit value of the fixed DC voltage terminal limit value, and the upper limit value of the fixed DC voltage terminal limit value is inverted to obtain the lower limit value of the fixed DC voltage terminal limit value; Figure 6 As shown, lim_HD_U is the upper limit of the fixed DC voltage terminal limit value, and lim_LD_U is the lower limit of the fixed DC voltage terminal limit value.

[0092] The change rate of the current limit value of the fixed frequency control end outer loop is processed by the first-order inertia link to obtain the upper limit of the fixed frequency control end limit value. The upper limit of the fixed frequency control end limit value is inverted to obtain the lower limit of the fixed frequency control end limit value, such as Figure 7 As shown, im_HD_f is the upper limit of the limit value of the fixed frequency control end, and lim_LD_f is the lower limit of the limit value of the fixed frequency control end.

[0093] The output value of the inner loop current controller at the fixed DC voltage end is determined based on the fixed DC voltage end amplitude limit, and the output value of the inner loop current controller at the fixed frequency control end is determined based on the fixed DC voltage end amplitude limit and the fixed frequency control end amplitude limit, including:

[0094] respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system;

[0095] Determine the output value of the inner loop current controller of the fixed DC voltage terminal based on the actual value of the DC voltage and the limit value of the fixed DC voltage terminal;

[0096] The output value of the inner loop current controller of the fixed frequency control terminal is determined based on the actual value of the DC voltage, the actual value of the frequency, the limit value of the fixed DC voltage terminal and the limit value of the fixed frequency control terminal.

[0097] The fault ride-through on the AC side of the flexible DC transmission system is controlled based on the output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end, including:

[0098] The output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end are respectively subjected to the inner loop current control link and the dq coordinate system inverse transformation to obtain a positive sequence modulation wave control signal;

[0099] Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

[0100] Based on the AC bus voltage at the constant DC voltage control end and the AC bus voltage at the constant frequency control end, a base value reference value of the outer loop current limit amplitude at the constant DC voltage end and a base value reference value of the outer loop current limit amplitude at the constant frequency control end are determined respectively, including:

[0101] The product of the AC bus voltage at the fixed DC voltage terminal and the fixed DC voltage terminal limit base value amplification coefficient is limited by the upper and lower limits of the fixed DC voltage terminal amplitude base value to obtain the fixed DC voltage terminal outer loop current limit base value reference value; Figure 2 As shown, V1 is the AC bus voltage at the fixed DC voltage end, k2 is the fixed DC voltage end limit base value magnification coefficient, k3 is the limit upper limit of the fixed DC voltage end amplitude base value, k4 is the limit lower limit of the fixed DC voltage end amplitude base value, and MIN_U is the reference value of the fixed DC voltage end outer loop current limit base value;

[0102] The product of the AC bus voltage at the fixed frequency control end and the base amplitude limit amplification coefficient at the fixed frequency control end is subjected to the upper and lower amplitude limit of the base amplitude limit of the fixed frequency control end to obtain the base amplitude limit reference value of the outer loop current at the fixed frequency control end; Figure 3 As shown, V2 is the AC bus voltage of the fixed frequency control end, k5 is the fixed frequency control end limit base value amplification factor, k6 is the limit upper limit of the fixed frequency control end amplitude base value, k7 is the limit lower limit of the fixed frequency control end amplitude base value, and MIN_f is the reference value of the fixed frequency control end outer loop current limit base value.

[0103] Based on the base value reference value of the outer loop current limit value at the constant DC voltage end and the base value reference value of the outer loop current limit value at the constant frequency control end, respectively determining the change rate of the outer loop current limit value at the constant DC voltage end and the change rate of the outer loop current limit value at the constant frequency control end, including:

[0104] The base value reference value of the current limit amplitude of the outer loop of the fixed DC voltage terminal is processed by the first-order inertia link and derivation operation is performed to obtain the first voltage derivation result; if the voltage derivation result is greater than zero, that is, the voltage rises, the positive change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; if the voltage derivation result is less than zero, that is, the voltage drops, the negative change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; Figure 4 As shown, T is the time constant of the first-order inertia link, du1 / dt is the first voltage derivative result, k8 is the positive change rate of the fixed DC voltage end limit, k9 is the negative change rate of the fixed DC voltage end limit, rateD1 is the change rate of the fixed DC voltage end outer loop current limit value;

[0105] The base value reference value of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link and derivation operation is performed to obtain the second voltage derivation result; if the second voltage derivation result is greater than zero, that is, the voltage rises, the positive change rate of the fixed frequency control end limit is used as the change rate of the current limit value of the outer loop of the fixed frequency control end; if the second voltage derivation result is less than zero, that is, the voltage drops, the negative change rate of the fixed frequency control end limit is used as the change rate of the current limit value of the outer loop of the fixed frequency control end, such as Figure 5 As shown, du2 / dt is the second voltage derivative result, k10 is the positive change rate of the fixed frequency control end limit, k11 is the negative change rate of the fixed frequency control end limit, rateD2 is the change rate of the fixed frequency control end outer loop current limit value;

[0106] The output value of the inner loop current controller at the fixed DC voltage end is determined based on the actual value of the DC voltage and the limit value of the fixed DC voltage end, including:

[0107] The difference between the preset DC voltage reference value and the actual DC voltage value of the flexible DC transmission system is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage end limit value and the lower limit of the fixed DC voltage end limit value to obtain the output value of the fixed DC voltage end inner loop current controller. Figure 8 As shown, U dcref_pu is the preset DC voltage reference value of the flexible DC transmission system, U dc_pu is the actual value of the normalized DC voltage, I dref1 is the output value of the inner loop current controller at the fixed DC voltage end.

[0108] The output value of the inner loop current controller of the fixed frequency control terminal is determined based on the actual value of the DC voltage, the actual value of the frequency, the limit value of the fixed DC voltage terminal and the limit value of the fixed frequency control terminal, including:

[0109] The difference between the preset frequency reference value and the actual frequency value of the flexible DC transmission system is passed through the PI control link, and then the upper limit of the fixed frequency control end limit value and the lower limit of the fixed frequency control end limit value are limited to obtain the upper limit of the fixed high margin DC voltage control outer loop current limit value; Fig. 9 As shown, f ref_pu is the preset frequency reference value of the flexible DC transmission system, f pu is the actual value of the normalized frequency, lim_U2 is the upper limit of the current limit of the outer loop of the fixed height margin DC voltage control;

[0110] The product of the preset flexible DC transmission system DC voltage reference value and the fixed high margin DC voltage limit value lower limit coefficient is subtracted from the actual DC voltage value, and the difference is passed through the PI control link, and then the fixed high margin DC voltage control outer loop current limit value upper limit and the fixed DC voltage terminal limit value lower limit are limited to obtain the fixed high margin DC voltage control outer loop current limit value lower limit; Fig.10 As shown, k12 is the lower limit coefficient of the fixed height margin DC voltage limit value, and lim_U1 is the lower limit of the fixed height margin DC voltage control outer loop current limit value;

[0111] The product of the preset flexible DC transmission system DC voltage reference value and the upper limit coefficient of the fixed high margin DC voltage limit value is subtracted from the actual DC voltage value, and the difference is passed through the PI control link, and then the upper limit of the fixed DC voltage end limit value and the lower limit of the fixed high margin DC voltage control outer loop current limit value are limited to obtain the output value of the fixed frequency control end inner loop current controller, such as Fig.11 As shown, k13 is the upper limit coefficient of the DC voltage limit value of the fixed height margin, I dref2 It is the output value of the inner loop current controller at the fixed frequency control end.

[0112] Example 2

[0113] Based on the same inventive concept, Embodiment 2 of the present invention further provides a fault ride-through voltage margin control device for a flexible DC power transmission system, such as Fig.12 As shown, including:

[0114] A first determination module is used to determine the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end respectively based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end;

[0115] A second determination module is used to determine the fixed DC voltage end amplitude limit value and the fixed frequency control end amplitude limit value based on the change rate of the fixed DC voltage end outer loop current amplitude limit value and the change rate of the fixed frequency control end outer loop current amplitude limit value respectively;

[0116] A third determination module is used to determine the output value of the inner loop current controller of the fixed DC voltage terminal based on the fixed DC voltage terminal amplitude limit value, and determine the output value of the inner loop current controller of the fixed frequency control terminal based on the fixed DC voltage terminal amplitude limit value and the fixed frequency control terminal amplitude limit value;

[0117] The control module is used to control the fault ride-through on the AC side of the flexible DC transmission system based on the output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end.

[0118] The first determination module includes:

[0119] A reference value determination unit, used to determine a base value reference value of an outer loop current amplitude limit value at a constant DC voltage terminal and a base value reference value of an outer loop current amplitude limit value at a constant frequency control terminal respectively based on an AC bus voltage at a constant DC voltage control terminal and an AC bus voltage at a constant frequency control terminal;

[0120] The change rate determination unit is used to determine the change rate of the fixed DC voltage end outer loop current limit value and the change rate of the fixed frequency control end outer loop current limit value based on the fixed DC voltage end outer loop current limit value base reference value and the fixed frequency control end outer loop current limit value base reference value.

[0121] The second determination module is specifically used for:

[0122] The change rate of the current limit value of the outer loop of the fixed DC voltage terminal is processed by the first-order inertia link to obtain the upper limit value of the fixed DC voltage terminal limit value, and the upper limit value of the fixed DC voltage terminal limit value is inverted to obtain the lower limit value of the fixed DC voltage terminal limit value;

[0123] The change rate of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the limit value of the fixed frequency control end, and the upper limit of the limit value of the fixed frequency control end is inverted to obtain the lower limit of the limit value of the fixed frequency control end.

[0124] The third determination module includes:

[0125] An acquisition unit, used to respectively acquire an actual value of a DC voltage and an actual value of a frequency of the flexible DC transmission system;

[0126] A first output value determination unit, used to determine an output value of a fixed DC voltage terminal inner loop current controller based on an actual DC voltage value and a fixed DC voltage terminal amplitude limit value;

[0127] The second output value determination unit is used to determine the output value of the inner loop current controller of the fixed frequency control terminal based on the actual value of the DC voltage, the actual value of the frequency, the fixed DC voltage terminal limit value and the fixed frequency control terminal limit value.

[0128] The control module is specifically used for:

[0129] The output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end are respectively subjected to the inner loop current control link and the dq coordinate system inverse transformation to obtain a positive sequence modulation wave control signal;

[0130] Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

[0131] The reference value determination unit is specifically used for:

[0132] The product of the AC bus voltage at the fixed DC voltage terminal and the fixed DC voltage terminal limit base value amplification coefficient is limited by the upper and lower limits of the fixed DC voltage terminal amplitude base value to obtain a fixed DC voltage terminal outer loop current limit base value reference value;

[0133] The product of the AC bus voltage at the fixed frequency control end and the base amplitude limit amplification coefficient of the fixed frequency control end is limited by the upper and lower limits of the base amplitude limit of the fixed frequency control end to obtain the base amplitude limit reference value of the outer loop current at the fixed frequency control end.

[0134] The change rate determination unit is specifically used for:

[0135] The base value reference value of the current limit amplitude of the outer loop of the fixed DC voltage terminal is processed by a first-order inertia link and a derivative operation is performed to obtain a first voltage derivative result; if the voltage derivative result is greater than zero, the positive change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; if the voltage derivative result is less than zero, the negative change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal;

[0136] The base value reference value of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link and a derivative operation is performed to obtain a second voltage derivative result; if the second voltage derivative result is greater than zero, the positive change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end; if the second voltage derivative result is less than zero, the negative change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end.

[0137] The first output value determination unit is specifically used for:

[0138] The difference between the preset DC voltage reference value of the flexible DC transmission system and the actual DC voltage value is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage terminal limit value and the lower limit of the fixed DC voltage terminal limit value to obtain the output value of the fixed DC voltage terminal inner loop current controller.

[0139] The second output value determination unit is specifically used for:

[0140] The difference between the preset frequency reference value and the actual frequency value of the flexible DC transmission system is passed through the PI control link, and then the upper limit of the fixed frequency control end limit value and the lower limit of the fixed frequency control end limit value are limited to obtain the upper limit of the fixed high margin DC voltage control outer loop current limit value;

[0141] The product of the preset flexible direct current transmission system direct current voltage reference value and the fixed high margin direct current voltage limit value lower limit coefficient is subtracted from the actual direct current voltage value, and the difference is passed through the PI control link, and then the fixed high margin direct current voltage control outer loop current limit value upper limit and the fixed direct current voltage terminal limit value lower limit are limited to obtain the fixed high margin direct current voltage control outer loop current limit value lower limit;

[0142] The product of the preset flexible DC voltage reference value of the DC transmission system and the upper limit coefficient of the fixed high margin DC voltage limit value is subtracted from the actual DC voltage value, and the difference is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage end limit value and the lower limit of the fixed high margin DC voltage control outer loop current limit value, to obtain the output value of the fixed frequency control end inner loop current controller.

[0143] For the convenience of description, the various parts of the above device are divided into various modules or units according to their functions and described separately. Of course, when implementing the present application, the functions of each module or unit can be implemented in the same or multiple software or hardware.

[0144] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0145] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes 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 generate 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.

[0146] 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.

[0147] 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.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Ordinary technicians in the relevant field can still modify or make equivalent substitutions to the specific implementation methods of the present invention with reference to the above embodiments. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the present invention to be approved.

Claims

1. A method for controlling fault ride-through voltage margin of a flexible direct current transmission system, characterized in that: include: Determine the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end respectively based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end; Determine the fixed DC voltage end limit value and the fixed frequency control end limit value based on the fixed DC voltage end outer loop current limit value change rate and the fixed frequency control end outer loop current limit value change rate; Determine the output value of the inner loop current controller at the fixed DC voltage end based on the fixed DC voltage end amplitude limit, and determine the output value of the inner loop current controller at the fixed frequency control end based on the fixed DC voltage end amplitude limit and the fixed frequency control end amplitude limit; Controlling the fault ride-through on the AC side of the flexible DC transmission system based on the output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end; The output value of the inner loop current controller at the fixed DC voltage end is determined based on the fixed DC voltage end amplitude limit, and the output value of the inner loop current controller at the fixed frequency control end is determined based on the fixed DC voltage end amplitude limit and the fixed frequency control end amplitude limit, including: respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system; Determine the output value of the inner loop current controller of the fixed DC voltage terminal based on the actual value of the DC voltage and the limit value of the fixed DC voltage terminal; The output value of the inner loop current controller of the fixed frequency control terminal is determined based on the actual value of the DC voltage, the actual value of the frequency, the limit value of the fixed DC voltage terminal and the limit value of the fixed frequency control terminal.

2. The method for controlling fault ride-through voltage margin of a flexible DC transmission system according to claim 1, characterized in that: The method of respectively determining the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end includes: Determine a base value reference value of an outer loop current amplitude limit value at a constant DC voltage end and a base value reference value of an outer loop current amplitude limit value at a constant frequency control end based on an AC bus voltage at a constant DC voltage control end and an AC bus voltage at a constant frequency control end; Based on the base value reference value of the outer loop current limit value at the fixed DC voltage end and the base value reference value of the outer loop current limit value at the fixed frequency control end, the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end are determined respectively.

3. The method for controlling fault ride-through voltage margin of a flexible DC transmission system according to claim 1, characterized in that: The method of determining the fixed DC voltage end amplitude limit value and the fixed frequency control end amplitude limit value based on the change rate of the fixed DC voltage end outer loop current amplitude limit value and the change rate of the fixed frequency control end outer loop current amplitude limit value respectively includes: The change rate of the current limit value of the outer loop of the fixed DC voltage terminal is processed by the first-order inertia link to obtain the upper limit value of the fixed DC voltage terminal limit value, and the upper limit value of the fixed DC voltage terminal limit value is inverted to obtain the lower limit value of the fixed DC voltage terminal limit value; The change rate of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the limit value of the fixed frequency control end, and the upper limit of the limit value of the fixed frequency control end is inverted to obtain the lower limit of the limit value of the fixed frequency control end.

4. The method for controlling fault ride-through voltage margin of a flexible DC transmission system according to claim 1, characterized in that: The method of controlling the fault ride-through on the AC side of the flexible DC power transmission system based on the output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end includes: The output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end are respectively subjected to the inner loop current control link and the dq coordinate system inverse transformation to obtain a positive sequence modulation wave control signal; Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

5. The method for controlling fault ride-through voltage margin of a flexible DC transmission system according to claim 2, characterized in that: The method of respectively determining a base value reference value of an outer loop current amplitude limit value at a constant DC voltage terminal and a base value reference value of an outer loop current amplitude limit value at a constant frequency control terminal based on an AC bus voltage at a constant DC voltage control terminal and an AC bus voltage at a constant frequency control terminal comprises: The product of the AC bus voltage at the fixed DC voltage terminal and the fixed DC voltage terminal limit base value amplification coefficient is limited by the upper and lower limits of the fixed DC voltage terminal amplitude base value to obtain a fixed DC voltage terminal outer loop current limit base value reference value; The product of the AC bus voltage at the fixed frequency control end and the base amplitude limit amplification coefficient of the fixed frequency control end is limited by the upper and lower limits of the base amplitude limit of the fixed frequency control end to obtain the base amplitude limit reference value of the outer loop current at the fixed frequency control end.

6. The method for controlling fault ride-through voltage margin of a flexible DC transmission system according to claim 2, characterized in that: The method of respectively determining the change rate of the outer loop current amplitude limit value at the fixed DC voltage end and the change rate of the outer loop current amplitude limit value at the fixed frequency control end based on the base value reference value of the outer loop current amplitude limit value at the fixed DC voltage end and the base value reference value of the outer loop current amplitude limit value at the fixed frequency control end comprises: The base value reference value of the current limit amplitude of the outer loop of the fixed DC voltage terminal is processed by a first-order inertia link and a derivative operation is performed to obtain a first voltage derivative result; if the voltage derivative result is greater than zero, the positive change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; if the voltage derivative result is less than zero, the negative change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; The base value reference value of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link and a derivative operation is performed to obtain a second voltage derivative result; if the second voltage derivative result is greater than zero, the positive change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end; if the second voltage derivative result is less than zero, the negative change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end.

7. The method for controlling fault ride-through voltage margin of a flexible DC transmission system according to claim 1, characterized in that: The method of determining the output value of the inner loop current controller at the fixed DC voltage end based on the actual DC voltage value and the fixed DC voltage end amplitude limit value includes: The difference between the preset DC voltage reference value of the flexible DC transmission system and the actual DC voltage value is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage terminal limit value and the lower limit of the fixed DC voltage terminal limit value to obtain the output value of the fixed DC voltage terminal inner loop current controller.

8. The method for controlling fault ride-through voltage margin of a flexible DC transmission system according to claim 1, characterized in that: The method of determining the output value of the inner loop current controller of the fixed frequency control terminal based on the actual value of the DC voltage, the actual value of the frequency, the fixed DC voltage terminal limit value and the fixed frequency control terminal limit value includes: The difference between the preset frequency reference value and the actual frequency value of the flexible DC transmission system is passed through the PI control link, and then the upper limit of the fixed frequency control end limit value and the lower limit of the fixed frequency control end limit value are limited to obtain the upper limit of the fixed high margin DC voltage control outer loop current limit value; The product of the preset flexible direct current transmission system direct current voltage reference value and the fixed high margin direct current voltage limit value lower limit coefficient is subtracted from the actual direct current voltage value, and the difference is passed through the PI control link, and then the fixed high margin direct current voltage control outer loop current limit value upper limit and the fixed direct current voltage terminal limit value lower limit are limited to obtain the fixed high margin direct current voltage control outer loop current limit value lower limit; The product of the preset flexible DC voltage reference value of the DC transmission system and the upper limit coefficient of the fixed high margin DC voltage limit value is subtracted from the actual DC voltage value, and the difference is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage end limit value and the lower limit of the fixed high margin DC voltage control outer loop current limit value, to obtain the output value of the fixed frequency control end inner loop current controller.

9. A fault ride-through voltage margin control device for a flexible DC transmission system, characterized in that: include: A first determination module is used to determine the change rate of the outer loop current limit value at the fixed DC voltage end and the change rate of the outer loop current limit value at the fixed frequency control end respectively based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end; A second determination module is used to determine the fixed DC voltage end amplitude limit value and the fixed frequency control end amplitude limit value based on the change rate of the fixed DC voltage end outer loop current amplitude limit value and the change rate of the fixed frequency control end outer loop current amplitude limit value respectively; A third determination module is used to determine the output value of the inner loop current controller of the fixed DC voltage terminal based on the fixed DC voltage terminal amplitude limit value, and determine the output value of the inner loop current controller of the fixed frequency control terminal based on the fixed DC voltage terminal amplitude limit value and the fixed frequency control terminal amplitude limit value; A control module, used for controlling the fault ride-through on the AC side of the flexible DC transmission system based on an output value of an inner loop current controller at a fixed DC voltage end and an output value of an inner loop current controller at a fixed frequency control end; The third determination module comprises: An acquisition unit, used to respectively acquire an actual value of a DC voltage and an actual value of a frequency of the flexible DC transmission system; A first output value determination unit, used to determine an output value of a fixed DC voltage terminal inner loop current controller based on an actual DC voltage value and a fixed DC voltage terminal amplitude limit value; The second output value determination unit is used to determine the output value of the inner loop current controller of the fixed frequency control terminal based on the actual value of the DC voltage, the actual value of the frequency, the fixed DC voltage terminal limit value and the fixed frequency control terminal limit value.

10. The fault ride-through voltage margin control device for a flexible DC power transmission system according to claim 9, characterized in that: The first determining module comprises: A reference value determination unit, used to determine a base value reference value of an outer loop current amplitude limit value at a constant DC voltage terminal and a base value reference value of an outer loop current amplitude limit value at a constant frequency control terminal respectively based on an AC bus voltage at a constant DC voltage control terminal and an AC bus voltage at a constant frequency control terminal; The change rate determination unit is used to determine the change rate of the fixed DC voltage end outer loop current limit value and the change rate of the fixed frequency control end outer loop current limit value based on the fixed DC voltage end outer loop current limit value base reference value and the fixed frequency control end outer loop current limit value base reference value.

11. The fault ride-through voltage margin control device for a flexible direct current transmission system according to claim 10, characterized in that: The second determining module is specifically used for: The change rate of the current limit value of the outer loop of the fixed DC voltage terminal is processed by the first-order inertia link to obtain the upper limit value of the fixed DC voltage terminal limit value, and the upper limit value of the fixed DC voltage terminal limit value is inverted to obtain the lower limit value of the fixed DC voltage terminal limit value; The change rate of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the limit value of the fixed frequency control end, and the upper limit of the limit value of the fixed frequency control end is inverted to obtain the lower limit of the limit value of the fixed frequency control end.

12. The fault ride-through voltage margin control device for a flexible DC power transmission system according to claim 9, characterized in that: The control module is specifically used for: The output value of the inner loop current controller at the fixed DC voltage end and the output value of the inner loop current controller at the fixed frequency control end are respectively subjected to the inner loop current control link and the dq coordinate system inverse transformation to obtain a positive sequence modulation wave control signal; Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

13. The fault ride-through voltage margin control device for a flexible DC power transmission system according to claim 10, characterized in that: The reference value determination unit is specifically used for: The product of the AC bus voltage at the fixed DC voltage terminal and the fixed DC voltage terminal limit base value amplification coefficient is limited by the upper and lower limits of the fixed DC voltage terminal amplitude base value to obtain a fixed DC voltage terminal outer loop current limit base value reference value; The product of the AC bus voltage at the fixed frequency control end and the base amplitude limit amplification coefficient of the fixed frequency control end is limited by the upper and lower limits of the base amplitude limit of the fixed frequency control end to obtain the base amplitude limit reference value of the outer loop current at the fixed frequency control end.

14. The fault ride-through voltage margin control device for a flexible DC power transmission system according to claim 10, characterized in that: The change rate determination unit is specifically used for: The base value reference value of the current limit amplitude of the outer loop of the fixed DC voltage terminal is processed by a first-order inertia link and a derivative operation is performed to obtain a first voltage derivative result; if the voltage derivative result is greater than zero, the positive change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; if the voltage derivative result is less than zero, the negative change rate of the limit amplitude of the fixed DC voltage terminal is used as the change rate of the current limit amplitude of the outer loop of the fixed DC voltage terminal; The base value reference value of the current limit value of the outer loop of the fixed frequency control end is processed by the first-order inertia link and a derivative operation is performed to obtain a second voltage derivative result; if the second voltage derivative result is greater than zero, the positive change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end; if the second voltage derivative result is less than zero, the negative change rate of the limit value of the fixed frequency control end is used as the change rate of the current limit value of the outer loop of the fixed frequency control end.

15. The fault ride-through voltage margin control device for a flexible DC power transmission system according to claim 9, characterized in that: The first output value determining unit is specifically used for: The difference between the preset DC voltage reference value of the flexible DC transmission system and the actual DC voltage value is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage terminal limit value and the lower limit of the fixed DC voltage terminal limit value to obtain the output value of the fixed DC voltage terminal inner loop current controller.

16. The fault ride-through voltage margin control device for a flexible direct current transmission system according to claim 9, characterized in that: The second output value determining unit is specifically used for: The difference between the preset frequency reference value and the actual frequency value of the flexible DC transmission system is passed through the PI control link, and then the upper limit of the fixed frequency control end limit value and the lower limit of the fixed frequency control end limit value are limited to obtain the upper limit of the fixed high margin DC voltage control outer loop current limit value; The product of the preset flexible direct current transmission system direct current voltage reference value and the fixed high margin direct current voltage limit value lower limit coefficient is subtracted from the actual direct current voltage value, and the difference is passed through the PI control link, and then the fixed high margin direct current voltage control outer loop current limit value upper limit and the fixed direct current voltage terminal limit value lower limit are limited to obtain the fixed high margin direct current voltage control outer loop current limit value lower limit; The product of the preset flexible DC voltage reference value of the DC transmission system and the upper limit coefficient of the fixed high margin DC voltage limit value is subtracted from the actual DC voltage value, and the difference is passed through the PI control link, and then limited by the upper limit of the fixed DC voltage end limit value and the lower limit of the fixed high margin DC voltage control outer loop current limit value, to obtain the output value of the fixed frequency control end inner loop current controller.

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