A method and device for controlling fault ride-through on the AC side of a flexible DC transmission system

Abstract

The present invention provides a method and device for controlling fault ride-through on the AC side 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 outer loop current limit value limit value at the fixed direct current voltage end and the outer loop current limit value 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 an inner loop current controller at the fixed frequency control end, and control the fault ride-through on the AC 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 fault ride-through on the alternating current side 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 fault ride-through on the AC side of a flexible DC power 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 limit value of the outer loop current amplitude limit value at the fixed DC voltage end and the limit value of the outer loop current amplitude limit value at the fixed frequency control end respectively based on 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;

[0007] Based on the limit value of the outer loop current limit value of the fixed DC voltage end and the limit value of the outer loop current limit value of the fixed frequency control end, the output value of the inner loop current controller of the fixed DC voltage end and the output value of the inner loop current controller of the fixed frequency control end are determined respectively;

[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 outer loop current amplitude limit value and the fixed frequency control end outer loop current amplitude limit value based on the fixed DC voltage end outer loop current amplitude limit value change rate and the fixed frequency control end outer loop current amplitude limit value change rate respectively includes:

[0013] Determine the primary amplitude limit value of the fixed DC voltage terminal based on the change rate of the outer loop current amplitude limit value of the fixed DC voltage terminal, and determine the primary amplitude limit value of the fixed frequency control terminal based on the change rate of the outer loop current amplitude limit value of the fixed frequency control terminal;

[0014] The outer loop current amplitude limit value of the fixed DC voltage terminal is determined based on the primary amplitude limit value of the fixed DC voltage terminal, and the outer loop current amplitude limit value of the fixed frequency control terminal is determined based on the primary amplitude limit value of the fixed frequency control terminal.

[0015] The method of respectively determining 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 based on the outer loop current amplitude limit value at the fixed DC voltage end and the outer loop current amplitude limit value at the fixed frequency control end comprises:

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

[0017] The difference between the preset DC voltage reference value and the actual DC voltage value of the flexible DC transmission system is controlled by the PI control link, and then limited by the current limit value of the outer loop of the fixed DC voltage end to obtain the output value of the inner loop current controller of the fixed DC voltage end;

[0018] 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 limited by the outer loop current limit value of the fixed frequency control end to obtain the output value of the inner loop current controller of the fixed frequency control end.

[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 primary amplitude limit value of the fixed DC voltage terminal based on the change rate of the external loop current amplitude limit value of the fixed DC voltage terminal, and determining the primary amplitude limit value of the fixed frequency control terminal based on the change rate of the external loop current amplitude limit value of the fixed frequency control terminal, comprises:

[0029] 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 of the primary limit value of the fixed DC voltage terminal, and the upper limit of the primary limit value of the fixed DC voltage terminal is inverted to obtain the lower limit of the primary limit value of the fixed DC voltage terminal;

[0030] The change rate of the outer loop current limit value of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the primary limit value of the fixed frequency control end, and the upper limit of the primary limit value of the fixed frequency control end is inverted to obtain the lower limit of the primary limit value of the fixed frequency control end.

[0031] The method of determining the current amplitude limit value of the outer loop of the fixed DC voltage terminal based on the primary amplitude limit value of the fixed DC voltage terminal, and determining the current amplitude limit value of the outer loop of the fixed frequency control terminal based on the primary amplitude limit value of the fixed frequency control terminal, comprises:

[0032] The difference between the preset maximum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the upper limit of the primary limit value of the fixed DC voltage end, so as to obtain the upper limit of the external loop current limit value of the fixed DC voltage end; and the difference between the preset minimum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the lower limit of the primary limit value of the fixed DC voltage end, so as to obtain the lower limit of the external loop current limit value of the fixed DC voltage end;

[0033] The difference between the preset maximum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the upper limit of the primary limit value of the fixed frequency control end, so as to obtain the upper limit of the outer loop current limit value of the fixed frequency control end; and the difference between the preset minimum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the lower limit of the primary limit value of the fixed frequency control end, so as to obtain the lower limit of the outer loop current limit value of the fixed frequency control end.

[0034] On the other hand, the present invention also provides an AC side fault ride-through control device for a flexible DC power 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 outer loop current amplitude limit value and the fixed frequency control end outer loop current amplitude limit value limit value respectively based on the fixed DC voltage end outer loop current amplitude limit value change rate and the fixed frequency control end outer loop current amplitude limit value change rate;

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

[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 determination module includes:

[0043] A primary amplitude limit value determination unit, used to determine the primary amplitude limit value of the fixed DC voltage terminal based on the change rate of the external loop current amplitude limit value of the fixed DC voltage terminal, and to determine the primary amplitude limit value of the fixed frequency control terminal based on the change rate of the external loop current amplitude limit value of the fixed frequency control terminal;

[0044] The outer loop current amplitude limit is used to determine the outer loop current amplitude limit at the fixed DC voltage end based on the primary amplitude limit at the fixed DC voltage end, and to determine the outer loop current amplitude limit at the fixed frequency control end based on the primary amplitude limit at the fixed frequency control end.

[0045] The third determination module is specifically used for:

[0046] respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system;

[0047] The difference between the preset DC voltage reference value and the actual DC voltage value of the flexible DC transmission system is controlled by the PI control link, and then limited by the current limit value of the outer loop of the fixed DC voltage end to obtain the output value of the inner loop current controller of the fixed DC voltage end;

[0048] 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 limited by the outer loop current limit value of the fixed frequency control end to obtain the output value of the inner loop current controller of the fixed frequency control end.

[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 primary amplitude limit value is specifically used for:

[0059] 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 of the primary limit value of the fixed DC voltage terminal, and the upper limit of the primary limit value of the fixed DC voltage terminal is inverted to obtain the lower limit of the primary limit value of the fixed DC voltage terminal;

[0060] The change rate of the outer loop current limit value of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the primary limit value of the fixed frequency control end, and the upper limit of the primary limit value of the fixed frequency control end is inverted to obtain the lower limit of the primary limit value of the fixed frequency control end.

[0061] The outer loop current limit amplitude limit is specifically used for:

[0062] The difference between the preset maximum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the upper limit of the primary limit value of the fixed DC voltage end, so as to obtain the upper limit of the external loop current limit value of the fixed DC voltage end; and the difference between the preset minimum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the lower limit of the primary limit value of the fixed DC voltage end, so as to obtain the lower limit of the external loop current limit value of the fixed DC voltage end;

[0063] The difference between the preset maximum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the upper limit of the primary limit value of the fixed frequency control end, so as to obtain the upper limit of the outer loop current limit value of the fixed frequency control end; and the difference between the preset minimum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the lower limit of the primary limit value of the fixed frequency control end, so as to obtain the lower limit of the outer loop current limit value of the fixed frequency control end.

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

[0065] The present invention provides a method for controlling fault ride-through on the AC side of a flexible DC power transmission system, wherein 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 are determined based on the AC bus voltage at the fixed DC voltage end and the AC bus voltage at the fixed frequency control end; the outer loop current amplitude limit value limit value at the fixed DC voltage end and the outer loop current amplitude limit value limit value at the fixed frequency control end are determined based on 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; 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 determined based on the limit value of the outer loop current amplitude limit value at the fixed DC voltage end and the limit value of the outer loop current amplitude limit value at the fixed frequency control end; the AC side fault ride-through of the flexible DC power 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, thereby greatly reducing the fluctuation of the flexible DC power 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 with two ends connected to a passive AC system at one end. When a temporary fault occurs in the passive AC system at any 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 and smoothly pass through the AC transient process. 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 ensured, 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 restores power transmission in a very short time after the fault is eliminated, and enables the entire DC power transmission system to have AC side fault ride-through capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is a flow chart of a method for controlling fault ride-through on the AC side of a flexible DC transmission system according to 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 51 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 primary amplitude limit value of a fixed DC voltage terminal in an embodiment of the present invention;

[0074] Figure 7 1 is a flow chart of determining the primary amplitude limit value of a constant frequency control terminal in an embodiment of the present invention;

[0075] Figure 8 1 is a flow chart for determining the upper limit of the current limit value of the outer loop at a given DC voltage terminal according to an embodiment of the present invention;

[0076] Fig. 9 1 is a flow chart for determining the lower limit of the current amplitude limit value of the outer loop at a given DC voltage terminal according to an embodiment of the present invention;

[0077] Fig.10 1 is a flow chart for determining the upper limit of the current limit value of the outer loop of the constant frequency control terminal according to an embodiment of the present invention;

[0078] Fig.11 1 is a flow chart for determining the lower limit of the current amplitude limit value of the outer loop of the constant frequency control terminal according to an embodiment of the present invention;

[0079] Fig.12 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;

[0080] Fig.13 It 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. DETAILED DESCRIPTION

[0081] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0082] Example 1

[0083] Embodiment 1 of the present invention provides a method for controlling fault ride-through on the AC side of a flexible direct current transmission system, wherein one end of the flexible direct current transmission system is connected to a passive AC system, and when a temporary fault occurs in the passive AC system and during the recovery process of the passive AC 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 AC system, and the AC transient process is smoothly passed, which can ensure the safe operation of the flexible direct current transmission systems at both ends during the transient fault of the passive AC system and the fault recovery process, and can dynamically adjust the DC control characteristics according to the fault characteristics to achieve AC fault ride-through. The specific flow chart of Embodiment 1 of the present invention is as follows: Figure 1 As shown, the specific process is as follows:

[0084] 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;

[0085] S102: Determine the outer loop current amplitude limit value of the fixed DC voltage end and the outer loop current amplitude limit value of the fixed frequency control end respectively based on the change rate of the outer loop current amplitude limit value of the fixed DC voltage end and the change rate of the outer loop current amplitude limit value of the fixed frequency control end;

[0086] S103: Determine the output value of the inner loop current controller at the constant DC voltage end and the output value of the inner loop current controller at the constant frequency control end respectively based on the outer loop current amplitude limit value at the constant DC voltage end and the outer loop current amplitude limit value at the constant frequency control end;

[0087] S104: Controlling the fault ride-through on the AC side of the 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.

[0088] In S101, 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 includes:

[0089] 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;

[0090] 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.

[0091] In S102, based on 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, the outer loop current limit value at the constant DC voltage end and the outer loop current limit value at the constant frequency control end are respectively determined, including:

[0092] Determine the primary amplitude limit value of the fixed DC voltage terminal based on the change rate of the outer loop current amplitude limit value of the fixed DC voltage terminal, and determine the primary amplitude limit value of the fixed frequency control terminal based on the change rate of the outer loop current amplitude limit value of the fixed frequency control terminal;

[0093] The outer loop current amplitude limit value of the fixed DC voltage terminal is determined based on the primary amplitude limit value of the fixed DC voltage terminal, and the outer loop current amplitude limit value of the fixed frequency control terminal is determined based on the primary amplitude limit value of the fixed frequency control terminal.

[0094] In S103, based on the outer loop current limit value of the fixed DC voltage end and the outer loop current limit value of the fixed frequency control end, the output value of the inner loop current controller of the fixed DC voltage end and the output value of the inner loop current controller of the fixed frequency control end are determined respectively, including:

[0095] respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system;

[0096] 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 the output value of the inner loop current controller at the fixed DC voltage end is obtained after the outer loop current limit value at the fixed DC voltage end is limited. Fig.12 As shown, where 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 dref_U is the output value of the inner loop current controller at the fixed DC voltage end;

[0097] The difference between the preset frequency reference value and the actual frequency value of the flexible DC transmission system is controlled by the PI control link, and then the current limit value of the outer loop of the fixed frequency control end is limited to obtain the output value of the inner loop current controller of the fixed frequency control end, such as Fig.13 As shown, where 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, I dref_VF It is the output value of the inner loop current controller at the fixed frequency control end.

[0098] In S104, the AC side fault ride-through 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:

[0099] 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;

[0100] Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

[0101] The above S101, based on the AC bus voltage of the constant DC voltage control terminal and the AC bus voltage of the constant frequency control terminal, respectively determines the base value reference value of the outer loop current amplitude limit value of the constant DC voltage terminal and the base value reference value of the outer loop current amplitude limit value of the constant frequency control terminal, including:

[0102] 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;

[0103] 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, such as 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.

[0104] 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:

[0105] 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 a derivative operation is performed to obtain a first voltage derivative result; if the first voltage derivative 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 first voltage derivative 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;

[0106] 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 5As 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;

[0107] The primary amplitude limit value of the fixed DC voltage terminal is determined based on the change rate of the external loop current amplitude limit value of the fixed DC voltage terminal, and the primary amplitude limit value of the fixed frequency control terminal is determined based on the change rate of the external loop current amplitude limit value of the fixed frequency control terminal, including:

[0108] The change rate of the outer loop current limit value at the constant DC voltage end is processed by the first-order inertia link to obtain the upper limit of the primary limit value at the constant DC voltage end. The upper limit of the primary limit value at the constant DC voltage end is inverted to obtain the lower limit of the primary limit value at the constant DC voltage end, such as Figure 6 As shown, lim_HD_U is the upper limit of the primary amplitude limit value at the constant DC voltage end, and lim_LD_U is the lower limit of the primary amplitude limit value at the constant DC voltage end.

[0109] The change rate of the outer loop current limit value of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the primary limit value of the fixed frequency control end. The upper limit of the primary limit value of the fixed frequency control end is inverted to obtain the lower limit of the primary limit value of the fixed frequency control end, such as Figure 7 As shown, lim_HD_VF is the upper limit of the primary amplitude limit value of the fixed frequency control end, and lim_LD_VF is the lower limit of the primary amplitude limit value of the fixed frequency control end.

[0110] The outer loop current amplitude limit value of the fixed DC voltage terminal is determined based on the primary amplitude limit value of the fixed DC voltage terminal, and the outer loop current amplitude limit value of the fixed frequency control terminal is determined based on the primary amplitude limit value of the fixed frequency control terminal, including:

[0111] The difference between the preset maximum active power reference value of the constant DC voltage terminal and the actual active power value is passed through the PI control link, and then limited by the upper limit of the primary limit value of the constant DC voltage terminal to obtain the upper limit of the external loop current limit value of the constant DC voltage terminal; Figure 8 As shown, where P ref_max is the preset maximum value of the active power reference value at the constant DC voltage terminal, P_ pu is the normalized actual value of active power, lim_U1 is the upper limit of the current limit of the outer loop at the constant DC voltage end; and the difference between the preset minimum active power reference value of the constant DC voltage end and the actual value of active power is controlled by the PI control link, and then limited by the lower limit of the primary limit value of the constant DC voltage end, so as to obtain the lower limit of the current limit of the outer loop at the constant DC voltage end; Fig. 9 As shown, where P ref_min is the preset minimum reference value of active power at the constant DC voltage terminal, P_ puis the actual value of the normalized active power, and lim_U2 is the lower limit of the outer loop current limit at the fixed DC voltage end.

[0112] The difference between the preset maximum active power reference value of the fixed frequency control end and the actual active power value is passed through the PI control link, and then the upper limit of the primary limit value of the fixed frequency control end is limited to obtain the upper limit of the outer loop current limit value of the fixed frequency control end; Fig.10 As shown, where P ref_max_VF is the preset maximum value of the active power reference value of the fixed frequency control end, lim_VF1 is the upper limit of the current limit value of the outer loop of the fixed frequency control end, and the difference between the preset minimum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then through the lower limit of the primary limit value of the fixed frequency control end to obtain the lower limit of the current limit value of the outer loop of the fixed frequency control end, such as Fig.11 As shown, where P ref_min_VF is the preset minimum active power reference value of the fixed frequency control end, and lim_VF2 is the lower limit of the outer loop current limit value of the fixed frequency control end.

[0113] Example 2

[0114] Based on the same inventive concept, Embodiment 2 of the present invention further provides an AC side fault ride-through control device for a flexible DC power transmission system, comprising:

[0115] 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;

[0116] A second determination module is used to determine the fixed DC voltage end outer loop current amplitude limit value and the fixed frequency control end outer loop current amplitude limit value limit value respectively based on the fixed DC voltage end outer loop current amplitude limit value change rate and the fixed frequency control end outer loop current amplitude limit value change rate;

[0117] A third determination module is used to determine the output value of the inner loop current controller of the fixed DC voltage end and the output value of the inner loop current controller of the fixed frequency control end respectively based on the outer loop current limit value of the fixed DC voltage end and the outer loop current limit value of the fixed frequency control end;

[0118] 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.

[0119] The first determination module includes:

[0120] 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;

[0121] 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.

[0122] The second determination module includes:

[0123] A primary amplitude limit value determination unit, used to determine the primary amplitude limit value of the fixed DC voltage terminal based on the change rate of the external loop current amplitude limit value of the fixed DC voltage terminal, and to determine the primary amplitude limit value of the fixed frequency control terminal based on the change rate of the external loop current amplitude limit value of the fixed frequency control terminal;

[0124] The outer loop current amplitude limit is used to determine the outer loop current amplitude limit at the fixed DC voltage end based on the primary amplitude limit at the fixed DC voltage end, and to determine the outer loop current amplitude limit at the fixed frequency control end based on the primary amplitude limit at the fixed frequency control end.

[0125] The third determination module is specifically used for:

[0126] respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system;

[0127] The difference between the preset DC voltage reference value and the actual DC voltage value of the flexible DC transmission system is controlled by the PI control link, and then limited by the current limit value of the outer loop of the fixed DC voltage end to obtain the output value of the inner loop current controller of the fixed DC voltage end;

[0128] 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 limited by the outer loop current limit value of the fixed frequency control end to obtain the output value of the inner loop current controller of the fixed frequency control end.

[0129] The control module is specifically used for:

[0130] 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;

[0131] Fault ride-through control is performed on the AC side of the flexible DC transmission system based on positive sequence modulation wave control signal.

[0132] The reference value determination unit is specifically used for:

[0133] 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;

[0134] 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.

[0135] The change rate determination unit is specifically used for:

[0136] 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;

[0137] 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.

[0138] The primary limit value is specifically used for:

[0139] 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 of the primary limit value of the fixed DC voltage terminal, and the upper limit of the primary limit value of the fixed DC voltage terminal is inverted to obtain the lower limit of the primary limit value of the fixed DC voltage terminal;

[0140] The change rate of the outer loop current limit value of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the primary limit value of the fixed frequency control end, and the upper limit of the primary limit value of the fixed frequency control end is inverted to obtain the lower limit of the primary limit value of the fixed frequency control end.

[0141] The outer loop current limit value is specifically used for:

[0142] The difference between the preset maximum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the upper limit of the primary limit value of the fixed DC voltage end, so as to obtain the upper limit of the external loop current limit value of the fixed DC voltage end; and the difference between the preset minimum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the lower limit of the primary limit value of the fixed DC voltage end, so as to obtain the lower limit of the external loop current limit value of the fixed DC voltage end;

[0143] The difference between the preset maximum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the upper limit of the primary limit value of the fixed frequency control end, so as to obtain the upper limit of the outer loop current limit value of the fixed frequency control end; and the difference between the preset minimum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the lower limit of the primary limit value of the fixed frequency control end, so as to obtain the lower limit of the outer loop current limit value of the fixed frequency control end.

[0144] For the convenience of description, the above parts of the 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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 on the AC side of a flexible DC 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 limit value of the outer loop current amplitude limit value at the fixed DC voltage end and the limit value of the outer loop current amplitude limit value at the fixed frequency control end respectively based on 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 limit value of the outer loop current limit value of the fixed DC voltage end and the limit value of the outer loop current limit value of the fixed frequency control end, the output value of the inner loop current controller of the fixed DC voltage end and the output value of the inner loop current controller of the fixed frequency control end are determined respectively; 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 method of determining the fixed DC voltage end outer loop current amplitude limit value and the fixed frequency control end outer loop current amplitude limit value based on the fixed DC voltage end outer loop current amplitude limit value change rate and the fixed frequency control end outer loop current amplitude limit value change rate respectively includes: Determine the primary amplitude limit value of the fixed DC voltage terminal based on the change rate of the outer loop current amplitude limit value of the fixed DC voltage terminal, and determine the primary amplitude limit value of the fixed frequency control terminal based on the change rate of the outer loop current amplitude limit value of the fixed frequency control terminal; Determine the limit value of the outer loop current amplitude limit value of the fixed DC voltage terminal based on the limit value of the primary amplitude limit value of the fixed DC voltage terminal, and determine the limit value of the outer loop current amplitude limit value of the fixed frequency control terminal based on the limit value of the primary amplitude limit value of the fixed frequency control terminal; The method of determining the current amplitude limit value of the outer loop of the fixed DC voltage terminal based on the primary amplitude limit value of the fixed DC voltage terminal, and determining the current amplitude limit value of the outer loop of the fixed frequency control terminal based on the primary amplitude limit value of the fixed frequency control terminal, comprises: The difference between the preset maximum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the upper limit of the primary limit value of the fixed DC voltage end, so as to obtain the upper limit of the external loop current limit value of the fixed DC voltage end; and the difference between the preset minimum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the lower limit of the primary limit value of the fixed DC voltage end, so as to obtain the lower limit of the external loop current limit value of the fixed DC voltage end; The difference between the preset maximum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the upper limit of the primary limit value of the fixed frequency control end, so as to obtain the upper limit of the outer loop current limit value of the fixed frequency control end; and the difference between the preset minimum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the lower limit of the primary limit value of the fixed frequency control end, so as to obtain the lower limit of the outer loop current limit value of the fixed frequency control end.

2. The method for controlling AC side fault ride-through of a flexible DC power 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 AC side fault ride-through of a flexible DC power transmission system according to claim 1, characterized in that: The method of respectively determining 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 based on the outer loop current amplitude limit value at the fixed DC voltage end and the outer loop current amplitude limit value at the fixed frequency control end comprises: respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system; The difference between the preset DC voltage reference value and the actual DC voltage value of the flexible DC transmission system is controlled by the PI control link, and then limited by the current limit value of the outer loop of the fixed DC voltage end to obtain the output value of the inner loop current controller of the fixed DC voltage end; 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 limited by the outer loop current limit value of the fixed frequency control end to obtain the output value of the inner loop current controller of the fixed frequency control end.

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

8. A fault ride-through control device for the AC side of 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 outer loop current amplitude limit value and the fixed frequency control end outer loop current amplitude limit value limit value respectively based on the fixed DC voltage end outer loop current amplitude limit value change rate and the fixed frequency control end outer loop current amplitude limit value change rate; A third determination module is used to determine the output value of the inner loop current controller of the fixed DC voltage end and the output value of the inner loop current controller of the fixed frequency control end respectively based on the outer loop current limit value of the fixed DC voltage end and the outer loop current limit value of the fixed frequency control end; 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 second determination module includes: A primary amplitude limit value determination unit, used to determine the primary amplitude limit value of the fixed DC voltage terminal based on the change rate of the external loop current amplitude limit value of the fixed DC voltage terminal, and to determine the primary amplitude limit value of the fixed frequency control terminal based on the change rate of the external loop current amplitude limit value of the fixed frequency control terminal; The outer loop current amplitude limit is used to determine the outer loop current amplitude limit of the fixed DC voltage terminal based on the primary amplitude limit of the fixed DC voltage terminal, and to determine the outer loop current amplitude limit of the fixed frequency control terminal based on the primary amplitude limit of the fixed frequency control terminal; The outer loop current limit amplitude limit is specifically used for: The difference between the preset maximum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the upper limit of the primary limit value of the fixed DC voltage end, so as to obtain the upper limit of the external loop current limit value of the fixed DC voltage end; and the difference between the preset minimum active power reference value of the fixed DC voltage end and the actual active power value is passed through the PI control link, and then is limited by the lower limit of the primary limit value of the fixed DC voltage end, so as to obtain the lower limit of the external loop current limit value of the fixed DC voltage end; The difference between the preset maximum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the upper limit of the primary limit value of the fixed frequency control end, so as to obtain the upper limit of the outer loop current limit value of the fixed frequency control end; and the difference between the preset minimum value of the active power reference value of the fixed frequency control end and the actual value of the active power is passed through the PI control link, and then limited by the lower limit of the primary limit value of the fixed frequency control end, so as to obtain the lower limit of the outer loop current limit value of the fixed frequency control end.

9. The AC side fault ride-through control device of the flexible DC power transmission system according to claim 8, 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.

10. The AC side fault ride-through control device of the flexible DC power transmission system according to claim 9, characterized in that: The third determination module is specifically used for: respectively obtaining the actual value of the DC voltage and the actual value of the frequency of the flexible DC transmission system; The difference between the preset DC voltage reference value and the actual DC voltage value of the flexible DC transmission system is controlled by the PI control link, and then limited by the current limit value of the outer loop of the fixed DC voltage end to obtain the output value of the inner loop current controller of the fixed DC voltage end; 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 limited by the outer loop current limit value of the fixed frequency control end to obtain the output value of the inner loop current controller of the fixed frequency control end.

11. The AC side fault ride-through control device of a flexible DC power transmission system according to claim 8, 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.

12. The AC side fault ride-through control device of the flexible DC power transmission system according to claim 9, 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.

13. The AC side fault ride-through control device of the flexible DC power transmission system according to claim 9, 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.

14. The AC side fault ride-through control device of the flexible DC power transmission system according to claim 8, characterized in that: The primary amplitude limit value 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 of the primary limit value of the fixed DC voltage terminal, and the upper limit of the primary limit value of the fixed DC voltage terminal is inverted to obtain the lower limit of the primary limit value of the fixed DC voltage terminal; The change rate of the outer loop current limit value of the fixed frequency control end is processed by the first-order inertia link to obtain the upper limit of the primary limit value of the fixed frequency control end, and the upper limit of the primary limit value of the fixed frequency control end is inverted to obtain the lower limit of the primary limit value of the fixed frequency control end.

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