MMC flexible DC converter valve submodule fault positioning method and device

Abstract

The invention discloses an MMC flexible DC converter valve submodule fault positioning method and device, and belongs to the technical field of DC power transmission. The method is composed of two links of fault monitoring and fault positioning, the fault monitoring link depends on the bridge arm voltage deviation value of the MMC system to monitor whether the system has a fault and position the fault to the bridge arm level, and the fault positioning link constructs a sliding mode observer for each sub-module of the fault bridge arm, estimates the capacitor voltage value of the sub-module and positions the fault to the bridge arm level. And comparing with a capacitor voltage measurement value to generate a residual sequence, and then comparing with an adaptive threshold value to locate a fault to a specific sub-module. According to the method, a preposed foundation is provided for submodule fault removal isolation and fault-tolerant operation of the subsequent MMC flexible direct current converter valve system, and the reliability of the MMC flexible direct current converter valve system is improved.

Description

Technical Field

[0001] The invention relates to a method and a device for locating a fault of a MMC flexible direct current converter valve submodule, belonging to the technical field of direct current transmission. Background Art

[0002] The Modular Multilevel Converter (MMC) was first proposed by Professor R. Marquardt in 2001. It is composed of multiple cascaded sub-modules (SM) with the same structure. The structure of the sub-module can be divided into three types: half-H bridge type, full H bridge type and double clamp sub-module type. The Modular Multilevel Converter (MMC) has the advantages of low harmonic content, flexible control, low loss, high output power quality, and easy expansion of voltage and power. It has received extensive attention and application in the fields of flexible DC transmission. At the same time, there are a large number of MMC circuit sub-modules. Each bridge arm contains a sub-module in high-voltage and high-power situations. The large number of sub-modules increases the probability of various faults. Once a sub-module fails, if it is not detected and isolated in time, it will have a serious impact on the performance of the MMC system. Each half-bridge sub-module contains two IGBTs, a storage capacitor, and a voltage sensor, and different types of component failures may occur. For different types of faults, how to quickly and accurately locate the faults to facilitate subsequent MMC system fault removal, isolation and fault-tolerant operation has become a crucial issue. Summary of the invention

[0003] The purpose of the present invention is to propose a method and device for locating the fault of a submodule of an MMC flexible direct current converter valve, which realizes the arm-level positioning of multiple types of faults through a fault monitoring link, and realizes the submodule-level positioning of multiple types of faults through a fault locating link.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a method for locating a fault of an MMC flexible direct current converter valve submodule, comprising:

[0006] Acquire the actual value of the bridge arm voltage and the measured value of the bridge arm voltage of the three-phase six-bridge arm of the MMC, and obtain the bridge arm voltage deviation based on the difference between the actual value of the bridge arm voltage and the measured value of the bridge arm voltage;

[0007] Calculating a bridge arm fault detection variable based on the bridge arm voltage deviation;

[0008] Determine whether the MMC fails based on the bridge arm fault detection variable, and locate the fault to the bridge arm level;

[0009] A capacitor voltage sliding mode observer is constructed for each submodule of the faulty bridge arm to obtain an estimated value of the submodule capacitor voltage;

[0010] For each submodule, the submodule capacitance voltage estimation value is compared with the submodule capacitance voltage measurement value to generate a submodule capacitance voltage residual value;

[0011] Based on the submodule capacitor voltage residual value, it is determined whether a submodule fails, and the fault is located in a specific submodule.

[0012] Preferably, the obtaining of the actual value of the bridge arm voltage of the MMC three-phase six-bridge arm includes: , in, For the The actual value of the bridge arm voltage on the phase, For the The actual value of the bridge arm voltage of the lower bridge arm of the phase, is the DC bus voltage, Indicates The output phase voltage of the phase, is the bridge arm inductance, For the The bridge arm current of the upper bridge arm, For the The bridge arm current of the lower bridge arm, ,express Three phase.

[0013] Preferably, the bridge arm voltage measurement value is calculated as follows: , in, For the The measured value of the bridge arm voltage of the bridge arm on the phase, For the The measured value of the bridge arm voltage of the lower bridge arm of the phase, For the Phase upper bridge arm The switch function on each submodule, For the Phase lower bridge arm The switch function on each submodule, For the Phase upper bridge arm The capacitor voltage measurement value of each submodule, For the Phase lower bridge arm The capacitor voltage measurement value of each submodule, is the number of submodules.

[0014] Preferably, the calculating of the bridge arm fault detection variable based on the bridge arm voltage deviation comprises: , in, Indicates Xiangdi Fault detection variables of the bridge arm, , represents the upper bridge arm, represents the lower bridge arm, Indicates Xiangdi The bridge arm voltage deviation of the bridge arm, For time, It is the fault monitoring cycle.

[0015] Preferably, judging whether a fault occurs in the MMC based on the bridge arm fault detection variable and locating the fault to the bridge arm level includes: The sliding window method is used to calculate the arm fault detection variables of the three-phase six bridge arms one by one. when When it is established, let the count value of the fault monitoring counter C nt_Falut_D Start to automatically add 1, is the bridge arm fault threshold; If the condition is satisfied within a continuous power frequency cycle , it is determined that the MMC is faulty and the fault location occurs in the Phase, first Bridge arm; like , then let the count value C nt_Falut_D Reset to zero and restart counting.

[0016] Preferably, the fault monitoring period is set to a power frequency period;

[0017] The sliding window is set to 1 / 20 of the power frequency period.

[0018] Preferably, the bridge arm fault threshold Set to 10% of.

[0019] Preferably, constructing a capacitor voltage sliding mode observer for each submodule of the faulty bridge arm to obtain a submodule capacitor voltage estimation value includes: Define the sliding surface , Based on the sliding mode surface, the submodule capacitor voltage sliding mode observer is established as follows: , in, For the Xiangdi The bridge arm The output value of the capacitor voltage sliding mode observer of each submodule is: For the Xiangdi The bridge arm The capacitor voltage measurement value of each submodule, is the observation gain, is the saturation function, Represents the width of the unsaturated region of the saturation function; Select As a Lyapunov function, by adjusting the observation gain , the submodule capacitor voltage sliding mode observer is controlled to the sliding mode surface The output value of the capacitor voltage sliding mode observer is the estimated value of the sub-module capacitor voltage.

[0020] Preferably, judging whether a submodule fails based on the submodule capacitor voltage residual value and locating the fault to a specific submodule includes: In each sampling period, the submodule capacitor voltage value measured by the voltage sensor is compared with the submodule capacitor voltage estimation value output by the capacitor voltage sliding mode observer to generate a residual value. ; when When it is established, let the count value of the fault location counter C nt_Uc_Err Start to automatically add 1, is the submodule fault threshold; If the condition is satisfied within a continuous power frequency cycle , it is determined that the submodule is faulty; like , then let the count value C nt_Uc_Err Reset to zero and restart counting.

[0021] In a second aspect, the present invention provides a MMC flexible direct current converter valve submodule fault locating device, which is used to implement the MMC flexible direct current converter valve submodule fault locating method, and the device comprises:

[0022] The first calculation module is used to obtain the actual value of the bridge arm voltage and the measured value of the bridge arm voltage of the three-phase six bridge arms of the MMC, and obtain the bridge arm voltage deviation based on the difference between the actual value of the bridge arm voltage and the measured value of the bridge arm voltage;

[0023] A second calculation module, used for calculating a bridge arm fault detection variable based on the bridge arm voltage deviation;

[0024] A first detection module, used for judging whether the MMC fails based on the bridge arm fault detection variable, and locating the fault to the bridge arm level;

[0025] A third calculation module is used to construct a capacitor voltage sliding mode observer for each submodule of the faulty bridge arm to obtain an estimated value of the capacitor voltage of the submodule;

[0026] A fourth calculation module, configured to compare, for each submodule, the submodule capacitance voltage estimation value with the submodule capacitance voltage measurement value to generate a submodule capacitance voltage residual value;

[0027] The second detection module is used to determine whether a submodule fails based on the submodule capacitor voltage residual value, and locate the fault to a specific submodule.

[0028] The beneficial effects of the present invention are as follows:

[0029] The present invention provides a method for locating a submodule fault of an MMC flexible direct current converter valve, which consists of two links: fault monitoring and fault locating. The fault monitoring link locates the fault to the bridge arm level, and the fault locating link locates the fault to a specific submodule, thereby providing a pre-condition for subsequent MMC flexible direct current converter valve system to perform submodule fault removal, isolation and fault-tolerant operation, thereby improving the reliability of the MMC flexible direct current converter valve system.

[0030] In the fault monitoring link of the present invention, the input quantities such as output phase voltage, bridge arm current, switch modulation signal, etc. required in the calculation process are all sampling quantities required for MMC modulation and voltage balancing, so there is no need to add additional sampling circuits.

[0031] In the fault location link of the present invention, the fault location processes between the submodules are completely independent and autonomous, and parallel calculation can be performed to realize simultaneous location of multiple faults of different types.

[0032] By adopting the method of the present invention, various types of faults of the MMC flexible direct current converter valve submodule can be located within 25 ms, and it is suitable for the rapid positioning of various types of faults of the MMC submodule, including the submodule IGBT upper switch open circuit fault, IGBT lower switch open circuit fault, voltage sensor disconnection fault, voltage sensor stuck fault, and voltage sensor gain fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 MMC topology diagram provided for an embodiment of the present invention;

[0034] Figure 2 for Figure 1 The MMC submodule topology diagram in the MMC topology diagram shown;

[0035] Figure 3 A schematic diagram of a sliding mode observer for an MMC submodule provided in an embodiment of the present invention;

[0036] Figure 4A schematic flow chart of a method for locating a fault of a submodule of an MMC flexible direct current converter valve based on a sliding mode observer provided in an embodiment of the present invention;

[0037] Figure 5 It is a simulation waveform diagram of switch open circuit fault monitoring and fault location on the sub-module IGBT in an embodiment of the present invention;

[0038] Figure 6 It is a simulation waveform diagram of the switch open circuit fault monitoring and fault location under the sub-module IGBT in the embodiment of the present invention;

[0039] Figure 7 It is a simulation waveform diagram of the submodule voltage sensor gain fault monitoring and fault location in an embodiment of the present invention;

[0040] Figure 8 It is a simulation waveform diagram of the submodule voltage sensor disconnection fault monitoring and fault location in an embodiment of the present invention;

[0041] Fig. 9 It is a simulation waveform diagram of the stuck fault monitoring and fault location of the submodule voltage sensor in the embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0043] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0044] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0045] It should be noted here that the step marks mentioned below do not limit the order of the steps, but it should be understood that the steps can be executed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be executed simultaneously.

[0046] The first embodiment of the present invention provides a method for locating faults of MMC flexible direct current converter valve submodules based on a sliding mode observer, which can realize rapid and accurate fault location of multiple types of faults such as two types of IGBT open circuit faults and three types of voltage sensor faults of MMC submodules. The method specifically includes:

[0047] Step S1: The actual value of the bridge arm voltage of the three-phase six-bridge arm of the MMC is calculated by the DC bus voltage, the output phase voltage, the bridge arm current sampling value, etc.; the measured value of the bridge arm voltage of the three-phase six-bridge arm of the MMC is calculated by the bridge arm PWM switching sequence and the capacitor voltage sampling sequence; the deviation between the actual value of the bridge arm voltage and the measured value of the bridge arm voltage is calculated; the fault detection variable is calculated by sliding to obtain the average value of the bridge arm voltage deviation of the three-phase six-bridge arm, and whether the MMC fails is determined based on the fault detection variable, and the fault is located at the bridge arm level.

[0048] Step S2: For the bridge arm determined to be faulty, a sliding mode observer is constructed for all submodules of the faulty bridge arm, the capacitance and voltage values ​​of all submodules are estimated, and compared with the capacitance and voltage measurement values ​​of the submodules measured by the voltage sensor to generate a residual sequence, and then the fault is located in the specific submodule by comparing it with the adaptive threshold.

[0049] In the embodiment of the present invention, whether the MMC fails is determined based on the calculated bridge arm voltage deviation, and the fault is located at the bridge arm level. The specific implementation process is as follows:

[0050] See also Figure 1 The MMC topology shown in the figure is that each phase in the MMC flexible DC converter includes an upper and a lower bridge arm, and each bridge arm includes N submodules (SM in the figure) and a bridge arm reactor.

[0051] In the figure and Respectively expressed as Xiangdi The sum of the voltages of all submodules on the bridge arm and the bridge arm current, ,express Three-phase, , represents the upper bridge arm, represents the lower bridge arm, and Indicates The output phase voltage and phase current of the phase, is the DC bus voltage, is the bridge arm inductance, , , Respectively Phase AC side grid voltage, is the grid-side inductance.

[0052] Kirchhoff voltage equations are written for the upper and lower bridge arms as follows:

[0053] (1)

[0054] in and Respectively expressed as Xiangdi The sum of the voltages of all submodules on the bridge arm and the bridge arm current,

[0055] When the nearest level approximation modulation is adopted, the number of sub-modules put into use in the upper and lower bridge arms of each phase is as follows:

[0056] (2)

[0057] in, For the Phase reference modulation wave, , Respectively The number of submodules put into use in the upper and lower bridge arms of the phase, The function represents the rounding function on both sides.

[0058] After adopting the circulating current suppression strategy, the bridge arm current is:

[0059] (3)

[0060] in, is the DC bus current, Indicates Mutually The output phase current at the moment, Transmits power to the MMC system.

[0061] The switch function of the MMC system submodule is defined as shown in formula (4), and the submodule schematic diagram is shown in Figure 2 As shown, the submodule port voltage is defined as , the current flowing through each submodule is the bridge arm current , the actual value of the submodule capacitor voltage is , the submodule capacitor voltage measurement value is .

[0062] (4)

[0063] in Indicates submodules, when When Xiangdi The bridge arm Switch on each submodule On, lower switch Shutdown, when When Xiangdi The bridge arm Switch on each submodule Shut down, switch down Conductivity.

[0064] During normal operation, the submodule port voltage can be expressed as:

[0065] (5)

[0066] When there is no voltage sensor failure, the actual value of the submodule capacitor voltage is equal to the measured value:

[0067] (6)

[0068] When the switch When an open circuit fault occurs, if the bridge arm current And the switch function , due to the upper switch Open the way, it should flow through The bridge arm current that discharges the capacitor is forced to flow to The anti-parallel diode , at this time, the capacitor current is 0, the capacitor loses the discharge state, and the submodule port voltage changes from equation (5) under normal working conditions to equation (7),

[0069] (7)

[0070] Current switch When an open circuit fault occurs, if the bridge arm current And the switch function ,because Open the way, it should flow through The bridge arm current is forced to flow to The anti-parallel diode And charge the capacitor. At this time, the capacitor current is greater than 0, and the capacitor is forced to enter the charging state. The voltage at the submodule port changes from equation (5) under normal working conditions to equation (8),

[0071] (8)

[0072] When a submodule voltage sensor disconnection fault occurs, the bridge arm current When the number of submodules in the faulty bridge arm is ≠0, the faulty submodule will be in the charging state; if the number of submodules in the faulty bridge arm is 0, the faulty submodule will be in the bypass cut-off state; when the bridge arm current When , if the number of submodules put into operation in the faulty bridge arm is ≠N, the faulty submodule will always be in the bypass cut-off state; if the number of submodules put into operation in the faulty bridge arm is N, the faulty submodule will always be in the discharge state, the average value of the faulty submodule capacitance will continue to jump and increase, and the measured submodule capacitance voltage increment will always be 0. The faulty submodule port voltage is shown in formula (9), where Represents logical AND.

[0073] (9)

[0074] When a submodule voltage sensor gain fault occurs, the gain coefficient after the gain fault is set to Then when When the bridge arm current When the bridge arm current is When , the submodule will be in the bypass cut-off state. In the early stage of the fault, the faulty submodule capacitor only has a charging process, but no discharging process. The actual submodule capacitance average value continues to increase, and the capacitor voltage increment is only in the positive half cycle and is 0 in the negative half cycle. When the fault occurs, the charging and discharging process is reversed. At the end of the fault, the measured capacitor voltage is equal to the actual capacitor voltage value of other normal submodules. At this time, the charging and discharging process of the faulty submodule returns to normal, and the actual capacitor voltage value is the normal value. times. At the initial stage of the fault, the voltage at the fault submodule port is as shown in formula (10):

[0075] (10)

[0076] From the above analysis, it can be seen that when a sub-module IGBT failure or a voltage sensor failure occurs, the sub-module port voltage will deviate from the port voltage in the normal working mode, and the sum of the port voltages of all sub-modules on the bridge arm constitutes the bridge arm voltage. Therefore, this embodiment will construct a fault monitoring variable based on the measured value and actual value of the bridge arm voltage.

[0077] In this embodiment, the fault monitoring variable It will be used to determine whether the MMC converter system has a fault, locate the fault at the bridge arm level, and define the fault monitoring variables As shown in formula (11),

[0078] (11)

[0079] in Indicates Xiangdi The deviation between the actual value of the bridge arm voltage and the measured value of the bridge arm voltage is shown in formula (12): The fault monitoring period is set to a power frequency period of 20ms.

[0080] Actual value of bridge arm voltage It can be deduced from formula (1), as shown in formula (13):

[0081] (12)

[0082] (13)

[0083] The bridge arm voltage measurement value measured by the voltage sensor As shown in formula (14),

[0084] (14)

[0085] The input quantities required in the calculation process, such as output phase voltage, bridge arm current, switch modulation signal, etc., are all the sampling quantities required for MMC modulation and voltage balancing, so there is no need to add additional sampling circuits.

[0086] Assume A submodule fails, and the capacitor voltage value of the faulty submodule is recorded as , then the bridge arm voltage measurement value is:

[0087] (15)

[0088] The bridge arm voltage deviation is shown in formula (16):

[0089] (16)

[0090] When the upper switch IGBT fails, substitute into formula (7) to calculate the bridge arm voltage deviation at this time, as shown in formula (17),

[0091] (17)

[0092] When the lower switch IGBT fails, the bridge arm voltage deviation can be calculated by substituting the port voltage into formula (8). Since the submodule capacitor voltage gradually increases when the lower switch IGBT fails, the bridge arm voltage deviation also gradually increases, as shown in formula (18).

[0093] (18)

[0094] When a voltage sensor disconnection fault occurs, the bridge arm voltage deviation is calculated by substituting into formula (9) as shown in formula (19):

[0095] (19)

[0096] When a voltage sensor stuck fault occurs, the voltage deviation of the fault bridge arm is as shown in formula (20), where is the capacitor voltage when the voltage sensor is stuck. It is the capacitor voltage value of the normal submodule in the same bridge arm when the voltage sensor is stuck.

[0097] (20)

[0098] When a voltage sensor gain fault occurs, at the initial stage of the fault, the bridge arm voltage deviation is calculated by substituting the port voltage formula (10) into the formula (21) and formula (22).

[0099] like , then the bridge arm voltage deviation is obtained by formula (21):

[0100] (twenty one)

[0101] like , then the bridge arm voltage deviation is obtained by formula (22):

[0102] (twenty two)

[0103] From equations (17) to (22), we can see that if a fault occurs, its fault monitoring variable It will deviate from the zero value and exceed the bridge arm fault threshold, thereby locating the fault to a specific bridge arm.

[0104] Fault Detection Variables is the bridge arm voltage deviation The average value within a power frequency cycle. In the actual MMC fault diagnosis system, the voltage deviation of each bridge arm of the three-phase six bridge arms is obtained by sliding, and each sliding window can be 1 / 20 of the power frequency cycle.

[0105] When the fault detection variable When the system fails, it can be considered that the fault occurs and the fault location occurs at Phase, first A bridge arm.

[0106] It should be noted that the bridge arm fault threshold Can be set to It not only takes into account the fault monitoring rate and accuracy, but also enhances the system's robustness to DC side voltage fluctuations, avoiding false alarms and missed alarms in fault detection.

[0107] In the embodiment of the present invention, after the fault is located at the bridge arm level in the fault monitoring link, the fault arm fault flag is set to 1, and the subroutine of the fault location link is started. The principle of the fault location link is as follows:

[0108] Considering that under the nearest level approach modulation, the switching period is much smaller than the fundamental period, the bridge arm current The change within a switching cycle can be ignored. Therefore, the capacitor voltage can be averaged within a switching cycle and the switching function is defined. The average value of the duty cycle in one switching cycle , as shown in formula (23),

[0109] (twenty three)

[0110] in, is the capacitance value, is the measured value of the submodule capacitor voltage.

[0111] The submodule capacitance voltage observation equation (24) is established.

[0112] (twenty four)

[0113] in, is the output value of the submodule capacitor voltage observer, is the observation gain, is a saturation function.

[0114] Define the sliding surface , subtracting equation (23) from the submodule capacitor voltage observation equation (24) to obtain the submodule sliding mode observer as follows: Equation (25):

[0115] (25)

[0116] in, Represents the width of the unsaturated region of the saturation function, beyond or , the function output is clipped to the upper or lower bound.

[0117] Figure 3 Schematic diagram of the sliding mode observer of the MMC submodule. is a Lyapunov function, then its derivative is equation (26), by adjusting Parameters, the observation system can be controlled to the sliding surface The stable state, at this time the sliding surface It will jump back and forth around 0. At this time, the observed value is equal to the measured value, that is, the estimated value of the submodule capacitor voltage is obtained; when a fault occurs, Will deviate This produces the residual:

[0118] (26)

[0119] in, express The derivative of express The derivative of .

[0120] Just guarantee , which means that its derivative is always less than 0, that is, it is guaranteed that the observation error of the sliding mode observer can converge to 0 when the system is operating normally. When the sliding mode observer observes a small disturbance, , substituting into formula (25) we can obtain:

[0121] (27)

[0122] This formula shows that if the sliding mode observer deviates from the initial value due to a small disturbance , then it decays exponentially, and the decay rate is determined by the parameter Decide.

[0123] The residual sequence is given by the sliding surface Calculated by comparing the residual sequence with the submodule fault threshold By comparing the two modules, the fault can be located in the specific sub-module.

[0124] Based on this, the MMC flexible direct current converter valve submodule multi-type fault location method based on sliding mode observer provided in the embodiment of the present invention is shown in FIG. Figure 4 , including the following steps:

[0125] S1, calculating the actual value of the bridge arm voltage according to the bridge arm current, output phase voltage and switch modulation signal;

[0126] S2. Calculate the fault detection variable based on the actual value of the bridge arm voltage and the measured value of the bridge arm voltage ;

[0127] S3, when When it is established, let the count value of the fault monitoring counter C nt_Falut_D Start to automatically add 1, if it appears in the middle If the situation is, it is considered to be a jitter phenomenon, and the count value C nt_Falut_D Return to zero, otherwise loop calculation until the count value reaches 20 (i.e. within one consecutive power frequency cycle) Both greater than ), the system is considered to have a fault, and the fault location occurs at Phase, first bridge arms;

[0128] S4, set the fault bridge arm flag position to 1;

[0129] S5. Construct a capacitor voltage sliding mode observer for each submodule of the faulty bridge arm to obtain the estimated value of the submodule capacitor voltage; and compare it with the capacitor voltage value measured by the voltage sensor to generate a residual value. ;

[0130] S6. When When it is established, let the count value of the fault location counter C nt_Uc_Err Start to automatically add 1, if it appears in the middle If the situation is, it is considered to be a jitter phenomenon, and the count value C nt_Uc_Err Return to zero, otherwise loop calculation until the count value reaches 20 (i.e. within one consecutive power frequency cycle) Both greater than ), it can be considered that the system fails and the fault location occurs in the sub-module, the fault sub-module flag position is 1, so that the fault can be located in the specific sub-module.

[0131] A simulation test is now conducted on the multi-type fault location method of the MMC flexible direct current converter valve submodule based on the sliding mode observer provided in the embodiment of the present invention, as follows:

[0132] A Simulink simulation model was built with a DC bus voltage of 5000V. A half-bridge sub-module structure was adopted, with 20 sub-modules in each bridge arm, 7mF sub-module bypass capacitor capacitance, 250V sub-module initial voltage, 10mH bridge arm inductance, 1mF DC side capacitor, and a sorting voltage balancing algorithm for capacitor voltage balance. PIR control was used for circulating current suppression.

[0133] When writing the fault monitoring module program, under various types of faults, the DC bus voltage, output phase voltage, and bridge arm current sampling values ​​are extracted to calculate the actual bridge arm voltage value; the bridge arm PWM switching sequence and capacitor voltage sampling sequence are extracted to calculate the bridge arm voltage measurement value; then the fault monitoring variable is calculated and compared with the threshold to locate the specific faulty bridge arm. The results are as follows Figure 5 , Figure 6 , Figure 7 , Figure 8 and Fig. 9 As shown in the figure, (a) curve is the output phase current of the three phases, (b) curve is the fault arm current and fault arm voltage deviation, (c) curve is the fault detection variable and threshold, (d) curve is the fault submodule capacitor voltage measurement value and the estimated value obtained by the sliding mode observer, (e) curve is the output residual sequence and positive and negative thresholds, Indicates the capacitor voltage measurement value of the faulty submodule. represents the observed value of the capacitor voltage of the fault submodule, represents the fault bridge arm current, It can be seen from the curves (b) and (c) in the figure that under the five different types of faults, the fault monitoring variables all exceed the threshold within 10ms (half the power frequency cycle), accurately locating the faulty bridge arm.

[0134] Write a fault location program for each submodule of the faulty bridge arm, build a sliding mode observer to observe the submodule capacitor voltage, and generate a residual sequence with the submodule capacitor voltage measurement value measured by the voltage sensor, and then compare it with the threshold to locate the fault to a specific submodule, such as Figure 5 , Figure 6 , Figure 7 , Figure 8 and Fig. 9 As shown in the figure, it can be seen from the (d) curve and (e) curve that the residual sequence of the faulty sub-module exceeds the threshold within 15ms, accurately locating the specific sub-module, laying a preliminary foundation for the subsequent fault isolation and fault-tolerant operation of the MMC system.

[0135] Based on the same inventive concept, an embodiment of the present invention further provides a MMC flexible direct current converter valve submodule fault locating device, which is used to implement the MMC flexible direct current converter valve submodule fault locating method of the above embodiment, and the device includes:

[0136] The first calculation module is used to obtain the actual value of the bridge arm voltage and the measured value of the bridge arm voltage of the three-phase six bridge arms of the MMC, and obtain the bridge arm voltage deviation based on the difference between the actual value of the bridge arm voltage and the measured value of the bridge arm voltage;

[0137] A second calculation module, used for calculating a bridge arm fault detection variable based on the bridge arm voltage deviation;

[0138] A first detection module, used for judging whether the MMC fails based on the bridge arm fault detection variable, and locating the fault to the bridge arm level;

[0139] A third calculation module is used to construct a capacitor voltage sliding mode observer for each submodule of the faulty bridge arm to obtain an estimated value of the capacitor voltage of the submodule;

[0140] A fourth calculation module, configured to compare, for each submodule, the submodule capacitance voltage estimation value with the submodule capacitance voltage measurement value to generate a submodule capacitance voltage residual value;

[0141] The second detection module is used to determine whether a submodule fails based on the submodule capacitor voltage residual value, and locate the fault to a specific submodule.

[0142] It is worth pointing out that the device embodiment corresponds to the above-mentioned method embodiment, and the implementation methods of the above-mentioned method embodiments are all applicable to the device embodiment and can achieve the same or similar technical effects, so they will not be repeated here.

[0143] 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 combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0144] 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.

[0145] 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.

[0146] 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 A step that specifies a function in one or more boxes.

[0147] 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. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for locating faults of MMC flexible direct current converter valve submodules, characterized in that: include: Acquire the actual value of the bridge arm voltage and the measured value of the bridge arm voltage of the three-phase six-bridge arm of the MMC, and obtain the bridge arm voltage deviation based on the difference between the actual value of the bridge arm voltage and the measured value of the bridge arm voltage; Calculating a bridge arm fault detection variable based on the bridge arm voltage deviation; Determine whether the MMC fails based on the bridge arm fault detection variable, and locate the fault to the bridge arm level; A capacitor voltage sliding mode observer is constructed for each submodule of the faulty bridge arm to obtain an estimated value of the capacitor voltage of the submodule; For each submodule, the submodule capacitance voltage estimation value is compared with the submodule capacitance voltage measurement value to generate a submodule capacitance voltage residual value; It is determined whether a submodule fails based on the submodule capacitor voltage residual value, and the fault is located in a specific submodule.

2. A method for locating a fault of a MMC flexible direct current converter valve submodule according to claim 1, characterized in that: The obtaining of the actual value of the bridge arm voltage of the MMC three-phase six-bridge arm includes: ， in, For the The actual value of the bridge arm voltage on the phase, For the The actual value of the bridge arm voltage of the lower bridge arm of the phase, is the DC bus voltage, Indicates The output phase voltage of the phase, is the bridge arm inductance, For the The bridge arm current of the upper bridge arm, For the The bridge arm current of the lower bridge arm, ,express Three phase.

3. A method for locating faults of MMC flexible direct current converter valve submodules according to claim 2, characterized in that: The bridge arm voltage measurement value is calculated as follows: ， in, For the The measured value of the bridge arm voltage of the bridge arm on the phase, For the The measured value of the bridge arm voltage of the lower bridge arm of the phase, For the Phase upper bridge arm The switch function on each submodule, For the Phase lower bridge arm The switch function on each submodule, For the Phase upper bridge arm The capacitor voltage measurement value of each submodule, For the Phase lower bridge arm The capacitor voltage measurement value of each submodule, is the number of submodules.

4. A method for locating a fault of a MMC flexible direct current converter valve submodule according to claim 3, characterized in that: The calculating of the bridge arm fault detection variable based on the bridge arm voltage deviation comprises: ， in, Indicates Xiangdi Fault detection variables of the bridge arm, , represents the upper bridge arm, represents the lower bridge arm, Indicates Xiangdi The bridge arm voltage deviation of the bridge arm, For time, It is the fault monitoring cycle.

5. A method for locating faults of MMC flexible direct current converter valve submodules according to claim 4, characterized in that: The determining whether the MMC fails based on the bridge arm fault detection variable and locating the fault to the bridge arm level includes: The sliding window method is used to calculate the arm fault detection variables of the three-phase six bridge arms one by one. when When it is established, let the count value C of the fault monitoring counter nt_Falut_D Start to automatically add 1, is the bridge arm fault threshold; If the condition is satisfied within a continuous power frequency cycle , it is determined that the MMC is faulty and the fault location occurs in the Phase, first Bridge arm; like , then let the count value C nt_Falut_D Reset to zero and restart counting.

6. A method for locating faults of MMC flexible direct current converter valve submodules according to claim 5, characterized in that: The fault monitoring period is set to a power frequency period; The sliding window is set to 1 / 20 of the power frequency period.

7. A method for locating a fault of a MMC flexible direct current converter valve submodule according to claim 5, characterized in that: The bridge arm fault threshold Set to 10% of.

8. A method for locating faults of MMC flexible direct current converter valve submodules according to claim 5, characterized in that: The step of constructing a capacitor voltage sliding mode observer for each submodule of the faulty bridge arm to obtain a submodule capacitor voltage estimation value includes: Define the sliding surface , Based on the sliding mode surface, the submodule capacitor voltage sliding mode observer is established as follows: ， in, For the Xiangdi The bridge arm The output value of the capacitor voltage sliding mode observer of each submodule is: For the Xiangdi The bridge arm The capacitor voltage measurement value of each submodule, is the observation gain, is a saturation function, Represents the width of the unsaturated region of the saturation function; Select As a Lyapunov function, by adjusting the observation gain , the submodule capacitor voltage sliding mode observer is controlled to the sliding mode surface The output value of the capacitor voltage sliding mode observer is the estimated value of the sub-module capacitor voltage.

9. A method for locating faults of MMC flexible direct current converter valve submodules according to claim 8, characterized in that: The determining whether a submodule fails based on the submodule capacitor voltage residual value and locating the fault to a specific submodule includes: In each sampling period, the submodule capacitor voltage value measured by the voltage sensor is compared with the submodule capacitor voltage estimation value output by the capacitor voltage sliding mode observer to generate a residual value. ; when When it is established, let the count value of the fault location counter C nt_Uc_Err Start to automatically add 1, is the submodule fault threshold; If the condition is satisfied within a continuous power frequency cycle , it is determined that the submodule is faulty; like , then let the count value C nt_Uc_Err Reset to zero and restart counting.

10. A fault location device for a MMC flexible direct current converter valve submodule, characterized in that: The device is used to implement the MMC flexible direct current converter valve submodule fault locating method according to any one of claims 1 to 9, and comprises: The first calculation module is used to obtain the actual value of the bridge arm voltage and the measured value of the bridge arm voltage of the three-phase six bridge arms of the MMC, and obtain the bridge arm voltage deviation based on the difference between the actual value of the bridge arm voltage and the measured value of the bridge arm voltage; A second calculation module, used for calculating a bridge arm fault detection variable based on the bridge arm voltage deviation; A first detection module, used for judging whether the MMC fails based on the bridge arm fault detection variable, and locating the fault to the bridge arm level; A third calculation module is used to construct a capacitor voltage sliding mode observer for each submodule of the faulty bridge arm to obtain an estimated value of the capacitor voltage of the submodule; A fourth calculation module, configured to compare, for each submodule, the submodule capacitance voltage estimation value with the submodule capacitance voltage measurement value to generate a submodule capacitance voltage residual value; The second detection module is used to determine whether a submodule fails based on the submodule capacitor voltage residual value, and locate the fault to a specific submodule.

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