Cascade SVG driving signal fault detection method

Abstract

The invention discloses a cascade SVG driving signal fault detection method, and relates to the technical field of power electronics, and the method comprises the steps: collecting the DC voltage data of each cascade module in a static var generator in real time, and carrying out the pulse-free pre-charging of a DC side capacitor in a bypass resistor grid-connected state; when pre-charging of the direct current side capacitor is completed, protection operation is executed on the static var generator; based on the detection target type, averagely grouping a plurality of H-bridge sub-modules in the static var generator to obtain a plurality of sub-module groups; and giving a pulse signal with a preset modulation ratio to the static var generator based on the modulation period with a preset continuous number of times. According to the method, grid-connected operation is prevented from being affected by faults generated during formal grid connection, fault modules of the cascaded SVG are positioned before grid connection, and grid connection failures and unnecessary damage to components caused by misconnection of driving signals of the fault modules are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a cascaded SVG drive signal fault detection method. BACKGROUND

[0002] With the rapid development of new power networks, the proportion of power electronic devices in the power grid is also increasing. The large number of power electronic devices connected to the grid has led to more and more challenges, and at the same time, higher and higher requirements for the safety and reliability of electrical equipment.

[0003] Static var generators (SVG) are widely used in photovoltaic power stations and wind farms, and play an irreplaceable role in reactive power regulation. However, due to the large number of power elements, drive faults may occur during engineering implementation. Due to the large number of sub-modules and drive signals, it is inevitable to have a pulse signal misconnection problem during installation. Traditional low-voltage detection is difficult to completely troubleshoot the misconnection problem, so how to ensure the safe and reliable grid connection of SVG is a widespread concern for power stations. SUMMARY

[0004] Therefore, it is necessary to provide a cascaded SVG drive signal fault detection method to solve the above technical problems.

[0005] The present application provides a cascaded SVG drive signal fault detection method, which comprises:

[0006] Real-time acquisition of DC voltage data of each cascaded module in the static var generator, and pre-charging of the DC side capacitor without pulse under the bypass resistance grid connection state;

[0007] When the DC side capacitor pre-charging is completed, the static var generator is executed for protection operation;

[0008] Based on the detection target type, the H-bridge sub-modules in the static var generator are evenly grouped to obtain a plurality of sub-module groups;

[0009] Based on the modulation period of the preset continuous number of times, the static var generator is given a pulse signal with a preset modulation ratio;

[0010] Observing the real-time acquisition of DC voltage data, based on the voltage change trend and harmonic content, identifying the pulse signal receiving state of the current sub-module group, diagnosing and correcting the drive signal fault;

[0011] After the current sub-module group is detected, the next sub-module group is continued to be detected.

[0012] Further, the protection operation of the static var generator comprises:

[0013] Shielding the circuit breaker signal, and driving the bypass resistance to continue grid operation, to suppress the damage of components exceeding the preset current threshold, and to realize the hardware protection of the static var generator.

[0014] Further, the H-bridge submodule comprises a DC side capacitor and two commutation bridge arms, each of which comprises two switching units and each of which is connected in parallel with a reverse diode.

[0015] The switching unit is an insulated gate bipolar transistor element.

[0016] Further, the two switching units in the same commutation bridge arm are a group of pulse signals, and the pulse signals of the two switching units in the same commutation bridge arm are complementary.

[0017] Further, based on the voltage change trend and the harmonic content, the pulse signal receiving state of the current submodule group is identified, the driving signal is fault diagnosed and corrected, which comprises:

[0018] Based on the DC voltage data and the voltage change trend of the current submodule group, it is determined whether the H-bridge submodule in the submodule group has driving signal abnormality;

[0019] If the H-bridge submodule in the current submodule group has driving signal abnormality, the harmonic component of the DC voltage data is extracted by Fourier transform, and the reverse connection type of the driving signal fault is identified;

[0020] The faulty H-bridge submodule in the submodule group is corrected and re-detected.

[0021] Further, based on the DC voltage data and the voltage change trend of the current submodule group, it is determined whether the H-bridge submodule in the submodule group has driving signal abnormality, which comprises:

[0022] If the voltage change trend of all DC voltage data in the current submodule group is consistent and the numerical value is consistent, it is determined that the current submodule group has no fault;

[0023] If the voltage change trend of the H-bridge submodule in the current submodule group is opposite to that of other H-bridge submodules, it is determined that the H-bridge submodule has driving signal abnormality.

[0024] Further, the Fourier transform is used to extract the harmonic component of the DC voltage data to identify the reverse connection type of the driving signal fault, which comprises:

[0025] The DC voltage data collected within a preset time period is integrated to form voltage recording data, and the voltage recording data is subjected to Fourier analysis to obtain harmonic components and harmonic initial angles;

[0026] If the voltage variation trend of the H-bridge sub-module is different from the current variation trend of other normal H-bridge sub-modules, and there is no harmonic component, it is determined that the H-bridge sub-module has a fault of the double-group bridge arm driving signal being reversed;

[0027] If the voltage variation trend of the H-bridge sub-module is different from the current variation trend of other normal H-bridge sub-modules, and there is a harmonic component greater than a preset harmonic threshold, it is determined that the H-bridge sub-module has a fault of the single-group bridge arm driving signal being reversed;

[0028] If the H-bridge sub-module has a fault of the single-group bridge arm driving signal being reversed, based on the number of H-bridge sub-modules in the current sub-module group, a corresponding analysis mode is selected to analyze the reversed type of the driving signal fault and the fault bridge arm of the H-bridge sub-module.

[0029] Further, according to the number of all H-bridge sub-modules contained in a single sub-module group, the analysis mode is divided into an even analysis mode and an odd analysis mode.

[0030] Further, when the sub-module group is in the even analysis mode, analyzing the reversed type of the driving signal fault and the fault bridge arm of the H-bridge sub-module includes:

[0031] According to the content of the harmonic component, the harmonics generated by several times of Fourier transformation are sorted from high to low, and a preset number of harmonics are selected as sample harmonics;

[0032] The initial phase of the sample harmonics of the first half number of H-bridge sub-modules in the sub-module group is obtained, if the initial phase is located at 0° to 180°, it is determined that the driving signals of the two switch units of the second group bridge arm are reversed, if the initial phase is located at -180° to 0°, it is determined that the driving signals of the two switch units of the first group bridge arm are reversed;

[0033] The initial phase of the sample harmonics of the second half number of H-bridge sub-modules in the sub-module group is obtained, if the initial phase is located at 0° to 180°, it is determined that the driving signals of the two switch units of the first group bridge arm are reversed, if the initial phase is located at -180° to 0°, it is determined that the driving signals of the two switch units of the second group bridge arm are reversed.

[0034] Further, when the sub-module group is in the odd analysis mode, analyzing the reversed type of the driving signal fault and the fault bridge arm of the H-bridge sub-module includes:

[0035] According to the content of the harmonic component, the harmonics generated by several times of Fourier transformation are sorted from high to low, and a preset number of harmonics are selected as sample harmonics;

[0036] The initial phase of the sample harmonic of all H-bridge sub-modules before the middle position in the sub-module group is acquired, if the initial phase is located at 0°-180°, it is determined that the two switch unit driving signals of the second group of bridge arms are connected reversely, if the initial phase is located at -180°-0°, it is determined that the two switch unit driving signals of the first group of bridge arms are connected reversely;

[0037] The initial phase of the sample harmonic of all H-bridge sub-modules after the middle position in the sub-module group is acquired, if the initial phase is located at 0°-180°, it is determined that the two switch unit driving signals of the first group of bridge arms are connected reversely, if the initial phase is located at -180°-0°, it is determined that the two switch unit driving signals of the second group of bridge arms are connected reversely;

[0038] The H-bridge sub-modules at the middle position in the sub-module group are observed, the four switch units are respectively given the conducting signals of 0, 1, 0 and 1, if the H-bridge alternating current side output voltage is a positive value, it is determined that the driving signals of the first group of bridge arms are connected reversely, if the H-bridge alternating current side output voltage is a negative value, it is determined that the driving signals of the second group of bridge arms are connected reversely.

[0039] The beneficial effects of the application are that: the DC voltage of each H-bridge sub-module is fed back to the monitoring page of the main control in real time through the optical fiber, the DC voltage data is monitored in real time in the pre-charging stage and the test stage, and whether the DC voltage is abnormal is determined by taking the DC voltage change trend of the normal unit as the standard, and then the abnormal sub-module DC voltage data is analyzed, so that the positioning and type determination of the fault sub-module are completed, the influence of the fault on the grid connection operation is avoided, the positioning of the fault module of the cascaded SVG before grid connection is realized, the grid connection failure caused by the wrong connection of the driving signal of the fault module is avoided, and unnecessary damage to the components is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0040] The drawings described herein are used to provide further understanding of the application, and form a part of the application. The illustrative embodiments of the application and their descriptions are used to explain the application, and do not constitute an improper limitation on the application. In the drawings:

[0041] Figure 1 It is a flow chart of a cascaded SVG driving signal fault detection method according to an embodiment of the application;

[0042] Figure 2 It is a chain SVG (static reactive power generator) structure schematic diagram according to an embodiment of the application;

[0043] Figure 3 It is a chain SVG sub-module structure diagram according to an embodiment of the application;

[0044] Figure 4 It is a DC voltage waveform diagram of the first driving fault according to an embodiment of the application;

[0045] Figure 5 is a direct current voltage waveform diagram of the second driving fault according to the embodiment of the application. DETAILED DESCRIPTION

[0046] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0047] Please refer to Figure 1 A cascaded SVG driving signal fault detection method, the method comprises:

[0048] S1, real-time acquisition of the direct current voltage data of each cascaded module in the static var generator, and pre-charging the direct current side capacitor without pulse in the bypass resistance grid-connected state.

[0049] S2, when the direct current side capacitor pre-charging is completed, performing protection operation on the static var generator.

[0050] In the description of the present application, the protection operation performed on the static var generator comprises:

[0051] Shielding the circuit breaker signal and driving the bypass resistance to continue the grid-connected work to suppress the damaged components exceeding the preset current threshold, and realizing the hardware protection of the static var generator.

[0052] S3, based on the detection target type, the H-bridge sub-modules in the static var generator are evenly grouped to obtain a plurality of sub-module groups.

[0053] In the description of the present application, the H-bridge sub-module (hereinafter referred to as sub-module) comprises a direct current side capacitor and two converter bridge arms, each converter bridge arm contains two switching units and each switching unit is connected in parallel with a reverse diode.

[0054] The switching unit is an insulated gate bipolar transistor (IGBT) element.

[0055] In addition, the two switching units located in the same converter bridge arm are a group of pulse signals, and the pulse signals of the two switching units located in the same converter bridge arm are complementary.

[0056] S4, based on the preset number of continuous times of the modulation period, the static var generator is given a preset modulation ratio pulse signal.

[0057] Specifically, the static var generator is given a modulation ratio pulse signal of 0.5, and only lasts for 5 to 10 periods for observation and analysis.

[0058] S5, observing the real-time collected direct current voltage data, identifying the pulse signal receiving state of the current sub-module group based on the voltage change trend and harmonic content, performing fault diagnosis on the driving signal and correcting.

[0059] In the description of the application, the identification of the pulse signal receiving state of the current sub-module group based on the voltage change trend and harmonic content, the fault diagnosis on the driving signal and the correction include:

[0060] S51, determining whether there is driving signal abnormality in the H-bridge sub-module in the current sub-module group based on the direct current voltage data and voltage change trend of the current sub-module group.

[0061] In the description of the application, the determination of whether there is driving signal abnormality in the H-bridge sub-module in the current sub-module group based on the direct current voltage data and voltage change trend of the current sub-module group includes:

[0062] S511, if the voltage change trend of all direct current voltage data in the current sub-module group is consistent and the numerical value is consistent, it is determined that the current sub-module group has no fault.

[0063] S512, if the voltage change trend of the H-bridge sub-module in the current sub-module group is opposite to the current change trend of other H-bridge sub-modules, it is determined that the H-bridge sub-module has driving signal abnormality.

[0064] S52, if there is driving signal abnormality in the H-bridge sub-module in the current sub-module group, the harmonic component of the direct current voltage data is extracted by using Fourier transform to identify the reverse type of driving signal fault.

[0065] In the description of the application, the identification of the reverse type of driving signal fault by using Fourier transform to extract the harmonic component of the direct current voltage data includes:

[0066] S521, based on the fault recording function of the cascade SVG itself and the transmission of pulse and voltage signals by optical fiber as a medium, the direct current voltage data is called and analyzed and the test pulse signal is given; the direct current voltage data collected in the preset time is integrated to form voltage recording data, and the voltage recording data is analyzed by Fourier analysis to obtain the harmonic component and the harmonic initial angle.

[0067] S522, if the voltage change trend of the H-bridge sub-module is different from the current change trend of other normal H-bridge sub-modules, and there is no harmonic component, it is determined that the H-bridge sub-module has the fault of driving signal double bridge arm driving signal reverse connection.

[0068] S523, if the voltage variation trend of the H-bridge submodule is different from the current variation trend of other normal H-bridge submodules, and there is a harmonic component greater than the preset harmonic threshold, it is determined that the H-bridge submodule has a fault of reverse connection of the driving signal of the single group of bridge arms.

[0069] S524, if the H-bridge submodule has a fault of reverse connection of the driving signal of the single group of bridge arms, based on the number of H-bridge submodules in the current submodule group, a corresponding analysis mode is selected to analyze the reverse connection type and the fault bridge arm of the driving signal fault of the H-bridge submodule.

[0070] In the description of the present application, according to the number of all H-bridge submodules contained in a single submodule group, the analysis mode is divided into an even analysis mode and an odd analysis mode.

[0071] In the description of the present application, when the submodule group is in the even analysis mode, analyzing the reverse connection type and the fault bridge arm of the driving signal fault of the H-bridge submodule comprises:

[0072] S5241', according to the content of the harmonic component, the harmonics generated by several Fourier transformations are sorted from high to low, and a preset number of harmonics are selected as sample harmonics.

[0073] S5241', the initial phase of the sample harmonics of the H-bridge submodules in the first half number (the first N / 2 submodules) of the submodule group is obtained, if the initial phase is located at 0° to 180°, it is determined that the driving signals of the two switch units of the second group of bridge arms are reversed (i.e. Figure 3 the driving signals of sw3 and sw4 are reversed), and if the initial phase is located at -180° to 0°, it is determined that the driving signals of the two switch units of the first group of bridge arms are reversed (i.e. Figure 3 the driving signals of sw1 and sw2 are reversed).

[0074] S5242', the initial phase of the sample harmonics of the H-bridge submodules in the second half number (the second N / 2 submodules) of the submodule group is obtained, if the initial phase is located at 0° to 180°, it is determined that the driving signals of the two switch units of the first group of bridge arms are reversed (i.e. Figure 3 the driving signals of sw1 and sw2 are reversed), and if the initial phase is located at -180° to 0°, it is determined that the driving signals of the two switch units of the second group of bridge arms are reversed (i.e. Figure 3 the driving signals of sw3 and sw4 are reversed).

[0075] In the description of the present application, when the submodule group is in the odd analysis mode, analyzing the reverse connection type and the fault bridge arm of the driving signal fault of the H-bridge submodule comprises:

[0076] S5241", according to the content of the harmonic component, the harmonics generated by several times Fourier transform are sorted from high to low, and a preset number of harmonics are selected as sample harmonics.

[0077] S5242", the initial phase of the sample harmonics of all H-bridge sub-modules before the middle position in the sub-module group (the first (N-1) / 2 sub-modules) is obtained, if the initial phase is located at 0° to 180°, it is determined that the two switch unit driving signals of the second group of bridge arms are reversed (that is, the sw3, sw4 driving signal is reversed), if the initial phase is located at -180° to 0°, it is determined that the two switch unit driving signals of the first group of bridge arms are reversed (that is, the sw1, sw2 driving signal is reversed). Figure 3 Figure 3

[0078] S5243", the initial phase of the sample harmonics of all H-bridge sub-modules after the middle position in the sub-module group (the last (N-1) / 2 sub-modules) is obtained, if the initial phase is located at 0° to 180°, it is determined that the two switch unit driving signals of the first group of bridge arms are reversed (that is, the sw1, sw2 driving signal is reversed), if the initial phase is located at -180° to 0°, it is determined that the two switch unit driving signals of the second group of bridge arms are reversed (that is, the sw3, sw4 driving signal is reversed). Figure 3 Figure 3

[0079] S5244", all H-bridge sub-modules at the middle position in the sub-module group (the ((N-1) / 2) +1th sub-module) are observed, and the four switch units are respectively given a conduction signal of 0, 1, 0, 1, if the H-bridge alternating current side output voltage is positive, it is determined that the driving signal of the first group of bridge arms is reversed, if the H-bridge alternating current side output voltage is negative, it is determined that the driving signal of the second group of bridge arms is reversed.

[0080] S53, the H-bridge sub-module with the fault existing in the sub-module group is corrected, and the detection is performed again.

[0081] S6, after the current sub-module group detection is completed, the fault detection of the next sub-module group is continued.

[0082] Specifically, if the DC voltage data is normal in the pre-charging operation and the pulse signal test of the first group of sub-modules (that is, the first sub-module group), the next group test is performed. If it is found that the DC voltage is abnormal after the modulation wave is given, the abnormal sub-module is corrected, and then the detection is performed again, and after the DC voltage is normal, the next group is switched to.

[0083] ​​​​The SVG driving signal fault detection method provided by the application is mainly aimed at the cascaded SVG, the SVG has the characteristics of more H-bridge sub-modules, so more driving signals are given, for example, 144 power elements exist in single phase in the common 36-level SVG, which is extremely prone to driving signal connection error problems. In the normal cascaded SVG, the upper and lower driving signals on each bridge arm are complementary, and there are two pairs of driving signals. In the construction process, the upper and lower bridge arm driving signals are often connected in reverse, and there are single pair driving signal connection error and two pairs of driving signal connection error. Therefore, there are three fault conditions.

[0084] In the application, in the detection stage, the change trend of the direct current voltage is collected by giving a fixed modulation ratio pulse signal to determine the fault module of the driving signal connection error, and the grouping test observation is carried out according to the actual module quantity, so as to avoid the missed detection due to too many module quantities. If the voltage of a unit module appears in the opposite direction during the detection process, it can be determined that the two pairs of pulse signals of the module exist the problem of the upper and lower pulse signal connection error, that is, the forward conduction of the module becomes reverse conduction, and the forward bypass becomes reverse bypass. If in the actual grid connection, the working state of the module will be opposite to that of the normal module, which will cause the SVG to trip and shut down, and report the direct current voltage fault. At present, the SVG manufacturers mainly use low voltage test to detect whether each group of modules of the SVG is running normally. The detection method determines whether the module is running normally by observing the alternating current side voltage of each H-bridge. If the two pairs of pulse signals of the module are connected in reverse, the alternating current side voltage waveform will be opposite to the normal waveform. Because it is an alternating current signal, it is difficult to judge without real-time comparison of the normal waveform. Therefore, the detection method mentioned in the application can effectively make up for the missed detection problem of the low voltage test, realize accurate positioning of the fault unit module of the SVG, and avoid the loss caused by missed detection in the normal grid connection.

[0085] In the application, the four power elements (switching units) of a single H-bridge sub-module are numbered as sw1, sw2, sw3 and sw4, sw1 and sw2 are a group, and sw3 and sw4 are a group. In the normal use process, the pulse signals of each group are complementary, and the upper and lower power elements cannot be turned on at the same time. Therefore, in the engineering implementation, the controller gives each group of power elements one pulse signal, and the other pulse signal is obtained by inverting the module itself control circuit. Therefore, the application discriminates and judges the two types of faults of single group connection error and two group connection error.

[0086] Because the pulse single group connects the two working conditions: sw1 and sw2 are connected reversely, sw3 and sw4 are connected reversely. The DC voltage feedback of the two fault working conditions is also different from that of the two groups connected reversely, and the conduction state sequence also changes, so a certain amount of harmonics is inevitably generated in the DC side voltage. Because the structure parameters of each H bridge (commutation bridge arm) are consistent, the specific fault type can be determined through the waveform analysis of the DC voltage and according to the characteristics of different working conditions.

[0087] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the present application.

[0088] In the examples of the present application, in order to protect the equipment, the bypass resistance exit signal is withdrawn during the implementation process of the examples of the present application, so that the bypass resistance always participates in the charging process and the inverter process of the cascaded SVG. First, the DC side capacitor is pre-charged, at this time, no driving signal is issued, and the parallel diode on the IGBT is relied on for uncontrolled rectification process to charge the DC side capacitor, at this time, all modules have consistent charging trend, if there is abnormal DC voltage fluctuation, it can be judged that the hardware equipment of the sub-module is abnormal, this process provides the basic conditions for the detection process. When the test driving signal is provided, if there is an individual module DC voltage trend anomaly, it is judged that the two pairs of upper and lower bridge arm driving signals are connected reversely, if there is a large harmonic in the DC voltage of an individual module, it is judged that there is a single pair of upper and lower bridge arm driving signal connected reversely, further FFT analysis of the harmonic can determine the specific driving signal abnormal module, the detection method is simple and effective, can effectively locate the module of the cascaded SVG driving signal misconnection, and is also a leak detection and supplement to the conventional low voltage detection method, realizing the fault detection of the cascaded SVG before grid connection.

[0089] The present application will be described below in conjunction with the drawings.

[0090] Referring to Figure 2 which is shown as the structure of chain SVG, the circulating circuit comprises: single module H bridge commutation circuit; multi-module three-phase chain structure circuit; filter capacitor; bypass resistance and bypass switch.

[0091] Each unit module (H bridge sub-module, referred to as sub-module) has the same structure parameters, each phase is composed of a plurality of unit sub-modules in series, and the number of sub-modules in each phase is equal, and each phase is connected in star.

[0092] Referring to Figure 3The structural diagram of the single sub-module is shown, including two converter bridge arms, each bridge arm having two IGBT elements and each IGBT having a parallel reverse diode, four switching units sw1, sw2, sw3, sw4 and four diodes D1, D2, D3, D4, and a DC capacitor C.

[0093] Based on the above element structure, the example of the application provides a method for judging driving failure based on module voltage, and an implementation flowchart of the method for judging driving failure based on module voltage implemented by the example of the application is shown, and the specific steps are as follows:

[0094] Step 101: Real-time acquisition of SVG cascade module voltage data through an optical fiber, and no-pulse pre-charging mode for the DC side capacitor in the state that the bypass resistance is not cut off.

[0095] Wherein there are a large number of H-bridge sub-modules with the same structure parameters in each phase of the cascade SVG, and the cell voltage refers to the capacitor voltage in the sub-module.

[0096] In the example of the application, data interaction between the sub-modules and the main control is performed through an optical fiber, in the pre-charging stage, whether the sub-module hardware is abnormal is determined by observing the cell voltage change trend of each stage of the sub-module, so as to preliminarily detect the basic conditions and avoid affecting the subsequent detection due to hardware damage and the like.

[0097] Step 102: When the pre-charging is completed, the circuit breaker signal is shielded, the bypass resistance continues to work in parallel with the grid to suppress excessive current damage to components, and the SVG to be checked is protected.

[0098] In the example of the application, since the cascade SVG belongs to the direct hanging type SVG, the inverter voltage is high, and when detecting, the impact current caused by the fault module is avoided to damage the equipment and affect the power grid, the bypass resistance is in the parallel state during the detection process, and the harm of the large current to the equipment and the power grid is avoided.

[0099] Step 103: Grouping the sub-modules of the SVG to be detected.

[0100] In the example of the application, since there are many high-voltage cascade SVG sub-modules, in order to ensure that the change process of all sub-modules is observed, the sub-modules are grouped, the number of each group is operated according to the actual working condition, and taking a common 36 cascade SVG as an example, in order to facilitate observation and intuition, and considering the influence of the DSP chip calculation processing resource, 12 sub-modules are selected as a group.

[0101] Step 104: Providing a pulse signal with a modulation ratio of 0.5 to the SVG for 7 cycles.

[0102] In the example of the present application, the modulation of the pulse signal is realized by setting a lower fixed modulation ratio of the modulation signal, there are two switching units on the same bridge arm, sw1 and sw2 form a group, the pulse signals of which are complementary, and sw3 and sw4 form a group, the pulse signals of which are complementary. The lower modulation ratio signal ensures that the output voltage of the cascaded SVG port inverts according to the proportion of the modulation ratio. Since the modulation ratio in the embodiment is set to be smaller than the normal operation modulation ratio, which is selected as 0.5pu in this paper, the output port voltage is lower than the grid side voltage, and the current flows to the DC side capacitor. Therefore, the DC voltage will maintain an upward trend during the detection period, and the capacitor is in a charging state. The example of the present application will determine whether the pulse signal is abnormal according to the change trend of the DC voltage.

[0103] Step 105: observing the voltage trend of the detected submodules from the master display, and determining the receiving state of the pulse signal of the submodule according to the change trend.

[0104] Step 105 includes:

[0105] Step 1051: when the pulse signal is given, if the first group of DC voltage signals has a consistent increasing trend and the same size, it is determined that the group of submodules has no fault;

[0106] Step 1052: if there is an abnormal DC voltage signal, it is determined that the submodule with abnormal DC voltage has a problem with the driving signal.

[0107] In the example of the present application, 12 modules are selected for collective observation each time. Under normal circumstances, the pulse signals of most modules are in a normal connection trigger state, and the parameters and structures of each module are consistent, and the modulation wave is consistent. Therefore, the change trend of the DC voltage will also be consistent. If there is one or more modules with abnormal DC voltage data compared with the majority of module data during testing, it is determined that the DC voltage abnormal module has a pulse fault. The number of fault modules in each group in the example of the present application is not limited, and the number of modules in each group can be flexibly selected according to the specific test object and test requirements.

[0108] Step 1053: if the DC voltage changes in a reverse trend during the working stage, it means that the two pairs of pulse signals are connected reversely.

[0109] In the example, the DC voltage feedback is the capacitor voltage connected to the DC side of the H bridge. The voltage change feedback by the DC voltage indicates that the DC voltage is in a fixed working state. The opposite change trend of the DC voltage during the test period indicates that the H bridge is in the opposite working mode.

[0110] Referring to Table 1, when sw1 exchanges pulse signals with sw2 and sw3 and sw4, the on state of sw1 changes, and the original switching sequence changes from forward conduction, forward bypass, reverse conduction, reverse bypass to reverse conduction, forward bypass, forward conduction, forward bypass. Therefore, when two groups of pulse signals exchange, the port voltage changes from +Vdc, 0, -Vdc, 0 to -Vdc, 0, +Vdc, 0.

[0111] Table 1: Switching unit pulse signal exchange table

[0112] SW1 SW2 SW3 SW4 Port voltage Forward conduction 1 0 0 1 +Vdc Reverse conduction 0 1 1 0 -Vdc Forward bypass 0 1 0 1 0 Reverse bypass 1 0 1 0 0

[0113] In this example, 12 sub-modules are taken as a group, and the DC voltage transmitted to the master control optical fiber data is observed. If there is a single or multiple DC voltage in the downward trend, and the trend is relatively smooth and there is no obvious harmonic, as shown in Figure 4 , it is determined that the abnormally changed module has a driving fault condition, and it can be determined that the sw1 and sw2 pulse signals are reversed, and the sw3 and sw4 pulse signals are reversed. Conversely, if the DC voltage can be normally charged and the waveform is smooth, it is determined that the modules in the group can normally work.

[0114] It should be noted that because the pulse modulation method of the cascaded SVG is carrier phase shift, that is, the pulse modulation of each sub-module is realized by shifting the carrier by a fixed angle, therefore, a small amount of shift of each group of DC voltage on the time axis is a normal phenomenon, which does not affect the change trend of the DC voltage and the observation and judgment.

[0115] Step 1054: If there is a harmonic component greater than 0.5V in the DC voltage in the working stage, the DC voltage recording data is analyzed by FFT (Fast Fourier Transform). Because the test carrier frequency is 300Hz, more 5th harmonics are selected for analysis. Because of the influence of the single-pole frequency multiplication carrier phase shift technology, the initial angle of the harmonic of the fault sub-module changes by the corresponding carrier change angle. Taking the 36-level SVG in this example as an example, if the initial phase of the 5th harmonic of the first 18 sub-modules is located at 0° to 180°, it is determined that the sw3 and sw4 driving signals are reversed, and if the initial phase is located at -180° to 0°, it is determined that the sw1 and sw2 driving signals are reversed. If the initial phase of the 5th harmonic of the last 18 sub-modules is located at 0° to 180°, it is determined that the sw1 and sw2 driving signals are reversed, and if the initial phase is located at -180° to 0°, it is determined that the sw3 and sw4 driving signals are reversed.

[0116] Set the fault condition, and the DC voltage is as shown in Figure 5As shown, if the DC recording data has obvious harmonics during the work period, the amplitude is about 1V, then the FFT analysis is performed on the waveform, the harmonic component is affected by the modulation ratio, the greater the modulation ratio, the smaller the harmonic component, so the working condition based on 0.5 modulation ratio is considered comprehensively.

[0117] The DC voltage recording data of the test period is analyzed by FFT based on the fundamental frequency of the modulation wave, the initial phase of the 5th harmonic of the fault module is-82°, and the module is located in the first 18 groups, so it is judged that sw1 and sw2 are connected reversely, sw3 and sw4 are connected normally, which is consistent with the actual fault condition.

[0118] Optionally, in order to make the FFT analysis result more obvious, the pulse signal enable time can be increased according to the self detection needs, that is, the test signal period, the longer the test time, the more accurate the FFT analysis result.

[0119] According to table 1, if sw1 and sw2 pulse signals are connected reversely, their working state changes accordingly, the forward conduction becomes forward bypass, the reverse conduction becomes reverse bypass, the forward bypass becomes forward conduction, and the reverse bypass becomes reverse bypass, and the working sequence also changes to forward bypass, forward conduction, reverse bypass and reverse conduction, the working conduction sequence is opposite, and the initial state is phase shifted.

[0120] Change the fault condition, and perform FFT analysis on the DC voltage recording data of the test period, the initial phase of the 5th harmonic is 90°, and the module is located in the first 18 groups, so it is judged that sw3 and sw4 are connected reversely, sw1 and sw2 are connected normally, which is consistent with the actual fault condition.

[0121] Similarly, if sw3 and sw4 pulse signals are connected reversely, their working state changes to reverse bypass, reverse conduction, forward bypass and forward conduction, the conduction sequence is the same as that of sw1 and sw2 after being reversed, but the switch state is different by half a period, so the initial phase of the two is different by half a period, that is, 180°.

[0122] If there are non-ignorable harmonics on the DC voltage side, and the two pairs of pulse signals are connected reversely, it is judged that if only one pair of switch trigger signals is connected reversely, the conduction sequence is opposite, and because the initial states corresponding to the two kinds of fault conditions are different by half a conduction period, the FFT analysis is performed on the DC voltage recording data with harmonics, taking 50Hz as the fundamental frequency, if the initial phase of the 5th harmonic is negative within ±180°, it indicates that sw1 and sw2 pulse signals are connected reversely, if the initial phase of the 5th harmonic is positive within ±180°, it indicates that sw3 and sw4 pulse signals are connected reversely.

[0123] Step 1055: correct the fault module and retest.

[0124] Step 106: If the group of DC voltage trends and waveforms are normal, switch to the next group of modules and repeat the above operation.

[0125] In the embodiment of the application, the DC voltage signals fed back by each module are observed by the master control based on a fixed small modulation ratio pulse signal. If the DC voltage exists in a relatively smooth trend for discharge work, it is judged that the two pairs of pulse signals of the two bridge arms are connected reversely; if the DC voltage exists in a large harmonic, it is judged that only the pulse signal of a single bridge arm is connected reversely. On this basis, the recording and broadcasting data are processed by FFT, and according to the phase, it can be judged which upper and lower pulse signals of the bridge arm are connected reversely.

[0126] The example of the application is mainly applied to self-detection before grid connection of cascaded SVG. The traditional low-voltage test observes the AC end voltage in a superimposed staircase waveform, which can only roughly observe the running state of the SVG sub-module, but when two groups of driving signals are connected reversely, the port voltage cannot be observed. The example of the application analyzes the DC voltage side to make up for this shortcoming, and can directly and conveniently present the misconnection state of the driving signal.

[0127] To sum up, by means of the technical scheme of the application, the DC voltage of each H-bridge sub-module is fed back to the monitoring page of the master control in real time through an optical fiber, and the DC voltage data is monitored in real time in the pre-charging stage and the test stage, and the change trend of the DC voltage of the normal unit is taken as a standard to judge whether the DC voltage is abnormal, and then the abnormal sub-module DC voltage data is analyzed, so as to complete the positioning and type determination of the faulty sub-module, avoid the influence of the fault on grid connection operation when formally connected to the grid, realize the positioning of the faulty module of the cascaded SVG before grid connection, avoid grid connection failure caused by the misconnection of the driving signal of the faulty module, and avoid unnecessary damage to the components.

[0128] It should be understood that, although each step in the flowchart of the accompanying drawings is displayed in sequence according to the direction of the arrow, these steps are not necessarily executed in sequence according to the direction of the arrow. Unless otherwise specified herein, the execution of these steps is not strictly limited in sequence, and they can be executed in other sequences. Moreover, at least part of the steps in the flowchart of the accompanying drawings can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence is not necessarily sequential, but can be executed in rotation or alternation with at least part of other steps or sub-steps or stages of other steps.

Claims

1. A method for detecting faults in cascaded SVG drive signals, characterized in that, The method includes: The DC voltage data of each stage module in the static var generator is collected in real time, and the DC side capacitor is pre-charged without pulses under the condition of grid connection of bypass resistor; When the DC side capacitor pre-charging is complete, a protective operation is performed on the static var generator. Based on the type of detection target, several H-bridge sub-modules in the static var generator are averaged into multiple sub-module groups. A pulse signal with a preset modulation ratio is applied to the static var generator based on a modulation period of a preset duration. By observing the real-time collected DC voltage data, and based on the voltage change trend and harmonic content, the pulse signal receiving status of the current submodule group is identified, and fault diagnosis and correction of the drive signal are performed. After the current submodule group has been checked, the fault detection of the next submodule group will be performed.

2. The method for detecting faults in cascaded SVG drive signals according to claim 1, characterized in that, The protective operation performed on the static var generator includes: The circuit breaker signal is shielded, and the bypass resistor is driven to continue working in parallel with the grid to suppress damage to components that exceed the preset current threshold, thereby achieving hardware protection for the static var generator.

3. The method for detecting faults in cascaded SVG drive signals according to claim 1, characterized in that, The H-bridge submodule includes a DC-side capacitor and two commutator arms. Each commutator arm contains two switching units and each switching unit is connected in parallel with a reverse diode. The switching unit is an insulated gate bipolar transistor (IGBT) element.

4. The method for detecting faults in cascaded SVG drive signals according to claim 3, characterized in that, Two switching units located in the same converter bridge arm share a set of pulse signals, and the pulse signals of the two switching units located in the same converter bridge arm are complementary.

5. The method for detecting faults in cascaded SVG drive signals according to claim 3, characterized in that, The step of identifying the pulse signal reception status of the current submodule group based on voltage change trends and harmonic content, and diagnosing and correcting faults in the drive signal, includes: Based on the current DC voltage data and voltage change trend of the submodule group, determine whether there is an abnormal drive signal in the H-bridge submodule within the submodule group. If the H-bridge submodule in the current submodule group has an abnormal drive signal, the harmonic components of the DC voltage data are extracted using Fourier transform to identify the reverse connection type of the drive signal fault. Correct any faulty H-bridge submodules within the submodule group and retest them.

6. The method for detecting faults in cascaded SVG drive signals according to claim 5, characterized in that, The determination of whether there is a drive signal abnormality in the H-bridge submodule within the current submodule group based on the DC voltage data and voltage change trend of the current submodule group includes: If the voltage change trend of all DC voltage data in the current submodule group is consistent and the values ​​are consistent, then the current submodule group is determined to be fault-free. If the voltage change trend of an H-bridge submodule within the current submodule group is opposite to the current change trend of other H-bridge submodules, then it is determined that the H-bridge submodule has an abnormal drive signal.

7. The method for detecting faults in cascaded SVG drive signals according to claim 5, characterized in that, The method of extracting harmonic components from DC voltage data using Fourier transform and identifying reverse connection types of drive signal faults includes: The DC voltage data collected within a preset time period is integrated to form voltage waveform data. Fourier analysis is performed on the voltage waveform data to obtain the harmonic components and the initial angle of the harmonics. If the voltage change trend of the H-bridge module is different from the current change trend of other normal H-bridge modules, and there are no harmonic components, then the H-bridge module is determined to have a fault where the drive signals of both groups of bridge arms are reversed. If the voltage change trend of the H-bridge module is different from the current change trend of other normal H-bridge modules, and there are harmonic components greater than the preset harmonic threshold, then the H-bridge module is determined to have a fault where the drive signal of a single bridge arm is reversed. If the H-bridge submodule has a fault where the drive signal of a single bridge arm is reversed, then based on the number of H-bridge submodules in the current submodule group, the corresponding analysis mode is selected to analyze the reverse connection type of the drive signal fault in the H-bridge submodule and the faulty bridge arm.

8. The method for detecting faults in cascaded SVG drive signals according to claim 7, characterized in that, The analysis modes are divided into even-number analysis modes and odd-number analysis modes based on the number of all H-bridge submodules contained in a single submodule group.

9. The method for detecting faults in cascaded SVG drive signals according to claim 8, characterized in that, When the submodule group is in the even-number analysis mode, the analysis of the reverse connection type of the drive signal fault and the faulty bridge arm in the H-bridge submodule includes: Based on the content of harmonic components, the harmonics generated by several Fourier transforms are sorted from high to low, and a preset number of harmonics are selected as sample harmonics. Obtain the initial phase of the sample harmonics of the first half of the H-bridge submodules in the submodule group. If the initial phase is between 0° and 180°, it is determined that the two switch unit drive signals of the second bridge arm are reversed. If the initial phase is between -180° and 0°, it is determined that the two switch unit drive signals of the first bridge arm are reversed. Obtain the initial phase of the sample harmonics of the second half of the H-bridge submodules in the submodule group. If the initial phase is between 0° and 180°, it is determined that the two switch unit drive signals of the first bridge arm are reversed. If the initial phase is between -180° and 0°, it is determined that the two switch unit drive signals of the second bridge arm are reversed.

10. The method for detecting faults in cascaded SVG drive signals according to claim 8, characterized in that, When the submodule group is in the odd-number analysis mode, the analysis of the reverse connection type of the drive signal fault and the faulty bridge arm in the H-bridge submodule includes: Based on the content of harmonic components, the harmonics generated by several Fourier transforms are sorted from high to low, and a preset number of harmonics are selected as sample harmonics. Obtain the initial phase of the sample harmonics of all H-bridge submodules before the middle position in the submodule group. If the initial phase is between 0° and 180°, it is determined that the two switch unit drive signals of the second bridge arm are reversed. If the initial phase is between -180° and 0°, it is determined that the two switch unit drive signals of the first bridge arm are reversed. Obtain the initial phase of the sample harmonics of all H-bridge submodules after the middle position within the submodule group. If the initial phase is between 0° and 180°, it is determined that the two switch unit drive signals of the first group of bridge arms are reversed. If the initial phase is between -180° and 0°, it is determined that the two switch unit drive signals of the second group of bridge arms are reversed. Observe all H-bridge submodules in the middle position within the submodule group. Apply 0, 1, 0, and 1 conduction signals to the four switching units respectively. If the output voltage on the AC side of the H-bridge is positive, it is determined that the drive signal of the first group of bridge arms is reversed. If the output voltage on the AC side of the H-bridge is negative, it is determined that the drive signal of the second group of bridge arms is reversed.

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