Insulation state detecting and positioning method and device for conversion system

Abstract

The invention discloses an insulation state detecting and positioning method and device for a conversion system, the conversion system comprises a converter module and a connecting element, the converter module comprises n conversion units, n is greater than or equal to 2, each conversion unit comprises a transformer, each transformer comprises a first winding and a second winding, the connecting element is connected between the first winding and the second winding of the transformer; the insulation state detecting and positioning method comprises the following steps of: S1, changing the state of at least one switch in the conversion system, so that voltage applied between a first winding and a second winding of a transformer of at least one of n conversion units is changed; s2, before and after the state of the at least one switch is changed, respectively detecting the quantity reflecting the current flowing through the connecting element; and S3, comparing the quantity of the current flowing through the connecting element before and after the state of the at least one switch is changed, and determining which insulation abnormity occurs in the n conversion units according to the comparison result.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a method and a device for detecting and positioning the insulation state of a conversion system. Background Art

[0002] The main power transformer in the medium-high voltage and high-frequency isolation converter is an important component for electrical isolation of high and low voltage circuits. It needs to withstand the long-term working voltage in the system and the overvoltage stress under fault conditions. As the converter system develops towards high frequency, high voltage and high power density, the size of the isolation transformer decreases, and the main insulation structure between the primary and secondary sides of the transformer will be subjected to higher electric field stress. The higher the electric field stress, the higher the risk of insulation abnormality. At the same time, long-term electric field stress aging and insulation abnormality will increase the risk of insulation failure, thereby causing major accidents and causing loss of life and property.

[0003] Currently, the common medium-high voltage and high-frequency isolation converter systems are often composed of multiple modules in cascade, and the converter system often contains multiple high-frequency isolation transformers. When the converter system has insulation abnormalities and needs to be repaired, the existing methods cannot accurately locate which module in the system has insulation abnormalities, and it is often necessary to check the modules in the system one by one, which requires a lot of labor costs to dismantle the machine for repair, and expensive high-voltage detection devices are also required for auxiliary detection.

[0004] Therefore, it is urgent to propose a method and device for detecting and locating the insulation status of a conversion system, which can locate the position of a module with insulation abnormality in the conversion system, simplify fault maintenance work, and reduce maintenance costs. Summary of the invention

[0005] The object of the present invention is to provide a method and device for detecting and locating the insulation state of a conversion system, which can solve one or more defects of the prior art.

[0006] In order to achieve the above object, the present invention proposes an insulation state detection and positioning method for a conversion system, the conversion system includes a converter module and a connecting element, the converter module includes n conversion units, n≥2, each conversion unit includes a transformer, the transformer includes a first winding and a second winding, the connecting element is connected between the first winding and the second winding of the transformer, and the insulation state detection and positioning method includes:

[0007] Step S1: changing the state of at least one switch in the conversion system so that the voltage between the first winding and the second winding of the transformer applied to at least one of the n conversion units changes;

[0008] Step S2: detecting the amount of current flowing through the connection element before and after the state of at least one switch changes; and

[0009] Step S3: Compare the state of at least one switch before and after the change, reflecting the amount of current flowing through the connection element, and determine which of the n conversion units have insulation abnormalities according to the comparison result.

[0010] In order to achieve the above-mentioned purpose, the present invention also proposes an insulation state detection and positioning device for a conversion system, characterized in that the conversion system includes a converter module and a connecting element, the converter module includes n conversion units, n≥2, each conversion unit includes a transformer, the transformer includes a first winding and a second winding, the connecting element is connected between the first winding and the second winding of the transformer, and the insulation state detection and positioning device includes a control unit, an insulation detection unit and a processing unit, the control unit is connected to the converter module, and is used to change the state of at least one switch in the conversion system, so that the voltage between the first winding and the second winding of the transformer applied to at least one of the n conversion units changes; the insulation detection unit is sleeved on the connecting element and connected to the control unit, and is used to detect the amount of current flowing through the connecting element before and after the state of at least one switch is changed; the processing unit is connected to the insulation detection unit, and is used to compare the amount of current flowing through the connecting element before and after the state of at least one switch is changed, and determine which of the n conversion units have insulation abnormalities according to the comparison result.

[0011] The present invention provides a method and device for detecting and locating the insulation status of a conversion system, which can locate the position of a module with insulation abnormality in the conversion system, simplify fault maintenance work, and reduce maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions implemented in the present invention, the following briefly introduces the drawings required for use in the embodiments.

[0013] Figure 1 1 is a schematic diagram of the structure of an insulation state detection and positioning device for a conversion system according to a first embodiment of the present invention;

[0014] Figure 2 The insulation status detection and positioning method process of the first embodiment is Figure 1 ;

[0015] Figure 3 The insulation status detection and positioning method process of the first embodiment is Figure 2 ;

[0016] Figure 4 The insulation status detection and positioning method process of the first embodiment is Figure 3 ;

[0017] Figure 5 is a structural schematic diagram of an insulation state detection and positioning device for a conversion system according to a second embodiment of the present invention;

[0018] Figure 6 The insulation status detection and positioning method process of the second embodiment Figure 1 ;

[0019] Figure 7 The insulation status detection and positioning method process of the second embodiment Figure 2 ;

[0020] Figure 8 The insulation status detection and positioning method process of the second embodiment Figure 3 ;

[0021] Fig. 9 is a structural schematic diagram of a conversion unit of an insulation state detection and positioning device for a conversion system according to Embodiment 2;

[0022] Fig.10 The insulation status detection and positioning method process of the second embodiment Figure 4 ;

[0023] Fig.11 The insulation status detection and positioning method process of the second embodiment Figure 5 ;

[0024] Fig.12 The insulation status detection and positioning method process of the second embodiment Figure 6 ;

[0025] Fig.13 1 is a schematic diagram of the structure of an insulation state detection and positioning device for a conversion system according to a third embodiment of the present invention;

[0026] Fig.14 The insulation status detection and positioning method process of embodiment 3 Figure 1 ;

[0027] Fig.15 The insulation status detection and positioning method process of embodiment 3 Figure 2 . DETAILED DESCRIPTION

[0028] Example embodiments will now be described more fully with reference to the accompanying drawings, however, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; on the contrary, these embodiments are provided so that the present invention will be comprehensive and complete and will fully and completely convey the concept of the example embodiments to those skilled in the art.

[0029] When introducing the elements / components / etc. described and / or illustrated herein, the terms "one", "an", "the", "said" and "at least one" are used to indicate the presence of one or more elements / components / etc. The terms "comprise", "include" and "have" are used to indicate an open-ended inclusion and mean that there may be additional elements / components / etc. in addition to the listed elements / components / etc. In addition, the terms "first", "second", etc. in the claims are used only as marks and are not numerical restrictions on their objects. The same numbers in the drawings represent the same or similar components. On the other hand, well-known components and steps are not described in the embodiments to avoid unnecessary limitations on the present invention. In addition, for the sake of simplifying the drawings, some known conventional structures and elements will be illustrated in the drawings in a simple schematic manner. Finally, "coupling" or "connection" used in the present invention may refer to two or more elements making direct physical or electrical contact, or making physical or electrical contact with each other indirectly.

[0030] Figure 1 is a schematic diagram of the structure of the insulation state detection and positioning device for the conversion system according to the first embodiment of the present invention. Figure 1 As shown, the conversion system includes a converter module 11, an excitation source 12, a coupling impedance unit 13 and a connecting element 14, wherein the converter module 11 includes n conversion units, n≥1. Each conversion unit includes a transformer 111, and the transformer 111 includes a first winding W1 and a second winding W2. The excitation source 12 is electrically connected to the first winding W1 of the transformer 111. The connecting element 14 is connected between the first winding W1 and the second winding W2 of the transformer 111. The coupling impedance unit 13 is connected in series with the connecting element 14, and a ground end is connected to the connecting element 14. In some other embodiments, the excitation source 12 is electrically connected to the second winding W2 of the transformer 111. In some embodiments, the connecting element 14 is a cable or PCB trace or sheet metal with low impedance. In some embodiments, the connecting element 14 may include a switch, for example, a converter.

[0031] The insulation state detection and positioning device comprises a control unit 151, an insulation state detection unit 152 and a processing unit 153. The control unit 151 is connected to the converter module 11, and is used to change the state of at least one switch in the conversion system, so that the voltage between the first winding W1 and the second winding W2 of the transformer 111 applied to at least one of the n conversion units changes. The insulation state detection unit 152 is sleeved on the connection element 14 and connected to the control unit 151, and is used to detect the amount of current flowing through the connection element 14 before and after the state of at least one switch changes. The processing unit 153 is connected to the insulation state detection unit 152, and is used to compare the amount of current flowing through the connection element 14 before and after the state of at least one switch changes, and determine which of the n conversion units has insulation abnormalities according to the comparison result. In some other embodiments, the insulation state detection unit 152 does not need to be sleeved on the connection element 14, and only needs to have an electrical or magnetic connection with the connection element 14 to detect the amount of current flowing through the connection element 14.

[0032] Figure 2 for Figure 1 The flowchart of the insulation state detection and positioning method 100 of the insulation state detection and positioning device is shown. Figure 1 and Figure 2 , the insulation status detection and positioning method 100 comprises:

[0033] Step S1: changing the state of at least one switch in the conversion system so that the voltage between the first winding W1 and the second winding W2 of the transformer 111 applied to at least one of the n conversion units changes;

[0034] Step S2: detecting the amount of current flowing through the connecting element 14 before and after the state of at least one switch changes; and

[0035] Step S3: Compare the state of at least one switch before and after the change, reflecting the amount of current flowing through the connecting element 14, and determine which of the n conversion units have insulation abnormalities according to the comparison result.

[0036] Further, in another embodiment of the present invention, Figure 5 As shown, the conversion system may further include a first switch K1, the first switch being connected between the excitation source 22 and the input end of the converter module 21, and each conversion unit further includes a first capacitor C1. Figure 3 As shown, before step S1, the insulation status detection and positioning method 100 further includes:

[0037] Step S11: close the first switch K1, and the power supply pre-charges the first capacitor C1 until the voltage of the first capacitor C1 is charged to a preset voltage value, and then open the first switch K1.

[0038] In another embodiment of the present invention, Figure 5 As shown, the conversion system may further include a second switch K2, the second switch K2 and the connecting element 24 are connected in series, and each conversion unit includes a first capacitor C1. Figure 4 As shown, before step S1, the insulation status detection and positioning method 100 further includes:

[0039] Step S11 ′: when the voltage of the first capacitor C1 reaches or exceeds a preset voltage value, the second switch K2 is controlled to be turned on to start insulation state detection.

[0040] Figure 5 FIG. 1 is a schematic diagram of the structure of an insulation state detection and positioning device for a conversion system according to a second embodiment of the present invention. Figure 5 As shown, the conversion system includes a conversion module 21, an excitation source 22 (power source Vin), a coupling impedance unit 23 (for example, a capacitor), a connecting element 24, a first switch K1 and a second switch K2. The conversion module 21 includes n conversion units (Unit 1, Unit 2...Unit n), n≥1, each conversion unit includes a transformer 211, and the transformer 211 includes a first winding W1 and a second winding W2. Each conversion unit also includes an AC / DC converter 212, a DC / AC converter 213 and a first capacitor C1. The AC / DC converter 212, the DC / AC converter 213 and the transformer 211 are electrically connected in sequence. The first capacitor C1 is connected in parallel to the DC side of the AC / DC converter 212, and the AC sides of the AC / DC converters 212 of the first conversion unit Unit 1 to the nth conversion unit Unit n are connected in series in sequence, and the voltage across the first capacitor C1 is Vdc. The excitation source 22 is electrically connected to the first winding W1 of the transformer 211. The connecting element 24 is connected between the first winding W1 and the second winding W2 of the transformer 211. The coupling impedance unit 23 is connected in series with the connecting element 24. A ground terminal is connected to the connecting element 24.

[0041] The insulation state detection and positioning device comprises a control unit 251, an insulation state detection unit 252 (for example, a current transformer) and a processing unit 253. The control unit 251, the insulation state detection unit 252 and the processing unit 253 and Figure 1 The structures and functions shown in are the same, so they will not be repeated here.

[0042] First, the first switch K1 of the conversion system is closed, and the power supply Vin is used to pre-charge the first capacitor C1 until the voltage of the first capacitor C1 is charged to a preset voltage value, and the first switch K1 is disconnected, and the second switch K2 is controlled to be turned on, and the insulation state detection begins. In some embodiments, before the insulation detection begins, the voltage across the first capacitor C1 is greater than the preset value. For example, when the converter system is just switched from the running state to the shutdown state, the voltage on the DC capacitor is still greater than the preset value, and no pre-charging is required at this time.

[0043] Figure 6 The insulation state detection and positioning method 200 for the insulation state detection and positioning device of the conversion system provided by the second embodiment of the present invention is shown, which locates the position of the conversion unit with insulation abnormality by reducing the voltage excitation at both ends of the transformer under test and according to the disappearance of the insulation abnormality. Figure 5 and Figure 6 When the absolute values ​​of the AC side voltages of the AC / DC converters 212 of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning method 200 includes:

[0044] Step R1: bypass one conversion unit at a time. Bypassing one conversion unit means making the AC side voltage of the conversion unit equal to 0. Beginning with the first conversion unit Unit 1, bypassing is performed in sequence. If when bypassing to the i-th conversion unit, 1≤i≤n, the insulation abnormality disappears, then the bypass is stopped, and it is determined that the i-th conversion unit has an insulation abnormality. If when bypassing to the n-th conversion unit in sequence, the insulation abnormality still does not disappear, then step R2 is executed;

[0045] Step R2: Each time two conversion units are bypassed, the sequence number of the conversion unit with the smallest sequence number among the two conversion units is increased sequentially from 1. If the conversion unit with the smallest sequence number among the two conversion units is the kth conversion unit when bypassed, 1≤k≤n-1, and the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality occurs in the kth conversion unit. If the insulation abnormality still does not disappear when the conversion unit with the smallest sequence number among the two conversion units is the n-1th conversion unit when bypassed, then step Rm is executed;

[0046] Step Rm: m conversion units are bypassed each time, and the value of m starts from 3. The sequence number of the conversion unit with the smallest sequence number among the m conversion units increases from 1 in sequence. If the conversion unit with the smallest sequence number among the m conversion units is the jth conversion unit, 1≤j≤n-m+1, and the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality occurs in the jth conversion unit. If the insulation abnormality still does not disappear when the conversion unit with the smallest sequence number among the m conversion units is the n-m+1th conversion unit, then m is increased. When m increases to n-2, if the insulation abnormality still does not disappear, then step Rn-1 is executed; and

[0047] Step Rn-1: Bypass the 1st conversion unit to the n-1th conversion unit at the same time. If the insulation abnormality disappears, it is determined that the n-1th conversion unit has an insulation abnormality. If the insulation abnormality does not disappear, it is determined that the nth conversion unit has an insulation abnormality.

[0048] Figure 7 The figure shows an insulation state detection and positioning method 300 for an insulation detection device of a conversion system provided by the second embodiment of the present invention, combined with Figure 5 and Figure 7 When the absolute values ​​of the AC side voltages of the AC / DC converters 213 of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning method 300 includes:

[0049] Step Q1: bypassing one conversion unit at a time, and bypassing from the first conversion unit to the nth conversion unit in sequence, wherein bypassing one conversion unit means making the AC side voltage of the conversion unit equal to 0;

[0050] Step Q2: bypassing two transform units each time, the sequence number of the transform unit with the smallest sequence number among the two transform units is increased from 1 to n-1 in sequence;

[0051] Step Qm: m transform units are bypassed each time, and the sequence number of the transform unit with the smallest sequence number among the m transform units is increased from 1 to n-m+1 in sequence, where m=3, 4...n-2;

[0052] Step Qn-1: bypassing the 1st transformation unit to the n-1th transformation unit at the same time; and

[0053] Step Qn: Determine which conversion unit has insulation abnormality.

[0054] Reference Figure 5 A third switch K3 is connected in parallel to the AC side of the AC / DC converter 212 of each conversion unit. By turning on the third switch K3, the corresponding conversion unit is bypassed, so that the AC side voltage of the conversion unit is equal to 0.

[0055] In other embodiments, the corresponding conversion unit may be bypassed by controlling the state of the switch tube in the AC / DC converter 212. Fig. 9As shown, the conversion system includes a conversion module 21, and the conversion module 21 includes n conversion units (Unit1, Unit 2...Unit n), n≥1. Each conversion unit also includes an AC / DC converter 212, a DC / AC converter 213 and a transformer that are electrically connected in sequence. The AC / DC converter 212 converter adopts a full-bridge circuit, including upper switch tubes Q1, Q3 and lower switch tubes Q2, Q4. By turning on all the upper switches Q1, Q3 of the AC / DC converter 212, the corresponding conversion unit is bypassed. Among them, the converter switch is a power switching device such as MOSFET, IGBT, IGCT, etc. Since the switching device generates an interference signal at the moment of switching from the off state to the on state or from the on state to the off state, in order to avoid the interference signal from affecting the insulation detection, in some embodiments, the control unit 251 shields the insulation detection signal at the moment of switching the switching device, and responds to the insulation detection signal when the switching device is stably turned on or off.

[0056] In some embodiments, the order of all the aforementioned insulation positioning steps and the bypassing of the conversion unit can be changed.

[0057] For example, m conversion units can be bypassed each time, and the other nm conversion units are in the active state, where m can be 1 to n. All bypass combinations are completed.

[0058] In this way, 1 conversion unit is bypassed each time, 2 conversion units are bypassed each time, and so on. After all bypass combinations of n conversion units are completed each time, it can be determined which conversion unit has insulation abnormality by comparing all bypass combinations.

[0059] Figure 8 The figure shows an insulation state detection and positioning method 300' for an insulation detection device of a conversion system provided by the second embodiment of the present invention, combined with Figure 5 and Figure 8 When the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all Vdc, the insulation state detection and positioning method 300' comprises the steps of:

[0060] Step H1: Select m transform units to bypass from the n transform units, and complete Bypass combination;

[0061] Step H2: m takes a value from the set {1, 2, ..., n}, and step H1 is executed once for each value of m; and

[0062] Step H3: Determine which conversion unit has insulation abnormality.

[0063] Fig.10 The insulation state detection and positioning method 400 of the insulation detection device for the conversion system provided in the second embodiment of the present invention is shown, which increases the voltage excitation at both ends of the transformer under test and locates the position of the conversion unit where the insulation abnormality occurs according to the phenomenon of the insulation abnormality. Figure 5 and Fig.10 When the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning method 400 includes:

[0064] Step V1: Connect one conversion unit at a time, wherein connecting one conversion unit means making the absolute value of the AC side voltage of the conversion unit equal to Vdc, and connecting in sequence from the first conversion unit. If when the i-th conversion unit is connected, 1≤i≤n, an insulation abnormality occurs, then the connection is stopped, and it is determined that the i-th conversion unit has an insulation abnormality. If when the n-th conversion unit is connected, no insulation abnormality still occurs, then step V2 is executed;

[0065] Step V2: Each time two conversion units are connected, the sequence number of the conversion unit with the smallest sequence number among the two conversion units is increased sequentially from 1. If the conversion unit with the smallest sequence number among the two conversion units connected is the kth conversion unit, 1≤k≤n-1, and an insulation abnormality occurs, then the connection is stopped, and it is determined that the insulation abnormality occurs in the kth conversion unit. If the conversion unit with the smallest sequence number among the two conversion units connected is the n-1th conversion unit, and no insulation abnormality occurs, then step Vm is executed;

[0066] Step Vm: each time m conversion units are accessed, the value of m starts from 3, and the sequence number of the conversion unit with the smallest sequence number among the m conversion units increases from 1 in sequence. If the conversion unit with the smallest sequence number among the m conversion units is the jth conversion unit, 1≤j≤n-m+1, and an insulation abnormality occurs, then the access is stopped, and it is determined that the insulation abnormality occurs in the jth conversion unit. If the conversion unit with the smallest sequence number among the m conversion units is the n-m+1th conversion unit, and no insulation abnormality occurs, then m increases in sequence. When m increases to n-2, and no insulation abnormality occurs, then step Vn-1 is executed; and

[0067] Step Vn-1: Simultaneously connect the 1st conversion unit to the n-1th conversion unit. If an insulation abnormality occurs, determine that the n-1th conversion unit has an insulation abnormality. If no insulation abnormality occurs, determine that the nth conversion unit has an insulation abnormality.

[0068] Fig.11 The figure shows an insulation state detection and positioning method 500 for an insulation detection device of a conversion system provided by the second embodiment of the present invention, combined with Figure 5and Fig.11 When the absolute values ​​of the AC side voltages of the AC / DC converters 213 of the n conversion units are all 0, the insulation state detection and positioning method 500 includes:

[0069] Step P1: connecting one conversion unit at a time, from the first conversion unit to the nth conversion unit in sequence, wherein connecting one conversion unit means making the absolute value of the AC side voltage of the conversion unit equal to Vdc;

[0070] Step P2: Each time two transform units are connected, the sequence number of the transform unit with the smallest sequence number among the two transform units is increased from 1 to n-1 in sequence;

[0071] Step Pm: Each time m transform units are accessed, the sequence number of the transform unit with the smallest sequence number among the m transform units is increased from 1 to n-m+1, m=3, 4...n-2;

[0072] Step Pn-1: simultaneously accessing the 1st transformation unit to the n-1th transformation unit; and

[0073] Step Pn: Determine which conversion unit has the insulation state.

[0074] In some embodiments, the order of all the aforementioned insulation positioning steps and the input of the conversion unit can be changed.

[0075] For example, m transform units can be connected at a time, and the other nm transform units are in bypass state, where m can be 1 to n. All access combinations are completed.

[0076] In this way, after all access combinations of 1 conversion unit, 2 conversion units, etc. are completed each time, it can be determined which conversion unit has insulation abnormality by comparing all access combinations.

[0077] Fig.12 The figure shows an insulation state detection and positioning method 500' for an insulation detection device of a conversion system provided by the second embodiment of the present invention, combined with Figure 5 and Fig.12 When the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning method 500' comprises the steps of:

[0078] Step F1: Select m transform units from the n transform units to access, and complete Access combinations;

[0079] Step F2: m takes a value from the set {1, 2, ..., n}, and step F1 is executed once for each value of m; and

[0080] Step F3: Determine which conversion unit has insulation abnormality.

[0081] Fig.13 FIG. 1 is a schematic diagram of the structure of an insulation detection and positioning device for a conversion system provided by Embodiment 3 of the present invention. Fig.13 As shown, the conversion system includes a conversion module 31, an excitation source 32 (power supply Vin), a coupling impedance unit 33, a connecting element 34, a first switch K1 and a second switch K2. Among them, the conversion module 31 includes n conversion units (Unit 1, Unit 2...Unit n), n≥1. Each conversion unit includes a transformer 311, and the transformer 311 includes a first winding W1 and a second winding W2. Each conversion unit also includes a DC / AC converter 312, an AC / DC converter 313, a first capacitor C1 and a second capacitor C2. The DC / AC converter 312, the transformer 311 and the AC / DC converter 313 are electrically connected in sequence. The first capacitor C1 is connected in parallel to the DC side of the DC / AC converter 312. The second capacitor C2 is connected in parallel to the DC side of the AC / DC converter 313. The first winding W1 is electrically connected to the DC / AC converter 312, and the second winding W2 is electrically connected to the AC / DC converter 313. The DC sides of the DC / AC converters 312 of the n conversion units are connected in parallel, and the DC sides of the AC / DC converters 313 of the n conversion units are connected in parallel. The excitation source 32 is electrically connected to the first winding W1 of the transformer 311. The connecting element 34 is connected between the first winding W1 and the second winding W2 of the transformer 311. The coupling impedance unit 33 is connected in series with the connecting element 34. A ground terminal is connected to the connecting element 34.

[0082] In some embodiments, the DC sides of the DC / AC converters 312 of the n conversion units may also be connected in series.

[0083] In this embodiment, the insulation detection and positioning device comprises a control unit 351, an insulation detection unit 352 and a processing unit 353. The control unit 351, the insulation detection unit 352 and the processing unit 353 and Figure 1 The structures and functions shown in are the same, so they will not be repeated here.

[0084] In one implementation of the third embodiment of the present invention, through the control unit, the first winding W1 of each conversion unit is first connected to the positive electrode of the first capacitor C1 of the corresponding conversion unit, and the second winding W2 of each conversion unit is connected to the negative electrode of the second capacitor C2 of the corresponding conversion unit.

[0085] Continue to refer to Fig.13In each conversion unit, the DC / AC converter 312 and the AC / DC converter 313 both use a full-bridge circuit. The DC / AC converter 312 includes upper switches S11, S12 and lower switches S13, S14. The AC / DC converter 313 includes upper switches S21, S22 and lower switches S23, S24. By turning on all upper switches of the DC / AC converter 312, the first winding W1 corresponding to the DC / AC converter 312 is connected to the positive electrode of the first capacitor C1, and by turning on all lower switches of the AC / DC converter 313, the second winding W2 corresponding to the AC / DC converter 313 is connected to the negative electrode of the second capacitor C2.

[0086] Fig.14 The insulation state detection and positioning method 600 of the insulation detection device for the conversion system provided in the third embodiment of the present invention is shown, which locates the position of the conversion unit where the insulation abnormality occurs by reducing the voltage excitation at both ends of the transformer under test and according to the phenomenon that the insulation abnormality disappears. The insulation state detection and positioning method 600 includes:

[0087] 601: Connect the first winding W1 of each conversion unit to the positive electrode of the first capacitor C1 of the corresponding conversion unit, and connect the second winding W2 of each conversion unit to the negative electrode of the second capacitor C2 of the corresponding conversion unit;

[0088] 602: When an insulation abnormality occurs in the conversion system, the first winding W1 of the transformer 311 in the i-th conversion unit is electrically connected to the negative electrode of the first capacitor C1 of the corresponding conversion unit, 1≤i≤n. If the insulation abnormality disappears, it is determined that the i-th conversion unit has an insulation abnormality.

[0089] In another implementation manner of the third embodiment of the present invention, through the control unit, first, the first winding of each conversion unit is connected to the negative electrode of the first capacitor of the corresponding conversion unit, and the second winding of each conversion unit is connected to the negative electrode of the second capacitor of the corresponding conversion unit, that is, all the lower switches S13 and S14 of the DC / AC converter 312 are turned on to connect the first winding W1 corresponding to the DC / AC converter 312 to the negative electrode of the first capacitor C1, and all the lower switches S23 and S24 of the AC / DC converter 313 are turned on to connect the second winding W2 corresponding to the AC / DC converter 313 to the negative electrode of the second capacitor C2.

[0090] Fig.15 The insulation state detection and positioning method 700 of the insulation detection device for the conversion system provided in the third embodiment of the present invention is shown, which increases the voltage excitation at both ends of the transformer under test and locates the position of the conversion unit where the insulation abnormality occurs according to the phenomenon of the insulation abnormality. The insulation state detection and positioning method 700 includes:

[0091] 701: Connect the first winding of each of the conversion units to the negative electrode of the first capacitor of the corresponding conversion unit, and connect the second winding of each of the conversion units to the negative electrode of the second capacitor of the corresponding conversion unit;

[0092] 702: electrically connect the first winding of the transformer in the i-th conversion unit to the positive electrode of the first capacitor of the corresponding conversion unit, 1≤i≤n. If an insulation abnormality occurs, it is determined that the i-th conversion unit has an insulation abnormality.

[0093] In summary, the present invention proposes an insulation state detection and positioning method for a conversion system, the conversion system includes a converter module and a connection element, the converter module includes n conversion units, n≥2, each conversion unit includes a transformer, the transformer includes a first winding and a second winding, the connection element is connected between the first winding and the second winding of the transformer, and the insulation state detection and positioning method includes:

[0094] Step S1: changing the state of at least one switch in the conversion system so that the voltage between the first winding and the second winding of the transformer applied to at least one of the n conversion units changes;

[0095] Step S2: detecting the amount of current flowing through the connection element before and after the state of at least one switch changes; and

[0096] Step S3: Compare the state of at least one switch before and after the change, reflecting the amount of current flowing through the connection element, and determine which of the n conversion units have insulation abnormalities according to the comparison result.

[0097] The present invention also proposes an insulation state detection and positioning device for a conversion system, characterized in that the conversion system includes a converter module and a connecting element, the converter module includes n conversion units, n≥2, each conversion unit includes a transformer, the transformer includes a first winding and a second winding, the connecting element is connected between the first winding and the second winding of the transformer, and the insulation state detection and positioning device includes a control unit, an insulation detection unit and a processing unit, the control unit is connected to the converter module, and is used to change the state of at least one switch in the conversion system so that the voltage between the first winding and the second winding of the transformer applied to at least one of the n conversion units changes; the insulation detection unit is mounted on the connecting element and connected to the control unit, and is used to detect the amount of current flowing through the connecting element before and after the state of at least one switch is changed; the processing unit is connected to the insulation detection unit, and is used to compare the amount of current flowing through the connecting element before and after the state of at least one switch is changed, and determine which of the n conversion units have insulation abnormalities according to the comparison result.

[0098] The present invention adjusts the state of the switch in the conversion system in a conventional medium- and high-voltage converter insulation state detection system, adjusts the insulation state test excitation voltage value of the corresponding conversion unit, and locates the position of the conversion unit with insulation abnormality through the change of the insulation state detection signal of the conversion system, which has the following advantages:

[0099] (1) Widely used in partial discharge detection of multi-module medium and high voltage isolation converters;

[0100] (2) It helps to simplify fault maintenance work and reduce maintenance costs;

[0101] (3) No additional components are required, easy to implement and low cost.

[0102] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of protection of the present invention shall be subject to the scope defined by the appended claims.

Claims

1. A method for detecting and locating the insulation state of a conversion system, characterized in that: The transformation system comprises: A converter module, comprising n conversion units, n≥2, each of the conversion units comprising a transformer, and the transformer comprising a first winding and a second winding; and A connecting element is connected between the first winding and the second winding of the transformer; the insulation state detection and positioning method comprises: Step S1: changing the state of at least one switch in the conversion system so that the voltage between the first winding and the second winding of the transformer applied to at least one of the n conversion units changes; Step S2: detecting the amount of current flowing through the connection element before and after the state of the at least one switch changes; as well as Step S3: comparing the state of the at least one switch before and after the change to reflect the amount of current flowing through the connection element, and determining which of the n conversion units have insulation abnormalities according to the comparison result.

2. The insulation status detection and positioning method according to claim 1, characterized in that: The conversion system further includes a first switch connected between a power source and an input terminal of the converter module. Each of the conversion units includes a first capacitor. Before step S1, the system further includes: Step S11: the first switch is closed, and the power supply pre-charges the first capacitor until the voltage of the first capacitor is charged to a preset voltage value, and the first switch is opened.

3. The insulation status detection and positioning method according to claim 1, characterized in that: The conversion system further includes a second switch, the second switch and the connecting element are connected in series, each of the conversion units includes a first capacitor, and before step S1, includes: Step S11: when the voltage of the first capacitor reaches or exceeds a preset voltage value, the second switch is controlled to be turned on to start insulation state detection.

4. The insulation status detection and positioning method according to claim 1, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, when the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning method includes: Step R1: bypassing one conversion unit at a time, wherein bypassing one conversion unit means making the AC side voltage of the conversion unit equal to 0, and bypassing is performed sequentially from the first conversion unit. If when bypassing to the i-th conversion unit, 1≤i≤n, the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality of the i-th conversion unit occurs. If when bypassing to the n-th conversion unit in sequence, the insulation abnormality still does not disappear, then step R2 is executed; Step R2: bypassing two conversion units each time, the sequence number of the conversion unit with the smallest sequence number among the two conversion units is increased sequentially from 1, if when the conversion unit with the smallest sequence number among the two conversion units is bypassed to the kth conversion unit, 1≤k≤n-1, the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality occurs in the kth conversion unit, if when the conversion unit with the smallest sequence number among the two conversion units is bypassed to the n-1th conversion unit, the insulation abnormality still does not disappear, then executing step Rm; Step Rm: m conversion units are bypassed each time, and the value of m starts from 3. The sequence number of the conversion unit with the smallest sequence number among the m conversion units increases from 1 in sequence. If the conversion unit with the smallest sequence number among the m conversion units is the jth conversion unit when bypassed, 1≤j≤n-m+1, and the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality occurs in the jth conversion unit. If the insulation abnormality still does not disappear when the conversion unit with the smallest sequence number among the m conversion units is the n-m+1th conversion unit when bypassed, then m increases. When m increases to n-2, if the insulation abnormality still does not disappear, then step Rn-1 is executed; and Step Rn-1: Bypass the 1st conversion unit to the n-1th conversion unit at the same time. If the insulation abnormality disappears, it is determined that the n-1th conversion unit has an insulation abnormality. If the insulation abnormality does not disappear, it is determined that the nth conversion unit has an insulation abnormality.

5. The insulation status detection and positioning method according to claim 1, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, when the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning method includes: Step Q1: bypassing one conversion unit at a time, and bypassing from the first conversion unit to the nth conversion unit in sequence, wherein bypassing one conversion unit means making the AC side voltage of the conversion unit equal to 0; Step Q2: bypassing two transform units each time, the sequence number of the transform unit with the smallest sequence number among the two transform units is increased from 1 to n-1 in sequence; Step Qm: m transform units are bypassed each time, and the sequence number of the transform unit with the smallest sequence number among the m transform units is increased from 1 to n-m+1 in sequence, where m=3, 4...n-2; Step Qn-1: bypassing the 1st transformation unit to the n-1th transformation unit at the same time; and Step Qn: Determine which conversion unit has insulation abnormality.

6. The insulation status detection and positioning method according to claim 1, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, when the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning method includes: Step H1: Select m transform units to bypass from the n transform units, and complete Bypass combination; Step H2: m takes a value from the set {1, 2, ..., n}, and step H1 is executed once for each value of m; and Step H3: Determine which conversion unit has insulation abnormality.

7. The insulation status detection and positioning method according to claim 4, characterized in that: A third switch is connected in parallel to the AC side of the AC / DC converter of each conversion unit, and the corresponding conversion unit is bypassed by turning on the third switch.

8. The insulation status detection and positioning method according to claim 4, characterized in that: The AC / DC converter adopts a full-bridge circuit, and the corresponding conversion unit is bypassed by turning on all upper switches of the AC / DC converter.

9. The insulation status detection and positioning method according to claim 1, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, and when the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning method includes: Step V1: Connect one conversion unit at a time, wherein connecting one conversion unit means making the absolute value of the AC side voltage of the conversion unit equal to Vdc, and connecting in sequence from the first conversion unit. If when the i-th conversion unit is connected, 1≤i≤n, an insulation abnormality occurs, then the connection is stopped, and it is determined that the i-th conversion unit has an insulation abnormality. If when the n-th conversion unit is connected, no insulation abnormality still occurs, then step V2 is executed; Step V2: Each time two conversion units are connected, the sequence number of the conversion unit with the smallest sequence number among the two conversion units is increased sequentially from 1. If the conversion unit with the smallest sequence number among the two conversion units connected is the kth conversion unit, 1≤k≤n-1, and an insulation abnormality occurs, then the connection is stopped, and it is determined that the insulation abnormality occurs in the kth conversion unit. If the conversion unit with the smallest sequence number among the two conversion units connected is the n-1th conversion unit, and no insulation abnormality occurs, then step Vm is executed; Step Vm: each time m conversion units are accessed, the value of m starts from 3, and the sequence number of the conversion unit with the smallest sequence number among the m conversion units increases from 1 in sequence. If the conversion unit with the smallest sequence number among the m conversion units is the jth conversion unit, 1≤j≤n-m+1, and an insulation abnormality occurs, then the access is stopped, and it is determined that the insulation abnormality occurs in the jth conversion unit. If the conversion unit with the smallest sequence number among the m conversion units is the n-m+1th conversion unit, and no insulation abnormality occurs, then m increases in sequence. When m increases to n-2, and no insulation abnormality occurs, then step Vn-1 is executed; and Step Vn-1: Simultaneously connect the 1st conversion unit to the n-1th conversion unit. If an insulation abnormality occurs, determine that the n-1th conversion unit has an insulation abnormality. If no insulation abnormality occurs, determine that the nth conversion unit has an insulation abnormality.

10. The insulation status detection and positioning method according to claim 1, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, and when the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning method includes: Step P1: connecting one conversion unit at a time, from the first conversion unit to the nth conversion unit in sequence, wherein connecting one conversion unit means making the absolute value of the AC side voltage of the conversion unit equal to Vdc; Step P2: Each time two transform units are connected, the sequence number of the transform unit with the smallest sequence number among the two transform units is increased from 1 to n-1 in sequence; Step Pm: Each time m transform units are accessed, the sequence number of the transform unit with the smallest sequence number among the m transform units is increased from 1 to n-m+1, m=3, 4...n-2; Step Pn-1: simultaneously accessing the 1st transformation unit to the n-1th transformation unit; and Step Pn: Determine which conversion unit has insulation abnormality.

11. The insulation status detection and positioning method according to claim 1, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, and when the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning method includes: Step F1: Select m transform units from the n transform units to access, and complete Access combinations; Step F2: m takes a value from the set {1, 2, ..., n}, and step F1 is executed once for each value of m; and Step F3: Determine which conversion unit has insulation abnormality.

12. The insulation status detection and positioning method according to claim 1, characterized in that: Each of the conversion units further includes a DC / AC converter, an AC / DC converter, a first capacitor and a second capacitor. The DC / AC converter, the transformer and the AC / DC converter are electrically connected in sequence. The first capacitor is connected in parallel to the DC side of the DC / AC converter, the second capacitor is connected in parallel to the DC side of the AC / DC converter, the first winding is electrically connected to the DC / AC converter, the second winding is electrically connected to the AC / DC converter, the DC sides of the DC / AC converters of the n conversion units are connected in series or in parallel, and the DC sides of the AC / DC converters of the n conversion units are connected in parallel. Step S12 is also included before step S1: The first winding of each of the conversion units is connected to the positive electrode of the first capacitor of the corresponding conversion unit, and the second winding of each of the conversion units is connected to the negative electrode of the second capacitor of the corresponding conversion unit.

13. The insulation status detection and positioning method according to claim 12, characterized in that: When an insulation abnormality occurs in the conversion system, the first winding of the transformer in the i-th conversion unit is electrically connected to the negative electrode of the first capacitor of the corresponding conversion unit, 1≤i≤n. If the insulation abnormality disappears, it is determined that the i-th conversion unit has an insulation abnormality.

14. The insulation status detection and positioning method according to claim 1, characterized in that: Each of the conversion units further includes a DC / AC converter, an AC / DC converter, a first capacitor and a second capacitor. The DC / AC converter, the transformer and the AC / DC converter are electrically connected in sequence. The first capacitor is connected in parallel to the DC side of the DC / AC converter, the second capacitor is connected in parallel to the DC side of the AC / DC converter, the first winding is electrically connected to the DC / AC converter, the second winding is electrically connected to the AC / DC converter, the DC sides of the DC / AC converters of the n conversion units are connected in series or in parallel, and the DC sides of the AC / DC converters of the n conversion units are connected in parallel. Step S13 is also included before step S1: The first winding of each of the conversion units is connected to the negative electrode of the first capacitor of the corresponding conversion unit, and the second winding of each of the conversion units is connected to the negative electrode of the second capacitor of the corresponding conversion unit.

15. The insulation status detection and positioning method according to claim 14, characterized in that: The first winding of the transformer in the i-th conversion unit is electrically connected to the positive electrode of the first capacitor of the corresponding conversion unit, 1≤i≤n. If an insulation abnormality occurs, it is determined that the i-th conversion unit has an insulation abnormality.

16. The insulation status detection and positioning method according to claim 12, characterized in that: The DC / AC converter and the AC / DC converter both adopt a full-bridge circuit. By turning on all the upper switches of the DC / AC converter, the first winding corresponding to the DC / AC converter is connected to the positive electrode of the first capacitor. By turning on all the lower switches of the AC / DC converter, the second winding corresponding to the AC / DC converter is connected to the negative electrode of the second capacitor.

17. An insulation status detection and positioning device for a conversion system, characterized in that: The transformation system comprises: A converter module, comprising n conversion units, n≥2, each of the conversion units comprising a transformer, and the transformer comprising a first winding and a second winding; and A connecting element is connected between the first winding and the second winding of the transformer; the insulation state detection and positioning device comprises: a control unit connected to the converter module, configured to change a state of at least one switch in the conversion system so as to change a voltage between the first winding and the second winding of a transformer applied to at least one of the n conversion units; an insulation detection unit, which is sleeved on the connection element and connected to the control unit, and is used to detect the amount of current flowing through the connection element before and after the state of the at least one switch changes; as well as The processing unit is connected to the insulation detection unit and is used to compare the state of the at least one switch before and after the change, reflecting the amount of current flowing through the connection element, and determining which of the n conversion units have insulation abnormalities according to the comparison result.

18. The insulation status detection and positioning device according to claim 17, characterized in that: The conversion system also includes a first switch connected between a power supply and the input end of the converter module. Each of the conversion units includes a first capacitor. The first switch is configured to be turned on before the power supply pre-charges the first capacitor and to be disconnected after the voltage of the first capacitor is charged to a preset voltage value.

19. The insulation status detection and positioning device according to claim 17, characterized in that: The conversion system further includes a second switch, which is connected in series with the connecting element. Each of the conversion units includes a first capacitor, and the second switch is configured to be turned on when the voltage of the first capacitor reaches or exceeds a preset voltage value.

20. The insulation status detection and positioning device according to claim 17, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, when the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning device performs the following steps: Step R1: bypassing one conversion unit at a time, wherein bypassing one conversion unit means making the AC side voltage of the conversion unit equal to 0, and bypassing is performed sequentially from the first conversion unit. If when bypassing to the i-th conversion unit, 1≤i≤n, the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality of the i-th conversion unit occurs. If when bypassing to the n-th conversion unit in sequence, the insulation abnormality still does not disappear, then step R2 is executed; Step R2: bypassing two conversion units each time, the sequence number of the conversion unit with the smallest sequence number among the two conversion units is increased sequentially from 1, if when the conversion unit with the smallest sequence number among the two conversion units is bypassed to the kth conversion unit, 1≤k≤n-1, the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality occurs in the kth conversion unit, if when the conversion unit with the smallest sequence number among the two conversion units is bypassed to the n-1th conversion unit, the insulation abnormality still does not disappear, then executing step Rm; Step Rm: m conversion units are bypassed each time, and the value of m starts from 3. The sequence number of the conversion unit with the smallest sequence number among the m conversion units increases from 1 in sequence. If the conversion unit with the smallest sequence number among the m conversion units is the jth conversion unit when bypassed, 1≤j≤n-m+1, and the insulation abnormality disappears, then the bypass is stopped, and it is determined that the insulation abnormality occurs in the jth conversion unit. If the insulation abnormality still does not disappear when the conversion unit with the smallest sequence number among the m conversion units is the n-m+1th conversion unit when bypassed, then m increases. When m increases to n-2, if the insulation abnormality still does not disappear, then step Rn-1 is executed; and Step Rn-1: Bypass the 1st conversion unit to the n-1th conversion unit at the same time. If the insulation abnormality disappears, it is determined that the n-1th conversion unit has an insulation abnormality. If the insulation abnormality does not disappear, it is determined that the nth conversion unit has an insulation abnormality.

21. The insulation status detection and positioning device according to claim 17, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, when the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning device performs the following steps: Step Q1: bypassing one conversion unit at a time, and bypassing from the first conversion unit to the nth conversion unit in sequence, wherein bypassing one conversion unit means making the AC side voltage of the conversion unit equal to 0; Step Q2: bypassing two transform units each time, the sequence number of the transform unit with the smallest sequence number among the two transform units is increased from 1 to n-1 in sequence; Step Qm: m transform units are bypassed each time, and the sequence number of the transform unit with the smallest sequence number among the m transform units is increased from 1 to n-m+1 in sequence, where m=3, 4...n-2; Step Qn-1: bypassing the 1st transformation unit to the n-1th transformation unit at the same time; and Step Qn: Determine which conversion unit has insulation abnormality.

22. The insulation status detection and positioning device according to claim 17, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, when the absolute values ​​of the AC side voltages of the AC / DC converters of the n conversion units are all Vdc, if insulation abnormality occurs in the conversion system, the insulation state detection and positioning device performs the following steps: Step H1: Select m transform units to bypass from the n transform units, and complete Bypass combination; Step H2: m takes a value from the set {1, 2, ..., n}, and step H1 is executed once for each value of m; and Step H3: Determine which conversion unit has insulation abnormality.

23. The insulation state detection and positioning device according to claim 20, characterized in that: A third switch is connected in parallel to the AC side of the AC / DC converter of each conversion unit.

24. The insulation state detection and positioning device according to claim 20, characterized in that: The AC / DC converter adopts a full-bridge circuit.

25. The insulation status detection and positioning device according to claim 17, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, and when the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning device performs the following steps: Step V1: Connect one conversion unit at a time, wherein connecting one conversion unit means making the absolute value of the AC side voltage of the conversion unit equal to Vdc, and connecting in sequence from the first conversion unit. If when the i-th conversion unit is connected, 1≤i≤n, an insulation abnormality occurs, then the connection is stopped, and it is determined that the i-th conversion unit has an insulation abnormality. If when the n-th conversion unit is connected, no insulation abnormality still occurs, then step V2 is executed; Step V2: Each time two conversion units are connected, the sequence number of the conversion unit with the smallest sequence number among the two conversion units is increased sequentially from 1. If the conversion unit with the smallest sequence number among the two conversion units connected is the kth conversion unit, 1≤k≤n-1, and an insulation abnormality occurs, then the connection is stopped, and it is determined that the insulation abnormality occurs in the kth conversion unit. If the conversion unit with the smallest sequence number among the two conversion units connected is the n-1th conversion unit, and no insulation abnormality occurs, then the following steps are performed; Step Vm: m conversion units are accessed each time, and the value of m starts from 3. The sequence number of the conversion unit with the smallest sequence number among the m conversion units increases from 1 in sequence. If the conversion unit with the smallest sequence number among the m conversion units is the jth conversion unit, 1≤j≤n-m+1, and an insulation abnormality occurs, then the access is stopped, and it is determined that the insulation abnormality occurs in the jth conversion unit. If the conversion unit with the smallest sequence number among the m conversion units is the n-m+1th conversion unit, and no insulation abnormality occurs, then m increases in sequence. When m increases to n-2, and no insulation abnormality occurs, then the following steps are performed; as well as Step Vn-1: Simultaneously connect the 1st conversion unit to the n-1th conversion unit. If an insulation abnormality occurs, determine that the n-1th conversion unit has an insulation abnormality. If no insulation abnormality occurs, determine that the nth conversion unit has an insulation abnormality.

26. The insulation status detection and positioning device according to claim 17, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, and when the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning device performs the following steps: Step P1: connecting one conversion unit at a time, from the first conversion unit to the nth conversion unit in sequence, wherein connecting one conversion unit means making the absolute value of the AC side voltage of the conversion unit equal to Vdc; Step P2: Each time two transform units are connected, the sequence number of the transform unit with the smallest sequence number among the two transform units is increased from 1 to n-1 in sequence; Step Pm: Each time m transform units are connected, the sequence number of the transform unit with the smallest sequence number among the m transform units is increased from 1 to n-m+1, m=3, 4...n-2; Step Pn-1: simultaneously accessing the 1st transformation unit to the n-1th transformation unit; and Step Pn: Determine which conversion unit has insulation abnormality.

27. The insulation status detection and positioning device according to claim 17, characterized in that: The n conversion units include the first conversion unit to the nth conversion unit, each of the conversion units further includes an AC / DC converter, a DC / AC converter and a first capacitor, the AC / DC converter, the DC / AC converter and the transformer are electrically connected in sequence, the first capacitor is connected in parallel to the DC side of the AC / DC converter, the AC sides of the AC / DC converters of the first conversion unit to the nth conversion unit are connected in series in sequence, the voltage across the first capacitor is Vdc, and when the AC side voltages of the AC / DC converters of the n conversion units are all 0, the insulation state detection and positioning device performs the following steps: Step F1: Select m transform units from the n transform units to access, and complete Access combinations; Step F2: m takes a value from the set {1, 2, ..., n}, and step F1 is executed once for each value of m; and Step F3: Determine which conversion unit has insulation abnormality.

28. The insulation status detection and positioning device according to claim 17, characterized in that: Each of the conversion units further includes a DC / AC converter, an AC / DC converter, a first capacitor and a second capacitor. The DC / AC converter, the transformer and the AC / DC converter are electrically connected in sequence. The first capacitor is connected in parallel to the DC side of the DC / AC converter, and the second capacitor is connected in parallel to the DC side of the AC / DC converter. The first winding is electrically connected to the DC / AC converter, and the second winding is electrically connected to the AC / DC converter. The DC sides of the DC / AC converters of the n conversion units are connected in series or in parallel, and the DC sides of the AC / DC converters of the n conversion units are connected in parallel. The control unit connects the first winding of each conversion unit to the positive electrode of the first capacitor of the corresponding conversion unit, and connects the second winding of each conversion unit to the negative electrode of the second capacitor of the corresponding conversion unit.

29. The insulation status detection and positioning device according to claim 28, characterized in that: When an insulation abnormality occurs in the conversion system, the first winding of the transformer in the i-th conversion unit is electrically connected to the negative electrode of the first capacitor of the corresponding conversion unit, 1≤i≤n. If the insulation abnormality disappears, it is determined that the i-th conversion unit has an insulation abnormality.

30. The insulation status detection and positioning device according to claim 17, characterized in that: Each of the conversion units further includes a DC / AC converter, an AC / DC converter, a first capacitor and a second capacitor. The DC / AC converter, the transformer and the AC / DC converter are electrically connected in sequence. The first capacitor is connected in parallel to the DC side of the DC / AC converter, and the second capacitor is connected in parallel to the DC side of the AC / DC converter. The first winding is electrically connected to the DC / AC converter, and the second winding is electrically connected to the AC / DC converter. The DC sides of the DC / AC converters of the n conversion units are connected in series or in parallel, and the DC sides of the AC / DC converters of the n conversion units are connected in parallel. The control unit connects the first winding of each conversion unit to the negative electrode of the first capacitor of the corresponding conversion unit, and connects the second winding of each conversion unit to the negative electrode of the second capacitor of the corresponding conversion unit.

31. The insulation status detection and positioning device according to claim 30, characterized in that: The first winding of the transformer in the i-th conversion unit is electrically connected to the positive electrode of the first capacitor of the corresponding conversion unit, 1≤i≤n. If an insulation abnormality occurs, it is determined that the i-th conversion unit has an insulation abnormality.

32. The insulation status detection and positioning device according to claim 28, characterized in that: The DC / AC converter and the AC / DC converter both adopt full-bridge circuits.

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