A converter system and a method for fault protection thereof

Abstract

This application discloses a converter system and its fault protection method, belonging to the field of converter technology. The converter system includes multiple converters, with the AC sides of power modules within the same converter connected together. A module capacitor is connected between the positive and negative DC terminals of the power modules. The positive DC terminal of the power module is connected to a positive busbar via a positive fuse, and / or the negative DC terminal is connected to a negative busbar via a negative fuse. The converter system of this application utilizes module capacitors. When any power module fails, the corresponding module capacitor of the non-faulty power module discharges, actively injecting fusing energy into the fuse of the faulty module. The instantaneous large current generated by the discharge of the module capacitor causes the positive and negative fuses of the faulty module to blow in a very short time, thereby effectively protecting the non-faulty modules.

Description

Technical Field

[0001] This application relates to the field of converter technology, specifically to a converter system and its fault protection method. Background Technology

[0002] With the continuous development of the new energy industry, voltage source converters are being used in more and more applications, especially in wind power, photovoltaics, energy storage, and green electricity hydrogen production. At the same time, the capacity requirements for voltage source converters are also increasing. To meet the demand for large-capacity development of voltage source converters, parallel expansion of power modules is often adopted. When a short-circuit fault occurs in a power transistor within a single power module, the short-circuit fault current flows through the positive or negative busbar between modules into the body diode of the power transistor in the non-faulty power module connected in parallel, causing damage to the power transistor in the non-faulty module. Summary of the Invention

[0003] A converter system and its fault protection method are provided to improve the problem of short-circuit fault current flowing into non-faulty power modules through the busbar between modules, causing damage to the power transistors in the non-faulty modules.

[0004] In a first aspect, embodiments of this application provide a converter system, comprising: Multiple converters, each converter including at least one power module, the AC side of the power module of the same converter being connected to each other, and a module capacitor being connected between the positive and negative DC side terminals of the power module. The positive terminal of the DC side of the power module is connected to the positive busbar through a positive fuse, and / or the negative terminal of the DC side of the power module is connected to the negative busbar through a negative fuse. The converter system is configured such that, in the event of a failure of any of the power modules, the positive fuse and / or the negative fuse corresponding to the faulty power module is blown by discharging the module capacitor corresponding to the non-faulty power module.

[0005] In some embodiments, the converter system further includes: A capacitor bank, wherein the positive terminal of the capacitor bank is connected to the positive busbar, and the negative terminal of the capacitor bank is connected to the negative busbar; The converter system is also configured to, in the event of a failure in any of the power modules, discharge through the capacitor bank to blow the positive fuse and / or the negative fuse corresponding to the faulty power module.

[0006] In some embodiments, the capacitor bank includes a plurality of capacitors connected in series and / or in parallel, and the capacitors include at least one of film capacitors, electrolytic capacitors, and supercapacitors.

[0007] In some embodiments, the capacitance value of the capacitor bank is determined based on at least one of the number of power modules, the capacitance value of the module capacitors, the fusing value of the positive fuse, the fusing time of the positive fuse, the fusing value of the negative fuse, and the fusing time of the negative fuse.

[0008] In some embodiments, the fault types of the power module include AC to DC side short circuit faults and DC positive and negative short circuit faults. The converter system is also configured to lock out the power transistors of all the power modules and disconnect the AC interfaces of the multiple converters before discharging the module capacitors corresponding to the non-faulty power modules and blowing the positive and / or negative fuses corresponding to the faulty power modules. In the case of an AC-to-DC short circuit fault in the power module, all power transistors in the bridge arm containing the faulty power transistor are turned on. In the event that the fault type of the power module is a DC positive and negative short circuit fault, all the power transistors shall remain locked.

[0009] In some embodiments, the power module includes a two-level three-phase bridge circuit or a three-level three-phase bridge circuit.

[0010] In some embodiments, the AC sides of the power modules in the same converter are connected in parallel via reactors to form the AC interface of the converter; the AC interface is used to connect to one of the following: power grid, motor, electrolytic cell, battery, capacitor, and coil. When the AC interface is connected to the power grid, the positive terminal of the DC side of the power module is connected to the positive busbar through the positive fuse, and the negative terminal of the DC side of the power module is connected to the negative busbar through the negative fuse.

[0011] Secondly, embodiments of this application also provide a fault protection method for a converter system, the converter system comprising: a plurality of converters, each converter comprising at least one power module, the AC side of the power module of the same converter being connected to each other, and a module capacitor being connected between the positive terminal of the DC side and the negative terminal of the DC side of the power module. The positive terminal of the DC side of the power module is connected to the positive busbar through a positive fuse, and / or the negative terminal of the DC side of the power module is connected to the negative busbar through a negative fuse. The fault protection method includes: In the event of a failure of any of the power modules, the positive fuse and / or the negative fuse corresponding to the faulty power module will be blown by discharging the module capacitor corresponding to the non-faulty power module.

[0012] In some embodiments, before discharging the module capacitor corresponding to the non-faulty power module and blowing the positive fuse and / or the negative fuse corresponding to the faulty power module, the fault protection method further includes: Lock out the power transistors of all the power modules and disconnect the AC interfaces of the multiple converters; In the case of an AC-to-DC short circuit fault in the power module, all power transistors in the bridge arm containing the faulty power transistor are turned on. In the event that the fault type of the power module is a DC positive and negative short circuit fault, all the power transistors shall remain locked.

[0013] In some embodiments, the converter system further includes a capacitor bank, the positive terminal of which is connected to the positive busbar, and the negative terminal of which is connected to the negative busbar; The fault protection method further includes: in the event of a fault in any of the power modules, discharging the capacitor bank to blow the positive fuse and / or the negative fuse corresponding to the faulty power module.

[0014] The beneficial effects of this application are as follows: The converter system of this application utilizes module capacitors. When any power module fails, the corresponding module capacitor of the non-faulty power module discharges, actively injecting fusing energy into the fuse of the faulty module. The instantaneous large current generated by the discharge of the module capacitor causes the positive and negative fuses of the faulty module to blow in a very short time, thereby effectively protecting the non-faulty modules. This improves the problem of short-circuit fault current flowing into the non-faulty power module through the busbar between modules, causing damage to the power transistors in the non-faulty modules. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a converter system architecture diagram provided in the embodiments of this application; Figure 2 This is a schematic diagram of a power module based on a two-level three-phase bridge circuit provided in an embodiment of this application; Figure 3 This is a schematic diagram of a power module based on a three-level three-phase bridge circuit provided in an embodiment of this application; Figure 4 This is a schematic diagram showing that all the converters provided in the embodiments of this application are connected to the power grid; Figure 5 This is a schematic diagram showing the converter provided in the embodiments of this application connected to the power grid and the motor respectively; Figure 6 This is an architecture diagram of the control system provided in an embodiment of this application; Figure 7 This is a schematic diagram illustrating the steps of the fault protection method implemented by the control system provided in the embodiments of this application.

[0017] Explanation of reference numerals in the attached figures: 1. Converter; 11. First Converter; 12. Second Converter; 13. AC Interface; 2. Power Module; 21. Power Transistor; 211. Upper Arm Power Transistor; 212. Lower Arm Power Transistor; 3. Module Capacitor; 31. First Capacitor; 32. Second Capacitor; 41. Positive Fuse; 42. Negative Fuse; 51. Positive Busbar; 52. Negative Busbar; 6. Capacitor Bank; 71. First Power Grid; 72. Second Power Grid; 73. Motor; 81. First Isolation Transformer; 82. Second Isolation Transformer; 9. Reactor; 101. Fault Identification Unit; 102. Fault Lockout Unit; 103. Conduction Control Unit; 104. Disconnection Control Unit; P. DC Side Positive; N. DC Side Negative; O. DC Midpoint; D1. Upper Arm Diode; D2. Lower Arm Diode. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0020] like Figure 1 As shown in the figure, this application provides a converter system, including: Multiple converters 1, each converter 1 including at least one power module 2. The number of power modules 2 included in each converter 1 can be the same or different, and can be arbitrarily selected according to actual capacity requirements.

[0021] All power modules 2 within the same converter 1 are connected on their AC sides. In some embodiments, each power module 2 is provided with a reactor 9 on its AC side. The AC sides of all power modules 2 are connected through the reactor 9 to form the AC interface 13 of the converter 1. The AC interface 13 of the converter 1 can be connected to different external devices, such as the power grid, motor 73, electrolytic cell, battery, capacitor or coil, depending on the application scenario.

[0022] Each power module 2 has a positive and a negative terminal on its DC side. A module capacitor 3 is connected between the positive terminal P and the negative terminal N on the DC side. The module capacitor 3 can be placed inside or outside the power module 2, depending on the structural requirements.

[0023] The positive terminal P of the DC side of the power module 2 is connected to the positive busbar 51 through the positive fuse 41, and / or the negative terminal N of the DC side of the power module 2 is connected to the negative busbar 52 through the negative fuse 42. That is to say, depending on different application scenarios, a fuse can be configured only on the positive terminal P of the DC side, or only on the negative terminal N of the DC side, or fuses can be configured on both the positive terminal P of the DC side and the negative terminal N of the DC side.

[0024] The converter system is configured such that, in the event of a failure of any power module 2, the module capacitor 3 corresponding to the non-faulty power module discharges, thereby blowing the positive fuse 41 and / or negative fuse 42 corresponding to the faulty power module.

[0025] When any power module 2 in the converter system experiences an internal short-circuit fault, this application does not rely on the short-circuit current provided by the external power grid. Instead, it can utilize the energy stored in the module capacitor 3 of the parallel non-faulty power module to discharge to the fuse of the faulty power module, thereby quickly blowing the positive fuse 41 and / or negative fuse 42 of the faulty power module and achieving isolation between the faulty power module and the DC bus.

[0026] The following examples illustrate some failure scenarios: assuming... Figure 1 A short circuit fault occurred inside the first power module 2 of the inverter 1 located at the top. At this time, the positive fuse 41 and the negative fuse 42 of the faulty power module have not yet blown, and the faulty power module is still connected to the positive bus 51 and the negative bus 52.

[0027] If no measures are taken, the short-circuit current will flow from the grid side through the fault point. At the same time, the module capacitor 3 in other non-faulty modules connected in parallel with the faulty power module will also discharge to the fault point through the positive bus 51 and the negative bus 52. Because the discharge current is dispersed and lasts for a long time, the fuse blows slowly, causing the body diode of the power transistor 21 inside the non-faulty module to fail before the fuse.

[0028] In this embodiment, after detecting a fault in power module 2, the energy stored in the module capacitor 3 of the non-faulty power module is actively released to the positive fuse 41 and negative fuse 42 of the faulty power module. Because the discharge current is much greater than the conventional short-circuit current and the energy is concentrated, the positive fuse 41 and negative fuse 42 will melt in a very short time, thereby quickly disconnecting the faulty power module and protecting the non-faulty power module.

[0029] Compared to the basic implementation scheme where fuses rely on short-circuit current supplied by the power grid for fusing, the high internal resistance of the power grid and the slow rise rate of the short-circuit current mean that it takes milliseconds or even longer for the fuse to reach the required fusing value. This application utilizes the discharge of module capacitor 3 in the non-faulty power module. The instantaneous current of the capacitor discharge is large and the rise rate is fast, which can cause the fuse to blow in milliseconds or even less time.

[0030] In some embodiments, the power transistor 21 may be an insulated-gate bipolar transistor (IGBT). Since IGBTs have relatively low withstand values, for example, on the order of tens to hundreds of ampere-square seconds, their withstand time is, for example, tens to hundreds of microseconds. In some basic embodiments, the fuse's fusing time is much longer than the body diode's withstand time, causing the body diode of a non-faulty module to fail before the fuse trips. This application effectively protects non-faulty modules by significantly shortening the fusing time, making the fuse's fusing time much shorter than the body diode's withstand time.

[0031] Based on the above embodiments, in order to further improve the fuse breaking speed in case of failure, or in cases where it is not convenient to increase the capacitance value of the module capacitor 3 of each power module 2, for example, due to limitations such as the size, cost or heat dissipation conditions of the power module 2, this application provides another improvement in some embodiments.

[0032] In some embodiments, the converter system further includes: Capacitor bank 6, the positive terminal of capacitor bank 6 is connected to positive bus 51, and the negative terminal of capacitor bank 6 is connected to negative bus 52. The converter system is also configured to, in the event of a failure of any power module 2, discharge through capacitor bank 6 to blow the positive fuse 41 and / or negative fuse 42 corresponding to the faulty power module.

[0033] In this embodiment, the positive terminal of capacitor bank 6 is connected to positive bus 51, and the negative terminal of capacitor bank 6 is connected to negative bus 52. That is, capacitor bank 6 is connected in parallel between positive bus 51 and negative bus 52, and is connected in parallel with the DC side of all power modules 2.

[0034] The capacitor bank 6 may include multiple capacitors connected in series and / or in parallel to meet different capacitance requirements. The capacitor types may include at least one of film capacitors, electrolytic capacitors, and supercapacitors.

[0035] In practice, one or more of the above capacitors can be flexibly selected for series and parallel combinations based on factors such as voltage level, expected discharge current, and installation space.

[0036] When any power module 2 experiences a short-circuit fault, the fuse can be blown by the discharge of the module capacitor 3 inside the non-faulty power modules. However, the discharge energy is limited by the capacitance of the module capacitor 3 and the number of non-faulty power modules. If the number of power modules 2 connected in parallel is small, or the capacitance of the module capacitor 3 is small, the discharge energy may be insufficient to blow the fuse within the required time. This application adds a capacitor bank 6, where the energy stored in the capacitor bank 6 is also discharged to the fault point through the fuse of the faulty power module, significantly increasing the available fusing energy and thus ensuring that the fuse blows within the required time.

[0037] In some embodiments, the module capacitor 3 inside the power module 2 mainly serves the functions of DC-side filtering and voltage support. Its capacitance value is determined based on the ripple voltage requirements under normal operating conditions and is typically small. Intentionally increasing the capacitance value of the module capacitor 3 for fault-tolerant fusing could significantly increase the size of the power module 2. This application, by adding a capacitor bank 6, allows the module capacitor 3 to continue performing its normal operating function, while the capacitor bank 6 provides the large current energy storage required for fault-tolerant fusing. Therefore, the module capacitor 3 of each power module 2 can maintain a small capacitance value, reducing the size of the power module 2.

[0038] In some embodiments, when the number of power modules 2 connected in parallel is small, such as only 2 or 3, the number of non-faulty power modules is limited, and the total energy stored in the module capacitors 3 of the non-faulty power modules may not be sufficient to quickly blow the fuse of the faulty power module. This application addresses this by adding a capacitor bank 6, which ensures that the capacitor bank 6 always provides sufficient fusing energy regardless of the number of power modules 2 connected in parallel, thereby guaranteeing that the fuse blows within the required time.

[0039] In some embodiments, the capacitance value of capacitor bank 6 is determined based on at least one of the number of power modules 2, the capacitance value of module capacitor 3, the fusing value of positive fuse 41, the fusing time of positive fuse 41, the fusing value of negative fuse 42, and the fusing time of negative fuse 42.

[0040] The more power modules 2 there are, the greater the total energy storage of the capacitors in the non-faulty power modules, thus the capacitance requirement for capacitor bank 6 can be appropriately reduced; conversely, the fewer power modules 2 there are, the larger the capacitance of capacitor bank 6 needs to be configured. If the DC-side capacitor value of power module 2 is small, a larger capacitance of capacitor bank 6 needs to be configured; if the module capacitor 3 already has a large capacitance, capacitor bank 6 can be configured to be smaller, or capacitor bank 6 can be omitted. Since each fuse has characteristic parameters required for fusing, in some embodiments, the expression for the characteristic parameters required for fusing can be the value of I²t, where I represents the current (amperes) and t represents the current duration (seconds). The larger the value of I²t, the more energy is required for fusing, and correspondingly, a larger capacitance of capacitor bank 6 needs to be configured.

[0041] In some embodiments, the fault types of the power module 2 include AC to DC side short circuit fault and DC positive and negative short circuit fault. The converter system is also configured to lock out the power transistors 21 of all power modules 2 and disconnect the AC interfaces 13 of multiple converters 1 before discharging the module capacitor 3 corresponding to the non-faulty power module and blowing the positive fuse 41 and / or negative fuse 42 corresponding to the faulty power module. When the fault type of power module 2 is AC to DC side short circuit fault, all power transistors 21 in the bridge arm where the faulty power transistor is located are turned on; In the event of a DC positive and negative short circuit fault in power module 2, all power transistors 21 remain locked.

[0042] In this embodiment, the fault types of the power module 2 include AC to DC side short circuit fault and DC positive and negative short circuit fault.

[0043] An AC-to-DC short circuit fault refers to a short circuit occurring between the AC side of power module 2 and the positive P or negative N of the DC side.

[0044] In some embodiments, the AC-to-DC short circuit of the module includes a short circuit to the positive P terminal of the AC-to-DC side and a short circuit to the negative N terminal of the AC-to-DC side. The AC-to-DC positive P terminal short circuit is a short circuit between any power transistor 21 on the AC side and the positive terminal of the power module 2. The AC-to-DC negative N terminal short circuit is a short circuit between any power transistor 21 on the AC side and the negative terminal of the power module 2. The DC positive and negative short circuit is when all power transistors 21 of the same bridge arm of the power module 2 are simultaneously turned on.

[0045] Different control methods are adopted in the embodiments of this application for the different fault types mentioned above. Therefore, this application needs to identify the fault type first. In some embodiments of this application, the signals used for fault type identification include: short-circuit fault signals of the power transistors 21 of each power module 2, DC side voltage signals of the power module 2, AC side current signals of the power module 2, etc.

[0046] In some embodiments, the fault identification logic of this application includes: If the short-circuit fault signal of power transistor 21 is valid, the DC voltage of power module 2 is higher than the undervoltage protection value, and the AC current of power module 2 is higher than the overcurrent protection value, it is determined to be an AC to DC side short-circuit fault. If the short-circuit fault signal of power transistor 21 is valid, the DC voltage of power module 2 is lower than the undervoltage protection value, and the AC current of power module 2 is higher than the overcurrent protection value, then a DC positive and negative short-circuit fault is determined.

[0047] The principle behind the above fault identification logic is that, under an AC-to-DC short-circuit fault, the short-circuit point is located between the AC and DC sides. Due to the presence of AC side voltage, the DC side capacitor will be reverse-charged by the AC side voltage through the short-circuit point or will maintain a higher voltage. Therefore, the DC voltage will not drop rapidly and will remain at a high level.

[0048] In the event of a DC short-circuit fault, the short-circuit point is directly connected to the DC positive and negative terminals. The energy stored in module capacitor 3 will be discharged through the short-circuit point, causing the DC voltage to drop to a very low level, even close to zero, in a very short time. Therefore, this application uses whether the DC voltage is lower than the undervoltage protection value to distinguish the fault type.

[0049] When a fault is detected in any power module 2, the initial protection action is executed first. Regardless of the fault type, the power transistors 21 of all power modules 2 will be locked out.

[0050] In some embodiments, locking the power transistors 21 of all power modules 2 includes sending a lockout signal to all power of all power modules 2, stopping the drive pulses of all power transistors 21, so as to prevent the fault current in the faulty module from further expanding, and to prevent the power transistors 21 in the non-faulty module from being mis-turned on.

[0051] Furthermore, the converter system cuts off the energy injection from the AC side by disconnecting the switches connected to the AC interface 13 of each converter 1, thus preventing the continuous input of short-circuit current from the AC side. After completing the initial protection actions described above, the converter system executes the corresponding control actions based on the fault type.

[0052] In the case of an AC to DC side short circuit fault, all power transistors 21 of the bridge arm containing the faulty power transistor are turned on, that is, the upper and lower transistors of the bridge arm are turned on simultaneously.

[0053] Taking a short circuit between the AC and DC sides of the lower tube in phase A as an example, the fault is that the lower tube is short-circuited. At this time, the converter system actively turns on the upper tube of phase A. After the upper tube turns on, a low-impedance discharge circuit is formed, flowing from the positive busbar 51 through the positive fuse 41 corresponding to the faulty power module 2, the upper tube, the lower tube, the negative fuse 42, and the negative busbar 52. Through the low-impedance discharge circuit, the energy stored in the module capacitors 3 of all parallel non-faulty power modules and the capacitor bank 6 is discharged rapidly. The discharge current flows through the positive fuse 41 and the negative fuse 42 of the faulty power module, causing the positive fuse 41 and the negative fuse 42 to blow in a very short time, thereby disconnecting the faulty power module.

[0054] When it is detected that the switch of AC interface 13 has been disconnected, the conduction signal of the faulty bridge arm is blocked to avoid unnecessary continuous conduction.

[0055] In the event of a DC short circuit fault, all power transistors 21 remain locked and no additional power transistors 21 are turned on.

[0056] Since a short circuit has already formed between the positive busbar 51, the faulty bridge arm, and the negative busbar 52 when the DC positive and negative terminals are short-circuited, no additional conduction is required. If other power transistors 21 are turned on, the energy stored in the capacitors of more parallel power modules 2 may be introduced to discharge to the short-circuit point, causing all fuses of the high-power modules 2 to withstand large currents, which may cause all fuses to blow.

[0057] This embodiment addresses AC-to-DC short-circuit faults by rapidly isolating the faulty power module and protecting the non-faulty power modules by conducting all power transistors 21 in the bridge arm containing the faulty power transistor. For DC positive-to-negative short-circuit faults, the positive bus 51, the faulty bridge arm, and the negative bus 52 already form a short-circuit loop, eliminating the need for additional conduction. Simultaneously, maintaining the blocked power transistors 21 avoids introducing additional discharge energy and reduces the risk of fault escalation.

[0058] In some embodiments, such as Figure 2 As shown, power module 2 includes a two-level three-phase bridge circuit. This circuit includes six power transistors 21. The upper bridge arm includes three power transistors 211, whose collectors are connected to the positive DC terminal P, and whose emitters are connected to the three-phase nodes A, B, and C. The lower bridge arm includes three power transistors 212, whose emitters are connected to the negative DC terminal N, and whose collectors are connected to the three-phase nodes A, B, and C.

[0059] In some embodiments, such as Figure 3 As shown, the power module 2 includes a three-level three-phase bridge circuit. In addition to the DC positive terminal P and the DC negative terminal N, the DC side of the power module 2 also includes the DC midpoint O. The module capacitor 3 includes a first capacitor 31 connected between the DC positive terminal P and the DC midpoint O, and a second capacitor 32 connected between the DC negative terminal N and the DC midpoint O.

[0060] In some embodiments, each phase arm of the three-level three-phase bridge circuit includes four power transistors 21 and two diodes, for a total of twelve power transistors 21. Each phase upper arm includes two upper arm power transistors 211 connected in series and one upper arm diode D1. The upper ends of the two upper arm power transistors 211 connected in series are connected to the positive terminal P of the DC side, and the lower ends of the two upper arm power transistors 211 connected in series are connected to the three-phase node. The positive terminal of the upper arm diode D1 is connected to the clamping node, and the negative terminal of the upper arm diode D1 is connected to the connection node of the two power transistors 21 connected in series.

[0061] Each lower bridge arm includes two lower bridge arm power transistors 212 connected in series and one lower bridge arm diode D2. The upper ends of the two lower bridge arm power transistors 212 connected in series are respectively connected to the three-phase node, and the lower ends of the two lower bridge arm power transistors 212 connected in series are connected to the negative terminal N of the DC side. The negative terminal of the lower bridge arm diode D2 is connected to the clamping node, and the positive terminal of the lower bridge arm diode D2 is connected to the connection node of the two power transistors 212 connected in series.

[0062] In some embodiments, the AC side of the power module 2 in the same converter 1 is connected in parallel through the reactor 9 to form the AC interface 13 of the converter 1; the AC interface 13 is used to connect one of the following: the power grid, the motor 73, the electrolytic cell, the battery, the capacitor, and the coil.

[0063] In some embodiments, when the AC interface 13 is connected to the power grid, the DC positive terminal P of the power module 2 is connected to the positive busbar 51 through the positive fuse 41, and the DC negative terminal N of the power module 2 is connected to the negative busbar 52 through the negative fuse 42.

[0064] In some embodiments, when the AC interface 13 is connected to one of the following: motor 73, electrolytic cell, battery, capacitor, or coil: The positive terminal P of the DC side of power module 2 is connected to the positive busbar 51 through the positive fuse 41, or; The DC side negative terminal N of power module 2 is connected to the negative busbar 52 through the negative terminal fuse 42, or; The positive terminal P of the DC side of the power module 2 is connected to the positive busbar 51 through the positive fuse 41.

[0065] That is, the DC side of power module 2 can be configured with either a positive fuse 41 or a negative fuse 42, or both positive fuse 41 and negative fuse 42.

[0066] In some embodiments, such as Figure 4 As shown, the converter system includes two converters 1: a first converter 11 and a second converter 12. The AC interface 13 of the first converter 11 is connected to the first power grid 71 via a first isolation transformer 81. The AC interface 13 of the second converter 12 is connected to the second power grid 72 via a second isolation transformer 82. The positive DC terminal P of the power module 2 of both the first and second converters 11 is connected to the positive busbar 51 via a positive fuse 41. The positive and negative terminals of the capacitor bank 6 are connected to the positive busbar 51 and the negative busbar 52, respectively.

[0067] In some embodiments, such as Figure 5 As shown, the converter system includes two converters 1: a first converter 11 and a second converter 12. The AC interface 13 of the first converter 11 is connected to the first power grid 71 through a first isolation transformer 81. The AC interface 13 of the second converter 12 is connected to the motor 73 through a second isolation transformer 82. The difference from the previous embodiment is that the positive DC terminal P of the power module 2 of the first converter 11 is connected to the positive busbar 51 through a positive fuse 41. Similarly, the positive DC terminal P of the power module 2 of the second converter 12 is connected to the positive busbar 51 through a positive fuse 41. The positive and negative terminals of the capacitor bank 6 are connected to the positive busbar 51 and the negative busbar 52, respectively.

[0068] In some embodiments, converter 1 includes voltage source converter 1.

[0069] The embodiments of this application also provide a fault protection method for a converter system. The converter system includes: a plurality of converters 1, each converter 1 including at least one power module 2, the AC side of the power module 2 of the same converter 1 being connected to each other, and a module capacitor 3 being connected between the positive terminal P of the DC side and the negative terminal N of the DC side of the power module 2. The positive terminal P of the DC side of the power module 2 is connected to the positive busbar 51 through the positive fuse 41, and / or the negative terminal N of the DC side of the power module 2 is connected to the negative busbar 52 through the negative fuse 42. Fault protection methods include: In the event of a failure of any power module 2, the module capacitor 3 corresponding to the non-faulty power module discharges, thereby blowing the positive fuse 41 and / or negative fuse 42 corresponding to the faulty power module.

[0070] In some embodiments, before discharging through the module capacitor 3 corresponding to the non-faulty power module and blowing the positive fuse 41 and / or negative fuse 42 corresponding to the faulty power module, the fault protection method further includes: Lock out the power transistors 21 of all power modules 2, and disconnect the AC interfaces 13 of multiple converters 1; When the fault type of power module 2 is AC to DC side short circuit fault, all power transistors 21 in the bridge arm where the faulty power transistor is located are turned on; In the event of a DC positive and negative short circuit fault in power module 2, all power transistors 21 remain locked.

[0071] In some embodiments, the AC-to-DC short circuit of the module includes a short circuit to the positive P terminal of the AC-to-DC side and a short circuit to the negative N terminal of the AC-to-DC side. The AC-to-DC positive P terminal short circuit is a short circuit between any power transistor 21 on the AC side and the positive terminal of the power module 2. The AC-to-DC negative N terminal short circuit is a short circuit between any power transistor 21 on the AC side and the negative terminal of the power module 2. The DC positive and negative short circuit is when all power transistors 21 of the same bridge arm of the power module 2 are simultaneously turned on.

[0072] In some embodiments, the converter system further includes a capacitor bank 6, with the positive terminal of the capacitor bank 6 connected to a positive busbar 51 and the negative terminal of the capacitor bank 6 connected to a negative busbar 52. The fault protection method also includes: in the event of a fault in any power module 2, discharging through capacitor bank 6 to blow the positive fuse 41 and / or negative fuse 42 corresponding to the faulty power module.

[0073] Based on the converter system hardware topology described in the above embodiments, this application provides a control system for implementing a fault protection method in some embodiments, such as... Figure 6 As shown, the control system includes a fault identification unit 101, a fault interlocking unit 102, a conduction control unit 103, and a disconnection control unit 104.

[0074] The fault identification unit 101 is used to monitor the short-circuit fault signals of all power transistors 21 in the module, the DC voltage signal and AC current signal of the power module 2 in real time, and identify the fault status, including AC to DC side positive P short circuit, AC to DC side negative N short circuit and short circuit between the positive and negative terminals of the module 2.

[0075] If the fault identification unit 101 detects a short-circuit fault signal of power transistor 21 in a power module 2, and the DC voltage of the power module 2 is higher than the undervoltage protection value, and the AC current of the power module 2 is higher than the overcurrent protection value, then it identifies an AC-to-DC short-circuit fault in the power module 2 and reports the location of the faulty power transistor to the communication control unit 103.

[0076] If the fault identification unit 101 detects a short circuit fault signal of power transistor 21 in a power module 2, and the DC voltage of the power module 2 is lower than the undervoltage protection value, and the AC current of the power module 2 is higher than the overcurrent protection value, then it identifies a positive and negative short circuit fault in the power module 2 and reports the location of the faulty power transistor to the communication control unit 103.

[0077] The fault blocking unit 102 is used to block the drive pulses of the power transistors 21 of all power modules 2; after the fault blocking unit 102 blocks the drive pulses of the power transistors 21 of all power modules 2, the conduction control unit 103 can still conduct all power transistors 21 of the bridge arm where the faulty power transistor is located.

[0078] The control system based on the above-mentioned fault protection method can quickly identify, accurately judge, and differentiate short-circuit faults, and quickly isolate faulty modules.

[0079] The above control system implements fault protection methods, such as Figure 7 As shown, it includes the following steps: Step S1: The fault identification unit 101 monitors the operating status of the converter system in real time. If a short-circuit fault is detected, the fault status signal is immediately reported to the fault blocking unit 102 and the disconnection control unit 104. The fault status signal, fault type and location of the fault power tube are reported to the conduction control unit 103. In step S2, after receiving the fault status signal, the fault interlocking unit 102 immediately interlocks the drive pulse signal of the power module 2; after receiving the fault status signal, the disconnecting unit control immediately disconnects the connection switch at the AC interface 13. In step S3, the control unit 103 receives a fault status signal. If a cross-pair positive or cross-pair negative short circuit fault occurs, it immediately turns on all power transistors 21 in the bridge arm where the faulty power transistor is located. If a positive or negative short circuit fault occurs, it still blocks the pulses of all power transistors 21. The positive fuse 41 and / or negative fuse 42 of the faulty power module are blown by discharging the DC side capacitor (excluding the faulty module) to the short circuit point through the fuse.

[0080] In step S4, after the conduction control unit 103 detects that the AC interface 13 is disconnected, it immediately blocks the conduction signal of the power tube 21 of the faulty bridge arm of the power module 2.

[0081] The present application provides a detailed description of a converter system and its fault protection method. Specific examples have been used to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present application. At the same time, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the ideas of the present application. Therefore, the content of this specification should not be construed as a limitation of the present application.

Claims

1. A converter system, characterized in that, include: Multiple converters, each converter including at least one power module, the AC side of the power module of the same converter being connected to each other, and a module capacitor being connected between the positive and negative DC side terminals of the power module. The positive terminal of the DC side of the power module is connected to the positive busbar through a positive fuse, and / or the negative terminal of the DC side of the power module is connected to the negative busbar through a negative fuse. The converter system is configured such that, in the event of a failure of any of the power modules, the positive fuse and / or the negative fuse corresponding to the faulty power module is blown by discharging the module capacitor corresponding to the non-faulty power module.

2. The converter system according to claim 1, characterized in that, The converter system also includes: A capacitor bank, wherein the positive terminal of the capacitor bank is connected to the positive busbar, and the negative terminal of the capacitor bank is connected to the negative busbar; The converter system is also configured to, in the event of a failure in any of the power modules, discharge through the capacitor bank to blow the positive fuse and / or the negative fuse corresponding to the faulty power module.

3. The converter system according to claim 2, characterized in that, The capacitor bank includes multiple capacitors connected in series and / or in parallel, and the capacitors include at least one of film capacitors, electrolytic capacitors, and supercapacitors.

4. The converter system according to claim 2, characterized in that, The capacitance value of the capacitor bank is determined based on at least one of the following: the number of power modules, the capacitance value of the module capacitors, the fusing value of the positive fuse, the fusing time of the positive fuse, the fusing value of the negative fuse, and the fusing time of the negative fuse.

5. The converter system according to claim 1, characterized in that, The fault types of the power module include AC to DC side short circuit fault and DC positive and negative short circuit fault. The converter system is also configured to lock out the power transistors of all the power modules and disconnect the AC interfaces of the multiple converters before discharging the module capacitors corresponding to the non-faulty power modules and blowing the positive and / or negative fuses corresponding to the faulty power modules. In the case of an AC-to-DC short circuit fault in the power module, all power transistors in the bridge arm containing the faulty power transistor are turned on. In the event that the fault type of the power module is a DC positive and negative short circuit fault, all the power transistors shall remain locked.

6. The converter system according to claim 1, characterized in that, The power module includes a two-level three-phase bridge circuit or a three-level three-phase bridge circuit.

7. The converter system according to claim 1, characterized in that, The AC sides of the power modules in the same converter are connected in parallel via reactors to form the AC interface of the converter; the AC interface is used to connect to one of the following: power grid, motor, electrolytic cell, battery, capacitor, and coil. When the AC interface is connected to the power grid, the positive terminal of the DC side of the power module is connected to the positive busbar through the positive fuse, and the negative terminal of the DC side of the power module is connected to the negative busbar through the negative fuse.

8. A fault protection method for a converter system, characterized in that, The converter system includes: multiple converters, each converter including at least one power module, the AC side of the power module of the same converter being connected to each other, and a module capacitor being connected between the positive and negative DC side terminals of the power module. The positive terminal of the DC side of the power module is connected to the positive busbar through a positive fuse, and / or the negative terminal of the DC side of the power module is connected to the negative busbar through a negative fuse. The fault protection method includes: In the event of a failure of any of the power modules, the positive fuse and / or the negative fuse corresponding to the faulty power module will be blown by discharging the module capacitor corresponding to the non-faulty power module.

9. The fault protection method according to claim 8, characterized in that, Before discharging the module capacitor corresponding to the non-faulty power module and blowing the positive fuse and / or the negative fuse corresponding to the faulty power module, the fault protection method further includes: Lock out the power transistors of all the power modules and disconnect the AC interfaces of the multiple converters; In the case of an AC-to-DC short circuit fault in the power module, all power transistors in the bridge arm containing the faulty power transistor are turned on. In the event that the fault type of the power module is a DC positive and negative short circuit fault, all the power transistors shall remain locked.

10. The fault protection method according to claim 8, characterized in that, The converter system further includes a capacitor bank, the positive terminal of which is connected to the positive busbar, and the negative terminal of which is connected to the negative busbar. The fault protection method further includes: in the event of a fault in any of the power modules, discharging the capacitor bank to blow the positive fuse and / or the negative fuse corresponding to the faulty power module.

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