Power conversion system and method for fault protection thereof

Abstract

The application discloses a power conversion system and a fault protection method thereof, and relates to the technical field of electronic power, which comprises the following steps: a power conversion unit is provided with at least two capacitors on the first side, and an intermediate node is formed between two adjacent capacitors; a first protection unit and a second protection unit are arranged between the first side of the power conversion unit and a DC bus; the first protection unit is connected with the positive electrode of the first side of the power conversion unit, the positive DC bus and at least one intermediate node, the second protection unit is connected with the negative electrode of the first side of the power conversion unit, the negative DC bus and at least one intermediate node, and the first and second protection units are connected with the capacitors to form a voltage division protection branch; and in the case of a DC bus fault, the connection between the power conversion unit and the DC bus is cut off through the protection unit. The application can cut off the fault path quickly, block the diffusion path of the fault and prevent the fault from spreading in a large range under the high-voltage operation condition.

Description

Technical Field

[0001] This invention relates to the field of electronic power technology, and in particular to a power conversion system and its fault protection method. Background Technology

[0002] As the installed capacity of power conversion systems continues to increase, the operating voltage level of the systems is also increasing. For example, under high-voltage operating conditions of 1000Vdc and above, the electric field energy stored in the DC bus is greater, and a fault will release a large amount of fault energy instantaneously. Once a partial short circuit fault occurs in the DC bus, the fault path cannot be quickly cut off, which can easily cause energy diffusion within the high-voltage system and form a fault chain propagation effect, seriously reducing the operational stability and reliability of the power conversion system.

[0003] Therefore, in order to improve the reliability, fault tolerance and safety protection of power conversion systems under high voltage operation, it is urgent to solve the technical problem of not being able to quickly cut off the fault path when the DC bus fails under high voltage operation conditions, so as to block the spread path of DC bus faults, prevent the fault from spreading on a large scale, and avoid the shutdown of the entire system or damage to equipment. Summary of the Invention

[0004] This invention discloses a power conversion system that can quickly cut off the fault path and block the spread of the fault when a DC bus fault occurs under high-voltage operating conditions, preventing the fault from spreading on a large scale and avoiding the shutdown of the entire system or damage to the equipment. The power conversion system includes: at least one power conversion unit, wherein at least two capacitors connected in series are provided on the first side of the power conversion unit, and an intermediate node is formed between each two adjacent capacitors. A protection unit is provided between the first side of at least one power conversion unit and the DC bus, the protection unit including a first protection unit and a second protection unit; The first protection unit is connected to the positive terminal, the positive DC bus and at least one intermediate node on the first side of the power conversion unit, so that the first protection unit and the capacitor form a first voltage divider protection branch. The second protection unit is connected to the negative terminal, negative DC bus and at least one intermediate node on the first side of the power conversion unit, so that the second protection unit and the capacitor form a second voltage divider protection branch. The protection unit is used to disconnect the power conversion unit connected to the protection unit from the DC bus in the event of a DC bus fault.

[0005] Optionally, the first protection unit includes at least one first switch module and at least one first unidirectional conduction module; The second protection unit includes at least one second switch module and at least one second unidirectional conduction module.

[0006] Optionally, each first switch module and each first unidirectional conduction module, together with at least one capacitor, constitute a first voltage divider protection branch; each second switch module and each second unidirectional conduction module, together with at least one capacitor, constitute a second voltage divider protection branch.

[0007] Optionally, when the number of the first switching module and the first unidirectional conduction module is 1, the first end of the first switching module is connected to the positive terminal of the first side of the power conversion unit, and the second end is connected to the positive DC bus and the first end of the first unidirectional conduction module; the second end of the first unidirectional conduction module is connected to an intermediate node. Alternatively, if the number of first switching modules and first unidirectional conduction modules is greater than 1, multiple first switching modules are connected in series between the positive terminal and the positive DC bus on the first side of the power conversion unit; the first end of each first unidirectional conduction module is connected to the second end of a first switching module, and the second end of each first unidirectional conduction module is connected to an intermediate node.

[0008] Optionally, when the number of the second switching module and the second unidirectional conduction module is 1, the second end of the second switching module is connected to the negative terminal of the first side of the power conversion unit, the first end is connected to the negative DC bus and the second end of the second unidirectional conduction module; the first end of the second unidirectional conduction module is connected to an intermediate node. Alternatively, if the number of second switching modules and second unidirectional conduction modules is greater than 1, multiple second switching modules are connected in series between the negative terminal and the negative DC bus on the first side of the power conversion unit; the second end of each second unidirectional conduction module is connected to the first end of a second switching module, and the first end of each second unidirectional conduction module is connected to an intermediate node.

[0009] Optionally, the protection unit is used to shut down the first and second switch modules in the event of a DC bus fault, thereby disconnecting the power conversion unit from the DC bus.

[0010] Optionally, turning off the first switch module and the second switch module includes turning off the first switch module sequentially according to a preset first timing sequence; and / or turning off the second switch module sequentially according to a preset second timing sequence.

[0011] Optionally, the protection unit further includes a third protection unit; the third protection unit is disposed between the positive DC bus and the first protection unit, and / or, the third protection unit is disposed between the negative DC bus and the second protection unit; The third protection unit is used to disconnect the power conversion unit from the DC bus in the event of a fault in the power conversion unit connected to the third protection unit.

[0012] Optionally, the power conversion system includes at least one power conversion module, the power conversion module includes multiple power conversion units, the first side of the multiple power conversion units is connected in parallel to the combiner point and then connected to the DC bus, and a main circuit protection unit is set between the combiner point and the DC bus. The main circuit protection unit is used to disconnect the power conversion module from the DC bus in the event of a fault in the power conversion unit of the power conversion module and / or a fault in the DC bus.

[0013] This invention also provides a fault protection method for a power conversion system. Under high-voltage operating conditions, in the event of a DC bus fault, the fault path can be quickly cut off, blocking the fault propagation path and preventing widespread fault spread, thus avoiding system shutdown or equipment damage. This method is applied to the aforementioned power conversion system and includes: In the event of a DC bus fault, the protection unit connected to the power conversion unit disconnects the power conversion unit from the DC bus.

[0014] In this embodiment of the invention, the power conversion system includes at least one power conversion unit. At least two capacitors connected in series are disposed on the first side of the power conversion unit, with an intermediate node formed between each pair of adjacent capacitors. A protection unit is disposed between the first side of the at least one power conversion unit and a DC bus. The protection unit includes a first protection unit and a second protection unit. The first protection unit connects the positive terminal of the first side of the power conversion unit, the positive DC bus, and at least one intermediate node, so that the first protection unit and the capacitors form a first voltage divider protection branch. The second protection unit connects the negative terminal of the first side of the power conversion unit, the negative DC bus, and at least one intermediate node, so that the second protection unit and the capacitors form a second voltage divider protection branch. The protection unit is used to disconnect the connection between the power conversion unit connected to it and the DC bus in the event of a DC bus fault. Thus, under high-voltage conditions, by utilizing the bus capacitors on the first side of the power conversion unit and the protection unit to construct a voltage divider protection branch, if a DC bus fault occurs, the connection between each power conversion unit and the DC bus can be disconnected through the protection unit between each power conversion unit and the DC bus, thereby preventing fault propagation and avoiding system failure or damage to critical equipment. Attached Figure Description

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

[0016] In the attached diagram: Figure 1 A schematic diagram of an existing power conversion system; Figure 2 This is a schematic diagram of a DC-DC circuit topology; Figure 3 This is a schematic diagram of another DC-DC circuit topology; Figure 4 This is a schematic diagram of a DCAC circuit topology; Figure 5 A structural diagram of a power conversion system provided in an embodiment of the present invention; Figure 6 This is a connection diagram of a protection unit when the number of capacitors is 3, provided in an embodiment of the present invention; Figure 7 This is a connection diagram of another protection unit when the number of capacitors is 3, as provided in an embodiment of the present invention. Figure 8 This is a connection diagram of a protection unit when the number of capacitors is 4, provided in an embodiment of the present invention; Figure 9 This is a structural diagram of another power conversion system provided in an embodiment of the present invention; Figure 10 This is a structural diagram of another power conversion system provided in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0018] In the description of this specification, the terms "comprising," "including," "having," and "containing" are open-ended terms, meaning that they include but are not limited to. The terms "an embodiment," "a specific embodiment," "some embodiments," and "for example," etc., refer to specific features, structures, or characteristics described in connection with that embodiment or example that are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. The order of steps involved in the various embodiments is used to illustrate the implementation of this application, and the order of steps is not limited and can be adjusted appropriately as needed.

[0019] In the description of this specification, the terms "first" and "second," etc., are used to distinguish different objects or to distinguish different treatments of the same object, rather than to describe a specific order of objects.

[0020] In the description of this specification, "and / or" is merely a way of describing the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0021] Research has revealed that existing power conversion systems urgently need to address the technical challenge of rapidly cutting off fault paths when a DC bus fault occurs under high-voltage operating conditions. This is to block the propagation path of the DC bus fault, prevent the fault from spreading widely, and avoid causing the entire system to shut down or equipment to be damaged.

[0022] For example, refer to Figure 1 This is a schematic diagram of an existing power conversion system, consisting of one or more DC power supplies and DC-DC converters connected in parallel, exchanging energy with a DC-AC converter via a DC bus. Typically, in high-voltage power conversion systems of 1000Vdc and above, [the following is a description of a similar system] can be used. Figure 2 and Figure 3 The DCDC circuit topology shown and Figure 4 The DCAC circuit topology shown has the problem of not being able to provide timely protection and fault isolation if the DC bus fails under high voltage conditions.

[0023] Based on this, embodiments of the present invention provide a power conversion system. The power conversion system includes at least one power conversion unit, and N capacitors connected in series are disposed on the first side of the power conversion unit, where N is an integer greater than or equal to 2, and an intermediate node is formed between every two adjacent capacitors, for a total of N-1 intermediate nodes.

[0024] A protection unit is provided between the first side of at least one power conversion unit and the DC bus. The protection unit includes a first protection unit and a second protection unit. The first protection unit is connected to the positive terminal, the positive DC bus and at least one intermediate node on the first side of the power conversion unit, so that the first protection unit and the capacitor form a first voltage divider protection branch. The second protection unit is connected to the negative terminal, negative DC bus and at least one intermediate node on the first side of the power conversion unit, so that the second protection unit and the capacitor form a second voltage divider protection branch. The protection unit is used to disconnect the power conversion unit connected to the protection unit from the DC bus in the event of a DC bus fault.

[0025] Thus, in this embodiment of the invention, the bus capacitor on the first side of the power conversion unit and the protection unit are used to construct a voltage divider protection branch. Under high voltage conditions, if the DC bus fails, the connection between the power conversion unit and the DC bus can be cut off through the protection unit between each power conversion unit and the DC bus, thereby preventing the fault from spreading and also preventing the entire system from being paralyzed or the critical equipment from being damaged.

[0026] It should be noted that the power conversion unit in the embodiments of the present invention can be a DC-DC conversion unit, an AC-DC conversion unit, or a bidirectional DC-AC conversion unit, etc. It is only necessary to ensure that the first side of the power conversion unit connected to the DC bus has at least two capacitors connected in series (i.e., bus capacitors).

[0027] It should also be noted that a protection unit may be set only between the first side of some power conversion units and the DC bus; or a protection unit may be set between the first side of each power conversion unit and the DC bus. The specific settings can be differentiated based on the actual application scenario.

[0028] In one embodiment, the first protection unit may include at least one first switch module and at least one first unidirectional conduction module; the second protection unit may include at least one second switch module and at least one second unidirectional conduction module.

[0029] In specific implementation, the first switching module and the second switching module can be a single switching transistor or multiple switching transistors connected in parallel; the first unidirectional conduction module and the second unidirectional conduction module can be a single diode or multiple diodes connected in series or a switching transistor with anti-parallel diodes.

[0030] In this embodiment of the invention, the total number of the first switch module and the second switch module, and the total number of the first unidirectional conduction module and the second unidirectional conduction module are related to the number of capacitors: the total number of the first switch module and the second switch module, and the total number of the first unidirectional conduction module and the second unidirectional conduction module are all the same as the number of capacitors, or the total number of the first switch module and the second switch module, and the total number of the first unidirectional conduction module and the second unidirectional conduction module are less than the number of capacitors.

[0031] In one embodiment, when the total number of the first switch module and the second switch module, and the total number of the first unidirectional conduction module and the second unidirectional conduction module are set to be the same as the number of capacitors, each first switch module and each first unidirectional conduction module, together with a capacitor, constitute a first voltage divider protection branch; each second switch module and each second unidirectional conduction module, together with a capacitor, constitute a second voltage divider protection branch.

[0032] In one embodiment, when the total number of the first switch module and the second switch module, and the total number of the first unidirectional conduction module and the second unidirectional conduction module are set to be less than the number of capacitors, each first switch module and each first unidirectional conduction module, together with one or more capacitors, constitute a first voltage divider protection branch; each second switch module and each second unidirectional conduction module, together with one or more capacitors, constitute a second voltage divider protection branch.

[0033] In one embodiment, the number of first switch modules and first unidirectional conduction modules is the same in the first protection unit; the number of second switch modules and second unidirectional conduction modules is the same in the second protection unit.

[0034] Specifically, when the number of the first switching module and the first unidirectional conduction module is 1, the first end of the first switching module is connected to the positive terminal of the first side of the power conversion unit, and the second end is connected to the positive DC bus and the first end of the first unidirectional conduction module; the second end of the first unidirectional conduction module is connected to an intermediate node. Alternatively, if the number of first switching modules and first unidirectional conduction modules is greater than 1, multiple first switching modules are connected in series between the positive terminal and the positive DC bus on the first side of the power conversion unit; the first end of each first unidirectional conduction module is connected to the second end of a first switching module, and the second end of each first unidirectional conduction module is connected to an intermediate node.

[0035] Specifically, when the number of the second switching module and the second unidirectional conduction module is 1, the second end of the second switching module is connected to the negative terminal of the first side of the power conversion unit, and the first end is connected to the negative DC bus and the second end of the second unidirectional conduction module; the first end of the second unidirectional conduction module is connected to an intermediate node. Alternatively, if the number of second switching modules and second unidirectional conduction modules is greater than 1, multiple second switching modules are connected in series between the negative terminal and the negative DC bus on the first side of the power conversion unit; the second end of each second unidirectional conduction module is connected to the first end of a second switching module, and the first end of each second unidirectional conduction module is connected to an intermediate node.

[0036] In this way, the first and second protection units mentioned above can form a multi-stage voltage divider protection branch with the capacitor. Under high-voltage conditions, the multi-stage voltage divider protection branch divides the voltage step by step along the direction of voltage transmission. The switching transistor of the first switching module only needs to withstand 1 / n of the total input voltage (where n is the number of voltage divider stages), which significantly reduces the voltage withstand requirements of the switching transistor. There is no need to use ultra-high voltage withstand power devices, greatly reducing the cost of high-voltage power devices. Moreover, it can avoid the risks of breakdown and leakage caused by the switching transistor being subjected to excessively high voltage, and the reliability of the switching transistor under high-voltage conditions is significantly improved.

[0037] In one embodiment, the protection unit is used to shut down the first and second switch modules in the event of a DC bus fault, thereby disconnecting the power conversion unit from the DC bus.

[0038] The process of turning off the first switch module and the second switch module may include turning off the first switch module sequentially according to a preset first timing sequence; and / or turning off the second switch module sequentially according to a preset second timing sequence.

[0039] Specifically, if there is only one first switch module and one second switch module, then the first switch module and the second switch module can be directly turned off.

[0040] If there are multiple first switch modules and only one second switch module, the first switch modules can be turned off sequentially according to a preset first timing sequence, and the second switch module can be turned off directly.

[0041] If there is one first switch module and multiple second switch modules, the second switch modules can be turned off sequentially according to the preset second timing sequence, and the first switch module can be turned off directly.

[0042] If there are multiple first switch modules and multiple second switch modules, the first switch modules can be turned off sequentially according to a preset first timing sequence, and the second switch modules can be turned off sequentially according to a preset second timing sequence.

[0043] The aforementioned preset first timing sequence can be to turn off the first switching module step by step along the positive terminal to the positive DC bus direction of the first side of the power conversion unit; the aforementioned preset second timing sequence can be to turn off the second switching module step by step along the negative terminal to the negative DC bus direction of the first side of the power conversion unit.

[0044] In this way, by turning off the corresponding switching modules step by step along the direction from the power conversion unit to the DC bus, the potential on both sides of the power conversion unit can be continuously clamped during the turn-off process to avoid overvoltage breakdown of the power switch caused by potential floating. At the same time, the energy stored in the discharge circuit is discharged step by step to suppress the voltage spikes and inrush currents at the moment of turn-off, reduce the electrical stress of the power devices, and improve the safety and operational reliability of disconnecting the power conversion unit from the DC bus.

[0045] As an example, see reference Figure 5 This is a structural diagram of a power conversion system provided in an embodiment of the present invention. Figure 5 In the diagram, the power conversion system includes two power conversion units 1. Each power conversion unit 1 has two capacitors (N=2) connected in series on its first side, namely C1 and C2, and an intermediate node P is formed between adjacent capacitors C1 and C2. The first side of the two power conversion units 1 is connected to the DC bus.

[0046] In this embodiment, a protection unit 2 is provided between the first side of each power conversion unit 1 and the DC bus; the protection unit 2 includes a first protection unit 21 and a second protection unit 22.

[0047] The first protection unit 21 is connected to the positive terminal, intermediate node P and positive DC bus of the first side of the power conversion unit 1. The first protection unit 21 and capacitor C1 form a first voltage divider protection branch. The second protection unit 22 is connected to the negative terminal, intermediate node P and negative DC bus of the first side of the power conversion unit 1. The second protection unit 22 and capacitor C2 form a second voltage divider protection branch.

[0048] Based on this, if the DC bus fails, the connection between each power conversion unit 1 and the DC bus can be cut off by the protection unit 2 connected to the power conversion unit 1. In this way, the impact of the fault on the normally operating power conversion unit can be avoided, thereby preventing the entire system from being paralyzed or the critical equipment from being damaged.

[0049] Furthermore, the first protection unit and the second protection unit together with the capacitor on the first side of the power conversion unit form a voltage divider protection branch. Under high voltage conditions, the voltage divider protection branch divides the voltage of the DC bus, reducing the voltage withstand requirements of the switching transistors and eliminating the need to select ultra-high voltage withstand power devices, thus significantly reducing the cost of high voltage power devices.

[0050] Specifically, the first protection unit 21 includes a first switch module Q1 and a first unidirectional conduction module D1, and the second protection unit includes a second switch module Q2 and a second unidirectional conduction module D2.

[0051] In specific implementation, refer to Figure 5 The first protection unit 21 may include a first switch module Q1 and a first unidirectional conduction module D1; the second protection unit 22 includes a second switch module Q2 and a second unidirectional conduction module D2.

[0052] The first switching module Q1 and the second switching module Q2 can be a single power switch or multiple power switches connected in parallel; the first unidirectional conduction module D1 and the second unidirectional conduction module D2 can be diodes or switching transistors with anti-parallel diodes.

[0053] When the number of capacitors N=2, the connection method of the first protection unit 21 and the second protection unit 22 in the power conversion system can be as follows: the first end of Q1 is connected to the positive terminal of the first side of the power conversion unit 1, the second end of Q1 is connected to the cathode (first end) of D1 and the positive DC bus, and the anode (second end) of D1 is connected to the intermediate node P; the first end of Q2 is connected to the anode (second end) of D2 and the negative DC bus, the second end of Q2 is connected to the negative terminal of the first side of the power conversion unit 1, and the cathode (first end) of D2 is connected to the intermediate node P.

[0054] It should be noted that the first and second terminals of Q1 and Q2 can be the source or drain of the power switching transistor. The connection method varies depending on the type of power switching transistor, and no specific limitation is made here. Q1 and Q2 are used to control the on / off connection between the power conversion unit and the DC bus. D1 and D2 serve as the current freewheeling path for the capacitors they are connected to.

[0055] The protection unit, in the event of a fault in the power conversion unit connected to it or a fault in the DC bus, shuts off the first switch module Q1 and the second switch module Q2 to disconnect the power conversion unit from the DC bus.

[0056] In this way, Q1, D1, and C1 form the first voltage divider protection branch, and Q2, D2, and C2 form the second voltage divider protection branch. The bus capacitor can be used as a turn-off buffer and voltage clamp. Compared with the existing technology that uses a single high-voltage power transistor or two low-voltage power transistors connected in series to form a protection unit, there is no problem of difficult switch selection, which can reduce costs. It can also avoid the problem of one transistor being overstressed due to different turn-off speeds of the two low-voltage power transistors connected in series, thus reducing control complexity.

[0057] As an example, see reference Figure 6 This is a structural diagram of a protection unit connection method provided in an embodiment of the present invention. When the number of capacitors N=3, there is a first intermediate node P1 and a second intermediate node P2. The first protection unit 21 may include a first switch module Q1 and a first unidirectional conduction module D1; the second protection unit 22 includes a second switch module Q2 and a second unidirectional conduction module D2.

[0058] The connection method of the first protection unit 21 and the second protection unit 22 in the power conversion system can be as follows: the first end of Q1 is connected to the positive terminal of the first side of the power conversion unit 1, the second end of Q1 is connected to the cathode (first end) of D1 and the positive DC bus, and the anode (second end) of D1 is connected to the second intermediate node P2; the first end of Q2 is connected to the anode (second end) of D2 and the negative DC bus, the second end of Q2 is connected to the negative terminal of the first side of the power conversion unit 1, and the cathode (first end) of D2 is connected to the first intermediate node P1. In this way, Q1, D1, C1 and C2 constitute the first voltage divider protection branch, and Q2, D2, C2 and C3 constitute the second voltage divider protection branch.

[0059] As an example, see reference Figure 7 This is a structural diagram of another protection unit connection method provided in an embodiment of the present invention. Figure 6 The difference is, Figure 7In the first protection unit 21, there are two first switch modules Q11 and Q12, and two first unidirectional conduction modules D11 and D12; the second protection unit 22 includes one second switch module Q2 and one second unidirectional conduction module D2.

[0060] The connection method of the first protection unit 21 and the second protection unit 22 in the power conversion system can be as follows: the first end of Q11 is connected to the positive terminal of the first side of the power conversion unit 1, and the second end of Q11 is connected to the first end of Q12 and the cathode (first end) of D11; the second end of Q12 is connected to the positive DC bus and the cathode (first end) of D12, that is, Q11 and Q12 are connected in series between the positive terminal and the positive DC bus of the first side of the power conversion unit; the anode (second end) of D11 is connected to the first intermediate node P1; the anode (second end) of D12 is connected to the second intermediate node P2. The first end of Q2 is connected to the anode (second end) of D2 and the negative DC bus, the second end of Q2 is connected to the negative terminal of the first side of the power conversion unit 1, and the cathode (first end) of D2 is connected to the second intermediate node P2. Thus, Q11, D11, and C1 constitute the first voltage divider protection branch of the first level, Q12, D12, C1, and C2 constitute the first voltage divider protection branch of the second level, forming a multi-level first voltage divider protection branch; Q2, D2, and C3 constitute the second voltage divider protection branch.

[0061] In the event of a DC bus fault, the aforementioned protection unit can, when shutting down the first and second switch modules, first shut down Q11, then Q12, and directly shut down the second switch module Q2 according to a preset first timing sequence, thereby cutting off the connection between the power conversion unit and the DC bus.

[0062] As an example, see reference Figure 8 When N=4, the intermediate nodes include the first intermediate node P1, the second intermediate node P2 and the third intermediate node P3. The first protection unit 21 includes two first switch modules Q11 and Q12, and two first unidirectional conduction modules D11 and D12. The second protection unit 22 includes two second switch modules Q21 and Q22, and two second unidirectional conduction modules D21 and D22.

[0063] The connection method of the first protection unit and the second protection unit in the power conversion system can be as follows: the first end of Q11 is connected to the positive terminal of the first side of the power conversion unit 1, and the second end of Q11 is connected to the first end of Q12 and the cathode (first end) of D11; the second end of Q12 is connected to the positive DC bus and the cathode (first end) of D12, that is, Q11 and Q12 are connected in series between the positive terminal and the positive DC bus of the first side of the power conversion unit; the anode (second end) of D11 is connected to the first intermediate node P1; the anode (second end) of D12 is connected to the second intermediate node P2. The second end of Q21 is connected to the negative terminal of the first side of the power conversion unit, the first end of Q21 is connected to the anode (second end) of D21 and the second end of Q22, and the first end of Q22 is connected to the negative DC bus, that is, Q21 and Q22 are connected in series between the negative terminal and the negative DC bus of the first side of the power conversion unit; the cathode (first end) of D21 is connected to the third intermediate node P3, and the cathode (first end) of D22 is connected to the second intermediate node P2. Thus, Q11, D11, and C1 constitute the first voltage divider protection branch of the first level, Q12, D12, C1, and C2 constitute the first voltage divider protection branch of the second level, forming a multi-level first voltage divider protection branch; Q21, D21, and C4 constitute the second voltage divider protection branch of the first level, and Q22, D22, C3, and C4 constitute the second voltage divider protection branch of the second level, forming a multi-level second voltage divider protection branch.

[0064] In the event of a DC bus fault, the aforementioned protection unit can, when shutting down the first and second switch modules, first shut down Q11 and then Q12 according to a preset first timing sequence, and then shut down Q21 and then Q22 according to a preset second timing sequence, thereby cutting off the connection between the power conversion unit and the DC bus.

[0065] In one embodiment, the protection unit may further include a third protection unit F1; the third protection unit is disposed between the positive DC bus and the first protection unit, and / or, the third protection unit is disposed between the negative DC bus and the second protection unit; The third protection unit is used to disconnect the power conversion unit from the DC bus in the event of a fault in the power conversion unit connected to the third protection unit.

[0066] In specific implementation, for example, Figure 9 As shown, the third protection unit F1 is located between the positive DC bus and the first protection unit. The third protection unit F1 can be a fuse, circuit breaker, etc. The third protection unit F1 can be an overcurrent protection device connected in series in the circuit. When the power conversion unit connected to the third protection unit fails, the current in the circuit increases, which in turn causes the third protection unit to burn out or disconnect. In this way, it can ensure that the fault circuit is disconnected and electrically isolated when the power conversion unit fails, so as to avoid affecting the operation of the entire system.

[0067] In one embodiment, the power conversion system may further include at least one power conversion module, each power conversion module including multiple power conversion units, the first side of the multiple power conversion units being connected in parallel to the busbar and then connected to the DC bus, and a main circuit protection unit being provided between the busbar and the DC bus. The main circuit protection unit is used to disconnect the power conversion module from the DC bus in the event of a fault in any power conversion unit of the power conversion module.

[0068] In specific implementation, for example, refer to Figure 10 The power conversion system includes two power conversion modules, each power conversion module includes two power conversion units 1. The first side of the two power conversion units 1 is connected in parallel to the busbar and then connected to the DC bus. In this embodiment of the invention, a main circuit protection unit 3 is set between the busbar of each power conversion module and the DC busbar. The main circuit protection unit 3 can be a power switch, circuit breaker, disconnector, etc. The switching form of the main circuit protection unit 3 can be set according to actual needs and is not specifically limited here.

[0069] In this way, by setting a main circuit protection unit between the busbar of each power conversion module and the DC bus, in the event of a fault in any power conversion unit of the power conversion module, the main circuit protection unit disconnects the power conversion module from the DC bus, thereby ensuring that other power conversion modules or power conversion units connected to the DC bus can operate normally.

[0070] Based on the power conversion system described above, this embodiment of the invention also provides a fault protection method for the power conversion system. Since the principle of this fault protection method in solving the problem is similar to that of the power conversion system described above, the implementation of this fault protection method can refer to the implementation of the power conversion system, and the repeated parts will not be described again.

[0071] Fault protection methods for power conversion systems include: In the event of a DC bus fault, the protection unit connected to the power conversion unit will disconnect the power conversion unit from the DC bus.

[0072] In one embodiment, it also includes: In the event of a power conversion unit failure, the connection between the power conversion unit and the DC bus is severed by disconnecting the third protection unit.

[0073] In one embodiment, it also includes: In the event of a power conversion unit failure and / or a DC bus failure in the power conversion module, the connection between the power conversion module and the DC bus will be disconnected through the main circuit protection unit of the power conversion module.

[0074] In this embodiment of the invention, when a DC bus fault occurs, the connection between each power conversion unit and the DC bus can be cut off through the protection unit between each power conversion unit and the DC bus, thereby preventing the fault from spreading and avoiding system paralysis or damage to critical equipment. Furthermore, by constructing a voltage divider protection branch using the bus capacitor on the first side of the power conversion unit and the protection unit, high-voltage power switching transistors are not required for the selection of the first and second switching modules, reducing hardware costs. It also eliminates the need to connect multiple low-voltage power switching transistors in series for protection. The first and second voltage divider protection branches utilize the bus capacitor as a turn-off buffer and voltage clamp, preventing overstress issues caused by inconsistent turn-off speeds of the series-connected power switching transistors, thus improving the system's tolerance to control errors.

[0075] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0076] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0077] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0078] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0079] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A power conversion system, characterized by, It includes at least one power conversion unit, and the first side of the power conversion unit is provided with at least two capacitors connected in series, and an intermediate node is formed between each pair of adjacent capacitors; A protection unit is provided between the first side of at least one power conversion unit and the DC bus, the protection unit including a first protection unit and a second protection unit; The first protection unit is connected to the positive terminal, the positive DC bus and at least one intermediate node on the first side of the power conversion unit, so that the first protection unit and the capacitor form a first voltage divider protection branch. The second protection unit is connected to the negative terminal, negative DC bus and at least one intermediate node on the first side of the power conversion unit, so that the second protection unit and the capacitor form a second voltage divider protection branch. The protection unit is used to disconnect the power conversion unit connected to the protection unit from the DC bus in the event of a DC bus fault.

2. The power conversion system as described in claim 1, characterized in that, The first protection unit includes at least one first switch module and at least one first unidirectional conduction module; The second protection unit includes at least one second switch module and at least one second unidirectional conduction module.

3. The power conversion system as described in claim 2, characterized in that, Each first switch module and each first unidirectional conduction module, together with at least one capacitor, constitute a first voltage divider protection branch; each second switch module and each second unidirectional conduction module, together with at least one capacitor, constitute a second voltage divider protection branch.

4. The power conversion system according to any one of claims 2-3, characterized in that, When the number of the first switching module and the first unidirectional conduction module is 1, the first end of the first switching module is connected to the positive terminal of the first side of the power conversion unit, and the second end is connected to the positive DC bus and the first end of the first unidirectional conduction module; the second end of the first unidirectional conduction module is connected to an intermediate node. Alternatively, if the number of first switching modules and first unidirectional conduction modules is greater than 1, multiple first switching modules are connected in series between the positive terminal and the positive DC bus on the first side of the power conversion unit; the first end of each first unidirectional conduction module is connected to the second end of a first switching module, and the second end of each first unidirectional conduction module is connected to an intermediate node.

5. The power conversion system as described in claim 4, characterized in that, When the number of the second switching module and the second unidirectional conduction module is 1, the second end of the second switching module is connected to the negative terminal of the first side of the power conversion unit, the first end is connected to the negative DC bus and the second end of the second unidirectional conduction module; the first end of the second unidirectional conduction module is connected to an intermediate node. Alternatively, if the number of second switching modules and second unidirectional conduction modules is greater than 1, multiple second switching modules are connected in series between the negative terminal and the negative DC bus on the first side of the power conversion unit; the second end of each second unidirectional conduction module is connected to the first end of a second switching module, and the first end of each second unidirectional conduction module is connected to an intermediate node.

6. The power conversion system as described in claim 2, characterized in that, The protection unit is used to shut down the first and second switch modules in the event of a DC bus fault, thereby disconnecting the power conversion unit from the DC bus.

7. The power conversion system as described in claim 6, characterized in that, The shutting off of the first switch module and the second switch module includes shutting off the first switch module sequentially according to a preset first timing sequence; and / or shutting off the second switch module sequentially according to a preset second timing sequence.

8. The power conversion system as described in claim 1, characterized in that, The protection unit further includes a third protection unit; the third protection unit is disposed between the positive DC bus and the first protection unit, and / or, the third protection unit is disposed between the negative DC bus and the second protection unit; The third protection unit is used to disconnect the power conversion unit from the DC bus in the event of a fault in the power conversion unit connected to the third protection unit.

9. The power conversion system as described in claim 1, characterized in that, The power conversion system includes at least one power conversion module, and the power conversion module includes multiple power conversion units. The first side of the multiple power conversion units is connected in parallel to the combiner point and then connected to the DC bus. A main circuit protection unit is set between the combiner point and the DC bus. The main circuit protection unit is used to disconnect the power conversion module from the DC bus in the event of a fault in the power conversion unit of the power conversion module and / or a fault in the DC bus.

10. A fault protection method for a power conversion system, characterized in that, Applied to the power conversion system as described in any one of claims 1-9, the method comprises: In the event of a DC bus fault, the protection unit connected to the power conversion unit disconnects the power conversion unit from the DC bus.

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