Energy storage commutation circuit and system

Abstract

The invention discloses an energy storage commutation circuit and system, and the circuit comprises an energy storage module which comprises a plurality of energy storage units which are connected in series; the energy storage module is used for controlling the input and output of a plurality of energy storage units so as to generate periodic multi-level voltage; the current conversion module is connected with the energy storage module and comprises a first bridge arm group and a second bridge arm group; the auxiliary reversing module is connected in series with the plurality of energy storage units, or is connected with at least one of the first bridge arm group and the second bridge arm group; the auxiliary commutation module is used for forming a resonance circuit with stray inductance on a loop in a commutation time interval; and the commutation module is used for carrying out commutation on the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group in the commutation time interval under the condition that the loop current meets the zero current condition so as to generate a single-phase alternating current voltage. According to the invention, commutation can be carried out under a zero-current condition, the turn-off loss of the device is reduced, and the service life of the device is prolonged.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to an energy storage commutation circuit and system. Background Art

[0002] Energy storage equipment in the power grid can store and release electrical energy, and can play an important role in scenarios such as peak and frequency regulation, new energy consumption, and large-scale new energy transmission. It is one of the important equipment that is indispensable for building a new power system.

[0003] Currently, MCCs (Modular Commuted Converters) can be used to connect three-phase energy storage to the AC grid. Each phase circuit can include a DC energy storage module and a high-load commutation H-bridge circuit. The DC energy storage module includes multiple battery modules, each connected to a corresponding half-bridge module. The half-bridge module controls the switching on and off of the battery modules. Using multi-level technology, the half-bridge module controls the switching on and off of the battery, and can output N+1 voltage levels between 0 and N times Ubat (N is the number of battery modules, and Ubat is the battery voltage), thus achieving multi-level voltage output.

[0004] Because the DC energy storage module uses a half-bridge module, it can only output a positive AC voltage signal, equivalent to an AC voltage signal in the positive half-cycle. By utilizing a high-load commutation H-bridge circuit, it is possible to achieve multi-level voltage output in both positive and reverse directions by controlling the conduction of the switching devices in the H-bridge circuit. For example, in two consecutive positive AC voltage cycles, the H-bridge circuit can reverse the AC voltage signal in the second cycle, generating an AC voltage signal equivalent to a sinusoidal signal at the output.

[0005] However, in the aforementioned embodiment, due to the typical distance between the DC energy storage module and the H-bridge circuit, a certain amount of stray inductance is generated when connecting them via cables. Since the DC current in the loop is high during commutation, the current reversal during commutation will produce a large current change, i.e., a large current change rate di / dt. At this high current change rate, the stray inductance in the loop cable will generate an excessively high induced voltage, thereby affecting the normal commutation process of the H-bridge circuit and even causing damage to the device. Summary of the Invention

[0006] The present application provides an energy storage commutation circuit and system, which can improve the technical problem that a large induced voltage is generated during the commutation process of the multi-level technology, thereby affecting the commutation process of the multi-level voltage.

[0007] In a first aspect, the present application provides an energy storage commutation circuit, comprising:

[0008] An energy storage module, comprising a plurality of energy storage units connected in series; the energy storage module is used to control the switching on and off of the plurality of energy storage units to generate a periodic multi-level voltage;

[0009] The commutation module is connected to the energy storage module and includes a first bridge arm group and a second bridge arm group;

[0010] An auxiliary commutation module is connected in series with the plurality of energy storage units, or is connected to at least one of the first bridge arm group and the second bridge arm group; the auxiliary commutation module is used to form a resonant circuit with the stray inductance on the loop during the commutation time interval;

[0011] The commutation module is used to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group within the commutation time interval and when the loop current meets the zero current condition to generate a single-phase AC voltage.

[0012] Optionally, the auxiliary reversing module includes:

[0013] A first commutation unit, comprising a first capacitor; the first commutation unit is connected in series with a plurality of energy storage units, the first commutation unit being configured to switch the first capacitor on during a commutation time interval and switch the first capacitor off when a voltage across the first capacitor satisfies a zero voltage condition;

[0014] The commutation module is used to commutate the first bridge arm group and the second bridge arm group within the commutation time interval and when the loop current meets the zero current condition.

[0015] Optionally, the first commutation unit includes:

[0016] a first capacitor;

[0017] A first full-bridge circuit is connected to the first capacitor; the commutation time interval includes a first time period, a second time period, a third time period and a fourth time period in sequence;

[0018] During the first time period and the fourth time period, the first full-bridge circuit is used to switch out the first capacitor;

[0019] During the second and third time periods, the first full-bridge circuit is used to connect the first capacitor so that the first capacitor and the stray inductance on the loop form a resonant circuit.

[0020] Optionally, the first full-bridge circuit includes:

[0021] a first switching device, wherein a first end of the first switching device is connected to a first end of the first capacitor; a second end of the first switching device is connected to a positive line, or connected to the positive line through at least one energy storage unit; and the positive line is connected between a first end of the energy storage module and a first end of the converter module;

[0022] a second switching device, wherein a first terminal of the second switching device is connected to a second terminal of the first switching device, and a second terminal of the second switching device is connected to a second terminal of the first capacitor;

[0023] a third switching device, wherein a first end of the third switching device is connected to a first end of the first capacitor; a second end of the third switching device is connected to a negative line, or connected to the negative line through at least one energy storage unit; and the negative line is connected between a second end of the energy storage module and a second end of the converter module;

[0024] a fourth switching device, wherein a first end of the fourth switching device is connected to the second end of the third switching device, and a second end of the fourth switching device is connected to the second end of the first capacitor;

[0025] The first switching device, the second switching device, the third switching device and the fourth switching device each include a first fully-controlled component that is unidirectionally conductive and a first freewheeling component that is unidirectionally conductive, and the conduction directions of the first fully-controlled component and the first freewheeling component are opposite;

[0026] During the first period, the second switching device and the fourth switching device are in the on state;

[0027] During the second period and the third period, the second switching device and the third switching device are in the on state;

[0028] During the fourth period, the first switching device and the third switching device are in the on state.

[0029] Optionally, the energy storage commutation circuit further includes:

[0030] A first current detection unit, used to detect a current signal of the positive line or the negative line;

[0031] a first voltage detection unit, connected in parallel with the first capacitor, for detecting the voltage across both ends of the first capacitor;

[0032] During the second and third time periods, the commutation module is configured to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group when the first current detection unit detects a zero current signal;

[0033] During the second period and the third period, the first full-bridge circuit is used to switch out the first capacitor when the first voltage detection unit detects a zero voltage signal.

[0034] Optionally, the first bridge arm group includes a first upper bridge arm and a first lower bridge arm, and the second bridge arm group includes a second upper bridge arm and a second lower bridge arm; the first upper bridge arm, the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm include a plurality of power switching devices connected in series;

[0035] The auxiliary reversing module includes:

[0036] a plurality of second commutation units, each of the second commutation units including a second capacitor, the second commutation unit being connected in parallel with a power switching device of the first upper bridge arm, the first lower bridge arm, the second upper bridge arm, or the second lower bridge arm; the second commutation unit being configured to switch the second capacitor on during a commutation time interval and switch the second capacitor off when the loop current meets a zero current condition;

[0037] The commutation module is used to commutate the first bridge arm group and the second bridge arm group within the commutation time interval and when the loop current meets the zero current condition.

[0038] Optionally, the second commutation unit includes:

[0039] a second capacitor;

[0040] a fifth switching device connected in series with the second capacitor; the fifth switching device includes a second fully-controlled component that is unidirectionally conductive and a second freewheeling component that is unidirectionally conductive, the second fully-controlled component and the second freewheeling component having opposite conduction directions;

[0041] The switching time intervals include the fifth period, the sixth period, and the seventh period in sequence;

[0042] In the fifth time period, the fifth switching device corresponding to the target power switching device is used to switch out the second capacitor; the target power switching device is a power switching device that is in a conducting state before commutation;

[0043] In a sixth time period, the target power switch device is switched to an off state, and the fifth switch device corresponding to the target power switch device is used to switch the second capacitor on;

[0044] In the seventh time period, the fifth switching device corresponding to the target power switching device is used to switch out the second capacitor, and the commutation module is used to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group.

[0045] Optionally, during the time interval when the energy storage module outputs the multi-level voltage, the fifth switching device corresponding to the target power switching device is used to connect the second capacitor to the loop to release the stored energy of the second capacitor.

[0046] Optionally, the energy storage commutation circuit further includes:

[0047] A second current detection unit, used to detect a current signal of the positive line or the negative line;

[0048] During the sixth and seventh time periods, the commutation module is configured to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group when the second current detection unit detects a zero current signal;

[0049] During the sixth and seventh time periods, the fifth switching device corresponding to the target power switching device is configured to switch off the second capacitor when the current detection unit detects a zero current signal.

[0050] In the second aspect, the present application provides an energy storage commutation system, comprising three energy storage commutation circuits of the first aspect, wherein the first voltage output ends of the three energy storage commutation circuits are respectively connected to the three-phase AC ends of the AC power grid through corresponding inductors, and the second voltage output ends of the three energy storage commutation circuits are connected to the same ground end.

[0051] The energy storage commutation circuit and system of the present application absorbs energy stored in stray inductance through an auxiliary commutation module during the commutation time interval, thereby reducing the inductive current in the loop. When the inductive current meets the zero-current condition, the switching state of the switching devices of the first bridge arm group and the second bridge arm group in the commutation module can be controlled. For devices that need to be shut down, the current change rate of the loop current can be suppressed by adding an auxiliary commutation module, allowing the commutation module to switch states under zero-current conditions. This can avoid the generation of large induced voltages during the commutation process, reduce device shutdown losses, and increase the service life of the switching devices in the commutation module. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0053] Figure 1 This is a structural diagram of an energy storage commutation circuit provided in one embodiment of the present application;

[0054] Figure 2 This is a schematic diagram of the principle of a multi-level AC voltage provided by an embodiment of the present application;

[0055] Figure 3 is a structural diagram of an energy storage commutation circuit provided by another embodiment of the present application;

[0056] Figure 4 Schematic diagram of the corresponding relationship between the inductor current and the capacitor voltage in the oscillation circuit provided in one embodiment of the present application;

[0057] Figure 5 This is a structural diagram of an energy storage commutation circuit provided in another embodiment of the present application;

[0058] Figure 6 This is a structural diagram of a first converter unit provided in one embodiment of the present application;

[0059] Figure 7is a structural schematic diagram of a first converter unit provided in another embodiment of the present application;

[0060] Figure 8 is a schematic diagram of current flow during a first period of time provided by an embodiment of the present application;

[0061] Figure 9 is a schematic diagram of current flow during the second period provided by an embodiment of the present application;

[0062] Figure 10 is a schematic diagram of current flow during the third period provided by an embodiment of the present application;

[0063] Figure 11 is a schematic diagram of current flow during a fourth period provided by an embodiment of the present application;

[0064] Figure 12 This is one of the structural diagrams of the energy storage commutation circuit provided in yet another embodiment of the present application;

[0065] Figure 13 This is the second structural diagram of the energy storage commutation circuit provided in yet another embodiment of the present application;

[0066] Figure 14 is a structural diagram of a second commutation unit provided in one embodiment of the present application;

[0067] Figure 15 1 is a schematic diagram of current flow during the fifth period provided by an embodiment of the present application;

[0068] Figure 16 1 is a schematic diagram of current flow during a sixth period provided by an embodiment of the present application;

[0069] Figure 17 1 is a schematic diagram of current flow during the seventh period provided by an embodiment of the present application;

[0070] Figure 18 This is a schematic diagram of current flow during multi-level output provided by an embodiment of the present application;

[0071] Figure 19 This is a structural diagram of an energy storage commutation system provided in one embodiment of the present application;

[0072] In the attached figure:

[0073] 10. Energy storage module; 11. Energy storage unit; 20. Commutation module; 21. First bridge arm group; 22. Second bridge arm group; 211. First upper bridge arm; 212. First lower bridge arm; 221. Second upper bridge arm; 222. Second lower bridge arm; 30. Auxiliary commutation module; Ls, stray inductance; 31. First commutation unit; C1, first capacitor; 311, first full-bridge circuit; T1, first switching device; T2, second switching device; T3, third switching device; T4, fourth switching device;

[0074] K1, first fully-controlled component; D1, first freewheeling component; 41, first current detection unit; 42, first voltage detection unit; 32, second commutation unit; C2, second capacitor; T5, fifth switching device; K2, second fully-controlled component; D2, second freewheeling component; 43, second current detection unit; L, reactor; AC, AC grid. DETAILED DESCRIPTION

[0075] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present application by illustrating the examples of the present application.

[0076] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0077] Energy storage equipment in the power grid can store and release electrical energy, and can play an important role in scenarios such as peak and frequency regulation, new energy consumption, and large-scale new energy transmission. It is one of the important equipment that is indispensable for building a new power system.

[0078] Currently, MCCs (Modular Commuted Converters) can be used to connect three-phase energy storage to the AC grid. Each phase circuit can include a high-load commutation H-bridge circuit in a DC energy storage module. The DC energy storage module includes multiple battery modules, each connected to a corresponding half-bridge module. The half-bridge module controls the switching on and off of the battery modules. Using multi-level technology, the half-bridge module controls the switching on and off of the batteries, and can output N+1 voltage levels between 0 and N times Ubat (N is the number of battery modules, and Ubat is the battery voltage), thus achieving multi-level voltage output.

[0079] Because the DC energy storage module uses a half-bridge module, it can only output a positive AC voltage signal, equivalent to an AC voltage signal in the positive half-cycle. By utilizing a high-load commutation H-bridge circuit, it is possible to achieve multi-level voltage output in both positive and reverse directions by controlling the conduction of the switching devices in the H-bridge circuit. For example, in two consecutive positive AC voltage cycles, the H-bridge circuit can reverse the AC voltage signal in the second cycle, generating an AC voltage signal equivalent to a sinusoidal signal at the output.

[0080] However, in the aforementioned embodiment, due to the typical distance between the DC energy storage module and the H-bridge circuit, a certain amount of stray inductance is generated when connecting them via cables. Since the DC current in the loop is high during commutation, the current reversal during commutation will produce a large current change, i.e., a large current change rate di / dt. At this high current change rate, the stray inductance in the loop cable will generate an excessively high induced voltage, thereby affecting the normal commutation process of the H-bridge circuit and even causing damage to the device.

[0081] In order to solve at least one of the above technical problems, the embodiments of the present application provide an energy storage commutation circuit and system. The energy storage commutation circuit provided in the embodiments of the present application is first introduced below.

[0082] Figure 1 FIG2 shows a schematic diagram of the structure of an energy storage commutation circuit provided by an embodiment of the present application. The energy storage commutation circuit includes an energy storage module 10 , a commutation module 20 and an auxiliary commutation module 30 .

[0083] The energy storage module 10 may include a plurality of energy storage units 11 connected in series, each energy storage unit 11 may include a battery module and a half-bridge module connected to the battery module. The half-bridge module can realize the input and output of the battery module. For example, when the energy storage module 10 includes N energy storage units 11 connected in series, each half-bridge module is used to control the input and output of the corresponding battery module, and N+1 levels between 0 and N times Ubat can be output (N is the number of battery modules, and Ubat is the battery voltage), that is, multi-level voltage output is realized.

[0084] like Figure 2 As shown, in the energy storage module 10, by controlling the input and output of multiple energy storage units 11, a periodic multi-level voltage close to the sinusoidal signal |sinωt| can be generated, that is, Figure 2 The waveform of the DC voltage is shown in FIG.

[0085] The commutation module 20 can be connected to the energy storage module 10, such as Figure 3 As shown, the commutation module 20 may be an H-bridge circuit formed by a first bridge arm group 21 and a second bridge arm group 22 .

[0086] Please continue to refer to Figure 2 When the energy storage module 10 outputs a multi-level voltage for two consecutive cycles, the converter module 20 can reverse the output voltage in the second cycle. Figure 2 As shown in the waveform of the control signal of the commutation module 20, the control levels of the power switching devices in the commutation module 20 are inverted. At this time, the voltage output by the commutation module 20 is reversed, so the voltage output in the second cycle is the voltage of the negative half cycle.

[0087] like Figure 2 As shown in the waveform of the AC voltage, through the commutation of the commutation module 20, the output end of the commutation module 20 can generate an AC voltage close to the sinusoidal signal sinωt.

[0088] like Figure 1 As shown, the auxiliary reversing module 30 can be connected in series with multiple energy storage units 11. Figure 3 As shown, the auxiliary commutation module 30 may also be connected to at least one of the first bridge arm group 21 and the second bridge arm group 22. The auxiliary commutation module 30 can form a resonant circuit with the stray inductance Ls of the entire loop during the commutation time interval.

[0089] Please continue to refer to Figure 2 The switching time interval is the time interval during which the multi-level voltage is at level 0 when the energy storage module 10 generates two consecutive cycles of the multi-level voltage. That is, during the switching time interval, the battery modules in all energy storage units 11 are in the switched-off state.

[0090] During the commutation time interval, when the auxiliary commutation module 30 forms a resonant circuit with the stray inductance Ls in the loop, the energy stored in the stray inductance Ls can be transferred to the auxiliary commutation module 30, gradually reducing the loop current. When the loop current meets the zero current condition, the commutation module 20 can control the switching states of the various components in the first bridge arm group 21 and the second bridge arm group 22 to achieve commutation.

[0091] After the commutation module 20 completes commutation, the multi-level voltage output by the energy storage module 10 is converted into an AC voltage of a negative half cycle, which forms a single-cycle AC voltage signal together with the AC voltage of the positive half cycle in the previous cycle.

[0092] In this embodiment, during the commutation time interval, the auxiliary commutation module 30 absorbs the energy stored in the stray inductance Ls, thereby reducing the inductive current in the loop. When the inductive current meets the zero-current condition, the switching states of the first bridge arm group 21 and the second bridge arm group 22 in the commutation module 20 can be controlled. For devices that need to be shut down, the addition of the auxiliary commutation module 30 can suppress the rate of change of the loop current, allowing the commutation module 20 to switch states under zero-current conditions. This can avoid the generation of large induced voltages during the commutation process, reduce device turn-off losses, and increase the service life of the switching devices in the commutation module 20.

[0093] Please refer to Figure 5 In some embodiments, the auxiliary commutation module 30 may include a first commutation unit 31 .

[0094] The first commutation unit 31 may include a first capacitor C1 and may be connected in series with multiple energy storage units 11. During the commutation time interval, the battery modules in all energy storage units 11 are switched off. During this time, the first commutation unit 31 may adjust the switching states of its internal components to switch the first capacitor C1 on.

[0095] After the first capacitor C1 is put into operation, it can form a resonant circuit with the stray inductance Ls in the entire loop, and the energy stored in the stray inductance Ls can be transferred to the first capacitor C1.

[0096] Figure 4 The figure shows the corresponding relationship between the voltage across the capacitor and the current on the stray inductance Ls during the energy transfer between the stray inductance Ls and the capacitor. Figure 4As shown in the figure, when the capacitor is first connected, the voltage across it is zero. At this time, the current flowing through the stray inductance Ls is at its forward peak current. As the stray inductance Ls releases energy, the voltage across the capacitor continues to rise. When the voltage across the capacitor reaches its peak voltage, the inductor current reaches zero. At this point, the capacitor begins to release energy, the voltage across it continues to decrease, and the inductor current increases in the reverse direction. When the voltage across the capacitor reaches zero again, the inductor current reaches its reverse peak.

[0097] based on Figure 4 As shown in the corresponding relationship, when the inductor current meets the zero current condition, the voltage across the first capacitor C1 reaches the peak voltage. At this time, the commutation module 20 can commutate the first bridge arm group 21 and the second bridge arm group 22 when the inductor current meets the zero current condition.

[0098] After the commutation module 20 completes commutation, in the resonant circuit formed by the first capacitor C1 and the stray inductance Ls, after the voltage across the first capacitor C1 reaches its peak voltage, the energy stored in the first capacitor C1 can be transferred to the stray inductance Ls. At this time, the direction of the current in the stray inductance Ls changes.

[0099] When the current on the stray inductance Ls reaches its reverse peak, the energy stored in the first capacitor C1 is completely discharged. At this time, the voltage across the first capacitor C1 just meets the zero voltage condition, and the first converter unit 31 can disconnect the first capacitor C1 at this time. Because the voltage across the first capacitor C1 meets the zero voltage condition, there is no need to discharge the charge of the first capacitor C1 after disconnecting it.

[0100] After the first commutation unit 31 switches off the first capacitor C1 , the energy storage module 10 can generate a multi-level voltage by controlling the switching on and off of each energy storage unit 11 .

[0101] In some embodiments, the first converter unit 31 may include a first capacitor C1 and a first full-bridge circuit. Figure 6 As shown, the first full-bridge circuit is composed of a first switching device T1, a second switching device T2, a third switching device T3 and a fourth switching device T4.

[0102] The first full-bridge circuit is connected to the first capacitor C1 . The first full-bridge circuit can switch the first capacitor C1 on and off by adjusting the switching state of the switching device.

[0103] A single switching time interval may include a first period, a second period, a third period, and a fourth period in sequence.

[0104] When all the energy storage units 11 in the energy storage module 10 cut out the battery module, the voltage output by the energy storage module 10 is at a zero level, which may be the starting moment of the first period.

[0105] During the first time period, the first full-bridge circuit controls the first capacitor C1 to be in a cut-out state, that is, during the first time period, the first capacitor C1 is not connected to the loop.

[0106] The first full-bridge circuit adjusts the switching state of the switching device, and the moment when the first capacitor C1 is connected can be used as the starting moment of the second time period.

[0107] During the second and third time periods, the first capacitor C1 is in the on state and can form a resonant circuit with the stray inductance Ls in the loop. The first capacitor C1 can achieve mutual energy transfer with the stray inductance Ls.

[0108] As the stray inductance Ls transfers energy to the first capacitor C1, the loop current continuously decreases. When the loop current drops to a zero current condition, the commutation module 20 controls the first bridge arm group 21 and the second bridge arm group 22 to commutate. This may be the start of the third period, and the voltage across the first capacitor C1 reaches its peak voltage.

[0109] In the third time period, the first capacitor C1 transfers energy to the stray inductance Ls. At this time, the direction of the loop current is opposite to the direction of the loop current in the second time period. When the voltage across the first capacitor C1 drops to meet the zero voltage condition, the loop current on the stray inductance Ls reaches a reverse peak, which can be the starting moment of the fourth time period.

[0110] During the fourth period, the first full-bridge circuit may cut out the first capacitor C1 .

[0111] Through the above four time periods, the first capacitor C1 can be used to absorb the energy stored in the stray inductance Ls during the commutation process, and the commutation module 20 can be controlled to perform commutation when the loop current meets the zero current condition, so as to avoid generating a higher induced voltage during the commutation process, reduce the turn-off loss of the device, and improve the service life of the switching device in the commutation module 20.

[0112] Please continue to refer to Figure 6 In some embodiments, the first full-bridge circuit may include a first switching device T1, a second switching device T2, a third switching device T3, and a fourth switching device T4.

[0113] The first end of the first switching device T1 is connected to the first end of the first capacitor C1; the second end of the first switching device T1 is connected to the positive line, or is connected to the positive line through at least one energy storage unit 11; the positive line is connected between the first end of the energy storage module 10 and the first end of the converter module 20.

[0114] A first end of the second switch device T2 is connected to the second end of the first switch device T1, and a second end of the second switch device T2 is connected to the second end of the first capacitor C1;

[0115] A first end of the third switching device T3 is connected to a first end of the first capacitor C1; a second end of the third switching device T3 is connected to a negative line, or connected to the negative line through at least one energy storage unit 11; the negative line is connected between a second end of the energy storage module 10 and a second end of the converter module 20;

[0116] A first end of the fourth switch device T4 is connected to the second end of the third switch device T3 , and a second end of the fourth switch device T4 is connected to the second end of the first capacitor C1 .

[0117] It can be understood that the above-mentioned first full-bridge circuit can be connected in series at the heads of multiple energy storage units 11, that is, the first energy storage unit 11 is connected to the positive line through the first full-bridge circuit; the first full-bridge circuit can also be connected in series at the tails of multiple energy storage units 11, that is, the last energy storage unit 11 is connected to the negative line through the first full-bridge circuit; the first full-bridge circuit can also be connected in series in the middle of multiple energy storage units 11, that is, the first full-bridge circuit is connected to the positive line through a part of the energy storage units 11, and is connected to the negative line through another part of the energy storage units 11.

[0118] Please refer to Figure 7 The above-mentioned first switching device T1, the second switching device T2, the third switching device T3 and the fourth switching device T4 all include a first unidirectionally conducting full-control component K1 and a first unidirectionally conducting freewheeling component D1, and the conduction directions of the first full-control component K1 and the first freewheeling component D1 are opposite.

[0119] The first fully-controlled component K1 may be an IGCT (Integrated Gate Commutated Thyristor) or an IGBT (Insulated Gate Bipolar Transistor). The first freewheeling component D1 may be a diode connected in reverse parallel to the first fully-controlled component K1 to achieve reverse current flow.

[0120] like Figure 8 As shown, in the first period, the second switch device T2 and the fourth switch device T4 are in the on state. At this time, the current flows to the positive line through the first full-control component K1 of the fourth switch device T4 and the first freewheeling component D1 of the second switch device T2.

[0121] like Figure 9As shown, during the second period, the second switching device T2 and the third switching device T3 are in the on state. At this time, current flows to the positive line through the first freewheeling component D1 of the third switching device T3, the first capacitor C1, and the first freewheeling component D1 of the second switching device T2. During the second period, the first capacitor C1 is in the on state, capable of absorbing the energy released by the stray inductance Ls in the loop. The voltage across the first capacitor C1 continues to rise until it reaches the peak voltage.

[0122] like Figure 10 As shown, during the third time period, the second and third switching devices T2 and T3 are in the on state, and the loop current reverses direction. Current now flows to the negative line through the first fully-controlled component K1 of the second switching device T2, the first capacitor C1, and the first fully-controlled component K1 of the third switching device T3. During the third time period, the first capacitor C1 is in the on state and can release energy. The voltage across the first capacitor C1 continuously decreases from the peak voltage until it reaches zero voltage.

[0123] like Figure 11 As shown, during the fourth time period, the first switching device T1 and the third switching device T3 are in the on state. Current flows to the negative line through the first freewheeling component D1 of the first switching device T1, the first capacitor C1, and the first fully-controlled component K1 of the third switching device T3. During the fourth time period, the first capacitor C1 is in the off state.

[0124] above Figures 8 to 11 The figure shows the current flow during the commutation process, where the current direction switches from flowing to the positive line to flowing to the negative line. It is understood that the commutation process from flowing to the negative line to flowing to the positive line can be achieved by reversing the switching of the on and off states of the switching devices in the four time periods.

[0125] In some embodiments, the energy storage commutation circuit may further include a first current detection unit (not shown) and a first voltage detection unit (not shown).

[0126] The first current detection unit can detect the current signal on the positive or negative line. For example, the first current detection unit can be a contact current sensor or a contactless current sensor. A contact current sensor can be connected in series with the positive or negative line; a contactless current sensor can be mounted on the positive or negative line, such as a Hall effect current sensor.

[0127] The first voltage detection unit may be connected in parallel to the first capacitor C1 to detect the voltage across both ends of the first capacitor C1.

[0128] During the second and third time periods, the first current detection unit may generate a corresponding control signal when a zero current signal is detected. Based on the control signal, the commutation module 20 may commutate the multi-level voltage output by the energy storage module 10 through the first bridge arm group 21 and the second bridge arm group 22. For example, if the upper bridge arm of the first bridge arm group 21 is turned on and the lower bridge arm of the second bridge arm group 22 is turned on before commutation, then after commutation, the lower bridge arm of the first bridge arm group 21 is turned on and the upper bridge arm of the second bridge arm group 22 is turned on.

[0129] It can be understood that the moment when the commutation module 20 commutates is the dividing point between the second period and the third period. Before the commutation module 20 commutates, it is in the second period; after the commutation module 20 commutates, it is in the third period.

[0130] During the second and third time periods, the first voltage detection unit can measure the voltage across the first capacitor C1. At the start of the second time period, when the first capacitor C1 is just put into operation, the voltage across the first capacitor C1 is essentially zero. During the process of energy transfer from the stray inductance Ls to the first capacitor C1, the voltage across the first capacitor C1 gradually increases. When the loop current meets the zero current condition, the voltage across the first capacitor C1 also reaches the peak voltage, which is the start of the third time period. During the third time period, the first capacitor C1 transfers energy to the stray inductance Ls. At this time, if the first voltage detection unit detects a zero voltage signal, it indicates that the energy of the first capacitor C1 has been released, and the loop current is at a reverse peak.

[0131] The first full-bridge circuit can cut out the first capacitor C1 based on the zero voltage signal generated by the first current detection unit, and the third time period ends.

[0132] In the fourth period, the first capacitor C1 is in a cut-off state. The energy storage module 10 can output a multi-level voltage by adjusting the number of battery modules used.

[0133] As an optional embodiment, the energy storage commutation circuit may further include a processing unit, which may be electrically connected to the first current detection unit and the first voltage detection unit, and to the commutation module 20 and the first full-bridge circuit. Upon receiving a zero-current signal generated by the first current detection unit, the processing unit may send a commutation control signal to the commutation module 20; upon receiving a zero-voltage signal generated by the first voltage detection unit, the processing unit may send a cut-out control signal to the first full-bridge circuit.

[0134] In the above embodiment, the voltage across the first capacitor C1 increases from zero voltage to peak voltage, and then decreases from peak voltage to zero voltage. When the voltage across the first capacitor C1 returns to zero voltage, the first full-bridge circuit can control the first capacitor C1 to be cut out.

[0135] When the first capacitor C1 is in the on state, the loop current in the LC oscillation circuit formed by the first capacitor C1 and the stray inductance Ls in the loop is expressed as:

[0136]

[0137] Where i(t) is the loop current at time t, I ac is the current mean value, L is the equivalent inductance value of the stray inductance Ls, and C is the capacitance value of the first capacitor C1.

[0138] Similarly, the voltage across the first capacitor C1 is expressed as:

[0139]

[0140] Wherein, u(t) is the voltage across the first capacitor C1 at time t, I ac is the current mean value, L is the equivalent inductance value of the stray inductance Ls, and C is the capacitance value of the first capacitor C1.

[0141] Please refer to Figure 12 In some embodiments, the first bridge arm group 21 includes a first upper bridge arm 211 and a first lower bridge arm 212, and the second bridge arm group 22 includes a second upper bridge arm 221 and a second lower bridge arm 222. The first upper bridge arm 211, the first lower bridge arm 212, the second upper bridge arm 221, and the second lower bridge arm 222 include multiple power switching devices connected in series. A single power switching device may include an IGCT or an IGBT, and a diode connected in anti-parallel with the IGCT or IGBT. That is, the upper and lower bridge arms may be IGCT valve strings or IGBT valve strings.

[0142] Please refer to Figure 13 The auxiliary commutation module 30 may include multiple second commutation units 32, each of which may include a second capacitor C2. The second commutation unit 32 may be connected in parallel with a power switch in the first upper bridge arm 211, the first lower bridge arm 212, the second upper bridge arm 221, or the second lower bridge arm 222. For example, the auxiliary commutation module 30 may include four second commutation units 32, each of which may be connected in parallel with a power switch in the first upper bridge arm 211, the first lower bridge arm 212, the second upper bridge arm 221, or the second lower bridge arm 222.

[0143] During the commutation time interval, the second commutation unit 32 corresponding to the conductive bridge arm can control the second capacitor C2 to be put into operation. At this time, the second capacitor C2 can form a resonant circuit with the stray inductance Ls in the conductive loop to achieve mutual energy transfer. In the process of the second capacitor C2 absorbing the energy released by the stray inductance Ls, the loop current is continuously reduced. When the loop current meets the zero current condition, the second commutation unit 32 can cut out the second capacitor C2. And at the same time, the commutation module 20 can control the first bridge arm group 21 and the second bridge arm group 22 to commutate. That is, when the loop current is in the zero current condition, the cutting out of the second capacitor C2 and the commutation of the commutation module 20 can be performed synchronously.

[0144] It should be noted that when the second capacitor C2 is cut out under zero current conditions, the voltage across the second capacitor C2 will reach a peak voltage. Therefore, during the subsequent multi-level output period, the second capacitor C2 can also be put into the loop to release the energy stored in the second capacitor C2.

[0145] Please refer to Figure 14 In some embodiments, the second commutation unit 32 may include a second capacitor C2 and a fifth switching device T5.

[0146] The fifth switch device T5 is connected in series with the second capacitor C2. The fifth switch device T5 includes a unidirectional second full-control component K2 and a unidirectional second freewheeling component D2. The conduction directions of the second full-control component K2 and the second freewheeling component D2 are opposite.

[0147] The second fully-controlled component K2 may be an IGCT (Integrated Gate Commutated Thyristor) or an IGBT (Insulated Gate Bipolar Transistor). The second freewheeling component D2 may be a diode connected in reverse parallel to the second fully-controlled component K2 to achieve reverse current flow.

[0148] The switching time interval may include a fifth period, a sixth period, and a seventh period in sequence. During the switching time interval, the battery modules in all the energy storage units 11 are in a switched-off state.

[0149] In the fifth time period, it can be determined whether the power switch device is the target power switch device according to the switching state of the power switch device corresponding to each fifth switch device T5.

[0150] For example, four fifth switching devices T5 are connected in parallel with one power switching device in the first upper bridge arm 211, the first lower bridge arm 212, the second upper bridge arm 221, or the second lower bridge arm 222. If the first upper bridge arm 211 and the second lower bridge arm 222 are in the on state before commutation, the power switching device corresponding to the fifth switching device T5 in the first upper bridge arm 211 is the target power device. Similarly, the power switching device corresponding to the fifth switching device T5 in the second lower bridge arm 222 is also the target power device.

[0151] After determining the target power switching device, such as Figure 15 As shown, the corresponding fifth switch device T5 can be controlled to maintain the second capacitor C2 in the cut-out state. That is, in the first upper bridge arm 211 and the second lower bridge arm 222, the second full-control component K2 of the corresponding fifth switch device T5 is in the disconnected state, and the second capacitor C2 is not connected to the loop.

[0152] In the sixth period, the target power switch device in the first upper bridge arm 211 and the second lower bridge arm 222 is switched from the on state to the off state, and the fifth switch device T5 corresponding to the target power switch device can be switched to the on state to realize the input of the second capacitor C2. Figure 16 As shown, at this time, the current passes through the second freewheeling component D2 of the fifth switch device T5 and the second capacitor C2. The second capacitor C2 can achieve energy transfer with the stray inductance Ls in the loop in the switched-on state.

[0153] like Figure 17 As shown, during the seventh time period, when the current in the loop meets the zero current condition, the fifth switch device T5 corresponding to the target power switch device can switch out the second capacitor C2. At the same time, the commutation module 20 can also commutate the multi-level voltage output by the energy storage module 10 through the first bridge arm group 21 and the second bridge arm group 22. For example, if the power switches of the first upper bridge arm 211 and the second lower bridge arm 222 are turned on before commutation, the power switches of the second upper bridge arm 221 and the first lower bridge arm 212 are turned on after commutation.

[0154] Please refer to Figure 18 In some embodiments, after the commutation time interval, during the time interval when the energy storage module 10 normally outputs the multi-level voltage, the fifth switch device T5 corresponding to the target power switch device can connect the second capacitor C2 to the loop.

[0155] Since the loop current meets the zero-current condition when the fifth switch device T5 switches off the second capacitor C2, the voltage across the second capacitor C2 is at its peak voltage when the second capacitor C2 is switched off. To discharge the charge from the second capacitor C2, the fifth switch device T5 can be turned on within the multi-level voltage interval after the commutation process. At this time, the charge from the second capacitor C2 can be discharged through the second fully-controlled device in the fifth switch device T5 and the anti-parallel diodes of the other power switch devices in the bridge arm.

[0156] In some embodiments, the energy storage commutation circuit may further include a second current detection unit (not shown). The second current detection unit may detect the current signal on the positive line or the negative line. For example, the second current detection unit may be a contact current sensor or a contactless current sensor. For a contact current sensor, it may be connected in series with the positive line or the negative line; for a contactless current sensor, it may be mounted on the positive line or the negative line, for example, a Hall current sensor may be used.

[0157] During the sixth and seventh time periods, the second current detection unit can detect whether the loop current is a zero current signal. When the loop current meets the zero current condition, the commutation module 20 can control the first bridge arm group 21 and the second bridge arm group 22 to commutate the multi-level voltage output by the energy storage module 10.

[0158] Similarly, since the switching-out time point of the second capacitor C2 can be consistent with the commutation time point of the commutation module 20 , the fifth switching device T5 corresponding to the target power switching device can switch out the second capacitor C2 under a zero current signal.

[0159] Please refer to Figure 19 The embodiment of the present application further provides an energy storage commutation system. The energy storage commutation system includes three energy storage commutation circuits 100 in the above-mentioned embodiments.

[0160] The first voltage output terminals of the three energy storage commutation circuits 100 are respectively connected to the three-phase AC terminals of the AC grid AC through corresponding reactors L, and the second voltage output terminals of the three energy storage commutation circuits 100 are connected to the same ground terminal.

[0161] It is understandable that the three energy storage commutation circuits 100 mentioned above may adopt the same topology.

[0162] The functional blocks shown in the above-described block diagram can be implemented as hardware, software, firmware or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of the present application are programs or code segments that are used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link by a data signal carried in a carrier wave. "Machine-readable medium" can include any medium that can store or transmit information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROMs, flash memories, erasable ROMs (EROMs), floppy disks, CD-ROMs, optical disks, hard disks, optical fiber media, radio frequency (RF) links, etc. The code segment can be downloaded via a computer network such as the Internet, an intranet, etc.

[0163] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0164] This article uses specific examples to illustrate the principles and implementation methods of this application. The above examples are only used to help understand the method and core ideas of this application. The above are only preferred implementation methods of this application. It should be pointed out that due to the limitations of textual expression, there are objectively infinite specific structures. For ordinary technicians in this technical field, without departing from the principles of this application, they can make several improvements, modifications or changes, and can also combine the above technical features in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the concept and technical solution of this application to other occasions without improvement, should be regarded as the scope of protection of this application.

Claims

1. An energy storage commutation circuit, characterized in that: include: An energy storage module comprising a plurality of energy storage units connected in series; the energy storage module is used to control the switching on and off of the plurality of energy storage units to generate a periodic multi-level voltage; a commutation module, connected to the energy storage module, comprising a first bridge arm group and a second bridge arm group; an auxiliary commutation module connected in series with the plurality of energy storage units, or connected to at least one of the first bridge arm group and the second bridge arm group; the auxiliary commutation module is configured to form a resonant circuit with the stray inductance on the loop during a commutation time interval; The commutation module is configured to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group within the commutation time interval and when the loop current meets the zero current condition, so as to generate a single-phase AC voltage.

2. The energy storage commutation circuit according to claim 1, characterized in that: The auxiliary reversing module includes: a first commutation unit, comprising a first capacitor; the first commutation unit being connected in series with the plurality of energy storage units, the first commutation unit being configured to switch the first capacitor on during the commutation time interval, and switch the first capacitor off when the voltage across the first capacitor satisfies a zero voltage condition; The commutation module is used to commutate the first bridge arm group and the second bridge arm group within the commutation time interval and when the loop current meets the zero current condition.

3. The energy storage commutation circuit according to claim 2, characterized in that: The first commutation unit includes: a first capacitor; A first full-bridge circuit is connected to the first capacitor; the commutation time interval includes a first period, a second period, a third period and a fourth period in sequence; During the first time period and the fourth time period, the first full-bridge circuit is used to switch out the first capacitor; During the second time period and the third time period, the first full-bridge circuit is used to connect the first capacitor so that the first capacitor and the stray inductance on the loop form a resonant circuit.

4. The energy storage commutation circuit according to claim 3, characterized in that: The first full-bridge circuit comprises: a first switching device, wherein a first terminal of the first switching device is connected to a first terminal of the first capacitor; The second end of the first switching device is connected to the positive line, or connected to the positive line through at least one energy storage unit; the positive line is connected between the first end of the energy storage module and the first end of the converter module; a second switching device, wherein a first terminal of the second switching device is connected to the second terminal of the first switching device, and a second terminal of the second switching device is connected to the second terminal of the first capacitor; a third switching device, wherein a first end of the third switching device is connected to the first end of the first capacitor; a second end of the third switching device is connected to a negative line, or connected to the negative line through at least one energy storage unit; the negative line is connected between the second end of the energy storage module and the second end of the converter module; a fourth switching device, wherein a first end of the fourth switching device is connected to the second end of the third switching device, and a second end of the fourth switching device is connected to the second end of the first capacitor; The first switching device, the second switching device, the third switching device and the fourth switching device each include a first fully-controlled component that is unidirectionally conductive and a first freewheeling component that is unidirectionally conductive, and the first fully-controlled component and the first freewheeling component have opposite conduction directions; During the first period, the second switching device and the fourth switching device are in an on state; During the second period and the third period, the second switching device and the third switching device are in the on state; During the fourth period, the first switching device and the third switching device are in the on state.

5. The energy storage commutation circuit according to claim 4, characterized in that: The energy storage commutation circuit further includes: a first current detection unit, configured to detect a current signal of the positive line or the negative line; a first voltage detection unit, connected in parallel with the first capacitor, and configured to detect a voltage across both ends of the first capacitor; During the second period and the third period, the commutation module is configured to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group when the first current detection unit detects a zero current signal; During the second time period and the third time period, the first full-bridge circuit is configured to switch out the first capacitor when the first voltage detection unit detects a zero voltage signal.

6. The energy storage commutation circuit according to claim 1, characterized in that: The first bridge arm group includes a first upper bridge arm and a first lower bridge arm, and the second bridge arm group includes a second upper bridge arm and a second lower bridge arm; the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm include a plurality of power switching devices connected in series; The auxiliary reversing module includes: a plurality of second commutation units, each of the second commutation units including a second capacitor, the second commutation unit being connected in parallel with a power switch device of the first upper bridge arm, the first lower bridge arm, the second upper bridge arm, or the second lower bridge arm; the second commutation unit being configured to switch the second capacitor on during the commutation time interval and switch off the second capacitor when the loop current meets a zero current condition; The commutation module is used to commutate the first bridge arm group and the second bridge arm group within the commutation time interval and when the loop current meets the zero current condition.

7. The energy storage commutation circuit according to claim 6, characterized in that: The second commutation unit includes: a second capacitor; a fifth switching device connected in series with the second capacitor; the fifth switching device includes a second fully-controlled component that is unidirectionally conductive and a second freewheeling component that is unidirectionally conductive, wherein the second fully-controlled component and the second freewheeling component have opposite conduction directions; The switching time intervals include a fifth period, a sixth period, and a seventh period in sequence; During the fifth time period, a fifth switching device corresponding to the target power switching device is used to switch out the second capacitor; the target power switching device is a power switching device that is in a conducting state before commutation; During the sixth time period, the target power switch device is switched to an off state, and a fifth switch device corresponding to the target power switch device is used to connect the second capacitor; During the seventh time period, the fifth switching device corresponding to the target power switching device is used to switch out the second capacitor, and the commutation module is used to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group.

8. The energy storage commutation circuit according to claim 7, characterized in that: During the time interval when the energy storage module outputs the multi-level voltage, the fifth switch device corresponding to the target power switch device is used to connect the second capacitor to the loop to release the stored energy of the second capacitor.

9. The energy storage commutation circuit according to claim 7, characterized in that: The energy storage commutation circuit further includes: A second current detection unit, used to detect a current signal of the positive line or the negative line; During the sixth time period and the seventh time period, the commutation module is configured to commutate the multi-level voltage output by the energy storage module through the first bridge arm group and the second bridge arm group when the second current detection unit detects a zero current signal; During the sixth period and the seventh period, the fifth switching device corresponding to the target power switching device is configured to switch off the second capacitor when the current detection unit detects a zero current signal.

10. An energy storage commutation system, characterized in that: It comprises three energy storage commutation circuits according to any one of claims 1 to 9, wherein the first voltage output terminals of the three energy storage commutation circuits are respectively connected to the three-phase AC terminals of the AC power grid through corresponding reactors, and the second voltage output terminals of the three energy storage commutation circuits are connected to the same ground terminal.

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