CN214959327U - Energy storage circuit and modular multilevel converter - Google Patents
Energy storage circuit and modular multilevel converter Download PDFInfo
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- CN214959327U CN214959327U CN202120964973.2U CN202120964973U CN214959327U CN 214959327 U CN214959327 U CN 214959327U CN 202120964973 U CN202120964973 U CN 202120964973U CN 214959327 U CN214959327 U CN 214959327U
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Abstract
The application relates to an energy storage circuit and a modular multilevel converter, wherein two ends of a first energy storage bridge arm, a second energy storage bridge arm, a third energy storage bridge arm, a fourth energy storage bridge arm, a fifth energy storage bridge arm and a sixth energy storage bridge arm are respectively connected with a diode in a reverse parallel mode. When a bipolar short-circuit fault occurs on the direct current side of the energy storage system, before protection action, fault current flows through an energy storage bridge arm; after protection, the energy storage bridge arm is locked, most of short-circuit fault current forms a loop through the anti-parallel diodes, and the current passing through the energy storage bridge arm is small, so that the energy storage bridge arm is prevented from being damaged. The short-circuit fault processing is carried out through the scheme, under the same voltage level, the number of required devices is small, the cost and the system structure can be effectively reduced, meanwhile, extra half-control devices such as thyristors are not required to be added, extra control is not required, and the short-circuit fault processing circuit has the advantage of easiness in implementation.
Description
Technical Field
The application relates to the technical field of energy storage, in particular to an energy storage circuit and a modular multilevel converter.
Background
With the increasing occupation ratio of new energy power generation such as wind power and solar energy, the problems of intermittence, volatility and the like generated in the new energy power generation process become more and more prominent. Smoothing wind and photovoltaic power generation power with a battery energy storage system is an effective way to solve this problem. The battery energy storage system relates to an alternating current-direct current conversion technology, and compared with a traditional voltage source Converter, the Modular Multilevel Converter (MMC) has high modularization and expandability, avoids direct series connection of power switch devices, reduces the loss of the Converter due to low switching frequency, introduces redundant sub-modules and is high in operation reliability.
However, during the operation of the battery energy storage system, the dc line inevitably has a short-circuit fault, and the dc bipolar short-circuit fault is one of the most serious faults of the MMC. At present, the following schemes are mainly used for handling the fault of the MMC on the dc side: firstly, a direct current breaker is adopted to rapidly remove direct current faults; secondly, a novel topology with fault ride-through capability is adopted; and thirdly, a single thyristor or two anti-parallel thyristors are connected in parallel on the alternating current side of the submodule, so that the uncontrolled rectification effect of the diode is eliminated, and the direct current can be naturally attenuated.
However, in the cleaning scheme of the direct current breaker, the direct current breaker is expensive; the novel topology with fault ride-through capability can greatly increase the number of switching devices, so that the system is more complex and has higher steady-state operation loss; the direct current protection scheme with the added thyristors needs to connect the thyristors in anti-parallel in each submodule, so that the cost of the system is seriously increased. Therefore, the conventional battery energy storage system still has the disadvantages of complex system structure and high cost.
SUMMERY OF THE UTILITY MODEL
In view of the above, it is necessary to provide an energy storage circuit and a modular multilevel converter for solving the problems of complex structure and high cost of the conventional battery energy storage system.
A tank circuit, comprising: a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a first energy storage bridge arm, a second energy storage bridge arm, a third energy storage bridge arm, a fourth energy storage bridge arm, a fifth energy storage bridge arm and a sixth energy storage bridge arm,
the cathode of the first diode is connected with the first end of the first energy storage bridge arm, the anode of the first diode is connected with the cathode of the second diode and the second end of the first energy storage bridge arm, the first end of the second energy storage bridge arm is connected with the second end of the first energy storage bridge arm, the public end of the second energy storage bridge arm is used for connecting a first phase line of a three-phase power grid, the anode of the second diode is connected with the second end of the second energy storage bridge arm, the cathode of the first diode is used for connecting the positive end of a direct-current power grid, and the anode of the diode is used for connecting the negative end of the direct-current power grid;
the cathode of the third diode is connected with the first end of the first energy storage bridge arm and the first end of the third energy storage bridge arm, the anode of the third diode is connected with the cathode of the fourth diode and the second end of the third energy storage bridge arm, the first end of the fourth energy storage bridge arm is connected with the second end of the third energy storage bridge arm, the public end of the fourth energy storage bridge arm is used for connecting a second phase line of the three-phase power grid, and the anode of the fourth diode is connected with the second end of the second energy storage bridge arm and the second end of the fourth energy storage bridge arm;
the cathode of the fifth diode is connected with the first end of the third energy storage bridge arm and the first end of the fifth energy storage bridge arm, the anode of the fifth diode is connected with the cathode of the sixth diode and the second end of the fifth energy storage bridge arm, the first end of the sixth energy storage bridge arm is connected with the second end of the fifth energy storage bridge arm, the public end of the sixth energy storage bridge arm is used for being connected with the third phase line of the three-phase power grid, and the anode of the sixth diode is connected with the second end of the fourth energy storage bridge arm and the second end of the sixth energy storage bridge arm.
In one embodiment, the energy storage circuit further includes a first inductor, a second inductor, a third inductor, a fourth inductor, a fifth inductor and a sixth inductor, the second end of the first energy storage bridge arm is connected to the first end of the first inductor, the second end of the first inductor is connected to the first end of the second inductor and the anode of the first diode, the common end is used for connecting the first phase line of the three-phase power grid, and the second end of the second inductor is connected to the first end of the second energy storage bridge arm; the second end of the third energy storage bridge arm is connected with the first end of the third inductor, the second end of the third inductor is connected with the first end of the fourth inductor and the anode of the third diode, the public end of the third inductor is used for connecting a second phase line of the three-phase power grid, and the second end of the fourth inductor is connected with the first end of the fourth energy storage bridge arm; the second end of the fifth energy storage bridge arm is connected with the first end of the fifth inductor, the second end of the fifth inductor is connected with the first end of the sixth inductor and the anode of the fifth diode, the public end of the fifth inductor is used for being connected with the third phase line of the three-phase power grid, and the second end of the sixth inductor is connected with the first end of the sixth energy storage bridge arm.
In one embodiment, the energy storage circuit further comprises a seventh inductor, an eighth inductor and a ninth inductor, the second end of the first inductor is connected with the first end of the second inductor and the anode of the first diode, and the common end is connected with the first phase line of the three-phase power grid through the seventh inductor; the second end of the third inductor is connected with the first end of the fourth inductor and the anode of the third diode, and the public end of the third inductor is connected with the second phase line of the three-phase power grid through the eighth inductor; and the second end of the fifth inductor is connected with the first end of the sixth inductor and the anode of the fifth diode, and the public end of the fifth inductor is connected with the third phase line of the three-phase power grid through the ninth inductor.
In one embodiment, each of the plurality of energy storage legs comprises a plurality of energy storage cells connected in series.
In one embodiment, the energy storage unit comprises a first switching device, a second switching device, a first freewheeling diode, a second freewheeling diode and an energy storage device, the control end of the first switching device and the control end of the second switching device are respectively used for connecting an external control device, a first terminal of the switching device is connected to the cathode of the first freewheeling diode and to a first terminal of the energy storage device, a second terminal of the first switching device is connected to an anode of the first freewheeling diode and a first terminal of the second switching device, a cathode of the second freewheeling diode is connected to a first terminal of the second switching device, a second terminal of the second switching device is connected to an anode of the second freewheeling diode and a second terminal of the energy storage device, the second end of the first switching device is used as the first end of the energy storage unit, and the second end of the second switching device is used as the second end of the energy storage unit.
In one embodiment, the energy storage unit further includes a filter capacitor, a first terminal of the filter capacitor is connected to the first terminal of the first switching device and the first terminal of the energy storage device, and a second terminal of the filter capacitor is connected to the second terminal of the second switching device and the second terminal of the energy storage device.
In one embodiment, the energy storage device is a battery.
In one embodiment, the first switching device and the second switching device are all controlled semiconductor switching devices.
In one embodiment, the number of energy storage cells in each energy storage leg is the same.
A modular multilevel converter comprises the energy storage circuit.
According to the energy storage circuit and the modular multilevel converter, the first energy storage bridge arm is connected with the second energy storage bridge arm, the third energy storage bridge arm is connected with the fourth energy storage bridge arm, and the fifth energy storage bridge arm is connected with the sixth energy storage bridge arm to form a phase cluster respectively, the first end of the first energy storage bridge arm, the first end of the third energy storage bridge arm and the first end of the fifth energy storage bridge arm are connected as direct current positive electrodes to be connected to a positive end of a direct current power grid, and the second end of the second energy storage bridge arm, the second end of the fourth energy storage bridge arm and the second end of the sixth energy storage bridge arm are connected as direct current negative electrodes to be connected to a negative end of the direct current power grid. And two ends of the first energy storage bridge arm, the second energy storage bridge arm, the third energy storage bridge arm, the fourth energy storage bridge arm, the fifth energy storage bridge arm and the sixth energy storage bridge arm are respectively connected with a diode in parallel in a reverse direction. When a bipolar short-circuit fault occurs on the direct current side of the energy storage system, before protection action, fault current flows through an energy storage bridge arm; after protection, the energy storage bridge arm is locked, most of short-circuit fault current forms a loop through the anti-parallel diodes, and the current passing through the energy storage bridge arm is small, so that the energy storage bridge arm is prevented from being damaged. The short-circuit fault processing is carried out through the scheme, under the same voltage level, the number of required devices is small, the cost and the system structure can be effectively reduced, meanwhile, extra half-control devices such as thyristors are not required to be added, extra control is not required, and the short-circuit fault processing circuit has the advantage of easiness in implementation.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of an embodiment of a tank circuit;
FIG. 2 is a schematic diagram of an alternative embodiment of a tank circuit;
FIG. 3 is a schematic diagram of an embodiment of an energy storage unit;
fig. 4 is a schematic structural diagram of an energy storage unit in another embodiment.
Detailed Description
To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present application are illustrated in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Referring to fig. 1, a tank circuit includes: a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a first energy storage bridge arm 10, a second energy storage bridge arm 20, a third energy storage bridge arm 30, a fourth energy storage bridge arm 40, a fifth energy storage bridge arm 50 and a sixth energy storage bridge arm 60, wherein the cathode of the first diode D1 is connected with the first end of the first energy storage bridge arm 10, the anode of the first diode D1 is connected with the cathode of the second diode D2 and the second end of the first energy storage bridge arm 10, the first end of the second energy storage bridge arm 20 is connected with the second end of the first energy storage bridge arm 10, the common end of the second diode D1 is connected with the first phase line of the three-phase grid, the anode of the second diode D2 is connected with the second end of the second energy storage bridge arm 20, the cathode of the first diode D1 is connected with the positive end of the direct-current grid, and the anode of the diode is connected with the negative end of the direct-current grid; the cathode of a third diode D3 is connected with the first end of the first energy storage bridge arm 10 and the first end of the third energy storage bridge arm 30, the anode of a third diode D3 is connected with the cathode of a fourth diode D4 and the second end of the third energy storage bridge arm 30, the first end of the fourth energy storage bridge arm 40 is connected with the second end of the third energy storage bridge arm 30, the common end of the fourth energy storage bridge arm is used for connecting a second phase line of a three-phase power grid, and the anode of a fourth diode D4 is connected with the second end of the second energy storage bridge arm 20 and the second end of the fourth energy storage bridge arm 40; the cathode of the fifth diode D5 is connected to the first end of the third energy storage bridge arm 30 and the first end of the fifth energy storage bridge arm 50, the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6 and the second end of the fifth energy storage bridge arm 50, the first end of the sixth energy storage bridge arm 60 is connected to the second end of the fifth energy storage bridge arm 50, the common end of the sixth energy storage bridge arm is used for connecting the third phase line of the three-phase power grid, and the anode of the sixth diode D6 is connected to the second end of the fourth energy storage bridge arm 40 and the second end of the sixth energy storage bridge arm 60.
Specifically, the energy storage bridge arms are bridge arms for storing electric energy, in the scheme of this embodiment, two bridge arms are connected to form a phase cluster, that is, the first energy storage bridge arm 10 is connected to the second energy storage bridge arm 20 to form a first phase cluster, the third energy storage bridge arm 30 is connected to the fourth energy storage bridge arm 40 to form a second phase cluster, and the fifth energy storage bridge arm 50 is connected to the sixth energy storage bridge arm 60 to form a third phase cluster. In each phase cluster, the common end points of the two energy storage bridge arms are respectively connected to the alternating current side of the energy storage system, that is, to an alternating current power grid, the first end of the first energy storage bridge arm 10, the first end of the third energy storage bridge arm 30 and the first end of the fifth energy storage bridge arm 50 are connected to the direct current side of the energy storage system, that is, to the positive end of the direct current power grid, and the second end of the second energy storage bridge arm 20, the second end of the fourth energy storage bridge arm 40 and the second end of the sixth energy storage bridge arm 60 are connected to the negative end of the direct current power grid, so that the mutual conversion between alternating current and direct current in the energy storage system can be realized.
Further, according to the scheme of the embodiment, each bridge arm is reversely connected with one diode in parallel, and two diodes in each phase cluster are connected in series. By the arrangement mode, when a bipolar short-circuit fault occurs on the direct current side of the energy storage system, before protection action, fault current flows through the energy storage bridge arm; after protection, the energy storage bridge arm is locked, most of short-circuit fault current forms a loop through the anti-parallel diodes, and the current passing through the energy storage bridge arm is small, so that the energy storage bridge arm is prevented from being damaged.
It should be noted that in one embodiment, to ensure that the individual diodes can withstand the current flowing through the storage circuit after the protective action, the diodes should be selected to withstand a large current. For example, in one embodiment, a diode of the type that can withstand a pulse current of greater than 1000A for a short period of time may be selected to provide a wider range of usage scenarios for the tank circuit. In a more detailed embodiment, the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5 and the sixth diode D6 are all anti-reverse diodes of the type MDK55a1600V, and the diodes have a withstand voltage of 1600V and can bear a pulse current of 1300A in a short time.
Referring to fig. 2, in an embodiment, the energy storage circuit further includes a first inductor L1, a second inductor L2, a third inductor L3, a fourth inductor L4, a fifth inductor L5, and a sixth inductor L6, a second end of the first energy storage leg 10 is connected to a first end of the first inductor L1, a second end of the first inductor L1 is connected to a first end of the second inductor L2 and an anode of the first diode D1, a common end is used for connecting a first phase line of a three-phase power grid, and a second end of the second inductor L2 is connected to a first end of the second energy storage leg 20; a second end of the third energy storage bridge arm 30 is connected with a first end of a third inductor L3, a second end of the third inductor L3 is connected with a first end of a fourth inductor L4 and an anode of a third diode D3, a common end of the third inductor L3 is used for connecting a second phase line of a three-phase power grid, and a second end of the fourth inductor L4 is connected with a first end of a fourth energy storage bridge arm 40; the second end of the fifth energy-storage bridge arm 50 is connected to the first end of a fifth inductor L5, the second end of the fifth inductor L5 is connected to the first end of a sixth inductor L6 and the anode of a fifth diode D5, the common end of the fifth inductor L5 is used for connecting a third phase line of a three-phase power grid, and the second end of the sixth inductor L6 is connected to the first end of the sixth energy-storage bridge arm 60.
Specifically, in the technical scheme of this embodiment, each bridge arm of the energy storage circuit is further provided with an inductor to realize connection between the bridge arms, that is, two bridge arms in each phase cluster are respectively provided with an inductor, and two bridge arms in the same phase cluster are connected through two inductors. In the scheme of this embodiment, the first inductor L1, the second inductor L2, the third inductor L3, the fourth inductor L4, the fifth inductor L5, and the sixth inductor L6 are arranged, so that the grid-connection requirement of the ac interface can be met, and the harmonic in the outlet current of the ac side is filtered; and the functions of suppressing the inter-phase commutation and suppressing the fault current rise rate in the case of a fault of the direct current bus.
It should be noted that in one embodiment, in order to minimize the size of the tank circuit and reduce the circuit cost, an inductor with an inductance value of 11mH may be selected as the connecting inductor between the bridge arms.
With reference to fig. 2, in an embodiment, the energy storage circuit further includes a seventh inductor L7, an eighth inductor L8, and a ninth inductor L9, the second terminal of the first inductor L1 is connected to the first terminal of the second inductor L2 and the anode of the first diode D1, and the common terminal is connected to the first phase line of the three-phase grid through the seventh inductor L7; a second end of the third inductor L3 is connected to a first end of the fourth inductor L4 and an anode of the third diode D3, and a common end is connected to a second phase line of the three-phase power grid through the eighth inductor L8; a second terminal of the fifth inductor L5 is connected to the first terminal of the sixth inductor L6 and the anode of the fifth diode D5, and the common terminal is connected to the third phase line of the three-phase grid through the ninth inductor L9.
Specifically, the scheme of this embodiment further provides three ac-side connection inductors in the energy storage circuit, a common end of the first inductor L1 and the second inductor L2 is connected to the first phase of the ac power grid through the seventh inductor L7, a common end of the third inductor L3 and the fourth inductor L4 is connected to the second phase of the ac power grid through the eighth inductor L8, and a common end of the fifth inductor L5 and the sixth inductor L6 is connected to the third phase of the ac power grid through the ninth inductor L9. The setting of inductance is connected through the interchange side to this embodiment, can further filter the current harmonic of interchange side export, guarantees energy storage circuit's operational reliability.
It should be noted that, in an embodiment, after the ac-side connection inductor takes the filtering effect into consideration, an inductor with an inductance of 1mH may be used as the ac-side connection inductor, that is, the seventh inductor L7, the eighth inductor L8, and the ninth inductor L9 may all be inductors with an inductance of 1 mH.
With continued reference to fig. 2, in one embodiment, each of the plurality of energy storage legs includes a plurality of energy storage cells connected in series.
Specifically, in this embodiment, the first energy storage bridge arm 10, the second energy storage bridge arm 20, the third energy storage bridge arm 30, the fourth energy storage bridge arm 40, the fifth energy storage bridge arm 50, and the sixth energy storage bridge arm 60 all include a plurality of energy storage units, and in each energy storage bridge arm, the energy storage units are connected in series, that is, the first end of the first energy storage unit is used as the first end of the energy storage bridge arm, the second end of the first energy storage unit is connected to the first end of the second energy storage unit, the second end of the second energy storage unit is connected to the first end … … of the third energy storage unit until the last energy storage unit, and the second end of the last energy storage unit is used as the second end of the energy storage bridge arm, that is, the series connection of the energy storage units is realized.
It can be understood that the number of energy storage cells in each energy storage bridge arm is not unique, and in a more detailed embodiment, the number of energy storage cells in each bridge arm may be the same, that is, the number of energy storage cells connected in series in the first energy storage bridge arm 10, the second energy storage bridge arm 20, the third energy storage bridge arm 30, the fourth energy storage bridge arm 40, the fifth energy storage bridge arm 50, and the sixth energy storage bridge arm 60 is the same.
Further, in an embodiment, each phase cluster may be provided with 40 energy storage cells, that is, the number of the energy storage cells in each bridge arm is 20, and each of the first energy storage bridge arm 10, the second energy storage bridge arm 20, the third energy storage bridge arm 30, the fourth energy storage bridge arm 40, the fifth energy storage bridge arm 50, and the sixth energy storage bridge arm 60 is formed by connecting 20 energy storage cells in series.
It should be noted that the structure of the energy storage unit is not exclusive, and referring to fig. 3 in combination, in an embodiment, the energy storage unit includes a first switching device T1, a second switching device T2, a first freewheeling diode D7, a second freewheeling diode D8 and an energy storage device U, a control terminal of the first switching device T1 and a control terminal of the second switching device T2 are respectively used for connecting an external control device, a first terminal of the switching device is connected to a cathode of the first freewheeling diode D7 and a first terminal of the energy storage device U, a second terminal of the first switching device T1 is connected to an anode of the first freewheeling diode D7 and a first terminal of the second switching device T2, a cathode of the second freewheeling diode D8 is connected to a first terminal of the second switching device T2, a second terminal of the second switching device T2 is connected to an anode of the second freewheeling diode D8 and a second terminal of the energy storage device U, a second terminal of the first switching device T1 is used as a first terminal of the energy storage unit, a second terminal of the second switching device T2 serves as a second terminal of the energy storage unit.
Specifically, in the scheme of this embodiment, the second terminal of the first switching device T1 is used as the first terminal of the energy storage unit, and the second terminal of the second switching device T2 is used as the second terminal of the energy storage unit, and the energy storage units can be connected in series by using the above manner. The energy storage unit comprises two switching devices, freewheeling diodes corresponding to the switching devices and an energy storage device U. When a bipolar short-circuit fault occurs on the direct current side of the energy storage system, before protection action, fault current flows through a switching device in the energy storage unit; after the protection action, the switching device is locked, the short-circuit fault current mostly forms a loop through the anti-parallel large-current diodes (namely the first diode D1 to the sixth diode D6), and the current passing through the first freewheeling diode D7 and the second freewheeling diode D8 in the energy storage unit is small, so that the freewheeling diodes are prevented from being damaged.
Further, in an embodiment, referring to fig. 4, the energy storage unit further includes a filter capacitor C0, a first terminal of the filter capacitor C0 is connected to the first terminal of the first switching device T1 and the first terminal of the energy storage device U, and a second terminal of the filter capacitor C0 is connected to the second terminal of the second switching device T2 and the second terminal of the energy storage device U.
Specifically, this embodiment still has filter capacitor C0 in parallel at energy storage device U's both ends, can effectively filter the clutter in the energy storage unit through this filter capacitor C0, effectively improves the operational reliability of energy storage unit.
It is to be understood that the specific type of energy storage device U is not exclusive and in one embodiment, the energy storage device U is a battery. Further, a lithium titanate battery can be used as the energy storage device U. In a more detailed embodiment, a high lithium titanate battery is used with a nominal voltage of 48V and a nominal capacity of 55 Ah.
Likewise, the specific types of the first and second switching devices T1 and T2 are not exclusive, as long as on/off control can be performed according to whether a double short circuit fault occurs on the dc side. For example, in one embodiment, the first switching device T1 and the second switching device T2 are all-controlled semiconductor switching devices.
Specifically, the fully-controlled semiconductor switching device is also called a self-turn-off device, and refers to a power electronic device that can be controlled to be turned on and turned off by a control signal. Gate turn-off thyristors, electric field effect transistors, insulated gate bipolar transistors, etc. are all included in this category. In this embodiment, the first switching device T1 and the second switching device T2 both adopt fully-controlled semiconductor switching devices, which have high control reliability, thereby improving the working reliability of the energy storage circuit.
Further, in a more detailed embodiment, the first switching device T1 and the second switching device T2 are both mosfets. Metal-Oxide-Semiconductor Field Effect transistors (MOSFETs) can be classified into an N-channel type in which electrons are dominant and a P-channel type in which holes are dominant, which are generally called N-type Metal-Oxide-Semiconductor Field Effect transistors (NMOSFETs) and P-type Metal-Oxide-Semiconductor Field Effect transistors (PMOSFETs), according to their channel polarities, and which type of MOSFET is specifically used may be selected by a user in various ways according to a specific scenario.
In one embodiment, to ensure that the tank circuit can be used in a higher voltage environment, the voltage resistance of the selected MOSFET should be 100V-150V. Further, in a more detailed embodiment, a power MOSFET of type SFG180N10PF is selected as the switching device of the energy storage unit, which allows a continuous drain current of 180A to pass and a pulsed drain current of 540A to be sustained. In the same energy storage unit, two MOSFETs are connected in a half-bridge structure and are connected with a filter capacitor C0 and an energy storage device U in parallel, and the capacity of the filter capacitor C0 is 6800 uF.
To facilitate an understanding of the various embodiments of the present application, the present application is explained below with reference to specific embodiments. The battery energy storage circuit of the embodiment is applied to a 60kW/380V battery energy storage system, the short-circuit capacity is 6MVA, and the rated voltage of a direct current side is 750V. The rated capacity of a transformer in a power distribution network connected with the energy storage system is 250 kVA. The energy storage unit of this embodiment includes: 2 switching elements and its freewheeling diode, 1 filter capacitor C0 and 1 energy storage battery constitute the energy storage unit according to the mode that connects in parallel. Each phase cluster comprises 40 energy storage units, and each bridge arm comprises 20 energy storage units (that is, each energy storage bridge arm comprises 20 energy storage units connected in series), and the energy storage units are connected in the manner shown in fig. 2 to form the whole energy storage circuit.
In this embodiment, the energy storage device U of the energy storage unit is a lithium titanate battery, and has a rated voltage of 48V and a nominal capacity of 55 Ah. The bridge arm connection inductors (i.e. the first inductor L1 to the sixth inductor L6) connected between the bridge arms mainly have three functions: firstly, the grid-connected requirement of an alternating current interface is met, and harmonic waves in outlet current of an alternating current side are filtered; secondly, inhibiting the phase-to-phase commutation; and thirdly, the fault current rising rate when the direct current bus fails is restrained. Due to the limitation of cost and volume, the bridge arm connection inductance selected in the embodiment is 1 mH. The inductance of the ac side connecting inductors (i.e. the seventh inductor L7 to the ninth inductor L9) is selected to be 1mH after considering the filtering effect. The switching devices (namely the first switching device T1 and the second switching device T2) of the energy storage unit are MOSFETs, the withstand voltage is 100V-150V, and the MOSFETs with the model number of SFG180N10PF are selected as the switching devices of the energy storage unit, the allowable continuous drain current is 180A, and the sustainable pulse drain current is 540A. The 2 MOSFETs are connected in a half-bridge structure and connected with a filter capacitor C0 and a storage battery in parallel, and the capacity of the filter capacitor C0 is 6800 uF. The diodes (i.e., the first diode D1 to the sixth diode D6) which can withstand a large current are anti-reverse diodes of MDK55a1600V, have a withstand voltage of 1600V, and can withstand a pulse current of 1300A in a short time.
When a bipolar short-circuit fault occurs on the direct-current side of the energy storage system, before protection action, fault current flows through the switching device; after the protection action, the switching device is locked, most of short-circuit fault current forms a loop through the anti-parallel large-current diode, and the current passing through the freewheeling diode of the switching device is small, so that the freewheeling diode of the switching device is prevented from being damaged. The embodiment has the advantages that under the same voltage level, the number of required devices is small, and the cost of the system is low; the structure is simple, and the cost for modifying the existing system is lower; and an additional semi-control device such as a thyristor does not need to be added, so that additional control is not needed, and the method is easy to realize.
In the energy storage circuit, the first energy storage bridge arm 10 is connected with the second energy storage bridge arm 20, the third energy storage bridge arm 30 is connected with the fourth energy storage bridge arm 40, and the fifth energy storage bridge arm 50 is connected with the sixth energy storage bridge arm 60 to form a cluster, the first end of the first energy storage bridge arm 10, the first end of the third energy storage bridge arm 30 and the first end of the fifth energy storage bridge arm 50 are connected as direct current positive electrodes to be connected to a positive end of a direct current power grid, and the second end of the second energy storage bridge arm 20, the second end of the fourth energy storage bridge arm 40 and the second end of the sixth energy storage bridge arm 60 are connected as direct current negative electrodes to be connected to a negative end of the direct current power grid. Meanwhile, two ends of the first energy storage bridge arm 10, the second energy storage bridge arm 20, the third energy storage bridge arm 30, the fourth energy storage bridge arm 40, the fifth energy storage bridge arm 50 and the sixth energy storage bridge arm 60 are respectively connected with a diode in a reverse parallel mode. When a bipolar short-circuit fault occurs on the direct current side of the energy storage system, before protection action, fault current flows through an energy storage bridge arm; after protection, the energy storage bridge arm is locked, most of short-circuit fault current forms a loop through the anti-parallel diodes, and the current passing through the energy storage bridge arm is small, so that the energy storage bridge arm is prevented from being damaged. The short-circuit fault processing is carried out through the scheme, under the same voltage level, the number of required devices is small, the cost and the system structure can be effectively reduced, meanwhile, extra half-control devices such as thyristors are not required to be added, extra control is not required, and the short-circuit fault processing circuit has the advantage of easiness in implementation.
A modular multilevel converter comprises the energy storage circuit.
Specifically, as shown in the above embodiments and the accompanying drawings, two bridge arms are connected to form a phase cluster, that is, the first energy storage bridge arm 10 is connected to the second energy storage bridge arm 20 to form a first phase cluster, the third energy storage bridge arm 30 is connected to the fourth energy storage bridge arm 40 to form a second phase cluster, the fifth energy storage bridge arm 50 is connected to the sixth energy storage bridge arm 60 to form a third phase cluster, in each phase cluster, the public end points of the two energy storage bridge arms are respectively connected to the ac side of the energy storage system, that is, to the ac power grid, the first end of the first energy storage bridge arm 10, the first end of the third energy storage bridge arm 30 and the first end of the fifth energy storage bridge arm 50 are connected to the dc side of the energy storage system, that is, to the positive end of the dc power grid, the second end of the second energy storage bridge arm 20, the second end of the fourth energy storage bridge arm 40 and the second end of the sixth energy storage bridge arm 60 are connected to the negative end of the dc power grid, therefore, the interconversion between the alternating current and the direct current in the energy storage system can be realized.
Further, according to the scheme of the embodiment, a diode is connected in parallel in each bridge arm in a reverse direction, and two diodes in each phase cluster are connected in series. By the arrangement mode, when a bipolar short-circuit fault occurs on the direct current side of the energy storage system, before protection action, fault current flows through the energy storage bridge arm; after protection, the energy storage bridge arm is locked, most of short-circuit fault current forms a loop through the anti-parallel diodes, and the current passing through the energy storage bridge arm is small, so that the energy storage bridge arm is prevented from being damaged.
In the modular multilevel converter, the first energy storage bridge arm 10 is connected with the second energy storage bridge arm 20, the third energy storage bridge arm 30 is connected with the fourth energy storage bridge arm 40, and the fifth energy storage bridge arm 50 is connected with the sixth energy storage bridge arm 60 to form a cluster, the first end of the first energy storage bridge arm 10, the first end of the third energy storage bridge arm 30 and the first end of the fifth energy storage bridge arm 50 are connected as direct current positive electrodes to be connected to a positive end of a direct current power grid, and the second end of the second energy storage bridge arm 20, the second end of the fourth energy storage bridge arm 40 and the second end of the sixth energy storage bridge arm 60 are connected as direct current negative electrodes to be connected to a negative end of the direct current power grid. Meanwhile, two ends of the first energy storage bridge arm 10, the second energy storage bridge arm 20, the third energy storage bridge arm 30, the fourth energy storage bridge arm 40, the fifth energy storage bridge arm 50 and the sixth energy storage bridge arm 60 are respectively connected with a diode in a reverse parallel mode. When a bipolar short-circuit fault occurs on the direct current side of the energy storage system, before protection action, fault current flows through an energy storage bridge arm; after protection, the energy storage bridge arm is locked, most of short-circuit fault current forms a loop through the anti-parallel diodes, and the current passing through the energy storage bridge arm is small, so that the energy storage bridge arm is prevented from being damaged. The short-circuit fault processing is carried out through the scheme, under the same voltage level, the number of required devices is small, the cost and the system structure can be effectively reduced, meanwhile, extra half-control devices such as thyristors are not required to be added, extra control is not required, and the short-circuit fault processing circuit has the advantage of easiness in implementation.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the claims. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A tank circuit, comprising: the energy storage bridge comprises a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a first energy storage bridge arm, a second energy storage bridge arm, a third energy storage bridge arm, a fourth energy storage bridge arm, a fifth energy storage bridge arm and a sixth energy storage bridge arm;
the cathode of the first diode is connected with the first end of the first energy storage bridge arm, the anode of the first diode is connected with the cathode of the second diode and the second end of the first energy storage bridge arm, the first end of the second energy storage bridge arm is connected with the second end of the first energy storage bridge arm, the public end of the second energy storage bridge arm is used for connecting a first phase line of a three-phase power grid, the anode of the second diode is connected with the second end of the second energy storage bridge arm, the cathode of the first diode is used for connecting the positive end of a direct-current power grid, and the anode of the diode is used for connecting the negative end of the direct-current power grid;
the cathode of the third diode is connected with the first end of the first energy storage bridge arm and the first end of the third energy storage bridge arm, the anode of the third diode is connected with the cathode of the fourth diode and the second end of the third energy storage bridge arm, the first end of the fourth energy storage bridge arm is connected with the second end of the third energy storage bridge arm, the public end of the fourth energy storage bridge arm is used for connecting a second phase line of the three-phase power grid, and the anode of the fourth diode is connected with the second end of the second energy storage bridge arm and the second end of the fourth energy storage bridge arm;
the cathode of the fifth diode is connected with the first end of the third energy storage bridge arm and the first end of the fifth energy storage bridge arm, the anode of the fifth diode is connected with the cathode of the sixth diode and the second end of the fifth energy storage bridge arm, the first end of the sixth energy storage bridge arm is connected with the second end of the fifth energy storage bridge arm, the public end of the sixth energy storage bridge arm is used for being connected with the third phase line of the three-phase power grid, and the anode of the sixth diode is connected with the second end of the fourth energy storage bridge arm and the second end of the sixth energy storage bridge arm.
2. The energy storage circuit according to claim 1, further comprising a first inductor, a second inductor, a third inductor, a fourth inductor, a fifth inductor and a sixth inductor, wherein the second end of the first energy storage bridge arm is connected to the first end of the first inductor, the second end of the first inductor is connected to the first end of the second inductor and the anode of the first diode, the common end is used for connecting the first phase line of the three-phase power grid, and the second end of the second inductor is connected to the first end of the second energy storage bridge arm; the second end of the third energy storage bridge arm is connected with the first end of the third inductor, the second end of the third inductor is connected with the first end of the fourth inductor and the anode of the third diode, the public end of the third inductor is used for connecting a second phase line of the three-phase power grid, and the second end of the fourth inductor is connected with the first end of the fourth energy storage bridge arm; the second end of the fifth energy storage bridge arm is connected with the first end of the fifth inductor, the second end of the fifth inductor is connected with the first end of the sixth inductor and the anode of the fifth diode, the public end of the fifth inductor is used for being connected with the third phase line of the three-phase power grid, and the second end of the sixth inductor is connected with the first end of the sixth energy storage bridge arm.
3. The energy storage circuit according to claim 2, further comprising a seventh inductor, an eighth inductor and a ninth inductor, wherein the second terminal of the first inductor is connected to the first terminal of the second inductor and the anode of the first diode, and the common terminal is connected to the first phase line of the three-phase power grid through the seventh inductor; the second end of the third inductor is connected with the first end of the fourth inductor and the anode of the third diode, and the public end of the third inductor is connected with the second phase line of the three-phase power grid through the eighth inductor; and the second end of the fifth inductor is connected with the first end of the sixth inductor and the anode of the fifth diode, and the public end of the fifth inductor is connected with the third phase line of the three-phase power grid through the ninth inductor.
4. The tank circuit according to any of claims 1-3 wherein each of the tank legs comprises a plurality of tank cells connected in series.
5. The energy storage circuit according to claim 4, wherein the energy storage unit comprises a first switching device, a second switching device, a first freewheeling diode, a second freewheeling diode and an energy storage device, a control terminal of the first switching device and a control terminal of the second switching device are respectively used for connecting an external control device, a first terminal of the switching device is connected to a cathode of the first freewheeling diode and a first terminal of the energy storage device, a second terminal of the first switching device is connected to an anode of the first freewheeling diode and a first terminal of the second switching device, a cathode of the second freewheeling diode is connected to a first terminal of the second switching device, a second terminal of the second switching device is connected to an anode of the second freewheeling diode and a second terminal of the energy storage device, and a second terminal of the first switching device is used as a first terminal of the energy storage unit, the second end of the second switching device is used as the second end of the energy storage unit.
6. The energy storage circuit of claim 5, wherein the energy storage unit further comprises a filter capacitor, a first terminal of the filter capacitor is connected to the first terminal of the first switching device and the first terminal of the energy storage device, and a second terminal of the filter capacitor is connected to the second terminal of the second switching device and the second terminal of the energy storage device.
7. The energy storage circuit of claim 5, wherein the energy storage device is a battery.
8. The tank circuit of claim 5 wherein the first switching device and the second switching device are all-controlled semiconductor switching devices.
9. The tank circuit of claim 4 wherein the number of tank cells in each tank leg is the same.
10. A modular multilevel converter comprising a tank circuit according to any of claims 1-9.
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| WO2024051217A1 (en) * | 2022-09-06 | 2024-03-14 | 南方电网调峰调频发电有限公司储能科研院 | Battery energy storage circuit and system |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2024051217A1 (en) * | 2022-09-06 | 2024-03-14 | 南方电网调峰调频发电有限公司储能科研院 | Battery energy storage circuit and system |
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