Grid-connected inverter system and power generation equipment

Abstract

The utility model discloses a grid-connected inverter system and power generation equipment. The grid-connected inverter system is used for being connected between a bus and a grid-connected point, and comprises a plurality of neutral-point-clamped three-level inverters and a plurality of filter circuits, wherein alternating current sides and direct current sides of the neutral-point-clamped three-level inverters are respectively connected in parallel; the positive half bus access end and the negative half bus access end of the neutral point clamping type three-level inverter are respectively connected with the positive end and the negative end of the bus; an inversion output end used for outputting voltage in the neutral point clamping type three-level inverter is connected with a filtering input end of a filtering circuit, so that the voltage output by the inversion output end is filtered by the filtering circuit and then is output by a filtering output end of the filtering circuit; a voltage output end formed by connecting the filter output ends of the filter circuits for outputting the same phase voltage in all the filter circuits is connected with a grid-connected point; and bus midpoints of all the midpoint clamping type three-level inverters are connected. According to the technical scheme disclosed by the utility model, the operation stability of the grid-connected inverter system can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of power electronics, in particular to a grid-connected inverter system and a power generation device. Background Art

[0002] At present, in order to cope with energy and environmental problems, distributed generation technologies based on renewable energy have been widely studied and scaled up. As a key interface between renewable energy and the power grid, the power electronic grid-connected inverter device directly affects and even determines the performance of the grid-connected system. However, limited by the capacity and temperature limitations of power devices, the energy that a single inverter can provide is limited, making it difficult to be applied to grid-connected systems with large capacity requirements. Therefore, in order to increase the capacity of the power system and improve the power level, a multi-module grid-connected inverter system has emerged.

[0003] The existing multi-module grid-connected inverter system is composed of multiple neutral point clamped (NPC) three-level inverters connected in parallel on the AC side. It has the advantages of high power density, flexible capacity ratio, and low cost. However, it places higher requirements on the performance of NPC three-level inverters when used in parallel. When any one of the parallel NPC three-level inverters is disturbed, it will affect the stable operation of the entire grid-connected inverter system. Among them, when multiple NPC three-level inverters are used in parallel, in order to reduce the volume and cost of the grid-connected inverter system, a common DC bus connection method is usually adopted. On the DC side of the NPC three-level inverter, the positive DC sides of all NPC three-level inverters are connected together, and the negative DC sides of all NPC three-level inverters are connected together. Further, the A, B, and C phases on the AC side of multiple parallel NPC three-level inverters are connected together and then connected to the grid connection point.

[0004] However, due to the differences in the parasitic parameters of the hardware of multiple NPC three-level inverters in the grid-connected inverter system, and the control signals of the grid-connected inverter system cannot be completely synchronized, the potentials of the bus midpoints of each NPC three-level inverter cannot be kept consistent, resulting in zero-sequence circulating current in the common DC bus connection method. On the one hand, the zero-sequence circulating current will increase the stress on the power devices in the NPC three-level inverter, causing additional losses, and thus reducing the operating efficiency and reliability of the NPC three-level inverter. On the other hand, it will also affect the quality of the output current waveform of the NPC three-level inverter and reduce the operating stability of the NPC three-level inverter. Therefore, the operating stability of the existing multi-module grid-connected inverter system is relatively low. Summary of the Utility Model

[0005] In view of this, the present utility model provides a grid-connected inverter system and a power generation device, mainly aiming to solve the technical problem of relatively low operation stability of a multi-module grid-connected inverter system.

[0006] To achieve the above object, the present utility model first provides a grid-connected inverter system for connecting between a bus and a grid connection point. The grid-connected inverter system includes a plurality of filter circuits and a plurality of neutral-point clamped three-level inverters with their AC sides and DC sides connected in parallel respectively.

[0007] The positive half-bus access end of the neutral-point clamped three-level inverter is connected to the positive extreme of the bus, and the negative half-bus access end of the neutral-point clamped three-level inverter is connected to the negative extreme of the bus.

[0008] The inverter output end for outputting voltage in the neutral-point clamped three-level inverter is connected to the filter input end of one of the filter circuits. The filter circuit is used to filter the voltage output from the inverter output end and output the filtered voltage at the filter output end of the filter circuit. Among them, the inverter output end and the filter circuit are in one-to-one correspondence.

[0009] Among all the filter circuits, the filter output ends of the filter circuits outputting the same-phase voltage are connected together to form a voltage output end, and the voltage output end is connected to the grid connection point.

[0010] The bus midpoints of all the neutral-point clamped three-level inverters are connected to each other.

[0011] In an embodiment of the present utility model, the filter circuit includes an inverter-side filter inductor, a grid-side filter inductor and a filter capacitor. The first end of the inverter-side filter inductor is connected to the inverter output end. The second end of the inverter-side filter inductor is respectively connected to the first end of the grid-side filter inductor and the first end of the filter capacitor. The second end of the grid-side filter inductor is connected to the grid connection point. The second ends of the filter capacitors in all the filter circuits corresponding to the same neutral-point clamped three-level inverter are connected to each other.

[0012] In an embodiment of the present utility model, among all the filter circuits connected to the neutral-point clamped three-level inverter, the second end of each filter capacitor is connected to the bus midpoint of the neutral-point clamped three-level inverter.

[0013] In an embodiment of the present utility model, the switching tubes in the neutral-point clamped three-level inverter are insulated gate bipolar transistors.

[0014] In an embodiment of the present utility model, the grid-connected inverter system further includes an inverter controller; the control ends of the inverter controller are respectively connected to the control ends of each switching tube in all the neutral-point clamped three-level inverters, and are used to control the conduction or disconnection of the switching tubes.

[0015] In an embodiment of the present utility model, the inverter controller has a remote communication port; the inverter controller is used to establish a communication connection with a remote host computer through the remote communication port.

[0016] In an embodiment of the present utility model, the inverter controller has a human-machine interaction interface.

[0017] In an embodiment of the present utility model, the grid-connected inverter system further includes an operating indicator light; the light control end of the inverter controller is connected to the operating indicator light and is used to control the operating indicator light to emit light information.

[0018] In an embodiment of the present utility model, the grid-connected inverter system further includes a speaker; the sound control end of the inverter controller is connected to the speaker and is used to control the speaker to emit sound alarm information.

[0019] In addition, to achieve the above object, the present utility model further provides a power generation device, and the power generation device includes the grid-connected inverter system as described above.

[0020] A grid-connected inverter system and a power generation device provided by the present utility model can connect the bus midpoints of a plurality of neutral-point clamped three-level inverters connected in parallel on the AC side to each other, so that the potentials of the bus midpoints of the plurality of neutral-point clamped three-level inverters connected in parallel on the AC side are kept consistent, and further the midpoint potentials of each neutral-point clamped three-level inverter are the same, thereby eliminating the excitation source of the on-state zero-sequence circulating current, significantly reducing the negative impact of the zero-sequence circulating current on the inverter, and further significantly improving the operation stability of the grid-connected inverter system.

[0021] The above description is only an overview of the technical solution of the present utility model. In order to be able to understand the technical means of the present utility model more clearly, it can be implemented according to the content of the specification. And in order to make the above and other objects, features and advantages of the present utility model more obvious and understandable, the specific embodiments of the present utility model are specifically listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the present utility model and constitute a part of the present utility model. The schematic embodiments of the present utility model and their descriptions are used to explain the present utility model and do not constitute an improper limitation of the present utility model. In the drawings:

[0023] Figure 1Shows one of the schematic structural diagrams of a grid-connected inverter system provided by an embodiment of the present invention;

[0024] Figure 2 Shows a schematic structural diagram of an exemplary grid-connected inverter system provided by an embodiment of the present invention;

[0025] Figure 3 Shows the second schematic structural diagram of a grid-connected inverter system provided by an embodiment of the present invention;

[0026] Figure 4a Shows a path schematic diagram of single-phase on-state zero-sequence circulating current when single-phase on-state zero-sequence circulating current appears in an existing grid-connected inverter system provided by an embodiment of the present invention;

[0027] Figure 4b Shows a path schematic diagram of single-phase on-state zero-sequence circulating current when negative half-bus single-phase on-state zero-sequence circulating current appears in an existing grid-connected inverter system provided by an embodiment of the present invention;

[0028] Figure 4c Shows a path schematic diagram of single-phase on-state zero-sequence circulating current in a grid-connected inverter system where the bus midpoints of a neutral-point clamped three-level inverter are interconnected provided by an embodiment of the present invention. Detailed implementation manners

[0029] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0030] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended utility model purpose, the following describes in detail the specific implementation manners, structures, features, and their effects of the application according to the present invention in conjunction with the drawings and preferred embodiments. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0031] The following combines Figures 1 to 4c Describe the grid-connected inverter system and power generation equipment according to some embodiments of the present invention.

[0032] Such as Figure 1As shown, a grid-connected inverter system proposed in an embodiment of the present utility model is used to connect between a bus and a grid connection point. The grid-connected inverter system includes a plurality of filter circuits and a plurality of neutral-point clamped three-level inverters with their AC sides and DC sides connected in parallel respectively. Here, the bus can be a DC bus for outputting direct current in new energy power stations such as power generation stations; further, the grid connection point can be a power access point device such as a step-up transformer for connecting a new energy power station to an external power grid system. Here, the structures of the plurality of neutral-point clamped three-level inverters in the grid-connected inverter system are the same, and the number of neutral-point clamped three-level inverters in the grid-connected inverter system can be determined according to actual situations and is also applicable to this embodiment.

[0033] Specifically, the positive half-bus access terminal Bus+ of the neutral-point clamped three-level inverter is connected to the positive extreme of the bus (not shown in the figure), and the negative half-bus access terminal Bus- of the neutral-point clamped three-level inverter is connected to the negative extreme of the bus (not shown in the figure). Among them, the positive half-bus access terminals Bus+ of each neutral-point clamped three-level inverter can be connected to each other and then connected to the positive extreme of the bus, and the negative half-bus access terminals Bus- of each neutral-point clamped three-level inverter can be connected to each other and then connected to the negative extreme of the bus to achieve parallel connection on the DC side. Here, the switching tubes in each neutral-point clamped three-level inverter in the grid-connected inverter system are Insulate-Gate Bipolar Transistors (IGBTs).

[0034] Among them, the neutral-point clamped three-level inverter is a common inverter, which includes multiple power conversion units, and each power conversion unit is used to output a phase voltage through its own inverter output terminal. Here, the A-phase power conversion unit for outputting the A-phase voltage is a full-bridge circuit, including the fifth A-phase clamping diode Da5, the sixth A-phase clamping diode Da6, and 4 insulated gate bipolar transistors with anti-parallel diodes. The 4 insulated gate bipolar transistors with anti-parallel diodes are respectively the first A-phase insulated gate bipolar transistor Ta1, the second A-phase insulated gate bipolar transistor Ta2, the third A-phase insulated gate bipolar transistor Ta3, and the fourth A-phase insulated gate bipolar transistor Ta4. Further, the B-phase power conversion unit for outputting the B-phase voltage includes the fifth B-phase clamping diode Db5, the sixth B-phase clamping diode Db6, and the first B-phase insulated gate bipolar transistor Tb1, the second B-phase insulated gate bipolar transistor Tb2, the third B-phase insulated gate bipolar transistor Tb3, and the fourth B-phase insulated gate bipolar transistor Tb4 with anti-parallel diodes respectively. Further, the C-phase power conversion unit for outputting the C-phase voltage includes the fifth C-phase clamping diode Dc5, the sixth C-phase clamping diode Dc6, and the first C-phase insulated gate bipolar transistor Tc1, the second C-phase insulated gate bipolar transistor Tc2, the third C-phase insulated gate bipolar transistor Tc3, and the fourth C-phase insulated gate bipolar transistor Tc4 with anti-parallel diodes respectively.

[0035] Further, the inverter output terminal for outputting voltage in the neutral-point clamped three-level inverter is connected to the filter input terminal of one of the filter circuits. The filter circuit is used to filter the voltage output by the inverter output terminal and output the filtered voltage at the filter output terminal of the filter circuit. Among them, the inverter output terminal and the filter circuit are in one-to-one correspondence. Further, the number of filter circuits in the system is the same as the number of inverter output terminals included in all the neutral-point clamped three-level inverters in the system. Further, the filter input terminal of the filter circuit is connected to an inverter output terminal to obtain a voltage, and after filtering the voltage, the filtered voltage is output through the filter output terminal of the filter circuit.

[0036] Further, in all the filter circuits, the filter output terminals of the filter circuits outputting the same phase voltage are connected to form a voltage output terminal, and the voltage output terminal is connected to the point of common coupling.

[0037] As an example, in all the neutral-point-clamped three-level inverters, each inverter output terminal for outputting phase-A electricity is respectively connected to the filter input terminal of a different filter circuit, and the filter output terminal of the above filter circuit is used to output the filtered phase-A voltage; further, the filter output terminals of each filter circuit for outputting phase-A voltage are connected to each other to form a voltage output terminal for outputting phase-A voltage, and the voltage output terminal for outputting phase-A voltage is connected to the grid connection point to output phase-A voltage to the grid connection point.

[0038] Similarly, in all the neutral-point-clamped three-level inverters, each inverter output terminal for outputting phase-B electricity is respectively connected to the filter input terminal of a different filter circuit, and the filter output terminal of the above filter circuit is used to output the filtered phase-B voltage; further, the filter output terminals of each filter circuit for outputting phase-B voltage are connected to each other to form a voltage output terminal for outputting phase-B voltage, and the voltage output terminal for outputting phase-B voltage is connected to the grid connection point to output phase-B voltage to the grid connection point.

[0039] Similarly, in all the neutral-point-clamped three-level inverters, each inverter output terminal for outputting phase-C electricity is respectively connected to the filter input terminal of a different filter circuit, and the filter output terminal of the above filter circuit is used to output the filtered phase-C voltage; further, the filter output terminals of each filter circuit for outputting phase-C voltage are connected to each other to form a voltage output terminal for outputting phase-C voltage, and the voltage output terminal for outputting phase-C voltage is connected to the grid connection point to output phase-C voltage to the grid connection point.

[0040] Further, each of the inverter output terminals in the neutral-point-clamped three-level inverter can be respectively connected to the grid connection point through a filter circuit. Here, the filter input terminal of the filter circuit is connected to the inverter output terminal, and the filter output terminal of the filter circuit is connected to the grid connection point; specifically, the filter circuit includes an inverter-side filter inductor, a grid-side filter inductor, and a filter capacitor. The first end of the inverter-side filter inductor is connected to the inverter output terminal, the second end of the inverter-side filter inductor is respectively connected to the first end of the grid-side filter inductor and the first end of the filter capacitor, and the second end of the grid-side filter inductor is connected to the grid connection point; further, in all the filter circuits connected to the same neutral-point-clamped three-level inverter, the second ends of each filter capacitor are connected to each other. Here, the filter circuits connected to each inverter output terminal are different.

[0041] Further, as an example, such as Figure 2As shown, the grid-connected inverter system includes three neutral-point-clamped three-level inverters, namely the first neutral-point-clamped three-level inverter, the second neutral-point-clamped three-level inverter, and the third neutral-point-clamped three-level inverter. Among them, the first neutral-point-clamped three-level inverter, the second neutral-point-clamped three-level inverter, and the third neutral-point-clamped three-level inverter, the 3 neutral-point-clamped three-level inverters each include 3 power conversion units, and each power conversion unit is connected to a filter circuit through the inverter output terminal of the power conversion unit. Here, the inverter output terminal of the first neutral-point-clamped three-level inverter includes the first phase-A inverter output terminal a1, the first phase-B inverter output terminal b1, and the first phase-C inverter output terminal c1; the inverter output terminal of the second neutral-point-clamped three-level inverter includes the second phase-A inverter output terminal a2, the second phase-B inverter output terminal b2, and the second phase-C inverter output terminal c2; the inverter output terminal of the third neutral-point-clamped three-level inverter includes the third phase-A inverter output terminal a3, the third phase-B inverter output terminal b3, and the third phase-C inverter output terminal c3.

[0042] Specifically, the filter circuit connected to the first phase-A inverter output terminal a1 for outputting the phase-A voltage in the first neutral-point-clamped three-level inverter includes the first phase-A inverter-side filter inductor L11, the first phase-A filter capacitor Cf11, and the first phase-A grid-side filter inductor Lg11; among them, the first phase-A inverter output terminal a1 is connected to the first end of the first phase-A inverter-side filter inductor L11, the second end of the first phase-A inverter-side filter inductor L11 is respectively connected to the first end of the first phase-A filter capacitor Cf11 and the first end of the first phase-A grid-side filter inductor Lg11, and the second end of the first phase-A grid-side filter inductor Lg11 is connected to the grid connection point to output the phase-A voltage to the grid connection point.

[0043] Further, the filter circuit connected to the first phase-B inverter output terminal b1 for outputting the phase-B voltage in the first neutral-point-clamped three-level inverter includes the first phase-B inverter-side filter inductor L12, the first phase-B filter capacitor Cf12, and the first phase-B grid-side filter inductor Lg12; among them, the first phase-B inverter output terminal b1 is connected to the first end of the first phase-B inverter-side filter inductor L12, the second end of the first phase-B inverter-side filter inductor L12 is respectively connected to the first end of the first phase-B filter capacitor Cf12 and the first end of the first phase-B grid-side filter inductor Lg12, and the second end of the first phase-B grid-side filter inductor Lg12 is connected to the grid connection point to output the phase-B voltage to the grid connection point.

[0044] Further, the filtering circuit connected to the first C-phase inverter output terminal c1 for outputting the C-phase voltage in the first neutral-point clamped three-level inverter includes a first C-phase inverter-side filtering inductor L13, a first C-phase filtering capacitor Cf13, and a first C-phase grid-side filtering inductor Lg13; wherein, the first C-phase inverter output terminal c1 is connected to the first end of the first C-phase inverter-side filtering inductor L13, and the second end of the first C-phase inverter-side filtering inductor L13 is respectively connected to the first end of the first C-phase filtering capacitor Cf13 and the first end of the first C-phase grid-side filtering inductor Lg13, and the second end of the first C-phase grid-side filtering inductor Lg13 is connected to the grid connection point to output the C-phase voltage to the grid connection point.

[0045] Similarly, the filtering circuit connected to the second A-phase inverter output terminal a2 for outputting the A-phase voltage in the second neutral-point clamped three-level inverter includes a second A-phase inverter-side filtering inductor L21, a second A-phase filtering capacitor Cf21, and a second A-phase grid-side filtering inductor Lg21; wherein, the second A-phase inverter output terminal a2 is connected to the first end of the second A-phase inverter-side filtering inductor L21, and the second end of the second A-phase inverter-side filtering inductor L21 is respectively connected to the first end of the second A-phase filtering capacitor Cf21 and the first end of the second A-phase grid-side filtering inductor Lg21, and the second end of the second A-phase grid-side filtering inductor Lg21 is connected to the grid connection point to output the A-phase voltage to the grid connection point.

[0046] Further, the filtering circuit connected to the second B-phase inverter output terminal b2 for outputting the B-phase voltage in the second neutral-point clamped three-level inverter includes a second B-phase inverter-side filtering inductor L22, a second B-phase filtering capacitor Cf22, and a second B-phase grid-side filtering inductor Lg22; wherein, the second B-phase inverter output terminal b2 is connected to the first end of the second B-phase inverter-side filtering inductor L22, and the second end of the second B-phase inverter-side filtering inductor L22 is respectively connected to the first end of the second B-phase filtering capacitor Cf22 and the first end of the second B-phase grid-side filtering inductor Lg22, and the second end of the second B-phase grid-side filtering inductor Lg22 is connected to the grid connection point to output the B-phase voltage to the grid connection point.

[0047] Further, the filtering circuit connected to the second C-phase inverter output terminal c2 for outputting the C-phase voltage in the second neutral-point clamped three-level inverter includes a second C-phase inverter-side filtering inductor L23, a second C-phase filtering capacitor Cf23, and a second C-phase grid-side filtering inductor Lg23; wherein, the second C-phase inverter output terminal c2 is connected to the first end of the second C-phase inverter-side filtering inductor L23, and the second end of the second C-phase inverter-side filtering inductor L23 is respectively connected to the first end of the second C-phase filtering capacitor Cf23 and the first end of the second C-phase grid-side filtering inductor Lg23, and the second end of the second C-phase grid-side filtering inductor Lg23 is connected to the grid connection point to output the C-phase voltage to the grid connection point.

[0048] Similarly, the filter circuit connected to the third A-phase inverter output terminal a3 for outputting the A-phase voltage in the third neutral-point clamped three-level inverter includes a third A-phase inverter-side filter inductor L31, a third A-phase filter capacitor Cf31, and a third A-phase grid-side filter inductor Lg31; wherein, the third A-phase inverter output terminal a3 is connected to the first end of the third A-phase inverter-side filter inductor L31, and the second end of the third A-phase inverter-side filter inductor L31 is respectively connected to the first end of the third A-phase filter capacitor Cf31 and the first end of the third A-phase grid-side filter inductor Lg31, and the second end of the third A-phase grid-side filter inductor Lg31 is connected to the grid connection point to output the A-phase voltage to the grid connection point.

[0049] Further, the filter circuit connected to the third B-phase inverter output terminal b3 for outputting the B-phase voltage in the third neutral-point clamped three-level inverter includes a third B-phase inverter-side filter inductor L32, a third B-phase filter capacitor Cf32, and a third B-phase grid-side filter inductor Lg32; wherein, the third B-phase inverter output terminal b3 is connected to the first end of the third B-phase inverter-side filter inductor L32, and the second end of the third B-phase inverter-side filter inductor L32 is respectively connected to the first end of the third B-phase filter capacitor Cf32 and the first end of the third B-phase grid-side filter inductor Lg32, and the second end of the third B-phase grid-side filter inductor Lg32 is connected to the grid connection point to output the B-phase voltage to the grid connection point.

[0050] Further, the filter circuit connected to the third C-phase inverter output terminal c3 for outputting the C-phase voltage in the third neutral-point clamped three-level inverter includes a third C-phase inverter-side filter inductor L33, a third C-phase filter capacitor Cf33, and a third C-phase grid-side filter inductor Lg33; wherein, the third C-phase inverter output terminal c3 is connected to the first end of the third C-phase inverter-side filter inductor L33, and the second end of the third C-phase inverter-side filter inductor L33 is respectively connected to the first end of the third C-phase filter capacitor Cf33 and the first end of the third C-phase grid-side filter inductor Lg33, and the second end of the third C-phase grid-side filter inductor Lg33 is connected to the grid connection point to output the C-phase voltage to the grid connection point.

[0051] Further, the second ends of the first A-phase grid-side filter inductor Lg11, the second A-phase grid-side filter inductor Lg21, and the third A-phase grid-side filter inductor Lg31 are connected to each other; the second ends of the first B-phase grid-side filter inductor Lg12, the second B-phase grid-side filter inductor Lg22, and the third B-phase grid-side filter inductor Lg32 are connected to each other; the second ends of the first C-phase grid-side filter inductor Lg13, the second C-phase grid-side filter inductor Lg23, and the third C-phase grid-side filter inductor Lg33 are connected to each other.

[0052] In an actual use environment, if the grid-connected inverter system includes other numbers of neutral-point-clamped three-level inverters, and each neutral-point-clamped three-level inverter includes other numbers of power conversion units, the connection method of each neutral-point-clamped three-level inverter in the grid-connected inverter system to the grid connection point, and the parallel connection method of the AC side of each neutral-point-clamped three-level inverter can refer to Figure 2 the corresponding examples, which will not be elaborated here and are also applicable to this embodiment.

[0053] Furthermore, as Figure 1 shown, the bus midpoints of all the neutral-point-clamped three-level inverters are connected. As an example, as Figure 2 shown, the grid-connected inverter system includes three neutral-point-clamped three-level inverters, namely the first neutral-point-clamped three-level inverter, the second neutral-point-clamped three-level inverter, and the third neutral-point-clamped three-level inverter. If the bus midpoint of the first neutral-point-clamped three-level inverter is the first midpoint O1, the bus midpoint of the second neutral-point-clamped three-level inverter is the second midpoint O2, and the bus midpoint of the third neutral-point-clamped three-level inverter is the third midpoint O3, then the first midpoint O1, the second midpoint O2, and the third midpoint O3 can be connected to each other.

[0054] The grid-connected inverter system proposed in the embodiment of the present utility model can make the potentials of the bus midpoints of multiple parallel neutral-point-clamped three-level inverters on the AC side consistent by connecting the bus midpoints of multiple parallel neutral-point-clamped three-level inverters on the AC side to each other, and further make the bus midpoint potentials of each neutral-point-clamped three-level inverter the same, thereby eliminating the excitation source of the on-state zero-sequence circulating current; furthermore, the connection method of sharing the bus midpoint can change the current path of the on-state zero-sequence circulating current when multiple neutral-point-clamped three-level inverters are connected in parallel, so that it directly forms a closed loop through the neutral line, and thus no longer flows through the positive and negative buses, which can significantly reduce the negative impact of the zero-sequence circulating current on the inverter, and further significantly improve the operation stability of the grid-connected inverter system.

[0055] In an alternative embodiment, as Figure 3 shown, in all the filter circuits connected to the neutral-point-clamped three-level inverter, the second end of each filter capacitor is connected to the bus midpoint of the neutral-point-clamped three-level inverter. If the grid-connected inverter system includes multiple neutral-point-clamped three-level inverters, the circuit structures of the neutral-point-clamped three-level inverters are the same, and the second ends of all the filter capacitors connected to each neutral-point-clamped three-level inverter are connected to the bus midpoint of this neutral-point-clamped three-level inverter. The embodiment provided in this application can effectively suppress the high-frequency components of the zero-sequence circulating current and improve the reliability of the grid-connected inverter system.

[0056] Furthermore,Figure 4a and Figure 4b respectively show the path schematic diagrams of the single-phase on-state zero-sequence circulating current when two neutral-point clamped three-level inverters do not share the connection of the bus neutral point in the existing grid-connected inverter system. Here, the on-state zero-sequence circulating current does not pass through the filter capacitor, so the filter capacitor will not affect the on-state zero-sequence circulating current, but the filter capacitor has a stronger attenuation ability for the high-frequency components of the switching zero-sequence circulating current.

[0057] Further, as an example, as Figure 4a shown, the two neutral-point clamped three-level inverters are the first neutral-point clamped three-level inverter and the second neutral-point clamped three-level inverter respectively. When a single-phase on-state zero-sequence circulating current appears between the two neutral-point clamped three-level inverters, the single-phase on-state zero-sequence circulating current will flow through the positive half-bus capacitors of the two neutral-point clamped three-level inverters respectively, causing additional losses in the positive half-bus capacitors. This loss is manifested in the form of heat, which makes the temperature of the positive half-bus capacitors rise during operation and shortens the service life of the positive half-bus capacitors.

[0058] Further, as an example, as Figure 4b shown, the two neutral-point clamped three-level inverters are the first neutral-point clamped three-level inverter and the second neutral-point clamped three-level inverter respectively. When a single-phase on-state zero-sequence circulating current appears between the two neutral-point clamped three-level inverters, the single-phase on-state zero-sequence circulating current will flow through the negative half-bus capacitors of the neutral-point clamped three-level inverters, causing additional losses in the negative half-bus capacitors. This loss is manifested in the form of heat, which makes the temperature of the negative half-bus capacitors rise during operation and shortens the service life of the negative half-bus capacitors.

[0059] Further, Figure 4c shows the schematic diagram of the single-phase on-state zero-sequence circulating current loop in the grid-connected inverter system in the embodiment of the present application. The bus neutral points of the neutral-point clamped three-level inverters in the grid-connected inverter system are connected to each other; it can be seen from the figure that the electrical connection method of the grid-connected inverter system provided by the present application will completely eliminate the excitation source for generating the on-state zero-sequence circulating current, change the path of the on-state zero-sequence circulating current, so that the zero-sequence circulating current does not flow through the positive half-bus capacitor and the negative half-bus capacitor, thereby suppressing the negative impact brought by the zero-sequence circulating current to the multi-grid-connected inverter parallel power system.

[0060] In one embodiment, the grid-connected inverter system further includes an inverter controller; wherein, the inverter controller can be a computer device with certain computing capabilities, such as a single-chip microcomputer, a digital signal processor and other computer devices. Further, the control terminals of the inverter controller are respectively connected to the control terminals of each switching tube in all the neutral-point clamped three-level inverters, and are used to control the conduction or disconnection of the switching tubes. Among them, the switching tube can be an insulated gate bipolar transistor.

[0061] Specifically, the inverter controller can be connected to the gates of each insulated gate bipolar transistor in all neutral point clamped three-level inverters. The insulated gate bipolar transistor is turned on by sending a voltage to its gate, and turned off by stopping sending a voltage to its gate. In the embodiment provided in the present application, the on / off states of each switch tube in all neutral point clamped three-level inverters can be controlled by the inverter controller, and thus the AC voltage sent by the grid-connected inverter system to the grid connection point can be controlled, improving the operability of the grid-connected inverter system.

[0062] In one embodiment, the inverter controller has a remote communication port; herein, the inverter controller is used to establish a communication connection with a host computer at a remote end through the remote communication port. Among them, the host computer can be a computer terminal at a remote control room or other locations, and relevant staff can remotely control the operating state of the inverter controller based on the host computer. Specifically, cables such as optical fibers and twisted pairs can be used to connect the host computer to the remote communication port of the inverter controller to establish a communication connection between the host computer and the inverter controller. The embodiment provided in the present application enables relevant staff to remotely control the grid-connected inverter system through the host computer, improving the operability of the grid-connected inverter system.

[0063] In one embodiment, the inverter controller has a human-machine interface. Among them, the human-machine interface can be a serial port touch screen. Specifically, the inverter controller can have a rigid housing, and the human-machine interface is arranged on an outer surface of the rigid housing, facilitating relevant staff to operate the inverter controller at the location of the inverter controller. The embodiment provided in the present application enables relevant staff to read the working information of the grid-connected inverter system through the human-machine interface and can operate the inverter controller, thereby realizing the control of the grid-connected inverter system and improving the operation convenience of the grid-connected inverter system.

[0064] In one embodiment, the grid-connected inverter system further includes an operating indicator light; the light control terminal of the inverter controller is connected to the operating indicator light and is used to control the operating indicator light to emit light information. During actual use, when the grid-connected inverter system is connected to an external AC power grid, the inverter controller can control the operating indicator light to emit a constant light or a flash of a specific color to indicate that the grid-connected inverter system is in a grid-connected operation state. The embodiment provided in the present application enables relevant staff to determine the operating state of the grid-connected inverter system through the lighting state of the operating indicator light, so that relevant staff can intuitively confirm the operating state of the grid-connected inverter system.

[0065] In one embodiment, the grid-connected inverter system further includes a speaker; the sound control terminal of the inverter controller is connected to the speaker and is used to control the speaker to emit a sound alarm message. During actual use, when the grid-connected inverter system is abnormal, the inverter controller can control the speaker to emit a preset alarm prompt sound to indicate that the grid-connected inverter system is in an abnormal state. In the embodiment provided by the present application, when the grid-connected inverter system is abnormal, a sound alarm can be issued so that relevant staff can understand the operating state of the grid-connected inverter system in a timely manner and take corresponding measures.

[0066] It should be noted that the selection of the neutral-point clamped three-level inverter, the inverter controller, and the internal circuit connection method can be determined according to the actual situation, and specific limitations are not made in this embodiment. In addition, the connection method of each device can be determined according to the specific selection of the device, and specific limitations are not made in this embodiment either. The functions of the grid-connected inverter system provided in this embodiment are mainly realized through the circuit connection relationship between each module, rather than depending on the program module in a certain module. In addition, each module in the grid-connected inverter system can be realized by an analog circuit or a digital circuit, and for the inverter controller that can implant a program module, the realization of its module functions can be achieved through the program modules provided by the prior art.

[0067] On the other hand, an embodiment of the present invention provides a power generation device, and the power generation device includes the grid-connected inverter system as described above. Here, the power generation device can be a new energy power generation device such as a wind turbine, a water turbine generator, and a photovoltaic power generation device. The busbar at the AC output end of the power generation device can be connected to the external power grid through the grid-connected inverter system to transmit power to the external power grid.

[0068] The above embodiments only represent several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the utility model patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the utility model patent shall be subject to the appended claims.

Claims

1. A grid-connected inverter system for connecting between a bus and a grid connection point, characterized in that, The grid-connected inverter system includes a plurality of filter circuits and a plurality of neutral-point clamped three-level inverters with the AC side and the DC side connected in parallel respectively; The positive half-bus access terminal of the neutral-point clamped three-level inverter is connected to the positive extreme of the bus, and the negative half-bus access terminal of the neutral-point clamped three-level inverter is connected to the negative extreme of the bus; The inverter output terminal for outputting voltage in the neutral-point clamped three-level inverter is connected to the filter input terminal of a filter circuit. The filter circuit is used to filter the voltage output from the inverter output terminal and output the filtered voltage at the filter output terminal of the filter circuit. Among them, the inverter output terminal and the filter circuit are in one-to-one correspondence; Among all the filter circuits, the filter output terminals of the filter circuits that output the same-phase voltage are connected to form a voltage output terminal, and the voltage output terminal is connected to the grid connection point; The bus midpoints of all the neutral-point clamped three-level inverters are interconnected.

2. The grid-connected inverter system according to claim 1, wherein The filter circuit includes an inverter-side filter inductor, a grid-side filter inductor and a filter capacitor. The first end of the inverter-side filter inductor is connected to the inverter output terminal. The second end of the inverter-side filter inductor is respectively connected to the first end of the grid-side filter inductor and the first end of the filter capacitor. The second end of the grid-side filter inductor is connected to the grid connection point. The second ends of the filter capacitors in all the filter circuits corresponding to the same neutral-point clamped three-level inverter are interconnected.

3. The grid-connected inverter system according to claim 2, characterized in that, Among all the filter circuits connected to the neutral-point clamped three-level inverter, the second end of each filter capacitor is connected to the bus midpoint of the neutral-point clamped three-level inverter.

4. The grid-connected inverter system according to claim 1, characterized in that The switching tubes in the neutral-point clamped three-level inverter are insulated gate bipolar transistors.

5. The grid-connected inverter system according to claim 1, wherein, The grid-connected inverter system further includes an inverter controller; The control terminals of the inverter controller are respectively connected to the control terminals of each switching tube in all the neutral-point clamped three-level inverters, and are used to control the switching tubes to conduct or disconnect.

6. The grid-connected inverter system according to claim 5, characterized in that, The inverter controller has a remote communication port; The inverter controller is used to establish a communication connection with a remote host computer through the remote communication port.

7. The grid-connected inverter system according to claim 5, characterized in that, The inverter controller has a human-machine interface.

8. The grid-connected inverter system according to claim 5, characterized in that The grid-connected inverter system further includes an operation indicator light; The light control terminal of the inverter controller is connected to the operation indicator light, and is used to control the operation indicator light to emit light information.

9. The grid-connected inverter system according to claim 5, wherein The grid-connected inverter system further includes a speaker; The sound control terminal of the inverter controller is connected to the speaker, and is used to control the speaker to emit sound alarm information.

10. A power generation device, characterized in that, The power generation equipment includes the grid-connected inverter system according to any one of claims 1 to 9.

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