CN111224572A - Gating unit and high-efficiency non-isolated three-level grid-connected inverter - Google Patents

Gating unit and high-efficiency non-isolated three-level grid-connected inverter Download PDF

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Publication number
CN111224572A
CN111224572A CN201911169627.9A CN201911169627A CN111224572A CN 111224572 A CN111224572 A CN 111224572A CN 201911169627 A CN201911169627 A CN 201911169627A CN 111224572 A CN111224572 A CN 111224572A
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China
Prior art keywords
diode
module
terminal
switch
connection
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CN201911169627.9A
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Chinese (zh)
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汪洪亮
朱晓楠
岳秀梅
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Hunan University
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Hunan University
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Priority to CN201911169627.9A priority Critical patent/CN111224572A/en
Publication of CN111224572A publication Critical patent/CN111224572A/en
Priority to PCT/CN2020/121684 priority patent/WO2021103842A1/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control

Abstract

The application discloses a gating unit and a high-efficiency non-isolated three-level grid-connected inverter, and belongs to the field of inverters. The gating unit includes: and the gating circuit module is provided with four terminals including a first terminal, a second terminal, a third terminal and a fourth terminal, provides five working modes under the control of the control signal, and respectively controls the conduction and the disconnection between different terminals under the five different working modes so that the common-mode voltage can keep a constant value in each working mode. The high-efficiency non-isolated three-level grid-connected inverter comprises one gating unit, and compared with an HERIC topological structure, the high-efficiency non-isolated three-level grid-connected inverter has the advantages that one active switch is omitted, and the cost of the active switch in an inverter system occupies a larger proportion, so that the cost is saved. The problem of the dc-to-ac converter leakage current has been solved effectively to this application, in addition, adopts unipolar pulse width modulation mode, and output current ripple is little, and output electric energy quality is high.

Description

Gating unit and high-efficiency non-isolated three-level grid-connected inverter
Technical Field
The embodiment of the application relates to the field of inverters, in particular to a gating unit and a high-efficiency non-isolated three-level grid-connected inverter.
Background
The non-isolated grid-connected inverter structure does not contain a transformer, has the advantages of high conversion efficiency, low volume, weight, cost and the like, the highest conversion efficiency of the system can reach more than 98 percent, and the system is rapidly paid attention by scientific researchers of various countries and pursuing of the industry. The non-isolated grid-connected inverter has two forming modes: single stage and two stage. The single-stage type DC converter is suitable for higher DC input voltage, the lowest input voltage is required to be not lower than the peak value of the grid voltage, and the conversion efficiency of the system is higher and can reach 98.8% at most. The double-stage type can adapt to a wider input voltage range, and the system is optimized and controlled in a grading manner, so that the whole system is very convenient to design. When the non-isolated grid-connected inverter is applied to a photovoltaic power generation system, the advantages of high efficiency, small size, light weight, low cost and the like are brought, and meanwhile, the electrical connection between a battery panel and a power grid is caused. Due to the presence of the parasitic capacitance of the panel to ground, the switching action of the grid-connected inverter power device may cause a high-frequency time-varying voltage to act on the parasitic capacitance, and in a resonant circuit composed of the parasitic capacitance of the panel, the dc/ac filter, the grid impedance, and the like, the impedance is very low in consideration of the optimization of the converter efficiency, so that the common-mode current (also called leakage current or ground current) generated in the circuit may exceed an allowable range. The generation of high frequency common mode currents can cause conducted and radiated interference, and increase of harmonic waves and loss of network access current, and even endanger the safety of equipment and personnel. Therefore, the elimination of the common mode current becomes a barrier that must be overcome in order for the non-isolated grid-connected inverter to be popularized, and becomes one of the hot spots for the research of the photovoltaic grid-connected inverter.
For the leakage current problem of the non-isolated inverter, domestic and foreign scholars propose a plurality of improved topological structures, and typical structures include H5, H6, improved H6, mixed H6, HERIC and other topological structures, and the main thought is as follows: a new follow current loop is constructed, so that the photovoltaic battery side and the alternating current network side are disconnected in a follow current stage, the level of the follow current loop is clamped to a fixed value in combination with a switch modulation mode, even if common-mode voltage is kept unchanged, and therefore generation of leakage current is restrained. Referring to fig. 1, for the HERIC topology proposed by Sunways, a freewheeling circuit consisting of two switching tubes and two diodes is added on the ac side. The switching tubes S1-S4 share most of the switching loss and the conduction loss in the active state. The topological structure device has balanced loss distribution, and is beneficial to prolonging the service life of the switching tube. However, the HERIC topology requires at least six switching devices and six anti-parallel diodes, resulting in increased system cost.
Disclosure of Invention
It is an aim of embodiments of the present application to overcome the above problems or to at least partially solve or mitigate them.
According to an aspect of an embodiment of the present application, there is provided a gating cell including:
a gate circuit module having four terminals including a first terminal, a second terminal, a third terminal and a fourth terminal, and providing five operation modes under the control of a control signal:
under a first working mode, controlling to conduct the connection between the first terminal and the third terminal, conduct the connection between the fourth terminal and the second terminal, and disconnect the other end-to-end connections of the four terminals;
under a second working mode, controlling to conduct the connection between the second end and the fourth end in a unidirectional way, conducting the connection between the third end and the first end in a unidirectional way, and disconnecting other end-to-end connections in the four terminals;
under a third working mode, controlling to conduct the connection between the first end and the fourth end, conducting the connection between the third end and the second end, and disconnecting the other end-to-end connection of the four terminals;
under a fourth working mode, controlling to conduct the connection between the second end and the third end in a unidirectional way, conducting the connection between the fourth end and the first end in a unidirectional way, and disconnecting other end-to-end connections in the four terminals;
and under a fifth working mode, controlling to break the connection between the first end and the second end, conducting the connection between the third end and the fourth end to form a follow current loop, and breaking the connection between other ends of the four terminals.
Optionally, the gating circuit module includes: the first circuit submodule, the second circuit submodule and the third circuit submodule;
the first circuit sub-module and the second circuit sub-module are provided with a first end, a second end and a third end; the third circuit sub-module has a first end, a second end, a third end, and a fourth end;
the first end of the first circuit sub-module, the first end of the second circuit sub-module and the first end of the third circuit sub-module are simultaneously connected with the first end of the gating circuit module;
the second end of the first circuit sub-module, the second end of the second circuit sub-module and the second end of the third circuit sub-module are simultaneously connected with the second end of the gating circuit module;
the third end of the first circuit submodule is connected with the third end of the gating circuit module;
the third end of the second circuit sub-module is connected with the fourth end of the gating circuit module;
the third end and the fourth end of the third circuit sub-module are respectively connected with the third end and the fourth end of the gating circuit module;
the first circuit sub-module provides three working states under the control of the control signal: only the connection between the first terminal and the third terminal is conducted; only conducting the connection between the second terminal and the third terminal; disconnecting all end-to-end connections;
the second circuit sub-module provides three working states under the control of the control signal: only the connection between the first terminal and the third terminal is conducted; only conducting the connection between the second terminal and the third terminal; disconnecting all end-to-end connections;
the third circuit sub-module provides four working states under the control of the control signal: only conducting the connection between the third end and the first end and the connection between the second end and the fourth end; only conducting the connection between the fourth end and the first end and the connection between the second end and the third end; only conducting the connection between the third terminal and the fourth terminal; all connections between end-to-end are broken.
Optionally, the first circuit sub-module includes: a first switch and a second switch;
the first switch is provided with a first end and a second end which are respectively connected with the first end and the third end of the gating circuit module;
the second switch is provided with a first end and a second end, the first end of the second switch is simultaneously connected with the second end of the first switch and the third end of the gating circuit module, and the second end of the second switch is connected with the second end of the gating circuit module.
Optionally, the first switch and the second switch are all full-control devices whose turn-on and turn-off are controllable.
Optionally, the second circuit sub-module includes: a third switch and a fourth switch;
the third switch is provided with a first end and a second end which are respectively connected with the first end and the fourth end of the gating circuit module;
the fourth switch is provided with a first end and a second end, the first end of the fourth switch is simultaneously connected with the second end of the third switch and the fourth end of the gating circuit module, and the second end of the fourth switch is connected with the second end of the gating circuit module.
Optionally, the third switch and the fourth switch are all full-control devices whose on and off are controllable.
Optionally, the third circuit sub-module includes: the first diode, the second diode, the third diode, the fourth diode, the fifth diode, the sixth diode and the fifth switch;
the negative electrode of the first diode is connected with the first end of the gating circuit module;
the cathode of the second diode is connected with the cathode of the fifth diode;
the anode of the second diode is connected with the cathode of the third diode;
the anode of the third diode is connected with the anode of the sixth diode;
the anode of the fourth diode is connected with the second end of the gating circuit module;
the anode of the fifth diode is connected with the cathode of the sixth diode;
the fifth switch has a first end and a second end;
the common end of the second diode and the common end of the fifth diode are connected with the anode of the first diode and the first end of the fifth switch at the same time, the common end of the second diode and the third diode are connected with the third end of the gating circuit module, the common end of the third diode and the sixth diode are connected with the cathode of the fourth diode and the second end of the fifth switch at the same time, and the common end of the fifth diode and the sixth diode is connected with the fourth end of the gating circuit module.
Optionally, the fifth switch is a full-control device whose on and off are controllable.
According to another aspect of the embodiments of the present application, there is provided a high-efficiency non-isolated three-level grid-connected inverter, including: a filter and a gating cell as described above, the filter comprising a first inductance and a second inductance, each having a first terminal and a second terminal;
the first end of the first inductor is connected with the third end of the gating circuit module;
the second end of the second inductor is connected with the fourth end of the gating circuit module;
the second end of the first inductor and the first end of the second inductor are connected to two ends of a power grid.
According to the technical scheme provided by the embodiment of the application, the common-mode voltage can be kept at a constant value in each mode, so that leakage current cannot be generated, and the leakage current suppression effect same as that of a HERIC topological structure can be achieved. In addition, the problem of leakage current generated by a non-isolated three-level grid-connected inverter is effectively solved by matching with a corresponding modulation strategy, and a unipolar pulse width modulation mode is adopted, so that output current ripples are small, and the output electric energy quality is high.
The above and other objects, advantages and features of the present application will become more apparent to those skilled in the art from the following detailed description of specific embodiments thereof, taken in conjunction with the accompanying drawings.
Drawings
Some specific embodiments of the present application will be described in detail hereinafter by way of illustration and not limitation with reference to the accompanying drawings. The same reference numbers in the drawings identify the same or similar elements or components. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale. In the drawings:
FIG. 1 is a prior art HERIC topology block diagram;
fig. 2 is a topology structure diagram of a high-efficiency non-isolated three-level grid-connected inverter according to an embodiment of the present application;
FIG. 3 is a schematic diagram of a modulation strategy according to another embodiment of the present application;
FIG. 4 is a schematic diagram of a first mode of operation of an inverter according to another embodiment of the present application;
FIG. 5 is a schematic diagram of a second mode of operation of an inverter according to another embodiment of the present application;
FIG. 6 is a schematic diagram of a third mode of operation of an inverter according to another embodiment of the present application;
FIG. 7 is a schematic diagram of a fourth mode of operation of an inverter according to another embodiment of the present application;
FIG. 8 is a schematic diagram of a fifth mode of operation of an inverter according to another embodiment of the present application;
fig. 9 is a flow chart of a method of suppressing leakage current according to another embodiment of the present application.
Detailed Description
The high-efficiency non-isolated three-level grid-connected inverter provided by the embodiment of the application has the following output voltage: three + Vdc, 0 and-Vdc, which may be represented by three levels of +1, 0 and-1, respectively. The output of the inverter includes five cases: outputting +1 level (+ Vdc) and active power, outputting +1 level and reactive power, outputting-1 level and active power, outputting-1 level (-Vdc) and reactive power, and outputting 0 level, respectively corresponding to the first to fifth operating modes of the inverter. Where Vdc represents the dc input voltage.
According to an embodiment of the present application, there is provided a gating cell including:
a gate circuit module having four terminals including a first terminal, a second terminal, a third terminal and a fourth terminal, and providing five operation modes under the control of a control signal:
under a first working mode, controlling to conduct the connection between the first end and the third end, conduct the connection between the fourth end and the second end, and disconnect the other end-to-end connections of the four terminals;
under a second working mode, the connection between the second end and the fourth end is controlled to be conducted in a unidirectional mode, the connection between the third end and the first end is controlled to be conducted in a unidirectional mode, and the connection between other ends of the four terminals is disconnected;
under a third working mode, controlling to conduct the connection between the first end and the fourth end, conduct the connection between the third end and the second end, and disconnect the other end-to-end connections of the four terminals;
under a fourth working mode, the connection between the second end and the third end of the unidirectional conduction and the connection between the fourth end and the first end of the unidirectional conduction are controlled, and the connection between other end-to-end of the four terminals is disconnected;
and under a fifth working mode, the connection between the first end and the second end is controlled to be disconnected, the connection between the third end and the fourth end is conducted, a follow current loop is formed, and the connection between the other ends of the four terminals is disconnected.
According to another embodiment of the present application, there is provided a high-efficiency non-isolated three-level grid-connected inverter, including: a filter and a gating cell as described above, the filter comprising a first inductance and a second inductance, each having a first terminal and a second terminal; the first end of the first inductor is connected with the third end of the gating circuit module; the second end of the second inductor is connected with the fourth end of the gating circuit module; the second end of the first inductor and the first end of the second inductor are connected to two ends of the power grid.
Fig. 2 is a topology structure diagram of a high-efficiency non-isolated three-level grid-connected inverter according to an embodiment of the present application. Referring to fig. 2, the gate circuit module has a first terminal at a point P, a second terminal at a point N, a third terminal at a point a, and a fourth terminal at a point B, and controls to turn on the connection between the two points PA and turn on the connection between the two points BN and to turn off the connection between the other ends of the four terminals, for example, in the first operation mode.
In this embodiment, optionally, the gating circuit module includes: the first circuit submodule, the second circuit submodule and the third circuit submodule. The first circuit sub-module and the second circuit sub-module are respectively provided with a first end, a second end and a third end; the third circuit sub-module has a first end, a second end, a third end, and a fourth end.
The first end of the first circuit sub-module, the first end of the second circuit sub-module and the first end of the third circuit sub-module are simultaneously connected with the first end of the gating circuit module; the second end of the first circuit sub-module, the second end of the second circuit sub-module and the second end of the third circuit sub-module are simultaneously connected with the second end of the gating circuit module; the third end of the first circuit submodule is connected with the third end of the gating circuit module; the third end of the second circuit sub-module is connected with the fourth end of the gating circuit module; the third end and the fourth end of the third circuit sub-module are respectively connected with the third end and the fourth end of the gating circuit module;
the first circuit sub-module provides three operating states under control of the control signal: only the connection between the first terminal and the third terminal is conducted; only conducting the connection between the second terminal and the third terminal; disconnecting all end-to-end connections;
the second circuit sub-module provides three working states under the control of the control signal: only the connection between the first terminal and the third terminal is conducted; only conducting the connection between the second terminal and the third terminal; disconnecting all end-to-end connections;
the third circuit sub-module provides four working states under the control of the control signal: only conducting the connection between the third end and the first end and the connection between the second end and the fourth end; only conducting the connection between the fourth end and the first end and the connection between the second end and the third end; only conducting the connection between the third terminal and the fourth terminal; all connections between end-to-end are broken.
Referring to fig. 2, the first circuit sub-module is a first bridge arm formed by switching devices S1 and S2, a first end of the first bridge arm is connected to a point P of a first end of the gating circuit module, a second end of the first bridge arm is connected to a point N of a second end of the gating circuit module, and a third end, that is, a midpoint of the first bridge arm, is connected to a point a of a third end of the gating circuit module. The second circuit sub-module is a second bridge arm consisting of switching devices S3 and S4, a first end of the second bridge arm is connected with a point P at a first end of the gating circuit module, a second end of the second bridge arm is connected with a point N at a second end of the gating circuit module, and a third end, namely the midpoint of the second bridge arm, is connected with a point B at a fourth end of the gating circuit module. The third circuit sub-module is a circuit composed of a switching device S5 and diodes D1-D6, a first end of the third circuit sub-module is connected with a point P of a first end of the gating circuit module, a second end of the third circuit sub-module is connected with a point N of a second end of the gating circuit module, a third end of the third circuit sub-module is connected with a point A of a third end of the gating circuit module, and a fourth end of the third circuit sub-module is connected with a point B of a fourth end.
In this embodiment, optionally, the first circuit sub-module includes: a first switch and a second switch; the first switch is provided with a first end and a second end which are respectively connected with the first end and the third end of the gating circuit module; the second switch is provided with a first end and a second end, the first end of the second switch is simultaneously connected with the second end of the first switch and the third end of the gating circuit module, and the second end of the second switch is connected with the second end of the gating circuit module. Optionally, the first switch and the second switch are all fully-controlled devices whose turn-on and turn-off are controllable.
Referring to fig. 2, the first circuit sub-module includes: and switching devices S1 and S2, wherein a first terminal and a second terminal of the switching device S1 are respectively connected to a first terminal P point and a third terminal A point of the gating circuit module, and a first terminal and a second terminal of the switching device S2 are respectively connected to a third terminal A point and a second terminal N point of the gating circuit module.
In this embodiment of the application, optionally, the second circuit sub-module includes: a third switch and a fourth switch; the third switch is provided with a first end and a second end which are respectively connected with the first end and the fourth end of the gating circuit module; the fourth switch is provided with a first end and a second end, the first end of the fourth switch is simultaneously connected with the second end of the third switch and the fourth end of the gating circuit module, and the second end of the fourth switch is connected with the second end of the gating circuit module. Optionally, the third switch and the fourth switch are all full-control devices whose on and off are controllable.
Referring to fig. 2, the second circuit sub-module includes: and switching devices S3 and S4, wherein a first terminal and a second terminal of the switching device S3 are respectively connected to a first terminal P point and a fourth terminal B point of the gating circuit module, and a first terminal and a second terminal of the switching device S4 are respectively connected to a fourth terminal B point and a second terminal N point of the gating circuit module.
In this embodiment, optionally, the third circuit sub-module includes: the first diode, the second diode, the third diode, the fourth diode, the fifth diode, the sixth diode and the fifth switch; the negative electrode of the first diode is connected with the first end of the gating circuit module; the cathode of the second diode is connected with the cathode of the fifth diode; the anode of the second diode is connected with the cathode of the third diode; the anode of the third diode is connected with the anode of the sixth diode; the anode of the fourth diode is connected with the second end of the gating circuit module; the anode of the fifth diode is connected with the cathode of the sixth diode; the fifth switch has a first end and a second end; the common end of the second diode and the common end of the fifth diode are connected with the anode of the first diode and the first end of the fifth switch at the same time, the common end of the second diode and the third diode are connected with the third end of the gating circuit module, the common end of the third diode and the sixth diode are connected with the cathode of the fourth diode and the second end of the fifth switch at the same time, and the common end of the fifth diode and the sixth diode is connected with the fourth end of the gating circuit module. Optionally, the fifth switch is a fully-controlled device whose on and off are controllable.
Referring to fig. 2, the third circuit sub-module includes: the switching device S5 and the diodes D1 to D6 have a first end connected to the point P of the first end of the gating circuit module, a second end connected to the point N of the second end of the gating circuit module, a third end connected to the point A of the third end of the gating circuit module, and a fourth end connected to the point B of the fourth end of the gating circuit module.
Referring to fig. 2, the high-efficiency non-isolated three-level grid-connected inverter provided in an embodiment of the present application may specifically include:
a photovoltaic panel PV, a capacitor C, switching devices S1, S2, S3, S4, and S5, diodes D1, D2, D3, D4, D5, and D6, and a filter;
the switching devices S1 and S2 form a first bridge arm, and the switching devices S3 and S4 form a second bridge arm; the first bridge arm and the second bridge arm are respectively connected with a capacitor C in parallel, and the capacitor C is connected with the photovoltaic cell panel PV in parallel;
the diode D1, the switching device S5 and the diode D4 are connected in series and then connected with the capacitor C in parallel; the diodes D2 and D3 are connected in series and then connected in parallel with the switching device S5; the diodes D5 and D6 are connected in series and then connected in parallel with the switching device S5;
the midpoint A of the first bridge arm and the midpoint B of the second bridge arm are respectively connected with the first end and the second end of the filter; the anode of diode D2 and the cathode of D3 are both connected to midpoint A of the first leg, and the anode of diode D5 and the cathode of D6 are both connected to midpoint B of the second leg.
In this embodiment, optionally, the modulation wave of the inverter includes: the device comprises a first modulation wave and a second modulation wave, wherein the first modulation wave and the second modulation wave are sine waves and have a phase difference of 180 degrees; the carrier wave of the inverter includes: the carrier wave carrier device comprises a first carrier wave and a second carrier wave, wherein the first carrier wave and the second carrier wave are same-direction stacked carrier waves.
Fig. 3 is a schematic diagram of a modulation strategy according to another embodiment of the present application. Referring to fig. 3, the modulation wave of the inverter includes: first modulated wave um+And a second modulated wave um-They are two sine modulation waves with phase difference of 180 degrees, and are weak current control signals. The carrier wave of the inverter includes: first carrier uaAnd a second carrier ubThey are co-directional stacked carriers. Each pulse in the figure is a control signal for the switching device, a high level indicating that the switching device is controlled to be on, and a low level indicating that the switching device is controlled to be off. The amplitude of the modulation wave is proportional to the amplitude of the AC output of the inverter, so that the amplitude of the modulation wave is largeThe magnitude of the amplitude of the output alternating voltage of the inverter is determined by the magnitude of the output alternating voltage of the inverter. The two sinusoidal modulated waves are compared with the two triangular carrier waves to generate control signals for the switching devices S1-S5, as shown. First modulated wave um+With the first carrier uaComparing the control signals S1 and S4 to obtain a second modulated wave um-And a second carrier ubThe comparison results in the control signals of S2 and S3. E.g. um+Greater than uaThen the control signal of the switching device S1 is high, indicating that S1 is turned on; u. ofm+Less than uaThen the control signal of the switching device S1 is low, indicating that S1 is turned off. The switching device S5 turns on when the switching devices S1, S2, S3, S4 turn off at the same time, thereby providing a zero level freewheeling loop.
Fig. 4 is a schematic diagram of a first mode of operation of an inverter according to another embodiment of the present application. Referring to fig. 4, in the first operation mode, the switching devices S1 and S4 are turned on through comparison of the first modulation wave and the first carrier, the switching devices S2 and S3 are turned off through comparison of the second modulation wave and the second carrier, current flows from the positive bus through S1, L1, L2, S4 to the negative bus, and the inverter outputs +1 level (+ Vdc) and active power.
The common-mode voltage calculation method of the inverter is as follows: common mode voltage (output voltage of the first leg + output voltage of the second leg)/2. Output voltage V of the first bridge armANIs + Vdc, output voltage V of the second legBN0, common mode voltage is Vdc/2; wherein Vdc is the dc input voltage.
Fig. 5 is a schematic diagram of a second mode of operation of an inverter according to another embodiment of the present application. Referring to fig. 5, in the second operation mode, the switching devices S1 and S4 are turned off through the comparison of the first modulation wave and the first carrier, the switching devices S2 and S3 are turned off through the comparison of the second modulation wave and the second carrier, the diodes D1, D2, D4 and D6 are turned on, the current is returned from the negative bus to the positive bus through the diodes D4, D6, L2, L1, D2 and D1, and the inverter outputs +1 level (+ Vdc) and reactive power. Output voltage V of the first bridge armANIs + Vdc, output voltage V of the second legBNIs 0 and the common mode voltage is Vdc/2.
FIG. 6 is a schematic representation of a system according to the present applicationPlease refer to a schematic diagram of a third operation mode of the inverter according to another embodiment. Referring to fig. 6, in the third operation mode, the switching devices S1 and S4 are turned off by comparison of the first modulated wave with the first carrier, the switching devices S2 and S3 are turned on by comparison of the second modulated wave with the second carrier, current flows from the positive bus through S3, L2, L1, S2 to the negative bus, and the inverter outputs-1 level (-Vdc) and active power. Output voltage V of the first bridge armAN0, output voltage V of the second armBNIs + Vdc and the common mode voltage is Vdc/2.
Fig. 7 is a schematic diagram of a fourth mode of operation of an inverter according to another embodiment of the present application. Referring to fig. 7, in the fourth operation mode, the switching devices S1 and S4 are turned off through the comparison of the first modulation wave with the first carrier, the switching devices S2 and S3 are turned off through the comparison of the second modulation wave with the second carrier, the diodes D3, D4, D1, and D5 are turned on, the current returns to the positive bus through the negative bus via the diodes D4, D3, L1, L2, D5, and D1, and the inverter outputs a level-1 (-Vdc) and reactive power. Output voltage V of the first bridge armAN0, output voltage V of the second armBNIs + Vdc and the common mode voltage is Vdc/2.
Fig. 8 is a schematic diagram of a fifth mode of operation of an inverter according to another embodiment of the present application. Referring to fig. 8, in the fifth operating mode, the ac output of the inverter is decoupled from the dc input, i.e. the Grid G is not directly connected to the photovoltaic panel PV, a bidirectional freewheeling loop is formed by the switching device S5 and the diodes D2, D3, D5 and D6, the inverter outputs 0 level, and the common mode voltage maintains Vdc/2 unchanged (see references l.zhang, k.sun, y.xing and m.xing, "H6 transformerless full-Bridge PV Grid-Tied Inverters" in IEEE Transactions on Power Electronics, vol.29, No. 2263, pp.1229-1238, ch mar doi: 10.1109/tpel.2013.0178). When the output level is 0 and the current is positive, a freewheeling loop is formed by a point A through L1, L2, a diode D5, a switching device S5 and a diode D3; when the output is at 0 level and the current is negative, another freewheeling circuit is formed by point B via L2, L1, diode D2, switching device S5 and diode D6.
According to the high-efficiency non-isolated three-level grid-connected inverter, an active branch and a reactive branch in a topological structure are complementary, namely, all active switching devices in the active branch are not multiplexed in the reactive branch, so that all the active switching devices do not need anti-parallel diodes, and the cost is saved.
In this application, optionally, the filter includes a first inductor L1 and a second inductor L2; the first inductor L1 has a first terminal connected to the third terminal (point a) of the gate circuit module and a second terminal L2 has a first terminal and a second terminal connected to the fourth terminal (point B) of the gate circuit module, and the second terminal of the first inductor L1 and the first terminal of the second inductor L2 are connected to two terminals of the grid G. Preferably, the inductive reactance of the first inductor L1 and the second inductor L2 are the same.
According to the inverter provided by the embodiment, the common-mode voltage can be kept at a constant value in each mode, the problem of leakage current generated by a non-isolated three-level grid-connected inverter is effectively solved, and the leakage current suppression effect same as that of a HERIC topological structure can be achieved. Compared with the HERIC topology, the inverter system has the advantages that one active switch is omitted in number of devices, and the cost of the active switch in the inverter system occupies a larger proportion, so that the system cost is saved. In addition, a unipolar pulse width modulation mode is adopted, output current ripples are small, and output electric energy quality is high.
For convenience of description, the efficient non-isolated three-level grid-connected inverter provided by the application is illustrated by taking the application to a photovoltaic power generation system as an example, but is not limited to the application to the photovoltaic power generation system.
The above description is only for the preferred embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (10)

1. A gating cell, comprising:
a gate circuit module having four terminals including a first terminal, a second terminal, a third terminal and a fourth terminal, and providing five operation modes under the control of a control signal:
under a first working mode, controlling to conduct the connection between the first terminal and the third terminal, conduct the connection between the fourth terminal and the second terminal, and disconnect the other end-to-end connections of the four terminals;
under a second working mode, controlling to conduct the connection between the second end and the fourth end in a unidirectional way, conducting the connection between the third end and the first end in a unidirectional way, and disconnecting other end-to-end connections in the four terminals;
under a third working mode, controlling to conduct the connection between the first end and the fourth end, conducting the connection between the third end and the second end, and disconnecting the other end-to-end connection of the four terminals;
under a fourth working mode, controlling to conduct the connection between the second end and the third end in a unidirectional way, conducting the connection between the fourth end and the first end in a unidirectional way, and disconnecting other end-to-end connections in the four terminals;
and under a fifth working mode, controlling to break the connection between the first end and the second end, conducting the connection between the third end and the fourth end to form a follow current loop, and breaking the connection between other ends of the four terminals.
2. The gating cell of claim 1, wherein the gating circuit module comprises: the first circuit submodule, the second circuit submodule and the third circuit submodule;
the first circuit sub-module and the second circuit sub-module are provided with a first end, a second end and a third end; the third circuit sub-module has a first end, a second end, a third end, and a fourth end;
the first end of the first circuit sub-module, the first end of the second circuit sub-module and the first end of the third circuit sub-module are simultaneously connected with the first end of the gating circuit module;
the second end of the first circuit sub-module, the second end of the second circuit sub-module and the second end of the third circuit sub-module are simultaneously connected with the second end of the gating circuit module;
the third end of the first circuit submodule is connected with the third end of the gating circuit module;
the third end of the second circuit sub-module is connected with the fourth end of the gating circuit module;
the third end and the fourth end of the third circuit sub-module are respectively connected with the third end and the fourth end of the gating circuit module;
the first circuit sub-module provides three working states under the control of the control signal: only the connection between the first terminal and the third terminal is conducted; only conducting the connection between the second terminal and the third terminal; disconnecting all end-to-end connections;
the second circuit sub-module provides three working states under the control of the control signal: only the connection between the first terminal and the third terminal is conducted; only conducting the connection between the second terminal and the third terminal; disconnecting all end-to-end connections;
the third circuit sub-module provides four working states under the control of the control signal: only conducting the connection between the third end and the first end and the connection between the second end and the fourth end; only conducting the connection between the fourth end and the first end and the connection between the second end and the third end; only conducting the connection between the third terminal and the fourth terminal; all connections between end-to-end are broken.
3. The gating cell of claim 2, wherein the first circuit sub-module comprises: a first switch and a second switch;
the first switch is provided with a first end and a second end which are respectively connected with the first end and the third end of the gating circuit module;
the second switch is provided with a first end and a second end, the first end of the second switch is simultaneously connected with the second end of the first switch and the third end of the gating circuit module, and the second end of the second switch is connected with the second end of the gating circuit module.
4. The gating cell of claim 3, wherein the first switch and the second switch are all fully controlled devices that are controllable to turn on and off, and are connected in anti-parallel with a single-direction conducting device.
5. The gating cell of claim 2, wherein the second circuit sub-module comprises: a third switch and a fourth switch;
the third switch is provided with a first end and a second end which are respectively connected with the first end and the fourth end of the gating circuit module;
the fourth switch is provided with a first end and a second end, the first end of the fourth switch is simultaneously connected with the second end of the third switch and the fourth end of the gating circuit module, and the second end of the fourth switch is connected with the second end of the gating circuit module.
6. The gating cell of claim 5, wherein the third switch and the fourth switch are all fully controlled devices that are controllable to turn on and off, and are connected in parallel with one unidirectionally conducting device in reverse.
7. The gating cell of claim 2, wherein the third circuit sub-module comprises: the first diode, the second diode, the third diode, the fourth diode, the fifth diode, the sixth diode and the fifth switch;
the negative electrode of the first diode is connected with the first end of the gating circuit module;
the cathode of the second diode is connected with the cathode of the fifth diode;
the anode of the second diode is connected with the cathode of the third diode;
the anode of the third diode is connected with the anode of the sixth diode;
the anode of the fourth diode is connected with the second end of the gating circuit module;
the anode of the fifth diode is connected with the cathode of the sixth diode;
the fifth switch has a first end and a second end;
the common end of the second diode and the common end of the fifth diode are connected with the anode of the first diode and the first end of the fifth switch at the same time, the common end of the second diode and the third diode are connected with the third end of the gating circuit module, the common end of the third diode and the sixth diode are connected with the cathode of the fourth diode and the second end of the fifth switch at the same time, and the common end of the fifth diode and the sixth diode is connected with the fourth end of the gating circuit module.
8. The gating cell of claim 7, wherein the fifth switch is a fully controlled device that is controllable to turn on and off, and is connected in reverse parallel with a unidirectional conducting device.
9. A high-efficiency non-isolated three-level grid-connected inverter is characterized by comprising:
a filter and a gating cell as claimed in any of claims 1 to 8, the filter comprising a first inductance and a second inductance and each having a first terminal and a second terminal;
the first end of the first inductor is connected with the third end of the gating circuit module;
the second end of the second inductor is connected with the fourth end of the gating circuit module;
the second end of the first inductor and the first end of the second inductor are connected to two ends of a power grid.
10. The non-isolated three-level grid-connected inverter according to claim 9, further comprising: a DC power supply and a capacitor;
the positive electrode of the direct current power supply is connected with the first end of the gating circuit module;
the negative electrode of the direct current power supply is connected with the second end of the gating circuit module;
and the capacitor is connected in parallel at two ends of the direct current power supply.
CN201911169627.9A 2019-11-26 2019-11-26 Gating unit and high-efficiency non-isolated three-level grid-connected inverter Pending CN111224572A (en)

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