CN115149833A - Three-level ANPC inverter, control method and photovoltaic system - Google Patents
Three-level ANPC inverter, control method and photovoltaic system Download PDFInfo
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- CN115149833A CN115149833A CN202210886972.XA CN202210886972A CN115149833A CN 115149833 A CN115149833 A CN 115149833A CN 202210886972 A CN202210886972 A CN 202210886972A CN 115149833 A CN115149833 A CN 115149833A
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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
- H02M7/487—Neutral point clamped inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/0048—Circuits or arrangements for reducing losses
- H02M1/0054—Transistor switching losses
- H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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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
- H02M7/53—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
- H02M7/5387—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 in a bridge configuration
- H02M7/53871—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 in a bridge configuration with automatic control of output voltage or current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The application discloses three-level ANPC inverter, control method and photovoltaic system, the inverter includes: the circuit comprises an absorption capacitor, four bridge arm switching tubes, two clamping tubes and a controller; the four bridge arm switch tubes comprise a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series; an absorption capacitor is connected in parallel between the common end of the first switching tube and the second switching tube and the common end of the third switching tube and the fourth switching tube; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor, and the common end of the two clamping tubes is used for connecting a neutral point; and the controller controls the three-level ANPC inverter to output zero level when the three-level ANPC inverter performs zero-crossing switching or envelope, controls all switching tubes of the three-level ANPC inverter to be switched off, and cuts off a discharging path of the absorption capacitor. The absorption capacitor is prevented from discharging to zero when zero-crossing switching or wave-blocking is carried out, the voltage is maintained at half of the direct-current bus voltage, and the safety of the absorption capacitor and the switch tube is protected.
Description
Technical Field
The application relates to the technical field of power electronics, in particular to a three-level ANPC inverter, a control method and a photovoltaic system.
Background
Three-level inverters are commonly used in photovoltaic systems at present, and for example, the existing 1100V or 1500V photovoltaic inverters basically adopt three-level inverters. Common three-level inverters include type I three-level, type T three-level, and Active Neutral Point Clamped (ANPC) three-level.
Referring to fig. 1, a schematic diagram of a three-level ANPC inverter is shown.
The bridge arm comprises four switch tubes T1, T2, T3 and T4 which are sequentially connected in series, wherein the T1 and the T4 are outer tubes, and the T2 and the T3 are inner tubes. And the two ends of the T2 and the T3 after being connected in series are also connected in parallel with the clamping tubes T5 and T6 after being connected in series.
Compared with a three-level NPC inverter, the three-level ANPC inverter has the advantages of more flexible modulation, more balanced loss, capability of realizing active clamping of all switching tubes and the like. The modulation strategy of the three-level ANPC inverter includes two types: the first method is that the outer tube high frequency inner tube power frequency modulation method has short current conversion loop and is suitable for being applied to high power occasions. The high-frequency tubes are large in quantity and large in loss. Secondly, the outer tube power frequency inner tube high frequency modulation method is suitable for medium and small power occasions, the outer tube basically only has conduction loss, and the loss is low; however, the high-frequency tube belongs to a long commutation loop, and the stress borne by the high-frequency tube is higher than that of the first scheme.
In practical application, when the three-level ANPC inverter performs zero-cross switching or envelope, if a circulating current loop of the switching tube is relatively long, the three-level ANPC inverter is unsafe.
Disclosure of Invention
In view of this, the application provides a three-level ANPC inverter, a control method and a photovoltaic system, which can ensure safe operation of the inverter when zero-crossing switching or closing is performed.
In order to solve the above problems, the technical solution provided by the present application is as follows:
the application provides a three-level ANPC inverter, includes: the device comprises an absorption capacitor, four bridge arm switching tubes, two clamping tubes and a controller;
the four bridge arm switch tubes comprise a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series;
an absorption capacitor is connected in parallel between the common end of the first switching tube and the second switching tube and the common end of the third switching tube and the fourth switching tube; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor, and the common end of the two clamping tubes is used for connecting a neutral point;
and the controller is used for controlling the three-level ANPC inverter to output zero level when the three-level ANPC inverter performs zero-crossing switching or wave sealing, controlling all switching tubes of the three-level ANPC inverter to be switched off, and cutting off a discharging path of the absorption capacitor.
Preferably, the controller is specifically configured to control the three-level ANPC inverter to output a zero level when the three-level ANPC inverter performs zero-crossing switching or envelope, turn off the first switching tube and the fourth switching tube, turn off the second switching tube, the third switching tube, the fifth switching tube and the sixth switching tube, and cut off a discharge path of the absorption capacitor.
Preferably, when the three-level ANPC inverter performs zero-crossing switching, the controller is further configured to control the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located after the zero-crossing switching to be conducted, and then control the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located after the zero-crossing switching to be conducted; the bridge arm outer pipe comprises a first switching pipe and a fourth switching pipe, and the bridge arm inner pipe comprises a second switching pipe and a third switching pipe.
Preferably, when the three-level ANPC inverter performs zero-cross switching from the positive half cycle to the negative half cycle, the controller controls the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the zero-cross switching, and then controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the zero-cross switching, which specifically includes:
and the second switching tube and the fifth switching tube are controlled to be conducted, and then the fourth switching tube is controlled to be conducted.
Preferably, when the three-level ANPC inverter performs zero-cross switching from the negative half cycle to the positive half cycle, the controller controls the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the zero-cross switching, and then controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the zero-cross switching, which specifically includes:
and controlling the conduction of the third switching tube and the sixth switching tube and then controlling the conduction of the first switching tube.
Preferably, the method further comprises the following steps: a plurality of voltage-sharing resistors connected in series;
and a plurality of series-connected voltage-sharing resistors are connected with four bridge arm switching tubes in series in parallel.
Preferably, the voltage equalizing resistor is three resistors with the same resistance value.
The application provides a control method of a three-level ANPC inverter, and the three-level ANPC inverter comprises: the circuit comprises an absorption capacitor, four bridge arm switching tubes and two clamping tubes; the four bridge arm switching tubes comprise a first switching tube, a second switching tube, a third switching tube and a fourth switching tube which are sequentially connected in series; an absorption capacitor is connected in parallel between the common end of the first switching tube and the second switching tube and the common end of the third switching tube and the fourth switching tube; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor, and the common end of the two clamping tubes is used for connecting a neutral point;
the control method comprises the following steps:
judging whether the three-level ANPC inverter needs to perform zero-crossing switching or wave sealing;
if the three-level ANPC inverter needs to perform zero-crossing switching or wave sealing, controlling the three-level ANPC inverter to output zero level;
and controlling all switching tubes of the three-level ANPC inverter to be switched off, and cutting off a discharge path of the absorption capacitor.
Preferably, controlling all switching tubes of the three-level ANPC inverter to be turned off specifically includes:
the first switching tube and the fourth switching tube are turned off first, and then the second switching tube, the third switching tube, the fifth switching tube and the sixth switching tube are turned off.
Preferably, when the three-level ANPC inverter performs zero-crossing switching, the method further includes:
controlling the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after zero-crossing switching, and then controlling the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after zero-crossing switching; the bridge arm outer pipe comprises a first switching pipe and a fourth switching pipe, and the bridge arm inner pipe comprises a second switching pipe and a third switching pipe.
Preferably, when the three-level ANPC inverter performs zero-cross switching from the positive half cycle to the negative half cycle, the bridge arm inner tube and the clamp tube corresponding to the half cycle where the three-level ANPC inverter is located after the zero-cross switching are controlled to be conducted, and then the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located after the zero-cross switching is controlled to be conducted, specifically including:
and the second switching tube and the fifth switching tube are controlled to be conducted, and then the fourth switching tube is controlled to be conducted.
Preferably, when the three-level ANPC inverter performs zero-cross switching from the negative half cycle to the positive half cycle, the bridge arm inner tube and the clamp tube corresponding to the half cycle where the three-level ANPC inverter is located after the zero-cross switching are controlled to be conducted, and then the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located after the zero-cross switching is controlled to be conducted, specifically including:
and the conduction of the third switching tube and the sixth switching tube is controlled, and then the conduction of the first switching tube is controlled.
The application provides a photovoltaic system, which is characterized by comprising a three-level ANPC inverter;
the input end of the three-level ANPC inverter is used for being connected with the photovoltaic array.
Therefore, the application has the following beneficial effects:
the application provides a three-level ANPC inverter, includes: the circuit comprises an absorption capacitor, four bridge arm switching tubes, two clamping tubes and a controller; the four bridge arm switch tubes comprise a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series; an absorption capacitor is connected in parallel between the common end of the first switching tube and the second switching tube and the common end of the third switching tube and the fourth switching tube; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor, and the common end of the two clamping tubes is used for connecting a neutral point;
when the three-level ANPC inverter performs zero-crossing switching or wave-sealing, the zero level is also forcibly output, then all the switching tubes are switched off, and the charging and discharging loop of the absorption capacitor is cut off, so that the absorption capacitor is ensured not to be charged and discharged, and is prevented from being discharged to zero when the zero-crossing switching or wave-sealing is performed, the voltage of the absorption capacitor is maintained at half of the voltage of the direct-current bus, various problems are prevented, and the safety of the absorption capacitor and the switching tubes is protected.
Drawings
FIG. 1 is a schematic diagram of a three-level ANPC inverter;
fig. 2 is a schematic diagram of a three-level ANPC inverter according to an embodiment of the present disclosure;
fig. 3 is a schematic diagram of a three-level ANPC inverter outputting zero level according to an embodiment of the present disclosure;
fig. 4 is a schematic diagram of a three-level ANPC inverter shutdown bridge arm outer tube according to an embodiment of the present disclosure;
fig. 5 is a schematic diagram of a three-level ANPC inverter shutdown bridge arm inner tube and a clamp tube according to an embodiment of the present disclosure;
fig. 6 is a schematic diagram illustrating conduction of a bridge arm inner tube and a clamp tube corresponding to a negative half cycle zero level provided in the embodiment of the present application;
fig. 7 is a schematic diagram illustrating conduction of the outer tube of the bridge arm in a negative half cycle after zero-crossing switching according to the embodiment of the present application;
FIG. 8 is a schematic diagram of another three-level ANPC inverter provided in an embodiment of the present application;
fig. 9 is a flowchart of a control method of a three-level ANPC inverter according to an embodiment of the present disclosure;
fig. 10 is a flowchart of a control method for zero-crossing switching of a three-level ANPC inverter according to an embodiment of the present disclosure;
fig. 11 is a flowchart of a control method for time-clipping a three-level ANPC inverter according to an embodiment of the present disclosure.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, embodiments accompanying the drawings are described in detail below.
For a three-level ANPC inverter, in order to reduce the voltage stress of the switching tube during the state switching process, an external absorption measure is generally provided, such as an absorption capacitor, see fig. 1, which is a schematic diagram of a three-level ANPC inverter with an absorption capacitor.
The three-level ANPC inverter comprises an absorption capacitor Cnp, four bridge arm switching tubes and two clamping tubes.
The four bridge arm switching tubes are respectively a first switching tube T1, a second switching tube T2, a third switching tube T3 and a fourth switching tube T4. The first switch tube T1 and the fourth switch tube T4 are outer bridge arm tubes, and the second switch tube T2 and the third switch tube T3 are inner bridge arm tubes.
Two ends of the first switching tube T1 are respectively connected to the positive input terminal DC + of the three-level ANPC inverter and the first end of the second switching tube T2, the second end of the second switching tube T2 is connected to the first end of the third switching tube T3, the second end of the third switching tube T3 is connected to the first end of the fourth switching tube T4, and the second end of the fourth switching tube T4 is connected to the negative input terminal DC-.
And the second end of the second switching tube T2 serves as a bridge arm output end AC.
The two clamping tubes are a fifth switch tube T5 and a sixth switch tube T6 respectively, wherein two ends of the fifth switch tube T5 are connected with the first end and the neutral point of the second switch tube T2 respectively, and two ends of the sixth switch tube T6 are connected with the neutral point and the first end of the fourth switch tube T4 respectively.
Two ends of the absorption capacitor Cnp are respectively connected with the first end of the fifth switch tube T5 and the second end of the sixth switch tube T6.
During steady state operation, the absorption capacitor Cnp will be held at half bus voltage; if the commutation loop of the switching tube is long, the absorption capacitor Cnp with a large capacitance value is needed, and zero-crossing switching of the three-level ANPC inverter may cause the absorption capacitor Cnp to be completely discharged, for example, the following working conditions may occur when the upper half cycle is switched to the lower half cycle and zero-crosses:
after the outer tube T1 is turned off, the absorption capacitor Cnp is discharged first, and then current flows from zero level. The absorption capacitance will discharge to 0, mainly including the following hazards:
1) When the absorption capacitor Cnp is charged and discharged, the absorption capacitor Cnp can vibrate with the circuit stray inductance, and the stress of T2 and T3 is possibly overproof;
2) The charging and discharging current of the absorption capacitor Cnp can pass through the switching tube, so that the switching process of the switching tube exceeds the risk of a safe working area;
3) The anti-du/dt capacity of the absorption capacitor Cnp is limited, and the reliability of the absorption capacitor Cnp is reduced;
therefore, in order to solve the technical problems, the absorption capacitor is ensured not to be charged and discharged when the three-level ANPC inverter is in a zero crossing point or wave-sealing working condition, and the voltage on the absorption capacitor is not discharged to 0, so that the safety of the three-level ANPC inverter is ensured.
Referring to fig. 2, the diagram is a schematic diagram of a three-level ANPC inverter according to an embodiment of the present disclosure.
The present embodiment provides a three-level ANPC inverter, including: the device comprises an absorption capacitor Cnp, four bridge arm switching tubes, two clamping tubes and a controller;
the four bridge arm switch tubes comprise a first switch tube T1, a second switch tube T2, a third switch tube T3 and a fourth switch tube T4 which are sequentially connected in series, and the specific connection relationship refers to the corresponding description in FIG. 1; wherein, DC + is the positive input end of the three-level ANPC inverter, and DC-is the negative input end of the three-level ANPC inverter.
An absorption capacitor Cnp is connected in parallel between the common end of the first switching tube T1 and the second switching tube T2 and the common end of the third switching tube T3 and the fourth switching tube T4; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor Cnp, and the two clamping tubes are respectively the common ends of the two clamping tubes of the fifth switch tube T5 and the sixth switch tube T6 and are used for connecting a neutral point DC _ N;
the controller 100 is configured to control the three-level ANPC inverter to output a zero level when the three-level ANPC inverter performs zero-crossing switching or envelope, control all switching tubes of the three-level ANPC inverter to be turned off, that is, T1 to T6 to be turned off, and cut off a discharging path of the absorption capacitor Cnp after all switching tubes are turned off, so that it is ensured that the voltage of the absorption capacitor Cnp is not discharged to zero.
It should be understood that each of the switching tubes in the technical solution provided in the embodiment of the present application is a controllable switching tube, that is, the controller 100 sends a driving signal to a gate of the switching tube, so as to control a switching state of the switching tube. Each switching tube comprises an anti-parallel diode, which may be integrated inside the switching tube.
The operation principle of the three-level ANPC inverter according to the embodiment of the present application will be described in detail with reference to the accompanying drawings. In order to prevent the absorption capacitor from discharging to zero during zero-crossing switching, the first switching tube and the fourth switching tube are turned off first, then the second switching tube, the third switching tube, the fifth switching tube and the sixth switching tube are turned off, and a discharging path of the absorption capacitor is cut off. It should be understood that, in actual operation, due to different working states, some switching tubes are already in the off state, and at this time, only the other switching tubes need to be turned off.
When the three-level ANPC inverter performs zero-crossing switching, the controller is also used for controlling the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching, and then controlling the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching; the bridge arm outer pipe comprises a first switching pipe and a fourth switching pipe, and the bridge arm inner pipe comprises a second switching pipe and a third switching pipe.
Since the three-level ANPC inverter performs zero-cross switching from the positive half cycle to the negative half cycle, and the corresponding outer tube, inner tube and clamp tube are different from those when performing zero-cross switching from the negative half cycle to the positive half cycle, the following two cases are possible:
when the three-level ANPC inverter performs zero-crossing switching from a positive half cycle to a negative half cycle, the controller controls the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching, and then controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching, and the method specifically comprises the following steps:
and the second switching tube and the fifth switching tube are controlled to be conducted, and then the fourth switching tube is controlled to be conducted.
When the three-level ANPC inverter is switched from the negative half cycle to the positive half cycle in a zero-crossing mode, the controller controls the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter is switched from the zero-crossing mode, and then controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter is switched from the zero-crossing mode, and the method specifically comprises the following steps:
and controlling the conduction of the third switching tube and the sixth switching tube and then controlling the conduction of the first switching tube.
First, the operation principle of zero-crossing switching of the three-level ANPC inverter will be described, and in order to make the skilled person easily understand, the following description will be given by taking the positive half cycle to the negative half cycle switching zero-crossing as an example.
Referring to fig. 3, the graph is a schematic diagram of a three-level ANPC inverter outputting zero level according to an embodiment of the present application.
And a controller (not shown in the figure), which is specifically configured to perform zero-crossing switching in the three-level ANPC inverter, and control the three-level ANPC inverter to output a zero level. For example, the transition is made from the positive half cycle to the output zero level, at which time the outer tube T1 corresponding to the positive half cycle is already turned on, but the output zero level is forcibly controlled, that is, the sixth switching tube T6 and the third switching tube T3 are controlled to be turned on, and the second switching tube T2, the fifth switching tube T5 and the fourth switching tube T4 are turned off.
Referring to fig. 4, the figure is a schematic diagram of a three-level ANPC inverter shutdown bridge arm outer tube according to an embodiment of the present application.
After the zero level is output, the outer tube of the bridge arm is turned off, namely the first switch tube T1 and the fourth switch tube T4 are turned off, and the fourth switch tube T4 is in a turn-off state, so that the first switch tube T1 can be turned off, and the sixth switch tube T6 and the third switch tube T3 are continuously conducted.
And then switching off the bridge arm inner tube and the two clamping tubes.
Referring to fig. 5, the figure is a schematic diagram of a three-level ANPC inverter shutdown bridge arm inner tube and a clamp tube according to an embodiment of the present disclosure.
Comparing fig. 4 and fig. 5, it can be seen that the inner tube T3 of the bridge arm in fig. 5 is turned off, and the clamp switching tube T6 is turned off, so far, four switching tubes included in the bridge arm are all turned off, and two clamp switching tubes are also turned off, that is, all the switching tubes are turned off, and the freewheeling current passes through the anti-parallel diodes of the third switching tube T3 and the fourth switching tube T4.
Since the three-level ANPC inverter performs zero-crossing switching from the positive half cycle to the negative half cycle, and needs to transition to the negative half cycle after the zero-crossing is completed, the bridge arm inner tube and the clamp tube corresponding to the negative half cycle zero level after the zero-crossing switching need to be conducted, see fig. 6, which is a schematic diagram of conducting the bridge arm inner tube and the clamp tube corresponding to the negative half cycle zero level provided in the embodiment of the present application.
As can be seen from fig. 6, the bridge arm inner tube T2 corresponding to the negative half cycle zero level is turned on, and the clamp tube T5 corresponding to the negative half cycle zero level is turned on, at this time, the three-level ANPC inverter continues to output the zero level.
Further, preparation is made for the negative half-cycle transition, that is, the bridge arm outer tube in the negative half cycle after the zero-crossing switching is conducted, see fig. 7, which is a schematic diagram of conducting the bridge arm outer tube in the negative half cycle after the zero-crossing switching provided in the embodiment of the present application.
As can be seen from fig. 7, the outer tube T4 of the bridge arm corresponding to the negative half cycle is turned on, and at this time, the three-level ANPC inverter continues to output the zero level, and is ready for outputting the-1 level.
From a combination of fig. 4-7, fig. 3-5, it can be seen that the voltage at T2 is half the dc bus voltage, i.e., U T2 ＝U BUS Voltage of/2, T3 is U T3 And =0. As can be seen in FIGS. 6-7, the voltage at T3 is half the DC bus voltage, i.e., U T3 ＝U BUS Voltage of/2, T2 is U T2 ＝0。
From the above analysis, it can be seen that the three-level ANPC inverter is always maintained at the half bus voltage during the zero-crossing switching process because the absorption capacitor Cnp is not charged or discharged, because the inner tube voltage does not exceed the half bus.
In addition, since the three-level ANPC inverter has no voltage on the absorption capacitor when it is just started, and after the three-level ANPC inverter is started, the absorption capacitor may be charged with large oscillation or the charging current may damage the switching tube, so as to protect the absorption capacitor and the switching tube, the embodiment of the present application adds the voltage equalizing resistor, which is described in detail below with reference to the accompanying drawings.
Referring to fig. 8, a schematic diagram of another three-level ANPC inverter according to an embodiment of the present disclosure is shown.
The three-level ANPC inverter that this application embodiment provided still includes: a plurality of voltage-sharing resistors connected in series;
and a plurality of series-connected voltage-sharing resistors are connected with four bridge arm switching tubes in series in parallel.
The number of the resistors connected in series is not specifically limited in the embodiment of the present application, and may be two, three, or even more. In addition, other electric elements can be adopted to realize voltage division, namely, when the three-level ANPC inverter is started, initial voltage is provided for the absorption capacitor.
In fig. 8, three resistors are connected in series as an example, and include a first resistor R1, a second resistor R2, and a third resistor R3, the resistances of the three resistors are not limited, and in order to implement voltage sharing, the three resistors may have the same resistance, specifically, R1, R2, and R3 are connected in series and then connected between the positive input terminal DC + and the negative input terminal DC-of the three-level ANPC inverter, and T1 to T4 are also connected in series and then connected between DC + and DC-.
Based on the three-level ANPC inverter provided in the above embodiments, the embodiments of the present application also provide a control method of the three-level ANPC inverter, which is described in detail below with reference to the accompanying drawings.
Referring to fig. 9, the figure is a flowchart of a control method of a three-level ANPC inverter according to an embodiment of the present application.
In the method for controlling a three-level ANPC inverter according to this embodiment, the three-level ANPC inverter includes: the circuit comprises an absorption capacitor, four bridge arm switching tubes and two clamping tubes; the four bridge arm switching tubes comprise a first switching tube, a second switching tube, a third switching tube and a fourth switching tube which are sequentially connected in series; an absorption capacitor is connected in parallel between the common end of the first switching tube and the second switching tube and the common end of the third switching tube and the fourth switching tube; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor, and the common end of the two clamping tubes is used for connecting a neutral point;
the control method comprises the following steps:
s901: judging whether the three-level ANPC inverter needs to perform zero-crossing switching or wave sealing;
s902: if the three-level ANPC inverter needs to perform zero-crossing switching or wave sealing, controlling the three-level ANPC inverter to output a zero level;
s903: and controlling all switching tubes of the three-level ANPC inverter to be switched off, and cutting off a discharge path of the absorption capacitor.
Controlling all switching tubes of the three-level ANPC inverter to be turned off specifically comprises:
the first switching tube and the fourth switching tube are turned off first, and then the second switching tube, the third switching tube, the fifth switching tube and the sixth switching tube are turned off.
The control method for the zero-crossing switching of the three-level ANPC inverter is described below.
Referring to fig. 10, the flowchart of a control method when the three-level ANPC inverter performs zero-crossing switching is shown.
S1001: identifying that zero-crossing switching is required;
s1002: and controlling to output a zero level, namely forcibly outputting the zero level.
S1003: and turning off all bridge arm outer pipes.
S1004: and turning off all bridge arm inner tubes and the clamping tubes.
S1005: and switching on the bridge arm inner tube and the clamping tube corresponding to the half-cycle zero level after zero-crossing switching. For example, when the positive half cycle is switched to the negative half cycle zero crossing, the bridge arm inner tube T2 and the clamp tube T5 are conducted.
S1006: and conducting the outer pipe of the bridge arm in the half cycle after zero-crossing switching. For example, if the zero-crossing switch is followed by a negative half cycle, T4 is turned on. So far, normal end and zero-crossing switching end can be realized.
The bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located after zero-crossing switching are controlled to be conducted, and then the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located after zero-crossing switching is controlled to be conducted; the bridge arm outer tube comprises a first switch tube and a fourth switch tube, and the bridge arm inner tube comprises a second switch tube and a third switch tube.
When the three-level ANPC inverter performs zero-crossing switching from a positive half cycle to a negative half cycle, controlling the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching, and then controlling the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching, specifically comprising the following steps:
and the second switching tube and the fifth switching tube are controlled to be conducted, and then the fourth switching tube is controlled to be conducted.
When the three-level ANPC inverter performs zero-crossing switching from a negative half cycle to a positive half cycle, controlling the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching, and then controlling the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after the three-level ANPC inverter performs zero-crossing switching, specifically comprising the following steps:
and controlling the conduction of the third switching tube and the sixth switching tube and then controlling the conduction of the first switching tube.
According to the control method provided by the embodiment of the application, when the three-level ANPC inverter performs zero-crossing switching, the zero level is forcibly output, then all the switch tubes are turned off, the charging and discharging loop of the absorption capacitor is cut off, and the absorption capacitor is ensured not to be charged and discharged, so that the absorption capacitor is prevented from being discharged to zero when the zero-crossing switching is performed, the voltage of the absorption capacitor is maintained at half of the direct-current bus voltage, various problems are prevented, and the safety of the absorption capacitor and the switch tubes is protected.
The control method during the time-slicing of the three-level ANPC inverter is described below.
Referring to fig. 11, it is a flowchart of a control method for time-sealing of a three-level ANPC inverter according to an embodiment of the present disclosure.
S1101: the signal of the wave seal is identified, and the signal of the wave seal is received when the wave seal is generally carried out, and the wave seal is instructed.
S1102: and controlling to output a zero level, namely forcibly outputting the zero level.
S1103: and turning off all bridge arm outer pipes.
S1104: and turning off all bridge arm inner tubes and the clamping tubes. And at this point, all the switch tubes are turned off, and the wave sealing is finished.
The control method that this application embodiment provided, when three-level ANPC inverter envelope, also force output zero level earlier, and turn off all switch tubes again, cut off absorption capacitor's charge-discharge circuit, ensure that absorption capacitor can not charge-discharge to prevent that absorption capacitor can not discharge to zero when the envelope, make its voltage maintain at half direct current bus voltage, thereby prevent various problems, protect the safety of absorption capacitor and switch tube.
In addition, the embodiment of the present application also provides a photovoltaic system, and the photovoltaic system includes the three-level ANPC inverter described in the above embodiment.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (13)
1. A three-level ANPC inverter, comprising: the device comprises an absorption capacitor, four bridge arm switching tubes, two clamping tubes and a controller;
the four bridge arm switch tubes comprise a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series;
the absorption capacitor is connected in parallel between the common end of the first switching tube and the second switching tube and the common end of the third switching tube and the fourth switching tube; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor, and the common end of the two clamping tubes is used for connecting a neutral point;
the controller is used for controlling the three-level ANPC inverter to output a zero level when the three-level ANPC inverter performs zero-crossing switching or wave sealing, controlling all switching tubes of the three-level ANPC inverter to be switched off, and cutting off a discharging path of the absorption capacitor.
2. The inverter of claim 1, wherein the controller is specifically configured to, when the three-level ANPC inverter performs zero-crossing switching or blanking, control the three-level ANPC inverter to output a zero level, and turn off the first switching tube and the fourth switching tube first, and then turn off the second switching tube, the third switching tube, the fifth switching tube and the sixth switching tube, so as to cut off a discharge path of the absorption capacitor.
3. The inverter of claim 2, wherein when the three-level ANPC inverter performs zero-crossing switching, the controller is further configured to control the bridge arm inner tube and the clamp tube corresponding to a half cycle where the three-level ANPC inverter is located to conduct after the zero-crossing switching, and then control the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to conduct after the zero-crossing switching; the bridge arm outer pipe comprises the first switch pipe and the fourth switch pipe, and the bridge arm inner pipe comprises the second switch pipe and the third switch pipe.
4. The inverter of claim 3, wherein when the three-level ANPC inverter performs zero-crossing switching from a positive half cycle to a negative half cycle, the controller controls the bridge arm inner tube and the clamp tube corresponding to the half cycle where the three-level ANPC inverter performs zero-crossing switching to be conducted, and then controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter performs zero-crossing switching to be conducted, and the method specifically includes:
and controlling the second switching tube to be conducted with the fifth switching tube, and then controlling the fourth switching tube to be conducted.
5. The inverter according to claim 1, wherein when the three-level ANPC inverter performs zero-cross switching from a negative half cycle to a positive half cycle, the controller controls the bridge arm inner tube and the clamp tube corresponding to the half cycle where the three-level ANPC inverter performs zero-cross switching after the zero-cross switching to be conducted, and then controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter performs zero-cross switching to be conducted, and specifically includes:
and controlling the third switching tube and the sixth switching tube to be conducted, and then controlling the first switching tube to be conducted.
6. The inverter according to any one of claims 1 to 5, further comprising: a plurality of voltage-sharing resistors connected in series;
the voltage-sharing resistors connected in series are connected in parallel with the four bridge arm switching tubes connected in series.
7. The inverter according to claim 6, wherein the voltage equalizing resistor is three resistors having the same resistance.
8. A method of controlling a three-level ANPC inverter, the three-level ANPC inverter comprising: the circuit comprises an absorption capacitor, four bridge arm switching tubes and two clamping tubes; the four bridge arm switch tubes comprise a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are sequentially connected in series; the absorption capacitor is connected in parallel between the common end of the first switching tube and the second switching tube and the common end of the third switching tube and the fourth switching tube; the two clamping tubes are connected in series and then connected in parallel at two ends of the absorption capacitor, and the common end of the two clamping tubes is used for connecting a neutral point;
the control method comprises the following steps:
judging whether the three-level ANPC inverter needs to perform zero-crossing switching or wave sealing;
if the three-level ANPC inverter needs to perform zero-crossing switching or wave sealing, controlling the three-level ANPC inverter to output a zero level;
and controlling all switching tubes of the three-level ANPC inverter to be switched off, and cutting off a discharging path of the absorption capacitor.
9. The control method according to claim 8, wherein the controlling of all switching tubes of the three-level ANPC inverter to be off comprises:
the first switching tube and the fourth switching tube are turned off first, and then the second switching tube, the third switching tube, the fifth switching tube and the sixth switching tube are turned off.
10. The control method of claim 8, wherein when the three-level ANPC inverter performs zero-crossing switching, further comprising:
controlling the bridge arm inner tube and the clamping tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after zero-crossing switching, and then controlling the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter is located to be conducted after zero-crossing switching; the bridge arm outer pipe comprises the first switch pipe and the fourth switch pipe, and the bridge arm inner pipe comprises the second switch pipe and the third switch pipe.
11. The control method according to claim 10, wherein when the three-level ANPC inverter performs zero-crossing switching from a positive half cycle to a negative half cycle, the control unit controls the bridge arm inner tube and the clamp tube corresponding to the half cycle where the three-level ANPC inverter performs zero-crossing switching to be conducted, and controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter performs zero-crossing switching to be conducted, specifically includes:
and controlling the second switching tube to be conducted with the fifth switching tube, and then controlling the fourth switching tube to be conducted.
12. The control method according to claim 10, wherein when the three-level ANPC inverter performs zero-crossing switching from a negative half cycle to a positive half cycle, the control method controls the bridge arm inner tube and the clamp tube corresponding to the half cycle where the three-level ANPC inverter performs zero-crossing switching to be conducted, and then controls the bridge arm outer tube corresponding to the half cycle where the three-level ANPC inverter performs zero-crossing switching to be conducted, specifically includes:
and controlling the third switching tube and the sixth switching tube to be conducted, and then controlling the first switching tube to be conducted.
13. A photovoltaic system comprising a three-level ANPC inverter according to any of claims 1-7;
and the input end of the three-level ANPC inverter is used for being connected with the photovoltaic array.
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