CN116345888B - Three-level converter, starting method thereof and electronic equipment - Google Patents
Three-level converter, starting method thereof and electronic equipment Download PDFInfo
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- CN116345888B CN116345888B CN202310618788.1A CN202310618788A CN116345888B CN 116345888 B CN116345888 B CN 116345888B CN 202310618788 A CN202310618788 A CN 202310618788A CN 116345888 B CN116345888 B CN 116345888B
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- 238000000034 method Methods 0.000 title claims abstract description 15
- 239000003990 capacitor Substances 0.000 claims abstract description 160
- 238000010586 diagram Methods 0.000 description 17
- 230000003213 activating effect Effects 0.000 description 4
- HEZMWWAKWCSUCB-PHDIDXHHSA-N (3R,4R)-3,4-dihydroxycyclohexa-1,5-diene-1-carboxylic acid Chemical compound O[C@@H]1C=CC(C(O)=O)=C[C@H]1O HEZMWWAKWCSUCB-PHDIDXHHSA-N 0.000 description 2
- 229910002601 GaN Inorganic materials 0.000 description 2
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 2
- 229910010271 silicon carbide Inorganic materials 0.000 description 2
- 238000010276 construction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
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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
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac 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
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac 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
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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
- H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
- H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
- H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
- H02J9/061—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems for DC powered loads
-
- 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
- H02M1/36—Means for starting or stopping converters
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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
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Business, Economics & Management (AREA)
- Emergency Management (AREA)
- Dc-Dc Converters (AREA)
Abstract
The application relates to a three-level converter, a starting method thereof and electronic equipment, wherein the three-level converter comprises the following components: a main circuit and a start pre-charging circuit; the input power supply, the first inductor, the second diode, the first diode and the bus capacitor of the main circuit are sequentially connected in series to form a loop, the collector electrode of the first switch tube is connected with the positive electrode of the second diode, the emitter electrode of the first switch tube is connected with the collector electrode of the second switch tube, the emitter electrode of the second switch tube is connected with the negative electrode of the input power supply, the first end of the flying capacitor of the main circuit is connected with the negative electrode of the second diode, and the second end of the flying capacitor is connected with the emitter electrode of the first switch tube; the starting pre-charging circuit is connected with the main circuit and is used for pre-charging the flying capacitor when the input power supply is connected with the first voltage, so that the voltage of the flying capacitor reaches the second voltage, the flying capacitor is pre-charged before the switching tube of the three-level converter is conducted, and overvoltage damage of the switching tube can be avoided.
Description
Technical Field
The application relates to the technical field of power electronics, in particular to a three-level converter, a starting method thereof and electronic equipment.
Background
The series-type inverter consists of a plurality of boosting circuits and an inverter circuit, and in order to reduce the construction cost of the photovoltaic power station, the voltage level of the photovoltaic inverter is increased from 1000V to 1500V, which leads to the three-level boosting boost circuit to gradually replace the two-level boosting circuit. Compared with other three-level circuits, the flying capacitor three-level boost has the advantages of less power devices, low common mode noise and the like, and is widely used in 1500V photovoltaic inverter systems.
As shown in FIG. 1, when the input voltage Vin is connected, the flying capacitor Cf has no voltage, which is equivalent to a short circuit, and the input voltage Vin is all applied to the switching tube T2, which is easy to cause overvoltage damage of the switching tube T2.
Disclosure of Invention
The technical problem which is mainly solved by the embodiment of the application is to provide the three-level converter, the starting method thereof and the electronic equipment, and the flying capacitor of the three-level converter can be precharged, so that a switching tube is protected from being damaged.
In order to solve the technical problems, one technical scheme adopted by the embodiment of the application is as follows: there is provided a three-level converter including: a main circuit and a start pre-charging circuit; the main circuit includes: the device comprises an input power supply, a first inductor, a first diode, a second diode, a first switch tube, a second switch tube, a bus capacitor and a flying capacitor, wherein the input power supply, the first inductor, the second diode, the first diode and the bus capacitor are sequentially connected in series to form a loop, the collector of the first switch tube is connected with the positive electrode of the second diode, the emitter of the first switch tube is connected with the collector of the second switch tube, the emitter of the second switch tube is connected with the negative electrode of the input power supply, the first end of the flying capacitor is connected with the negative electrode of the second diode, and the second end of the flying capacitor is connected with the emitter of the first switch tube; the starting precharge circuit is connected with the main circuit, and is used for precharging the flying capacitor when the input power supply is connected with the first voltage, so that the voltage of the flying capacitor reaches the second voltage.
In some embodiments, the enabling precharge circuit includes: a third diode and a first capacitor; the anode of the third diode is connected with the second end of the flying capacitor, the cathode of the third diode is connected with the first end of the first capacitor, and the second end of the first capacitor is connected with the cathode of the input power supply.
In some embodiments, the capacitance of the first capacitor is given by the formula: c3 = (vin_max-v2_max) Cf/v2_max; wherein C3 is the capacitance of the first capacitor, and the unit is Farad; vin_max is the maximum voltage of the input power supply in volts; v2_max is the maximum voltage that the second switching tube can withstand, in volts; cf is the capacitance of the flying capacitor in Farad.
In some embodiments, the capacitance of the flying capacitor is greater than the capacitance of the first capacitor.
In some embodiments, the enabling precharge circuit further comprises: a first resistor and a second resistor; the first end of the first resistor is connected with the second end of the first inductor, the second end of the first resistor is connected with the emitter of the first switch tube, the first end of the second resistor is connected with the second end of the first resistor, and the second end of the second resistor is connected with the negative electrode of the input power supply.
In some embodiments, the resistances of the first and second resistances should satisfy the following condition: vin_min R1/(r1+r2) > vcf_start, and R1> R2; wherein R1 is the resistance of the first resistor, and the unit is ohm; r2 is the resistance of the second resistor, and the unit is ohm; vin_min is the minimum voltage of the input power supply, and is in volts; vcf_start is the start-up voltage of the flying capacitor in volts.
In some embodiments, the three-level converter further comprises: a second main circuit and a second start-up precharge circuit; the second main circuit is connected with the second starting precharge circuit, a first output end of the second main circuit is connected with a first output end of the main circuit, and a second output end of the second main circuit is connected with a second output end of the main circuit.
In order to solve the technical problems, another technical scheme adopted by the embodiment of the application is as follows: there is provided a start-up method applied to a three-level converter as described above, comprising: controlling the three-level converter to enter a starting state at the moment when the input power supply outputs a first voltage; wherein said controlling the three-level converter to enter a start-up state comprises: and charging the flying capacitor through the starting pre-charging circuit so that the voltage of the flying capacitor is a second voltage.
In some embodiments, said charging said flying capacitor by said start-up precharge circuit comprises: the input power supply charges the flying capacitor and the first capacitor of the starting precharge circuit at the same time; when the voltage of the first capacitor is the third voltage, the input power supply charges the flying capacitor through the second resistor of the starting pre-charging circuit until the voltage of the flying capacitor reaches the second voltage.
In some embodiments, the method of starting further comprises: when the voltage of the flying capacitor is the first voltage, the input power supply continuously outputs the first voltage so as to enable the working state of the three-level converter to be switched to a stable state.
Unlike the case of the related art, the present application provides a three-level converter including: a main circuit and a start pre-charging circuit; the main circuit includes: the device comprises an input power supply, a first inductor, a first diode, a second diode, a first switch tube, a second switch tube, a bus capacitor and a flying capacitor, wherein the input power supply, the first inductor, the second diode, the first diode and the bus capacitor are sequentially connected in series to form a loop, the collector of the first switch tube is connected with the positive electrode of the second diode, the emitter of the first switch tube is connected with the collector of the second switch tube, the emitter of the second switch tube is connected with the negative electrode of the input power supply, the first end of the flying capacitor is connected with the negative electrode of the second diode, and the second end of the flying capacitor is connected with the emitter of the first switch tube; the starting precharge circuit is connected with the main circuit, and is used for precharging the flying capacitor when the input power supply is connected with the first voltage, so that the voltage of the flying capacitor reaches the second voltage, and the flying capacitor is precharged before the switching tube of the three-level converter is conducted, and damage of the switching tube due to overvoltage is avoided.
Drawings
One or more embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which the figures of the drawings are not to scale, unless expressly stated otherwise.
FIG. 1 is a schematic diagram of a circuit configuration of a conventional flying capacitor three-level circuit;
fig. 2 is a schematic circuit diagram of a three-level converter according to an embodiment of the present application;
fig. 3 is an equivalent circuit schematic diagram of the three-level converter according to the embodiment of the present application in a start state;
fig. 4 is an equivalent circuit schematic diagram of the three-level converter according to the embodiment of the present application in a stable state;
FIG. 5 is a schematic diagram of voltage waveforms of elements of a three-level converter at start-up in an embodiment of the present application;
FIG. 6 is a schematic diagram of the voltage waveform obtained by amplifying the partial waveform taken in FIG. 5;
FIG. 7 is a schematic diagram of a circuit structure in which multiple boost circuit outputs are connected in parallel, according to an embodiment of the present application;
fig. 8 is a schematic diagram of a circuit structure of another output parallel connection of a multi-path boost circuit according to an embodiment of the present application.
Detailed Description
The present application will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present application, but are not intended to limit the application in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present application.
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
It should be noted that, if not in conflict, the features of the embodiments of the present application may be combined with each other, which is within the protection scope of the present application. In addition, while functional block division is performed in a device diagram and logical order is shown in a flowchart, in some cases, the steps shown or described may be performed in a different order than the block division in the device, or in the flowchart. Moreover, the words "first," "second," "third," "fourth," and the like as used herein do not limit the data and order of execution, but merely distinguish between identical or similar items that have substantially the same function and effect. It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" as used in this specification includes any and all combinations of one or more of the associated listed items.
In addition, the technical features of the embodiments of the present application described below may be combined with each other as long as they do not collide with each other.
In particular, embodiments of the present application are further described below with reference to the accompanying drawings.
Referring to fig. 1, fig. 1 is a schematic circuit diagram of a conventional flying capacitor three-level circuit. As shown in fig. 1, in the conventional flying capacitor three-level circuit, when the input voltage Vin is connected, the flying capacitor Cf has no voltage, which is equivalent to a short circuit, and the input voltage Vin is all applied to the switching tube T2, which is easy to cause overvoltage damage of the switching tube T2. Therefore, the embodiment of the application provides a three-level converter, a starting method thereof and electronic equipment. Before the switching tube of the three-level converter is conducted, the pre-charging circuit is started to pre-charge the flying capacitor of the main circuit, and meanwhile, the voltage at two ends of the switching tube of the main circuit is kept within a safe range, so that the switching tube is protected from being damaged due to overvoltage.
Referring to fig. 2, fig. 2 is a schematic circuit diagram of a three-level converter according to an embodiment of the application. As shown in fig. 2, the three-level converter 100 includes a main circuit and a start-up precharge circuit 10. The main circuit includes: the input power DC, the first inductor Lf, the first diode D1, the second diode D2, the first switching tube T1, the second switching tube T2, the bus capacitor Cn and the flying capacitor Cf are sequentially connected in series to form a loop, the collector of the first switching tube T1 is connected with the positive electrode of the second diode D2, the emitter of the first switching tube T1 is connected with the collector of the second switching tube T2, the emitter of the second switching tube T2 is connected with the negative electrode of the input power DC, the first end of the flying capacitor Cf is connected with the negative electrode of the second diode D2, and the second end of the flying capacitor Cf is connected with the emitter of the first switching tube T1. The start-up pre-charging circuit 10 is connected to the main circuit, and the start-up pre-charging circuit 10 is configured to pre-charge the flying capacitor Cf when the input power DC is connected to the first voltage, so that the voltage of the flying capacitor Cf reaches the second voltage.
Wherein, the first inductance Lf is used for filtering. The first voltage is the input voltage of the input power supply DC, the value range of the first voltage is [ vin_min, vin_max ], vin_min is the minimum voltage of the input power supply DC, and vin_max is the maximum voltage of the input power supply DC. The value of vin_min and the value of vin_max can be reasonably set according to actual requirements.
Specifically, the value of the second voltage needs to be greater than or equal to the starting voltage of the flying capacitor Cf. The start voltage of the flying capacitor Cf is a voltage that just enables the three-level converter 100 to perform the boosting operation when the first switching tube T1 or the second switching tube T2 of the three-level converter 100 is turned on.
In some embodiments, activating the precharge circuit 10 includes: a third diode D3 and a first capacitance C3. The positive pole of the third diode D3 is connected with the second end of the flying capacitor Cf, the negative pole of the third diode D3 is connected with the first end of the first capacitor C3, and the second end of the first capacitor C3 is connected with the negative pole of the input power supply DC.
In some embodiments, activating the precharge circuit 10 further includes: a first resistor R1 and a second resistor R2. The first end of the first resistor R1 is connected with the second end of the first inductor Lf, the second end of the first resistor R1 is connected with the emitter of the first switch tube T1, the first end of the second resistor R2 is connected with the second end of the first resistor R1, and the second end of the second resistor R2 is connected with the negative electrode of the input power supply DC.
The first diode D1, the second diode D2, and the third diode D3 are all diodes of the types silicon carbide diode, fast recovery diode (Fast recovery diode, FRD), and the like.
The first capacitor C3 may be an electrolytic capacitor, or a capacitor of other materials.
The first switching tube T1 and the second switching tube T2 may be semiconductor full-control devices such as IGBTs (Insulated Gate Bipolar Transistor, insulated gate bipolar transistors), siC mosfets (silicon carbide field effect transistors), gaN (gallium nitride) transistors, and the like.
In the embodiment of the present application, the three-level converter 100 includes two operating states, i.e., a start-up state and a steady state. The starting state is a state in which the first switching tube T1 and the second switching tube T2 are not turned on at the moment when the three-level converter 100 is connected to the input power DC, and the voltage across the flying capacitor Cf and the voltage across the first capacitor C3 are not stable and unchanged. The stable state is that the first switching tube T1 and the second switching tube T2 of the three-level converter 100 are not turned on, and the voltage across the flying capacitor Cf and the voltage across the first capacitor C3 reach stable and unchanged states.
When the three-level converter 100 is in the start-up state, the voltage of the first switching tube T1 is equal to the voltage across the flying capacitor Cf, and the voltage of the second switching tube T2 is equal to the voltage across the first capacitor C3.
When the three-level converter 100 is in a stable state, the voltage of the first switching tube T1 is equal to the voltage of the first resistor R1, and the voltage of the second switching tube T2 is equal to the voltage of the second resistor R2.
Referring to fig. 2 and fig. 3 together, fig. 3 is an equivalent circuit schematic diagram of the three-level converter according to the embodiment of the application in a start-up state.
When the three-level converter is in the on state, the first switching tube T1 and the second switching tube T2 are both in an off state.
The start-up state of fig. 3 is the state of the three-level converter at the instant of switching in the input power supply DC. At this time, the first diode D1, the second diode D2, and the third diode D3 are all turned on, the voltage across the first switching tube T1 is equal to the voltage across the flying capacitor Cf, and the voltage across the second switching tube T2 is also equal to the voltage across the first capacitor C3.
At this time, neglecting the influence of the first inductance Lf, the voltages at the two ends of the flying capacitor Cf and the first capacitor C3 are respectively: VCf =vin×c3/(cf+c3), vc3=vin×cf/(cf+c3). Wherein VCf is the voltage across the flying capacitor Cf in volts; VC3 is the voltage across the first capacitor C3 in volts; vin is the voltage of the input power DC in volts; cf is the capacitance of the flying capacitor Cf in Farad; c3 is the capacitance of the first capacitor C3 in farads.
It should be noted that, by reasonably setting the capacitance of the first capacitor C3 and the capacitance of the flying capacitor Cf, the voltage of the first switching tube T1 and the voltage of the second switching tube T2 can be controlled within a reasonable range at the moment of accessing the input power DC.
In some embodiments, the capacitance of the flying capacitor Cf is greater than the capacitance of the first capacitor C3. In order to make the first capacitor C3 fully charged faster, and to make the voltage across the flying capacitor Cf reach the start-up voltage, it is necessary to set the capacitance of the first capacitor C3 smaller than that of the flying capacitor Cf.
In some embodiments, the capacitance of the first capacitor C3 is given by the formula: c3 = (vin_max-v2_max) Cf/v2_max. Wherein C3 is the capacitance of the first capacitor C3, and the unit is Farad; vin_max is the maximum voltage of the input power DC in volts; v2_max is the maximum voltage that the second switching tube can withstand, in volts; cf is the capacitance of the flying capacitor Cf in Farad.
In order to save costs, the smaller the capacitance of the first capacitor C3, the better. Therefore, the capacitance of the first capacitor C3 needs to satisfy the condition that the voltage across the second switching tube T2 is smaller than the maximum voltage that it can withstand.
Due to the presence of the first capacitor C3, the overvoltage problem of the second switching tube T2 does not occur at the instant of switching on the input power DC. Because of the third diode D3, when the second switching tube T2 needs to be turned on, the electric quantity of the first capacitor C3 does not bleed through the second switching tube T2, and the first capacitor C3 does not affect the normal operation of the three-level converter 100.
Referring to fig. 2 and fig. 4 together, fig. 4 is an equivalent circuit schematic diagram of the three-level converter according to the embodiment of the application in a stable state.
When the three-level converter is in a steady state, the first switching tube T1 and the second switching tube T2 are both in an off state. At this time, the first diode D1 and the second diode D2 are both turned on, the voltage across the first switching tube T1 is equal to the voltage across the first resistor R1, and the voltage across the second switching tube T2 is also equal to the voltage across the second resistor R2. The flying capacitor Cf and the first capacitor C3 are no longer active, and the voltage distribution of the first switching tube T1 and the second switching tube T2 is determined by the first resistor R1 and the second resistor R2. At this time, the voltage across the flying capacitor Cf reaches the start voltage.
At this time, the voltages at two ends of the first switching tube T1 and the second switching tube T2 are respectively: v1=vjn×r1/(r1+r2), v2=vjn×r2/(r1+r2). Wherein VT1 is the voltage at two ends of the first switch tube T1, and the unit is volt; vin is the voltage of the input power DC in volts; VT2 is the voltage at two ends of the second switch tube T2, and the unit is volt; r1 is the resistance of the first resistor R1, and the unit is ohm; r2 is the resistance of the second resistor R2 in ohms.
It should be noted that, by reasonably setting the resistance value of the first resistor R1 and the resistance value of the second resistor R2, the voltage of the first switching tube T1 and the voltage of the second switching tube T2 can be controlled within a reasonable range when the three-level converter 100 is in a stable state, and the voltage of the flying capacitor Cf can reach the starting voltage, so that the first diode D2 is ensured not to be over-voltage when the first switching tube T1 or the second switching tube T2 is turned on.
In some embodiments, the resistances of the first resistor R1 and the second resistor R2 should satisfy the following conditions: vin_min R1/(r1+r2) > vcf_start, and R1> R2. Wherein R1 is the resistance of the first resistor R1, and the unit is ohm; r2 is the resistance of the second resistor R2, and the unit is ohm; vin_min is the minimum voltage of the input power DC in volts; vcf_start is the start-up voltage of the flying capacitor Cf in volts.
In order to make the voltage across the flying capacitor Cf reach the starting voltage, the resistance value of the first resistor R1 and the resistance value of the second resistor R2 need to be reasonably set according to the minimum voltage of the input power.
The starting voltage of the flying capacitor Cf is a voltage that just enables the three-level converter 100 to perform the boosting operation when the first switching tube T1 or the second switching tube T2 of the three-level converter 100 is turned on.
Referring to fig. 5 and fig. 6, fig. 5 is a schematic voltage waveform diagram of each element of the three-level converter in the embodiment of the application when the three-level converter is started, and fig. 6 is a schematic voltage waveform diagram obtained by amplifying a part of the waveforms cut in fig. 5.
In fig. 5 and 6, the abscissa indicates time in seconds; the ordinate is voltage in V. The voltage of the input power DC is 1200V.
As shown in fig. 5, at 0.1 seconds, the input power DC inputs 1200V of direct current to the three-level converter 100, and at the moment of inputting 1200V of voltage, both the voltage VCf of the flying capacitor Cf and the voltage VT1 of the first switching tube T1 rise to 400V, and both the voltage VC3 of the first capacitor C3 and the voltage VT2 of the second switching tube T2 rise to 800V. The capacitance of the first capacitor C3 is smaller than the capacitance of the flying capacitor Cf, so that the first capacitor C3 is filled up quickly and the voltage VC3 is kept at 800V.
As shown in fig. 6, after the 1200V voltage is input, the three-level converter is in a start-up state, the voltage VC3 across the first capacitor C3 rapidly rises to 800V, and the voltage VCf across the flying capacitor Cf rapidly rises to 400V.
In fig. 5, in the period of 0.1 to 1 second, the three-level converter 100 is in the start-up state, the first capacitor C3 and the flying capacitor Cf are both charged, the first capacitor C3 is fully charged after being powered up, the flying capacitor Cf gradually reaches the start-up voltage after being powered up, and the start-up voltage is 700V in fig. 5.
In fig. 5, three-level converter 100 is in a steady state after 1 second. The voltage across the flying capacitor Cf reaches the start-up voltage, 700V. Since the flying capacitor Cf is not yet full at this time, the voltage VT1 across the first switching tube T1 is also 700V. The voltage VT2 across the second switching tube T2 is 500V. At this time, the voltage of the first switching tube T1 and the voltage of the second switching tube T2 are determined by the resistance of the first resistor R1 and the resistance of the second resistor R2.
In some embodiments, the three-level converter further comprises: a second main circuit and a second start-up precharge circuit. The second main circuit is connected with the second starting precharge circuit, a first output end of the second main circuit is connected with a first output end of the main circuit, and a second output end of the second main circuit is connected with a second output end of the main circuit.
Referring to fig. 7, fig. 7 is a schematic circuit structure diagram of a multi-path boost circuit output parallel connection according to an embodiment of the present application.
As shown in fig. 7, the first output terminal A1 of the main circuit is connected to the first output terminal A2 of the second main circuit, and the second output terminal B1 of the main circuit is connected to the second output terminal B2 of the second main circuit.
The one-path boost circuit comprises one-path main circuit and one-path starting pre-charging circuit.
In some embodiments, as shown in fig. 7, the three-level converter may include multiple boost circuits, the outputs of which are all connected in parallel.
In practical application, the input end of each path of boost circuit can be connected with the solar panel, and the input power supply is the electric energy PV output by the solar panel.
In some embodiments, referring to fig. 8, fig. 8 is a schematic circuit diagram of another multi-path boost circuit output parallel circuit according to an embodiment of the present application.
As shown in fig. 8, the three-level converter includes a multi-path boost circuit, the multi-path boost circuit shares a capacitor C3, and outputs of the multi-path boost circuit are connected in parallel.
It should be noted that, when the capacitor C3 is shared by multiple boost circuits, the capacitance of the capacitor C3 needs to be sufficiently large.
It should be noted that the three-level converter provided by the embodiment of the application can be applied to a photovoltaic system, and plays a role in boosting voltage in the photovoltaic system. The photovoltaic system may further include: solar panels, DCDC converters, inverters, loads, power grids, etc.
The three-level converter provided by the embodiment of the application can also be applied to UPS (Uninterruptible Power Supply ). The UPS may further include: batteries, bi-directional DCDC circuits, PFC circuits, etc.
The present application provides a three-level converter comprising: a main circuit and a start pre-charging circuit; the main circuit includes: the device comprises an input power supply, a first inductor, a first diode, a second diode, a first switching tube, a second switching tube, a bus capacitor and a flying capacitor, wherein the input power supply, the first inductor, the second diode, the first diode and the bus capacitor are sequentially connected in series to form a loop, the collector electrode of the first switching tube is connected with the positive electrode of the second diode, the emitter electrode of the first switching tube is connected with the collector electrode of the second switching tube, the emitter electrode of the second switching tube is connected with the negative electrode of the input power supply, the first end of the flying capacitor is connected with the negative electrode of the second diode, and the second end of the flying capacitor is connected with the emitter electrode of the first switching tube; the starting pre-charging circuit is connected with the main circuit and is used for pre-charging the flying capacitor when the input power supply is connected with the first voltage, so that the voltage of the flying capacitor reaches the second voltage. The embodiment of the application can prevent the first switching tube and the second switching tube from overvoltage at the moment of accessing the input power supply, and precharge the flying capacitor before the switching tube of the three-level converter is conducted so as to avoid overvoltage of the first diode, and no additional auxiliary power supply or additional control circuit is needed.
The embodiment of the application also provides a starting method which is applied to the three-level converter, and comprises the following steps: controlling the three-level converter to enter a starting state at the moment of inputting the power DC and outputting the first voltage; wherein controlling the three-level converter to enter the start-up state comprises: the flying capacitor Cf is charged by activating the precharge circuit 10 so that the voltage of the flying capacitor Cf is the second voltage.
The first voltage is the voltage of the input three-level converter 100 of the input power DC, the value range of the first voltage is [ vin_min, vin_max ], vin_min is the minimum voltage of the input power DC, and vin_max is the maximum voltage of the input power DC. The value of vin_min and the value of vin_max can be reasonably set according to actual requirements.
Specifically, the value of the second voltage needs to be greater than or equal to the starting voltage of the flying capacitor Cf. The start voltage of the flying capacitor Cf is a voltage that just enables the three-level converter 100 to perform the boosting operation when the first switching tube T1 or the second switching tube T2 of the three-level converter 100 is turned on.
In some embodiments, charging flying capacitor Cf by activating precharge circuit 10 includes: the input power supply DC charges the flying capacitor Cf and the first capacitor C3 of the starting precharge circuit 10 at the same time; when the voltage of the first capacitor C3 is the third voltage, the input power DC charges the flying capacitor Cf by starting the second resistor R2 of the precharge circuit 10 until the voltage of the flying capacitor Cf reaches the second voltage.
The third voltage is a voltage when the first capacitor C3 is fully charged.
In some embodiments, the method of starting further comprises: when the voltage of the flying capacitor Cf is the first voltage, the input power DC continues to output the first voltage, so that the operating state of the three-level converter is switched to a stable state.
And after the working state of the three-level converter reaches a stable state, starting and pre-charging of the three-level converter is completed. At this time, the switching transistor of the three-level converter can be controlled to start to be turned on and perform boosting operation.
It should be noted that the above starting method may be applied to the three-level converter provided by the embodiment of the present application. Technical details not described in detail in the starting method embodiment may be referred to the three-level converter provided in the embodiment of the present application.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting; the technical features of the above embodiments or in the different embodiments may also be combined within the idea of the application, the steps may be implemented in any order, and there are many other variations of the different aspects of the application as described above, which are not provided in detail for the sake of brevity; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the application.
Claims (7)
1. A three-level converter, comprising:
a main circuit and a start pre-charging circuit;
the main circuit includes: the device comprises an input power supply, a first inductor, a first diode, a second diode, a first switch tube, a second switch tube, a bus capacitor and a flying capacitor, wherein the input power supply, the first inductor, the second diode, the first diode and the bus capacitor are sequentially connected in series to form a loop, the collector of the first switch tube is connected with the positive electrode of the second diode, the emitter of the first switch tube is connected with the collector of the second switch tube, the emitter of the second switch tube is connected with the negative electrode of the input power supply, the first end of the flying capacitor is connected with the negative electrode of the second diode, and the second end of the flying capacitor is connected with the emitter of the first switch tube;
the start-up precharge circuit includes: the anode of the third diode is connected with the second end of the flying capacitor, the cathode of the third diode is connected with the first end of the first capacitor, and the second end of the first capacitor is connected with the cathode of the input power supply;
the start-up precharge circuit further includes: a first resistor and a second resistor; the first end of the first resistor is connected with the second end of the first inductor, the second end of the first resistor is connected with the emitter of the first switch tube, the first end of the second resistor is connected with the second end of the first resistor, and the second end of the second resistor is connected with the negative electrode of the input power supply;
the resistances of the first resistor and the second resistor should satisfy the following conditions:
vin_min R1/(r1+r2) > vcf_start, and R1> R2;
wherein R1 is the resistance of the first resistor, and the unit is ohm; r2 is the resistance of the second resistor, and the unit is ohm; vin_min is the minimum voltage of the input power supply, and is in volts; vcf_start is the starting voltage of the flying capacitor in volts;
the starting precharge circuit is connected with the main circuit, and is used for precharging the flying capacitor when the input power supply is connected with the first voltage, so that the voltage of the flying capacitor reaches the second voltage.
2. The three-level converter according to claim 1, wherein the capacitance of the first capacitor has a formula:
C3=(Vin_max-VT2_max)*Cf/VT2_max；
wherein C3 is the capacitance of the first capacitor, and the unit is Farad; vin_max is the maximum voltage of the input power supply in volts; v2_max is the maximum voltage that the second switching tube can withstand, in volts; cf is the capacitance of the flying capacitor in Farad.
3. The three-level converter of claim 2, wherein the flying capacitor has a capacitance greater than a capacitance of the first capacitor.
4. A three-level converter according to any of claims 1-3, characterized in that the three-level converter further comprises:
a second main circuit and a second start-up precharge circuit;
the second main circuit is connected with the second starting precharge circuit, a first output end of the second main circuit is connected with a first output end of the main circuit, and a second output end of the second main circuit is connected with a second output end of the main circuit.
5. A starting method applied to the three-level converter according to any one of claims 1 to 4, comprising:
controlling the three-level converter to enter a starting state at the moment when the input power supply outputs a first voltage;
wherein said controlling the three-level converter to enter a start-up state comprises: and charging the flying capacitor through the starting pre-charging circuit so that the voltage of the flying capacitor is a second voltage.
6. The method of starting up of claim 5, wherein said charging the flying capacitor by the start-up precharge circuit comprises:
the input power supply charges the flying capacitor and the first capacitor of the starting precharge circuit at the same time;
when the voltage of the first capacitor is the third voltage, the input power supply charges the flying capacitor through the second resistor of the starting pre-charging circuit until the voltage of the flying capacitor reaches the second voltage.
7. The method of starting up of claim 6, further comprising:
when the voltage of the flying capacitor is the first voltage, the input power supply continuously outputs the first voltage so as to enable the working state of the three-level converter to be switched to a stable state.
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| CN212381111U (en) * | 2020-03-25 | 2021-01-19 | 上海正泰电源系统有限公司 | Three-level power conversion circuit capable of being precharged by flying capacitor |
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| CN115242092A (en) * | 2022-08-18 | 2022-10-25 | 阳光电源股份有限公司 | Flying capacitor three-level DCDC converter, photovoltaic system and control method |
| CN115955108A (en) * | 2023-02-09 | 2023-04-11 | 四川嘉义雷科电子技术有限公司 | Flying capacitor three-level buck circuit and flying capacitor pre-charging method |
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| CN114641924A (en) * | 2019-11-06 | 2022-06-17 | 宜普电源转换公司 | Multilevel converter with voltage divider for precharging a flying capacitor |
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| CN111245220A (en) * | 2020-02-24 | 2020-06-05 | 上海正泰电源系统有限公司 | Three-level power conversion circuit and voltage clamping method |
| CN212381111U (en) * | 2020-03-25 | 2021-01-19 | 上海正泰电源系统有限公司 | Three-level power conversion circuit capable of being precharged by flying capacitor |
| JP2021175260A (en) * | 2020-04-23 | 2021-11-01 | パナソニックＩｐマネジメント株式会社 | Dc/dc conversion device |
| CN115242092A (en) * | 2022-08-18 | 2022-10-25 | 阳光电源股份有限公司 | Flying capacitor three-level DCDC converter, photovoltaic system and control method |
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