CN114710021B - Three-level BOOST converter of suspension capacitor and starting control method thereof - Google Patents
Three-level BOOST converter of suspension capacitor and starting control method thereof Download PDFInfo
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- CN114710021B CN114710021B CN202210628036.9A CN202210628036A CN114710021B CN 114710021 B CN114710021 B CN 114710021B CN 202210628036 A CN202210628036 A CN 202210628036A CN 114710021 B CN114710021 B CN 114710021B
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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
- H02M1/36—Means for starting or stopping converters
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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
- 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
- H02M3/156—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 with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—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 with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
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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
Abstract
The invention provides a three-level BOOST converter of a suspension capacitor and a starting control method thereof, wherein when the input voltage of a main circuit in the three-level BOOST converter of the suspension capacitor is smaller than the starting threshold value of the suspension capacitor in the main circuit, a pre-charging circuit is controlled to charge the suspension capacitor by using the input voltage, so that the voltage of the suspension capacitor reaches the preset voltage; and then, the two switching tubes in the main circuit are controlled to work to charge and discharge the floating capacitor, and the charging time is longer than the discharging time, so that the voltage of the floating capacitor reaches a startup threshold value, the main circuit can be controlled to work normally, and the three-level BOOST circuit with lower input voltage can also work normally.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a three-level BOOST converter of a suspension capacitor and a starting control method thereof.
Background
In order to improve the power generation efficiency of the photovoltaic module, a first-stage boosting unit is usually added in the photovoltaic power generation system between the photovoltaic array and the inverter DC bus, and as shown in fig. 1, the boosting unit is usually formed by connecting a plurality of DC/DC converters in parallel through output terminals.
For the specific circuit selection of the DC/DC converter, compared with a two-level BOOST circuit, the voltage stress of a power device of the three-level BOOST circuit is reduced by half, so that the voltage output of a higher level can be realized by using a power device with a lower voltage-withstanding level, and the size and the cost of an inductor can be greatly reduced due to the fact that the input current ripple is greatly reduced, so that the three-level BOOST circuit has a wide application prospect in a high-voltage photovoltaic system.
In order to avoid the problem of overvoltage breakdown of a switching tube at the moment of power-on of a three-level BOOST circuit, a scheme in the prior art is that the input voltage of the three-level BOOST circuit is used for pre-charging a floating capacitor of the three-level BOOST circuit so as to balance the bearing size of two switching tubes on the input voltage at the moment of power-on; however, when a plurality of three-level BOOST circuits are applied in parallel, it is not excluded that the input voltage of each BOOST circuit is low due to the shielding of the connected photovoltaic components, and the like, and at this time, it cannot be ensured that the BOOST circuit can charge the floating capacitor to the start threshold, and further the normal operation of the BOOST circuit is affected.
Disclosure of Invention
In view of this, the present application provides a floating capacitor three-level BOOST converter and a start control method thereof, so that a three-level BOOST circuit with a lower input voltage can work normally.
In order to achieve the above purpose, the present application provides the following technical solutions:
in a first aspect of the present application, a start control method for a floating capacitor three-level BOOST converter is provided, where a main circuit of the floating capacitor three-level BOOST converter includes: the circuit comprises an inductor, a first diode, a second diode, a first switching tube, a second switching tube, a floating capacitor and a pre-charging circuit, wherein the inductor, the first diode and the second diode are sequentially arranged in a transmission branch of one electrode; the starting control method comprises the following steps:
when the input voltage is smaller than the starting threshold value of the suspension capacitor, controlling the pre-charging circuit to charge the suspension capacitor by using the input voltage, so that the voltage of the suspension capacitor reaches a preset voltage;
controlling the first switch tube and the second switch tube to work, and charging and discharging the suspension capacitor, wherein the charging time is longer than the discharging time, so that the voltage of the suspension capacitor reaches the startup threshold;
and controlling the main circuit to work normally.
Optionally, controlling the first switch tube and the second switch tube to work, for the floating capacitor performs charging and discharging, and the charging duration is longer than the discharging duration, so that the voltage of the floating capacitor reaches the start threshold, including:
determining the modulation duty ratio and the initial phase difference of the first switching tube and the second switching tube;
determining the turn-on duration of the first switch tube and the second switch tube; the switching-on time of the first switching tube connected to the same-pole transmission branch circuit with the suspension capacitor is shorter than that of the second switching tube;
and generating two modulation signals according to the modulation duty ratio, the initial phase difference and the two on-periods, and respectively outputting the two modulation signals to corresponding switch tubes until the voltage of the suspension capacitor reaches the start threshold.
Optionally, the modulation duty ratio is the same as the modulation duty ratio of the two switching tubes in normal operation;
the initial phase difference is the same as the initial phase difference of the first switching tube and the second switching tube in normal operation.
Optionally, determining the on-time of the first switch tube and the second switch tube includes:
calculating the normal on-time of the first switch tube and the second switch tube in normal work;
reducing a preset time length on the basis of the normal on-time length to obtain the discharge time length which is used as the on-time length of the first switch tube;
and adding one preset time length on the basis of the normal on-time length to obtain the charging time length which is used as the on-time length of the second switch tube.
Optionally, controlling the main circuit to normally operate includes:
determining the modulation duty ratio, the initial phase difference and the normal turn-on time of the first switching tube and the second switching tube during normal work;
and generating and outputting two modulation signals to corresponding switch tubes according to the modulation duty ratio, the initial phase difference and the normal turn-on duration.
Optionally, determining the modulation duty ratio, the initial phase difference, and the normal on-time of the first switching tube and the second switching tube during normal operation includes:
taking the ratio of the boosted value and the output voltage of the main circuit as the modulation duty ratio;
taking the product of the modulation duty ratio and the modulation period as the normal on-time;
and taking half of the modulation period as the initial phase difference.
Optionally, the output end of the main circuit is connected with a direct current bus of the inverter;
before controlling the pre-charge circuit to charge the floating capacitor with the input voltage, the method further includes: acquiring the input voltage, the voltage of the suspension capacitor and the bus voltage of the direct current bus;
the starting threshold value is as follows: half of the bus voltage.
Optionally, in the main circuit, a first controllable switch is arranged between a connection point of two switching tubes and the suspension capacitor; and the precharge circuit includes: the second controllable switch and the resistor are arranged between the suspension capacitor and the negative electrode of the output end of the main circuit or the midpoint of the output end of the main circuit and are connected in series; in the start control method, controlling the pre-charge circuit to charge the floating capacitor with the input voltage to make the voltage of the floating capacitor reach a preset voltage includes:
controlling the first controllable switch to be switched off and controlling the second controllable switch to be switched on;
judging whether the voltage of the suspension capacitor reaches the preset voltage or not;
and if so, controlling the first controllable switch to be closed and controlling the second controllable switch to be opened.
Optionally, the preset voltage is within a preset range of the input voltage.
Optionally, the method further includes:
when the input voltage is greater than or equal to the starting threshold, charging the suspension capacitor by using the input voltage, so that the voltage of the suspension capacitor reaches the starting threshold;
and then executing the step of controlling the normal work of the main circuit.
A second aspect of the present application provides a floating capacitor three-level BOOST converter, comprising: a main circuit and a controller; wherein the content of the first and second substances,
the main circuit is a suspension capacitor three-level BOOST circuit, and comprises: the circuit comprises an inductor, a first diode, a second diode, a first switch tube, a second switch tube, a suspension capacitor, a pre-charging circuit, an input capacitor and an output capacitor;
the inductor, the first diode and the second diode are sequentially arranged in the one-pole transmission branch; the other end of the inductor is used as a corresponding pole of an input end of the main circuit, and the other end of the second diode is used as a corresponding pole of an output end of the main circuit;
the connection point of the inductor and the first diode is connected with the other pole transmission branch circuit through the first switch tube and the second switch tube in sequence;
one end of the suspension capacitor is connected with a connection point of the first switch tube and the second switch tube; the other end of the suspension capacitor is connected with a connection point of the first diode and the second diode;
the pre-charging circuit is used for charging the suspension capacitor by using the input voltage of the main circuit;
the input capacitor is arranged between the positive and negative poles of the input end of the main circuit, and the output capacitor is arranged between the positive and negative poles of the output end of the main circuit;
the first switch tube, the second switch tube and the pre-charge circuit are all controlled by the controller, and the controller is configured to execute the start-up control method of the floating capacitor three-level BOOST converter according to any one of the first aspect.
Optionally, a first controllable switch is disposed between the connection point of the first switch tube and the second switch tube and the suspension capacitor;
the precharge circuit includes: the second controllable switch and the resistor are connected in series, and a branch circuit after the series connection is arranged between the suspension capacitor and the negative electrode of the output end of the main circuit or the midpoint of the output end of the main circuit;
the first controllable switch and the second controllable switch are both controlled by the controller.
Optionally, the first controllable switch is a normally open relay or a power semiconductor switch tube, and the second controllable switch is a normally closed relay or a power semiconductor switch tube.
When the input voltage of a main circuit in the three-level BOOST converter of the floating capacitor is smaller than the start threshold of the floating capacitor in the main circuit, a pre-charging circuit is controlled to charge the floating capacitor by using the input voltage, so that the voltage of the floating capacitor reaches the preset voltage; and then, the two switching tubes in the main circuit are controlled to work to charge and discharge the floating capacitor, and the charging time is longer than the discharging time, so that the voltage of the floating capacitor reaches a startup threshold value, the main circuit can be controlled to work normally, and the three-level BOOST circuit with lower input voltage can also work normally.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a photovoltaic power generation system provided by the prior art;
fig. 2 is a schematic diagram of a main circuit structure of a floating capacitor three-level BOOST converter according to an embodiment of the present invention;
fig. 3 is a flowchart of a start control method of a floating capacitor three-level BOOST converter according to an embodiment of the present invention;
fig. 4 is another flowchart of a start control method of a floating capacitor three-level BOOST converter according to an embodiment of the present invention;
fig. 5a and 5b are schematic diagrams of two specific structures of a main circuit of a floating capacitor three-level BOOST converter according to an embodiment of the present invention;
FIG. 6 is a complete flow chart of the start-up control method for the main circuit of FIG. 5 a;
fig. 7 is a schematic timing diagram of the switching tube modulation signal in step S104 in the start-up control method according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In this application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The application provides a starting control method of a three-level BOOST converter of a floating capacitor, so that a three-level BOOST circuit with lower input voltage can work normally.
Fig. 2 shows a typical floating capacitor three-level BOOST topology, in which an input capacitor Cin is disposed between the positive and negative electrodes of the input end thereof, an inductor L, a first diode D1 and a second diode D2 are sequentially disposed in the positive transmission branch thereof, a first switch Q1 and a second switch Q2 are connected in series between the anode of the first diode D1 and the negative transmission branch of the topology, one end of a floating capacitor Cf is connected to a connection point of a first diode D1 and a second diode D2, the other end of the floating capacitor Cf is connected to a connection point of a first switch Q1 and a second switch Q2, and an output capacitor Cout is disposed between the positive and negative electrodes of the output end of the topology; vin is the input voltage of the topology, and when the output end of the topology is connected with the direct current bus of the inverter, the output voltage of the topology is the bus voltage Vbus of the direct current bus.
It should be noted that fig. 2 only shows the main circuit of the floating capacitor three-level BOOST converter by taking a common-negative-electrode topology as an example, in practical applications, the main circuit may also adopt a common-positive-electrode topology, which depends on the specific application environment, and both are within the protection scope of the present application.
Referring to fig. 3, the method for controlling the start-up of the floating capacitor three-level BOOST converter includes:
s101, acquiring input voltage of a main circuit in a three-level BOOST converter of a suspension capacitor and voltage of the suspension capacitor.
In practical application, the input voltage Vin and the floating capacitor voltage Vcf of the main circuit can be respectively collected through corresponding voltage sensors. When the output end of the main circuit is connected with a direct current bus of the inverter, the bus voltage Vbus can be obtained simultaneously.
The subsequent steps can then be performed based on these parameters.
And S102, judging whether the input voltage is larger than or equal to a starting threshold of a suspension capacitor in the main circuit.
Under normal conditions, in the early morning, the voltage of each photovoltaic module gradually rises along with the increase of the illumination amplitude, so that the input voltage Vin of a main circuit in a three-level BOOST converter of a suspension capacitor connected with the photovoltaic module rises along with the increase of the illumination amplitude; when the input voltage Vin rises to a certain preset value, the floating capacitor Cf can be charged by the pre-charging circuit shown in fig. 2; when the voltage Vcf of the suspension capacitor rises to be larger than the startup threshold value, the main circuit can be controlled to enter a normal working state. The start threshold value can be close to half of the input voltage Vin, so that two switching tubes Q1 and Q2 can equally divide the input voltage Vin at the moment of power-on without breakdown damage caused by overvoltage; the upper limit of the value range of the starting threshold is not more than the voltage stress of the first switch tube Q1, and the lower limit of the value range is not less than the difference value of the input voltage Vin minus the voltage stress of the second switch tube Q2; if the main circuit output ends of the plurality of floating capacitor three-level BOOST converters are connected in parallel to the dc bus of the inverter, the start threshold may be half of the bus voltage Vbus, but is not limited thereto.
However, in practical applications, when the input voltage Vin of the main circuit of the rear stage floating capacitor three-level BOOST converter of the photovoltaic module is lower, for example, lower than the start-up threshold due to shielding, etc., if the pre-charging circuit shown in fig. 2 has a simple structure and does not have a boosting function, for example, only a transmission loop with a controllable switch and a voltage divider, the floating capacitor voltage Vcf cannot be charged to the start-up threshold higher than the input voltage Vin. For example, the main circuit output ends of the plurality of floating capacitor three-level BOOST converters are connected in parallel, before each main circuit works, the bus voltage Vbus obtained by the parallel connection is determined by the main circuit with the highest input voltage Vin, and when the input voltage Vin of a certain main circuit is less than 1/2 bus voltage Vbus, the floating capacitor voltage Vcf of the floating capacitor Cf in the main circuit cannot be charged to 1/2 bus voltage Vbus. At this time, in the case that the input voltage Vin is smaller than the start-up threshold, steps S103 and S104 need to be executed successively.
S103, controlling the pre-charging circuit to charge the floating capacitor by using the input voltage, so that the voltage of the floating capacitor reaches a preset voltage.
Although the input voltage Vin is used to charge the floating capacitor Cf, the floating capacitor Cf cannot reach the start threshold, but the voltage Vcf of the floating capacitor may also rise to a preset voltage, for example, a value close to the input voltage Vin may be reached, that is, the preset voltage is within a preset range of the input voltage Vin, and values of the preset range may be determined according to an application environment of the floating capacitor Cf, and are all within a protection range of the present application.
The floating capacitor voltage Vcf can be increased in one stage in step S103, and then, in order to reach the start threshold and make the main circuit operate normally, the main circuit can be increased in the next stage in step S104.
And S104, controlling the first switch tube and the second switch tube to work, and charging and discharging the suspension capacitor, wherein the charging time is longer than the discharging time, so that the voltage of the suspension capacitor reaches a startup threshold value.
When the first switch tube Q1 is controlled to be switched off and the second switch tube Q2 is controlled to be switched on, the input capacitor Cin, the inductor L, the first diode D1, the floating capacitor Cf and the second switch tube Q2 form a loop to charge the floating capacitor Cf; when the first switch tube Q1 is turned on and the second switch tube Q2 is turned off, the input capacitor Cin, the inductor L, the first switch tube Q1, the floating capacitor Cf and the second diode D2 form a loop, so that the floating capacitor Cf is discharged; in practical applications, in order to enable the floating capacitor voltage Vcf to be charged to exceed the input voltage Vin, a time when both the two switching tubes Q1 and Q2 are turned on needs to exist, at this time, the input capacitor Cin, the inductor L, the first switching tube Q1, and the second switching tube Q2 form a loop, so that the input voltage Vin stores energy in the inductor L to prepare for subsequently charging the floating capacitor Cf, and at this time, the floating capacitor voltage Vcf on the floating capacitor Cf is kept unchanged.
Since the charging duration is longer than the discharging duration, the voltage Vcf of the floating capacitor can be further increased by each charging and discharging, that is, the voltage Vcf of the floating capacitor can reach the startup threshold through the periodic charging and discharging actions.
Thereafter, step S105 is performed.
And S105, controlling the main circuit to work normally.
In the start control method of the three-level BOOST converter of the floating capacitor provided by this embodiment, when the input voltage of the main circuit is less than the start threshold of the floating capacitor, the input voltage is first used to charge the floating capacitor, so that the voltage of the floating capacitor reaches the preset voltage; and then, the two switching tubes in the main circuit are controlled to work to charge and discharge the floating capacitor, and the charging time is longer than the discharging time, so that the voltage of the floating capacitor reaches a startup threshold value, the main circuit can be controlled to work normally, and the three-level BOOST circuit with lower input voltage can also work normally.
On the basis of the above embodiment, specifically, the step S104 may specifically include, as shown in fig. 4:
s201, determining the modulation duty ratio and the initial phase difference of the first switching tube and the second switching tube.
Preferably, the modulation duty cycle is the same as the modulation duty cycle of the two switching tubes during normal operation, and the initial phase difference is also the same as the initial phase difference of the two switching tubes during normal operation, that is, the present embodiment may not change the modulation logic of the main circuit, and may implement seamless switching of the modulation strategy during steady-state operation after the start-up pre-charge adjustment is completed.
S202, determining the on-time of the first switch tube and the second switch tube.
The switch tube connected to the same pole transmission branch as the floating capacitor, such as the first switch tube Q1 connected to the positive pole transmission branch together with the floating capacitor Cf shown in fig. 2, has an on-time shorter than that of the other switch tube; in combination with the above description of the charge and discharge circuit of the floating capacitor in the previous embodiment, it can be obtained that the setting that the charging time period is longer than the discharging time period can be realized at this time.
Preferably, the step S202 may specifically include: calculating the normal on-time of the first switch tube and the second switch tube during normal operation, and then reducing a preset time on the basis of the normal on-time to obtain a discharge time as the on-time of a switch tube (such as Q1 shown in fig. 2) connected to the same pole transmission branch circuit with the suspension capacitor; meanwhile, a preset time length is added on the basis of the normal on-time length to obtain a charging time length as the on-time length of another switching tube (such as Q2 shown in fig. 2). The value of the preset duration is not specifically limited, and is determined according to the application environment, and is within the protection scope of the application.
Of course, in practical applications, the difference between the two on-time lengths and the normal on-time length may be different, and the two on-time lengths may not change on the basis of the normal on-time length, as long as it is ensured that the charging time length of the floating capacitor is greater than the discharging time length, which are all within the protection scope of the present application.
And S203, generating two modulation signals according to the modulation duty ratio, the initial phase difference and the two on-periods, and respectively outputting the two modulation signals to corresponding switch tubes until the voltage of the suspension capacitor reaches a startup threshold value.
The step S203 may refer to an existing PWM (Pulse Width Modulation) process, which is not described herein.
In practical applications, step S105 may also specifically include, as shown in fig. 4:
s301, determining the modulation duty ratio, the initial phase difference and the normal on-time of the first switching tube and the second switching tube in normal work.
In practical application, the modulation duty ratio is specifically the ratio of the boost value to the output voltage of the main circuit, and for the main circuit shown in fig. 2 connected in parallel to the dc bus, the output voltage is the bus voltage Vbus, and the boost value is Vbus-Vin, so that the modulation duty ratio D = (Vbus-Vin)/Vbus.
The normal on-time is the product of the modulation duty cycle D and the modulation period T, i.e. DT.
The starting phase difference may be half the modulation period T, i.e. T/2.
And S302, generating and outputting two modulation signals to corresponding switch tubes according to the modulation duty ratio, the initial phase difference and the normal on-time.
The step S302 may also refer to the existing PWM process, which is not described herein.
In addition, as shown in fig. 4, the startup control method, after step S102, further includes: if the input voltage is greater than or equal to the start-up threshold, step S106 is executed to charge the floating capacitor with the input voltage, so that the voltage of the floating capacitor reaches the start-up threshold. Then step S105 may be performed.
Fig. 5a and 5b provide two alternatives for the pre-charge circuit in fig. 2, in which a second controllable switch K2 and a resistor R are arranged in series (in an unlimited series order) between the floating capacitor Cf and the negative pole of the output terminal (as shown in fig. 5 a) or the midpoint of the output terminal (as shown in fig. 5 b) of the main circuit; a first controllable switch K1 is arranged between the middle point of the two switching tubes Q1 and Q2 and the suspension capacitor Cf; in this case, in the start control method, step S103 includes: firstly, the first controllable switch K1 is controlled to be opened, and the second controllable switch K2 is controlled to be closed; then judging whether the voltage Vcf of the suspension capacitor reaches a preset voltage or not; if so, the first controllable switch K1 is controlled to close and the second controllable switch K2 is controlled to open.
Taking the structure shown in fig. 5a as an example, the second controllable switch K2 and the resistor R are added by the inductor L and the first diode D1 to form a pre-charge circuit of the floating capacitor Cf, and the first controllable switch K1 can prevent the second switch Q2 from being broken down by overvoltage at the moment of power-on of the input high voltage. In order to ensure that the topology can work normally, the voltage of the floating capacitor Cf needs to be precharged to be half of the bus voltage Vbus connected to the output side. If the input voltage Vin can be greater than or equal to the startup threshold, after the input is powered on, the second controllable switch K2 is closed, and the voltage of the floating capacitor Cf is gradually charged to the bus voltage Vbus 1/2 through a loop formed by the input voltage Vin, the first diode D1, the floating capacitor Cf, the second controllable switch K2 and the resistor R. However, in practical applications, it is not guaranteed that the input voltage Vin of each of the plurality of main circuits connected in parallel is equal to or greater than the start-up threshold, and therefore, for each main circuit shown in fig. 5a, the start-up control method can be as follows, with reference to fig. 6, after the input voltage Vin, the bus voltage Vbus, and the floating capacitor voltage Vcf are obtained:
if Vin is more than or equal to Vbus/2, closing a second controllable switch K2 to charge the floating capacitor Cf, and directly charging the voltage Vcf of the floating capacitor to the half bus voltage Vbus/2 by using the pre-charging circuit; then the second controllable switch K2 is opened, the first controllable switch K1 is closed, and the two switching tubes Q1 and Q2 can be driven to work alternately, and the three-level BOOST converter of the floating capacitor is started to work normally.
If Vin is less than Vbus/2, first closing the second controllable switch K2 to charge the floating capacitor Cf, charging the voltage Vcf of the floating capacitor to a preset voltage (close to the input voltage Vin) by using the pre-charging circuit, then opening the second controllable switch K2, closing the first controllable switch K1, and adjusting and distributing the on-time of the two switching tubes Q1 and Q2 based on the calculated modulation duty ratio D = (Vbus-Vin)/Vbus, wherein the on-time of the first switching tube Q1 is set to be (D- Δ) T, the on-time of the second switching tube Q2 is set to be (D + Δ) T, and Δ T is the preset time; and the two switching tubes Q1 and Q2 drive the phase difference T/2, as shown in fig. 7, the on duration of the second switching tube Q2 is slightly longer than the on duration of the first switching tube Q1, so that the charging duration of the floating capacitor Cf is longer than the discharging duration in each modulation period T, and the voltage Vcf of the floating capacitor rises; after n modulation periods, the voltage Vcf of the suspension capacitor precharges the start threshold (namely Vbus/2), and the three-level BOOST converter of the suspension capacitor can be ensured to work normally. Then, the two switching tubes Q1 and Q2 are turned on again to be the normal on time DT at all times, and at this time, the floating capacitor Cf is in a charge-discharge balance state, and the start threshold (i.e. Vbus/2) is maintained unchanged. Therefore, seamless switching between the starting precharge process and the steady-state working process can be realized.
Referring to fig. 7, when the main circuit shown in fig. 5a faces the case of Vin <1/2Vbus, i.e. D >1/2, within each modulation period T in step S104:
1) the interval of 0-t1 is,
the two switching tubes Q1 and Q2 are simultaneously turned on, the input capacitor Cin, the inductor L, the first switching tube Q1 and the second switching tube Q2 form a loop, the input voltage Vin stores energy in the inductor L, and the voltage Vcf of the floating capacitor is maintained; the duration of this interval is DT-T/2-DeltaT.
2) the interval T1-T/2,
the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, the input capacitor Cin, the inductor L, the first diode D1, the suspension capacitor Cf, the first controllable switch K1 and the second switch tube Q2 form a loop, the inductor L releases energy, and the suspension capacitor Cf charges; the duration of this interval is T-DT +. DELTA.T.
3) The interval from T/2 to T2,
the first switch tube Q1 and the second switch tube Q2 are turned on simultaneously, the input capacitor Cin, the inductor L, the first switch tube Q1 and the second switch tube Q2 form a loop, the input voltage Vin stores energy to the inductor L, and the voltage Vcf of the floating capacitor is maintained; the duration of this interval is DT +. DELTA.T-T/2.
4) the interval T2-T is,
the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the input capacitor Cin, the inductor L, the first switch tube Q1, the first controllable switch K1, the suspension capacitor Cf and the second diode D2 form a loop, the inductor L releases energy, and the suspension capacitor Cf discharges; the duration of this interval is T-DT- Δ T.
It can be seen that in one modulation period T, the floating capacitor Cf in the interval T1-T/2 is charged, the floating capacitor Cf in the interval T2-T is discharged, and the voltage Vcf of the floating capacitor in the other two intervals is kept unchanged, and as the time length of the interval T1-T/2 is longer than the time length of the interval T2-T, namely the charging time length of the floating capacitor Cf is longer than the discharging time length, the voltage Vcf of the floating capacitor can be charged to the startup threshold (namely Vbus/2) after a plurality of modulation periods.
On the basis of not increasing the cost, the problem of pre-charging of the voltage of the floating capacitor of the three-level BOOST converter corresponding to the floating capacitor of the low-voltage input circuit when the bus is high-voltage is solved; and moreover, the modulation strategy logic of the three-level BOOST converter of the floating capacitor is not changed, and the seamless switching of the switching tube modulation strategy under the steady-state operation can be realized after the start-up pre-charging adjustment is completed.
Another embodiment of the present application further provides a floating capacitor three-level BOOST converter, including: a main circuit and a controller; wherein:
the main circuit is a three-level BOOST circuit of a floating capacitor, such as a common-negative topology shown in fig. 2 or a common-positive topology in the prior art, and specifically includes: the circuit comprises an inductor L, a first diode D1, a second diode D2, a first switch tube Q1, a second switch tube Q2, a floating capacitor Cf, a pre-charging circuit, an input capacitor Cin and an output capacitor Cout; wherein:
an inductor L, a first diode D1 and a second diode D2, which are sequentially disposed in a one-pole transmission branch (such as the positive transmission branch shown in fig. 2); the other end of the inductor L is used as the corresponding pole of the input end of the main circuit, and the other end of the second diode D2 is used as the corresponding pole of the output end of the main circuit.
The junction point of the inductor L and the first diode D1 passes through the first switch Q1 and the second switch Q2 in sequence, and is connected to another pole transmission branch (such as the negative pole transmission branch shown in fig. 2).
One end of the floating capacitor Cf is connected with the connection point of the first switch tube Q1 and the second switch tube Q2; the other end of the floating capacitor Cf is connected to a connection point of the first diode D1 and the second diode D2.
The pre-charging circuit is used for charging the floating capacitor Cf by using the input voltage Vin of the main circuit.
The input capacitor Cin is arranged between the positive and negative poles of the input end of the main circuit, and the output capacitor Cout is arranged between the positive and negative poles of the output end of the main circuit.
The first switch Q1, the second switch Q2 and the pre-charge circuit are all controlled by a controller, and the controller is used for executing the start-up control method of the floating capacitor three-level BOOST converter according to any of the embodiments. The specific process and principle of the start control method may also refer to the above embodiments, and details are not repeated here.
In order to realize the precharge circuit, in practical application, a first controllable switch (e.g. K1 shown in fig. 5a and 5 b) may be disposed between the connection point of the first switch tube Q1 and the second switch tube Q2 and the floating capacitor Cf; the precharge circuit includes: a second controllable switch (e.g. K2 shown in fig. 5a and 5 b) and a resistor (e.g. R shown in fig. 5a and 5 b) connected in series, and the branch after the series connection is arranged between the floating capacitor Cf and the negative pole (shown in fig. 5 a) of the output end or the midpoint (shown in fig. 5 b) of the main circuit. The first controllable switch K1 and the second controllable switch K2 are also controlled by the controller.
In practical applications, the first controllable switch K1 may be a normally open relay, and the second controllable switch K2 may be a normally closed relay; wherein the first controllable switch K1 and the second controllable switch K2 may also be replaced by power semiconductor switching devices, such as: MOS (Insulated Gate field effect Transistor), IGBT (Insulated Gate Bipolar Transistor), GTO (Gate Turn-Off Thyristor), and the like, which are not limited herein, depending on the specific application environment. In addition, a bypass device, such as a diode or a relay, may be further disposed between the input end anode and the output end anode of the main circuit, and other settings of the floating capacitor three-level BOOST converter may refer to the prior art, which is not described herein any more, as long as the controller thereof can implement the above-mentioned start control method, and all are within the protection scope of the present application.
It should be noted that, in both the structures shown in fig. 5a and fig. 5b, the inductor L and the first diode D1 are used, and only the second controllable switch K2 and the resistor R are added to form the precharge circuit. In practical applications, any circuit structure capable of charging the floating capacitor Cf with the input voltage Vin of the main circuit may be used as the pre-charging circuit, and is not limited to the structures shown in fig. 5a and 5b, and for example, a controllable switch disposed between the positive electrode of the input end of the main circuit and the connection point of the two diodes may also achieve the above functions, and is also within the scope of the present application.
The same and similar parts among the various embodiments in the present specification are referred to each other, and each embodiment focuses on differences from other embodiments. In particular, the system or system embodiments, which are substantially similar to the method embodiments, are described in a relatively simple manner, and reference may be made to some descriptions of the method embodiments for relevant points. The above-described system and system embodiments are only illustrative, wherein the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
Those of skill would further appreciate that the various illustrative components and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the components and steps of the various examples have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
In the above description of the disclosed embodiments, the features described in the embodiments in this specification may be replaced or combined with each other to enable those skilled in the art to make or use the invention. 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 invention. Thus, the present invention 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 starting control method of a floating capacitor three-level BOOST converter is characterized in that a main circuit of the floating capacitor three-level BOOST converter comprises the following steps: the circuit comprises an inductor, a first diode, a second diode, a first switching tube, a second switching tube, a floating capacitor and a pre-charging circuit, wherein the inductor, the first diode and the second diode are sequentially arranged in a one-pole transmission branch, the first switching tube and the second switching tube are connected between a connection point of the inductor and the first diode and between another-pole transmission branch in series, the floating capacitor is arranged between the connection point of the two diodes and the connection point of the two switching tubes, and the pre-charging circuit charges the floating capacitor by using the input voltage of a main circuit; the starting control method comprises the following steps:
when the input voltage is smaller than the starting threshold value of the suspension capacitor, controlling the pre-charging circuit to charge the suspension capacitor by using the input voltage, so that the voltage of the suspension capacitor reaches a preset voltage;
controlling the first switching tube and the second switching tube to work, determining the modulation duty ratio, the initial phase difference and the turn-on time of the first switching tube and the second switching tube, generating and outputting two modulation signals to the corresponding switching tubes according to the modulation duty ratio, the initial phase difference and the turn-on time, and charging and discharging the suspension capacitor, wherein the charging time is longer than the discharging time, so that the voltage of the suspension capacitor reaches the start threshold;
and controlling the main circuit to work normally.
2. The method as claimed in claim 1, wherein the step of controlling the first switch tube and the second switch tube to operate to charge and discharge the floating capacitor for a time period longer than a discharge time period to make the voltage of the floating capacitor reach the start-up threshold includes:
determining the modulation duty ratio and the initial phase difference of the first switching tube and the second switching tube;
determining the turn-on duration of the first switch tube and the second switch tube; the switching-on time of the first switching tube connected to the same-pole transmission branch circuit with the suspension capacitor is shorter than that of the second switching tube;
and generating two modulation signals according to the modulation duty ratio, the initial phase difference and the two on-periods, and respectively outputting the two modulation signals to corresponding switch tubes until the voltage of the suspension capacitor reaches the start threshold value.
3. The method for controlling starting of a three-level BOOST converter according to claim 2, wherein said modulation duty cycle is the same as the modulation duty cycle of two said switching tubes during normal operation;
the initial phase difference is the same as the initial phase difference of the first switching tube and the second switching tube in normal operation.
4. The method for controlling starting of a floating capacitor three-level BOOST converter according to claim 2, wherein determining the on-duration of the first switch tube and the second switch tube comprises:
calculating the normal turn-on time of the first switch tube and the second switch tube in normal work;
reducing a preset time length on the basis of the normal on-time length to obtain the discharge time length which is used as the on-time length of the first switch tube;
and adding one preset time length on the basis of the normal on-time length to obtain the charging time length which is used as the on-time length of the second switch tube.
5. The method as claimed in claim 1, wherein the controlling the main circuit to operate normally comprises:
determining the modulation duty ratio, the initial phase difference and the normal turn-on time of the first switching tube and the second switching tube during normal work;
and generating and outputting two modulation signals to corresponding switch tubes according to the modulation duty ratio, the initial phase difference and the normal on-time.
6. The method as claimed in claim 5, wherein the determining the modulation duty cycle, the initial phase difference and the normal on-time of the first switch tube and the second switch tube during normal operation comprises:
taking the ratio of the boosted value and the output voltage of the main circuit as the modulation duty ratio;
taking the product of the modulation duty ratio and the modulation period as the normal on-time;
and taking half of the modulation period as the initial phase difference.
7. The start-up control method of the flying capacitor three-level BOOST converter according to any one of claims 1 to 6, characterized in that the output end of the main circuit is connected with the DC bus of the inverter;
before controlling the pre-charge circuit to charge the floating capacitor with the input voltage, the method further includes: acquiring the input voltage, the voltage of the suspension capacitor and the bus voltage of the direct current bus;
the starting threshold value is as follows: half of the bus voltage.
8. The method for controlling starting of a three-level BOOST converter according to any one of claims 1 to 6, wherein a first controllable switch is arranged between the connection point of two switching tubes and the floating capacitor in the main circuit; and the precharge circuit includes: the second controllable switch and the resistor are arranged between the suspension capacitor and the negative electrode of the output end of the main circuit or the midpoint of the output end of the main circuit and are connected in series; in the start control method, controlling the pre-charge circuit to charge the floating capacitor with the input voltage to make the voltage of the floating capacitor reach a preset voltage includes:
controlling the first controllable switch to be switched off and controlling the second controllable switch to be switched on;
judging whether the voltage of the suspension capacitor reaches the preset voltage or not;
and if so, controlling the first controllable switch to be closed and controlling the second controllable switch to be opened.
9. A method for controlling the start-up of a flying capacitor three-level BOOST converter as claimed in any one of claims 1 to 6, wherein said predetermined voltage is within a predetermined range of said input voltage.
10. The method for controlling the start-up of a flying capacitor three-level BOOST converter as claimed in any one of claims 1 to 6, further comprising:
when the input voltage is greater than or equal to the starting threshold, charging the suspension capacitor by using the input voltage, so that the voltage of the suspension capacitor reaches the starting threshold;
and then executing the step of controlling the normal work of the main circuit.
11. A floating capacitor three-level BOOST converter, comprising: a main circuit and a controller; wherein the content of the first and second substances,
the main circuit is a suspension capacitor three-level BOOST circuit, and comprises: the circuit comprises an inductor, a first diode, a second diode, a first switch tube, a second switch tube, a suspension capacitor, a pre-charging circuit, an input capacitor and an output capacitor;
the inductor, the first diode and the second diode are sequentially arranged in the one-pole transmission branch; the other end of the inductor is used as a corresponding pole of an input end of the main circuit, and the other end of the second diode is used as a corresponding pole of an output end of the main circuit;
the connection point of the inductor and the first diode is connected with the other pole transmission branch circuit through the first switch tube and the second switch tube in sequence;
one end of the suspension capacitor is connected with a connection point of the first switch tube and the second switch tube; the other end of the suspension capacitor is connected with a connection point of the first diode and the second diode;
the pre-charging circuit is used for charging the suspension capacitor by using the input voltage of the main circuit;
the input capacitor is arranged between the positive and negative poles of the input end of the main circuit, and the output capacitor is arranged between the positive and negative poles of the output end of the main circuit;
the first switch tube, the second switch tube and the pre-charge circuit are all controlled by the controller, and the controller is used for executing the starting control method of the floating capacitor three-level BOOST converter according to any one of claims 1 to 10.
12. The floating-capacitor three-level BOOST converter according to claim 11, wherein a first controllable switch is disposed between the connection point of the first switch tube and the second switch tube and the floating capacitor;
the precharge circuit includes: the second controllable switch and the resistor are connected in series, and a branch circuit after series connection is arranged between the suspension capacitor and the negative electrode of the output end or the midpoint of the output end of the main circuit;
the first controllable switch and the second controllable switch are both controlled by the controller.
13. The flying capacitor three-level BOOST converter according to claim 12, wherein said first controllable switch is a normally open relay or a power semiconductor switch tube, and said second controllable switch is a normally closed relay or a power semiconductor switch tube.
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| CN103441658A (en) * | 2013-08-30 | 2013-12-11 | 深圳市汇顶科技股份有限公司 | Boost controller and Boost converter |
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