A flying capacitor dc boost converter and photovoltaic system

Abstract

The application provides a flying capacitor type direct current boost converter and a photovoltaic system. An inductor and a buffer capacitor are connected to a positive input end of the converter, and the buffer capacitor and a second switch tube are connected to a negative input end of the converter. The second switch tube is connected to a first switch tube, and the first switch tube and the inductor are connected to a positive electrode of a first anti-reverse unit. A negative electrode of the first anti-reverse unit is connected to a positive electrode of a second anti-reverse unit. A flying capacitor and a scheduling unit are connected to a negative electrode of the first anti-reverse unit, and the flying capacitor is also connected to a second end of the second switch tube. A negative electrode of the second anti-reverse unit and a first capacitor are connected to a positive output end of the converter, and one pole of a second capacitor is connected to a negative output end of the converter. A second end of the scheduling unit is connected between the first capacitor and the second capacitor. Through the scheduling unit, the voltage balance control problem of the flying capacitor is solved by using a bus, so that the voltage of the flying capacitor after charging is kept near a rated value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electric power, in particular to a flying capacitor type DC boost converter and photovoltaic system. BACKGROUND

[0002] With the increasing demand for voltage level of string photovoltaic inverter in large ground photovoltaic power station, multi-level converter gradually replaces the traditional two-level topology structure due to its technical advantages. At present, the mainstream string photovoltaic inverter adopts two-stage power conversion architecture, the front stage is configured with a boost circuit for maximum power point tracking, and the rear stage realizes grid-connected control through an inverter circuit. Among them, the three-level flying capacitor type DC boost converter (boost converter) is concerned due to its unique topological characteristics. The structure can reduce the voltage stress of the switching device and significantly improve the system reliability.

[0003] However, in practical application, the three-level flying capacitor type DC boost converter still faces multiple technical challenges, including the voltage balance control problem of flying capacitor, which has become a difficult problem for those skilled in the art. SUMMARY

[0004] The purpose of the present application is to provide a flying capacitor type DC boost converter and photovoltaic system to improve the above problems.

[0005] In order to achieve the above purpose, the technical scheme adopted by the embodiments of the present application is as follows:

[0006] In a first aspect, the embodiments of the present application provide a flying capacitor type DC boost converter, comprising: a first anti-flow unit, a second anti-flow unit, a first switch tube, a second switch tube, a flying capacitor, a buffer capacitor, an inductor, a scheduling unit, a first capacitor and a second capacitor.

[0007] One end of the inductor and one pole of the buffer capacitor are connected to the positive input end of the converter, and the other pole of the buffer capacitor and the first end of the second switch tube are connected to the negative input end of the converter.

[0008] The second end of the second switch tube is connected to the first end of the first switch tube, the second end of the first switch tube and the other end of the inductor are connected to the positive pole of the first anti-flow unit, and the negative pole of the first anti-flow unit is connected to the positive pole of the second anti-flow unit.

[0009] One pole of the flying capacitor and the first end of the scheduling unit are connected to the negative pole of the first anti-flow unit, and the other pole of the flying capacitor is connected to the second end of the second switch tube.

[0010] The negative pole of the second anti-reverse flow unit and one pole of the first capacitor are connected to the positive output end of the converter, and one pole of the second capacitor is connected to the negative output end of the converter.

[0011] The second end of the scheduling unit is connected between the first capacitor and the second capacitor.

[0012] Optionally, the DC boost converter further comprises a controller, which is connected to the control end of the first switch tube, the control end of the second switch tube, and the control end of the scheduling unit respectively.

[0013] When the DC boost converter is in a normal working mode, the controller is configured to control the first switch tube to be turned on in a first time period in a working cycle, and control the second switch tube and the scheduling unit to be turned on in a second time period in the working cycle, the first time period and the second time period being non-overlapping.

[0014] Optionally, when the DC boost converter is in an initialization mode, the controller is configured to control the second switch tube and the scheduling unit to be turned on to pre-charge the flying capacitor.

[0015] Optionally, the controller is configured to obtain a buffer voltage and a bus voltage, wherein the buffer voltage is the voltage between the two poles of the buffer capacitor.

[0016] The controller is configured to determine that the DC boost converter is in the initialization mode when the buffer voltage is greater than a first voltage threshold and the bus voltage is less than a second voltage threshold.

[0017] Optionally, when the DC boost converter is in a disabled mode, the controller is configured to control the scheduling unit to be turned on to charge the flying capacitor.

[0018] Optionally, the controller is configured to obtain a buffer voltage and a bus voltage, wherein the buffer voltage is the voltage between the two poles of the buffer capacitor.

[0019] The controller is configured to determine that the DC boost converter is in the disabled mode when the buffer voltage is less than the second voltage threshold and the bus voltage is greater than the first voltage threshold.

[0020] Optionally, the scheduling unit comprises a third NMOS tube and a fourth NMOS tube.

[0021] The drain of the third NMOS tube is connected to the drain of the fourth NMOS tube, the source of the third NMOS tube serves as the first end of the scheduling unit, and the source of the fourth NMOS tube serves as the second end of the scheduling unit.

[0022] Optionally, the scheduling unit further comprises a current-limiting resistor.

[0023] One end of the current-limiting resistor is connected to the source of the fourth NMOS tube, and the other end of the current-limiting resistor is connected to the second end of the scheduling unit.

[0024] Optionally, the first anti-reverse flow unit and the second anti-reverse flow unit are diodes.

[0025] In a second aspect, an embodiment of the present application provides a photovoltaic system, comprising the flying capacitor type direct current boost converter.

[0026] Compared with the prior art, the flying capacitor type direct current boost converter and the photovoltaic system provided by the embodiment of the present application have the following advantages: one end of the inductor and one pole of the buffer capacitor are connected to the positive input end of the converter, the other pole of the buffer capacitor and the first end of the second switch tube are connected to the negative input end of the converter; the second end of the second switch tube is connected to the first end of the first switch tube, the second end of the first switch tube and the other end of the inductor are connected to the positive pole of the first anti-reverse flow unit, the negative pole of the first anti-reverse flow unit is connected to the positive pole of the second anti-reverse flow unit; one pole of the flying capacitor and the first end of the scheduling unit are connected to the negative pole of the first anti-reverse flow unit, the other pole of the flying capacitor is connected to the second end of the second switch tube; the negative pole of the second anti-reverse flow unit and one pole of the first capacitor are connected to the positive output end of the converter, one pole of the second capacitor is connected to the negative output end of the converter; the second end of the scheduling unit is connected between the first capacitor and the second capacitor. By arranging the scheduling unit, the voltage balance control problem of the flying capacitor is solved by using the bus, so that the voltage of the flying capacitor after charging is kept near the rated value.

[0027] In order to make the above object, characteristics and advantages of the present application more obvious and easy to understand, the following preferred embodiments are described in detail below, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0029] Figure 1 The topological diagram of the flying capacitor type direct current boost converter provided by the embodiment of the present application.

[0030] Figure 2 The current path diagram of the flying capacitor type direct current boost converter provided by the embodiment of the present application.

[0031] Figure 3The connection schematic diagram of the flying capacitor type direct current boost converter is provided for the embodiment of the present application.

[0032] Figure 4 The working timing schematic diagram is provided for the embodiment of the present application.

[0033] Figure 5 The second current path schematic diagram of the flying capacitor type direct current boost converter is provided for the embodiment of the present application.

[0034] Figure 6 The third current path schematic diagram of the flying capacitor type direct current boost converter is provided for the embodiment of the present application.

[0035] Figure 7 The fourth current path schematic diagram of the flying capacitor type direct current boost converter is provided for the embodiment of the present application.

[0036] Figure 8 The fifth current path schematic diagram of the flying capacitor type direct current boost converter is provided for the embodiment of the present application. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0039] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. Meanwhile, in the description of the present application, the terms "first", "second" and the like are only used to distinguish description, and cannot be understood as indicating or implying relative importance.

[0040] It is to be noted that the relative terms such as first and second and the like in this context are used only to differentiate one entity or operation from another, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In addition, the terms "comprising", "containing" or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, method, article or apparatus that includes a list of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent in such process, method, article or apparatus. Without more limitations, the element defined by the phrase "comprising a" does not exclude the presence of additional identical elements in the process, method, article or apparatus that includes the element.

[0041] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present application is usually placed, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0042] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms "provided", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0043] Some embodiments of the present application will be described in detail below with reference to the accompanying drawings. The following examples and features in the examples can be combined with each other without conflict.

[0044] The embodiment of the present application provides a flying capacitor type DC boost converter, which can also be called a three-level flying capacitor type DC boost converter. Please refer to Figure 1 , Figure 1 The flying capacitor type DC boost converter provided by the embodiment of the present application is shown in the topological diagram.

[0045] The flying capacitor type DC boost converter comprises a first anti-reverse flow unit D1, a second anti-reverse flow unit D2, a first switch tube T1, a second switch tube T2, a flying capacitor Cf, a buffer capacitor Cpv, an inductor Lb, a scheduling unit, a first capacitor C1 and a second capacitor C2.

[0046] Wherein, the first anti-reverse flow unit D1 and the second anti-reverse flow unit D2 can be but not limited to the diode as shown. Figure 1 The first switch tube T1 and the second switch tube T2 are taken as examples of NMOS tubes, and it should be noted that the first switch tube T1 and the second switch tube T2 can also be IGBT tubes, and the connection relationship is adjusted adaptively, which is not described here.

[0047] One end of the inductor Lb and one pole of the buffer capacitor Cpv are connected to the positive input end of the converter (for connecting the positive output end of the photovoltaic module string), and the other pole of the buffer capacitor Cpv and the first end of the second switch tube T2 (the source of the NMOS tube) are connected to the negative input end of the converter (for connecting the negative output end of the photovoltaic module string).

[0048] The second end (the drain of the NMOS tube) of the second switch tube T2 is connected to the first end (the source of the NMOS tube) of the first switch tube T1, and the second end (the drain of the NMOS tube) of the first switch tube T1 and the other end of the inductor Lb are connected to the positive pole of the first anti-reverse flow unit D1, and the negative pole of the first anti-reverse flow unit D1 is connected to the positive pole of the second anti-reverse flow unit D2.

[0049] One pole of the flying capacitor Cf and the first end of the scheduling unit are connected to the negative pole of the first anti-reverse flow unit D1 (between the first anti-reverse flow unit D1 and the second anti-reverse flow unit D2), and the other pole of the flying capacitor Cf is connected to the second end of the second switch tube T2 (between the first switch tube T1 and the second switch tube T2).

[0050] The negative pole of the second anti-reverse flow unit D2 and one pole of the first capacitor C1 are connected to the positive output end of the converter (for connecting the positive access end of the bus), and one pole of the second capacitor C2 is connected to the negative output end of the converter (for connecting the negative access end of the bus), and optionally, the negative output end of the converter is conductive with the negative input end of the converter.

[0051] The other pole of the first capacitor C1 is connected to the other pole of the second capacitor C2, the second end of the scheduling unit is connected between the first capacitor C1 and the second capacitor C2, and is connected to the midpoint of the DC bus.

[0052] Wherein, the control end of the first switch tube T1, the control end of the second switch tube T2 and the control end of the scheduling unit are used for accessing corresponding control signals, and under the control of the control signals, the state switching of conduction and disconnection is carried out, so as to realize the autonomous balance adjustment of the flying capacitor under the voltage imbalance working condition. The control signal can be provided by the upper computer, or can be provided by the controller in the following.

[0053] One of the improvements of the embodiment of the application is to introduce the scheduling unit. Without the scheduling unit, it is equivalent to the scheduling unit being in the off state. The following will be described in combination with the schematic diagram of the application. Figure 2, the problems that may exist in the non-quoted scheduling unit are described. Please refer to Figure 2 , Figure 2 The current path schematic diagram of the flying capacitor type DC boost converter provided by the embodiment of the present application is shown. Without introducing the scheduling unit, the flying capacitor type DC boost converter has three working modes, mode one corresponding to the current path 1, mode two corresponding to the current path 2, and mode three corresponding to the current path 3.

[0054] Mode one: the first switch T1 is turned on, the second switch T2 is turned off, and the scheduling unit is turned off and disconnected. At this time, the current flows through the first switch T1 -> the flying capacitor Cf -> the second anti-flow unit D2 into the DC bus, the flying capacitor Cf is discharged, and the flying capacitor voltage U cf drops.

[0055] Mode two: the first switch T1 and the second switch T2 are turned off, and the scheduling unit is turned off and disconnected. At this time, the current flows through the first anti-flow unit D1 -> the second anti-flow unit D2 into the DC bus, and the flying capacitor voltage U cf remains unchanged.

[0056] Mode three: the second switch T2 is turned on, the first switch T1 is turned off, and the scheduling unit is turned off and disconnected. At this time, the current flows through the first anti-flow unit D1 -> the flying capacitor Cf -> the second switch T2 back to the input, the flying capacitor Cf is charged, and the flying capacitor voltage U cf rises.

[0057] In the actual circuit, due to the characteristics deviation of the switching device, the non-ideal synchronization of the driving signal, and the line parasitic parameters and other factors, the charging and discharging process of the flying capacitor Cf is difficult to achieve strict charge balance (such as the symmetry error of the conduction time or the current), which causes the voltage across the flying capacitor to produce cumulative fluctuations and gradually deviate from the rated value (which can be but is not limited to half of the bus voltage Vdc / 2). This voltage imbalance can cause the power device to bear uneven voltage stress, and further cause the risk of local overvoltage breakdown, threatening the overall reliability of the system.

[0058] In order to overcome this problem, an optional embodiment provided by the embodiment of the present application is as follows: Figure 3 , Figure 3 The connection schematic diagram of the flying capacitor type DC boost converter provided by the embodiment of the present application is shown. The DC boost converter further includes a controller, which is connected with the control end of the first switch T1, the control end of the second switch T2, and the control end of the scheduling unit, respectively.

[0059] When the DC boost converter is in the normal working mode, the controller is configured to control the first switch T1 to be turned on in a first period in a working cycle, and control the second switch T2 and the scheduling unit to be turned on in a second period in the working cycle, and the first period and the second period do not overlap.

[0060] Please refer to Figure 4 , Figure 4 The working timing diagram is provided for the embodiment of the present application. Among them, the third switch tube T3 and the fourth switch tube T4 correspond to the scheduling unit, the first time period corresponds to t1, and the second time period corresponds to t2. Figure 4 As shown, the working timing of the second switch tube T2 and the scheduling unit is consistent.

[0061] The interval between the start time of the second time period of the i-th working cycle and the end time of the first time period of the i-th working cycle is greater than the preset time length, and the interval between the end time of the second time period of the i-th working cycle and the start time of the first time period of the i+1-th working cycle is greater than the preset time length, thereby avoiding the first switch tube T1 and the second switch tube T2 from being turned on at the same time.

[0062] In the first time period t1, the first switch tube T1 is turned on, and the second switch tube T2 and the scheduling unit are both in the off state, at this time the DC boost converter works in the above-mentioned mode one, the flying capacitor Cf is discharged, and the flying capacitor voltage U cf drops.

[0063] In the second time period t2, the second switch tube T2 and the scheduling unit are turned on, and the first switch tube T1 is in the off state, at this time the DC boost converter works in the above-mentioned mode three, the flying capacitor Cf is charged, and the flying capacitor voltage U cf rises. There are two possibilities in the second time period t2, the flying capacitor voltage U cf is less than the half bus voltage U m , corresponding to the current path 4; the flying capacitor voltage U cf is greater than the half bus voltage U m , corresponding to the current path 5. Please refer to Figure 5 and Figure 6 , Figure 5 The current path diagram two of the flying capacitor type DC boost converter provided by the embodiment of the present application is shown in the figure, Figure 6 The current path diagram three of the flying capacitor type DC boost converter provided by the embodiment of the present application is shown in the figure.

[0064] When the flying capacitor voltage U cf is less than the half bus voltage U m , as shown in the current path 4, in addition to charging the flying capacitor Cf by the photovoltaic string, the bus current can charge the flying capacitor Cf through the scheduling unit. Compared with the original mode three, the newly added charging loop speeds up the flying capacitor voltage rise until it reaches the half bus voltage.

[0065] When the flying capacitor voltage U cf is greater than the half bus voltage U mWhen the photovoltaic string charges the flying capacitor Cf, as shown in the current path 5, the charging current can flow to the bus through the scheduling unit, which splits the charging current of the original flying capacitor Cf and suppresses the rising amplitude of the flying capacitor voltage, so that the flying capacitor voltage slowly falls to the half bus voltage.

[0066] In the flying capacitor type DC boost converter provided by the embodiment of the application, based on the on-off logic of the switching tube, autonomous equalization adjustment of the flying capacitor under the voltage imbalance condition is realized, so that the voltage of the flying capacitor after charging is kept near the rated value (deviation is less than a preset amplitude), and the rated value can be but is not limited to the half bus voltage. The advantage is autonomous equalization without sampling, which guides the directional migration of charges between the capacitor branches through the switching sequence in the preset working period, without relying on voltage sampling and dynamic pulse width modulation (PWM) feedback control, and significantly reduces the algorithm complexity.

[0067] On the basis of the foregoing, the embodiment of the application also provides an optional implementation for how to realize the pre-charging of the flying capacitor, please refer to Figure 7 , Figure 7 Figure 4 is a fourth schematic diagram of the current path of the flying capacitor type DC boost converter provided by the embodiment of the application.

[0068] When the DC boost converter is in the initialization mode, the controller is configured to control the second switching tube T2 and the scheduling unit to be turned on to pre-charge the flying capacitor Cf.

[0069] As shown in Figure 7 , when the second switching tube T2 and the scheduling unit are turned on and the first switching tube T1 is turned off, the flying capacitor Cf is pre-charged through the current path 6 therein, so that the flying capacitor voltage is pre-charged to be close to the half bus voltage, so as to ensure the subsequent normal operation of the flying capacitor type DC boost converter.

[0070] Optionally, the controller sends a short pulse control signal to the second switching tube T2 and the scheduling unit at a preset frequency, and the second switching tube T2 and the scheduling unit are switched to the on state when receiving the short pulse control signal, thereby completing the pre-charging of the flying capacitor Cf. The purpose of sending the short pulse control signal is to prevent the inductance Lb current from being too large and reduce the operation risk. The short pulse refers to a square wave signal with a frequency of 10KHz~20KHz and a pulse width of 50%, which is consistent with the waveform shown in Figure 4 .

[0071] In an optional implementation, the controller is configured to obtain a buffer voltage and a bus voltage, wherein the buffer voltage is the voltage between the two poles of the buffer capacitor Cpv.

[0072] The controller is configured to determine that the DC voltage booster is in the initialization mode when the buffer voltage is greater than a first voltage threshold (which can be but is not limited to 550 V) and the bus voltage is less than a second voltage threshold (which can be but is not limited to 100 V).

[0073] Optionally, the initialization mode is exited when the buffer voltage is equal to the bus voltage and greater than the first voltage threshold.

[0074] Based on the foregoing, when multiple flying-capacitor-type DC voltage boosters connected to photovoltaic strings are connected in parallel on the bus, how to avoid the flying capacitor from collapsing in the disabled mode and maintain the flying capacitor voltage to avoid device overvoltage failure is described. Figure 8 , Figure 8 A fifth current path schematic diagram of the flying-capacitor-type DC voltage booster provided in the embodiments of the present application.

[0075] When the DC voltage booster is in the disabled mode, the controller is configured to control the switching unit to be turned on to charge the flying capacitor Cf.

[0076] It should be noted that when some photovoltaic strings enter the disabled state due to shading, failure or light difference, the DC voltage booster is in the disabled mode.

[0077] As shown in Figure 8 , when the switching unit is turned on and the first switch T1 and the second switch T2 are turned off. Because there is a point in the bus, the switching unit and the body diode in the first switch T1 form a path, i.e., the current path 7. The flying capacitor Cf is charged through the current path 7, so that the flying capacitor voltage is maintained at a voltage close to half the bus voltage, thereby avoiding the flying capacitor from collapsing, maintaining the flying capacitor voltage to avoid device overvoltage failure, and ensuring the normal operation of the flying-capacitor-type DC voltage booster.

[0078] In the embodiments of the present application, the first capacitor C1 and the second capacitor C2 are the same, the capacity of the flying capacitor Cf is less than the capacity of the second capacitor C2, and the capacity of the flying capacitor Cf is more than 5 times the capacity of the buffer capacitor Cpv.

[0079] In an optional embodiment, the controller is configured to obtain the buffer voltage and the bus voltage, wherein the buffer voltage is the voltage between the two poles of the buffer capacitor Cpv.

[0080] The controller is configured to determine that the DC voltage booster is in the disabled mode when the buffer voltage is less than the second voltage threshold and the bus voltage is greater than the first voltage threshold.

[0081] Optionally, the disabled mode is exited when the buffer voltage is greater than the first voltage threshold.

[0082] Please continue to refer to Figure 1 In an alternative embodiment, the scheduling unit comprises a third NMOS transistor T3 and a fourth NMOS transistor T4.

[0083] The drain of the third NMOS transistor T3 is connected to the drain of the fourth NMOS transistor T4, the source of the third NMOS transistor T3 is the first end of the scheduling unit (connected to the negative electrode of the first anti-reverse unit D1), and the source of the fourth NMOS transistor T4 is the second end of the scheduling unit (connected between the first capacitor C1 and the second capacitor C2).

[0084] As shown in Figure 3 The gate of the third NMOS transistor T3 and the gate of the fourth NMOS transistor T4 are connected to the controller.

[0085] In this way, the body diode leakage can be avoided when the third NMOS transistor T3 and the fourth NMOS transistor T4 are turned off.

[0086] Please continue to refer to Figure 1 In an alternative embodiment, the scheduling unit further comprises a current-limiting resistor R1.

[0087] One end of the current-limiting resistor R1 is connected to the source of the fourth NMOS transistor T4, and the other end of the current-limiting resistor R1 is the second end of the scheduling unit (connected between the first capacitor C1 and the second capacitor C2).

[0088] By connecting the current-limiting resistor in series in the balancing path, the amplitude of the balancing current across the capacitor is constrained, so that the MOS switch tube selection can be based on a low current specification (such as below 10A), which greatly reduces the device cost and driving power consumption.

[0089] The embodiment of the present application also provides a photovoltaic system comprising the flying capacitor type DC boost converter described above.

[0090] In summary, the fly capacitor type direct current boost converter and photovoltaic system provided by the embodiment of the present application has the following advantages: one end of the inductor and one pole of the buffer capacitor are connected to the positive input end of the converter, the other pole of the buffer capacitor and the first end of the second switch tube are connected to the negative input end of the converter; the second end of the second switch tube is connected to the first end of the first switch tube, the second end of the first switch tube and the other end of the inductor are connected to the positive pole of the first anti-flow unit, the negative pole of the first anti-flow unit is connected to the positive pole of the second anti-flow unit; one pole of the fly capacitor and the first end of the scheduling unit are connected to the negative pole of the first anti-flow unit, the other pole of the fly capacitor is connected to the second end of the second switch tube; the negative pole of the second anti-flow unit and one pole of the first capacitor are connected to the positive output end of the converter, one pole of the second capacitor is connected to the negative output end of the converter; the second end of the scheduling unit is connected between the first capacitor and the second capacitor. By setting the scheduling unit, the voltage balance control problem of the fly capacitor is solved by using the bus, so that the voltage of the fly capacitor after charging is kept near the rated value.

[0091] The above only describes preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0092] It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims.

Claims

1. A flying capacitor type DC-boost converter characterized by comprising: The DC boost converter comprises: a first anti-inrush unit, a second anti-inrush unit, a first switch tube, a second switch tube, a flying capacitor, a buffer capacitor, an inductor, a scheduling unit, a first capacitor, and a second capacitor; one end of the inductor and one pole of the buffer capacitor are connected to a positive input end of the converter, and the other pole of the buffer capacitor and a first end of the second switch tube are connected to a negative input end of the converter; a second end of the second switch tube is connected to a first end of the first switch tube, a second end of the first switch tube and the other end of the inductor are connected to a positive pole of the first anti-inrush unit, and a negative pole of the first anti-inrush unit is connected to a positive pole of the second anti-inrush unit; one pole of the flying capacitor and a first end of the scheduling unit are connected to a negative pole of the first anti-inrush unit, and the other pole of the flying capacitor is connected to the second end of the second switch tube; a negative pole of the second anti-inrush unit and one pole of the first capacitor are connected to a positive output end of the converter, and one pole of the second capacitor is connected to a negative output end of the converter; a second end of the scheduling unit is connected between the first capacitor and the second capacitor; the DC boost converter further comprises a controller, which is connected to a control end of the first switch tube, a control end of the second switch tube, and a control end of the scheduling unit, respectively; when the DC boost converter is in a normal working mode, the controller is configured to control the first switch tube to be turned on in a first time period in a working cycle, and control the second switch tube and the scheduling unit to be turned on in a second time period in the working cycle, and the first time period and the second time period do not overlap.

2. The DC boost converter of the flying capacitor type according to claim 1, wherein when the DC boost converter is in an initialization mode, the controller is configured to control the second switch tube and the scheduling unit to be turned on to pre-charge the flying capacitor.

3. The DC boost converter of the flying capacitor type according to claim 2, wherein the controller is configured to obtain a buffer voltage and a bus voltage, wherein the buffer voltage is a voltage between two poles of the buffer capacitor; the controller is configured to determine that the DC boost converter is in the initialization mode when the buffer voltage is greater than a first voltage threshold and the bus voltage is less than a second voltage threshold.

4. The DC boost converter of the flying capacitor type according to claim 1, wherein when the DC boost converter is in a disabled mode, the controller is configured to control the scheduling unit to be turned on to charge the flying capacitor.

5. The DC boost converter of the flying capacitor type according to claim 4, wherein the controller is configured to obtain a buffer voltage and a bus voltage, wherein the buffer voltage is a voltage between two poles of the buffer capacitor; the controller is configured to determine that the DC boost converter is in the disabled mode when the buffer voltage is less than a second voltage threshold and the bus voltage is greater than a first voltage threshold.

6. The flying capacitor type DC boost converter according to any one of claims 1 to 5, wherein the scheduling unit comprises a third NMOS tube and a fourth NMOS tube. The drain of the third NMOS tube is connected with the drain of the fourth NMOS tube, the source of the third NMOS tube is the first end of the scheduling unit, and the source of the fourth NMOS tube is the second end of the scheduling unit.

7. The flying capacitor type DC boost converter according to claim 6, wherein The scheduling unit further comprises a current-limiting resistor. One end of the current-limiting resistor is connected to the source of the fourth NMOS tube, and the other end of the current-limiting resistor is the second end of the scheduling unit.

8. The flying capacitor type DC boost converter according to any one of claims 1 to 5, wherein The first anti-backflow unit and the second anti-backflow unit are diodes.

9. A photovoltaic system characterized by, The flying capacitor type direct current boost converter of any one of claims 1-8.

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