Buck-Boost conversion circuit and photovoltaic power generation system

Abstract

The present invention discloses a Buck-Boost conversion circuit and a photovoltaic power generation system. The Buck-Boost conversion circuit includes: one end of a first controllable switch and the anode of a second diode are connected to the positive electrode of an input voltage, the cathode of the second diode is connected in series with the second controllable switch and an adjustable inductor in sequence and then connected to the negative electrode of the input voltage, one end of an adjustable capacitor is connected to the other end of the first controllable switch, the other end of the adjustable capacitor is connected to the cathode of the second diode, the other end of the first controllable switch is connected to the anode of the first diode and the cathode of a third diode, the cathode of the first diode is connected to the junction of the second controllable switch and the adjustable inductor, the anode of the third diode is connected to the negative electrode of the input voltage after being connected in series with a resistor, the capacitor is connected in parallel with the resistor, and the first controllable switch and the second controllable switch are controlled to be connected or disconnected at the same time. Through the present invention, power loss caused by multiple control of the circuit can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to a Buck-Boost conversion circuit and a photovoltaic power generation system. Background Art

[0002] At present, the existing technology provides a photovoltaic energy storage inverter topology structure, such as Figure 1 As shown, it includes: Buck-Boost circuit on the PV side, single-stage bidirectional DC-DC circuit on the battery side, DC-AC circuit on the AC side and a battery module. One end of the Buck-Boost circuit on the PV side is connected to the PV panel, and the other end is connected to the DC bus; one end of the single-stage bidirectional DC-DC circuit on the battery side is connected to the battery module, and the other end is connected to the DC bus; one end of the DC-AC inverter circuit on the AC side is connected to the DC bus, and the other end is connected to the grid.

[0003] The specific structure of the Buck-Boost circuit on the PV side includes: a first energy storage inductor L1, a first power switch tube K1, a second power switch tube K2, a first power diode d1, a second power diode d2 and a first filter capacitor C1. One end of the first power switch tube K1 is connected to PV+, and the other end is connected to PV- through the power diode d1. One end of the first energy storage inductor L1 is connected to the cathode of the first power diode d1, and the other end is connected to the junction of the second power switch tube K2 and the second power diode d2. One end of the second power switch tube K2 is connected to the anode of the second power diode d2, and the other end is connected to the anode of the first power diode d1. One end of the first filter capacitor C1 is connected to the cathode of the second power diode d2 and the DC bus DC_Bus+.

[0004] The working mode of the PV side Buck-Boost circuit is that when the PV voltage is greater than the set threshold value such as 380V, the circuit works in Buck mode, at which time the first power switch tube K1 is working and the second power switch tube K2 is in the OFF state; when the PV voltage is less than the set threshold value such as 380V, the circuit works in Boost mode, at which time the first power switch tube K1 is in the ON state and the second power switch tube K2 is working.

[0005] However, this topology causes power loss problems due to multiple circuit controls, and no effective solution has been proposed yet. Summary of the invention

[0006] A Buck-Boost conversion circuit and a photovoltaic power generation system are provided in the embodiments of the present invention to solve the problem of power loss caused by multiple controls of the Buck-Boost circuit in the prior art.

[0007] In order to solve the above technical problems, the present invention provides a Buck-Boost conversion circuit, wherein the Buck-Boost conversion circuit includes: a first controllable switch, a second controllable switch, an adjustable inductor, an adjustable capacitor, a first diode, a second diode, a third diode, a capacitor and a resistor, wherein:

[0008] One end of the first controllable switch and the anode of the second diode are connected to the positive electrode of the input voltage, the cathode of the second diode is connected in series with the second controllable switch and the adjustable inductor in sequence and then connected to the negative electrode of the input voltage, one end of the adjustable capacitor is connected to the other end of the first controllable switch, the other end of the adjustable capacitor is connected to the cathode of the second diode, the other end of the first controllable switch is connected to the anode of the first diode and the cathode of the third diode, the cathode of the first diode is connected to the junction of the second controllable switch and the adjustable inductor, the anode of the third diode is connected in series with the resistor and then connected to the negative electrode of the input voltage, the capacitor is connected in parallel with the resistor, and the first controllable switch and the second controllable switch are controlled to be connected or disconnected at the same time.

[0009] Furthermore, the first controllable switch and the second controllable switch are controlled to be connected or disconnected at the same time by a soft switch control method.

[0010] Furthermore, the adjustable capacitor includes a preset number of capacitors connected in series; and the adjustable inductor includes a preset number of inductors connected in series.

[0011] Furthermore, the preset number is 5.

[0012] The present invention also provides a photovoltaic power generation system, wherein the photovoltaic power generation system includes: a photovoltaic cell array; a grid-connected inverter, the grid-connected inverter includes the Buck-Boost conversion circuit described in any one of claims 1 to 4, the input end of the Buck-Boost conversion circuit is connected to the output end of the photovoltaic cell array; a first central processor, the first central processor is connected to the first controllable switch and the second controllable switch in the Buck-Boost conversion circuit, and is used to control the first controllable switch and the second controllable switch to be connected or disconnected at the same time; a second central processor, the second central processor is connected to the adjustable inductor and the adjustable capacitor in the Buck-Boost conversion circuit, and is used to adjust the inductance value of the adjustable inductor and the capacitance value of the adjustable capacitor.

[0013] Furthermore, the first central processor is specifically used to generate a PWM wave according to the requirements of boost and buck, and transmit the PWM wave to the MPPT controller in the grid-connected inverter; the MPPT controller is used to control the first controllable switch and the second controllable switch to be connected or disconnected at the same time according to the PWM wave.

[0014] Furthermore, the first central processing unit generates the PWM wave according to a conductance increment method.

[0015] Furthermore, the second central processor is specifically used to control one or more of the adjustable inductors to close and adjust the inductance value of the adjustable inductors when the open-circuit voltage of the grid-connected inverter fluctuates; and / or the second central processor controls one or more of the adjustable capacitors to close and adjust the capacitance value of the adjustable capacitors.

[0016] Furthermore, the second central processing unit is connected one-to-one with the inductors in the adjustable inductors through switches, and is connected one-to-one with the capacitors in the adjustable capacitors through switches.

[0017] Furthermore, the above photovoltaic power generation system also includes:

[0018] A storage battery is connected to the output end of the Buck-Boost conversion circuit.

[0019] By applying the technical solution of the present invention, an improved Buck-Boost conversion circuit structure is provided. The unique circuit structure of the improved buck-boost conversion circuit greatly simplifies the control of the switch tube, and realizes that the first controllable switch and the second controllable switch can be controlled to be connected or disconnected at the same time, thereby avoiding power loss caused by multiple controls of the circuit, and further facilitating improving the output efficiency of the system; at the same time, the improved buck-boost conversion circuit includes an adjustable capacitor and an adjustable inductor, and the loss can be further reduced by regulating the capacitance value of the adjustable capacitor and the inductance value of the adjustable inductor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the topological structure of a photovoltaic energy storage inverter in the prior art;

[0021] Figure 2 is a schematic structural diagram of a Buck-Boost conversion circuit according to an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of the principle of a photovoltaic power generation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0025] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0026] It should be understood that, although the terms first, second, third, etc. may be used to describe controllable switches and diodes in the embodiments of the present invention, they should not be limited to these terms. These terms are only used to distinguish controllable switches, diodes, etc. For example, without departing from the scope of the embodiments of the present invention, the first controllable switch may also be referred to as the second controllable switch, and similarly, the second controllable switch may also be referred to as the first controllable switch.

[0027] As used herein, the words "if" and "if" may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0028] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0029] The optional embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0030] Embodiment 1

[0031] Figure 2 is a schematic diagram of the structure of a Buck-Boost conversion circuit according to an embodiment of the present invention. Figure 2 As shown, the Buck-Boost conversion circuit includes: a first controllable switch S1, a second controllable switch S2, an adjustable inductor Lr, an adjustable capacitor Cr, a first diode D1, a second diode D2, a third diode D3, a capacitor Co and a resistor R, wherein:

[0032] One end of the first controllable switch S1 and the anode of the second diode D2 are connected to the positive electrode of the input voltage, and the cathode of the second diode D2 is connected to the negative electrode of the input voltage after the second controllable switch S2 and the adjustable inductor Lr are connected in series in sequence.

[0033] One end of the adjustable capacitor Cr is connected to the other end of the first controllable switch S1, and the other end of the adjustable capacitor Cr is connected to the cathode of the second diode D2.

[0034] The other end of the first controllable switch S1 is connected to the anode of the first diode D1 and the cathode of the third diode D3, the cathode of the first diode D1 is connected to the junction of the second controllable switch S2 and the adjustable inductor Lr, and the anode of the third diode D3 is connected in series with the resistor R and then connected to the negative electrode of the input voltage.

[0035] The capacitor Co is connected in parallel with the resistor R, and the first controllable switch S1 and the second controllable switch S2 are controlled to be connected or disconnected at the same time.

[0036] The buck-boost conversion circuit mentioned above is mainly composed of a controllable switch, an inductor, and a buffer capacitor. The resonant circuit of the capacitor part is equivalent to the traditional buck-boost conversion circuit, which is composed of a series of switches, diodes, and capacitors. Through the connection or disconnection control of the controllable switch, it can be equivalent to a lossless buffer circuit.

[0037] In order to conveniently and effectively control the first controllable switch S1 and the second controllable switch S2 to be connected or disconnected at the same time, the first controllable switch S1 and the second controllable switch S2 can be controlled to be connected or disconnected at the same time by a soft switch control method, that is, the first controllable switch S1 and the second controllable switch S2 are controlled to be connected or disconnected at the same time by a soft switch control technology.

[0038] In order to further reduce the loss, this embodiment proposes a buck-boost conversion circuit including an adjustable capacitor with adjustable capacitance value and an adjustable inductor with adjustable inductance value. In order to adjust the capacitance and inductance required by the circuit to achieve maximum power tracking, it is proposed that the adjustable capacitor includes a preset number of capacitors connected in series; the adjustable inductor includes a preset number of inductors connected in series. The adjustable capacitor Cr can be called a capacitor interlocking switching switch, which is connected in parallel with the first controllable switch S1. The adjustable inductor can be called an inductor interlocking switching switch, which is connected in series with the second controllable switch S2. For specific connection methods, see Figure 2 The connection method of Cr and Lr.

[0039] The specific value of the preset number can be determined according to the specific adjustment requirements of the inductor and the capacitor. For example, the preset number can be 5, that is, the capacitor interlocking switching switch is formed by five capacitors connected in series, and the inductor interlocking switching switch is formed by five inductors connected in series. In this way, the power loss of the capacitor and the inductor in the circuit can be controlled by controlling the closing or opening of part of the capacitor in the capacitor interlocking switching switch and part of the inductor in the inductor interlocking switching switch, and then the conversion efficiency of the tracking circuit can be controlled.

[0040] Embodiment 2

[0041] based on Figure 2 The Buck-Boost conversion circuit described above, this embodiment provides a photovoltaic power generation system, the photovoltaic power generation system comprising:

[0042] Photovoltaic cell arrays;

[0043] A grid-connected inverter, the grid-connected inverter comprising any of the above-mentioned Buck-Boost conversion circuits, the input end of the Buck-Boost conversion circuit being connected to the output end of the photovoltaic cell array;

[0044] a first central processor, the first central processor being connected to the first controllable switch and the second controllable switch in the Buck-Boost conversion circuit, and being used for controlling the first controllable switch and the second controllable switch to be connected or disconnected at the same time;

[0045] A second central processor is connected to the adjustable inductor and the adjustable capacitor in the Buck-Boost conversion circuit, and is used to adjust the inductance value of the adjustable inductor and the capacitance value of the adjustable capacitor.

[0046] The photovoltaic cell array uses photovoltaic panels (eg, solar panels) of appropriate size to convert photovoltaic energy into electrical energy.

[0047] The function of the above-mentioned grid-connected inverter is to convert the DC power generated by the photovoltaic power generation system into AC power. At the same time, its automatic voltage stabilization function can also improve the power supply quality of the system. The input end of the grid-connected inverter is connected to the output end of the photovoltaic cell array, and the output end of the grid-connected inverter is connected to the load or directly connected to the grid if only grid feeding is required and no power supply is required.

[0048] In this embodiment, the maximum power tracking of the photovoltaic cell array (photovoltaic cell panel) can be realized. Figure 3 As shown, a first central processor 1 is proposed, which is specifically used to generate PWM waves with different duty cycles according to the requirements of boosting and bucking the DC power, and transmit the PWM waves to the MPPT controller in the grid-connected inverter; then the MPPT controller is used to control the first controllable switch and the second controllable switch to be connected or disconnected at the same time according to the PWM wave.

[0049] The principle of achieving boost and buck is: first, a pulse signal (i.e., PWM wave) is sent through PWM modulation technology. When the pulse signal acts on the first controllable switch S1 and the second controllable switch S2, a voltage will be generated at both ends of the adjustable capacitor Cr, that is, the adjustable capacitor Cr is charged. At this time, due to the principle of soft switching technology, the first controllable switch S1 and the second controllable switch S2 will be closed at the same time, and after closing, the adjustable inductor Lr will be charged. D3 is a voltage-stabilizing diode. In the charging stage, the capacitor Co supplies power to the load (inductor) R. When the inductor R is charged, the first controllable switch S1 and the second controllable switch S2 are turned off. At this time, the adjustable inductor Lr supplies power to the load R. This is a completed boost and buck cycle. How to achieve the setting of the two modes of boost and buck is to adjust by changing the duty cycle of the PWM signal, and the output voltage U = E*(a / 1-a). E is the input voltage, and a is the conduction ratio. That is, the ratio of the on time and off time of the tube (i.e., the first controllable switch S1 and the second controllable switch S2) in one cycle. This enables the voltage of DC power to be stepped up and down.

[0050] The purpose of designing the adjustable capacitor Cr in this way is to form an auxiliary commutation loop with the first controllable switch S1 and the second controllable switch S2 through the adjustable capacitor Cr and the adjustable inductor Lr, so that the first controllable switch S1 and the second controllable switch S2 are turned off at the same time, thereby reducing the switching loss of the switches.

[0051] The first central processor 1 can generate the PWM wave according to the conductance increment method, and the PWM wave periodically controls the first controllable switch and the second controllable switch to be connected or disconnected at the same time, so as to avoid power loss caused by multiple control of the circuit, thereby improving the output efficiency of the system.

[0052] The full name of PWM is pulse-width modulation, which is a way to reduce the average power transmitted by the electrical signal by dispersing the effective electrical signal into discrete forms; therefore, according to the area equivalence law, the waveform of the corresponding amplitude and frequency required to be synthesized can be equivalently obtained by changing the time width of the pulse, that is, the above-mentioned PWM wave.

[0053] Maximum Power Point Tracking (MPPT) is a core technology in photovoltaic power generation systems. It refers to adjusting the output power of the photovoltaic array according to different external ambient temperature, light intensity and other characteristics, so that the photovoltaic array always outputs maximum power.

[0054] In this embodiment, the capacitance and inductance required by the circuit can be adjusted to achieve maximum power tracking. Figure 3 As shown, a second central processor 2 is proposed, which is specifically used for dynamically controlling one or more inductors in the adjustable inductor to close to adjust the inductance value of the adjustable inductor when the open-circuit voltage of the grid-connected inverter fluctuates; and / or, the second central processor can dynamically control one or more capacitors in the adjustable capacitor to close to adjust the capacitance value of the adjustable capacitor. That is, the second central processor changes the inductance value or capacitance value by changing the number of inductors connected in series in the adjustable inductor or the number of capacitors connected in series in the adjustable capacitor when there is power loss in the capacitor and the inductor, thereby reducing the loss.

[0055] For example, when the lighting conditions change, the open-circuit voltage of the grid-connected inverter (that is, the voltage at the output end of the photovoltaic cell array) will fluctuate. At this time, the power will not be maintained at the maximum power point, so maximum mppt tracking is required. At this time, the second central processor 2 can be used to calculate the capacitance and inductance values ​​required for the circuit, and calculate how many capacitors need to be closed in the adjustable capacitor to adjust the capacitance value of the adjustable capacitor, and calculate how many inductors need to be closed in the adjustable inductor to adjust the inductance value of the adjustable inductor. According to the calculation results, the capacitance value of the adjustable capacitor Cr and the inductance value of the adjustable inductor Lr in the Buck-Boost conversion circuit are dynamically adjusted in the form of a control signal to reduce power loss.

[0056] The above-mentioned second central processor 2 is connected one-to-one with the inductance in the adjustable inductor through a switch, and is connected one-to-one with the capacitance in the adjustable capacitor through a switch, so that the second central processor 2 can control the closing or opening of each switch to control the closing or opening of the corresponding capacitance or the corresponding inductance.

[0057] For example, Figure 3As shown, the second central processor 2 is connected one-to-one with the capacitor in the adjustable capacitor (i.e., the capacitor interlocking switching switch) through switches a, b, c, d, and e, and is connected one-to-one with the inductor in the adjustable inductor (i.e., the inductor interlocking switching switch) through switches f, g, h, i, and j. Then, when the illumination conditions at the current stage change, i.e., when the open circuit voltage changes, the second central processor 2 can dynamically change the capacitance value of Cr and the inductance value of Lr in the Buck-Boost conversion circuit by controlling the closing or opening of switches a, b, c, d, e, f, g, h, i, and j, so as to realize the power loss of the capacitor and inductor in the control circuit, thereby reducing the power loss and improving the system operation efficiency.

[0058] In order to ensure stable power supply, the present embodiment proposes that the photovoltaic power generation system further includes: a battery connected to the output end of the Buck-Boost conversion circuit. The charging and discharging of the battery can be uniformly managed by the intelligent management core. The battery stores excess electrical energy and provides energy to the load to ensure stable electrical energy when the power generation is insufficient.

[0059] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Buck-Boost conversion circuit, characterized in that: The Buck-Boost conversion circuit includes: a first controllable switch, a second controllable switch, an adjustable inductor, an adjustable capacitor, a first diode, a second diode, a third diode, a capacitor and a resistor, wherein: One end of the first controllable switch and the anode of the second diode are connected to the positive electrode of the input voltage, and the cathode of the second diode is connected to the negative electrode of the input voltage after the second controllable switch and the adjustable inductor are connected in series in sequence. One end of the adjustable capacitor is connected to the other end of the first controllable switch, and the other end of the adjustable capacitor is connected to the cathode of the second diode. The other end of the first controllable switch is connected to the anode of the first diode and the cathode of the third diode, the cathode of the first diode is connected to the junction of the second controllable switch and the adjustable inductor, and the anode of the third diode is connected in series with the resistor and then connected to the negative electrode of the input voltage. The capacitor is connected in parallel with the resistor, and the first controllable switch and the second controllable switch are controlled to be connected or disconnected at the same time.

2. The Buck-Boost conversion circuit according to claim 1, characterized in that: The first controllable switch and the second controllable switch are controlled to be connected or disconnected at the same time by a soft switch control method.

3. The Buck-Boost conversion circuit according to claim 1 or 2, characterized in that: The adjustable capacitor includes a preset number of capacitors connected in series; the adjustable inductor includes a preset number of inductors connected in series.

4. The Buck-Boost conversion circuit according to claim 3, characterized in that: The preset number is 5.

5. A photovoltaic power generation system, characterized in that: The photovoltaic power generation system comprises: Photovoltaic cell arrays; A grid-connected inverter, the grid-connected inverter comprising the Buck-Boost conversion circuit according to any one of claims 1 to 4, the input end of the Buck-Boost conversion circuit being connected to the output end of the photovoltaic cell array; a first central processor, the first central processor being connected to the first controllable switch and the second controllable switch in the Buck-Boost conversion circuit, and being used for controlling the first controllable switch and the second controllable switch to be connected or disconnected at the same time; A second central processor is connected to the adjustable inductor and the adjustable capacitor in the Buck-Boost conversion circuit, and is used to adjust the inductance value of the adjustable inductor and the capacitance value of the adjustable capacitor.

6. The photovoltaic power generation system according to claim 5, characterized in that: The first central processor is specifically used to generate PWM waves with different duty cycles according to the requirements of boosting and bucking the direct current, and transmit the PWM waves to the MPPT controller in the grid-connected inverter; The MPPT controller is used to control the first controllable switch and the second controllable switch to be connected or disconnected at the same time according to the PWM wave.

7. The photovoltaic power generation system according to claim 6, characterized in that: The first central processing unit generates the PWM wave according to a conductance increment method.

8. The photovoltaic power generation system according to claim 5, characterized in that: The second central processor is specifically used to control one or more of the adjustable inductors to close and adjust the inductance value of the adjustable inductors when the open-circuit voltage of the grid-connected inverter fluctuates; and / or the second central processor controls one or more of the adjustable capacitors to close and adjust the capacitance value of the adjustable capacitors.

9. The photovoltaic power generation system according to any one of claims 5 to 8, characterized in that: The second central processing unit is connected one-to-one with the inductors in the adjustable inductors through switches, and is connected one-to-one with the capacitors in the adjustable capacitors through switches.

10. The photovoltaic power generation system according to any one of claims 5 to 8, characterized in that: Also includes: A storage battery is connected to the output end of the Buck-Boost conversion circuit.

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