Photovoltaic boost circuit

Abstract

The invention discloses a photovoltaic booster circuit, which comprises n capacitors connected in parallel with a photovoltaic panel PV, n inductors, n switching tubes, a diode and a bus capacitor, wherein one capacitor, one inductor and one switch tube form one PV path; the n PV paths share a diode; the maximum power point tracking of each PV path is realized by controlling the conduction duty ratio of the n switching tubes, and the voltage of the serially connected PVs is boosted to the required bus voltage. According to the invention, independent tracking of the maximum power point of the PV path is realized by using fewer switch tubes, the system conversion efficiency is improved, the generating capacity is increased, and the cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic industry, and in particular relates to a photovoltaic boost circuit. Background Art

[0002] At present, fossil energy is increasingly scarce, and the prices of fuels such as oil and coal are rising. At the same time, their combustion process pollutes the environment. Due to the shortage of energy and environmental protection, there is an urgent need to find clean energy to replace traditional energy. Solar energy is inexhaustible and pollution-free. It is an ideal alternative to fossil energy. However, how to use solar energy efficiently and at low cost is the direction people have been working hard on. The inverter plays an important role in the solar power generation system. It is responsible for converting the DC power output by the solar panel into the commonly used AC power in life, realizing photovoltaic grid-connected power generation or off-grid power generation.

[0003] With the advancement of technology, the current of a single solar photovoltaic panel is getting bigger and bigger, and the voltage of the photovoltaic panel is getting lower and lower at the same power, so it is necessary to introduce a corresponding boost circuit. For photovoltaic panels with large string current, the input voltage of the boost circuit is relatively low, which increases the loss of the boost circuit, reduces the system conversion efficiency, and reduces the power generation. At the same time, the greater the loss, the higher the cost. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a photovoltaic boost circuit. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0005] The present invention provides a photovoltaic boost circuit, comprising:

[0006] n photovoltaic panels PV are connected in parallel with capacitors, n inductors, n switches, diodes and bus capacitors; among them, 1 capacitor, 1 inductor and 1 switch form 1 PV path; n PV paths share a diode;

[0007] The maximum power point tracking of each PV path is achieved by controlling the conduction duty cycle of n switching tubes, and the voltage of the series-connected PVs is boosted to the required bus voltage.

[0008] In one embodiment of the present invention, each PV path includes:

[0009] Capacitors, inductors, and switch tubes; among them,

[0010] The first end of the capacitor is connected to the first end of the external photovoltaic panel PV, and the second end is connected to the second end of the external photovoltaic panel PV;

[0011] The first end of the inductor is connected to the first end of the capacitor, and the second end is connected to the first end of the switch tube, serving as the first end of the current PV path;

[0012] The second end of the switch tube serves as the second end of the current PV path.

[0013] In one embodiment of the present invention, the switch tube comprises:

[0014] Field effect transistor FET, insulated gate bipolar transistor IGBT or triode BJT.

[0015] In one embodiment of the present invention, the PV paths are connected in series.

[0016] In one embodiment of the present invention, ignoring the transient state of dead zone control, the working state of the PV path includes:

[0017] A first working state, a second working state and a third working state.

[0018] In one embodiment of the present invention, the first working state includes:

[0019] The switch tubes in all PV paths are turned on and the diodes are turned off.

[0020] In one embodiment of the present invention, the second working state includes:

[0021] Among all the switch tubes in the PV path, one switch tube is turned off, and the remaining switch tubes are turned on, and the diode is turned on for freewheeling.

[0022] In one embodiment of the present invention, the third working state includes:

[0023] Among all the switch tubes in the PV path, one switch tube is turned off and the rest of the switch tubes are turned on. After the current of the diode reaches 0, it stops flowing and is turned off.

[0024] Beneficial effects of the present invention:

[0025] In the solution provided by the present invention, the maximum power point tracking of each PV path is achieved by controlling the conduction duty cycle of n switch tubes, and the voltage of the PV connected in series is boosted to the required bus voltage. The present invention uses fewer switch tubes to achieve independent tracking of the maximum power point of the PV path, improves the system conversion efficiency, increases the power generation, and reduces the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of a traditional photovoltaic boost circuit and inverter circuit;

[0027] Figure 2A schematic diagram of the structure of a photovoltaic boost circuit and an inverter circuit provided by an embodiment of the present invention;

[0028] Figure 3 A schematic diagram of the structure of a photovoltaic boost circuit and an inverter circuit composed of two PV paths provided in an embodiment of the present invention;

[0029] Figure 4 A schematic diagram of the structure of a photovoltaic boost circuit consisting of two PV paths provided by an embodiment of the present invention;

[0030] Figure 5 A schematic diagram of current flow in a first working state of a photovoltaic boost circuit composed of two PV paths provided by an embodiment of the present invention;

[0031] Figure 6 A schematic diagram of current flow in a second working state of a photovoltaic boost circuit composed of two PV paths provided by an embodiment of the present invention;

[0032] Figure 7 Another current flow diagram of a second working state in a photovoltaic boost circuit composed of two PV paths provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0034] The following is an example of a photovoltaic grid-connected inverter. Figure 1 As shown, it is usually divided into a two-stage structure, the first stage can be a boost circuit, and the second stage can be an inverter circuit. The embodiment of the present invention mainly considers the boost circuit part. It can be understood that Figure 1 It is a topology with two boost circuits. In practice, the inverter can be one or more than two. Each boost circuit can track the maximum power point of the photovoltaic panels connected to this string. With the advancement of technology, the current of a single photovoltaic panel is getting bigger and bigger, and the voltage of the photovoltaic panel is getting lower and lower under the same power. For example, a 6kW dual-channel MPPT (maximum power point tracking) single-phase grid-connected inverter, a single-channel MPPT power of 3kW, the current of the solar panel is calculated according to 20A, the photovoltaic panel voltage is 150V, for 220V voltage applications, the bus voltage is generally greater than 360V, so the boost circuit needs to boost the 150V voltage to more than 360V, for photovoltaic panels with large string current, the input voltage of the boost circuit is relatively low, which increases the loss of the boost circuit, reduces the system conversion efficiency, and reduces the power generation. At the same time, the greater the loss, the higher the cost.

[0035] In order to improve conversion efficiency and reduce losses, an embodiment of the present invention provides a photovoltaic boost circuit, such as Figure 2 The boost circuit section shown in the figure may include:

[0036] n photovoltaic panels PV are connected in parallel with capacitors, n inductors, n switches, diodes and bus capacitors; among them, 1 capacitor, 1 inductor and 1 switch form 1 PV path; n PV paths share a diode;

[0037] The maximum power point tracking of each PV path is achieved by controlling the conduction duty cycle of n switching tubes, and the voltage of the series-connected PVs is boosted to the required bus voltage.

[0038] Understandably, Figure 2 In the figure, the left part is the boost circuit proposed in the embodiment of the present invention, and the right part is the inverter circuit.

[0039] In actual use, the value range of n can be a natural number greater than or equal to 2, and the specific value can be freely selected by the user according to needs. The embodiment of the present invention does not specify whether the inverter output terminal is connected to the power grid or the electrical appliance, and mainly emphasizes the boost part. The embodiment of the present invention uses the PV path to achieve independent tracking of the maximum power point by a multi-channel topology structure, thereby improving the system conversion efficiency, reducing the loss of the boost circuit, and outputting the boosted voltage, thereby increasing the power generation and reducing the cost.

[0040] For ease of understanding, each module of the boost circuit proposed in the embodiment of the present invention is introduced separately below.

[0041] PV Pathway

[0042] from Figure 2 It can be seen that each PV channel includes:

[0043] Capacitors, inductors, and switch tubes; among them,

[0044] A first end of the capacitor is connected to a first end of an external photovoltaic panel PV, and a second end of the capacitor is connected to a second end of the external photovoltaic panel PV;

[0045] The first end of the inductor is connected to the first end of the capacitor, and the second end is connected to the first end of the switch tube, serving as the first end of the current PV path;

[0046] The second end of the switch tube serves as the second end of the current PV path.

[0047] Taking the nth PV path in the series of n PV paths as an example, it can be seen that Cn is a capacitor, Qn is a switch tube, and Ln is an inductor.

[0048] The switch tube may include:

[0049] Field effect transistor FET, insulated gate bipolar transistor IGBT or triode BJT.

[0050] The PV paths can be connected in series.

[0051] The switch tube is responsible for boosting the total photovoltaic panel voltage and adjusting the output current of each photovoltaic panel PV.

[0052] from Figure 2 It can be seen that in the series connection of n PV paths, the capacitor and switch tube in the first PV path are respectively connected to the capacitor and switch tube in the second PV path. And the capacitor and switch tube in the first PV path are connected through the inductor in the second PV path.

[0053] The working status of the PV pathway can include:

[0054] A first working state, a second working state and a third working state.

[0055] The specific working process under each working state will be introduced in detail later.

[0056] diode

[0057] The first end of the diode is connected to the first end of the first path of the n PV paths connected in series, and the second end of the diode is connected to the first end of the bus capacitor.

[0058] Bus Capacitor

[0059] It can be understood that the bus capacitance is Figure 2 In Cbus, the first end of the bus capacitor is connected to the second end of the diode as the first end of the boost circuit; the second end is connected to the second end of the last of the n PV paths as the second end of the boost circuit. Its function is to stabilize the bus voltage.

[0060] To facilitate understanding, a detailed introduction is given below using a two-way photovoltaic string as an example.

[0061] A schematic diagram of a photovoltaic boost circuit and an inverter circuit composed of two PV paths provided in an embodiment of the present invention is shown in FIG. Figure 3 ,from Figure 3 As can be seen, the left part represents the structure of the boost circuit, which includes two PV paths, and the right part represents the structure of the inverter circuit, which is a conventional structure.

[0062] For a schematic diagram of the photovoltaic boost circuit consisting of two PV paths, see Figure 4 ; By adjusting Figure 4The conduction time of Q1 and Q2 can realize the maximum power point tracking control of the two photovoltaic strings. Since the input side of the boost circuit is a series connection of two PV strings, the input voltage of the boost circuit is higher than that of the traditional solution. Taking the 20A string current of a 6kW inverter as an example, the input voltage is 300V. If the bus voltage is 360V, the boost circuit boosts the input voltage from 300V to 360V, thereby improving the system efficiency, reducing the heat dissipation cost and increasing the power generation. Considering the cost issue, the inductor L2 does not need to be designed according to the current parameters of L1. For example, when the currents of the two strings are completely equal, the average current of L2 can be 0, and it is not necessary for the two inductors to run full current like the traditional solution, thereby further reducing the loss. Because the currents between the actual multi-way photovoltaic panel strings are usually close, unless there is a shadow or other special circumstances, the design current of L2 can be reduced to reduce the cost during design, thereby achieving the optimal cost. In a photovoltaic grid-connected inverter with two PV paths, if the currents flowing through PV1 and PV2 are equal, the average current of L2 can be reduced to 0; if the currents flowing through PV1 and PV2 are not equal, the difference current flows through L2.

[0063] Assuming that the PV1 voltage U1=100V and the PV2 voltage U2=200V, their maximum power point currents may be Impp1=15A and Impp2=20A respectively, and the bus voltage across the bus capacitor Cbus is 360V.

[0064] In order to facilitate the understanding of the working state of the PV path, the following is a detailed description of the specific working state of the two PV paths in the entire control cycle. Figure 5-Figure 7 In the embodiment, the capacitor connected in parallel with the photovoltaic panel PV is incorporated into the photovoltaic panel PV and regarded as a whole.

[0065] Ignoring the transient state of dead-band control, the operating states of the PV path can include:

[0066] A first working state, a second working state and a third working state.

[0067] Specifically, the first working state may include:

[0068] The switch tubes in all PV paths are turned on and the diodes are turned off.

[0069] Take two PV paths as an example. In the first working state, Q1 and Q2 are turned on, and the current in the PV path flows as follows: Figure 5 As shown by the middle arrow, the current flows through Q1 and Q2, and D1 is reverse-cut off.

[0070] The second working state may include:

[0071] Among all the switch tubes in the PV path, one switch tube is turned off, and the remaining switch tubes are turned on, and the diode is turned on for freewheeling.

[0072] Take the two PV paths as an example. In the second working state, Q1 is off and Q2 is on. The current in the PV path flows as follows: Figure 6 As shown by the arrow in the middle, the current of inductor L1 flows through D1, and also includes Q2 disconnection and Q1 conduction. The current flow in the PV path is as follows: Figure 7 As shown by the arrows in the middle, the currents of the inductors L1 and L2 flow through D1.

[0073] The third working state may include:

[0074] Among all the switch tubes in the PV path, one switch tube is turned off and the rest of the switch tubes are turned on. After the current of the diode reaches 0, it stops flowing and is turned off.

[0075] Take the two PV paths as an example. In the second working state, Q1 is off and Q2 is on. The current in the PV path flows as follows: Figure 6 As shown by the arrow in the middle, the current of the inductor L1 flows through D1. If the inductor current is intermittent, the diode current may be disconnected naturally after reaching zero in this working state. It also includes Q2 disconnection and Q1 conduction. The current flow in the PV path is as follows Figure 7 As shown by the middle arrow, the current of inductors L1 and L2 flows through D1. If the inductor current is intermittent, the diode may be disconnected naturally after the current reaches zero in this working state.

[0076] It can be understood that the above three working states are three state cycles, and there is no fixed order between each state. At the same time, there is no restriction on the switching order between each switch tube. In specific use, the working order may not be exactly the same as described above.

[0077] The boost circuit proposed in the embodiment of the present invention realizes the maximum power point tracking of each PV path by controlling the conduction duty cycle of n switch tubes, and at the same time boosts the voltage of the PV after series connection to the required bus voltage. The present invention realizes the independent tracking of the maximum power point of the PV path with fewer switch tubes, improves the system conversion efficiency, increases the power generation, and reduces the cost.

[0078] It should be noted that in the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A photovoltaic boost circuit, characterized in that: include: n photovoltaic panels PV are connected in parallel with capacitors, n inductors, n switches, diodes and bus capacitors; among them, 1 capacitor, 1 inductor and 1 switch form 1 PV path; n PV paths share a diode; The maximum power point tracking of each PV path is achieved by controlling the conduction duty cycle of n switching tubes, and the voltage of the series-connected PVs is boosted to the required bus voltage.

2. A photovoltaic boost circuit according to claim 1, characterized in that: Each PV channel includes: Capacitors, inductors, and switch tubes; among them, The first end of the capacitor is connected to the first end of the external photovoltaic panel PV, and the second end is connected to the second end of the external photovoltaic panel PV; The first end of the inductor is connected to the first end of the capacitor, and the second end is connected to the first end of the switch tube, serving as the first end of the current PV path; The second end of the switch tube serves as the second end of the current PV path.

3. A photovoltaic boost circuit according to claim 2, characterized in that: The switch tube comprises: Field effect transistor FET, insulated gate bipolar transistor IGBT or triode BJT.

4. A photovoltaic boost circuit according to claim 1, characterized in that: The PV paths are connected in series.

5. A photovoltaic boost circuit according to claim 2, characterized in that: The working status of the PV pathway includes: A first working state, a second working state and a third working state.

6. A photovoltaic boost circuit according to claim 5, characterized in that: The first working state includes: The switch tubes in all PV paths are turned on and the diodes are turned off.

7. A photovoltaic boost circuit according to claim 5, characterized in that: The second working state includes: Among all the switch tubes in the PV path, one switch tube is turned off, and the remaining switch tubes are turned on, and the diode is turned on for freewheeling.

8. A photovoltaic boost circuit according to claim 7, characterized in that: The third working state includes: Among all the switch tubes in the PV path, one switch tube is turned off and the rest of the switch tubes are turned on. After the current of the diode reaches 0, it stops flowing and is turned off.

Images