External boost type non-isolated high-gain converter based on photovoltaic power generation system

Abstract

The invention discloses an external boost type non-isolated high-gain converter based on a photovoltaic power generation system, which is characterized in that a traditional Boost converter is connected with a switched capacitor converter in a cascading manner, and the voltage gain performance obviously superior to that of a traditional topology is realized; the Boost converter serves as a first-stage boosting unit to primarily boost input voltage, and then output voltage is further multiplied through the switched capacitor network connected with the Boost converter in series. By reasonably configuring the positions and working time sequences of the inductors, the capacitors and the switching devices, the circuit structure of the converter is optimized, and the current waveform characteristic of the input end is also remarkably improved. In the whole working period, the input current shows more continuous and smooth characteristics, and the ripple amplitude of the input current is greatly reduced. The characteristic is particularly important for the application of power supplies such as a photovoltaic power generation system and a fuel cell which have high requirements on input stability, and is beneficial to improving the overall efficiency and electromagnetic compatibility of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic power generation, and in particular relates to an external boost type non-isolated high-gain converter based on a photovoltaic power generation system. Background Art

[0002] Power electronic converters are commonly used in renewable energy systems to regulate the output voltage of RE power sources. However, due to the low output voltage of photovoltaic modules (20-40V), a high-voltage DC-DC converter is required to boost the low DC voltage of the photovoltaic system to 400V, and then convert it into AC voltage through a power inverter.

[0003] The traditional boost converter is widely used due to its simple operation and low component count. Theoretically, its voltage gain can extend from 1 (at a duty cycle of 0) to infinity (at a duty cycle of 1). However, when operating at a high duty cycle, its voltage gain drops sharply due to the presence of parasitic components. Furthermore, the voltage stress on its semiconductor devices is high, equal to the output voltage. To overcome these shortcomings of the boost converter, researchers at home and abroad have proposed various converter topologies. These include switching element technology (switched inductor and switched capacitor), cascade technology (series output and converter), and magnetic coupling. Connecting the front-stage filter inductor of a traditional boost cascade converter in series with the output capacitor reduces the current ripple of the filter inductor, but the voltage stress on the downstream switching transistor remains high. Therefore, a non-isolated high-gain external boost converter based on a photovoltaic power generation system is needed to address these issues. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an external boost-type non-isolated high-gain converter based on a photovoltaic power generation system, which achieves high voltage gain by cascading a traditional Boost converter and a switched capacitor converter. At the same time, a new topology formation method is adopted to achieve low input current ripple, thereby reducing the voltage stress of semiconductor devices and back-end capacitors.

[0005] In order to achieve the above technical effects, the technical solution adopted by the present invention is: An external boost type non-isolated high-gain converter based on a photovoltaic power generation system, comprising a cascade-connected Boost converter and a switched capacitor converter; DC voltage source Positive connection inductor One end, The second end is also connected to the active switching device The drain and diode The anode constitutes the input path; Cathode connection capacitance Positive electrode and inductor First end, Cathode connection capacitance Positive electrode and inductor First end, Cathode connection capacitance positive electrode, Negative electrode and The negative electrodes are connected to the reference ground to form a Boost converter unit; Anode connected to diode anode, Cathode connection capacitance Anode and diode anode, Cathode connection capacitance positive electrode, Negative connection positive electrode, The negative electrode is connected to the reference ground to form a switched capacitor converter unit; The output is taken from Positive electrode, load resistor Connected between the output terminal and the reference ground, the DC voltage source The negative pole and the negative poles of all capacitors are connected to the reference ground to form the output and grounding path.

[0006] Preferably, the steady-state analysis satisfies the following assumptions: Ignore the on-resistance of the power MOSFET , the forward voltage drop of the diode and on-resistance ; The inductor and capacitor are ideal components, and the equivalent series resistance of the inductor is ignored. and capacitor equivalent series resistance ; The capacitor and inductor are large enough so that the capacitor voltage and inductor current are constant.

[0007] Preferably, the continuous conduction mode (CCM) includes two operating modes: Mode 1, Range: exist When the power switch Conductivity, diode 、 and Shutdown, The inductor current rises linearly and the capacitor 、 、 discharge, Charging; In the modal state, by applying Kirchhoff's voltage law on the equivalent circuit, the following relationship is derived: ; (1) In the formula, in the formula, Indicates the input voltage, Inductance Voltage, Indicates capacitance Voltage, Inductance Voltage; Mode 2, Range: exist When the power switch Disconnect, diode 、 and conduction, Turn off, the inductor current decreases linearly, and the capacitor 、 、 Charge, Discharge; In mode 2, by applying Kirchhoff's voltage law on the equivalent circuit, the following relationship is derived: ; (2) Where, Indicates the input voltage, Indicates capacitance Voltage.

[0008] Preferably, there is a third mode in the discontinuous conduction mode DCM: switch Maintaining off, the inductor The current drops to zero, the diode - The current is zero, in the off state, the capacitor 、 、 In discharge state.

[0009] Preferably, the voltage gain analysis in continuous conduction mode (CCM) is as follows: Through the inductor and Applying the volt-second balance rule, combining equations (1) and (2), we get: ; (3) The input voltage of the proposed converter is derived from formula (3): and output voltage Relationship: ; (4) The voltage gain of the converter is thus: ; (5) Where D represents the duty cycle.

[0010] Preferably, the voltage gain analysis in discontinuous conduction mode DCM is as follows: From the equivalent circuits of each mode, we can get that the output diode Current For inductance Half the current, so ; (6) in, Inductor in DCM mode The current value is calculated as follows: ; (7) in, Output diode The peak current size is calculated as follows: ; (8) Output diode The average current in one cycle is equal to the output current ,have to: ; (9) The combined equations (6)-(9) can be used to calculate the duty cycle under DCM: , as shown in formula (10): ; (10) in, is the proportional coefficient, which can be obtained from formula (10): ; (11) Applying the volt-second balance rule to the three inductors yields: ; (12) Solving equation (12), we can get the voltage gain in DCM mode: expression: ; (13) Where, Indicates the duty cycle in DCM mode.

[0011] Preferably, when the converter operates in boundary conduction mode (BCM), equal , the normalized inductance time constant can be obtained , as shown in formula (14); ; (14) > When , the converter operates in CCM, otherwise it operates in DCM.

[0012] Preferably, the voltage stress expression of the semiconductor device is derived based on the equivalent circuits of each mode under CCM: ; (15) Where, It is a power switch The voltage at is a resistor The voltage at .

[0013] Preferably, it is assumed that the converter operates in a lossless state, i.e. ; Therefore, the inductor current and The calculation is as follows: ; (16) in is the output current.

[0014] Preferably, by applying Kirchhoff's current law on the DCM equivalent circuit, the current stress on the power switch and the diode is derived as follows: ; (17) Where, Indicates capacitance The discharge current, Indicates capacitance The charging current, Indicates capacitance Charging current; Indicates resistance The current at Indicates power switch The current at .

[0015] The beneficial effects of the present invention are as follows: 1. This patent introduces a cascade structure for voltage coordinated protection optimization, which is particularly suitable for the needs of photovoltaic power generation systems. The system structure should be protected with emphasis. Since the photovoltaic array voltage is significantly affected by ambient light fluctuations, in order to prevent the Boost switch device from breaking down due to excessive input voltage, the photovoltaic array output voltage is sampled in real time through a high-precision resistor divider network, and the sampled value is compared with the preset safety voltage threshold. Once the input voltage exceeds the set upper limit threshold, the comparator immediately sends an overvoltage signal to the main control chip. After receiving the signal, the main control chip quickly executes the protection control logic, and by turning off the PWM control signal, the Boost main switch device stops conducting, thereby blocking energy transmission and preventing the subsequent circuit from being subjected to excessive voltage shock.

[0016] This patent introduces overcurrent and overtemperature protection for switching devices. All high-frequency switching devices, including the Boost main switch and each switch in the SCC stage, are equipped with current sensing resistors or Hall effect current sensors, and are combined with temperature sensors to implement dynamic power management. When overcurrent or temperature exceeding a set threshold is detected, the control logic immediately implements current limiting or shutdown protection strategies to prevent device damage.

[0017] 3. This patent introduces overcurrent and overtemperature protection for switching devices. All high-frequency switching devices are equipped with current detection resistors or Hall current sensors, and combined with temperature sensors to achieve dynamic power management. When overcurrent or temperature exceeding a set threshold is detected, the control logic immediately implements current limiting or shutdown protection strategies to prevent device damage.

[0018] This patent introduces a temperature-dependent dynamic frequency modulation control strategy. To address the heat accumulation generated by high-frequency switching devices during continuous operation, the system integrates a temperature sensor module. When the device temperature exceeds a warning threshold, the controller automatically reduces the switching frequency or duty cycle, thereby reducing heat generation and achieving dynamic temperature control to prevent overheating and burnout.

[0019] 5. This patented structure cleverly combines a traditional boost converter with a switched-capacitor converter in a cascade configuration, achieving significantly superior voltage gain performance compared to conventional topologies. Specifically, in this structure, the boost converter, acting as the first-stage step-up unit, initially boosts the input voltage. The output voltage is then further multiplied by a series-connected switched-capacitor network. This effectively overcomes the duty cycle limitations and reduced efficiency inherent in traditional boost converters in high-gain scenarios. Furthermore, to further enhance system performance, this patent innovatively introduces a novel topology formation method. By rationally configuring the placement and timing of the inductor, capacitor, and switching components, this not only optimizes the converter's circuit structure but also significantly improves the input current waveform. Throughout the entire operating cycle, the input current exhibits a more continuous and smooth characteristic, significantly reducing input current ripple. This characteristic is particularly important for power supply applications requiring high input stability, such as photovoltaic power generation systems and fuel cells, helping to improve overall system efficiency and electromagnetic compatibility. This topology also offers the advantage of reducing device voltage stress. Through a rational energy transfer path design and capacitor voltage distribution mechanism, the voltage stress on the main power switch and rectifier diode is effectively alleviated, and the voltage withstand requirement of the output-side filter capacitor is also reduced, thereby allowing the use of semiconductor devices and passive components with lower rated voltages, smaller size, and higher performance. This feature not only helps improve the overall reliability and service life of the system, but also provides strong support for cost control and system miniaturization design. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the topological structure of the converter of the present invention; Figure 2 The converter in one switching cycle in the embodiment of the present invention The trigger pulse diagram and main waveform diagram inside; Figure 3 This is a mode 1 equivalent circuit diagram in an embodiment of the present invention; Figure 4 This is a mode 2 equivalent circuit diagram in an embodiment of the present invention; Figure 5 : is a modal three equivalent circuit diagram in an embodiment of the present invention; Figure 6 This is the boundary condition between CCM and DCM operation of the converter in the embodiment of the present invention. DETAILED DESCRIPTION

[0021] Example 1: like Figure 1 As shown, an external boost type non-isolated high gain converter based on a photovoltaic power generation system includes a cascade-connected Boost converter and a switched capacitor converter; DC voltage source Positive connection inductor One end, The second end is also connected to the active switching device The drain and diode The anode constitutes the input path; Cathode connection capacitance Positive electrode and inductor First end, Cathode connection capacitance Positive electrode and inductor First end, Cathode connection capacitance positive electrode, Negative electrode and The negative electrodes are connected to the reference ground to form a Boost converter unit; Anode connected to diode anode, Cathode connection capacitance Anode and diode anode, Cathode connection capacitance positive electrode, Negative connection positive electrode, The negative electrode is connected to the reference ground to form a switched capacitor converter unit; The output is taken from Positive electrode, load resistor Connected between the output terminal and the reference ground, the DC voltage source The negative pole and the negative poles of all capacitors are connected to the reference ground to form the output and grounding path.

[0022] Preferably, the steady-state analysis satisfies the following assumptions: Ignore the on-resistance of the power MOSFET , the forward voltage drop of the diode and on-resistance ; The inductor and capacitor are ideal components, and the equivalent series resistance of the inductor is ignored. and capacitor equivalent series resistance ; The capacitor and inductor are large enough so that the capacitor voltage and inductor current are constant.

[0023] like Figure 2 As shown, preferably, there are two operating modes in the continuous conduction mode CCM: Mode 1, Range: exist When the power switch Conductivity, diode 、 and Shutdown, conduction, the equivalent circuit is as follows Figure 3 As shown. At this time, the inductor current rises linearly and the capacitor 、 、 discharge, Charge; in mode, by Figure 3 Applying Kirchhoff's voltage law to the equivalent circuit shown, the following relationship is derived: ; (1) In the formula, in the formula, Indicates the input voltage, Inductance Voltage, Indicates capacitance Voltage, Inductance Voltage; Mode 2, Range: exist When the power switch Disconnect, diode 、 and conduction, Turn off, the equivalent circuit is as follows Figure 4 As shown; at this time, the inductor current decreases linearly and the capacitor 、 、 Charge, Discharge; in mode 2, by Figure 4 Applying Kirchhoff's voltage law to the equivalent circuit shown, the following relationship is derived: ; (2) Where, Indicates the input voltage, Indicates capacitance Voltage.

[0024] Preferably, there is a third mode in the discontinuous conduction mode DCM: switch Maintaining off, the inductor The current drops to zero, the diode - The current is zero, in the off state, the capacitor 、 、 In discharge state.

[0025] Preferably, the voltage gain analysis in continuous conduction mode (CCM) is as follows: Through the inductor and Applying the volt-second balance rule, combining equations (1) and (2), we get: ; (3) The input voltage of the proposed converter is derived from formula (3): and output voltage Relationship: ; (4) The voltage gain of the converter is thus: ; (5) Where D represents the duty cycle.

[0026] Preferably, the voltage gain analysis in discontinuous conduction mode DCM is as follows: From the equivalent circuits of each mode, we can get that the output diode Current For inductance Half the current, so ; (6) in, Inductor in DCM mode The current value is calculated as follows: ; (7) in, Output diode The peak current size is calculated as follows: ; (8) Output diode The average current in one cycle is equal to the output current ,have to: ; (9) The combined equations (6)-(9) can be used to calculate the duty cycle under DCM: , as shown in formula (10): ; (10) in, is the proportional coefficient, which can be obtained from formula (10): ; (11) Applying the volt-second balance rule to the three inductors yields: ; (12) Solving equation (12), we can get the voltage gain in DCM mode: expression: ; (13) Where, Indicates the duty cycle in DCM mode.

[0027] Preferably, when the converter operates in boundary conduction mode (BCM), equal , the normalized inductance time constant can be obtained , as shown in formula (14); ; (14) > When , the converter operates in CCM, otherwise it operates in DCM; Figure 6 Drawn The relationship curve with D.

[0028] Preferably, by Figure 3 and Figure 4 The voltage stress expression of semiconductor devices is derived based on the equivalent circuits of each mode under CCM: ; (15) Where, It is a power switch The voltage at is a resistor The voltage at .

[0029] Preferably, it is assumed that the converter operates in a lossless state, i.e. ; Therefore, the inductor current and The calculation is as follows: ; (16) in is the output current.

[0030] Preferably, by Figure 5 Applying Kirchhoff's current law to the DCM equivalent circuit shown, the current stress on the power switch and diode is derived as follows: ; (17) Where, Indicates capacitance The discharge current, Indicates capacitance The charging current, Indicates capacitance Charging current; Indicates resistance The current at Indicates power switch The current at .

[0031] Example 2: This embodiment provides a specific application of an external boost-type non-isolated high-gain converter based on a photovoltaic power generation system, including the following steps: 1. Design the converter topology and make assumptions about the converter's steady-state structure: This embodiment proposes a novel boost converter that achieves high voltage gain by cascading a traditional boost converter and a switched capacitor converter. A novel topology formation method is also used to achieve low input current ripple, reducing voltage stress on semiconductor devices and downstream capacitors. This method can also be used to form a series of novel high-gain DC-DC converters. To facilitate analysis of the proposed converter, it is assumed that: (1) Ignore the on-resistance of the power MOSFET , the forward voltage drop of the diode and on-resistance .

[0032] (2) Both inductors and capacitors are ideal components, i.e. the equivalent series resistance of the inductor and capacitor components is ignored. , .

[0033] (3) The capacitor and inductor of the proposed converter are large enough, so the capacitor voltage and inductor current are assumed to be constant.

[0034] 2. Analysis of the switching state of the converter: The main waveforms of the proposed converter when operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are as follows: Figure 2 shown.

[0035] from Figure 2 It can be seen that the CCM down converter has two operating modes; the time of mode 1 is , the time of mode 2 is ,in is the switching period, is the duty cycle, and are the input and output voltages.

[0036] 3. Voltage stress gain analysis: 1) In continuous conduction mode, the relationship between the converter input voltage and output voltage is derived by applying volt-second balance to the inductor.

[0037] 2) In discontinuous conduction mode, applying volt-second balance to the inductor can obtain the voltage gain in DCM mode expression.

[0038] 3) In boundary conduction mode, compare and The relationship is obtained , through analytical transformation.

Claims

1. An external boost type non-isolated high gain converter based on a photovoltaic power generation system, characterized in that: The invention comprises a Boost converter and a switched capacitor converter connected in cascade; DC voltage source Positive connection inductor One end, The second end is also connected to the active switching device The drain and diode The anode constitutes the input path; Cathode connection capacitance Positive electrode and inductor The first end, Cathode connection capacitance Positive electrode and inductor First end, Cathode connection capacitance positive electrode, Negative electrode and The negative electrodes are connected to the reference ground to form a Boost converter unit; Anode connected to diode anode, Cathode connection capacitance Anode and diode anode, Cathode connection capacitance positive electrode, Negative connection positive electrode, The negative electrode is connected to the reference ground to form a switched capacitor converter unit; The output is taken from Positive electrode, load resistor Connected between the output terminal and the reference ground, the DC voltage source The negative pole and the negative poles of all capacitors are connected to the reference ground to form the output and grounding path.

2. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 1, characterized in that: The steady-state analysis meets the following assumptions: Ignore the on-resistance of the power MOSFET , the forward voltage drop of the diode and on-resistance ; The inductor and capacitor are ideal components, and the equivalent series resistance of the inductor is ignored. and capacitor equivalent series resistance ; The capacitor and inductor are large enough so that the capacitor voltage and inductor current are constant.

3. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 1, characterized in that: There are two operating modes in continuous conduction mode (CCM): Mode 1, Range: exist When the power switch Conductivity, diode 、 and Shutdown, Turn on; at this time, the inductor current rises linearly, and the capacitor 、 、 discharge, Charging; In the modal state, by applying Kirchhoff's voltage law on the equivalent circuit, the following relationship is derived: ；（1） In the formula, in the formula, Indicates the input voltage, Inductance Voltage, Indicates capacitance Voltage, Inductance Voltage; Mode 2, Range: exist When the power switch Disconnect, diode 、 and conduction, Turn off, the inductor current decreases linearly, and the capacitor 、 、 Charge, Discharge; In mode 2, by applying Kirchhoff's voltage law on the equivalent circuit, the following relationship is derived: ；（2） Where, Indicates the input voltage, Indicates capacitance Voltage.

4. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 3, characterized in that: There is a third mode in discontinuous conduction mode DCM: switch Maintaining off, the inductor The current drops to zero, the diode - The current is zero, in the off state, the capacitor 、 、 In discharge state.

5. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 4, characterized in that: The voltage gain analysis in continuous conduction mode (CCM) is as follows: Through the inductor and Applying the volt-second balance rule, combining equations (1) and (2), we get: ；（3） The input voltage of the proposed converter is derived from formula (3): and output voltage Relationship: ；（4） The voltage gain of the converter is thus: ；（5） Where, Indicates the duty cycle.

6. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 5, characterized in that: The voltage gain analysis in discontinuous conduction mode (DCM) is as follows: From the equivalent circuits of each mode, we can get that the output diode Current For inductance Half the current, so ；（6） in, Inductor in DCM mode The current value is calculated as follows: ；（7） in, Output diode The peak current size is calculated as follows: ；（8） Output diode The average current in one cycle is equal to the output current ,have to: ；（9） The combined equations (6)-(9) can be used to calculate the duty cycle under DCM: , as shown in formula (10): ；（10） in, is the proportional coefficient, which can be obtained from formula (10): ；（11） Applying the volt-second balance rule to the three inductors yields: ；（12） Solving equation (12), we can get the voltage gain in DCM mode: expression: ；（13） Where, Indicates the duty cycle in DCM mode.

7. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 6, characterized in that: When the converter operates in boundary conduction mode (BCM), equal , the normalized inductance time constant can be obtained , as shown in formula (14); ；（14） > When , the converter operates in CCM, otherwise it operates in DCM.

8. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 7, characterized in that: The voltage stress expression of semiconductor devices is derived based on the equivalent circuits of each mode under CCM: ； （15） Where, It is a power switch The voltage at is a resistor The voltage at .

9. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 8, characterized in that: Assume that the converter operates in a lossless state, that is, ; Therefore, the inductor current and The calculation is as follows: ；（16） in is the output current.

10. The external boost type non-isolated high gain converter based on a photovoltaic power generation system according to claim 9, characterized in that: By applying Kirchhoff’s current law on the DCM equivalent circuit, the current stress on the power switch and diode is derived as follows: ；（17） Where, Indicates capacitance The discharge current, Indicates capacitance The charging current, Indicates capacitance Charging current; Indicates resistance The current at Indicates power switch The current at .

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