Boost circuit, application of Boost circuit in photovoltaic charging device and photovoltaic charging device for charging electric automobile

Abstract

The invention belongs to the technical field of converters, and discloses a Boost circuit, application of the Boost circuit in a photovoltaic charging device and the photovoltaic charging device used for charging an electric vehicle. The Boost circuit comprises an input capacitor module, an output capacitor module, four capacitor modules, three inductance modules, seven diode modules and a switching tube S. An input end, the switching tube and an output end are in common ground, 20-time boosting is achieved under the condition of a small duty ratio, low inductive current stress is achieved, a digital controller does not need to be adopted, control is simple, and the control cost is low. The soft start circuit is low in implementation cost, free of voltage spikes, resonance and voltage abrupt change, low in voltage stress, free of isolation driving, small in electromagnetic interference, capable of working under the condition of full duty ratio, capable of conveniently achieving soft start and capable of reliably working within the wide input end voltage and full load range, and the input end, the output end and the source electrode of the switching tube are in common ground.

Description

Technical Field

[0001] This application relates to the technical field of converters, specifically to Boost boost circuits and their applications in photovoltaic charging devices and photovoltaic charging devices for electric vehicle charging. Background Art

[0002] When an electric vehicle is in motion, it does not emit tail gas, and its energy consumption per 100 kilometers is much lower than that of traditional fuel vehicles. However, it usually charges using the electrical energy from the power grid (mainly from thermal power generation), which has raised doubts about its "green purity". In order to effectively reduce the carbon footprint of electric vehicles and promote the paradigm shift from fuel vehicles to electric vehicles, it is necessary to significantly increase the penetration rate of photovoltaic grid-connected power generation systems so that their power generation can cover the electrical energy required for electric vehicle charging. Moreover, vigorously developing electric vehicle charging facilities based on distributed independent photovoltaic power generation systems is equally crucial. This is because it can not only solve the problem of electric vehicle charging in areas where the public power grid cannot reach (such as islands) or where the power supply is unreliable, but also help reduce the load impact on the power grid caused by the random charging behavior of a large number of electric vehicles.

[0003] Compared with traditional 400V electric vehicles, an 800V high-voltage electrical system can reduce in-vehicle cables, increase the charging speed, extend the cruising range, and provide more powerful power. It is recognized as the future technological evolution trend of electric vehicles. However, the high-voltage battery architecture brings new technical challenges to the design of distributed independent photovoltaic charging infrastructure.

[0004] Currently, most distributed photovoltaic charging systems adopt a string-type architecture, that is, a dozen or so photovoltaic modules are connected in series and connected to an 800V DC bus through a traditional Boost converter to charge an electric vehicle. The advantage of this system architecture is that the initial investment cost of the system is relatively low. However, under partial shading conditions, the power generation of solar cells drops significantly, affecting the user's income. Moreover, the 800V DC bus is extremely prone to arcing, leading to fires. The string-type architecture cannot disconnect the connection of photovoltaic modules, has a very high open-circuit voltage, is difficult to cut off the fire source, and poses a threat to the safety of firefighters.

[0005] In recent years, some scholars have proposed an electric vehicle charging system architecture based on a parallel-type photovoltaic optimizer. It integrates a photovoltaic module (or two photovoltaic modules connected in series) and a high-gain Boost converter, which is called a photovoltaic optimizer or a DC photovoltaic module; then, a large number of photovoltaic optimizers are connected in parallel to the DC bus to charge the electric vehicle. Compared with the string charging system architecture, this charging system architecture based on the parallel-type photovoltaic optimizer has the following advantages: 1) It can accurately track the maximum power point of each photovoltaic module, achieve the maximum power output of the solar cell under complex and variable actual lighting conditions, thereby maximizing the utilization of solar energy and shortening the charging time; 2) It allows the mixed use of photovoltaic modules with different specifications and degrees of aging, and has the ability of flexible capacity expansion; 3) It can realize component-level status monitoring, intelligent scheduling and rapid shutdown, reducing the system operation and maintenance cost and improving the safety and reliability.

[0006] The high-gain photovoltaic charging converter is the core component of the parallel optimizer charging system. Since the output voltage of a single photovoltaic module is relatively low (about 40 - 50V) and the output current is relatively large (more than about 12A), in order to achieve the efficient, reliable, and economical operation of the charging system, the parallel optimizer for 800V electric vehicle charging must meet special performance requirements: 1) It has extremely strong boost capability (more than 20 times), that is, ultra-high gain, to match the output voltage of the photovoltaic module (one or two in series) (about 40 - 100V) and the output terminal voltage of the electric vehicle (800V); 2) It has relatively low voltage and current stresses, to reduce the difficulty of device selection, and reduce switching losses and conduction losses, improve the charging efficiency, and shorten the investment payback period. 3) It can operate under full load and wide voltage range, and adapt to wide range changes in light and temperature. In addition, the photovoltaic charging converter also needs to meet the basic performance requirements of power electronic devices, such as low cost, easy implementation, small volume, and high reliability, etc. To meet the above performance requirements, in recent years, scholars from various countries have proposed a large number of ultra-high gain converter schemes with low voltage and current stresses. These schemes can be roughly divided into two categories: transformer (including coupled inductor) type and transformerless type. Compared with the former, it is more suitable to use the transformerless type converter as the main circuit topology of the parallel optimizer photovoltaic charging system. This is because it does not have the voltage spikes caused by transformer leakage inductance, does not require the use of active or passive clamping circuits, and the structure and control are simpler; the magnetic components have a smaller volume and relatively simple design, lower cost, and higher efficiency. The transformerless type ultra-high gain converter with low voltage and current stresses includes various schemes such as active switched inductor, current source half-bridge, and capacitor series connection. The active switched inductor Boost converter scheme has the following disadvantages: multiple non-grounded switching tubes are used, and isolated power supplies and isolated drivers are required, increasing the cost; there is a high-frequency potential difference at the input and output terminals, further increasing electromagnetic interference; the inductor values are inconsistent, causing voltage spikes and resonances, increasing the voltage stress. The switching tube drive signals of the current source half-bridge Boost converter are 180° out of phase with each other, so a digital controller must be used, increasing the cost; the duty cycle cannot be lower than 0.5, so it is difficult to achieve soft start and cannot adapt to wide range changes in the input terminal voltage and output power; there is a high-frequency potential difference at the input and output terminals, which may cause relatively large electromagnetic interference. The duty cycles of the switching tubes of the capacitor series connection Boost converter must meet special constraint relationships, so digital control must also be used; when the input terminal voltage or load changes within a wide range, there is a phenomenon of sudden change in voltage stress, and it is very difficult to achieve smooth switching of the control law, and the implementation is relatively complex. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a Boost boost circuit, its application in a photovoltaic charging device, and a photovoltaic charging device for electric vehicle charging, which can achieve a voltage gain of more than 20 times at a relatively small duty cycle.

[0008] To achieve the above object, the technical solution proposed by the present invention is as follows:

[0009] In a first aspect of the present invention, a Boost boost circuit is provided. The Boost boost circuit includes: an input capacitor module, an output capacitor module, a first capacitor module, a second capacitor module, a third capacitor module, a fourth capacitor module, a first inductor module, a second inductor module, a third inductor module, a first diode module, a second diode module, a third diode module, a fourth diode module, a fifth diode module, a sixth diode module, a seventh diode module, and a switching transistor S; a first end of the first inductor module is connected to an anode of the fourth diode module and a first end of the input capacitor module, and is used as a positive voltage input terminal; a second end of the first inductor module is connected to an anode of the first diode module and an anode of the second diode module; a cathode of the second diode module is connected to a first end of the first capacitor module and a first end of the second inductor module; a second end of the second inductor module is connected to an anode of the third diode module and a first end of the second capacitor module; a cathode of the third diode module is connected to a cathode of the fourth diode module and a first end of the third inductor module; a second end of the third inductor module is connected to a cathode of the first diode module, an anode of the fifth diode module, a first end of the fourth capacitor module, a second end of the second capacitor module, and a drain of the switching transistor; a cathode of the fifth diode module is connected to an anode of the sixth diode module and a first end of the third capacitor module; a cathode of the sixth diode module is connected to a second end of the fourth capacitor module and an anode of the seventh diode module; a cathode of the seventh diode module is connected to a first end of the output capacitor module and is used as a positive boost voltage output terminal; a source of the switching transistor S is connected to a second end of the input capacitor module, a second end of the first capacitor module, a second end of the third capacitor module, and a second end of the output capacitor module, and is used as a negative voltage input terminal and a negative boost voltage output terminal; a gate of the switching transistor S is used to connect to a PWM output circuit, and the switching transistor S is used to control the on / off between the source and the drain of the switching transistor S according to the received PWM signal.

[0010] In some embodiments of the present invention, the inductance values of the first inductor module, the second inductor module, and the third inductor module in the Boost boost circuit are designed.

[0011] The inductance value of the first inductor module satisfies:

[0012] The inductance value of the second inductor module satisfies:

[0013] The inductance value of the third inductor module satisfies:

[0014] Wherein, U b represents the output terminal voltage; D represents the duty cycle of the driving signal of the switching transistor S; f s represents the switching frequency of the switching transistor S; I L1,max represents the maximum average current of the first inductor module; I L2,max is the maximum average current of the second inductor module; I L3,max represents the maximum average current of the third inductor module.

[0015] In some embodiments of the present invention, the input terminal voltage of the Boost boost circuit is 40V - 100V, the maximum power is 500W, the switching frequency of the switching transistor S is 50kHz, the inductance value of the first inductor module is 400 microhenries, the inductance value of the second inductor module is 2.2 millihenries, and the inductance value of the third inductor module is 400 microhenries.

[0016] In a second aspect of the present invention, there is provided an application of the above-mentioned Boost boost circuit in a photovoltaic charging device.

[0017] In some embodiments of the present invention, the photovoltaic charging device is used for charging an electric vehicle.

[0018] In some embodiments of the present invention, the charging voltage of the electric vehicle is 800V.

[0019] In a third aspect of the present invention, there is provided a photovoltaic charging device for charging an electric vehicle, the photovoltaic charging device comprising: the above-mentioned Boost boost circuit; a photovoltaic module, an output terminal of the photovoltaic module is connected to an input terminal of the Boost boost circuit; a charging gun, the charging gun is connected to an output terminal of the Boost boost circuit.

[0020] In some embodiments of the present invention, the maximum power point voltage of the photovoltaic module is 40V - 100V.

[0021] Compared with the prior art, the Boost boost circuit proposed by the present invention, its application in a photovoltaic charging device, and the photovoltaic charging device for charging an electric vehicle have the following technical effects:

[0022] (1) The voltage gain of the Boost boost circuit proposed by the present invention is It can achieve a 20-fold voltage boost under the condition of a small duty cycle (D = 0.6), has an extremely high voltage gain, and low inductance current stress.

[0023] (2) The Boost boost circuit proposed by the present invention has only one switching tube, does not involve complex control between different switching tubes, does not require the use of a digital controller, and the Boost boost circuit of the present invention realizes common-ground drive, that is, the source electrode of the switching tube is connected to the negative electrode of the input terminal and the negative electrode of the output terminal, without isolation drive, with simple control and reduced cost.

[0024] (3) In the Boost boost circuit proposed by the present invention, it can work reliably under full-duty-cycle conditions, can easily achieve soft start. In addition, the voltage stress of the switching tube S is U b / 2, allowing the input terminal voltage to vary within a wide range.

[0025] (4) The input and output terminals share the same ground, simplifying the voltage sampling circuit and helping to reduce electromagnetic interference. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 For an embodiment, it is a schematic structural block diagram of the Boost boost circuit;

[0028] Figure 2 For an embodiment, it is a circuit diagram of the Boost boost circuit;

[0029] Figure 3 For an embodiment, it is an equivalent circuit diagram of each working mode of the Boost boost circuit;

[0030] Figure 4 For an embodiment, it is a key waveform diagram of the Boost boost circuit within one switching cycle;

[0031] Figure 5 For an embodiment, it is an average current equivalent circuit diagram of the Boost boost circuit;

[0032] Figure 6 is a steady-state simulation waveform diagram of the Boost boost circuit for an embodiment. Detailed Embodiments

[0033] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0034] In the first typical embodiment of the present invention, a Boost boost circuit is provided, as Figure 1 shown, including a first inductor module 100, a second inductor module 200, a third inductor module 300, an input capacitor module 400, a first capacitor module 500, a second capacitor module 600, a third capacitor module 700, a fourth capacitor module 800, an output capacitor module 900, a first diode module 1000, a second diode module 1100, a third diode module 1200, a fourth diode module 1300, a fifth diode module 1400, a sixth diode module 1500, a seventh diode module 1600, and a switching transistor S. The first end of the first inductor module 100 is connected to the anode of the fourth diode module 1300 and the first end of the input capacitor module 400, and is used as the positive voltage input terminal; the second end of the first inductor module 100 is connected to the anode of the first diode module 1000 and the anode of the second diode module 1100; the cathode of the second diode module 1100 is connected to the first end of the first capacitor module 500 and the first end of the second inductor module 200; the second end of the second inductor module 200 is connected to the anode of the third diode module 1200 and the first end of the second capacitor module 600; the cathode of the third diode module 1200 is connected to the cathode of the fourth diode module 1300 and the first end of the third inductor module 700; the second end of the third inductor module 700 is connected to the cathode of the first diode module 1000, the anode of the fifth diode module 1400, the first end of the fourth capacitor module 800, the second end of the second capacitor module 600, and the drain of the switching transistor S; the cathode of the fifth diode module 1400 is connected to the anode of the sixth diode module 1500 and the first end of the third capacitor module 700; the cathode of the sixth diode module 1500 is connected to the second end of the fourth capacitor module 800 and the anode of the seventh diode module 1600; the cathode of the seventh diode module 1600 is connected to the first end of the output capacitor module 900 and is used as the positive boost voltage output terminal; the source of the switching transistor S is connected to the second end of the input capacitor module 400, the second end of the first capacitor module 500, the second end of the third capacitor module 700, and the second end of the output capacitor module 900, and is used as the negative voltage input terminal and the negative boost voltage output terminal; the gate of the switching transistor S is used to connect to the PWM output circuit, and the switching transistor S is used to control the on / off between the source and the drain of the switching transistor S according to the received PWM signal.

[0035] Among them, the first inductance module 100 can be a circuit structure with inductance characteristics. For example, the first inductance module 100 can have the characteristic that the current flowing through this module cannot change suddenly. The actual circuit of the first inductance module 100 can include one or more inductors, or the equivalent circuit of the first inductance module 100 can be the same as the equivalent circuit of an inductor. It can be understood that the specific circuit structure of the first inductance module 100 can be determined according to actual situations such as the expected voltage gain and / or circuit size requirements. For example, the first inductance module 100 can be composed of multiple inductors connected in series in sequence. For the convenience of description, in some embodiments of this article, the first inductance module 100 is described by taking only the first inductor L1 as an example.

[0036] Similarly, the second inductance module 200 and the third inductance module 300 can be circuit structures with inductance characteristics, and can be understood by referring to the relevant description of the first inductance module 100. For the convenience of description, in some embodiments of this article, the second inductance module 200 is described by taking only the second inductor L2, and the third inductance module 300 is described by taking only L3 as an example. It can be understood that the first inductance module 100, the second inductance module 200, and the third inductance module 300 do not necessarily have the same circuit structure. In other words, among the first inductance module 100, the second inductance module 200, and the third inductance module 300, every two inductance modules can have the same or different circuit structures.

[0037] Compared with a single-inductor boost circuit, in the Boost boost circuit provided by the present invention, multiple inductors share the input current, reduce the current stress, and reduce the copper loss.

[0038] In the Boost boost circuit provided by the present invention, the first capacitance module 500 can be a circuit structure with capacitance characteristics. For example, the first capacitance module 500 can have the characteristic that the voltage across this module cannot change suddenly. The actual circuit of the first capacitance module 500 can include one or more capacitors, or the equivalent circuit of the first capacitance module 500 can be the same as the equivalent circuit of a capacitor. It can be understood that the specific circuit structure of the first capacitance module 500 can be determined according to actual situations such as the expected voltage gain and / or circuit size requirements, and specific limitations are not made herein. For example, the first capacitance module 500 can be composed of multiple capacitors, and the capacitors are connected in parallel with each other. For the convenience of description, in some embodiments of this article, the first capacitance module 500 is described by taking only the first capacitor C1 as an example.

[0039] Similarly, the second capacitor module 600, the third capacitor module 700, the fourth capacitor module 800, the input capacitor module 400, and the output capacitor module 900 can all be circuit structures with capacitance characteristics. For specific descriptions of the second capacitor module 600, the third capacitor module 700, the fourth capacitor module 800, the input capacitor module 400, and the output capacitor module 900, reference can be made to the description of the first capacitor module 500 above, which will not be elaborated herein. For ease of description, in some embodiments of this article, the second capacitor module 600 only includes the second capacitor C2, the third capacitor module 700 only includes the third capacitor C3, the fourth capacitor module 800 only includes the fourth capacitor C4, the input capacitor module 400 only includes the input capacitor C in , and the output capacitor module 900 only includes the output capacitor C o as an example for illustration. It can be understood that the first capacitor module 500, the second capacitor module 600, the third capacitor module 700, the fourth capacitor module 800, the input capacitor module 400, and the output capacitor module 900 do not necessarily have the same circuit structure. In other words, among the first capacitor module 500, the second capacitor module 600, the third capacitor module 700, the fourth capacitor module 800, the input capacitor module 400, and the output capacitor module 900, every two capacitor modules can have the same or different circuit structures.

[0040] It can be understood that the inductance value or equivalent inductance value of the first inductor module 100, the second inductor module 200, and the third inductor module 300 can be determined according to the actual situation. Similarly, the capacitance value or equivalent capacitance value of the first capacitor module 500, the second capacitor module 600, the third capacitor module 700, and the fourth capacitor module 800 can all be determined according to the actual situation. In one example, the inductance value of the first inductor module 100 can be 400 microhenries (uH), the inductance value of the second inductor module 200 can be 2.2 millihenries (mH), the inductance value of the third inductor module 300 can be 400 microhenries, the capacitance value of the first capacitor module 500 can be 10 microfarads (uF), the capacitance value of the second capacitor module 600 can be 10 microfarads, the capacitance value of the third capacitor module 700 can be 20 microfarads, the capacitance value of the fourth capacitor module 800 can be 20 microfarads, the capacitance value of the input capacitor module 400 can be 100 microfarads, and the capacitance value of the output capacitor module 900 can be 4.7 microfarads.

[0041] The first diode module 1000 can be a circuit module with forward conduction and reverse cut-off characteristics, which may include one or more diodes. It can be understood that the specific circuit structure of the first diode module 1000 can be determined according to actual situations such as the voltage stress borne by the module and the requirements for operating stability, and specific limitations in this regard are not made in this article. Similarly, the second diode module 1100, the third diode module 1200, the fourth diode module 1300, the fifth diode module 1400, the sixth diode module 1500, and the seventh diode 1600 module can be circuit modules with forward conduction and reverse cut-off characteristics. For specific descriptions of the second diode module 1100, the third diode module 1200, the fourth diode module 1300, the fifth diode module 1400, the sixth diode module 1500, and the seventh diode module 1600, reference can be made to the description of the first diode module 1000 above, and details are not repeated in this article. For ease of description, in some embodiments of this article, it is taken as an example that the first diode module 1000 only includes the first diode D1, the second diode module 1100 only includes the second diode D2, the third diode module 1200 only includes the third diode D3, the fourth diode module 1300 only includes the fourth diode D4, the fifth diode module 1400 only includes the fifth diode D5, the sixth diode module 1500 only includes the sixth diode D6, and the seventh diode module 1600 only includes the seventh diode D7 for illustration.

[0042] The switching transistor S is an N-channel MOS transistor.

[0043] The PWM output circuit is used to output a PWM signal to the switching transistor S according to a pre-determined pulse width modulation strategy to control the on / off state of the switching transistor S. Signal parameters such as the signal period and / or duty cycle of the PWM signal can be determined according to the expected voltage gain of the photovoltaic charging converter circuit, the rated parameters of circuit components, etc.

[0044] The switching transistor S can control the on / off between the first end and the second end of the switching transistor S according to the PWM signal output by the PWM output circuit. For example, when the switching transistor S is an N-type MOS transistor, if the currently received PWM signal is at a high level and the voltage difference between the gate and the source of the switching transistor S is greater than the conduction voltage threshold, the first end and the second end of the switching transistor S are turned on, and the branch where the switching transistor S is located is in a conducting state. If the currently received PWM signal is at a low level and the voltage difference between the gate and the source of the switching transistor S is less than the conduction voltage threshold, the first end and the second end of the switching transistor S are turned off, and the branch where the switching transistor S is located is in an open state.

[0045] In an embodiment of the present invention, a Boost boost circuit is provided, as Figure 2 shown, including an input capacitor C in and an output capacitor Co , the first capacitor C1, the second capacitor C2, the third capacitor C3, the fourth capacitor C4, the first inductor L1, the second inductor L2, the third inductor L3, the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6, the seventh diode D7, and the switching transistor S. The first end of the first inductor L1 is connected to the anode of the fourth diode D4 and the first end of the input capacitor C in and is used as the positive voltage input terminal; the second end of the first inductor L1 is connected to the anode of the first diode D1 and the anode of the second diode D2; the cathode of the second diode D2 is connected to the first end of the first capacitor C1 and the first end of the second inductor L2; the second end of the second inductor L2 is connected to the anode of the third diode D3 and the first end of the second capacitor C2; the cathode of the third diode D3 is connected to the cathode of the fourth diode D4 and the first end of the third inductor L3; the second end of the third inductor L3 is connected to the cathode of the first diode D1, the anode of the fifth diode D5, the first end of the fourth capacitor C4, the second end of the second capacitor C2, and the drain of the switching transistor; the cathode of the fifth diode D5 is connected to the anode of the sixth diode D6 and the first end of the third capacitor C3; the cathode of the sixth diode D6 is connected to the second end of the fourth capacitor C4 and the anode of the seventh diode D7; the cathode of the seventh diode D7 is connected to the first end of the output capacitor C o and is used as the positive boost voltage output terminal; the source of the switching transistor is connected to the second end of the input capacitor C in , the second end of the first capacitor C1, the second end of the third capacitor C3, and the second end of the output capacitor C o and is used as the negative voltage input terminal and the negative boost voltage output terminal; the source of the switching transistor S is connected to the second end of the input capacitor C in , the second end of the first capacitor C1, the second end of the third capacitor C3, and the second end of the output capacitor C o and is used as the negative voltage input terminal and the negative boost voltage output terminal.

[0046] In a typical embodiment of the present invention, an application of the above Boost boost circuit in a photovoltaic charging device is provided. The positive voltage input terminal and the negative voltage input terminal of the Boost boost circuit are respectively connected to the positive output terminal and the negative output terminal of the photovoltaic module.

[0047] In some embodiments of the present invention, the photovoltaic charging device is a photovoltaic charging device for charging an electric vehicle. The positive boost voltage output terminal and the negative boost voltage output terminal of the Boost boost circuit are respectively connected to the positive terminal and the negative terminal of the electric vehicle battery.

[0048] In some embodiments of the present invention, the photovoltaic module may be a photovoltaic panel with a maximum power point voltage of 40V - 100V, and the charging voltage of the electric vehicle battery is 800V.

[0049] The working principle of the energy storage converter shown below Figure 2 will be described.

[0050] To simplify the analysis, the following assumptions are made: The input capacitor C in , output capacitor C o , first capacitor C1, second capacitor C2, third capacitor C3, fourth capacitor C4, first inductor L1, second inductor L2, third inductor L3, first diode D1, second diode D2, third diode D3, fourth diode D4, fifth diode D5, sixth diode D6, seventh diode D7, and switch tube S are all ideal devices.

[0051] Based on the above assumptions, the steady-state working process of the Boost boost circuit shown in the present invention Figure 2 within one switching period T s can be divided into 3 modes. The equivalent circuits of each mode are as shown in Figure 3 and the main waveforms are as shown in Figure 4 .

[0052] Mode 1, stage t0 - t1 (equivalent circuit as shown in Figure 3 (a)).

[0053] At time t0, the switch tube S is turned on and Mode 1 starts. The first diode D1, fourth diode D4, and sixth diode D6 are forward-biased, and the rest of the diodes are reverse-biased. The output capacitor C o alone supplies energy to the load. The third capacitor C3 charges the fourth capacitor C4 through the sixth diode D6. The first inductor L1 and the third inductor L3 are subjected to a positive voltage U in , and the second inductor L2 is subjected to a positive voltage U C1 +U C2 , so the inductor currents i L1 , i L2 , and i L3 all rise linearly. During this period, there is:

[0054]

[0055] where U in is the input terminal voltage, U C1 and U C2 are the terminal voltages of the first capacitor C1 and the second capacitor C2 respectively, and L1, L2, L3 are the inductance values of the first inductor L1, the second inductor L2, and the third inductor L3 respectively.

[0056] Mode 2, from t1 to t2 (the equivalent circuit is as shown in Figure 3 (b)).

[0057] At time t1, the charging current of the third capacitor C3 to the fourth capacitor C4 drops to zero, and the charging process ends. The sixth diode D6 turns off naturally. The inductor currents i L1 , i L2 and i L3 all continue to rise linearly at the original rate of change. During this period, there is:

[0058]

[0059] where U b is the output terminal voltage, and U C3 and U C4 are the terminal voltages of the third capacitor C3 and the fourth capacitor C4 respectively.

[0060] Mode 3, from t2 to t3 (the equivalent circuit is as shown in Figure 3 (c)).

[0061] At time t2, the switch tube S is turned off, and Mode 3 starts. In this mode, the second diode D2, the third diode D3, the fifth diode D5, and the seventh diode D7 are forward-biased, and the first diode D1 and the fourth diode D4 are reverse-biased. The first inductor L1, the second inductor L2, and the third inductor L3 respectively bear negative voltages U C1 - U in , U b - U C1 - U C2 - U C4 and U C2 , so they all start to discharge linearly. During this period, there is:

[0062]

[0063] where U in is the input terminal voltage, U b is the output terminal voltage, U C1 , U C2 and U C4 are the terminal voltages of the first capacitor C1, the second capacitor C2, and the fourth capacitor C4 respectively, and L1, L2, L3 are the inductance values of the first inductor L1, the second inductor L2, and the third inductor L3 respectively.

[0064] Based on the above working principle, the steady-state characteristics of the Boost boost circuit proposed by the present invention are analyzed below.

[0065] According to the volt-second balance of the first inductor L1, the second inductor L2, and the third inductor L3, it can be obtained that:

[0066]

[0067] Wherein, U in is the input terminal voltage, U b is the output terminal voltage, U C1 , U C2 and U C4 are the terminal voltages of the first capacitor C1, the second capacitor C2 and the fourth capacitor C4 respectively, D is the duty cycle of the driving signal of the switching transistor S, and T s is a switching cycle of the switching transistor S.

[0068] According to Equation (4), the voltage gain of the Boost boost circuit proposed by the present invention can be obtained as:

[0069]

[0070] Wherein, U in is the input terminal voltage, U b is the output terminal voltage, and D is the duty cycle of the driving signal of the switching transistor S.

[0071] According to Equation (2) and Equation (4), the voltage stresses of the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are:

[0072]

[0073] The voltage stresses of the switching transistor S and all the diodes can be expressed as:

[0074]

[0075] Wherein, U S is the voltage stress of the switching transistor S, and U D1 , U D2 , U D3 , U D4 , U D5 , U D6 , U D7 are the voltage stresses of the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6, and the seventh diode D7 respectively.

[0076] After entering the steady state, the average currents of the input capacitor C in , the output capacitor C o , the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are zero.

[0077] The average current equivalent circuit of the Boost boost circuit proposed by the present invention is as Figure 5 shown, and the following conclusions can be obtained:

[0078]

[0079] Wherein, I in is the average value of the input current; I o is the average value of the output current; I L1 , I L2 and I L3 are respectively the average values of the currents of the first inductor L1, the second inductor L2 and the third inductor L3; I D1 , I D2 , I D3 , I D4 , I D5 , I D6 and I D7 are respectively the average values of the currents of the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6 and the seventh diode D7.

[0080] According to Figure 5 it can be known that the first diode D1 and the diode D2 conduct complementarily, and the third diode D3 and the fourth diode D4 conduct complementarily. Therefore, there is:

[0081]

[0082] From Equation (8) and Equation (9), it can be obtained that:

[0083]

[0084] According to Equation (5) and Equation (10), it can be obtained that:

[0085]

[0086] Wherein, P o is the output power.

[0087] Next, the main circuit parameter design method of the Boost boost circuit proposed by the present invention will be described in conjunction with specific examples.

[0088] The design indexes of the converter proposed by the present invention are: switching frequency f s = 50 kHz, U in = 40 V - 102.85 V, U b = 800 V, maximum output power P o,max = 500 W.

[0089] According to the above indexes, from Equation (5), the variation range of the duty cycle can be obtained: D = 0.4 - 0.6.

[0090] The maximum average value of the inductor current is:

[0091]

[0092] Wherein, D max is the maximum duty cycle, I L1,max is the average maximum current of the first inductor L1, I L2,max is the average maximum current of the second inductor L2, I L3,max is the average maximum current of the third inductor module L3.

[0093] The peak-to-peak current of the first inductor L1 is:

[0094]

[0095] Wherein, D min is the minimum duty cycle, L1 is the inductance value of the first inductor L1, ΔI L1,max is the peak-to-peak maximum current of the first inductor L1.

[0096] The peak-to-peak current of the second inductor L2 is:

[0097]

[0098] Wherein, L2 is the inductance value of the second inductor L2, ΔI L2,max is the peak-to-peak maximum current of the second inductor L2.

[0099] Design each inductance value according to the peak-to-peak maximum current of the inductor current not exceeding 30% of the average maximum current. Therefore, combining Equation (12) and Equation (13), we can obtain:

[0100]

[0101] Actually, the inductance value of the first inductor L1 is taken as L1 = 400 μH.

[0102] Combining Equation (12) and Equation (14), we can obtain:

[0103]

[0104] Actually, the inductance value of the second inductor L2 is taken as L2 = 2.2 mH.

[0105] Combining Equation (12) and Equation (13), we can obtain:

[0106]

[0107] Actually, the inductance value of the third inductor L3 is taken as L3 = 400 μH.

[0108] In order to verify the feasibility of the Boost boost circuit proposed by the present invention, a simulation circuit is built using Saber simulation software. The specific technical indicators and main circuit parameters are set as follows: switching frequency f s= 50 kHz, the input voltage U in = 40 V - 100 V, the output voltage U of the electric vehicle b = 800 V, the maximum output power P o,max = 500 W; the input capacitor C in = 100 μF, the output capacitor C o = 4.7 μF, the first capacitor C1 = 10 μF, the second capacitor C2 = 10 μF, the third capacitor C3 = 20 μF, the fourth capacitor C4 = 20 μF; the inductance value of the first inductor L1, L1 = 400 μH, the inductance value of the second inductor L2, L2 = 2.2 mH, the inductance value of the third inductor L3, L3 = 400 μH.

[0109] As shown in Fig. 6(a), the driving signal u of the switching transistor S gs,S , the input voltage U in , the output voltage U b simulation waveforms. It can be seen that the measured duty cycle is 0.6, which is exactly the same as the theoretical value; Fig. 6(b) shows the first inductor current i L1 , the second inductor current i L2 , the third inductor current i L3 simulation waveforms. It can be seen that the average current simulation measurement values of the first inductor L1, the second inductor L2 and the third inductor L3 are 7.76 A, 3.06 A and 7.76 A respectively, all of which are basically in line with the theoretical values; the peak-to-peak current measurement values of the first inductor L1, the second inductor L2 and the third inductor L3 are 0.67 A, 0.86 A and 0.67 A respectively, all of which do not exceed 30% of their respective maximum current averages, meeting the design requirements.

[0110] As shown in Fig. 6(c), the terminal voltage u of the switching transistor S s , the output voltage U b , the terminal voltage u of the first capacitor C1 C1 , the terminal voltage u of the second capacitor C2 C2 , the terminal voltage u of the third capacitor C3 C3 , the terminal voltage u of the fourth capacitor C4 C4 simulation waveforms. It can be seen that the output voltage U b = 800 V, the voltage stress of the first capacitor is U C1 = 100.5 V, the voltage stress of the second capacitor is U C2 = 60.5 V, the voltage stress of the third capacitor is U C3 = 400.4 V, the voltage stress of the fourth capacitor is U C4 = 399.7 V, the voltage stress of the switching transistor S is U s = 400.4 V. The above simulation measurement values are basically consistent with the theoretical values.

[0111] The Boost boost circuit provided by the present invention, its application in a photovoltaic charging device, and the photovoltaic charging device for electric vehicle charging have the following advantages:

[0112] (1) The voltage gain of the Boost boost circuit proposed by the present invention is It can achieve a 20-fold boost under the condition of a small duty cycle (D = 0.6), has an extremely high voltage gain, and low inductance current stress.

[0113] (2) The Boost boost circuit proposed by the present invention has only one switching tube, does not involve complex control between different switching tubes, does not require the use of a digital controller, and the Boost boost circuit of the present invention realizes common-ground drive, that is, the source electrode of the switching tube is connected to the negative electrode of the input end and the negative electrode of the output end, without isolation drive, the control is simple, and the cost is reduced.

[0114] (3) In the Boost boost circuit proposed by the present invention, it can work reliably under the condition of full duty cycle, can easily realize soft start, and in addition, the voltage stress of the switching tube S is U b / 2, allowing a wide range of input voltage variations.

[0115] (4) The input and output ends are common-grounded, simplifying the voltage sampling circuit and helping to reduce electromagnetic interference.

[0116] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0117] The description of the above embodiments is only used to help understand the method and its core idea of the present invention, rather than to limit it. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A Boost boost circuit, characterized in that, The Boost boost circuit includes: an input capacitor module, an output capacitor module, a first capacitor module, a second capacitor module, a third capacitor module, a fourth capacitor module, a first inductor module, a second inductor module, a third inductor module, a first diode module, a second diode module, a third diode module, a fourth diode module, a fifth diode module, a sixth diode module, a seventh diode module, and a switching transistor S; The first end of the first inductor module is connected to the anode of the fourth diode module and the first end of the input capacitor module, and is used as the positive voltage input terminal; The second end of the first inductor module is connected to the anode of the first diode module and the anode of the second diode module; The cathode of the second diode module is connected to the first end of the first capacitor module and the first end of the second inductor module; The second end of the second inductor module is connected to the anode of the third diode module and the first end of the second capacitor module; The cathode of the third diode module is connected to the cathode of the fourth diode module and the first end of the third inductor module; The second end of the third inductor module is connected to the cathode of the first diode module, the anode of the fifth diode module, the first end of the fourth capacitor module, the second end of the second capacitor module, and the drain of the switching transistor; The cathode of the fifth diode module is connected to the anode of the sixth diode module and the first end of the third capacitor module; The cathode of the sixth diode module is connected to the second end of the fourth capacitor module and the anode of the seventh diode module; The cathode of the seventh diode module is connected to the first end of the output capacitor module and is used as the positive boost voltage output terminal; The source of the switching transistor S is connected to the second end of the input capacitor module, the second end of the first capacitor module, the second end of the third capacitor module, and the second end of the output capacitor module, and is used as the negative voltage input terminal and the negative boost voltage output terminal; The gate of the switching transistor S is used to connect to the PWM output circuit, and the switching transistor S is used to control the on-off between the source and the drain of the switching transistor S according to the received PWM signal.

2. The Boost boost circuit according to claim 1, wherein, The inductance value of the first inductor module satisfies: The inductance value of the second inductor module satisfies: The inductance value of the third inductor module satisfies: Among them, U b represents the output terminal voltage; D represents the duty cycle of the driving signal of the switching transistor S; f s represents the switching frequency of the switching transistor S; I L1,max represents the maximum average current of the first inductor module; I L2,max is the maximum average current of the second inductor module; I L3,max represents the maximum average current of the third inductor module.

3. The Boost boost circuit according to claim 1, characterized in that The input voltage of the Boost boost circuit is 40V - 100V, the maximum power is 500W, the switching frequency of the switching transistor S is 50kHz, the inductance value of the first inductor module is 400 microhenries, the inductance value of the second inductor module is 2.2 millhenries, and the inductance value of the third inductor module is 400 microhenries.

4. The application of the Boost boost circuit according to any one of claims 1 - 3 in a photovoltaic charging device.

5. The application according to claim 4, characterized in that The photovoltaic charging device is used for charging an electric vehicle.

6. The application according to claim 5, characterized in that The charging voltage of the electric vehicle is 800V.

7. A photovoltaic charging device for electric vehicle charging, characterized in that, The photovoltaic charging device includes: The Boost boost circuit according to any one of claims 1 - 3; A photovoltaic module, the output end of the photovoltaic module is connected to the input end of the Boost boost circuit; Charging gun, and the charging gun is connected to the output end of the Boost boost circuit.

8. The photovoltaic charging device according to claim 7, characterized in that, The maximum power point voltage of the photovoltaic module is 40V - 100V.

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