DC-DC converter and its control method, photovoltaic energy storage system

Abstract

This application discloses a DC-DC converter and its control method, as well as a photovoltaic-energy storage system, relating to the field of switching power supply technology. It includes a push-pull resonant circuit, a photovoltaic input circuit, and an energy storage input circuit. This application uses a push-pull resonant circuit as a unified energy conversion core, allowing the photovoltaic input and energy storage input to share key components such as transformers, resonant networks, and switching transistors. This replaces the independent multi-stage converters of traditional solutions with a single-stage structure, simplifying the system architecture and reducing size, weight, and cost. Through resonant soft-switching technology, the switching transistors operate under zero-voltage or zero-current conditions, reducing switching losses and achieving high-efficiency energy transfer. Simultaneously, a third switching circuit at the photovoltaic end is dedicated to tracking the maximum power point, while the energy storage end is independently controlled for charging and discharging via a bidirectional circuit, ensuring both photovoltaic energy harvesting efficiency and flexible power scheduling and smoothing fluctuations.

Description

Technical Field

[0001] This application relates to the technical field of switching power supplies, and more particularly to a DC-DC converter and its control method, and a photovoltaic energy storage system. Background Technology

[0002] Solar energy has great development potential due to its advantages such as being pollution-free and having zero emissions. However, its power supply is easily interrupted and unstable due to irradiance and environmental impact. Therefore, it is necessary to use the charging and discharging of energy storage units to compensate for the power of the DC grid and achieve a stable supply.

[0003] Traditional photovoltaic-storage systems require separate DC-DC converters to connect the photovoltaic and energy storage ends to the load end, or to use multi-stage converters to complete the energy conversion. These systems generally suffer from problems such as large system size, complex control, low transmission efficiency, and high cost. The complex control methods also affect the system reliability and dynamic response speed. Summary of the Invention

[0004] The main purpose of this application is to provide a DC-DC converter and its control method, as well as a photovoltaic-energy storage system, which aims to solve the technical problems of complex structure, large size and high cost caused by the need for two independent converters for photovoltaic and energy storage in traditional photovoltaic-energy storage systems.

[0005] To achieve the above objectives, this application proposes a DC-DC converter, comprising:

[0006] The push-pull resonant circuit includes a transformer, a primary-side switching circuit electrically connected to the primary winding of the transformer, and a resonant network and rectifier circuit electrically connected to the secondary winding of the transformer.

[0007] A photovoltaic input circuit includes a third switching circuit, the input terminal of which is used to connect to a photovoltaic module, and the output terminal of which is electrically connected to the center tap of the primary winding of the transformer.

[0008] An energy storage input circuit includes an energy storage device, a first end of which is used to connect to an energy storage module, and a second end of which is electrically connected to the center tap of the primary winding of the transformer.

[0009] The primary-side switching circuit is used to convert the DC signal input to the photovoltaic module and / or the energy storage module into an AC signal.

[0010] The third switching circuit is used to adjust the output power of the photovoltaic module so that the output power of the photovoltaic module is maintained at the corresponding maximum power point.

[0011] In one embodiment, the primary-side switching circuit includes a first switching transistor and a second switching transistor, the input terminals of the first switching transistor and the second switching transistor are respectively electrically connected to the two ends of the primary-side winding, and the output terminals of the first switching transistor and the second switching transistor are grounded.

[0012] The primary-side switching circuit is used to convert the DC signal input to the photovoltaic module and / or the energy storage module into an AC signal by alternately turning on the first and second switching transistors.

[0013] In one embodiment, the third switching circuit includes a third switching transistor, the input terminal of which is electrically connected to the positive terminal of the photovoltaic module, and the output terminal of which is electrically connected to the center tap of the primary winding of the transformer, and the negative terminal of the photovoltaic module is grounded.

[0014] The DC-DC converter also includes a control circuit, which is electrically connected to the control terminals of the first switch, the second switch and the third switch, and is used to generate and output drive signals.

[0015] The driving signal of the third switch is generated based on the driving signals of the first switch and the second switch.

[0016] In one embodiment, the energy storage device of the energy storage input circuit is an energy storage inductor, which is used to absorb the power output by the energy storage component when the first switch and the second switch are simultaneously turned on.

[0017] In addition, it is used to release energy to the push-pull resonant circuit when the first switch and the third switch are turned on simultaneously, or when the second switch and the third switch are turned on simultaneously.

[0018] In one embodiment, the photovoltaic input circuit further includes:

[0019] The anti-reverse-feedback diode has its anode connected to the positive electrode of the photovoltaic module, and its cathode electrically connected to the center tap of the primary winding of the transformer via the third switching transistor.

[0020] In one embodiment, the photovoltaic input circuit further includes an input filter capacitor connected in parallel across the two ends of the photovoltaic module, used to filter out high-frequency ripple in the photovoltaic input circuit and provide energy buffer for the push-pull resonant circuit.

[0021] In one embodiment, the DC-DC converter includes:

[0022] Multiple photovoltaic input circuits;

[0023] And / or, multiple energy storage input circuits;

[0024] And / or, the first end of the energy storage device is connected to multiple energy storage components.

[0025] Furthermore, to achieve the above objectives, this application also proposes a control method for a DC-DC converter, implemented based on the DC-DC converter as described above, the method comprising:

[0026] A set of complementary drive signals is generated to control the first and second switching transistors of the primary-side switching circuit to conduct alternately.

[0027] The driving signal of the third switching circuit is generated based on the driving signal of the first switching transistor and the driving signal of the second switching transistor to control the conduction and disconnection of the third switching transistor of the third switching circuit.

[0028] By adjusting the duty cycle of the drive signals of the first and second switching transistors, the output power of the photovoltaic module is adjusted so that the output power of the photovoltaic module is maintained at the corresponding maximum power point.

[0029] The output voltage of the DC-DC converter is stabilized by adjusting the switching frequencies of the first and second switching transistors.

[0030] In one embodiment of the control method, it further includes:

[0031] The voltages of the energy storage module and the photovoltaic module are collected;

[0032] Based on the voltage of the energy storage component and the photovoltaic component, the duty cycle of the third switching transistor is adjusted to regulate the distribution of photovoltaic power and energy storage power.

[0033] In addition, to achieve the above objectives, this application also proposes a photovoltaic energy storage system, including the DC-DC converter as described above, as well as photovoltaic modules and energy storage modules.

[0034] One or more technical solutions proposed in this application have at least the following technical effects:

[0035] This application employs a push-pull resonant circuit as the unified energy conversion core, allowing the photovoltaic input and energy storage input to share key components such as transformers, resonant networks, and switching transistors. This replaces the independent multi-stage converters of traditional solutions with a single-stage structure, simplifying the system architecture and reducing size, weight, and cost. Through resonant soft-switching technology, the switching transistors operate under zero-voltage or zero-current conditions, reducing switching losses and achieving high-efficiency energy transfer. Simultaneously, a third switching circuit at the photovoltaic end is dedicated to tracking the maximum power point, while the energy storage end uses a bidirectional circuit to independently control charging and discharging. The two power sources converge at the middle tap of the transformer, ensuring both photovoltaic energy harvesting efficiency and flexible power scheduling and smoothing fluctuations. This effectively solves the problems of complex structure, low efficiency, and control redundancy in traditional photovoltaic-energy storage systems. While achieving a low-cost dual-input system, it significantly expands the system gain range, enabling it to adapt to different photovoltaic and battery voltage levels, improving the flexibility of on-site configuration, and expanding the application scenarios and scope of the device. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a structural diagram of a DC-DC converter according to this application;

[0039] Figure 2 This is a circuit diagram of a DC-DC converter according to a first embodiment of this application;

[0040] Figure 3 This is a circuit diagram of a second embodiment of a DC-DC converter according to this application;

[0041] Figure 4 This is a drive signal control logic diagram of a DC-DC converter according to a third embodiment of this application;

[0042] Figure 5 The waveform diagram of the third switch of the DC-DC converter of this application with a duty cycle d = 0.5 is shown.

[0043] Figure 6 This is a control block diagram of an embodiment of this application;

[0044] Figure 7 The simulation waveform of a DC-DC converter according to this application. Figure 1 ;

[0045] Figure 8 The simulation waveform of a DC-DC converter according to this application. Figure 2 ;

[0046] Figure 9 The simulation waveform of a DC-DC converter according to this application. Figure 3 ;

[0047] Figure 10 This is a schematic flowchart illustrating a DC-DC converter control method according to an embodiment of this application.

[0048] Explanation of reference numerals: Transformer 01, Primary-side switching circuit 02, Resonant network 03, Rectifier circuit 04, Photovoltaic input circuit 05, Third switching circuit 51, Anti-reverse current diode 52, Energy storage input circuit 06, Energy storage device 61.

[0049] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0050] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.

[0051] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0052] This application proposes a DC-DC converter, such as... Figure 1 and Figure 2 As shown, it includes:

[0053] The push-pull resonant circuit includes a transformer 01, a primary-side switching circuit 02 electrically connected to the primary winding of the transformer 01, and a resonant network 03 and a rectifier circuit 04 electrically connected to the secondary winding of the transformer 01; the photovoltaic input circuit 05 includes a third switching circuit 51, the input terminal of which is used to connect to a photovoltaic module, and the output terminal of which is electrically connected to the center tap of the primary winding of the transformer 01; the energy storage input circuit 06 includes an energy storage device 61, the first end of which is used to connect to an energy storage module, and the second end of which is electrically connected to the center tap of the primary winding of the transformer 01.

[0054] The primary-side switching circuit 02 is used to convert the DC signal input to the photovoltaic module and / or energy storage module into an AC signal; the third switching circuit 51 is used to adjust the output power of the photovoltaic module so that the output power of the photovoltaic module is maintained at the corresponding maximum power point.

[0055] More specifically, solar energy, as a clean and renewable energy source, has the core advantage of zero pollution and zero emissions in its power generation process, and is therefore considered an important component of the future energy structure. However, this energy form inherently suffers from intermittency and volatility. The fundamental reason for this is that solar radiation intensity is significantly affected by environmental factors such as weather changes, day-night cycles, and cloud cover, leading to highly unstable power output from photovoltaic modules. To address this issue and ensure a continuous and stable power supply to loads, especially the DC grid, the current common technical approach is to introduce energy storage units into the photovoltaic system. Energy storage batteries are charged when there is surplus power generation and discharged when there is insufficient power generation to smooth and compensate for the system's net output power.

[0056] Traditional solutions typically involve configuring separate DC-DC converters for photovoltaic arrays and energy storage batteries, or using a complex multi-stage converter architecture to connect them to the system. The direct consequences of this approach are bulky equipment, high overall cost, and loss of transmission efficiency due to the multiple energy conversions required. A deeper challenge lies in the fact that managing multiple converters requires a complex and coordinated control system. This not only increases the difficulty of system design but also introduces potential points of failure, thus limiting the overall reliability of the system and slowing down its dynamic response to changes in illumination or load.

[0057] To address the aforementioned challenges, this application proposes a resonant converter device, comprising a push-pull resonant circuit, a photovoltaic input circuit 05, and an energy storage input circuit 06. This application abandons the traditional approach of equipping photovoltaic and energy storage with separate converters, and instead creatively integrates multiple functions such as photovoltaic input, energy storage access, DC-AC conversion, power regulation, and isolation rectification into a single-stage power conversion platform centered on a push-pull resonant transformer. This aims to achieve high hardware reuse, reduce the number of components, and thus fundamentally reduce system size, lower costs, and improve efficiency.

[0058] The push-pull circuit is a classic power amplifier or switching converter circuit. It uses two identical switching transistors that operate alternately, thus synthesizing a complete and continuous energy waveform across the load. The driver circuit of the push-pull circuit generates two complementary pulse-width modulation signals with dead time, which control the on and off states of the two switching transistors respectively. A resonant circuit is a circuit composed of an inductor and a capacitor that exhibits resonance at its resonant frequency. At the resonant frequency, the circuit impedance reaches its minimum or maximum value, and energy is efficiently exchanged between the magnetic field of the inductor and the electric field of the capacitor, forming a large-amplitude sinusoidal oscillation. In switching power supplies, the resonant circuit is not used to generate continuous oscillation, but rather, in conjunction with the switching transistors, it creates soft-switching conditions by controlling the switching timing.

[0059] In traditional hard switching, the voltage and current overlap during the turn-on and turn-off moments, resulting in significant switching losses and noise. The resonant circuit modifies the voltage and current waveforms across the switch, making them sinusoidal. Just before the switch turns on, the existing current in the resonant network (03) charges and discharges the parasitic capacitance of the switch, bringing the voltage across it to zero. When the switch is turned on at this point, the conduction loss is almost zero because the voltage is zero. Just before the switch turns off, the resonant current naturally crosses zero. Turning off the switch when the current crosses zero results in almost zero turn-off losses.

[0060] The push-pull resonant circuit of this application possesses the functions and advantages of the aforementioned push-pull and resonant circuits. Specifically, it includes a transformer 01, a primary-side switching circuit 02 electrically connected to the primary winding of the transformer 01, and a resonant network 03 and a rectifier circuit 04 electrically connected to the secondary winding of the transformer 01. The primary-side switching circuit 02 inverts the DC power input from the photovoltaic module and / or energy storage module into high-frequency AC power. This circuit typically consists of two main switching transistors, respectively connected to both ends of the primary winding of the transformer 01. The control system generates two complementary pulse drive signals with a slight dead time, which are applied to the two switching transistors respectively. This causes the two switching transistors to alternately turn on and off like a saw: when one is on, current flows through half of the primary winding of the transformer 01; when the other is on, the current flows in the opposite direction through the other half of the winding, generating a high-frequency AC square wave voltage on the primary side of the transformer 01. Transformer 01 raises or lowers the high-frequency AC voltage generated on the primary side to the voltage level required by the load, and transfers energy through magnetic coupling to achieve electrical isolation between the primary side (photovoltaic / energy storage side) and the secondary side (load side), thereby enhancing the system's safety and anti-interference capabilities.

[0061] The resonant network 03 on the secondary side creates soft-switching conditions, significantly reducing switching losses. The rectifier circuit 04 is responsible for converting the high-frequency AC current from the secondary side of transformer 01 into DC current. The resonant network 03, composed of inductors and capacitors connected in a specific manner, resonates near the operating frequency of the switching circuit. The physical characteristics of resonance cause the waveform of the current flowing through the switching transistor and the voltage across it to change from a steep square wave to a smooth sine wave. Just before the switching transistor turns on, the resonant current charges and discharges the transistor's parasitic capacitance, causing the voltage across it to oscillate naturally to zero. When the switching transistor is then turned on, the conduction loss is reduced to extremely low levels because the voltage is zero at the moment of turn-on. Just before the switching transistor turns off, the resonant current naturally crosses zero. When the switching transistor is then turned off, the turn-off loss is negligible because the current is zero at the moment of turn-off. This technique of using resonance to achieve zero-voltage or zero-current switching overcomes the shortcomings of traditional hard switching, such as high losses and severe electromagnetic interference, and is the core of improving the overall efficiency of the device. The high-frequency sinusoidal alternating current after passing through the resonant network 03 is sent to the rectifier circuit 04. The rectifier circuit 04 flips the waveform of its negative half-cycle, turning it into pulsating direct current. After being smoothed by the output filter capacitor, the stable direct current required by the load is finally obtained.

[0062] Based on the aforementioned push-pull resonant core, a photovoltaic input circuit and an energy storage input circuit 06 are integrated. The photovoltaic input circuit 05 includes a third switching circuit 51. The input terminal of the third switching circuit 51 is used to connect to the photovoltaic module, and the output terminal of the third switching circuit 51 is electrically connected to the center tap of the primary winding of the transformer 01. The third switching circuit 51 is the control core on the photovoltaic side. By dynamically adjusting its duty cycle, it continuously changes the operating point of the photovoltaic module, thereby tracking and locking its maximum power point in real time. This means that regardless of changes in solar irradiance, this circuit can ensure that the photovoltaic module always outputs electrical energy at the highest efficiency under the current conditions. The DC power optimized by Maximum Power Point Tracking (MPPT) is directly fed into the center tap of the primary winding of the transformer 01.

[0063] The energy storage input circuit 06 includes an energy storage device 61. The first end of the energy storage device 61 is connected to the energy storage module, and the second end of the energy storage device 61 is electrically connected to the center tap of the primary winding of the transformer 01. The energy storage input circuit 06 is directly connected to the energy storage module. Its bidirectional design means it can intelligently determine the direction of energy flow based on the real-time power balance of the system. When the photovoltaic power generation exceeds the load demand, the circuit operates in charging mode, storing the excess energy in the battery. When photovoltaic power generation is insufficient or there is no light at night, it switches to discharging mode, releasing the energy stored in the battery and injecting it into the system through the same center tap to support load operation.

[0064] Meanwhile, the center tap of the primary winding of transformer 01 becomes the power convergence point for the entire system. The electrical energy generated by the photovoltaic system and the electrical energy absorbed or released by the energy storage battery are superimposed here. The push-pull resonant circuit, acting as a fast-response power processor, efficiently converts and transmits this combined total power to the secondary side. This architecture allows fluctuations in photovoltaic energy to be compensated in real time by the charging and discharging actions of the energy storage unit, ultimately smoothing the net output power of the entire system and providing a stable and continuous power supply to the load.

[0065] This application employs a push-pull resonant circuit as the unified energy conversion core, allowing the photovoltaic input and energy storage input to share key components such as transformer 01, resonant network 03, and switching transistors. This replaces the independent multi-stage converters of traditional solutions with a single-stage structure, simplifying the system architecture and reducing size, weight, and cost. Through resonant soft-switching technology, the switching transistors operate under zero-voltage or zero-current conditions, reducing switching losses and achieving high-efficiency energy transfer. Simultaneously, the third switching circuit 51 at the photovoltaic end is dedicated to tracking the maximum power point, while the energy storage end independently controls charging and discharging through a bidirectional circuit. The two power sources converge at the middle tap of transformer 01, ensuring both photovoltaic energy harvesting efficiency and flexible power scheduling and smoothing fluctuations. This effectively solves the problems of complex structure, low efficiency, and control redundancy in traditional photovoltaic-energy storage systems. While achieving a low-cost dual-input system, it significantly expands the system gain range, enabling it to adapt to different photovoltaic and battery voltage levels, improving the flexibility of on-site configuration, and expanding the application scenarios and applicability of the device.

[0066] In one embodiment, such as Figure 2 As shown, the primary-side switching circuit 02 includes a first switching transistor S1 and a second switching transistor S2. The input terminals of the first switching transistor S1 and the second switching transistor S2 are electrically connected to the two ends of the primary winding, respectively. The output terminals of the first switching transistor S1 and the second switching transistor S2 are grounded. The primary-side switching circuit 02 is used to convert the DC signal input from the photovoltaic module and / or energy storage module into an AC signal by alternately turning on the first switching transistor S1 and the second switching transistor S2.

[0067] In this embodiment, the primary-side switching circuit 02 is configured with a first switch S1 and a second switch S2 in a classic push-pull configuration. It efficiently and reliably converts the DC power input from the photovoltaic module and energy storage module into high-frequency AC power for subsequent transmission and conversion via the transformer 01. The first switch S1 and the second switch S2 are typically fully controllable power semiconductor devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated-gate bipolar transistors (IGBTs). They are required to have identical electrical characteristics to ensure the symmetry of the push-pull operation.

[0068] Connection method: The input terminal of the first switching transistor S1 is connected to one end of the primary winding of transformer 01, and the input terminal of the second switching transistor S2 is connected to the other end of the primary winding. The output terminals of both switching transistors are connected to a common ground reference point, providing two alternating paths for current flow. The working principle of the primary-side switching circuit 02 is essentially to chop the DC power supply and drive transformer 01 through the high-frequency, alternating conduction of the two switching transistors. The specific process can be broken down as follows:

[0069] When the control system issues a command to turn on the first switch S1, the second switch S2 remains off. At this time, the positive current from the DC input power supply (from photovoltaic and / or energy storage) flows from the center tap of the primary winding, through the upper half of the winding, through the turned-on first switch S1, and finally back to the negative terminal of the power supply. As the current flows through the upper half of the primary winding, it generates an upward magnetic flux in the transformer 01 core, establishing a magnetic field. It is important to note that there is a preset dead time between the turn-off of the first switch S1 and the turn-on of the second switch S2. During this extremely short period, both switches remain off. The setting of this dead time is crucial to absolutely prevent the two switches from turning on simultaneously due to overlapping control signals, which could lead to a short circuit and catastrophic damage to the devices. However, this application sets the energy of the DC input power supply when the first switch S1 and the second switch S2 are simultaneously turned on through the energy storage device 61 of the energy storage input circuit 06. Therefore, this application does not need to set the simultaneous turn-off time of the two switches, and the duty cycle of the two can be set to be greater than 0.5.

[0070] The control system turns on the second switch S2, while the first switch S1 remains on, entering an overlapping conduction period. After the overlapping conduction period ends, the path of the DC current changes again, still entering from the middle tap of the primary winding, but this time flowing through the lower half of the winding and then returning to ground through the turned-on second switch S2. Since the current direction is opposite to that of the upper half of the primary winding, it generates a downward magnetic flux in the transformer 01 core, opposite to the direction of the magnetic field in the previous stage.

[0071] By continuously and alternately turning on and off the first switch S1 and the second switch S2 at extremely high frequencies, the current flowing through the primary winding of transformer 01 alternates direction continuously, generating a high-frequency AC square wave voltage on the primary side of transformer 01. This alternating voltage applied to transformer 01 induces a corresponding AC electromotive force in the secondary winding. Since the photovoltaic and energy storage inputs share the center tap of the primary winding, this switching circuit naturally becomes the mixing and dispatching center of the two energy sources. By controlling the duty cycle and timing of the two switches, it is possible to flexibly determine which source of energy to draw from and how much energy to draw. Its push-pull operation, in close coordination with the subsequent resonant network 03, provides the necessary circuit operating conditions for achieving zero-voltage turn-on or zero-current turn-off of the switches.

[0072] In one embodiment, the third switching circuit 51 includes a third switching transistor S3. The input terminal of the third switching transistor S3 is electrically connected to the positive terminal of the photovoltaic module, and the output terminal is electrically connected to the center tap of the primary winding of the transformer 01. The negative terminal of the photovoltaic module is grounded. The DC-DC converter also includes a control circuit, which is electrically connected to the control terminals of the first switching transistor S1, the second switching transistor S2, and the third switching transistor S3, and is used to generate and output drive signals. Figure 4 As shown, the drive signal of the third switch S3 is generated based on the drive signals of the first switch S1 and the second switch S2.

[0073] In this embodiment, the third switching circuit 51 is composed of a third switching transistor S3. The input terminal of the third switching transistor S3 is connected to the positive terminal of the photovoltaic module, and its output terminal is connected to the center tap of the primary winding of transformer 01. The negative terminal of the photovoltaic module is grounded. The primary winding of transformer 01 is symmetrically divided into upper and lower parts by the center tap, and the endpoints of these two parts are respectively connected to the first switching transistor S1 and the second switching transistor S2. The first switching transistor S1 and the second switching transistor S2 constitute a typical push-pull circuit, and the direction of the current flowing through the primary winding is controlled by their alternating conduction.

[0074] The DC-DC converter is also equipped with a control circuit, which is connected to the control terminals of the first switch S1, the second switch S2, and the third switch S3, and is responsible for generating and outputting drive signals. Specifically, the drive signal control logic is as follows: Figure 4As shown, Vs represents the output voltage waveform of transformer 01. The control circuit generates two drive signals to control the first switch S1 and the second switch S2, respectively. These two signals are complementary and symmetrical, meaning they are 180 degrees out of phase and both have a duty cycle D greater than 0.5. This means that at any given moment, at least one of the first switch S1 and the second switch S2 is conducting, and there may even be a period of "overlapping time" where both are conducting simultaneously. The drive signal for the third switch S3 is not generated independently, but is obtained by performing a "NAND" logic operation on the drive signals of the first switch S1 and the second switch S2. Within one main switching cycle (frequency fs), the combined states of S1 and S2 will each undergo one change, resulting in two pulses in the drive signal of S3. Therefore, the actual switching frequency of the third switch S3 is twice the main switching frequency fs, i.e., 2fs. This can be understood as the third switch S3 being a time-division multiplexing circuit, effectively doubling the system's regulation frequency without increasing the number of switching operations of the first and second switches S1 and S2.

[0075] It is worth noting that in the description of this application, the duty cycle of the first switch S1 and the second switch S2 is denoted as D, and the duty cycle of the third switch S3 is denoted as d. D and d are two independent variables, and the formulas involved in this application are calculated according to the above-mentioned variable definitions.

[0076] The main switch frequency of this application is fs, and the energy storage element and voltage regulation are equivalent to operating under a 2fs condition. Therefore, it has a frequency doubling effect in terms of both inductor ripple and magnetic component size. While ensuring reduced inductor ripple, improved battery life, and reduced system size, it also reduces the switching loss of the main switch and improves system efficiency. Furthermore, due to the frequency doubling relationship, the actual voltage regulation duty cycle d of the third switch S3 is within the range of [0, 1], i.e., fully adjustable. From the overall effect of the photovoltaic power injection system, within one main cycle T, the total conduction time of the third switch S3 is 2... (d T / 2) =d T, such as Figure 5 As shown, Figure 5 This is the operating waveform when d = 0.5. Therefore, the equivalent duty cycle of the photovoltaic current injection, relative to the dominant frequency fs, is d. The change of d from 0 to 1 is equivalent to the continuous adjustment of the photovoltaic current from complete shutdown to maximum possible injection. The operating point of the photovoltaic module will shift over a wide range with changes in illumination and temperature. The voltage corresponding to the maximum power point (MPP) is... V_mp It can be very high or very low. Continuously adjustable duty cycle d within the range of [0, 1] is the fundamental guarantee for achieving accurate MPPT across the entire operating voltage range.

[0077] Specifically, for the input inductor, the volt-second balance expression is written as follows: V Bat (D -0.5) = ( V Cc -V Bat ) (1-D). Therefore V Cc = V Bat / [2 [(1-D)]; Assuming the period T = Ts / 2, then d = 1 - (1-D) Ts / (Ts / 2) = 1 - 2 (1-D), therefore V Cc = V Bat / (1- d). Among them, V Bat The voltage of the energy storage component. V Cc Let be the capacitor voltage, and D be the duty cycle of the first switch S1. Clearly, d ranges from [0,1]. Therefore, although the main switch operates at frequency fs, the addition of the third switch S3, combined with the existing control algorithm, gives the topology a frequency multiplication effect. That is, without increasing the number of interleaved parallel devices and the main switch losses, the inductor operates in a frequency multiplication state, achieving smaller inductor current ripple and smaller magnetic component size. If the transformer 01 turns ratio is 1:n, then... u tank = n V Cc Combined with fundamental frequency analysis (FHA), the resonant cavity gain is obtained. M LLC ,but V o = M LLC u tank =M LLC n V Bat / [2 (1-D)]. Among them, u tank Where is the input voltage of the resonant cavity, and n is the transformer turns ratio. V o This is the output voltage.

[0078] In one embodiment, the resonant network 03 is an LLC resonant cavity, including a resonant inductor, a resonant capacitor, and a magnetizing inductor. The resonant inductor and the resonant capacitor are connected in series and electrically connected to both ends of the secondary winding of the transformer 01. The magnetizing inductor is connected in parallel to both ends of the secondary winding of the transformer 01. The rectifier circuit 04 includes a rectifier bridge and an output filter capacitor. The input end of the rectifier bridge is electrically connected to the LLC resonant cavity, and the output end is connected in parallel with the output filter capacitor.

[0079] In this embodiment, as Figure 2 As shown, the output side of the device employs a high-performance LLC resonant network 03 and a rectifier circuit 04 to efficiently and smoothly convert the high-frequency AC power from the secondary winding of transformer 01 into the DC power required by the load. The LLC resonant cavity consists of three key passive components. The resonant inductor and resonant capacitor are connected in series in the circuit, while the magnetizing inductor is connected in parallel across the secondary winding of transformer 01. By designing the resonant parameters and operating the switching frequency near the resonant point, the LLC resonant cavity circuit can achieve soft switching across the entire load range, thereby minimizing switching losses. Simultaneously, the LLC topology exhibits extremely high efficiency near the rated operating point and possesses inherent short-circuit protection capabilities, enhancing system reliability and conversion efficiency. The rectifier bridge rectifies the high-frequency sinusoidal AC power output from the LLC resonant cavity into DC power, while the output filter capacitor smooths and filters the rectified voltage, ultimately outputting a stable DC voltage to meet the stringent requirements of the DC grid or load.

[0080] Compared to the traditional push-pull LLC topology, this scheme adds only a third switch S3 and an energy storage device L, successfully achieving dual-input port integration, a wide voltage gain range, and fast dynamic response while maintaining the inherent advantages of LLC. The reuse of the energy storage port capacitor and the photovoltaic input filter capacitor further optimizes the component count. The calculation method is the same as that for traditional LLC resonant cavities. L r / C r / L m Let be the resonant cavity parameters, where L r and C r The resonant frequency is: , L r 、C r and L m The resonant frequency is: .

[0081] Furthermore, to achieve power control across the three ports, the switching frequency fs and the duty cycle D of the switching transistor are used as two control variables, employing a hybrid modulation method of PWM+PFM. The duty cycle D is used to achieve voltage matching and power transfer control between the two primary-side ports, while the switching frequency fs is used to stabilize the output voltage and control the output energy. The hybrid modulation strategy of PWM and PFM balances steady-state accuracy and dynamic response. Pulse frequency modulation, by fine-tuning the switching frequency of the main switching transistor, can change the equivalent impedance of the LLC resonant cavity, thereby adjusting its voltage gain. When load or input changes cause output voltage fluctuations, the control system can quickly pull it back to the set value by changing the frequency. Simultaneously, PFM ensures that the switching frequency always operates within a range that enables soft switching, maintaining the high efficiency foundation of the system. Pulse width modulation, by adjusting the duty cycle of the main switching transistor, can change the voltage at the energy storage battery terminal, thereby flexibly achieving the voltage adaptation required for photovoltaic maximum power point tracking and intelligently scheduling the power distribution between the photovoltaic system and the energy storage battery.

[0082] Traditional pure PFM-LLC systems require a wide range of frequency adjustments to respond to drastic load changes, resulting in relatively slow response times. In this design, PWM regulation provides a faster intrinsic power regulation mechanism. When the load changes abruptly, the energy level delivered to transformer 01 can be immediately altered by rapidly adjusting the duty cycle. Working in conjunction with the PFM, this significantly accelerates the system's dynamic response.

[0083] Specifically, refer to Figures 7-9 , Figure 7 This is a simulation waveform diagram when d = 0.5 and fs = 100k. Figure 8 This is a simulation waveform diagram when d < 0.5 and fs = 100k. Figure 9 The simulation waveforms are shown when d = 0.5 and fs = 80kHz. When the switching frequency fs is kept constant while the duty cycle d is adjusted, the photovoltaic port voltage changes accordingly, demonstrating the precise control capability of d over the photovoltaic operating point and power distribution. The voltage gain change is consistent with the theoretical analysis. When the duty cycle d is kept constant while the switching frequency fs is adjusted, the DC output voltage changes accordingly, demonstrating the independent control effect of fs on output voltage regulation. The voltage gain change also conforms to the LLC resonance theory. The driving waveforms of the switching devices clearly show that they achieve zero-voltage turn-on and zero-current or zero-voltage turn-off, verifying the effectiveness of soft switching. Furthermore, the secondary inductor current exhibits frequency doubling characteristics. At the same switching frequency, doubling the fundamental current means that the size of the magnetic components can be significantly reduced, and the power density can be improved. Simultaneously, thanks to the inherent characteristics and optimized design of the LLC resonance converter, the energy storage battery port exhibits a smooth inductor current waveform. The smaller ripple characteristics greatly reduce internal battery losses and heat generation, which is beneficial for extending battery life and improving charge and discharge efficiency.

[0084] In summary, this control strategy based on hybrid modulation of PWM and PFM enables precise execution of photovoltaic MPPT, intelligent scheduling of energy storage charging and discharging, rapid stabilization of output voltage, and high-efficiency operation with full-range soft switching, demonstrating the comprehensive advantages of this integrated push-pull resonant converter in terms of performance, efficiency, and reliability.

[0085] In one embodiment, the energy storage device 61 of the energy storage input circuit 06 is an energy storage inductor. The energy storage inductor is used to absorb the power output by the energy storage component when the first switch S1 and the second switch S2 are turned on simultaneously; and to release energy to the push-pull resonant circuit when the first switch S1 and the third switch S3 are turned on simultaneously, or when the second switch S2 and the third switch S3 are turned on simultaneously.

[0086] In this embodiment, the energy storage device 61 of the energy storage input circuit 06 is an energy storage inductor. When the first switch S1 and the second switch S2 are simultaneously turned on according to the drive signal, the voltage across the energy storage component is directly applied to the two ends of the energy storage inductor. When the switching state is switched to the first switch S1 and the third switch S3 being turned on, or the second switch S2 and the third switch S3 being turned on, the circuit topology changes. At this time, the energy storage inductor is no longer directly connected back to the negative terminal of the battery, but its positive terminal is connected to the center tap of the primary winding of the transformer 01 through the turned-on S3. Since the inductor current needs to remain continuous, the previously stored magnetic energy begins to be released, and the inductor current decreases linearly. This released current merges with the current input from the photovoltaic module at the center tap and is injected together into the primary side of the push-pull transformer 01, and finally transmitted to the output terminal.

[0087] Energy storage inductors naturally regulate the voltage at the energy storage battery terminals through their volt-second balance principle. By controlling the duration of simultaneous conduction of S1 / S2, the average current of the energy storage inductor can be precisely controlled, thereby determining the amount of power drawn from the battery terminals and achieving power distribution and voltage matching between the photovoltaic and energy storage input ports. The energy stored in the inductor can be considered a rapid energy buffer. When the system load requires instantaneous high power, the energy storage inductor can quickly release its stored energy to replenish it, complementing the photovoltaic input and thus improving the overall system's dynamic response to sudden load changes.

[0088] In one embodiment, such as Figure 3 As shown, the photovoltaic input circuit 05 also includes: a reverse-current protection diode 52, the anode of which is connected to the positive terminal of the photovoltaic module, and the cathode of which is electrically connected to the center tap of the primary winding of the transformer 01 via the third switch S3; and an input filter capacitor, which is connected in parallel across the two ends of the photovoltaic module to filter out the high-frequency ripple of the photovoltaic input circuit 05 and to provide energy buffer for the push-pull resonant circuit.

[0089] In this embodiment, the photovoltaic input circuit 05 integrates two components: an anti-reverse current diode 52 and an input filter capacitor. Under normal sunlight conditions, the photovoltaic module generates electricity, and current flows out from the positive terminal of the module, passing through the anti-reverse current diode 52 and being injected into the converter. At this time, the diode is in a forward biased conducting state, and the voltage drop is very small. However, at night, on cloudy days, or when the photovoltaic panel is shaded, or under conditions of no or weak sunlight, the photovoltaic module itself cannot generate electricity, and its output voltage may be lower than the internal voltage of the system. Without this diode, energy from the energy storage battery or the load side may flow backward into the photovoltaic panel through the circuit. This reverse current not only wastes energy, but more seriously, it may cause irreversible hot spot effects and other damage to the photovoltaic cells, greatly shortening their lifespan.

[0090] The anti-reverse current diode 52, through its unidirectional conductivity, allows current to flow only from the photovoltaic module to the system interior, while blocking any possibility of reverse flow. This, combined with software protections in the control algorithm such as duty cycle limiting, forms a dual protection mechanism integrating hardware and software, greatly improving the system's robustness and security.

[0091] The switching transistors in this device, especially the third switching transistor S3 operating at a frequency multiplier, result in a current drawn from the photovoltaic side containing abundant high-frequency harmonics during high-frequency switching. This large-capacity input filter capacitor, connected in parallel across the photovoltaic module, provides a low-impedance bypass path for these high-frequency ripple currents, preventing them from flowing entirely through the photovoltaic module itself. This effectively smooths the operating current of the photovoltaic panel, making it closer to pure DC. This not only helps in more accurate maximum power point tracking but also reduces potential stress on the photovoltaic panel caused by current ripple. Furthermore, the capacitor can rapidly discharge to replenish energy when the switching transistor is on and the system requires a large instantaneous current; when demand decreases, it can be charged to store energy. This rapid charging and discharging process smooths the instantaneous fluctuations in the photovoltaic module's output power, providing a voltage-stable and responsive energy source for the subsequent push-pull resonant circuit, ensuring the continuity and stability of energy transmission.

[0092] In one embodiment, the DC-DC converter includes:

[0093] Multiple photovoltaic input circuits 05; and / or multiple energy storage input circuits 06; and / or, the first end of the energy storage device 61 is connected to multiple energy storage components.

[0094] This application implies that the proposed DC-DC converter possesses strong scalability. The device can integrate multiple photovoltaic input circuits 05, simultaneously connecting multiple photovoltaic arrays of different specifications to achieve centralized convergence and maximum power point tracking of multiple photovoltaic energy sources, thereby improving the deployment flexibility and total power generation of the photovoltaic system. The device also supports the integration of multiple energy storage input circuits 06, or the connection of multiple energy storage components, allowing the system to connect multiple battery packs or different types of energy storage devices 61. This enhances the system's energy dispatch capability and reliability, allowing for flexible configuration of energy storage scale as needed, and enabling group management and redundancy backup of energy storage units. Furthermore, this modular and scalable architecture allows the converter to easily adapt to application scenarios of varying scales, from residential energy storage and communication base stations to large-scale photovoltaic-energy storage power stations.

[0095] In summary, this application achieves integrated energy flow paths between photovoltaic (PV), battery, and DC loads through a highly integrated single topology. PV power can be prioritized for the load, with excess power stored in the battery; when PV power is insufficient, battery energy can seamlessly supplement the load. This flexible scheduling is accomplished in real-time within a single topology using an advanced hybrid modulation strategy, achieving true high-efficiency "source-load-storage" coordination. Through efficient internal energy scheduling, the system can maximize the local absorption of PV power generation, reducing dependence on and impact on the upper-level power grid, thereby improving the utilization efficiency of new energy sources.

[0096] Furthermore, as mentioned earlier, complex functions are achieved with only a few additional components, resulting in a simple topology and fewer main power devices. This not only reduces hardware costs but also means fewer points of failure and higher system reliability. Reliable electrical isolation, achieved through transformer 01, ensures the safety of equipment and personnel. Soft-switching characteristics across the entire load range are key to ensuring efficient operation. Reduced switching losses allow the system to operate at high frequencies while achieving extremely high peak efficiency and high performance across a wide load range. A wide voltage gain range is another major highlight of this device. It can easily adapt to photovoltaic modules with different output voltage levels and also allows batteries to operate normally over a wider voltage range. This provides system integrators with significant configuration flexibility, allowing them to flexibly select the models and combinations of photovoltaic panels and batteries based on actual resource conditions and cost considerations, thus broadening the product's applicability.

[0097] Furthermore, this application also proposes a control method for a DC-DC converter, implemented based on the DC-DC converter described above, such as... Figure 10 As shown, the method includes:

[0098] S100: Generates a set of complementary drive signals to control the first switch S1 and the second switch S2 of the primary-side switching circuit to conduct alternately.

[0099] S200: Based on the drive signal of the first switch S1 and the drive signal of the second switch S2, a drive signal for the third switch circuit is generated to control the conduction and disconnection of the third switch S3 of the third switch circuit.

[0100] S300: By adjusting the duty cycle of the drive signals of the first switch S1 and the second switch S2, the output power of the photovoltaic module is adjusted so that the output power of the photovoltaic module is maintained at the corresponding maximum power point.

[0101] S400: The output voltage of the DC-DC converter is stabilized by adjusting the switching frequency of the first switch S1 and the second switch S2.

[0102] This can be understood as follows: In step S100, the controller generates a set of complementary drive signals with dead time, which control the first switch S1 and the second switch S2 of the primary-side push-pull circuit to conduct alternately. This establishes the basic operating frequency fs and timing reference for the entire system. In step S200, the drive signal for the third switch S3 is synthesized from the drive signals of the first switch S1 and the second switch S2 through a logical AND-NOT relationship.

[0103] Step S300 manages energy distribution by adjusting the duty cycle D of the drive signals of the first switch S1 and the second switch S2. The duty cycle directly determines the ratio of the charging time to the releasing time of the energy storage inductor, thereby precisely regulating the power drawn from the energy storage port. The control system samples the voltage and current of the photovoltaic module, calculates its output power in real time, and dynamically adjusts the duty cycle to ensure that the photovoltaic module always operates at its maximum power point (MPPT). Experimental and theoretical analysis show that, with a fixed switching frequency fs, adjusting the duty cycle can effectively and linearly regulate the operating voltage and power on the photovoltaic side, achieving flexible power scheduling.

[0104] Step S400 stabilizes the output voltage by fine-tuning the switching frequencies fs of the first switch S1 and the second switch S2. This method utilizes the voltage gain characteristics of the LLC resonant network: near the rated load, fine-tuning the frequency can smoothly adjust the voltage gain. With the duty cycle D remaining constant, i.e., the power distribution relationship between photovoltaic and energy storage is fixed, adjusting the switching frequency can effectively stabilize the output voltage at the target value, and the gain change is highly consistent with the theoretical derivation.

[0105] This application combines control timing to ensure that all switching transistors can achieve soft switching (ZVS or ZCS) over a wide load range, reducing switching losses and improving efficiency. Simultaneously, the inherent frequency doubling effect means that the inductor current ripple frequency is doubled at the same main switching frequency. This not only allows for the use of smaller magnetic components, contributing to high power density, but also results in lower current ripple flowing into / out of the battery, which is more beneficial to battery life. A hybrid PWM and PFM modulation strategy is employed, with the duty cycle dedicated to fast power dispatch and the switching frequency responsible for precise voltage regulation. Utilizing the fast response of duty cycle adjustment, the slow dynamic response of traditional LLC converters relying solely on frequency-based voltage regulation can be effectively compensated for. It can rapidly adjust the transmitted power during load changes, and combined with fine calibration using frequency-based voltage regulation, a perfect balance between dynamic response and steady-state accuracy is achieved. By coordinating and controlling the duty cycle and frequency, the device can intelligently and seamlessly switch between multiple operating modes, including: pure battery power supply mode SISO1, pure photovoltaic power supply mode SISO2, photovoltaic-storage combined power supply mode DISO, and photovoltaic simultaneous power supply and charging mode SIDO, comprehensively covering all typical operating scenarios of photovoltaic-storage systems.

[0106] In one embodiment of the control method, it further includes:

[0107] The voltages of the energy storage module and the photovoltaic module are collected; based on the voltages of the energy storage module and the photovoltaic module, the upper limit of the duty cycle of the third switching circuit is calculated, and the actual duty cycle of the third switching tube S3 is controlled to work within the upper limit threshold in order to manage the distribution of photovoltaic power and energy storage power.

[0108] like Figure 6 As shown, the control method in this embodiment is used to calculate and limit the upper limit of the duty cycle of the third switch S3 in real time. Specifically, the control system continuously collects the voltage of the energy storage component. V Bat and the voltage of photovoltaic modules V pv Based on these two key parameters, the algorithm dynamically calculates a safe upper limit for the duty cycle, d, in real time. max The core logic behind this upper limit is to ensure that under any operating condition, the voltage relationship in the circuit will not cause current to flow backward into the photovoltaic module. This is achieved by strictly limiting the actual duty cycle of the third switch S3 to d. max Within this system, the control system proactively and preventively cuts off the circuit conditions for photovoltaic backfeeding at the software level. When the third switch S3 is turned on, the photovoltaic port voltage... V pv With capacitor voltage V Cc Direct comparison. From the circuit topology and the volt-second balance relationship, it can be seen that... V Cc With battery voltageV Bat And the duty cycle D satisfies: V Cc = V Bat / [2 (1-D)]. Therefore, to prevent backflow, the following must be met. V Bat / [2 (1-D)] ≤ V pv Therefore, the safe upper limit of the main switch duty cycle D can be derived. D max for: D max =1 V Bat / 2 V pv .

[0109] And d = 1 - (1 - D) Ts / (Ts / 2) = 1 - 2 (1-D), therefore, we get d max =1 V Bat / V pv The control system samples the battery voltage in real time. V Bat With photovoltaic voltage V pv Calculate the current allowed upper limit of S3 duty cycle based on the above formula. d max During PWM modulation, regardless of the value of the duty cycle instruction d output by the MPPT algorithm or other control logic, the final executed duty cycle d must satisfy d ≤ d max This method ensures the unidirectionality of the photovoltaic input channel at the control algorithm level, forming a dual hardware and software protection system together with the anti-reverse diode in the hardware.

[0110] This software protection measure, together with the essential anti-reverse-current diode at the photovoltaic input end—a hardware barrier—forms a dual protection mechanism combining software and hardware. The software limiting acts as the first line of active defense, intervening before abnormal situations occur; the hardware diode serves as the final physical safety net. This enhances the system's robustness and security, effectively protecting valuable photovoltaic assets.

[0111] In addition, this application also proposes a photovoltaic-energy storage system, including the DC-DC converter as described above, as well as photovoltaic modules and energy storage modules.

[0112] This application can be understood as constructing a complete photovoltaic-storage system. This system uses the DC-DC converter described in this invention as its core hub, organically integrating photovoltaic modules and energy storage modules to form a collaborative whole. The photovoltaic modules convert solar energy into DC power, and their output voltage and power vary drastically with sunlight and temperature. The energy storage modules are responsible for time-shifting energy, storing energy when photovoltaic power generation is excessive and releasing energy when power generation is insufficient or at night, ensuring the continuity of power supply to the load. The DC-DC converter intelligently schedules the flow and volume between photovoltaic power and energy storage power according to real-time operating conditions, ensuring that the photovoltaic modules always generate power at maximum efficiency and converting the changing input voltage into a stable and controllable DC output voltage to supply the load or invert it into AC power.

[0113] By placing the DC-DC converter of this invention within a photovoltaic-storage system, all its aforementioned technical advantages are translated into system-level benefits. Thanks to soft-switching technology and an efficient hybrid modulation strategy, losses in energy conversion and transfer between photovoltaic, storage, and load are minimized, improving the overall system's power generation revenue and operational economy. The device's simple topology reduces potential failure points, while dual hardware and software anti-backflow protection mechanisms ensure the long-term safe operation of the two core assets—the photovoltaic panels and the batteries—under complex operating conditions. The device's wide voltage gain range allows system designers greater flexibility in selecting photovoltaic panels and batteries of different specifications, easily adapting to various application scenarios and reducing the difficulty and constraints of system integration.

[0114] In addition, the system can automatically and smoothly switch between multiple working modes to achieve efficient coordination of source-grid-load-storage, maximize the utilization of solar energy, and improve the capacity for new energy consumption.

[0115] The above description is only a part of the embodiments of this application and does not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. A DC conversion device, characterized by comprising: include: The push-pull resonant circuit includes a transformer, a primary-side switching circuit electrically connected to the primary winding of the transformer, and a resonant network and rectifier circuit electrically connected to the secondary winding of the transformer; the primary-side switching circuit includes a first switching transistor and a second switching transistor; the primary-side switching circuit is used to convert the DC signal input to the photovoltaic module and the energy storage module into an AC signal; The photovoltaic input circuit includes a third switching circuit, which includes a third switching transistor. The input terminal of the third switching transistor is electrically connected to the positive terminal of the photovoltaic module, and the output terminal is electrically connected to the center tap of the primary winding of the transformer. The negative terminal of the photovoltaic module is grounded. An energy storage input circuit includes an energy storage device, a first end of which is used to connect to an energy storage module, and a second end of which is electrically connected to the center tap of the primary winding of the transformer. The photovoltaic input circuit and the energy storage input circuit converge at the center tap to transfer energy to the secondary winding through the alternating conduction of the first and second switching transistors. The third switch is used to adjust the output power of the photovoltaic module so that the output power of the photovoltaic module is maintained at the corresponding maximum power point; the drive signal of the third switch is generated based on the drive signals of the first switch and the second switch so that the operating frequency of the third switch is twice the operating frequency of the first switch.

2. The DC conversion device according to claim 1, wherein The input terminals of the first and second switching transistors are electrically connected to the two ends of the primary winding, respectively, and the output terminals of the first and second switching transistors are grounded.

3. The DC-DC converter as described in claim 2, characterized in that, The DC-DC converter also includes a control circuit, which is electrically connected to the control terminals of the first, second, and third switching transistors and is used to generate and output drive signals.

4. The DC conversion device according to claim 3, wherein The energy storage device in the energy storage input circuit is an energy storage inductor, which is used to absorb the power output by the energy storage component when the first switch and the second switch are turned on simultaneously. In addition, it is used to release energy to the push-pull resonant circuit when the first switch and the third switch are turned on simultaneously, or when the second switch and the third switch are turned on simultaneously.

5. The DC conversion device of claim 3, wherein The photovoltaic input circuit also includes: The anti-reverse-feedback diode has its anode connected to the positive terminal of the photovoltaic module, and its cathode electrically connected to the center tap of the primary winding of the transformer via the third switching transistor.

6. The DC conversion device of claim 2, wherein The photovoltaic input circuit also includes: An input filter capacitor is connected in parallel across the two ends of the photovoltaic module to filter out high-frequency ripple in the photovoltaic input circuit and to provide energy buffer for the push-pull resonant circuit.

7. The DC conversion device according to any one of claims 1 to 6, wherein The DC-DC converter includes: Multiple photovoltaic input circuits; And / or, multiple energy storage input circuits; And / or, the first end of the energy storage device is connected to multiple energy storage components.

8. A control method for a DC-DC converter, characterized in that, Based on the DC-DC converter as described in any one of claims 1-7, the method includes: A set of complementary drive signals is generated to control the first and second switching transistors of the primary-side switching circuit to conduct alternately. The driving signal of the third switching circuit is generated based on the driving signal of the first switching transistor and the driving signal of the second switching transistor to control the conduction and disconnection of the third switching transistor of the third switching circuit. By adjusting the duty cycle of the drive signals of the first and second switching transistors, the output power of the photovoltaic module is adjusted so that the output power of the photovoltaic module is maintained at the corresponding maximum power point. The output voltage of the DC-DC converter is stabilized by adjusting the switching frequencies of the first and second switching transistors.

9. The control method for the DC-DC converter as described in claim 8, characterized in that, Also includes: The voltages of the energy storage module and the photovoltaic module are collected; Based on the voltage of the energy storage component and the photovoltaic component, the duty cycle of the third switching transistor is adjusted to regulate the distribution of photovoltaic power and energy storage power.

10. A photovoltaic energy storage system, characterized in that, It includes the DC-DC converter as described in any one of claims 1 to 7, as well as photovoltaic modules and energy storage modules.

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