A resonant three-port dc converter topology and its fixed-frequency pwm modulation method

Abstract

The application provides a resonant three-port DC converter topology suitable for a light storage system and a fixed-frequency PWM modulation method thereof, and the three-port DC converter topology comprises a photovoltaic port V pv , a battery port V bat , a load port V o , a first filter capacitor C 1, an input half-bridge, an output half-bridge and a first DC inductor L 1, a first resonant capacitor C r , a first coupled inductor, wherein the input half-bridge comprises a first switch tube S 1, a second switch tube S 2, a second filter capacitor C 2 and a third filter capacitor C 3, the output half-bridge comprises a third switch tube S 3, a fourth switch tube S 4, a fourth filter capacitor C 4 and a fifth filter capacitor C 5, by adopting the double active half-bridge structure and the coupled inductor, the number of switch tubes and magnetic elements is reduced while ensuring electrical isolation between the load and the photovoltaic / battery, the device cost is reduced and the device power density is improved, flexible energy management between the ports is realized under the single-stage structure and the fixed switching frequency, and full-range soft switching is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic devices, and in particular to a resonant three-port DC converter topology suitable for a photovoltaic storage system and a fixed-frequency PWM modulation method thereof. Background Art

[0002] Renewable energy, with its clean and renewable advantages, is gradually replacing traditional power generation methods, typically thermal power. In photovoltaic energy storage systems, the output of photovoltaic arrays is susceptible to environmental factors such as sunlight, necessitating the inclusion of energy storage units to ensure continuous and stable power supply to the load. DC converters, which control energy flow and regulate loads, are a crucial component of photovoltaic energy storage systems. Traditional solutions use multiple two-port converters to achieve energy control between the photovoltaic array, battery, and load, but this presents challenges with multi-stage energy conversion and decentralized control. To improve system efficiency, three-port DC converters, which enable single-stage energy conversion, are widely used. Three-port converters can be categorized by isolation type: non-isolated, fully isolated, and partially isolated. Non-isolated three-port converters offer a simple structure and a small number of components, but are only suitable for applications where the voltage levels of the ports are similar. Fully isolated three-port converters achieve electrical isolation between all ports, but require a large number of components and complex transformer design. Partially isolated three-port converters combine the advantages of fewer components and load isolation, making them a preferred choice for photovoltaic energy storage systems. Among existing partially isolated three-port converters, the topology based on the forward circuit is simple but difficult to achieve soft switching of all switches; the topology based on two-phase interleaved boost and dual active DC converter has soft switching capability but has the problem of a large number of switches and magnetic components; the topology based on the resonant converter also has the problem of a large number of magnetic components or switches, and it is difficult to meet the requirements of the photovoltaic storage system for a wide voltage gain range under frequency modulation.

[0003] After searching, the invention patent with Chinese patent publication number CN117458883A proposes a photovoltaic storage type CLLC resonant three-port DC-DC converter, which belongs to the field of power electronic converters in hybrid energy storage systems, especially a photovoltaic storage type CLLC resonant three-port DC-DC converter. The converter consists of three parts: a primary circuit, a secondary circuit, and a transformer plus a CLLC resonant network. The primary circuit and the secondary circuit are integrated with a dual-path staggered parallel bidirectional Buck-Boost circuit and a dual active bridge. The present invention forms a three-port DC-DC converter by integrating a dual-path staggered parallel bidirectional Buck-Boost circuit with a dual active bridge, realizing switch tube reuse, effectively reducing the number of switch tubes, reducing converter cost, and improving system power density. The CLLC resonant network, the first inductor L1, and the second inductor L2 of the present invention enable the eight switch tubes of the DC-DC converter to achieve soft switching, thereby reducing the switching loss of the converter.

[0004] The present application is compared with the above-mentioned patent as follows:

[0005] A transformer in a light storage CLLC resonant three-port DC-DC converter is integrated with a two-phase interleaved bidirectional Buck-Boost circuit and a full-bridge CLLC resonant converter, containing five magnetic elements (two DC inductors, two resonant inductors, and one transformer) and eight switching tubes; the transformer of the present patent is integrated with a single-phase bidirectional Buck-Boost circuit and a half-bridge LLC resonant converter, containing two magnetic elements and four switching tubes, with fewer devices. The two have essential differences in the design idea of integrating topological devices.

[0006] A transformer in a light storage CLLC resonant three-port DC-DC converter adopts a duty cycle + phase shift control method, and the specific details are not elaborated; the transformer of the present patent adopts a fixed-frequency PWM control method, and the switching frequency of the transformer is equal to the resonant frequency. The maximum power tracking of photovoltaic or the overcharge protection of the battery is achieved by adjusting the duty cycle of the primary side switching tube, and the output voltage control is achieved by adjusting the duty cycle of the secondary side switching tube. Under this method, the voltage gain and port power of the transformer are decoupled. The two have essential differences in the design idea of the control method.

[0007] After searching, the invention patent with Chinese patent publication number CN118074533A proposes a LCC type current-fed three-port light storage hydrogen production DC converter and control method, wherein the converter includes a first port DC input capacitor, a second port interleaved parallel input inductor, an inverter full-bridge, an LCC resonant cavity, a high-frequency isolation transformer, a diode uncontrolled rectification full-bridge, and a third port DC output inductor; the converter adopts a variable duty cycle and variable frequency composite control method, which adjusts the input voltage of the first port or the input voltage of the second port by changing the duty cycle, and adjusts the output voltage or output current of the third port by changing the switching frequency. The present invention uses a three-port DC converter to integrate energy storage for new energy electrolysis hydrogen production. The energy storage can effectively smooth the power fluctuation of photovoltaic and other new energy sources, improve the dynamic adaptability and operation reliability of the electrolysis hydrogen production system; at the same time, the three-port topology can reduce the number of power electronic devices used and the power conversion links, thereby reducing the cost and volume of the converter and improving the conversion efficiency.

[0008] The present application is compared with the above-mentioned patent as follows:

[0009] The output port of the converter in the LCC type current feeding three-port optical storage hydrogen production DC converter and control method is a unidirectional port, a two-phase staggered bidirectional Buck-Boost circuit and a unidirectional full-bridge LCC resonant converter are integrated, and the converter comprises four magnetic elements (two direct-current inductors, a resonant inductor and a transformer), four switching tubes and four rectifier diodes; the output port of the converter in the patent is a bidirectional port, a single-phase bidirectional Buck-Boost circuit and a half-bridge LLC resonant converter are integrated, and only two magnetic elements and four switching tubes are included, the number of devices is smaller, and the working principle of the LLC converter is different from that of the LCC type converter. There are essential differences between the two in the design idea of the converter topology.

[0010] The converter in the LCC type current feeding three-port optical storage hydrogen production DC converter and control method adopts PWM + frequency modulation control, the original side two ports are controlled by adjusting the duty cycle of the original side switching tube, the output port of the secondary side is controlled by adjusting the switching frequency, and there are problems of complex magnetic element design and limited voltage regulation range under frequency modulation control; the converter in the patent adopts a fixed-frequency PWM control method, the switching frequency of the converter is equal to the resonant frequency, the maximum power tracking of photovoltaic or the overcharge protection of the battery is realized by adjusting the duty cycle of the original side switching tube, the output voltage control is realized by adjusting the duty cycle of the secondary side switching tube, and the converter can realize wide voltage gain under the fixed switching frequency. There are essential differences between the two in the design idea of the control method. SUMMARY

[0011] The present application provides a resonant three-port DC converter topology suitable for optical storage systems and a fixed-frequency PWM modulation method, which aims to reduce the number of switching tubes and magnetic elements, reduce device cost and improve device power density, realize flexible energy management between ports in a single-stage structure and fixed switching frequency, and realize full-range soft switching.

[0012] To achieve the above object, the technical scheme adopted by the present application is:

[0013] A resonant three-port DC converter topology, characterized in that it comprises a photovoltaic port V pv , a battery port V bat , a load port V o , a first filter capacitor C1, an input half-bridge, an output half-bridge, a first direct-current inductor L1, a first resonant capacitor C r , a first coupled inductor,

[0014] The input half-bridge includes a first switch tube S1, a second switch tube S2, a second filter capacitor C2, and a third filter capacitor C3. The source of the first switch tube S1 is connected to the drain of the second switch tube S2 to form a first switch bridge arm, the negative electrode of the second filter capacitor C2 is connected to the positive electrode of the third filter capacitor C3 to form a first filter capacitor bridge arm, the drain of the first switch tube S1 is connected to the positive electrode of the second filter capacitor C2, and the source of the second switch tube S2 is connected to the negative electrode of the third filter capacitor C3.

[0015] The source of the first switch tube S1 is the midpoint A of the first switch bridge arm, and the cathode of the second filter capacitor C2 is the midpoint B of the first filter capacitor bridge arm;

[0016] The output half-bridge includes a third switch tube S3, a fourth switch tube S4, a fourth filter capacitor C4, and a fifth filter capacitor C5. The source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 to form a second switch bridge arm, the negative electrode of the fourth filter capacitor C4 is connected to the positive electrode of the fifth filter capacitor C5 to form a second filter capacitor bridge arm, the drain of the third switch tube S3 is connected to the positive electrode of the fourth filter capacitor C4, and the source of the fourth switch tube S4 is connected to the negative electrode of the fifth filter capacitor C5.

[0017] The source of the third switch tube S3 is the midpoint C of the second switch bridge arm, and the cathode of the fourth filter capacitor C4 is the midpoint D of the second filter capacitor bridge arm;

[0018] The photovoltaic port V pv The positive and negative electrodes are connected to the positive and negative electrodes of the third filter capacitor C3 respectively, and the battery port V bat The positive electrode of the battery is connected to the drain of the first switch tube S1 and the positive electrode of the second filter capacitor C2. bat The negative electrode of the second switch tube S2 and the source of the photovoltaic port V pv The negative connection of the load port V o The positive electrode of is connected to the drain of the third switch tube S3 and the positive electrode of the fourth filter capacitor C4, and the load port V o The negative electrode of the first resonant capacitor C is connected to the source of the fourth switch tube S4 and the negative electrode of the fifth filter capacitor C5; the two ends of the first DC inductor L1 are respectively connected to the midpoint A of the first switch bridge arm and the midpoint B of the first filter capacitor bridge arm, and the first resonant capacitor C r One side is connected to the midpoint A of the first switch bridge arm, and the other side is connected to the positive electrode of the primary side of the first coupling inductor, the negative electrode of the primary side of the first coupling inductor is connected to the midpoint B of the first filter capacitor bridge arm, and the positive and negative electrodes of the first coupling inductor are respectively connected to the midpoint C of the second switch bridge arm and the midpoint D of the second filter capacitor bridge arm.

[0019] The voltage between the first switch bridge arm midpoint A and the first filter capacitor bridge arm midpoint B is a transformer primary side bridge arm midpoint voltage v AB ; the voltage between the second switch bridge arm midpoint C and the second filter capacitor bridge arm midpoint D is a transformer secondary side bridge arm midpoint voltage v CD .

[0020] As a preferred technical solution of the present application: the first filter capacitor C1, the second filter capacitor C2, the third filter capacitor C3, the fourth filter capacitor C4 and the fifth filter capacitor C5 are used to filter high-frequency components in the photovoltaic port V pv , the battery port V bat , the load port V o current.

[0021] As a preferred technical solution of the present application: the first resonant capacitor C r is used to constitute a resonant network with the first coupled inductor to transfer energy;

[0022] The first direct current inductor L1 is used to transfer energy and assist the first switch tube and the second switch tube to realize soft switching;

[0023] The first coupled inductor is used to realize electrical isolation, voltage conversion and constitute a resonant network.

[0024] As a preferred technical solution of the present application: the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 in the first switch bridge arm and the second switch bridge arm all adopt power transistors with anti-parallel diodes and drain-source parasitic capacitances.

[0025] In the above structure: the present application is provided with an input half-bridge and an output half-bridge, wherein the input half-bridge includes a first switch tube, a second switch tube, a second filter capacitor and a third filter capacitor, the first switch tube S1 and the second switch tube S2 in the first switch bridge arm in the input half-bridge are complementary on, when the first switch tube S1 is on, the voltage applied to the first direct current inductor L1 is equal to V pv , when the second switch tube S2 is on, the voltage applied to the first direct current inductor L1 is equal to V pv -V bat According to the volt-second balance principle, it can be concluded that the voltage gain from the photovoltaic port V pv to the battery port V bat is 1 / D p , therefore, by adjusting the duty cycle D p of the switch tube S1, the voltage gain from the photovoltaic port V pv to the battery port V bat is adjusted, so as to realize the MPPT of photovoltaic or the overcharge protection of battery.

[0026] The output half-bridge includes a third switch tube, a fourth switch tube, a fourth filter capacitor and a fifth filter capacitor. The third switch tube S3 and the fourth switch tube S4 in the output half-bridge are complementary turned on. When the third switch tube S3 is turned on, the midpoint voltage v CD =Equal to the voltage on the fourth filter capacitor C4. When the fourth switch S4 is turned on, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD Equal to the negative value of the voltage on the fifth filter capacitor C5, by adjusting the duty cycle D of the third switch tube S3 s Adjust the resonant cavity port voltage v CD The waveform of the photovoltaic port V can be deduced by fundamental wave analysis. pv To the load port V o The voltage gain is sin(πD p ) / [D p sin(πD s )], so the output voltage is regulated by controlling the duty cycle of the third switch tube D s accomplish.

[0027] Therefore, by adjusting the phase shift angle between the first switch S1 and the third switch S3 to be equal to (D p -D s ) / 2 to maintain the transformer primary and secondary side bridge midpoint voltage v AB and v CD The central symmetry enables the fundamental voltage synchronization of the ports on both sides of the resonant cavity to match, thus achieving decoupling of voltage gain and transmission power.

[0028] A 500W converter prototype was constructed with a PV port voltage of 60V to 120V, a battery port voltage of 160V to 200V, and an output voltage of 400V. All switching elements in the switching network used power MOSFETs with anti-parallel diodes and drain-source parasitic capacitance. The main circuit drive signal was generated by a TI TMS320F28335 digital signal processor. Under these experimental conditions, the prototype resonant three-port DC / DC converter for a photovoltaic storage system operated normally under fixed-frequency PWM modulation under various operating conditions.

[0029] The present invention reduces the number of switching tubes and magnetic components in the converter by adopting a dual active half-bridge structure and coupled inductors, thereby reducing device costs and device size; adopts fixed-frequency PWM modulation and realizes flexible energy management through two-degree-of-freedom PWM control; the converter can achieve a wide voltage gain at a fixed switching frequency, meeting the voltage gain requirements in the context of photovoltaic storage applications; all switching tubes can achieve full-range soft switching, reducing switching losses and facilitating efficiency improvement; the converter has consistent driving logic in all power transmission modes, which can achieve smooth switching between modes.

[0030] A fixed-frequency PWM modulation method, characterized in that it includes the following steps:

[0031] S1. Implementation of overcharge protection:

[0032] S11, the first switch tube S1 and the second switch tube S2 in the first switch bridge arm are complementary turned on, and the first switch tube S1 is turned on. At this time, the voltage applied to both ends of the first DC inductor L1 is equal to V pv , turn on the second switch tube S2, at this time, the voltage applied to both ends of the first DC inductor L1 is equal to V pv -V bat ,

[0033] S12, according to the volt-second balance principle, the photovoltaic port V pv To the battery port V bat The voltage gain is 1 / D p ,

[0034] S13, by adjusting the duty cycle D of the switch tube S1 p To adjust the photovoltaic port V pv To the battery port V bat Voltage gain to achieve MPPT of photovoltaic or overcharge protection of battery;

[0035] S2. Implementation of output voltage regulation:

[0036] S21, the third switch tube S3 and the fourth switch tube S4 are complementary turned on, and the third switch tube S3 is turned on. At this time, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD = is equal to the voltage on the fourth filter capacitor C4, turning on the fourth switch S4. At this time, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD is equal to the negative value of the voltage on the fifth filter capacitor C5,

[0037] S22, by adjusting the duty cycle D of the third switch tube S3 s Adjust the resonant cavity port voltage v CD The waveform,

[0038] S23, through the fundamental wave analysis method, the photovoltaic port V pv To the load port V o The voltage gain is: sin(πD p ) / [D p sin(πD s )],

[0039] S24, by controlling the duty cycle D of the third switch tube s Realize output voltage regulation;

[0040] S3, port decoupling control:

[0041] S31, by adjusting the phase shift angle between the first switch S1 and the third switch tube S3 to be equal to (Dp-Ds) / 2 to maintain the transformer primary and secondary side bridge arm midpoint voltage v AB and v CD Central symmetry,

[0042] S32. Match the fundamental synchronous voltage of the port voltages on both sides of the resonant cavity to achieve decoupling of voltage gain and transmission power.

[0043] In the above method: the first switch tube S1 and the second switch tube S2 are complementary turned on, and there is a dead zone between the drive signals to prevent a direct short circuit; the third switch tube S3 and the fourth switch tube S4 are complementary turned on, and there is a dead zone between the drive signals to prevent a direct short circuit; the switching frequency of all the switch tubes is equal to the resonant frequency, and the MPPT of the photovoltaic port or the overcharge protection of the battery is achieved by controlling the duty cycle Dp of the first switch tube S1, and the output voltage control is achieved by controlling the duty cycle Ds of the third switch tube S3; at the same time, the phase shift angle between the first switch tube S1 and the third switch tube S3 is controlled to be equal to (Dp-Ds) / 2, so that the midpoint voltage v AB and the transformer secondary side bridge arm midpoint voltage v CD Central symmetry.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention proposes a resonant three-port DC converter topology suitable for photovoltaic storage systems and a fixed-frequency PWM modulation method thereof. By adopting a dual active half-bridge structure and coupled inductors, the topology reduces the number of switches and magnetic components while ensuring electrical isolation between the load and the photovoltaic / battery, thereby reducing device costs and improving the power density of the device. The converter can achieve flexible energy management between each port in a single-stage structure and a fixed switching frequency, and all switches can achieve full-range soft switching, reducing switching losses. The converter has consistent drive logic in all power transmission modes, which can achieve smooth switching between modes, and the voltage gain is decoupled from the transmission power, which helps to reduce the control complexity of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the topological structure of a resonant three-port DC converter according to an embodiment of the present invention.

[0047] Figure 2 1 is a working waveform diagram of the fixed-frequency PWM modulation method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0049] like Figure 1 As shown, the present invention proposes a resonant three-port DC converter topology suitable for photovoltaic storage system, including photovoltaic port V pv , battery port V bat , load port V o , first filter capacitor C1, input half bridge, output half bridge, first DC inductor L1, first resonant capacitor C r , the first coupled inductor,

[0050] The input half-bridge includes a first switch tube S1, a second switch tube S2, a second filter capacitor C2, and a third filter capacitor C3. The source of the first switch tube S1 is connected to the drain of the second switch tube S2 to form a first switch bridge arm, the negative electrode of the second filter capacitor C2 is connected to the positive electrode of the third filter capacitor C3 to form a first filter capacitor bridge arm, the drain of the first switch tube S1 is connected to the positive electrode of the second filter capacitor C2, and the source of the second switch tube S2 is connected to the negative electrode of the third filter capacitor C3.

[0051] The source of the first switch tube S1 is the midpoint A of the first switch bridge arm, and the cathode of the second filter capacitor C2 is the midpoint B of the first filter capacitor bridge arm;

[0052] The output half-bridge includes a third switch tube S3, a fourth switch tube S4, a fourth filter capacitor C4, and a fifth filter capacitor C5. The source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 to form a second switch bridge arm, the negative electrode of the fourth filter capacitor C4 is connected to the positive electrode of the fifth filter capacitor C5 to form a second filter capacitor bridge arm, the drain of the third switch tube S3 is connected to the positive electrode of the fourth filter capacitor C4, and the source of the fourth switch tube S4 is connected to the negative electrode of the fifth filter capacitor C5.

[0053] The source of the third switch tube S3 is the midpoint C of the second switch bridge arm, and the cathode of the fourth filter capacitor C4 is the midpoint D of the second filter capacitor bridge arm;

[0054] The photovoltaic port V pv The positive and negative electrodes are connected to the positive and negative electrodes of the third filter capacitor C3 respectively, and the battery port V bat The positive electrode of the battery is connected to the drain of the first switch tube S1 and the positive electrode of the second filter capacitor C2. bat The negative electrode of the second switch tube S2 and the source of the photovoltaic port V pv The negative connection of the load port V o The positive electrode of is connected to the drain of the third switch tube S3 and the positive electrode of the fourth filter capacitor C4, and the load port V oThe negative electrode of the first resonant capacitor C is connected to the source of the fourth switch tube S4 and the negative electrode of the fifth filter capacitor C5; the two ends of the first DC inductor L1 are respectively connected to the midpoint A of the first switch bridge arm and the midpoint B of the first filter capacitor bridge arm, and the first resonant capacitor C r One side is connected to the midpoint A of the first switch bridge arm, and the other side is connected to the positive electrode of the primary side of the first coupling inductor, the negative electrode of the primary side of the first coupling inductor is connected to the midpoint B of the first filter capacitor bridge arm, and the positive and negative electrodes of the first coupling inductor are respectively connected to the midpoint C of the second switch bridge arm and the midpoint D of the second filter capacitor bridge arm.

[0055] The voltage between the midpoint A of the first switch bridge arm and the midpoint B of the first filter capacitor bridge arm is the transformer primary side bridge arm midpoint voltage v AB The voltage between the midpoint C of the second switch bridge arm and the midpoint D of the second filter capacitor bridge arm is the midpoint voltage v of the transformer secondary side bridge arm CD .

[0056] The first filter capacitor C1, the second filter capacitor C2, the third filter capacitor C3, the fourth filter capacitor C4 and the fifth filter capacitor C5 are used to filter out the photovoltaic port V pv , battery port V bat , load port V o High-frequency components in current.

[0057] The first resonant capacitor C r Used to form a resonant network with the first coupled inductor to transfer energy;

[0058] The first DC inductor L1 is used to transfer energy and assist the first switching tube and the second switching tube to achieve soft switching;

[0059] The first coupled inductor is used to achieve electrical isolation, voltage conversion and form a resonant network.

[0060] The first switch tube S1 , the second switch tube S2 , the third switch tube S3 , and the fourth switch tube S4 in the first switch bridge arm and the second switch bridge arm are all power transistors with anti-parallel diodes and drain-source parasitic capacitances.

[0061] The present invention is provided with an input half-bridge and an output half-bridge, wherein the input half-bridge includes a first switch tube, a second switch tube, a second filter capacitor and a third filter capacitor. The first switch tube S1 and the second switch tube S2 in the first switch bridge arm of the input half-bridge are complementary turned on. When the first switch tube S1 is turned on, the voltage applied to both ends of the first DC inductor L1 is equal to V pv When the second switch tube S2 is turned on, the voltage across the first DC inductor L1 is equal to V pv -V bat According to the volt-second balance principle, the photovoltaic port V pvTo the battery port V bat The voltage gain is 1 / D p Therefore, by adjusting the duty cycle D of the switch tube S1 p To adjust the photovoltaic port V pv To the battery port V bat The voltage gain can be increased to achieve MPPT of photovoltaic or overcharge protection of battery.

[0062] The output half-bridge includes a third switch tube, a fourth switch tube, a fourth filter capacitor and a fifth filter capacitor. The third switch tube S3 and the fourth switch tube S4 in the output half-bridge are complementary turned on. When the third switch tube S3 is turned on, the midpoint voltage v CD =Equal to the voltage on the fourth filter capacitor C4. When the fourth switch S4 is turned on, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD Equal to the negative value of the voltage on the fifth filter capacitor C5, by adjusting the duty cycle D of the third switch tube S3 s Adjust the resonant cavity port voltage v CD The waveform of the photovoltaic port V can be deduced by fundamental wave analysis. pv To the load port V o The voltage gain is sin(πD p ) / [D p sin(πD s )], so the output voltage is regulated by controlling the duty cycle of the third switch tube D s accomplish.

[0063] Therefore, by adjusting the phase shift angle between the first switch S1 and the third switch S3 to be equal to (Dp-Ds) / 2, the transformer primary and secondary side bridge midpoint voltage v AB and v CD The central symmetry enables the fundamental voltage synchronization of the ports on both sides of the resonant cavity to match, thus achieving decoupling of voltage gain and transmission power.

[0064] A 500W converter prototype was constructed with a PV port voltage of 60V to 120V, a battery port voltage of 160V to 200V, and an output voltage of 400V. All switching elements in the switching network used power MOSFETs with anti-parallel diodes and drain-source parasitic capacitance. The main circuit drive signal was generated by a TI TMS320F28335 digital signal processor. Under these experimental conditions, the prototype resonant three-port DC / DC converter for a photovoltaic storage system operated normally under fixed-frequency PWM modulation under various operating conditions.

[0065] The present invention reduces the number of switching tubes and magnetic components in the converter by adopting a dual active half-bridge structure and coupled inductors, thereby reducing device costs and device size; adopts fixed-frequency PWM modulation and realizes flexible energy management through two-degree-of-freedom PWM control; the converter can achieve a wide voltage gain at a fixed switching frequency, meeting the voltage gain requirements in the context of photovoltaic storage applications; all switching tubes can achieve full-range soft switching, reducing switching losses and facilitating efficiency improvement; the converter has consistent driving logic in all power transmission modes, which can achieve smooth switching between modes.

[0066] like Figure 2 As shown, a fixed-frequency PWM modulation method proposed by the present invention includes the following steps:

[0067] S1. Implementation of overcharge protection:

[0068] S11, the first switch tube S1 and the second switch tube S2 in the first switch bridge arm are complementary turned on, and the first switch tube S1 is turned on. At this time, the voltage applied to both ends of the first DC inductor L1 is equal to V pv , turn on the second switch tube S2, at this time, the voltage applied to both ends of the first DC inductor L1 is equal to V pv -V bat ,

[0069] S12, according to the volt-second balance principle, the photovoltaic port V pv To the battery port V bat The voltage gain is 1 / D p ,

[0070] S13, by adjusting the duty cycle D of the switch tube S1 p To adjust the photovoltaic port V pv To the battery port V bat Voltage gain to achieve MPPT of photovoltaic or overcharge protection of battery;

[0071] S2. Implementation of output voltage regulation:

[0072] S21, the third switch tube S3 and the fourth switch tube S4 are complementary turned on, and the third switch tube S3 is turned on. At this time, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD = is equal to the voltage on the fourth filter capacitor C4, turning on the fourth switch S4. At this time, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD is equal to the negative value of the voltage on the fifth filter capacitor C5,

[0073] S22, by adjusting the duty cycle D of the third switch tube S3 s Adjust the resonant cavity port voltage v CD The waveform,

[0074] S23, through the fundamental wave analysis method, the photovoltaic port V pv To the load port V o The voltage gain is: sin(πD p ) / [D p sin(πD s )],

[0075] S24, by controlling the duty cycle D of the third switch tube s Realize output voltage regulation;

[0076] S3, port decoupling control:

[0077] S31, by adjusting the phase shift angle between the first switch S1 and the third switch tube S3 to be equal to (Dp-Ds) / 2 to maintain the transformer primary and secondary side bridge arm midpoint voltage v AB and v CD Central symmetry,

[0078] S32. Match the fundamental synchronous voltage of the port voltages on both sides of the resonant cavity to achieve decoupling of voltage gain and transmission power.

[0079] In the above method: the first switch tube S1 and the second switch tube S2 are complementary turned on, and there is a dead zone between the drive signals to prevent a direct short circuit; the third switch tube S3 and the fourth switch tube S4 are complementary turned on, and there is a dead zone between the drive signals to prevent a direct short circuit; the switching frequency of all the switch tubes is equal to the resonant frequency, and the MPPT of the photovoltaic port or the overcharge protection of the battery is achieved by controlling the duty cycle Dp of the first switch tube S1, and the output voltage control is achieved by controlling the duty cycle Ds of the third switch tube S3; at the same time, the phase shift angle between the first switch tube S1 and the third switch tube S3 is controlled to be equal to (Dp-Ds) / 2, so that the midpoint voltage v AB and the transformer secondary side bridge arm midpoint voltage v CD Central symmetry.

[0080] The present invention proposes a resonant three-port DC converter topology suitable for photovoltaic storage systems and a fixed-frequency PWM modulation method thereof. By adopting a dual active half-bridge structure and coupled inductors, the topology reduces the number of switches and magnetic components while ensuring electrical isolation between the load and the photovoltaic / battery, thereby reducing device costs and improving the power density of the device. The converter can achieve flexible energy management between each port in a single-stage structure and a fixed switching frequency, and all switches can achieve full-range soft switching, reducing switching losses. The converter has consistent drive logic in all power transmission modes, which can achieve smooth switching between modes, and the voltage gain is decoupled from the transmission power, which helps to reduce the control complexity of the system.

[0081] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any other form, and any modification or equivalent variation made according to the technical essence of the present application still falls within the scope of the present application.

Claims

1. A resonant three-port DC / DC converter topology, characterized in that: Including photovoltaic port V pv , battery port V bat , load port V o , first filter capacitor C1, input half bridge, output half bridge, first DC inductor L1, first resonant capacitor C r , the first coupled inductor, The input half-bridge includes a first switch tube S1, a second switch tube S2, a second filter capacitor C2, and a third filter capacitor C3. The source of the first switch tube S1 is connected to the drain of the second switch tube S2 to form a first switch bridge arm, the negative electrode of the second filter capacitor C2 is connected to the positive electrode of the third filter capacitor C3 to form a first filter capacitor bridge arm, the drain of the first switch tube S1 is connected to the positive electrode of the second filter capacitor C2, and the source of the second switch tube S2 is connected to the negative electrode of the third filter capacitor C3. The source of the first switch tube S1 is the midpoint A of the first switch bridge arm, and the cathode of the second filter capacitor C2 is the midpoint B of the first filter capacitor bridge arm; The output half-bridge includes a third switch tube S3, a fourth switch tube S4, a fourth filter capacitor C4, and a fifth filter capacitor C5. The source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 to form a second switch bridge arm, the negative electrode of the fourth filter capacitor C4 is connected to the positive electrode of the fifth filter capacitor C5 to form a second filter capacitor bridge arm, the drain of the third switch tube S3 is connected to the positive electrode of the fourth filter capacitor C4, and the source of the fourth switch tube S4 is connected to the negative electrode of the fifth filter capacitor C5. The source of the third switch tube S3 is the midpoint C of the second switch bridge arm, and the cathode of the fourth filter capacitor C4 is the midpoint D of the second filter capacitor bridge arm; The photovoltaic port V pv The positive and negative electrodes are connected to the positive and negative electrodes of the third filter capacitor C3 respectively, and the battery port V bat The positive electrode of the battery is connected to the drain of the first switch tube S1 and the positive electrode of the second filter capacitor C2. bat The negative electrode of the second switch tube S2 and the source of the photovoltaic port V pv The negative connection of the load port V o The positive electrode of is connected to the drain of the third switch tube S3 and the positive electrode of the fourth filter capacitor C4, and the load port V o The negative electrode of the first resonant capacitor C is connected to the source of the fourth switch tube S4 and the negative electrode of the fifth filter capacitor C5; the two ends of the first DC inductor L1 are respectively connected to the midpoint A of the first switch bridge arm and the midpoint B of the first filter capacitor bridge arm, and the first resonant capacitor C r One side is connected to the midpoint A of the first switch bridge arm, and the other side is connected to the positive electrode of the primary side of the first coupling inductor, the negative electrode of the primary side of the first coupling inductor is connected to the midpoint B of the first filter capacitor bridge arm, and the positive and negative electrodes of the first coupling inductor are respectively connected to the midpoint C of the second switch bridge arm and the midpoint D of the second filter capacitor bridge arm.

2. A resonant three-port DC converter topology according to claim 1, characterized in that: The voltage between the midpoint A of the first switch bridge arm and the midpoint B of the first filter capacitor bridge arm is the transformer primary side bridge arm midpoint voltage v AB The voltage between the midpoint C of the second switch bridge arm and the midpoint D of the second filter capacitor bridge arm is the midpoint voltage v of the transformer secondary side bridge arm CD .

3. The resonant three-port DC converter topology according to claim 1, characterized in that: The first filter capacitor C1, the second filter capacitor C2, the third filter capacitor C3, the fourth filter capacitor C4 and the fifth filter capacitor C5 are used to filter out the photovoltaic port V pv , battery port V bat , load port V o High-frequency components in current.

4. The resonant three-port DC converter topology according to claim 1, characterized in that: The first resonant capacitor C r Used to form a resonant network with the first coupled inductor to transfer energy; The first DC inductor L1 is used to transfer energy and assist the first switching tube and the second switching tube to achieve soft switching; The first coupled inductor is used to achieve electrical isolation, voltage conversion and form a resonant network.

5. The resonant three-port DC converter topology according to claim 1, characterized in that: The first switch tube S1 , the second switch tube S2 , the third switch tube S3 , and the fourth switch tube S4 in the first switch bridge arm and the second switch bridge arm are all power transistors with anti-parallel diodes and drain-source parasitic capacitances.

6. A constant-frequency PWM modulation method for a resonant three-port DC converter topology according to any one of claims 1 to 5, characterized in that: The process includes the following steps: S1. Implementation of overcharge protection: S11, the first switch tube S1 and the second switch tube S2 in the first switch bridge arm are complementary turned on, and the first switch tube S1 is turned on. At this time, the voltage applied to both ends of the first DC inductor L1 is equal to V pv , turn on the second switch tube S2, at this time, the voltage applied to both ends of the first DC inductor L1 is equal to V pv -V bat , S12, according to the volt-second balance principle, the photovoltaic port V pv To the battery port V bat The voltage gain is 1 / D p , S13, by adjusting the duty cycle D of the switch tube S1 p To adjust the photovoltaic port V pv To the battery port V bat Voltage gain to achieve MPPT of photovoltaic or overcharge protection of battery; S2. Implementation of output voltage regulation: S21, the third switch tube S3 and the fourth switch tube S4 are complementary turned on, and the third switch tube S3 is turned on. At this time, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD = is equal to the voltage on the fourth filter capacitor C4, turning on the fourth switch S4. At this time, the midpoint voltage of the bridge arm on the secondary side of the transformer v CD is equal to the negative value of the voltage on the fifth filter capacitor C5, S22, by adjusting the duty cycle D of the third switch tube S3 s Adjust the resonant cavity port voltage v CD The waveform, S23, through the fundamental wave analysis method, the photovoltaic port V pv To the load port V o The voltage gain is: sin(πD p ) / [D p sin(πD s )], S24, by controlling the duty cycle D of the third switch tube s Realize output voltage regulation; S3, port decoupling control: S31, by adjusting the phase shift angle between the first switch S1 and the third switch tube S3 to be equal to (Dp-Ds) / 2 to maintain the transformer primary and secondary side bridge arm midpoint voltage v AB and v CD Central symmetry, S32. Match the fundamental synchronous voltage of the port voltages on both sides of the resonant cavity to achieve decoupling of voltage gain and transmission power.

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