Resonant three-port direct-current converter topology and fixed-frequency PWM (Pulse Width Modulation) method thereof

Abstract

The invention provides a resonant three-port direct-current converter topology and a fixed-frequency PWM (Pulse Width Modulation) method of the resonant three-port direct-current converter topology, which are suitable for an optical storage system, and the three-port direct-current converter topology comprises a photovoltaic port Vpv, a battery port Vbat, a load port Vo, a first filter capacitor C1, an input half bridge, an output half bridge, a first direct-current inductor L1, a first resonant capacitor Cr and a first coupling inductor, the input half-bridge comprises a first switch tube S1, a second switch tube S2, a second filter capacitor C2 and a third filter capacitor C3, and the output half-bridge comprises a third switch tube S3, a fourth switch tube S4, a fourth filter capacitor C4 and a fifth filter capacitor C5. By adopting a dual-active half-bridge structure and a coupling inductor, the load is ensured to be electrically isolated from a photovoltaic / battery, and the load is effectively isolated from the photovoltaic / battery; the number of switching tubes and magnetic elements is reduced, the device cost is reduced, the power density of the device is improved, flexible energy management among ports is realized under a single-stage structure and a 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] New energy is gradually replacing traditional power generation represented by thermal power generation due to its clean and renewable advantages. In the photovoltaic storage system, the output of the photovoltaic array is easily affected by environmental factors such as light, so it is necessary to add energy storage units to ensure continuous and stable power supply to the load. The DC converter used to achieve energy flow control and load regulation is an important part of the photovoltaic energy storage system. Under the traditional scheme, multiple two-port converters are used to achieve energy control between the photovoltaic array, battery and load, but there are problems of multi-level energy conversion and decentralized control. In order to improve the efficiency of the system, three-port DC converters that can achieve single-stage energy conversion are widely used. Three-port converters can be divided into three types according to the isolation type: non-isolated, fully isolated and partially isolated. Among them, the non-isolated three-port converter has a simple structure and a small number of components, but it is only suitable for occasions where the voltage levels of each port are close; each port in the fully isolated three-port converter can achieve electrical isolation, but the number of components is large and the transformer design is complex; the partially isolated three-port converter has the advantages of fewer components and load isolation, and is the preferred choice for photovoltaic energy storage system applications. In the existing partially isolated three-port converters, the topology based on the forward circuit is simple but it is difficult to achieve soft switching of all switches; the topology based on the 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, which is composed 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 obtained by integrating a dual-path staggered parallel bidirectional Buck-Boost circuit with 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, realizes switch tube reuse, effectively reduces the number of switch tubes, reduces converter cost, and improves 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 comparison between this application and the above patent is as follows:

[0005] The converter in a photo-storage CLLC resonant three-port DC-DC converter is a two-phase interleaved bidirectional Buck-Boost circuit integrated with a full-bridge CLLC resonant converter, including five magnetic components (two DC inductors, two resonant inductors and a transformer) and eight switch tubes; the converter of this patent is a single-phase bidirectional Buck-Boost circuit integrated with a half-bridge LLC resonant converter, including two magnetic components and four switch tubes, with fewer devices. The two have essential differences in the design ideas of topological device integration.

[0006] The converter in a photovoltaic storage CLLC resonant three-port DC-DC converter adopts a duty cycle + phase shift control method, but the specific details are not described; the converter of this patent adopts a fixed-frequency PWM control method, and the converter switching frequency is equal to the resonant frequency. The maximum photovoltaic power tracking or battery overcharge protection is achieved by adjusting the duty cycle of the primary switch tube, and the output voltage control is achieved by adjusting the duty cycle of the secondary switch tube. Under this method, the converter voltage gain is decoupled from the port power. There is an essential difference between the two in the design ideas of the control method.

[0007] After searching, the invention patent with Chinese patent publication number: CN118074533A proposes an LCC type current-fed three-port photovoltaic storage hydrogen production DC converter and control method, wherein the converter includes a first-port DC input capacitor, a second-port staggered parallel input inductor, an inverter full bridge, an LCC resonant cavity, a high-frequency isolation transformer, a diode uncontrolled rectifier full bridge and a third-port DC output inductor; the converter adopts a variable duty ratio variable frequency composite control method, and adjusts the input voltage of the first port or the input voltage of the second port by changing the duty ratio, and adjusts the output voltage or output current of the third port by changing the switching frequency. The present invention adopts a three-port DC converter integrated with energy storage for new energy electrolysis hydrogen production. Energy storage can effectively smooth the power fluctuations of new energy such as photovoltaics, and 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 link, thereby reducing the cost and volume of the converter and improving the conversion efficiency.

[0008] The comparison between this application and the above patent is as follows:

[0009] The output port of the converter in an LCC-type current-fed three-port photovoltaic storage hydrogen production DC converter and control method is a unidirectional port, and a two-phase staggered bidirectional Buck-Boost circuit and a unidirectional full-bridge LCC resonant converter are integrated, including four magnetic elements (two DC inductors, one resonant inductor, and one transformer), four switch tubes, and four rectifier diodes; the output port of the converter of this patent is a bidirectional port, and a single-phase bidirectional Buck-Boost circuit and a half-bridge LLC resonant converter are integrated, including only two magnetic elements and four switch tubes, with fewer devices, and the working principle of the LLC converter is different from that of the LCC converter. The two are essentially different in the design ideas of the converter topology.

[0010] The converter in an LCC type current-fed three-port photovoltaic storage hydrogen production DC converter and control method adopts PWM+frequency modulation control, controls the two ports of the primary side by adjusting the duty cycle of the primary switch tube, and controls the output port of the secondary side by adjusting the switching frequency. The frequency modulation control has the problems of complex magnetic component design and limited voltage regulation range; the converter of this patent adopts a fixed-frequency PWM control method, the converter switching frequency is equal to the resonant frequency, and the photovoltaic maximum power tracking or battery overcharge protection is achieved by adjusting the duty cycle of the primary switch tube, and the output voltage control is achieved by adjusting the duty cycle of the secondary switch tube. The converter can achieve a wide voltage gain at a fixed switching frequency. There is an essential difference between the two in the design ideas of the control method. Summary of the invention

[0011] The present invention proposes a resonant three-port DC converter topology suitable for a photovoltaic storage system and a fixed-frequency PWM modulation method thereof, the purpose of which is to reduce the number of switching tubes and magnetic components, reduce the cost of the device and improve the power density of the device, realize flexible energy management between ports under a single-stage structure and a fixed switching frequency, and realize full-range soft switching.

[0012] To achieve the above object, the technical solution adopted by the present invention is:

[0013] A resonant three-port DC converter topology, characterized in that: it includes a 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,

[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. 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, 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 terminal of the load port is connected to 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; 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] As a preferred technical solution of the present invention: 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 .

[0020] As a preferred technical solution of the present invention: 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.

[0021] As a preferred technical solution of the present invention: the first resonant capacitor C r Used to form a resonant network with the first coupled inductor to transfer energy;

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

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

[0024] As a preferred technical solution of the present invention: 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.

[0025] In the above structure: 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, and the first switch tube S1 and the second switch tube S2 in the first switch bridge arm of the input half-bridge are complementary and 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 pv To 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.

[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 is equal to the voltage on the fourth filter capacitor C4. When the fourth switch tube S4 is turned on, 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, 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 port voltages on both sides of the resonant cavity to match, thus achieving the decoupling of voltage gain and transmission power.

[0028] A 500W converter prototype was built when the PV port voltage was 60V-120V, the battery port voltage was 160V-200V and the output voltage was 400V. All switch networks used power transistor MOSFETs with anti-parallel diodes and drain-source parasitic capacitance. The driving signal of the main circuit was generated by the TI digital signal processor TMS320F28335. Under this experimental condition, the resonant three-port DC converter prototype for the photovoltaic storage system can operate normally under different working conditions under fixed-frequency PWM modulation.

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

[0030] A fixed frequency PWM modulation method, characterized in that it comprises 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 turned on complementary, and the third switch tube S3 is turned on. At this time, the midpoint voltage v CD = is equal to the voltage on the fourth filter capacitor C4, turning on the fourth switch tube 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 of

[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 the regulation of output voltage;

[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, matching 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 complementarily turned on, and there is a dead zone between the drive signals to prevent a straight-through short circuit; the third switch tube S3 and the fourth switch tube S4 are complementarily turned on, and there is a dead zone between the drive signals to prevent a straight-through 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 of the bridge arm on the primary side of the transformer AB 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 a photovoltaic storage system and a fixed-frequency PWM modulation method thereof. By adopting a dual active half-bridge structure and a coupled inductor, the number of switching tubes and magnetic components is reduced while ensuring electrical isolation between the load and the photovoltaic / battery, which is beneficial to reducing device costs and improving device power density; the converter can achieve flexible energy management between ports under a single-stage structure and a fixed switching frequency, and all switching tubes can achieve full-range soft switching, reducing switching losses; the converter has consistent driving logic in all power transmission modes, can achieve smooth switching between modes, and the voltage gain is decoupled from the transmission power, which is beneficial to reducing 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 in conjunction with 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 a photovoltaic storage system, including a 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. 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, 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 terminal of the load port is connected to 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; 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 switch tube and the second switch 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 comprises a first switch tube, a second switch tube, a second filter capacitor and a third filter capacitor, and 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, and 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 is equal to the voltage on the fourth filter capacitor C4. When the fourth switch tube S4 is turned on, 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, 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 tube S3 to be equal to (Dp-Ds) / 2, the transformer primary and secondary side bridge arm midpoint voltage v AB and v CD The central symmetry enables the fundamental voltage synchronization of the port voltages on both sides of the resonant cavity to match, thus achieving the decoupling of voltage gain and transmission power.

[0064] A 500W converter prototype was built when the PV port voltage was 60V-120V, the battery port voltage was 160V-200V and the output voltage was 400V. All switch networks used power transistor MOSFETs with anti-parallel diodes and drain-source parasitic capacitance. The driving signal of the main circuit was generated by the TI digital signal processor TMS320F28335. Under this experimental condition, the resonant three-port DC converter prototype for the photovoltaic storage system can operate normally under different working conditions under fixed-frequency PWM modulation.

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

[0066] like Figure 2 As shown, a fixed-frequency PWM modulation method proposed by the present invention comprises 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 turned on complementary, and the third switch tube S3 is turned on. At this time, the midpoint voltage v CD = is equal to the voltage on the fourth filter capacitor C4, turning on the fourth switch tube 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 of

[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 the regulation of output voltage;

[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, matching 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 complementarily turned on, and there is a dead zone between the drive signals to prevent a straight-through short circuit; the third switch tube S3 and the fourth switch tube S4 are complementarily turned on, and there is a dead zone between the drive signals to prevent a straight-through 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 of the bridge arm on the primary side of the transformer AB 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 a photovoltaic storage system and a fixed-frequency PWM modulation method thereof. By adopting a dual active half-bridge structure and a coupled inductor, the number of switching tubes and magnetic components is reduced while ensuring electrical isolation between the load and the photovoltaic / battery, which is beneficial to reducing device costs and improving device power density; the converter can achieve flexible energy management between ports under a single-stage structure and a fixed switching frequency, and all switching tubes can achieve full-range soft switching, reducing switching losses; the converter has consistent driving logic in all power transmission modes, can achieve smooth switching between modes, and the voltage gain is decoupled from the transmission power, which is beneficial to reducing the control complexity of the system.

[0081] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A resonant three-port 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. 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, 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 terminal of the load port is connected to 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; 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. A 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. A 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 switch tube and the second switch tube to achieve soft switching; The first coupled inductor is used to achieve electrical isolation, voltage conversion and form a resonant network.

5. A 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 according to any one of claims 1 to 5, characterized in that: The steps include: 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 turned on complementary, and the third switch tube S3 is turned on. At this time, the midpoint voltage v CD = is equal to the voltage on the fourth filter capacitor C4, turning on the fourth switch tube 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 of 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 the regulation of output voltage; 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, matching 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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