Single-stage high-frequency isolated bidirectional DC converter and grid-connected energy storage system

Abstract

The present invention relates to a single-stage high-frequency isolated bidirectional DC converter, comprising: a boost energy storage module, an input switch network, a transformer module, a resonance module, an output switch network electrically connected in sequence, and a switching control module connected to the boost energy storage module and the resonance module, wherein the boost energy storage module is connected to the positive and negative poles of the input power supply; the switching control module is used to control the boost energy storage module to be switched on and the resonance module to be switched off during forward conversion, and to control the boost energy storage module to be switched off and the resonance module to be switched on during reverse conversion. The present invention also relates to a grid-connected energy storage system. By adopting a switching control module, the present invention can meet a wide input voltage range with a single-stage topology structure in a low-cost and high-efficiency manner.

Description

Technical Field

[0001] The present invention relates to the field of power supply modules, and more specifically, to a single-stage high-frequency isolated bidirectional DC converter and a grid-connected energy storage system comprising the single-stage high-frequency isolated bidirectional DC converter. Background Art

[0002] With the increasing energy crisis and the improvement of people's environmental awareness, green and efficient use of energy has become the focus of research and application in various countries, and the research of high-frequency isolated wide-range DC converters is even more important. At present, in engineering applications, the input voltage range of single-stage high-frequency isolated bidirectional DC converters is usually too narrow to meet the wide input voltage range. Bidirectional high-frequency isolated DC converters with a wide input voltage range mostly adopt a two-stage topology. For example, BUCKBOOST+LLC circuit cascade, the input voltage range is increased by the BUCKBOOST circuit, and high-frequency isolation is achieved through the transformer of the LLC circuit. Or BUCKBOOST+phase-shifted full-bridge circuit cascade, the input voltage range is also increased by the BUCKBOOST circuit, and high-frequency isolation is achieved through the transformer of the phase-shifted full-bridge circuit. However, whether it is BUCKBOOST+LLC circuit cascade or BUCKBOOST+phase-shifted full-bridge circuit cascade, it increases the cost of switching devices and reduces the energy conversion efficiency compared to the single-stage topology. Summary of the invention

[0003] The technical problem to be solved by the present invention is that, in view of the above-mentioned defects of the prior art, a single-stage high-frequency isolated bidirectional DC converter and a grid-connected energy storage system including the single-stage high-frequency isolated bidirectional DC converter are provided, which are used to meet the wide input voltage range in a single-stage topology structure with low cost and high efficiency.

[0004] The technical solution adopted by the present invention to solve its technical problem is: constructing a single-stage high-frequency isolated bidirectional DC converter, including: a boost energy storage module, an input switch network, a transformer module, a resonance module, an output switch network electrically connected in sequence, and a switching control module connected to the boost energy storage module and the resonance module for control, wherein the boost energy storage module is connected to the positive and negative poles of the input power supply; the switching control module is used to control the boost energy storage module to be switched in and the resonance module to be switched out during forward conversion, and to control the boost energy storage module to be switched out and the resonance module to be switched in during reverse conversion.

[0005] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the resonance module includes a first resonance unit and a second resonance unit, the first resonance unit is connected between the first end of the secondary side of the transformer module and the first input end of the output switch network, and the second resonance unit is connected between the first end of the secondary side and the second end of the secondary side of the transformer module via the resonance switching control unit.

[0006] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the switching control module includes a boost switching control unit for controlling the boost energy storage module to be switched in during forward conversion and to be switched out during reverse conversion, and a resonance switching control unit for controlling the first resonance unit and the second resonance unit to be switched out during forward conversion and to be switched in during reverse conversion.

[0007] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the first resonant unit includes a first inductor and a first capacitor, and the second resonant unit includes a second inductor. The first end of the first inductor is connected to the first end of the secondary side of the transformer module, and the second end is connected to the first input end of the output switch network via the first capacitor; the first end of the second inductor is connected to the first end of the secondary side of the transformer module via the resonant switching control unit, and the second end of the second inductor is connected to the second end of the secondary side of the transformer module.

[0008] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the resonant switching control unit includes a first resonant switch connected in parallel with the first inductor and a second resonant switch connected in series with the second inductor.

[0009] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the boost energy storage module includes a boost energy storage inductor connected to the positive electrode of the input power supply and the first input end of the input switch network.

[0010] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the boost switching control unit includes a boost switching switch connected in parallel at both ends of the boost energy storage inductor.

[0011] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the boost energy storage module further includes an input filter capacitor connected between the positive and negative electrodes of the output power supply and an absorption unit connected between the first input end and the second input end of the input switch network.

[0012] In the single-stage high-frequency isolated bidirectional DC converter described in the present invention, the input switch network and the output switch network include a full-bridge switch tube network or a half-bridge switch tube network; the absorption unit includes an absorption diode, an absorption capacitor and an absorption resistor, the anode of the absorption diode is connected to the first input end of the input switch network, and the cathode is connected to the second input end of the input switch network via the absorption capacitor, and the absorption resistor is connected in parallel to the absorption diode or the absorption capacitor.

[0013] Another technical solution adopted by the present invention to solve its technical problem is to construct a grid-connected energy storage system, including a battery module, a photovoltaic component, a DC / DC module, a DC filter module, a DC / AC module, an AC filter module, a relay, a load, a power grid module and the single-stage high-frequency isolated bidirectional DC converter. The photovoltaic component is connected to the DC filter module via the DC / DC module, the battery module is connected to the DC filter module via the single-stage high-frequency isolated bidirectional DC converter, and the DC filter module is further connected to the load or power grid module via the DC / AC module, the AC filter module and the relay in sequence.

[0014] The single-stage high-frequency isolated bidirectional DC converter and grid-connected energy storage system of the present invention adopts a switching control module, and during forward conversion, a boost energy storage module is put in and a resonant module is put out, so as to realize the conversion of a wide input range voltage to a relatively stable output voltage. During reverse conversion, the boost energy storage module is put in and the resonant module is put in, so as to convert a relatively stable input voltage into an output voltage with a wide output range. Therefore, a single-stage topology structure can meet a wide input voltage range in a low-cost and high-efficiency manner. Compared with a pure resonant LLC converter, it can increase the input voltage range without adding additional circuits. Compared with a traditional phase-shifted full-bridge converter, it can also increase the input voltage range; and the LLC topology advantages can be used to improve the efficiency of reverse conversion of DC power. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0016] Figure 1 It is a principle block diagram of a first preferred embodiment of a single-stage high-frequency isolated bidirectional DC converter of the present invention;

[0017] Figure 2 It is a principle block diagram of a second preferred embodiment of a single-stage high-frequency isolated bidirectional DC converter of the present invention;

[0018] Figure 3 is a circuit diagram of a third preferred embodiment of a single-stage high-frequency isolated bidirectional DC converter of the present invention;

[0019] Figures 4A-4CShows Figure 3 The schematic diagram of charging energy and positive and negative energy transfer during forward conversion of a single-stage high-frequency isolated bidirectional DC converter shown in FIG.

[0020] Figure 5 yes Figure 3 The schematic diagram of the switch tube driving wave of the DC forward conversion of the single-stage high-frequency isolated bidirectional DC converter shown in FIG.

[0021] Figure 6 yes Figure 3 The control block diagram of the DC forward conversion of the single-stage high-frequency isolated bidirectional DC converter shown in FIG.

[0022] Figure 7A-7B Shows Figure 3 The schematic diagram of positive and negative energy transfer during reverse conversion of a single-stage high-frequency isolated bidirectional DC converter shown in FIG.

[0023] Figure 8 yes Figure 3 The schematic diagram of the switch tube driving wave generation of the DC reverse conversion of the single-stage high-frequency isolated bidirectional DC converter shown;

[0024] Fig. 9 yes Figure 3 A control block diagram of a DC reverse conversion of a single-stage high-frequency isolated bidirectional DC converter shown in FIG.

[0025] Figures 10A-10B The schematic diagram of the application circuit of the single-stage high-frequency isolated bidirectional DC converter of the present invention is shown;

[0026] Fig.11 is a circuit diagram of a fourth preferred embodiment of a single-stage high-frequency isolated bidirectional DC converter of the present invention;

[0027] Fig.12 is a principle block diagram of a first preferred embodiment of a grid-connected energy storage system of the present invention;

[0028] Figures 13A-13C Shows a single-phase optional implementation of the DA / AC module;

[0029] Figures 14A-14C A three-phase optional implementation of the DA / AC module is shown. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] The present invention relates to a single-stage high-frequency isolated bidirectional DC converter, comprising: a boost energy storage module, an input switch network, a transformer module, a resonance module, an output switch network electrically connected in sequence, and a switching control module connected to the boost energy storage module and the resonance module, wherein the boost energy storage module is connected to the positive and negative poles of the input power supply; the switching control module is used to control the boost energy storage module to be put in and the resonance module to be put out during forward conversion, and to control the boost energy storage module to be put out and the resonance module to be put in during reverse conversion. The present invention adopts a switching control module to put in the boost energy storage module and put out the resonance module during forward conversion, thereby realizing the conversion of a wide input range voltage to a relatively stable output voltage, and to put out the boost energy storage module and put in the resonance module during reverse conversion, thereby converting a relatively stable input voltage into an output voltage with a wide output range, so that a single-stage topology structure with low cost and high efficiency can meet the wide input voltage range.

[0032] The requirements of voltage conversion range, power density, cost, volume and efficiency are indispensable for bidirectional DC conversion system. However, since the traditional topology usually adopts a two-stage structure, the input voltage range is increased by adding an additional step-up and step-down circuit. Therefore, due to the increase of switching devices, the traditional two-stage topology inevitably leads to a series of problems such as increased cost, reduced power density, reduced conversion efficiency, and increased control difficulty. Most of the existing products are combined into a bidirectional DC converter with larger capacity and wider range by using multiple circuits in series and parallel. However, the inventor of this application creatively thought of combining the BOOST boost module with the high-frequency isolated DC conversion module, and achieved the purpose of step-up and step-down by combining the BOOST boost module with the high-frequency transformer; the bidirectional DC reverse conversion adopts the traditional LLC resonant circuit to reduce switching losses and improve system efficiency. This move breaks through the conventional thinking mode in this field.

[0033] Figure 1 1 is a schematic block diagram of a first preferred embodiment of a single-stage high-frequency isolated bidirectional DC converter according to the present invention. Figure 1 As shown, the single-stage high-frequency isolated bidirectional DC converter of the present invention comprises: a boost energy storage module 100, an input switch network 200, a transformer module 300, a resonance module 400, an output switch network 500 electrically connected in sequence, and a switching control module 600 connected to the boost energy storage module 100 and the resonance module 400, wherein the boost energy storage module 100 is connected to the positive and negative electrodes of the input power supply. The switching control module 600 is used to control the boost energy storage module 100 to be switched on and the resonance module 400 to be switched off during forward conversion, and to control the boost energy storage module 100 to be switched off and the resonance module 400 to be switched on during reverse conversion.

[0034] In a preferred embodiment of the present invention, the boost energy storage module 100 can be constructed using any known capacitors and inductors. The transformer module 300 can include one or more transformers connected in series. The input switch network 200 and the output switch network 500 can include any known full-bridge switch tube network or half-bridge switch tube network. The resonant module 400 can be any LLC resonant module, CLLC resonant module, LC resonant module, etc. The switching control module 600 can be any hardware switch or circuit, such as an air switch, a power switch tube, a relay or a contactor, or any soft switch module or device.

[0035] The present invention adopts a switching control module to switch on and off the boost energy storage module and switch on the resonance module during forward conversion, thereby realizing the conversion of a wide input range voltage to a relatively stable output voltage. During reverse conversion, the boost energy storage module is switched off and the resonance module is switched on, thereby converting a relatively stable input voltage into an output voltage with a wide output range. Therefore, a single-stage topology structure can meet the wide input voltage range in a low-cost and high-efficiency manner.

[0036] Figure 2 1 is a schematic diagram of a second preferred embodiment of a single-stage high-frequency isolated bidirectional DC converter according to the present invention. Figure 2 In the illustrated embodiment, the single-stage high-frequency isolated bidirectional DC converter of the present invention comprises: a boost energy storage module 100, an input switch network 200, a transformer module 300, a resonance module 400, an output switch network 500 electrically connected in sequence, and a switching control module 600 connected to the boost energy storage module 100 and the resonance module 400, wherein the boost energy storage module 100 is connected to the positive and negative electrodes of the input power supply. Further, the resonance module 400 comprises a first resonance unit 410 and a second resonance unit 420.

[0037] The first resonant unit 410 is connected between the first end of the secondary side of the transformer module 300 and the first input end of the output switch network 500, and the second resonant unit 420 is connected between the first end of the secondary side and the second end of the secondary side of the transformer module 300. The switching control module 600 includes a boost switching control unit 610 for controlling the boost energy storage module 100 to be switched in forward conversion and to be switched out in reverse conversion, and a resonant switching control unit 620 for controlling the first resonant unit 410 and the second resonant unit 420 to be switched out in forward conversion and to be switched in reverse conversion.

[0038] In a preferred embodiment of the present invention, the boost energy storage module 100 can be constructed using any known capacitors and inductors. The transformer module 300 may include one or more transformers connected in series. The input switch network 200 and the output switch network 500 may include any known full-bridge switch tube network or half-bridge switch tube network. The first resonant unit 410 and the second resonant unit 420 may be any LC resonant module. The boost switching control unit 610 and the resonant switching control unit 620 may be any hardware switch or circuit, such as an air switch, a power switch tube, a relay or a contactor, or any soft switch module or device.

[0039] The present invention adopts a switching control module to switch on and off the boost energy storage module and switch on the resonance module during forward conversion, thereby realizing the conversion of a wide input range voltage to a relatively stable output voltage. During reverse conversion, the boost energy storage module is switched off and the resonance module is switched on, thereby converting a relatively stable input voltage into an output voltage with a wide output range. Therefore, a single-stage topology structure can meet the wide input voltage range in a low-cost and high-efficiency manner.

[0040] Figure 3 1 is a circuit diagram of a third preferred embodiment of a single-stage high-frequency isolated bidirectional DC converter of the present invention. Figure 3 As shown, the single-stage high-frequency isolated bidirectional DC converter of the present invention comprises: a boost energy storage module 100, an input switch network 200, a transformer module 300, a resonance module 400, an output switch network 500 electrically connected in sequence, and a switching control module 600 connected to the boost energy storage module 100 and the resonance module 400, wherein the boost energy storage module 100 is connected to the positive and negative electrodes of the input power supply. Further, the resonance module 400 comprises a first resonance unit 410 and a second resonance unit 420. The switching control module 600 comprises a boost switching control unit 610 and a resonance switching control unit 620.

[0041] exist Figure 3 In the preferred embodiment shown, the boost energy storage module 100 includes an input filter capacitor C connected between the positive electrode BAT+ and the negative electrode BAT- of the input power supply. in and a boost energy storage inductor L connected to the input power positive electrode BAT+ and the first input terminal of the input switch network 200 boost The input switch network 200 includes a switch tube Q 1 -Q 4 And the reverse parallel diode D 1 -D 4 The first resonant unit 410 comprises a first inductor L r and the first capacitor C 1The second resonant unit 420 includes a second inductor L m The first inductor L r The first end of the first capacitor C is connected to the first end of the secondary side of the transformer module 300. The second end is connected to the first end of the secondary side of the transformer module 300. 1 is connected to the first input terminal of the output switch network 500. The second inductor L m The first end of the second inductor L is connected to the first end of the secondary side of the transformer module 300 through the resonant switching control unit 620. m The second end of the output switch network 500 is connected to the second end of the secondary side of the transformer module 300. 5 -Q 8 And the reverse parallel diode D 5 -D 8 The output switch network 500 may further include an output filter capacitor C out The output filter capacitor C out Connect the positive and negative bus bars at both ends.

[0042] In this embodiment, the resonant switching control unit includes a first inductor L r The first resonant switch K connected in parallel llc and the second inductor L m The second resonant switch K in series m The boost switching control unit includes a boost energy storage inductor L connected in parallel with the boost energy storage inductor L boost The boost switch K at both ends boost In this preferred embodiment, the first resonant switch K llc , the second resonant switch K m And boost switch K boost Air switches are used. In a preferred embodiment of the present invention, the switch tube can be a metal-oxide semiconductor field effect transistor, an insulated gate bipolar transistor, a power transistor, an insulated gate field effect transistor, a gate turn-off thyristor or a thyristor. The input end of the boost energy storage module 100 can be connected to a battery module or a load module, a single-phase passive power factor correction circuit, a single-phase active power factor correction circuit, a three-phase passive power factor correction circuit, or a three-phase active power factor correction circuit.

[0043] In a further preferred embodiment of the present invention, the boost energy storage module further comprises an absorption unit connected between the first input terminal and the second input terminal of the input switch network. Fig.11 In the embodiment shown, the absorption unit includes an absorption diode D f , absorption capacitor C f And the absorption resistor R f The absorption diode Df The anode is connected to the first input terminal of the input switch network 200, and the cathode is connected to the absorption capacitor C f The second input terminal of the input switch network 200 is connected to the absorption resistor R f In parallel with the absorption capacitor C f Of course, the absorption resistor R f It is also possible to connect the absorption diode D f In other preferred embodiments of the present invention, the absorption unit may also adopt other structures or include other elements.

[0044] Figures 4A-4C and Figure 7A-7B The schematic diagrams of charging energy, positive and negative energy transfer during forward transformation and positive and negative energy transfer during reverse transformation are shown respectively. Figure 5 and 8 The schematic diagrams of the switch tube driving the wave generator for the DC forward and reverse conversion are shown respectively. Figure 6 and 9 The control block diagrams of its DC forward conversion and DC reverse conversion are shown respectively. Figures 10A-10B The following is a schematic diagram of the application circuit. Figure 3-10B The principle of the present invention is explained as follows.

[0045] In the forward transformation stage:

[0046] In step 1, disconnect the air switch K boost , disconnect the air switch K lm , Close the air switch K llc , combining BOOST boost with transformer module to realize step-up and step-down from input power side to output side.

[0047] In step 2, the switch tube of the high-voltage side full-bridge circuit of the transformer module is controlled in the following manner: switch tube Q 1 , switch tube Q 3 The drive is the same, the switch tube Q 2 , switch tube Q 4 The drive is the same, the switch tube Q 1 , switch tube Q 2 The driving duty cycle is the same and the phase is staggered by 180 degrees;

[0048] In step 3, when the high-voltage side switch tube Q of the transformer module 1 , switch tube Q 2 , switch tube Q 3 , switch tube Q 4 When all are turned on, the input power is supplied to the inductor L boost Charging; at this time, the low-voltage side switch tube Q of the transformer module 5 , switch tube Q6 , switch tube Q 7 , switch tube Q 8 All are turned off, the specific circuit diagram is as follows Figure 4A shown.

[0049] In step 4, when the high-voltage side switch tube Q of the transformer module 1 , switch tube Q 3 Turn on, switch tube Q 2 , switch tube Q 4 When off, the input power supply and the inductor L boost At this time, the low-voltage side switch tube Q 5 , switch tube Q 7 Turn on, switch tube Q 6 , switch tube Q 8 Turn off and perform synchronous rectification; the specific circuit diagram is as follows Figure 4B shown.

[0050] In step 5, when the high-voltage side switch tube Q of the transformer module 1 , switch tube Q 3 Turn off, switch tube Q 2 , switch tube Q 4 When turned on, the power supply and the inductor L boost At this time, the low-voltage side switch tube Q 5 , switch tube Q 7 Turn off, switch tube Q 6 , switch tube Q 8 Turn on to perform synchronous rectification; the specific circuit diagram is as follows Figure 4C shown.

[0051] The control goal of the forward conversion is to stabilize the output voltage (i.e., bus voltage), limit power, and improve current ripple. Therefore, voltage and current dual closed-loop control is adopted: the current reference value is calculated by the BUS voltage PI loop, and the BOOST duty cycle is calculated by the current PI loop, and the actual control switch duty cycle is calculated by adding the feedforward amount; the specific wave control method is as follows: Figure 5 As shown in the control block diagram Figure 6 shown.

[0052] In the inverse transformation stage:

[0053] In step 1, close the air switch K boost , close the air switch K lm , disconnect the air switch K llc , combining the LLC resonant module with the transformer module to achieve step-up and step-down from the output side to the power supply side; the switch tube Q 1 , switch tube Q 2 , switch tube Q 3 , switch tube Q4 , switch tube Q 5 , switch tube Q 6 , switch tube Q 7 , switch tube Q 8 They are all controlled with a constant duty cycle, and the reverse output voltage is controlled by adjusting the switching frequency (frequency modulation).

[0054] In step 2, the switch tube of the low-voltage side full-bridge circuit of the transformer module is controlled in the following manner: switch tube Q 5 , switch tube Q 7 The drive is the same, the switch tube Q 6 , switch tube Q 8 The drive is the same, the switch tube Q 5 , switch tube Q 8 The drives are complementary, and the duty cycle is controlled by adjusting the dead time.

[0055] In step 3, when the low-voltage side switch tube Q of the transformer module 5 , switch tube Q 7 Turn on, switch tube Q 6 , switch tube Q 8 When turned off, the output side transfers energy to the power side through the transformer module; at this time, the high-voltage side switch tube Q of the transformer module 1 , switch tube Q 3 Turn on, switch tube Q 2 , switch tube Q 4 Turn off and perform synchronous rectification; the specific circuit diagram is as follows Fig. 7A shown.

[0056] In step 4, when the low-voltage side switch tube Q of the transformer module 5 , switch tube Q 7 Turn off, switch tube Q 6 , switch tube Q 8 When it is turned on, the output side transfers energy to the power supply side through the transformer module; at this time, the high-voltage side switch tube Q 1 , switch tube Q 3 Turn off, switch tube Q 2 , switch tube Q 4 Turn on to perform synchronous rectification; the specific circuit diagram is as follows Figure 7B shown.

[0057] The reverse conversion control goal is to stabilize the power supply voltage and limit the power at the same time. It adopts voltage and current double closed-loop control: the current reference value is calculated by the power supply voltage PI loop, and then the LLC frequency adjustment is calculated through the current PI loop. Finally, the feedforward amount is added to calculate the actual control switch frequency. The specific wave control method is as follows: Figure 8 As shown in the control block diagram Fig. 9In the constant current control stage, the power supply voltage PI loop is saturated; in the constant voltage control stage and the floating charge stage, the power supply voltage PI loop will be desaturated.

[0058] The single-stage high-frequency isolated bidirectional DC converter proposed in the present invention innovatively combines the BOOST boost circuit with the high-frequency isolated LLC resonant module to realize the function of boosting the high-voltage side of the high-frequency transformer, and then reduces the voltage through the high-frequency transformer ratio. The low-voltage side can use low-voltage switch devices to save costs; under the premise of effectively widening the input voltage range, no switch devices are added, which can reduce the system volume and simplify the control; the present invention realizes bidirectional DC conversion with a wide input voltage range through a single-stage power conversion circuit, which can improve the system conversion efficiency. The voltage and current dual closed-loop control strategy is simple to control and easy to promote and apply; the compact single-stage power conversion is adopted, which is more efficient and less costly.

[0059] Fig.12 1 is a principle block diagram of the first preferred embodiment of the grid-connected energy storage system of the present invention. Fig.12 As shown, the grid-connected energy storage system includes a battery module 101, a photovoltaic module 301, a DC / DC module 401, a DC filter module 501, a DC / AC module 601, an AC filter module 701, a relay 801, a load 1001, a power grid module 901, and a single-stage high-frequency isolated bidirectional DC converter 201. The photovoltaic module 301 is connected to the DC filter module 501 via the DC / DC module 401, the battery module 101 is connected to the DC filter module 501 via the single-stage high-frequency isolated bidirectional DC converter 201, and the DC filter module is further connected to the load 10011 or the power grid module 901 via the DC / AC module 601, the AC filter module 701, and the relay 801 in sequence.

[0060] Those skilled in the art know that the battery module 101, the photovoltaic assembly 301, the DC / DC module 401, the DC filter module 501, the DC / AC module 601, the AC filter module 701, the relay 801, the load 1001, and the grid module 901 can adopt any relevant modules known in the art. Figures 13A-13C A single-phase alternative implementation of the DA / AC module is shown. Figures 14A-14C The three-phase optional implementation of the DA / AC module is shown. The photovoltaic module 301 can be a PV photovoltaic module. The single-stage high-frequency isolated bidirectional DC converter 201 can be constructed with reference to any of the above embodiments.

[0061] In a preferred embodiment of the present invention, a current sensor is connected in series in the circuit of the battery module 101; a current sensor is connected in series in the circuit of the PV photovoltaic component 301; a current sensor is connected in series in the circuit of the power grid module 901; a current sensor is connected in series in the circuit of the load 1001; the input and output AC voltages of the relay network 801 are sampled respectively through voltage sensors; the DC voltages at both ends of the battery module 101, the PV photovoltaic component 301 and the DC filter module 501 are sampled respectively through resistor series-parallel connection and a linear optocoupler circuit.

[0062] The working principle of the grid-connected energy storage system of the present invention is described in detail below, and the specific steps are as follows:

[0063] Step 1: Detect the access status of the battery module 101, the PV photovoltaic assembly 301, and the grid module 901.

[0064] Step 2: If there is only the battery module 101 , it works in the off-grid operation mode: the battery module 101 discharges to supply power to the load 1001 .

[0065] Step 3: If only the PV photovoltaic module 301 is used, it works in the off-grid operation mode: the PV photovoltaic module 301 discharges to supply power to the load 1001 .

[0066] Step 4: If only the grid module 901 is connected, it works in the grid-connected operation mode: the grid module 901 supplies power to the load 1001.

[0067] Step 5. If only the PV photovoltaic module 301 and the grid module 901 are connected, it works in the grid-connected operation mode and is the same as the PV grid-connected inverter: first, the bus soft start is mainly to control the non-isolated DC / DC module 401 to convert the voltage of the PV photovoltaic module 301 into an ideal voltage output; secondly, the software phase lock is mainly to perform software phase lock on the phase of the grid module 901; thirdly, the relay detection is mainly to detect the relay module 801, close the relay, and connect the grid module 901 and the load 1001 to the system; finally, the maximum power tracking is mainly to track the maximum power point of the PV photovoltaic module 301.

[0068] Step 6: If only the PV photovoltaic component 301 and the battery module 101 are connected, it works in the off-grid operation mode: when the load is light, the energy of the PV photovoltaic component 301 is transmitted to the battery module 101 and the load 1001, and the battery module 101 is in the charging mode; when the load is heavy, the energy of the PV photovoltaic component 301 and the battery module 101 is transmitted to the load 1001, and the battery module 101 is in the discharging mode.

[0069] Step 7. If only the battery module 101 and the grid module 901 are connected, it works in the grid-connected operation mode similar to the photovoltaic grid-connected inverter: first, the bus soft start mainly controls the single-stage high-frequency isolated bidirectional DC converter 201 to convert the voltage of the battery module 101 into an ideal voltage output; secondly, the software phase lock mainly performs software phase lock on the phase of the grid module 901; thirdly, the relay detection mainly detects the relay module 801, closes the relay, and connects the grid module 901 and the load 1001 to the system; finally, the power flow control of the battery module 101 mainly determines whether the battery module 101 is in charging mode or discharging mode.

[0070] Step 8: If the battery module 101, PV photovoltaic component 301 and grid module 901 are connected, it works in the grid-connected operation mode similar to the photovoltaic grid-connected inverter: first, the bus soft start mainly controls the single-stage high-frequency isolated bidirectional DC converter 201 to convert the voltage of the battery module 101 into an ideal voltage output or controls the non-isolated DC / DC module 401 to convert the voltage of the PV photovoltaic component 301 into an ideal voltage output; secondly, software phase lock mainly performs software phase lock on the phase of the grid module 901; thirdly, relay detection mainly detects the relay network 801, closes the relay, and connects the grid module 901 and the load 1001 to the system; finally, maximum power tracking mainly tracks the maximum power point of the PV photovoltaic component 301, and at the same time determines the power flow direction of the battery module 101, that is, whether the battery module 101 is in charging mode or discharging mode.

[0071] Further analysis of the charging and discharging principle of the single-stage high-frequency isolated bidirectional DC converter 201

[0072] Discharge operation mode:

[0073] In step 1, disconnect the air switch K boost , disconnect the air switch K lm , Close the air switch K llc , combining BOOST boost with transformer module to realize step-up and step-down of input power supply to output side. By adjusting the duty ratio of high-voltage side switch tube of transformer module and low-voltage side switch tube of transformer module, the discharge step-up and step-down and high-frequency isolation functions of battery module 101 are realized.

[0074] Specifically, the duty cycle of the high-voltage side switch tube of the transformer module is soft-started to a maximum of 50%, and the initial duty cycle value is obtained, and the switch devices in the same bridge arm are driven with the same duty cycle, the phase is staggered by 180 degrees, and the relative switch devices in different bridge arms are driven in the same way. The voltage of the required DC filter module 501 is given as the discharge voltage closed-loop reference value, and the actual DC voltage at both ends of the DC filter module 501 is used as the discharge voltage closed-loop feedback value, and the discharge current closed-loop given value is output. The current value sampled by the series current sensor in the battery module 101 loop is used as the feedback value of the discharge current closed-loop, and the duty cycle adjustment amount of the high-voltage side switch tube of the transformer module is output.

[0075] The calculated duty cycle adjustment is added to the initial duty cycle to obtain the duty cycle of the switch device that actually controls the high-voltage side switch tube of the transformer module. The duty cycle of the switch device is used as a reference to calculate the duty cycle required for the synchronous rectification control of the low-voltage side switch tube of the transformer module, which is slightly smaller than the ideal calculated value to avoid energy backflow.

[0076] Charging operation mode:

[0077] Close air switch K boost , close the air switch K lm , disconnect the air switch K llc , combining the LLC resonant module with the transformer module to realize the buck-boost from the output side to the power supply side; by adjusting the switching frequency and duty cycle of the high-voltage side switch tube of the transformer module and the low-voltage side switch tube of the transformer module, the charging buck-boost and high-frequency isolation functions are realized.

[0078] Specifically: according to the initially set switching frequency and duty cycle, slowly reduce the dead time of the low-voltage side switch tube of the transformer module to the set value, and ensure that the switching devices in the same bridge arm are complementary, and the relative switching devices in different bridge arms are driven the same.

[0079] The required voltage of the battery module 101 is given as a charging voltage closed-loop reference value, the actual DC voltage across the battery module 101 is used as a charging voltage closed-loop feedback value, and a charging current closed-loop given value is output.

[0080] The current value sampled by the series current sensor in the battery module 101 loop is used as the feedback value of the reverse current closed loop, and the switching frequency adjustment value of the low-voltage side switch tube of the transformer module is output.

[0081] The calculated switching frequency adjustment amount is added to the initially set switching frequency to obtain the switching frequency of the low-voltage side switch tube of the actual control transformer module. The calculated switching frequency and duty cycle of the low-voltage side switch tube of the actual control transformer module are used as a reference to calculate the switching frequency and duty cycle required for synchronous rectification control of the high-voltage side switch tube of the transformer module, where the frequency is the same and the duty cycle is slightly smaller than the ideal calculated value to avoid energy backflow.

[0082] The grid-connected energy storage system proposed in the present invention innovatively combines BOOST boost with high-frequency isolated LLC resonant module to realize the function of boosting the high-voltage side of the high-frequency transformer, and then reduces the voltage through the high-frequency transformer ratio. The low-voltage side can use low-voltage switch devices to save costs; under the premise of effectively widening the input voltage range, no switch devices are added, which can reduce the system volume and simplify the control; the present invention realizes bidirectional DC conversion with a wide input voltage range through a single-stage power conversion circuit, which can improve the system conversion efficiency. The voltage and current dual closed-loop control strategy is simple to control and easy to promote and apply; the compact single-stage power conversion is adopted, which is more efficient and less costly.

[0083] Although the present invention is described by specific embodiments, it should be understood by those skilled in the art that various changes and equivalent substitutions may be made to the present invention without departing from the scope of the present invention. In addition, various modifications may be made to the present invention for specific situations or materials without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed, but should include all implementation methods falling within the scope of the claims of the present invention.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A single-stage high-frequency isolated bidirectional DC converter, characterized in that: include: A boost energy storage module, an input switch network, a transformer module, a resonance module, an output switch network, and a switching control module connected to the boost energy storage module and the resonance module, wherein the boost energy storage module is connected to the positive and negative electrodes of the input power supply; the switching control module is used to control the boost energy storage module to be switched on and the resonance module to be switched off during forward conversion, and to control the boost energy storage module to be switched off and the resonance module to be switched on during reverse conversion; The resonance module includes a first resonance unit and a second resonance unit, wherein the first resonance unit is connected between the first end of the secondary side of the transformer module and the first input end of the output switch network, and the second resonance unit is connected between the first end of the secondary side of the transformer module and the second end of the secondary side via a resonance switching control unit; The switching control module includes a boost switching control unit for controlling the boost energy storage module to be switched in forward conversion and the boost energy storage module to be switched out in reverse conversion, and a resonance switching control unit for controlling the first resonance unit and the second resonance unit to be switched out in forward conversion and the first resonance unit and the second resonance unit to be switched in reverse conversion; The first resonant unit includes a first inductor and a first capacitor, and the second resonant unit includes a second inductor, wherein a first end of the first inductor is connected to a first end of a secondary side of the transformer module, and a second end of the first inductor is connected to a first input end of the output switch network via the first capacitor; a first end of the second inductor is connected to a first end of a secondary side of the transformer module via the resonant switching control unit, and a second end of the second inductor is connected to a second end of a secondary side of the transformer module; The resonant switching control unit includes a first resonant switch connected in parallel with the first inductor and a second resonant switch connected in series with the second inductor; the boost energy storage module includes a boost energy storage inductor connected to the positive electrode of the input power supply and the first input end of the input switch network; the boost switching control unit includes a boost switching switch connected in parallel at both ends of the boost energy storage inductor.

2. The single-stage high-frequency isolated bidirectional DC converter according to claim 1, characterized in that: The boost energy storage module further includes an input filter capacitor connected between the positive electrode and the negative electrode of the output power supply and an absorption unit connected between the first input terminal and the second input terminal of the input switch network.

3. The single-stage high-frequency isolated bidirectional DC converter according to claim 2, characterized in that: The input switch network and the output switch network include a full-bridge switch tube network or a half-bridge switch tube network, the absorption unit includes an absorption diode, an absorption capacitor and an absorption resistor, the anode of the absorption diode is connected to the first input end of the input switch network, and the cathode is connected to the second input end of the input switch network via the absorption capacitor, and the absorption resistor is connected in parallel to the absorption diode or the absorption capacitor.

4. A grid-connected energy storage system, comprising a battery module, a photovoltaic component, a DC / DC module, a DC filter module, a DC / AC module, an AC filter module, a relay, a load, a power grid module and a single-stage high-frequency isolated bidirectional DC converter according to any one of claims 1 to 3, wherein the photovoltaic component is connected to the DC filter module via the DC / DC module, the battery module is connected to the DC filter module via the single-stage high-frequency isolated bidirectional DC converter, and the DC filter module is further connected to a load or a power grid module via a DC / AC module, an AC filter module and a relay in sequence.

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