A bidirectional DCDC conversion circuit and its charge and discharge control method

Abstract

The present invention provides a bidirectional DCDC conversion circuit and a charge and discharge control method thereof. By setting a switching switch, the turn ratio of the windings connecting a bus side converter and a high-frequency inverter is changed, thereby adjusting the output voltage of the high-frequency transformer. The bidirectional DCDC conversion circuit can increase the transformation ratio of the high-frequency transformer by switching the switch to increase the bus voltage when the battery is discharged and the battery voltage is low, thereby avoiding that the bus voltage is greatly reduced with the reduction of the battery voltage, thereby causing the inverter voltage to be clipped. The bidirectional DCDC conversion circuit can also increase the transformation ratio of the high-frequency transformer by switching the switch to reduce the bus voltage when the battery is charged and the battery voltage is increased, thereby avoiding that the bus voltage is greatly increased with the increase of the battery voltage, thereby causing the inverter switch tube voltage stress to be too high and damaged. The variation range of the bus voltage is reduced by the cooperation of the first connection point, the second connection point and the switching switch, thereby replacing a special buck-boost circuit, saving costs, and being conducive to achieving green energy-saving effects.

Description

Technical Field

[0001] The present invention relates to the technical field of bidirectional DCDC conversion, and more specifically to a bidirectional DCDC conversion circuit and a charge and discharge control method thereof. Background Art

[0002] The bidirectional DCDC conversion circuit can change the direction of the current according to the actual needs while keeping the input and output voltage polarities unchanged. It can convert the high voltage on the bus side into the low voltage on the battery side, and also convert the low voltage on the battery side into the high voltage on the bus side. This bidirectional energy conversion feature makes the bidirectional DCDC conversion circuit an indispensable component in applications such as energy storage systems and electric vehicles. The common bidirectional DCDC conversion circuits are usually as follows Figure 1 or Figure 2 shown.

[0003] like Figure 1 As shown, a first-stage LLC bidirectional converter and a first-stage BUCK-BOOST bidirectional converter are used between the battery and the bus, and a smooth voltage output is achieved through a complex filtering network, including C2, L2, T_DIS, T_CHG, and C3. In this way, whether in battery discharge mode or battery charging mode, the bus voltage can be controlled within a very small variation range within the battery voltage variation range. The disadvantage is that the cost is relatively high. The first-stage conversion can only adjust the DC voltage to a value that follows the battery voltage change, and then it is further converted through another stage of change to obtain the required voltage value with little fluctuation. The process is complicated, occupies more control resources, and has low efficiency.

[0004] like Figure 2 As shown, only one LLC resonant converter is used to realize bidirectional DCDC conversion, and only a filter is used between the bus and the bus-side converter. The disadvantage is that the bus voltage will decrease significantly as the battery voltage decreases during the discharge process. During the charging process, as the battery voltage increases, the bus voltage needs to be greatly increased to complete the fast charging of the battery according to the required current. In this case, the bus voltage changes greatly, and when the bus voltage is too high, the transistor stress in the inverter circuit will exceed the standard, so that higher-level transistors have to be selected under special circumstances. Therefore, the bidirectional DCDC conversion circuit is not conducive to the stable operation of the system, and reduces the operating efficiency of the system, and cannot achieve green energy saving.

[0005] Therefore, it is difficult for the existing bidirectional DCDC conversion circuit to reduce the bus voltage variation range under the conditions of low cost and green energy saving. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provide a bidirectional DCDC conversion circuit and a charge and discharge control method thereof to solve the technical problem that the existing bidirectional DCDC conversion circuit is difficult to achieve both low cost and reduced bus voltage variation range.

[0007] In a first aspect, an embodiment of the present invention provides a bidirectional DCDC conversion circuit, which is applied to a battery and a busbar of an inverter, and includes:

[0008] Main circuit and control circuit; the main circuit includes: a battery access terminal, a battery side filter, a battery side converter, a high-frequency transformer, a switching switch, a bus side converter, a bus side filter and a bus access terminal connected in sequence; the high-frequency transformer is provided with a first connection point and a second connection point, and the winding turns ratio of the second connection point is smaller than the winding turns ratio of the first connection point; the control circuit is used to control the first connection point or the second connection point to be connected so as to adjust the output voltage of the high-frequency transformer.

[0009] Among them, the switching switch is provided with a static contact, a first moving contact and a second moving contact; the static contact is connected to the input end of the bus side converter, the first moving contact and the second moving contact are respectively connected to the first connection point and the second connection point; the static contact is connected to the first moving contact or the second moving contact.

[0010] Wherein, the high frequency transformer comprises: a battery side winding and a bus side winding, the battery side winding is connected to the battery side converter, and the switching switch is connected to the bus side converter;

[0011] The busbar side winding is provided with a main tap and a middle tap, and the first connection point and the second connection point are respectively located at the main tap and the middle tap.

[0012] The battery side converter comprises: four switch units, the four switch units and the battery side of the high frequency transformer form a first H-bridge circuit; the switch unit comprises: a Moss tube and a first diode, the Moss tube is connected in parallel with the first diode; the first H-bridge circuit is connected in parallel with the battery side filter;

[0013] The bus-side converter comprises: four crystal units, the four crystal units and the bus side of the high-frequency transformer form a second H-bridge circuit; the crystal unit comprises: a transistor and a second diode, the transistor and the second diode are connected in parallel; the second H-bridge circuit is connected in parallel with the bus-side filter;

[0014] The battery-side filter and the bus-side filter are both capacitors.

[0015] Wherein, the control circuit comprises:

[0016] A first voltage detection module, connected between the battery access terminal and the battery side filter circuit, for detecting the battery voltage;

[0017] A second voltage detection module, connected between the bus access terminal and the bus side filter circuit, for detecting the bus voltage;

[0018] A first transistor driving module, used for controlling the battery side converter to work or shut down;

[0019] A second transistor driving module, used for controlling the bus side converter to operate or shut down;

[0020] A first current detection module, used for collecting the working current of the battery side converter;

[0021] A second current detection module, used for collecting the working current of the bus-side converter;

[0022] A switch driving module, used for driving the switch to connect to the first connection point or the second connection end;

[0023] The signal processing module, the first voltage detection module, the second voltage detection module, the first transistor driving module, the second transistor driving module, the first current detection module, the second current detection module, and the switching switch driving module are electrically connected to the signal processing module respectively.

[0024] Wherein, the main circuit further includes:

[0025] A first Hall element is provided between the battery side converter and the high frequency transformer, and is used to detect the working current of the battery side converter; the first current detection module is connected to the first Hall element;

[0026] The second Hall element is arranged between the high-frequency transformer and the bus-side converter, and is used to detect the operating current of the bus-side converter; the second current detection module is connected to the second Hall element.

[0027] In a second aspect, an embodiment of the present invention further provides a charging control method for a bidirectional DCDC conversion circuit, the method being performed by the bidirectional DCDC conversion circuit as described above, and comprising the following steps:

[0028] Step 1: Check whether the bus voltage is higher than the preset bus voltage threshold Vb; if yes, go to step 2; otherwise, jump to step 4;

[0029] Step 2, driving the switch to connect the first connection point, and driving the bus-side converter to operate at a frequency fa;

[0030] Step 3, detecting whether the battery voltage is lower than the preset battery voltage threshold Va; if so, maintaining the current charging state, otherwise proceeding to step 4;

[0031] Step 4, driving the switch to connect the second connection point, and driving the bus-side converter to operate at a frequency fb;

[0032] Step 5, detecting whether the battery voltage is higher than the battery preset high voltage threshold value Vfull; if so, ending the charging, otherwise returning to step 4; wherein the battery preset high voltage threshold value Vfull is greater than the battery preset voltage threshold value Va.

[0033] Wherein, before step 4, the following steps are also included:

[0034] Driving the bus-side converter to shut down;

[0035] Wait for the operating current of the bus-side converter to drop to zero.

[0036] In a third aspect, an embodiment of the present invention further provides a discharge control method of a bidirectional DCDC conversion circuit, the method being executed by the above-mentioned bidirectional DCDC conversion circuit, and comprising the following steps:

[0037] Step 1: Check whether the battery voltage is higher than the preset battery voltage threshold Va; if yes, go to step 2; otherwise, go to step 4;

[0038] Step 2, driving the switch to connect the second connection point, and driving the battery side converter to operate at a frequency fb;

[0039] Step 3: Check whether the bus voltage is lower than the preset bus voltage threshold Vb; if so, proceed to step 4; otherwise, maintain the current discharge state;

[0040] Step 4, driving the switch to connect the first connection point, and driving the battery side converter to operate at a frequency fa;

[0041] Step 5, detecting whether the battery voltage is lower than a preset low voltage threshold value Vlow of the battery; if so, the discharge is terminated, otherwise, the process returns to step 4; wherein the preset low voltage threshold value Vlow of the battery is smaller than the preset voltage threshold value Va of the battery.

[0042] Wherein, before step 4, the following steps are also included:

[0043] Driving the battery side converter to shut down;

[0044] Wait for the operating current of the battery side converter to drop to zero.

[0045] Compared with the prior art, the present invention has the following beneficial effects: the present invention changes the winding turns ratio of the bus-side converter connected to the high-frequency converter by setting a switching switch, thereby adjusting the output voltage of the high-frequency transformer; the bidirectional DCDC conversion circuit can increase the transformation ratio of the high-frequency transformer by switching the switch to increase the bus voltage when the battery is discharged and the battery voltage is low, thereby compensating for the deficiency of the bus voltage and avoiding the bus voltage from being greatly reduced as the battery voltage is reduced, thereby causing the inverter voltage to be clipped; the bidirectional DCDC conversion circuit can also increase the transformation ratio of the high-frequency transformer by switching the switch to reduce the bus voltage when the battery is charged and the battery voltage is increased, thereby avoiding the bus voltage from being greatly increased as the battery voltage is increased, thereby causing the inverter switch tube voltage stress to be too high and damaged; the bus voltage variation range is reduced by cooperating with the first connection point, the second connection point and the switching switch, thereby replacing a special buck-boost circuit, saving costs, and being conducive to achieving green energy-saving effects.

[0046] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a structural schematic diagram of an existing bidirectional DCDC conversion circuit;

[0048] Figure 2 It is a structural schematic diagram of another existing bidirectional DCDC conversion circuit;

[0049] Figure 3 A schematic diagram of the structure of a main circuit of a bidirectional DCDC conversion circuit provided by the present invention;

[0050] Figure 4 A schematic diagram of the structure of a control circuit of a bidirectional DCDC conversion circuit provided by the present invention;

[0051] Figure 5 A flow chart of a charging control circuit of a bidirectional DCDC conversion circuit provided by the present invention;

[0052] Figure 6 The present invention provides a flow chart of a discharge control circuit of a bidirectional DCDC conversion circuit.

[0053] Reference numerals:

[0054] 1. Main circuit; 11. Battery access terminal; 12. Battery side filter; 13. Battery side converter; 14. High frequency transformer; 15. Resonant network; 16. Bus side converter; 17. Bus side filter; 18. Bus access terminal; 2. Control circuit; 21. First voltage detection module; 22. Second voltage detection module; 23. First transistor drive module; 24. Second transistor drive module; 25. First current detection module; 26. Second current detection module; 27. Switch drive module; 28. Signal processing module. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail in conjunction with the accompanying drawings and specific implementation methods. The technical solution in the embodiment of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0057] Embodiment 1, see attached Figure 3-4 As shown, this embodiment provides a bidirectional DCDC conversion circuit, which is applied to the battery and bus of the inverter. The bidirectional DCDC conversion circuit includes: a main circuit 1 and a control circuit 2; the main circuit 1 includes: a battery access terminal 11, a battery side filter 12, a battery side converter 13, a high-frequency transformer 14, a switching switch K1, a bus side converter 16, a bus side filter 17 and a bus access terminal 18 connected in sequence; the high-frequency transformer 14 is provided with a first connection point and a second connection point, and the winding turns ratio of the second connection point is smaller than the winding turns ratio of the first connection point; the control circuit 2 is used to control the first connection point or the second connection point to be connected to adjust the output voltage of the high-frequency transformer 14.

[0058] The switch K1 of this embodiment is used to change the winding turns ratio of the bus-side converter 16 connected to the high-frequency inverter, and then adjust the output voltage of the high-frequency transformer 14, so that the bus voltage can be controlled within a very small variation range within the battery voltage variation range. That is, the bidirectional DCDC conversion circuit can increase the transformation ratio of the high-frequency transformer 14 by switching the switch K1 during the battery discharge process and when the battery voltage is low, so as to increase the bus voltage, thereby compensating for the lack of bus voltage, and avoiding the bus voltage from being greatly reduced as the battery voltage decreases, thereby causing the inverter voltage to be clipped; the bidirectional DCDC conversion circuit can also increase the transformation ratio of the high-frequency transformer 14 by switching the switch K1 during the battery charging process and as the battery voltage gradually increases, thereby reducing the bus voltage, thereby avoiding the bus voltage from being greatly increased as the battery voltage increases, thereby causing the inverter switch tube voltage stress to be too high and damaged. This embodiment reduces the variation range of the bus voltage through the cooperation of the first connection point, the second connection point and the switch K1, replaces the complex filtering network, greatly saves costs, and is conducive to achieving green energy-saving effects.

[0059] Among them, the switching switch K1 is provided with a static contact c, a first moving contact a and a second moving contact b; the static contact c is connected to the input end of the bus side converter 16, the first moving contact a and the second moving contact b are respectively connected to the first connection point and the second connection point; the static contact c is connected to the first moving contact a or the second moving contact b. The output voltage of the high-frequency transformer 14 affects the battery voltage and the bus voltage. In the discharge state, the output voltage of the high-frequency transformer 14 is high, and the bus voltage input to the bus increases. In the charging state, the output voltage of the high-frequency transformer 14 is low, and the battery voltage input to the battery decreases. Therefore, the bidirectional DCDC conversion circuit of this embodiment realizes flexible adjustment of different voltage requirements. In practical applications, if the output voltage of the high-frequency transformer 14 needs to be reduced, the static contact c is connected to the first moving contact a, and if the output voltage of the high-frequency transformer 14 needs to be increased, the static contact c is connected to the second moving contact b.

[0060] Among them, the high-frequency transformer 14 includes: a battery side winding and a bus side winding, the battery side winding is connected to the battery side converter 13, and the switch K1 is connected to the bus side converter 16; the bus side winding is provided with a main tap and a middle tap, and the first connection point and the second connection point are respectively located at the main tap and the middle tap. The bus side winding includes a winding N2 and a winding N3, and the middle tap and the main tap are respectively arranged corresponding to the winding N2 and the winding N3; the middle tap is located in the middle of the bus side winding, and the main tap can be located at the end of the bus side winding, or between the end of the bus side winding and the middle tap. The addition of the middle tap reduces the bus voltage variation amplitude of the bidirectional DCDC conversion circuit of this embodiment without significantly increasing the cost, thereby ensuring the stability and safety of the battery and the bus. In other embodiments, the high-frequency transformer 14 can be an adjustable transformer, that is, a mobile connection point is used to replace the middle tap and the main tap.

[0061] Among them, the battery side converter 13 includes: four switch units, the four switch units and the battery side of the high-frequency transformer 14 form a first H-bridge circuit; the switch unit includes: a Morse tube and a first diode, the Morse tube is connected in parallel with the first diode; the first H-bridge circuit is connected in parallel with the battery side filter 12, and the D pole and S pole of the Morse tube are respectively connected to the output end and input end of the first diode; the bus side converter 16 includes: four crystal units, the four crystal units and the bus side of the high-frequency transformer 14 form a second H-bridge circuit; the crystal unit includes: a transistor and a second diode, the transistor and the second diode are connected in parallel, and the A pole and K pole of the transistor are respectively connected to the output end and input end of the second diode; the second H-bridge circuit is connected in parallel with the bus side filter 17; the battery side filter 12 and the bus side filter 17 are both capacitors. Figure 3 As shown, the four switch units are PRI1_T1, PRI1_T2, PRI1_T3, and PRI1_T4, and the four crystal units are H1, H2, H3, and H4. The battery and the bus are connected to the bidirectional DCDC conversion circuit through the battery access terminal 11 and the bus access terminal 18 respectively. The DC power output by the battery or the bus needs to be transformed by the high-frequency transformer 14 before it can be transmitted to each other. The battery side converter 13 and the bus side converter 16 are used to rectify the high-frequency AC power output by the high-frequency transformer 14 and to control the output voltage of the high-frequency transformer 14. The bus side filter 17 does not require a complex filtering network. Only by the joint action of the switching switch K1 and the high-frequency transformer 14, the bus voltage change amplitude can be accurately controlled.

[0062] The main circuit 1 further includes: a resonant network 15; the switch K1 is connected to the bus-side converter 16 through the resonant network 15; the resonant network 15 includes: a resonant inductor Lr and a resonant capacitor Cr; the resonant inductor Lr and the resonant capacitor Cr are sequentially connected in series between the switch K1 and the bus-side converter 16. The resonant network 15 is conducive to voltage shaping, reduces harmonic distortion, improves the quality of the output voltage or current, and can suppress high-frequency noise and interference, filter out unnecessary frequency components, and provide pure and stable output; the resonant inductor Lr and the resonant capacitor Cr can store and transfer energy, and the energy is exchanged back and forth between the resonant inductor Lr and the resonant capacitor Cr through the resonance effect, which improves the efficient transmission of energy, helps to reduce power loss, and thus improves the overall efficiency of the system.

[0063] The control circuit 2 includes: a first voltage detection module 21, connected between the battery access terminal 11 and the battery side filter circuit, for detecting the battery voltage; a second voltage detection module 22, connected between the bus access terminal 18 and the bus side filter circuit, for detecting the bus voltage; a first transistor driving module 23, for controlling the operation or shutdown of the battery side converter 13; a second transistor driving module 24, for controlling the operation or shutdown of the bus side converter 16; a first current detection module 25, for collecting the working current of the battery side converter 13; a second current detection module 26, for collecting the working current of the bus side converter 16; a switching switch driving module 27, for driving the switching switch K1 to connect the first connection point or the second connection point end; signal processing module 28, first voltage detection module 21, second voltage detection module 22, first transistor driving module 23, second transistor driving module 24, first current detection module 25, second current detection module 26, switching switch driving module 27 are electrically connected to the signal processing; specifically, four switch units are respectively connected to the first transistor driving module 23, the first transistor driving module 23 is used to drive the four Morse tubes to be turned on and off, and four crystal units are respectively connected to the second transistor driving module 24, the second transistor driving module 24 is used to drive the four transistors to be turned on and off; the G pole of the Morse tube is connected to the first transistor driving module 23, and the G pole of the transistor is connected to the second transistor driving module 24. The first voltage detection module 21, the second voltage detection module 22, the first transistor driving module 23, the second transistor driving module 24, the first current detection module 25, the second current detection module 26, and the switching switch driving module 27 are formed by the existing voltage detection circuit, transistor driving circuit, current detection circuit, and switch driving circuit, and the specific structure is not repeated here. The signal processing module 28 is formed by a DSP signal processing circuit, which is used to collect the detection voltage of the first voltage detection circuit and the second voltage detection circuit, and to collect the detection current of the first current detection circuit and the second current detection circuit, and to drive the switch unit or the crystal unit to work and shut down according to the preset logic.

[0064] The main circuit 1 further includes: a first Hall element HALL1, which is arranged between the battery side converter 13 and the high frequency transformer 14, and is used to detect the working current of the battery side converter 13; a first current detection module 25 connected to the first Hall element HALL1; a first Hall element HALL1, which is arranged between the high frequency transformer 14 and the bus side converter 16, and is used to detect the working current of the bus side converter 16; and a second current detection module 26 connected to the first Hall element HALL1. The first Hall element HALL1 and the first Hall element HALL1 are built into the bidirectional DCDC conversion circuit for current detection, which reduces the transmission path of the detection current and improves the efficiency of current electrical measurement. Compared with current electrical measurement elements such as fluxgate sensors and shunts, they also have lower costs, which is conducive to achieving green energy saving.

[0065] Embodiment 2, see attached Figure 5 This embodiment further provides a charging control method for a bidirectional DCDC conversion circuit. The method is performed by the bidirectional DCDC conversion circuit of the first embodiment, and comprises the following steps:

[0066] S11, detect whether the bus voltage is higher than the bus preset voltage threshold Vb; if so, go to S12, otherwise jump to S14;

[0067] S12, driving the switch K1 to connect to the first connection point, and driving the bus-side converter 16 to operate at the frequency fa;

[0068] S13, detecting whether the battery voltage is lower than the preset battery voltage threshold Va; if so, maintaining the current charging state, otherwise entering S14;

[0069] S14, driving the switch K1 to connect to the second connection point, and driving the bus-side converter 16 to operate at the frequency fb;

[0070] S15, detecting whether the battery voltage is higher than the preset high voltage threshold Vfull of the battery; if so, ending the charging, otherwise returning to S14; wherein the preset high voltage threshold Vfull of the battery is greater than the preset voltage threshold Va of the battery.

[0071] That is, before the charging mode starts, the initial battery voltage is low. During the continuous charging process, the battery voltage gradually increases, and the bus voltage needs to be increased to ensure continuous high-current charging of the battery. The bus voltage increases much faster than the battery voltage, so the first stage of the charging process is to switch the switch K1 to the second connection point so that the high-frequency transformer 14 works at a lower winding turns ratio; as the battery voltage increases, the bus voltage also gradually increases until the bus voltage reaches the bus preset voltage threshold Vb, driving the switch K1 to connect to the first connection point, so that the turns ratio of the bus side winding of the high-frequency transformer 14 increases, and the bus voltage is reduced. Even if the battery voltage increases, it will not cause a significant increase in the bus voltage; when the charging process reaches the battery preset high-voltage threshold Vfull greater than the battery preset voltage threshold Va, the battery is full and the charging mode ends.

[0072] Among them, before S14, the following steps are also included:

[0073] Drive the bus-side converter 16 to shut down; wait for the operating current of the bus-side converter 16 to drop to zero.

[0074] There is a voltage difference between the second connection point and the first connection point when switching. When the switching switch K1 changes the connection point, if the bus-side converter 16 is still working and has an operating current, the voltage at this moment may cause a current mutation, thereby generating a current spike. The current spike will cause stress to the components in the bidirectional DCDC conversion circuit and may even damage the components. By first shutting down the bus-side converter 16 and waiting for its operating current to drop to zero, the generation of current spikes can be avoided, and instantaneous short circuits or overcurrent conditions during the switching process can be avoided, thereby ensuring the service life of the components; and during the switching process, if the bus-side converter 16 is still working, it is easy to cause an increase in the energy loss required for switching. By shutting down the bus-side converter 16 and waiting for the current to drop to zero, it is helpful to reduce energy loss, thereby improving the overall conversion efficiency of the bidirectional DCDC conversion circuit.

[0075] Embodiment 3, see attached Figure 6 This embodiment further provides a discharge control method for a bidirectional DCDC conversion circuit. The method is performed by the bidirectional DCDC conversion circuit of the first embodiment, and comprises the following steps:

[0076] S21, detect whether the battery voltage is higher than the preset battery voltage threshold Va; if so, go to S22, otherwise jump to S23;

[0077] S22, driving the switch K1 to connect to the second connection point, and driving the battery side converter 13 to operate at a frequency fb;

[0078] S23, detect whether the bus voltage is lower than the bus preset voltage threshold Vb; if so, enter S24, otherwise maintain the current discharge state;

[0079] S24, driving the switch K1 to connect to the first connection point, and driving the battery side converter 13 to operate at a frequency fa;

[0080] S25, detecting whether the battery voltage is lower than a preset low voltage threshold Vlow of the battery; if so, the discharge is terminated, otherwise, the process returns to S24; wherein the preset low voltage threshold Vlow of the battery is lower than the preset voltage threshold Va of the battery.

[0081] That is, in the discharge mode, if the battery has sufficient power (the voltage is higher than the preset battery voltage threshold Va), the bus is powered by the lower high-frequency transformer 14 output to avoid bus overvoltage. Otherwise, the bus is powered by the higher high-frequency transformer 14 output, thereby achieving bus voltage compensation and avoiding a significant decrease in the bus voltage as the battery voltage decreases, so that the bus voltage reaches a safe working state. During the discharge process, the bus voltage detected by the second voltage measuring circuit can be monitored by the signal processing module 28. When the bus voltage is too small, such as when the bus load is large, the switching switch K1 is promptly controlled to connect to the first connection point to increase the bus voltage. Otherwise, when the bus voltage is too large, such as when the bus load is small or the battery voltage is large, the switching switch K1 is promptly controlled to connect to the second connection point to reduce the bus voltage.

[0082] Among them, before S24, the following steps are also included:

[0083] Driving the battery side converter 13 to shut down; waiting for the operating current of the battery side converter 13 to drop to zero.

[0084] There is a voltage difference between the second connection point and the first connection point during switching. By first shutting down the battery side converter 13 and waiting for its operating current to drop to zero, the generation of current spikes can be avoided, and momentary short circuits or overcurrent conditions during the switching process can be avoided, thereby ensuring the service life of components and helping to reduce energy loss, thereby improving the overall conversion efficiency of the bidirectional DCDC conversion circuit.

[0085] A bidirectional DCDC conversion circuit and a charge and discharge control method thereof of the present embodiment, by setting a switching switch, changes the turns ratio of the windings connected between the bus side converter and the high-frequency inverter, thereby adjusting the output voltage of the high-frequency transformer; the bidirectional DCDC conversion circuit can increase the transformation ratio of the high-frequency transformer by switching the switch to increase the bus voltage when the battery is discharged and the battery voltage is low, thereby compensating for the deficiency of the bus voltage and avoiding the bus voltage from being greatly reduced as the battery voltage decreases, thereby causing the inverter voltage to be clipped; the bidirectional DCDC conversion circuit can also increase the transformation ratio of the high-frequency transformer by switching the switch to reduce the bus voltage when the battery is charged and the battery voltage increases, thereby avoiding the bus voltage from being greatly increased as the battery voltage increases, thereby causing the inverter switch tube voltage stress to be too high and damaged; the bus voltage variation range is reduced by the cooperation of the first connection point, the second connection point and the switching switch, thereby replacing a special buck-boost circuit, saving costs, and achieving green energy-saving effects.

[0086] The above examples are only used to further illustrate the technical content of the present invention, so that readers can understand it more easily, but they do not mean that the implementation of the present invention is limited to this. Any technical extension or re-creation made according to the present invention is protected by the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A bidirectional DCDC conversion circuit, applied to the battery and busbar of an inverter, characterized in that: include: Main circuit and control circuit; The main circuit includes: a battery access terminal, a battery side filter, a battery side converter, a high-frequency transformer, a switching switch, a bus side converter, a bus side filter and a bus access terminal connected in sequence; the high-frequency transformer is provided with a first connection point and a second connection point, and the winding turns ratio of the second connection point is smaller than the winding turns ratio of the first connection point; the control circuit is used to control the first connection point or the second connection point to be connected to adjust the output voltage of the high-frequency transformer; the switching switch is provided with a static contact, a first moving contact and a second moving contact; the static contact is connected to the input terminal of the bus side converter, and the first moving contact and the second moving contact are respectively connected to the first connection point and the second connection point; the static contact is connected to the first moving contact or the second moving contact; The main circuit further includes: a resonant network; the switching switch is connected to the bus-side converter via the resonant network; the resonant network includes: a resonant inductor and a resonant capacitor; the resonant inductor and the resonant capacitor are sequentially connected in series between the switching switch and the bus-side converter; The main circuit also includes: a first Hall element and a second Hall element, the first Hall element is arranged between the battery side converter and the high-frequency transformer, and the second Hall element is arranged between the high-frequency transformer and the bus side converter; the first Hall element and the second Hall element are respectively used to detect the operating current of the battery side converter and the bus side converter, when the battery side converter is turned off and the operating current of the battery side converter is about to reach zero, the switching switch is switched from connecting the second connection point to connecting the first connection point, and when the bus side converter is turned off and the operating current of the bus side converter is about to reach zero, the switching switch is switched from connecting the first connection point to connecting the second connection point.

2. The bidirectional DCDC conversion circuit according to claim 1, characterized in that: The high frequency transformer comprises: a battery side winding and a bus side winding, the battery side winding is connected to the battery side converter, and the switch is connected to the bus side converter; The busbar side winding is provided with a main tap and a middle tap, and the first connection point and the second connection point are respectively located at the main tap and the middle tap.

3. The bidirectional DCDC conversion circuit according to claim 1, characterized in that: The battery side converter comprises: four switch units, the four switch units and the battery side of the high frequency transformer form a first H-bridge circuit; the switch unit comprises: a MOS tube and a first diode, the MOS tube is connected in parallel with the first diode; the first H-bridge circuit is connected in parallel with the battery side filter; The bus-side converter comprises: four crystal units, the four crystal units and the bus side of the high-frequency transformer form a second H-bridge circuit; the crystal unit comprises: a transistor and a second diode, the transistor and the second diode are connected in parallel; the second H-bridge circuit is connected in parallel with the bus-side filter; The battery-side filter and the bus-side filter are both capacitors.

4. The bidirectional DCDC conversion circuit according to claim 1, characterized in that: The control circuit comprises: A first voltage detection module, connected between the battery access terminal and the battery side filter circuit, for detecting the battery voltage; A second voltage detection module, connected between the bus access terminal and the bus side filter circuit, for detecting the bus voltage; A first transistor driving module, used for controlling the battery side converter to work or shut down; A second transistor driving module, used for controlling the bus side converter to operate or shut down; A first current detection module, used for collecting the working current of the battery side converter; A second current detection module, used for collecting the working current of the bus-side converter; A switch driving module, used for driving the switch to connect to the first connection point or the second connection end; The signal processing module, the first voltage detection module, the second voltage detection module, the first transistor driving module, the second transistor driving module, the first current detection module, the second current detection module, and the switching switch driving module are electrically connected to the signal processing module respectively.

5. The bidirectional DCDC conversion circuit according to claim 4, characterized in that: The first current detection module is connected to the first Hall element; the second current detection module is connected to the second Hall element.

6. A charging control method for a bidirectional DCDC conversion circuit, the method being performed by the bidirectional DCDC conversion circuit according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: Check whether the bus voltage is higher than the preset bus voltage threshold Vb; if yes, go to step 2; otherwise, jump to step 4; Step 2, driving the switch to connect the first connection point, and driving the bus-side converter to operate at a frequency fa; Step 3, detecting whether the battery voltage is lower than the preset battery voltage threshold Va; if so, maintaining the current charging state, otherwise proceeding to step 4; Step 4, driving the switch to connect the second connection point, and driving the bus-side converter to operate at a frequency fb; Step 5, detecting whether the battery voltage is higher than the battery preset high voltage threshold value Vfull; if so, ending the charging, otherwise returning to step 4; wherein the battery preset high voltage threshold value Vfull is greater than the battery preset voltage threshold value Va.

7. The charging control method of the bidirectional DCDC conversion circuit according to claim 6, characterized in that: Before step 4, the following steps are also included: Driving the bus-side converter to shut down; Wait for the operating current of the bus-side converter to drop to zero.

8. A discharge control method for a bidirectional DCDC conversion circuit, the method being performed by the bidirectional DCDC conversion circuit according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: Check whether the battery voltage is higher than the preset battery voltage threshold Va; if yes, go to step 2; otherwise, go to step 4; Step 2, driving the switch to connect the second connection point, and driving the battery side converter to operate at a frequency fb; Step 3: Check whether the bus voltage is lower than the preset bus voltage threshold Vb; if so, proceed to step 4; otherwise, maintain the current discharge state; Step 4, driving the switch to connect the first connection point, and driving the battery side converter to operate at a frequency fa; Step 5, detecting whether the battery voltage is lower than a preset low voltage threshold value Vlow of the battery; if so, the discharge is terminated, otherwise, the process returns to step 4; wherein the preset low voltage threshold value Vlow of the battery is smaller than the preset voltage threshold value Va of the battery.

9. The discharge control method of the bidirectional DCDC conversion circuit according to claim 8, characterized in that: Before step 4, the following steps are also included: Driving the battery side converter to shut down; Wait for the operating current of the battery side converter to drop to zero.

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