A bidirectional DC-DC conversion circuit and control method thereof and charging device

Abstract

The present invention discloses a bidirectional DC-DC conversion circuit suitable for realizing wide-range voltage regulation and having soft switching characteristics, a control method thereof, and a charging device. The bidirectional DC-DC conversion circuit is used to realize the bidirectional flow of electric energy between a first DC power supply and a second DC power supply; it comprises: a first switch network, a second switch network, a third switch network, and two transformers; the first switch network and the second switch network are both connected to the first DC power supply and both include a plurality of controllable switches; the third switch network is connected to the second DC power supply and includes a plurality of controllable switches and has three switch bridge arms connected in parallel to each other, and each switch bridge arm has a bridge arm midpoint; the first side windings of the two transformers are respectively connected to the first switch network and the second switch network, and the second side windings thereof are connected in series and define two non-common ends and one common end respectively connected to the three bridge arm midpoints of the third switch network.

Description

Technical Field

[0001] The present invention relates to the technical field of charging pile systems, and in particular to a bidirectional DC-DC conversion circuit and a control method and a charging device thereof. Background Art

[0002] Nowadays, the new energy electric vehicle industry is developing rapidly. The charging pile system of electric vehicles mainly includes AC-DC converters (hereinafter referred to as PFC modules) and DC-DC converters. As one of the core components, the DC-DC conversion circuit is mainly used to match the battery voltage of electric vehicles and adjust the corresponding output voltage. The direction of power flow in traditional charging pile systems is usually unidirectional. Electric vehicles only act as a load. When the power grid fluctuates, the charging pile system cannot change dynamically, which greatly reduces the stability of the charging pile system.

[0003] In this regard, the prior art proposes a bidirectional DC-DC converter based on an LLC resonant cavity, which includes two full-bridge circuits composed of MOS tubes, an LLC resonant cavity and an isolation transformer, one end of the two full-bridge circuits is respectively connected to the two sides of the isolation transformer and the other end of the two full-bridge circuits is respectively connected to the output end of the PFC module and the battery, and the MOS tubes of the two full-bridge circuits are switched by the host computer controller to achieve bidirectional control of the flow of electric energy. In other words, the bidirectional DC-DC converter switches working states between the charging mode and the discharging mode. The above-mentioned bidirectional DC-DC conversion circuit adjusts the output voltage by frequency modulation, and in the charging mode, the soft switching of each MOS tube in the two full-bridge circuits on each PFC side and the battery side can be ensured by controlling the switching frequency to be higher than the resonant frequency of the LLC resonant cavity.

[0004] However, the above-mentioned bidirectional DC-DC converter has a natural structural defect that the output voltage on the battery side has a narrow voltage regulation range. Especially when the voltage on the battery side is low, the voltage regulation method using frequency modulation not only fails to achieve the corresponding output voltage, but may also cause hard switching. Summary of the invention

[0005] The object of the present invention is to overcome at least one defect or problem existing in the background technology and to provide a bidirectional DC-DC conversion circuit and a control method and a charging device thereof, which are suitable for achieving a wider voltage regulation range.

[0006] To achieve the above-mentioned purpose, the first aspect of the present invention provides a bidirectional DC-DC conversion circuit for realizing bidirectional flow of electric energy between a first DC power supply and a second DC power supply; comprising: a first switch network and a second switch network, both of which are connected to the first DC power supply and both include a plurality of controllable switches coupled to each other; a third switch network, which is connected to the second DC power supply and includes a plurality of controllable switches coupled to each other; it also has three switch bridge arms connected in parallel to each other, each switch bridge arm includes two controllable switches connected in series and defines a bridge arm midpoint located between the two controllable switches; and two transformers, whose first side windings are respectively connected to the first switch network and the second switch network, and whose second side windings are connected and define two non-common ends and one common end respectively connected to the three bridge arm midpoints of the third switch network.

[0007] Further, the first DC power supply has a positive level terminal, a neutral point terminal and a negative level terminal; the first switch network is a full-bridge switch network, which includes a first switch, a second switch, a third switch and a fourth switch, which are all configured as controllable switches; the first switch and the third switch, the second switch and the fourth switch are respectively connected in series to form a switch bridge arm; the first switch and the second switch are both connected to the positive level terminal of the first DC power supply, and the third switch and the fourth switch are both connected to the neutral point terminal of the first DC power supply; the second switch network is a full-bridge switch network, which includes a fifth switch, a sixth switch, a seventh switch and an eighth switch, which are all configured as controllable switches; the fifth switch and the seventh switch are connected in series to form a switch bridge arm, and the sixth switch and the eighth switch are connected in series to form a switch bridge arm; the fifth switch and the sixth switch are both connected to the neutral point terminal of the first DC power supply, and the seventh switch and the eighth switch are both connected to the negative level terminal of the first DC power supply; the third switch network includes a ninth switch, a tenth switch, an eleventh switch, a twelfth switch, a thirteenth switch and a fourteenth switch, which are all configured as controllable switches; the ninth switch and the tenth switch, the eleventh switch and the twelfth switch, the tenth switch and the twelfth switch, the thirteenth switch and the fourteenth switch are connected to the neutral point terminal of the first DC power supply, and the thirteenth switch and the twelfth switch are connected to the negative level terminal of the first DC power supply. The third switch and the fourteenth switch are connected in series and constitute a switch bridge arm; the ninth switch, the eleventh switch and the thirteenth switch are all connected to one end of the second DC power supply, and the tenth switch, the twelfth switch and the fourteenth switch are all connected to the other end of the second DC power supply; the two transformers are respectively a first transformer and a second transformer; the same-name end of the first-side winding of the first transformer is connected to the common point of the second switch and the fourth switch, the opposite-name end of the first-side winding of the first transformer is connected to the common point of the first switch and the third switch, the same-name end of the second-side winding of the first transformer is connected to the common point of the eleventh switch and the twelfth switch, and the opposite-name end of the second-side winding of the first transformer is connected to the common point of the ninth switch and the tenth switch; the same-name end of the first-side winding of the second transformer is connected to the common point of the sixth switch and the eighth switch, the opposite-name end of the first-side winding of the second transformer is connected to the common point of the fifth switch and the seventh switch, the same-name end of the second-side winding of the second transformer is connected to the common point of the ninth switch and the tenth switch, and the opposite-name end of the second-side winding of the second transformer is connected to the common point of the thirteenth switch and the fourteenth switch.

[0008] Furthermore, each of the controllable switches is a MOS tube.

[0009] Furthermore, it also includes: a first resonant tank, which is composed of a first inductor and a first capacitor, the two ends of the first inductor are respectively connected to the same-name end of the first side winding of the first transformer and the common point of the second switch and the fourth switch, and the two ends of the first capacitor are respectively connected to the opposite-name end of the first side winding of the first transformer and the common point of the first switch and the third switch; a second resonant tank, which is composed of a second inductor and a second capacitor, the two ends of the second inductor are respectively connected to the same-name end of the first side winding of the second transformer and the common point of the sixth switch and the eighth switch, and the two ends of the second capacitor are respectively connected to the opposite-name end of the first side winding of the second transformer and the common point of the fifth switch and the seventh switch; a third resonant tank, which is composed of a third capacitor, the two ends of the third capacitor are respectively connected to the same-name end of the second side winding of the first transformer and the common point of the eleventh switch and the twelfth switch; and a fourth resonant tank, which is composed of a fourth capacitor, the two ends of the fourth capacitor are respectively connected to the opposite-name end of the second side winding of the second transformer and the common point of the thirteenth switch and the fourteenth switch.

[0010] To achieve the above-mentioned purpose, the second aspect of the present invention provides a control method for a bidirectional DC-DC conversion circuit, wherein the bidirectional DC-DC conversion circuit is the bidirectional DC-DC conversion circuit as described in the above-mentioned technical solution, and the bridge arm connecting the common ends of the two transformers in the third switch network is defined as the first bridge arm; the method comprises: obtaining a flow direction instruction and a voltage of the second DC power supply; wherein the flow direction instruction is used to indicate the working flow direction of the bidirectional DC-DC conversion circuit; according to the voltage of the second DC power supply, switching the bidirectional DC-DC conversion circuit to a first connection state or a second connection state; wherein, When the second DC power supply is in a high-voltage mode, the bidirectional DC-DC conversion circuit is in a first connection state, and the first bridge arm does not work; when the second DC power supply is in a low-voltage mode, the bidirectional DC-DC conversion circuit is in a second connection state, and the first bridge arm works; the switching frequency of the inflow side switch network corresponding to the flow direction instruction is determined through a control loop, and the driving phase difference of each of the switch networks is determined according to the switching frequency, the flow direction instruction and the connection state of the bidirectional DC-DC conversion circuit; the corresponding controllable switch of each of the switch networks is driven and controlled according to the switching frequency and the driving phase difference.

[0011] Furthermore, the control loop is a control loop for controlling the output voltage of the bidirectional DC-DC conversion circuit.

[0012] Furthermore, when the flow direction instruction is from the first DC power supply to the second DC power supply, the corresponding inflow side switch network is the first switch network and the second switch network; when the flow direction instruction is from the second DC power supply to the first DC power supply, the corresponding inflow side switch network is the third switch network.

[0013] Further, the driving phase difference of each of the switch networks is determined according to the switching frequency, the flow direction instruction and the connection state of the bidirectional DC-DC conversion circuit, including: when the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the driving phase difference between the first switch network and the second switch network is 0°, and the third switch network follows the corresponding inflow side switch network for synchronous rectification; when the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the driving phase difference between the first switch network and the second switch network is 180°, and the third switch network follows the corresponding inflow side switch network for synchronous rectification; when the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state When the driving phase difference between the first switch network and the second switch network is 0°, the first switch network and the second switch network follow the corresponding inflow side switch network for synchronous rectification; wherein, when the switching frequency is lower than the resonant frequency of each of the resonant tanks, each controllable switch of the third switch network is synchronously turned on and delayed turned off compared with the corresponding controllable switches of the first switch network and the second switch network; when the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the driving phases of the first switch network and the second switch network are spaced 180° apart, and the first switch network and the second switch network follow the corresponding inflow side switch network for synchronous rectification; wherein, when the switching frequency is lower than the resonant frequency of each of the resonant tanks, each controllable switch of the third switch network is synchronously turned on and delayed turned off compared with the corresponding controllable switches of the first switch network and the second switch network.

[0014] Further, when the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the first switch, the fourth switch, the fifth switch and the eighth switch are turned on and off at the same time, and the second switch, the third switch, the sixth switch and the seventh switch are turned on and off at the same time; the eleventh switch and the fourteenth switch are turned on and off at the same time as the second switch, and the twelfth switch and the thirteenth switch are turned on and off at the same time as the first switch; when the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the first switch, the fourth switch, the sixth switch and the seventh switch are turned on and off at the same time, and the second switch, the third switch, the fifth switch and the eighth switch are turned on and off at the same time. The tenth switch, the eleventh switch, the thirteenth switch and the second switch are turned on and off at the same time, and the ninth switch, the twelfth switch, and the fourteenth switch are turned on and off at the same time as the first switch; when the flow direction instruction is that the second DC power supply flows to the first DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the eleventh switch and the fourteenth switch are turned on and off at the same time, and the twelfth switch and the thirteenth switch are turned on and off at the same time; the eleventh switch and the twelfth switch are complementarily turned on; the first switch, the fourth switch, the fifth switch and the eighth switch are turned on and off at the same time, and the second switch, the third switch, the sixth switch and the seventh switch are turned on and off at the same time; when the switching frequency is higher than the resonant frequency of each of the resonant slots, the eleventh switch and the fourth ... twelfth switch and the eighth switch are turned on and off at the same time. The second switch, the third switch, the sixth switch and the seventh switch are turned on and off at the same time, and the twelfth switch is turned on and off at the same time as the first switch, the fourth switch, the fifth switch and the eighth switch; when the switching frequency is lower than the resonant frequency of each of the resonant tanks, the eleventh switch is turned on and off synchronously with the second switch, the third switch, the sixth switch and the seventh switch, and the twelfth switch is turned on and off synchronously with the first switch, the fourth switch, the fifth switch and the eighth switch, and the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the tenth switch, the eleventh switch and the thirteenth switch are turned on and off simultaneously, and the ninth switch, the twelfth switch and the fourteenth switch are turned on and off simultaneously, and the The eleventh switch is complementary to the twelfth switch; the first switch, the fourth switch, the sixth switch and the seventh switch are turned on and off at the same time, and the second switch, the third switch, the fifth switch and the eighth switch are turned on and off at the same time; when the switching frequency is higher than the resonant frequency of each of the resonant slots, the eleventh switch is turned on and off at the same time as the second switch, the third switch, the fifth switch and the eighth switch, and the twelfth switch is turned on and off at the same time as the first switch, the fourth switch, the sixth switch and the seventh switch; when the switching frequency is lower than the resonant frequency of each of the resonant slots, the eleventh switch is turned on synchronously with the second switch, the third switch, the fifth switch and the eighth switch and turned off with a delay, and the twelfth switch is turned on synchronously with the first switch, the fourth switch, the sixth switch and the seventh switch and turned off with a delay.

[0015] To achieve the above objectives, the third aspect of the present invention provides a charging device, which includes a bidirectional DC-DC conversion circuit and a controller as described in the above technical solution; the controller is used to execute the method described in the above technical solution.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The bidirectional DC-DC conversion circuit of the present invention adopts two transformers, and the two transformers are respectively configured such that the first side windings thereof are respectively connected to two switch networks, the second side windings thereof are connected and define two non-common ends and one common end, and the third switch network having three bridge arms is connected through the two non-common ends and one common end, so that it is suitable to change the phase angle of the two switch networks connecting the first side windings of the two transformers on this basis, so that the two second side windings of the two transformers are switched between series connection and parallel connection and change the basic gain ratio between the output end and the output end of the conversion circuit, and on this basis, a conventional frequency modulation voltage regulation method is adopted to achieve a wider voltage regulation range. In addition, in the bidirectional DC-DC conversion circuit of the present invention, a resonant slot network is provided between the first side winding and the AC side of the corresponding switch network, which is conducive to realizing the soft switching of each controllable switch. Further, when each resonant slot constitutes a CLLC resonant network as a whole, both sides of the transformer have a resonant structure, which is suitable for realizing the soft switching of the switch networks on both sides in both the charging mode and the discharging mode.

[0018] On the basis of the above-mentioned bidirectional DC-DC conversion circuit, the corresponding control method provided by the present invention determines the connection state of the bidirectional DC-DC conversion circuit according to the flow direction instruction and the voltage of the second DC power supply, and switches the working state of the first bridge arm, so as to further determine the driving mode of the bidirectional DC-DC conversion circuit in different working directions and when the second DC power supply is in different modes according to the switching frequency calculated by the control loop, combined with the three factors of the flow direction instruction and the connection state. In the case of wide range input or output, by adjusting the driving phase difference of each switch network, when the excitation current of the bidirectional DC-DC conversion circuit under various working conditions is equal to the resonant cavity current, the current on the synchronous rectification side is 0, thereby realizing soft switching under wide range voltage regulation under various working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1The circuit structure diagram of the bidirectional DC-DC conversion circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are preferred embodiments of the present invention and should not be regarded as excluding other 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.

[0022] In the claims, description and the above-mentioned drawings of the present invention, unless otherwise clearly defined, the use of terms such as "first", "second" or "third" etc. are for distinguishing different objects rather than for describing a specific order.

[0023] In the claims, description and drawings of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0024] In the claims, specification and the above-mentioned drawings of the present invention, unless otherwise clearly defined, the terms "connected", "connected" and the like may include both direct electrical connection and indirect electrical connection; the term "coupled" may refer to the fact that two electrical parts have a specific circuit function after being electrically connected.

[0025] An embodiment of the present invention provides a bidirectional DC-DC conversion circuit for realizing a bidirectional flow of electric energy between a first DC power supply and a second DC power supply. In this embodiment, the first DC power supply is a three-level DC power supply having a positive level terminal, a neutral point terminal and a negative level terminal. In other embodiments, the first DC power supply may also be a two-level DC power supply. In this embodiment, the first DC power supply is a DC power supply after PFC rectification of the power grid, and the second DC power supply is a battery of a new energy vehicle.

[0026] Reference Figure 1 The bidirectional DC-DC conversion circuit includes a first switch network, a second switch network, a third switch network, a first transformer T1, a second transformer T2, a first resonant tank, a second resonant tank, a third resonant tank and a fourth resonant tank.

[0027] The first switch network and the second switch network are both connected to the first DC power supply and both include a plurality of controllable switches coupled to each other. In this embodiment, the first switch network is connected to the positive level terminal and the neutral point terminal of the first DC power supply, and the second switch network is connected to the neutral point terminal and the negative level terminal of the first DC power supply. When the first DC power supply is a two-level DC power supply, the first switch network and the second switch network are connected in parallel to each other and are both connected to the two ends of the first DC power supply.

[0028] In the specific structure of this embodiment, the first switch network is a full-bridge switch network, which includes a first switch S1, a second switch S2, a third switch S3 and a fourth switch S4, which are all configured as controllable switches. The first switch S1 and the third switch S3, the second switch S2 and the fourth switch S4 are connected in series and form a switch bridge arm. The first switch S1 and the second switch S2 are both connected to the positive level end of the first DC power supply, and the third switch S3 and the fourth switch S4 are both connected to the neutral point end of the first DC power supply. The second switch network is also a full-bridge switch network, which includes a fifth switch S5, a sixth switch S6, a seventh switch S7 and an eighth switch S8, which are all configured as controllable switches. The fifth switch S5 and the seventh switch S7 are connected in series and form a switch bridge arm, and the sixth switch S6 and the eighth switch S8 are connected in series and form a switch bridge arm. The fifth switch S5 and the sixth switch S6 are both connected to the neutral point end of the first DC power supply, and the seventh switch and the eighth switch S8 are both connected to the negative level end of the first DC power supply. In other embodiments, the first switch network and the second switch network may also be other power switch topologies, such as a half-bridge switch network.

[0029] The third switch network is connected to the second DC power supply and includes a plurality of controllable switches coupled to each other. It also has three switch bridge arms connected in parallel to each other, each switch bridge arm includes two controllable switches connected in series and defines a bridge arm midpoint located between the two controllable switches. In the specific structure of this embodiment, the third switch network includes a ninth switch S9, a tenth switch S10, an eleventh switch S11, a twelfth switch S12, a thirteenth switch S13 and a fourteenth switch, all of which are configured as controllable switches. The ninth switch S9 and the tenth switch S10, the eleventh switch S11 and the twelfth switch S12, the thirteenth switch S13 and the fourteenth switch S14 are connected in series and form a switch bridge arm. The ninth switch S9, the eleventh switch S11 and the thirteenth switch S13 are all connected to one end of the second DC power supply, and the tenth switch S10, the twelfth switch S12 and the fourteenth switch S14 are all connected to the other end of the second DC power supply. In this embodiment, each of the above-mentioned controllable switches is a MOS tube, and in other embodiments, each of the controllable switches can also be an IGBT.

[0030] The first side windings of the first transformer T1 and the second transformer T2 are connected to the AC side of the first switch network and the second switch network respectively, and the second side windings thereof are connected and define two non-common ends and one common end respectively connected to the midpoints of the three bridge arms of the third switch network. In the specific structure, the same-name end of the first side winding of the first transformer T1 is connected to the common point of the second switch S2 and the fourth switch S4, the opposite-name end of the first side winding of the first transformer T1 is connected to the common point of the first switch S1 and the third switch S3, the same-name end of the second side winding of the first transformer T1 is connected to the common point of the eleventh switch S11 and the twelfth switch S12, and the opposite-name end of the second side winding of the first transformer T1 is connected to the common point of the ninth switch S9 and the tenth switch S10. The same-name end of the first side winding of the second transformer T2 is connected to the common point of the sixth switch S6 and the eighth switch S8, the opposite-name end of the first side winding of the second transformer T2 is connected to the common point of the fifth switch S5 and the seventh switch S7, the same-name end of the second side winding of the second transformer T2 is connected to the common point of the ninth switch S9 and the tenth switch S10, and the opposite-name end of the second side winding of the second transformer T2 is connected to the common point of the thirteenth switch S13 and the fourteenth switch S14.

[0031] The first resonant tank is composed of a first inductor L1 and a first capacitor C1, the two ends of the first inductor L1 are respectively connected to the same-name end of the first side winding of the first transformer T1 and the common point of the second switch S2 and the fourth switch S4, and the two ends of the first capacitor C1 are respectively connected to the opposite-name end of the first side winding of the first transformer T1 and the common point of the first switch S1 and the third switch S3. The second resonant tank is composed of a second inductor L2 and a second capacitor C2, the two ends of the second inductor L2 are respectively connected to the same-name end of the first side winding of the second transformer T2 and the common point of the sixth switch S6 and the eighth switch S8, and the two ends of the second capacitor C2 are respectively connected to the opposite-name end of the first side winding of the second transformer T2 and the common point of the fifth switch S5 and the seventh switch S7. The third resonant tank is composed of a third capacitor C3, the two ends of the third capacitor C3 are respectively connected to the same-name end of the second side winding of the first transformer T1 and the common point of the eleventh switch S11 and the twelfth switch S12. The fourth resonant tank is formed by a fourth capacitor C4, and two ends of the fourth capacitor C4 are respectively connected to the opposite-name end of the second side winding of the second transformer T2 and a common point between the thirteenth switch S13 and the fourteenth switch S14.

[0032] It goes without saying that the bidirectional DC-DC conversion circuit can also use other resonant tank structures to form different resonant tank networks. Generally speaking, the resonant tank network includes a plurality of resonant devices that are coupled to each other and form a resonant cavity, and are connected between the first side winding of the transformer and the AC side of the corresponding switch network. The resonant device includes an inductor and a capacitor.

[0033] The bidirectional DC-DC conversion circuit of the present invention adopts two transformers, and the two transformers are respectively configured such that the first side windings thereof are respectively connected to two switch networks, the second side windings thereof are connected and define two non-common ends and one common end, and the third switch network having three bridge arms is connected through the two non-common ends and one common end, so that it is suitable to change the phase angle of the two switch networks connecting the first side windings of the two transformers on this basis, so that the two second side windings of the two transformers are switched between series connection and parallel connection and change the basic gain ratio between the output end and the output end of the conversion circuit, and on this basis, a conventional frequency modulation voltage regulation method is adopted to achieve a wider voltage regulation range. In addition, in the bidirectional DC-DC conversion circuit of the present invention, a resonant slot network is provided between the first side winding and the AC side of the corresponding switch network, which is conducive to realizing the soft switching of each controllable switch. Further, when each resonant slot constitutes a CLLC resonant network as a whole, both sides of the transformer have a resonant structure, which is suitable for realizing the soft switching of the switch networks on both sides in both the charging mode and the discharging mode.

[0034] Based on the above bidirectional DC-DC conversion circuit, the present invention further provides a corresponding control method, wherein the bridge arm in the third switch network connecting the common ends of the two transformers is defined as the first bridge arm. The method comprises:

[0035] Acquire a flow direction instruction and a voltage of the second DC power supply, wherein the flow direction instruction is used to indicate the working flow direction of the bidirectional DC-DC conversion circuit.

[0036] According to the voltage of the second DC power supply, the bidirectional DC-DC conversion circuit is switched to the first connection state or the second connection state. When the second DC power supply is in the high voltage mode, the bidirectional DC-DC conversion circuit is in the first connection state, and the first bridge arm does not work, that is, the ninth switch S9 and the tenth switch S10 do not work. When the second DC power supply is in the low voltage mode, the bidirectional DC-DC conversion circuit is in the second connection state, and the first bridge arm works, that is, the ninth switch S9 and the tenth switch S10 work.

[0037] The switching frequency of the inflow side switch network corresponding to the flow direction instruction is determined by the control loop, and the driving phase difference of each switch network is determined according to the switching frequency, the flow direction instruction and the connection state of the bidirectional DC-DC conversion circuit. In this embodiment, the control loop is a control loop for controlling the output voltage of the bidirectional DC-DC conversion circuit. In other embodiments, the control loop can also be a control loop for controlling the output current of the bidirectional DC-DC conversion circuit. It can be specifically selected according to needs. The present invention does not limit the sampled input electrical parameters and specific algorithms of the control loop. For example, the sampled input electrical parameters can be input voltage, output voltage or input current, and the control loop can be a PI control loop or a PID control loop. In addition, it can be understood that when the flow direction instruction is from the first DC power supply to the second DC power supply, the corresponding inflow side switch network is the first switch network and the second switch network. When the flow direction instruction is from the second DC power supply to the first DC power supply, the corresponding inflow side switch network is the third switch network.

[0038] The corresponding controllable switches of each of the switch networks are driven and controlled according to the switching frequency and the driving phase difference to control the on and off of each controllable switch, thereby controlling the bidirectional DC-DC conversion circuit to operate according to the working flow direction corresponding to the flow direction instruction and output the corresponding voltage.

[0039] Specifically, determining the driving phase difference of each of the switch networks according to the switching frequency, the flow direction instruction and the connection state of the bidirectional DC-DC conversion circuit includes:

[0040] When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the driving phase difference between the first switch network and the second switch network is 0°, and the third switch network follows the corresponding inflow side switch network for synchronous rectification.

[0041] When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the driving phase difference between the first switch network and the second switch network is 180°, and the third switch network follows the corresponding inflow side switch network for synchronous rectification.

[0042] When the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the driving phase difference between the first switch network and the second switch network is 0°, and the first switch network and the second switch network follow the corresponding inflow side switch network for synchronous rectification; wherein, when the switching frequency is lower than the resonant frequency of each resonant tank, each controllable switch of the third switch network is synchronously turned on and delayed turned off compared with the corresponding controllable switches of the first switch network and the second switch network.

[0043] When the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the driving phases of the first switch network and the second switch network are spaced 180° apart, and the first switch network and the second switch network follow the corresponding inflow side switch network for synchronous rectification; wherein, when the switching frequency is lower than the resonant frequency of each resonant tank, each controllable switch of the third switch network is synchronously turned on and delayed turned off compared with the corresponding controllable switches of the first switch network and the second switch network.

[0044] Specifically, according to the control method of the embodiment of the present invention, the DC-DC conversion circuit has the following working process.

[0045] (1) When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the bidirectional DC-DC conversion circuit operates in the high-voltage charging mode. At this time, the battery voltage is relatively high, the driving phase difference between the first switch network and the second switch network is 0°, the second side windings of the two transformers (T1, T2) are connected in series, and the basic gain ratio is 1. In other words, the first switch S1, the fourth switch S4, the fifth switch S5 and the eighth switch S8 are opened and closed at the same time, the second switch S2, the third switch S3, the sixth switch S6 and the seventh switch S7 are opened and closed at the same time, and the output voltage is adjusted by adjusting the switching frequency, and the switching frequency is limited to be greater than the resonant frequency of each resonant slot by reasonably adjusting the voltage of the first DC power supply. In addition, the ninth switch S9 and the tenth switch S10 do not work in this mode, and the eleventh switch S11, the twelfth switch S12, the thirteenth switch S13 and the fourteenth switch S14 perform synchronous rectification. At this time, the eleventh switch S11 and the fourteenth switch S14 are opened and closed at the same time as the second switch S2, and the twelfth switch S12 and the thirteenth switch S13 are opened and closed at the same time as the first switch S1.

[0046] (2) When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the bidirectional DC-DC conversion circuit operates in a low-voltage charging mode. At this time, the battery voltage is low, the driving phase difference between the first switch network and the second switch network is 180°, the second side windings of the two transformers (T1, T2) are connected in parallel, and the basic gain ratio is 0.5. In other words, the first switch S1, the fourth switch S4, the sixth switch S6 and the seventh switch S7 are opened and closed at the same time, the second switch S2, the third switch S3, the fifth switch S5 and the eighth switch S8 are opened and closed at the same time, and the output voltage is adjusted by adjusting the switching frequency, and the switching frequency is limited to be greater than the resonant frequency of each resonant slot by reasonably adjusting the voltage of the first DC power supply. In addition, the ninth switch S9, the tenth switch S10, the eleventh switch S11, the twelfth switch S12, the thirteenth switch S13 and the fourteenth switch S14 perform synchronous rectification. At this time, the tenth switch S10, the eleventh switch S11, the thirteenth switch S13 and the second switch S2 are opened and closed at the same time, and the ninth switch S9, the twelfth switch S12, the fourteenth switch S14 are opened and closed at the same time as the first switch S1.

[0047] (3) When the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the bidirectional DC-DC conversion circuit operates in the high-voltage discharge mode. At this time, the battery voltage is relatively high, the driving phase difference between the first switch network and the second switch network is 0°, the second side windings of the two transformers (T1, T2) are connected in series, and the basic gain ratio is 1. In other words, the ninth switch S9 and the tenth switch S10 do not work in this mode, the eleventh switch S11 and the fourteenth switch S14 are opened and closed at the same time, the twelfth switch S12 and the thirteenth switch S13 are opened and closed at the same time, the eleventh switch S11 and the twelfth switch S12 are complementary, the duty cycle is 50%, and the output voltage is adjusted by adjusting the switching frequency. In addition, the first switch network and the second switch network perform synchronous rectification, at this time, the first switch S1, the fourth switch S4, the fifth switch S5 and the eighth switch S8 are opened and closed at the same time, and the second switch S2, the third switch S3, the sixth switch S6 and the seventh switch S7 are opened and closed at the same time.

[0048] Preferably, if the switching frequency of the third switch network is greater than or equal to the resonant frequency of each resonant tank, the eleventh switch S11 is opened and closed at the same time as the second switch S2, the third switch S3, the sixth switch S6 and the seventh switch S7, and the twelfth switch S12 is opened and closed at the same time as the first switch S1, the fourth switch S4, the fifth switch S5 and the eighth switch S8. If the switching frequency of the third switch network is less than the resonant frequency of each resonant tank, the eleventh switch S11 is opened at the same time as the second switch S2, the third switch S3, the sixth switch S6 and the seventh switch S7, but is turned off later than the second switch S2, the third switch S3, the sixth switch S6 and the seventh switch S7; the twelfth switch S12 is opened at the same time as the first switch S1, the fourth switch S4, the fifth switch S5 and the eighth switch S8, but is turned off later than the first switch S1, the fourth switch S4, the fifth switch S5 and the eighth switch S8, so that the bidirectional DC-DC conversion circuit can also keep the excitation current equal to the resonant cavity current under this working condition, and the current on the synchronous rectification side is 0, thereby realizing soft switching.

[0049] (4) When the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the bidirectional DC-DC conversion circuit operates in a low-voltage discharge mode. At this time, the battery voltage is low, the driving phase difference between the first switch network and the second switch network is 180°, the second side windings of the two transformers (T1, T2) are connected in series, and the basic gain ratio is 2. In other words, the tenth switch S10, the eleventh switch S11 and the thirteenth switch S13 are opened and closed at the same time, the ninth switch S9, the twelfth switch S12 and the fourteenth switch S14 are opened and closed at the same time, the eleventh switch S11 is complementary to the twelfth switch S12, the duty cycle is 50%, and the output voltage is adjusted by adjusting the switching frequency. In addition, the first switch network and the second switch network perform synchronous rectification, at this time, the first switch S1, the fourth switch S4, the sixth switch S6 and the seventh switch S7 are opened and closed at the same time, and the second switch S2, the third switch S3, the fifth switch S5 and the eighth switch S8 are opened and closed at the same time.

[0050] Preferably, if the switching frequency of the third switch network is greater than or equal to the resonant frequency of each resonant tank, the eleventh switch S11 is opened and closed at the same time as the second switch S2, the third switch S3, the fifth switch S5 and the eighth switch S8, and the twelfth switch S12 is opened and closed at the same time as the first switch S1, the fourth switch S4, the sixth switch S6 and the seventh switch S7. If the switching frequency of the third switch network is less than the resonant frequency of each resonant tank, the eleventh switch S11 is opened at the same time as the second switch S2, the third switch S3, the fifth switch S5 and the eighth switch S8, but is turned off later than the second switch S2, the third switch S3, the fifth switch S5 and the eighth switch S8; the twelfth switch S12 is opened at the same time as the first switch S1, the fourth switch S4, the sixth switch S6 and the seventh switch S7, but is turned off later than the first switch S1, the fourth switch S4, the sixth switch S6 and the seventh switch S7, so that the bidirectional DC-DC conversion circuit can also keep the excitation current equal to the resonant cavity current under this working condition, and the current on the synchronous rectification side is 0, thereby realizing soft switching.

[0051] It can be seen that the corresponding control method provided by the present invention determines the connection state of the bidirectional DC-DC conversion circuit according to the flow direction instruction and the voltage of the second DC power supply, and switches the working state of the first bridge arm, so as to further determine the driving mode of the bidirectional DC-DC conversion circuit in different working directions and when the second DC power supply is in different modes according to the switching frequency calculated by the control loop, combined with the three factors of the flow direction instruction and the connection state. In the case of a wide range of input or output, the driving phase difference of each switch network is adjusted so that when the excitation current of the bidirectional DC-DC conversion circuit under various working conditions is equal to the resonant cavity current, the current on the synchronous rectification side is 0, thereby realizing soft switching under a wide range of voltage regulation under various working conditions.

[0052] In addition, an embodiment of the present invention further provides a charging device, which includes the bidirectional DC-DC conversion circuit and a controller of the present embodiment. The controller is used to execute the control method of the above embodiment, thereby inheriting all its advantages.

[0053] The description of the above specification and embodiments is used to explain the protection scope of the present invention, but does not constitute a limitation on the protection scope of the present invention. Through the enlightenment of the present invention or the above embodiments, ordinary technicians in this field can obtain modifications, equivalent substitutions or other improvements to the embodiments of the present invention or part of the technical features thereof through logical analysis, reasoning or limited experiments, which should be included in the protection scope of the present invention.

Claims

1. A control method for a bidirectional DC-DC conversion circuit, characterized in that: The bidirectional DC-DC conversion circuit is used to realize the bidirectional flow of electric energy between the first DC power supply and the second DC power supply; the first DC power supply has a positive level terminal, a neutral point terminal and a negative level terminal; The bidirectional DC-DC conversion circuit includes a first switch network, a second switch network, a third switch network, two transformers, a first resonant tank, a second resonant tank, a third resonant tank and a fourth resonant tank; A first switch network and a second switch network, both connected to the first DC power source and both comprising a plurality of controllable switches coupled to each other; a third switch network connected to the second DC power source and comprising a plurality of controllable switches coupled to each other; the third switch network further comprising three switch bridge arms connected in parallel to each other, each switch bridge arm comprising two controllable switches connected in series and defining a bridge arm midpoint located between the two controllable switches; Two transformers, whose first side windings are respectively connected to the first switch network and the second switch network, and whose second side windings are connected and define two non-common ends and one common end respectively connected to the midpoints of the three bridge arms of the third switch network; The first switch network is a full-bridge switch network, which includes a first switch, a second switch, a third switch and a fourth switch, all of which are configured as controllable switches; the first switch and the third switch, the second switch and the fourth switch are respectively connected in series and form a switch bridge arm; the first switch and the second switch are both connected to the positive level end of the first DC power supply, and the third switch and the fourth switch are both connected to the neutral point end of the first DC power supply; The second switch network is a full-bridge switch network, which includes a fifth switch, a sixth switch, a seventh switch and an eighth switch, all of which are configured as controllable switches; the fifth switch and the seventh switch are connected in series to form a switch bridge arm, and the sixth switch and the eighth switch are connected in series to form a switch bridge arm; the fifth switch and the sixth switch are both connected to the neutral point end of the first DC power supply, and the seventh switch and the eighth switch are both connected to the negative level end of the first DC power supply; The third switch network includes a ninth switch, a tenth switch, an eleventh switch, a twelfth switch, a thirteenth switch and a fourteenth switch, all of which are configured as controllable switches; the ninth switch and the tenth switch, the eleventh switch and the twelfth switch, the thirteenth switch and the fourteenth switch are respectively connected in series to form a switch bridge arm; the ninth switch, the eleventh switch and the thirteenth switch are all connected to one end of the second DC power supply, and the tenth switch, the twelfth switch and the fourteenth switch are all connected to the other end of the second DC power supply; The two transformers are respectively a first transformer and a second transformer; The same-name end of the first-side winding of the first transformer is connected to a common point of the second switch and the fourth switch, the opposite-name end of the first-side winding of the first transformer is connected to a common point of the first switch and the third switch, the same-name end of the second-side winding of the first transformer is connected to a common point of the eleventh switch and the twelfth switch, and the opposite-name end of the second-side winding of the first transformer is connected to a common point of the ninth switch and the tenth switch; The same-name end of the first-side winding of the second transformer is connected to the common point of the sixth switch and the eighth switch, the opposite-name end of the first-side winding of the second transformer is connected to the common point of the fifth switch and the seventh switch, the same-name end of the second-side winding of the second transformer is connected to the common point of the ninth switch and the tenth switch, and the opposite-name end of the second-side winding of the second transformer is connected to the common point of the thirteenth switch and the fourteenth switch; A first resonant tank, which is composed of a first inductor and a first capacitor, wherein two ends of the first inductor are respectively connected to the same-name end of the first side winding of the first transformer and a common point of the second switch and the fourth switch, and two ends of the first capacitor are respectively connected to the opposite-name end of the first side winding of the first transformer and a common point of the first switch and the third switch; a second resonant tank, which is composed of a second inductor and a second capacitor, wherein two ends of the second inductor are respectively connected to the same-name end of the first-side winding of the second transformer and a common point of the sixth switch and the eighth switch, and two ends of the second capacitor are respectively connected to the opposite-name end of the first-side winding of the second transformer and a common point of the fifth switch and the seventh switch; a third resonant tank, which is composed of a third capacitor, and two ends of the third capacitor are respectively connected to the same-name end of the second side winding of the first transformer and a common point of the eleventh switch and the twelfth switch; a fourth resonant tank, which is composed of a fourth capacitor, wherein two ends of the fourth capacitor are respectively connected to the opposite-name end of the second side winding of the second transformer and a common point of the thirteenth switch and the fourteenth switch; Define a bridge arm in the third switch network that is connected to common ends of the two transformers as a first bridge arm; The method comprises: Acquire a flow direction instruction and a voltage of the second DC power supply; wherein the flow direction instruction is used to indicate the working flow direction of the bidirectional DC-DC conversion circuit; According to the voltage of the second DC power supply, the bidirectional DC-DC conversion circuit is switched to a first connection state or a second connection state; wherein, when the second DC power supply is in a high voltage mode, the bidirectional DC-DC conversion circuit is in the first connection state, and the first bridge arm does not work; when the second DC power supply is in a low voltage mode, the bidirectional DC-DC conversion circuit is in the second connection state, and the first bridge arm works; Determine the switching frequency of the inflow-side switch network corresponding to the flow direction instruction through a control loop, and determine the driving phase difference of each of the switch networks according to the switching frequency, the flow direction instruction and the connection state of the bidirectional DC-DC conversion circuit; Driving and controlling the corresponding controllable switches of each of the switch networks according to the switching frequency and the driving phase difference; When the flow direction instruction is from the first DC power supply to the second DC power supply, the corresponding inflow side switch network is the first switch network and the second switch network; when the flow direction instruction is from the second DC power supply to the first DC power supply, the corresponding inflow side switch network is the third switch network; Determining the driving phase difference of each of the switch networks according to the switching frequency, the flow direction instruction and the connection state of the bidirectional DC-DC conversion circuit includes: When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the driving phase difference between the first switch network and the second switch network is 0°, and the third switch network follows the corresponding inflow side switch network for synchronous rectification; When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the driving phase difference between the first switch network and the second switch network is 180°, and the third switch network follows the corresponding inflow side switch network for synchronous rectification; When the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the driving phase difference between the first switch network and the second switch network is 0°, and the first switch network and the second switch network follow the corresponding inflow side switch network for synchronous rectification; wherein, when the switching frequency is lower than the resonant frequency of each resonant tank, each controllable switch of the third switch network is synchronously turned on and delayed turned off compared with the corresponding controllable switches of the first switch network and the second switch network; When the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the driving phases of the first switch network and the second switch network are spaced 180° apart, and the first switch network and the second switch network follow the corresponding inflow side switch network for synchronous rectification; wherein, when the switching frequency is lower than the resonant frequency of each resonant tank, each controllable switch of the third switch network is synchronously turned on and delayed turned off compared with the corresponding controllable switches of the first switch network and the second switch network.

2. The control method of a bidirectional DC-DC converter circuit according to claim 1, characterized in that: When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the first connection state, the first switch, the fourth switch, the fifth switch and the eighth switch are opened and closed at the same time, the second switch, the third switch, the sixth switch and the seventh switch are opened and closed at the same time; the eleventh switch and the fourteenth switch are opened and closed at the same time as the second switch, and the twelfth switch and the thirteenth switch are opened and closed at the same time as the first switch; When the flow direction instruction is from the first DC power supply to the second DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the first switch, the fourth switch, the sixth switch and the seventh switch are opened and closed at the same time, the second switch, the third switch, the fifth switch and the eighth switch are opened and closed at the same time; the tenth switch, the eleventh switch and the thirteenth switch are opened and closed at the same time as the second switch, and the ninth switch, the twelfth switch and the fourteenth switch are opened and closed at the same time as the first switch; When the flow direction instruction is that the second DC power source flows to the first DC power source and the bidirectional DC-DC conversion circuit is in the first connection state, the eleventh switch and the fourteenth switch are turned on and off at the same time, and the twelfth switch and the thirteenth switch are turned on and off at the same time; the eleventh switch and the twelfth switch are complementary to each other; the first switch, the fourth switch, the fifth switch and the eighth switch are turned on and off at the same time, and the second switch, the third switch, the sixth switch and the seventh switch are turned on and off at the same time; when the switching frequency is higher than the resonant frequency of each of the resonant tanks, the eleventh switch and the second switch, the third switch, the sixth switch and the seventh switch are turned on and off at the same time, and the twelfth switch and the first switch, the fourth switch, the fifth switch and the eighth switch are turned on and off at the same time; when the switching frequency is lower than the resonant frequency of each of the resonant tanks, the eleventh switch and the second switch, the third switch, the sixth switch and the seventh switch are turned on and off with a delay, and the twelfth switch and the first switch, the fourth switch, the fifth switch and the eighth switch are turned on and off with a delay; When the flow direction instruction is from the second DC power supply to the first DC power supply and the bidirectional DC-DC conversion circuit is in the second connection state, the tenth switch, the eleventh switch and the thirteenth switch are opened and closed at the same time, the ninth switch, the twelfth switch and the fourteenth switch are opened and closed at the same time, and the eleventh switch is complementary to the twelfth switch; the first switch, the fourth switch, the sixth switch and the seventh switch are opened and closed at the same time, and the second switch, the third switch, the fifth switch and the eighth switch are opened and closed at the same time; when the switching frequency is higher than the resonant frequency of each of the resonant tanks, the eleventh switch is opened and closed at the same time as the second switch, the third switch, the fifth switch and the eighth switch, and the twelfth switch is opened and closed at the same time as the first switch, the fourth switch, the sixth switch and the seventh switch; when the switching frequency is lower than the resonant frequency of each of the resonant tanks, the eleventh switch is opened synchronously with the second switch, the third switch, the fifth switch and the eighth switch and is turned off with a delay, and the twelfth switch is opened synchronously with the first switch, the fourth switch, the sixth switch and the seventh switch and is turned off with a delay.

3. The control method of a bidirectional DC-DC converter circuit according to claim 1, characterized in that: The control loop is a control loop for controlling the output voltage of the bidirectional DC-DC conversion circuit.

4. The control method of a bidirectional DC-DC converter circuit according to claim 1, characterized in that: Each of the controllable switches is a MOS tube.

5. A charging device, characterized in that: It comprises the bidirectional DC-DC conversion circuit and a controller; the controller is used to execute the method as described in any one of claims 1-4.

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