Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, the "plurality" generally includes at least two, but does not exclude the case of at least one.
It should be understood that the term "and/or" as used herein is merely one relationship describing the association of the associated objects, meaning that there may be three relationships, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.
It should be understood that the terms "comprises," "comprising," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising … …" does not exclude the presence of other like elements in a process, method, article or apparatus that comprises the element.
It should be noted that, in the embodiment of the present application, directional indications (such as up, down, left, right, front, and rear … …) are referred to, and the directional indications are merely used to explain the relative positional relationship, movement conditions, and the like between the components in a specific posture (as shown in the drawings), and if the specific posture is changed, the directional indications are correspondingly changed.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments.
Referring to fig. 1, fig. 1 is a schematic structural diagram of an embodiment of a bidirectional DC/DC converter of the present application. As shown in fig. 1, the high-voltage side circuit 11 includes at least two switching circuits connected in series. The high-voltage side circuit 11 is connected to a first power supply port, and specifically, two switch circuits of the high-voltage side circuit 11 are respectively connected to the positive and negative electrodes of the first power supply port. The first power port is used for being connected with the front bus 101 of the inverter circuit of the energy storage device. The bus 101 may be used to directly connect to a dc load or a dc power supply, or may be connected to an ac load or an ac power supply.
The low-side circuit 12 comprises two sets of two switching circuits connected in series, each set of switching circuits being connected in parallel with each other. The low-voltage side circuit 12 is used for connecting a second power supply port, specifically, two ends of two switch circuits in each group in the low-voltage side circuit 12 are respectively connected with the positive electrode and the negative electrode of the second power supply port. Wherein the second power port is connected to the energy storage device 102. The energy storage device 102 is a device having an electric energy storage capability, and may be, for example, a lithium battery or the like.
The transformer circuit 13 has a high voltage side N1 near the high voltage side circuit 11 and a low voltage side N2 near the low voltage side circuit 12. Wherein, two ends of the high voltage side N1 are respectively connected to the connection of the two switch circuits in the high voltage side circuit 11 and the resonance circuit 14, and two ends of the low voltage side N2 are respectively connected to the connection of the two switch circuits in one group of half-bridge circuits and the connection of the two switch circuits in the other group of half-bridge circuits in the low voltage side circuit 12. Specifically, one end of the high-voltage side N1 is connected to the connection of the two switching circuits of the half-bridge circuit in the high-voltage side circuit 11, and the other end is connected to the resonant circuit 14, wherein the resonant circuit 14 is composed of an inductance and a capacitance. One end of the low-voltage side N2 is connected with the connection part of two switch circuits of one group of half-bridge circuits of the low-voltage side circuit 12, and the other end is connected with the connection part of two switch circuits of the other group of half-bridge circuits of the low-voltage side circuit 12.
It should be noted that the half-bridge circuit is composed of two switching circuits connected in series. The high-side circuit 11 is composed of at least one half-bridge circuit, and the low-side circuit 12 is also composed of at least one half-bridge circuit.
The current detection circuit 15 is disposed between the low-voltage side circuit 12 and the energy storage device 102, and is configured to collect a value of a current flowing through the energy storage device 102. The resistor current detection circuit and other current detection circuits are included.
The control circuit 16 is connected to the switch circuits of the low-voltage side circuit 12 and the high-voltage side circuit 11 and the current detection circuit 15, and is configured to determine an operation mode of the bidirectional DC/DC converter according to the current value detected by the current detection circuit 15, and adjust the duty ratio of the switch circuits of the low-voltage side circuit 12 and the high-voltage side circuit 11 according to the current value, so as to maintain the stability of the current value flowing through the energy storage device 102.
Specifically, when the output current is detected to be reduced, the switching circuit is controlled to increase the duty ratio thereof, so that the output power is increased, and the output current is increased, whereas when the output current is detected to be increased, the switching circuit is controlled to decrease the duty ratio thereof, so that the output power is reduced, the output current is reduced, and the steady state of the current is maintained.
The beneficial effects of the embodiment are as follows: the duty ratio of each switching circuit under fixed frequency is regulated by the control circuit, so that the purpose of power transmission equalization is achieved, bus voltage is regulated in an equalization manner along with the voltage of the energy storage device, the highest conversion efficiency of the DC/DC converter is achieved, and the economical efficiency and the reliability of the bidirectional DC/DC converter are improved.
Wherein the resonant circuit 14 comprises at least a capacitive circuit and an inductive circuit. One end of the high-voltage side of the transformer circuit 13 is connected to the capacitor circuit, and the other end is connected to the inductor circuit, so that the high-voltage side of the transformer circuit 13 is connected to the high-voltage side circuit 11 via the resonance circuit 14. In this embodiment, the capacitive circuit comprises two capacitors connected in series, and the inductive circuit comprises a resonant inductor. That is, the resonant circuit 14 includes two capacitors in series and one resonant inductance. In other embodiments, the resonant inductance Lr of the resonant circuit 14 is formed by the leakage inductance in the transformer circuit 13, and in other embodiments, the leakage inductance of the transformer circuit may be replaced by a separate magnetic inductance device, where the resonant inductance is the sum of the separate inductance and the leakage inductance of the transformer circuit. In other embodiments, the resonant circuit 14 may also be formed by a capacitor in series with an inductor. In this embodiment, specifically, as shown in fig. 1, the resonant circuit 14 includes a first capacitor C1 and a second capacitor C2, and a resonant inductor Lr, where the first capacitor C1 and the second capacitor C2 are connected in series.
In the present embodiment, the control circuit 16 determines each of the switching circuits in the high-voltage side circuit 11 and the low-voltage side circuit 12 as a target switching circuit and a freewheel switching circuit according to the operation mode, and controls on-off of the target switching circuit and the freewheel switching circuit. In the present embodiment, the control circuit 16 mainly controls the target switching circuit and the freewheel switching circuit not to be turned on at the same time. In this embodiment, the target switching circuit and the freewheel switching circuit may be turned off at the same time, which is not limited herein. The working mode refers to a charging mode or a discharging mode. The target switch circuit is firstly conducted, the follow current switch circuit is then conducted, and the follow current switch circuit is not conducted at the same time, so that a resonant circuit is formed. Specifically, the step of the control circuit 16 adjusting the duty ratio of each of the switching circuits in the low-voltage side circuit and the high-voltage side circuit at the fixed operating frequency according to the current value includes: and increasing the duty ratio of the target switching circuit and the follow current switching circuit when the current value is smaller than a preset threshold value, and decreasing the duty ratio of the target switching circuit and the follow current switching circuit when the current value is larger than the preset threshold value, wherein the target switching circuit and the follow current switching circuit are ensured not to be conducted simultaneously when the duty ratio of the target switching circuit and the follow current switching circuit is increased. The phase of the control circuit 16 adjusting the duty ratio according to the current value detected by the current detection circuit 15 is that the duty ratio of each switching circuit is kept stable when each switching circuit is operated before each switching circuit is operated. The preset threshold may be set by itself, which is not limited herein. The duty ratio refers to the proportion of the energization time of the switching circuit relative to the total time.
In this embodiment, each switching circuit includes at least one MOS transistor, and each MOS transistor includes a body diode. Specifically, referring to fig. 2, fig. 2 is a schematic circuit diagram of a bidirectional DC/DC converter according to a first embodiment of the present application.
In the present embodiment, the high-voltage side circuit 11 includes a first switching circuit Q1 and a second switching circuit Q2. The control circuit determines that the first switch circuit Q1 is a target switch circuit, the second switch circuit Q2 is a follow current switch circuit, and controls the second switch circuit Q2 to be turned off when the first switch circuit Q1 is turned on, and controls the second switch circuit Q2 to be turned on when the first switch circuit Q1 is turned off. And decreasing the duty ratio of the first switching circuit Q1 and the second switching circuit Q2 when the current value is greater than a preset threshold value; the duty ratio of the first switching circuit Q1 and the second switching circuit Q2 is increased when the current value is smaller than a preset threshold value. The turn-off time of the second switch circuit Q2 is slightly longer than that of the first switch circuit Q1, so that the inductor in the transformer circuit 13 is completely released.
In the present embodiment, the low-voltage side circuit 12 includes a third switching circuit Q3, a fourth switching circuit Q4, a fifth switching circuit Q5, and a sixth switching circuit Q6. The third switching circuit Q3 and the fourth switching circuit Q4 are connected in series to form a group of half-bridge circuits, and the fifth switching circuit Q5 and the sixth switching circuit Q6 are connected in series to form a second group of half-bridge circuits. Wherein, two ends of the half-bridge circuit are respectively connected with the positive electrode and the negative electrode of the energy storage device 102. Specifically, the third switching circuit Q3 and the fifth switching circuit Q5 are connected in parallel to the positive electrode of the energy storage device 102, and the fourth switching circuit Q4 and the sixth switching circuit Q6 are connected in parallel to the negative electrode of the energy storage device 102, which is not limited herein. The control circuit 16 determines the fourth switching circuit Q4 and the fifth switching circuit Q5 as target switching circuits and determines the third switching circuit Q3 and the sixth switching circuit Q6 as freewheel switching circuits according to the operation mode. When the fourth switching circuit Q4 and the fifth switching circuit Q5 are simultaneously turned on, the third switching circuit Q3 and the sixth switching circuit Q6 are controlled to be simultaneously turned off, and when the fourth switching circuit Q4 and the fifth switching circuit Q5 are simultaneously turned off, the third switching circuit Q3 and the sixth switching circuit Q6 are controlled to be simultaneously turned on.
In particular, when the operating mode is a charging mode, energy is transferred from the high voltage side to the low voltage side, and we divide the cycle into a-F. Referring to fig. 3A-3F, the broken line indicates that the MOS transistor is turned off, the solid line indicates that the MOS transistor is turned on, and I is the current direction. The current resonance circuit operates at each cycle as follows:
fig. 3A is a schematic diagram of the bi-directional DC/DC transformer of the present application in the a-phase. In phase a, the first switching circuit Q1 is turned on and the second switching circuit Q2 is turned off, the resonant circuit has a current ID1 flowing through it, and energy is stored in the resonant circuit 14. The high-side winding voltage Lp of the transformer causes the transformer circuit 13 to transfer energy to the low-side N2 due to the decrease in the voltage of the first capacitor C1 and the increase in the second capacitor C2 in the resonant circuit 14. Meanwhile, the fourth and fifth switching circuits Q4 and Q5 are turned on, and the third and sixth switching circuits Q3 and Q6 are turned off. At the same time, the first capacitor C1 is energized, the voltage of the first capacitor C1 decreases, the second capacitor C2 is energized, and the voltage of the second capacitor C2 increases until the high-side winding voltage cannot maintain the energy to the low-side, at which time the high-side no longer transmits energy to the low-side.
Fig. 3B is a schematic diagram of the bi-directional DC/DC transformer of the present application in B-stage conduction. In the B-stage, after the low-side current is zero, the exciting current is zero, and the resonance current still flows in the resonance circuit 14.
Fig. 3C is a schematic diagram of the bi-directional DC/DC transformer of the present application in the C phase. In phase C, there is dead time between the target switching circuit turning off and the freewheel switching circuit turning on, and in this phase, both the first switching circuit Q1 and the second switching circuit Q2 are in an off state. In phase C, the first switching circuit Q1 is closed and the energy stored in the resonant circuit 14 is released through the second capacitor C2. At this time, the voltage of the first capacitor C1 increases, and the voltage of the second capacitor C2 decreases. The current-ID 2 flows into the body diode of the second switching circuit Q2, and when the forward voltage of the second switching circuit Q2 drops to the voltage VF2 of the body diode of the second switching circuit Q2, the voltage of the second switching circuit Q2 is clamped to VF2.
Fig. 3D is a schematic diagram of the bi-directional DC/DC transformer of the present application in the D phase. In the D stage, the second switching circuit Q2 is turned on, and since the Q2 voltage is clamped to VF2 at this time, approximately 0, ZVS (zero voltage switching) can be realized. The high voltage winding voltage of the transformer is added by the voltage of the first capacitor C1, and the transformer transfers energy to the low voltage side. Meanwhile, the third switching circuit Q3 and the sixth switching circuit Q6 are turned on, and the fifth switching circuit Q5 and the fourth switching circuit Q4 are turned off, and because the low-voltage side current is 0 at this time, ZCS (zero current switching) can be realized, thereby reducing power consumption generated by turning off the MOS transistor. At the same time, the first capacitor C1 charges, the voltage of the first capacitor C1 rises, the second capacitor C2 discharges, and the voltage of the second capacitor C2 drops until the high-side winding voltage cannot maintain the energy of the low-side.
Fig. 3E shows the conduction condition of the bidirectional DC/DC transformer in the E phase. In the E phase, after the low-side current is zero, the exciting current is zero, and the resonance current still flows in the resonance circuit 14.
Fig. 3F is a schematic diagram of the bi-directional DC/DC transformer of the present application in the F phase. In the F stage, there is dead time between the freewheel switch circuit turning off to the target switch circuit turning on, and in this stage, both the first switch circuit Q1 and the second switch circuit Q2 are in an off state. When the second switching circuit Q2 is closed, energy is stored into the resonant circuit 14. a-ID 1 current flows to charge the second capacitor C2. When the second capacitor C2 voltage increases to the input voltage, -ID1 current flows into the body diode of the first switching circuit Q1, and the voltage of the first switching circuit Q1 is clamped at the value VF 1.
The above cycle is repeated and energy is transferred from the high side circuit 11 to the low side circuit 12, thereby effecting charging of the energy storage device 102.
In the case of discharging a lithium battery, energy is transferred from the low voltage side to the high voltage side by the control circuit 16 controlling the on and off of Q1, Q2, Q3, Q4, Q5, Q6. Similarly, the switching circuits are turned on and off repeatedly in the above a-F periods, wherein the current flows in the opposite direction to the charging process.
In this embodiment, the voltage of the bidirectional DC/DC converter is designed in an open loop, that is, the bus DC voltage in this embodiment is balanced along with the voltage of the lithium battery according to the turn ratio of the transformer circuit, and is multiplied.
In the present embodiment, the lithium battery voltage Vo and the bus dc voltage VIN The relation of (2) is as follows:
wherein n is the turn ratio of the high-voltage side and the low-voltage side of the transformer, and Vd is the conduction voltage drop of the low-voltage side switch circuit.
When the turn ratio in the transformer circuit is determined and the number of the low-voltage side switch circuits is determined, the lithium battery voltage is linearly related to the bus voltage. The turn ratio in the transformer circuit and the conduction voltage drop of the low-voltage side switch circuit are determined by hardware.
In this embodiment, when the transformer turn ratio is determined, the energy storage device voltage corresponds to the bus voltage in proportion, and the topology frequency is no longer adjusted according to the load or the voltage of the energy storage device, and the bus voltage constant voltage is not required to be maintained. The bus voltage varies with the fixed proportion of the energy storage device voltage, so that the DC/DC converter can reach the highest conversion efficiency. The current of the embodiment adopts a closed loop design, namely, the control circuit detects the current flowing into or flowing out of the energy storage device through the current detection circuit, and adjusts the duty ratio of each switching circuit under fixed frequency, so that the purpose of power transmission equalization is achieved. Specifically, the control circuit detects the input and output voltages of the bidirectional DC/DC converter, gives a target current according to an algorithm, compares the given target current with the sampled current, reduces the duty ratio when the current is larger, and increases the duty ratio when the current is smaller until the given target current is equal to the sampled current, and completes the power transmission balance.
In this embodiment, the control circuit further includes controlling the operating frequency of each switching circuit to be near the resonance frequency of the resonance circuit, thereby ensuring high-efficiency power conversion and reducing power consumption. Specifically, the operating frequency of each switching circuit is not more than ±30% of the resonant frequency of the resonant circuit, that is, the switching circuit operates within a range not exceeding ±30% of the resonant frequency. Wherein the method comprises the steps ofThe resonant frequency is determined by capacitance and leakage inductance of the transformer circuit, and the calculation formula isWherein Lr is leakage inductance of the high-voltage side of the transformer, and Cr is the sum of C1 and C2.
The beneficial effects of this embodiment are: the control circuit is used for detecting the current flowing into or out of the energy storage device according to the current detection circuit and adjusting the duty ratio of each switching circuit under fixed frequency, so that the bus voltage and the voltage of the energy storage device form a multiple relation, and the purpose of balancing power transmission is achieved.
In other embodiments, the voltage ring can also adopt a semi-closed ring scheme, that is, according to the sampled input and output voltage, the duty ratio limiting function is increased, the busbar voltage or the energy storage device voltage can be finely adjusted, when the bidirectional DC/DC converter works unidirectionally, the output busbar voltage or the voltage fluctuation range of the energy storage device is reduced, the control effect of outputting a narrow voltage range is realized, and the control effect is close to the busbar voltage constant voltage mode.
In this embodiment, the switching circuits Q1, Q2, Q3, Q4, Q5, Q6 are MOS transistors. Each switching circuit can comprise a plurality of MOS tubes connected in parallel. In this embodiment, the switching circuit includes a MOS transistor. In other embodiments, the switching circuit may further include a plurality of MOS transistors connected in parallel. Referring to fig. 4, fig. 4 is a schematic circuit diagram of a second embodiment of the bidirectional DC/DC converter according to the present invention. As shown in fig. 4, the first switching circuit Q1 includes two parallel first MOS transistors 1 and second MOS transistors 2; the second switching circuit Q2 includes two parallel third MOS transistors 3 and fourth MOS transistor 4, where the first MOS transistor 1 and the second MOS transistor 2 are turned on simultaneously, and the third MOS transistor 3 and the fourth MOS transistor 4 are turned on simultaneously. In other embodiments, the other switching circuit may also include two MOS transistors, which are not listed here. The control circuit 16 is further configured to determine the number of turned-on MOS transistors according to the charging power or the discharging power. The larger the number of MOS tubes connected in parallel is, the larger the voltage the circuit can bear.
In the present embodiment, the resonance circuit 14 is composed of the first and second capacitances C1 and C2 and the resonance inductance Lr. In other embodiments, the resonant circuit 14 may also be composed of a capacitor and an inductor, that is, in series with the resonant inductor or the transformer winding, which may also achieve the effects of this embodiment. Specifically, referring to fig. 5, fig. 5 is a schematic circuit diagram of a bidirectional DC/DC converter according to a third embodiment of the present application.
In the third embodiment, the resonant circuit 14 includes one capacitor C1 and one inductor Lr. In one embodiment, the capacitor C1 and the inductor Lr are respectively connected to two ends of the high voltage side of the transformer circuit 13, and in another embodiment, the capacitor C1 and the inductor Lr are connected to one end of the high voltage side of the transformer circuit 13, which is not limited herein.
In the present embodiment, the high-voltage side circuit 11 includes one set of half-bridge circuits, and in other embodiments, the high-voltage side circuit 11 may also include two sets of half-bridge circuits. Referring to fig. 6 specifically, fig. 6 is a schematic circuit diagram of a bidirectional DC/DC converter according to a fourth embodiment of the present application. As shown in fig. 6, the high-voltage side circuit 11 includes a first switching circuit Q1 and a second switching circuit Q2 connected in series, and a seventh switching circuit Q7 and an eighth switching circuit Q8 connected in series, wherein the first switching circuit Q1 and the second switching circuit Q2 are connected in parallel with the seventh switching circuit Q7 and the eighth switching circuit Q8. The first switching circuit Q1 and the second switching circuit Q2 constitute a group of half-bridge circuits, and the seventh switching circuit Q7 and the eighth switching circuit Q8 constitute a group of half-bridge circuits, so that the high-side circuit 11 forms a full-bridge circuit.
In the fourth embodiment, one end of the high-voltage side of the transformer circuit 13 is connected to the junction of the first switching circuit Q1 and the second switching circuit Q2, and the other end is connected to the junction of the seventh switching circuit Q7 and the eighth switching circuit Q8. The control circuit 16 determines the first switching circuit Q1 and the eighth switching circuit Q8 as target switching circuits and determines the second switching circuit Q2 and the seventh switching circuit Q7 as freewheel switching circuits according to the operation mode. That is, the eighth switching circuit Q8 is turned on or off simultaneously with the first switching circuit Q1, and the seventh switching circuit Q7 is turned on or off simultaneously with the second switching circuit Q2, so that the first switching circuit Q1 and the eighth switching circuit Q8 control the conduction of the two ends of the transformer circuit 13 in the first stage, and the second switching circuit Q2 and the seventh switching circuit Q7 control the conduction of the two ends of the transformer circuit 13 in the second stage. The first stage refers to the A-B stage, and the second stage refers to the D-E stage. The conduction of each other switch circuit is shown in fig. 3A-3F, and will not be described herein.
In the application, the target switch circuit and the follow current switch circuit in the high-voltage side circuit and the low-voltage side circuit are determined, relay conduction of the target switch circuit and the follow current switch circuit is controlled, so that charging from the high-voltage side to the low-voltage side or discharging from the low-voltage side to the high-voltage side is realized, the working frequency of the converter is fixed through the control circuit, the duty ratio of the target switch circuit and the follow current switch circuit under the fixed working frequency is regulated, and the purpose of balancing power transmission is achieved on the premise that the DC/DC converter works in the state of highest conversion efficiency is ensured, so that the economical efficiency and reliability of the bidirectional DC/DC converter are improved.
The foregoing is only examples of the present application, and is not intended to limit the scope of the patent application, and all equivalent structures or equivalent processes using the descriptions and the contents of the present application or other related technical fields are included in the scope of the patent application.