Control method for resonant conversion circuit, and energy storage apparatus

Abstract

Provided in the present application are a control method for a resonant conversion circuit, and an energy storage apparatus. The resonant conversion circuit is connected to other resonant conversion circuits in parallel, wherein the resonant conversion circuit comprises a transformer, a high-voltage-side bridge circuit, a resonant network and a low-voltage-side bridge circuit, the high-voltage-side bridge circuit is connected to a primary side of the transformer by means of the resonant network, and the low-voltage-side bridge circuit is connected to a secondary side of the transformer. The control method comprises: determining a droop control curve on the basis of operating parameters of a resonant conversion circuit, wherein the droop control curve indicates a linear droop relationship between a high-voltage-side direct-current voltage and a high-voltage-side current of a high-voltage-side bridge circuit; and controlling the operation of the resonant conversion circuit on the basis of the droop control curve. The control method of the present application can limit the voltage change range of the resonant conversion circuit, and can thus reduce the frequency change range and facilitate the resonant conversion circuit operating at a resonant frequency, thereby improving the efficiency.

Description

Control method and energy storage device of resonant conversion circuit

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 20, 2024, with application number 202410329873.0 and application name “Control Method and Energy Storage Device for Resonant Conversion Circuit”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of resonant conversion circuits, and in particular to a control method and energy storage device for a resonant conversion circuit. Background Art

[0003] Due to its simple structure and easy soft switching, the resonant converter circuit is widely used in server power supplies, vehicle power supplies, energy storage power supplies and other fields. In the field of energy storage power supplies, bidirectional operation of the resonant converter circuit and parallel connection of multiple machines are often required. Since the voltage variation range of the energy storage power supply is relatively wide, the frequency variation range of the resonant converter circuit is also relatively wide, making it difficult to operate near the resonant frequency, which is not conducive to efficiency improvement. Moreover, in actual operation, the voltage drop caused by the line impedance, the internal resistance of the device, etc. will increase with the increase of load power, thereby affecting the gain, resulting in the need for the resonant converter circuit to further adjust the frequency to compensate for this part of the gain. However, this will make the frequency variation range wider, making it more difficult to achieve optimal efficiency. Summary of the Invention

[0004] In view of this, the present application provides a control method and an energy storage device for a resonant conversion circuit to solve the problem of low efficiency of the resonant conversion circuit in the prior art due to a wide frequency variation range.

[0005] In a first aspect, the present application provides a control method for a resonant conversion circuit, wherein the resonant conversion circuit is connected in parallel with other resonant conversion circuits, the resonant conversion circuit comprising a transformer, a high-voltage side bridge circuit, a resonant network, and a low-voltage side bridge circuit, wherein the high-voltage side bridge circuit is connected to the primary side of the transformer via the resonant network, and the low-voltage side bridge circuit is connected to the secondary side of the transformer; the control method comprises:

[0006] Determining a droop control curve according to operating parameters of the resonant conversion circuit, the droop control curve being used to indicate a linear droop relationship between a high-side DC voltage and a high-side current of the high-side bridge circuit;

[0007] The operation of the resonant converter circuit is controlled according to the droop control curve.

[0008] In one embodiment, the expression of the droop control curve is: V HV =V LV ·nI HV ·Rv

[0009] Among them, V HV is the high-side DC voltage, V LV is the low-voltage side DC voltage of the low-voltage side bridge circuit, n is the primary-to-secondary turns ratio of the transformer, I HV is the DC current on the high voltage side, and Rv is the set virtual resistance.

[0010] In one embodiment, the operating parameters of the resonant conversion circuit include the primary-to-secondary turns ratio of the transformer, the high-voltage side DC voltage, the high-voltage side current, and the low-voltage side DC voltage of the low-voltage side bridge circuit;

[0011] The linear droop relationship between the high-side DC voltage and the high-side current of the high-side bridge circuit is determined according to the operating parameters of the resonant conversion circuit, including:

[0012] After obtaining the high-side DC voltage given value of the high-side bridge circuit each time, the resonant conversion circuit is controlled according to the high-side DC voltage given value;

[0013] Obtaining an actual value of the high-side current of the high-side bridge circuit, an actual value of the low-side DC voltage of the low-voltage side bridge circuit, and a switching frequency of the resonant conversion circuit;

[0014] Calculate the resistance based on the transformer's primary-to-secondary turns ratio, the high-voltage side DC voltage set value, the high-voltage side current actual value, the low-voltage side DC voltage actual value, and the droop control curve expression;

[0015] The resistance corresponding to the time when the difference between the switching frequency and the resonant frequency of the resonant network is minimum is determined as the set virtual resistance.

[0016] In one embodiment, the low-voltage side bridge circuit is also used to access the battery pack;

[0017] Determining a linear droop relationship between a high-side DC voltage and a high-side current of a high-side bridge circuit according to operating parameters of the resonant conversion circuit also includes:

[0018] Obtain a given value of the high-voltage side DC voltage according to the battery voltage of the battery pack;

[0019] The high-voltage side DC voltage given value obtained each time is different and is not greater than the product of the battery voltage of the battery pack and the primary-to-secondary turns ratio of the transformer.

[0020] In one embodiment, the droop control curve fits the natural droop characteristic curve of the resonant conversion circuit, and the voltage variation range of the droop control curve is smaller than the voltage variation range of the natural droop characteristic curve, wherein the natural droop characteristic curve is used to indicate the droop characteristics between the high-voltage side DC voltage and the high-voltage side current of the resonant conversion circuit itself.

[0021] In one embodiment, when the energy of the resonant conversion circuit flows from the high-voltage side bridge circuit to the low-voltage side bridge circuit, the droop control curve indicates a linear droop relationship between the high-voltage side DC voltage and the high-voltage side current, wherein the high-voltage side current is a negative current;

[0022] When the energy of the resonant conversion circuit flows from the low-voltage side bridge circuit to the high-voltage side bridge circuit, the droop control curve indicates a linear droop relationship between the high-voltage side DC voltage and the high-voltage side current, wherein the high-voltage side current is a positive current.

[0023] In one embodiment, the control method further includes:

[0024] The operation of each parallel resonant conversion circuit is controlled according to the droop control curve.

[0025] A second aspect of the present application provides an energy storage device, which includes a battery pack, a resonant conversion circuit and a controller. The resonant conversion circuit includes a transformer, a high-voltage side bridge circuit, a resonant network and a low-voltage side bridge circuit. The high-voltage side bridge circuit is connected to the primary side of the transformer through the resonant network, one end of the low-voltage side bridge circuit is connected to the secondary side of the transformer, and the other end of the low-voltage side bridge circuit is connected to the battery pack; the resonant conversion circuit is used to be connected in parallel with other resonant conversion circuits; the controller is connected to the resonant conversion circuit, and the controller is used to control the operation of the resonant conversion circuit according to a droop control curve, wherein the droop control curve is used to indicate the linear droop relationship between the high-voltage side DC voltage and the high-voltage side current of the high-voltage side bridge circuit.

[0026] In one embodiment, the high-voltage side bridge circuit includes a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube. The first switching tube and the second switching tube are connected in series to form a first bridge arm, the third switching tube and the fourth switching tube are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel.

[0027] The low-voltage side bridge circuit includes a fifth switching tube, a sixth switching tube, a seventh switching tube, and an eighth switching tube. The fifth switching tube and the sixth switching tube are connected in series to form a third bridge arm. The seventh switching tube and the eighth switching tube are connected in series to form a fourth bridge arm. The third bridge arm and the fourth bridge arm are connected in parallel.

[0028] The resonant network includes a resonant capacitor, a resonant inductor and an excitation inductor. The resonant capacitor and the resonant inductor are connected in series between the midpoint of the first bridge arm and one terminal of the primary side of the transformer. The midpoint of the second bridge arm is connected to the other terminal of the primary side of the transformer. The excitation inductor is connected in parallel to the primary side of the transformer. The midpoints of the third bridge arm and the fourth bridge arm are connected to the secondary side of the transformer.

[0029] In one embodiment, during the operation of the resonant conversion circuit controlled according to the droop control curve, the first switch tube and the second switch tube are alternately turned on, the third switch tube and the fourth switch tube are alternately turned on, the fifth switch tube and the sixth switch tube are alternately turned on, and the seventh switch tube and the eighth switch tube are alternately turned on, and the switching frequency of the resonant conversion circuit is close to or equal to the resonant frequency of the resonant network.

[0030] Compared with the prior art, this application has at least the following advantages:

[0031] 1. Taking into account the natural droop characteristics of the resonant conversion circuit, the present application proposes a droop control curve to perform droop control on the resonant conversion circuit. This can achieve compensation for the gain change of the resonant conversion circuit under different loads and the internal resistance voltage drop change under different loads (i.e., compensation for the natural droop characteristics of the gain and internal resistance). When the resonant conversion circuit is operating unidirectionally or bidirectionally, the switching frequency variation range of the resonant conversion circuit can be reduced, which helps to improve the efficiency of the resonant conversion circuit.

[0032] 2. When the resonant conversion circuit is used in the field of multiple machines in parallel, the control method of the present application uses the droop control curve required for current sharing to compensate for the parameter differences between different resonant conversion circuits, thereby achieving the current sharing characteristics of multiple machines in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0034] FIG1 is a circuit topology diagram of a resonant conversion circuit;

[0035] FIG2 is an AC equivalent circuit diagram of the high-voltage side bridge circuit in the resonant conversion circuit shown in FIG1 ;

[0036] FIG3 is a gain curve diagram of the resonant converter circuit shown in FIG1 during forward operation;

[0037] 4 is a schematic diagram showing changes in the high-voltage side DC voltage and the high-voltage side current when the resonant converter circuit shown in FIG1 is in forward operation;

[0038] FIG5 is a gain curve diagram of the resonant conversion circuit shown in FIG1 during reverse operation;

[0039] 6 is a schematic diagram showing changes in the high-voltage side DC voltage and the high-voltage side current when the resonant conversion circuit shown in FIG1 is in reverse operation;

[0040] FIG7 is a characteristic curve diagram of the internal resistance of the resonant conversion circuit shown in FIG1;

[0041] FIG8 is a schematic diagram of a plurality of resonant conversion circuits shown in FIG1 connected in parallel;

[0042] FIG9 is a flow chart of a control method of a resonant conversion circuit provided by an embodiment of the present application;

[0043] FIG10 is a flow chart of step S10 in FIG9 ;

[0044] FIG11 is a schematic diagram of a droop control curve provided in an embodiment of the present application;

[0045] FIG12 is a comparison diagram of the droop control curve shown in FIG11 and the natural droop characteristic curve of the resonant conversion circuit;

[0046] FIG13 is a schematic diagram of a power conversion device provided in an embodiment of the present application;

[0047] FIG14 is a schematic diagram of an energy storage device provided in an embodiment of the present application.

[0048] Explanation of Reference Numerals 100 - resonant conversion circuit; 10 - high-voltage side bridge circuit; 20 - resonant network; 30 - low-voltage side bridge circuit; 200 - controller; 300 - power conversion device; 400 - battery pack; 500 - energy storage device DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of this application. In the absence of conflict, the features in the following different embodiments and embodiments can be combined with each other.

[0050] Please refer to Figure 1, which shows the circuit topology of a resonant converter circuit. Resonant converter circuit 100 includes a transformer T, a high-voltage-side bridge circuit 10, a resonant network 20, and a low-voltage-side bridge circuit 30. In actual use, the primary side of transformer T typically serves as the high-voltage side, and the secondary side serves as the low-voltage side. Therefore, the high-voltage-side bridge circuit 10 is connected to the primary side of transformer T via the resonant network 20, while the low-voltage-side bridge circuit 30 is connected to the secondary side of transformer T.

[0051] Specifically, the high-voltage side bridge circuit 10 and the low-voltage side bridge circuit 30 can be full-bridge circuits. The high-voltage side bridge circuit 10 includes a first switch tube Q1, a second switch tube Q2, a third switch tube Q3, and a fourth switch tube Q4. The first switch tube Q1 and the second switch tube Q2 are connected in series to form a first bridge arm, the third switch tube Q3 and the fourth switch tube Q4 are connected in series to form a second bridge arm, the first bridge arm and the second bridge arm are connected in parallel, and the two switches in the same bridge arm are alternately turned on. The low-voltage side bridge circuit 30 includes a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7, and an eighth switch tube Q8. The fifth switch tube Q5 and the sixth switch tube Q6 are connected in series to form a third bridge arm, the seventh switch tube Q7 and the eighth switch tube Q8 are connected in series to form a fourth bridge arm, the third bridge arm and the fourth bridge arm are connected in parallel, and the two switches in the same bridge arm are alternately turned on. For ease of demonstration, the switch tubes Q1 to Q8 in the embodiments of the present application are all demonstrated using MOS tubes as an example. Of course, in other embodiments, the switch tubes Q1 to Q8 may also use other types of semiconductor switch tubes, which does not constitute a limitation to the present application.

[0052] The resonant network 20 includes a resonant capacitor Cr, a resonant inductor Lr, and an excitation inductor Lm. The resonant capacitor Cr and the resonant inductor Lr are connected in series between the midpoint a of the first bridge arm and one terminal of the primary side of the transformer T. The midpoint b of the second bridge arm is connected to the other terminal of the primary side of the transformer T. The excitation inductor Lm is connected in parallel to the primary side of the transformer T. In one embodiment, the excitation inductor Lm can also be integrated into the transformer T. The midpoint c of the third bridge arm and the midpoint d of the fourth bridge arm are connected to the secondary side of the transformer T.

[0053] Based on this design, the resonant conversion circuit 100 constitutes a bidirectional LLC resonant conversion circuit. The ends of the first bridge arm and the second bridge arm in the high-voltage side bridge circuit 10 can serve as the input ports of the resonant conversion circuit 100, and the ends of the third bridge arm and the fourth bridge arm in the low-voltage side bridge circuit 30 can serve as the output ports of the resonant conversion circuit 100. The input port of the resonant conversion circuit 100 is used to connect to a DC power supply, and the output port of the resonant conversion circuit 100 is used to connect to a load. Therefore, the high-voltage side bridge circuit 10 can convert the high-voltage side DC voltage V HV After DC / AC conversion into the bridge arm midpoint voltage Vab, it is fed to the primary side of the transformer T through the resonant network 20. The voltage Vab is coupled to the secondary side of the transformer T through the magnetic field of the transformer T, generating the bridge arm midpoint voltage Vcd. The voltage Vcd is then converted by AC / DC by the low-voltage side bridge circuit 30 and outputs the low-voltage side DC voltage V LV The third and fourth bridge arms can also be connected in parallel with capacitor C1, which can provide voltage stabilization. During this process, energy flows from the high-voltage side bridge circuit 10 to the low-voltage side bridge circuit 30. For ease of description, this process can be referred to as the forward operation (or charging) process of the resonant converter circuit 100.

[0054] Alternatively, the ends of the first and second bridge arms in the high-voltage side bridge circuit 10 may serve as output ports of the resonant conversion circuit 100, and the ends of the third and fourth bridge arms in the low-voltage side bridge circuit 30 may serve as input ports of the resonant conversion circuit 100. In this case, the operation of the resonant conversion circuit 100 is the reverse of the forward operation described above, so this process can be referred to as the reverse operation (or discharge) process of the resonant conversion circuit 100. For details, please refer to the forward operation described above and will not be described in detail here. During this process, energy flows from the high-voltage side bridge circuit 10 to the low-voltage side bridge circuit 30.

[0055] When the resonant converter circuit 100 is operating in the forward direction, the high-voltage side bridge circuit 10 can be equivalent to the AC equivalent circuit diagram shown in FIG2 . Since the switches in each bridge arm are alternately turned on, the bridge arm midpoint voltage Vab is an AC voltage. Therefore, FIG2 illustrates Vab as equivalent to an AC power supply.

[0056] There is an equivalent resistance R on the primary side of transformer T ac , whose expression is:

[0057] Where V LV is the low-voltage side DC voltage, I LV is the low voltage side current.

[0058] The inductance k of the resonant converter circuit 100 is:

[0059] The resonant frequency fr of the resonant network 20 is:

[0060] The normalized frequency fn of the resonant conversion circuit 100 is:

[0061] Wherein, fs is the switching frequency of the switch tube in the resonant conversion circuit 100. It can be understood that when the switching frequency fs of the resonant conversion circuit 100 is fs=fr, the energy transmission efficiency of the resonant conversion circuit 100 is the highest.

[0062] The quality factor Q of the resonant converter circuit 100 is:

[0063] When the resonant converter circuit 100 is running in the forward direction, it can be deduced from the fundamental wave analysis method that the gain M of the resonant converter circuit 100 is charge The expression is:

[0064] Therefore, the gain of the resonant converter circuit 100 changes with the high-voltage side current during forward operation as shown in the curve in FIG3 . In FIG3 , the horizontal axis is the high-voltage side current I HV , the vertical axis is the gain M charge As can be seen from Figure 3, the gain of the resonant converter circuit 100 decreases as the high-voltage side current increases. It should be noted that the data on the horizontal and vertical axes in Figure 3 are only examples and do not constitute a limitation of this application. The same applies to Figures 4 to 7 and 12 below.

[0065] It can be understood that the high-side DC voltage V of the resonant converter circuit 100 during forward operation is HV The expression is:

[0066] Therefore, the change of the high-side DC voltage of the resonant converter circuit 100 with the high-side current during forward operation can be shown as the curve in FIG4 . In FIG4 , the horizontal axis is the high-side current I HV , the vertical axis is the high voltage side DC voltage V HV As can be seen from FIG4 , during forward operation, the DC voltage on the high-voltage side of the resonant converter circuit 100 increases as the current on the high-voltage side increases.

[0067] When the resonant converter circuit 100 is in reverse operation, it can be deduced from the fundamental wave analysis method that the gain M of the resonant converter circuit 100 is discharge The expression is:

[0068] Therefore, the gain of the resonant converter circuit 100 changes with the high-voltage side current during reverse operation as shown in the curve in FIG5 . In FIG5 , the horizontal axis is the high-voltage side current I HV , the vertical axis is the gain M discharge As can be seen from FIG5 , when operating in reverse, the gain of the resonant converter circuit 100 decreases as the high-voltage side current increases.

[0069] It can be understood that the high-side DC voltage V of the resonant conversion circuit 100 during reverse operation is HV The expression is: V HV =V LV ·n·M discharge (9)

[0070] Therefore, the variation of the high-side DC voltage of the resonant converter circuit 100 with the high-side current during reverse operation can be shown as the curve in FIG6 . In FIG6 , the horizontal axis is the high-side current I HV , the vertical axis is the high voltage side DC voltage V HV As can be seen from FIG6 , the high-voltage side DC voltage of the resonant conversion circuit 100 decreases as the high-voltage side current increases.

[0071] In summary, when the resonant conversion circuit 100 is running in the forward direction, the high-voltage side DC voltage increases as the high-voltage side current increases, and when it is running in the reverse direction, the high-voltage side DC voltage decreases as the high-voltage side current increases. For the convenience of description, the high-voltage side current during forward operation is defined as a negative current, and the high-voltage side current during reverse operation is defined as a positive current. The variation curve of the high-voltage side DC voltage can be referred to the natural droop characteristic curve shown in Figure 12 (combined with Figures 4 and 6). It can be seen that the influence of the high-voltage side current on the high-voltage side DC voltage presents a droop characteristic (or a droop trend). This can be regarded as the gain of the resonant conversion circuit 100 itself having a droop characteristic.

[0072] In addition, the high-voltage side current also has a certain impact on the internal resistance Rin (including the equivalent resistance of the switch tube, line impedance, etc.) of the resonant converter circuit 100 equivalent to the secondary side of the transformer T. Assuming that the impact of the high-voltage side current on the gain of the resonant converter circuit 100 is ignored, the voltage drop V Rin The expression of V can be: Rin =V LV ·nI HV ·R in (10)

[0073] Therefore, the voltage drop V Rin The change with the high-voltage side current can be shown as the curve in Figure 7. It can be seen that the influence of the high-voltage side current on the internal resistance also presents a droop characteristic (or a droop trend).

[0074] Understandably, the resonant converter circuit 100 is widely used in server power supplies, vehicle power supplies, energy storage power supplies, and other fields due to its simple structure and ease of soft switching. In the energy storage power field, bidirectional operation of the resonant converter circuit 100 and parallel connection of multiple units are often required.

[0075] For example, see Figure 8, which shows a controller 200 and at least two resonant conversion circuits 100 with identical structures and parameters. In energy storage power supply applications, the first and second bridge arms of each resonant conversion circuit 100 can be connected to the DC side of the same inverter (not shown in Figure 8), and the third and fourth bridge arms of each resonant conversion circuit 100 can be connected to corresponding battery packs (not shown in Figure 8). During forward operation, the inverter acts as a DC power source and the battery pack acts as a load. During reverse operation, the battery pack acts as a DC power source and the inverter acts as a load. After connecting to the corresponding battery pack, the input and output ports of all resonant conversion circuits 100 are connected in parallel, thereby providing sufficient current to the loads connected to the output ports. The controller 200 can be an MCU (Micro Controller Unit) or other control element / circuit. The controller 200 is connected to each resonant conversion circuit 100 and is used to perform current sharing control on each resonant conversion circuit 100, that is, to control the operating state of each resonant conversion circuit 100 to be consistent, thereby outputting the same current.

[0076] Because the voltage range of the energy storage power supply is relatively wide, the switching frequency range of the resonant converter circuit 100 is also relatively wide, making it difficult to operate near the resonant frequency, which is not conducive to improving efficiency. Moreover, in actual operation, the voltage drop caused by line impedance, device equivalent resistance, etc. will increase with the increase of load power, thereby affecting the gain, resulting in the resonant converter circuit 100 needing to further adjust the frequency to compensate for this part of the gain. However, this will make the switching frequency range even wider, making it more difficult to achieve optimal efficiency.

[0077] Therefore, an embodiment of the present application provides a control method for a resonant conversion circuit. This control method can be executed by the controller 200 and can limit the voltage variation range of the resonant conversion circuit 100, thereby reducing the switching frequency variation range, helping the resonant conversion circuit 100 to operate at the resonant frequency, so that the efficiency can be improved.

[0078] Specifically, the embodiment of the present application proposes a droop control curve to control the droop of the resonant conversion circuit 100 in consideration of the natural droop characteristics of the resonant conversion circuit 100. Referring to FIG9 , this control method includes:

[0079] Step S1 : determining a droop control curve according to operating parameters of the resonant conversion circuit 100 , where the droop control curve indicates a linear droop relationship between the high-side DC voltage and the high-side current of the high-side bridge circuit 10 .

[0080] In this embodiment, the operating parameters of the resonant conversion circuit 100 may include the primary-to-secondary turns ratio of the transformer, the high-voltage side DC voltage, the high-voltage side current, and the low-voltage side DC voltage of the low-voltage side bridge circuit 30 .

[0081] The expression of the droop control curve can be: V HV =V LV ·nI HV ·Rv (11)

[0082] Among them, Rv is the set virtual resistance. It can also be seen from this expression that V HV with I HV There is a linear negative correlation between them, in other words, there is a linear droop relationship.

[0083] Therefore, the schematic diagram of the droop control curve can be shown as the oblique line in FIG10 , where the horizontal coordinate of the oblique line is I HV , the vertical axis is V HV , the voltage at the intersection with the vertical axis is V LV ·n, the slope is Rv.

[0084] In one embodiment, the low-voltage side bridge circuit 30 can be connected to the battery pack, that is, the battery pack serves as a DC power source or load. Therefore, in step S1, the controller 200 can obtain a high-voltage side DC voltage given value based on the battery voltage of the battery pack. For example, the controller 200 can use the battery voltage as the high-voltage side DC voltage given value, or adjust the battery voltage down as the high-voltage side DC voltage given value. As a further example, when the battery voltage is 420V, the high-voltage side DC voltage given value can be 420V, 414V or other voltage values ​​less than 420V. Among them, the battery voltage can be adjusted multiple times to obtain multiple high-voltage side DC voltage given values. The high-voltage side DC voltage given value obtained each time is different, and is not greater than the product of the battery voltage of the battery pack and the primary-to-secondary turns ratio n of the transformer T, that is, the high-voltage side DC voltage given value ≤V LV ·n.

[0085] As shown in FIG11 , the process of determining the droop control curve according to the operating parameters of the resonant conversion circuit 100 in step S1 may specifically include:

[0086] Step S11 : After obtaining the high-side DC voltage set value of the high-side bridge circuit 10 each time, controlling the resonant conversion circuit 100 according to the high-side DC voltage set value.

[0087] In step S11, the controller 200 controls the resonant converter circuit 100 shown in FIG1 to operate in the forward direction according to the high-voltage side DC voltage setpoint, wherein the switches Q1 to Q8 are switched on and off at a certain switching frequency. During this process, the high-voltage side bridge circuit 10 generates current, and the low-voltage side bridge circuit 30 also outputs corresponding voltage and current. The switching frequency can be set accordingly based on actual conditions (such as the high-voltage side DC voltage setpoint, the voltage and current requirements of the load connected to the low-voltage side bridge circuit 30, the selection parameters of the switch tubes, losses, etc.), and is not specifically limited here.

[0088] Step S12 , obtaining the actual value of the high-side current of the high-side bridge circuit 10 , the actual value of the low-side DC voltage of the low-side bridge circuit 30 , and the switching frequency of the resonant conversion circuit 100 .

[0089] The controller 200 can obtain the actual value of the high-voltage side current and the actual value of the low-voltage side DC voltage through a sampling circuit.

[0090] Step S13: Calculate the resistance based on the primary-to-secondary turns ratio of the transformer, the given value of the high-voltage side DC voltage, the actual value of the high-voltage side current, the actual value of the low-voltage side DC voltage, and the expression of the droop control curve.

[0091] Specifically, each time the high-voltage side DC voltage given value of the high-voltage side bridge circuit 10 is obtained, the primary-to-secondary turns ratio of the corresponding transformer, the high-voltage side DC voltage given value, the high-voltage side current actual value, and the low-voltage side DC voltage actual value are substituted into the expression of the droop control curve, that is, in formula (11), so that the size of the corresponding resistance Rv can be calculated. Therefore, when the high-voltage side DC voltage given value of the high-voltage side bridge circuit 10 is obtained multiple times, multiple different resistances Rv can be calculated. It is understandable that when the working conditions of the resonant conversion circuit 100 (such as the parameter specifications of the connected battery pack, the parameter specifications of the inverter, the switching frequency fs, the primary-to-secondary turns ratio n of the transformer T, etc.) are different, the calculated resistance Rv is different.

[0092] Step S14 : determining the resistance corresponding to the minimum difference between the switching frequency and the resonant frequency of the resonant network 20 as the set virtual resistance.

[0093] Therefore, by substituting the determined virtual resistance into formula (11), the quantitative expression of the droop control curve can be obtained.

[0094] It is understandable that in the field of energy storage power supply applications, facing different energy transmission requirements, the low-voltage side bridge circuit 30 can be connected to battery packs of corresponding different voltage specifications. Correspondingly, the primary-to-secondary turns ratio of the transformer T, the set value of the high-voltage side DC voltage, the actual value of the high-voltage side current, and the actual value of the low-voltage side DC voltage all change accordingly. Therefore, the quantitative expression of the droop control curve is also different. However, in general, the quantitative expression of the droop control curve conforms to Equation (11).

[0095] Step S2: Control the operation of the resonant conversion circuit 100 according to the droop control curve.

[0096] Specifically, as shown in FIG12 , when the resonant converter circuit 100 is controlled to operate in the forward direction (i.e., energy flows from the high-voltage side bridge circuit 10 to the low-voltage side bridge circuit 30) according to the droop control curve, the high-voltage side DC voltage and the high-voltage side current exhibit a linear droop relationship, where the high-voltage side current is defined as a negative current. When the resonant converter circuit 100 is controlled to operate in the reverse direction (i.e., energy flows from the low-voltage side bridge circuit 30 to the high-voltage side bridge circuit 10) according to the droop control curve, the high-voltage side DC voltage and the high-voltage side current exhibit a linear droop relationship, where the high-voltage side current is defined as a positive current. Thus, it can be seen that the changing trend of the droop control curve is basically consistent with the changing trend of the natural droop characteristic curve.

[0097] Because the droop control curve indicates a linear droop relationship between the high-side DC voltage and the high-side current, when the operation of the resonant converter circuit 100 is controlled according to the droop control curve, when the high-side current is within a certain range of variation, the high-side DC voltage is correspondingly limited to the corresponding range of variation, such that the voltage variation range of the droop control curve is smaller than the voltage variation range of the natural droop characteristic curve. For example, in FIG12 , the natural droop characteristic curve is a curve with a voltage variation range of approximately 398V to 415V; the droop control curve is a sloping straight line with a voltage variation range limited to approximately 401.5V to 414V. Although the droop control curve in FIG12 is relatively close to the natural droop characteristic curve overall, with multiple intersections, the voltage variation range of the droop control curve is smaller than the voltage variation range of the natural droop characteristic curve.

[0098] In other words, the droop control curve determined in step S11 can closely match (or fit) the natural droop characteristic curve of the resonant converter circuit 100. Under this premise, the voltage variation range of the high-voltage side DC voltage is also limited. Therefore, the embodiment of the present application controls the resonant converter circuit 100 according to the droop control curve, which can effectively compensate for the natural droop characteristics of the resonant converter circuit 100.

[0099] It should be understood that, as shown in FIG7 , the voltage drop equivalent to the internal resistance Rin of the secondary side of the transformer T also has a natural droop characteristic. Since the droop control curve of the embodiment of the present application is obtained after determining the virtual resistance through steps S11 to S14, the determined virtual resistance actually already includes the resistance value of the internal resistance Rin. Therefore, the embodiment of the present application controls the resonant conversion circuit 100 according to the droop control curve. What is actually compensated is the natural droop characteristic of the entire resonant conversion circuit 100 after the voltage drop of the internal resistance Rin is superimposed on the high-voltage side DC voltage. That is, what is compensated is the influence of the high-voltage side current on the gain and internal resistance of the resonant conversion circuit 100.

[0100] Therefore, the resonant converter circuit 100 does not need to further adjust its frequency to compensate for the gain variation caused by the voltage drop across the internal resistor Rin combined with the overall natural droop of the high-side DC voltage. Consequently, the switching frequency variation range of the resonant converter circuit 100 can be reduced, making it easier for the switching frequency fs of the resonant converter circuit 100 to approach or reach the resonant frequency fr, thereby improving the conversion efficiency of the resonant converter circuit 100.

[0101] It is understandable that when the control method of the embodiment of the present application is applied to the scenario where multiple resonant conversion circuits 100 are connected in parallel as shown in FIG8 , the control method may further include:

[0102] The operation of each resonant converter circuit 100 connected in parallel is controlled according to the droop control curve.

[0103] That is to say, in Figure 8, the controller 200 controls each resonant conversion circuit 100 connected in parallel according to the same droop control curve, so that the current generated by each resonant conversion circuit 100 is the same, thereby ensuring that the multiple resonant conversion circuits 100 are controlled for equal current. Moreover, the parameter differences between different resonant conversion circuits 100 can be compensated, avoiding the problem of different resonant conversion circuits 100 operating under different parameters due to different operating conditions (such as some resonant conversion circuits 100 running at full load, and other resonant conversion circuits 100 running at no load), which in turn causes circulating currents between circuits and affects the service life of the circuits.

[0104] In summary, the control method of the embodiment of the present application can compensate for the gain change of the resonant conversion circuit 100 under different loads and the internal resistance voltage drop change under different loads (that is, the natural droop characteristics of the compensation gain and internal resistance). When the resonant conversion circuit 100 is operating unidirectionally or bidirectionally, the switching frequency variation range of the resonant conversion circuit 100 can be reduced, so that the switching frequency can be closer to or reach the resonant frequency, thereby helping to improve the efficiency of the resonant conversion circuit 100.

[0105] When the resonant conversion circuit 100 is applied in the field of multiple machines in parallel, the control method of the embodiment of the present application uses the droop control curve required for current sharing to compensate for the natural droop characteristics of the resonant conversion circuit 100, thereby achieving the current sharing characteristics of multiple machines in parallel.

[0106] Referring to Figure 13 , an embodiment of the present application further provides a power conversion device, which can be applied to server power supplies, vehicle power supplies, energy storage power supplies, and other fields.

[0107] As shown in FIG13 , a power conversion device 300 includes a resonant conversion circuit 100 and a controller 200. The resonant conversion circuit 100 and the controller 200 can be integrated or separate, depending on actual needs. The controller 200 can be used to execute the aforementioned control method for the resonant conversion circuit, thereby controlling the resonant conversion circuit 100. The resonant conversion circuit 100, the controller 200, and the control method can be found in the relevant descriptions of the aforementioned method embodiments and will not be repeated here.

[0108] Please refer to FIG. 14 . An embodiment of the present application further provides an energy storage device.

[0109] As shown in Figure 14, the energy storage device 500 includes a resonant conversion circuit 100, a battery pack 400, and a controller 200. The resonant conversion circuit 100, the battery pack 400, and the controller 200 can be provided separately or at least partially integrated together, depending on actual needs. The battery pack 400 can serve as a DC power supply or load for the resonant conversion circuit 100, and the controller 200 can be used to execute the control method of the resonant conversion circuit described above. Among them, the battery pack 400, the resonant conversion circuit 100, the controller 200, and the control method can be found in the relevant description of the aforementioned method embodiment, which will not be repeated here.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A control method for a resonant conversion circuit, wherein the resonant conversion circuit is used to be connected in parallel with other resonant conversion circuits, the resonant conversion circuit comprising a transformer, a high-voltage side bridge circuit, a resonant network, and a low-voltage side bridge circuit, wherein the high-voltage side bridge circuit is connected to the primary side of the transformer through the resonant network, and the low-voltage side bridge circuit is connected to the secondary side of the transformer; wherein: The control method includes: determining a droop control curve according to the operating parameters of the resonant conversion circuit, wherein the droop control curve is used to indicate a linear droop relationship between the high-side DC voltage and the high-side current of the high-side bridge circuit; The operation of the resonant converter circuit is controlled according to the droop control curve.

2. The control method according to claim 1, wherein: The expression of the droop control curve is: V HV =V LV ·nI HV ·Rv Among them, V HV is the high-side DC voltage, V LV is the low-voltage side DC voltage of the low-voltage side bridge circuit, n is the primary-to-secondary turns ratio of the transformer, I HV is the high voltage side DC current, and Rv is the set virtual resistance.

3. The control method according to claim 2, wherein: The operating parameters of the resonant conversion circuit include the primary-to-secondary turns ratio of the transformer, the high-voltage side DC voltage, the high-voltage side current, and the low-voltage side DC voltage of the low-voltage side bridge circuit; The determining, according to the operating parameters of the resonant conversion circuit, a linear droop relationship between the high-side DC voltage and the high-side current of the high-side bridge circuit includes: After obtaining a high-side DC voltage given value of the high-side bridge circuit each time, controlling the resonant conversion circuit according to the high-side DC voltage given value; Obtaining an actual value of the high-side current of the high-side bridge circuit, an actual value of the low-side DC voltage of the low-voltage side bridge circuit, and a switching frequency of the resonant conversion circuit; Calculating resistance according to the primary-to-secondary turns ratio of the transformer, the given value of the high-voltage side DC voltage, the actual value of the high-voltage side current, the actual value of the low-voltage side DC voltage, and the expression of the droop control curve; The resistance corresponding to when the difference between the switching frequency and the resonant frequency of the resonant network is minimum is determined as the set virtual resistance.

4. The control method according to claim 3, wherein: The low-voltage side bridge circuit is also used to access the battery pack; The step of determining the linear droop relationship between the high-side DC voltage and the high-side current of the high-side bridge circuit according to the operating parameters of the resonant conversion circuit further includes: Obtaining the high-voltage side DC voltage given value according to the battery voltage of the battery pack; The high-voltage side DC voltage given value obtained each time is different and is not greater than the product of the battery voltage of the battery pack and the primary-to-secondary turns ratio of the transformer.

5. The control method according to any one of claims 1 to 4, wherein: The droop control curve fits the natural droop characteristic curve of the resonant conversion circuit, and the voltage variation range of the droop control curve is smaller than the voltage variation range of the natural droop characteristic curve, wherein the natural droop characteristic curve is used to indicate the droop characteristics between the high-voltage side DC voltage and the high-voltage side current of the resonant conversion circuit itself.

6. The control method according to any one of claims 1 to 5, wherein: When the energy of the resonant conversion circuit flows from the high-voltage side bridge circuit to the low-voltage side bridge circuit, the droop control curve indicates a linear droop relationship between the high-voltage side DC voltage and the high-voltage side current, wherein the high-voltage side current is a negative current; When the energy of the resonant conversion circuit flows from the low-voltage side bridge circuit to the high-voltage side bridge circuit, the droop control curve indicates a linear droop relationship between the high-voltage side DC voltage and the high-voltage side current, wherein the high-voltage side current is a positive current.

7. The control method according to any one of claims 1 to 6, wherein: The control method further includes: The operation of each of the parallel-connected resonant conversion circuits is controlled according to the droop control curve.

8. An energy storage device, wherein: The energy storage device includes a resonant conversion circuit, a battery pack and a controller. The resonant conversion circuit includes a transformer, a high-voltage side bridge circuit, a resonant network and a low-voltage side bridge circuit. The high-voltage side bridge circuit is connected to the primary side of the transformer through the resonant network, one end of the low-voltage side bridge circuit is connected to the secondary side of the transformer, and the other end of the low-voltage side bridge circuit is connected to the battery pack. The resonant conversion circuit is used to be connected in parallel with other resonant conversion circuits; the controller is connected to the resonant conversion circuit, and the controller is used to: The operation of the resonant conversion circuit is controlled according to a droop control curve, wherein the droop control curve is used to indicate a linear droop relationship between a high-side DC voltage and a high-side current of the high-side bridge circuit.

9. The energy storage device according to claim 8, wherein: The high-voltage side bridge circuit includes a first switching tube, a second switching tube, a third switching tube and a fourth switching tube, the first switching tube and the second switching tube are connected in series to form a first bridge arm, the third switching tube and the fourth switching tube are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel; The low-voltage side bridge circuit includes a fifth switching tube, a sixth switching tube, a seventh switching tube, and an eighth switching tube, wherein the fifth switching tube and the sixth switching tube are connected in series to form a third bridge arm, the seventh switching tube and the eighth switching tube are connected in series to form a fourth bridge arm, and the third bridge arm and the fourth bridge arm are connected in parallel; The resonant network includes a resonant capacitor, a resonant inductor and an excitation inductor. The resonant capacitor and the resonant inductor are connected in series between the midpoint of the first bridge arm and one terminal of the primary side of the transformer. The midpoint of the second bridge arm is connected to the other terminal of the primary side of the transformer. The excitation inductor is connected in parallel to the primary side of the transformer. The midpoint of the third bridge arm and the midpoint of the fourth bridge arm are connected to the secondary side of the transformer.

10. The energy storage device according to claim 9, wherein: During the operation of the resonant conversion circuit controlled according to the droop control curve, the first switching tube and the second switching tube are alternately turned on, the third switching tube and the fourth switching tube are alternately turned on, the fifth switching tube and the sixth switching tube are alternately turned on, and the seventh switching tube and the eighth switching tube are alternately turned on, and the switching frequency of the resonant conversion circuit is close to or equal to the resonant frequency of the resonant network.

Images