Control method for wide voltage range cllc resonant converter for energy storage systems

Abstract

The application is a control method of a wide voltage range CLLL resonant converter for an energy storage system, which comprises the control of the energy storage system in three different stages of constant current charging, constant voltage charging and constant current discharging s The bridge phase shift angle is used to realize wide voltage gain control, and the switching frequency f s is adjusted to be equal to the resonant frequency f r to realize constant voltage gain control, and the switching frequency f s is adjusted to realize wide voltage gain control. In the control of the three different stages, all the switching devices of the CLLL resonant converter can realize soft switching operation. Compared with the frequency control, the switching frequency of the converter in the control method does not exceed the resonant frequency, the switching frequency is lower, the variation range of the switching frequency is narrower, which is beneficial to the design of the transformer and the driving circuit, and the converter has a wider voltage adjustment range in the step-down mode.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically a control method for a wide voltage range CLLLC resonant converter used in energy storage systems. Background Technology

[0002] In energy storage systems, bidirectional DC-DC converters serve as the interface connecting the DC bus and the energy storage battery, playing a crucial role in bidirectional energy control, electrical isolation, and voltage level conversion. Among numerous bidirectional DC-DC converter topologies, the CLLLC resonant converter has attracted widespread attention due to its advantages such as symmetrical structure, good soft-switching characteristics, and low turn-off losses. For CLLLC resonant converters, a full-bridge two-level topology is typically used on both the DC bus and energy storage battery sides. However, as the DC bus voltage level increases, the voltage stress on the switching devices in the two-level topology becomes significant, leading to the development of the DNPC-CLLLC resonant converter. In this converter, the voltage stress on the switching devices is reduced to half of the DC bus voltage. The DNPC-CLLLC resonant converter refers to replacing the full-bridge two-level topology on the DC bus side with a half-bridge diode midpoint clamped (DNPC stands for diode midpoint clamped) three-level topology.

[0003] CLLLC resonant converters are generally controlled by frequency conversion control, which regulates the output voltage and transmitted power by changing the switching frequency of the inverter bridge. However, since the voltage variation range on the battery side in energy storage systems is typically wide, frequency conversion control requires the switching frequency to vary over a wide range to achieve wide voltage regulation, which increases the design complexity of the transformer and drive. Furthermore, while CLLLC resonant converters can achieve buck operation at switching frequencies higher than the resonant frequency, the inability of the rectifier diodes to achieve zero-current turn-off leads to reduced converter efficiency and a narrower voltage adjustment range. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides a control method for a wide-voltage-range CLLLC resonant converter for energy storage systems. This invention combines the constant-current and constant-voltage charging characteristics of energy storage batteries and designs the operating modes and control methods of the CLLLC resonant converter in the constant-current charging stage, the constant-voltage charging stage, and the constant-current discharging stage. It can meet the requirements of wide-range battery voltage variation within a narrow switching frequency range, and achieves soft switching of all switching devices in all three stages, enabling the CLLLC resonant converter to operate with high efficiency.

[0005] To achieve the above-mentioned objectives, the technical solution adopted is as follows:

[0006] A control method for a wide-voltage-range CLLLC resonant converter for an energy storage system is disclosed. The CLLLC resonant converter includes a DC bus-side topology, an energy storage battery-side topology, and a symmetrical CLLLC resonant network. For example, the DC bus-side topology can be a DC bus-side half-bridge DNPC three-level topology or a DC bus-side full-bridge two-level topology, and the energy storage battery-side topology can be an energy storage battery-side full-bridge two-level topology or an energy storage battery-side DNPC three-level topology. The DC bus voltage remains constant, and the energy storage battery must be charged according to a constant current and constant voltage two-stage charging method.

[0007] During the constant current charging phase, both the switching devices on the DC bus side and the switching devices on the energy storage battery side are driven by drive signals, and the switching frequency f of the CLLLC resonant converter is required to be constant. s Less than the resonant frequency f r The CLLLC resonant converter operates in buck mode. Since all switching devices can provide corresponding drive signals, the inter-bridge phase shift angle between the DC bus-side topology and the energy storage battery-side topology is adjusted. It can be actively controlled to achieve wide voltage control;

[0008] Obtain the equivalent circuit of the CLLLC resonant converter and calculate the expression for the resonant current on both sides of the symmetrical CLLLC resonant network under constant current charging mode.

[0009] Substitute the switching time t=0 into the expression for the resonant current on the primary side, and simultaneously... Substituting the expression for the resonant current on the secondary side, we obtain the switching frequency f. s Phase shift angle between bridges The relationship between them describes the soft-switching region. At the boundary of the soft-switching region, the switching frequency f is adjusted. s and inter-bridge phase shift angle To achieve soft switching of all switching devices, where ω s The switching angular frequency;

[0010] During the constant voltage charging phase, only the switching devices on the DC bus side topology are driven by drive signals, while the switching devices on the energy storage battery side topology are not driven by drive signals. Simultaneously, the switching frequency f is required to... s Equal to the resonant frequency f r The CLLLC resonant converter operates in voltage matching mode, which means that constant voltage control is achieved and all switching devices are soft-switched.

[0011] During the constant current discharge phase, only the switching devices on the battery-side topology are driven by a drive signal, while the switching devices on the DC bus-side topology are not driven by a drive signal. Simultaneously, the switching frequency f of the CLLLC resonant converter is required to... s Less than the resonant frequency fr The CLLLC resonant converter operates in boost mode, adjusting the switching frequency f. s It enables wide voltage control and soft switching of all switching devices.

[0012] In the DC bus topology, if a half-bridge DNPC three-level topology is adopted on the DC bus side, then the switching devices S1 and S2 are connected in series to form the upper bridge arm of the half-bridge DNPC three-level topology, and the switching devices S3 and S4 are connected in series to form the lower bridge arm of the half-bridge DNPC three-level topology; if a full-bridge two-level topology is adopted on the DC bus side, then the switching devices S1 and S2 are connected in series to form a pair of bridge arms of the full-bridge two-level topology, with S1 being the upper bridge arm and S2 being the lower bridge arm, and the switching devices S3 and S4 are connected in series to form another pair of bridge arms of the full-bridge two-level topology, with S3 being the upper bridge arm and S4 being the lower bridge arm.

[0013] In the energy storage battery side topology, if the energy storage battery side adopts a full-bridge two-level topology, then the switching devices S5 and S6 are connected in series to form a pair of bridge arms of the full-bridge two-level topology, with S5 being the upper bridge arm and S6 being the lower bridge arm. The switching devices S7 and S8 are connected in series to form another pair of bridge arms of the full-bridge two-level topology, with S7 being the upper bridge arm and S8 being the lower bridge arm. If the energy storage battery side adopts a half-bridge DNPC three-level topology, then the switching devices S5 and S6 are connected in series to form the upper bridge arm of the half-bridge DNPC three-level topology, and the switching devices S7 and S8 are connected in series to form the lower bridge arm of the half-bridge DNPC three-level topology.

[0014] Furthermore, when switching devices S1-S8 are driven by drive signals, the duty cycle of the given drive signals is 50%. In the DC bus side topology, if it is a DC bus side half-bridge DNPC three-level topology, then the drive signals of S1 and S2 are the same and complementary to S3 and S4; if it is a DC bus side full-bridge two-level topology, then the drive signals of S1 and S4 are the same and complementary to S2 and S3. In the energy storage battery side topology, if it is an energy storage battery side full-bridge two-level topology, then the drive signals of S5 and S8 are the same and complementary to S6 and S7; if it is an energy storage battery side half-bridge DNPC three-level topology, then the drive signals of S5 and S6 are the same and complementary to S7 and S8.

[0015] The primary resonant capacitor C in the symmetrical CLLLC resonant network r1 With secondary resonant capacitor C r2 The relationship is C r1 =C r2 / N 2 Primary resonant inductor L r1 With secondary resonant inductor L r2 The relationship is L r1 =N 2 L r2 N is the transformer turns ratio, and the resonant frequency f r The expression is:

[0016]

[0017] During the constant current charging phase, after characterizing the soft-switching region, the switching frequency f is used... s Phase shift angle between bridges The relationship between the two points is used to find the boundary of the soft-switching region, obtaining the complete boundary curve. The two endpoints of the soft-switching region boundary are points C and F. Simultaneously, the inter-bridge phase shift angle is set to -π / 2 to obtain the switching frequency f at point C. s First, determine the coordinates of point C. Then, find point E with the same current as point C. Determine the corresponding point E from point C. Next, determine the selected partial soft-switching region boundary curve EF on the complete soft-switching region boundary curve CEF. On the selected partial soft-switching region boundary curve EF for different voltage transfer ratios d, select the corresponding switching frequency f according to the required charging current. s Phase angle between bridges This enables soft switching of all switching devices during the constant current charging stage.

[0018] The beneficial effects of the technical solution provided by this invention are as follows:

[0019] The control method proposed in this invention can achieve wide-range adjustment of battery voltage during the charging and discharging process of energy storage battery. At the same time, all switching devices in the converter achieve soft switching, reducing switching losses and enabling the converter to operate with high efficiency.

[0020] The control method of this invention includes the control of the energy storage system in three different stages: constant current charging, constant voltage charging, and constant current discharging. During the constant current charging stage, the switching frequency f is adjusted. s Phase angle between bridges To achieve wide voltage gain control, the switching frequency f is adjusted during the constant voltage charging phase. s Equal to the resonant frequency f r To achieve constant voltage gain control, the switching frequency f is adjusted during the constant current discharge phase. s Wide voltage gain control is achieved. In the three different control stages, all switching devices of the CLLLC resonant converter can achieve soft-switching operation. Compared with frequency conversion control, the switching frequency of the converter in the control method proposed in this invention does not exceed the resonant frequency, the switching frequency is lower, and the range of switching frequency variation is narrower, which is beneficial to the design of transformer and drive circuit. Furthermore, the converter has a wider voltage adjustment range in buck mode. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the circuit structure of the DNPC-CLLLC resonant converter in this invention.

[0022] Figure 2This is a charging curve of the energy storage battery in this invention under a constant current and constant voltage two-stage charging method.

[0023] Figure 3 This is a diagram showing the drive signal waveform and working waveform of the DNPC-CLLLC resonant converter in the constant current charging stage under buck mode operation.

[0024] Figure 4 This is the equivalent circuit of the DNPC-CLLLC resonant converter in the constant current charging stage under buck mode operation in this invention.

[0025] Figure 5 This is the soft-switching region boundary curve of the DNPC-CLLLC resonant converter in this invention when the voltage transfer ratio d = 0.8.

[0026] Figure 6 The switching frequency f of the DNPC-CLLLC resonant converter in this invention is when different charging currents are used for constant current charging. s Phase angle between bridges The curve showing the change.

[0027] Figure 7 This is a diagram showing the drive signal waveform and operating waveform of the DNPC-CLLLC resonant converter in the constant voltage charging stage under voltage matching mode.

[0028] Figure 8 This is the fundamental equivalent circuit of the DNPC-CLLLC resonant converter in the constant voltage charging stage under voltage matching mode operation in this invention.

[0029] Figure 9 This is a diagram showing the drive signal waveform and operating waveform of the DNPC-CLLLC resonant converter in the constant current discharge stage under boost mode operation.

[0030] Figure 10 This is the fundamental equivalent circuit of the DNPC-CLLLC resonant converter in the constant current discharge stage under boost mode operation in this invention. Detailed Implementation

[0031] The technical solution of the present invention will now be described in detail and completely with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In an embodiment of the present invention, a control method for a wide voltage range CLLLC resonant converter for an energy storage system is provided. The CLLLC resonant converter is a DNPC-CLLLC resonant converter, and the structure of the DNPC-CLLLC resonant converter is as follows. Figure 1 As shown, it includes a DC bus-side half-bridge DNPC three-level topology, a battery-side full-bridge two-level topology, and a symmetrical CLLLC resonant network.

[0033] Figure 1 In the above, the DC bus-side half-bridge DNPC three-level topology includes switching devices S1-S4, clamping diodes D1-D2, and bus capacitor C. i1 -C i2 The full-bridge two-level topology on the energy storage battery side includes switching devices S5-S8 and filter capacitor C. o The symmetrical CLLLC resonant network includes a primary-side resonant capacitor C. r1 Primary resonant inductor L r1 Secondary resonant inductor L r2 Secondary resonant capacitor C r2 And high-frequency transformers, which have built-in magnetizing inductance L. m Among them, the primary side resonant capacitor C r1 With secondary resonant capacitor C r2 The relationship is C r1 =C r2 / N 2 Primary resonant inductor L r1 With secondary resonant inductor L r2 The relationship is L r1 =N 2 L r2 N is the transformer turns ratio.

[0034] The resonant frequency f of the DNPC-CLLLC resonant converter r The expression is:

[0035]

[0036] The energy storage battery adopts a two-stage constant current and constant voltage charging method, and its charging curve is as follows: Figure 2 As shown, during the constant current charging stage, the charging current remains constant, and the battery voltage continuously rises. After reaching a certain value, it enters the constant voltage charging stage, where the battery voltage remains constant and the charging current gradually decreases. The energy storage battery discharge process uses a constant current discharge method. This stage is the opposite of the constant current charging stage; the discharge current remains constant, and the battery voltage continuously decreases.

[0037] In the three different stages of energy storage battery charging—constant current charging, constant voltage charging, and constant current discharging—the DC bus voltage remains constant, while the battery voltage varies over a wide range. Based on the relationship between the DC bus voltage and the battery voltage, the DNPC-CLLLC resonant converter is designed as a forward buck mode in the constant current charging stage, a forward voltage matching mode in the constant voltage charging stage, and a reverse boost mode in the constant current discharging stage.

[0038] The control method for wide-voltage-range DNPC-CLLLC resonant converters used in energy storage systems includes control of three different stages in the energy storage system: constant current charging, constant voltage charging, and constant current discharging.

[0039] Constant current charging stage

[0040] During the constant current charging phase, both the switching devices on the DC bus side topology and the switching devices on the energy storage battery side topology are driven by drive signals, and the switching frequency f of the DNPC-CLLLC resonant converter is required to be... s Less than the resonant frequency f r The DNPC-CLLLC resonant converter operates in buck mode. The inter-bridge phase shift angle between the DC bus-side topology and the energy storage battery-side topology is... Able to actively control

[0041] Figure 3 This diagram shows the drive signal waveforms and operating waveforms of the DNPC-CLLLC resonant converter in buck mode during the constant current charging phase. The duty cycle of the drive signals for switching devices S1-S8 is 50%. The drive signals for S1 and S2 are identical and complementary to those for S3 and S4. The drive signals for S5 and S8 are identical and complementary to those for S6 and S7. The angle by which the drive signal for S1 leads the drive signal for S5 is the inter-bridge phase shift angle. Phase shift angle between bridges during constant current charging stage Less than zero, switching frequency f s Less than the resonant frequency f r Phase shift angle between bridges This enables the converter to have a wide voltage range regulation capability, while simultaneously adjusting the switching frequency f. s Ensure that the switching devices achieve soft switching, thereby improving converter efficiency.

[0042] During the constant current charging phase, the equivalent circuit of the DNPC-CLLLC resonant converter is as follows: Figure 4 As shown, C' r2 L' r2 These are the secondary resonant capacitor and resonant inductor, respectively, after being referred to the primary side, and their values ​​satisfy C'. r2 =C r2 / N 2 L' r2 =N 2 Lr2 i1 and u1 are the primary-side resonant current and the port voltage of the DC bus-side topology equivalent to the symmetrical CLLLC resonant network, respectively; i'2 and u'2 are the secondary-side resonant current after being referred to the primary side and the port voltage of the energy storage battery-side topology equivalent to the symmetrical CLLLC resonant network, respectively, with values ​​satisfying i'2=i2 / N and u'2=Nu2, where i2 and u2 are the secondary-side resonant current before being referred to the primary side and the port voltage of the energy storage battery-side topology equivalent to the symmetrical CLLLC resonant network, respectively. m This is the magnetizing inductor current.

[0043] Based on the two-port network theory, the expressions for the resonant currents i1 and i'2 on both sides of the symmetrical CLLLC resonant network under constant current charging mode are derived using the frequency analysis method, as shown in Equations (1) and (2):

[0044]

[0045]

[0046] In the formula, U dc1 U is the DC bus voltage. dc2 k is the energy storage battery voltage; k is the magnetizing inductance L m With resonant inductor L r1 The ratio, k = L m / L r1 ;ω s ω is the switching angular frequency. s =(2πf s );ω n For the normalized angular frequency, ω n =(2πf s ) / (2πf r );Z o Z is the characteristic impedance. o =2πf r L r1 n represents the switching frequency, and t represents time.

[0047] Substituting t=0 into formula (1), Substituting into formula (2), we obtain formula (3). The condition in formula (3) is met, which enables soft switching of all switching devices, thereby reducing the switching losses of the converter.

[0048]

[0049] The DC bus voltage U is represented by the voltage transfer ratio d. dc1 With energy storage battery voltage U dc2 The relationship is that the voltage transfer ratio d = 2NU dc2 / U dc1During the constant current charging stage, d<1 indicates that the DNPC-CLLLC resonant converter is operating in buck mode, while d=1 indicates that the DNPC-CLLLC resonant converter has entered voltage matching mode. According to formula (3), the switching frequency f s Phase angle between bridges Characterize the fixed energy storage battery voltage U dc2 The soft-switching region under a fixed voltage transfer ratio d is the soft-switching region under a fixed voltage transfer ratio d.

[0050] When the selected switching frequency f s Phase angle between bridges Within the soft-switching region and on the boundary curve of the soft-switching region, soft switching of all switching devices can be achieved; furthermore, the switching frequency f is selected on the boundary curve of the soft-switching region. s Phase angle between bridges Compared to selecting within the soft-switching region, a smaller turn-off current can be obtained, thereby reducing the turn-off losses of the switching devices.

[0051] Figure 5 The curve CEF represents the boundary curve of the soft-switching region for the DNPC-CLLLC resonant converter at a voltage transfer ratio d = 0.8. The curve CEF is the complete boundary curve of the soft-switching region. Figure 5 The dashed line in the middle represents the charging current curve corresponding to curve CEF, and the charging current I... o Phase angle shifts between bridges The charging current first increases monotonically and then decreases monotonically; the charging current at points C and E is the same. To ensure the charging current I... o Due to the monotonicity of the curve EF, the switching frequency f is selected based on the magnitude of the charging current. s Phase angle between bridges Point E is designed to be the location of the maximum charging current, while the charging current at point F is 0.

[0052] During constant current charging, the energy storage battery voltage U dc2 The voltage transfer ratio d changes, causing changes in the soft-switching region characterized by formula (3) and the boundary curve CEF of the complete soft-switching region, thus also causing changes in the selected soft-switching region boundary curve EF; however, the switching frequency f at point C... s Phase angle between bridges Since the voltage transfer ratio d is fixed and does not change with the voltage transfer ratio d, the DNPC-CLLLC resonant converter is designed based on point C. Since the charging current is the same at point C and point E, when the voltage transfer ratio d changes, the corresponding point E is determined by point C, and then the selected part of the soft-switching region boundary curve EF is determined on the complete soft-switching region boundary curve CEF.

[0053] Specifically, the switching frequency f at point Cs Phase angle between bridges The relationship is shown in formula (4):

[0054]

[0055] Furthermore, on the boundary curves EF of the selected soft-switching regions at different voltage transfer ratios d, the corresponding switching frequency f is selected according to the required charging current. s Phase angle between bridges This enables soft switching of all switching devices during the constant current charging stage.

[0056] Figure 6 The switching frequency f of the DNPC-CLLLC resonant converter under constant current charging with different charging currents s Phase angle between bridges The curve of change, I in the figure omax This represents the maximum charging current of the energy storage battery; during charging, the energy storage battery voltage U... dc2 As the voltage of the energy storage battery increases, the switching frequency f also gradually increases, reaching 1 at the end of the constant current charging process. s Gradually moving towards the resonant frequency f r Closer, phase shift angle between bridges Gradually approaching zero, the control quantity avoids abrupt changes from the constant current charging stage to the constant voltage charging stage.

[0057] Constant voltage charging stage

[0058] During the constant voltage charging phase, only the switching devices on the DC bus side topology are driven by drive signals, while the switching devices on the energy storage battery side topology are not driven by drive signals. Simultaneously, the switching frequency f is required to... s Equal to the resonant frequency f r The DNPC-CLLLC resonant converter operates in voltage matching mode.

[0059] Figure 7 This is a diagram showing the drive signal waveforms and operating waveforms of a DNPC-CLLLC resonant converter in voltage matching mode during the constant voltage charging phase. The duty cycle of the drive signals S1-S4 is 50%. The drive signals S1 and S2 are identical and complementary to those of S3 and S4. The switching frequency f... s Equal to the resonant frequency f r The voltages at both ports of the symmetrical CLLLC resonant network are matched and are independent of the load size. Therefore, during the constant voltage charging phase, the battery voltage remains constant as the charging current gradually decreases.

[0060] Figure 8 This is the fundamental equivalent circuit of the DNPC-CLLLC resonant converter during the constant voltage charging stage. R in the figure...eq1 This is the equivalent load resistance referred from the secondary side to the primary side.

[0061] At this time, during the operation of the converter, the switching devices S1-S4 of the DC bus side half-bridge DNPC three-level topology achieve zero-voltage turn-on; the resonant current on the energy storage battery side is in phase with the voltage, and its rectifier achieves zero-current turn-off, that is, all switching devices achieve soft switching.

[0062] Constant current discharge stage

[0063] During the constant current discharge phase, only the switching devices on the battery-side topology are driven by a drive signal, while the switching devices on the DC bus-side topology are not driven by a drive signal. Simultaneously, the switching frequency f of the DNPC-CLLLC resonant converter is required to... s Less than the resonant frequency f r The DNPC-CLLLC resonant converter operates in boost mode.

[0064] Figure 9 This invention presents the drive signal waveforms and operating waveforms of the DNPC-CLLLC resonant converter in boost mode during the constant current discharge phase. The duty cycle of the drive signals S5-S8 is 50%. The drive signals S5 and S8 are identical and complementary to those of S6 and S7. Energy is transferred from the energy storage battery side to the DC bus side. At this time, the switching frequency f is adjusted... s To achieve voltage regulation.

[0065] Figure 10 This is the fundamental equivalent circuit of the DNPC-CLLLC resonant converter during the constant current discharge stage. R in the figure... eq2 This is the equivalent load resistance on the primary side.

[0066] Based on the equivalent circuit, the AC voltage gain M of the converter in constant current discharge mode is derived. AC expression:

[0067]

[0068] In the formula, Q is the quality factor of the DNPC-CLLLC resonant converter, Q = 2πf r L r1 / R eq2 .

[0069] According to formula (5), in order to achieve boost operation, the switching frequency f is required to be... s Below the resonant frequency f r At this time, the switching devices S5-S8 of the full-bridge two-level topology on the energy storage battery side achieve zero-voltage turn-on; the resonant current on the DC bus side is opposite to the voltage phase, and its rectifier tube achieves zero-current turn-off, that is, all switching devices achieve soft switching.

[0070] The control method for a wide-voltage-range DNPC-CLLLC resonant converter in energy storage systems provided in this embodiment enables soft-switching operation of all switching devices in the three stages of constant current charging, constant voltage charging, and constant current discharging. Furthermore, compared to traditional frequency conversion control, the switching frequency of the converter in the proposed method does not exceed the resonant frequency; the switching frequency is lower, and the range of switching frequency variation is narrower, which is more beneficial for the design of the transformer and drive circuit.

[0071] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

[0072] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A control method for a wide voltage range CLLLC resonant converter for an energy storage system, characterized in that, The CLLLC resonant converter includes a DC bus-side topology, an energy storage battery-side topology, and a symmetrical CLLLC resonant network. The DC bus voltage remains constant, and the energy storage battery must be charged in a constant current and constant voltage two-stage charging mode. The control method includes control of three different stages in the energy storage system: constant current charging, constant voltage charging, and constant current discharging. During the constant current charging phase, both the switching devices on the DC bus side and the battery side are driven by drive signals, and the switching frequency of the CLLLC resonant converter is required to be adjusted. f s Less than the resonant frequency f r The CLLLC resonant converter operates in buck mode. Since all switching devices can provide corresponding drive signals, the inter-bridge phase shift angle between the DC bus-side topology and the energy storage battery-side topology is adjusted. It can be actively controlled to achieve wide voltage control; Obtain the equivalent circuit of the CLLLC resonant converter and calculate the expression for the resonant current on both sides of the symmetrical CLLLC resonant network under constant current charging mode. Switching time t Substituting 0 into the expression for the resonant current on the primary side, and simultaneously considering the switching timing... Substituting the expression for the resonant current on the secondary side, we obtain the switching frequency. f s Phase shift angle between bridges The relationship between these factors characterizes the soft-switching region. At the boundary of this region, the switching frequency is adjusted. f s and inter-bridge phase shift angle To achieve soft switching of all switching devices, among which The switching angular frequency; During the constant voltage charging phase, only the switching devices on the DC bus side topology are driven by drive signals, while the switching devices on the energy storage battery side topology are not driven by drive signals. Simultaneously, the switching frequency is required to... f s equal to the resonant frequency f r The CLLLC resonant converter operates in voltage matching mode, which means that constant voltage control is achieved and all switching devices are soft-switched. During the constant current discharge phase, only the switching devices on the battery-side topology are driven by a drive signal, while the switching devices on the DC bus-side topology are not driven by a drive signal. Simultaneously, the switching frequency of the CLLLC resonant converter is required to... f s Less than the resonant frequency f r The CLLLC resonant converter operates in boost mode, adjusting the switching frequency. f s It enables wide voltage control and soft switching of all switching devices.

2. The control method for a wide voltage range CLLLC resonant converter for an energy storage system according to claim 1, characterized in that, The DC bus-side topology is either a DC bus-side half-bridge DNPC three-level topology or a DC bus-side full-bridge two-level topology, and the energy storage battery-side topology is either an energy storage battery-side full-bridge two-level topology or an energy storage battery-side DNPC three-level topology.

3. The control method for a wide voltage range CLLLC resonant converter for an energy storage system according to claim 1, characterized in that, The CLLLC resonant converter is a DNPC-CLLLC resonant converter, comprising a DC bus-side half-bridge DNPC three-level topology, a battery-side full-bridge two-level topology, and a symmetrical CLLLC resonant network; the DC bus-side half-bridge DNPC three-level topology includes switching devices. S 1- S 4. Clamping diode D 1- D 2. Bus capacitor C i1 - C i2 Switching devices S 1. S Two components are connected in series to form the upper bridge arm of a half-bridge DNPC three-level topology, using switching devices. S 3. S Four series-connected components form the lower arm of a half-bridge DNPC three-level topology. The connection point between the upper and lower arms is connected to one end of the primary side port of a symmetrical CLLLC resonant network; clamping diodes are also included. D 1's positive terminal and clamping diode D The negative terminal of 2 is connected, and the connection point of both is connected to the other end of the primary side port of the symmetrical CLLLC resonant network, clamping diode. D The negative terminal of 1 and the switching device S 1 and switching devices S Connection point 2, clamping diode D 2's positive terminal and switching device S 3 and switching devices S 4. Connection point connection; bus capacitor C i1 , C i2 The bus capacitor is connected in series across both ends of the DC bus. C i1 and C i2 Connection point and clamping diode D 1 and D 2. Connection point connection; The energy storage battery-side full-bridge two-level topology includes switching devices. S 5- S 8 and filter capacitor C o Switching devices S 5 and switching devices S A pair of bridge arms, connected in series, form a full-bridge two-level topology; switching devices. S 7 and switching devices S Eight series-connected components form another pair of bridge arms in a two-level full-bridge topology; switching devices S 5 and switching devices S 6 Connection points and switching devices S 7 and switching devices S The connection points of 8 are respectively connected to the two ends of the secondary side port of the symmetrical CLLLC resonant network; filter capacitor C o Connected to both ends of the energy storage battery; the symmetrical CLLLC resonant network includes a primary resonant capacitor. C r1 Primary resonant inductor L r1 Secondary resonant inductor L r2 Secondary resonant capacitor C r2 And high-frequency transformers; primary-side resonant capacitors C r1 One end serves as one end of the primary side port of the symmetrical CLLLC resonant network, and the other end is connected to the primary side resonant inductor. L r1 One end is connected to the primary resonant inductor. L r1 The other end is connected to one end of the primary side of the high-frequency transformer. The other end of the primary side of the high-frequency transformer serves as the other end of the primary side port of the symmetrical CLLLC resonant network. The high-frequency transformer has its own magnetizing inductance. L m Magnetizing inductor L m The capacitor is connected in parallel across the primary side; the secondary side resonant capacitor... C r2 One end serves as one end of the secondary side port of the symmetrical CLLLC resonant network, and the other end is connected to the secondary resonant inductor. L r2 One end is connected to the secondary resonant inductor. L r2 The other end is connected to one end of the secondary side of the high-frequency transformer, and the other end of the secondary side of the high-frequency transformer serves as the other end of the secondary side port of the symmetrical CLLLC resonant network.

4. The control method for a wide-range CLLLC resonant converter for an energy storage system according to claim 3, characterized in that, The resonant current on both sides of the symmetrical CLLLC resonant network in the constant current charging mode i 1 and i The expressions for '2' are formula (1) and formula (2): （1） （2） In the formula, U dc1 This is the DC bus voltage. U dc2 This refers to the voltage of the energy storage battery. k Magnetizing inductor L m With resonant inductor L r1 The ratio, k = L m / L r1 ; The switching angular frequency, =(2π f s ); For normalized angular frequency, =(2π f s ) / (2π f r ); Z o Characteristic impedance; n The switching frequency. t For time; i 1 represents the primary resonant current. i '2' represents the secondary resonant current; N For transformer turns ratio; The switching frequency f s Phase shift angle between bridges The relationship between them is given by equation (3). The condition in equation (3) is met to achieve soft switching of all switching devices. （3）。 5. The control method for a wide voltage range CLLLC resonant converter for an energy storage system according to claim 1, characterized in that, In the DC bus-side topology, if a half-bridge DNPC three-level topology is used on the DC bus side, then the switching devices... S 1. S Two components are connected in series to form the upper bridge arm of a half-bridge DNPC three-level topology, using switching devices. S 3. S Four components are connected in series to form the lower arm of a half-bridge DNPC three-level topology; if a full-bridge two-level topology is used on the DC bus side, then the switching devices... S 1. S Two bridge arms connected in series form a two-level full-bridge topology. S 1 is the upper bridge arm, S 2 is the lower bridge arm, a switching device. S 3. S The other pair of bridge arms, connected in series, form another pair of bridge arms in a two-level full-bridge topology. S 3 is the upper bridge arm, S 4 is the lower bridge arm; In the energy storage battery side topology, if a full-bridge two-level topology is adopted on the energy storage battery side, then the switching devices... S 5. S A pair of bridge arms, connected in series, form a two-level full-bridge topology. S 5 is the upper bridge arm, S 6 is the lower bridge arm, a switching device. S 7. S The other pair of bridge arms, consisting of 8 series connections, form a two-level full-bridge topology. S 7 is the upper bridge arm, S 8 represents the lower bridge arm; if a half-bridge DNPC three-level topology is used on the energy storage battery side, then the switching devices... S 5. S Six components are connected in series to form the upper bridge arm of a half-bridge DNPC three-level topology, using switching devices. S 7. S Eight components are connected in series to form the lower bridge arm of a half-bridge DNPC three-level topology.

6. The control method for a wide voltage range CLLLC resonant converter for an energy storage system according to claim 5, characterized in that, Switching devices S 1- S 8. When driven by a drive signal, the duty cycle of the given drive signal is 50%; in the DC bus side topology, if it is a DC bus side half-bridge DNPC three-level topology, then S 1. S 2. The drive signals are the same and S 3. S 4. Complementary; if it is a two-level full-bridge topology on the DC bus side, then S 1. S 4. The drive signals are the same and S 2. S 3. Complementary; In the energy storage battery side topology, if it is a full-bridge two-level topology on the energy storage battery side, then S 5. S 8 drive signals are the same and S 6. S 7. Complementary; if it is a battery-side half-bridge DNPC three-level topology, S 5. S 6. The drive signals are the same and S 7. S 8. Complementary.

7. A control method for a wide-range CLLLC resonant converter for an energy storage system according to claim 1, characterized in that, The primary resonant capacitor in the symmetrical CLLLC resonant network C r1 With secondary resonant capacitor C r2 The relationship is C r1 = C r2 / N 2 Primary resonant inductor L r1 With secondary resonant inductor L r2 The relationship is L r1 = N 2 L r2 , N The transformer turns ratio, the resonant frequency f r The expression is: 。 8. A control method for a wide-range CLLLC resonant converter for an energy storage system according to claim 3, characterized in that, During the constant current charging phase, after defining the soft-switching region, the switching frequency is... f s Phase shift angle between bridges The relationship between the two points is used to find the boundary of the soft-switching region, obtaining the complete boundary curve. The two endpoints of the soft-switching region boundary are points C and F. Simultaneously, the inter-bridge phase shift angle is set to -π / 2 to obtain the switching frequency at point C. f s First, determine the coordinates of point C. Then, find point E with the same current as point C. Determine the corresponding point E from point C. Finally, determine the selected portion of the soft-switching region boundary curve EF on the complete soft-switching region boundary curve CEF, and apply this to different voltage transfer ratios. d On the selected soft-switching region boundary curve EF, the corresponding switching frequency is selected according to the required charging current. f s Phase angle between bridges This enables soft switching of all switching devices during the constant current charging stage.

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