Control method of asymmetric CLLC resonant converter

Abstract

The invention discloses a control method of an asymmetric CLLC resonant converter adopting mixed control of track control and PI control. PI control is adopted during steady-state operation of the asymmetric CLLC resonant converter, when input voltage fluctuation is detected, trajectory control is introduced, the frequency of the converter entering the steady state again after the input voltage fluctuation is calculated through the geometrical relationship of a state plane, and steady-state errors are eliminated through a PI controller. The method has the advantages that the combination of the state track control and the linear controller can reduce the voltage change of the output side and shorten the adjustment time when the input voltage fluctuates, so that the problem of severe fluctuation of the output voltage caused by the sudden change of the input voltage when the resonant converter operates is solved, the dynamic performance of the converter is remarkably improved, and the reliability of the converter is improved. Finally, the problems existing in the process of designing the linear controller are solved, the problem of voltage abrupt change of the input side is solved, and the requirements for rapidity and stability are met.

Description

TECHNICAL FIELD

[0001] The present application relates to a control method of a power electronic power converter, in particular to a control method of an asymmetric CLLC resonant converter using hybrid control of trajectory control and PI control. BACKGROUND

[0002] The asymmetric CLLC resonant converter can realize bidirectional transmission of electrical energy between the DC bus and the energy storage device. Due to its natural soft switching characteristics, it has the advantages of high efficiency and high power density, and is widely used in microgrids, V2G and other fields. However, during the process of bidirectional transmission of electrical energy, input voltage fluctuations inevitably occur. Linear controller is a commonly used control method to maintain output voltage stability. However, in the process of designing linear controller, bandwidth and phase margin are mutually restricted. Higher bandwidth can improve the response speed of the system and shorten the adjustment time, but may result in a larger overshoot of the output voltage. Larger phase margin can reduce the overshoot of the output voltage, but will increase the adjustment time. Therefore, only using linear controller cannot meet the requirements of the system on dynamic performance, and a new type of control method is needed.

[0003] The state trajectory control method takes the state variable as the coordinate axis, and can draw the state trajectory of a single switching period of the nonlinear converter on the state plane, accurately describing the dynamic process of the converter in one period. Therefore, the state trajectory can also describe the dynamic process of the asymmetric CLLC resonant converter when the input voltage fluctuates. State trajectory control has been widely used in LLC resonant converters, symmetric CLLC resonant converters and other fields, but existing researches mostly focus on solving the problem of load mutation of resonant converters. However, input voltage mutation is a common phenomenon during the operation of resonant converters, so it is difficult to solve. Therefore, how to solve the problem of input voltage mutation has become a technical problem to be solved. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a control method of an asymmetric CLLC resonant converter that can solve the problems existing in the process of designing linear controller, solve the problem of input voltage mutation, and meet the requirements of rapidity and stability.

[0005] In order to solve the above technical problems, the control method of the asymmetric CLLC resonant converter of the present application uses PI control when the asymmetric CLLC resonant converter is in steady state operation, and introduces trajectory control when input voltage fluctuation is detected. The frequency of the converter when it enters steady state again after input voltage fluctuation is calculated through the geometric relationship of the state plane, and the steady state error is eliminated through the PI controller.

[0006] The specific method of state trajectory control is to establish a time-domain model for some operating modes of the asymmetric CLLC resonant converter and a state trajectory model for all operating modes, and perform geometric calculations in the state plane to obtain the frequency at which the converter re-enters a steady state after the input voltage fluctuation, thereby enabling the converter to smoothly transition to a new steady state.

[0007] The asymmetrical CLLC resonant converter has eight switching transistors Q1-Q8 on both the primary and secondary sides, each with an anti-parallel diode. During forward operation, the four primary-side transistors Q1-Q4 form an inverter bridge, and the four secondary-side transistors Q5-Q8 form a rectifier bridge. Conversely, during reverse operation, the four secondary-side transistors Q5-Q8 form an inverter bridge, and the four primary-side transistors Q1-Q4 form a rectifier bridge. A transformer connects the primary-side resonant cavity and the secondary-side resonant capacitor. The transformer has a primary-to-secondary turns ratio of n:1, and the primary and secondary structures are asymmetrical. A resonant inductor is incorporated into the primary-side resonant cavity. and resonant capacitor The secondary side is equipped with a resonant capacitor. In addition, a load of R is also set. L The excitation inductor With resonant inductor The ratio is Secondary resonant capacitor After normalizing to the original edge, we get The and resonant capacitor The ratio is .

[0008] The asymmetric CLLC resonant converter operates in six modes during normal operation. State equations for each of the six modes are written, and corresponding state trajectory models are established by solving these equations. Combining the state trajectories of multiple modes yields the complete operating trajectory of the converter. The horizontal axis of the asymmetric CLLC resonant converter's state trajectory is... The vertical axis is Forward and reverse operations share the same coordinate axis.

[0009] The asymmetric CLLC resonant converter is based on the switching frequency f. s The different resonant frequencies can be categorized into three states: underresonance, quasi-resonance, and overresonance; the resonant frequency... When f s < When f is in an underresonant state, the converter is in a subresonant state; when f s = When f is in a quasi-resonant state, the converter is in a quasi-resonant state; when f s > At that time, the converter is in an over-resonance state; in all three operating states, there exists a mode one, and the resonant capacitance at the initial moment of this mode is... Voltage Resonant current Resonant capacitor Voltage and resonant current All of these can be calculated; after normalizing these four variables and substituting them into the coordinate axes of the state trajectory, the coordinates of the initial moment of the quasi-resonant mode can be obtained, denoted as [missing information] during forward operation. When running in reverse, it is denoted as The trajectory corresponding to mode one is a standard circle, and the radius of the trajectory during forward running is denoted as . The trajectory radius during reverse running is denoted as .

[0010] When the input voltage increases, the converter increases the switching frequency to maintain a stable output voltage; during forward operation, the state trajectory control calculates the output frequency as follows: Since the system has two modes, buck and boost, they are denoted as follows for easy differentiation during calculation: and Similarly, in reverse operation, the frequency of the state trajectory control calculation output is... In the buck and boost modes, they are respectively denoted as and The final output drive frequency of the state trajectory control and PI hybrid control is: Forward and reverse execution are respectively denoted as and The calculation process is the same whether running in the forward or reverse direction, except for the radius. , The coordinates of points S1 and S2 are different.

[0011] The frequency calculated by the state trajectory control when the positive operating input voltage suddenly increases is denoted as... As shown below;

[0012]

[0013] In the formula, ; . D is a point on the state plane; This represents the effective value of the resonant current on the inductor side of the mode-1 resonant in positive operation. It is a constant; similarly, when the input voltage suddenly increases during reverse operation, the calculated frequency is denoted as... As shown below

[0014]

[0015] In the formula, ; ; This is the equivalent input voltage during reverse operation. ; The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during reverse operation;

[0016] When the input voltage decreases, the converter needs to reduce the switching frequency to maintain a stable output voltage. The switching frequency calculated by the state trajectory control during forward operation is denoted as:

[0017]

[0018]

[0019]

[0020] In the formula, ; ; ; ; In the formula, A point on the state plane; The x-coordinate of the initial point S1 of the mode during forward operation; It is the radius of the mode-1 state trajectory circle during forward operation.

[0021] Similar to forward operation, the switching frequency calculated for state trajectory control during reverse operation is denoted as:

[0022]

[0023]

[0024] In the formula, ; ; ; .

[0025] Similar to forward execution, A point on the state plane; The x-coordinate of the initial point S2 of mode 1 during reverse operation; It is the radius of the mode-1 state trajectory circle during reverse runtime.

[0026] The resonant frequency of the asymmetric CLLC resonant converter is f. r The resonant frequency of the three elements is f m f r and f m The expression is:

[0027]

[0028] In the formula, , For a constant, the expression is:

[0029]

[0030] The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during forward operation is expressed as follows: , The load connected to the output side during forward operation. The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during reverse operation is expressed as follows: , For loads connected to the output side during reverse operation; This represents the initial phase of the resonant current on the resonant inductor side during forward operation. and The expression is:

[0031]

[0032] The radius of the state trajectory circle corresponding to mode one during forward running is expressed as:

[0033]

[0034] The radius of the state trajectory circle corresponding to mode one during reverse runtime is expressed as:

[0035]

[0036] Point S1 is the coordinate of the initial moment of the quasi-resonant mode during forward operation, denoted as... , and The expression is:

[0037]

[0038] Point S2 is the coordinate of the initial moment of the quasi-resonant mode during reverse operation, denoted as... , and The expression is:

[0039] .

[0040] The advantages of this invention are:

[0041] This invention retains the PI control method for asymmetrical CLLC resonant converters and introduces state trajectory control on this basis. It adopts a hybrid control method combining state trajectory and PI, and calculates the switching frequency when the output converter re-enters steady state by calculating the geometric relationship between the state trajectories of different operating modes. This achieves state trajectory control. The combination of state trajectory control and linear controller can reduce the output voltage change when the input voltage fluctuates, shorten the adjustment time, and solve the problem of drastic output voltage fluctuation caused by sudden input voltage changes during the operation of the resonant converter. This significantly improves the dynamic performance of the converter. Ultimately, it solves the problems existing in the design of linear controllers and the problem of sudden input voltage changes, meeting the requirements of speed and stability. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the asymmetric CLLC resonant converter of the present invention, which employs a hybrid control strategy of trajectory control and PI control.

[0043] Figure 2 This is the equivalent circuit diagram of the asymmetric CLLC resonant converter mode one in this invention;

[0044] Figure 3 This is a mode-state trajectory diagram of the asymmetric CLLC resonant converter in this invention;

[0045] Figure 4 This is a state trajectory diagram of the asymmetric CLLC resonant converter in this invention at quasi-resonance.

[0046] Figure 5 This is the state trajectory diagram of mode two of the asymmetric CLLC resonant converter in this invention;

[0047] Figure 6 This is the state trajectory diagram of mode three of the asymmetric CLLC resonant converter in this invention;

[0048] Figure 7 This is the state trajectory diagram of mode four of the asymmetric CLLC resonant converter in this invention;

[0049] Figure 8 This is the state trajectory diagram of mode five of the asymmetric CLLC resonant converter in this invention;

[0050] Figure 9 This is the state trajectory diagram of mode six of the asymmetric CLLC resonant converter in this invention;

[0051] Figure 10 This is a state trajectory diagram of the buck mode of the asymmetric CLLC resonant converter in this invention;

[0052] Figure 11This is a state trajectory diagram of the boost mode of the asymmetric CLLC resonant converter in this invention;

[0053] Figure 12 This is a simulation output voltage waveform diagram of the input voltage drop during the forward operation of the asymmetric CLLC resonant converter in this invention.

[0054] Figure 13 This is a simulation output voltage waveform diagram of the input voltage surge during the forward operation of the asymmetric CLLC resonant converter in this invention.

[0055] Figure 14 This is a simulation output voltage waveform diagram of the input voltage drop during reverse operation of the asymmetric CLLC resonant converter in this invention.

[0056] Figure 15 This is a simulation output voltage waveform diagram of the input voltage surge during the reverse operation of the asymmetric CLLC resonant converter in this invention. Detailed Implementation

[0057] The control method of the asymmetric CLLC resonant converter of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] The control method for the asymmetric CLLC resonant converter of the present invention employs PI control during steady-state operation of the asymmetric CLLC resonant converter. When an input voltage fluctuation is detected, trajectory control is introduced. The frequency at which the converter re-enters steady state after the input voltage fluctuation is calculated through the geometric relationship of the state plane. The steady-state error is then eliminated through the PI controller. Specifically, the trajectory control method involves establishing a time-domain model for some operating modes of the asymmetric CLLC resonant converter and a state trajectory model for all operating modes. Geometric calculations are performed on the state plane to obtain the frequency at which the converter re-enters steady state after the input voltage fluctuation, thereby enabling the converter to smoothly transition to the new steady state. In particular, the present invention requires continuous sampling of the input voltage and comparison with a given input voltage value to obtain a voltage difference ΔU. The control frequency is then calculated and output based on ΔU. When a decrease in input voltage is detected, the voltage difference ΔU < 0, and the system enters boost mode. The state trajectory calculation predicts the switching frequency when the system re-enters steady state based on ΔU, and reduces the switching frequency accordingly. When an increase in input voltage is detected, the voltage difference ΔU > 0, and the system enters buck mode. The state trajectory calculation predicts the switching frequency when the system re-enters steady state based on the difference ΔU, and increases the switching frequency accordingly. By adding the signal output by the PI controller, the system finally outputs a drive signal, realizing a hybrid control combining state trajectory control and PI control. This control method significantly reduces output voltage fluctuations, shortens output voltage adjustment time, and improves dynamic performance.

[0059] Furthermore, such as Figure 1As shown, the asymmetric CLLC resonant converter has eight switching transistors Q1-Q8 on both the primary and secondary sides, each with an anti-parallel diode. During forward operation, the four primary-side transistors Q1-Q4 form an inverter bridge, and the four secondary-side transistors Q5-Q8 form a rectifier bridge. Conversely, during reverse operation, the four secondary-side transistors Q5-Q8 form an inverter bridge, and the four primary-side transistors Q1-Q4 form a rectifier bridge, thus enabling bidirectional energy transfer. A transformer connects the primary-side resonant cavity and the secondary-side resonant capacitor. The transformer's primary-to-secondary turns ratio is n:1, and the primary and secondary structures are asymmetric. A resonant inductor is incorporated into the primary-side resonant cavity. and resonant capacitor The secondary side only has a resonant capacitor. The load is R L Magnetizing inductor With resonant inductor The ratio is Secondary resonant capacitor After normalizing to the original edge, we get The and resonant capacitor The ratio is .

[0060] Furthermore, the asymmetric CLLC resonant converter operates in six modes during normal operation. State equations for each of the six modes are written, and corresponding state trajectory models are established by solving these equations. Combining the state trajectories of multiple modes yields the complete operating trajectory of the converter. The horizontal axis of the asymmetric CLLC resonant converter's state trajectory is... The vertical axis is Forward and reverse operations share the same coordinate axis.

[0061] Furthermore, the asymmetric CLLC resonant converter is based on the switching frequency f s The different states can be divided into three types: underresonance, quasi-resonance, and overresonance; resonant frequency When f s < When f is in an underresonant state, the converter is in a subresonant state; when f s = When f is in a quasi-resonant state, the converter is in a quasi-resonant state; when f s > At that time, the converter is in an over-resonance state; in all three operating states, there exists a mode one, and the resonant capacitance at the initial moment of this mode is... Voltage Resonant current Resonant capacitor ,Voltage and resonant current All of these can be calculated; after normalizing these four variables and substituting them into the coordinate axes of the aforementioned state trajectory, the coordinates of the initial moment of the quasi-resonant mode can be obtained, denoted as […] during forward operation. When running in reverse, it is denoted as The trajectory corresponding to mode one is a standard circle, and the radius of the trajectory during forward running is denoted as . The trajectory radius during reverse running is denoted as .

[0062] Let ΔU be the difference between the input voltage setpoint and the actual value. When the input voltage increases, the converter increases the switching frequency to maintain a stable output voltage. During forward operation, the frequency of the output calculated by the state trajectory control is... Since the system has two modes, buck and boost, they are denoted as follows for easy differentiation during calculation: and Similarly, in reverse operation, the frequency of the state trajectory control calculation output is... In the buck and boost modes, they are respectively denoted as and The final output drive frequency of the state trajectory control and PI hybrid control is: Forward and reverse execution are respectively denoted as and The calculation process is the same whether running in the forward or reverse direction, except for the radius. , The coordinates of points S1 and S2 are different.

[0063] The frequency calculated by the state trajectory control when the input voltage suddenly increases during forward operation is denoted as: As shown below;

[0064]

[0065] In the formula, ; . D is a point on the state plane, and its specific location is already shown in the diagram. Figure 10 Marking; This represents the effective value of the resonant current on the inductor side of the mode-1 resonant in positive operation. It is a constant;

[0066] Similarly, when the input voltage suddenly increases during reverse operation, the calculated frequency is denoted as... As shown below

[0067]

[0068] In the formula, ; Because they share the same trajectory when running in both directions, The location of point D is similar to that during forward movement; its specific location is already shown in [the original text]. Figure 10 Marking; This is the equivalent input voltage during reverse operation. ; The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during reverse operation;

[0069] When the input voltage decreases, the converter needs to reduce the switching frequency to maintain a stable output voltage. The switching frequency calculated by the state trajectory control during forward operation is denoted as:

[0070]

[0071]

[0072]

[0073] In the formula, ; ; ; ; In the formula, A point on the state plane, its specific location is already shown. Figure 11 Marking; The x-coordinate of the initial point S1 of the mode during forward operation; It is the radius of the mode-1 state trajectory circle during forward operation.

[0074] Similar to forward operation, the switching frequency calculated for state trajectory control during reverse operation is denoted as:

[0075]

[0076]

[0077] In the formula, ; ; ; .

[0078] Similar to forward execution, A point on the state plane, its specific location is already shown. Figure 11 Marking; The x-coordinate of the initial point S2 of mode 1 during reverse operation; It is the radius of the mode-1 state trajectory circle during reverse runtime.

[0079] Furthermore, the resonant frequency of the asymmetric CLLC resonant converter is f. r The resonant frequency of the three elements is f m f rand f m The expression is:

[0080]

[0081] In the formula, , For a constant, the expression is:

[0082]

[0083] The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during forward operation is expressed as follows: , The load connected to the output side during forward operation. The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during reverse operation is expressed as follows: , For loads connected to the output side during reverse operation; This represents the initial phase of the resonant current on the resonant inductor side during forward operation. and The expression is:

[0084]

[0085] The radius of the state trajectory circle corresponding to mode one during forward running is expressed as:

[0086]

[0087] The radius of the state trajectory circle corresponding to mode one during reverse runtime is expressed as:

[0088]

[0089] Point S1 is the coordinate of the initial moment of the quasi-resonant mode during forward operation, denoted as... , and The expression is:

[0090]

[0091] Point S2 is the coordinate of the initial moment of the quasi-resonant mode during reverse operation, denoted as... , and The expression is:

[0092] .

[0093] To more clearly express the intent of this invention, its technical solution is described in detail below:

[0094] To achieve hybrid control combining state trajectory control and PI control of the asymmetric CLLC resonant converter, state trajectory models need to be established for each of the six modes of the converter, and a time-domain model needs to be established for mode one under quasi-resonant operating conditions. Taking mode one in forward operation as an example, the equivalent circuit is as follows: Figure 2 As shown, a system of equations is written based on this equivalent circuit diagram. Solve the system of equations and linearly combine the state variables to obtain the expression. .

[0095] The system of state equations is as follows:

[0096]

[0097] Solving this system of equations and linearly combining the state variables yields the following expression for the state trajectory corresponding to mode one. Mode middle, , , Where is a constant, and M is the DC voltage gain. ; C and D are determined by the initial values ​​of each state variable. , , The expressions for C and D are as follows.

[0098]

[0099] Mode middle, This is the ratio of the magnetizing inductance to the resonant inductance. ; The effective value of the resonant current on the resonant inductor side during forward quasi-resonance operation is expressed as follows: ; For loads connected to the output side during forward operation, This represents the initial phase of the resonant current on the resonant inductor side during forward operation. and The expression is:

[0100]

[0101] According to the formula ,by The x-axis is... Using the vertical axis as the ordinate, the state trajectory of mode one can be plotted, and its trajectory is based on... Let r be a standard circle with center r1. ,like Figure 3 As shown.

[0102] M is the DC voltage gain. When the converter operates in quasi-resonance mode, M equals... In the quasi-resonant operating state, the state trajectories of modes one and two coincide, both being circles centered at (0,0), as shown below. Figure 4 As shown, point S is the initial moment of this mode, denoted as S1 during forward operation, with coordinates S1. The expression is as follows.

[0103]

[0104] Mode middle, Characteristic impedance, .

[0105] Figure 10 This is the state trajectory diagram of an asymmetric CLLC resonant converter in buck mode, corresponding to the over-resonance operating state. The circular trajectory centered at O2 corresponds to mode one, and the circular trajectory centered at O1 corresponds to mode two. Mode two is similar to mode one, only the input voltage polarity is reversed. Point B is the initial point of mode one in the over-resonance operating state, and the coordinates of point B are the coordinates of point S offset to the right by OO1. A straight line perpendicular to the horizontal axis is drawn through point A and intersects the trajectory of mode two at point [missing information]. It intersects the horizontal axis at point D, because The duration of the corresponding mode is extremely short, and can be considered as... The coordinates of point A and point B are the same, that is... , Let A be the x-coordinate of the initial point S1 of mode one during quasi-resonance operation in the forward direction. Draw a straight line parallel to the x-axis through point A, intersecting the trajectory of mode two at point [missing information]. , The coordinates of point A are offset to the right by O1O2; passing through Draw a line perpendicular to the horizontal axis from point E, intersecting the horizontal axis at point E. The time calculated by the state trajectory control is... The time corresponding to the trajectory minus the time of one resonant cycle. When the input voltage suddenly increases during forward operation, the control switching frequency of the state trajectory control output is denoted as... The expression is:

[0106]

[0107] Mode middle, ; .

[0108] Figure 11 This is the state trajectory diagram of an asymmetric CLLC resonant converter in boost mode, corresponding to the underresonant operating state. The circular trajectory centered at O1 corresponds to mode one, and the circular trajectory centered at O2 corresponds to mode two. Mode two is similar to mode one, except that the input voltage polarity is reversed. Point A represents the last moment of mode two in this operating state, and its coordinates are... The point is shifted to the left by OO1. Point A is symmetrical to point S1 about the origin. A straight line parallel to the horizontal axis is drawn through point A, intersecting the mode-1 trajectory at point P, where the coordinates of point P are O1O2 offset to the right of point A. A tangent line to the mode-1 trajectory is drawn through point P, and a line segment perpendicular to the tangent line is drawn through point A, intersecting the tangent line at point [missing information]. Draw a line perpendicular to the horizontal axis through point P, intersecting the horizontal axis at point T; Draw a line perpendicular to line segment AP, intersecting AP at point H and the horizontal axis at point Q. (Approximate point) It coincides with point B, and the two points have the same coordinates, that is... . The trajectory corresponds to a three-element resonant mode, where the excitation current equals the resonant current on the resonant inductor side. Since the excitation inductance is much larger than the resonant inductance, it is assumed that the resonant current on the resonant inductor side and the excitation current remain constant in this mode. The time corresponding to the trajectory can be approximated by the time corresponding to line segment AH. The time calculated by state trajectory control is the time corresponding to line segment AH. The corresponding time is added to the time of one resonant cycle. The switching control frequency of the state trajectory control output when the input voltage suddenly drops during forward operation is denoted as: The expression is as follows.

[0109]

[0110] In the formula, ; ; ; ;

[0111] In reverse operation, the state trajectory is completely identical to that in forward operation, and the state trajectory control calculation method is also completely identical. The state trajectory diagrams for boost and buck modes are also completely identical to those in forward operation, with only the expressions for the coordinates of each point in the diagram differing. During calculation, the input voltage needs to be converted to the resonant inductor L. r1 Side, denoted as , .

[0112] When running in reverse, the initial point of the quasi-resonant mode is denoted as S2, and its coordinates are S2. The expression is:

[0113]

[0114] Mode middle, The effective value of the resonant inductor side current in the quasi-resonant mode during reverse operation is expressed as: , The load connected to the output side during reverse operation.

[0115] When running in reverse, the radius of the circle corresponding to the state trajectory of the quasi-resonant mode is denoted as . The expression is as follows.

[0116]

[0117] When the input voltage suddenly increases, the control switching frequency of the reverse running state trajectory control output is denoted as: The expression is as follows.

[0118]

[0119] In the formula, ; Since the trajectory during reverse running is consistent with that during forward running, The location of the point is consistent with the forward running direction; the specific location is already shown in [the original text]. Figure 10 Marked at the location.

[0120] When the input voltage suddenly drops, the control switching frequency of the reverse running state trajectory control output is denoted as: The expression is as follows:

[0121]

[0122] In the formula, ; ; ; Consistent with forward execution, A point on the state plane, its specific location is already shown. Figure 11 Marked at the location.

[0123] Figure 12 For forward operation, given an input voltage of 400V and an output voltage of 240V, when t=0.04s, the input voltage suddenly drops by 20V. The simulation diagram of the output voltage using state trajectory control and PI hybrid control is shown.

[0124] Figure 13For forward operation, given an input voltage of 400V and an output voltage of 240V, when t=0.04s, the input voltage suddenly increases by 20V. The simulation diagram of the output voltage using state trajectory control and PI hybrid control is shown.

[0125] Figure 14 When operating in reverse, given an input voltage of 240V (equivalent input voltage 360V) and an output voltage of 400V, the input voltage suddenly drops by 20V at t=0.04s (equivalent input voltage drop of 30V). The simulation diagram of the output voltage using state trajectory control and PI hybrid control is shown.

[0126] Figure 15 When operating in reverse, given an input voltage of 240V (equivalent input voltage 360V) and an output voltage of 400V, the input voltage suddenly increases by 20V at t=0.04s (equivalent input voltage suddenly increases by 30V). The simulation diagram of the output voltage using state trajectory control and PI hybrid control is shown.

[0127] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A control method for an asymmetric CLLC resonant converter, characterized in that: In the steady-state operation of the asymmetric CLLC resonant converter, PI control is used. When the input voltage fluctuation is detected, trajectory control is introduced. The frequency at which the converter re-enters steady state after the input voltage fluctuation is calculated through the geometric relationship of the state plane, and then the steady-state error is eliminated by the PI controller.

2. The control method for the asymmetric CLLC resonant converter according to claim 1, characterized in that: The specific method of trajectory control is to establish a time-domain model for some operating modes of the asymmetric CLLC resonant converter and a state trajectory model for all operating modes, and perform geometric calculations in the state plane to obtain the frequency at which the converter re-enters a steady state after the input voltage fluctuation, thereby enabling the converter to smoothly transition to a new steady state.

3. The control method for the asymmetric CLLC resonant converter according to claim 1 or 2, characterized in that: The asymmetrical CLLC resonant converter has eight switching transistors Q1-Q8 on both the primary and secondary sides, each with an anti-parallel diode. During forward operation, the four primary-side transistors Q1-Q4 form an inverter bridge, and the four secondary-side transistors Q5-Q8 form a rectifier bridge. Conversely, during reverse operation, the four secondary-side transistors Q5-Q8 form an inverter bridge, and the four primary-side transistors Q1-Q4 form a rectifier bridge. A transformer connects the primary-side resonant cavity and the secondary-side resonant capacitor. The transformer has a primary-to-secondary turns ratio of n:1, and the primary and secondary structures are asymmetrical. A resonant inductor is incorporated into the primary-side resonant cavity. and resonant capacitor The secondary side is equipped with a resonant capacitor. In addition, a load of R is also set. L The excitation inductor With resonant inductor The ratio is Secondary resonant capacitor After normalizing to the original edge, we get The and resonant capacitor The ratio is .

4. The control method for the asymmetric CLLC resonant converter according to claim 3, characterized in that: The asymmetric CLLC resonant converter operates in six modes during normal operation. State equations for each of the six modes are written, and corresponding state trajectory models are established by solving these equations. Combining the state trajectories of multiple modes yields the complete operating trajectory of the converter. The horizontal axis of the asymmetric CLLC resonant converter's state trajectory is... The vertical axis is Forward and reverse operations share the same coordinate axis.

5. The control method for the asymmetric CLLC resonant converter according to claim 4, characterized in that: The asymmetric CLLC resonant converter is based on the switching frequency f. s The different resonant frequencies can be categorized into three states: underresonance, quasi-resonance, and overresonance; the resonant frequency... When f s < When f is in an underresonant state, the converter is in a subresonant state; when f s = When f is in a quasi-resonant state, the converter is in a quasi-resonant state; when f s > At that time, the converter is in an over-resonance state; in all three operating states, there exists a mode one, and the resonant capacitance at the initial moment of this mode is... Voltage Resonant current Resonant capacitor Voltage and resonant current All four variables were obtained through calculation; after normalizing these four variables and substituting them into the coordinate axes of the state trajectory, the coordinates of the initial moment of the quasi-resonant mode can be obtained, denoted as [missing information] during forward operation. When running in reverse, it is denoted as The trajectory corresponding to mode one is a standard circle, and the radius of the trajectory during forward running is denoted as . The trajectory radius during reverse running is denoted as .

6. The control method for the asymmetric CLLC resonant converter according to claim 1, 2, 4 or 5, characterized in that: When the input voltage increases, the converter increases the switching frequency to maintain a stable output voltage; during forward operation, the state trajectory control calculates the output frequency as follows: Since the system has both buck and boost modes, they are denoted as follows in the calculation: and Similarly, in reverse operation, the frequency of the state trajectory control calculation output is... In the buck and boost modes, they are respectively denoted as and The final output drive frequency of the state trajectory control and PI hybrid control is: Forward and reverse execution are respectively denoted as and ; The calculation process is the same whether running in the forward or reverse direction.

7. The control method for the asymmetric CLLC resonant converter according to claim 6, characterized in that: The frequency calculated by the state trajectory control when the positive operating input voltage suddenly increases is denoted as... As shown below; ； In the formula, ; , D is a point on the state plane; This represents the effective value of the resonant current on the inductor side of the mode-1 resonant in positive operation. It is a constant; similarly, when the input voltage suddenly increases during reverse operation, the calculated frequency is denoted as... As shown below; ； In the formula, ; ; This is the equivalent input voltage during reverse operation. ; The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during reverse operation; When the input voltage decreases, the converter needs to reduce the switching frequency to maintain a stable output voltage. The switching frequency calculated by the state trajectory control during forward operation is denoted as: ； ； ； In the formula, ; ; ; ; In the formula, A point on the state plane; The x-coordinate of the initial point S1 of the mode during forward operation; The radius of the mode-1 state trajectory circle during forward operation; The reverse operation is similar to the forward operation; the switching frequency calculated by the state trajectory control is denoted as: ； ； In the formula, ; ; ; ; The same applies to forward execution. A point on the state plane; The x-coordinate of the initial point S2 of mode 1 during reverse operation; It is the radius of the mode-1 state trajectory circle during reverse runtime.

8. The control method for the asymmetric CLLC resonant converter according to claim 7, characterized in that: The resonant frequency of the asymmetric CLLC resonant converter is f. r The resonant frequency of the three elements is f m f r and f m The expression is: ； In the formula, , For a constant, the expression is: ； The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during forward operation is expressed as follows: , The load connected to the output side during forward operation; The effective value of the resonant current on the resonant inductor side in the quasi-resonant mode during reverse operation is expressed as follows: , For loads connected to the output side during reverse operation; This represents the initial phase of the resonant current on the resonant inductor side during forward operation. and The expression is: ； The radius of the state trajectory circle corresponding to mode one during forward running is expressed as: ； The radius of the state trajectory circle corresponding to mode one during reverse runtime is expressed as: ； Point S1 is the coordinate of the initial moment of the quasi-resonant mode during forward operation, denoted as... , and The expression is: ； Point S2 is the coordinate of the initial moment of the quasi-resonant mode during reverse operation, denoted as... , and The expression is: 。

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