Three-Pulse Burst Optimal Trajectory Control Method for CLLC Resonant Converter

Abstract

The present invention discloses a three-pulse Burst mode optimal trajectory control method for a CLLC resonant converter. This method fixes the conduction time of the switching tube through the three-pulse mode, enabling the converter to continuously switch between the standby and working states. Meanwhile, according to the theoretical state trajectory of the CLLC resonant converter under the light load mode, the width of the first conduction pulse is optimized, enabling the state variables of the converter to quickly reach the target trajectory. The second and third conduction pulses ensure the stable operation of the converter on the theoretical trajectory. This method effectively reduces the switching frequency of the system, optimizes the light load efficiency, and reduces the output voltage ripple.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converters, and particularly relates to a three-pulse Burst optimal trajectory control method for a CLLC resonant converter. Background Art

[0002] With the rapid development of the information technology industry, the demand for energy in human society is increasing, and the requirements for the efficiency and power density of power supplies are also continuously improving. Resonant converters have been widely used in DC-DC converters because they are suitable for both high power density designs and high efficiency designs. Resonant converters are widely used in new energy application fields such as distributed power generation systems, energy storage systems, and electric vehicles. The CLLC resonant converter, which is extended from the traditional LLC resonant converter, not only has the advantages of high efficiency and high power density of the LLC resonant converter, but also has the characteristic of bidirectional energy transfer, and is very suitable for bidirectional DC-DC application scenarios.

[0003] The CLLC resonant converter has high efficiency under heavy loads, but its efficiency under light loads is less than satisfactory. This is mainly due to load-independent losses such as drive losses and transformer core losses. The Burst mode is an effective method to improve the efficiency under light loads, and its concept is to switch back and forth between pulse conduction and turn-off. During the pulse conduction time, the CLLC resonant converter operates at the ideal efficiency, and its instantaneous output power is equal to the output power corresponding to the ideal efficiency. During the pulse off-time, the CLLC resonant converter does not operate and the output power is zero. By controlling the ratio of the pulse conduction time to the pulse turn-off time, the average power output in the Burst mode can be controlled, and the output voltage can be adjusted accordingly.

[0004] However, due to the dynamic characteristics of the resonant cavity of the resonant converter, the hard switching losses during the start and turn-off of the Burst mode are still relatively large, which limits the improvement of the light load efficiency of the traditional Burst mode. At the same time, because the resonant converter switches back and forth between pulse conduction and pulse turn-off, there is a large low-frequency ripple in the output voltage of the resonant converter.

[0005] Therefore, there is an urgent need for a control method to improve the efficiency of the Burst mode and thus improve the efficiency of the CLLC resonant converter under light loads. Summary of the Invention

[0006] The purpose of the present invention is to provide a three-pulse Burst optimal trajectory control method for a CLLC resonant converter to optimize the efficiency of the CLLC resonant converter under light loads and reduce the output voltage ripple in the Burst mode.

[0007] The technical solution for achieving the object of the present invention is: a three-pulse Burst optimal trajectory control method for a CLLC resonant converter, comprising the following steps:

[0008] Step 1, taking the voltage u of the first resonant capacitor on the primary side of the CLLC resonant converter Cr1 , the voltage u of the second resonant capacitor on the secondary side Cr2 , the current i of the first resonant inductor on the primary side Lr1 , and the current i of the second resonant inductor on the secondary side Lr2 as state variables, to establish a state trajectory model of the CLLC resonant converter;

[0009] Step 2, when the CLLC resonant converter is working, detect the output voltage of the CLLC resonant converter, and determine whether the CLLC resonant converter is working in a light load state;

[0010] If the CLLC resonant converter is not working in a light load state, adopt a method including proportional integral, with the controlled object being the output voltage, and adjust the voltage gain by adjusting the switching frequency of the CLLC resonant converter;

[0011] If the CLLC resonant converter is working in a light load state, sample the voltage value of the first resonant capacitor on the primary side, calculate the width of the first pulse wave corresponding to this case, and drive the primary side switch tube of the CLLC resonant converter according to the calculated pulse width.

[0012] Preferably, the CLLC resonant converter includes a first switch tube S on the primary side 1 , a first anti-parallel diode D in parallel with the first switch tube S on the primary side 1 and a first parasitic capacitor C on the primary side 1 ; a second switch tube S on the primary side 2 , a second anti-parallel diode D in parallel with the second switch tube S on the primary side 2 , a second parasitic capacitor C on the primary side 2 ; a third switch tube S on the primary side 2 , a third anti-parallel diode D in parallel with the third switch tube S on the primary side 3 ; a fourth switch tube S on the primary side 3 , a fourth anti-parallel diode D in parallel with the fourth switch tube S on the primary side 3 ; a fourth parasitic capacitor C on the primary side 3 ; a first resonant inductor L on the primary side 4 , a first resonant capacitor C on the primary side 4 , and a first resonant capacitor C on the primary side 4 , a fourth anti-parallel diode D in parallel with the fourth switch tube S on the primary side 4 ; a fourth parasitic capacitor C on the primary side r1 ; a first resonant inductor L on the primary side r1 , a first resonant capacitor C on the primary side m, the exciting inductance L of the transformer m , a transformer with a turns ratio of n:1, the fifth switching transistor S on the secondary side 5 , with the fifth switching transistor S on the secondary side 5 , the fifth anti-parallel diode D on the secondary side connected in parallel with it 5 , the fifth parasitic capacitor C on the secondary side 5 ; the sixth switching transistor S on the secondary side 6 , with the sixth switching transistor S on the secondary side 6 , the sixth anti-parallel diode D on the secondary side connected in parallel with it 6 , the sixth parasitic capacitor C on the secondary side 6 ; the seventh switching transistor S on the secondary side 7 , with the seventh switching transistor S on the secondary side 7 , the seventh anti-parallel diode D on the secondary side connected in parallel with it 7 , the seventh parasitic capacitor C on the secondary side 7 ; the eighth switching transistor S on the secondary side 8 , with the eighth switching transistor S on the secondary side 8 , the eighth anti-parallel diode D on the secondary side connected in parallel with it 8 , the eighth parasitic capacitor C on the secondary side 8 ; the second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 , the output capacitor C o , the input voltage V in and the output voltage V o , the first switching transistor S on the primary side 1 and the second switching transistor S 2 are connected in series to form the first bridge arm, and the third switching transistor S on the primary side 3 and the fourth switching transistor S 4 are connected in series to form the second bridge arm; the first resonant inductor L on the primary side r1 , the first resonant capacitor C on the primary side r1 , the second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 and the transformer with a turns ratio of n:1 form the resonant cavity of the CLLC resonant converter.

[0013] Preferably, the specific method for establishing the state trajectory model of the CLLC resonant converter is as follows:

[0014] Normalize all the voltage quantities in the CLLC resonant converter with the input voltage V in , normalize all the current quantities in the CLLC resonant converter with V in / Z 0 , and normalize all the impedance quantities in the CLLC resonant converter with Z 0 , where Z 0 is the first resonant inductor L on the primary sider1 and the primary side first resonant capacitor C r1 characteristic impedance;

[0015] Normalize the primary and secondary resonant inductor currents i Lr1 、i Lr2 and the primary and secondary resonant capacitor voltages u Cr1 、u Cr2 to obtain i Lr1N 、i Lr2N and u Cr1N 、u Cr2N respectively. Taking u Cr1N +u Cr2N as the abscissa and i Lr1 +i Lr2 as the ordinate, establish the state-plane locus diagram of the CLLC resonant converter. When the CLLC resonant converter operates at the two-element series resonance frequency f 0 , its locus is a circle centered at the origin, and the equation is as follows

[0016] (i Lr1N +i Lr2N ) 2 +(u Cr1N +u Cr2N ) 2 =ρ 2

[0017] where ρ is the radius of the locus circle.

[0018] Preferably, the calculation formula for the two-element series resonance frequency f 0 of the primary side of the CLLC resonant converter is as follows:

[0019]

[0020] where L r1 is the primary side first resonant inductor and C r1 is the primary side first resonant capacitor.

[0021] Preferably, it is judged whether the CLLC resonant converter operates in a light load state by detecting the output voltage of the CLLC resonant converter. If the output voltage is lower than the reference voltage, the CLLC resonant converter operates in a light load state, otherwise, it does not operate in a light load state.

[0022] Preferably, if the CLLC resonant converter operates in a light load state, the three-pulse Burst optimal trajectory control method is adopted. By sampling the voltage of the first resonant capacitor on the primary side, the width of the first pulse is calculated, so that the CLLC resonant converter reaches the steady state at the highest efficiency load in the first pulse. Subsequently, the durations of the next two pulses are not only equal, both being half of the series resonance period of the two components, but also make the CLLC resonant converter operate at the steady state of the highest efficiency load and last for an entire series resonance period of the two components.

[0023] Preferably, if the CLLC resonant converter operates under light load, the total conduction time of the three pulses remains unchanged, and the output voltage is adjusted by adjusting the length of the pulse-off time.

[0024] Preferably, the method for determining the durations of the three pulses is as follows:

[0025] When the CLLC resonant converter operates at the load with the highest efficiency, the operating frequency is f s = f 0 , then

[0026]

[0027] where, T 0 is the series resonance period of the two components on the primary side of the CLLC resonant converter, V 0 is the output voltage of the CLLC resonant converter, L m is the magnetizing inductance of the CLLC resonant converter;

[0028] Thus, it is calculated that

[0029]

[0030] where, ρ is the radius of the trajectory circle, R L is the load at the highest efficiency, n is the turns ratio of the transformer, is the characteristic impedance of the CLLC converter, t 0 is the start time of the first pulse, t 3 is the end time of the third pulse, u Cr1N (t 0 ) + u Cr2N (t 0 ) is the abscissa of the trajectory circle corresponding to the start time of the first pulse, u Cr1N (t 3 ) + u Cr2N (t 3 ) is the abscissa of the trajectory circle corresponding to the end time of the third pulse, i Lr1N (t 3 ) + i Lr2N (t 3) is the vertical coordinate of the trajectory circle corresponding to the end time of the third pulse;

[0031] It is calculated that the duration of the first pulse is

[0032]

[0033] where f 1 is the series resonance frequency of the three components on the primary side of the CLLC resonant converter;

[0034] The durations of the second and third pulses are

[0035]

[0036] where T 0 is the series resonance period of the two components on the primary side.

[0037] Preferably, the calculation formula for the series resonance frequency f 1 of the three components on the primary side of the CLLC resonant converter is as follows:

[0038]

[0039] In the formula, L r1 is the first resonant inductor on the primary side, L m is the exciting inductor of the transformer, and C r1 is the first resonant capacitor on the primary side.

[0040] Preferably, the method for determining the radius of the state trajectory circle is:

[0041] When the CLLC resonant converter operates at the highest efficiency load, the operating frequency is f s , and f s = f 0 , the current i Lr1 of the first resonant inductor on the primary side is a sine wave, and the current i Lm of the exciting inductor of the transformer is a triangular wave. The effective value I Lr1 of the current i rms of the first resonant inductor on the primary side is calculated as:

[0042]

[0043] The calculated effective value I rms_2 of the current of the second resonant inductor on the secondary side is:

[0044]

[0045] where T 0 is the series resonance period of the two components on the primary side, L m is the exciting inductor in the transformer, and RL For the load at the highest efficiency, n is the turns ratio of the transformer, and V 0 is the output voltage of the CLLC resonant converter;

[0046] It is calculated that the radius of the state trajectory circle is:

[0047]

[0048] where V in is the input voltage of the CLLC resonant converter, is the characteristic impedance of the CLLC resonant converter.

[0049] Compared with the prior art, the significant advantages of the present invention are as follows: The present invention can not only improve the efficiency, but also reduce the ripple of the output voltage, and does not require an additional output voltage filter; the control method provided by the present invention is simple, and for different light loads, only the pulse-off time needs to be adjusted to achieve stable modulation of the output voltage. Therefore, this control method has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is the circuit diagram of the CLLC resonant converter which is the controlled object of the present invention.

[0051] Figure 2 is the overall control flowchart of the present invention.

[0052] Figure 3 is the schematic diagram of modulating the output voltage of the present invention.

[0053] Figure 4 is the schematic diagram of three-pulse state trajectory analysis of the present invention.

[0054] Figure 5 is the schematic diagram of time-domain waveform analysis of the present invention under the action of three pulses.

[0055] Figure 6 is the simulation diagram of three-pulse state estimation analysis of the present invention.

[0056] Figure 7 is the time-domain waveform simulation diagram of the present invention under the action of three pulses. DETAILED DESCRIPTION OF THE INVENTION

[0057] The following further elaborates the solution of the present invention in conjunction with the drawings and specific examples.

[0058] The present invention proposes a three-pulse Burst optimal trajectory control method for a CLLC resonant converter. By detecting the voltage of the first resonant capacitor on the primary side and adjusting the duration of the first pulse based on state-plane analysis, the CLLC resonant converter reaches the steady state of the highest-efficiency load under the first pulse, achieving high-efficiency operation, fast response of the CLLC resonant converter under light load, and reducing the output voltage ripple, thus eliminating the need for an additional output filter. The present invention selects the capacitor voltage and inductor current to establish the state trajectory. By detecting the voltage of the first resonant capacitor on the primary side and optimizing the duration of the first pulse according to the optimal trajectory of the state plane, the CLLC resonant converter can operate in the steady state corresponding to the highest-efficiency load with only one pulse, realizing the operation of the CLLC resonant converter under light load quickly and with low ripple, including the following steps:

[0059] Step 1: Taking the voltage u of the first resonant capacitor on the primary side of the CLLC resonant converter, Cr1 the voltage u of the second resonant capacitor on the secondary side, Cr2 the current i of the first resonant inductor on the primary side, Lr1 and the current i of the second resonant inductor on the secondary side Lr2 as state variables, establish the state trajectory model of the CLLC resonant converter;

[0060] Step 2: When the CLLC resonant converter is operating, detect the output voltage of the CLLC resonant converter and determine whether the CLLC resonant converter is operating under light load;

[0061] If the CLLC resonant converter is not operating under light load, the system enters the linear control mode;

[0062] If the CLLC resonant converter is operating under light load, the system enters the three-pulse Burst control mode. The system detects the voltage of the first resonant capacitor on the primary side, calculates the duration of the first pulse, that is, the system gives the duration of the first pulse in the three-pulse Burst mode of the CLLC resonant converter, and then gives two pulses immediately. The durations of these two pulses are equal and both are half of the two-element resonant period. Under the action of these two pulses, the CLLC resonant converter continuously operates for a whole two-element resonant period in the steady state corresponding to the highest-efficiency load;

[0063] Keep the total time of the three pulses given by the system unchanged, and adjust the output voltage and keep the output voltage stable by adjusting the length of the pulse-off time.

[0064] In a further embodiment, Figure 1 shown is the CLLC resonant converter as the controlled object. The described CLLC resonant converter includes the first switching tube S on the primary side 1 and the first switching tube S on the primary side1 The first anti-parallel diode D on the primary side in parallel 1 and the first parasitic capacitor C on the primary side 1 ; The second switching tube S on the primary side 2 , and the second switching tube S on the primary side 2 The second anti-parallel diode D in parallel on the primary side 2 , the second parasitic capacitor C on the primary side 2 ; The third switching tube S on the primary side 3 , and the third switching tube S on the primary side 3 The third anti-parallel diode D in parallel on the primary side 3 , the third parasitic capacitor C on the primary side 3 ; The fourth switching tube S on the primary side 4 , and; The fourth switching tube S on the primary side 4 The fourth anti-parallel diode D in parallel on the primary side 4 , the fourth parasitic capacitor C on the primary side 4 ; The first resonant inductor L on the primary side r1 , the first resonant capacitor C on the primary side r1 , the exciting inductor L of the transformer m , the transformer with a turn ratio of n:1, the fifth switching tube S on the secondary side 5 , and the fifth switching tube S on the secondary side 5 The fifth anti-parallel diode D in parallel on the secondary side 5 , the fifth parasitic capacitor C on the secondary side 5 ; The sixth switching tube S on the secondary side 6 , and the sixth switching tube S on the secondary side 6 The sixth anti-parallel diode D in parallel on the secondary side 6 , the sixth parasitic capacitor C on the secondary side 6 ; The seventh switching tube S on the secondary side 7 , and the seventh switching tube S on the secondary side 7 The seventh anti-parallel diode D in parallel on the secondary side 7 , the seventh parasitic capacitor C on the secondary side 7 ; The eighth switching tube S on the secondary side 8 , and the eighth switching tube S on the secondary side 8 The eighth anti-parallel diode D in parallel on the secondary side 8 , the eighth parasitic capacitor C on the secondary side 8 ; The second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 , the output capacitor C o , the input voltage V in and the output voltage V o , the first switching tube S on the primary side 1 and the second switching tube S 2are connected in series to form the first bridge arm, and the third switching transistor S on the primary side 3 and the fourth switching transistor S 4 are connected in series to form the second bridge arm; the first resonant inductor L on the primary side r1 , the first resonant capacitor C on the primary side r1 , the second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 and a transformer with a turns ratio of n:1 form the resonant cavity of the CLLC resonant converter; the anti-parallel diodes D 5 -D 8 on the secondary side switching transistors form the rectification path of the CLLC resonant converter, and the switching transistors S 1 -S 8 are all MOS transistors.

[0065] In a further embodiment, before using the three-pulse Burst optimal trajectory control method, taking the voltage u of the first resonant capacitor on the primary side of the CLLC resonant converter Cr1 , the voltage u of the second resonant capacitor on the secondary side Cr2 , the current i of the first resonant inductor on the primary side Lr1 , and the current i of the second resonant inductor on the secondary side Lr2 as state variables, a state trajectory model of the CLLC resonant converter is established. The specific method is as follows: The CLLC resonant converter operates at its primary side two-element series resonant frequency f 0 , and the calculation formula for the two-element series resonant frequency is as follows:

[0066]

[0067] In the formula, L r1 is the first resonant inductor on the primary side, and C r1 is the first resonant capacitor on the primary side.

[0068] The CLLC resonant converter operates at the primary side three-element series resonant frequency f 1 , and the calculation formula for the three-element series resonant frequency is as follows:

[0069]

[0070] The voltage variables of the CLLC resonant converter are normalized according to the input voltage V in , and all its current variables are normalized according to V in / Z o , where Z o is the characteristic impedance of the first resonant capacitor C r1 on the primary side and the first resonant inductor L r1 on the primary side:

[0071]

[0072] The resonant inductor currents i Lr1 、i Lr2 in the primary and secondary sides of the state variables, and the resonant capacitor voltages u Cr1 、u Cr2 after per-unit conversion are i Lr1N 、i Lr2N and u Cr1N 、u Cr2N . Taking u Cr1N +u Cr2N as the abscissa and i Lr1 +i Lr2 as the ordinate, a state-plane trajectory diagram of the CLLC resonant converter is established. When the converter operates at the two-element series resonance frequency f 0 , there is V in =nV o , where n is the turns ratio of the transformer. At this time, the state trajectory of the CLLC resonant converter is a circle centered at the origin, and its equation is as follows

[0073] (i Lr1N +i Lr2N ) 2 +(u Cr1N +u Cr2N ) 2 =ρ 2 (4)

[0074] The control flow chart of the three-pulse Burst optimal trajectory control method is as Figure 2 shown.

[0075] Figure 3 shown is the waveform schematic diagram of adjusting the output voltage in the present invention. The present invention adjusts the magnitude of the output voltage by adjusting the time length of the pulse disconnection. Among them, the time lengths of the disconnections of the three pulses are marked as Figure 3 T off on Figure 3 . And the durations of the three pulses, that is, the total conduction time of the three pulses each time, are constant. Among them, the conduction times of the three pulses are marked as on T

[0076] Figure 4 shown is the state trajectory schematic diagram in the three-pulse Burst optimal trajectory control method of the present invention. Among them, the first pulse corresponds to Figure 4 t 0 ~t 1 at, and the second and third pulses respectively correspond to Figure 4 t 1 ~t 2 and t2 ~t 3 Before the first pulse arrives, the current i of the first resonant inductor on the primary side of the CLLC resonant converter Lr1 , and the current i of the second resonant inductor on the secondary side Lr2 are both zero. At this time, the state of the CLLC resonant converter corresponds to Figure 4 at t 0 . When the first pulse arrives, the state of the CLLC resonant converter changes from Figure 4 at t 0 to Figure 4 at t 1 . Because the primary side is in a three-element series resonance state at this time, the resonant frequency corresponding to t Figure 4 in 0 ~t 1 is the three-element series resonant frequency f 1 . At Figure 4 at t 1 , the CLLC resonant converter has reached the steady-state trajectory corresponding to the highest efficiency, and its trajectory is a circle with the origin as the center and ρ as the radius. The durations of the second and third pulses are both half of the two-element series resonance period, enabling the CLLC resonant converter to continuously operate for a complete two-element series resonance period at the steady state of the highest efficiency.

[0077] Figure 5 is a schematic diagram of the time-domain waveform analysis of the present invention under the action of three pulses. At Figure 5 in t 0 , the current i of the first resonant inductor on the primary side of the CLLC resonant converter Lr1 , and the current i of the second resonant inductor on the secondary side Lr2 are both zero. When the first pulse arrives, that is, at Figure 5 in t 0 ~t 1 , the current i of the first resonant inductor on the primary side Lr1 , and the current i of the second resonant inductor on the secondary side Lr2 rise simultaneously. At Figure 5 in t 1 ~t 2 and at t 2 ~t 3 , which correspond to the second and third pulses respectively, the CLLC resonant converter is already operating at the steady state corresponding to the highest efficiency, and the current i of the first resonant inductor on the primary side Lr1 is approximately a sine wave, and the current i of the second resonant inductor on the secondary side Lr2 is approximately a triangular wave.

[0078] Observing Figure 4 and Figure 5 , due to the current i of the first resonant inductor on the primary sideLr1 Approximately a sine wave, the second resonant inductor current i on the secondary side Lr2 is approximately a triangular wave. Through Figure 5 the current symmetry relationship of the positive and negative half cycles of the time-domain waveform of the shown CLLC resonant converter, the effective value I of the first resonant current on the primary side can be calculated rms as:

[0079]

[0080] where, T 0 = 1 / f 0 , L m is the magnetizing inductance in the transformer, and R L is the load at the highest efficiency steady state.

[0081] The calculated effective value I of the second resonant inductor current on the secondary side rms_2 is:

[0082]

[0083] Thus, it is calculated that at Figure 4 when the switching frequency in is the series resonant frequency f of the two components 0 , the radius of the state trajectory circle is:

[0084]

[0085] Figure 4 The t 3 of the state trajectory circle corresponds to the t Figure 5 of the 3 waveform diagram. It can be intuitively seen from the waveform that simultaneously i Lr2 (t 3 ) = 0. Combining with Equation (7), it can be calculated that:

[0086]

[0087] At Figure 4 the t 1 of the state trajectory circle, there is u Cr1N (t 1 ) + u Cr2N (t 1 ) ≈ ρ. At the same time, from the t 0 to the t 1 of the state trajectory circle, the secondary resonant inductor current is zero, and the primary side operates in the three-component series resonance state, and the three-component series resonance frequency is f 1 . The time ΔT from the t 0 to the t 1 of the state trajectory circle can be calculated as

[0088]

[0089] By Figure 4 and Figure 6 comparison, it can be seen that the CLLC resonant converter can reach the steady state corresponding to the highest efficiency under the action of the first pulse, and continuously operates at the steady state corresponding to the highest efficiency under the action of the second and third pulses, and its trajectory is a circle centered at the origin.

[0090] By Figure 5 and Figure 7 comparison, it can be seen that under the action of the first pulse of the CLLC resonant converter, the primary-side first resonant inductor current i Lr1 , and the secondary-side second resonant inductor current i Lr2 rises from zero, and under the action of the second and third pulses, the primary-side first resonant inductor current i Lr1 is approximately a sine wave, and the secondary-side second resonant inductor current i Lr2 is approximately a triangular wave.

Claims

1. A three - pulse Burst optimal trajectory control method for a CLLC resonant converter, characterized in that, it includes the following steps: Step 1, taking the voltage u of the first resonant capacitor on the primary side of the CLLC resonant converter Cr1 , the voltage u of the second resonant capacitor on the secondary side Cr2 , the current i of the first resonant inductor on the primary side Lr1 , the current i of the second resonant inductor on the secondary side Lr2 as state variables, a state trajectory model of the CLLC resonant converter is established. The specific method is as follows: With the input voltage V in Normalize all voltage quantities in the per-unit CLLC resonant converter with V in / Z 0 Normalize all current quantities in the per-unit CLLC resonant converter with Z 0 Normalize all impedance quantities in the per-unit CLLC resonant converter, where Z 0 is the characteristic impedance of the first resonant inductor L r1 on the primary side and the first resonant capacitor C r1 on the primary side; Normalize the primary and secondary resonant inductor currents \(i\) Lr1 and \(i\) Lr2 , and the primary and secondary resonant capacitor voltages \(u\) Cr1 and \(u\) Cr2 . After normalization, we get \(i\) Lr1N , \(i\) Lr2N , \(u\) Cr1N , and \(u\) Cr2N . Taking \(u\) Cr1N + \(u\) Cr2N as the abscissa and \(i\) Lr1 + \(i\) Lr2 as the ordinate, establish the state-plane trajectory diagram of the CLLC resonant converter. When the CLLC resonant converter operates at the two-element series resonant frequency \(f\) 0 , its trajectory is a circle centered at the origin, and the equation is as follows (i Lr1N + i Lr2N ) 2 +(u Cr1N + u Cr2N ) 2 = ρ 2 where ρ is the radius of the trajectory circle; Step 2, when the CLLC resonant converter is working, detect the output voltage of the CLLC resonant converter and determine whether the CLLC resonant converter is working in a light - load state; If the CLLC resonant converter is not working in a light - load state, adopt a method including proportional - integral, with the controlled object being the output voltage, and adjust the voltage gain by regulating the switching frequency of the CLLC resonant converter; If the CLLC resonant converter is working in a light - load state, sample the voltage value of the first resonant capacitor on the primary side, calculate the width of the first pulse wave in this case, and drive the primary - side switch tube of the CLLC resonant converter according to the calculated pulse width.

2. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 1, characterized in that, The CLLC resonant converter includes a first primary-side switching transistor S 1 、a first anti-parallel diode D 1 in parallel with the first primary-side switching transistor S 1 and a first parasitic capacitor C 1 on the primary side; a second primary-side switching transistor S 2 、a second anti-parallel diode D 2 in parallel with the second primary-side switching transistor S 2 、a second parasitic capacitor C 2 on the primary side; a third primary-side switching transistor S 3 、a third anti-parallel diode D 3 in parallel with the third primary-side switching transistor S 3 、a third parasitic capacitor C 3 on the primary side; a fourth primary-side switching transistor S 4 、a fourth anti-parallel diode D 4 in parallel with the fourth primary-side switching transistor S 4 、a fourth parasitic capacitor C 4 on the primary side; a first primary-side resonant inductor L r1 、a first primary-side resonant capacitor C r1 、a transformer excitation inductor L m 、a transformer with a turn ratio of n:1, a fifth secondary-side switching transistor S 5 、a fifth anti-parallel diode D 5 in parallel with the fifth secondary-side switching transistor S 5 、a fifth parasitic capacitor C 5 on the secondary side; a sixth secondary-side switching transistor S 6 、a sixth anti-parallel diode D 6 in parallel with the sixth secondary-side switching transistor S 6 、a sixth parasitic capacitor C 6 on the secondary side; a seventh secondary-side switching transistor S 7 、a seventh anti-parallel diode D 7 in parallel with the seventh secondary-side switching transistor S 7 、a seventh parasitic capacitor C 7 on the secondary side; an eighth secondary-side switching transistor S 8 、an eighth anti-parallel diode D 8 in parallel with the eighth secondary-side switching transistor S 8 、an eighth parasitic capacitor C 8 on the secondary side; a second secondary-side resonant inductor L r2 、a second secondary-side resonant capacitor C r2 、an output capacitor C o 、an input voltage V in and an output voltage V o , the first primary-side switch tube S 1 and the second switch tube S 2 are connected in series to form the first bridge arm, and the third primary-side switch tube S 3 and the fourth switch tube S 4 are connected in series to form the second bridge arm; the first primary-side resonant inductor L r1 , the first primary-side resonant capacitor C r1 , the second secondary-side resonant inductor L r2 , the second secondary-side resonant capacitor C r2 and a transformer with a turns ratio of n:1 form the resonant cavity of the CLLC resonant converter.

3. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 1, characterized in that, The series resonance frequency f of two components on the primary side of the CLLC resonant converter 0 is calculated as follows: Among them, L r1 is the first resonance inductor on the primary side, and C r1 is the first resonance capacitor on the primary side.

4. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 1, characterized in that, Judge whether the CLLC resonant converter is working in a light - load state by detecting the output voltage of the CLLC resonant converter. If the output voltage is lower than the reference voltage, the CLLC resonant converter is working in a light - load state; otherwise, it is not working in a light - load state.

5. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 1, characterized in that, If the CLLC resonant converter is working in a light - load state, then adopt the three - pulse Burst optimal trajectory control method. By sampling the voltage of the first resonant capacitor on the primary side, calculate the width of the first pulse, so that the CLLC resonant converter reaches the steady state at the highest - efficiency load during the first pulse. Subsequently, the durations of the following two pulses are not only equal, both being half of the series - resonance period of the two components, but also make the CLLC resonant converter work in the steady state of the highest - efficiency load and last for an entire series - resonance period of the two components.

6. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 1, characterized in that, If the CLLC resonant converter is working under light - load, the total conduction time of the three pulses remains unchanged, and the output voltage is regulated by adjusting the length of the pulse - off time.

7. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 1, characterized in that, The method for determining the durations of the three pulses is: At the load where the CLLC resonant converter operates at the highest efficiency, the operating frequency is f s = f 0 , then Among them, T 0 is the series resonance period of two components on the primary side of the CLLC resonant converter, V 0 is the output voltage of the CLLC resonant converter, L m is the magnetizing inductance of the CLLC resonant converter; Thus, it is calculated that where ρ is the radius of the trajectory circle, R L is the load at the highest efficiency, n is the turn ratio of the transformer, is the characteristic impedance of the CLLC converter, t 0 is the start time of the first pulse, t 3 is the end time of the third pulse, u Cr1N (t 0 ) + u Cr2N (t 0 ) is the abscissa of the trajectory circle corresponding to the start time of the first pulse, u Cr1N (t 3 ) + u Cr2N (t 3 ) is the abscissa of the trajectory circle corresponding to the end time of the third pulse, i Lr1N (t 3 ) + i Lr2N (t 3 ) is the ordinate of the trajectory circle corresponding to the end time of the third pulse; The calculated duration of the first pulse is where, f 1 is the series resonance frequency of the three components on the primary side of the CLLC resonant converter; The durations of the second and third pulses are where T 0 is the series resonance period of the two components on the primary side.

8. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 7, characterized in that, The series resonance frequency f of the three components on the primary side of the CLLC resonant converter 1 is calculated as follows: Wherein, L r1 is the first resonance inductor on the primary side, L m is the excitation inductor of the transformer, and C r1 is the first resonance capacitor on the primary side.

9. The three - pulse Burst optimal trajectory control method for a CLLC resonant converter according to claim 7, characterized in that, The method for determining the radius of the state trajectory circle is: The load at which the CLLC resonant converter operates at the highest efficiency, with the operating frequency being f s , and having f s = f 0 , the primary-side first resonant inductor current i Lr1 is a sine wave, and the transformer magnetizing inductor current i Lm is a triangular wave. The calculated rms value I Lr1 of the primary-side first resonant inductor current i rms is: The effective value I of the current of the second resonant inductor on the secondary side is calculated as follows: rms_2 For: Among them, T 0 is the series resonance period of the two original side components, L m is the exciting inductance in the transformer, R L is the load at the highest efficiency, n is the turn ratio of the transformer, V 0 is the output voltage of the CLLC resonant converter; The calculated radius of the state trajectory circle is as follows: Among them, V in is the input voltage of the CLLC resonant converter, and is the characteristic impedance of the CLLC resonant converter.

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