Efficiency optimization control method for buck-boost LLC converter

Abstract

The application discloses an efficiency optimization control method of a Buck-Boost LLC converter, which changes the control margin of the Buck-Boost LLC converter through phase shift control and dead time adjustment, and then realizes the efficiency optimization of the Buck-Boost LLC converter; specifically, the phase difference of PWM signals between the Buck bridge arm and the integrated bridge arm is adjusted, the primary side conduction loss is reduced under the premise of realizing the soft switching of primary side switch tubes S1 and S2 on the Buck bridge arm, and the efficiency of the Buck-Boost LLC converter is improved; in addition, the dead time of the integrated bridge arm switch tube is adjusted, the time of transferring energy from the primary side to the secondary side is increased under the premise of realizing the soft switching of primary side switch tubes S3 and S4 on the integrated bridge arm, the dead time is shortened, the loss generated by the primary side circulating current of the converter is reduced, and the efficiency of the Buck-Boost LLC converter is further improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of direct current converters, and more particularly relates to an efficiency optimization control method for a Buck-Boost LLC converter. BACKGROUND

[0002] The Buck-Boost LLC converter (boost-buck resonant converter) combines the advantages of the four-switch Buck-Boost converter in wide voltage regulation range and the half-bridge LLC resonant converter in high efficiency, so that the LLC converter works at the resonant frequency point, and the Buck-Boost converter adjusts the converter gain. The BBLLC converter can realize soft switching of all switches in a wide gain range and is widely used in direct current conversion occasions requiring wide voltage input and high efficiency.

[0003] The Buck-Boost LLC converter realizes soft switching of the Buck bridge arm switch by adjusting the phase difference between the PWM signals of the Buck bridge arm and the integrated bridge arm. In theory, there are many phase shift values that can realize soft switching of the Buck bridge arm, and the current effective value of the primary side of the Buck-Boost LLC converter is different when different phase shift values are used, so the conduction loss is different. Therefore, by adjusting the phase difference between the PWM signals of the two bridge arms, the conduction loss of the primary side can be minimized under the premise of realizing soft switching of the switch, and the efficiency of the Buck-Boost LLC converter can be improved.

[0004] The Buck-Boost LLC converter enhances the soft switching capability of the LLC converter in the rear stage by bridge arm integration, but the existing control scheme does not release the soft switching potential of the rear stage, and still uses the dead time before bridge arm integration. During the dead time, the primary side LLC resonant cavity does not transfer energy to the secondary side, and at this time the current circulates in the primary side, resulting in loss. Therefore, reducing the dead time of the switch under the premise of ensuring soft switching can reduce the primary side circulating time, thereby improving the efficiency of the Buck-Boost LLC converter. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide an efficiency optimization control method for a Buck-Boost LLC converter. By adjusting the phase difference between the PWM signals of the Buck bridge arm and the integrated bridge arm, the conduction loss of the primary side can be minimized under the premise of realizing soft switching of the primary side switches S1 and S2. Then by adjusting the dead time of the integrated bridge arm switch, the time for the primary side LLC resonant cavity to transfer energy to the secondary side can be increased under the premise of realizing soft switching of the primary side switches S3 and S4, thereby further improving the efficiency of the Buck-Boost LLC converter.

[0006] To achieve the above object, the application discloses an efficiency optimization control method of a Buck-Boost LLC converter, which is characterized by comprising the following steps.

[0007] (1) According to the topology structure of the Buck-Boost LLC converter, the primary side switch tubes S1-S4 and the secondary side rectifier tubes SR1 and SR2 are marked, and the phase-shift inductance L is marked. b ; the expected output voltage V o_ref of the Buck-Boost LLC converter is given; in the open-loop theoretical duty ratio D0 of the primary side switch tube S1 is given;

[0008] (2) The input voltage V in , the output voltage V o and the load current I o of the Buck-Boost LLC converter under each working condition are obtained through a sampling module;

[0009] (3) The optimal phase-shift value of the Buck-Boost LLC converter under each working condition is calculated;

[0010] (3.1) The upper limit p up of the phase-shift value required for the primary side switch tubes S1 and S2 to realize soft switching function is calculated as follows:

[0011]

[0012]

[0013]

[0014] wherein, C oss is the junction capacitance value of each primary side switch tube; η is the estimated efficiency of the Buck-Boost LLC converter; and are the upper limits of the soft switching boundaries of S1 and S2 respectively; p up is the upper limit of the phase-shift value required for the primary side switch tubes S1 and S2 to realize soft switching function, and the smaller one of p S1 and p S2 is taken; n is the turns ratio of the transformer of the Buck-Boost LLC converter;

[0015] (3.2) The lower limit p down of the phase-shift value required for the primary side switch tubes S1 and S2 to realize soft switching function is calculated as follows:

[0016]

[0017] (3.3) Calculate the phase shift extreme value P of the minimum conduction loss in each working condition con_loss ;

[0018]

[0019] Where, R dson is the on-resistance of each primary switch tube; i Lr (t) is the LLC resonant current;

[0020] (3.4) Determine whether the phase shift extreme value P con_loss is within the soft switching boundary [p up , p down ], if P con_loss is within [p up , p down ], then let P con_loss be the optimal phase shift value, denoted as p optimal ; otherwise, take the value closest to P up from p down and p con_loss , denoted as p optimal ;

[0021] (4) Calculate the initial currents i b (t0), i Lb (t1), i Lb (t2), i Lb (t3) of the phase shift inductance L Lb in different modes;

[0022]

[0023] i Lb (t1) = i Lb (t0)

[0024]

[0025]

[0026] Where, t0-t3 represent the starting time of the four modes respectively; V bus is the intermediate bus voltage of the Buck-Boost LLC converter;

[0027] (5) According to the initial current, calculate the minimum dead time T d3 and T d4 required for the primary side switch tubes S3 and S4 to realize soft switching function;

[0028]

[0029]

[0030] wherein, I Lm is the LLC-level excitation current;

[0031] (6) Establishing the optimal phase-shifting value and minimum dead-time lookup table under each working condition;

[0032] Each column of the lookup table is two input variables corresponding to three output variables, wherein the two input variables are input voltage V in and output current I o under different working conditions, and the output variables are the optimal phase-shifting value p optimal and the minimum dead-time T d3 , T d4 under the corresponding working condition;

[0033] (7) Real-time acquisition of input voltage V in , output voltage V o and output current I o of the Buck-Boost LLC converter through the sampling module;

[0034] (8) Calculate the difference between the output voltage V o and the expected output voltage V o_ref , get the duty ratio D1 of the switch tube S1 through the PID regulator, and then get the duty ratio D2 of the switch tube S2 complementary to D1, D2 = 1-D1;

[0035] (9) Find the optimal phase-shifting value p optimal and the minimum dead-time T d3 , T d4 in the lookup table according to the input voltage V in and the output current I o , and then get the duty ratios D3, D4 of the switch tubes S3, S4 and the duty ratios D SR1 , D SR2 of the secondary rectifier tubes;

[0036] D3 = 0.5-T d3

[0037] D4 = 0.5-T d4

[0038] D SR1 = D4

[0039] D SR2 = D3

[0040] (10) The duty ratios D1-D4 and D SR1 , D SR2The signal is sent to the driver module, which then drives the primary-side switching transistors and the secondary-side synchronous rectifier transistors to complete the efficiency optimization control of the Buck-Boost LLC converter.

[0041] The objective of this invention is achieved as follows:

[0042] This invention discloses an efficiency optimization control method for a Buck-Boost LLC converter. By adjusting phase-shift control and dead-time, the control margin of the Buck-Boost LLC converter is altered, thereby optimizing its efficiency. Specifically, by adjusting the phase difference of the PWM signal between the Buck arm and the integrated bridge arm, the primary-side conduction loss is reduced while achieving soft switching of the primary-side switches S1 and S2 on the Buck arm, thus improving the efficiency of the Buck-Boost LLC converter. Furthermore, by adjusting the dead time of the integrated bridge arm switches, the time for energy transfer from the primary side to the secondary side is increased while achieving soft switching of the primary-side switches S3 and S4 on the integrated bridge arm. This shortens the dead time and reduces the losses caused by the primary-side circulating current, further improving the efficiency of the Buck-Boost LLC converter.

[0043] Meanwhile, the efficiency optimization control method for a Buck-Boost LLC converter of the present invention also has the following advantages:

[0044] Beneficial effects:

[0045] (1) This invention utilizes the principle of minimum conduction loss to calculate the optimal phase shift value among numerous phase shift values ​​that can achieve soft switching of the Buck arm switches. The optimal phase shift value can, under the premise of achieving soft switching of the Buck arm switches, ensure that the phase-shifting inductor current i of the BBLLC converter is... Lb The peak-to-peak value and RMS value are minimized, thereby reducing the conduction loss on the primary side of the BBLLC converter and improving the efficiency of the BBLLC converter.

[0046] (2) This invention adjusts the dead time of the integrated bridge arm switches S3 and S4 to select, from among many dead times that can achieve soft switching of the integrated bridge arm switches, the dead time T that allows the switches to achieve soft switching under the current operating conditions. d3 and T d4 During the dead time T d3 and T d4 Inside the primary-side LLC resonant cavity, the excitation current equals the resonant current. At this time, no energy is transferred from the primary side to the secondary side, and a circulating current is generated in the primary side of the BBLLC converter, resulting in circulating current losses. This invention proposes a minimum dead time T... d3 and T d4The time increases the time of transferring energy from the primary side to the secondary side in the switching period under the premise of realizing soft switching of the integrated bridge arm switch tube, reduces the loss generated by the circulation of the primary side current, and improves the efficiency of the BBLLC converter.

[0047] (3) The present application reduces the conduction loss and circulation loss of the primary side of the BBLLC converter by using the optimal phase shift value and the minimum dead time, so that the heat generated when the converter works is less, thereby reducing the requirement of the converter on the heat dissipation condition, and making it more suitable for high power density application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a flow chart of the efficiency optimization control method of the Buck-Boost LLC converter.

[0049] Figure 2 is a control system principle diagram of the Buck-Boost LLC converter.

[0050] Figure 3 is a topology structure of the Buck-Boost LLC converter.

[0051] Figure 4 is a schematic diagram of the current waveform of the post-stage LLC resonant cavity.

[0052] Figure 5 is a lookup table establishment flow chart. DETAILED DESCRIPTION

[0053] The specific embodiments of the present application will be described below with reference to the accompanying drawings, so that those skilled in the art can better understand the present application. It should be particularly noted that in the following description, when the detailed description of the known functions and designs may obscure the main content of the present application, these descriptions will be omitted here.

[0054] EMBODIMENT

[0055] Figure 1 is a flow chart of the efficiency optimization control method of the Buck-Boost LLC converter.

[0056] In this embodiment, as shown in Figure 2 , the Buck-Boost LLC converter control system comprises a Buck-Boost LLC converter, a sampling module, a digital controller module and a driver module. The digital controller module comprises a lookup table module, a PID regulator and a PWM generator. The lookup table module stores different input voltages V in and output currents I oThe optimal phase shift value and minimum dead time are determined to make the converter most efficient under any operating condition.

[0057] The sampling module connects to the input and output terminals of the Buck-Boost LLC converter and is used to sample the input voltage V of the Buck-Boost LLC converter. in Output voltage V o Output current I o Perform sampling.

[0058] The driver module connects the Buck-Boost LLC converter and the digital controller module. It is used to perform level conversion on the signal generated by the PWM generator in the digital controller, thereby driving the primary-side switching transistors and secondary-side synchronous rectifier transistors of the Buck-Boost LLC converter.

[0059] Below we combine Figure 2 This invention provides a detailed description of an efficiency optimization control method for a Buck-Boost LLC converter, such as... Figure 1 As shown, it includes the following steps:

[0060] S1, Topology initialization;

[0061] like Figure 3 As shown, based on the topology of the Buck-Boost LLC converter, primary-side switches S1-S4 and secondary-side rectifiers SR1 and SR2 are labeled, and phase-shifting inductor L is also labeled. b ; Given the desired output voltage V of the Buck-Boost LLC converter o_ref Given input voltage V in The theoretical open-loop duty cycle of the primary-side switch S1 is D0;

[0062] S2. Collect input and output parameters under various operating conditions;

[0063] The input voltage V of the Buck-Boost LLC converter under various operating conditions is obtained through the sampling module. in Output voltage V o Load current I o ;

[0064] S3. Calculate the optimal phase shift value of the Buck-Boost LLC converter under each operating condition;

[0065] S3.1 During the dead time of primary-side switches S1 and S2, the phase-shifting inductor L b With the junction capacitance C of the switching transistor oss Resonance, and i LbThe amplitude gradually decreases. The necessary condition for the soft switching of the primary side switch S1 and S2 is that the Buck bridge arm midpoint voltage V a should be greater than V in in the dead time of the primary side switch S1, and V a should be less than V in in the dead time of the primary side switch S2, so that the upper limit p up of the phase shift value required for the soft switching of the primary side switch S1 and S2 is:

[0066]

[0067]

[0068]

[0069] wherein, C oss is the junction capacitance of each primary side switch; η is the estimated efficiency of the Buck-Boost LLC converter; and and are the upper limits of the soft switching boundaries of S1 and S2, respectively; p up is the upper limit of the phase shift value required for the soft switching of the primary side switch S1 and S2, and is the smaller one of p S1 and p S2 ; and n is the turns ratio of the transformer of the Buck-Boost LLC converter.

[0070] S3.2, the bus voltage is reduced in proportion by adjusting the duty cycle D1 of the primary side switch S1, and the switching frequency of the LLC stage is fixed at the resonant frequency. When S1 is turned on, energy is transferred from the input capacitor C in to the inductor L b . When S3 is turned on, energy is transferred from L b to the bus capacitor C bus . By adjusting the phase shift value between the Buck bridge arm and the integrated bridge arm, the current of the phase shift inductor L b is shaped into a quadrilateral containing positive and negative parts, i Lb . The positive and negative parts are used to realize the soft switching of all switches. Thus, the lower limit p down of the phase shift value required for the soft switching of the primary side switch S1 and S2 is:

[0071]

[0072] S3.3, the phase shift values within the upper and lower limits can ensure the soft switching of the switches, but the conduction losses of the primary side switches are different under different phase shift values. Therefore, there is a phase shift extreme value P con_loss;

[0073]

[0074] wherein R dson is the on-resistance of each primary switch; i Lr (t) is the LLC resonant current;

[0075] S3.4, judging whether the phase-shift extreme value P con_loss is within the soft-switching boundary [p up , p down ], if P con_los is within [p up , p down ], then P con_loss is the optimal phase-shift value, denoted as p optimal ; otherwise, the value closest to P up from p down and p con_loss is denoted as p optimal ;

[0076] S4, calculating the phase-shift inductance L b under different modes, initial currents i Lb (t0), i Lb (t1), i Lb (t2), i Lb (t3);

[0077]

[0078] i Lb (t1) = i Lb (t0)

[0079]

[0080]

[0081] wherein t0-t3 represent the starting time of the four modes respectively; V bus is the intermediate bus voltage of the Buck-Boost LLC converter;

[0082] S5, calculating the minimum dead-time T d3 and T d4 required for the primary switch S3 and S4 to realize soft-switching function according to the initial current;

[0083] The phase-shift inductance L b provides soft-switching energy for the switch S3, even if i Lb is negative, it can also provide sufficient soft-switching energy within the dead-time, only need to ensure that the integrated bridge arm midpoint voltage Vb Charging to V bus , the soft switching of switch S3 can be realized, and the dead time required by S3 is the minimum dead time T d3 :

[0084]

[0085] S4 junction capacitance is discharged through phase-shift inductance L b connected directly to the ground, providing a discharge circuit for S4 junction capacitance, only need to ensure that at the end of the dead time phase V b discharged to 0, the soft switching of primary side switch S4 can be realized, and the dead time required by S4 is the minimum dead time T d4 :

[0086]

[0087] Where, I Lm is the LLC excitation current;

[0088] In this embodiment, as Figure 4 shown, in a switching cycle T, the energy transferred from the primary side to the secondary side is the resonant current i Lr (t) minus the excitation current I Lm . In the dead time T d3 and T d4 , the resonant current i Lr (t) and the excitation current I Lm are equal, at this time the primary side does not transfer energy to the secondary side, and the current produces circulating loss in the primary side. Therefore, under the premise of ensuring the soft switching of switch S3 and S4, reducing the dead time T d3 and T d4 can improve the efficiency of the converter.

[0089] S6, establish the optimal phase-shift value and minimum dead time lookup table under each working condition;

[0090] Each column of the lookup table is two input variables corresponding to three output variables, where the two input variables are input voltage V in and output current I o under different working conditions, and the output variables are the optimal phase-shift value p optimal and the minimum dead time T d3 , T d4 under the corresponding working condition;

[0091] In this embodiment, Table 1 is the optimal phase-shift value and the shortest dead time lookup table when the efficiency of the converter is the highest under different working conditions, and the specific process of establishing the lookup table can be referred to Figure 5 , and Table 1 is only an example, so only part of the data is listed in the table.

[0092]

[0093] Table 1

[0094] S7, collecting the input voltage V of the Buck-Boost LLC converter in real time through the sampling module in , the output voltage V o and the output current I o ;

[0095] S8, calculating the duty cycles of the primary side switch tubes S1 and S2;

[0096] calculating the difference between the output voltage V o and the expected output voltage V o_ref , obtaining the duty cycle D1 of the primary side switch tube S1 through the PID regulator, and then obtaining the duty cycle D2 of the primary side switch tube S2 complementary to D1, D2 = 1-D1;

[0097] S9, calculating the duty cycles of the primary side switch tubes S3, S4 and the secondary side rectifier tubes SR1, SR2;

[0098] According to the input voltage V in and the output current I o , finding the optimal phase shift value p optimal and the minimum dead time T d3 , T d4 in the lookup table, and then obtaining the duty cycles D3, D4 of the switch tubes S3, S4 and the duty cycles D SR1 , D SR2 of the secondary side rectifier tubes;

[0099] D3 = 0.5-T d3

[0100] D4 = 0.5-T d4

[0101] D SR1 = D4

[0102] D SR2 = D3

[0103] S10, realizing the efficiency optimization control of the converter through the driving module;

[0104] Sending the duty cycles D1-D4 and D SR1 , D SR2 to the driving module, driving the primary side switch tubes and the secondary side synchronous rectifier tubes by the driving module, and completing the efficiency optimization control of the Buck-Boost LLC converter.

[0105] While the foregoing specific embodiments of the application have been described in some detail to provide a clear understanding thereof, it will be apparent to those of ordinary skill in the art that numerous modifications can be made to the specific embodiments described without departing from the spirit and scope of the application defined by the appended claims.

Claims

1. An efficiency optimization control method for a Buck-Boost LLC converter, characterized in that, Includes the following steps: (1) Based on the topology of the Buck-Boost LLC converter, label the primary-side switches S1-S4 and the secondary-side rectifiers SR1 and SR2, and label the phase-shifting inductor Lb; given the desired output voltage of the Buck-Boost LLC converter... Given input voltage The theoretical open-loop duty cycle of the primary-side switch S1 is: ; (2) Obtain the input voltage of the Buck-Boost LLC converter under various operating conditions through the sampling module. Output voltage Load current ; (3) Calculate the optimal phase shift value of the Buck-Boost LLC converter under each operating condition; (3.1) Calculate the upper boundary of the phase shift value required for the primary-side switching transistors S1 and S2 to achieve soft switching function. for: ； in, Coss is the junction capacitance value of each primary-side switch transistor; This is the estimated efficiency of the Buck-Boost LLC converter; and These are the upper limits of the soft-switching boundaries of S1 and S2, respectively; pup is the upper limit of the phase shift value required for the primary-side switching transistors S1 and S2 to achieve the soft-switching function, which is the smaller of pS1 and pS2; n is the turns ratio of the transformer in the Buck-Boost LLC converter. (3.2) Calculate the lower boundary of the phase shift value required for the primary-side switching transistors S1 and S2 to achieve soft switching function. for: ； (3.3) Calculate the phase shift extreme value of minimum conduction loss under each operating condition. ; ； in, The on-resistance of each primary-side switch transistor; This is the LLC level resonant current; (3.4) Determining the phase shift extremes Is it at the soft-switching boundary? Inside, if exist Inside, then order The optimal phase shift value is denoted as . Otherwise, take and Zhongyu The closest value is denoted as ; (4) Calculate the initial current of the phase-shifting inductor Lb in different modes. ; ； in, These represent the start times corresponding to the four modes; This refers to the intermediate stage bus voltage of the Buck-Boost LLC converter. (5) Calculate the minimum dead time required for primary-side switching transistors S3 and S4 to achieve soft-switching function based on the initial current. and ; ； ； in, This is the excitation current for LLC level; (6) Establish lookup tables for optimal phase shift values ​​and minimum dead time under various operating conditions; Each column of the lookup table represents two input variables corresponding to three output variables. The two input variables are the input voltages under different operating conditions. and output current The output variable is the optimal phase shift value under the corresponding operating condition. and minimum dead time , ; (7) The input voltage of the Buck-Boost LLC converter is acquired in real time through the sampling module. Output voltage and output current ; (8) Calculate the output voltage With the desired output voltage The difference is used to obtain the duty cycle D1 of the switching transistor S1 through the PID controller, and then the duty cycle D2 of the switching transistor S2, which is complementary to D1, is obtained, where D2 = 1 - D1. (9) Based on the input voltage and output current Find the optimal phase shift value in the lookup table. And the minimum dead time Td3, Td4, and then the duty cycles D3, D4 of the switching transistors S3, S4, and the duty cycles DSR1, DSR2 of the secondary rectifier transistors SR1, SR2 are obtained; ； (10) Send the duty cycles D1-D4 and DSR1, DSR2 to the drive module, which drives the primary-side switching transistor and the secondary-side synchronous rectifier transistor to complete the efficiency optimization control of the Buck-Boost LLC converter.

2. The efficiency optimization control method for a Buck-Boost LLC converter according to claim 1, characterized in that, The excitation current The calculation method is as follows: ； Where Lm is the excitation inductance value of LLC level.

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