A high-efficiency wide-input half-bridge LLC resonant converter control system

Abstract

The present invention discloses a high-efficiency wide-input half-bridge LLC resonant converter control system, which includes a control system composed of a sampling module, a mode monitoring module, a PID module, and a duty cycle output total module. This control system is connected to a controlled half-bridge LLC resonant converter switching power supply to form a closed-loop system, achieving high-efficiency output of a constant voltage within a 0-100% load range under a wide input voltage range. Through the control of the sampling module, the mode monitoring module, the PID module, and the switching method, the present invention enables the half-bridge LLC resonant converter to achieve a very wide gain range within a 0-100% load range under a wide input voltage range, and can achieve considerable sampling accuracy and constant voltage accuracy. Moreover, the proposed mode can obtain higher conversion efficiency compared with the traditional variable-frequency mode through reasonable parameter design.

Description

Technical Field

[0001] The present invention relates to a switching power supply, and more particularly to a high-efficiency wide-input half-bridge LLC resonant converter control system. Background Art

[0002] Switching power supplies are often used as power sources for various electrical devices, and have the function of converting an unprocessed DC or AC input voltage into a processed DC or AC output voltage. Moreover, since switching power supplies have the advantages of high efficiency and small size compared to traditional linear power supplies, they are widely used in power electronics. For example, in today's electric vehicle applications, the converter can convert the input voltage of the charging pile or the power battery pack into an output voltage that meets the different index requirements of the power and in-vehicle electrical appliances of the electric vehicle, enabling the electric vehicle to not only facilitate people's travel but also protect the environment.

[0003] In switching power supplies, resonant converters are widely used due to their almost zero loss when the switching transistors are turned on or off, that is, the soft-switching characteristic. In particular, half-bridge LLC resonant converters have received extensive attention in recent years due to their ability to maintain high power density and efficiency over a wide input voltage range and their relatively simple circuit topology.

[0004] The charging of on-vehicle lithium-ion battery packs for electric vehicles is usually divided into two stages: constant current (CC) and constant voltage (CV). Frequency modulation (FM) is mainly used to regulate the output voltage of LLC resonant converters. During the charging process, the converter inevitably operates under light load conditions, such as the trickle charging stage. Generally, the duration of light load operation is much longer than that of other charging stages and cannot be ignored. This makes it very important to optimize the light load performance of LLC converters. However, when the switching frequency fs is higher than the resonant frequency fr, the traditional LLC resonant converter adopts the FM control method. The LLC resonant converter can control the magnitude of the output voltage by changing the switching frequency fs of the converter. The constant-frequency LLC resonant converters studied in previous literature only guarantee the best efficiency under nominal operating conditions (nominal switching frequency, full load and other nominal indicators), and lose ZVS when the load decreases and the input voltage range is wide. The traditional variable-frequency LLC resonant converter requires a wide switching frequency range and a high-quality factor (Q) resonant circuit to regulate the voltage under light load. A high Q value will result in a large size of the resonant circuit, an increase in magnetic loss, and a high circulating current for a wide range of load and input voltage variations. The LLC resonant circuit based on low Q design may allow the converter to operate efficiently under low voltage stress between the magnetic field and the capacitor, but they will lose zero voltage switching (ZVS) at light load. Neither method can achieve high efficiency in a wide input voltage range. Therefore, a new control method needs to be proposed, which can be applied regardless of the Q value of the half-bridge LLC resonant converter. Therefore, a control method that can meet the gain requirements in the 0-100% load range within a wide input voltage range, while maintaining zero voltage switching (ZVS) and being able to improve efficiency can greatly optimize the overall performance of the converter.

[0005] In summary, it is necessary to research and design a simple control method, which can enable the half-bridge LLC resonant converter to maintain the zero voltage switching (ZVS) of the main switching tube under an extremely wide input voltage range and 0-100% output load conditions, and achieve the low-cost and high-efficiency operation of the half-bridge LLC resonant converter. Summary of the Invention

[0006] To overcome the limitations and deficiencies of the prior art, the present invention proposes a high-efficiency wide-input half-bridge LLC resonant converter control system, which can achieve a high-efficiency constant voltage output of the half-bridge LLC resonant converter within a 0-100% load range in an extremely wide input voltage range at low cost, making the application range of the half-bridge LLC resonant converter wider, more practical and more efficient;

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A high-efficiency wide-input half-bridge LLC resonant converter control system, including a control system composed of a sampling module, a mode monitoring module, a PID module, and a duty cycle output total module, etc. This control system is connected to the controlled half-bridge LLC resonant converter switching power supply to form a closed-loop system, achieving high-efficiency output of a constant voltage within a 0-100% load range over a wide input voltage range. The sampling module is used to sample the switching voltage and current of the half-bridge LLC resonant converter; and process the sampled data in combination with the switching period Ts and the switching signals of the two main switching tubes of the half-bridge LLC resonant converter, and output a signal Vo_S representing the magnitude of the output voltage, a signal Vin_S representing the magnitude of the input voltage, and a signal Ii_S representing the magnitude of the input current.

[0009] The mode monitoring module is used for judging the input voltage range; its inputs are the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, and the switching period Ts, and it outputs a mode switching signal mode_ctrl to the PID module.

[0010] The inputs of the PID module are the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, the signal Vo_S representing the magnitude of the output voltage, the mode switching signal mode_ctrl, and the switching period Ts; this module is used to calculate the next switching period length Ts_pi and the switching duty cycle D_pi at different input voltages and loads.

[0011] The inputs of the duty cycle output total module are the switching period Ts_pi and the switching duty cycle D_pi output by the PID module. It determines the switching conduction time Ton and the dead time t according to the switching period Ts_pi and the switching duty cycle D_pi dead , generates duty cycle signals duty1 and duty2, and outputs a voltage with a changing duty cycle waveform to perform loop control on the gate electrodes of the switching tubes of the half-bridge LLC resonant converter.

[0012] Furthermore, the sampling module includes a sampling circuit and a sampling control module. The inputs of the sampling circuit are the analog quantity Vo_sense representing the magnitude of the output voltage, the analog quantity Vin_sense representing the magnitude of the input voltage, and the analog quantity Ii_sense representing the magnitude of the input current, which are output to the sampling control module. The sampling control module performs corresponding control and calculations according to the signal to be processed output by the sampling circuit, in combination with the input switching period Ts and the switching signals duty1 and duty2 of the two main switching tubes of the half-bridge LLC resonant converter, and respectively obtains the signal Vo_S representing the magnitude of the output voltage, the signal Vin_S representing the magnitude of the input voltage, and the signal Ii_S representing the magnitude of the input current.

[0013] Further, the inputs of the mode monitoring module are the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, and the switching period Ts. The output is the mode switching signal mode_ctrl, which is passed to the PID module. The mode monitoring module starts to judge the input voltage range. Its main functions are as follows: Define the minimum value V of the converter input voltage in_min_th , and its calculation method is:

[0014] V in_min_th = 2·n·V o (1)

[0015] In Equation (1), Vo is the output equivalent voltage, which is the sum of the output capacitor voltage and the output diode voltage. n is the ratio of the number of turns Np of the primary winding of the transformer to the number of turns Ns1 or Ns2 of the secondary winding, that is:

[0016]

[0017] When the actual input voltage Vin is greater than the theoretical minimum value V of the input voltage in_min_th , the mode switching signal mode_ctrl is set to "1"; when the actual input voltage Vin is less than or equal to the theoretical minimum value V of the input voltage in_min_th , the mode switching signal mode_ctrl is set to "2".

[0018] Further, the inputs of the PID module are the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, the signal Vo_S representing the magnitude of the output voltage, the mode switching signal mode_ctrl, and the switching period Ts. This module mainly calculates the length Ts_pi of the next switching period under different input voltages and loads. Its implementation functions are as follows:

[0019] Step 1: Set the initial value of the switching frequency of the PID module to the resonant frequency fr, and the duty cycle is 50%. The resonant frequency fr is defined as:

[0020]

[0021] In Equation (3), L r is the resonant inductor, and C r is the resonant capacitor.

[0022] Step 2: Define the maximum value f s_max_FM and the minimum value f s_min_FM of the theoretically allowed switching frequency change range when the converter is controlled using the traditional frequency modulation mode (FM).

[0023]

[0024]

[0025]

[0026]

[0027] In formulas (4) and (5), k is the inductance ratio coefficient. G max and G min are respectively the maximum and minimum gains set for the converter. Formulas (6) and (7) give the calculation methods for G max and G min , where V in_min and V in_max are respectively the minimum and maximum input voltages set for the converter.

[0028] Step 3: When the PID module receives the mode switching signal mode_ctrl set to "2", that is, when the actual input voltage Vin is less than or equal to the theoretical minimum value V in_min_th of the input voltage: First, the PID module sets the adjustment range of the switching frequency fs to f s_min_FM < f s ≤ f r . At the same time, the switching frequency fs starts from fr and decreases within the adjustment range of f s_min_FM < f s ≤ f r , and the switching frequency fs is adjusted based on the magnitude of the actual input voltage Vin (see formula (8a)) or the magnitude of the actual output power Po (see formula (8b)).

[0029] |f r - f s | = α 1 ·|V n - V in | (8a)

[0030] |f r |f s | = α 2 ·|P n |P o | (8b)

[0031] In formula (8a), α 1 is the proportionality coefficient and is greater than 0, and Vn is the nominal input voltage; in formula (8b), α 2 is the proportionality coefficient and is greater than 0, and Pn is the nominal output voltage.

[0032] When the PID module receives the mode switching signal mode_ctrl set to "1", that is, when the actual input voltage Vin is greater than the theoretical minimum value V in_min_thTime: First, the PID module sets the adjustment range of the switching frequency fs to f s_min_FM < f s < f s_max_FM . If the signal Vin_S representing the magnitude of the input voltage is less than the reference value Vn_ref corresponding to the nominal voltage Vn of the half-bridge LLC resonant converter circuit, the switching frequency fs starts from fr, and f s_min_FM < f s ≤ f r is used as the adjustment range for decreasing, and the switching frequency fs is adjusted based on the magnitude of the actual input voltage Vin (see Equation (8a)) or the magnitude of the actual output power Po (see Equation (8b)); if the signal Vin_S representing the magnitude of the input voltage is greater than or equal to the reference value Vn_ref corresponding to the nominal voltage Vn of the half-bridge LLC resonant converter circuit, the switching frequency fs starts from fr, and f r ≤ f s < f s_max_FM is used as the adjustment range for increasing, and the switching frequency fs is adjusted based on the magnitude of the actual input voltage Vin (see Equation (8a)) or the magnitude of the actual output power Po (see Equation (8b)).

[0033] Step Four: After obtaining the switching frequency fs, according to Equation (9), the switching frequency fs is used to calculate the corresponding switching period Ts_pi.

[0034]

[0035] Step Five: While determining the change range of the switching frequency, the PID module also needs to determine the duty cycle D_pi.

[0036] Therefore, while adjusting the switching frequency fs, the PID module performs PID operations according to the input signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, and the signal Vo_S representing the magnitude of the output voltage. The PID operation adjusts the duty cycle D_pi based on the magnitude of the actual input voltage Vin (see Equation (10a)) or the magnitude of the actual output power Po (see Equation (10b)).

[0037] |50% - D _pi | = β 1 ·|V n - V in | (10a)

[0038] |50% - D _pi | = β 2 ·|P n - P o | (10b)

[0039] In Equation (10a), β1 is a proportionality coefficient and generally satisfies 0 < α 1 < β 1 , Vn is the nominal input voltage of the converter; in Equation (10b), β 2 is a proportionality coefficient and generally satisfies 0 < α 2 < β 2 , Pn is the nominal output voltage of the converter.

[0040] Calculate the corresponding switching duty cycle D_pi of the converter, so that the switching period Ts_pi output by the PID module at this time and the signal Vo_S representing the magnitude of the output voltage of the converter controlled by the switching duty cycle D_pi are equal to the reference value Vo_ref corresponding to the required output voltage, so as to achieve the set constant voltage output. At this time, the switching period Ts_pi and the switching duty cycle D_pi corresponding to Vin_S and Ii_S are stably output to the total duty cycle output module.

[0041] Furthermore, the total duty cycle output module includes a duty cycle generation module and a driving module. The input of the duty cycle generation module is the switching period Ts_pi and the switching duty cycle D_pi output by the PID module. The duty cycle generation module calculates the switch-on time Ton and the dead time t according to the switching period Ts_pi and the switching duty cycle D_pi dead , generates output duty cycle signals duty1 and duty2, and outputs a voltage with a changing duty cycle waveform through the driving module to realize loop control of the gates of the switching tubes of the half-bridge LLC resonant converter; then the system samples the analog quantity Vo_sense representing the magnitude of the output voltage, the analog quantity Vin_sense representing the magnitude of the input voltage, and the analog quantity Ii_sense representing the magnitude of the input current of the half-bridge LLC resonant converter circuit again for control and calculation, and repeats the above process for cyclic control of the on and off of the main switching tubes of the half-bridge LLC resonant converter, so that the system is more stable, thereby obtaining a higher dynamic response.

[0042] Repeating the above sampling, mode monitoring, PID precise calculation, and control of the switching method can enable the half-bridge LLC resonant converter to achieve a very wide gain range in the 0-100% load range under a wide input voltage range, and can achieve considerable sampling accuracy and constant voltage accuracy, and the proposed mode can obtain higher conversion efficiency than the traditional variable frequency mode through reasonable parameter design.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) The present invention can achieve high-efficiency output control under the conditions of 0-100% load of the half-bridge LLC resonant converter. Compared with the traditional frequency modulation (FM), the working efficiency (especially under light load conditions) is significantly improved;

[0045] (2) The present invention can achieve a very wide output gain range, is applicable to an extremely wide input voltage range from low voltage to high voltage, and has the universality and flexibility for applications.

[0046] (3) Since the proposed control system can obtain a higher gain than frequency modulation (FM) under light load conditions, the output voltage can be regulated within a relatively narrow switching frequency change range; therefore, the magnetic components can be optimized in design. This reduces the size of the magnetic components and conduction losses, thus providing high efficiency under nominal operation and high power density.

[0047] (4) The present invention can be applied to isolated or non-isolated converters. In an isolated converter, it can adopt primary side feedback technology or secondary side feedback technology. When collecting output voltage information using primary side feedback technology, it can greatly reduce the control cost and improve the system reliability.

[0048] (5) The present invention can be widely applied to various switching power supply circuit structures, and has universality, reusability, and portability. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is the system structure block diagram of the control method of the present invention.

[0050] Figure 2 is the typical circuit structure diagram of a primary side feedback half-bridge LLC resonant converter.

[0051] Figure 3(a) is Figure 1 the flow of the sampling control module in the case of taking the primary side feedback half-bridge LLC resonant converter as an example; Figure 3(b) is the control block diagram of the present invention in the case of taking the primary side feedback half-bridge LLC resonant converter as an example.

[0052] Figure 4 is the specific working method and key waveform diagram of the duty cycle output total module under light load conditions in the case of taking the primary side feedback half-bridge LLC resonant converter as an example.

[0053] Figure 5(a) is the working waveform diagram of traditional frequency modulation (FM) under the conditions of an input voltage of 250V and an output load of 10% of the full load; Figure 5(b) is the working waveform diagram of the present invention under the same conditions of an input voltage of 250V and an output load of 10% of the full load.

[0054] Figure 6(a) is the working waveform diagram of traditional frequency modulation (FM) under the conditions of an input voltage of 250V and an output load of 5% of the full load; Figure 6(b) is the working waveform diagram of the present invention under the same conditions of an input voltage of 250V and an output load of 5% of the full load.

[0055] Figure 7(a) is the working waveform diagram of traditional frequency modulation (FM) under the conditions of an input voltage of 500V and an output load of 10% of the full load; Figure 7(b) is the working waveform diagram of the present invention under the same conditions of an input voltage of 500V and an output load of 10% of the full load.

[0056] Figure 8(a) is the working waveform diagram of traditional frequency modulation (FM) under the conditions of an input voltage of 500V and an output load of 5% of the full load; Figure 8(b) is the working waveform diagram of the present invention under the same conditions of an input voltage of 500V and an output load of 5% of the full load.

[0057] Figure 9 This is the efficiency broken line graph of the present invention and traditional frequency modulation (FM) under light load conditions. Specific embodiments

[0058] Refer to Figure 1 , the control system of the present invention includes a sampling module, a mode monitoring module, a PID module, and a duty cycle output total module. The sampling module includes a sampling circuit and a sampling control module. The inputs of the sampling circuit, namely the analog quantity Vo_sense representing the output voltage magnitude, the analog quantity Vin_sense representing the input voltage magnitude, and the analog quantity Ii_sense representing the input current magnitude, are output to the sampling control module. The sampling control module performs corresponding control and calculations based on the signal to be processed output by the sampling circuit, in combination with the input switching period Ts, the switching signals duty1 and duty2 of the two main switching tubes of the half-bridge LLC resonant converter, and respectively obtains the signal Vo_S representing the output voltage magnitude, the signal Vin_S representing the input voltage magnitude, and the signal Ii_S representing the input current magnitude. The mode monitoring module performs mode monitoring and control based on the signal Vin_S representing the input voltage magnitude and the signal Ii_S representing the input current magnitude output by the sampling control module, in combination with the switching period Ts, and outputs the corresponding mode switching signal mode_ctrl and the input voltage status signal Vin_state to the PID module. The PID performs corresponding operations based on the switched mode and the input voltage status, in combination with the switching period Ts, and outputs the switching period Ts_pi and D_pi to the duty cycle generation module. The duty cycle generation module calculates and outputs the duty cycle signals duty1 and duty2 and the dead time tdead to the driving module, and the driving module generates voltages Vg1 and Vg2 with changing duty cycle waveforms to achieve loop control of the gates of the two main switching tubes of the half-bridge LLC resonant converter.

[0059] Figure 2It is a circuit structure diagram with the primary-side feedback half-bridge LLC resonant converter as an example. According to Equation (11), the primary-side feedback technology can obtain the information Vaux_S representing the magnitude of the output voltage by sampling the voltage Vaux of the primary-side auxiliary winding. Compared with the traditional secondary-side feedback technology that directly samples the output voltage, it removes the optocoupler and the secondary circuit, improves the reliability and lifespan of the converter, and also reduces costs. Q1 and Q2 are two main switching transistors, and the transformer has four windings (Np: Ns1: Ns2: Na). Among them, the sampling resistor R sVin The resistance value Vin_sense on the resistor, the voltage value VIi_sense on the series sampling resistor of the DC input, and the voltage Vaux_sense on the sampling resistor after the voltage of the primary-side transformer auxiliary winding is divided by the resistor are input to the control system. The control system obtains the output voltage, load, etc. based on the above three sampling signals and conducts switching control. The two secondary output rectifier diodes D1 and D2 rectify the secondary-side voltage of the transformer, and Vg1 and Vg2 represent the turn-on and turn-off signals of the main switching transistors.

[0060]

[0061] In Equation (11), Vo is the output equivalent voltage, which is the sum of the output capacitor voltage and the output diode voltage, V aux_max is the maximum value of the primary-side auxiliary winding Vaux in each switching cycle, Ns1 and Ns2 are the turns of the secondary-side windings of the transformer, and Na is the turns of the primary-side auxiliary winding of the transformer.

[0062] Figure 3(a) shows the specific sampling, control, and calculation processes of the sampling control module in the sampling module with the primary-side feedback half-bridge LLC resonant converter as an example. Since the input voltage Vin and the input current Ii are direct current values and their parameters do not change with time, signals Vin_S (voltage Vin) representing the magnitude of the input voltage and Ii_S representing the magnitude of the input current are output after sampling at fixed times Ts1 and Ts2 within the switching period Ts of the switching transistor and sent to the mode monitoring module and the PID module. When using the primary-side feedback technology to sample the output voltage magnitude information of the half-bridge LLC resonant converter, since the voltage of the auxiliary winding of the transformer is an approximate square wave with equal absolute values of positive and negative peaks, and there is a fixed proportional relationship between this absolute value and the magnitude of the output voltage, the sampling control module uses the resistor-divided ADC_Vaux of the primary-side auxiliary winding voltage collected by the sampling circuit, and takes the magnitude Vaux_min of the lowest ADC_Vaux corresponding to different input voltages as the judgment reference, and only intercepts the part greater than Vaux_min. In this way, the useless part with an approximate square wave amplitude less than or equal to 0 is filtered out, and only the part that can accurately represent the output voltage magnitude information is retained. Due to the limitation of the sampling rate of the analog-to-digital conversion chip ADC and the interference of the analog measured peripheral circuit, there is a slight discrete fluctuation in the peak value of the intercepted part. In order to more accurately obtain the maximum value Vaux_max of the intercepted part peak ADC_Vaux within each switching period, according to the input switching period signal T_ctrl, the two floating discrete values Vaux_1 and Vaux_2 of the intercepted part peak according to the switching transistor duty cycle signal law within each switching period are compared. When Vaux_1 is higher than or equal to Vaux_2, the comparison result is output as Vaux_1; when Vaux_1 is lower than Vaux_2, the comparison result is output as Vaux_2. This comparison result is the maximum value Vaux_max of the intercepted part peak ADC_Vaux within each switching period. Connecting the Vaux_max of each sampling period together is another output of the sampling control module: the auxiliary winding voltage signal Vaux_S representing the output voltage information, that is, Vo_S.

[0063] The specific control process of the described mode monitoring module and PID module with the primary-side feedback half-bridge LLC resonant converter as an example is shown in Figure 3(b). The mode monitoring module first judges the input voltage range. Its main function is: define the minimum value V of the converter input voltage in_min_th , and its calculation method is:

[0064] V in_min_th = 2·n·V o

[0065] Wherein, Vo is the output equivalent voltage, which is the sum of the output capacitor voltage and the output diode voltage, and n is the ratio of the number of turns Np of the primary winding of the transformer to the number of turns Ns1 or Ns2 of the secondary winding, that is:

[0066]

[0067] The mode monitoring module needs to determine whether the signal Vin_S representing the magnitude of the input voltage is less than or equal to the minimum value V of the input voltage of the converter theoretically. in_min_th The converted voltage reference value V in_min_ref .

[0068] When the signal Vin_S representing the magnitude of the input voltage is greater than the voltage reference value V in_min_ref , the mode switching signal mode_ctrl is set to "1";

[0069] When the signal Vin_S representing the magnitude of the input voltage is less than or equal to the voltage reference value V in_min_ref , the mode switching signal mode_ctrl is set to "2".

[0070] The inputs of the PID module are the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, the signal Vo_S representing the magnitude of the output voltage, the mode switching signal mode_ctrl, and the switching period Ts. This module mainly calculates the length Ts_pi of the next switching period under different input voltages and loads. Its functions are as follows:

[0071] Step 1: The initial value of the switching frequency of the PID module is set to the resonance frequency fr, and the duty cycle is 50%.

[0072]

[0073] (3) Wherein, L r is the resonance inductor, and C r is the resonance capacitor.

[0074] Step 2: Define the maximum value f s_max_FM and the minimum value f s_min_FM of the allowable switching frequency change range of the converter theoretically when the converter is controlled using the traditional frequency modulation mode (FM).

[0075]

[0076]

[0077]

[0078]

[0079] where k is the inductance ratio coefficient, G max and G min are the maximum and minimum gains set for the converter respectively.

[0080] The formula gives the calculation method of G max and G min where V in_min and V in_max are the minimum and maximum input voltages set for the converter respectively.

[0081] Step 3: When the PID module receives the mode switching signal mode_ctrl set to "2", which means the signal Vin_S representing the magnitude of the input voltage is less than or equal to the voltage reference value V in_min_ref : First, the PID module sets the adjustment range of the switching frequency fs to f s_min_FM < f s ≤ f r . At the same time, starting from fr, the switching frequency fs is decreased within the adjustment range of f s_min_FM < f s ≤ f r and the switching frequency fs is adjusted based on the magnitude of the actual input voltage Vin (see the following formula) or the magnitude of the actual output power Po (see the following formula).

[0082] |f r - f s | = α 1 ·|V n - V in |

[0083] |f r - f s | = α 2 ·|P n - P o |

[0084] where α 1 is the proportionality coefficient and greater than 0, and Vn is the nominal input voltage; where α 2 is the proportionality coefficient and greater than 0, and Pn is the nominal output voltage.

[0085] When the PID module receives the mode switching signal mode_ctrl set to "1", which means the actual input voltage Vin is greater than the theoretical minimum value V of the input voltage in_min_th : First, the PID module sets the adjustment range of the switching frequency fs to f s_min_FM < f s < f s_max_FMIf the signal Vin_S representing the magnitude of the input voltage is less than the reference value Vn_ref corresponding to the nominal voltage Vn of the half-bridge LLC resonant converter circuit, the switching frequency fs starts from fr, and f s_min_FM < f s ≤ f r is decreased within the adjustment range, and the switching frequency fs is adjusted based on the magnitude of the actual input voltage Vin (see the following formula) or the magnitude of the actual output power Po (see the following formula); if the signal Vin_S representing the magnitude of the input voltage is greater than or equal to the reference value Vn_ref corresponding to the nominal voltage Vn of the half-bridge LLC resonant converter circuit, the switching frequency fs starts from fr, and f r ≤ f s < f s_max_FM is increased within the adjustment range, and the switching frequency fs is adjusted based on the magnitude of the actual input voltage Vin (see the following formula) or the magnitude of the actual output power Po (see the following formula)

[0086] |f r - f s | = α 1 ·|V n - V in |

[0087] |f r - f s | = α 2 ·|P n - P o |

[0088] Step Four: After obtaining the switching frequency fs, calculate the corresponding switching period Ts_pi according to the switching frequency fs..

[0089]

[0090] Step Five: While determining the switching frequency change range, the PID module also needs to determine the duty cycle D_pi.

[0091] Therefore, while adjusting the switching frequency fs, the PID module performs PID operations according to the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, and the signal Vo_S representing the magnitude of the output voltage input. The PID operation adjusts the duty cycle D_pi based on the magnitude of the actual input voltage Vin (see the following formula) or the magnitude of the actual output power Po (see the following formula).

[0092] |50% - D _pi | = β 1 ·|V n - V in |

[0093] |50% - D_pi | = β 2 ·|P n -P o |

[0094] Wherein, β 1 is a proportionality coefficient and generally satisfies 0 < α 1 < β 1 , Vn is the nominal input voltage of the converter; wherein, β 2 is a proportionality coefficient and generally satisfies 0 < α 2 < β 2 , Pn is the nominal output voltage of the converter.

[0095] Calculate the corresponding switching duty ratio D_pi of the converter, so that the switching period Ts_pi output by the PID module at this time and the signal Vaux_S representing the output voltage magnitude controlled by the switching duty ratio D_pi of the converter are equal to the reference value Vaux_ref corresponding to the required output voltage, so as to achieve the set constant voltage output. At this time, the switching period Ts_pi and the switching duty ratio D_pi corresponding to Vin_S and Ii_S are stably output to the duty ratio output total module.

[0096] Figure 4 Shows the driving and control logic waveforms of the duty ratio output total module described above with the primary side feedback half-bridge LLC resonant converter as an example under light load conditions. The rising edge and falling edge of the gate pulse of the main switch tube Q2 are symmetrically placed with the rising edge and falling edge of the gate of the main switch tube Q1 to achieve zero voltage switching of Q1 and Q2. Vs1 and Vs2 are control signals generated by adding or subtracting half of the calculated switch-on time Ton plus or minus Vs_max / 2, and this signal generates symmetric gate pulses for Q1 and Q2. The resulting LLC resonant cavity input voltage Va is more symmetrical. Compared with the traditional waveform, this will reduce the peak stress on the circuit components. The resonant capacitor Cr acts as a DC blocking capacitor to prevent DC bias in the high-frequency transformer.

[0097] Repeating the above sampling, mode monitoring, PID precise calculation, and control of the switching method can enable the half-bridge LLC resonant converter to achieve a very wide gain range in the 0-100% load range under a wide input voltage range, and can achieve considerable sampling accuracy and constant voltage accuracy, and the proposed mode can obtain higher conversion efficiency compared with the traditional variable frequency mode through reasonable parameter design.

[0098] Figure 5(b) , 6(b) 、7(b), 8(b) are the working waveforms of the half-bridge LLC resonant converter using the proposed control method under extremely light load conditions of 5% and 10% load as an example, v ais the input voltage of the resonant cavity of the half - bridge LLC resonant circuit, i a is the current of the resonant cavity of the half - bridge LLC resonant circuit. The reason for choosing the extremely light load condition is that in the heavy load condition, the proposed control method is not much different from the traditional frequency modulation (FM) (the duty cycle is close to 50% in both cases), but the zero - voltage switching (ZVS) of the main switch tube of the converter in the worst - case scenario means zero - voltage switching of the main switch tube of the converter under all possible operating conditions. The method and system used in the present invention can also be used in other types of switching power supply circuit structures. Here, only the half - bridge LLC resonant converter using the primary - side feedback technology to sample the output voltage signal is taken as an example. The input of the half - bridge LLC resonant converter is 250 - 500V, the output is a constant voltage of 48V, the nominal output power is 300W, the full - load is 7.68Ω, the effective value of the output current is 6.25A, the size of the resonant capacitor Cr is 32nF, the size of the resonant inductor Lr is 78uH, the circuit quality factor Q is 0.2728 (<0.5), the size of the transformer exciting inductor Lm is 470uH, and the turn ratios of the primary winding, auxiliary winding, and two secondary windings of the transformer are 31 / 2 / 8 / 8. The LLC resonant frequency is 100kHz.

[0099] As a test control, Figure 5(a) 、 6(a) Figures 7(a) and 8(a) are the working waveforms of the half - bridge LLC resonant converter controlled by the traditional frequency modulation (FM) under the extremely light load conditions of 5% and 10% load under the same conditions.

[0100] Figures 5(a) and 5(b) are respectively the working waveforms of the half - bridge LLC resonant converter when using the traditional frequency modulation (FM) and the proposed control method when the load is 10% load and the input is the lowest input voltage of 250V. It can be seen that when using the traditional frequency modulation (FM), at 10% load, the switching frequency drops to f s = 29kHz (f n = 0.29), and at the same time, the ZVS of the main switch tube cannot be achieved; while when using the proposed control method, the switching frequency drops to f s = 63kHz (f n = 0.63), and the effective duty cycle is D eff = 12.5%. The difference between the switching frequency fs of the proposed control method and the resonant frequency f r = 100kHz is only half of that of the frequency modulation (FM), greatly reducing the switching frequency variation range. At the same time, the proposed control method enables the switch tube to achieve zero - voltage switching, thus greatly improving the efficiency.

[0101] Similarly, Fig. 6(a) and Fig. 6(b) are the operating waveforms of the half-bridge LLC resonant converter when the load is 5% and the lowest input voltage is 250V, using traditional frequency modulation (FM) and the proposed control method, respectively. It can be seen that when using traditional frequency modulation (FM), at an ultra-low load of 5%, the switching frequency drops to f s = 28 kHz (f n = 0.28), and at the same time, zero voltage switching (ZVS) of the main switching tube still cannot be achieved; while when using the proposed control method, the switching frequency drops to f s = 62 kHz (f n = 0.62), and the effective duty cycle is D eff = 8.6%. Similar to the 10% load case, the difference between the switching frequency fs of the proposed control method and the resonant frequency f r = 100 kHz is only half of that of frequency modulation (FM), greatly reducing the switching frequency variation range. At the same time, the proposed control method enables the switching tube to achieve zero voltage switching, thus greatly improving the efficiency.

[0102] Fig. 7(a) and Fig. 7(b) are the operating waveforms of the half-bridge LLC resonant converter when the load is 10% and the highest input voltage is 500V, using traditional frequency modulation (FM) and the proposed control method, respectively. It can be seen that under traditional frequency modulation (FM), at a 10% load, if the switching frequency fs is increased to regulate the output voltage, it will rise to f s = 2250 kHz (f n = 22.5), so the control system chooses to reduce the frequency to f s = 22.6 kHz (f n = 0.226) to select the smallest switching frequency variation range, but the switching tube still cannot ensure zero voltage switching at light load. When using the proposed control method at a 10% load, the switching frequency rises to f s = 125 kHz (f n = 1.25), and the effective duty cycle is D eff = 6.9%; the difference between the switching frequency fs of the proposed control method and the resonant frequency f r = 100 kHz is only 1 / 3 of that of frequency modulation (FM), greatly reducing the switching frequency variation range. At the same time, it ensures that the switching tube achieves zero voltage switching, thus greatly improving the converter efficiency.

[0103] Similarly, FIGS. 8(a) and 8(b) respectively show the operating waveforms of a half-bridge LLC resonant converter when the load is 5% and the maximum input voltage is 500V, using traditional frequency modulation (FM) and the proposed control method. It can be seen that when using traditional frequency modulation (FM), at an ultra-low load of 5%, the switching frequency drops to f s = 11 kHz (f n = 0.11), and at the same time, zero-voltage switching (ZVS) of the main switching transistor still cannot be achieved; while when using the proposed control method, the switching frequency drops to f s = 130 kHz (f n = 1.3), and the effective duty cycle is D eff = 4.6%. Similar to the 10% load case, the difference between the switching frequency fs of the proposed control method and the resonant frequency f r = 100 kHz is only 1 / 3 of that of frequency modulation (FM), greatly reducing the range of variation of the switching frequency. At the same time, it ensures that the switching transistors achieve zero-voltage switching, thus greatly improving the efficiency of the converter.

[0104] Figure 9 FIG. is a graph showing the efficiency curves of the half-bridge LLC resonant converter embodiment under light load conditions when using the present invention and traditional variable frequency modulation (FM). Obviously, when using the present invention, the efficiency is greatly improved compared to traditional variable frequency modulation (FM) under light load conditions, especially at the full load condition with the lowest input voltage of 250V and a load of 10%, where the efficiency is increased by 16%.

[0105] As can be seen from the above examples, after adopting the present invention, especially for the half-bridge LLC resonant converter system, when using the proposed control method, the system can greatly reduce the range of variation of the switching frequency in the load range of 0 to 100%, especially under light load conditions, while ensuring that the main switching transistors obtain zero-voltage switching (ZVS), thereby greatly improving the light load efficiency.

[0106] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. The present invention described herein can have many variations (the duty cycle can be equivalent to the conduction time of the switching transistor, the selection of the switching frequency and the duty cycle adjustment method), and such variations cannot deviate from the spirit and scope of the present invention artificially. Therefore, all changes obvious to those skilled in the art are included within the scope covered by this claim.

Claims

1. A high-efficiency wide-input half-bridge LLC resonant converter control system, characterized in that: it includes a sampling module, a mode monitoring module, a PID module, and a duty cycle output total module. The control system is connected to the controlled half-bridge LLC resonant converter switching power supply to form a closed-loop system; the sampling module is used to sample the switching voltage and current of the half-bridge LLC resonant converter; and process the sampled data in combination with the switching period Ts and the switching signals of the two main switching tubes of the half-bridge LLC resonant converter, and output a signal Vo_S representing the magnitude of the output voltage, a signal Vin_S representing the magnitude of the input voltage, and a signal Ii_S representing the magnitude of the input current; the mode monitoring module is used for input voltage range judgment; its inputs are the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, and the switching period Ts, and it outputs a mode switching signal mode_ctrl to the PID module; the inputs of the PID module are the signal Vin_S representing the magnitude of the input voltage, the signal Ii_S representing the magnitude of the input current, the signal Vo_S representing the magnitude of the output voltage, the mode switching signal mode_ctrl, and the switching period Ts; this module is used to calculate the length Ts_pi of the next switching period and the switching duty cycle D_pi under different input voltages and loads; The input of the duty cycle output total module is the switching period Ts_pi and the switching duty cycle D_pi output by the PID module. The switching conduction time Ton and the dead time t are determined according to the switching period Ts_pi and the switching duty cycle D_pi dead , generate duty cycle signals duty1 and duty2, and output a voltage with a changing duty cycle waveform to perform loop control on the gates of the switching tubes of the half-bridge LLC resonant converter; the voltage range judgment performed by the mode monitoring module includes: Define the minimum input voltage V of the half-bridge LLC resonant converter in_min_th , as follows: V in_min_th = 2·n·V o (1) where Vo is the output equivalent voltage, and n is the ratio of the number of turns Np of the primary winding of the transformer in the half-bridge LLC resonant converter to the number of turns Ns1 or Ns2 of the secondary winding, that is: When the actual input voltage Vin is greater than the minimum input voltage V in_min_th , the mode switching signal mode_ctrl is set to 1; When the actual input voltage Vin is less than or equal to the minimum input voltage V in_min_th , the mode switching signal mode_ctrl is set to 2.

2. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 1, characterized in that: the sampling module includes a sampling circuit and a sampling control module. The input of the sampling circuit is the analog quantity Vo_sense representing the magnitude of the output voltage, the analog quantity Vin_sense representing the magnitude of the input voltage, and the analog quantity Ii_sense representing the magnitude of the input current of the half-bridge LLC resonant converter, and outputs them to the sampling control module; the sampling control module processes the input data and outputs a signal Vo_S representing the magnitude of the output voltage, a signal Vin_S representing the magnitude of the input voltage, and a signal Ii_S representing the magnitude of the input current.

3. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 2, characterized in that: The sampling control module uses the resistor-divided ADC_Vaux of the primary auxiliary winding voltage in the converter. Taking the magnitude Vaux_min of the lowest ADC_Vaux corresponding to different input voltages as the judgment reference, it intercepts the part greater than Vaux_min. According to the input switching period signal T_ctrl, it compares the two floating discrete values Vaux_1 and Vaux_2 that intercept part of the peak value according to the switching tube duty cycle signal rule within each switching period. When Vaux_1 is higher than or equal to Vaux_2, the comparison result is output as Vaux_1; when Vaux_1 is lower than Vaux_2, the comparison result is output as Vaux_2. This comparison result is the maximum value Vaux_max of the intercepted part of the peak ADC_Vaux within each switching period. Connecting the Vaux_max of each sampling period together is an output of the sampling control module: the auxiliary winding voltage signal Vaux_S representing the output voltage information, that is, the signal Vo_S representing the magnitude of the output voltage.

4. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 1, characterized in that: The PID module calculates the next switching period length Ts_pi and the switching duty cycle D_pi under different input voltages and loads, specifically including: Setting the initial value of the switching frequency of the PID module to the resonant frequency fr and the duty cycle to 50%; Calculate the maximum value \(f\) of the switching frequency variation range s_max_FM and the minimum value \(f\) s_min_FM ; Based on the switching frequency change range, starting from the resonant frequency fr, the switching frequency fs is adjusted under the mode switching signal; Determine the switching period Ts_pi based on the switching frequency fs; that is Based on the magnitude of the actual input voltage Vin or the magnitude of the actual output power Po, the duty cycle D_pi is determined.

5. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 4, characterized in that, The resonant frequency is: Wherein, L r is the resonant inductor, and C r is the resonant capacitor.

6. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 4, characterized in that, The maximum value f s_max_FM and the minimum value f s_min_FM of the switching frequency change range are as follows: where k is the inductance ratio coefficient, L r is the resonant inductor, and L m is the exciting inductor of the transformer. G max and G min are the maximum and minimum gains of the converter, respectively. V in_min and V in_max are the minimum and maximum input voltages set for the converter, respectively.

7. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 4, characterized in that, The adjustment of the switching frequency fs under the mode switching signal specifically includes: When the PID module receives the mode switching signal mode_ctrl set to 2: Set the adjustment range of the switching frequency fs to f s_min_FM < f s ≤ f r , and at the same time, starting from fr, decrease the switching frequency fs within the adjustment range of f s_min_FM < f s ≤ f r and adjust the switching frequency fs according to the following formula; |f r -f s | = α 1 ·|V n -V in |; |f r -f s | = α 2 ·|P n -P o |; (8) where α 1 is a proportionality coefficient and greater than 0, and Vn is the nominal input voltage; α 2 is a proportionality coefficient and greater than 0, Pn is the nominal output voltage, Vin is the magnitude of the actual input voltage, i.e., Vin_S, and Po is the magnitude of the actual output power; When the PID module receives the mode switching signal mode_ctrl which is set to 1: set the adjustment range of the switching frequency fs to f s_min_FM < f s < f s_max_FM , if the signal Vin_S representing the magnitude of the input voltage is less than the reference value Vn_ref corresponding to the nominal voltage Vn of the half-bridge LLC resonant converter circuit, starting from fr, the switching frequency fs will decrease within the adjustment range of f s_min_FM < f s ≤ f r and the switching frequency fs is adjusted based on the following formula; |f r -f s | = α 1 ·|V n -V in | |f r -f s | = α 2 ·|P n -P o | (9) If the signal Vin_S representing the magnitude of the input voltage is greater than or equal to the reference value Vn_ref corresponding to the nominal voltage Vn of the half-bridge LLC resonant converter circuit, the switching frequency fs starts from fr, and f r ≤f s <f s_max_FM rises within the adjustment range, and the switching frequency fs is adjusted based on the above formula.

8. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 4, characterized in that, The duty cycle D_pi is: |50%-D _pi | = β 1 ·|V n -V in |; |50%-D _pi | = β 2 ·|P n -P o |; (10) Wherein, β 1 is a proportionality coefficient and satisfies 0 < α 1 < β 1 , Vn is the nominal input voltage of the converter, and β 2 is a proportionality coefficient and satisfies 0 < α 2 < β 2 , and Pn is the nominal output voltage of the converter.

9. The high-efficiency wide-input half-bridge LLC resonant converter control system according to claim 4, characterized in that, The duty cycle output total module includes a duty cycle generation module and a driving module. The inputs of the duty cycle generation module are the switching period Ts_pi and the switching duty cycle D_pi output by the PID module. The duty cycle generation module calculates the switch-on time Ton and the dead time t according to the switching period Ts_pi and the switching duty cycle D_pi dead , and generates the output duty cycle signals duty1 and duty2.

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