Control method of LLC resonant converter and related device

Abstract

The invention discloses a control method of an LLC resonant converter, and the method comprises the steps: controlling the LLC resonant converter through a PFM mode and a Burst mode when the switching frequency is smaller than or equal to the maximum switching frequency, and controlling the LLC resonant converter to stably output a target voltage in a mode of adjusting the switching frequency within the limiting range of the maximum switching frequency. And when the switching frequency is greater than the maximum switching frequency, controlling the LLC resonant converter through a PWM mode and a Burst mode, and controlling the LLC resonant converter to stably output the target voltage through a mode of adjusting the duty ratio of a driving signal. According to the LLC resonant converter, the advantages of symmetric PWM and Brust are combined, stable output of the LLC resonant converter is achieved, the switching frequency is effectively reduced, and the situation that due to the fact that the switching frequency is too large, the switching frequency greatly exceeds the designed frequency is avoided. By combining the advantages of the three modes, the switching loss can be reduced on the basis of widening and adjusting the output voltage range.

Description

Technical Field

[0001] The present application relates to the technical field, and in particular to a control method and related device of an LLC resonant converter. Background Art

[0002] Non-vehicle DC charging piles have become the preferred charging facilities for large charging stations due to their safety, reliability, fast charging, and high power. As an important component of a DC charging pile, the power unit is usually an AC / DC module composed of Vienna in the front stage and a DC / DC module composed of LLC resonant converter in the back stage.

[0003] However, in practical applications, the load state is variable and it is difficult for the LLC resonant converter to maintain a stable output voltage when the load changes. Summary of the invention

[0004] In view of this, the present application provides a control method and related device of an LLC resonant converter.

[0005] In a first aspect, an embodiment of the present application provides a control method for an LLC resonant converter, comprising:

[0006] Obtaining a switching frequency of an LLC resonant converter; the switching frequency is determined according to an output voltage and an output current of the LLC resonant converter;

[0007] When the switching frequency is less than or equal to the maximum switching frequency, the LLC resonant converter is controlled by a first hybrid mode so that the LLC resonant converter outputs a target voltage; the first hybrid mode includes a pulse frequency modulation PFM mode and a hiccup Brust mode;

[0008] When the switching frequency is greater than the maximum switching frequency, the LLC resonant converter is controlled by a second hybrid mode so that the LLC resonant converter outputs the target voltage; the second hybrid mode includes a symmetrical pulse width modulation (PWM) mode and the Brust mode.

[0009] In a possible implementation, the adopting the first hybrid mode to control the LLC resonant converter includes:

[0010] When a first preset condition is met, controlling the switching frequency of the LLC resonant converter through the PFM mode so that the LLC resonant converter outputs the target voltage;

[0011] Alternatively, when a second preset condition is met, the switch tube in the LLC resonant converter is controlled to be disconnected through the Brust mode, so that the LLC resonant converter outputs the target voltage.

[0012] In a possible implementation, the adopting the second hybrid mode to control the LLC resonant converter includes:

[0013] When a first preset condition is met, controlling the duty cycle of the driving signal of the LLC resonant converter through the PWM mode so that the LLC resonant converter outputs the target voltage;

[0014] Alternatively, when a second preset condition is met, the switch tube in the LLC resonant converter is controlled to be disconnected through the Brust mode, so that the LLC resonant converter outputs the target voltage.

[0015] In a possible implementation, the first preset condition includes: the output current of the LLC resonant converter is greater than or equal to a first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0; or, the output current of the LLC resonant converter is greater than or equal to the first reference current, and the difference between the target voltage and the output voltage is less than 0; or, the output current of the LLC resonant converter is less than the first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0;

[0016] The second preset condition is that the output current is less than the first reference current, and the difference between the target voltage and the output voltage is less than 0;

[0017] Wherein, the first reference current is determined according to the target voltage.

[0018] In a possible implementation manner, when the first preset condition is that the output current of the LLC resonant converter is greater than or equal to the first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0, controlling the switching frequency of the LLC resonant converter by the PFM mode includes:

[0019] Controlling the switching frequency of the LLC resonant converter to decrease by the PFM mode;

[0020] When the first preset condition is that the output current of the LLC resonant converter is greater than or equal to a first reference current, and the difference between the target voltage and the output voltage is less than 0, controlling the switching frequency of the LLC resonant converter by the PFM mode includes:

[0021] Controlling the switching frequency of the LLC resonant converter to increase through the PFM mode;

[0022] When the first preset condition is that the output current is less than the first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0, controlling the switching frequency of the LLC resonant converter by the PFM mode includes:

[0023] The switching frequency of the LLC resonant converter is increased by controlling the PFM mode.

[0024] In a possible implementation manner, controlling the duty cycle value of the driving signal of the LLC resonant converter by using the PWM mode includes:

[0025] Using the difference between the target voltage and the output voltage as an input of a voltage PI regulator to obtain a second reference current;

[0026] The difference between the second reference current and the output current is used as an input of a current PI regulator to obtain the duty cycle value.

[0027] In a possible implementation, the duty cycle value is less than 0.5, and the duty cycle value is greater than a minimum duty cycle value; wherein the minimum duty cycle value is a minimum duty cycle capable of maintaining a soft switching state.

[0028] In a possible implementation, obtaining the switching frequency of the LLC resonant converter includes:

[0029] Determining a voltage loop switching frequency and a current loop switching frequency of the LLC resonant converter;

[0030] The minimum value between the voltage loop switching frequency and the current loop switching frequency is used as the switching frequency.

[0031] In a possible implementation, determining the voltage loop switching frequency and the current loop switching frequency of the LLC resonant converter includes:

[0032] obtaining the output voltage and the output current;

[0033] Using the difference between the output voltage and the target voltage as the input of the voltage PI regulator to obtain the voltage loop switching frequency;

[0034] The difference between the output current and the second reference current is used as an input of the current PI regulator to obtain the current loop switching frequency; the second reference current is determined according to the target voltage and the rated power of the LLC resonant converter.

[0035] In a second aspect, an embodiment of the present application provides an LLC resonant converter, comprising a primary circuit, a secondary circuit, a resonant circuit, a transformer and a controller; the primary circuit is connected to a primary winding of the transformer through the resonant circuit, and the secondary circuit is connected to a secondary winding of the transformer;

[0036] The controller is used to execute the method as described in any one of the first aspects to control the LLC resonant converter.

[0037] In a third aspect, an embodiment of the present application provides a control device, characterized in that it includes a processor and a memory, the memory is used to store programs, instructions or codes, and the processor is used to execute the programs, instructions or codes in the memory to complete the control method of the LLC resonant converter as described in any one of the first aspects.

[0038] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium, characterized in that a computer program is stored therein, and the computer program is loaded by a processor to execute the control method of the LLC resonant converter as described in any one of the first aspects.

[0039] The embodiment of the present application provides a control method for an LLC resonant converter, which combines the switching frequency and maximum switching frequency of the LLC resonant converter to control the LLC resonant converter in different modes. When the switching frequency is less than or equal to the maximum switching frequency, the LLC resonant converter is controlled by the PFM mode and the Burst mode, and within the limit of the maximum switching frequency, the LLC resonant converter is controlled to stably output the target voltage by adjusting the switching frequency. When the switching frequency is greater than the maximum switching frequency, the LLC resonant converter is controlled by the PWM mode and the Burst mode, and the LLC resonant converter is controlled to stably output the target voltage by adjusting the duty cycle of the drive signal. In the embodiment of the present application, the advantages of symmetrical PWM and Brust are combined, while achieving the stable output of the LLC resonant converter, the switching frequency is effectively reduced to avoid excessive switching frequency, which causes the switching frequency to greatly exceed the designed frequency. Combining the advantages of these three modes, the switching loss can be reduced on the basis of widening the range of the adjustable output voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A topological diagram of an LLC resonant converter provided in an embodiment of the present application;

[0041] Figure 2 A flow chart of a control method for an LLC resonant converter provided in an embodiment of the present application;

[0042] Figure 3 A schematic diagram of a control method for an LLC resonant converter provided in an embodiment of the present application;

[0043] Figure 4 A schematic diagram of an implementation process of controlling a duty cycle value D in a symmetrical PWM mode provided in an embodiment of the present application;

[0044] Figure 5 A control device for an LLC resonant converter is provided in an embodiment of the present application. DETAILED DESCRIPTION

[0045] The LLC resonant converter consists of a resonant inductor (Lr), a resonant capacitor (Cr) and a transformer (Tr). Efficient power conversion is achieved through the coupling of the resonant inductor, the resonant capacitor and the transformer. In the LLC resonant converter, the resonant inductor and the resonant capacitor form an LC resonant circuit. The LC resonant circuit can produce resonance at a specific switching frequency. By adjusting the switching frequency, the working state of the resonant circuit can be changed, thereby controlling the output voltage of the LLC resonant converter.

[0046] When facing different load conditions, that is, facing different voltage requirements, the LLC resonant converter can be controlled by adjusting the switching frequency to output the corresponding voltage. However, under some special working conditions (such as low voltage or light load), the LLC resonant converter cannot stably output the specified voltage by changing the switching frequency.

[0047] For example, under light load conditions, the load current of the LLC resonant converter is small and the impedance of the resonant circuit is high. The switching frequency needs to be increased to improve the power conversion efficiency of the LLC resonant converter. However, as the switching frequency increases, the resonance point of the resonant circuit may shift, causing the switching frequency to weaken the gain regulation effect or even cause imbalance, which in turn causes the output voltage of the LLC resonant converter to be unstable.

[0048] In view of this technical problem, the embodiment of the present application provides a control method for an LLC resonant converter, which combines the switching frequency and the maximum switching frequency of the LLC resonant converter, and uses different modes to control the LLC resonant converter. When the switching frequency is less than or equal to the maximum switching frequency, the LLC resonant converter is controlled by the pulse frequency modulation (Pulse Frequency Modulation, PFM) mode and the hiccup (Burst) mode, and within the limit range of the maximum switching frequency, the LLC resonant converter is controlled to output the target voltage stably by adjusting the switching frequency. When the switching frequency is greater than the maximum switching frequency, the LLC resonant converter is controlled by the symmetric pulse width modulation (Symmetric Pulse Width Modulation, PWM) mode and the Burst mode, and the LLC resonant converter is controlled to output the target voltage stably by adjusting the duty cycle of the drive signal. In the embodiment of the present application, combining the advantages of symmetrical PWM and Brust, while achieving the stable output of the LLC resonant converter, the switching frequency is effectively reduced to avoid excessive switching frequency, which causes the switching frequency to greatly exceed the designed frequency. Combining the advantages of these three modes, the switching loss can be reduced on the basis of widening the range of the output voltage adjustment.

[0049] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the embodiments of the present application are further described in detail below in combination with the accompanying drawings and specific implementation methods.

[0050] Exemplarily, an embodiment of the present application provides a topology diagram of an LLC resonant converter, such as Figure 1 shown.

[0051] The LLC resonant converter includes a primary circuit, a secondary circuit, a resonant circuit and a transformer; the primary circuit is connected to the primary winding of the transformer through the resonant circuit, and the secondary circuit is connected to the complex winding of the transformer. The specific connection relationship is as follows:

[0052] The first switch tube Q1 and the second switch tube Q2 are connected in series to form a first bridge arm, the third switch tube Q3 and the fourth switch tube Q4 are connected in series to form a second bridge arm, and the fifth switch tube Q5 and the sixth switch tube Q6 are connected in series to form a third bridge arm; the first bridge arm, the second bridge arm, the third bridge arm and the first capacitor C1 are connected in parallel.

[0053] One end of the second capacitor C2 is connected to a common point between the first switch tube Q1 and the second switch tube Q2, and the other end of the second capacitor C2 is connected to one end of the first inductor L1; the other end of the first inductor L1 is connected to the first end of the primary winding of the winding T1.

[0054] One end of the third capacitor C3 is connected to the common point between the third switch tube Q3 and the fourth switch tube Q4, and the other end of the third capacitor C3 is connected to one end of the second inductor L2; the other end of the second inductor L2 is connected to the first end of the primary winding of the winding T2.

[0055] One end of the fourth capacitor C4 is connected to the common point between the fifth switch tube Q5 and the sixth switch tube Q6, and the other end of the fourth capacitor C4 is connected to one end of the third inductor L3; the other end of the third inductor L3 is connected to the first end of the primary winding of the winding T3.

[0056] The second end of the primary winding of winding T1 , the second end of the primary winding of winding T2 , and the second end of the primary winding of winding T3 are connected.

[0057] The anode of the first diode D1 and the cathode of the second diode D2 are connected to form a fourth bridge arm, the anode of the third diode D3 and the cathode of the fourth diode D4 are connected to form a fifth bridge arm, and the anode of the fifth diode D5 and the cathode of the sixth diode D6 are connected to form a sixth bridge arm; the fourth bridge arm, the fifth bridge arm, the sixth bridge arm and the fifth capacitor C5 are connected in parallel.

[0058] The first end of the secondary winding of winding T1 is connected between the anode of the first diode D1 and the cathode of the second diode D2, the first end of the secondary winding of winding T2 is connected between the anode of the third diode D3 and the cathode of the fourth diode D4, and the first end of the secondary winding of winding T3 is connected between the anode of the fifth diode D5 and the cathode of the sixth diode D6.

[0059] The second end of the secondary winding of the winding T1 , the second end of the secondary winding of the winding T2 , and the second end of the secondary winding of the winding T3 are connected.

[0060] The switching frequencies of the first switch tube Q1 , the second switch tube Q2 , the third switch tube Q3 , the fourth switch tube Q4 , the fifth switch tube Q5 and the sixth switch tube Q6 are the same, and the driving signals of the switch tubes are also the same.

[0061] like Figure 2 As shown, Figure 2 A control method for an LLC resonant converter provided in an embodiment of the present application includes:

[0062] S201: Obtain the switching frequency f of the LLC resonant converter S .

[0063] Switching frequency f S Refers to the number of times the switch tube in the LLC resonant converter switches on and off per second. The switching frequency is one of the key parameters of the LLC resonant converter operation and has a direct impact on the performance, efficiency and stability of the LLC resonant converter. Switching frequency f SThe selection and adjustment of mainly depends on the output voltage U and output current I of LLC resonant converter. The current switching frequency f of LLC resonant converter S It can be determined based on the current output voltage U and output current I of the LLC resonant converter. Figure 1 The switching frequencies of the various switching tubes shown are the same, so the switching frequency of a certain switching tube only needs to be determined in step S201.

[0064] like Figure 3 As shown, in the embodiment of the present application, the output voltage U of the LLC resonant converter and the target voltage U ref Determine the voltage loop switching frequency f US , and based on the output current I of the LLC resonant converter and the second reference current I ref Determine the current loop switching frequency f IS , and then according to the voltage loop switching frequency f US and the current loop switching frequency f IS Determine the switching frequency f S .

[0065] Specifically, the output voltage U and output current I of the LLC resonant converter are determined; then the target voltage U ref The voltage error △U of the output voltage U is used as the input of the voltage PI (proportional-integral) regulator to obtain the voltage loop switching frequency f US ; and the second reference current I ref The current error △I of the output current I is used as the input of the current PI (proportional-integral) regulator to obtain the current loop switching frequency f IS ; Finally, the voltage loop switching frequency f US and the current loop switching frequency f IS The minimum value among them is taken as the switching frequency f S .

[0066] In the above process, the target voltage U ref It refers to the required voltage of the load, which is the voltage that the LLC resonant controller needs to output stably. ref It can be a value or a range of values. The embodiment of the present application controls the LLC resonant controller so that the LLC resonant controller can stably output the target voltage U ref The output voltage U is the actual output voltage of the LLC resonant converter, and the output current I is the actual output current of the LLC resonant converter. The second reference current I ref It is determined based on the target voltage and the rated power of the LLC resonant converter, that is, the output current when the output power of the LLC resonant converter is the rated power and the output voltage is the target voltage.

[0067] Voltage loop switching frequency f US It is the switching frequency calculated by the voltage PI regulator and is used as a reference to adjust the switching frequency of the LLC resonant converter so that the output voltage U reaches the target voltage U ref . Voltage loop switching frequency f US Reflects the need to adjust the output voltage U to the target voltage U ref The required switching frequency adjustment. Similarly, the current loop switching frequency f IS It is the switching frequency calculated by the current PI regulator and is used to adjust the switching frequency of the LLC resonant converter so that the output current I reaches the second reference current I ref . Current loop switching frequency f IS Reflects the need to adjust the output current I to the second reference current I ref The amount of switching frequency adjustment required.

[0068] Since the voltage loop switching frequency f US and the current loop switching frequency f IS The difference may be large. Directly using a larger switching frequency may lead to increased switching losses, and the characteristics of the resonant circuit may deviate from the design expectations, affecting system performance. Therefore, in the embodiment of the present application, the smaller of the voltage loop switching frequency and the current loop switching frequency is selected as the switching frequency f S For reference (ie MIN_F(f Us ,f Is )) to avoid excessive switching losses and gain curve imbalance caused by too high switching frequency. By selecting the voltage loop switching frequency f US and the current loop switching frequency f IS The minimum value in can balance the needs of voltage control and current control to a certain extent and ensure a balance between the two. In addition, a lower switching frequency usually helps to achieve soft switching, thereby reducing switching losses and electromagnetic interference. Selecting the minimum value can ensure that the switching frequency is within the acceptable range of soft switching, thereby improving the efficiency and reliability of the system.

[0069] After determining the switching frequency of the LLC resonant converter, compare the switching frequency f S With the maximum switching frequency f max When the switching frequency f S Less than or equal to the maximum switching frequency f max When the switching frequency f S is greater than the maximum switching frequency f max , execute step S203.

[0070] Maximum switching frequency f maxRefers to the highest switching frequency allowed in the design and operation of the LLC resonant converter. This frequency is the maximum switching frequency that the converter can achieve within the range of safe and effective operation.

[0071] S202: Control the LLC resonant converter using a first hybrid mode.

[0072] When the switching frequency f of the LLC resonant converter S Less than or equal to the maximum switching frequency f max When the LLC resonant converter is switched at the current frequency f S The maximum value does not exceed the specified value. Therefore, the output voltage of the LLC resonant converter can be controlled by adjusting the switching frequency. In the process of adjusting the switching frequency, the duty cycle value can be kept unchanged, that is, Figure 1 The duty cycle value of the driving signal of each switching tube shown remains unchanged.

[0073] In the embodiment of the present application, the first hybrid mode includes the PFM mode and the Brust mode.

[0074] PFM mode is a method of controlling the output power by adjusting the switching frequency. In this mode, the switching frequency is not fixed, but dynamically adjusted according to the actual demand of the load.

[0075] Brust mode is a method of controlling the LLC resonant converter by controlling the switch tube in the LLC resonant converter. Under light load or no-load conditions, Brust mode reduces power consumption by reducing the switching time, and no switching operation is performed during the off cycle, thereby significantly reducing switching losses.

[0076] Based on the above two modes, at the switching frequency f S Less than or equal to the maximum switching frequency f max In this case, the LLC resonant converter is controlled by a hybrid mode of PFM mode and Brust mode. The output voltage of the LLC resonant converter can be dynamically adjusted according to the actual load conditions and energy efficiency requirements, thereby optimizing the performance and reliability of the converter. In this way, the LLC resonant converter can not only efficiently cope with various load conditions, but also stably output the target voltage U ref ; It can also effectively reduce power consumption and switching losses under light load, and improve the overall performance and stability of the system.

[0077] Based on step S202, the embodiment of the present application further provides how to control the LLC resonant converter using the first hybrid mode, as follows:

[0078] When the first preset condition is met, the switching frequency f of the LLC resonant converter is controlled by the PFM mode.S , so that the LLC resonant converter outputs the target voltage U ref ;

[0079] Alternatively, when the second preset condition is met, the switch tube in the LLC resonant converter is disconnected by controlling the Brust mode so that the LLC resonant converter outputs the target voltage U ref .

[0080] When the first preset condition is met, the switching frequency f S It will be adjusted according to actual needs so that the output voltage of the LLC resonant converter reaches the target voltage U ref . That is, synchronous regulation Figure 1 The switching frequency of each switch tube in the LLC resonant converter is shown.

[0081] When the second preset condition is met, the switch tube of the LLC resonant converter is disconnected through the Brust mode, thereby quickly reducing the output voltage of the LLC resonant converter, thereby adjusting the output voltage. Figure 1 The switching frequency of each switch tube in the LLC resonant converter is shown.

[0082] The first preset condition includes, for example:

[0083] The output current I of the LLC resonant converter is greater than or equal to the first reference current I N , and the target voltage U ref The difference with the output voltage U is greater than or equal to 0;

[0084] Alternatively, the output current I of the LLC resonant converter is greater than or equal to the first reference current I N , and the target voltage U ref The difference with the output voltage U is less than 0;

[0085] Alternatively, the output current I of the LLC resonant converter is less than the first reference current I N , and the target voltage U ref The difference with the output voltage U is greater than or equal to 0.

[0086] The second preset condition includes, for example:

[0087] The output current I is less than the first reference current I N , and the target voltage U ref The difference with the output voltage U is less than 0.

[0088] When the switching frequency f of the LLC resonant converter S Less than or equal to the maximum switching frequency f max, and the output condition of the LLC resonant converter satisfies any one of the first preset conditions, that is, the LLC resonant converter is controlled by the PFM mode.

[0089] Among them, the first reference current I N Equal to M times the second reference current I ref The value of M can be determined according to the actual working condition or load condition. The second reference current I ref Based on the target voltage U ref and the rated power of the LLC resonant converter, therefore, it can be understood as the first reference current I N According to the target voltage U ref As an example, the first reference current I N =0.2*second reference current I ref .

[0090] In the above process, the first reference current I N As a reference standard. When the output current I is greater than or equal to the first reference current I N When the LLC resonant converter outputs a higher current (higher load conditions), the PFM mode can dynamically adjust the switching frequency to maintain a stable output voltage and current while optimizing the converter efficiency.

[0091] When the output current I is less than the first reference current I N When the output voltage U is further compared with the target voltage U ref If the target voltage U ref The difference with the output voltage U is greater than or equal to 0, that is, the target voltage U ref -Output voltage U≥0, that is, the current output voltage is smaller than the expected target voltage, or the current output voltage is equal to the expected target voltage. At this time, the load is light, and the PFM mode can provide more precise voltage regulation and improve the overall efficiency of the system.

[0092] If the target voltage U ref The difference with the output voltage U is less than 0, that is, the target voltage U ref - Output voltage U<0, that is, the current output voltage is greater than the expected target voltage, then it can be switched to Brust mode, directly turning off the switch tube in the LLC resonant converter, reducing switching losses and maintaining low power consumption.

[0093] Through the above method, the most appropriate control mode can be flexibly selected to control the LLC resonant converter under different load conditions and voltage requirements, so that the LLC resonant converter can stably output the target voltage, and the power consumption of the LLC resonant converter can also be optimized.

[0094] Furthermore, when the output current of the LLC resonant converter is greater than or equal to the first reference current I N In the case of ref The difference between the switching frequencies can be used to fine-tune the switching frequency, as follows:

[0095] At the target voltage U ref When the difference between the output voltage U of the LLC resonant converter is greater than or equal to 0, the target voltage U ref -Output voltage U≥0, switching frequency f controlled by PFM mode S reduce;

[0096] At the target voltage U ref When the difference with the output voltage U is less than 0, that is, the target voltage U ref -Output voltage U<0, switching frequency f is controlled by PFM mode S Increase.

[0097] If the target voltage U ref The difference between the output voltage U of the LLC resonant converter is greater than or equal to 0, that is, the target voltage U ref When it is greater than or equal to the current output voltage U, it means that the output voltage U needs to be increased. In PFM mode, by reducing the switching frequency f S , which can increase the gain of the LLC resonant converter, thereby helping to increase the output voltage U to the target voltage U ref .

[0098] Similarly, if the target voltage U ref The difference between the output voltage U of the LLC resonant converter is less than 0, that is, the target voltage U ref When it is less than the current output voltage U, it means that the output voltage U needs to be reduced. In PFM mode, by increasing the switching frequency f S , the gain of the LLC resonant converter can be reduced, thereby reducing the output voltage U to the target voltage U ref .

[0099] It should be noted that the control switching frequency f S During the process, the duty cycle value of the driving signal of the LLC resonant converter remains unchanged.

[0100] It can be understood that in the above process of controlling the LLC resonant converter based on the PFM mode, when the target voltage U ref The difference obtained by subtracting the output voltage U is positive and the larger the difference is, the higher the switching frequency f S Adjust to a smaller value; when the target voltage U ref The difference obtained by subtracting the output voltage U is negative and the smaller the difference is, the higher the switching frequency fS Adjust to a larger value.

[0101] In the above process, the LLC resonant converter is allowed to operate under heavy load according to the target voltage U ref The real-time difference between the output voltage U and the switching frequency f is dynamically adjusted. S , to achieve precise voltage control and efficient energy conversion. Through the flexible application of PFM mode, it can ensure that the converter can provide stable output voltage under different working conditions and optimize the overall system performance.

[0102] S203: Control the LLC resonant converter using a second hybrid mode.

[0103] When the switching frequency f of the LLC resonant converter S Greater than the maximum switching frequency f max When the LLC resonant converter is switched at the current frequency f S The maximum value has been exceeded. Therefore, if the output voltage of the LLC resonant converter is controlled by adjusting the switching frequency, the components of the LLC resonant converter may overheat and the stability may be reduced.

[0104] In the embodiment of the present application, the second hybrid mode includes a symmetrical PWM mode and a Brust mode.

[0105] Symmetrical PWM mode is a pulse width modulation control technique commonly used to control power converters and motor drives. It uses a symmetrical pulse width modulation signal, in which the pulse width of each cycle has equal rise and fall times around the symmetry point. That is, the high level time (pulse width) and low level time (idle time) of the drive signal are symmetrical within one cycle.

[0106] Based on the above two modes, when the symmetrical PWM mode is adopted, by increasing the switching frequency f S Maintain a fixed value within the design frequency range, that is, the switching frequency f S Fixed to be less than or equal to the maximum switching frequency f max Then, the output voltage is controlled by adjusting the duty cycle of the driving signal to ensure that the LLC resonant converter can provide the required voltage output when the load changes. Brust mode control can also be used at light loads, which can effectively reduce power consumption and switching losses and improve the overall efficiency and stability of the system.

[0107] In a possible implementation, when the symmetrical PWM mode control is adopted, the switching frequency f S Fixed to the maximum switching frequency f maxAt this fixed frequency, the output voltage is controlled by adjusting the duty cycle of the drive signal to keep the LLC resonant converter outputting a stable voltage within a safe operating range.

[0108] Based on step S203, the embodiment of the present application further provides how to control the LLC resonant converter using the second hybrid mode, as follows:

[0109] When the first preset condition is met, the duty cycle of the driving signal of the LLC resonant converter is controlled by the symmetrical PWM mode so that the LLC resonant converter outputs the target voltage U ref ;

[0110] Alternatively, when the second preset condition is met, the switch tube in the LLC resonant converter is disconnected by controlling the Brust mode so that the LLC resonant converter outputs the target voltage U ref .

[0111] When the first preset condition D is met, the duty cycle value of the LLC resonant converter drive signal is adjusted according to actual needs through the symmetrical PWM mode so that the output voltage of the LLC resonant converter reaches the target voltage U ref .

[0112] When the second preset condition is met, the switch tube of the LLC resonant converter is disconnected through the Brust mode, thereby quickly reducing the output voltage of the LLC resonant converter, thereby adjusting the output voltage.

[0113] Among them, the first preset condition is the same as the first preset condition introduced in step S202, and the second preset condition is also the same as the second preset condition introduced in step S202, which will not be repeated here.

[0114] When the output current I of the LLC resonant converter is greater than or equal to the first reference current I N In the case of , the duty cycle value D of the driving signal of the LLC resonant converter is controlled by the symmetrical PWM mode;

[0115] When the output current I is less than the first reference current I N , and the target voltage U ref When the difference with the output voltage U is greater than or equal to 0, the duty cycle value D is controlled by the symmetrical PWM mode;

[0116] When the output current I is less than the first reference current I N , and the target voltage U ref When the difference with the output voltage U is less than 0, the switching frequency f is controlled by the Brust mode S .

[0117] In the embodiment of the present application, the first reference current I N As a reference standard. When the output current I is greater than or equal to the first reference current I N When the LLC resonant converter outputs a high current (high load condition), the symmetrical PWM mode can be used to stabilize the output voltage U by adjusting the duty cycle value D. The symmetrical PWM mode can control the output voltage U by changing the pulse width at a fixed switching frequency, ensuring the stability and effectiveness of the LLC resonant converter under high load conditions. When adjusting the duty cycle value of the drive signal, the same is true for synchronous adjustment. Figure 1 The duty cycle value of the driving signal of each switch tube is shown.

[0118] When the output current I is less than the first reference current I N When the output voltage U is further compared with the target voltage U ref If the target voltage U ref The difference with the output voltage U is greater than or equal to 0, that is, the target voltage U ref -Output voltage U≥0, that is, the current output voltage is smaller than the expected target voltage, or the current output voltage is equal to the expected target voltage. At this time, the load is light, and the symmetrical PWM mode can provide more precise voltage regulation and improve the overall efficiency of the system.

[0119] If the target voltage U ref The difference with the output voltage U is less than 0, that is, the target voltage U ref - If the output voltage U is less than 0, that is, the current output voltage is greater than the target voltage expected to be output, it can be switched to Brust mode to directly turn off the switch tube in the LLC resonant converter, reduce switching losses, and maintain low power consumption.

[0120] In the above process of controlling LLC resonant converter based on PWM mode, when the target voltage U ref The difference obtained by subtracting the output voltage U is positive and the larger the difference is, the larger the duty cycle value D is adjusted to; when the target voltage U ref The difference obtained by subtracting the output voltage U is negative and the smaller the difference is, the larger the duty cycle value D is adjusted to.

[0121] It should be noted that in the process of controlling the duty cycle value D through the symmetrical PFM mode, the switching frequency f of the LLC resonant converter is controlled. S Equal to the maximum switching frequency f max .

[0122] In the above process, by real-time monitoring and mode switching of the LLC resonant converter's operating status, accurate voltage and current control can be achieved under different load conditions. When the output current is high, the symmetrical PWM mode is used to stabilize the system; when the load is light and the relationship between the target voltage and the output voltage is different, it is switched to the symmetrical PWM mode or Brust mode in time to optimize energy efficiency and control performance. This hybrid control strategy can effectively improve the flexibility, stability and overall efficiency of the system.

[0123] The embodiment of the present application also provides an implementation process of controlling the duty cycle value D in the symmetrical PWM mode, as follows: Figure 4 shown.

[0124] The target voltage U ref The voltage error △U with the output voltage U is used as the input of the voltage PI regulator to obtain the second reference current I ref ;

[0125] The second reference current I ref The current error △I with the output current I is used as the input of the current PI regulator to obtain the duty cycle value D.

[0126] In the above process, firstly according to the target voltage U ref Calculate the voltage error △U (△U=U ref -U), and use the voltage error △U as the input of the voltage PI regulator, and use the voltage PI regulator to calculate the second reference current I according to the voltage error △U ref Then, according to the second reference current I ref Calculate the current error △I (△I=I ref -I), the current PI regulator is used to calculate the duty cycle value D according to the current error △I, and then the driving signal (PWM signal) of the LLC resonant converter is controlled according to the duty cycle value D. In the symmetrical PWM mode, the duty cycle value D determines the high level duration of the driving signal, thereby controlling the output voltage of the LLC resonant converter.

[0127] In one possible implementation, the minimum duty cycle value D min <Duty cycle value D<0.5, where. Minimum duty cycle value D min The duty cycle D is the minimum duty cycle that can maintain the soft switching state. In the embodiment of the present application, the duty cycle value D is adjusted in real time according to the output of the LLC resonant converter and the load demand, and the duty cycle value D is maintained within a set range to prevent the duty cycle value from being lower than the minimum value or exceeding the safety range, thereby protecting the normal operation of the LLC resonant converter.

[0128] The PI regulator is a commonly used control strategy for adjusting system errors. P is used to reduce system deviations, and I is used to eliminate steady-state errors. For a specific topology, testers can adjust the PI value based on the specific topology.

[0129] Through the control method of the LLC resonant converter provided in the embodiment of the present application, when the switching frequency is lower than the maximum switching frequency, the LLC resonant converter is controlled based on the PFM mode and the Brust mode, and the output voltage regulation of the LLC resonant converter can be achieved by controlling the switching frequency; when the switching frequency is lower than the maximum switching frequency, that is, when the voltage control cannot be achieved by adjusting the switching frequency, the LLC resonant converter is controlled based on the PWM mode and the Brust mode, and the output voltage of the LLC resonant converter is controlled by controlling the duty cycle value of the drive signal.

[0130] Through the above hybrid mode control method, not only can the LLC resonant converter output a stable voltage, but also the adjustment range of the LLC resonant converter output voltage can be widened. On the basis of PFM mode control, combined with the advantages of symmetrical PWM mode and Brust mode, while achieving the stable output of the LLC resonant converter, the switching frequency is effectively reduced to avoid the switching frequency exceeding the maximum switching frequency. Based on the symmetrical PWM mode, soft switching within the full load range is achieved, which effectively reduces the switching loss. The introduction of the Brust mode reduces the switching time of the switch tube in the LLC resonant converter and reduces the switching loss.

[0131] Based on the above embodiments, the present application also provides a control device, see Figure 5 , which is a schematic diagram of a control device provided in an embodiment of the present application.

[0132] The control device may include a memory 501 and a processor 502. The processor 502 may be connected to the power converter and may drive switches in each power conversion circuit in the power converter. Figure 5 As shown, the memory may be a random access memory (RAM), a flash memory, a read only memory (ROM), an EPROM memory, an Electronic Programmable ROM (EPROM), a register, a hard disk, a removable disk, etc.

[0133] The memory 501 may store computer instructions. When the computer instructions stored in the memory 501 are executed by the processor 502, the processor 502 may be used to control the LLC resonant converter. The memory 501 may also store data.

[0134] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on the computer, the process or function according to the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (digital subscriber line, DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. The computer-readable storage medium can be any available medium that can be accessed by the computer or a data storage device such as a server, data center, etc. that includes one or more available media integrated. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape) or a semiconductor medium (e.g., a solid state disk (SSD)), etc.

[0135] The present application also provides a readable storage medium for storing the method provided in the above embodiment, for example, a random access memory (RAM), a flash memory, a read only memory (ROM), an EPROM memory, an electronic programmable ROM (EPROM), a register, a hard disk, a removable disk or any other form of storage medium in the art.

[0136] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other. For the method disclosed in the embodiment, since it corresponds to the product embodiment disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the product embodiment part.

[0137] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for an LLC resonant converter, It is characterized in that include: Get the switching frequency of the LLC resonant converter; The switching frequency is determined according to the output voltage and output current of the LLC resonant converter; When the switching frequency is less than or equal to the maximum switching frequency, the LLC resonant converter is controlled by a first hybrid mode so that the LLC resonant converter outputs a target voltage; The first hybrid mode includes a pulse frequency modulation (PFM) mode and a hiccup (Brust) mode; When the switching frequency is greater than the maximum switching frequency, the LLC resonant converter is controlled by a second hybrid mode so that the LLC resonant converter outputs the target voltage; the second hybrid mode includes a symmetrical pulse width modulation (PWM) mode and the Brust mode.

2. The method according to claim 1, It is characterized in that The adopting the first hybrid mode to control the LLC resonant converter includes: When a first preset condition is met, controlling the switching frequency of the LLC resonant converter through the PFM mode so that the LLC resonant converter outputs the target voltage; Alternatively, when a second preset condition is met, the switch tube in the LLC resonant converter is controlled to be disconnected through the Brust mode, so that the LLC resonant converter outputs the target voltage.

3. The method according to claim 1, It is characterized in that The adopting the second hybrid mode to control the LLC resonant converter includes: When a first preset condition is met, controlling the duty cycle of the driving signal of the LLC resonant converter through the PWM mode so that the LLC resonant converter outputs the target voltage; Alternatively, when a second preset condition is met, the switch tube in the LLC resonant converter is controlled to be disconnected through the Brust mode, so that the LLC resonant converter outputs the target voltage.

4. The method according to claim 2 or 3, It is characterized in that The first preset condition includes: the output current of the LLC resonant converter is greater than or equal to the first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0; or, the output current of the LLC resonant converter is greater than or equal to the first reference current, and the difference between the target voltage and the output voltage is less than 0; or, the output current of the LLC resonant converter is less than the first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0; The second preset condition is that the output current is less than the first reference current, and the difference between the target voltage and the output voltage is less than 0; Wherein, the first reference current is determined according to the target voltage.

5. The method according to claim 2, It is characterized in that When the first preset condition is that the output current of the LLC resonant converter is greater than or equal to a first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0, controlling the switching frequency of the LLC resonant converter by the PFM mode includes: Controlling the switching frequency of the LLC resonant converter to decrease by the PFM mode; When the first preset condition is that the output current of the LLC resonant converter is greater than or equal to a first reference current, and the difference between the target voltage and the output voltage is less than 0, controlling the switching frequency of the LLC resonant converter by the PFM mode includes: Controlling the switching frequency of the LLC resonant converter to increase through the PFM mode; When the first preset condition is that the output current is less than the first reference current, and the difference between the target voltage and the output voltage is greater than or equal to 0, controlling the switching frequency of the LLC resonant converter by the PFM mode includes: The switching frequency of the LLC resonant converter is increased by controlling the PFM mode.

6. The method according to claim 3, It is characterized in that The step of controlling the duty cycle of the driving signal of the LLC resonant converter by the PWM mode includes: Using the difference between the target voltage and the output voltage as an input of a voltage PI regulator to obtain a second reference current; The difference between the second reference current and the output current is used as an input of a current PI regulator to obtain the duty cycle value.

7. The method according to claim 3 or 6, It is characterized in that The duty cycle value is less than 0.5, and the duty cycle value is greater than a minimum duty cycle value; wherein the minimum duty cycle value is a minimum duty cycle capable of maintaining a soft switching state.

8. The method according to claim 1, It is characterized in that The obtaining of the switching frequency of the LLC resonant converter includes: Determining a voltage loop switching frequency and a current loop switching frequency of the LLC resonant converter; The minimum value between the voltage loop switching frequency and the current loop switching frequency is used as the switching frequency.

9. The method according to claim 8, It is characterized in that Determining the voltage loop switching frequency and the current loop switching frequency of the LLC resonant converter includes: obtaining the output voltage and the output current; Using the difference between the output voltage and the target voltage as the input of the voltage PI regulator to obtain the voltage loop switching frequency; The difference between the output current and the second reference current is used as an input of the current PI regulator to obtain the current loop switching frequency; the second reference current is determined according to the target voltage and the rated power of the LLC resonant converter.

10. An LLC resonant converter, It is characterized in that It includes a primary circuit, a secondary circuit, a resonant circuit, a transformer and a controller; the primary circuit is connected to the primary winding of the transformer through the resonant circuit, and the secondary circuit is connected to the secondary winding of the transformer; The controller is used to execute the method according to any one of claims 1 to 9 to control the LLC resonant converter.

11. A control device, It is characterized in that It comprises a processor and a memory, wherein the memory is used to store programs, instructions or codes, and the processor is used to execute the programs, instructions or codes in the memory to complete the control method of the LLC resonant converter as described in any one of claims 1 to 9.

12. A computer-readable storage medium, It is characterized in that A computer program is stored, and the computer program is loaded by a processor to execute the control method of the LLC resonant converter according to any one of claims 1 to 9.

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