Voltage stabilization control method of LLC resonant converter and LLC resonant converter

Abstract

The invention discloses a voltage stabilization control method of an LLC resonant converter and the LLC resonant converter, according to the voltage stabilization control method, pre-stage feedback is introduced in PI control, one path of error is set to be a difference value between an output voltage and a set value, the other path of error is set to be a difference value between a pre-stage input voltage and a reference value, and the PI control is completed. And the sum of the two paths of errors forms an overall error and is introduced into a proportional-integral link for adjustment, so that the problem of unstable output end voltage caused by sudden voltage dramatic change at the input end of the switching power supply can be solved. In the LLC resonant converter, a main loop adopts a double-path full-bridge LLC topological structure, and an electrolytic capacitor is arranged at an input end, so that the condition of huge fall of preceding-stage voltage can be effectively handled; and the parallel tube is arranged on each group of switch tubes, so that the loss and the temperature rise of each switch tube can be reduced.

Description

Technical Field

[0001] The invention relates to a switching power supply, and in particular to a voltage stabilization control method of an LLC resonant converter and an LLC resonant converter. Background Art

[0002] LLC resonant converter is generally used as an interface between DC buses of different voltage levels to achieve DC conversion. It is a highly efficient isolated DC / DC converter. According to the requirements, LLC resonant converter can adopt a single-stage LLC topology or a two-stage LLC topology cascade. Currently, LLC resonant converter adopts the classic PI control strategy. When the input voltage fluctuates too much, it is difficult to achieve a stable voltage output. Summary of the invention

[0003] Purpose of the invention: The first purpose of the present invention is to provide a voltage stabilization control method for an LLC resonant converter to solve the problem of unstable output voltage caused by sudden and drastic voltage changes at the input end; the second purpose of the present invention is to provide an LLC resonant converter using the voltage stabilization control method.

[0004] Technical solution: A voltage stabilization control method for an LLC resonant converter of the present invention introduces a front-stage feedback into a PI algorithm. The PI algorithm formula is:

[0005]

[0006] Among them, U t is the regulating input, K p is the proportionality coefficient, K i is the integration coefficient; t is the time;

[0007] Error e t =error1+error2, where error1 is the output error and the previous stage error B is a constant; is the average value of the difference between the sampling points of the continuous n input voltages and the reference value; A2 is The variable coefficient is used to reflect the severity of the change in the previous stage voltage.

[0008] Furthermore, the reference value of the input voltage is determined by taking a number of consecutive sampling points of the input voltage and calculating the average value, then making a difference between the values ​​of these input voltage sampling points and the average value. If the absolute value of the difference is within the set value, the average value is used as the reference value of the input voltage. If there is a sampling point where the absolute value of the difference is greater than the set value, resampling is performed; the set value is taken as a percentage of the normal input voltage.

[0009] Furthermore, when the reference value is obtained, the difference between the sampling points of the consecutive n input voltages and the reference value is assumed to be e1, e2, ..., en , set the new value e a =k1e1+k2e2+k3e3+…+k n e n , e b =k n e1+k n-1 e2+k n-2 e3+…+k1e n , k is the weight of the difference between a single sampling point and the reference value, k1, k2, …, k n Take the arithmetic progression, the maximum is 1; use m*e b Subtract m*e a Get e c , m is a pending value, which is used to ensure e c The absolute value of e is less than 1; c If e c If it is not 0, it means that the trend of the error between the input voltage and the reference value is changing, and A2 needs to be changed accordingly. Suppose A2 obtained from the previous calculation is The current calculation of A2 is First, determine whether the error between the input voltage and the reference value is positive or negative. If the error is negative, then If the error is positive, then If the differences between the sampling points of the n input voltages and the reference values ​​are positive or negative, error2 is set to 0 directly; the initial A2 is determined by experience.

[0010] Furthermore, the control process is set in a frequency range, within which the change in frequency and the change in gain are similar to a linear relationship.

[0011] The present invention discloses an LLC resonant converter using the voltage stabilization control method, comprising a pre-charging circuit, a main circuit, an operation processing unit, a sampling unit, a driving unit, a communication unit and an auxiliary power supply. The main circuit adopts a dual-path full-bridge LLC topology structure. The pre-charging circuit is used to initially charge the electrolytic capacitor of the main circuit. When the electrolytic capacitor voltage reaches the set value of the pre-charging voltage, the pre-charging circuit is cut off, the main circuit is connected, and closed-loop control begins. The sampling unit is used to collect input stage voltage, output stage voltage, input stage current and output stage current, wherein the output stage voltage is used as a control and feedback signal and directly participates in the operation of the loop. The input stage current and the output stage current are used to protect the switch tube. The operation processing unit is used to generate a PWM waveform, and the driving unit is used to drive the switch tube according to the PWM waveform. The communication unit is used to communicate with the outside.

[0012] Furthermore, in the full-bridge LLC topology, each group of switch tubes has parallel tubes to reduce the loss and temperature rise of each switch tube.

[0013] Furthermore, in the full-bridge LLC topology, an electrolytic capacitor is provided at the input end of the entire topology for storing energy at the input stage to support short-term energy consumption.

[0014] Furthermore, in the full-bridge LLC topology, the diode on the secondary side adopts a Schottky type diode that can withstand high-frequency switching frequencies.

[0015] Furthermore, the sampling unit is also used to collect the resonant current in the switching tube loop, and at the same time set two resonant current uneven protection to prevent the two LLC loops from being unevenly loaded, causing one of them to be overloaded and cause thermal damage, and when the resonant current uneven protection occurs, it can reflect that there is a problem with at least one of the loops.

[0016] Furthermore, the operation processing unit adopts a chip, a programmable controller or an industrial computer.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention proposes a new feedforward idea, that is, considering the error effect caused by the change of input voltage in PI control, which can solve the problem of unstable output voltage caused by sudden and drastic voltage changes at the input end of the switching power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the PI control strategy with feedforward added in Example 1 of the present invention;

[0019] Figure 2 is a main loop circuit diagram of the LLC resonant converter in Embodiment 2 of the present invention;

[0020] Figure 3 It is a schematic diagram of selecting input voltage sampling points in Embodiment 2 of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings.

[0022] Example 1

[0023] Embodiment 1 provides a voltage stabilization control method for an LLC resonant converter, using a PI algorithm, and the formula is:

[0024] U t =K p *e t +K i ∫0 t e t dt

[0025] Among them, U t is the regulating input, K p is the proportionality coefficient, e tis the error; K i is the integration coefficient; t is the time.

[0026] Under normal circumstances, the output voltage of the next stage is stable and the output error error1 is zero, so the U t It remains the same as the previous cycle and keeps the output voltage stable.

[0027] When the input voltage of the previous stage changes greatly, the output voltage has not changed at this time, so the U calculated based on the output voltage t The value remains unchanged, but the input voltage has changed, so the obtained U t The value can no longer make the entire system stable, resulting in fluctuations in the output voltage of the subsequent stage when the input voltage of the previous stage changes, resulting in a certain lag.

[0028] To this end, the present invention introduces the front-stage feedback into the PI algorithm to reflect the change of the front-stage input voltage into the error. Specifically, the error e t =error1+error2, where error1 is the output error and the previous stage error B is a constant.

[0029] It is the average value of the difference between the sampling points of the continuous n input voltages and the reference value. Because there is electromagnetic interference in the operation of the switching power supply, interference is easy to occur in the analog-to-digital conversion, and using the average value as part of the control can effectively reduce the impact of such interference.

[0030] The method for determining the reference value is as follows: first, a number of consecutive input voltage sampling points are sampled and the average value is calculated, and then the difference between the values ​​of these input voltage sampling points and the average value is calculated. If the absolute value of the difference is within the set value, the average value is used as the reference value of the input voltage. If there is a sampling point where the absolute value of the difference is greater than the set value, re-sampling is performed. In this embodiment, the set value is 1% of the normal input voltage.

[0031] A2 is The variable coefficient is used to reflect the severity of the voltage change of the previous stage. When the reference value is obtained, the difference between the sampling points of the consecutive n input voltages and the reference value is set to e1, e2, …, e n , set the new value e a =k1e1+k2e2+k3e3+…+k n e n , e b =k n e1+k n-1 e2+k n-2 e3+…+k1e n, k is the weight of the difference between a single sampling point and the reference value, k1, k2, …, k n Take the arithmetic progression, the maximum is 1. Use m*e b Subtract m*e a Get e c , m is an undetermined value, which depends on the difference between the sampling point and the reference value. Its function is to ensure that e c The absolute value of is less than 1.

[0032] Judge c The positive or negative value of the input voltage is used to determine whether the amplitude of the input voltage change is increasing or decreasing. The sampling period is very short, so select e n The number of is limited, and the weight is taken according to an arithmetic progression. If the input voltage fluctuates, e c Normally, it will not be 0, e c is 0, it can be considered that the input voltage tends to be stable. c If it is not 0, it means that the trend of the error between the input voltage and the reference value is changing, and A2 needs to be changed accordingly. Suppose A2 obtained from the previous calculation is The current calculation of A2 is First, determine whether the error between the input voltage and the reference value is positive or negative. If the error is negative, then If the error is positive, then If the difference between the sampling points of the n input voltages and the reference value is positive or negative, error2 is set to 0 directly. Therefore, if the difference is positive or negative, and the number of sampling points selected is not large, it means that the input voltage is near the reference value. In this case, error2 does not need to participate in the control; the initial A2 is determined by experience. The PI control strategy with feedforward is as follows Figure 1 As shown in the figure, by taking the change of the front-end input voltage as a part of adjusting the switching frequency, the hysteresis of the conventional PI algorithm is effectively compensated.

[0033] Example 2

[0034] Embodiment 2 exemplarily provides an LLC resonant converter, and introduces the voltage stabilization control method described in Embodiment 1 in combination with the LLC resonant converter.

[0035] An LLC resonant converter comprises a pre-charging circuit, a main circuit, an operation processing unit, a sampling unit, a driving unit, a communication unit and an auxiliary power supply, wherein the functions of the sampling unit, the driving unit and the communication unit are realized based on corresponding circuits, and these units are essential components of the existing LLC resonant converter.

[0036] Figure 2The main circuit diagram is shown, which adopts a dual-path full-bridge LLC topology. Taking the full-bridge LLC topology on the upper side as an example, it includes a switch circuit, a resonant circuit, a transformer TX1, and a rectifier circuit, wherein the switch circuit includes switch tubes Q1, Q2, Q3, and Q4, the resonant circuit includes a resonant inductor Lr1, an excitation inductor Lm1, and a resonant capacitor Cr1, and the rectifier circuit includes diodes D1, D2, D3, and D4. In addition, the LLC main circuit input port is provided with a filter capacitor C6, which is connected in parallel with an electrolytic capacitor C1, and the output port is connected in parallel with a filter capacitor C3.

[0037] The full-bridge LLC topology structure on the lower side is not described in detail here. The cathode of the diode D7 and one end of the filter capacitor C8 are connected to the cathode of the diode D2 respectively.

[0038] The entire topology input end is provided with an electrolytic capacitor C9 for energy storage at the input stage to support short-term energy consumption and cope with the situation of a huge voltage drop in the previous stage.

[0039] The sampling unit is used to collect the input stage voltage, output stage voltage, input stage current, output stage current and resonant current in the switch tube loop. The output stage voltage is used as a control and feedback signal and directly participates in the operation of the loop, while the input stage current and output stage current are used to protect the switch tube to prevent damage to the switch tube due to excessive current. The resonant current sampling set in the switch tube loop can quickly, timely and effectively reflect the current in the main loop. At the same time, two resonant current uneven protections are set to prevent uneven loading of the two LLC loops, which may cause one of them to be overloaded and cause thermal damage. When the resonant current uneven protection occurs, it can reflect that at least one group of loops has a problem, and the switch power supply can be protected in time to avoid greater damage. The communication unit is used to communicate with the outside.

[0040] 220VDC is added to the input end and enters the main circuit. First, the input voltage is sampled and judged. When the voltage value is within the input range, the operation processing unit issues an instruction to open the pre-charge relay (used to control the on and off of the pre-charge circuit). The 220VDC voltage passes through the pre-charge circuit and charges the electrolytic capacitor of the main circuit through the pre-charge circuit. When the electrolytic capacitor voltage reaches the set value of the pre-charge voltage, the operation processing unit issues an instruction to close the pre-charge relay and open the main relay to start closed-loop control, that is, enter Figure 1 During the adjustment process, the processing unit generates a PWM waveform, and the driving unit drives the switch tube according to the PWM waveform.

[0041] The calculation processing unit can adopt a chip, a programmable controller or an industrial computer.

[0042] Under standard circumstances, the input voltage is 220VDC, the pre-charge voltage is set to 195VDC, and a voltage difference of 25VDC is reserved. On the one hand, when charging the electrolytic capacitor of the main circuit, the charging speed is relatively fast at the beginning, and then the rising speed begins to slow down. Excluding some losses, the 220VDC voltage cannot actually charge the capacitor to 220VDC. The reserved 25VDC voltage is an empirical value in practice. In this case, the instantaneous impact current when the main relay is closed will not be very large.

[0043] Considering the switching frequency of nearly 100K and the load of 8KW, each group of switch tubes in this embodiment has parallel tubes, for example, switch tube Q1 is connected in parallel with switch tube Q5, switch tube Q2 is connected in parallel with switch tube Q6, etc., so that on average, the loss on each switch tube will be smaller and the temperature will not be very high. The secondary side diode is a Schottky type diode that can withstand high-frequency switching frequencies and can effectively withstand high-frequency switching frequencies.

[0044] The current will first pass through a set of tube pairs, e.g. Figure 2 The middle switch tubes Q1 and Q4 form a loop through the resonant inductor Lr1, transformer TX1 and resonant capacitor Cr1. At this time, the other pair of tubes Q2 and Q3 will be in the off state. Then turn off Q1 and Q4, turn on Q2 and Q3, and the current will also pass through a pair of tubes, resonant inductor, transformer and resonant capacitor. By controlling the two pairs of tubes to be turned on at different times, the direction of the voltage on the transformer is controlled. When the two pairs of tubes are turned on, they are opposite, that is, the input DC voltage can be converted into AC voltage, and then transmitted to the secondary side through the transformer. Finally, the DC voltage is uncontrolled rectified by the diode and filtered by the capacitor into a smooth DC. The transformer can not only change the voltage, but also electrically isolate the primary and secondary sides, ensuring the insulation of the hardware.

[0045] Since the LLC gain curve and frequency are similar to a parabola, the operating frequency is set in one of the intervals. Within this interval, the frequency and gain curves are similar to a linear relationship. In this power supply, the frequency is set to be reduced from the initial frequency of 200k. Within this set interval, the smaller the frequency, the greater the gain.

[0046] Under normal circumstances, the sampled output voltage is compared with the set value of 640VDC. When the frequency is 200k, the gain is very small, and the voltage of 640VDC cannot be obtained at this frequency. At this time, the sampled output voltage is less than 640VDC, and error1 is formed between the sampled value and the set value. At this time, the input voltage is stable, error2 is 0, and the final error is only error1. The error is obtained by the PI algorithm to obtain a current frequency value less than 220k, and then the calculation processing unit will send out a PWM waveform at the current calculated frequency, and finally the output voltage is controlled by the driving unit to the switch tube, and then the output voltage is sampled again, and the control is cyclic. Finally, the output voltage reaches 640VDC by reducing the frequency to a suitable value. When the output is loaded, the back stage will be consumed. At this time, the 640VDC voltage will drop. After the output voltage is sampled, the frequency is reduced again after PI operation, so that the output voltage can be stable under load. Different frequency values ​​can be calculated after PI operation with different loads.

[0047] When the input voltage changes, the feedforward error error2 introduced at this time starts to work. First, take 100 consecutive input voltage sampling points, calculate the average value of the 100 input voltage sampling points, and then make a difference between these 100 points and the average value. If the absolute value of the difference is within 2V, the average value of these 100 points can be used as the reference value of the input voltage. If there is a point where the absolute value of the difference is greater than 2V, resample another set of 100 consecutive points.

[0048] When the reference value is obtained, the number of sampling points is set to 5, such as Figure 3 As shown, find the error between the 5 sampling points and the reference value, and then take the average value. The difference between the five consecutive sampling points and the reference value is the average value. The difference between the five consecutive sampling points and the reference value is e1, e2, e3, e4, e5. Let the new value e a =e1+0.8e2+0.6e3+0.4e4+0.2e5, e b =0.2e1+0.4e2+0.6e3+0.8e4+e5, using 0.01e b Subtract 0.01e a Get e c , judge e c If e c If it is not 0, it means that the trend of the error between the input voltage and the reference value is changing, and A2 needs to be changed accordingly. Suppose the previous A2 calculation is The current calculation of A2 is First, determine whether the error between the input voltage and the reference value is positive or negative. If the error is negative, then If the error is positive, then If the differences between the sampling points of the five input voltages and the reference values ​​are positive or negative, error2 is directly set to 0. The initial value of A2 is obtained from experience.

[0049] According to the above method, error2 in the current situation can be calculated. At this time, error1 and error2 together constitute the error amount. Because the error amount includes the feedback of the previous stage voltage, it makes obvious adjustments in the subsequent stage PI control process, and can achieve timely and effective stable output voltage.

[0050] The constant B can be selected according to different conditions. If it is not needed, it can also be set to 0. The reason for setting this value is that when the input change is not large, the detected e is relatively small, so the overall effect is relatively small. Adding an appropriate constant can adapt to a wide range of rapid adjustments.

[0051] When the input error is negative, it means that the input voltage is decreasing, which means that the input voltage is less than the standard value, indicating that the voltage of the previous stage is insufficient. In this case, if you want to keep the voltage of the next stage stable, you need to increase the LLC gain, reduce the input, and increase the gain. Only in this way can the output remain stable. In terms of the overall error, the effect of the overall error increases. At this time, A2 must be a positive value, and the greater the downward trend, It must be compared That is to say, the effect of error2 should be further amplified, and it is precisely because of the introduction of e c , in e c In the calculation of , the trend change can be naturally introduced. That is to say, according to the formula, after each calculation, the loop can gradually stabilize the output voltage when the input decreases and the trend changes. In this case, it is necessary to significantly increase the effect of the error amount, and the current coefficient It is obtained based on the previous coefficient, so that error2 can contain the downward trend of input voltage. In this formula, e c The generation of includes the trend of input error. In this case, a smaller frequency value without delay can be calculated by the PI loop.

[0052] When the detected input error is positive, At this time, the input voltage is in the rising stage, which means that the input voltage is higher than the standard value, indicating that the voltage of the previous stage rises sharply. In this case, if you want to keep the voltage of the next stage stable, you need to reduce the LLC gain, increase the input, and reduce the gain. Only in this way can the output remain stable. In terms of the overall error, the overall error effect is reduced. At this time, A2 must be a negative value, and the greater the upward trend, The absolute value of The absolute value of error2 is even larger, that is, the effect of error2 is also further amplified. That is to say, according to the formula, after each calculation, the loop can gradually stabilize the output voltage when the input rises and the trend changes. In this case, it is necessary to significantly reduce the effect of the error amount, and the current coefficient It is also obtained on the basis of the previous coefficient, so that error2 can also contain the rising trend of the input voltage. In this case, a larger frequency value without delay can be calculated through the PI loop. It is necessary to reduce the impact of the error, that is, it is necessary to increase the frequency, and introduce a negative absolute value in the generation process of A2 to reduce the overall error.

[0053] In summary, the present invention sets one error as the difference between the output voltage and the set value, and the other error as the difference between the input voltage of the previous stage and the reference value. The sum of the two errors constitutes the overall error and enters the proportional integral link for adjustment. Finally, after calculation and multiple feedback adjustments, a dynamic voltage stabilization effect is achieved. The LLC resonant converter is based on the LLC topology and adopts the classic frequency control modulation method, that is, the frequency of controlling the switch tube to turn off and on to increase or reduce the gain of the topology itself, and sets the control process in a frequency interval. Within this interval, the change in frequency and the change in gain can be similar to a linear relationship, so that the overall error obtained through all feedback can be finally applied to the frequency through the calculation and corresponding relationship of the PI loop. The operation processing unit calculates the frequency that needs to be controlled in order to make the output voltage reach the set value, and then the corresponding pin produces a PWM waveform of the corresponding frequency, which is amplified by the drive unit and finally acts on the switch tube to participate in the control of the main loop. Under the collective operation of the sampling unit, the drive unit and the operation processing unit, a dynamic adjustment effect is achieved.

[0054] It should be pointed out that the voltage stabilization control method provided by the present invention provides a feedforward concept at its core, that is, considering the input voltage change in PI control. Therefore, the application of the method is not limited to the LLC resonant converter provided in Example 2, and is also applicable to LLC resonant converters of other structures. The initial values ​​of many control parameters set in this embodiment are obtained from experience, and if used for the control of other LLC resonant converters, they need to be adjusted according to specific circumstances.

Claims

1. A voltage stabilization control method for an LLC resonant converter, characterized in that: Introducing the previous stage feedback into the PI algorithm, the PI algorithm formula is: Among them, U t is the regulating input, K p is the proportionality coefficient, K i is the integration coefficient; t is the time; Error e t =error1+error2, where error1 is the output error and the previous stage error B is a constant; is the average value of the difference between the sampling points of the continuous n input voltages and the reference value; A2 is The variable coefficient is used to reflect the severity of the change in the previous stage voltage.

2. The voltage stabilization control method of LLC resonant converter according to claim 1, characterized in that: The method for determining the reference value of the input voltage is to take a number of consecutive input voltage sampling points and calculate the average value, then make a difference between the values ​​of these input voltage sampling points and the average value. If the absolute value of the difference is within the set value, the average value is used as the reference value of the input voltage. If there is a sampling point where the absolute value of the difference is greater than the set value, re-sampling is performed; the set value is taken as a percentage of the normal input voltage.

3. The voltage stabilization control method of LLC resonant converter according to claim 2, characterized in that: When the reference value is obtained, the difference between the sampling points of the consecutive n input voltages and the reference value is set to e1, e2, …, e n , set the new value e a =k1e1+k2e2+k3e3+…+k n e n , e b =k n e1+k n-1 e2+k n-2 e3+…+k1e n , k is the weight of the difference between a single sampling point and the reference value, k1, k2, …, k n Take the arithmetic progression, the maximum is 1; use m*e b Subtract m*e a Get e c , m is a pending value, which is used to ensure e c The absolute value of e is less than 1; c If e c If it is not 0, it means that the trend of the error between the input voltage and the reference value is changing, and A2 needs to be changed accordingly. Suppose A2 obtained from the previous calculation is The current calculation of A2 is First, determine whether the error between the input voltage and the reference value is positive or negative. If the error is negative, then If the error is positive, then If the differences between the sampling points of the n input voltages and the reference values ​​are positive or negative, error2 is set to 0 directly; the initial A2 is determined by experience.

4. The voltage stabilization control method of LLC resonant converter according to claim 3, characterized in that: The control process is set in a frequency range, within which the change in frequency and the change in gain are similar to a linear relationship.

5. An LLC resonant converter using the voltage stabilization control method according to any one of claims 1 to 4, characterized in that: It includes a pre-charging circuit, a main circuit, an operation processing unit, a sampling unit, a driving unit, a communication unit and an auxiliary power supply. The main circuit adopts a dual-path full-bridge LLC topology structure. The pre-charging circuit is used to initially charge the electrolytic capacitor of the main circuit. When the electrolytic capacitor voltage reaches the set value of the pre-charging voltage, the pre-charging circuit is cut off, the main circuit is connected, and closed-loop control begins; the sampling unit is used to collect input stage voltage, output stage voltage, input stage current and output stage current, wherein the output stage voltage is used as a control and feedback signal and directly participates in the operation of the loop; the input stage current and the output stage current are used to protect the switch tube; the operation processing unit is used to generate a PWM waveform, and the driving unit is used to drive the switch tube according to the PWM waveform; The communication unit is used to communicate with the outside.

6. The LLC resonant converter according to claim 5, characterized in that: In the full-bridge LLC topology, each group of switch tubes has parallel tubes to reduce the loss and temperature rise of each switch tube.

7. The LLC resonant converter according to claim 5, characterized in that: In the full-bridge LLC topology, an electrolytic capacitor is provided at the input end of the entire topology for energy storage at the input stage to support short-term energy consumption.

8. The LLC resonant converter according to claim 5, characterized in that: In the full-bridge LLC topology, the secondary-side diode uses a Schottky-type diode that can withstand high-frequency switching frequencies.

9. The LLC resonant converter according to claim 5, characterized in that: The sampling unit is also used to collect the resonant current in the switching tube loop, and set two resonant current uneven protections to prevent the two LLC loops from being unevenly loaded, causing one of them to be overloaded and cause thermal damage. When the resonant current uneven protection occurs, it can reflect that there is a problem with at least one of the loops.

10. The LLC resonant converter according to claim 5, characterized in that: The calculation processing unit adopts a chip, a programmable controller or an industrial computer.

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