An Output Voltage Slope Control System Based on LLC Topology

Abstract

The present invention relates to a circuit scheme with controllable output voltage rising slope based on LLC topology, and the description includes a slope control circuit, an MCU control system, an input DC power supply, an LLC power circuit, an output capacitor and a load resistor. The circuit scheme can realize the control of the output voltage rising slope, and the time from starting rising to stabilization can be calculated more accurately by flexibly setting the slope threshold. The system is suitable for electrical equipment with strict restrictive requirements on the power supply voltage rising time and the change speed at the startup moment. The patent of the present invention can realize the controllable output voltage rising slope, and has a very convenient and fast way to adjust the slope, and the accuracy of the output startup voltage slope control is relatively high, the circuit structure is very simple, and the cost of the scheme is relatively low.

Description

Technical Field

[0001] The invention relates to the fields of power electronics and electronic information, and in particular to an output voltage slope control system based on LLC topology. Background Art

[0002] With the development of science and technology, new energy and intelligence have become the hot topics of today's era. In addition, the introduction of the "carbon neutrality" policy has further consolidated the status of new energy. Under the label of new energy, electricity is indispensable. Therefore, under the promotion of this policy and hot topics, power supply equipment will usher in an unprecedented development torrent. For the DCDC driver power supply used in the lighting industry, there is still a problem of output voltage transients at the moment of startup, resulting in frequent light flickering. This problem will affect the life of the lighting equipment at the least, and will directly damage the lighting equipment in severe cases. Summary of the invention

[0003] In order to solve the above technical problems, the present application provides an output voltage slope control system based on LLC topology, the system comprising:

[0004] Slope control circuit, MCU control system, input DC power supply, LLC power circuit, output capacitor and load resistor, among which:

[0005] An input DC power supply is used to provide a DC input power supply to the LLC power circuit;

[0006] Output capacitor, used to reduce the ripple of the output voltage of the LLC power circuit;

[0007] Load resistance is used to represent the electrical equipment in the actual circuit;

[0008] LLC power circuit, which includes LLC converter and drive circuit, is the execution system of digital DCDC converter. The output voltage of LLC power circuit is directly detected by control system for loop control, and the output current of LLC power circuit is detected by control system for overcurrent protection.

[0009] The MCU control system is the control center of the LLC power circuit. It detects the output voltage Uo of the LLC power circuit and makes a difference between the output voltage and the given voltage Uc. Then, through PID regulation, the voltage signal is converted into a frequency signal inside the MCU control system. The output voltage of the LLC power circuit is stabilized by adjusting the frequency of the output constant duty cycle pulse.

[0010] The slope control circuit is the hardware detection part of the output voltage rising slope. The slope control circuit is used to monitor the output voltage rising slope in real time, and convert the signal of the output slope being too fast or too slow into a high or low level signal through MOSFET and transmit it to the MCU control system.

[0011] In a possible implementation, the MCU control system is also used to detect the current signal of the LLC power circuit U1 to implement overcurrent protection.

[0012] In one possible implementation, the slope control circuit is used to send a signal S2 unidirectionally to the MCU control system. When the power supply is started and the output voltage slope of the LLC power circuit exceeds a set threshold, the signal S1 is transmitted to the slope control circuit, monitored and converted into a low-level signal by the slope control circuit, and transmitted to the MCU control circuit. When the output voltage slope returns to a normal value, a high-level signal is re-transmitted.

[0013] In a possible implementation, the signal S3 between the MCU control system and the LLC power circuit is bidirectionally transmitted. For the MCU control system, the drive signal is output, and the voltage and current signals are input detection.

[0014] In a possible implementation, the slope control circuit includes 1 capacitor, 2 resistors, 1 MOSFET tube and 1 variable resistor.

[0015] In a possible implementation, the output port of the LLC power circuit serves as an input monitoring terminal of the slope control circuit.

[0016] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0017] The present application can control the output voltage rising slope, and the way to adjust the slope is convenient and fast; the output voltage rising slope control accuracy is high; the circuit structure is simple and the cost is low.

[0018] The present application can realize the control of the rising slope of the output voltage when it is started. Through the control system, the time for the power supply output voltage to rise to a stable value can be accurately calculated, and the characteristic of the time controllable can be realized. The system is suitable for electrical equipment that has strict restrictions on the power supply voltage rise time and change speed at the startup moment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 An overall system structure diagram provided for an exemplary embodiment of the present invention;

[0021] Figure 2 An MCU control system slope monitoring execution flow chart provided for an exemplary embodiment of the present invention;

[0022] Figure 3 A slope control circuit diagram provided for an exemplary embodiment of the present invention;

[0023] Figure 4 An FHA equivalent diagram of an LLC power circuit provided by an exemplary embodiment of the present invention;

[0024] Figure 5 A waveform diagram showing an equivalent control rectifier output current provided by an exemplary embodiment of the present invention;

[0025] Figure 6 A simulation overall structure diagram provided for an exemplary embodiment of the present invention;

[0026] Figure 7 A simplified diagram of a slope control circuit simulation provided by an exemplary embodiment of the present invention;

[0027] Figure 8 An output voltage slope diagram when there is no simulation restriction provided by an exemplary embodiment of the present invention;

[0028] Fig. 9 A diagram of a simulated limited 100ms output voltage slope is provided for an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the inventive concept. These all belong to the protection scope of the present invention.

[0030] like Figures 1 to 9 This embodiment discloses an output voltage slope control system based on LLC topology. Figure 1 , including: an input DC power supply DC, an output capacitor Co, a load resistor RL, an LLC power circuit U1, an MCU control system U2 and a slope control circuit U3.

[0031] The input DC power supply DC is used to provide a stable DC input power supply to the LLC power circuit U1;

[0032] The output capacitor Co plays a filtering role in this system and is used to reduce the ripple of the output voltage of LLC power circuit U1;

[0033] The load resistance RL is used to represent the electrical equipment in the actual circuit;

[0034] LLC power circuit U1 includes LLC converter and MOSFET drive circuit inside. This part is used as the execution system of digital DCDC converter. The output voltage of LLC power circuit U1 is directly detected by MCU control system U2, thus forming a digital control loop of single voltage loop control. Then, the current of LLC power circuit U1 is detected by MCU control system U2 for overcurrent protection. Since the driving capability of MCU control system U2 is weak and cannot directly drive the MOSFET tube in LLC converter, the pulse drive signal output by MCU control system first reaches MOSFET drive circuit to amplify the driving capability, and then transmits the amplified drive signal to MOSFET tube in LLC power circuit U1, thereby achieving the effect that MCU control system U2 indirectly drives MOSFET tube in LLC converter.

[0035] The MCU control system U2 serves as the control center of the LLC power circuit U1. It detects the output voltage Uo of the LLC power circuit U1 and makes a difference between the output voltage and the given voltage Uc, and then converts the voltage signal into a frequency signal through PID regulation. It achieves the stability of the output voltage of the LLC power circuit U1 by adjusting the frequency of the output constant duty cycle pulse, thereby achieving the voltage single-loop control effect. The MCU control system U2 also detects the current signal of the LLC power circuit U1, which is used as an overcurrent protection OCP. When the current exceeds the set threshold, the system will stop all output pulses.

[0036] The slope control circuit is the hardware detection part of the output voltage rising slope. The slope control circuit is used to monitor the output voltage rising slope in real time, and convert the signal of the output slope being too fast or too slow into a high or low level signal through MOSFET and transmit it to the MCU control system.

[0037] Figure 1 In the figure, S3 is used between the MCU control system U2 and the LLC power circuit U1 to indicate that all types of transmitted signals are bidirectional. For the MCU control system U2, the drive signal is output, and the voltage and current signals are input detection. The MCU control system U2 also unidirectionally receives the signal S2 transmitted by the slope control circuit U3. When the power supply is started, when the output voltage slope of the LLC power circuit U1 exceeds the set threshold, it will be transmitted to the slope control circuit U3 through the signal S1, and then monitored and converted into a low-level signal by the slope control circuit U3, and transmitted to the MCU control circuit U2. When the output voltage slope returns to the normal value, a high-level signal will be re-transmitted. The MCU control circuit U2 that receives the low-level signal will immediately pull down all the output pulses. When a high-level signal is received, the output pulse signal will be restored to normal timing. The execution process of the MCU control system U2 is as follows: Figure 2 .

[0038] The slope control circuit U3 is composed of 1 capacitor, 2 resistors, 1 MOSFET tube and 1 variable resistor. The specific circuit is as follows: Figure 3 As shown, the output port of LLC power circuit U1 serves as the input monitoring terminal of the slope control circuit U3. The basic principle is: when LLC power circuit U1 is started, the output voltage starts to rise. Since the current waveform of the output port is the absolute value of a quasi-sine wave, the current waveform presents a pulsating waveform similar to a steamed bun in each cycle. Through such pulsating current waveforms, it flows to the output capacitor, and the input detection port of the slope control circuit U3 is connected to the position where the output capacitor is connected in parallel. Due to the high-frequency fluctuation of the current, the high-frequency current will flow through the capacitor C1 in the slope control circuit U3, and through C1, the fluctuating current will flow through the resistor R1. The current flowing through R1 will generate a voltage drop on R1, so that there is a certain voltage drop between the GS of the MOSFET. Since the current across the capacitor C1 is Therefore, the magnitude of the current fluctuation on the output side of the LLC power circuit U1 determines the magnitude of the rising slope of the output voltage. For the G-level resistor R2 connected in series with the MOSFET, its size determines the driving conduction speed of the MOSFET. At a certain moment, if the output current value is too large, the voltage divider value on R1 will be greater than the conduction voltage threshold of the MOSFET, so that the MOSFET tube is driven to conduct, and the I / O port that was originally pulled to a high level by R3 is instantly pulled to a low level and transmitted to the MCU control system U2. After being processed by the MCU control system U2, the drive pulse signal at this time is instantly lowered, and the MOSFET in the LLC power circuit U1 will be turned off, which will cause the current rising trend in the current cycle to be limited and reduced, so the output voltage The slope will also decrease; when the current reaches a certain moment in the downward trend, making the voltage divider value on R1 lower than the turn-off voltage threshold of the MOSFET, the MOSFET will be turned off and the I / O port of the MCU control system U2 will receive a high level. After being processed by the MCU control system U2, the output drive pulse signal returns to normal, and the current begins to show an upward trend, and finally the output voltage slope increases. The output voltage slope is controlled under such reciprocating working conditions. Due to the delay of the system and the difference in the on-off threshold voltage of the MOSFET, it will eventually fluctuate between being higher than the output voltage slope threshold and lower than the threshold, so that the output voltage rising slope fluctuates around the set rising slope and reaches a stable value of the output voltage.

[0039] To analyze the LLC power circuit U1, first perform FHA (first harmonic approximation equivalence) to obtain a simplified circuit as follows: Figure 4, in the FHA equivalent circuit, the fundamental wave of the input equivalent power supply can be obtained as a sine wave:

[0040]

[0041] V in the above formula dc is the input DC power supply, and f s is the resonant frequency at which the LLC power circuit operates.

[0042] Such as Figure 4 in the equivalent circuit, the voltage V s1 transmits the current to the secondary under the action of the inductor, capacitor and transformer. The voltage fundamental wave of this circuit is sinusoidal through FHA equivalence. Therefore, it is analyzed that the input current equivalent fundamental wave is also a sine wave, and the input current waveform is:

[0043]

[0044] where I s1_rms is the effective value of the input current, is the phase difference between the resonant current and the voltage.

[0045] For the secondary rectified output current to be a quasi-sine wave, its fundamental component can also be expressed as:

[0046]

[0047] where I r1_rms is the effective value of the fundamental component of the rectified current, is the phase difference between the rectified output current and the input voltage.

[0048] In the LLC circuit, there are two resonant operating frequencies, which are respectively:

[0049]

[0050]

[0051] Generally, the LLC circuit is designed to operate in region 1 and region 2, that is, the resonant frequency always operates at: fs > fr2

[0052] For operation at f s > f r1 and f s = f r1 When, since the secondary output diode is basically in a continuous operating state throughout the cycle, the equivalent circuit Figure 4 the voltage V in p is always clamped at nV o ; when operating at fr2 < fs < fr1, generally in the LLC circuit, the exciting current I p is very small. Here, only the analysis of the current I is considereds1 =I p Before, in this stage, the voltage V p Also clamped at nV o So in the LLC circuit, the voltage V p It can be regarded as being clamped at nV o Department:

[0053] V p =n·V o

[0054] Through the above analysis, the output diode always keeps current flowing in the clamped state, and the output rectified current waveform is always a high-frequency pulsating waveform. r1 It changes with time and presents a quasi-sinusoidal change. For the characteristics of capacitors that they pass high frequencies and block low frequencies, such a high-frequency pulsating current waveform will easily pass through the capacitor.

[0055] At the output rectifier port, a slope control circuit is connected. The capacitor C1 at the input detection end of the circuit has the following relationship at a certain moment:

[0056]

[0057] The current flowing through capacitor C1 also flows through resistor R1, so when the divided voltage on resistor R1 reaches the driving threshold U of MOSFET th Sometimes:

[0058] I r1 R1≥U th

[0059] When the above equation is true, the MOSFET will be triggered to turn on and generate a low level to be transmitted to the MCU control system, thereby lowering the drive signal of the MOSFET tube of the LLC power circuit at this time, forcibly cutting off the growth trend of the current and starting to decrease. Figure 5 As shown in the equivalent waveform diagram provided, x1 is the normal drive signal of the MCU control system, x2 is the signal transmitted to the MCU control system by the slope control circuit, x3 is the actual drive signal, and x4 is the quasi-sinusoidal current signal I of the output diode. r1 (including the signal when the slope is not controlled and the signal when the slope is controlled). At time t1, the fluctuating current I output by the diode r1 The voltage value obtained by the capacitor C1 of the slope control circuit flowing through the resistor R1 is exactly equal to the driving voltage U of the MOSFET. th , so that the slope control circuit transmits a low-level signal to the MCU control system at this moment, such as Figure 5 The x2 signal in is pulled low, and the MCU control system pulls the drive pulse signal low at this moment, such as Figure 5 x3 in the figure, so at this time the bridge arm in the LLC power circuit is turned off, and before the current reaches the top of the sine wave t2, the current in the resonant cavity is forced to continue to flow, so the current I r1 At t1, it also starts to decrease, because the current I r1 The decrease in will cause the MOSFET in the slope control circuit to turn off again, and the level signal transmitted to the MCU control system will return to a high level, and the MCU control system will drive the MOSFET in the LLC power circuit normally again. Through the above analysis, the critical moments of the slope control circuit are:

[0060] I r1 R1=U th

[0061] The current and voltage formulas across the combined capacitor C1 are:

[0062]

[0063] Therefore, the calculation formula for the output voltage slope to be controlled can be obtained through the above formula. By analyzing the above formula, changing the U of the MOSFET th The value (equivalent to changing the MOSFET model), the value of capacitor C1 and the value of resistor R1 can control the output voltage rising slope. th It is inconvenient to change the value of C1 and C2, so here we consider using a sliding rheostat as R1 in the actual circuit, which can realize convenient control of the output voltage rising slope. The accurate value of the voltage rising slope can be obtained by calculating the above formula.

[0064] Due to the delay in the transmission and processing of information in the circuit and the MOSFET tube production process, there are differences in the turn-on threshold and the turn-off threshold. In fact, the working mode of the rising slope does not completely conform to the slope value obtained by the theoretical calculation, but fluctuates around the slope value.

[0065] After the above analysis, if Figure 6 As shown in the figure, a power converter based on LLC topology with a full load power of 1000W and an output voltage of 48V was built through Simulink for simulation verification. Figure 7 The simplified simulation model of the slope control circuit is shown. By running the test under full load, the comparison of the output voltage and current when the output voltage slope is not limited and when the slope rise time is limited to 100ms is obtained. Figure 8 , Fig. 9 As shown. Figure 8 As shown in Figure 1, when the output voltage slope is not limited, the rise time is approximately 4.1ms. Fig. 9As shown, after the output voltage is limited, the rise time here is exactly equal to 100ms in the oscilloscope test. The output voltage after limitation remains basically unchanged from the output voltage before limitation, but there is a big change in the slope.

[0066] The invention concept is described in detail using specific examples herein, and the description of the above embodiments is only used to help understand the core idea of ​​the invention. It should be pointed out that any obvious modification, equivalent substitution or other improvement made by a person of ordinary skill in the art without departing from the invention concept should be included in the protection scope of the present invention.

[0067] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are considered to be exemplary only, and the true scope and spirit of the present application are indicated by the above-mentioned claims.

[0068] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

[0069] It should be understood that the "plurality" mentioned in this article refers to two or more. "And / or" describes the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0070] A person skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware or by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a disk or an optical disk, etc.

[0071] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An output voltage slope control system based on LLC topology, characterized in that: The system comprises: Slope control circuit, MCU control system, input DC power supply, LLC power circuit, output capacitor and load resistor, among which: An input DC power supply is used to provide a DC input power supply to the LLC power circuit; Output capacitor, used to reduce the ripple of the output voltage of the LLC power circuit; Load resistance is used to represent the electrical equipment in the actual circuit; LLC power circuit, which includes LLC converter and drive circuit, is the execution system of digital DCDC converter. The output voltage of LLC power circuit is directly detected by control system for loop control, and the output current of LLC power circuit is detected by control system for overcurrent protection. The MCU control system is the control center of the LLC power circuit. It detects the output voltage Uo of the LLC power circuit and makes a difference between the output voltage and the given voltage Uc. Then, through PID regulation, the voltage signal is converted into a frequency signal inside the MCU control system. The output voltage of the LLC power circuit is stabilized by adjusting the frequency of the output constant duty cycle pulse. The slope control circuit is composed of 1 capacitor, 2 resistors, 1 MOSFET tube and 1 variable resistor. The output port of LLC power circuit U1 serves as the input monitoring terminal of the slope control circuit U3, and transmits the output high and low level signals to the MCU control system through MOSFET.

2. The system according to claim 1, characterized in that The MCU control system is also used to detect the current signal of the LLC power circuit U1 to achieve overcurrent protection.

3. The system according to claim 1, characterized in that The slope control circuit is used to send a unidirectional signal S2 to the MCU control system. When the power supply is started and the output voltage slope of the LLC power circuit exceeds the set threshold, the signal S1 is transmitted to the slope control circuit, monitored and converted into a low-level signal by the slope control circuit, and transmitted to the MCU control circuit. When the output voltage slope returns to a normal value, a high-level signal is re-transmitted.

4. The system according to claim 1, characterized in that The signal S3 between the MCU control system and the LLC power circuit is bidirectionally transmitted. For the MCU control system, the drive signal is output, and the voltage and current signals are input detection.

5. The system according to claim 1, characterized in that The slope control circuit is composed of 1 capacitor, 2 resistors, 1 MOSFET tube and 1 variable resistor.

6. The system according to claim 5, characterized in that The output port of the LLC power circuit serves as the input monitoring terminal of the slope control circuit.

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