Staggered parallel LLC resonant converter current sharing control method based on switch control capacitor
Through the current equalization control method of the interleaved parallel LLC resonant converter based on the switching control capacitor, the resonant current of the parallel LLC resonant converter is detected in real time and the conduction angle is dynamically adjusted, which solves the problems of large current ripple and high thermal loss in the interleaved parallel LLC resonant converter when load is unbalanced, and improves the reliability and stability of the system.
Patent Information
- Application Number
- CN202510554982.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-29
- Publication Date
- 2025-08-15
AI Technical Summary
The existing interlaced parallel LLC resonant converters have problems such as large current ripple, high thermal loss and poor reliability when load unbalanced, and the existing current sharing control method is complex, low efficiency and high cost.
Through the current sharing control method of interleaved parallel LLC resonant converter based on switch control capacitors, the resonant current of the parallel LLC resonant converter is detected in real time, and the conduction angle of the switching control capacitors of each phase is dynamically adjusted to realize resonant current sharing control.
The current equalization of the LLC resonant converter under the deviation of circuit parameters is realized, which reduces the output current ripple, improves the reliability and stability of the system, and reduces heat loss.
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Figure CN120498227A_ABST
Abstract
Description
Technical Field
[0001] The embodiments of the present disclosure relate to the technical field of resonant converters, and in particular to a current sharing control method for an interleaved parallel LLC resonant converter based on switch-controlled capacitors. Background Art
[0002] With the development and utilization of green and efficient switching power supplies, the LLC resonant topology, with its advantages of soft switching, high efficiency, and high power density, has been widely adopted in the design of green home appliances and related products such as new energy power. However, with increasing power supply demands, single-phase LLC resonant converters can no longer fully meet market needs. Furthermore, when operating under heavy loads, the output current ripple is large, which seriously hinders the LLC resonant converter from achieving low-ripple output in high-power applications. Interleaved parallel technology can effectively solve this problem. This technology staggers the output ripple of the resonant converter, significantly reducing output ripple. At the same time, the parallel structure can increase output current and effectively improve output power. Furthermore, for the same output power, a multi-phase interleaved parallel resonant converter generates less heat than a single-phase resonant converter, reducing heat loss in the circuit.
[0003] The multi-phase interleaved parallel LLC resonant converter introduces interleaved parallel technology into the LLC resonant converter, which not only retains the good soft switching characteristics of the LLC resonant converter, but also improves the power of the converter, solves the power upper limit problem of a single LLC resonant converter, improves the output ripple problem, improves transmission efficiency, and enhances the redundancy and reliability of the LLC resonant converter.
[0004] However, due to process limitations and errors, the parameters of each module in a DC power supply system inherently vary. These differences can also increase due to external factors such as time and temperature. These differences prevent the modules from evenly sharing the load current when connected in parallel. Some modules may carry excessive current, increasing losses, shortening the life of switching components, and increasing the risk of damage. Furthermore, under heavy loads, the module with the highest current draw may trigger protection mechanisms, impacting the normal operation of the entire system. Therefore, current sharing technology is necessary to address these issues.
[0005] Currently, the current sharing methods for interleaved parallel LLC resonant converters mainly include passive current sharing and active current sharing.
[0006] The passive current sharing method uses the characteristics of passive components or improved topology to form a current balancing unit to achieve automatic current balancing. It mainly includes the following methods: ① Flying capacitor: A flying capacitor is connected in series to a two-phase half-bridge LLC resonant converter to compensate for the difference in voltage gain between phases, but this increases the complexity of the drive circuit.
[0007] ② A coupled inductor is inserted in series into the resonant cavity of each resonant converter, and the magnetic circuit coupling between the two resonant converters is used to achieve current sharing of the parallel resonant converter. The advantages are that there is no current sharing control circuit and the reliability is high. The disadvantage is that the series coupling inductor is not conducive to improving the converter efficiency and power density.
[0008] ③ Passive impedance matching: Changing the coupled inductor in the resonant cavity can achieve both current balancing and ripple cancellation. However, in low-voltage, high-current applications, the coupled inductor's size and conduction losses can be significant. Alternatively, introducing other impedances in the resonant cavity can achieve automatic current sharing, but this method suffers from poor current sharing performance under light loads. Alternatively, adding a filter at the output can significantly affect current sharing performance, necessitating a combination of other current sharing methods to minimize current sharing errors.
[0009] ④ Y / Δ connection: According to Kirchhoff's current law, the vector sum of the primary three-phase resonant currents is always zero, so this topology can achieve current balance. However, the Y / Δ connection structure is only applicable to three-phase topologies and cannot be extended to any phase. As the resonant parameter tolerance increases, the current sharing performance deteriorates.
[0010] Active current sharing requires a closed-loop control scheme to achieve current balance in a multi-phase LLC resonant converter. The controller detects and compares the output currents of each phase and adjusts the controlled variable to reduce the current difference in the multi-phase converter. This method mainly includes the following: ① Direct frequency control method: This method relies on the adjustment of the switching frequency to ensure the consistency of the voltage gain of each module, but this will cause the output current ripple caused by the frequency difference to have periodic and large fluctuations.
[0011] ② Asymmetric resonant parameter design: This method uses asymmetric resonant parameter design to ensure that the voltage gain curves of each LLC converter module intersect under various loads, allowing the converter to achieve current balance within the same switching cycle. However, the voltage gain of these converters must be adjusted with load changes.
[0012] ③ Equivalent voltage regulation: This method compensates for gain differences caused by resonant component tolerances by changing the equivalent input or output voltage amplitude of the resonant tank. This can be achieved through phase shifting or by adding a PWM rectifier to the secondary side. However, this method weakens the ripple suppression effect and increases the complexity of the control scheme.
[0013] ④ Controlling resonant component parameters: By adding auxiliary circuitry, the parameters of the resonant components are adjusted to compensate for parameter differences caused by tolerances. The tolerances of the resonant capacitor and inductor are the primary cause of current imbalance. Current sharing can be controlled by adjusting the parameters of the resonant capacitor and inductor.
[0014] From the above analysis, it can be seen that although the above method can perform current sharing control to a certain extent and achieve power balance of the interleaved parallel LLC resonant converter, it also brings new problems such as complex control, increased cost, reduced efficiency, and poor reliability.
[0015] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.
[0016] It should be noted that this section is intended to provide background or context for the technical solutions of the present disclosure stated in the claims. The description herein is not admitted to be prior art by virtue of being included in this section. Summary of the Invention
[0017] The purpose of the embodiments of the present disclosure is to provide a current sharing control method for an interleaved parallel LLC resonant converter based on switch-controlled capacitors, thereby overcoming one or more problems caused by the limitations and defects of related technologies to at least a certain extent.
[0018] According to an embodiment of the present disclosure, a current sharing control method for an interleaved parallel LLC resonant converter based on switch-controlled capacitors is provided, the method comprising: Constructing an interleaved parallel LLC resonant converter; wherein the interleaved parallel LLC resonant converter includes a digital control circuit, a main power circuit, and an auxiliary circuit; the main power circuit includes a first-phase LLC resonant converter and a second-phase LLC resonant converter connected in parallel; the first-phase LLC resonant converter and the second-phase LLC resonant converter are electrically connected to the digital control circuit and the auxiliary circuit, respectively; Generate multiple PWM drive signals with the same frequency and staggered phases through a digital control circuit to control the operation of the switches of the first-phase LLC resonant converter and the second-phase LLC resonant converter respectively, so that the first-phase LLC resonant converter generates a first resonant current and the second-phase LLC resonant converter generates a second resonant current; Acquire the first resonant current and the second resonant current in real time, and calculate the resonant current sharing error according to the first resonant current and the second resonant current; When the resonant current sharing error exceeds the set sharing error threshold, the conduction angle of each phase switch control capacitor is dynamically adjusted until the resonant current sharing error is less than the sharing error threshold to output the current.
[0019] Furthermore, the first-phase LLC resonant converter specifically includes: Capacitor C in The two ends are connected in parallel at both ends of the input source, one end of the switch tube Q1 is electrically connected to the positive end of the input source, and the other end of the switch tube Q1 is connected in parallel with the switch tube Q2 and the resonant inductor L r1One end of the resonant cavity freewheeling diode D1 is electrically connected to the positive end of the input source, the other end of the resonant cavity freewheeling diode D1 is connected in parallel with the resonant cavity freewheeling diode D2, and the other end of the resonant cavity freewheeling diode D2 is electrically connected to the negative end of the input source; the resonant capacitor C r1 The two ends of the resonant cavity freewheeling diode D1 are connected in parallel, and the resonant capacitor C r2 The two ends of the resonant cavity freewheeling diode D2 are connected in parallel; the switch S1 is connected to the resonant capacitor C a1 In parallel with the resonant inductor L r1 , excitation inductance L m1 Resonant inductor L r1 , excitation inductance L m1 Series; the primary side of the transformer and the excitation inductance L in the resonant cavity m1 In parallel, the secondary side is connected to the rectifier circuit, the sources of the synchronous rectifier tubes SR1 and SR2 are connected in parallel to the ground of the output end, and the drains of the synchronous rectifier tubes SR1 and SR2 are connected to the secondary side of the transformer; the center tap of the transformer is electrically connected to the positive electrode of the output end; Among them, the output voltage C o And the load RL is connected in parallel at both ends of the output.
[0020] Furthermore, the second-phase LLC resonant converter specifically includes: One end of the switch tube Q3 is electrically connected to the positive end of the input source, the other end of the switch tube Q4 is connected in parallel with the switch tube Q4 and is electrically connected to one end of the resonant inductor Lr3, and the other end of the switch tube Q4 is electrically connected to the negative end of the input source; one end of the resonant cavity freewheeling diode D3 is electrically connected to the positive end of the input source, the other end of the resonant cavity freewheeling diode D3 is connected in parallel with the resonant cavity freewheeling diode D4, and the other end of the resonant cavity freewheeling diode D4 is electrically connected to the negative end of the input source; both ends of the resonant capacitor Cr3 are connected in parallel with both ends of the resonant cavity freewheeling diode D3, and the resonant capacitor Cr3 is connected in parallel with both ends of the resonant cavity freewheeling diode D3. The two ends of capacitor Cr4 are connected in parallel with the two ends of resonant cavity freewheeling diode D4; switch S2 is connected in parallel with resonant capacitor Ca2, and is connected in series with resonant inductor Lr2 and excitation inductor Lm2; the primary side of the transformer is connected in parallel with the excitation inductor Lm2 in the resonant cavity, the secondary side is connected to the rectifier circuit, the source of synchronous rectifier SR3 and synchronous rectifier SR4 are connected in parallel to the ground of the output end, and the drain of synchronous rectifier SR3 and synchronous rectifier SR4 is connected to the secondary side of the transformer; the center tap of the transformer is electrically connected to the positive electrode of the output end; Among them, the output voltage C o And the load RL is connected in parallel at both ends of the output.
[0021] Furthermore, the step of calculating the resonant current sharing error according to the first resonant current and the second resonant current includes: Get the first resonant current and the second resonant current ; According to the first resonant current and the second resonant current Calculate the average ; Calculate the resonant current sharing error based on the average value .
[0022] Furthermore, when the resonant current sharing error exceeds a set current sharing error threshold, the step of dynamically adjusting the conduction angle of each phase switch control capacitor until the resonant current sharing error is less than the current sharing error threshold includes: The conduction angle of the switch-controlled capacitor in the resonant cavity of the first-phase LLC resonant converter is and the conduction angle of the switch-controlled capacitor in the resonant cavity of the second-phase LLC resonant converter Initialize to initial value , ; When the resonant current sharing error Exceeds the set current sharing error threshold When the first resonant current Is it greater than the second resonant current ; If the first resonant current Greater than the second resonant current , then determine the conduction angle Whether it is the maximum conduction angle; If so, reduce the conduction angle If not, increase the conduction angle angle.
[0023] Furthermore, the method further comprises: If the second resonant current Greater than the first resonant current , then determine the conduction angle Whether it is the maximum conduction angle; If so, reduce the conduction angle If not, increase the conduction angle angle.
[0024] Furthermore, when the vibration current sharing error Less than the set current sharing error threshold When , the LLC resonant converters are staggered in parallel to achieve output current sharing.
[0025] Furthermore, it is characterized in that the conduction angle and conduction angle Adjust 0.01 degrees each time.
[0026] The technical solutions provided by the embodiments of the present disclosure may have the following beneficial effects: In the embodiments of the present disclosure, the above-mentioned staggered parallel LLC resonant converter current sharing control method based on switch-controlled capacitors is used. On the one hand, by detecting the first resonant current and the second resonant current of the first-phase LLC resonant converter and the second-phase LLC resonant converter, the size of the resonant capacitor of the resonant converter is closed-loop adjusted, so that the staggered parallel LLC resonant converter is not affected by the circuit parameter deviation and can control the resonant current sharing, thereby achieving the transmission power balance of the staggered parallel LLC resonant converter. Each LLC resonant converter independently adjusts the size of its own resonant capacitor without affecting the normal output of the staggered parallel LLC resonant converter. On the other hand, the switching signal frequency of each LLC resonant converter is the same and the phases are staggered, which reduces the output current ripple of the staggered parallel LLC resonant converter. The reliability and stability of the staggered parallel LLC resonant converter system are improved through this application. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification, are used to explain the principles of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on these drawings without inventive effort.
[0028] Figure 1 A diagram showing the steps of a current sharing control method for an interleaved parallel LLC resonant converter based on switch-controlled capacitors in an exemplary embodiment of the present disclosure is provided; Figure 2 A schematic diagram illustrating an interleaved parallel LLC resonant converter in an exemplary embodiment of the present disclosure is shown; Figure 3 A diagram showing the steps of a current sharing method for an interleaved parallel LLC resonant converter in an exemplary embodiment of the present disclosure is shown; Figure 4 Showing a four-way 90° staggered driving waveform diagram in an exemplary embodiment of the present disclosure; Figure 5 A schematic diagram showing an inverter circuit in an exemplary embodiment of the present disclosure; Figure 6 A schematic diagram showing a resonant cavity circuit in an exemplary embodiment of the present disclosure; Figure 7 A schematic diagram showing a rectifier and filter output circuit in an exemplary embodiment of the present disclosure is shown; Figure 8 The waveforms of the first resonant current, the second resonant current, the output current and the output voltage before current sharing control in an exemplary embodiment of the present disclosure are shown; Figure 9 The waveforms of the first resonant current, the second resonant current, the output current and the output voltage after current sharing control in an exemplary embodiment of the present disclosure are shown. DETAILED DESCRIPTION
[0029] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0030] In addition, the accompanying drawings are merely schematic illustrations of embodiments of the present disclosure and are not necessarily drawn to scale. Like reference numerals in the figures represent like or similar parts, and thus repeated descriptions thereof will be omitted. Some of the blocks shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically separate entities.
[0031] This example embodiment provides a current sharing control method for an interleaved parallel LLC resonant converter based on switch-controlled capacitors. Figure 1 As shown in , the current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors may include: Step S101: constructing an interleaved parallel LLC resonant converter; wherein the interleaved parallel LLC resonant converter includes a digital control circuit, a main power circuit, and an auxiliary circuit, the main power circuit includes a first-phase LLC resonant converter and a second-phase LLC resonant converter connected in parallel, the first-phase LLC resonant converter and the second-phase LLC resonant converter are electrically connected to the digital control circuit and the auxiliary circuit, respectively; Step S102: Generate multiple PWM drive signals with the same frequency and staggered phases through a digital control circuit to control the operation of switches of the first-phase LLC resonant converter and the second-phase LLC resonant converter, respectively, so that the first-phase LLC resonant converter generates a first resonant current and the second-phase LLC resonant converter generates a second resonant current; Step S103: acquiring the first resonant current and the second resonant current in real time, and calculating the resonant current sharing error according to the first resonant current and the second resonant current; Step S104: When the resonant current sharing error exceeds the set sharing error threshold, dynamically adjust the conduction angle of each phase switch control capacitor until the resonant current sharing error is less than the sharing error threshold to output the sharing current.
[0032] Through the above-mentioned staggered parallel LLC resonant converter current sharing control method based on switch-controlled capacitors, on the one hand, by detecting the first resonant current and the second resonant current of the first-phase LLC resonant converter and the second-phase LLC resonant converter, the size of the resonant capacitor of the resonant converter is closed-loop adjusted, so that the staggered parallel LLC resonant converter is not affected by the circuit parameter deviation and can control the resonant current sharing, thereby achieving the transmission power balance of the staggered parallel LLC resonant converter. Each LLC resonant converter independently adjusts the size of its own resonant capacitor without affecting the normal output of the staggered parallel LLC resonant converter. On the other hand, the switching signal frequency of each LLC resonant converter is the same and the phases are staggered, which reduces the output current ripple of the staggered parallel LLC resonant converter. The reliability and stability of the staggered parallel LLC resonant converter system are improved through this application.
[0033] Below, we will refer to Figures 1 to 9 Each step of the above-mentioned method for controlling current sharing of the interleaved parallel LLC resonant converter based on switch-controlled capacitors in this exemplary embodiment is described in more detail.
[0034] In one embodiment, Figure 2 The figure shows the schematic diagram of the structure of the staggered parallel LLC resonant converter, which mainly consists of three parts: digital control circuit, main power circuit and auxiliary circuit. The input and output of the two resonant converters are connected in parallel. Each LLC resonant converter shares the DC input voltage. The output end of each output rectifier filter circuit is connected in parallel to jointly provide the output voltage to the load. The digital control circuit is designed based on the STM32F334C8T6 microcontroller (Microcontroller Unit, MCU), and frequency reduction control is used to achieve soft start. The output voltage and output current after parallel connection are sampled by the output voltage and current sampling circuit and sent to the control circuit. The digital values of output voltage, output current and resonant current are obtained through the analog-to-digital converter (ADC). The proportional-integral-differential (PID) control algorithm is used to adjust the switching frequency to achieve closed-loop voltage regulation. The PID algorithm is applied in the current sharing control strategy to change the duty cycle of the SCC drive signal to achieve current sharing of the two-phase resonant cavity. The current sharing control algorithm is as follows: Figure 3 The main power circuit is an LLC full-bridge resonant converter or LLC half-bridge resonant converter, which converts DC input power and outputs it through rectification and filtering. It includes a full-bridge or half-bridge switching circuit, an LLC resonant circuit, a high-frequency transformer, and a rectification and filtering circuit. The auxiliary circuit mainly consists of a drive circuit, a startup protection circuit, a hardware protection circuit, and a sampling circuit.
[0035] The control circuit's MCU (which can be a DSP, single-chip microcomputer, ARM embedded processor, or FPGA programmable chip) outputs six PWM signals. Four of these PWM signals drive the inverter bridge arms of the two resonant converters, and two drive the switch-controlled capacitors. The switching signals for each resonant converter are set to have the same frequency and a 90° phase shift, forming an interleaved parallel structure. To balance the device tolerances within the two resonant cavities, a switch-controlled capacitor is connected in series with each resonant cavity circuit of the two-phase resonant converter. Turning switches S1 and S2 on and off changes the duty cycle of the PWM signals driving S1 and S2, thereby varying the size of the switch-controlled capacitors and, consequently, the equivalent resonant capacitance. This compensates for the voltage gain of the two phases at the same switching frequency, thus achieving current balancing.
[0036] The specific technical solutions are as follows: definition 、 is the resonant current of the two LLC resonant converters, then the average value of the two resonant currents is for The resonant current sharing error of the two-phase LLC resonant converter is defined as The closer the current sharing error is to 0, the more balanced the two resonant currents are, and the more balanced the power of the two resonant converters is. is the conduction angle of the switch-controlled capacitor in the resonant cavity of the first-phase LLC resonant converter, is the conduction angle of the switch-controlled capacitor in the resonant cavity of the second-phase LLC resonant converter.
[0037] First, and Initialize to initial value , Then, the resonant current, resonant voltage, output voltage, and output current of each phase resonant converter are sampled. When the circuit is in a stable state, the current sharing error is calculated. When the current sharing error Less than the set current sharing error threshold When , it is considered that the two-phase interleaved parallel LLC resonant converter has achieved current sharing, and the algorithm ends. When comparing the two resonant currents, increase the conduction angle of the switch control capacitor of the resonant converter with the larger resonant current. If it is already the maximum value ( ), the conduction angle of the other phase resonant converter is reduced until current sharing is achieved and the two resonant currents are balanced.
[0038] The current sharing control method for the interleaved parallel circuit of LLC resonant converters described in the present application is also applicable to the current sharing control of more than two LLC resonant converters connected in parallel.
[0039] In a specific embodiment, the following Figure 2 The embodiments of the present application are described. Figure 2 This is the structure diagram of the interleaved parallel half-bridge LLC resonant converter.
[0040] The converter input voltage is DC voltage , the output voltage is a constant DC voltage . It is the upper and lower LLC resonant converter switch tube, The upper and lower resonant cavity freewheeling diodes, the upper resonant cavity is composed of resonant capacitors , resonant inductor , excitation inductance The lower resonant cavity is composed of a resonant capacitor , resonant inductor , excitation inductance composition, They are high-frequency transformers for the upper and lower resonant converters respectively. For the output synchronous rectifier, is the rectifier filter capacitor, is the load resistance.
[0041] The control chip in the control circuit is an ARM embedded processor STM32F334 (which can be a DSP, single-chip microcomputer, ARM embedded processor or FPGA programmable chip). The control chip outputs two PWM drive signals. Each PWM signal outputs a set of complementary PWM drive signals. The two PWM drive signals have the same frequency and a phase difference of 90°, forming an interleaved parallel structure, such as Figure 4 The two PWM signals drive the switching tubes of the two resonant converters through the isolation drive circuit respectively.
[0042] The output voltage sampling circuit samples the voltage of the parallel output, and the output current sampling circuit samples the current of the parallel output, and sends the sampled values of the output voltage and output current to the A / D converter of the embedded processor to convert them into digital quantities for the system closed-loop control to output a stable voltage.
[0043] There are two resonant current sampling circuits, which respectively sample the resonant current of the two LLC resonant converters and convert them into digital quantities through the A / D converter of the embedded processor for use in system current sharing control.
[0044] The input voltage of the interleaved parallel LLC resonant converter is 48V; the output voltage is 24V; and the rated output power is 250W. The resonant frequency is 100kHz, the resonant inductance is 1.695uH, and the excitation inductance is 8.475uH. To facilitate verification of the validity of this application, the resonant parameters of the two resonant converters are set to different values to simulate the deviation of the resonant parameters. The resonant capacitance of the first resonant converter is 1340nF; the resonant capacitance of the second resonant converter is 1640nF, with a resonant capacitance deviation of 300nF.
[0045] Table 1 lists in detail the main technical indicators required for this application.
[0046] Table 1 Design index parameter table
[0047] Resonant cavity parameter design: The theoretical turns ratio of the transformer is:
[0048] in 0.5V is the forward conduction voltage drop of the diode.
[0049] Converter minimum gain for:
[0050] Maximum gain for:
[0051] Output load for:
[0052] Substituting the above formula into the primary side equivalent load can be obtained:
[0053] Minimum operating frequency At maximum gain we get:
[0054] The inductance coefficient is selected based on experience .
[0055] Maximum operating frequency At minimum gain we get:
[0056] Maximum quality factor for
[0057] Leaving a margin, the quality factor can be obtained:
[0058] The maximum resonant capacitance can be obtained for:
[0059] Characteristic impedance for:
[0060] Quality factor for:
[0061] Calculate the size of SCC according to and quality factor get The value of 、 and Substitution Get , and then substitute it into Get =957nF. and Substitution and Zhong Ke De =1492nF, = =2668.867nF.
[0062] and 、 The following relationship is satisfied:
[0063] but:
[0064] The resonant inductance can be obtained for:
[0065] The magnetizing inductance can be obtained for:
[0066] Calculate the effective value of the resonant cavity current for:
[0067] Power transformer parameter design: According to the above design indicators, the PC95 model is selected and the core area product method (AP method) is used for design.
[0068] The apparent power of the transformer is:
[0069] The calculation formula is:
[0070] Window coefficient Take 0.3, waveform coefficient Take 4.44, operating frequency Take 75.2kHz, maximum magnetic flux density Take 0.2T, current density Pick , we can get The values are:
[0071] According to the commonly used core parameter table, the window area of PQ3535 is , the effective area is , then the PQ3535 core skeleton The values are:
[0072] , the designed magnetic core meets the design requirements.
[0073] Transformer winding calculation: Calculate the number of turns of the transformer primary winding according to the volt-second balance principle. is the duty cycle of the switch, is the conduction time in one cycle, is the duty cycle of the switch tube, , is the magnetic flux density, is the rated input voltage.
[0074]
[0075] According to the circuit design indicators and the selected transformer core parameters, the number of turns of the transformer primary winding can be obtained:
[0076] Then the number of turns of the secondary winding is:
[0077] The primary winding can be obtained by rounding The secondary winding has 4 turns. It is 4 turns.
[0078] Use 0.2mm*25 strands / root enameled wire for transformer winding, and the maximum current density that each wire can withstand .
[0079] The number of primary winding wires is:
[0080] The number of secondary winding wires is:
[0081] Rounding off, the number of primary winding wires is The number of secondary winding wires is 4. For 2 pieces.
[0082] Inverter circuit design in the main power circuit: The inverter circuit designed in this application is as follows Figure 5 shown.
[0083] In the inverter circuit, Q1 and Q3 use FCH47N60 MOSFETs. To suppress the turn-off spike, a small capacitor is connected in parallel between the drain and source. Furthermore, to provide a discharge path for gate charge and achieve circuit protection, a resistor is connected in parallel between the gate and source. To suppress the spike caused by LC oscillation during turn-on, a resistor is added in series with the gate input.
[0084] Resonant cavity circuit design The circuit of the first LLC resonant converter designed in this application is as follows Figure 6 As shown, the structure of the second LLC resonant converter is the same as that of the first LLC resonant converter.
[0085] L2 ( ) is the resonant inductor, C30 ( )、C40( ) and the switch control capacitor C43 in series in the resonant cavity ( ) together form the resonant capacitor. By adjusting the duty cycle of the gate drive signal (SCC_HO_G) of Q5 (FCH47N60P), its on-time is changed. By dynamically adjusting the capacitance in the circuit, the resonant cavity current is controlled.
[0086] Rectifier circuit design: The full-wave rectifier filter circuit designed in this application is as follows Figure 7 shown.
[0087] The maximum current in this circuit for:
[0088] The maximum reverse voltage in the MOSFET for:
[0089] Taking into account the key parameters of the synchronous rectification circuit, such as the switching frequency and drive signal amplitude, this application uses the SRK2001 and STL130N6F7 chips. Considering extreme working conditions, C35, C36, C37, and C38 are selected as 470 / 100V to optimize filtering performance.
[0090] The following is a verification of the current sharing control of the interleaved parallel half-bridge LLC resonant converter. The current sharing control process is as follows: (1) Output drive signal, detect the resonant current of the two resonant converters in each switching cycle, and the effective value of the detected resonant current is recorded as and Calculate the average value of the effective value of the two resonant currents and resonant current sharing error ,like Greater than the set current sharing error threshold Proceed to the next step.
[0091] (2) Compare the magnitudes of the two resonant currents, increase the conduction angle of the switch control capacitor of the resonant converter with the larger resonant current, and reduce the conduction angle of the other resonant converter to balance the two resonant currents. When performing closed-loop control, the conduction angle adjustment range is .
[0092] (3) Repeat the process of (1) and (2) until the current equalization error is Less than the set current sharing error threshold , current sharing control ends.
[0093] The resonant current, output current and output voltage waveforms before current equalization control are as follows: Figure 8 As shown, the resonant current of the first resonant converter is 12.49A, and the resonant current of the second resonant converter is 4.28A. The resonant currents of the two resonant converters differ greatly, the power of the two resonant converters is unbalanced, and the output ripple is 15.11mV.
[0094] After adopting the current sharing control, the resonant current, output current and output voltage waveforms are as follows Figure 9 As shown, the resonant current of the first resonant converter is 7.41A, and the resonant current of the second resonant converter is 7.42A, which are basically equal to achieve current sharing. The power of the two resonant converters is balanced, and the output ripple is 5.61mV.
[0095] It can be seen from the implementation examples that although there are differences in the circuit parameters of each LLC resonant converter in the staggered parallel power supply system, resulting in inconsistent resonant currents of the two LLC resonant converters, after adopting the current equalization method proposed in this application, the resonant currents of the two LLC resonant converters are equal, the output ripple is significantly reduced, the transmission power is more balanced, and the reliability and stability of the entire power supply system are improved.
[0096] Through the above-mentioned staggered parallel LLC resonant converter current sharing control method based on switch-controlled capacitors, on the one hand, by detecting the first resonant current and the second resonant current of the first-phase LLC resonant converter and the second-phase LLC resonant converter, the size of the resonant capacitor of the resonant converter is closed-loop adjusted, so that the staggered parallel LLC resonant converter is not affected by the circuit parameter deviation and can control the resonant current sharing, thereby achieving the transmission power balance of the staggered parallel LLC resonant converter. Each LLC resonant converter independently adjusts the size of its own resonant capacitor without affecting the normal output of the staggered parallel LLC resonant converter. On the other hand, the switching signal frequency of each LLC resonant converter is the same and the phases are staggered, which reduces the output current ripple of the staggered parallel LLC resonant converter. The reliability and stability of the staggered parallel LLC resonant converter system are improved through this application.
[0097] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly indicate the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.
[0098] In the embodiments of the present disclosure, unless otherwise expressly specified or limited, the terms "installed," "electrically connected," "connected," "fixed," and the like should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integrated connections; they may refer to mechanical connections or electrical connections; they may refer to direct electrical connections or indirect electrical connections through an intermediate medium; they may refer to internal connectivity between two components or the interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present disclosure based on specific circumstances.
[0099] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.
[0100] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the appended claims.
Claims
1. A current sharing control method for an interleaved parallel LLC resonant converter based on switch-controlled capacitors, characterized in that: The method includes: Constructing an interleaved parallel LLC resonant converter; wherein the interleaved parallel LLC resonant converter includes a digital control circuit, a main power circuit, and an auxiliary circuit; the main power circuit includes a first-phase LLC resonant converter and a second-phase LLC resonant converter connected in parallel; the first-phase LLC resonant converter and the second-phase LLC resonant converter are electrically connected to the digital control circuit and the auxiliary circuit, respectively; Generate multiple PWM drive signals with the same frequency and staggered phases through a digital control circuit to control the operation of the switches of the first-phase LLC resonant converter and the second-phase LLC resonant converter respectively, so that the first-phase LLC resonant converter generates a first resonant current and the second-phase LLC resonant converter generates a second resonant current; Acquire the first resonant current and the second resonant current in real time, and calculate the resonant current sharing error according to the first resonant current and the second resonant current; When the resonant current sharing error exceeds the set sharing error threshold, the conduction angle of each phase switch control capacitor is dynamically adjusted until the resonant current sharing error is less than the sharing error threshold to output the current.
2. The current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors according to claim 1, characterized in that: The first-phase LLC resonant converter specifically includes: Capacitor C in The two ends are connected in parallel at both ends of the input source, one end of the switch tube Q1 is electrically connected to the positive end of the input source, and the other end of the switch tube Q1 is connected in parallel with the switch tube Q2 and the resonant inductor L r1 One end of the resonant cavity freewheeling diode D1 is electrically connected to the positive end of the input source, the other end of the resonant cavity freewheeling diode D1 is connected in parallel with the resonant cavity freewheeling diode D2, and the other end of the resonant cavity freewheeling diode D2 is electrically connected to the negative end of the input source; the resonant capacitor C r1 The two ends of the resonant cavity freewheeling diode D1 are connected in parallel, and the resonant capacitor C r2 The two ends of the resonant cavity freewheeling diode D2 are connected in parallel; the switch S1 is connected to the resonant capacitor C a1 In parallel with the resonant inductor L r1 , excitation inductance L m1 Resonant inductor L r1 , excitation inductance L m1 Series; the primary side of the transformer and the excitation inductance L in the resonant cavity m1 In parallel, the secondary side is connected to the rectifier circuit, the sources of the synchronous rectifier tubes SR1 and SR2 are connected in parallel to the ground of the output end, and the drains of the synchronous rectifier tubes SR1 and SR2 are connected to the secondary side of the transformer; the center tap of the transformer is electrically connected to the positive electrode of the output end; Among them, the output voltage C o And the load RL is connected in parallel at both ends of the output.
3. The current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors according to claim 2, characterized in that: The second-phase LLC resonant converter specifically includes: One end of the switch tube Q3 is electrically connected to the positive end of the input source, the other end of the switch tube Q4 is connected in parallel with the switch tube Q4 and is electrically connected to one end of the resonant inductor Lr3, and the other end of the switch tube Q4 is electrically connected to the negative end of the input source; one end of the resonant cavity freewheeling diode D3 is electrically connected to the positive end of the input source, the other end of the resonant cavity freewheeling diode D3 is connected in parallel with the resonant cavity freewheeling diode D4, and the other end of the resonant cavity freewheeling diode D4 is electrically connected to the negative end of the input source; both ends of the resonant capacitor Cr3 are connected in parallel with both ends of the resonant cavity freewheeling diode D3, and the resonant capacitor Cr3 is connected in parallel with both ends of the resonant cavity freewheeling diode D3. The two ends of capacitor Cr4 are connected in parallel with the two ends of resonant cavity freewheeling diode D4; switch S2 is connected in parallel with resonant capacitor Ca2, and is connected in series with resonant inductor Lr2 and excitation inductor Lm2; the primary side of the transformer is connected in parallel with the excitation inductor Lm2 in the resonant cavity, the secondary side is connected to the rectifier circuit, the source of synchronous rectifier SR3 and synchronous rectifier SR4 are connected in parallel to the ground of the output end, and the drain of synchronous rectifier SR3 and synchronous rectifier SR4 is connected to the secondary side of the transformer; the center tap of the transformer is electrically connected to the positive electrode of the output end; Among them, the output voltage C o And the load RL is connected in parallel at both ends of the output.
4. The current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors according to claim 3, characterized in that: The step of calculating the resonant current sharing error according to the first resonant current and the second resonant current includes: Get the first resonant current and the second resonant current ; According to the first resonant current and the second resonant current Calculate the average ; Calculate the resonant current sharing error based on the average value .
5. The current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors according to claim 4, characterized in that: When the resonant current sharing error exceeds a set current sharing error threshold, the conduction angle of each phase switch control capacitor is dynamically adjusted until the resonant current sharing error is less than the current sharing error threshold, including: The conduction angle of the switch-controlled capacitor in the resonant cavity of the first-phase LLC resonant converter is and the conduction angle of the switch-controlled capacitor in the resonant cavity of the second-phase LLC resonant converter Initialize to initial value , ; When the resonant current sharing error Exceeds the set current sharing error threshold When the first resonant current Is it greater than the second resonant current ; If the first resonant current Greater than the second resonant current , then determine the conduction angle Whether it is the maximum conduction angle; If so, reduce the conduction angle If not, increase the conduction angle angle.
6. The current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors according to claim 5, characterized in that: The method further includes: If the second resonant current Greater than the first resonant current , then determine the conduction angle Whether it is the maximum conduction angle; If so, reduce the conduction angle If not, increase the conduction angle angle.
7. The current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors according to claim 6, characterized in that: Current sharing error when oscillating current Less than the set current sharing error threshold When , the LLC resonant converters are staggered in parallel to achieve output current sharing.
8. The current sharing control method of the interleaved parallel LLC resonant converter based on switch-controlled capacitors according to claim 7, characterized in that: Conduction angle and conduction angle Adjust 0.01 degrees each time.