A control method, control device and switching power supply

Abstract

The application discloses a control method, a control device and a switching power supply, wherein the control method comprises the following steps: detecting whether a current turn-off event of a certain switch tube in a primary side inverter circuit of an N-phase LLC topology occurs in a current switching period; controlling the conduction time of each switch tube in the primary side inverter circuit in a next switching period according to the detection result; if the current turn-off event of the certain switch tube occurs in the current switching period, the time length between the conduction time of the certain switch tube in the current switching period and the time when the current turn-off event occurs is taken as the conduction time of each switch tube in the primary side inverter circuit in the next switching period; and if the current turn-off event of the certain switch tube does not occur in the current switching period, the conduction time of each switch tube in the primary side inverter circuit in the current switching period is increased by a set value and then taken as the conduction time of each switch tube in the primary side inverter circuit in the next switching period. The application can guarantee the current sharing characteristic of each phase and is beneficial to reducing the output ripple.

Description

Technical Field

[0001] This invention relates to power supplies, and more particularly to a control method, control device, and switching power supply. Background Technology

[0002] With the rapid development of power electronics technology, switching power supplies are evolving towards miniaturization and high power density. Multiphase LLC topologies are widely used in high-power power supply applications due to their advantages of soft switching and low current ripple. Figure 1 This is a schematic diagram of a typical three-phase LLC topology circuit. The primary-side inverter circuit includes a first bridge arm composed of switches Q1 and Q2, a second bridge arm composed of switches Q3 and Q4, and a third bridge arm composed of switches Q5 and Q6. The resonant branch connected to switches Q1 and Q2 includes a resonant inductor L1 and a resonant capacitor C2. The resonant branch connected to switches Q3 and Q4 includes a resonant inductor L3 and a resonant capacitor C3. The resonant branch connected to switches Q5 and Q6 includes a resonant inductor L5 and a resonant capacitor C4.

[0003] LLC topologies are divided into two types based on the sampling of the feedback signal:

[0004] (1) Voltage-type control: The secondary output voltage is used as the feedback signal. The deviation between the feedback signal and the setpoint is amplified by a comparator and compared with a sawtooth wave to generate a control pulse. Figure 2 for Figure 1 A voltage-type control timing diagram for a three-phase LLC topology, where θ1, θ2, and θ3 represent the phase angles between the three-phase drives. Starting with the first phase, the second and third phase drives lag by 120° phase, i.e., θ1 is 0°, θ2 is 120°, and θ3 is 240°. The frequency of the drive pulses of each bridge arm remains consistent. This control adopts a frequency modulation control strategy, which calculates the required operating frequency based on the feedback voltage, and calculates the delay time between the second and third phase drives based on the operating frequency, thereby providing the correct switching frequency and phase delay, and realizing closed-loop control of the electrical parameters output by the LLC topology to achieve the desired value.

[0005] (2) Current-type control includes two loops: an inner current loop with the primary side output current as the first feedback signal and an outer voltage loop with the secondary side output voltage as the second feedback signal. The output deviation of the outer voltage loop is used as the given value of the inner current loop and compared with the first feedback signal to generate a current shutdown event. This current shutdown event is a control quantity used to achieve closed-loop control of the electrical parameters of the N-phase LLC topology output to reach the desired value.

[0006] Voltage-controlled LLC topologies suffer from poor dynamic performance due to the influence of reactive power devices. Therefore, voltage-controlled systems are difficult to meet the design requirements of switching power supplies in applications with high dynamic performance requirements. Current-controlled LLC topologies reduce the LLC topology from a second-order system to a first-order system from a control perspective, widening the control bandwidth of the entire system and thus improving dynamic response performance. However, current-controlled methods suffer from current unevenness issues in three-phase LLC topologies, thus limiting their application. Currently, they are mainly used in single-phase LLC topologies.

[0007] The inventors of this application discovered through in-depth research that the reason for the uneven current problem in a three-phase LLC topology caused by the current-mode control method is that each phase of the three-phase LLC switching power supply needs to maintain a fixed angle, generally lagging by 120°. In the frequency modulation control of a three-phase LLC, the required operating frequency, i.e., the switching cycle, needs to be calculated in advance based on the feedback voltage of the switching power supply. Then, based on the calculated switching cycle, the angle required for the 120° lag is calculated sequentially, thereby determining the rise and fall times of each phase's switching. However, the turn-off of the switching transistor is determined by the resonant current and the loop feedback value. Therefore, the current-mode controlled LLC actually operates in a state of constantly changing frequency. This makes it impossible to determine the operating cycle of the switching power supply in advance, and thus impossible to determine the turn-on and turn-off times of each phase under the 120° lag. In other words, it is impossible to guarantee that each phase maintains a 120° phase lag sequentially, thus causing the problem of uneven current among the three phases.

[0008] It should be noted that the information disclosed in the background section is intended only to enhance the understanding of the overall background of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0009] Therefore, the technical problem to be solved by the present invention is to provide a control method, control device and switching power supply that can maintain a 120° phase lag between the three phases when using current-type control in a three-phase LLC topology, so as to achieve better dynamic response while ensuring current sharing of each phase.

[0010] As a first aspect of the present invention, the technical solution of the provided control method is as follows:

[0011] A control method is applied to an N-phase LLC topology with current-mode control, where N is a natural number greater than or equal to 2, wherein the control method includes:

[0012] The detection method detects whether a current turn-off event occurs in a certain switch in the primary-side inverter circuit of the N-phase LLC topology during the current switching cycle. The current turn-off event is a control quantity used to achieve closed-loop control of the electrical parameters output by the N-phase LLC topology to reach the desired value.

[0013] Based on the detection results, the conduction time of each switch in the primary-side inverter circuit of the next switching cycle is controlled as follows: If a current turn-off event occurs in a certain switch during the current switching cycle, the duration from the turn-on time of that switch to the time when the current turn-off event occurs is taken as the conduction time of each switch in the primary-side inverter circuit of the next switching cycle; if no current turn-off event occurs in a certain switch during the current switching cycle, the conduction time of each switch in the primary-side inverter circuit of the current switching cycle is increased by a set value and taken as the conduction time of each switch in the primary-side inverter circuit of the next switching cycle.

[0014] Furthermore, the current shutdown event is generated by comparing the sampled value of the resonant current in the resonant branch connected to the switch with the feedback value of the output voltage of the N-phase LLC topology, or by comparing the sampled value of the voltage across the resonant capacitor in the resonant branch connected to the switch with the feedback value of the output voltage of the N-phase LLC topology.

[0015] Furthermore, in the primary-side inverter circuit during the same switching cycle, the set value for the increase in conduction time of the upper and lower switching transistors of the same bridge arm is equal.

[0016] Furthermore, the set value for increasing the conduction time of each switch in the primary-side inverter circuit during different switching cycles is adjustable.

[0017] Furthermore, in each switching cycle, the upper and lower switches of each bridge arm in the primary-side inverter circuit are turned on alternately, and after ignoring the dead time, the conduction time of the upper and lower switches of each bridge arm is the same. At the same time, the phase of the driving pulse of each bridge arm is delayed by 360° / N in sequence.

[0018] As a second aspect of the present invention, the technical solution of the provided control device embodiment is as follows:

[0019] A control device is applied to a current-controlled N-phase LLC topology, where N is a natural number greater than or equal to 2, wherein the control device comprises:

[0020] The detection module is used to detect whether a certain switch in the primary-side inverter circuit of the N-phase LLC topology generates a current turn-off event during the current switching cycle. The current turn-off event is a control quantity used to achieve closed-loop control of the electrical parameters output by the N-phase LLC topology to reach the desired value.

[0021] The processing module is used to control the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle based on the detection results: if a certain switch generates a current turn-off event in the current switching cycle, the duration from the turn-on time of that switch in the current switching cycle to the time when the current turn-off event occurs is taken as the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle; if a certain switch does not generate a current turn-off event in the current switching cycle, the conduction duration of each switch in the primary-side inverter circuit in the current switching cycle is increased by a set value and taken as the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle.

[0022] As a third aspect of the present invention, the technical solution of the provided switching power supply embodiment is as follows:

[0023] A switching power supply employing a current-controlled N-phase LLC topology, wherein N is a natural number greater than or equal to 2, characterized in that the switching power supply includes the control device described in the second aspect above, used to control the conduction time of each switching transistor in the primary-side inverter circuit.

[0024] Preferably, N is 3.

[0025] Compared with the prior art, the three-phase LLC topology in this embodiment of the invention adopts current-type control, which reduces the second-order system to a first-order system compared with voltage-type control, thus widening the system bandwidth, making loop compensation easier, improving the dynamics of the system, and by applying the current turn-off event of the current cycle to the next switching cycle, it can maintain a fixed angle between each phase of the N-phase LLC topology, that is, the three phases are staggered by 360° / N, thereby ensuring the current sharing characteristics of each phase, which is beneficial to reducing the output ripple of the switching power supply and enhancing the reliability of the switching power supply. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a typical three-phase LLC topology circuit in the background art;

[0027] Figure 2 for Figure 1 A voltage-mode control timing diagram for a three-phase LLC topology;

[0028] Figure 3 This is a flowchart of the control method according to the first embodiment of the present invention;

[0029] Figure 4 A control timing diagram for a current-off event was generated for the control method of the first embodiment of the present invention;

[0030] Figure 5 This is a control timing diagram for the control method of the first embodiment of the present invention when no current shutdown event is generated;

[0031] Figure 6 This is a schematic block diagram of the control device according to the second embodiment of the present invention. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0034] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be used interchangeably where appropriate for the purposes of describing embodiments of this application herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0035] It should be understood that in the specification, claims, and drawings, when a step is described as continuing into another step, the step may directly continue into that other step or be continued into that other step through a third step; when an element / unit is described as "continuing" into another element / unit, the element / unit may be "directly connected" to that other element / unit or "connected" to that other element / unit through a third element / unit.

[0036] Furthermore, the accompanying drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions thereof will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0037] First Embodiment

[0038] This embodiment provides a control method applied to a current-controlled N-phase LLC topology, where N is a natural number greater than or equal to 2. The control method of this embodiment includes:

[0039] S101 detects whether a current turn-off event occurs in a certain switch in the primary-side inverter circuit of the N-phase LLC topology during the current switching cycle. The current turn-off event is a control quantity used to achieve closed-loop control of the electrical parameters output by the N-phase LLC topology to reach the desired value.

[0040] S102, based on the detection results, control the conduction duration of each switch in the primary-side inverter circuit of the next switching cycle: if a certain switch generates a current turn-off event in the current switching cycle, then the duration between the turn-on time of the certain switch in the current switching cycle and the time when the current turn-off event occurs is taken as the conduction duration of each switch in the primary-side inverter circuit of the next switching cycle; if a certain switch does not generate a current turn-off event in the current switching cycle, then the conduction duration of each switch in the primary-side inverter circuit of the current switching cycle is increased by a set value and taken as the conduction duration of each switch in the primary-side inverter circuit of the next switching cycle.

[0041] Figure 1 This embodiment uses a typical N-phase LLC topology for the control method, where N is 3 phases, the three-phase transformer is delta connected, the secondary side uses a three-phase full-wave rectifier circuit, and the rectifier tube is a diode.

[0042] It should be noted that the control method in this embodiment is applied to Figure 1 The three-phase LLC topology shown is just an example. Those skilled in the art can choose the number of phases, the connection method of the transformer, and the type of secondary rectifier circuit according to the actual situation. The specific selection of the LLC topology is not limited in this invention.

[0043] Furthermore, in the aforementioned S101 step, it detects whether a certain switch in the primary-side inverter circuit of the N-phase LLC topology generates a current turn-off event during the current switching cycle. This embodiment does not limit the switch to be detected; those skilled in the art can choose it themselves. For example, for... Figure 1 The circuit can detect any one of the switching transistors Q1 to Q6 in the primary-side inverter circuit. Of course, it is also possible to detect multiple switching transistors. In this case, the time between the turn-on and the current-generating turn-off event of each detected switching transistor in the same cycle is theoretically equal.

[0044] Among them, the current turn-off event is a control quantity used to achieve closed-loop control of the electrical parameters of the N-phase LLC topology output to reach the desired value. The electrical parameters reaching the desired value refers to achieving constant voltage output, constant current output, or constant power output of the LLC resonant converter, etc. This invention does not specify which electrical parameter reaches the desired value, and those skilled in the art can design it themselves as needed.

[0045] Preferably, the current-shutdown event is generated by comparing the sampled value of the resonant current in the resonant branch connected to the switching transistor with the feedback value of the N-phase LLC topology output voltage, or by comparing the sampled value of the voltage across the resonant capacitor in the resonant branch connected to the switching transistor with the feedback value of the N-phase LLC topology output voltage. The feedback value of the N-phase LLC topology output voltage is the feedback signal in the outer voltage loop, which characterizes the magnitude of the secondary-side output voltage.

[0046] Furthermore, in the primary-side inverter circuit during the same switching cycle, the set value for the increase in conduction time of the upper and lower switching transistors in the same bridge arm is equal, thereby ensuring that the turn-on time of the upper and lower transistors is the same and that the current and voltage are symmetrical.

[0047] Furthermore, the set value for increasing the conduction time of each switch in the primary-side inverter circuit during different switching cycles is adjustable, which helps to achieve the desired electrical parameters of the N-phase LLC topology output.

[0048] Furthermore, in each switching cycle, the upper and lower switches of each bridge arm in the primary-side inverter circuit are turned on alternately, and after ignoring the dead time, the conduction time of the upper and lower switches of each bridge arm is the same. At the same time, the phase of the driving pulse of each bridge arm is delayed by 360° / N in sequence.

[0049] The following is Figure 1 The working principle of the control method in this embodiment is explained using circuit topology as an example:

[0050] Figure 4 A control timing diagram for a current-turn-off event was generated for the control method of the first embodiment of the present invention. For example... Figure 4 As shown, since the driving pulses for every two phases in a three-phase LLC topology are the same, except that the phases lag by 120° sequentially, therefore Figure 4 Only two phases are shown in the text. Figure 1The rising edge of the drive of the intermediate phase switch Q1 is the start time. The current switching period T1 is determined by the current turn-off event in the previous switching period and is known. Therefore, the current switching period T1 is known before the start time of the drive of the intermediate phase switch Q1, and thus the turn-off time of the first phase is known. Furthermore, it can be known that the rising edge of the drive of the intermediate phase switch Q3 is 1 / 3T1 and the entire period of the second phase is T1. Correspondingly, the rising edge of the drive of the intermediate phase switch Q5 is 2 / 3T1 and the period is also T1. Therefore, the three phases can maintain a precise 120° phase delay. Assuming that after switch Q1 is turned on for TIpk 1 time, the sampled value of the resonant current in the resonant branch connected to switch Q1 is compared with the feedback signal of the voltage outer loop, resulting in a current turn-off event, then in the next switching cycle, both switch Q1 and switch Q2 will be turned on for TIpk 1 time. Thus, the next switching cycle T2 = 2 * TIpk 1 + 2 * Tdead, where Tdead is the dead time. During this period, both switch Q1 and switch Q2 will be turned off to prevent short circuits and burnout. The next switching cycle of the second phase can be determined as T2, with a phase delay of 1 / 3T2. The next switching cycle of the third phase can also be determined as T2, with a phase delay of 2 / 3T2. This ensures that the three phases strictly maintain a 120° phase delay when a current turn-off event occurs.

[0051] Figure 5 The control timing diagram for the first embodiment of the present invention where no current turn-off event is generated is shown below. Figure 5 As shown, only two phases are displayed. Figure 1 The rising edge of the drive of the switching transistor Q1 in the first phase is the starting moment. The current switching period T1 is determined by the current turn-off event in the previous switching period and is known. Therefore, the current switching period T1 is known before the start of the drive of the switching transistor Q1, and thus the turn-off time of the first phase is known. Furthermore, it can be known that the rising edge of the drive of the switching transistor Q3 in the second phase is 1 / 3T1 and the entire period of the second phase is T1. Correspondingly, the rising edge of the drive of the switching transistor Q5 in the third phase is 2 / 3T1 and the period is also T1. Therefore, a precise 120° phase delay can be maintained between the three phases. Assuming no current-turn-off event occurs during the conduction period (Ton1) of switch Q1, then in the next switching cycle, switch Q1 and switch Q2 will be on for a duration of Ton1 + Δt. Thus, the next switching cycle T2 = 2*(Ton1 + Δt) + 2*Tdead. The next switching cycle of the second phase can be determined as T2, with a phase delay of 1 / 3T2. The next switching cycle of the third phase can also be determined as T2, with a phase delay of 2 / 3T2. This ensures that the three phases strictly maintain a 120° phase delay when no current-turn-off event occurs.

[0052] Based on the above analysis of the working principle, it can be seen that this embodiment is similar to... Figure 2The difference in methods is that... Figure 2 The operating frequency is determined solely by the feedback signal of the secondary output voltage. However, in this embodiment, the operating frequency is related not only to the feedback signal of the outer voltage loop but also to the feedback signal of the inner current loop. Compared to voltage-type control, the control method in this embodiment reduces the second-order system to a first-order system, broadens the system bandwidth, facilitates loop compensation, and improves the system's dynamics. Furthermore, by applying the current turn-off event of the current cycle to the next switching cycle, it can maintain a fixed angle between each phase of the N-phase LLC topology, i.e., three-phase staggered 360° / N, thereby ensuring the current sharing characteristics of each phase, which helps reduce the output ripple of the switching power supply and enhances its reliability.

[0053] Second Embodiment

[0054] This embodiment provides a control device applied to a current-controlled N-phase LLC topology, where N is a natural number greater than or equal to 2. The control device includes:

[0055] The detection module is used to detect whether a certain switch in the primary-side inverter circuit of the N-phase LLC topology generates a current turn-off event during the current switching cycle. The current turn-off event is a control quantity used to achieve closed-loop control of the electrical parameters output by the N-phase LLC topology to reach the desired value.

[0056] The processing module is used to control the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle based on the detection results: if a certain switch generates a current turn-off event in the current switching cycle, the duration from the turn-on time of that switch in the current switching cycle to the time when the current turn-off event occurs is taken as the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle; if a certain switch does not generate a current turn-off event in the current switching cycle, the conduction duration of each switch in the primary-side inverter circuit in the current switching cycle is increased by a set value and taken as the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle.

[0057] This embodiment is a control device corresponding to the control method of the first embodiment, and the beneficial effects are the same. In addition, further refinements or improvements in the control method of the first embodiment are also applicable to the control device of this embodiment.

[0058] Third Embodiment

[0059] This embodiment provides a switching power supply that adopts a current-controlled N-phase LLC topology, where N is a natural number greater than or equal to 2. The switching power supply includes any of the control devices in the second embodiment, used to control the conduction time of each switching transistor in the primary-side inverter circuit.

[0060] Preferably, N is 3. Increasing the number of phases can reduce the output ripple current of LLC, but it will greatly increase the size of the switching power supply. Therefore, when N is 3, the optimal balance between the size of the switching power supply and the output ripple current can be achieved.

[0061] The above embodiments of the present invention are not intended to limit the scope of protection of the present invention. The implementation of the present invention is not limited thereto. All other modifications, substitutions or alterations made to the above structure of the present invention based on the above content of the present invention, in accordance with ordinary technical knowledge and common practice in the field, without departing from the basic technical idea of ​​the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A control method applied to an N-phase LLC topology with current-mode control, wherein N is a natural number greater than or equal to 2, characterized in that, The control method includes: The detection method detects whether a current turn-off event occurs in a certain switch in the primary-side inverter circuit of the N-phase LLC topology during the current switching cycle. The current turn-off event is a control quantity used to achieve closed-loop control of the electrical parameters output by the N-phase LLC topology to reach the desired value. Based on the detection results, the conduction time of each switch in the primary-side inverter circuit of the next switching cycle is controlled as follows: If a current turn-off event occurs in a certain switch during the current switching cycle, the duration from the turn-on time of that switch to the time when the current turn-off event occurs is taken as the conduction time of each switch in the primary-side inverter circuit of the next switching cycle; if no current turn-off event occurs in a certain switch during the current switching cycle, the conduction time of each switch in the primary-side inverter circuit of the current switching cycle is increased by a set value and taken as the conduction time of each switch in the primary-side inverter circuit of the next switching cycle.

2. The control method according to claim 1, characterized in that: The current shutdown event is generated by comparing the sampled value of the resonant current in the resonant branch connected to the switch with the feedback value of the output voltage of the N-phase LLC topology, or by comparing the sampled value of the voltage across the resonant capacitor in the resonant branch connected to the switch with the feedback value of the output voltage of the N-phase LLC topology.

3. The control method according to claim 1, characterized in that: In the same switching cycle, the set value for the increase in conduction time of the upper and lower switching transistors of the same bridge arm in the primary-side inverter circuit is equal.

4. The control method according to claim 1, characterized in that: The set value for increasing the conduction time of each switching transistor in the primary-side inverter circuit at different switching cycles is adjustable.

5. The control method according to any one of claims 1 to 4, characterized in that: In each switching cycle, the upper and lower switches of each bridge arm in the primary-side inverter circuit are turned on alternately. After ignoring the dead time, the conduction time of the upper and lower switches of each bridge arm is the same. At the same time, the phase of the driving pulse of each bridge arm is delayed by 360° / N.

6. A control device applied to a current-controlled N-phase LLC topology, wherein N is a natural number greater than or equal to 2, characterized in that, The control device includes: The detection module is used to detect whether a certain switch in the primary-side inverter circuit of the N-phase LLC topology generates a current turn-off event during the current switching cycle. The current turn-off event is a control quantity used to achieve closed-loop control of the electrical parameters output by the N-phase LLC topology to reach the desired value. The processing module is used to control the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle based on the detection results: if a certain switch generates a current turn-off event in the current switching cycle, the duration from the turn-on time of that switch in the current switching cycle to the time when the current turn-off event occurs is taken as the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle; if a certain switch does not generate a current turn-off event in the current switching cycle, the conduction duration of each switch in the primary-side inverter circuit in the current switching cycle is increased by a set value and taken as the conduction duration of each switch in the primary-side inverter circuit in the next switching cycle.

7. A switching power supply employing a current-controlled N-phase LLC topology, wherein N is a natural number greater than or equal to 2, characterized in that, The switching power supply includes the control device described in claim 6, used to control the conduction time of each switching transistor in the primary-side inverter circuit.

8. The switching power supply according to claim 7, characterized in that: The value of N is 3.

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