A control method of a single-stage flyback AC-DC converter
Patent Information
- Application Number
- CN202611213804.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-11
- Publication Date
- 2026-10-09
AI Technical Summary
该方案能够适应具有高效率要求的大功率应用场景，使主控制开关的应力被较好的控制，但由于增加了额外的开关器件、磁元件等，会存在成本较高、以及控制复杂度大幅提升的问题；
[0053]本发明通过在电流控制目标中主动加入谐波含量，能够实现主控制开关的电压应力降低，且无需新增其他任何开关器件，降低了主控制开关的电压应力和钳位电容的容量需求，使变压器峰值电流下降，实现了低成本的电压应力控制。
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Abstract
Description
Technical Field
[0001] This invention relates to the application of AC-DC converters, and in particular to a control method for a single-stage flyback AC-DC converter. Background Technology
[0002] Single-stage AC-DC converters can simultaneously achieve power factor correction (PFC) and isolated voltage regulation. Among them, single-stage flyback AC-DC converters have gained widespread application in the charging pile field due to their low system cost. Benefiting from the development of silicon carbide devices, single-stage flyback AC-DC converters can achieve higher power output.
[0003] As power output increases, the leakage inductance absorption problem in single-stage flyback AC-DC converters presents additional challenges. If the leakage inductance energy cannot be effectively controlled, the voltage stress on the main control switch will increase significantly. Currently, commonly used leakage inductance absorption schemes mainly include traditional RCD absorption schemes and active feedback absorption schemes.
[0004] Appendix Figure 1 The circuit diagram for the RCD absorption scheme is shown. The main control switch is the switching transistor Q1. The leakage inductance energy is absorbed by the RCD circuit composed of resistor R1, capacitor C1, and diode D1. It can adapt to low-power and low-cost scenarios. However, as the power output increases, in order to control the voltage stress on the control switch, only three measures can be taken: increasing the power consumption on resistor R1, increasing the capacitance of capacitor C1, and selecting a switching transistor Q1 with a higher voltage specification. These measures will either increase the system cost or reduce the system efficiency.
[0005] Appendix Figure 2 and attached Figure 3 This is a circuit diagram of an active feedback absorption scheme. The main control switch is transistor Q1. When Q1 is turned off, the leakage inductance energy can be absorbed by capacitor C1. Under appropriate switching transients, the capacitor energy can be fed back into the main circuit through transistor Q2, or through a circuit consisting of transistor Q2, diode D2, and inductor L1. This scheme can adapt to high-power applications with high efficiency requirements, and the stress on the main control switch is well controlled. However, due to the addition of extra switching devices and magnetic components, it suffers from higher costs and significantly increased control complexity.
[0006] Therefore, how to design a cost-effective and efficient voltage stress control scheme is a technical problem that the industry urgently needs to solve. Summary of the Invention
[0007] To address the problems existing in the leakage inductance absorption scheme in the prior art, this invention proposes a control method for a single-stage flyback AC-DC converter, aiming to reduce the voltage stress on the main control switch without increasing costs.
[0008] The technical solution of the present invention is to propose a control method for a single-stage flyback AC-DC converter, comprising: when controlling the operation of the single-stage flyback AC-DC converter, adding harmonic content to the current control target in the single-stage flyback AC-DC converter to reduce the voltage stress of the main control switch in the single-stage flyback AC-DC converter.
[0009] Furthermore, the single-stage flyback AC-DC converter includes:
[0010] A grid-side filter, which is connected to the AC power grid, is used to filter the AC power output from the AC power grid.
[0011] A rectifier bridge, connected to the output of the grid-side filter, is used to convert AC power into a single-phase full-wave rectified voltage and provide the single-phase full-wave rectified voltage to the input capacitor.
[0012] At least one DC-DC flyback module is connected between the input capacitor and the output capacitor to perform DC-DC voltage conversion and provide the DC-DC converted DC power to the output capacitor;
[0013] The control method for the single-stage flyback AC-DC converter includes at least four control strategies, including at least a first control strategy and a second control strategy that generate the current control target based on the input-side voltage or output-side voltage of the grid-side filter, and a third control strategy and a fourth control strategy that generate the current control target based on the input-side voltage or output-side voltage of the rectifier bridge.
[0014] Furthermore, the first control strategy includes:
[0015] The input voltage of the grid-side filter is detected, and a first current control target is generated based on the input voltage of the grid-side filter. The first current control target includes a first fundamental current control target and a first harmonic current control target. The first fundamental current control target is in phase and frequency with the grid voltage, and its amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0016] The input current of the grid-side filter is detected, the first current control target is subtracted from the detected input current to obtain a current error signal, and the current error signal is injected into the closed-loop controller.
[0017] The output of the closed-loop controller is input into the PWM module to generate the first PWM signal;
[0018] The first PWM signal controls the on / off state of the main control switch in the single-stage flyback AC-DC converter.
[0019] Furthermore, the first fundamental current control target is: i in_ref =I1sin(wt);
[0020] The first harmonic current control target is: i in_ref_extra =I2sin(2wt)+I3sin(3wt)+...+I n sin(nwt);
[0021] The grid voltage is v in =V m sin(wt);
[0022] Where w is the angular frequency of the grid voltage.
[0023] Furthermore, the second control strategy includes:
[0024] The input voltage of the grid-side filter is detected, and a second current control target is generated based on the input voltage of the grid-side filter. The second current control target includes a second fundamental current control target and a second harmonic current control target. The second fundamental current control target is in phase and frequency with the grid voltage, and its amplitude is set by an external command. It is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0025] The operating parameters of the single-stage flyback AC-DC converter are detected. The operating parameters are any current or voltage parameters in the single-stage flyback AC-DC converter other than the second current control target.
[0026] The operating parameters, the second fundamental current control target, and the second harmonic current control target are injected into the open-loop controller;
[0027] The output of the open-loop controller is input into the PWM module to generate a second PWM signal;
[0028] The second PWM signal controls the on / off state of the main control switch in the single-stage flyback AC-DC converter.
[0029] Furthermore, the second fundamental current control objective is: i in_ref =I1sin(wt);
[0030] The second harmonic current control target is: i in_ref_extra =I2sin(2wt)+I3sin(3wt)+...+I n sin(nwt);
[0031] The grid voltage is v in =V m sin(wt);
[0032] Where w is the angular frequency of the grid voltage.
[0033] Furthermore, the third control strategy includes:
[0034] The output voltage of the rectifier bridge is detected, and a third current control target is generated based on the output voltage of the rectifier bridge. The third current control target includes a third fundamental current control target and a third harmonic current control target. The waveform of the third fundamental current control target is consistent with the waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0035] The output current of the rectifier bridge is detected, the detected output current is subtracted from the third current control target to obtain a current error signal, and the current error signal is injected into the closed-loop controller.
[0036] The output of the closed-loop controller is input into the PWM module to generate a third PWM signal;
[0037] The third PWM signal is used to control the on / off state of the main control switch in the single-stage flyback AC-DC converter.
[0038] Furthermore, the target for controlling the third fundamental current is: i rec_ref =I1|sin(wt)|;
[0039] The control objective for the third harmonic current is: i rec_ref_extra =I2sin|(2wt)|+I3sin|(3wt)|+...+I n |sin(nwt)|;
[0040] The output voltage of the rectifier bridge is: v rec =|V m sin(wt)|;
[0041] Where w is the angular frequency of the grid voltage.
[0042] Furthermore, the fourth control strategy includes:
[0043] The output voltage of the rectifier bridge is detected, and a fourth current control target is generated based on the output voltage of the rectifier bridge. The fourth current control target includes a fourth fundamental current control target and a fourth harmonic current control target. The waveform of the fourth fundamental current control target is consistent with the waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0044] The operating parameters of the single-stage flyback AC-DC converter are detected. The operating parameters are any current or voltage parameters in the single-stage flyback AC-DC converter other than the fourth current control target.
[0045] The operating parameters, the fourth fundamental current control target, and the fourth harmonic current control target are injected into the open-loop controller;
[0046] The output of the open-loop controller is input into the PWM module to generate a fourth PWM signal;
[0047] The fourth PWM signal is used to control the on / off state of the main control switch in the single-stage flyback AC-DC converter.
[0048] Furthermore, the fourth fundamental current control target is: i rec_ref =I1|sin(wt)|;
[0049] The target for controlling the fourth harmonic current is: i rec_ref_extra =I2sin|(2wt)|+I3sin|(3wt)|+...+I n |sin(nwt)|;
[0050] The output voltage of the rectifier bridge is: v rec =|V m sin(wt)|;
[0051] Where w is the angular frequency of the grid voltage.
[0052] Compared with the prior art, the present invention has at least the following beneficial effects:
[0053] This invention reduces the voltage stress of the main control switch by actively adding harmonic content to the current control target without adding any other switching devices. This reduces the voltage stress of the main control switch and the capacity requirement of the clamping capacitor, thereby reducing the peak current of the transformer and achieving low-cost voltage stress control. Attached Figure Description
[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0055] Figure 1 This is a circuit diagram of an existing RCD absorption scheme;
[0056] Figure 2 and attached Figure 3 This is a circuit diagram of an existing active feedback absorption scheme.
[0057] Figure 4 This is a circuit diagram illustrating the application of the harmonic current injection method in the first embodiment of the present invention.
[0058] Figure 5 This is a circuit diagram illustrating the application of the harmonic current injection method in the second embodiment of the present invention.
[0059] Figure 6 This is a circuit diagram illustrating the application of the harmonic current injection method in the third embodiment of the present invention.
[0060] Figure 7 This is a circuit diagram illustrating the application of the harmonic current injection method in the fourth embodiment of the present invention.
[0061] Figure 8 This is the control flow of the harmonic current injection method in the first embodiment of the present invention;
[0062] Figure 9 This is the control flow of the harmonic current injection method in the second embodiment of the present invention;
[0063] Figure 10 This is the control flow of the harmonic current injection method in the third embodiment of the present invention;
[0064] Figure 11 This is the control flow of the harmonic current injection method in the fourth embodiment of the present invention;
[0065] Figure 12 A schematic diagram of the grid voltage and current waveforms when harmonic current is injected;
[0066] Figure 13 A schematic diagram of the grid voltage and current waveforms after injecting 33% third harmonic;
[0067] Figure 14 A schematic diagram of the grid voltage and current waveforms with 33% third harmonic and 10% fifth harmonic injected. Detailed Implementation
[0068] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0069] Therefore, a feature pointed out in this specification is used to describe one feature of one embodiment of the invention, and does not imply that every embodiment of the invention must have the described feature. Furthermore, it should be noted that this specification describes many features. Although certain features may be combined to illustrate possible system designs, these features may also be used in other combinations not explicitly stated. Therefore, unless otherwise stated, the described combinations are not intended to be limiting.
[0070] The principles and structure of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.
[0071] Currently, commonly used leakage inductance absorption schemes mainly include traditional RCD absorption schemes and active feedback absorption schemes. Figure 1 The circuit diagram shows the RCD absorption scheme, which can absorb leakage inductance energy through the RCD circuit composed of resistor R1, capacitor C1, and diode D1. However, it can only be used in low-power and low-cost scenarios. When the power output is increased, it is necessary to increase the power consumption on resistor R1, increase the capacitance of capacitor C1, or select a higher voltage switching transistor Q1. This will either increase the system cost or reduce the system efficiency.
[0072] Appendix Figure 2 and attached Figure 3 This is a circuit diagram of an active feedback absorption scheme, which can absorb leakage inductance energy through capacitor C1 and feed the capacitor energy back into the main circuit during appropriate switching transients. (Attached) Figure 2 The feedback of capacitor energy can be controlled by switching transistor Q2. Figure 3 The feedback of capacitor energy can be controlled by a circuit composed of switching transistor Q2, diode D2, and inductor L1. It can adapt to high-power application scenarios with high efficiency requirements and make the stress of the main control switch better controlled. However, due to the need to add additional switching devices, magnetic components, etc., there are problems such as increased cost and significantly increased control complexity.
[0073] To address the aforementioned problems, this invention proposes a control method for a single-stage flyback AC-DC converter. The aim is to reduce the voltage stress on the main control switch without increasing circuit hardware costs. The core solution lies in actively incorporating harmonic content into the current control target to reduce the voltage stress on the main control switch. Please refer to the appendix. Figure 4 The single-stage flyback AC-DC converter used in the first embodiment of the present invention consists of a grid-side filter, a rectifier bridge, a DC-DC flyback module, and a capacitor C. in and capacitor C o composition;
[0074] The grid-side filter is connected to the AC power grid and is used to filter the AC power output from the AC power grid. It can be implemented using traditional LC filtering or higher-order forms.
[0075] Diodes D3, D4, D5, and D6 form a rectifier bridge to rectify alternating current and convert it into a single-phase full-wave rectified voltage.
[0076] Resistor R1, capacitor C1, and diode D1 form an RCD circuit, which can absorb some leakage inductance energy. Switch Q1 acts as the main control switch to control the working state of the primary circuit. This part of the structure, together with the transformer and diode D2, constitutes a DC-DC flyback module for DC-DC voltage conversion.
[0077] Please see the appendix Figure 5 In the second embodiment of the present invention, multiple DC-DC flyback modules can be provided, where resistor R n Capacitor C n diode D pn diode D sn and the switching transistor Q n The nth DC-DC flyback module is set up, and its control method is slightly different from that of setting a single DC-DC flyback module. It needs to perform power sharing or current sharing control. However, its core solution is still to reduce the voltage stress of the main control switch by actively adding harmonic content to the current control target.
[0078] Please see the appendix Figure 6 In low-voltage charging scenarios, this invention can also adopt a synchronous rectification scheme for the secondary side circuit of the transformer. By using a MOSFET Q2 to replace the diode D2 in the above scheme, efficiency can be further improved and thermal design can be improved. However, its core solution still lies in actively adding harmonic content to the current control target to reduce the voltage stress of the main control switch.
[0079] Please see the appendix Figure 7 In high-power charging scenarios, in addition to using auxiliary Figure 5 The scheme shown with multiple DC-DC flyback modules can also adopt a structure of multiple transformers in parallel, or even a deep coupling scheme with multiple transformers sharing a magnetic core, to meet the needs of high-power charging scenarios. The core solution is still to reduce the voltage stress of the main control switch by actively adding harmonic content to the current control target.
[0080] It should be noted that the above appendix Figure 4 To be continued Figure 7The embodiments described above are mainly used to illustrate the implementation schemes of this application. They do not mean that the circuits used in this invention are limited to the above-described schemes. As long as they meet the core scheme of this invention, "by actively adding harmonic content to the current control target to reduce the voltage stress of the main control switch", they should be within the protection scope of this invention.
[0081] Based on the above circuit structure, this invention provides a corresponding control method for a single-stage flyback AC-DC converter, which specifically includes:
[0082] When controlling the operation of a single-stage flyback AC-DC converter, harmonic content is added to the current control target in the single-stage flyback AC-DC converter to reduce the voltage stress on the main control switch in the single-stage flyback AC-DC converter.
[0083] Under the above-described scheme, the present invention does not require any additional switching devices. It only needs to add harmonic content to the current control target to reduce the voltage stress on the main control switch, thereby achieving low-cost voltage stress control.
[0084] The control method for a single-stage flyback AC-DC converter provided by the present invention includes at least four control strategies, including at least a first control strategy and a second control strategy that generate current control target based on the input-side voltage or output-side voltage of the grid-side filter, and a third control strategy and a fourth control strategy that generate current control target based on the input-side voltage or output-side voltage of the rectifier bridge.
[0085] The first and third control strategies are used to perform closed-loop control, while the second and fourth control strategies are used to perform open-loop control.
[0086] It should be noted that the above four control strategies are only used to illustrate the method of injecting harmonic content in this invention. However, the specific method of injecting harmonic content is not limited to the above four. The core idea of this invention is to reduce the voltage stress of the main control switch by actively adding harmonic content. As long as it conforms to this design idea, it should fall within the protection scope of this invention.
[0087] The specific schemes of the first control strategy, the second control strategy, the third control strategy, and the fourth control strategy in this invention will be described below with reference to the accompanying drawings. Please refer to the attached drawings. Figure 8 The first control strategy in this invention includes the following steps:
[0088] The input voltage of the grid-side filter is detected, and a first current control target is generated based on the input voltage of the grid-side filter. The first current control target includes a first fundamental current control target and a first harmonic current control target. The first fundamental current control target is in phase and frequency with the grid voltage, and its amplitude is set by an external command. It is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0089] The input current of the detection grid-side filter is detected, the first current control target is subtracted from the detected input current to obtain the current error signal, and the current error signal is injected into the closed-loop controller.
[0090] The output of the closed-loop controller is input into the PWM module to generate the first PWM signal;
[0091] The on / off state of the main control switch in the single-stage flyback AC-DC converter is controlled by the first PWM signal.
[0092] Among them, the appendix Figure 8 i in in That is, the input current of the grid-side filter, which can be detected by a corresponding current sensor, i in_ref and i in_ref_extra The first fundamental current control target and the first harmonic current control target are respectively, which can be obtained by phase-locked tracking of the input voltage of the grid-side filter. By adding the above parameters together into the closed-loop controller, closed-loop control of the single-stage flyback AC-DC converter can be realized.
[0093] The output of the closed-loop controller is input to the PWM module, which can obtain the corresponding first PWM signal to control the on / off state of the main control switch.
[0094] Under the above control, the present invention can reduce the voltage stress of the main control switch and the capacity requirement of the clamping capacitor, thereby reducing the peak current of the transformer and achieving low-cost voltage stress control.
[0095] It should be noted that the above description is mainly used to illustrate the first control strategy. Other control strategies can only be implemented based on the input voltage of the grid-side filter. In other embodiments of the present invention, the current control target can also be generated based on the output voltage of the grid-side filter, which can also achieve the same technical effect.
[0096] Generally, the first fundamental current control target and the first harmonic current control target mentioned above can be obtained through phase-locked tracking. Please refer to the appendix. Figure 4 v in The grid voltage can be expressed as: v in =V m sin(wt), where w is the angular frequency of the grid voltage;
[0097] By performing phase-locked tracking on it, we can obtain: i in =I1sin(wt)+ I2sin(2wt)+ I3sin(3wt)+…+I n sin(nwt);
[0098] Here, I1sin(wt) represents the first fundamental current control target, I2sin(2wt) + I3sin(3wt) + ... + I n sin(nwt) represents the first harmonic current control target. This process is also the scheme in the first control strategy mentioned above that generates the current control target based on the input voltage of the grid-side filter.
[0099] The first fundamental current control target obtained through this scheme is in phase and frequency with the grid voltage, and its amplitude is set by external commands, which can achieve precise control of the input current or input power of a single-stage flyback AC-DC converter.
[0100] Please see the appendix Figure 9 The second control strategy in this invention includes the following steps:
[0101] The input voltage of the grid-side filter is detected, and a second current control target is generated based on the input voltage of the grid-side filter. The second current control target includes a second fundamental current control target and a second harmonic current control target. The second fundamental current control target is in phase and frequency with the grid voltage, and its amplitude is set by an external command. It is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0102] The operating parameters of a single-stage flyback AC-DC converter are detected. The operating parameters are any current or voltage parameters in the single-stage flyback AC-DC converter other than the second current control target.
[0103] The operating parameters, the second fundamental current control target, and the second harmonic current control target are injected into the open-loop controller;
[0104] The output of the open-loop controller is input into the PWM module to generate a second PWM signal;
[0105] The on / off state of the main control switch in the single-stage flyback AC-DC converter is controlled by the second PWM signal.
[0106] Among them, the appendix Figure 9 i in in_ref and i in_ref_extra These are the second fundamental current control target and the second harmonic current control target, respectively, which can be obtained by phase-locked tracking of the input voltage of the grid-side filter;
[0107] After obtaining the second fundamental current control target and the second harmonic current control target, the operating parameters of the single-stage flyback AC-DC converter are collected. Theoretically, these operating parameters can be any current or voltage parameter other than the second current control target. By performing relevant conversions and controls on the operating parameters, the second current control target can be indirectly controlled. In one embodiment of the present invention, the above-mentioned operating parameters can be selected as AC input voltage, clamping capacitor voltage, and output voltage. These parameters, along with the second fundamental current control target and the second harmonic current control target, are input to the open-loop controller to achieve open-loop control of the single-stage flyback AC-DC converter.
[0108] The output of the open-loop controller is input to the PWM module, which can obtain the corresponding second PWM signal to control the on / off state of the main control switch.
[0109] Based on the circuit model, although the input current of the single-stage flyback AC-DC converter is not monitored in real time in this second control strategy, the open-loop controller can calculate the required duty cycle and frequency based on the various voltage signals collected by the theoretical circuit model, thereby indirectly controlling the input current and tracking the current control target.
[0110] Under the above control, the present invention can reduce the voltage stress of the main control switch and the capacity requirement of the clamping capacitor, thereby reducing the peak current of the transformer and achieving low-cost voltage stress control.
[0111] It should be noted that the above description is mainly used to illustrate the second control strategy. The second control strategy can not only be implemented based on the input voltage of the grid-side filter. In other embodiments of the present invention, the current control target can also be generated based on the output voltage of the grid-side filter, which can also achieve the same technical effect.
[0112] Generally, the second fundamental current control target and the second harmonic current control target mentioned above can be obtained through phase-locked tracking. Please refer to the appendix. Figure 4 v in The grid voltage can be expressed as: v in =V m sin(wt), where w is the angular frequency of the grid voltage;
[0113] By performing phase-locked tracking on it, we can obtain: i in =I1sin(wt)+ I2sin(2wt)+ I3sin(3wt)+…+I n sin(nwt);
[0114] Here, I1sin(wt) represents the target of the second fundamental current control, I2sin(2wt) + I3sin(3wt) + ... + I nsin(nwt) represents the second harmonic current control target. This process is also the scheme in the second control strategy mentioned above that generates the current control target based on the input voltage of the grid-side filter.
[0115] The second fundamental current control target obtained through this scheme is in phase and frequency with the grid voltage, and its amplitude is set by external commands, which can achieve precise control of the input current or input power of a single-stage flyback AC-DC converter.
[0116] Please see the appendix Figure 10 The third control strategy in this invention includes the following steps:
[0117] The output voltage of the rectifier bridge is detected, and a third current control target is generated based on the output voltage of the rectifier bridge. The third current control target includes a third fundamental current control target and a third harmonic current control target. The waveform of the third fundamental current control target is consistent with the waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0118] The output current of the rectifier bridge is detected, the third current control target is subtracted from the detected output current to obtain the current error signal, and the current error signal is injected into the closed-loop controller.
[0119] The output of the closed-loop controller is input into the PWM module to generate a third PWM signal;
[0120] The on / off state of the main control switch in the single-stage flyback AC-DC converter is controlled by the third PWM signal.
[0121] Among them, the appendix Figure 10 i in rec That is, the output current of the rectifier bridge can be detected by a corresponding current sensor. Figure 10 i in rec_ref and i rec_ref_extra The third fundamental current control target and the third harmonic current control target are respectively, which can be obtained by phase-locked tracking of the output voltage of the rectifier bridge. By adding the above parameters together to the closed-loop controller, closed-loop control of the single-stage flyback AC-DC converter can be realized.
[0122] The output of the closed-loop controller is input to the PWM module, which can obtain the corresponding third PWM signal to control the on / off state of the main control switch.
[0123] Under the above control, the present invention can reduce the voltage stress of the main control switch and the capacity requirement of the clamping capacitor, thereby reducing the peak current of the transformer and achieving low-cost voltage stress control.
[0124] It should be noted that the above description is mainly used to illustrate the third control strategy. The non-third control strategy can only be implemented based on the output voltage of the rectifier bridge. In other embodiments of the present invention, the current control target can also be generated based on the input voltage of the rectifier bridge or by directly using the absolute value of the input voltage of the single-stage flyback AC-DC converter, which can also achieve the same technical effect.
[0125] Generally speaking, the aforementioned third fundamental current control target and third harmonic current control target can be obtained through phase-locked tracking, v rec The output voltage of the rectifier bridge can be expressed as: v rec =|V m sin(wt)|, where w is the angular frequency of the grid voltage;
[0126] By performing phase-locked tracking on it, we can obtain: i rec =I1|sin(wt)|+I2|sin(2wt)|+I3|sin(3wt)|+...+I n |sin(nwt)|;
[0127] Here, I1|sin(wt)| represents the target of the third fundamental current control, and I2|sin(2wt)|+I3|sin(3wt)|+...+I n |sin(nwt)| represents the third harmonic current control target, which is the scheme in the third control strategy mentioned above that generates the current control target based on the output voltage of the rectifier bridge.
[0128] The third fundamental current control target obtained through this scheme has a consistent waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command, which is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0129] Please see the appendix Figure 11 The fourth control strategy in this invention includes the following steps:
[0130] The output voltage of the rectifier bridge is detected, and a fourth current control target is generated based on the output voltage of the rectifier bridge. The fourth current control target includes a fourth fundamental current control target and a fourth harmonic current control target. The waveform of the fourth fundamental current control target is consistent with the waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0131] The operating parameters of a single-stage flyback AC-DC converter are detected. The operating parameters are any current or voltage parameters in the single-stage flyback AC-DC converter other than the fourth current control target.
[0132] The operating parameters, the fourth fundamental current control target, and the fourth harmonic current control target are injected into the open-loop controller;
[0133] The output of the open-loop controller is input into the PWM module to generate the fourth PWM signal;
[0134] The on / off state of the main control switch in the single-stage flyback AC-DC converter is controlled by the fourth PWM signal.
[0135] Among them, the appendix Figure 11 i in rec That is, the output current of the rectifier bridge, attached Figure 11 i in rec_ref and i rec_ref_extra These are the fourth fundamental current control target and the fourth harmonic current control target, respectively, which can be obtained by phase-locked tracking of the output voltage of the rectifier bridge;
[0136] After obtaining the fourth fundamental current control target and the fourth harmonic current control target, the operating parameters of the single-stage flyback AC-DC converter are collected. Theoretically, these operating parameters can be any current or voltage parameter other than the fourth current control target. By performing relevant conversions and controls on the operating parameters, the fourth current control target can be indirectly controlled. In one embodiment of the present invention, the above-mentioned operating parameters can be selected as AC input voltage, clamping capacitor voltage, and output voltage. These parameters, along with the fourth fundamental current control target and the fourth harmonic current control target, are input to the open-loop controller to realize open-loop control of the single-stage flyback AC-DC converter.
[0137] The output of the open-loop controller is input to the PWM module, which can obtain the corresponding fourth PWM signal to control the on / off state of the main control switch.
[0138] Based on the circuit model, although the output current of the rectifier bridge of the single-stage flyback AC-DC converter is not monitored in real time in this fourth control strategy, the open-loop controller can calculate the required duty cycle and frequency based on the various voltage signals collected by the theoretical circuit model, thereby indirectly controlling the output current of the rectifier bridge and tracking the current control target.
[0139] Under the above control, the present invention can reduce the voltage stress of the main control switch and the capacity requirement of the clamping capacitor, thereby reducing the peak current of the transformer and achieving low-cost voltage stress control.
[0140] It should be noted that the above description is mainly used to illustrate the fourth control strategy. Other control strategies can only be implemented based on the output voltage of the rectifier bridge. In other embodiments of the present invention, the current control target can also be generated based on the input voltage of the rectifier bridge or by directly using the absolute value of the input voltage of the single-stage flyback AC-DC converter, which can also achieve the same technical effect.
[0141] Generally speaking, the fourth fundamental current control target and the fourth harmonic current control target mentioned above can be obtained through phase-locked tracking. rec The output voltage of the rectifier bridge can be expressed as: v rec =|V m sin(wt)|, where w is the angular frequency of the grid voltage;
[0142] By performing phase-locked tracking on it, we can obtain: i rec =I1|sin(wt)|+I2|sin(2wt)|+I3|sin(3wt)|+...+I n |sin(nwt)|;
[0143] Here, I1|sin(wt)| represents the target of the fourth fundamental current control, and I2|sin(2wt)|+I3|sin(3wt)|+...+I n |sin(nwt)| represents the fourth harmonic current control target, which is the scheme in the fourth control strategy mentioned above that generates the current control target based on the output voltage of the rectifier bridge.
[0144] The fourth fundamental current control target obtained through this scheme has a consistent waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command, which is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter.
[0145] The above are the implementation schemes of the first, second, third, and fourth control strategies provided in this invention. In practical applications, it is generally only necessary to inject odd harmonics to make the even harmonic content zero. That is, when executing the first, second, third, and fourth control strategies, the control method of the single-stage flyback AC-DC converter further includes: controlling the even harmonic content in the harmonic current to be zero, i.e., I2=I4=…=I 2n =0, and mainly injects low-order harmonics.
[0146] It should be noted that the injected harmonic content usually needs to be controlled within the range required by the corresponding harmonic regulations and standards for the product.
[0147] Please see the appendix Figure 12This refers to the grid voltage and grid current waveforms without injected harmonic current. Please refer to the appendix. Figure 13 This represents the grid voltage and current waveforms after injecting 33% third harmonic, i.e., at this time i in =I1sin(wt)+ 0.33I1sin(3wt), from this appendix Figure 13 It can be clearly seen that the power grid current waveform decreases significantly at its peak, and the voltage stress of the corresponding main control switch is also significantly reduced.
[0148] Please see the appendix Figure 14 It represents the grid voltage and current waveforms after injecting 33% third harmonic and 10% fifth harmonic, i.e., at this time i in =I1sin(wt) + 0.33I1sin(3wt) + 0.1I1sin(5wt), from the attached... Figure 14 It is quite obvious that the waveform of the grid current has become smooth, and the voltage stress of the corresponding main control switch has also been significantly reduced.
[0149] In other words, by actively incorporating harmonic content into the current control target, this invention can reduce the voltage stress of the main control switch without adding any other switching devices, thus reducing the voltage stress of the main control switch and the capacitance requirement of the clamping capacitor.
[0150] This reduces the peak current of the transformer, achieving low-cost voltage stress control.
[0151] It should be noted that the terminology used above is for describing specific embodiments only and is not intended to limit the exemplary embodiments of the present invention. When the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The order of execution of actions, steps, etc., in the apparatus and methods in the specification and drawings can be implemented in any order unless a specific express order is specified, and as long as the output of a previous process is not used in a subsequent process. Similar sequential terms used for ease of description do not imply that such an order must be followed.
[0152] Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as constraints. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.
[0153] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A control method for a single-stage flyback AC-DC converter, characterized in that, include: When controlling the operation of the single-stage flyback AC-DC converter, harmonic content is added to the current control target of the single-stage flyback AC-DC converter to reduce the voltage stress of the main control switch in the single-stage flyback AC-DC converter.
2. The control method for a single-stage flyback AC-DC converter according to claim 1, characterized in that, The single-stage flyback AC-DC converter includes: A grid-side filter, which is connected to the AC power grid, is used to filter the AC power output from the AC power grid. A rectifier bridge, connected to the output of the grid-side filter, is used to convert AC power into a single-phase full-wave rectified voltage and provide the single-phase full-wave rectified voltage to the input capacitor. At least one DC-DC flyback module is connected between the input capacitor and the output capacitor to perform DC-DC voltage conversion and provide the DC-DC converted DC power to the output capacitor; The control method for the single-stage flyback AC-DC converter includes at least four control strategies, including at least a first control strategy and a second control strategy that generate the current control target based on the input-side voltage or output-side voltage of the grid-side filter, and a third control strategy and a fourth control strategy that generate the current control target based on the input-side voltage or output-side voltage of the rectifier bridge.
3. The control method for a single-stage flyback AC-DC converter according to claim 2, characterized in that, The first control strategy includes: The input voltage of the grid-side filter is detected, and a first current control target is generated based on the input voltage of the grid-side filter. The first current control target includes a first fundamental current control target and a first harmonic current control target. The first fundamental current control target is in phase and frequency with the grid voltage, and its amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter. The input current of the grid-side filter is detected, the first current control target is subtracted from the detected input current to obtain a current error signal, and the current error signal is injected into the closed-loop controller. The output of the closed-loop controller is input into the PWM module to generate the first PWM signal; The first PWM signal controls the on / off state of the main control switch in the single-stage flyback AC-DC converter.
4. The control method for a single-stage flyback AC-DC converter according to claim 3, characterized in that, The first fundamental current control target is: i in_ref =I1sin(wt); The first harmonic current control target is: i in_ref_extra =I2sin(2wt)+I3sin(3wt)+...+I n sin(nwt); The grid voltage is v in =V m sin(wt); Where w is the angular frequency of the grid voltage.
5. The control method for a single-stage flyback AC-DC converter according to claim 2, characterized in that, The second control strategy includes: The input voltage of the grid-side filter is detected, and a second current control target is generated based on the input voltage of the grid-side filter. The second current control target includes a second fundamental current control target and a second harmonic current control target. The second fundamental current control target is in phase and frequency with the grid voltage, and its amplitude is set by an external command. It is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter. The operating parameters of the single-stage flyback AC-DC converter are detected. The operating parameters are any current or voltage parameters in the single-stage flyback AC-DC converter other than the second current control target. The operating parameters, the second fundamental current control target, and the second harmonic current control target are injected into the open-loop controller; The output of the open-loop controller is input into the PWM module to generate a second PWM signal; The second PWM signal controls the on / off state of the main control switch in the single-stage flyback AC-DC converter.
6. The control method for a single-stage flyback AC-DC converter according to claim 5, characterized in that, The second fundamental current control target is: i in_ref =I1sin(wt); The second harmonic current control target is: i in_ref_extra =I2sin(2wt)+I3sin(3wt)+...+I n sin(nwt); The grid voltage is v in =V m sin(wt); Where w is the angular frequency of the grid voltage.
7. The control method for a single-stage flyback AC-DC converter according to claim 2, characterized in that, The third control strategy includes: The output voltage of the rectifier bridge is detected, and a third current control target is generated based on the output voltage of the rectifier bridge. The third current control target includes a third fundamental current control target and a third harmonic current control target. The waveform of the third fundamental current control target is consistent with the waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter. The output current of the rectifier bridge is detected, the detected output current is subtracted from the third current control target to obtain a current error signal, and the current error signal is injected into the closed-loop controller. The output of the closed-loop controller is input into the PWM module to generate a third PWM signal; The third PWM signal is used to control the on / off state of the main control switch in the single-stage flyback AC-DC converter.
8. The control method for a single-stage flyback AC-DC converter according to claim 7, characterized in that, The control objective of the third fundamental current is: i rec_ref =I1|sin(wt)|; The control objective for the third harmonic current is: i rec_ref_extra =I2sin|(2wt)|+I3sin|(3wt)|+...+I n |sin(nwt)|; The output voltage of the rectifier bridge is: v rec =|V m sin(wt)|; Where w is the angular frequency of the grid voltage.
9. The control method for a single-stage flyback AC-DC converter according to claim 2, characterized in that, The fourth control strategy includes: The output voltage of the rectifier bridge is detected, and a fourth current control target is generated based on the output voltage of the rectifier bridge. The fourth current control target includes a fourth fundamental current control target and a fourth harmonic current control target. The waveform of the fourth fundamental current control target is consistent with the waveform of the output voltage of the rectifier bridge, and the amplitude is set by an external command. This is used to achieve precise control of the input current or input power of the single-stage flyback AC-DC converter. The operating parameters of the single-stage flyback AC-DC converter are detected. The operating parameters are any current or voltage parameters in the single-stage flyback AC-DC converter other than the fourth current control target. The operating parameters, the fourth fundamental current control target, and the fourth harmonic current control target are injected into the open-loop controller; The output of the open-loop controller is input into the PWM module to generate a fourth PWM signal; The fourth PWM signal is used to control the on / off state of the main control switch in the single-stage flyback AC-DC converter.
10. The control method for a single-stage flyback AC-DC converter according to claim 9, characterized in that, The fourth fundamental current control objective is: i rec_ref =I1|sin(wt)|; The target for controlling the fourth harmonic current is: i rec_ref_extra =I2sin|(2wt)|+I3sin|(3wt)|+...+I n |sin(nwt)|; The output voltage of the rectifier bridge is: v rec =|V m sin(wt)|; Where w is the angular frequency of the grid voltage.