PFM / PWM control method used in bidirectional DC-DC power supply circuit

Abstract

The invention provides a PFC / PWM (Pulse Frequency Modulation / Pulse Width Modulation) control method used in a bidirectional DC-DC (Direct Current-Direct Current) power supply circuit. The DC / DC converter obtains a bus input voltage Ubus, and the bus input voltage Ubus is input to the battery after being subjected to voltage reduction processing; s2; a battery voltage sampling value Ubat is acquired through a battery voltage acquisition module, a voltage target value Uref is set, and the voltage target value Uref and the voltage sampling value are calculated through a PI controller to obtain a current target value Iref; (S3); a battery current sampling value Ibat is acquired through a battery current acquisition module, and a duty ratio D is obtained through calculation of a current target value Iref and the current sampling value Ibat through a PI controller; setting the minimum duty ratio as Dmin, comparing the minimum duty ratio Dmin with the duty ratio D, and judging whether the system is in a PWM (Pulse Width Modulation) control stage or a PFM (Pulse Frequency Modulation) control stage; smooth switching of the two control modes is realized by combining PWM and PFM technologies and utilizing the output duty ratio D of the PI controller, so that the voltage output range of the DC-DC converter is expanded, and meanwhile, the light load efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment, and more specifically to a PFM / PWM control method for a bidirectional DC-DC power supply circuit. Background Art

[0002] At present, the control schemes of DC-DC circuits for charging and discharging batteries in the new energy industry mostly use PWM (Pulse-Width Modulation) technology or PFM (Pulse frequency modulation) technology. Among them, PFM technology is usually applied to DC-DC converters to improve light load efficiency. The method used is single and cannot be continuous.

[0003] Most existing DC-DC control solutions use a single PWM technology or PFM technology, but they have the following defects:

[0004] 1. The cycle of single PWM technology control is fixed, and the duty cycle has a limited range of variation. When the duty cycle is less than a certain value, it cannot be reduced for control, and the PI controller outputs the value of the duty cycle.

[0005] 2. The duty cycle controlled by a single PFM technology is fixed. Due to the limitation of the operating frequency range of the hardware switch tube, the frequency modulation range of the PFM technology is limited, and the PI controller outputs the switching frequency of the switch tube.

[0006] As a result, these two single control methods will result in a limited voltage output range of the DC-DC output circuit. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a PFM / PWM control method for a bidirectional DC-DC power supply circuit, which can quickly cut off the non-electrical fault of the transformer and reduce the time the transformer can withstand the fault, in view of the shortcomings of the above technical solutions.

[0008] In one aspect, the present invention provides a PFM / PWM control method for a bidirectional DC-DC power supply circuit, the control method comprising the following steps:

[0009] S1; the DC / DC converter obtains the bus input voltage Ubus, and steps down the bus input voltage Ubus before inputting it into the battery;

[0010] S2: The battery voltage sampling value Ubat is collected by the battery voltage collection module, and the voltage target value is set as Uref. The voltage target value Uref and the voltage sampling value Ubat are calculated by the PI controller to obtain the current target value Iref;

[0011] S3: The battery current sampling value Ibat is collected by the battery current collection module, and the current target value Iref and the current sampling value Ibat are calculated by the PI controller to obtain the duty cycle D; the minimum duty cycle is set to Dmin, the minimum duty cycle Dmin is compared with the duty cycle D, and it is determined whether the system is in the PWM control stage or the PFM control stage;

[0012] S4: The duty cycle D is used to generate a pulse drive signal through a pulse generator, and the pulse drive signal controls the on and off of the switch tube in the DC / DC converter.

[0013] In the PFM / PWM control method for a bidirectional DC-DC power supply circuit described in the present invention; in the step S2, the calculation formula of the current target value Iref is: Iref=Kp(Uref-Ubat)+Ki*∫(Uref-Ubat), wherein Kp is the proportional coefficient and Ki is the integral coefficient.

[0014] In the PFM / PWM control method for a bidirectional DC-DC power supply circuit described in the present invention; in the step S3, the calculation formula of the duty cycle D is: D=Kp(Iref-Ibat)+Ki*∫(Iref-Ibat), wherein Kp is the proportional coefficient and Ki is the integral coefficient.

[0015] In the PFM / PWM control method for a bidirectional DC-DC power supply circuit of the present invention, step S3 includes the following steps:

[0016] S31; when the duty cycle D calculated by the PI controller is greater than or equal to the minimum duty cycle Dmin, the system is in the PWM control stage, the switching frequency of the switch tube in the DC / DC converter remains unchanged, and the conduction time of the switch tube in the DC / DC converter is adjusted by adjusting the duty cycle D.

[0017] In the PFM / PWM control method for a bidirectional DC-DC power supply circuit described in the present invention; in the step S31, when the system is in the PWM control stage, control is performed by changing the width of the pulse drive signal without changing the period of the pulse drive signal, and the switch-on time of the switch tube in the DC / DC converter in the PWM control stage is: Ton=T1*D; wherein T1 is the switching period of the PWM control stage, and the switching frequency remains unchanged.

[0018] In the PFM / PWM control method for a bidirectional DC-DC power supply circuit of the present invention, the step S3 further includes the following steps:

[0019] S32; when the duty cycle D calculated by the PI controller is less than the minimum duty cycle Dmin, the system switches from the PWM control stage to the PFM control stage, the on-time of the switch tube in the DC / DC converter remains unchanged, and the switching frequency of the switch tube in the DC / DC converter is calculated according to the duty cycle D calculated by the PI controller, and the switching frequency of the switch tube in the DC / DC converter is adjusted.

[0020] In the PFM / PWM control method for a bidirectional DC-DC power supply circuit described in the present invention; in the step S32, when the system is in the PFM control stage, the control is performed by changing the cycle of the pulse drive signal without changing the on-time of the switch tube in the DC / DC converter, and the on-time of the switch tube in the PFM control stage is: Ton=T1*Dmin, wherein T1 is the switching cycle of the PWM control stage, and Dmin is the minimum duty cycle; the switching cycle T2 of the PFM control stage is: T2=T1*Dmin / D; wherein T1 is the switching cycle of the PWM control stage, Dmin is the minimum duty cycle, and D is the duty cycle calculated by the PI controller.

[0021] On the other hand, the present invention also provides a PFM / PWM control system for a bidirectional DC-DC power supply circuit, the system comprising a battery voltage acquisition module, a battery current acquisition module, a DC / DC converter, a bus input voltage Ubus, a pulse generator, a mode switching module, an input capacitor C1 and an output capacitor C2;

[0022] The DC / DC converter is used to convert the bus input voltage Ubus into the voltage required for charging or discharging the battery; the input capacitor C1 is connected between the bus input voltage Ubus and the DC / DC converter; the output capacitor C2 is connected between the output end of the DC / DC converter and the battery;

[0023] The battery current acquisition module and the battery voltage acquisition module are both electrically connected to the battery, the battery current acquisition module is used to acquire the battery current sampling value Ibat; the battery voltage acquisition module is used to acquire the battery voltage sampling value Ubat;

[0024] The PI controller is used to calculate the current target value Iref according to the voltage target value Uref and the battery voltage sampling value Ubat, and calculate the duty cycle D according to the current target value Iref and the battery current sampling value Ibat;

[0025] The mode switching module is used to determine whether the system is in the PWM control stage or the PFM control stage according to the duty cycle D:

[0026] The pulse generator is used to generate a pulse signal according to the duty cycle D to control the on and off of the switch tube in the DC / DC converter.

[0027] The PFM / PWM control method for a bidirectional DC-DC power supply circuit of the present invention combines PWM and PFM technologies and utilizes the output duty cycle D of a PI controller to achieve smooth switching between the two control modes, thereby expanding the voltage output range of the DC-DC converter and improving the light load efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of a PFM / PWM control method in a bidirectional DC-DC power supply circuit of the present invention;

[0029] Figure 2 The present invention is a circuit topology diagram of a PFM / PWM control system in a bidirectional DC-DC power supply circuit. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0032] like Figure 1 As shown, Figure 1 The present invention is a flow chart of a PFM / PWM control method embodiment for a bidirectional DC-DC power supply circuit. A PFM / PWM control method for a bidirectional DC-DC power supply circuit is provided, and the control method comprises the following steps:

[0033] In step S1, the DC / DC converter obtains the bus input voltage Ubus, and steps down the bus input voltage Ubus before inputting it into the battery;

[0034] In step S2, the battery voltage sampling value Ubat is collected by the battery voltage collection module, and the voltage target value is set as Uref. The voltage target value Uref and the voltage sampling value Ubat are calculated by the PI controller to obtain the current target value Iref;

[0035] In step S3; the battery current sampling value Ibat is collected by the battery current collection module, and the current target value Iref and the current sampling value Ibat are calculated by the PI controller to obtain the duty cycle D; the minimum duty cycle is set to Dmin, the minimum duty cycle Dmin is compared with the duty cycle D, and it is determined whether the system is in the PWM control stage or the PFM control stage;

[0036] In step S4, the duty cycle D is used to generate a pulse drive signal through a pulse generator, and the pulse drive signal controls the on and off of the switch tube in the DC / DC converter.

[0037] In one embodiment, in the step S2, the calculation formula of the current target value Iref is: Iref=Kp(Uref-Ubat)+Ki*∫(Uref-Ubat), wherein Kp is the proportional coefficient and Ki is the integral coefficient.

[0038] In one embodiment, the calculation formula of the duty cycle D in step S3 is: D=Kp(Iref-Ibat)+Ki*∫(Iref-Ibat), wherein Kp is the proportional coefficient and Ki is the integral coefficient.

[0039] In one embodiment, the step S3 comprises the following steps:

[0040] In step S31; when the duty cycle D calculated by the PI controller is greater than or equal to the minimum duty cycle Dmin, the system is in the PWM control stage, the switching frequency of the switch tube in the DC / DC converter remains unchanged, and the conduction time of the switch tube in the DC / DC converter is adjusted by adjusting the duty cycle D.

[0041] In one embodiment, in step S31, when the system is in the PWM control stage, control is performed by changing the width of the pulse drive signal without changing the period of the pulse drive signal. The on-time of the switch tube in the DC / DC converter in the PWM control stage is: Ton=T1*D; wherein T1 is the switching period of the PWM control stage, and the switching frequency remains unchanged.

[0042] In one embodiment, the step S3 further includes the following steps:

[0043] In step S32; when the duty cycle D calculated by the PI controller is less than the minimum duty cycle Dmin, the system switches from the PWM control stage to the PFM control stage, the on-time of the switch tube in the DC / DC converter remains unchanged, and the switching frequency of the switch tube in the DC / DC converter is calculated according to the duty cycle D calculated by the PI controller, and the switching frequency of the switch tube in the DC / DC converter is adjusted.

[0044] In one embodiment, in step S32, when the system is in the PFM control stage, control is performed by changing the period of the pulse drive signal without changing the on-time of the switch tube in the DC / DC converter. The on-time of the switch tube in the PFM control stage is: Ton=T1*Dmin, wherein T1 is the switching period of the PWM control stage, and Dmin is the minimum duty cycle; the switching period T2 of the PFM control stage is: T2=T1*Dmin / D; wherein T1 is the switching period of the PWM control stage, Dmin is the minimum duty cycle, and D is the duty cycle calculated by the PI controller.

[0045] like Figure 2 As shown, the present invention also provides a PFM / PWM control system for a bidirectional DC-DC power supply circuit, the system comprising a battery voltage acquisition module, a battery current acquisition module, a DC / DC converter, a bus input voltage Ubus, a pulse generator, a mode switching module, an input capacitor C1 and an output capacitor C2;

[0046] The DC / DC converter is used to convert the bus input voltage Ubus into the voltage required for charging or discharging the battery; the input capacitor C1 is connected between the bus input voltage Ubus and the DC / DC converter; the output capacitor C2 is connected between the output end of the DC / DC converter and the battery;

[0047] The battery current acquisition module and the battery voltage acquisition module are both electrically connected to the battery, the battery current acquisition module is used to acquire the battery current sampling value Ibat; the battery voltage acquisition module is used to acquire the battery voltage sampling value Ubat;

[0048] The PI controller is used to calculate the current target value Iref according to the voltage target value Uref and the battery voltage sampling value Ubat, and calculate the duty cycle D according to the current target value Iref and the battery current sampling value Ibat;

[0049] The mode switching module is used to determine whether the system is in the PWM control stage or the PFM control stage according to the duty cycle D:

[0050] The pulse generator is used to generate a pulse signal according to the duty cycle D to control the on and off of the switch tube in the DC / DC converter.

[0051] Specifically, the battery current and battery voltage sampled by the battery voltage acquisition module and the battery current acquisition module are calculated by the PI controller to obtain the corresponding duty cycle D, and then the on-time and switching cycle of the switch tube in the DC / DC converter are calculated, and the pulse drive signal is output to control the on-off of the switch tube in the DC / DC converter. The voltage target value Uref is set by the user according to the actual situation. For example, if the user wants the battery voltage to be charged to a certain voltage value, a specific voltage target value Uref is set, and the control program in the DC / DC converter controls the output of the voltage to obtain the voltage target value Uref. The current target value Iref is calculated by the PI controller, and the calculation formula is as described in Iref=Kp(Uref-Ubat)+Ki*∫(Uref-Ubat). The calculation formula of the duty cycle is D=Kp(Iref-Ibat)+Ki*∫(Iref-Ibat). The on-time and switching cycle of the switch tube in the DC / DC converter are calculated, the value of the comparison register and the value of the period register are updated, and the corresponding pulse drive signal is output to the switch tube, and then the corresponding control is performed.

[0052] for example:

[0053] According to actual needs, the minimum duty cycle value Dmin=0.1 is limited. When the system is in the PWM stage, the control frequency of the switch tube in the DC / DC converter is 72kHz, that is, the period is T1=1 / (72kHz)=13.89us. When the duty cycle output by the PI controller is greater than 0.1, such as D=0.5, the system control is in the PWM control stage, the switching frequency of the switch tube in the DC / DC converter is 72kHz, and the on-time Ton of the switch tube in the DC / DC converter is Ton=D / (72kHz)=0.5 / (72kH z)=6.94us; when the duty cycle output by the PI controller is less than 0.1, such as 0.05, when the system switches from the PWM stage to the PFM control stage, the on-time of the switch tube in the DC / DC converter is Ton=Dmin / (72kHz)=0.1 / (72kHz)=1.39us, and the switching period of the switch tube in the DC / DC converter is T2=T1*Dmin / D=13.89*0.1 / 0.05=27.78us, that is, the control frequency of the switch tube in the DC / DC converter is 36kHz.

[0054] Specifically, the switch tubes S1 and S4 are turned on and off at the same time, the switch tubes S2 and S3 are turned on and off at the same time, when S1 is turned on, the switch tubes S5 and S8 are turned off, and when S2 is turned on, the switch tubes S5 and S7 are turned off.

[0055] It should be noted that, for the above-mentioned method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0056] Through the description of the above implementation methods, those skilled in the art can clearly understand that the method according to the above embodiment can be implemented by means of software plus a necessary general hardware platform, and of course can also be implemented by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes a number of instructions for a terminal device (which can be a mobile phone, computer, server, or network device, etc.) to execute the methods described in each embodiment of the present invention.

[0057] Therefore, the above is only a preferred specific implementation mode of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. The protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A PFM / PWM control method for a bidirectional DC-DC power supply circuit, characterized in that: The method comprises the following steps: S1; the DC / DC converter obtains the bus input voltage Ubus, and steps down the bus input voltage Ubus before inputting it into the battery; S2: The battery voltage sampling value Ubat is collected by the battery voltage collection module, and the voltage target value is set as Uref. The voltage target value Uref and the voltage sampling value Ubat are calculated by the PI controller to obtain the current target value Iref; S3: The battery current sampling value Ibat is collected by the battery current collection module, and the current target value Iref and the current sampling value Ibat are calculated by the PI controller to obtain the duty cycle D; the minimum duty cycle is set to Dmin, the minimum duty cycle Dmin is compared with the duty cycle D, and it is determined whether the system is in the PWM control stage or the PFM control stage; S4: The duty cycle D is used to generate a pulse drive signal through a pulse generator, and the pulse drive signal controls the on and off of the switch tube in the DC / DC converter.

2. The PFM / PWM control method for a bidirectional DC-DC power supply circuit according to claim 1, characterized in that: In the step S2, the calculation formula of the current target value Iref is: Iref=Kp(Uref-Ubat)+Ki*∫(Uref-Ubat), wherein Kp is the proportional coefficient and Ki is the integral coefficient.

3. The PFM / PWM control method for a bidirectional DC-DC power supply circuit according to claim 2, characterized in that: In step S3, the calculation formula of the duty cycle D is: D=Kp(Iref-Ibat)+Ki*∫(Iref-Ibat), wherein Kp is the proportional coefficient and Ki is the integral coefficient.

4. The PFM / PWM control method for a bidirectional DC-DC power supply circuit according to claim 3, characterized in that: The step S3 comprises the following steps: S31; when the duty cycle D calculated by the PI controller is greater than or equal to the minimum duty cycle Dmin, the system is in the PWM control stage, the switching frequency of the switch tube in the DC / DC converter remains unchanged, and the conduction time of the switch tube in the DC / DC converter is adjusted by adjusting the duty cycle D.

5. The PFM / PWM control method for a bidirectional DC-DC power supply circuit according to claim 4, characterized in that: In step S31, when the system is in the PWM control stage, control is performed by changing the width of the pulse drive signal without changing the period of the pulse drive signal. The on-time of the switch tube in the DC / DC converter in the PWM control stage is: Ton=T1*D; wherein T1 is the switching period of the PWM control stage, and the switching frequency remains unchanged.

6. The PFM / PWM control method for a bidirectional DC-DC power supply circuit according to claim 5, characterized in that: The step S3 further comprises the following steps: S32; when the duty cycle D calculated by the PI controller is less than the minimum duty cycle Dmin, the system switches from the PWM control stage to the PFM control stage, the on-time of the switch tube in the DC / DC converter remains unchanged, and the switching frequency of the switch tube in the DC / DC converter is calculated according to the duty cycle D calculated by the PI controller, and the switching frequency of the switch tube in the DC / DC converter is adjusted.

7. The PFM / PWM control method for a bidirectional DC-DC power supply circuit according to claim 6, characterized in that: In step S32, when the system is in the PFM control stage, control is performed by changing the cycle of the pulse drive signal without changing the on-time of the switch tube in the DC / DC converter. The on-time of the switch tube in the PFM control stage is: Ton=T1*Dmin, wherein T1 is the switching cycle of the PWM control stage, and Dmin is the minimum duty cycle; the switching cycle T2 of the PFM control stage is: T2=T1*Dmin / D; wherein T1 is the switching cycle of the PWM control stage, Dmin is the minimum duty cycle, and D is the duty cycle calculated by the PI controller.

8. A PFM / PWM control system for a bidirectional DC-DC power supply circuit, characterized in that: The system includes a battery voltage acquisition module, a battery current acquisition module, a DC / DC converter, a bus input voltage Ubus, a pulse generator, a mode switching module, an input capacitor C1 and an output capacitor C2; The DC / DC converter is used to convert the bus input voltage Ubus into the voltage required for charging or discharging the battery; the input capacitor C1 is connected between the bus input voltage Ubus and the DC / DC converter; the output capacitor C2 is connected between the output end of the DC / DC converter and the battery; The battery current acquisition module and the battery voltage acquisition module are both electrically connected to the battery, the battery current acquisition module is used to acquire the battery current sampling value Ibat; the battery voltage acquisition module is used to acquire the battery voltage sampling value Ubat; The PI controller is used to calculate the current target value Iref according to the voltage target value Uref and the battery voltage sampling value Ubat, and calculate the duty cycle D according to the current target value Iref and the battery current sampling value Ibat; The mode switching module is used to determine whether the system is in the PWM control stage or the PFM control stage according to the duty cycle D: The pulse generator is used to generate a pulse signal according to the duty cycle D to control the on and off of the switch tube in the DC / DC converter.

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