A four-switch buck-boost converter control method for self-generating system

Abstract

The present invention discloses a control method for a four-switch buck-boost converter for a self-generating system, including a converter and a digital controller, wherein the converter samples the input voltage and transmits it to the digital processor, wherein the digital processor determines the current working mode according to the received input voltage, and calculates the small signal input voltage feedforward amount, and feeds the feedforward amount to the duty cycle control amount output by the control loop to suppress voltage disturbance; the controller determines whether the current working mode has changed, and if so, sets the duty cycle control amount to zero and calculates the steady-state duty cycle under the current working mode and assigns it to the duty cycle control amount to achieve stable regulation of the output voltage. The present invention not only eliminates the influence of the input voltage disturbance on the output voltage by introducing dual input voltage feedforward in the control loop, but also achieves smooth switching between four working modes, effectively improving the stability of the output voltage of the four-switch buck-boost converter.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics and electrical engineering, and relates to a control method for a four-switch buck-boost converter for a self-generating system, and in particular to a control method for smooth switching of working modes of a four-mode four-switch buck-boost converter. Background Art

[0002] With the rapid development of power electronics technology, various airborne electronic devices have emerged in the aerospace field. Aircraft external pods have become one of the main ways to load electronic equipment on aircraft, and have been widely used in airborne military confrontation electronic equipment. Different airborne pods have different power supply requirements for their power systems due to the different types of pod equipment, and pod electronic equipment has high mobility and flexibility. It is unrealistic to require the aircraft's power supply system to meet the power supply performance of various special pod electronic equipment. Therefore, self-generation technology has been widely used in the power supply system of airborne pods.

[0003] In the self-generating power supply system, as the flight status and environment of the aircraft change, other forms of energy input to the generator will change greatly, and the output voltage of the generator will also change in a wide range. A converter with buck-boost and voltage regulation function is needed to stabilize the output voltage of the generator to provide a stable DC voltage for the load. Among various buck-boost circuits, the Four Switches Buck-Boost (FSBB) is widely used in wide input voltage range applications due to its advantages such as the same polarity of input and output voltages, low voltage stress, and few passive components. FSBB circuit topology is as follows: Figure 1 In this topology, there are two switch arms working complementary to each other and one inductor, so there are two control degrees of freedom: duty cycle d1 of Q1 and duty cycle d2 of Q3.

[0004] According to the inductor volt-second balance principle within a switching cycle, the input-output voltage relationship of FSBB can be obtained as follows:

[0005]

[0006] At present, the research on the working mode of FSBB can be roughly divided into the following four types: (1) single-mode control; (2) Buck / Boost two-mode control; (3) Buck / Buck-Boost / Boost three-mode control; (4) Buck / Buck-Boost mode I / Buck-Boost mode II / Boost four-mode control. Single-mode control only needs to control one duty cycle to achieve the buck-boost function, and there is no problem of working mode switching. However, the four switches work at the same time and the ripple and average value of the inductor current are large, so the circuit efficiency is low. Two-mode control judges the relationship between the input voltage and the output voltage to make the FSBB work in Buck or Boost mode respectively. In this mode, only two switches work and the switching loss is small. However, when the input voltage is close to the output voltage, there is a problem of extreme duty cycle in both Buck / Boost mode, and the output voltage ripple will increase at this point or even the system will be out of control. Three-mode control divides the input voltage range into three regions, making it work in Buck, Buck-Boost and Boost modes respectively, but the efficiency of the intermediate transition Buck-Boost mode is low. To further improve the efficiency of Buck / Buck-Boost / Boost three-mode control, Buck / Buck-Boost mode 1 / Buck-Boost mode 2 / Boost four-mode control is proposed. O and V O +△V uses a fixed duty cycle d2=D N , adjust d1 for single mode control, at V O -△V and V O A fixed duty cycle d1 = D M , adjust the single mode control of d2. However, the input-output voltage relationship of the four-mode control is different in different working modes. Therefore, when the working mode is switched, the steady-state duty cycle will suddenly change, and the output voltage will also fluctuate. The degree of fluctuation is related to the degree of sudden change of the steady-state duty cycle.

[0007] The use of traditional small-signal input voltage feedforward control can suppress the impact of input voltage disturbances on the output voltage. However, small-signal input voltage feedforward alone cannot solve the problem of steady-state duty cycle mutations when the working mode is switched. Therefore, when the working mode switching is accompanied by a large steady-state duty cycle mutation, the output voltage will fluctuate severely when the working mode is switched. Summary of the invention

[0008] The purpose of the present invention is to provide a four-switch buck-boost converter control method for a self-generating system, which can realize smooth switching of different working modes on the basis of suppressing input voltage disturbance, effectively alleviate the problem of severe output voltage fluctuation when the working mode is switched in traditional small signal input voltage feedforward control, and improve the output voltage regulation performance of the four-mode FSBB converter.

[0009] The present invention adopts the following technical solutions to achieve the above-mentioned purpose:

[0010] A control method for a four-switch buck-boost converter for a self-generating system includes a converter and a digital controller. The converter samples an input voltage and transmits it to the digital processor. The digital processor determines the current working mode according to the received input voltage and calculates a small signal input voltage feedforward amount. The feedforward amount is fed forward to a duty cycle control amount output by a control loop to suppress voltage disturbances. The controller determines whether the current working mode has changed. If so, the duty cycle control amount is reset to zero and a steady-state duty cycle under the current working mode is calculated and assigned to the duty cycle control amount to achieve stable regulation of the output voltage.

[0011] Beneficial effects:

[0012] (1) The present invention introduces small signal input voltage feedforward control in different working modes to eliminate the influence of input voltage disturbance on output voltage of the four-switch buck-boost converter in four working modes;

[0013] (2) The present invention calculates the duty cycle according to the input voltage and the working mode during the working mode switching process to perform feedforward to suppress the influence of the sudden change of the duty cycle during the working mode switching on the output voltage;

[0014] (3) The present invention introduces dual input voltage feedforward in the control loop, which not only eliminates the influence of input voltage disturbance on the output voltage but also realizes smooth switching between four working modes, thereby improving the stability of the output voltage. Compared with the single voltage loop regulation method, the feedforward regulation method has a faster regulation speed and a better regulation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of FSBB circuit topology in the prior art;

[0016] Figure 2 The figure is a block diagram of a dual input voltage feedforward control in one embodiment of the present invention.

[0017] Figure 3 A schematic diagram of a duty cycle mutation of a four-mode FSBB when switching between adjacent working modes according to an embodiment of the present invention;

[0018] Figure 4The output voltage regulation process of a four-mode FSBB without input voltage feedforward when switching between adjacent working modes according to an embodiment of the present invention; DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0020] like Figure 2 As shown, the present invention is a method for smoothly switching the operating modes of a four-switch buck-boost converter for a self-generating system.

[0021] The converter samples the input voltage during operation and transmits the current input voltage to a digital processor, such as a DSP, which determines the current operating mode based on the input voltage and calculates the small signal input voltage feedforward to feed forward to the digital processor. Figure 3 The duty cycle control quantity output by the control loop shown. In the controller, it is determined whether the current working mode has changed. If it has changed, the duty cycle control quantity is set to zero and the steady-state duty cycle in the current working mode is calculated and assigned to the duty cycle control quantity. The present invention realizes stable regulation of output voltage through dual input voltage feedforward.

[0022] The dual feedforward of the present invention is introduced separately below.

[0023] like Figure 3 As shown, the input voltage is divided into four working mode areas according to the relationship between the input voltage and the output voltage. When the converter is working, the working mode of FSBB will be determined according to the current input voltage sampling value, and the duty cycle control amount output by the controller will be given to the corresponding switch tube to adjust the output voltage. The four working modes are: Buck mode, Buck-Boost step-down mode, Buck-Boost step-up mode and Boost mode. The converter in this embodiment is a four-switch buck-boost converter. The small signal input voltage feedforward function of the four-switch buck-boost converter in four different working modes is different, and the input-output voltage relationship is also different. When the working mode is switched, a steady-state duty cycle mutation will occur, and the output voltage will fluctuate. The feedforward functions in the four working modes are specifically:

[0024] Buck mode:

[0025]

[0026] Buck-Boost step-down mode (fixed duty cycle d2 = D N ):

[0027]

[0028] Buck-Boost mode (fixed duty cycle d1 = D M ):

[0029]

[0030] Boost Mode:

[0031]

[0032] Where V in is the input voltage, V O is the output voltage, D'=1-D, R is the load resistance, V M is the amplitude of the PWM modulator. In the four working modes, the small signal input voltage feedforward amount in the current working mode is calculated according to the input voltage and equations (1-2) to (1-5), and the feedforward amount is superimposed on the duty cycle control amount output by the feedback control loop, thereby suppressing the influence of the input voltage disturbance on the output voltage.

[0033] The four-switch buck-boost converter has different small signal input voltage feedforward functions and different input-output voltage relationships in four different operating modes. When the operating mode is switched, a sudden change in the steady-state duty cycle will occur, causing the output voltage to fluctuate. Figure 4 As shown, it is a schematic diagram of the switching process of adjacent working modes under the four-mode control method without feedforward. It can be concluded from the figure that severe fluctuations in the inductor current and the output voltage occurred during the switching process between the Buck mode and the Buck-Boost step-down mode, the Buck-Boost step-down mode and the Buck-Boost step-up mode, and the Buck-Boost step-up mode and the Boost mode. When the working mode is switched, the present invention feeds forward the steady-state duty cycle in the current working mode to the duty cycle control amount to achieve rapid compensation for the sudden duty cycle, so as to achieve rapid stabilization of the output voltage. Specifically,

[0034] According to the input-output voltage relationship and the input voltage under the four working modes, the steady-state duty cycle under the current working mode is calculated. When the working mode is switched, the duty cycle control amount is set to zero and the steady-state duty cycle under the current working mode is fed forward to the duty cycle control amount, as shown in equations (1-6) to (1-9).

[0035] Buck mode:

[0036]

[0037] Buck-Boost mode:

[0038]

[0039] Buck-Boost mode:

[0040]

[0041] Boost Mode:

[0042]

[0043] Where VREF is the output reference voltage.

[0044] When the operating mode of the converter changes, the steady-state duty cycle of the current operating mode is calculated based on the input voltage and equations (1-6) to (1-9) and directly assigned to the duty cycle control value.

[0045] The working principle of the present invention is:

[0046] In converter modeling, there is a transfer function from input voltage to output voltage, so the disturbance signal in the input voltage will also be reflected in the output voltage. If only a single voltage loop is provided for regulation, there will be a certain delay and the regulation effect will be poor. Providing a small signal input voltage feedforward function can offset the impact of small signal disturbances in the input voltage on the output voltage. However, when the working mode is switched, the steady-state duty cycle will change suddenly, so the output voltage may fluctuate greatly when the working mode is switched. If the steady-state duty cycle in the current working mode is fed forward to the duty cycle control amount when the working mode is switched, the duty cycle mutation can be quickly compensated to achieve rapid stabilization of the output voltage.

[0047] The present invention proposes a method for smoothly switching the working modes of a four-switch buck-boost converter for a self-generating system. The method can realize fast and smooth switching of the working modes by introducing dual input voltage feedforward, thereby improving the regulation performance of the output voltage of the four-mode four-switch buck-boost converter.

[0048] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A four-switch buck-boost converter control method for a self-generating system, It is characterized in that The invention comprises a converter and a digital controller, wherein the converter samples an input voltage and transmits the sample to the digital controller, wherein the digital controller determines a current working mode according to the received input voltage, calculates a corresponding feedforward function according to a small signal model of a circuit of the converter in different working modes, obtains a small signal input voltage feedforward amount based on the feedforward function and the current input voltage, and feeds the feedforward amount to a duty cycle control amount output by a control loop to suppress voltage disturbances; The controller determines whether the current working mode has changed. If it has changed, the duty cycle control value is set to zero and the steady-state duty cycle under the current working mode is calculated and assigned to the duty cycle control value to achieve stable regulation of the output voltage. The converter is a four-mode four-switch buck-boost converter, which operates in Buck mode, Buck-Boost mode, Buck-Boost mode and Boost mode according to the relationship between the input voltage and the output voltage. The feedforward function in each mode is expressed as: Let V in is the input voltage, V O is the output voltage, R is the load resistance, V M is the amplitude of the PWM modulator, L is the inductance value, s is the complex domain variable in the Laplace transform, D is the duty cycle, D'=1-D, then the feedforward function in Buck mode is: The feed-forward function in Buck-Boost mode is: Among them, the fixed duty cycle d 2 =D N ; The feed-forward function in Buck-Boost mode is: Among them, the fixed duty cycle d 1 =D M ;The feedforward function in Boost mode is:

2. The four-switch buck-boost converter control method for a self-generating system according to claim 1, It is characterized in that The steady-state duty cycle in Buck mode is: The steady-state duty cycle in Buck-Boost step-down mode is: The steady-state duty cycle in Buck-Boost mode is: The steady-state duty cycle in Boost mode is: Among them, V REF is the output reference voltage.

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