A composite control method for Superbuck converter based on input voltage feedforward

Abstract

The present invention proposes a composite control method for a Superbuck converter based on input voltage feedforward, which belongs to the technical field of DC / DC converters; it includes the following steps: S0: constructing a circuit of a system based on a Superbuck converter; S1: using a state space averaging method to solve the circuit's small signal state equation, small signal model, and transfer function from the control system input to the system output; S2: configuring component parameters in the circuit; S3: designing a composite controller for the control system block diagram; S4: performing simulation analysis on the control system using the composite controller to verify the contents of steps S2 and S3. The present invention constructs a signal model of a Superbuck converter by using a state space averaging method, designs a controller with a lag-lead effect and an input voltage feedforward controller, and effectively suppresses the oscillation phenomenon of the output voltage caused by input voltage pulsation.

Description

Technical Field

[0001] The invention relates to the technical field of DC / DC converters, and in particular to a composite control method of a Superbuck converter based on input voltage feedforward. Background Art

[0002] With the development of power electronics technology, DC-DC technology is widely used in various fields. As one of the key components in satellite systems, compact, high-density and high-efficiency satellite power DC-DC converters for future space exploration applications are very important. However, for occasions where there is a pulsating load on the primary bus, such as SAR satellite power supply, when the load is turned on, it is equivalent to a working mode in which the input voltage of the conversion circuit is always disturbed. At present, the loop design of the power converter is designed based on the influence of the output disturbance on the control quantity, mainly for the working condition of stable input voltage. Therefore, for special occasions of input pulsation, the current solution simply relies on a large LC filter, which is not conducive to the lightweight demand of the power converter. Therefore, to further improve the performance of the power converter, it is necessary to carry out research on advanced control technology to replace the large LC filter to achieve the purpose of stable operation of the power converter under input voltage pulsation. Traditional second-order topology DC-DC converters such as Buck, Boost, Buck-Boost, etc. have problems such as discontinuous current on the input side or output side, different input and output polarities, or large current ripple.

[0003] The Superbuck converter is a dual-inductor step-down DC-DC converter. There have been many studies on the design of the topology of the Superbuck converter, but there are still few contents on improving the output voltage oscillation problem of the Superbuck converter when the bus voltage pulsates. Therefore, it is very necessary to provide a composite control method for the Superbuck converter based on input voltage feedforward, optimize the performance indicators of the Superbuck converter, improve the steady-state characteristics of the control system, and improve the output voltage oscillation problem. Summary of the invention

[0004] In view of this, the present invention proposes a composite control method of a Superbuck converter based on input voltage feedforward, which can improve the output voltage oscillation problem when the bus voltage pulsates and is suitable for DC-DC in specific scenarios.

[0005] The present invention provides a composite control method of a Superbuck converter based on input voltage feedforward, comprising the following steps:

[0006] S0: Build the circuit of the system based on Superbuck converter;

[0007] S1: Use the state space averaging method to solve the circuit's small signal state equation, small signal model, and transfer function from the control system input to the system output;

[0008] S2: configure the component parameters in the circuit;

[0009] S3: Design a composite controller based on the control system block diagram;

[0010] S4: Perform simulation analysis on the control system using the composite controller to verify the contents of steps S2 and S3.

[0011] On the basis of the above technical solution, preferably, the circuit of the system based on the Superbuck converter described in step S0 includes a power supply, a first inductor L1, a first capacitor C1, a switch tube Q1, a diode D, a second inductor L2, a second capacitor C2 and a load R; the positive electrode of the power supply is electrically connected to one end of the first inductor L1, the other end of the first inductor L1 is electrically connected to the drain of the switch tube Q1 and one end of the first capacitor C1 respectively, the other end of the first capacitor C1 is electrically connected to the anode of the diode D and one end of the second inductor L2 respectively, the source of the switch tube Q1 is electrically connected to the cathode of the diode D, one end of the second capacitor C2 and one end of the load R respectively, the other end of the second capacitor C2, the other end of the load R and the other end of the second inductor L2 are all electrically connected to the negative electrode of the power supply; the gate of the switch tube Q1 receives a square wave signal with a duty cycle to realize turning on or off.

[0012] Preferably, the small signal state equation of the circuit in step S1 is obtained by analyzing the circuit working mode when the switch tube Q1 is turned on and off, and obtaining a differential equation group of state variables within a switching cycle:

[0013]

[0014] The state variable i L1 、i L2 、v C1 、v C2 They represent the current on the first inductor L1, the current on the second inductor L2, the voltage on the first capacitor C1, and the voltage on the second capacitor C2 respectively; D represents the duty cycle of the square wave received by the gate of the switch tube Q1, v in is the input voltage of the power supply to the system, R is the resistance of the load; let the differential term be zero, and get the steady-state solution of the state variable:

[0015]

[0016] Where V in D is the steady-state value of the input voltage from the power supply to the system. s Represents the steady-state value of the square wave duty cycle, I L1 ,IL2 、V C1 and V C2 are state quantities i L1 、i L2 、v C1 、v C2 The steady-state solution of .

[0017] Further preferably, the small signal model solved in step S1 is an expression of the system small signal model obtained by introducing a small signal disturbance and ignoring the second-order disturbance. The expression of the small signal model in the form of a state space equation is:

[0018] in is the first-order derivative of the state variable x, and the state variable x, input u, output y, system matrix A, input matrix B and output matrix C are respectively:

[0019] C=(0 0 0 1); after rewriting the state variable into the form of steady-state component plus small-signal disturbance, ignoring the second-order term and eliminating the steady-state component, the above expression is obtained, where the parameters with sharp corners are the small-signal disturbances of the state variables; L1 and L2 are the inductances of the first inductor L1 and the second inductor L2 respectively; C1 and C2 are the capacitances of the first capacitor and the second capacitor respectively; the sharp-cornered symbols on the variables represent the estimated values ​​of the variables.

[0020] More preferably, the transfer function from the control system input to the system output in step S1 is further obtained according to the state space equation:

[0021] The transfer function G of the duty cycle of the switch tube Q1 to the system output vd (s) is:

[0022]

[0023] s is a variable in the complex plane; the transfer function of the system's input to output is G vg (s) is:

[0024]

[0025] Further preferably, the component parameters in the configuration circuit described in step S2 are to determine the inductance of the first inductor L1 and the second inductor L2, and the capacitance of the first capacitor C1 and the second capacitor C2. The values ​​of the inductors should avoid the right half plane zero of the open-loop transfer function of the system affecting the stability of the system. The open-loop transfer function of the system is: To avoid the molecular part G vd When (s) is 0, a positive solution appears, which needs to meet the following conditions: (1-Ds )L2>D s L1.

[0026] Further preferably, the composite controller is designed for the control system block diagram as described in step S3, which is to add a lead-lag compensator and a feedforward controller to the control system block diagram; the lead-lag compensator is used to maintain the system bandwidth range and improve the phase margin and stability of the system, and the feedforward controller is used to improve the tracking performance of the system.

[0027] Further preferably, the transfer function expression of the lead-lag compensator is:

[0028] Further preferably, the precise expression of the feedforward controller is:

[0029] The composite control method of a Superbuck converter based on input voltage feedforward provided by the present invention has the following beneficial effects compared with the prior art:

[0030] In traditional PI control, the frequency response characteristics of the PI controller determine its limited ability to compensate for the phase margin. Since the PI controller has good gain compensation characteristics in the low frequency band, it may not provide sufficient phase improvement in the high frequency band, which will lead to insufficient phase margin of the system. The PI controller mainly controls the dynamic response of the system by adjusting the proportion and integral gain, but this adjustment may cause instability when increasing the bandwidth, especially when the integral gain is large, the system is prone to oscillation and overshoot, which limits the improvement of bandwidth. The present invention constructs a signal model of the Superbuck converter by adopting the state space averaging method, and guides the controller parameter design based on this. By adopting the zero-pole compensation method and designing a controller with a lag-lead effect, the phase margin of the system is effectively increased, and the steady-state characteristics of the system are improved; by introducing the input voltage feedforward control method, the oscillation phenomenon of the output voltage caused by the input voltage pulsation is effectively suppressed; the present invention improves the deficiencies of the traditional PI control in the phase margin and bandwidth compensation, and effectively improves the performance index of the Superbuck converter in specific occasions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1A circuit diagram of a composite control method of a Superbuck converter based on input voltage feedforward according to the present invention;

[0033] Figure 2 A control system block diagram of a composite control method for a Superbuck converter based on input voltage feedforward according to the present invention;

[0034] Figure 3 A Bode diagram of an open-loop transfer function of a closed-loop control system of a composite control method for a Superbuck converter based on input voltage feedforward according to the present invention;

[0035] Figure 4 A Bode diagram of a feedforward controller of a composite control method of a Superbuck converter based on input voltage feedforward according to the present invention;

[0036] Figure 5 It is an amplitude-frequency curve diagram of a closed-loop transfer function from input voltage to output voltage of a composite control method of a Superbuck converter based on input voltage feedforward of the present invention;

[0037] Figure 6 The present invention is a composite control method of a Superbuck converter based on input voltage feedforward and a schematic diagram of the converter's operating waveform after input pulsation is considered. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Traditional second-order topology DC-DC converters such as Buck, Boost, Buck-Boost, etc. have problems such as discontinuous current on the input or output side, different input and output polarities, or large current ripple or output voltage oscillation. Figure 1 As shown, the present invention provides a composite control method of a Superbuck converter based on input voltage feedforward, comprising the following steps:

[0040] S0: Build the circuit of the Superbuck converter based system.

[0041] The circuit of the system based on the Superbuck converter in step S0 includes a power supply, a first inductor L1, a first capacitor C1, a switch tube Q1, a diode D, a second inductor L2, a second capacitor C2 and a load R; the positive electrode of the power supply is electrically connected to one end of the first inductor L1, the other end of the first inductor L1 is electrically connected to the drain of the switch tube Q1 and one end of the first capacitor C1 respectively, the other end of the first capacitor C1 is electrically connected to the anode of the diode D and one end of the second inductor L2 respectively, the source of the switch tube Q1 is electrically connected to the cathode of the diode D, one end of the second capacitor C2 and one end of the load R respectively, the other end of the second capacitor C2, the other end of the load R and the other end of the second inductor L2 are all electrically connected to the negative electrode of the power supply; the gate of the switch tube Q1 receives a square wave signal with a duty cycle to realize turning on or off.

[0042] The specific working process is: when the switch tube Q1 is turned off, the current passes through the first inductor L1, the first resistor C1, the diode D and the load R in sequence, and then returns to the power supply to form a loop; when the switch tube Q1 is turned on, the current passes through the first inductor L1, the switch tube Q1 and the load R in sequence, the diode D is cut off, and the power supply, the switch tube Q1, the first inductor L1 and the load R form a loop.

[0043] S1: Use the state-space averaging method to solve the circuit's small-signal state equation, small-signal model, and transfer function from the control system input to the system output.

[0044] The small signal state equation of the circuit is to analyze the circuit working mode when the switch tube Q1 is turned on and off, and obtain the differential equation group of the state variables within a switching cycle:

[0045]

[0046] The state variable i L1 、i L2 、v C1 、v C2 They represent the current on the first inductor L1, the current on the second inductor L2, the voltage on the first capacitor C1, and the voltage on the second capacitor C2 respectively; D represents the duty cycle of the square wave received by the gate of the switch tube Q1, v in is the input voltage of the power supply to the system, and R is the resistance of the load. Figure 1 The arrow in the figure points to the state variable i L1 and i L2 The reference direction; setting the differential term to zero, we obtain the steady-state solution of the state variables:

[0047]

[0048] Where V in D is the steady-state value of the input voltage from the power supply to the system. sRepresents the steady-state value of the square wave duty cycle, I L1 ,I L2 、V C1 and V C2 are state quantities i L1 、i L2 、v C1 、v C2 The steady-state solution of .

[0049] Solving the small signal model is to introduce small signal disturbances and ignore the second-order disturbance to obtain the expression of the system small signal model. The expression of the small signal model in the form of state space equations is:

[0050] in is the first-order derivative of the state variable x, and the state variable x, input u, output y, system matrix A, input matrix B and output matrix C are respectively:

[0051]

[0052] C=(0001); after rewriting the state variable into the form of steady-state component plus small-signal disturbance, ignoring the second-order term and eliminating the steady-state component, the above expression is obtained, wherein the parameters with sharp corners are the small-signal disturbances of the state variable; L1 and L2 are the inductances of the first inductor L1 and the second inductor L2 respectively; C1 and C2 are the capacitances of the first capacitor and the second capacitor respectively; the parameters with sharp corners represent the expressions obtained by rewriting the parameters into the form of signal plus small-signal disturbance, then ignoring the second-order term and eliminating the steady-state component.

[0053] Furthermore, the transfer function from the control system input to the system output described in step S1 is further obtained according to the state space equation:

[0054] The transfer function G of the duty cycle of the switch tube Q1 to the system output vd (s) is:

[0055]

[0056] s is a variable in the complex plane; the transfer function of the system's input to output is G vg (s) is:

[0057]

[0058] S2: Configure the component parameters in the circuit.

[0059] Specifically, the inductance of the first inductor L1 and the second inductor L2, as well as the capacitance of the first capacitor C1 and the second capacitor C2 are determined. In particular, when designing the inductor, in addition to considering the current ripple, the inductor value should also be considered to avoid the right half plane zero point of the system's open-loop transfer function affecting the stability of the system; the system's open-loop transfer function is To avoid the molecular part G vd When (s) is 0, a positive solution appears, which needs to meet the following conditions: (1-D s )L2>D s L1.

[0060] In this embodiment, the rated power of the Superbuck converter is 500W, and the steady-state value of the input voltage is V in is 44V, the steady-state value of the output voltage is V o is 28V, the inductance L1 of the inductor L1 is 60μH, the inductance L2 of the inductor L2 is 140μH, the capacitance value C1 of the capacitor C1 is 60μF, and the capacitance value C2 of the capacitor C2 is 200μF.

[0061] S3: Design a composite controller based on the control system block diagram.

[0062] Specifically, a lead-lag compensator and a feedforward controller are added to the control system block diagram; the lead-lag compensator is used to maintain the system bandwidth range and improve the phase margin and stability of the system, and the feedforward controller is used to improve the tracking performance of the system.

[0063] The transfer function expression of the lead-lag compensator is:

[0064] A feedforward controller is designed for input voltage pulsation. The precise expression of the feedforward controller is:

[0065] The function of the lead adjustment is to provide a lead phase angle, such as Figure 3 As shown in the frequency-phase curve in , the lead compensation can increase the phase in a specific frequency range, thereby increasing the phase margin of the system. The lag adjustment mainly reduces the system amplitude, reduces the crossover frequency, and can also increase the limit margin, such as Figure 4 and Figure 5 As shown, the reduction in peak value has been reduced.

[0066] When the system has a high frequency, large amplitude, measurable but uncontrollable disturbance, a feedforward controller can be used. The expression of the feedforward controller is related to the frequency. When the input disturbance frequency is less than the first zero or first pole frequency of the feedforward controller, it can be regarded as a proportional link. The simplified feedforward controller expression used in this embodiment is: Where V mis the modulation wave amplitude.

[0067] Combining the above content, the closed-loop transfer function A(s) from the input voltage to the output voltage of the control system can be obtained as follows:

[0068] S4: Perform simulation analysis on the control system using the composite controller to verify the contents of steps S2 and S3.

[0069] like Figure 3-Figure 6 As shown, according to the parameters of the composite control system in this example, the Bode diagram of the closed-loop transfer function from input voltage to output voltage is drawn, and the case where the input voltage contains disturbances is simulated and analyzed. It can be seen that the composite control method has a good control effect on the occasion of input voltage pulsation, and the converter performance is effectively improved.

[0070] Figure 6 Times in it represents time, ms / div represents the time interval represented by each scale of the horizontal axis, and the scale value of the vertical axis represents the instantaneous value of the input voltage or output voltage. Figure 6 (a) shows the input voltage signal with pulsation. Figure 6 (d) shows the system output voltage waveform when the input voltage jumps; Figure 6 (b) shows the output voltage signal with oscillation without feedforward control; Figure 6 (c) in the figure shows the output voltage waveform after the feedforward controller is introduced.

[0071] 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, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite control method for a Superbuck converter based on input voltage feedforward, characterized in that: The following steps are involved: S0: Build the circuit of the system based on Superbuck converter; S1: Use the state space averaging method to solve the circuit's small signal state equation, small signal model, and transfer function from the control system input to the system output; S2: configure the component parameters in the circuit; S3: Design a composite controller based on the control system block diagram; S4: Perform simulation analysis on the control system using the composite controller to verify the contents of steps S2 and S3.

2. The composite control method of a Superbuck converter based on input voltage feedforward according to claim 1, characterized in that: The circuit of the system based on the Superbuck converter described in step S0 includes a power supply, a first inductor L1, a first capacitor C1, a switch tube Q1, a diode D, a second inductor L2, a second capacitor C2 and a load R; the positive electrode of the power supply is electrically connected to one end of the first inductor L1, the other end of the first inductor L1 is electrically connected to the drain of the switch tube Q1 and one end of the first capacitor C1 respectively, the other end of the first capacitor C1 is electrically connected to the anode of the diode D and one end of the second inductor L2 respectively, the source of the switch tube Q1 is electrically connected to the cathode of the diode D, one end of the second capacitor C2 and one end of the load R respectively, the other end of the second capacitor C2, the other end of the load R and the other end of the second inductor L2 are all electrically connected to the negative electrode of the power supply; the gate of the switch tube Q1 receives a square wave signal with a duty cycle to realize turning on or off.

3. The composite control method of a Superbuck converter based on input voltage feedforward according to claim 2, characterized in that: The small signal state equation of the circuit in step S1 is obtained by analyzing the circuit working mode when the switch tube Q1 is turned on and off, and obtaining a differential equation group of state variables within a switching cycle: The state variable i L1 、i L2 、v C1 、v C2 They represent the current on the first inductor L1, the current on the second inductor L2, the voltage on the first capacitor C1, and the voltage on the second capacitor C2 respectively; D represents the duty cycle of the square wave received by the gate of the switch tube Q1, v in is the input voltage of the power supply to the system, and R is the resistance of the load; Setting the differential term to zero gives the steady-state solution of the state variables: Where V in is the steady-state value of the input voltage from the power supply to the system, D s Represents the steady-state value of the square wave duty cycle, I L1 ,I L2 、V C1 and V C2 are state quantities i L1 、i L2 、v C1 、v C2 The steady-state solution of .

4. The composite control method of a Superbuck converter based on input voltage feedforward according to claim 3 is characterized in that: The small signal model solved in step S1 is an expression of the system small signal model obtained by introducing a small signal disturbance and ignoring the second-order disturbance. The expression of the small signal model in the form of a state space equation is: in is the first-order derivative of the state variable x, and the state variable x, input u, output y, system matrix A, input matrix B and output matrix C are respectively: C＝(0001)； After rewriting the state variable into the form of steady-state component plus small-signal disturbance, ignoring the second-order term and eliminating the steady-state component, the above expression is obtained, where the parameters with sharp corners are the small-signal disturbances of the state variables; L1 and L2 are the inductances of the first inductor L1 and the second inductor L2 respectively; C1 and C2 are the capacitance values ​​of the first capacitor and the second capacitor respectively; the sharp-cornered symbols on the variables represent the estimated values ​​of the variables.

5. The composite control method of Superbuck converter based on input voltage feedforward according to claim 4, characterized in that: The transfer function from the control system input to the system output described in step S1 is further obtained based on the state space equation: The transfer function G of the duty cycle of the switch tube Q1 to the system output vd (s) is: s is a variable in the complex plane; the transfer function of the system's input to output is G vg (s) is:

6. The composite control method of Superbuck converter based on input voltage feedforward according to claim 5, characterized in that: The component parameters in the configuration circuit described in step S2 are to determine the inductance of the first inductor L1 and the second inductor L2, and the capacitance of the first capacitor C1 and the second capacitor C2. The value of the inductor should avoid the right half plane zero point of the open-loop transfer function of the system affecting the stability of the system; the open-loop transfer function of the system is To avoid the molecular part G vd When (s) is 0, a positive solution appears, which needs to meet the following conditions: (1-D s )L2>D s L1.

7. The composite control method of Superbuck converter based on input voltage feedforward according to claim 6, characterized in that: Designing a composite controller for the control system block diagram described in step S3 is to add a lead-lag compensator and a feedforward controller to the control system block diagram; the lead-lag compensator is used to maintain the system bandwidth range and improve the phase margin and stability of the system, and the feedforward controller is used to improve the tracking performance of the system.

8. The composite control method of Superbuck converter based on input voltage feedforward according to claim 7, characterized in that: The transfer function expression of the lead-lag compensator is:

9. The composite control method of Superbuck converter based on input voltage feedforward according to claim 7, characterized in that: The exact expression of the feedforward controller is:

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