Beat frequency control method applied to multiple power supply modules

Abstract

The invention discloses a beat frequency control method applied to multiple power supply modules. The beat frequency control method comprises the following steps: step 1, establishing a small signal model of a Buck circuit by using a state space averaging method; step 2, deducing calculation of a transfer function from an input end to an output end based on analysis of a small signal model of a Buck loop by a loop control method for deducing and suppressing beat frequency ripples; an RC low-pass filter is added in the Buck loop, and is added behind the amplification and compensation circuit and in front of the pulse width modulation circuit; and step 3, converting to a digital discrete domain. The method comprises the following steps: establishing a small signal model of a closed-loop Buck circuit; based on the small signal model, deducing a loop control method for suppressing beat frequency ripples; and finally, through a digital control technology, the layout area is optimized, and the use of devices is reduced. The method is mainly applied to all power supply systems needing to improve the beat frequency problem, and has high compatibility.

Description

Technical Field

[0001] The invention belongs to the field of switching power supplies, and in particular relates to a beat frequency control method applied to a multi-power supply module. Background Art

[0002] In the future, the power supply current of a certain chip may have a Class A power supply requirement. For this reason, it is necessary to integrate multiple power modules on a single board. Multi-switch power modules can provide higher power capacity and better reliability, but at the same time, it may also bring some impacts. For example, the use of a large number of power modules will increase the complexity of the system, requiring more power management and monitoring circuits, and increasing the difficulty of design and maintenance; there may be voltage and current imbalances between multiple power modules, and reasonable load balancing and power management are required to ensure that each power module can achieve maximum efficiency; there may be problems of mutual influence between multiple power modules, such as crosstalk and common mode noise between modules, and corresponding isolation and filtering measures are required. In summary, the use of multi-switch power modules requires attention to corresponding design and management issues to ensure the reliability and performance of the system.

[0003] The voltage regulator modules of the same batch will inevitably have deviations in actual operating frequencies, which will cause the differences in the switching frequencies of each module to form a low-frequency envelope signal, thus causing the beat frequency problem of the system. Beat frequency will directly lead to larger output ripples. The introduction of low-frequency disturbances will increase the difficulty of filtering and will also have a certain impact on the stability of the system. At the same time, due to the generation of additional frequency components (beat frequency), the traditional impedance concept is no longer a tool for beat frequency oscillation analysis, and a new model needs to be developed.

[0004] Currently, the traditional method to solve this beat frequency problem is to place an anti-beat frequency filtering LC on the tertiary power input side, but this will increase the layout area. Summary of the invention

[0005] The purpose of the present invention is to provide a beat frequency control method applied to multiple power supply modules, establish a small signal model of a closed-loop Buck circuit; then based on this small signal model, derive a loop control method for suppressing beat frequency ripple; finally, through digital control technology, optimize the board area and reduce the use of devices. The main application range includes all power supply systems that need to improve the beat frequency problem, with high compatibility to solve the technical problems existing in the background technology.

[0006] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0007] A beat frequency control method applied to a multi-power module comprises the following steps:

[0008] Step 1: Use the state space averaging method to establish a small signal model of the Buck circuit;

[0009] The Buck loop includes a DC source, a MOS tube Q1, a MOS tube Q2, an inductor L, a capacitor C, a load resistor R, a sampling circuit, an amplification and compensation circuit, and a pulse width modulation circuit;

[0010] The source, drain and gate of the MOS tube Q1 are respectively connected to a DC source, the source of the MOS tube Q2 and the output of the pulse width modulation circuit; the source, drain and gate of the MOS tube Q2 are respectively connected to the drain of the MOS tube Q1, the ground potential and the output of the pulse width modulation circuit; the inductor L is connected to the drain of the MOS tube Q1 and the source of the MOS tube Q2; the capacitor C is connected in parallel with the load resistor R; the sampling circuit is connected from the load resistor R, and the output is connected to a comparator for comparison with a reference voltage Vref; the comparison result is input to an amplification and compensation circuit; the output of the amplification and compensation circuit is connected to a pulse width modulation circuit; the output of the pulse width modulation circuit is connected to the gates of the MOS tube Q1 and the MOS tube Q2;

[0011] The small signal model of the Buck loop is: Input voltage V in After the power stage to the output voltage V out , and subtract the result from the Buck loop and input it to the LC filter; the power stage includes the duty cycle and the LC filter; the Buck loop includes the transfer function G of the LC filter LC (s), feedback transfer function H V (s), amplification and compensation transfer function G C (s), pulse width modulator transfer function G PMW (s) and the duty cycle to output transfer function G D (s); Input voltage V in Connected to the comparator through D, the output of the comparator is connected to the transfer function G of the LC filter LC (s); LC filter transfer function G LC The output of (s) is the output voltage V out , input to the feedback transfer function H V (s); feedback transfer function H V The output of (s) is connected to the amplification and compensation transfer function G C (s); after the signal is amplified and compensated, it is connected to the pulse width modulator transfer function G PWM (s); after generating the pulse width modulation signal, it enters the duty cycle to output transfer function G D (s), compared with the reference voltage, and enters the Buck loop again; where D is a constant;

[0012] Step 2, derive the loop control method for suppressing beat frequency ripple; derive the transfer function calculation from the input end to the output end based on the analysis of the small signal model of the Buck loop; add an RC low-pass filter in the Buck loop, after the amplification and compensation circuit, and before the pulse width modulation circuit;

[0013] Step 3: Convert to digital discrete domain.

[0014] Furthermore, in step 2, the transfer function calculation from the input to the output is derived based on the analysis of the small signal model of the Buck loop, as shown below:

[0015] H(s)=D*G LC (s)

[0016] T V (s) = G LC (s)*H V (s)*G C (s)*G PWM (s)*G D (s)

[0017]

[0018] Where H(s) is the power stage transfer function, T V (s) is the open-loop gain of the control loop; the gain from input to output is calculated as The smaller this gain is, the smaller the beat frequency ripple transmitted to the output side is; increase the mid- and low-frequency gain of the control loop, that is, the denominator of the gain from the input to the output 1+T V (s), reducing the gain from input to output, thereby reducing the beat frequency ripple at the output.

[0019] Furthermore, the transfer function of the RC low-pass filter added in step 2 in the Buck loop is as follows:

[0020]

[0021] C is the capacitance, R is the inductance, G is P (s) is the RC filter transfer function.

[0022] Furthermore, the MATLAB mathematical model and the SIMPLIS simulation model are given and compared to verify the correctness of the model; MATLAB draws the loop Bode plot through the transfer function, and the gain can be seen through the amplitude-frequency curve; SIMPLIS simulates the voltage output results by building a simulation circuit to verify the feasibility of the solution.

[0023] Furthermore, step 3 specifically includes the following steps: performing digital discretization, directly using the "c2d" function in MATLAB to convert the transfer function from the continuous domain to the digital domain, and using MATLAB to draw a Bode plot to demonstrate the improvement effect of adding an RC filter after digitization.

[0024] A control method for suppressing the beat frequency of a switching power supply according to the present invention has the following advantages:

[0025] 1. The control method adopted in the present invention is a control method for effectively suppressing the beat frequency interference generated at the input bus, which is derived after establishing a small signal model of a closed-loop Buck circuit and based on this model.

[0026] 2. The control method for suppressing the beat frequency of multiple power modules adopted by the present invention avoids damaging the stability of the system, which can be reflected by drawing the phase-frequency curve of the Bode diagram through MATLAB.

[0027] 3. The control method for suppressing the beat frequency of multiple power modules adopted in the present invention only requires the addition of a simple RC filter circuit without any other additional steps. It is simple to implement, has a stable effect, and has a low development cost.

[0028] 4. The control method for suppressing the beat frequency of multiple power modules adopted in the present invention is derived based on the most basic Buck closed-loop system small signal model and does not use any special structure, but only uses a simple RC filter circuit. Therefore, it has a very wide range of applications and is universal and highly compatible. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart of establishing the input bus beat frequency suppression method;

[0030] Figure 2 This is the schematic diagram of the Buck converter circuit;

[0031] Figure 3 It is a block diagram of the small signal model of a single power supply control structure;

[0032] Figure 4 Is a single power module T V Comparison of simulation and theoretical calculation of (s) and H(s);

[0033] Figure 5 This is the control structure block diagram after adding the RC filter;

[0034] Figure 6 Before and after adding the RC filter, T V (s) Gain comparison and output beat frequency ripple comparison diagram;

[0035] Figure 7 This is a comparison chart of the stability and dynamic performance of the power module before and after adding the RC filter;

[0036] Figure 8 This is the Bode plot before and after adding the RC filter in the z domain;

[0037] Fig. 9 This is a comparison chart of the beat frequency ripple size at the output ends of the two power converters. DETAILED DESCRIPTION

[0038] In order to better understand the purpose, structure and function of the present invention, a beat frequency control method applied to a multi-power module of the present invention is further described in detail below with reference to the accompanying drawings.

[0039] Figure 1 This is a flow chart of the method for suppressing the beat frequency of the input busbar of the present invention. It is mainly divided into three steps, namely, using the state space averaging method to establish a small signal model, deriving a loop control method for suppressing the beat frequency ripple, and converting to the digital domain to optimize the layout area. First, a Buck loop small signal model is established; on this basis, the derivation is continued, and the loop control method for suppressing the beat frequency ripple is obtained by combining the simulation software MATLAB and SIMPLIS; finally, the transfer function is directly converted to the discrete z domain using the "c2d" function in MATLAB, and digital control can optimize the layout area.

[0040] The present invention specifically comprises the following steps:

[0041] Step 1: Use the state space averaging method to establish a small signal model of the Buck loop;

[0042] The behavior of the converter is averaged within a switching cycle, so that the discontinuous, time-varying characteristics are converted into a continuous time-invariant nonlinear system model. The signals of all components in the system change continuously with time, and the size of the signal is a model quantity that can take any value, which is called a continuous system; as long as the form of the input signal remains unchanged, the output response form under different time inputs is the same, which is time-invariant; at the same time, as long as there is a component in the system whose characteristics cannot be described by a linear differential equation to describe its input and output relationship, it is called a nonlinear system; then after a series of linearization steps, a linear time-invariant model is obtained. The characteristics of the components of the linear system are all linear, and one or a group of linear differential equations can be used to describe the relationship between the system input and output.

[0043] The linearization step can adopt the perturbation method, that is, adding disturbance near the steady-state operating point, and substituting the disturbance result into the original formula to expand. Since the original system is approximated as a linear system at this time, the second-order terms obtained after expansion are ignored to obtain the linearized state space equation; the model is analyzed using linear system theory. The main process refers to obtaining the transfer function in the continuous domain after Laplace transform, and then using the amplitude-frequency curve and phase-frequency curve of the Bode plot to analyze the gain and stability of the system.

[0044] Figure 2 This is a schematic diagram of the Buck converter circuit. This diagram shows the basic structure of the Buck loop, which helps to understand what conditions will affect the circuit. Figure 3 Corresponding. Figure 2 As shown, the Buck loop includes a DC source, a MOS tube Q1, a MOS tube Q2, an inductor L, a capacitor C, a load resistor R, a sampling circuit, an amplification and compensation circuit, and a pulse width modulation circuit; the sampling circuit collects the voltage on the load, that is, the output voltage, and the reference voltage V ref The error voltage is obtained by making a difference, and is sent to the pulse width modulation circuit through the amplification and compensation circuit. The pulse width modulation circuit controls the duty cycle of the switch tube and adjusts the output voltage to achieve the purpose of voltage reduction.

[0045] The source, drain and gate of the MOS tube Q1 are respectively connected to a DC source, the source of the MOS tube Q2 and the output of the pulse width modulation circuit; the source, drain and gate of the MOS tube Q2 are respectively connected to the drain of the MOS tube Q1, the ground potential and the output of the pulse width modulation circuit; the inductor L is connected to the drain of the MOS tube Q1 and the source of the MOS tube Q2; the capacitor C and the load resistor R are connected in parallel; the sampling circuit is connected from the load resistor R, and the output is connected to a comparator for comparison with a reference voltage Vref; the comparison result is input to an amplification and compensation circuit; the output of the amplification and compensation circuit is connected to a pulse width modulation circuit; the output of the pulse width modulation circuit is connected to the gates of the MOS tube Q1 and the MOS tube Q2, forming a complete Buck loop.

[0046] The small signal model of the Buck loop is: Input voltage V in After the power stage to the output voltage V out , and subtract the result from the Buck loop and input it to the LC filter; the power stage includes the duty cycle and the LC filter; the Buck loop includes the transfer function G of the LC filter LC (s), feedback transfer function H V (s), amplification and compensation transfer function G C (s), pulse width modulator transfer function G PWM (s) and the duty cycle to output transfer function G D (s); Input voltage V inConnected to the comparator through D, the output of the comparator is connected to the transfer function G of the LC filter LC (s); LC filter transfer function G LC The output of (s) is the output voltage V out , input to the feedback transfer function H V (s); feedback transfer function H V The output of (s) is connected to the amplification and compensation transfer function G C (s); after the signal is amplified and compensated, it is connected to the pulse width modulator transfer function G PWM (s); after generating the pulse width modulation signal, it enters the duty cycle to output transfer function G D (s), compared with the reference voltage, and enters the Buck loop again; where D is a constant;

[0047] D times V in It can be regarded as a reference voltage that produces an error with the output; according to the accurate equivalent circuit model, G LC (s) actually includes the capacitor L, the inductor C and the parasitic resistance r of the two L and r C , we can derive the transfer function Feedback transfer function H V (s) only adjusts the output voltage coefficient, which is a gain module; the amplification and compensation transfer function G C (s) involves the design of the compensator, the main purpose of which is to ensure that the closed-loop system has sufficient stability and sufficient control bandwidth; modeling of the pulse width modulator, since this is analog control, it belongs to natural sampling PWM, using a continuous time modulated signal, and the wave of the natural sampling signal intersecting with the PWM will not have any delay, so it is customary to regard it as a gain module, Where V r is the amplitude of PWM carrier; G D (s) is a gain module;

[0048] Step 2 Figure 3 This is a closed-loop small signal model block diagram of a single power supply structure. The beat frequency ripple at the output of the power module is determined by the beat frequency ripple at the input and the gain from the input to the output of each power module. The beat frequency interference appears on the input side, that is, the smaller the gain, the smaller the beat frequency ripple transmitted to the output side. Take one of the power modules as an example, its structure diagram is as follows Figure 3 As shown, the input voltage V in After the power stage to the output voltage V out, and subtract the result from the control loop and input it to the LC filter. The power stage includes the duty cycle and LC filter parts; the control loop includes the LC filter, feedback transfer function, amplification and compensation transfer function, pulse width modulator transfer function and duty cycle to output transfer function. The transfer function corresponds to Figure 2 Each structure in Figure 3 exist Figure 2 The gain from the input to the output is Calculated by the following formula:

[0049] H(s)=D*G LC (s)

[0050] T V (s) = G LS (s)*H V (s)*G C (s)*G PWM (s)*G D (s)

[0051]

[0052] Where H(s) is the power stage transfer function, T V (s) is the open-loop gain of the control loop; taking into account the fact that the beat frequency interference appears on the input side, the gain from the input to the output is calculated The smaller this gain is, the smaller the beat frequency ripple transmitted to the output side is; the derivation concludes that increasing the mid- and low-frequency gain of the control loop, that is, the denominator of the gain from the input to the output, 1+T V (s), reducing the gain from input to output, thereby reducing the beat frequency ripple at the output.

[0053] Furthermore, under the premise of ensuring the stability of the power supply system, a method of improving the low-frequency gain in the control loop is studied, that is, adding an RC low-pass filter in the Buck loop, after the amplification and compensation circuit and before the pulse width modulation circuit. Figure 5 This is the control structure block diagram after adding the RC filter. LP (s) link, and the above derivation Figure 3 Control box Figure 1 The difference is that the signal is transferred from the amplification and compensation function G C After (s) comes out, it does not directly enter the pulse width modulator transfer function G PWM (s), but first through a G LP (s) link, this link is mainly composed of an RC filter. According to research, adding an RC low-pass filter in the loop can effectively improve the low-frequency gain in the control loop. The transfer function is as follows:

[0054]

[0055]

[0056] In the formula, C is the capacitance, R is the inductance, G is P (s) is the RC filter transfer function, G LP (s) is the transfer function after the RC filter is added to the loop through the connection method shown in the figure. LP The expression of (s) shows that a lag link is added to the system, thereby increasing the mid- and low-frequency loop gain. At the same time, it can be concluded from the above formula that at mid- and low-frequency The gain is very large, and the gain approaches 1 at mid-high frequencies, so adding an RC filter can effectively increase the low-frequency gain in the control loop while having little effect on the mid-high frequency gain; at the same time, The mid- and low-frequency gain is also significantly reduced.

[0057] The MATLAB mathematical model and the SIMPLIS simulation model are given and compared to verify the correctness of the model. Specifically, MATLAB mainly draws the loop Bode diagram through the transfer function, and the gain can be seen through the amplitude-frequency curve; SIMPLIS mainly simulates the voltage output results by building a simulation circuit to verify the feasibility of the solution.

[0058] Step 3: Convert to digital discrete domain;

[0059] Digital discretization is performed, and the transfer function is directly converted from the continuous domain to the digital domain using the “c2d” function in MATLAB. The Bode plot is drawn using MATLAB to demonstrate the improvement effect of adding an RC filter after digitization.

[0060] Figure 4 Is a single power module T V This figure shows the comparison between the SIMPLIS simulation and theoretical calculation results. The two are very consistent, proving the accuracy of the formula obtained in the previous article.

[0061] Figure 6 Before and after adding the RC filter, T V (s) Gain comparison and output end beat frequency ripple comparison. It can be clearly seen from the figure that adding an RC filter can effectively improve the mid- and low-frequency gain of the control loop and reduce The mid- and low-frequency gains of the control loop are verified, verifying the above analysis on the impact of adding an RC filter on the control loop. At the same time, through the comparison of the two cases with and without the RC filter in SIMPLIS simulation, it can be seen that after adding the RC filter, the beat frequency ripple is significantly reduced, proving the feasibility of this solution.

[0062] Figure 7 The stability and dynamic performance of the power module were tested before and after adding the RC filter. The purpose of adding the RC filter is only to improve the gain of the low frequency in the control loop, but it cannot affect the mid- and high-frequency gain of the control loop. As can be seen from the figure, it does not affect the mid- and high-frequency gain of the control loop, thereby affecting the stability and dynamic performance of the power module.

[0063] Figure 8 The Bode diagram before and after adding the RC filter is drawn by MATLAB, which is drawn by the transfer function in the z domain. The bilinear transformation method is mainly used to convert the transfer function in the system obtained above to the z domain through inverse bilinear mapping, calculate the transfer function of the compensator and the RC filter in the z domain, and draw the overall Bode diagram to prepare for digital implementation. It can be seen that the image drawn by the s domain transfer function is roughly the same. Adding an RC filter can increase the mid- and low-frequency gain and achieve the purpose.

[0064] Fig. 9 The comparison between the beat frequency ripple size at the output of the two power converters is shown, and the switching frequencies of the two power converters are set differently. Among them, the VOUT1 output is compared with and without the RC filter. The dotted line represents that the RC low-pass filter is not added, and the solid line represents that the RC low-pass filter is added. By comparing and observing, it can be seen that the beat frequency phenomenon is significantly improved.

[0065] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A beat frequency control method applied to a multi-power module, characterized in that: The following steps are involved: Step 1: Use the state space averaging method to establish a small signal model of the Buck circuit; The Buck loop includes a DC source, a MOS tube Q1, a MOS tube Q2, an inductor L, a capacitor C, a load resistor R, a sampling circuit, an amplification and compensation circuit, and a pulse width modulation circuit; The source, drain and gate of the MOS tube Q1 are respectively connected to a DC source, the source of the MOS tube Q2 and the output of the pulse width modulation circuit; the source, drain and gate of the MOS tube Q2 are respectively connected to the drain of the MOS tube Q1, the ground potential and the output of the pulse width modulation circuit; the inductor L is connected to the drain of the MOS tube Q1 and the source of the MOS tube Q2; the capacitor C is connected in parallel with the load resistor R; the sampling circuit is connected from the load resistor R, and the output is connected to a comparator for comparison with a reference voltage Vref; the comparison result is input to an amplification and compensation circuit; the output of the amplification and compensation circuit is connected to a pulse width modulation circuit; the output of the pulse width modulation circuit is connected to the gates of the MOS tube Q1 and the MOS tube Q2; The small signal model of the Buck loop is: Input voltage V in After the power stage to the output voltage V out , and subtract the result from the Buck loop and input it to the LC filter; the power stage includes the duty cycle and the LC filter; the Buck loop includes the transfer function G of the LC filter LC (s), feedback transfer function H V (s), amplification and compensation transfer function G C (s), pulse width modulator transfer function G PWM (s) and the duty cycle to output transfer function G D (s); Input voltage V in Connected to the comparator through D, the output of the comparator is connected to the transfer function G of the LC filter LS (s); LC filter transfer function G LC The output of (s) is the output voltage V out , input to the feedback transfer function H V (s); feedback transfer function H V The output of (s) is connected to the amplification and compensation transfer function G C (s); after the signal is amplified and compensated, it is connected to the pulse width modulator transfer function G PWM (s); after generating the pulse width modulation signal, it enters the duty cycle to output transfer function G D (s), compared with the reference voltage, and enters the Buck loop again; Where D is a constant; Step 2, derive the loop control method for suppressing beat frequency ripple; derive the transfer function calculation from the input end to the output end based on the analysis of the small signal model of the Buck loop; add an RC low-pass filter in the Buck loop, after the amplification and compensation circuit, and before the pulse width modulation circuit; Step 3: Convert to digital discrete domain.

2. The beat frequency control method applied to a multi-power module according to claim 1, characterized in that: In step 2, based on the analysis of the small signal model of the Buck loop, the transfer function calculation from the input to the output is derived as follows: H(s)=D*G LC (s) T V (s)=G LC (s)*H V (s)*G C (s)*G PWM (s)*G D (s) Where H(s) is the power stage transfer function, T V (s) is the open-loop gain of the control loop; the gain from input to output is calculated as The smaller this gain is, the smaller the beat frequency ripple transmitted to the output side is; increase the mid- and low-frequency gain of the control loop, that is, the denominator of the gain from the input to the output 1+T V (s), reducing the gain from input to output, thereby reducing the beat frequency ripple at the output.

3. The beat frequency control method applied to multiple power modules according to claim 2, characterized in that: The transfer function of the RC low-pass filter added in step 2 in the Buck loop is as follows: C is the capacitance, R is the inductance, G is P (s) is the RC filter transfer function.

4. The beat frequency control method applied to multiple power modules according to claim 3, characterized in that: The MATLAB mathematical model and SIMPLIS simulation model are given and compared to verify the correctness of the model; MATLAB draws the loop Bode plot through the transfer function and the gain can be seen through the amplitude-frequency curve; SIMPLIS simulates the voltage output results by building a simulation circuit to verify the feasibility of the solution.

5. The beat frequency control method applied to multiple power modules according to claim 4, characterized in that: Step 3 specifically includes the following steps: performing digital discretization, directly using the "c2d" function in MATLAB to convert the transfer function from the continuous domain to the digital domain, and using MATLAB to draw a Bode plot to demonstrate the improvement effect of adding an RC filter after digitization.

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