A beat frequency control method applied to multiple power supply modules

Abstract

The present invention discloses a beat frequency control method for a multi-power supply module, comprising the following steps: Step 1, establishing a small signal model of a Buck circuit using a state space averaging method; Step 2, deriving a loop control method for suppressing beat frequency ripple; deriving a transfer function calculation from the input end to the output end based on the analysis of the small signal model of the Buck loop; adding an RC low-pass filter in the Buck loop, after the amplification and compensation circuit and before the pulse width modulation circuit; Step 3, converting to a digital discrete domain. The present invention establishes a small signal model of a closed-loop Buck circuit; then, based on this small signal model, derives a loop control method for suppressing beat frequency ripple; finally, through digital control technology, optimizes the board area and reduces the use of devices. The main application scope includes all power supply systems that need to improve the beat frequency problem, and has high compatibility.

Description

Technical Field

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

[0002] In the future, a chip's power supply current may require Class A power supply. To achieve this, multiple power modules will need to be integrated on a single board. Multi-switch power modules can provide higher power capacity and better reliability, but this may also bring some impacts. For example, the use of a large number of power modules will increase system complexity, 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, requiring reasonable load balancing and power management 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, requiring corresponding isolation and filtering measures. In summary, the use of multi-switch power modules requires attention to corresponding design and management issues to ensure system reliability and performance.

[0003] Voltage regulator modules from the same batch inevitably experience deviations in their actual operating frequencies. This causes the differences in switching frequencies of each module to add up to form a low-frequency envelope signal, which can lead to beat frequency issues in the system. Beat frequency directly increases output ripple, introduces low-frequency disturbances that increase filtering difficulties, and can also affect system stability. Furthermore, due to the generation of additional frequency components (beat frequencies), traditional impedance concepts are no longer suitable for analyzing beat frequency oscillations, necessitating the development of new models.

[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 present invention aims to provide a beat frequency control method for multiple power supply modules. This method establishes a small-signal model of a closed-loop buck circuit. Based on this small-signal model, it derives a loop control method for suppressing beat frequency ripple. Finally, through digital control technology, it optimizes board layout and reduces component usage. The method is primarily applicable to all power supply systems requiring beat frequency improvement, and offers high compatibility, addressing the technical issues previously discussed.

[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, MOS transistor Q1, MOS transistor Q2, inductor L, capacitor C, load resistor R, sampling circuit, amplification and compensation circuit, and pulse width modulation circuit;

[0010] The source, drain, and gate of MOS transistor Q1 are respectively connected to a DC source, the source of MOS transistor Q2, and the output of a pulse width modulation circuit; the source, drain, and gate of MOS transistor Q2 are respectively connected to the drain of MOS transistor Q1, the ground potential, and the output of the pulse width modulation circuit; an inductor L is connected to the drain of MOS transistor Q1 and the source of MOS transistor Q2; a capacitor C is connected in parallel to a load resistor R; a sampling circuit is connected to the load resistor R, and its 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; and the output of the pulse width modulation circuit is connected to the gates of MOS transistors Q1 and Q2.

[0011] The small signal model of the Buck loop is: Input voltage V in Through the power stage to the output voltage V out , and the result of the Buck loop is subtracted and input 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); transfer function G of LC filter 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 a loop control method to suppress beat frequency ripple; derive the input-to-output transfer function based on the analysis of the small-signal model of the Buck loop; add an RC low-pass filter to the Buck loop, after the amplification and compensation circuits and before the pulse width modulation circuit;

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

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

[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 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 capacitor, R is the inductor, G P (s) is the RC filter transfer function.

[0022] Furthermore, a MATLAB mathematical model and a 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 prove 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 by 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.

[0026] 2. The control method adopted by the present invention to suppress the beat frequency of multiple power modules avoids damaging the system stability, 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 stable effects, and has low development costs.

[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. It 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 This is the block diagram of the small signal model of a single power supply control structure;

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

[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;

[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] Figure 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 present invention's method for suppressing input bus beat frequency. It mainly consists of three steps: establishing a small signal model using the state-space averaging method, deriving a loop control method for suppressing 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, further research and derivation are conducted, combining the simulation software MATLAB and SIMPLIS to derive a loop control method for suppressing beat frequency ripple; 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 that make up 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 a disturbance near the steady-state operating point and substituting the disturbance result into the original formula to expand it. Since the original system is approximated as a linear system at this time, the second-order terms obtained after expansion are ignored, and the linearized state space equation is obtained; the model is analyzed using linear system theory. The main process is to obtain the transfer function in the continuous domain after Laplace transform, and then use 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, helping to understand which conditions will affect the circuit. Figure 3 Corresponding. Figure 2 As shown in Figure 1, the Buck loop includes a DC source, MOS tube Q1, MOS tube Q2, inductor L, capacitor C, load resistor R, sampling circuit, amplification and compensation circuit, and 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 obtained by making a difference 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 MOS transistor Q1 are respectively connected to a DC source, the source of MOS transistor Q2, and the output of the pulse width modulation circuit; the source, drain, and gate of MOS transistor Q2 are respectively connected to the drain of MOS transistor Q1, the ground potential, and the output of the pulse width modulation circuit; an inductor L is connected to the drain of MOS transistor Q1 and the source of MOS transistor Q2; a capacitor C is connected in parallel to a load resistor R; a sampling circuit is connected from the load resistor R, and its output is connected to a comparator that compares it 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; and the output of the pulse width modulation circuit is connected to the gates of MOS transistors Q1 and Q2, forming a complete Buck loop.

[0046] The small signal model of the Buck loop is: Input voltage V in Through the power stage to the output voltage V out , and the result of the Buck loop is subtracted and input 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); transfer function G of LC filter 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 and 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; the pulse width modulator is modeled. Since this is analog control, it belongs to natural sampling PWM and uses a continuous time modulated signal. The wave of the naturally sampled signal intersecting with the PWM will not have any delay, so it is usually regarded as a gain module. Where V r is the amplitude of the PWM carrier; G D (s) is a gain block;

[0048] Step 2 Figure 3 This is a block diagram of a closed-loop small signal model with a complete 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 is shown in the figure below. Figure 3 As shown, the input voltage V in Through the power stage to the output voltage V out, and the result of the control loop is subtracted and input 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 input to 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, adding it after the amplification and compensation circuit and before the pulse width modulation circuit. Figure 5 This is the control structure diagram after adding RC filter. LP (s) link, and the previous deduction 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 go 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 of the control loop. The transfer function is as follows:

[0054]

[0055]

[0056] In the formula, C is the capacitor, R is the inductor, 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 shown in the figure. LP The expression of (s) shows that a lag link is added to the system, thereby improving 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- and high-frequency. Therefore, adding an RC filter can effectively improve the low-frequency gain of the control loop while having little effect on the mid- and high-frequency gain. At the same time, The mid- and low-frequency gain is also significantly reduced.

[0057] The correctness of the model was verified by comparing the MATLAB mathematical model and the SIMPLIS simulation model. Specifically, MATLAB primarily used the transfer function to draw the loop Bode plot, and the gain was visualized through the amplitude-frequency curve. SIMPLIS primarily used the simulation circuit to simulate the voltage output and 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. Bode plots are also drawn using MATLAB to demonstrate the improvement effect of adding an RC filter after digitization.

[0060] Figure 4 Is a single power supply module T V Comparison of simulation and theoretical calculations for (s) and H(s). This figure shows the comparison of the results of SIMPLIS simulation and theoretical calculations. The two are very consistent, proving the accuracy of the formulas obtained above.

[0061] Figure 6 Before and after adding the RC filter, T V (s) Gain comparison and output end beat frequency ripple comparison diagram. 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 circuit are verified, verifying the above analysis of 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 the beat frequency ripple is significantly reduced after adding the RC filter, 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 RC filter's purpose is to increase the control loop's low-frequency gain only, without affecting the control loop's mid- and high-frequency gain. The graph shows that the mid- and high-frequency gain of the control loop is not affected, thereby impacting the power module's stability and dynamic performance.

[0063] Figure 8 This Bode plot, created using MATLAB, compares the z-domain transfer function before and after adding the RC filter. The bilinear transformation method is employed to convert the system transfer function obtained above to the z-domain via an inverse bilinear mapping. The z-domain transfer functions of the compensator and RC filter are then calculated, and the overall Bode plot is plotted to prepare for digital implementation. As can be seen, the plot is largely identical to the plot of the s-domain transfer function, demonstrating that adding the RC filter improves mid- and low-frequency gain, achieving the desired result.

[0064] Figure 9 This figure shows a comparison of the beat frequency ripple at the output of two power converters, with different switching frequencies. The VOUT1 output is compared with and without an RC filter. The dashed line represents the output without an RC low-pass filter, while the solid line shows the output with an RC low-pass filter. The comparison shows a significant improvement in the beat frequency phenomenon.

[0065] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by 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 to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by 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, MOS transistor Q1, MOS transistor Q2, inductor L, capacitor C, load resistor R, sampling circuit, amplification and compensation circuit, and pulse width modulation circuit; The source, drain, and gate of MOS transistor Q1 are respectively connected to a DC source, the source of MOS transistor Q2, and the output of a pulse width modulation circuit; the source, drain, and gate of MOS transistor Q2 are respectively connected to the drain of MOS transistor Q1, the ground potential, and the output of the pulse width modulation circuit; an inductor L is connected to the drain of MOS transistor Q1 and the source of MOS transistor Q2; a capacitor C is connected in parallel to a load resistor R; a sampling circuit is connected to the load resistor R, and its 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; and the output of the pulse width modulation circuit is connected to the gates of MOS transistors Q1 and Q2. The small signal model of the Buck loop is: Input voltage V in Through the power stage to the output voltage V out , and the result of the Buck loop is subtracted and input 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); transfer function G of LC filter 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 a loop control method to suppress beat frequency ripple; derive the input-to-output transfer function based on the analysis of the small-signal model of the Buck loop; add an RC low-pass filter to the Buck loop, after the amplification and compensation circuits and before the pulse width modulation circuit; Step 3: Convert to digital discrete domain.

2. The beat frequency control method for 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 from input to 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 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 a multi-power module 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 capacitor, R is the inductor, G P (s) is the RC filter transfer function.

4. The beat frequency control method for a multi-power module according to claim 3, wherein: 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 for a multi-power module 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.

Images