A current sharing control method for a parallel DC buck converter system

Abstract

The present invention discloses a current sharing control method for a parallel DC buck converter system, suitable for high-precision control of the output voltage and inductor current sharing of the parallel DC buck converter system. The method adopts a voltage tracking approach. First, an extended state observer is designed to observe and estimate disturbances such as input voltage fluctuations and load resistance changes. Based on this, a sliding mode controller is designed to obtain a composite controller for controlling the parallel DC buck converter system. This controller can quickly and accurately track the target voltage and achieve current sharing control even in the presence of disturbances such as input voltage fluctuations and load resistance changes. The present invention is simple to implement and requires minimal parameter adjustment. It not only improves the parallel DC buck converter system's ability to quickly track a reference signal, but also effectively reduces the steady-state fluctuations of the parallel power electronic DC buck converter, meeting the application requirements of high-performance power electronic buck converter systems.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic direct current buck converter systems, and in particular to a current sharing control method for a parallel direct current buck converter system. Background Art

[0002] With the rapid development of modern science and technology, especially the tremendous progress in power electronics, microelectronics, digital control and modern control theory, favorable conditions have been created for the development of power electronic DC switching power supply systems. In particular, in areas such as robots, precision radars, military weapons, and new energy photovoltaic systems, which have increasingly higher requirements for DC switching power supply control performance, DC converter systems have received more and more attention.

[0003] In practical DC power supply equipment, DC converter systems often require very high output voltage accuracy and the ability to quickly adapt to a variety of operating conditions. However, the currently used PI controller, when operating under different operating conditions, primarily utilizes integration to eliminate the impact of disturbances on the output voltage. This passive and slow control method makes it difficult to quickly track a given voltage when the system encounters rapidly changing or periodic disturbances, such as load fluctuations and voltage input variations. If the controller does not quickly and proactively handle these disturbances, the closed-loop system will struggle to achieve fast and high-precision voltage output performance. Therefore, if the DC step-down power electronic converter system can promptly handle disturbances in the presence of disturbances, the tracking speed and accuracy of the power electronic converter system can be further improved, meeting the application requirements of power electronic systems in the field of high-precision voltage output. Summary of the Invention

[0004] This invention addresses the problem of parallel DC buck converters being susceptible to interference from changes in load resistance and input voltage. By first estimating the disturbance using extended state observer technology, and obtaining estimated information about the load resistance and input voltage disturbances present in the system, this method then incorporates sliding mode control technology to design a composite controller. This allows the parallel DC buck converter system to quickly and accurately track a given voltage and also to control the inductor current sharing. This method is easy to implement, with relatively simple parameter adjustment, and has excellent application value.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for controlling current sharing in a parallel DC buck converter system comprises the following steps:

[0007] Step 1: Based on the topology of the parallel DC buck converter and considering its strongly nonlinear switching characteristics, the state variables are weighted averaged using the state-space averaging method in the continuous modeling method to convert the nonlinear, time-varying switching circuit into an equivalent linear, time-invariant continuous circuit. The system's inductor current and capacitor voltage are used as state variables, and a state-space average model of the system is established using time averaging techniques.

[0008] Step 2: Considering the input voltage fluctuation and load resistance variation of the shunt DC converter, an extended state controller is designed to estimate the load resistance variation and input voltage fluctuation. Based on the unified model of the DC converter, the disturbance of the load resistance variation and input voltage fluctuation is estimated as d(t). An observer is designed based on the extended state observer technique to estimate the disturbance.

[0009] Step 3: Based on the disturbance estimation by the extended state observer, a continuous non-singular terminal sliding mode controller is designed under the consideration of the load resistance change and input voltage fluctuation. The composite controller can ensure that the output voltage Uc can still track the given reference voltage U faster when there is a disturbance in the system. d .

[0010] Furthermore, the specific steps of step 1 are as follows:

[0011] A parallel DC buck converter system is constructed. The system's inductor current and load voltage are used as state variables. Relying on time averaging technology, the time-varying, nonlinear switching circuit is converted into an equivalent time-invariant, linear continuous circuit. This allows large-signal transient analysis of the switching converter and the establishment of a state-space average model of the system. The parallel buck converter model is established with the two states of the switch tube μ = 0 or 1:

[0012] When the switch tube S1 is turned off, the control input is 0, that is, μ1 = 0, and the inductor current i L The current flows to the output side through the diode D1, and the stored energy of the inductor is transferred to the load and capacitor, charging the capacitor. At this time, the voltage applied to the inductor is -U c , so i L Linear decrease;

[0013]

[0014] When the switch tube S1 is turned on, the control input is 1, that is, μ1=1, and the power supply voltage E is added to the diode D1, the output filter inductor L1, and the output filter capacitor C through the switch tube S1. The diode D1 is cut off; at this time, the voltage applied to the inductor is EU c , so i L Linear increase;

[0015]

[0016] With the two states of the switch tube μ1 = 0 or 1, the above formula can be unified into:

[0017]

[0018] Since the two switches S1 and S2 are connected in parallel, the relationship between the inductor current and the load voltage of the S2 branch is consistent with the above derivation. Applying the relationship of a single buck chopper circuit to the parallel DC buck converter system, the voltage equation of the parallel DC buck converter system is obtained:

[0019]

[0020] Current equation:

[0021]

[0022] Furthermore, the specific steps of step 2 are as follows:

[0023] Considering the input voltage fluctuation and load resistance variation of the DC converter, an extended state observer is designed to estimate the load resistance variation and input voltage fluctuation.

[0024] According to the theory of extended state observer, the observer is designed as follows:

[0025]

[0026] In the formula is the estimated value of the difference between the output voltage and the nominal value of the output voltage,

[0027] is the estimated value after taking the derivative of the difference between the output voltage and the nominal output voltage,

[0028] is the disturbance estimate of the load resistance change and input voltage fluctuation, parameters β1, β2, β3>0, E0, R0 represent the nominal values ​​of input voltage and load resistance respectively, and let the two inductors L1=L2=L;

[0029] in:

[0030]

[0031] Furthermore, the specific steps of step 3 are as follows:

[0032] Design the sliding surface: s = kx1 + x2. Based on the designed extended state observer, design a composite controller that combines the extended state observer with sliding mode control technology for variable load resistance and fluctuating input voltage:

[0033]

[0034]

[0035] in η, k, and λ are adjustable parameters of the sliding mode controller. Under the designed control law, the output voltage U c Able to realize reference voltage U d Tracking; and realizing current sharing control so that

[0036] The present invention has the following beneficial results:

[0037] 1) The present invention applies a composite controller combining an extended state observer and sliding mode control technology to a parallel DC buck converter system. While ensuring the dynamic performance of the system, it can significantly suppress disturbances caused by load changes and input voltage fluctuations, thereby greatly improving the tracking speed and accuracy of the DC buck converter and achieving equal current control of the inductor current.

[0038] 2) The composite control method combining the extended state observer and the sliding mode controller is applied to the parallel DC buck converter system. While ensuring the original dynamic performance, the anti-interference performance and tracking performance of the parallel DC buck converter system can be significantly improved, meeting the application of DC buck converters in high-precision fields. Engineers only need to adjust the controller parameters less. Compared with the existing technology, it has the advantages of simple design principle, significant improvement of the speed and accuracy of the buck converter on the basis of ensuring dynamic performance, and good suppression of load disturbances and input voltage fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a control block diagram of the present invention;

[0040] Figure 2 It is a schematic diagram of the present invention;

[0041] Figure 3 This is a structural diagram of the extended state observer of the present invention;

[0042] Figure 4 The response diagram of the output voltage (A), output inductor current difference (B), and output control quantity (C) of the parallel DC buck converter system when the load resistance suddenly changes from 94Ω to 50Ω under the ESO-SMC composite controller of the present invention;

[0043] Figure 5 This is a response diagram of the output voltage (A), output inductor current difference (B), and output control quantity (C) of the parallel DC buck converter system when the input voltage suddenly changes from 30V to 29V under the ESO-SMC composite controller of the present invention. DETAILED DESCRIPTION

[0044] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings: This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific implementation process are given, but the protection scope of the present invention is not limited to the following examples.

[0045] Step 1:

[0046] like Figure 1 The structure diagram shown here establishes the basic structure of a DC buck converter. Using the system's inductor current and capacitor voltage as state variables, time averaging techniques are used to convert the time-varying, nonlinear switching circuit into an equivalent, time-invariant, linear, continuous circuit. This allows for large-signal transient analysis of the switching converter and establishes a state-space average model of the system. The buck converter model is established with the switch in two states: μ = 0 or 1.

[0047] When the switch S1 is turned off, the control input is 0, that is, μ = 0, and the inductor current i L The current flows to the output side through diode D1, and the stored energy of the inductor is transferred to the load and capacitor, charging the capacitor. At this time, the voltage applied to the inductor is -U c , so i L Decrease linearly.

[0048]

[0049] When the switch tube S1 is turned on, the control input is 1, that is, μ = 1, and the power supply voltage E is added to the diode D1, the output filter inductor L1, and the output filter capacitor C through the switch tube S1. The diode D1 is cut off. At this time, the voltage applied to the inductor is EU c , so i L Increase linearly.

[0050]

[0051] With the two states of the switch tube μ = 0 or 1, the above formula can be unified into

[0052]

[0053] Since the two switches S1 and S2 are connected in parallel, the relationship between the inductor current, load voltage and other variables in the S2 branch is consistent with the above derivation. Applying the relationship of a single buck chopper circuit to the parallel buck converter system, the voltage equation of the parallel DC buck converter system is obtained:

[0054]

[0055] Its current equation is:

[0056]

[0057] Step 2: If Figure 2 As shown in FIG, a block diagram of a parallel DC buck converter control system is shown. Considering the input voltage fluctuation and load resistance variation of the parallel DC converter, an extended state observer is designed to estimate the load resistance variation and input voltage fluctuation.

[0058] Its extended state observer can be designed as:

[0059]

[0060] In the formula is the estimated value of the difference between the output voltage and the nominal value of the output voltage, is the estimated value after taking the derivative of the difference between the output voltage and the nominal output voltage, is the disturbance estimate of the load resistance change and input voltage fluctuation, parameters β1, β2, β3>0, E0, R0 represent the nominal values ​​of the input voltage and load resistance respectively, and let the two inductors L1=L2=L.

[0061] in:

[0062]

[0063] Step 3: Design the sliding surface: s = kx1 + x2. Based on the designed extended state observer, design a composite controller that combines the extended state observer with sliding mode control technology for variable load resistance and fluctuating input voltage:

[0064]

[0065]

[0066] in η, k, λ are the adjustable parameters of the sliding mode controller. The output voltage U of the closed-loop system c This realizes the reference voltage U d And realize the current sharing control so that

[0067] The experimental platform in this example is a parallel DC buck converter system, which utilizes a fully digital control method based on an NI real-time control board and is programmed in LabView. The system's main components include a control circuit centered around the NI control board, a DC buck circuit centered around a unipolar power field-effect transistor (MOSFET), a load power resistor, sensors such as Hall effect devices, a keyboard, and a display module. The main functions of these components are as follows: the Hall effect sensor acquires current and voltage signals. The NI control board is the core of the entire DC buck converter system, responsible for collecting current and voltage signals, observing system errors, and calculating key operations such as the output PWM duty cycle. The host computer keyboard and display module are used to set parameters and display current system status. The power device driver circuit, centered around the MOSFET, controls the MOSFET's on and off times based on PWM control signals generated by the host computer.

[0068] To verify the anti-interference characteristics of the designed controller, we observed the control effect of the ESO-SMC controller. First, we considered the case with no input voltage fluctuation, an input voltage of 30V, a target value of 15V, and an ideal duty cycle of μ = 0.5.

[0069] describe Parameter Symbol Normal value Input voltage E 30(V) Reference output voltage <![CDATA[U c ]]> 15(V) inductance L 4.7 (mH) capacitance C 1(μF) load resistance R 94(Ω)

[0070] Table 1

[0071] When the load changes from 94Ω to 50Ω, the output voltage, inductor current and control quantity are as follows: Figure 4 As shown in Figure 2, the output voltage of the sliding mode controller based on the extended state observer recovers to 15V after a small disturbance when the load changes. Keeping the load resistance unchanged, when the input voltage changes from 30V to 29V, we see Figure 5 , the system output voltage recovers to 15V after a small disturbance. The parameters of the sliding mode controller are set to η=200, λ=10, k=200, and the parameters of the extended state observer are set to β1=157, β2=7000, β3=75000. Figure 4 and Figure 5 It can be seen that the ESO-SMC controller greatly improves the speed and accuracy of the parallel DC buck converter system, improves the anti-interference ability of the system and realizes the equal current control of the inductor current.

[0072] This embodiment uses a composite controller based on an extended state observer and sliding mode control technology to control a parallel DC buck converter system. When disturbances occur in the DC buck power electronic converter system, the system can promptly process them, further improving the tracking accuracy and speed of the power electronic converter system, meeting the application requirements of the power electronic DC buck converter system in high-performance voltage output applications. Experimental results demonstrate that this method is highly universal, exhibits excellent anti-disturbance performance in the presence of system disturbances, and significantly improves the tracking speed and accuracy of the parallel power electronic DC converter system. It effectively achieves precise tracking of the output voltage and equal current control of the inductor current.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several anticipated improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A current sharing control method for a parallel DC buck converter system, characterized in that: The following steps are involved: Step 1: Based on the topology of the parallel DC buck converter and considering its strongly nonlinear switching characteristics, the state variables are weighted averaged using the state-space averaging method in the continuous modeling method to convert the nonlinear, time-varying switching circuit into an equivalent linear, time-invariant continuous circuit. The system's inductor current and capacitor voltage are used as state variables, and a state-space average model of the system is established using time averaging techniques. The specific steps of step 1 are as follows: A parallel DC buck converter system is constructed. The system's inductor current and load voltage are used as state variables. Relying on time averaging technology, the time-varying, nonlinear switching circuit is converted into an equivalent time-invariant, linear continuous circuit. This allows large-signal transient analysis of the switching converter and the establishment of a state-space average model of the system. The parallel buck converter model is established with the two states of the switch tube μ = 0 or 1: When the switch tube S1 is turned off, the control input is 0, that is, μ1 = 0, and the inductor current i L The current flows to the output side through the diode D1, and the stored energy of the inductor is transferred to the load and capacitor, charging the capacitor. At this time, the voltage applied to the inductor is -U c , so i L Linear decrease; When the switch tube S1 is turned on, the control input is 1, that is, μ1=1, and the power supply voltage E is added to the diode D1, the output filter inductor L1, and the output filter capacitor C through the switch tube S1. The diode D1 is cut off; at this time, the voltage applied to the inductor is EU c , so i L Linear increase; With the two states of the switch tube μ1 = 0 or 1, the above formula can be unified into: Since the two switches S1 and S2 are connected in parallel, the relationship between the inductor current and the load voltage of the S2 branch is consistent with the above derivation. Applying the relationship of a single buck chopper circuit to the parallel DC buck converter system, the voltage equation of the parallel DC buck converter system is obtained: Current equation: Step 2: Considering the input voltage fluctuation and load resistance variation of the shunt DC converter, an extended state controller is designed to estimate the load resistance variation and input voltage fluctuation. Based on the unified model of the DC converter, the disturbance of the load resistance variation and input voltage fluctuation is estimated as d(t). An observer is designed based on the extended state observer technique to estimate the disturbance. The specific steps of step 2 are as follows: Considering the input voltage fluctuation and load resistance variation of the DC converter, an extended state observer is designed to estimate the load resistance variation and input voltage fluctuation. According to the theory of extended state observer, the observer is designed as follows: In the formula is the estimated value of the difference between the output voltage and the nominal value of the output voltage, is the estimated value after taking the derivative of the difference between the output voltage and the nominal output voltage, is the disturbance estimate of the load resistance change and input voltage fluctuation, parameters β1, β2, β3>0, E0, R0 represent the nominal values ​​of input voltage and load resistance respectively, and let the two inductors L1=L2=L; in: Step 3: Based on the disturbance estimation by the extended state observer, a linear sliding mode controller is designed taking into account the load resistance change and input voltage fluctuation. The composite controller can ensure that the output voltage U is constant when there is a disturbance in the system. c Still able to quickly track the given reference voltage U d ; The specific steps of step 3 are as follows: Design the sliding surface: s = kx1 + x2. Based on the designed extended state observer, design a composite controller that combines the extended state observer with sliding mode control technology for variable load resistance and fluctuating input voltage: in η, k, and λ are adjustable parameters of the sliding mode controller. Under the designed control law, the output voltage U c Able to realize reference voltage U d Tracking; and realizing current sharing control so that

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