Voltage Control Method of DCDC Converter with Discontinuous Current

Abstract

The present invention discloses a method for controlling the voltage of a DCDC converter when the current is discontinuous. The key point of the method is that when the inductor current is discontinuous, the voltage closed-loop control parameters should comply with the following points: 1) The zero point of the PI controller transfer function is determined by the transfer function of the DCDC converter small signal model; 2) The proportional coefficient of the PI controller after switching remains consistent with that before switching to prevent current shock caused by sudden changes in the control voltage; 3) The integral coefficient of the PI controller after switching is jointly determined by the proportional coefficient and the zero point. When the load is small and the inductor current is discontinuous, the present invention uses the voltage control parameters when the current is discontinuous, and the control voltage fluctuation is greatly improved; the proportional coefficient of the PI controller after the continuous and discontinuous switching of the inductor current remains consistent with that before switching to prevent current shock caused by sudden changes in the control voltage.

Description

Technical Field

[0001] The invention belongs to the technical field of DCDC converters, and in particular relates to a DCDC converter voltage control method when current is discontinuous. Background Art

[0002] The DCDC converter is a voltage converter that effectively outputs a fixed voltage after converting the input voltage. Figure 1 It is the circuit diagram of DCDC buck converter. Figure 2 This is the control principle diagram of the DCDC converter. In the figure, V REF is the voltage command value, G c (s) is the voltage closed-loop control transfer function, F m is the voltage / duty cycle conversion factor, G dv (s) is the transfer function of the DCDC converter system, H(s)e -sTs is the voltage sampling transfer function. The transfer function of the small signal model of the DCDC converter is:

[0003]

[0004] Where s is the Laplace operator, and the voltage closed-loop control PI parameters are usually designed based on this transfer function.

[0005] The voltage closed-loop control PI parameters are designed based on the transfer function (1) when the current is continuous. When the load is small, the current flowing through the inductor will be cut off, and there will be a period of zero current. During this period, the output voltage is the capacitor voltage. Compared with the continuous current, the output voltage increases.

[0006] like Figure 3 and Figure 4 As shown in the figure, when the load is small, the inductor current is discontinuous, and the voltage control parameters when the current is continuous are used, the output voltage △Vo of the voltage closed-loop PI control fluctuates greatly. At the same time, when the load is small and the inductor current is discontinuous, the voltage control parameters when the current is continuous are used, and the output voltage Vo will also fluctuate with the control voltage. Summary of the invention

[0007] The object of the present invention is to provide a method for controlling the voltage of a DCDC converter when the current is discontinuous, so as to solve the problem that the control voltage and the output voltage fluctuate greatly when the current is discontinuous.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A method for controlling a voltage of a DCDC converter when current is discontinuous, comprising:

[0010] Obtain the resonant frequency ωn of the DCDC converter system;

[0011] The zero-pole expression of the PI controller is defined as:

[0012]

[0013] In the formula, ω1 and ω z are all PI transfer function gains, and s is the Laplace operator;

[0014] The PI control zero point is determined by the system's resonant frequency ωn, and the PI controller when the current is continuous is:

[0015]

[0016] The PI parameters of the PI controller when the current is continuous are obtained as follows: From this, we can get the PI parameter k of the PI controller when the current is continuous P and k I ;

[0017] When the current is discontinuous, the system transfer function is:

[0018]

[0019] Where V I Indicates input voltage, V O represents the output voltage, C represents the DCDC converter capacitance, I O Represents the output current; when the current is discontinuous, the system zero point is

[0020] When the current is discontinuous, the PI controller is:

[0021]

[0022] The zero point is determined by the system zero point when the current is discontinuous, and we get:

[0023]

[0024] Proportional coefficient k' when current is discontinuous P The proportionality coefficient k when the system is continuous P Consistent, we get: k' P =k P =ω1 / w;

[0025] Then ω1=w*k P , and then determine the integral coefficient k' when the current is discontinuous I :k' I =ω1=w*k P .

[0026] Furthermore, the resonant frequency

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] 1) When the load is small and the inductor current is discontinuous, the voltage control parameters when the current is discontinuous are used to significantly improve the control voltage fluctuation.

[0029] 2) After the inductor current is switched between continuous and discontinuous, the proportional coefficient of the PI controller remains consistent with that before the switching, preventing current shock caused by sudden changes in the control voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the circuit diagram of a DCDC buck converter;

[0031] Figure 2 This is the control schematic diagram of the DCDC converter;

[0032] Figure 3 This is the voltage closed-loop PI control output voltage △Vo fluctuation diagram when this solution is not used;

[0033] Figure 4 This is the fluctuation diagram of output voltage Vo with control voltage when this solution is not used;

[0034] Figure 5 is a control voltage fluctuation diagram when the voltage control parameters of the present invention are used;

[0035] Figure 6 It is an output voltage fluctuation diagram when the voltage control parameters of the present invention are used. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] like Figure 3 and Figure 4 As shown, when the current is discontinuous, the voltage control parameters when the current is continuous are used, and the control voltage and output voltage fluctuate greatly; in addition, when the inductor current is switched between continuous and discontinuous, different control parameters will cause the control voltage to suddenly change. In order to solve the above technical problems, the present invention provides a voltage control method for a DCDC converter when the current is discontinuous.

[0038] The critical state of inductor current continuous / discontinuous, the load power Pc is:

[0039]

[0040] Where: T s is the sampling period, V I Indicates input voltage / voltage before conversion, V O Indicates the output voltage.

[0041] Under light load conditions, when the inductor current is discontinuous, the transfer function of the DCDC converter small signal model is:

[0042]

[0043] Where s is the Laplace operator.

[0044] It can be seen that compared with the transfer function (1) when the current is continuous, the transfer function is reduced to a first-order system and the system characteristics change.

[0045] Therefore, when the inductor current is discontinuous, the voltage closed-loop control parameters should comply with the following points:

[0046] 1) The zero point of the PI controller transfer function is determined by equation (3);

[0047] 2) The proportional coefficient of the PI controller after switching remains the same as before switching to prevent current shock caused by sudden changes in control voltage;

[0048] 3) After switching, the integral coefficient of the PI controller is determined by the proportional coefficient and the zero point. Specific embodiment:

[0050] V i =450V, output voltage command value V O =350V, load po=6kW, capacitance C=1mF, inductance L=75uh, r L =0.05Ω, r C =0.001Ω, PWM control frequency is 40khz.

[0051] When the current is continuous, the transfer function is:

[0052] The resonant frequency of the system:

[0053] The zero-pole expression of the PI controller can be defined as:

[0054] Where ω1 is the PI transfer function gain, ω z is the PI transfer function gain.

[0055] The PI control zero point is determined by the resonant frequency of the system, and the PI controller when the current is continuous is:

[0056]

[0057] According to the frequency domain control stability theory, it is necessary to ensure that the frequency domain phase angle margin is less than 180°. Under this premise, the controller gain has a maximum value, which not only satisfies the stability of the system frequency domain phase angle, but also enables the system to achieve the fastest response performance. The PI controller when the current is continuous is:

[0058]

[0059] Here: 1300 is the controller G when the system frequency domain phase angle stability is met c (s) maximum gain.

[0060] The PI parameters of the PI controller when the current is continuous are obtained as follows:

[0061] Get: k I =1300, k P =0.356.

[0062] When the current is discontinuous, the system transfer function is:

[0063]

[0064] When the current is discontinuous, the system zero point w is 101rad / s.

[0065] PI controller when current is discontinuous:

[0066]

[0067] The zero point is determined by the system zero point when the current is discontinuous, and we get:

[0068]

[0069] The proportional coefficient is consistent with the proportional coefficient when the system is continuous, so:

[0070] k' P =k P =0.356=ω1 / w

[0071] Then: ω1=w*k' P =w*k P =101*0.356=36;

[0072] Then determine the integral coefficient:

[0073] k' I =ω1=w*k P =101*0.356=36.

[0074] like Figure 5 and Figure 6As shown in the figure, when the load is small and the inductor current is discontinuous, the voltage control parameters when the current is discontinuous are used, and the control voltage fluctuation is greatly improved. After the inductor current is switched between continuous and discontinuous, the proportional coefficient of the PI controller remains the same as before the switching, preventing the current shock caused by the sudden change of the control voltage.

[0075] Those skilled in the art will easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling the voltage of a DCDC converter when the current is discontinuous, characterized in that: include: Obtain the resonant frequency ωn of the DCDC converter system; The zero-pole expression of the PI controller is defined as: In the formula, ω1 and ω z are all PI transfer function gains, and s is the Laplace operator; The PI control zero point is determined by the system's resonant frequency ωn, and the PI controller when the current is continuous is: The PI parameters of the PI controller when the current is continuous are obtained as follows: From this, we can get the PI parameter k of the PI controller when the current is continuous P and k I ; When the current is discontinuous, the system transfer function is: Where V I Indicates input voltage, V O represents the output voltage, C represents the DCDC converter capacitance, I O Indicates the output current; When the current is discontinuous, the system zero point is When the current is discontinuous, the PI controller is: The zero point is determined by the system zero point when the current is discontinuous, and we get: Proportional coefficient k' when current is discontinuous P The proportional coefficient is consistent with the continuous system, so: k' P =k P =ω1 / w; Then ω1=w*k P , and then determine the integral coefficient when the current is discontinuous: k' I =ω1=w*k P .

2. The method for controlling the voltage of a DCDC converter when the current is discontinuous according to claim 1, characterized in that: Resonance frequency

Images