Current prediction control method and circuit of direct current converter

Abstract

The embodiment of the invention provides a current prediction control method and circuit of a direct-current converter, which are used for reducing the calculation burden of a current prediction algorithm and improving the response performance of a system. Comprising the following steps: sampling the DC converter to obtain a current output voltage value, a current input voltage value and a current inductance current value of the DC converter; obtaining a target reference current value, and inputting the current output voltage value, the current input voltage value, the current inductance current value and the target reference current value into a duty ratio positioning model to obtain a duty ratio positioning value to be optimized; and inputting the to-be-optimized duty ratio positioning value, the current output voltage value, the current input voltage value, the current inductance current value and the target reference current value into a final target function model and a target current prediction model, performing secondary small-range optimization on the to-be-optimized duty ratio positioning value in preset optimization times, and outputting a target duty ratio positioning value. And converting the optimal duty ratio into a real-time pulse signal so as to control the direct current converter.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of wireless power transmission control, and in particular to a current prediction control method and circuit for a DC converter. Background Art

[0002] Wireless power transfer (WPT) technology is a technology that uses electromagnetic fields to transmit energy in space. It can wirelessly transmit electrical energy from the power source to the power-consuming device. This technology has a wide range of application scenarios, such as wireless charging of mobile phones and cars, smart homes, medical equipment, underwater detection equipment, and aerospace.

[0003] In the wireless power transmission system, the DC converter plays a vital role. Its main function is to rectify the AC power obtained by the secondary coil of the wireless power transmission system into DC power and adjust the voltage to meet the needs of different loads. At the receiving end, the wireless power transmission system may face fluctuations and changes in the output voltage, and the output side is generally connected to voltage source loads such as batteries. Therefore, an additional DC converter needs to be cascaded on the output side to adapt to the fluctuation of the output voltage of the WPT system and control the current on the output side, thereby ensuring the final wide range of current output capability and fast response capability.

[0004] In order to respond to the changes of the WPT system in time, model predictive control (MPC) can be used to ensure the rapidity of the system current response. MPC is an advanced control strategy that optimizes the control behavior by predicting future behavior and avoids the lag of the integral link in the PI controller. The core of MPC lies in a system model, which is used to predict the future behavior of the system under different control actions. However, when the traditional finite set model predictive compensation is used to control the output current of the DC converter, a large number of nonlinear terms and coupling terms will appear in the process of deriving the delay compensation model, which will increase the complexity of the derivation process and reduce the practicality of the algorithm. In addition, the traditional finite set model predictive control requires exhaustive calculation of all possibilities of the control quantity, which will increase the calculation burden of the controller and reduce the rapidity of the algorithm. In addition, in the exhaustive calculation, the control output will have a large mutation due to sampling interference or calculation error of the control system, further reducing the anti-interference ability of the algorithm. Summary of the invention

[0005] The embodiments of the present application provide a current prediction control method and circuit for a DC converter, which are used to reduce the computational burden of a current prediction algorithm and improve the dynamic response performance and anti-interference capability of the system.

[0006] A first aspect of an embodiment of the present application provides a current prediction control method for a DC converter, characterized in that the method is applied to a prediction control circuit, the prediction control circuit includes a DC converter, and the method includes:

[0007] Sampling the DC converter to obtain a current output voltage value, a current input voltage value, and a current inductor current value of the DC converter at a current moment;

[0008] Obtaining a target reference current value at a current moment, inputting the current output voltage value, the current input voltage value, the current inductor current value, and the target reference current value into a duty cycle positioning model, and obtaining a duty cycle positioning value to be optimized at a current moment;

[0009] The duty cycle positioning value to be optimized, the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value are input into the final objective function model and the target current prediction model, and the duty cycle positioning value to be optimized is optimized twice in a small range within a preset number of optimization times, and the target duty cycle positioning value is output, and the optimal duty cycle is converted into a real-time pulse signal to realize the control of the DC converter.

[0010] A second aspect of the embodiments of the present application provides a current prediction control circuit for a DC converter, the circuit comprising: a DC converter, a full-bridge rectifier circuit, a high-frequency inverter and a resonance unit;

[0011] The high-frequency inverter is located in the front-stage circuit of the prediction control circuit, and is used to invert the low-voltage direct current of the input power supply into high-frequency low-voltage alternating current, and input the high-frequency low-voltage alternating current into the resonance unit;

[0012] The resonance unit is used to make the high-frequency low-voltage alternating current undergo circuit resonance and input resonance excitation to the full-bridge rectifier circuit;

[0013] The full-bridge rectifier circuit is connected to the DC converter circuit and is located in the post-stage circuit of the predictive control circuit; the full-bridge rectifier circuit is used to rectify the resonant excitation and output the rectified current to the DC converter; the DC converter is used to determine the current output voltage value, the current input voltage value and the current inductor current value of the DC converter according to the current rectifier current, so as to control the DC converter according to the current output voltage value, the current input voltage value and the current inductor current value;

[0014] The DC converter also includes: an input voltage capacitor, a load resistor, a filter capacitor, a power inductor, a switch tube and a unidirectional diode;

[0015] The two ends of the input voltage capacitor are circuit-connected to the full-bridge rectifier circuit, and one end of the input voltage capacitor is connected to the drain of the switch tube, and the other end is respectively circuit-connected to one end of the load resistor, the positive electrode of the unidirectional diode, and one end of the filter capacitor, and the voltage value at the two ends of the input voltage capacitor is the current input voltage value;

[0016] The source of the switch tube is respectively connected to the cathode of the unidirectional diode and one end of the power inductor;

[0017] The other end of the power inductor is respectively connected to the other end of the filter capacitor and the other end of the load resistor, and the current value flowing through the power inductor is the current inductor current value;

[0018] The voltage value across the filter capacitor and the load resistor is the current output voltage value.

[0019] The prediction control circuit provided in the second aspect of the embodiment of the present application is used to execute the current prediction control method of the DC converter described in the first aspect.

[0020] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages: through the current prediction control method of a DC converter disclosed in the embodiments of the present application, a mechanism is sought on a simplified duty cycle positioning model without affecting the load current control effect, thereby obtaining a duty cycle positioning value to be optimized that is very close to the optimal duty cycle. Then, in order to achieve precise control, a secondary iterative optimization is performed based on the duty cycle positioning value to be optimized, and finally the optimal duty cycle for controlling the DC converter is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0022] Figure 1 A circuit diagram of a predictive control circuit disclosed in an embodiment of the present application;

[0023] Figure 2 A schematic flow chart of a current prediction control method for a DC converter disclosed in an embodiment of the present application;

[0024] Figure 3 A schematic flow chart of another current prediction control method for a DC converter disclosed in an embodiment of the present application;

[0025] Figure 4A schematic flow chart of another current prediction control method for a DC converter disclosed in an embodiment of the present application;

[0026] Figure 5 A control block diagram of a DC converter disclosed in an embodiment of the present application;

[0027] Figure 6 A steady-state output current response waveform diagram disclosed in an embodiment of the present application;

[0028] Figure 7 A converter switch duty cycle and steady-state output voltage waveform diagram disclosed in an embodiment of the present application;

[0029] Figure 8 A dynamic output current and duty cycle waveform diagram disclosed in an embodiment of the present application. DETAILED DESCRIPTION

[0030] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0031] It should be noted that the descriptions involving "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0032] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] For the technical issues described above, please refer to Figure 1 , Figure 1 A circuit diagram of a predictive control circuit disclosed in an embodiment of the present application.

[0034] Depend on Figure 1 As shown, the predictive control circuit includes: a DC converter, a full-bridge rectifier circuit, a high-frequency inverter and a resonance unit. The high-frequency inverter is located in the front-stage circuit of the predictive control circuit, and is used to invert the low-voltage DC power of the input power supply into a high-frequency low-voltage AC power, and input the high-frequency low-voltage AC power to the resonance unit. The resonance unit is used to resonate the high-frequency low-voltage AC power and input the resonance excitation to the full-bridge rectifier circuit. The full-bridge rectifier circuit is connected to the DC converter circuit and is located in the rear-stage circuit of the predictive control circuit. The full-bridge rectifier circuit is used to rectify the resonance excitation and output the current rectified current after rectification to the DC converter. The DC converter is used to determine the current output voltage value, the current input voltage value and the current inductor current value of the DC converter according to the current rectified current, so as to control the DC converter according to the current output voltage value, the current input voltage value and the current inductor current value.

[0035] The DC converter includes: input voltage capacitor C dc , load resistance R0 (equivalent resistance), filter capacitor C0 (equivalent capacitance), power inductor L B (equivalent inductance), switch tube S B And the unidirectional diode D B . Input voltage capacitor C dc The two ends of the capacitor C are connected to the full-bridge rectifier circuit, and the input voltage dc One end of the switch tube S B The other end is connected to one end of the load resistor R0 and the unidirectional diode D B The positive electrode of the filter capacitor C0 is connected to the circuit, and the input voltage capacitor C dc The voltage value at both ends is the current input voltage value u dc , the corresponding current value is i dc . Switching tube S B The source of each of the two diodes D B The negative pole, power inductor L B One end of the circuit is connected to the power inductor L B The other end of the filter capacitor C0 and the other end of the load resistor R0 are connected to the circuit, and the current flows through the power inductor L B The current value is the current inductor current value i L The voltage value across the filter capacitor C0 and the load resistor R0 is the current output voltage value U0. BBy controlling the voltage and current, the DC converter can be controlled.

[0036] It should be noted that the high-frequency inverter includes a first capacitor C1, a second capacitor C2, a first MOS transistor S1, a second MOS transistor S2, a third MOS transistor S3 and a fourth MOS transistor S4, and the low-voltage direct current corresponding to the input power supply is U in . Wherein, the first capacitor C1 and the second capacitor C2 are connected in series, and the other ends of the first capacitor C1 and the second capacitor C2 are connected to the positive electrode and the negative electrode of the input power supply respectively. The drain of the first MOS tube S1 and the drain of the second MOS tube S2 are connected to the positive electrode of the input power supply, the source of the third MOS tube S3 and the source of the fourth MOS tube S4 are connected to the negative electrode of the input power supply, the source of the first MOS tube S1 and the drain of the third MOS tube S3 are connected, and the source of the second MOS tube S2 and the drain of the fourth MOS tube S4 are connected. Furthermore, the intersection where the source of the first MOS tube S1 and the drain of the third MOS tube S3 are connected, the output current of the resonance unit is i Lf The intersection where the source of the second MOS tube S2 and the drain of the fourth MOS tube S4 are connected has a voltage u p Furthermore, the first MOS transistor S1, the second MOS transistor S2, the third MOS transistor S3 and the fourth MOS transistor S4 can be understood as a switch transistor, which will not be described in detail here. Furthermore, through the circuit connection relationship of the first capacitor C1, the second capacitor C2, the first MOS transistor S1, the second MOS transistor S2, the third MOS transistor S3 and the fourth MOS transistor S4, the low voltage DC power supply U of the input power supply can be realized. in Converted into high frequency alternating current.

[0037] It should be noted that the resonant unit includes a resonant inductor L f , resonant capacitor C f , resonant input capacitor C p , resonant input inductor L p , resonant output inductor L s and the resonant output capacitor C s Among them, the resonant input inductor L p With the resonant output inductor L s The inductance multiple between is M. The resonant inductance L f One end is connected to the intersection of the source of the first MOS tube S1 and the drain of the third MOS tube S3 in the high-frequency inverter, and the other end is connected to the resonant capacitor C f and the resonant input capacitor C p connected, flows through the resonant inductor L f The current is i Lf . Resonant capacitor C fThe other end is connected to the intersection of the source of the second MOS tube S2 and the drain of the fourth MOS tube S4, and its resonant capacitor C f The voltage is u cf , the current is i cf . Resonant input capacitor C p The other end of the resonant input inductor L p One end of the resonant input inductor L p The other end is connected to the intersection of the source of the second MOS tube S2 and the drain of the fourth MOS tube S4, wherein the resonant input capacitor C p The voltage is u cp , the current is i p . Resonant output inductor L s One end of the resonant output capacitor C s One end is connected to the full-bridge rectifier circuit, and the other end is connected to the resonant output capacitor C s The other end is also connected to the full-bridge rectifier circuit, where the current flowing through the resonant output inductor L s The current is i s , corresponding to the resonant output capacitor C s The voltage is u cs Thus, by connecting the various circuit devices in the resonant unit, the loop can be absorbed and the interference signal can be filtered out.

[0038] It should be noted that the full-bridge rectifier circuit includes a first diode D1, a second diode D2, a third diode D3 and a fourth diode D4. The anode of the first diode D1 is connected to the cathode of the third diode D3, and the intersection of the first diode D1 and the third diode D3 is connected to the resonant output capacitor C s The anode of the second diode D2 is connected to the cathode of the fourth diode D4, and the intersection of the second diode D2 and the fourth diode D4 is connected to the resonant output inductor L. s The cathode of the first diode D1 and the cathode of the second diode D2 are connected to the input voltage capacitor C dc The anode of the third diode D3 and the anode of the fourth diode D4 are connected to the input voltage capacitor C dc Furthermore, the potential difference between the intersection of the first diode D1 and the third diode D3, and the intersection of the second diode D2 and the fourth diode D4 is u s1 Thus, by connecting the various circuit components in the full-bridge rectifier circuit, the current of the full-bridge rectifier circuit is rectified by utilizing the unidirectional conductivity of the diode.

[0039] In one of the feasible technical solutions, the predictive control circuit is located in a digital control system, and the digital control system also includes a controller that can control a DC converter. Further, in one feasible technical solution, the embodiment of the present application is particularly directed to an LCC-S type WPT system based on BUCK converter control, and for ease of understanding, no further description will be given later.

[0040] To facilitate the above Figure 1 The control method of the DC converter is described in Figure 2 , Figure 2 The present invention is a flowchart of a current prediction control method for a DC converter disclosed in an embodiment of the present application, including steps 201 to 204.

[0041] 201. Sampling the DC converter to obtain a current output voltage value, a current input voltage value, and a current inductor current value of the DC converter at a current moment.

[0042] Depend on Figure 1 It can be seen that in order to realize the control of the DC converter, the DC converter needs to be sampled first, so as to obtain the current output voltage value, current input voltage value and current inductor current value of the DC converter at the current moment. Specifically, in this embodiment, an updated MPC method is used for model prediction.

[0043] In one specific embodiment, the voltage and current of the DC converter (a BUCK converter) are sampled to obtain the output voltage value, input voltage value and inductor current value of the DC converter at the current moment. Figure 1 As shown, the input voltage value at the current moment is the voltage capacitor C dc The corresponding voltage value, the output voltage value is the voltage value corresponding to the load resistance R0 or the filter capacitor C0, and the inductor current value is the current flowing through the power inductor L B Further, it should be noted that the load resistor R0 described in this embodiment is an equivalent resistor, specifically, it can be an equivalent resistor formed by multiple resistors connected in series or in parallel, and the details are not repeated here.

[0044] 202. Obtain the target reference current value at the current moment, input the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value into the duty cycle positioning model, and obtain the duty cycle positioning value to be optimized at the current moment.

[0045] It should be noted that the predicted current value does not need to be calculated in the duty cycle positioning model, and the duty cycle positioning model already includes the predicted current value.

[0046] In one of the specific embodiments, please combine Figure 1 , before controlling the DC converter, the reference current value of the DC converter at the current moment can be determined by the parameters of each circuit device of the entire predictive control circuit and the input voltage of the predictive control circuit. Thus, the target reference current value is obtained. Therefore, the target reference current value, the current output voltage value, the current input voltage value and the current inductor current value at the current moment can be substituted into the duty cycle positioning model for duty cycle positioning, so as to obtain the duty cycle positioning value to be optimized at the current moment. It should be noted that the duty cycle positioning value to be optimized at this time can be understood as a suboptimal duty cycle. This is because the duty cycle obtained at this time is not obtained through an accurate model, and there is still a certain deviation from the true optimal duty cycle, so it is necessary to perform secondary small-scale processing on the solution, and refer to step 203 for details.

[0047] 203. The duty cycle positioning value to be optimized, the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value are input into the final objective function model and the target current prediction model, and the duty cycle positioning value to be optimized is optimized twice in a small range within a preset number of optimizations, the target duty cycle positioning value is output, and the optimal duty cycle is converted into a real-time pulse signal to realize the control of the DC converter.

[0048] In one of the specific embodiments, the duty cycle positioning value to be optimized, the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value are first input into the derived target current prediction model. Because the digital control system needs to be considered to have a delay, it is necessary to calculate to other moments (in this embodiment, the k+2 moment can be selected to compensate for the system delay), so that the predicted current value at the k+2 moment can be obtained, and then the target reference current value and the predicted current value are input into the objective function model, so that the duty cycle in a single optimization process can be obtained. Furthermore, the target current prediction model and the objective function model are used to perform optimization within a preset optimization cycle, so as to determine the absolute value difference between the predicted current value and the target reference current value, that is, the optimal duty cycle when the objective function is minimized, and the optimal duty cycle positioning value is determined to be the target duty cycle positioning value.

[0049] Furthermore, the switch tube of the DC converter can be controlled according to the target duty cycle positioning value.

[0050] In one specific embodiment, the digital control system can control the switch tube of the DC converter by controlling the controller, and then use the target duty cycle positioning value to ensure the steady-state response of the current, thereby achieving control of the DC converter.

[0051] Through the current prediction control method of a DC converter disclosed in this embodiment, a mechanism is sought on a simplified duty cycle positioning model without affecting the load current control effect, thereby obtaining a duty cycle positioning value to be optimized that is very close to the optimal duty cycle. Then, in order to achieve precise control, a secondary iterative optimization is performed based on the duty cycle positioning value to be optimized, and finally the optimal duty cycle for controlling the DC converter is obtained.

[0052] To facilitate the description of the derivation process of the objective function model and the current prediction model, please refer to Figure 3 , Figure 3 This is a flow chart of another current prediction control method for a DC converter disclosed in an embodiment of the present application, including steps 301 to 306.

[0053] 301. According to the circuit switching state of the switch tube in the DC converter, the target discrete mathematical model of the DC converter is determined based on the current output voltage value, the current input voltage value and the current inductor current value.

[0054] It should be noted that this embodiment mainly describes the derivation process of the objective function model and the target current prediction model, and therefore, does not describe each electronic device in the DC converter in detail. In this embodiment, the target discrete mathematical model of the DC converter can be determined based on the current output voltage value, the current input voltage value, and the current inductor current value according to the circuit switching state of the switch tube in the DC converter.

[0055] Specifically, in one of the specific embodiments, it is necessary to first determine the load resistance value R0, the filter capacitor value C0, and the power inductor value L of the DC converter. B and the switching period T s It can be understood that, combined with the above description, R0, C0 or L B Then, according to the different switching states of the subsequent circuit, the initial state equation of the DC converter (BUCK converter) is established based on the current output voltage value, the current input voltage value and the current inductor current value, and the initial state equation is discretized to obtain an equivalent discrete mathematical model of the DC converter (i.e., an initial discrete mathematical model), wherein the initial discrete mathematical model is:

[0056] Where x=[u0 i L ] T , u(k)=u dc It should be noted that u dc is the current input voltage value, u0 is the current output voltage value, i L is the current inductor current value, E2 is the 2×2 unit matrix, xd (k+1) is used to represent the state variable value when the switch tube is in the closed state at the next moment, x 1-d (k+1) is used to represent the state variable value when the switch is in the off state at the next moment. Then, the initial discrete mathematical model can be weighted according to the duration of the switch corresponding to the closed state and the open state in the switching cycle, so as to obtain the integrated target discrete mathematical model, where the target discrete mathematical model is Where, M = E2 + AT s ,N=B1T s u dc , d(k) is the duty cycle positioning value at the current moment k. It should also be noted that the above M or N, etc., are simplified forms of overly long polynomials. For ease of understanding and description, the simplified polynomials will not be described in detail later.

[0057] 302. Determine an intermediate current prediction model of the DC converter at the next moment according to the target discrete mathematical model.

[0058] Specifically, in order to obtain the current prediction model, it is necessary to additionally write the output current variable y(k). Specifically, the initial current prediction model y(k)=i L (k) = Cx(k), where C is the coefficient matrix

[01] . Then, through the initial current prediction model and combined with the target discrete mathematical model in step 301, the current prediction expression y at time k+1 can be obtained: p (k+1), namely the intermediate current prediction model Among them, A x =CM, B d =CN. It should be noted that there is a correlation between the intermediate current prediction model and the output current of the DC converter.

[0059] 303. Determine the duty cycle change rate of the DC converter, and obtain a function model to be compensated according to the duty cycle change rate, the target reference current value and the intermediate current prediction model.

[0060] Furthermore, the intermediate current prediction model obtained in step 302 can be used to predict the inductor current value at time k+1, and the predicted current value is subtracted from the target reference current value to obtain Δi L , take the value that makes Δi L The minimum duty cycle is the optimal duty cycle at that moment, but in order to avoid the controller from having a significant change in duty cycle during the period from k-1 to k, which may lead to system oscillation, the duty cycle change rate also needs to be introduced into the function model to be compensated. Specifically, it is necessary to first determine the duty cycle change rate of the DC converter, and then obtain the function model to be compensated based on the duty cycle change rate, the target reference current value and the intermediate current prediction model.

[0061] In one specific embodiment, the current control weight value k1 and the duty cycle control weight value k2 corresponding to the duty cycle conversion rate are first determined in the DC converter. Among them, k1 can also be understood as the weight coefficient of the current control function G, and k2 can also be understood as the weight coefficient of the function model to be compensated G (specifically, it can be understood as a duty cycle change rate control function). Then, based on the current control weight value k1, the duty cycle control weight value k2 and the target reference current value, the initial function model G=k1(I ref -y p (k+1)) 2 +k2(d(k)-d(k-1)) 2 , where I ref is the target reference current value, and d(k-1) is the duty cycle positioning value at the previous moment. It should be noted that the duty cycle positioning value at the previous moment can be obtained by the predicted current value obtained by the intermediate current prediction model at the previous moment, and is calculated based on the predicted current value and the target reference current value. The details are not repeated here. Finally, the initial function model is combined with the intermediate current prediction model obtained in step 302 to derive the function model to be compensated.

[0062] 304. Perform compensation delay on the intermediate current prediction model to obtain a current prediction model to be optimized corresponding to the next moment, and update the compensation function model according to the current prediction model to be optimized to obtain a function model to be optimized.

[0063] Specifically, it is necessary to compensate the delay of the intermediate current prediction model to obtain the current prediction model to be optimized corresponding to the next moment, and then update the compensation function model according to the current prediction model to be optimized to obtain the function model to be optimized.

[0064] In one specific embodiment, if there is a delay in the digital control system based on time k+2, it is necessary to calculate the system delay. Specifically, the delay is compensated for the intermediate current prediction model to obtain the current prediction model to be optimized. in, M2=CA x B d , M3=CB d Then, the compensation function model to be optimized is updated according to the current prediction model to be optimized to obtain the function model to be optimized.

[0065]

[0066] 305. De-linearize the function model to be optimized, and perform differentiation to obtain a duty cycle positioning value that satisfies the minimum value of the function model to be optimized.

[0067] When the system compensation calculation reaches the k+2 moment, it is necessary to de-linearize the function model to be optimized and perform differentiation to obtain the duty cycle positioning value that satisfies the minimum value of the function model to be optimized.

[0068] In one specific embodiment, when the system compensation is calculated to time k+2, the function model obtained according to the above step 304 will produce more nonlinear terms and coupling terms, which makes the difficulty of model derivation suddenly increase. Therefore, the function model G to be optimized obtained in the above step 304 is optimized, and only the polynomial related to the control quantity d(k) is retained, and the nonlinear terms containing the state quantity are omitted.

[0069] Specifically, in this embodiment, the function model to be optimized can be optimized to retain the polynomial associated with the state variable value d(k), and the nonlinear term containing the state variable value in the function model to be optimized is removed, thereby obtaining a simplified function model to be optimized. Then, in order to avoid iterating the duty cycle from 0 to 1 in each calculation, the simplified function model to be optimized can be derived according to the uniqueness theorem of derivation. Specifically, in, D=2k1A x x(k)B d -2k1I ref B d =2k2d(k-1). Therefore, combined with the function model G to be optimized in step 305 of this embodiment, the duty cycle positioning value that minimizes the function model G can be obtained, that is, the duty cycle positioning model And get the duty cycle positioning value d opt (k), at this time, the compensation matrix D d =2k1M2M3d(k-1)-2k1M3I ref -2k2d(k-1).

[0070] 306. According to the duty cycle positioning value and the current prediction model to be optimized, optimization is performed at a preset optimization number of times to obtain a target current prediction model, and according to the target current prediction model and the target reference current value, an objective function model is obtained.

[0071] In one specific embodiment, based on the finite set model predictive control algorithm, the duty cycle positioning value is used as a reference, and the current prediction model to be optimized is optimized in a preset number of optimizations to obtain the target current prediction model y p (k+2)=M1x(k)+M2d(k-1)+M3(d opt(k)+Δd / n); where Δd is used to represent the optimization fluctuation range, and n is used to represent the preset optimization times. It should also be noted that Δd / n can be represented as the optimization step length. Then, based on the target reference current value, the target current prediction model is transformed into the simplified function model to be optimized, and the target function model G=|I ref -y p (k+2)|.

[0072] Specifically, the objective function obtained in step 305 is obtained after ignoring the nonlinear term x(k). It is a simplified result, not obtained by an accurate model. Therefore, the duty cycle calculated only by step 305 is not the optimal duty cycle, and there is still a certain deviation from the actual optimal duty cycle, so it is necessary to perform a secondary small-scale processing on the result. Adopting the idea of ​​finite set model predictive control, it can be considered that the result obtained in step 305 is a preliminary suboptimal duty cycle, and then a small-scale iterative optimization is performed near the suboptimal duty cycle to finally obtain a new objective function model and a new current prediction model.

[0073] Correspondingly, Δd can be understood as the fluctuation range of the optimization calculation, and n represents the number of optimization calculations. The calculation formula of step 306, d(k) brought into the iterative calculation includes the fluctuation range Δd, and the duty cycle obtained after the final secondary optimization of the objective function is the optimal duty cycle (target duty cycle positioning value) finally sent to the controller. Finally, the duty cycle is converted into a pulse signal to control the switch tube of the BUCK converter, and the whole control process is terminated.

[0074] Through the current prediction control method of a DC converter disclosed in this embodiment, the nonlinear terms of the model are optimized, the mathematical model with delay compensation and duty cycle change rate compensation is simplified, and the objective function is specifically simplified to a univariate function related only to the duty cycle, which reduces the coupling between model parameters and the calculation burden of the controller. Compared with the traditional model prediction compensation control, the complexity of model derivation is significantly simplified, the partial derivative process is omitted, and the practicality and extensiveness of the algorithm are improved. At the same time, an extreme value strategy and a small range optimization algorithm are adopted. First, through extreme value calculation, a suboptimal duty cycle close to the optimal duty cycle is obtained on the basis of a simplified equivalent model. According to the finite set prediction method, a secondary optimization iteration is performed in a very small range near the suboptimal duty cycle. Compared with the traditional finite set model prediction control, the calculation amount of the optimization iteration is reduced, the calculation speed of the finite set model prediction is improved, and the rapidity and timeliness of the algorithm are significantly improved.

[0075] For a more detailed description of the output duty cycle, see Figure 4 , Figure 4This is a flow chart of another current prediction control method for a DC converter disclosed in an embodiment of the present application, including steps 401 to 405.

[0076] 401. Determine the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value, determine the optimization fluctuation range during optimization according to the objective function model, and determine the preset optimization times.

[0077] It should be noted that since the objective function model and the target current prediction model used can be derived from the above embodiments, they will not be described in detail. In this embodiment, the main description is about the process of obtaining the target duty cycle positioning value.

[0078] In one specific embodiment, in order to achieve the derivation of the target duty cycle positioning value, it is necessary to obtain all parameters or related data in the process of deriving the target duty cycle positioning value. Figure 2 and Figure 3 The various algorithms or models shown need to determine the current output voltage value, the current input voltage value, the current inductor current value, the target reference current value and the related optimization step length, so as to use the above parameters and related values ​​as variables to perform optimization within the step length of the optimization calculation.

[0079] 402. Input the current output voltage value, the current input voltage value, the current inductor current value, the target reference current value, the optimization fluctuation range and the preset optimization times into the target current prediction model to obtain the predicted current value at the interval time at the current time.

[0080] It should be noted that the interval time between the current moment and the current moment is one next moment. In simple terms, if the current moment is moment k, the interval time between the current moment is moment k+2.

[0081] In one specific embodiment, in combination with the above Figure 3 The target current prediction model in step 306 shows that the suboptimal duty cycle d opt (k), where the calculation method here can be found in the above Figure 3 As shown in step 305, the duty cycle is positioned. Furthermore, in the actual sampling and control process, the specific values ​​of the relevant target reference current value, the optimization fluctuation range or the preset optimization times and other parameters can be preset. For example, in one of the feasible technical solutions, the preset optimization times can be set to 10 to 30 (for example, n=20), and the optimization fluctuation range Δdd=0.05 / n. At this time, the corresponding optimization times is i, and i=0. Furthermore, the target reference current value can be 30 to 50A (for example, 40A), then the corresponding target duty cycle positioning value is d * =dopt (k)±Δdd. It should be noted that the above is only one way of taking values ​​of various parameters, and this embodiment does not limit this.

[0082] Then, the target current prediction model in step 306 can be used to substitute the above parameters to calculate the predicted current value at the interval time at the current time. Furthermore, the predicted current value may be included in the duty cycle positioning model, which is not specifically limited here.

[0083] 403. Input the predicted current value at the interval time of the current time and the target reference current value into the objective function model to obtain the function value of the objective function model.

[0084] In one specific embodiment, the objective function model equation G=|I ref -y p (k+2)|, thereby obtaining the function value G of the objective function model at this time.

[0085] 404. If the current optimization number is greater than the preset optimization number, the input amount of the minimum function value of the objective function model is determined as the target duty cycle positioning value, and the step of sampling the DC converter at the next moment is executed.

[0086] Furthermore, based on step 403, in one specific embodiment, after obtaining the function value G of the objective function model, it is necessary to compare the current optimization times with the preset optimization times. Specifically, it is determined whether i is greater than n. If i>n at this time, step 404 is executed, and it is determined that the minimum G is obtained in all optimization processes, that is, the absolute value difference Δi between the predicted current value and the target reference current value is the smallest. L , as the optimal duty cycle at that moment, and then execute step 201, and then wait for the sampling at the next moment, and output the corresponding optimal duty cycle d at the next moment * .

[0087] 405. If the current number of optimization searches is less than the preset number of optimization searches, increase the current number of optimization searches, and execute the step of inputting the current output voltage value, the current input voltage value, the current inductor current value, the target reference current value, the optimization fluctuation range and the preset number of optimization searches into the target current prediction model to obtain the predicted current value at the interval moment at the current moment, so as to optimize the duty cycle positioning value.

[0088] Then, based on step 403, in one of the specific embodiments, after obtaining the function value G of the objective function model, it is necessary to compare the current optimization times with the preset optimization times. Specifically, it is determined whether i is greater than n. If i < n at this time, step 405 is executed, and then the polling operation of i = i + 1 is performed. Thus, the optimization operation of the duty cycle positioning value of the next round is re-executed, that is, the predicted current value is calculated. Execute step 402.

[0089] For easier understanding, please refer to Figure 6 , Figure 7 and Figure 8 ,in, Figure 6 A steady-state output current response waveform diagram disclosed in an embodiment of the present application. Figure 7 A converter switch duty cycle and steady-state output voltage waveform diagram disclosed in an embodiment of the present application. Figure 8 A dynamic output current and duty cycle waveform diagram disclosed in an embodiment of the present application.

[0090] like Figure 6 , Figure 7 The figure shows the steady-state response of the current and the fluctuation of the duty cycle. Compared with other controls, the proposed invention method (MPC algorithm) can make the duty cycle of the control system output quickly reach the target control value, and the output current tracking speed is also significantly accelerated. Specifically, Figure 6 As shown, the MPC algorithm proposed in the technical solution of this application can achieve the average value of the inductor current gradually stabilizing at t=5ms. ss1 =13ms, the filtering process of the inductor current can be realized and the corresponding anti-interference operation can be completed. On the contrary, the PI algorithm proposed in the prior art can only realize the gradual stabilization of the average value of the inductor current when t=25ms. ss1 =24ms, the filtering of the inductor current can be realized. At the same time, the stability of the inductor current (the inductor current value of a certain period of time intercepted in the small box diagram) of the MPC algorithm and the PI algorithm is also more stable. Figure 7 As shown, the MPC algorithm proposed in the technical solution of the present application can optimize the switch tube of the DC converter to the target duty cycle positioning value and the corresponding output voltage value in the time period of 0 to 10 ms. On the contrary, the PI algorithm proposed in the prior art can only optimize the target duty cycle positioning value and the corresponding output voltage value in the time period of 10 to 20 ms. It can be seen that the MPC algorithm proposed in the technical solution of the present application has a shorter optimization time.

[0091] Figure 8The response waveform of the inductor current in the DC converter is shown when the inductor current suddenly changes from 40A to 30A at 30ms. In the response process, the proposed fast prediction method (mainly using the MPC algorithm) can predict the inductor current in a short time. ss2 =1.5ms to quickly reach a new steady state, and the current drop value is also significantly reduced, only Δi L =9A. On the contrary, the PI algorithm of the prior art requires T ss2 =7ms to reach a new steady state, and the current drop value is relatively large, with Δi L =12A. In summary, the proposed method can maintain better robustness under multiple working conditions, and from the perspective of the entire control algorithm, it is not complicated to implement and has strong practicality. The above is only a preferred embodiment of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

[0092] Through the current predictive control method of a DC converter disclosed in this embodiment, the rate of change of the duty cycle is taken into account in the objective function, and the variation amplitude of the duty cycle is effectively suppressed in different control cycles. Compared with the traditional finite set model predictive control, the sudden change of the control output caused by sampling interference or the calculation accuracy of the control system is effectively reduced, and the anti-interference ability and robustness of the algorithm are significantly improved.

[0093] Therefore, in combination with the embodiment of the present application Figures 2 to 4 In the embodiment shown, the control algorithm of the DC converter can be understood as firstly theoretically deriving the BUCK converter of the subsequent stage to obtain the discretized mathematical model. However, due to the delay and sudden change of the output control quantity in the digital control system, the delay compensation and duty cycle change rate compensation are performed in the algorithm. The compensated mathematical model contains more nonlinear terms and coupling terms. In order to improve the practicality of the algorithm, the target model is optimized, and finally the simplified prediction model and objective function are obtained. Then, in order to reduce the computational burden of model predictive control, the extreme value is sought on the basis of the simplified model to obtain a suboptimal duty cycle that is very close to the optimal duty cycle. Finally, in order to achieve precise control of the system, a small range secondary iterative optimization is performed on the basis of the suboptimal duty cycle, and finally the optimal duty cycle sent to the controller is obtained. Then, the strategy of fast duty cycle prediction control of the DC converter is adopted. First, the capacitor voltage u on the input side is sampled. dc and the inductor current i on the output side L And the output voltage u0. Then the simplified compensation target extreme value function is applied to quickly find the suboptimal duty cycle d opt (k), and based on the simplified compensation prediction model, a small-scale optimization calculation of Δd is performed, and the results of the small-scale iterative calculation are sorted into a new set; combined with the above set, the duty cycle that minimizes the objective function G is selected as the optimal duty cycle d *The optimal duty cycle is converted into a corresponding pulse signal and applied to the converter, and finally the system can achieve the goal of quickly tracking the reference output current.

[0094] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0095] Although preferred embodiments of the present disclosure have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present disclosure. Obviously, those skilled in the art may make various changes and modifications to the present disclosure without departing from the spirit and scope of the present disclosure. Thus, if these modifications and variations of the present disclosure fall within the scope of the claims of the present disclosure and their equivalents, the present disclosure is also intended to include these modifications and variations.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure rather than to limit its protection scope. Although the present disclosure is described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the present disclosure, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the disclosed claims to be approved.

Claims

1. A current prediction control method for a DC converter, characterized in that: Applied to a predictive control circuit, the predictive control circuit includes a DC converter, and the method includes: Sampling the DC converter to obtain a current output voltage value, a current input voltage value, and a current inductor current value of the DC converter at a current moment; Obtaining a target reference current value at a current moment, inputting the current output voltage value, the current input voltage value, the current inductor current value, and the target reference current value into a duty cycle positioning model, and obtaining a duty cycle positioning value to be optimized at a current moment; The duty cycle positioning value to be optimized, the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value are input into the final objective function model and the target current prediction model, and the duty cycle positioning value to be optimized is optimized twice in a small range within a preset number of optimization times, and the target duty cycle positioning value is output, and the optimal duty cycle is converted into a real-time pulse signal to realize the control of the DC converter.

2. The current prediction control method of a DC converter according to claim 1, characterized in that: The derivation process of the objective function model includes: Determining a target discrete mathematical model of the DC converter according to a circuit switching state of the switch tube in the DC converter, based on the current output voltage value, the current input voltage value and the current inductor current value; Determine an intermediate current prediction model of the DC converter at the next moment according to the target discrete mathematical model; wherein the intermediate current prediction model is associated with the output current of the DC converter; Determine the duty cycle change rate of the DC converter, and obtain a function model to be compensated according to the duty cycle change rate, the target reference current value and the intermediate current prediction model; Performing compensation delay on the intermediate current prediction model to obtain a current prediction model to be optimized corresponding to the next moment, and updating the function model to be compensated according to the current prediction model to be optimized to obtain a function model to be optimized; De-linearizing the function model to be optimized and performing derivation to obtain a duty cycle positioning value that satisfies the minimum value of the function model to be optimized; According to the duty cycle positioning value and the current prediction model to be optimized, performing optimization for the preset optimization times to obtain the target current prediction model; The objective function model is obtained according to the target current prediction model and the target reference current value.

3. The current prediction control method of a DC converter according to claim 2, characterized in that: The step of determining the target discrete mathematical model of the DC converter according to the circuit switching state of the switch tube in the DC converter, based on the current output voltage value, the current input voltage value and the current inductor current value, includes: Determine the equivalent load resistance value R0, equivalent filter capacitance value C0, and equivalent power inductance value L of the DC converter B and the switching period T s ; According to the circuit switch state, the initial state equation of the DC converter is established based on the current output voltage value, the current input voltage value and the current inductor current value, and the initial state equation is discretized to obtain an initial discrete mathematical model of the DC converter, wherein the initial discrete mathematical model is: Wherein, x=[u0i L ] T , Said Said The u(k)=u dc , the u dc is the current input voltage value, u0 is the current output voltage value, and i L is the current inductor current value, E2 is a 2×2 unit matrix, and x d (k+1) is used to represent the state variable value when the switch tube is in the closed state at the next moment, and the x 1-d (k+1) is used to represent the state variable value when the switch tube is in the off state at the next moment; According to the duration of the switch tube in the switching cycle, the corresponding closed state and open state, the initial discrete mathematical model is weighted to obtain the target discrete mathematical model, wherein the target discrete mathematical model is Where, M = E2 + AT s ,N=B1T s u dc , the d(k) is the duty cycle positioning value at the current moment k.

4. The current prediction control method of a DC converter according to claim 3, characterized in that: Determining the intermediate current prediction model of the DC converter at the next moment according to the target discrete mathematical model includes: Determine the initial current prediction model y(k)=i L (k) = Cx(k), where C is a coefficient matrix [01]; Based on the initial current prediction model and in combination with the target discrete mathematical model, the intermediate current prediction model is obtained. Among them, the A x =CM, B d =CN.

5. The current prediction control method of a DC converter according to claim 4, characterized in that: The step of determining the duty cycle change rate of the DC converter and obtaining a function model to be compensated according to the duty cycle change rate, the target reference current value and the intermediate current prediction model includes: Determine a current control weight value k1 in the DC converter and a duty cycle control weight value k2 corresponding to the duty cycle conversion rate; An initial function model G=k1(I ref -y p (k+1)) 2 +k2(d(k)-d(k-1)) 2 , wherein said I ref is the target reference current value, d(k-1) is the duty cycle positioning value at the previous moment, the duty cycle positioning value at the previous moment is a predicted current value obtained by prediction by the intermediate prediction model, and is calculated based on the predicted current value and the target reference current value; The initial function model is combined with the intermediate current prediction model to obtain the function model to be compensated 6. The current prediction control method of a DC converter according to claim 5, characterized in that: The compensating delay of the intermediate current prediction model to obtain the current prediction model to be optimized corresponding to the next moment, and updating the function model to be compensated according to the current prediction model to be optimized to obtain the function model to be optimized, including: Based on the system delay at time k+2, the intermediate current prediction model is compensated for the delay to obtain the current prediction model to be optimized Among them, the M2=CA x B d , the M3=CB d ; The function model to be compensated is updated according to the current prediction model to be optimized to obtain the function model to be optimized 7. The current prediction control method of a DC converter according to claim 6, characterized in that: The step of de-linearizing the function model to be optimized and performing derivation to obtain a duty cycle positioning value when the function model to be optimized has a minimum value includes: The function model to be optimized is optimized to retain the polynomial associated with the state variable value d(k), and the nonlinear terms and coupling terms containing the state variable value in the function model to be optimized are removed to obtain a simplified function model to be optimized. The function model to be optimized is According to the uniqueness theorem of derivation, the simplified function model to be optimized is derived to obtain the duty cycle positioning model And obtain the duty cycle positioning value d opt (k), where the compensation matrix D d =2k1M2M3d(k-1)-2k1M3I ref -2k2d(k-1).

8. The current prediction control method of a DC converter according to claim 7, characterized in that: The step of performing optimization according to the duty cycle positioning value and the current prediction model to be optimized for the preset number of optimization times to obtain the target current prediction model includes: Based on the finite set model predictive control algorithm, taking the duty cycle positioning value as a benchmark, the current prediction model to be optimized is optimized at the preset optimization times to obtain the target current prediction model y p (k+2)=M1x(k)+M2d(k-1)+M3(d opt (k)+Δdn); wherein, Δd is used to represent the optimization fluctuation range, and n is used to represent the preset optimization number; The step of obtaining the objective function model according to the target current prediction model and the target reference current value includes: Based on the target reference current value, the target current prediction model is transformed into the simplified function model to be optimized to obtain the target function model G=|I ref -y p (k+2).

9. The current prediction control method of a DC converter according to claim 1, characterized in that: The step of inputting the duty cycle positioning value to be optimized, the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value into the final objective function model and the target current prediction model, performing a secondary small-range optimization on the duty cycle positioning value to be optimized within a preset number of optimization searches, and outputting the optimal target duty cycle positioning value includes: Determine the current output voltage value, the current input voltage value, the current inductor current value and the target reference current value, determine the optimization fluctuation range during optimization according to the objective function model, and determine the preset optimization times; The current output voltage value, the current input voltage value, the current inductor current value, the target reference current value, the optimization fluctuation range and the preset optimization times are input into the target current prediction model to obtain the predicted current value at the interval time of the current time; wherein the interval time of the current time is separated from the current time by a next time; Inputting the predicted current value at the interval time of the current time and the target reference current value into the objective function model to obtain the function value of the objective function model; If the current optimization number is greater than the preset optimization number, the input amount of the minimum function value of the objective function model is determined as the target duty cycle positioning value, and the step of sampling the DC converter at the next moment is performed; If the current optimization number is less than the preset optimization number, the current optimization number is increased, and the step of inputting the current output voltage value, the current input voltage value, the current inductor current value, the target reference current value, the optimization fluctuation range and the preset optimization number into the target current prediction model to obtain the predicted current value at the interval moment at the current moment is executed to optimize the duty cycle.

10. A current prediction control circuit for a DC converter, characterized in that: The circuit comprises: a DC converter, a full-bridge rectifier circuit, a high-frequency inverter and a resonance unit; The high-frequency inverter is located in the front-stage circuit of the prediction control circuit, and is used to invert the low-voltage direct current of the input power supply into high-frequency low-voltage alternating current, and input the high-frequency low-voltage alternating current into the resonance unit; The resonance unit is used to make the high-frequency low-voltage alternating current undergo circuit resonance and input resonance excitation to the full-bridge rectifier circuit; The full-bridge rectifier circuit is connected to the DC converter circuit and is located in the post-stage circuit of the predictive control circuit; the full-bridge rectifier circuit is used to rectify the resonant excitation and output the rectified current to the DC converter; the DC converter is used to determine the current output voltage value, the current input voltage value and the current inductor current value of the DC converter according to the current rectifier current, so as to control the DC converter according to the current output voltage value, the current input voltage value and the current inductor current value; The DC converter also includes: an input voltage capacitor, a load resistor, a filter capacitor, a power inductor, a switch tube and a unidirectional diode; The two ends of the input voltage capacitor are circuit-connected to the full-bridge rectifier circuit, and one end of the input voltage capacitor is connected to the drain of the switch tube, and the other end is respectively circuit-connected to one end of the load resistor, the positive electrode of the unidirectional diode, and one end of the filter capacitor, and the voltage value at the two ends of the input voltage capacitor is the current input voltage value; The source of the switch tube is respectively connected to the cathode of the unidirectional diode and one end of the power inductor; The other end of the power inductor is respectively connected to the other end of the filter capacitor and the other end of the load resistor, and the current value flowing through the power inductor is the current inductor current value; The voltage value across the filter capacitor and the load resistor is the current output voltage value.

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