Three-mode adaptive control duty ratio online optimization efficiency control method based on four-switch buck-boost

Abstract

The application discloses a three-mode adaptive control duty ratio online optimization efficiency control method based on a four-switch Buck-Boost, and belongs to the technical field of power electronics. When the output power is constant, the converter is operated in a three-mode state, and two-phase duty ratios and a phase difference in the converter are reduced to single variable control.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to an efficiency optimization control method and device based on a four-switch Buck-Boost converter. BACKGROUND

[0002] With the continuous development of the current automobile industry, the traditional linear voltage regulator in the industry is gradually replaced by high-efficiency direct current converters. With the continuous increase in the number of converters, the selection of the topology structure of the converter will have a significant impact on the improvement of the efficiency and the energy consumption of the automobile. With the continuous development of integrated circuits, the integration of the circuit is getting higher and higher, so the topology structure of the converter is coupled with small external magnetic elements with low inductance value or even integrated with package-level micro- inductors. If using small inductance has the typical disadvantage of causing higher current ripple and the resulting conduction loss, from the perspective of fully integrated design, the conversion topology with more switch numbers becomes a feasible choice and introduces additional degrees of freedom, which can be conveniently used for performance optimization purposes. In this and other load point scenarios, the demand for low-size solutions stimulates the development of strong integration and high-frequency topology structures, so the natural integrated circuit also continuously improves the requirements for the power supply, and the power supply is required to be more and more efficient. As a non-isolated type of Buck-Boost DC converter, the four-switch Buck-Boost has the characteristics of simple circuit structure and high voltage stress of the switch device.

[0003] How to improve the efficiency of the converter is also a problem that researchers continue to explore, so the application explores the relationship between the duty cycle of the control pulse of different bridge arms of the Buck-Boost DC converter and the phase difference between the bridge arm control pulses and the operating efficiency, and proposes an adaptive step optimization control strategy to improve the efficiency of the converter, so that the Buck-Boost works in a three-mode working state, effectively improving the operating efficiency of the converter. SUMMARY

[0004] In view of the deficiencies in the prior art, the application provides a three-mode adaptive control duty cycle online optimization control. An adaptive control algorithm is proposed for the four-switch Buck-Boost switch model to adjust the duty cycle Da, Db of the two half bridges and the control pulse phase difference three variables. Make the converter work in a three-mode state, in which mode, the starting time of A and B pulses is the same, and the phase difference is automatically determined by A and B pulses. When the output power is constant, adjust the value of Db, and then adjust the value of Da through PI to make the output power constant, which corresponds to a converter efficiency. In each cycle, adjust the duty cycle Db of the B bridge arm control pulse, that is, optimize the minimum input current value by adaptively controlling the duty cycle Db to optimize the highest efficiency point.

[0005] To achieve the above object, the technical scheme of the present application is as follows:

[0006] An adaptive control optimization efficiency control method based on a four-switch Buck-Boost converter, comprising the following steps:

[0007] Step 1: sample the current input inductor current I in (k) to determine whether it is the current sampling value under the first period Db value. If it is the first period, execute step 2; otherwise, execute step 3;

[0008] Wherein, I in (k) represents the input current value of the kth algorithm period. When the output power is constant, the input voltage is also constant, and the smaller the input current value, the higher the operating efficiency of the converter. Therefore, the purpose of the highest operating efficiency of the converter can be achieved by finding the minimum value of the input current.

[0009] Step 2: adjust the B-phase bridge arm duty cycle Db value by a constant value C. Then execute step 5;

[0010] Wherein, the constant value C is small, the purpose is to make a small change to Db to obtain the gradient value of the next period.

[0011] Step 3: calculate the gradient value of the current inductor current to the duty cycle according to the duty cycle and the input current of the last period, and the current duty cycle and the input current Then execute step 4;

[0012] Wherein, the gradient value The calculation formula is:

[0013]

[0014] In the above formula,

[0015] ΔI in =I in (k-I in (k-1), ΔDb=Db(k)-Db(k-1);

[0016] Step 4: calculate the adjustment step of the B-bridge arm duty cycle as Then execute step 5;

[0017] Wherein, λ is the step parameter, which is a fixed constant value, and is adjusted according to the magnitude of the converter power. The larger the converter power, the smaller the λ, and vice versa.

[0018] Step 5: subtract the calculated adjustment step from the current B-phase duty cycle Db to obtain the B-phase bridge arm duty cycle of the next control period, and then execute step 6;

[0019] wherein,

[0020]

[0021] In the above formula, Db(k+1) is the control pulse of the B-phase bridge arm in the next period, Db(k) is the control pulse in the current period, and the control pulse in the next period is decreased by one step in the gradient direction along the current pulse.

[0022] Step 6: control the B-phase bridge arm with the current Db, and adjust the A-phase duty cycle Da to make the output voltage constant through PI control. Since the starting time of the control pulse voltages of the A-phase and the B-phase is the same, the phase difference can be automatically determined, wherein the phase difference Then step 7 is performed.

[0023] In the above formula, since the four-switch Buck-Boost operates in the three-mode mode at this time, the switching time of Va and Vb at this time is the same, and different (Da, Db) combinations correspond to different phase differences , because of its operating characteristics, and Da, Db have the above fixed relationship.

[0024] Step 7: run a period with the current Da and Db values under the condition that the output power is constant, add one to the period number, and then perform step 1.

[0025] wherein Db is determined, and Da is also stabilized at a determined value under the condition that the output power is constant through PI adjustment. Control the converter in the k+1 algorithm period with the current stable Da and Db values, and let k=k+1.

[0026] Further, the topology of the above Buck-Boost converter comprises the following devices: an inductor (L), an input voltage stabilizing capacitor (C1), an output voltage stabilizing capacitor (C2), four Mosfet switch tubes (S1, S2, S3, S4), an output resistor (R), an input power supply (V in ), two half-bridges are formed by combining the four Mosfet tubes in pairs, the lower ends of the two half-bridges are connected to the negative electrode of the power supply, and the output capacitor C2 is connected in parallel with the output resistor.

[0027] Further, the Buck-Boost converter operates in the continuous conduction mode (CCM) of inductor current in the steady state.

[0028] Further, the adjustment direction of the B-phase control duty cycle Db of the converter is the negative gradient direction, and the descending speed in this direction is the fastest.

[0029] Further, the algorithm is based on the constant output voltage of the converter, and the output voltage is constant by PI regulation, so the output power is constant.

[0030] In summary, after adopting the technical scheme, the application has the following beneficial effects:

[0031] 1. The application proposes an adaptive control algorithm to adjust Da, Db and three variables based on the four-switch Buck-Boost switching model, and realizes efficiency optimization of the converter in the same three modes at the starting time. Due to the characteristics of the working mode, the problem is converted into adjusting Db to obtain the minimum value of the input power, that is, the minimum value of the input current Iin. The three-variable problem is successfully reduced to a single-variable extreme value problem. Based on the problem, an adaptive control algorithm is adopted to optimize the optimal Db value, and Da is adjusted by PI to make the output power constant, while the value is calculated by the working mode. .

[0032] 2. The application finds the relationship between the duty cycle and the efficiency of the converter in a working mode. The discrete steepest descent method is used to find the minimum value point of the input current, and the algorithm has the characteristics of fast speed and adaptive step adjustment, which can effectively optimize the highest efficiency point of the Buck-Boost converter. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Fig. 1 is a structural schematic diagram of the Buck-Boost converter.

[0034] Figure 2 Fig. 2 is a working mode diagram of the Buck-Boost converter when the output voltage is less than the input voltage.

[0035] Figure 3 Fig. 3 is a working mode diagram of the Buck-Boost converter when the output voltage is greater than the input voltage.

[0036] Figure 4 Fig. 4 is a flow chart of the adaptive control efficiency optimization.

[0037] Figure 5 Fig. 5 is the conduction state when Va and Vb are both turned on.

[0038] Figure 6 Fig. 6 is the circuit conduction state when Va is turned off and Vb is turned on.

[0039] Figure 7 Fig. 7 is the circuit conduction state when Va is turned on and Vb is turned off.

[0040] Figure 8 Fig. 8 is the circuit conduction state when Va and Vb are both turned off.

[0041] Figure 9 is 20V input, output constant to 10V, output load R o = 15Ω algorithm control Db and input current I in .

[0042] Figure 10 is 20V input, output constant to 10V, output load R o = 12Ω output voltage Vo by PI regulation.

[0043] Figure 11 is 20V input, output constant to 10V, output load R o = 15Ω algorithm control Db and input current I in .

[0044] Figure 12 is 20V input, output constant to 10V, output load R o = 12Ω output voltage Vo by PI regulation. DETAILED DESCRIPTION

[0045] The specific embodiments of the present application are described below to facilitate a better understanding of the present application for those skilled in the art.

[0046] The adaptive control algorithm proposed in the present application is for four-switch Buck-Boost converter, which is different from the general Buck-Boost converter, the control pulse phase difference is not 180°, but can be any angle. The duty cycle Da, Db of Va, Vb of each bridge arm can also be arbitrarily combined. Let the conduction time of Va, Vb be the same, when the converter works in the above mode, the phase difference can be determined by the duty cycle of the two, that is In addition, by PI regulation Da to make the output voltage constant, at this time, as long as the duty cycle Db of Vb is adjusted, it can be stabilized to a certain value by PI regulation Da, therefore, the phase difference is naturally determined.

[0047] The topology structure of Buck-Boost converter is shown in Figure 1 , including the following devices: inductance (L), input voltage stabilizing capacitor (C1), output voltage stabilizing capacitor (C2), four Mosfet switch tubes (S1, S2, S3, S4), output resistor (R), input power (V in );

[0048] Figure 2The operation mode of the converter when the output voltage is less than the input voltage is described, as shown in the figure. At this time, the output voltage is less than the input voltage, and the conduction time of the control pulses of Va and Vb is the same. When S1 and S4 are turned on, the inductor current rises, and at this time the circuit state is as shown in Figure 5 When S1 is turned off and S4 is turned on, the inductor current decreases, and at this time the circuit state is as shown in Figure 6 When S1 and S4 are both turned off, the inductor current remains unchanged, and at this time the circuit state is as shown in Figure 8

[0049] Figure 3 The operation mode of the converter when the output voltage is greater than the input voltage is described, as shown in the figure. At this time, the output voltage is greater than the input voltage, and the conduction time of the control pulses of Va and Vb is the same. When S1 and S4 are turned on, the inductor and the power source charge the output load, and the inductor current decreases, and at this time the circuit state is as shown in Figure 5 When S1 is turned on and S4 is turned off, the power source charges the inductor, and the inductor current rises, and at this time the circuit state is as shown in Figure 7 When S1 and S4 are both turned off, the inductor current remains unchanged, and at this time the circuit state is as shown in Figure 8

[0050] Figure 4 The flowchart of adaptive control efficiency optimization based on the above operation mode is described. First, the control algorithm sets the initial value k = 1 and the initial duty cycle Db, detects the k-th sampling circuit input current, if K = 1, fine tunes Db by a constant value C, then outputs the next control period Db(k+1), and sets k = k+1. Control is performed with the current Db, the output power is kept constant by PI regulation loop adjustment of Va duty cycle Da, and then the next cycle is entered;

[0051] Figure 4 If k is not equal to 1, the gradient value at k time is calculated based on the sampling current value Iin(k-1) and Db(k-1) value of the last period and the sampling current value I in (k) and Db(k) value of the current period. The adjustment step of Db is calculated based on the current gradient value, Db(k+1) of the (k+1) period is obtained and output, k = k+1 is set, the current Db is controlled, the output power is kept constant by PI regulation of Da, and then the next cycle is entered.

[0052] Figure 9 The algorithm control Db and input current I in when the output load R o = 15Ω is described. The algorithm sets the period to 0.2 seconds, from Figure 10 ​​As can be seen, within 0.2 seconds, after each Db adjustment, the time required for the output voltage to remain constant through PI regulation is less than 0.2 seconds. This means that the output power can be kept constant before the next adaptive control algorithm execution time, and the corresponding Da and... .from Figure 9 The upper part of the graph also shows that as Db is continuously adjusted, the input current I... in The current continuously decreases. The minimum input current is 0.353A, and Db is approximately 0.56. It can be seen that the algorithm quickly adjusts according to the gradient value and converges to the minimum current value. Its efficiency is effectively improved to 94.3%.

[0053] Figure 10 It describes a 20V input, a constant output to 10V, and an output load R. o The algorithm controls Db and input current I when the Ω is 12Ω. in The algorithm's period is also set to 0.2 seconds. Figure 10 As can be seen, within 0.2 seconds, after each Db adjustment, the time required for the output voltage to remain constant through PI regulation is less than 0.2 seconds. This means that the output power can be kept constant before the next adaptive control algorithm execution time, and the corresponding Da and... .from Figure 12 The upper part of the graph also shows that as Db is continuously adjusted, the input current I... in The current continuously decreases. The minimum input current is 0.49A, and Db is around 0.4. It can be seen that the algorithm quickly adjusts Db based on the gradient value and converges to the minimum current value. Its efficiency is effectively improved to 85%.

[0054] Figure 11 The waveform of the output voltage Vo shows that when the four-switch Buck-Boost converter operates at... Figure 9 When the adaptive steepest descent algorithm adjusts Db under load, the PI controller can adjust Da to keep the output voltage constant.

[0055] Figure 12 The waveform of the output voltage Vo shows that when the four-switch Buck-Boost converter operates at... Figure 10 When the adaptive steepest descent algorithm adjusts Db under load, the PI controller can adjust Da to keep the output voltage constant.

Claims

1. An adaptive control optimization efficiency control method based on a four-switch Buck-Boost converter, characterized in that, Includes the following steps: Step 1: Sample the input current for the current cycle I in (k) determines whether it is the current cycle duty cycle. D b Input current value at (k) value I in (k), if it is the current cycle, execute step 2; otherwise, execute step 3. in, I in (k) represents the input current value in the k-th algorithm cycle; D b (k) represents the duty cycle value of the switch on the B-phase bridge arm in the k-th algorithm cycle; the k-th algorithm cycle is defined as the current cycle; Step 2: Set the duty cycle for the current period D b The value of (k) is adjusted to a constant value C, and then step 5 is executed; Among them, the constant value C is relatively small, and its purpose is to control the duty cycle of the current period. D b The (k) value is slightly changed to obtain the gradient value for the next cycle; Step 3: Based on the duty cycle of the (k-1)th algorithm cycle D b The (k-1) value and the input current in the (k-1)th algorithm cycle. I in (k-1) value, and the current cycle duty cycle D b (k) and current cycle input current I in (k), calculate the input current of the current cycle I in (k) Duty cycle for the current period D b The gradient value of (k)▽ I in Then proceed to step 4; Among them, the gradient value ▽ I in The calculation formula is: ▽ I in =Δ I in / Δ D b ; In the formula, Δ I in = I in (k)- I in (k-1), Δ D b = D b (k)- D b (k-1); Step 4: The gradient value calculated for the current period ▽ I in Calculate the current cycle duty cycle D b The adjustment step size of (k) is λ*▽ I in Then proceed to step 5; Wherein, λ is the gradient coefficient, which is a fixed constant value and is adjusted according to the power level of the four-switch Buck-Boost converter; the higher the power of the converter, the smaller λ is, and vice versa. Step 5: Set the duty cycle for the current period D b (k) value minus the calculated adjustment step size λ*▽ I in The duty cycle of the (k+1)th algorithm cycle is obtained. D b (k+1), then proceed to step 6; in, D b (k+1)= D b (k)-λ*▽ I in ; In the formula, D b (k+1) represents the duty cycle of the switch on the B-phase bridge arm in the (k+1)th algorithm cycle. D b (k) represents the duty cycle value of the switch on the B-phase bridge arm in the k-th algorithm cycle; the duty cycle in the (k+1)-th algorithm cycle... D b (k+1) represents the duty cycle of the k-th algorithm cycle. D b (k) Decrease along the gradient direction by an adjustment step size λ*▽ I in λ is the gradient coefficient; Step 6: Using the current cycle duty cycle D b (k) Control phase B bridge arm and adjust the duty cycle of the switch on phase A bridge arm via PI control. D a (k) keeps the output voltage constant; due to the duty cycle D a (k) and duty cycle D b (k) Since the starting times are the same, the phase difference can be automatically determined, where the phase difference φ = ( D b (k)- D a (k)) / 2, then proceed to step 7; Among them, the duty cycle of the switch on phase A bridge arm D a (k) and duty cycle of the switching transistor on phase B bridge arm D b The switching start times of (k) are the same, according to the phase difference expression φ=( D b (k)- D a (k)) / 2, different duty cycles can be obtained. D a (k) D b (k) combinations correspond to different phase differences φ; due to their operating characteristics, the phase difference φ is related to the duty cycle. D a (k) D b (k) exists where φ=( D b (k)- D a The fixed relationship (k)) / 2; Step 7: Under constant output power conditions, with the current cycle duty cycle D a (k) D b The (k) value runs for one cycle, the cycle number is incremented by 1, and then step 1 is executed; Among them, the current cycle duty cycle D b Once the value of (k) is determined, the output power is kept constant through PI regulation, and the duty cycle of the current cycle is... D a (k) also stabilizes at a fixed value, with the current cycle's stable duty cycle. D a (k) D b The (k) value controls the operation of the converter in the (k+1)th algorithm cycle, and k = k+1.

2. The adaptive control optimization efficiency control method as described in claim 1, characterized in that, The topology of the aforementioned four-switch Buck-Boost converter includes the following components: inductor L, input voltage regulator C1, output voltage regulator C2, four switching transistors S1, S2, S3, and S4, output resistor R, and input power supply Vin. The four switching transistors are combined in pairs to form a half-bridge and then connected in parallel through an inductor. The lower ends of the two half-bridges are connected to the negative terminal of the power supply. The output capacitor C2 is connected in parallel with the output resistor.

3. The adaptive control optimization efficiency control method as described in claim 1, characterized in that, The four-switch Buck-Boost converter operates in steady-state mode in continuous conduction mode (CCM).

4. The adaptive control optimization efficiency control method as described in claim 1, characterized in that, Current cycle duty cycle of a four-switch Buck-Boost converter D b The adjustment direction of (k) is the negative gradient direction, and the descent speed is fastest in the negative gradient direction.

5. The adaptive control optimization efficiency control method as described in claim 1, characterized in that, PI regulation is used to keep the converter's output voltage constant.

6. The adaptive control optimization efficiency control method as described in claim 1, characterized in that, The discrete steepest descent method is used to find the minimum point of the input current Iin(k) in the current cycle.

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