Dual-input DC-DC control circuit and control method based on constant voltage control

Abstract

The present invention discloses a dual-input DC-DC control circuit and a control method based on constant voltage control. A photovoltaic input conversion module adopts a photovoltaic array input voltage, outputs a voltage through a conversion circuit, and performs closed-loop control through feedback of a PI controller. In the constant voltage input conversion module, the switching effect of a MOSFET tube is used to limit the input constant voltage, thereby ensuring the maximum value limit of the input voltage and improving the circuit conversion efficiency. The constant voltage input conversion module is used as an active conversion structure to realize auxiliary compensation and stable feedback for a main conversion structure, i.e., a photovoltaic input conversion module, so as to solve the problems of low energy utilization and unstable output voltage caused by changes in light sources in a traditional photovoltaic DC-DC conversion structure, thereby making the energy conversion of the photovoltaic array more efficient and the DC-DC conversion structure more stable.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic power generation integrated circuits, and in particular to a dual-input DC-DC control circuit and a control method based on constant voltage control. Background Art

[0002] Sunlight is greatly affected by external environmental factors, and the photovoltaic array will have a certain instability in converting solar energy into electric potential energy. In other words, the stability of the electric energy indicators generated by the photovoltaic array is poor. At present, photovoltaic power generation is mainly used for battery charging or grid connection, both of which require its operating point to be controlled at its maximum power point MMP. This output method is called maximum power point tracking mode MMPT, but the output voltage and current obtained by this output method are not constant, because the light intensity will change over time, which will cause the output voltage of the photovoltaic array to gradually fluctuate, further causing the DC voltage required for DC-DC post-conversion to deviate, thereby causing the charging voltage to be unstable and the energy conversion efficiency to be low.

[0003] Traditional DC-DC conversion to stabilize non-constant direct current has certain limitations, and the energy generated by non-high-intensity direct sunlight cannot be effectively utilized. The reason is the lack of constant voltage that can stabilize charging, which makes it difficult to achieve good results in the power and energy conversion rate of the charging part. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a dual-input DC-DC control circuit and control method based on constant voltage control, by using a constant voltage input conversion module as an active conversion structure to achieve auxiliary compensation and stable feedback for the main conversion structure, i.e., the photovoltaic input conversion module, so that the energy conversion of the photovoltaic input conversion is more efficient and the DC-DC conversion structure is more stable.

[0005] Technical solution: The present invention provides a dual-input DC-DC control circuit based on constant voltage control, comprising a photovoltaic input conversion module, a constant voltage input conversion module, and a voltage compensation addition module;

[0006] The photovoltaic input conversion module is used to sense changes in light intensity and adjust the duty cycle through a photovoltaic feedback compensation circuit. The photovoltaic input conversion module includes a photovoltaic array PV, a power switch tube N3, and a power switch tube N4. The photovoltaic array PV is used to sense light intensity, input a photovoltaic voltage according to the light intensity, obtain an output voltage through a boost-buck type conversion circuit, compare the output voltage with a reference voltage Vref to obtain an error value, compensate and adjust the error value, and input a PWM square wave after the duty cycle is changed into the power switch tube N3 and the power switch tube N4 to obtain a photovoltaic output voltage, and input the photovoltaic output voltage into a voltage compensation addition module;

[0007] The constant voltage input conversion module is used to sample the summed voltage obtained by the voltage compensation addition module, compare and adjust the summed voltage with the reference voltage, adjust the duty cycle through the constant voltage feedback compensation circuit and output the compensation voltage. The constant voltage input conversion module includes an error amplifier, a bandgap reference, a mosfet tube M1, a mosfet tube M2, a mosfet tube M3, and a power switch tube N1; the current paths of the mosfet tube M1 and the mosfet tube M2 are used for voltage division, the mosfet tube M1 works in the saturation region, the mosfet tube M2 works in the linear region, the drain voltage of the mosfet tube M2 controls the conduction or shutdown of the mosfet tube M3 and then controls the power switch tube N1 to obtain the compensation voltage, and output the compensation voltage to the voltage compensation addition module. The constant voltage feedback compensation circuit samples the summed voltage obtained by the voltage compensation addition module, compares and adjusts the summed voltage with the reference voltage to obtain a voltage error, compares and amplifies the voltage error through the error amplifier, adjusts the compensation voltage and further transmits the compensation voltage to the voltage compensation addition module;

[0008] The voltage compensation addition module is used to continuously add the photovoltaic output voltage and the compensation voltage to obtain the added voltage and output an effective constant voltage after stabilizing the ripple. The voltage compensation addition module includes an adder, an RC filter, and a fourth unit buffer; the added voltage is obtained by the adder, and the ripple is stabilized by the RC filter to obtain a stable effective voltage. The stable effective voltage is passed through the fourth unit buffer to obtain an effective constant voltage for output.

[0009] Further, the photovoltaic input conversion module further includes a filter RC3, an inductor L2, a capacitor C4, a resistor R5, a subtractor, a second ramp oscillator, a PI controller, a second comparator, a third unit buffer, a second third-order inverter, and a third third-order inverter;

[0010] The positive pole of the photovoltaic array PV is used as the input end of the photovoltaic input, the negative pole of the photovoltaic array PV is grounded, the two ends of the photovoltaic array PV are connected in parallel with the filter RC3, the two ends of the filter RC3 are connected in parallel with the inductor L2, the two ends of the inductor L2 are connected in parallel with the capacitor C4, the two ends of the capacitor C4 are connected in parallel with the resistor R5, the source of the power switch tube N3 is connected to one end of the capacitor in the filter RC3, the drain of the power switch tube N3 is connected to one end of the inductor L2, the drain of the power switch tube N3 is also connected to the source of the power switch tube N4, the drain of the power switch tube N4 is connected to the input end of the third third-order inverter, the output end of the third third-order inverter is connected to the out1 input end of the adder in the voltage compensation addition module, the filter RC3, the inductor L2, and the capacitor C4 , resistor R5, power switch tube N3, and power switch tube N4 together form a boost-buck type conversion circuit, the gate of the power switch tube N3 is connected to the output end of the third unit buffer, the input end of the third unit buffer is connected to the input end of the second third-order inverter, the input end of the third unit buffer is also connected to the output end of the second comparator, the non-inverting input end of the second comparator is connected to the second ramp oscillator, the inverting input end of the second comparator is connected to one end of the PI controller, the other end of the PI controller is connected to the output end of the subtractor, the non-inverting input end of the subtractor is used as the input end of the reference voltage Vref, and the inverting input end of the subtractor is connected to the out1 input end of the adder in the voltage compensation addition module.

[0011] Furthermore, the constant voltage input conversion module further includes a capacitor C1, a first unit buffer, a power switch tube N2, an inductor L1, a first three-phase inverter, a filter RC1, a resistor R4, a first comparator, a first ramp oscillator, a second unit buffer, and a bandgap reference;

[0012] The input end of the first unit buffer serves as the input end of the constant voltage input conversion module, the first unit buffer is connected in parallel with the capacitor C1, the output end of the first unit buffer is connected to the drain of the power switch tube N1, the mosfet tube M1 and the mosfet tube M2 are connected in series to form a voltage dividing structure, the gate of the mosfet tube M1 is connected to the gate of the mosfet tube M2, and is also connected to the drain of the mosfet tube M1, the drain of the mosfet tube M1 is connected to the output end of the first unit buffer, the source of the mosfet tube M2 is grounded, the drain of the mosfet tube M2 is connected to the source of the mosfet tube M1, the gate of the mosfet tube M3 is connected to the source of the mosfet tube M1, the source of the mosfet tube M3 is grounded, the drain of the mosfet tube M3 is connected to the gate of the power switch tube N1, the gate of the power switch tube N1 is also connected to the output end of the second unit buffer, the power switch tube N The drain of the power switch tube N1 is connected to one end of the inductor L1, the drain of the power switch tube N1 is also connected to the source of the power switch tube N2, the drain of the power switch tube N2 is grounded, the gate of the power switch tube N2 is connected to the output end of the first three-phase inverter, the input end of the first three-phase inverter is connected to the input end of the second unit buffer, the other end of the inductor L1 is connected to the filter RC1, and is also connected to one end of the resistor R4, the two ends of the filter RC1 are connected in parallel with the resistor R4, the other end of the resistor R4 is grounded, the other end of the inductor L1 is also connected to the out2 input end of the adder in the voltage compensation addition module, the non-inverting input end of the error amplifier is connected to the output end of the adder in the voltage compensation addition module, the inverting input end of the error amplifier is externally connected to the bandgap reference, the output end of the error amplifier is connected to the non-inverting input end of the first comparator, the inverting input end of the first comparator is connected to the first ramp oscillator, and the output end of the first comparator is connected to the input end of the second unit buffer.

[0013] Furthermore, in the voltage compensation adding module, the output end of the adder is connected to one end of the RC filter, the other end of the RC filter is grounded, and one end of the RC filter is simultaneously connected to the input end of the fourth unit buffer.

[0014] Furthermore, in the constant voltage input conversion module, the error amplifier samples the summed voltage obtained in the adder, compares it with the bandgap reference voltage, obtains a voltage error, compares and amplifies the voltage error through the error amplifier, and then outputs a square wave by comparing it with the first ramp oscillator through the first comparator, outputs a stable square wave through the second unit buffer and updates the adjustment compensation voltage value, transmits the compensation voltage value to the voltage compensation addition module, and outputs a voltage V out2 =D*Vin, where D is the duty cycle and Vin is the input voltage in the constant voltage input conversion module.

[0015] Furthermore, in the photovoltaic input conversion module, the voltage obtained at the output end of the third third-order inverter is used as a sampling value, the sampling value is input into the subtractor to compare with the reference voltage Vref, and the signal difference is output. The signal difference is adjusted by the PI controller, and the adjusted signal is adjusted by the second comparator and the second ramp oscillator to output the adjustment square wave and update the photovoltaic output voltage, and the photovoltaic output voltage is transmitted to the voltage compensation addition module, and the output voltage V out1 =D / (1-D).

[0016] The present invention provides a dual-input DC-DC control method based on constant voltage control, comprising the following steps:

[0017] S1, the photovoltaic array PV senses the light intensity, inputs the photovoltaic voltage according to the light intensity, the photovoltaic feedback compensation circuit controls the PWM modulation duty cycle through the voltage mode to obtain the photovoltaic output voltage, and inputs the photovoltaic output voltage into the voltage compensation addition module;

[0018] S2, the input voltage of the constant voltage input conversion module is converted into the compensation voltage input to the compensation addition module through the buck circuit, and the constant voltage feedback compensation circuit is adjusted according to the comparison between the added voltage output by the voltage addition compensation module and the reference voltage, and the duty cycle is adjusted through the current mode to update and adjust and output the compensation voltage, and the compensation voltage is input to the voltage compensation addition module;

[0019] S3, the photovoltaic array PV senses the light intensity, and inputs the photovoltaic voltage according to the light intensity. When the photovoltaic array PV senses the light intensity is weak, the output voltage of the photovoltaic input conversion module does not reach the required value. In the constant voltage input conversion module, the constant voltage feedback compensation circuit automatically samples the added voltage output by the voltage addition compensation module, adjusts and updates the compensation voltage, and inputs it into the voltage compensation addition module;

[0020] S4, the voltage compensation addition module continuously adds the photovoltaic output voltage and the compensation voltage to obtain the added voltage and outputs an effective constant voltage after stabilizing the ripple.

[0021] Beneficial effect: Compared with the prior art, the present invention has the following notable features: the photovoltaic input conversion module adopts the photovoltaic array input voltage, outputs the voltage through the conversion circuit, and performs closed-loop control through PI controller feedback; in the constant voltage input conversion module, the switching effect of the mosfet tube is used to limit the input constant voltage to ensure the maximum value of the input voltage, thereby improving the circuit conversion efficiency; the constant voltage input conversion module is used as an active conversion structure to realize auxiliary compensation and stable feedback for the main conversion structure, i.e., the photovoltaic input conversion module, thereby solving the problem of low energy utilization and unstable output voltage caused by changes in light sources in the traditional photovoltaic DC-DC conversion structure, thereby making the energy conversion of photovoltaic input conversion more efficient and the DC-DC conversion structure more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of the present invention

[0023] Figure 2 It is a circuit schematic diagram of the present invention;

[0024] Figure 3 It is an equivalent diagram of the simulation model when the constant voltage input is 0 in the present invention;

[0025] Figure 4 It is an equivalent diagram of the simulation model when the constant voltage input is not 0 in the present invention;

[0026] Figure 5 It is a voltage output waveform diagram when the constant voltage input is 0 in the present invention;

[0027] Figure 6 It is a voltage output waveform diagram when the constant voltage input is not 0 in the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0029] The present invention provides a dual-input DC-DC control circuit based on constant voltage control, comprising a photovoltaic input conversion module, a constant voltage input conversion module, and a voltage compensation addition module;

[0030] See also Figure 1 As shown, the photovoltaic array converts light energy into electrical energy, and the photovoltaic voltage enters the boost-buck type circuit of the conversion voltage through the photovoltaic input terminal 2 and is converted into the required constant voltage. The photovoltaic conversion input module compares the input voltage with the reference voltage through a third-order inverter, and adjusts the duty cycle to control the output through the photovoltaic feedback compensation circuit; when the light intensity is sufficient, the photovoltaic voltage output voltage is large, and the photovoltaic conversion module basically meets the output requirements. At this time, the switch tube of the constant voltage input conversion module will be closed all the time and is only used to compensate for ripples, and its out2 output is small; as the light intensity decreases, the conversion rate of the boost-buck type circuit will become lower, and the output out1 will not meet the constant voltage output requirements. At this time, the constant voltage input conversion module will adjust the duty cycle to ensure the required constant voltage output according to the output of the photovoltaic input conversion module and the constant voltage input conversion module and the feedback coefficient of the constant voltage conversion, thus completing the dual-input constant voltage single output control mode.

[0031] See also Figure 2As shown, the photovoltaic input conversion module is used to sense changes in light intensity and adjust the duty cycle through a photovoltaic feedback compensation circuit, including a photovoltaic array PV, a power switch tube N3, and a power switch tube N4; the photovoltaic array PV senses light intensity, inputs a photovoltaic voltage according to the light intensity, obtains an output voltage through a boost-buck type conversion circuit, compares the output voltage with a reference voltage Vref to obtain an error value, and compensates and adjusts the error value. At this time, the PWM square wave after the duty cycle is changed is input into the power switch tube N3 and the power switch tube N4 to obtain a photovoltaic output voltage, and the photovoltaic output voltage is input into a voltage compensation addition module;

[0032] The photovoltaic input conversion module further includes a filter RC3, an inductor L2, a capacitor C4, a resistor R5, a subtractor, a second ramp oscillator, a PI controller, a second comparator, a third unit buffer, a second third-order inverter, and a third third-order inverter;

[0033] The positive pole of the photovoltaic array PV is used as the input end of the photovoltaic input, the negative pole of the photovoltaic array PV is grounded, the two ends of the photovoltaic array PV are connected in parallel with the filter RC3, the two ends of the filter RC3 are connected in parallel with the inductor L2, the two ends of the inductor L2 are connected in parallel with the capacitor C4, the two ends of the capacitor C4 are connected in parallel with the resistor R5, the source of the power switch tube N3 is connected to one end of the capacitor in the filter RC3, the drain of the power switch tube N3 is connected to one end of the inductor L2, the drain of the power switch tube N3 is also connected to the source of the power switch tube N4, the drain of the power switch tube N4 is connected to the input end of the third third-order inverter, the output end of the third third-order inverter is connected to the out1 input end of the adder in the voltage compensation addition module, the filter RC3, the inductor L2, and the capacitor C4 , resistor R5, power switch tube N3, and power switch tube N4 together form a boost-buck type conversion circuit, the gate of the power switch tube N3 is connected to the output end of the third unit buffer, the input end of the third unit buffer is connected to the input end of the second third-order inverter, the input end of the third unit buffer is also connected to the output end of the second comparator, the non-inverting input end of the second comparator is connected to the second ramp oscillator, the inverting input end of the second comparator is connected to one end of the PI controller, the other end of the PI controller is connected to the output end of the subtractor, the non-inverting input end of the subtractor is used as the input end of the reference voltage Vref, and the inverting input end of the subtractor is connected to the out1 input end of the adder in the voltage compensation addition module.

[0034] The constant voltage input conversion module is used to sample the summed voltage obtained by the voltage compensation addition module, compare and adjust the summed voltage with the reference voltage, adjust the duty cycle and output the compensation voltage through the constant voltage feedback compensation circuit, and includes an error amplifier, a bandgap reference, a mosfet tube M1, a mosfet tube M2, a mosfet tube M3, and a power switch tube N1; the constant voltage input conversion module outputs the compensation voltage through a buck type conversion circuit, the current paths of the mosfet tubes M1 and M2 are used for voltage division, the mosfet tube M1 works in the saturation region, the mosfet tube M2 works in the linear region, the drain voltage of the mosfet tube M2 controls the conduction or shutdown of the mosfet tube M3 and then controls the power switch tube N1 to obtain the compensation voltage, and outputs the compensation voltage to the voltage compensation addition module, the constant voltage feedback compensation circuit samples the summed voltage obtained by the voltage compensation addition module, compares and adjusts the summed voltage with the reference voltage to obtain a voltage error, compares and amplifies the voltage error through the error amplifier, adjusts the compensation voltage value, and further transmits it to the voltage compensation addition module;

[0035] The constant voltage input conversion module further includes a capacitor C1, a first unit buffer, a power switch tube N2, an inductor L1, a first three-phase inverter, a filter RC1, a resistor R4, a first comparator, a first ramp oscillator, a second unit buffer, and a bandgap reference;

[0036] The input end of the first unit buffer serves as the input end of the constant voltage input conversion module, the first unit buffer is connected in parallel with the capacitor C1, the output end of the first unit buffer is connected to the drain of the power switch tube N1, the mosfet tube M1 and the mosfet tube M2 are connected in series to form a voltage dividing structure, the gate of the mosfet tube M1 is connected to the gate of the mosfet tube M2, and is also connected to the drain of the mosfet tube M1, the drain of the mosfet tube M1 is connected to the output end of the first unit buffer, the source of the mosfet tube M2 is grounded, the drain of the mosfet tube M2 is connected to the source of the mosfet tube M1, the gate of the mosfet tube M3 is connected to the source of the mosfet tube M1, the source of the mosfet tube M3 is grounded, the drain of the mosfet tube M3 is connected to the gate of the power switch tube N1, the gate of the power switch tube N1 is also connected to the output end of the second unit buffer, the drain of the power switch tube N1 The gate of the power switch tube N2 is connected to one end of the inductor L1, the drain of the power switch tube N1 is connected to the source of the power switch tube N2, the drain of the power switch tube N2 is grounded, the gate of the power switch tube N2 is connected to the output end of the first three-phase inverter, the input end of the first three-phase inverter is connected to the input end of the second unit buffer, the other end of the inductor L1 is connected to the filter RC1, and is connected to one end of the resistor R4, the two ends of the filter RC1 are connected in parallel with the resistor R4, the other end of the resistor R4 is grounded, the other end of the inductor L1 is connected to the out2 input end of the adder in the voltage compensation addition module, the non-inverting input end of the error amplifier is connected to the output end of the adder in the voltage compensation addition module, the inverting input end of the error amplifier is externally connected to the bandgap reference as a compensation circuit, the output end of the error amplifier is connected to the non-inverting input end of the first comparator, the inverting input end of the first comparator is connected to the first ramp oscillator, and the output end of the first comparator is connected to the input end of the second unit buffer.

[0037] When the power supply generates a high pulse signal when powered on, the first unit buffer is connected in parallel with the capacitor C1 to form an overvoltage protection structure. The capacitor C1 is charged immediately, and the first buffer will generate a signal delay to filter the high pulse. When the high pulse signal acts on the mosfet tube M1 and the mosfet tube M2, the mosfet tube M1 and the mosfet tube M2 are connected in series to make the current pass. Among them, the mosfet tube M1 works in the saturation region, and the mosfet tube M2 works in the linear region. The drain voltage of the mosfet tube M2 is used to control the interruption of the mosfet tube M3, thereby controlling the power switch tube N1, to achieve The function of the protection circuit is that when the voltage at the constant voltage input end is too high and the drain voltage of the mosfet tube M2 exceeds the threshold voltage Vth of the mosfet tube M3, the mosfet tube M3 will be turned on, pulling down the gate voltage of the power switch tube N1, thereby turning off the power switch tube N1, that is, the entire constant voltage input conversion module as the compensation feedback loop of the photovoltaic input conversion module is closed, achieving overvoltage protection and ensuring high energy efficiency; when the voltage at the constant voltage input end is less than a certain value, the drain voltage of the mosfet tube M2 will not be greater than the threshold voltage Vth of the mosfet tube M3, and the entire circuit operates normally.

[0038] The error amplifier samples the added voltage obtained in the adder and compares it with the bandgap reference voltage to obtain a voltage error. The voltage error is compared and amplified by the error amplifier and then output. Then, the first comparator compares it with the first ramp oscillator to output a square wave. After the second unit buffer outputs a stable square wave and updates the compensation voltage value, the compensation voltage value is transmitted to the voltage compensation addition module, and the output voltage V out2 =D*Vin, where D is the duty cycle and Vin is the input voltage in the constant voltage input conversion module.

[0039] The voltage obtained at the output end of the third third-order inverter is used as the sampling value, and the sampling value is input into the subtractor to compare with the reference voltage Vref, and the signal difference is output. The signal difference is adjusted by the PI controller, and the adjusted signal is adjusted by the second comparator and the second ramp oscillator to output the adjustment square wave and update the photovoltaic output voltage, and the photovoltaic output voltage is transmitted to the voltage compensation addition module, and the output voltage V out1 =D / (1-D).

[0040] The constant voltage input conversion module adjusts the parameters to adapt the output to a constant voltage output according to the light intensity and temperature, that is, the output voltage of the photovoltaic array, and reasonably adjusts and controls the constant voltage fixed value output in an adaptive manner; that is, according to the size of the photovoltaic input voltage, the constant voltage input module will switch between "compensation" and "feedback", and the constant voltage input conversion module is designed with an overvoltage limiting function to prevent high-voltage pulse signals from damaging the circuit and limiting the high voltage input that leads to low energy utilization, thereby solving the problem of unstable photovoltaic output voltage in traditional DC-DC control conversion circuits.

[0041] The voltage compensation addition module is used to continuously add the photovoltaic output voltage and the compensation voltage to obtain the added voltage and output an effective constant voltage after stabilizing the ripple, comprising an adder, an RC filter, and a fourth unit buffer; the output end of the adder is connected to one end of the RC filter, the other end of the RC filter is grounded, and one end of the RC filter is simultaneously connected to the input end of the fourth unit buffer, the added voltage is obtained through the adder, and the ripple is stabilized through the RC filter, wherein Rs=2k, Cs=1nF, to obtain a stable effective voltage, and the stable effective voltage is passed through the fourth unit buffer to obtain an effective constant voltage for output.

[0042] The present invention provides a dual-input DC-DC control method based on constant voltage control, comprising the following steps:

[0043] S1, the photovoltaic array PV senses the light intensity, inputs the photovoltaic voltage according to the light intensity, the photovoltaic feedback compensation circuit controls the PWM modulation duty cycle through the voltage mode to obtain the photovoltaic output voltage, and inputs the photovoltaic output voltage into the voltage compensation addition module;

[0044] S2, the input voltage of the constant voltage input conversion module is converted into the compensation voltage input to the compensation addition module through the buck circuit, and the constant voltage feedback compensation circuit is adjusted according to the comparison between the added voltage output by the voltage addition compensation module and the reference voltage, and the duty cycle is adjusted through the current mode to update and adjust and output the compensation voltage, and the compensation voltage is input to the voltage compensation addition module;

[0045] S3, the photovoltaic array PV senses the light intensity, and inputs the photovoltaic voltage according to the light intensity. When the photovoltaic array PV senses the light intensity is weak, the output voltage of the photovoltaic input conversion module does not reach the required value. In the constant voltage input conversion module, the constant voltage feedback compensation circuit automatically samples the added voltage output by the voltage addition compensation module, adjusts and updates the compensation voltage, and inputs it into the voltage compensation addition module;

[0046] S4, the voltage compensation addition module continuously adds the photovoltaic output voltage and the compensation voltage to obtain the added voltage and outputs an effective constant voltage after stabilizing the ripple.

[0047] Example 1

[0048] See also Figure 2 As shown, when the circuit is not powered on, the photovoltaic array PV is in a short-circuit state, and the circuit output is 0; when the circuit is powered on but the input of the constant voltage input terminal 1 is 0, the voltage generated by the photovoltaic array PV is first stabilized by the filter RC3 to stabilize the ripple of the photovoltaic array input, and the inductor L2 is charged through the power switch tube N3. At this time, the power switch tube N4 is turned off. When the PWM controls the power switch tube N4 to open and the power switch tube N3 to close, the inductor L2 is discharged and output. The output is stabilized by the capacitor C4 to filter out the sudden voltage and obtain the preliminary voltage. The preliminary voltage is inverted by the third-order inverter to output a positive voltage, and feedback is performed. The positive voltage is compared with the reference voltage and the PI control is used. The controller and the second comparator generate a PWM waveform, and independently adjust the duty cycle to control the opening and closing of the power switch tube N3 and the power switch tube N4 and adjust the output voltage. Since the input of the constant voltage input terminal 1 is 0, the output is an ordinary boost-buck type output. When the light intensity is not high, the output has a large deviation; at this time, when the constant voltage input terminal takes a certain voltage, the constant voltage input conversion module further uses the buck circuit for feedback, so that the out2 output terminal is at a certain output value, realizing the "compensation" effect, thereby achieving a constant voltage output effect. Even if the light intensity is sufficient, the constant voltage conversion module can also play a ripple-stabilized feedback role, thereby stabilizing the output and making more reasonable use of light energy.

[0049] See also Figure 3 and Figure 4 As shown, to verify the feasibility of the above analysis, a corresponding simulation mathematical model is built in Matlab / Simulink. The photovoltaic array model is 1Soltech1STH-215-P photovoltaic array (2X2). Figure 3 This is the conversion equivalent model when the constant voltage input terminal 1 is the reasonable input low voltage of 0. At this time, the light intensity is 200, the temperature is 20, the photovoltaic array PV output voltage is 4.55V, the required output voltage is 4V, and the actual output is 3.118V. Please refer to Figure 5 As shown, Figure 5 for Figure 3 Output simulation waveform; when the constant voltage input terminal 1 takes 18V, Figure 4 This is an equivalent conversion model. At this time, when the reference voltage is 4V, the output voltage is 3.997V, which is closer to the required standard. Please refer to Figure 6 As shown, Figure 6 for Figure 4 Output simulation curve, the upper curve corresponds to the output of the entire circuit, and the lower curve corresponds to the situation without adding the constant voltage input conversion module.

Claims

1. A dual-input DC-DC control circuit based on constant voltage control, characterized in that: It includes photovoltaic input conversion module, constant voltage input conversion module and voltage compensation addition module; The photovoltaic input conversion module is used to sense changes in light intensity and adjust the duty cycle through a photovoltaic feedback compensation circuit. The photovoltaic input conversion module includes a photovoltaic array PV, a power switch tube N3, and a power switch tube N4. The photovoltaic array PV is used to sense light intensity, input a photovoltaic voltage according to the light intensity, obtain an output voltage through a boost-buck type conversion circuit, compare the output voltage with a reference voltage Vref to obtain an error value, compensate and adjust the error value, and input a PWM square wave after the duty cycle is changed into the power switch tube N3 and the power switch tube N4 to obtain a photovoltaic output voltage, and input the photovoltaic output voltage into a voltage compensation addition module; The constant voltage input conversion module is used to sample the added voltage obtained by the voltage compensation addition module, compare and adjust the added voltage with the reference voltage, adjust the duty cycle through the constant voltage feedback compensation circuit and output the compensation voltage. The constant voltage input conversion module includes an error amplifier, a mosfet tube M1, a mosfet tube M2, a mosfet tube M3, and a power switch tube N1; the current paths of the mosfet tube M1 and the mosfet tube M2 are used for voltage division, the mosfet tube M1 works in the saturation region, the mosfet tube M2 works in the linear region, the drain voltage of the mosfet tube M2 controls the conduction or shutdown of the mosfet tube M3 and then controls the power switch tube N1 to obtain the compensation voltage, and output the compensation voltage to the voltage compensation addition module. The constant voltage feedback compensation circuit samples the added voltage obtained by the voltage compensation addition module, compares and adjusts the added voltage with the reference voltage to obtain a voltage error, compares and amplifies the voltage error through the error amplifier, adjusts the compensation voltage and further transmits the compensation voltage to the voltage compensation addition module; The voltage compensation adding module is used to continuously add the photovoltaic output voltage and the compensation voltage to obtain the added voltage and output an effective constant voltage after stabilizing the ripple. The voltage compensation adding module includes an adder, an RC filter, and a fourth unit buffer; The added voltage is obtained through the adder, and the ripple is stabilized by the RC filter to obtain a stable effective voltage. The stable effective voltage is passed through the fourth unit buffer to obtain an effective constant voltage for output.

2. The dual-input DC-DC control circuit based on constant voltage control according to claim 1, characterized in that: The photovoltaic input conversion module further includes a filter RC3, an inductor L2, a capacitor C4, a resistor R5, a subtractor, a second ramp oscillator, a PI controller, a second comparator, a third unit buffer, a second third-order inverter, and a third third-order inverter; The positive pole of the photovoltaic array PV is used as the input end of the photovoltaic input, the negative pole of the photovoltaic array PV is grounded, the two ends of the photovoltaic array PV are connected in parallel with the filter RC3, the two ends of the filter RC3 are connected in parallel with the inductor L2, the two ends of the inductor L2 are connected in parallel with the capacitor C4, the two ends of the capacitor C4 are connected in parallel with the resistor R5, the source of the power switch tube N3 is connected to one end of the capacitor in the filter RC3, the drain of the power switch tube N3 is connected to one end of the inductor L2, the drain of the power switch tube N3 is also connected to the source of the power switch tube N4, the drain of the power switch tube N4 is connected to the input end of the third third-order inverter, the output end of the third third-order inverter is connected to the out1 input end of the adder in the voltage compensation addition module, the filter RC3, the inductor L2, and the capacitor C4 , resistor R5, power switch tube N3, and power switch tube N4 together form a boost-buck type conversion circuit, the gate of the power switch tube N3 is connected to the output end of the third unit buffer, the input end of the third unit buffer is connected to the input end of the second third-order inverter, the input end of the third unit buffer is also connected to the output end of the second comparator, the non-inverting input end of the second comparator is connected to the second ramp oscillator, the inverting input end of the second comparator is connected to one end of the PI controller, the other end of the PI controller is connected to the output end of the subtractor, the non-inverting input end of the subtractor is used as the input end of the reference voltage Vref, and the inverting input end of the subtractor is connected to the out1 input end of the adder in the voltage compensation addition module.

3. The dual-input DC-DC control circuit based on constant voltage control according to claim 1, characterized in that: The constant voltage input conversion module further includes a capacitor C1, a first unit buffer, a power switch tube N2, an inductor L1, a first three-phase inverter, a filter RC1, a resistor R4, a first comparator, a first ramp oscillator, a second unit buffer, and a bandgap reference; The input end of the first unit buffer serves as the input end of the constant voltage input conversion module, the first unit buffer is connected in parallel with the capacitor C1, the output end of the first unit buffer is connected to the drain of the power switch tube N1, the mosfet tube M1 and the mosfet tube M2 are connected in series to form a voltage dividing structure, the gate of the mosfet tube M1 is connected to the gate of the mosfet tube M2, and is also connected to the drain of the mosfet tube M1, the drain of the mosfet tube M1 is connected to the output end of the first unit buffer, the source of the mosfet tube M2 is grounded, the drain of the mosfet tube M2 is connected to the source of the mosfet tube M1, the gate of the mosfet tube M3 is connected to the source of the mosfet tube M1, the source of the mosfet tube M3 is grounded, the drain of the mosfet tube M3 is connected to the gate of the power switch tube N1, the gate of the power switch tube N1 is also connected to the output end of the second unit buffer, the power switch tube N The drain of the power switch tube N1 is connected to one end of the inductor L1, the drain of the power switch tube N1 is also connected to the source of the power switch tube N2, the drain of the power switch tube N2 is grounded, the gate of the power switch tube N2 is connected to the output end of the first three-phase inverter, the input end of the first three-phase inverter is connected to the input end of the second unit buffer, the other end of the inductor L1 is connected to the filter RC1, and is also connected to one end of the resistor R4, the two ends of the filter RC1 are connected in parallel with the resistor R4, the other end of the resistor R4 is grounded, the other end of the inductor L1 is also connected to the out2 input end of the adder in the voltage compensation addition module, the non-inverting input end of the error amplifier is connected to the output end of the adder in the voltage compensation addition module, the inverting input end of the error amplifier is externally connected to the bandgap reference, the output end of the error amplifier is connected to the non-inverting input end of the first comparator, the inverting input end of the first comparator is connected to the first ramp oscillator, and the output end of the first comparator is connected to the input end of the second unit buffer.

4. The dual-input DC-DC control circuit based on constant voltage control according to claim 1, characterized in that: In the voltage compensation adding module, the output end of the adder is connected to one end of the RC filter, the other end of the RC filter is grounded, and one end of the RC filter is simultaneously connected to the input end of the fourth unit buffer.

5. The dual-input DC-DC control circuit based on constant voltage control according to claim 3, characterized in that: In the constant voltage input conversion module, the error amplifier samples the summed voltage obtained in the adder and compares it with the bandgap reference voltage to obtain a voltage error. The voltage error is compared and amplified by the error amplifier and then output. Then, the first comparator compares it with the first ramp oscillator to output a square wave. After the second unit buffer outputs a stable square wave and updates the adjustment compensation voltage value, the compensation voltage value is transmitted to the voltage compensation addition module, and the output voltage V out2 =D*Vin, where D is the duty cycle and Vin is the input voltage in the constant voltage input conversion module.

6. The dual-input DC-DC control circuit based on constant voltage control according to claim 1, characterized in that: In the photovoltaic input conversion module, the voltage obtained at the output end of the third third-order inverter is used as the sampling value, and the sampling value is input into the subtractor to compare with the reference voltage Vref, and the signal difference is output. The signal difference is adjusted by the PI controller, and the adjusted signal is adjusted by the second comparator and the second ramp oscillator to output the adjustment square wave and update the photovoltaic output voltage. The photovoltaic output voltage is transmitted to the voltage compensation addition module, and the output voltage V out1 =D / (1-D), where D is the duty cycle.

7. A dual-input DC-DC control method based on constant voltage control according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, the photovoltaic array PV senses the light intensity, inputs the photovoltaic voltage according to the light intensity, the photovoltaic feedback compensation circuit controls the PWM modulation duty cycle through the voltage mode to obtain the photovoltaic output voltage, and inputs the photovoltaic output voltage into the voltage compensation addition module; S2, the input voltage of the constant voltage input conversion module is converted into the compensation voltage input to the compensation addition module through the buck circuit, and the constant voltage feedback compensation circuit is adjusted according to the comparison between the added voltage output by the voltage addition compensation module and the reference voltage, and the duty cycle is adjusted through the current mode to update and adjust and output the compensation voltage, and the compensation voltage is input to the voltage compensation addition module; S3, the photovoltaic array PV senses the light intensity, and inputs the photovoltaic voltage according to the light intensity. When the photovoltaic array PV senses the light intensity is weak, the output voltage of the photovoltaic input conversion module does not reach the required value. In the constant voltage input conversion module, the constant voltage feedback compensation circuit automatically samples the added voltage output by the voltage addition compensation module, adjusts and updates the compensation voltage, and inputs it into the voltage compensation addition module; S4, the voltage compensation addition module continuously adds the photovoltaic output voltage and the compensation voltage to obtain the added voltage and outputs an effective constant voltage after stabilizing the ripple.

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