Photovoltaic greenhouse power conversion energy-saving device, control method and component selection method

Abstract

The present invention discloses a photovoltaic greenhouse power conversion energy-saving device, a control method and a component selection method thereof, and belongs to the field of smart agriculture and building energy-saving technology. It includes a photovoltaic module, a microprocessor, a Buck-Boost converter, a temperature and humidity sensor, an auxiliary power supply, a voltage and current transmitter and a display, wherein the photovoltaic module is respectively connected to the input port and the auxiliary power supply of the Buck-Boost converter, and the two output ports of the Buck-Boost converter are respectively connected to the inverter and the DC bus. The present invention reduces the power loss caused by the cascade and parallel converters and reduces the amount of components used, so as to realize the simultaneous output of high voltage and low voltage by the non-cascade circuit, which not only solves the voltage level required by the inverter, but also solves the power supply problem of the DC equipment, and adopts the flyback conversion to provide a higher voltage output and a wider voltage input range.

Description

Technical Field

[0001] The invention belongs to the technical field of electric energy conversion and building energy saving, and relates to a photovoltaic greenhouse electric power conversion energy saving device, a control method and a component selection method thereof. Background Art

[0002] Photovoltaic agriculture has various development models, such as photovoltaic agricultural greenhouses, fishery-photovoltaic complementarity, etc. These models can achieve the dual goals of clean electricity and efficient agricultural production without occupying new land resources. Photovoltaic greenhouse is an innovative agricultural model that combines solar power generation with modern agricultural planting. This model can not only generate clean electricity, but also improve the comprehensive utilization value of land, promote agricultural modernization and rural revitalization. The technical advantages of photovoltaic greenhouses include that the components can reduce the radiation intensity in the greenhouse and avoid the photosynthetic nap of greenhouse crops; at the same time, the distributed photovoltaic power generation system provides electricity for the load in the greenhouse, which improves the agricultural production efficiency and the utilization efficiency of the distributed photovoltaic system.

[0003] However, there are AC and DC devices in the photovoltaic greenhouse system, which usually requires multiple converters to be connected in parallel and cascaded to obtain the voltage level required by the equipment. The use of too many converters will increase the power loss of the equipment. Therefore, in terms of photovoltaic greenhouse converters, saving the number of components and reducing energy loss are issues to be solved. Summary of the invention

[0004] In order to solve the problems of large losses in photovoltaic high-voltage AC inversion and low-voltage DC supply, the present invention provides a photovoltaic greenhouse power conversion energy-saving device, a control method and a component selection method, so as to realize the simultaneous output of high voltage and low voltage in a non-cascade circuit, which not only solves the voltage level required for inversion, but also solves the power supply problem of DC equipment, and adopts flyback conversion to provide higher voltage output and wider voltage input range.

[0005] The present invention is realized by the following technical scheme: a photovoltaic greenhouse power conversion energy-saving device, including a photovoltaic module, a microprocessor, a new high-efficiency single-input multi-stage multi-output Buck-Boost converter, a temperature and humidity sensor, an auxiliary power supply, a voltage and current transmitter and a display, wherein the photovoltaic module is respectively connected to the input port and the auxiliary power supply of the Buck-Boost converter, and the two output ports of the Buck-Boost converter are respectively connected to the inverter and the DC bus; the communication port of the microprocessor is connected to the display; the ADC port of the microprocessor is connected to the temperature and humidity sensor and the voltage and current transmitter, and the data of multiple acquisition sources are read at the same time, including the acquisition of the output voltage V PVin , output current I PVinAs well as the output voltage and output current of the two output ports of the Buck-Boost converter, as well as the external temperature and humidity; the microprocessor serves as the core control unit controller to output PWM waves, and the PWM waveform uses the pulse width modulation module built into the microprocessor to output multiple PWM drives to achieve optimal control of electrical energy; the auxiliary power supply uses a 24V power supply module. If the voltage of the photovoltaic module is high, it can be stepped down by the 24V power supply module to supply power to the microprocessor; in addition to the Buck-Boost converter step-up and step-down processing of the photovoltaic module output voltage, it also powers the microprocessor through an auxiliary power supply module with a fixed output voltage, and uses the microprocessor program to control the single-input dual-output Buck-Boost converter to achieve step-up and step-down of the photovoltaic module output voltage.

[0006] The Buck-Boost converter includes an input port V in , the first output port V out1 , the second output port V out2 , a first power switch S1, a second power switch S2, a third power switch S3, a first diode D1, a second diode D2, a third diode D3, a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6 and a seventh capacitor C7;

[0007] The present invention stipulates that the direction of inductor charging is positive. inThe positive electrode of the first inductor L1 is connected in parallel with the seventh capacitor C7, the positive electrode of the first inductor L1 is connected to the positive electrode of the seventh capacitor C7, the collector of the first switch tube S1 is connected to the negative electrode of the first inductor L1, and the emitter of the first switch tube S1 is connected to the negative electrode of the seventh capacitor C7; the anode of the first diode D1 is connected to the negative electrode of the first inductor L1, and the cathode of the first diode D1 is connected to the positive electrode of the first capacitor C1; the negative electrode of the first capacitor C1 is connected to the negative electrode of the seventh capacitor C7; the collector of the second switch tube S2 is connected to the positive electrode of the first capacitor C1, and the emitter of the second switch tube S2 is connected to the positive electrode of the second inductor L2; the positive electrode of the second capacitor C2 is connected to the negative electrode of the first inductor L1, and the negative electrode of the second capacitor C2 is connected to the negative electrode of the second inductor The anode of the second diode D2 is connected to the negative electrode of the second capacitor L2, and the cathode of the second diode D2 is connected to the positive electrode of the third capacitor C3; the negative electrode of the third capacitor C3 is connected to the negative electrode of the seventh capacitor C7, and the positive electrode of the third capacitor C3 is also connected to the positive electrode of the third inductor L3; the emitter of the third switch tube S3 is connected to the positive electrode of the inductor L2, and the collector of the third switch tube S3 is connected to the negative electrode of the third inductor L3; the positive electrode of the third inductor L3 is also connected to the cathode of the second diode D2, the anode of the third diode D3 is connected to the negative electrode of the third inductor L3, and the cathode of the third diode D3 is connected to the positive electrode of the fourth capacitor C4; the positive electrode of the fourth capacitor C4 is also connected to the first output port V out1 The positive electrode of the fourth capacitor C4 is connected to the first output port V out1 The positive electrode of the fifth capacitor C5 is connected to the output port V out1 The positive electrode of the fifth capacitor C5 is connected to the output port V out1 The first output port V out1 The negative electrode of the first output port V out1 The positive electrode of the sixth capacitor C6 is also connected to the cathode of the third diode D3; the positive electrode of the sixth capacitor C6 is connected to the anode of the third diode D3, and the negative electrode of the sixth capacitor C6 is connected to the anode of the second diode D2; the second output port V out2 The positive electrode of the second output port V out2 The negative electrode of is connected to the negative electrode of the sixth capacitor C6.

[0008] The sixth capacitor C6, the fifth capacitor C5 and the fourth capacitor C4 play a filtering role, and the seventh capacitor C7 plays an input filtering role. There are two output ports, namely the first output port V out1 and the second output port V out2 .

[0009] Another object of the present invention is to provide: a method for photovoltaic greenhouse power conversion, using the above device, in a cycle of a PWM wave output by the microprocessor, there are two stages, namely, the switch tube conduction state and the switch tube closed state:

[0010] Phase 1: The PWM wave output by the microprocessor is at a high potential, the first power switch S1, the second power switch S2 and the third power switch S3 are all closed, and the photovoltaic module is connected through the input port V in The first inductor L1 is charged, the first capacitor C1 and the second capacitor C2 are connected in series to charge the second inductor L2, the second capacitor C2 and the third capacitor C3 are connected in series to charge the third inductor L3 and the second inductor L2, and the sixth capacitor C6 is connected to the second output port V out2 The fourth capacitor C4 and the fifth capacitor C5 are connected to the first output port V out1 Output of energy;

[0011] Phase 2: The PWM wave output by the microprocessor is at a low potential, the first power switch S1, the second power switch S2 and the third power switch S3 are all disconnected, and the photovoltaic module is connected through the input port V in The first inductor L1 is connected in series to charge the first capacitor C1, the second capacitor C2, and the third capacitor C3. The second inductor L2 and the third inductor L3 jointly charge the fifth capacitor C5 and the fourth capacitor C4 and the first output port V out1 The third inductor L3 alone provides energy to the sixth capacitor C6 and the second input port V out2 Provide energy.

[0012] By changing the time ratio of the two stages within a cycle, the converter can achieve voltage boost and voltage reduction. Since the components have a withstand voltage value, the voltage stress, current stress, capacitance of the capacitor and inductance of the inductor of each component must be calculated according to the input and output voltage and current of the converter to facilitate the selection of converter components for different scenarios.

[0013] The voltage stress and current stress to be borne by the first power switch S1, the second power switch S2 and the third power switch S3 are calculated by the following formulas, and the types are selected according to the calculation results:

[0014] (1)

[0015] (2)

[0016] (3)

[0017] (4)

[0018] (5)

[0019] (6)

[0020] In the formula, is the duty cycle of the power switch, V i is the maximum voltage of the input port, V S1 is the voltage stress of the first power switch S1, V S2 is the voltage stress of the second power switch S2, V S3 is the voltage stress of the third power switch S3, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, I S1 is the current stress of the first power switch S1, I S2 is the current stress of the second power switch S2, I S3 is the current stress of the third power switch S3.

[0021] The voltage stress and current stress to be borne by the first diode D1, the second diode D2 and the third diode D3 are calculated by the following formulas, and the types are selected according to the calculation results:

[0022] (7)

[0023] (8)

[0024] (9)

[0025] (10)

[0026] (11)

[0027] (12)

[0028] In the formula, d is the duty cycle of the power switch, V i is the maximum voltage of the input port, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, V D1 is the voltage stress of the first diode D1, V D2 is the voltage stress of the second diode D2, V D3 is the voltage stress of the third diode D3, I D1 is the current stress of the first diode D1, I D2 is the current stress of the second diode D2, I D3is the current stress of the third diode D3.

[0029] The first capacitor C1, the second capacitor C2, the third capacitor C3, the fifth capacitor C5, the sixth capacitor C6 and the seventh capacitor C7 are calculated by the following formula to have a minimum capacitance, and are selected according to the calculation results:

[0030] (13)

[0031] (14)

[0032] (15)

[0033] (16)

[0034] (17)

[0035] (18)

[0036] In the formula, d is the duty cycle of the power switch, T S is the time of one cycle of PWM wave, V i is the maximum voltage of the input port, I in is the maximum current of the input port, V o1 is the maximum output voltage of the first output port, V o2 is the maximum output voltage of the second output port, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, R1, R2, R3, R5, R6, and R7 are the voltage ripple rates of C1, C2, C3, C5, C6, and C7 respectively, and f is the system operating frequency;

[0037] The fourth capacitor C4 is mainly used to filter out high-frequency noise, and its capacitance should be much smaller than the output capacitor. The capacitance value of C5 and C4 in parallel should not differ too much from that of C5. Therefore, the capacitance of the fourth capacitor C4 is selected to be one thousandth of that of C5.

[0038] The first inductor L1, the second inductor L2 and the third inductor L3 are calculated by the following formula to have a minimum inductance, and are selected according to the calculation results:

[0039] (19)

[0040] (20)

[0041] (twenty one)

[0042] In the formula, d is the duty cycle of the power switch, T S is the time of one cycle of PWM wave, V i is the maximum voltage of the input port, V o1 is the maximum output voltage of the first output port, V o2 is the maximum output voltage of the second output port, V L3 is the voltage across the third inductor L3, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, r1, r2, r3 are the current ripple coefficients of the first inductor L1, the second inductor L2 and the third inductor L3 respectively.

[0043] The high-efficiency single-input multi-output Buck-Boost converter proposed in the present invention uses a microprocessor as a core control unit controller to output PWM waves to achieve optimal control of electric energy. The communication port of the microprocessor (inside the microprocessor) is connected to the data bus to monitor the voltage and current on the monitoring equipment; the ADC port of the microprocessor is connected to the external temperature and humidity sensor and the voltage and current transmitter to simultaneously read data from multiple collection sources, including the output voltage V of the photovoltaic module. PVin , output current I PVin , the output voltage and output current of the two output ports of the Buck-Boost converter, as well as the external temperature and humidity. The PWM waveform uses the pulse width modulation module built into the microprocessor to output multiple PWM drives; the photovoltaic modules are connected to the Buck-Boost converter and the auxiliary power supply respectively, where the auxiliary power supply uses a 24V output power module. If the voltage of the photovoltaic module is high, it can be stepped down by the step-down circuit and then powered by a 24V voltage output power module to supply power to the microprocessor. In addition to the step-up and step-down processing of the Buck-Boost converter, the output voltage of the photovoltaic module is also powered by an auxiliary power module with a fixed output voltage to supply power to the microprocessor. The specific system diagram is as follows Figure 1 shown.

[0044] When the output voltage source is stable and there is no power limit, the first output port V can be changed by changing the operating time or duty cycle of the two stages within a PWM wave cycle. out1 and the first output port V out2 The voltage of the first output port V of the converter can be obtained by using the inductor volt-second balance equation and the capacitor ampere-second balance equation. out1 and the first output port V out2 The voltage gain ratio is shown in formula (22) and formula (23):

[0045] (twenty two)

[0046] (twenty three)

[0047] In the formula, M1 represents the gain of the first output port, d is the duty cycle of the power switch, and V o1 is the maximum output voltage of the first output port, V i represents the maximum voltage of the input port, M2 represents the gain of the second output port, V o2 Indicates the maximum output voltage of the second output port.

[0048] When the PWM wave duty ratio of the first power switch S1, the second power switch S2, and the third power switch S3 is between 10% and 80%, it can be known from formula (22) and formula (23) that the first output port V out1 The voltage multiple range is 0.4 to 100 times. The second output port V out2 The voltage multiple range is 0.1 to 9 times. The topology can be adjusted based on the requirements between the sixth capacitor C6 and the second output port V out2 An additional switch is added between the two to control the second output port V out2 voltage.

[0049] It can be seen that the present invention proposes a converter with two voltage step-up ratios for use in DC and AC devices. The converter can save the number of components and reduce energy loss.

[0050] The present invention has a single input port and two output ports. Compared with two converters that respectively supply energy to the AC bus and the DC bus, the converter combines the two converters into one, saving the number of components and solving the problem of overall low efficiency caused by the use of multiple converters. According to the control of the first power switch S1, the second power switch S2 and the third power switch S3, high voltage and low voltage can be output simultaneously, and the converter has a very wide step-up ratio. When the PWM wave duty cycle is 0.1-0.9, the first output port V out1 The voltage multiple range is 0.4 to 100 times, which can meet the inverter voltage level of various inverters. The second output port V out2 The voltage multiple ranges from 0.1 to 9 times and is connected to the DC bus to supply energy to the DC load.

[0051] In order to reduce energy waste, achieve energy saving, increase automation and precise control, the present invention uses series-parallel photovoltaic modules, a new multi-level voltage output Buck-Boost circuit and a microprocessor. The first diode D1 and the second diode D2 form the main circuit, the seventh input filter capacitor C7 and the input port V in When the duty cycle is between 10% and 80%, the first output port V out1 The output voltage multiple is 0.4 to 100 times, the second output port Vout2 The output voltage multiple is 0.3 to 9 times, the maximum boost efficiency is 94%, and the maximum buck efficiency is 92%. out2 The output port is connected to the DC bus or directly connected to a DC device such as an LED lamp, and the output voltage is regulated by the switch tube. The first output port V out1 Use an inverter to connect to the AC bus.

[0052] The single-input multi-output Buck-Boost converter of the present invention is used as a step-up / step-down converter. The first power switch S1, the second power switch S2 and the third power switch S3 operate in parallel under the PI control stable operation mode. The PWM control signal generated by the microprocessor has the same frequency and the same phase. The circuit of the converter operates in the inductor current continuous mode. The first power switch S1, the second power switch S2 and the third power switch S3 operate with equal duty cycles and the same phase. The first inductor L1, the second inductor L2 and the third inductor L3 are equal. The fourth capacitor C4 and the fifth capacitor C5 are connected in parallel to filter out high-frequency and low-frequency clutter. When in the maximum power point operation mode, the microprocessor outputs a PWM waveform through a maximum power search algorithm to control the first power switch S1, the second power switch S2 and the third power switch S3, and detects the second output port V out2 Or the first output terminal V out1 The voltage is transmitted to the microcontroller, and then the microcontroller outputs a PWM waveform through the PI algorithm to achieve power reduction operation and stabilize the DC side output voltage.

[0053] When the power of the PV module is much greater than the power required by the load side, PI control is used to reduce the power in buck mode to improve system stability and eliminate the fluctuation of PV module output within a certain period of time.

[0054] The low-voltage port of the converter of the present invention supplies power to the DC load in the greenhouse, and the high-voltage port is input to the inverter to supply power to the AC load. The converter uses the existing maximum power point search algorithm to achieve maximum power point tracking, and then uses PI control to verify the maximum power point and achieve power reduction operation, solving the problem of power fluctuation caused by non-uniform illumination such as shadows and fallen leaves in photovoltaic modules. Compared with the traditional single-input single-output converter, the present invention has one input port and two output ports, which reduces the power loss caused by cascade and parallel converters and reduces the use of devices. It has a very wide voltage output range, strong environmental adaptability, and different voltage output levels can meet the voltage levels required by the DC bus and the AC bus. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the system of the present invention;

[0056] Figure 2 A schematic diagram of the topology of a single-input multi-output control BUCK-BOOST converter circuit of the present invention;

[0057] Figure 3 is a schematic diagram of circuit mode 1;

[0058] Figure 4 is a schematic diagram of circuit mode 2;

[0059] Figure 5 It is a schematic diagram of dual closed-loop voltage and current PI control; where K p The value is 20, K i A value of 3 can achieve stable output voltage with less fluctuation;

[0060] Figure 6 Detect the maximum power point for PI disturbance and reduce the power operation control flow chart;

[0061] Figure 7 It is a schematic diagram of the change of efficiency with duty cycle when the output load is 100 ohms in the embodiment;

[0062] Figure 8 It is a schematic diagram of efficiency under voltage reduction when the output load is 100 ohms in the embodiment. DETAILED DESCRIPTION

[0063] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0064] The photovoltaic greenhouse power conversion energy-saving device comprises a photovoltaic module, a microprocessor, a new high-efficiency single-input multi-stage multi-output Buck-Boost converter, a temperature and humidity sensor, an auxiliary power supply, a voltage and current transmitter and a display. The photovoltaic module is respectively connected to the input port and the auxiliary power supply of the Buck-Boost converter, and the two output ports of the Buck-Boost converter are respectively connected to the inverter and the DC bus; the communication port of the microprocessor is connected to the display; the ADC port of the microprocessor is connected to the temperature and humidity sensor and the voltage and current transmitter, and reads data from multiple collection sources at the same time, including collecting the output voltage V PVin , output current I PVinAs well as the output voltage and output current of the two output ports of the Buck-Boost converter, as well as the external temperature and humidity; the microprocessor serves as the core control unit controller to output PWM waves, and the PWM waveform uses the pulse width modulation module built into the microprocessor to output multiple PWM drives to achieve optimal control of electrical energy; the auxiliary power supply uses a 24V power supply module. If the voltage of the photovoltaic module is high, it can be stepped down by the 24V power supply module to supply power to the microprocessor; in addition to the Buck-Boost converter step-up and step-down processing of the photovoltaic module output voltage, it also powers the microprocessor through an auxiliary power supply module with a fixed output voltage, and uses the microprocessor program to control the single-input dual-output Buck-Boost converter to achieve step-up and step-down of the photovoltaic module output voltage.

[0065] The temperature and humidity sensors are commercially available products, such as the HDC1080DMBR temperature and humidity sensor of Texas Instruments; the auxiliary power supply is a commercially available product, such as the TAS50-24-W step-down power supply module of Tenda Power; the voltage and current transmitters are commercially available products, such as the QIDIAN QD-D14-12 DC current transmitter and the QIDIAN DC0-1000V voltage transmitter.

[0066] The Buck-Boost converter includes an input port V in , the first output port V out1 , the second output port V out2 , a first power switch S1, a second power switch S2, a third power switch S3, a first diode D1, a second diode D2, a third diode D3, a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6 and a seventh capacitor C7;

[0067] The present invention stipulates that the direction of inductor charging is positive. inThe positive electrode of the first inductor L1 is connected in parallel with the seventh capacitor C7, the positive electrode of the first inductor L1 is connected to the positive electrode of the seventh capacitor C7, the collector of the first switch tube S1 is connected to the negative electrode of the first inductor L1, and the emitter of the first switch tube S1 is connected to the negative electrode of the seventh capacitor C7; the anode of the first diode D1 is connected to the negative electrode of the first inductor L1, and the cathode of the first diode D1 is connected to the positive electrode of the first capacitor C1; the negative electrode of the first capacitor C1 is connected to the negative electrode of the seventh capacitor C7; the collector of the second switch tube S2 is connected to the positive electrode of the first capacitor C1, and the emitter of the second switch tube S2 is connected to the positive electrode of the second inductor L2; the positive electrode of the second capacitor C2 is connected to the negative electrode of the first inductor L1, and the negative electrode of the second capacitor C2 is connected to the negative electrode of the second inductor The anode of the second diode D2 is connected to the negative electrode of the second capacitor L2, and the cathode of the second diode D2 is connected to the positive electrode of the third capacitor C3; the negative electrode of the third capacitor C3 is connected to the negative electrode of the seventh capacitor C7, and the positive electrode of the third capacitor C3 is also connected to the positive electrode of the third inductor L3; the emitter of the third switch tube S3 is connected to the positive electrode of the inductor L2, and the collector of the third switch tube S3 is connected to the negative electrode of the third inductor L3; the positive electrode of the third inductor L3 is also connected to the cathode of the second diode D2, the anode of the third diode D3 is connected to the negative electrode of the third inductor L3, and the cathode of the third diode D3 is connected to the positive electrode of the fourth capacitor C4; the positive electrode of the fourth capacitor C4 is also connected to the first output port V out1 The positive electrode of the fourth capacitor C4 is connected to the first output port V out1 The positive electrode of the fifth capacitor C5 is connected to the output port V out1 The positive electrode of the fifth capacitor C5 is connected to the output port V out1 The first output port V out1 The negative electrode of the first output port V out1 The positive electrode of the sixth capacitor C6 is also connected to the cathode of the third diode D3; the positive electrode of the sixth capacitor C6 is connected to the anode of the third diode D3, and the negative electrode of the sixth capacitor C6 is connected to the anode of the second diode D2; the second output port V out2 The positive electrode of the second output port V out2 The negative electrode of is connected to the negative electrode of the sixth capacitor C6.

[0068] The sixth capacitor C6, the fifth capacitor C5 and the fourth capacitor C4 play a filtering role, and the seventh capacitor C7 plays an input filtering role. There are two output ports, namely the first output port V out1 and the second output port V out2 .

[0069] The microcontroller mainly uses PI control and MPPT control to realize the duty cycle adjustment of PWM wave, voltage and current feedback, and the formation of PWM wave is calculated and output by the microprocessor. After the initialization setting is completed, the rising waveform is used to control the PWM duty cycle by changing the values ​​of CMP1 and CMP2 of different PWM output ports, thereby changing the output voltage and power of the Buck-Boost converter output port. The PI controller is a controller with proportional and integral functions. The main function of the PI controller is to adjust the operation of the control system according to the error between the output value and the reference value, so that the error gradually decreases and reaches a steady state. At the same time, it can respond quickly and achieve steady-state control. The PI control of this system is mainly used to control the voltage and current of the output port. The outer loop of the double closed-loop control is the voltage detection loop, and the inner loop is the current detection loop. While detecting the current and voltage data, it can realize the steady-state control of the voltage and current. The soft start control can make the current not change suddenly when the system starts. At startup, the capacitor in the circuit will gradually charge and the voltage will gradually increase. The soft start controller controls the startup process so that the output voltage can follow the reference voltage to achieve stable operation of the system.

[0070] This system mainly uses the method of finding the maximum power point (MPPT) and then reducing the power:

[0071] First, the existing maximum power point search algorithm is used to find the maximum power point when working and the maximum power output of the photovoltaic module. Since various algorithms applied to photovoltaic modules may have errors, especially under extreme weather conditions, they need to be verified after the maximum power point is found.

[0072] After finding the maximum power point using the MPPT algorithm, the voltage at the maximum power point is detected. By changing the target voltage input of the PI control and the duty cycle of the PWM wave, the maximum power point is detected and verified using the PI disturbance control and the power reduction operation is achieved according to 90% of the maximum power point. The PI double closed-loop control block diagram is shown below: Figure 5 As shown, the maximum power point verification and power reduction operation flow chart is shown in Figure 6. The power reduction operation solves the problem of photovoltaic instability caused by temporary obstructions.

[0073] The auxiliary power module uses a 100-380V input and 24V output power module (purchased model: Tenda Power TAS50-24-W step-down power module). The output voltage and current of the photovoltaic module and the first output port V out1 and the second output port V out2 The output voltage and current are controlled by the MPPT algorithm and PID algorithm in the microprocessor to achieve the maximum power point search, verification and power reduction operation.

[0074] Furthermore, the photovoltaic greenhouse power conversion method adopts the above device, and within a cycle of a PWM wave output by the microprocessor, there are two stages, namely, the switch tube conduction state and the switch tube closed state:

[0075] Phase 1: The PWM wave output by the microprocessor is at a high potential, the first power switch S1, the second power switch S2 and the third power switch S3 are all closed, and the photovoltaic module is connected through the input port V in The first inductor L1 is charged, the first capacitor C1 and the second capacitor C2 are connected in series to charge the second inductor L2, the second capacitor C2 and the third capacitor C3 are connected in series to charge the third inductor L3 and the second inductor L2, and the sixth capacitor C6 is connected to the second output port V out2 The fourth capacitor C4 and the fifth capacitor C5 are connected to the first output port V out1 To output energy; the specific circuit diagram is as follows Figure 3 (Mode 1) shown;

[0076] Phase 2: The PWM wave output by the microprocessor is at a low potential, the first power switch S1, the second power switch S2 and the third power switch S3 are all disconnected, and the photovoltaic module is connected through the input port V in The first inductor L1 is connected in series to charge the first capacitor C1, the second capacitor C2, and the third capacitor C3. The second inductor L2 and the third inductor L3 jointly charge the fifth capacitor C5 and the fourth capacitor C4 and the first output port V out1 The third inductor L3 alone provides energy to the sixth capacitor C6 and the second input port V out2 Provide energy; the specific circuit diagram is as follows Figure 4 (Mode 2) shown.

[0077] Circuit device selection: Since the first power switch S1 needs to flow a large amount of current during operation, an IGBT suitable for large current is selected, and MOS tubes are selected for the other two power switches. The three switch tubes are synchronously controlled with a frequency of 20kHZ. Select the device according to the following calculation formula: the output resistance is 100 ohms, the voltage ripple is less than 5%, the inductor ripple rate is 0.4, and the switch tube frequency is 20KHz. The maximum input voltage is 40V, the maximum input current is 10A, and the duty cycle of the maximum power point is around 0.6.

[0078] The voltage stress and current stress to be borne by the first power switch S1, the second power switch S2 and the third power switch S3 are calculated by the following formulas, and the types are selected according to the calculation results:

[0079] (1)

[0080] (2)

[0081] (3)

[0082] (4)

[0083] (5)

[0084] (6)

[0085] In the formula, d is the duty cycle of the power switch, V i is the maximum voltage of the input port, V S1 is the voltage stress of the first power switch S1, V S2 is the voltage stress of the second power switch S2, V S3 is the voltage stress of the third power switch S3, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, I S1 is the current stress of the first power switch S1, I S2 is the current stress of the second power switch S2, I S3 is the current stress of the third power switch S3.

[0086] The voltage stress and current stress to be borne by the first diode D1, the second diode D2 and the third diode D3 are calculated by the following formulas, and the types are selected according to the calculation results:

[0087] (7)

[0088] (8)

[0089] (9)

[0090] (10)

[0091] (11)

[0092] (12)

[0093] In the formula, d is the duty cycle of the power switch, V i is the maximum voltage of the input port, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, V D1 is the voltage stress of the first diode D1, V D2 is the voltage stress of the second diode D2, VD3 is the voltage stress of the third diode D3, I D1 is the current stress of the first diode D1, I D2 is the current stress of the second diode D2, I D3 is the current stress of the third diode D3.

[0094] According to formula (13), by substituting the maximum input current, the duration of one PWM cycle and the minimum duty cycle, it can be concluded that the minimum value of the first capacitor C1 is 56.25uF.

[0095] (13)

[0096] The voltage ripple of the second capacitor C2 is 2%. According to formula (14), it can be calculated that the minimum value of the second capacitor C2 is 140.625uF.

[0097] (14)

[0098] According to formula (15), it can be calculated that the minimum value of the third capacitor C3 is 56.25uF.

[0099] (15)

[0100] Since the fifth capacitor C5 is an input capacitor, its voltage ripple should be less than 0.2%. When operating at the maximum power point, the maximum voltage is 190V, the current is 2A, and the duty cycle is 0.6. According to formula (16), the value of the fifth capacitor C5 is at least 94.7368uF.

[0101] (16)

[0102] The sixth capacitor C6 is still an output capacitor. Since the output voltage is low, the ripple requirement is less than 1%. When the maximum power point is running, the maximum voltage is 64.41, the output current is 0.9A, and the duty cycle is 0.6. According to formula (17), the minimum value of the sixth capacitor C6 is 175.7812uF.

[0103] (17)

[0104] The seventh capacitor C7 is an input capacitor with a maximum value of only 40V and a ripple of less than 5%. According to formula (18), the value of the seventh input capacitor C7 must be greater than 460.375uF.

[0105] (18)

[0106] The fourth capacitor C4 is mainly used to filter out high-frequency noise, and its capacitance should be much smaller than the output capacitor. The capacitance value of C5 and C4 in parallel should not differ too much from that of C5. Therefore, the capacitance of the fourth capacitor C4 is selected to be one thousandth of that of C5.

[0107] Since the first inductor L1 needs to charge multiple capacitors, its capacity requirement is relatively large. The first inductor L1 is the input inductor, so the maximum current is 10A, the ripple rate is set to 0.4, and the maximum input voltage is 40V. According to formula (19), the inductance of the output first inductor L1 is calculated to be at least 0.3mH.

[0108] (19)

[0109] The second inductor L2 only supplies energy to the first output port Vout1, and the ripple rate is 0.4. According to formula (20), the inductance of the second inductor L2 is calculated to be at least 4.75 mH.

[0110] (20)

[0111] (The third inductor L3 is the output inductor. According to formula (21), it can be calculated that the minimum value of the third inductor L3 is 4.379 mH.

[0112] (twenty one)

[0113] (Based on the minimum value calculated above, considering the safety margin, long-term reliability and future scalability, the specific value is larger than the calculated value when selecting the model. The specific selection is shown in Table 1.

[0114] Table 1 Device selection

[0115]

[0116] According to the above formula, the reverse withstand voltage of the power switch and the diode can be calculated, and the input port V in The maximum voltage of the first output port is 40V. out1 Maximum current I out1 For 2A, the second output port V out2 The maximum current is 0.9A, and the specific selection is shown in Table 2:

[0117] Table 2 Calculation of voltage and current stress of switch tube and diode

[0118]

[0119] The input port is 40V, the first output port V out1 and the second output port V out2When the load is 100Ω, the efficiency is as follows Figure 7 As shown in the figure, the maximum efficiency is 94.59% and the efficiency is always above 88% when the duty cycle is between 0.1 and 0.8. When the duty cycle is lower than 0.5, the second output port V out2 To achieve step-down, when the duty cycle is lower than 0.2, the first output port V out1 To achieve voltage reduction. Figure 8 Shown is the step-down efficiency for duty cycles from 0.1% to 10%.

[0120] The first output port V out1 The output resistance is 100 ohms. When the output voltage is 147.3V, the output voltage ripple is 0.26V, the ripple rate is 0.18%, and the current ripple is 1.8%. When the output voltage is 771.5V, the voltage ripple is 1.6V, and the ripple rate is 0.2%. The first output port V out1 The output ripple rate is shown in Table 3. When the output resistance is 100Ω, the second output port V out2 The output voltage is 59.02V, the ripple is 0.09V, and the ripple rate is 1.5%. When the output voltage is 157.6V, the ripple voltage is 0.3V, and the voltage ripple rate is 1.9%. The second output port V out2 The output ripple rate is shown in Table 4.

[0121] Table 3 V out1 Voltage and current ripple

[0122]

[0123] Table 4 V out2 Voltage and current ripple

[0124]

[0125] When the input of the Buck-Boost converter is connected to the DC bus, the first output port V out1 and the second output port V out2 The tests under no-load condition are shown in Table 5.

[0126] Table 5 No-load test under DC source input state

[0127]

[0128] When the output resistance is 100 ohms, the open circuit voltage of the photovoltaic module is 47V and the short circuit current is 10A. Using a single photovoltaic module as the input source, the duty cycle and output voltage characteristics when the output resistance is 100 ohms are shown in Table 6. Table 7 is the test of 1000 ohm output resistance under the input state of a single photovoltaic module. After test comparison, it is found that the larger the output resistance, the greater the boost multiple of the Buck-Boost converter under the same duty cycle conditions.

[0129] Table 6 100 ohm output resistance test of a single photovoltaic module under input state

[0130]

[0131] Table 7 1000 ohm output resistance test of a single photovoltaic module under input state

[0132]

Claims

1. A photovoltaic greenhouse power conversion energy-saving device, characterized in that: The invention comprises a photovoltaic module, a microprocessor, a Buck-Boost converter, a temperature and humidity sensor, an auxiliary power supply, a voltage and current transmitter and a display. The photovoltaic module is respectively connected to the input port of the Buck-Boost converter and the auxiliary power supply, and the two output ports of the Buck-Boost converter are respectively connected to the inverter and the DC bus; the communication port of the microprocessor is connected to the display; the ADC port of the microprocessor is connected to the temperature and humidity sensor and the voltage and current transmitter; The Buck-Boost converter includes an input port V in , the first output port V out1 , the second output port V out2 , a first power switch S1, a second power switch S2, a third power switch S3, a first diode D1, a second diode D2, a third diode D3, a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6 and a seventh capacitor C7; The input port V in The positive electrode of the first inductor L1 is connected in parallel with the seventh capacitor C7, the positive electrode of the first inductor L1 is connected to the positive electrode of the seventh capacitor C7, the collector of the first switch tube S1 is connected to the negative electrode of the first inductor L1, and the emitter of the first switch tube S1 is connected to the negative electrode of the seventh capacitor C7; the anode of the first diode D1 is connected to the negative electrode of the first inductor L1, and the cathode of the first diode D1 is connected to the positive electrode of the first capacitor C1; the negative electrode of the first capacitor C1 is connected to the negative electrode of the seventh capacitor C7; the collector of the second switch tube S2 is connected to the positive electrode of the first capacitor C1, and the emitter of the second switch tube S2 is connected to the positive electrode of the second inductor L2; the positive electrode of the second capacitor C2 is connected to the negative electrode of the first inductor L1, and the negative electrode of the second capacitor C2 is connected to the negative electrode of the second inductor The anode of the second diode D2 is connected to the negative electrode of the second capacitor L2, and the cathode of the second diode D2 is connected to the positive electrode of the third capacitor C3; the negative electrode of the third capacitor C3 is connected to the negative electrode of the seventh capacitor C7, and the positive electrode of the third capacitor C3 is also connected to the positive electrode of the third inductor L3; the emitter of the third switch tube S3 is connected to the positive electrode of the inductor L2, and the collector of the third switch tube S3 is connected to the negative electrode of the third inductor L3; the positive electrode of the third inductor L3 is also connected to the cathode of the second diode D2, the anode of the third diode D3 is connected to the negative electrode of the third inductor L3, and the cathode of the third diode D3 is connected to the positive electrode of the fourth capacitor C4; the positive electrode of the fourth capacitor C4 is also connected to the first output port V out1 The positive electrode of the fourth capacitor C4 is connected to the positive electrode of the first output port V out1 The positive electrode of the fifth capacitor C5 is connected to the output port V out1 The positive electrode of the fifth capacitor C5 is connected to the output port V out1 The first output port V out1 The negative electrode of the first output port V out1 The positive electrode of the sixth capacitor C6 is also connected to the cathode of the third diode D3; the positive electrode of the sixth capacitor C6 is connected to the anode of the third diode D3, and the negative electrode of the sixth capacitor C6 is connected to the anode of the second diode D2; the second output port V out2 The positive electrode of the second output port V out2 The negative electrode of is connected to the negative electrode of the sixth capacitor C6.

2. The photovoltaic greenhouse power conversion energy-saving device according to claim 1 is characterized in that: The voltage stress and current stress to be borne by the first power switch S1, the second power switch S2 and the third power switch S3 are calculated by the following formulas, and the types are selected according to the calculation results: （1）； （2）； （3）； （4）； （5）； （6）； In the formula, d is the duty cycle of the power switch, V i is the maximum voltage of the input port, V S1 is the voltage stress of the first power switch S1, V S2 is the voltage stress of the second power switch S2, V S3 is the voltage stress of the third power switch S3, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, I S1 is the current stress of the first power switch S1, I S2 is the current stress of the second power switch S2, I S3 is the current stress of the third power switch S3.

3. The photovoltaic greenhouse power conversion energy-saving device according to claim 1 is characterized in that: The voltage stress and current stress to be borne by the first diode D1, the second diode D2 and the third diode D3 are calculated by the following formulas, and the types are selected according to the calculation results: （7）； （8）； （9）； （10）； （11）； （12）； In the formula, d is the duty cycle of the power switch, V i is the maximum voltage of the input port, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, V D1 is the voltage stress of the first diode D1, V D2 is the voltage stress of the second diode D2, V D3 is the voltage stress of the third diode D3, I D1 is the current stress of the first diode D1, I D2 is the current stress of the second diode D2, I D3 is the current stress of the third diode D3.

4. The photovoltaic greenhouse power conversion energy-saving device according to claim 1 is characterized in that: The first capacitor C1, the second capacitor C2, the third capacitor C3, the fifth capacitor C5, the sixth capacitor C6 and the seventh capacitor C7 are calculated by the following formula to have a minimum capacitance, and are selected according to the calculation results: （13）； （14）； （15）； （16）； （17）； （18）； In the formula is the duty cycle of the power switch, T S is the time of one cycle of PWM wave, V i is the maximum voltage of the input port, I in is the maximum current of the input port, V o1 is the maximum output voltage of the first output port, V o2 is the maximum output voltage of the second output port, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, R1, R2, R3, R5, R6, and R7 are the voltage ripple rates of C1, C2, C3, C5, C6, and C7 respectively, and f is the system operating frequency; The capacitance of the fourth capacitor C4 is selected to be one thousandth of that of C5.

5. The photovoltaic greenhouse power conversion energy-saving device according to claim 1 is characterized in that: The first inductor L1, the second inductor L2 and the third inductor L3 are calculated by the following formula to have a minimum inductance, and are selected according to the calculation results: （19）； （20）； （21）； In the formula, d is the duty cycle of the power switch, T S is the time of one cycle of PWM wave, V i is the maximum voltage of the input port, V o1 is the maximum output voltage of the first output port, V o2 is the maximum output voltage of the second output port, V L3 is the voltage across the third inductor L3, I out1 is the maximum output current of the first output port, I out2 is the maximum output current of the second output port, r1, r2, r3 are the current ripple coefficients of the first inductor L1, the second inductor L2 and the third inductor L3 respectively.

6. A method for photovoltaic greenhouse power conversion, using any device of claims 1 to 5, characterized in that: There are two stages in a PWM wave cycle output by the microprocessor, namely the switch tube conduction state and the switch tube closed state: Phase 1: The PWM wave output by the microprocessor is at a high potential, the first power switch S1, the second power switch S2 and the third power switch S3 are all closed, and the photovoltaic module is connected through the input port V in The first inductor L1 is charged, the first capacitor C1 and the second capacitor C2 are connected in series to charge the second inductor L2, the second capacitor C2 and the third capacitor C3 are connected in series to charge the third inductor L3 and the second inductor L2, and the sixth capacitor C6 is connected to the second output port V out2 The fourth capacitor C4 and the fifth capacitor C5 are connected to the first output port V out1 Output of energy; Phase 2: The PWM wave output by the microprocessor is at a low potential, the first power switch S1, the second power switch S2 and the third power switch S3 are all disconnected, and the photovoltaic module is connected through the input port V in The first inductor L1 is connected in series to charge the first capacitor C1, the second capacitor C2, and the third capacitor C3. The second inductor L2 and the third inductor L3 jointly charge the fifth capacitor C5 and the fourth capacitor C4 and the first output port V out1 The third inductor L3 alone provides energy to the sixth capacitor C6 and the second input port V out2 Provide energy.

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