阅读说明：本技术 一种高转换效率的光伏离网逆变器及其控制方法 (Photovoltaic off-grid inverter with high conversion efficiency and control method thereof ) 是由 黄明华 熊芸 周杨 于 2021-01-08 设计创作，主要内容包括：本发明公开了一种高转换效率的光伏离网逆变器,其包括所包括锂电池组、直流输入防反接电路、直流输入电压采样电路、直流母线开关电流波形校正电路、控制单元、全桥架构MOS管电路、高频矩形脉冲波产生电路、输出电压及频率检测电路、交流输出滤波电路及输出电流检测电路。本发明还公开一种控制方法。本发明结构简单、成本低、实用性强、稳定性强,本发明通过全桥架构MOS管电路及高频矩形脉冲波产生电路提高逆变器转换效率的同时,还能够有效降低其在空载状态下逆变器自损耗电流,在同等负载条件下减少锂电池组的放电电流,延长锂电池组的使用寿命。(The invention discloses a photovoltaic off-grid inverter with high conversion efficiency, which comprises a lithium battery pack, a direct current input anti-reverse connection circuit, a direct current input voltage sampling circuit, a direct current bus switch current waveform correction circuit, a control unit, a full-bridge framework MOS (metal oxide semiconductor) tube circuit, a high-frequency rectangular pulse wave generation circuit, an output voltage and frequency detection circuit, an alternating current output filter circuit and an output current detection circuit. The invention also discloses a control method. The inverter has the advantages of simple structure, low cost, strong practicability and strong stability, improves the conversion efficiency of the inverter through the full-bridge framework MOS tube circuit and the high-frequency rectangular pulse wave generating circuit, and can effectively reduce the self-loss current of the inverter in a no-load state, reduce the discharge current of the lithium battery pack under the same load condition and prolong the service life of the lithium battery pack.)

1. The utility model provides a photovoltaic of high conversion efficiency is from net inverter which characterized in that: the photovoltaic off-grid inverter with high conversion efficiency comprises a lithium battery pack, a direct current input reverse connection prevention circuit, a direct current input voltage sampling circuit, a direct current bus switch current waveform correction circuit, a control unit, a full-bridge framework MOS tube circuit, a high-frequency rectangular pulse wave generation circuit, an output voltage and frequency detection circuit, an alternating current output filter circuit and an output current detection circuit, wherein the direct current input reverse connection prevention circuit, the direct current input voltage sampling circuit, the direct current bus switch current waveform correction circuit, the full-bridge framework MOS tube circuit, the high-frequency rectangular pulse wave generation circuit, the output voltage and frequency detection circuit, the alternating current output filter circuit and the output current detection circuit are all connected with the control unit, the negative electrode of the lithium battery pack is connected with the direct current input reverse connection prevention circuit, and the positive electrode of the lithium battery pack is connected with the direct current input voltage sampling circuit, the direct current bus switch current waveform correction circuit is connected with the direct current input voltage sampling circuit, the full-bridge framework MOS tube circuit is connected with the direct current bus switch current waveform correction circuit, the high-frequency rectangular pulse wave generation circuit is arranged between the control unit and the full-bridge framework MOS tube circuit, and the alternating current output filter circuit is connected with the full-bridge framework MOS tube circuit.

2. The high conversion efficiency photovoltaic off-grid inverter of claim 1, wherein: the direct current input voltage sampling circuit comprises a resistor R12 and a resistor R13, the resistor R12 and the resistor R13 are connected in series to form a voltage dividing resistor group, the control unit is provided with a plurality of A/D sampling ports, the resistor R13 is connected with one of the A/D sampling ports, the direct current input voltage sampling circuit is clamped by the resistor R12 and the resistor R13 after sampling and is sent to the A/D sampling port of the control unit, and whether the input voltage is within a rated range or not is judged after analyzing the sampling voltage.

3. The high conversion efficiency photovoltaic off-grid inverter of claim 2, wherein: the full-bridge structure MOS tube circuit comprises a power frequency transformer, four bridge arms and two groups of switch tube groups, the power frequency voltage device comprises a primary side and a secondary side, the primary side and the secondary side are both provided with two connectors, the four bridge arms comprise a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm, the first bridge arm and the second bridge arm form a first bridge arm group, the third bridge arm and the second bridge arm are arranged diagonally to form a second bridge arm group, two groups of switch tube groups are respectively connected between the first bridge arm and the second bridge arm and between the third bridge arm and the fourth bridge arm, two groups of switch tube groups are respectively formed by two switch tubes, when the first bridge arm group and the second bridge arm group are alternately conducted, the two switching tubes on the same bridge arm group are complementarily conducted, the switching tubes are controlled by the driving pulse, the output voltage and current are controlled by the pulse width modulation of the high-frequency rectangular pulse wave generating circuit so as to achieve the purpose of adjusting power output.

4. The high conversion efficiency photovoltaic off-grid inverter of claim 3, wherein: the control unit is a single chip microcomputer control unit, the single chip microcomputer control unit is provided with a peripheral connecting circuit, the single chip microcomputer control unit adopts an MC9S08PA32 single chip microcomputer, the control unit is further provided with an MCU oscillation starting rear signal output end, the high-frequency rectangular pulse wave generating circuit is composed of the MCU oscillation starting rear signal output end and a connecting driving waveform converting circuit, and the waveform converting circuit is of a circuit structure with four groups of independent waveforms.

5. The high-conversion-efficiency photovoltaic off-grid inverter and the control method thereof according to claim 4, wherein: the direct current bus switch current waveform correction circuit comprises an inductor L1, the inductor L1 is connected in series at the midpoint of the primary side of the power frequency transformer and the two bridge arms of the upper half bridge, and the inductor L1 is an amorphous magnetic core material inductor.

6. The high conversion efficiency photovoltaic off-grid inverter of claim 5, wherein: output voltage and frequency detection circuit comprise output voltage sampling circuit, frequency sampling circuit and operational amplifier, operational amplifier with the control unit connects, output voltage sampling circuit is equipped with voltage detection unit and high resistance value resistance one, frequency sampling circuit is equipped with frequency detection unit and high resistance value resistance two, high resistance value resistance one is established ties by resistance R14 and resistance R15 and constitutes, high resistance value resistance two is established ties by resistance R16 and resistance R17 and constitutes, carries out the equal proportion through operational amplifier after high resistance value resistance one and high resistance value resistance two voltage divisions, and the AD sample connection of singlechip main control unit is surveyed the signal according to the sine wave and is measured.

7. The high conversion efficiency photovoltaic off-grid inverter of claim 3, wherein: the turn ratio between the primary side and the secondary side of the power frequency transformer is 16V:230V, a magnetic core is arranged in the power frequency transformer, the power of the magnetic core is 3000W, a resistor R18 is connected in series between the second bridge arm and the third bridge arm, the first bridge arm comprises an MOS tube Q4, a resistor R4 and a resistor R5, the second bridge arm comprises an MOS tube Q7, a resistor R10 and a resistor 11, the third bridge arm comprises an MOS tube Q5, a resistor R6 and a resistor R7, and the first bridge arm comprises an MOS tube Q6, a resistor R8 and a resistor R9.

8. The high conversion efficiency photovoltaic off-grid inverter of claim 7, wherein: the output current detection circuit comprises an output current sampling circuit and a system temperature sampling circuit, the output current sampling circuit is a series of alternating current mutual inductor T2 on the output end of the alternating current inversion, the alternating current mutual inductor T2 is provided with a resistor R18, when the output current detection circuit passes through a certain alternating current, the output end of the alternating current mutual inductor T2 generates a voltage drop after the induction current with equal proportion flows through a load resistor, the voltage drop is further amplified and then is sent to an A/D sampling port of a main control unit of the single chip microcomputer, the output current feedback is completed, the system temperature sampling circuit comprises a negative temperature coefficient thermistor, and the system temperature sampling circuit carries out voltage division sampling and then sends the voltage to the A/D sampling port of the single chip microcomputer to carry out signal measurement.

9. A control method to implement a high conversion efficiency photovoltaic off-grid inverter according to claims 1-8, characterized in that it comprises the following steps:

(1) the lithium battery pack is connected through a direct-current input end, the lithium battery pack is conducted after the polarity of the lithium battery pack is detected to be correct through a direct-current input anti-reverse connection circuit, a detection signal is sent to a main control unit of the single chip microcomputer after the direct-current input voltage sampling circuit passes through, and when the direct-current input voltage is detected within a rated input voltage range, the control unit conducts conduction control;

(2) the control unit sequentially sends two paths of high-frequency rectangular pulse wave drives and two paths of low-frequency square wave drives, and the high-frequency rectangular pulse wave signals enable the direct-current input voltage sampling circuit to be conducted to form a direct-current input voltage sampling circuit loop;

(3) the full-bridge framework MOS tube circuit acts simultaneously, an MOS tube Q4 and an MOS tube Q7 in the full-bridge framework MOS tube circuit form a geminate transistor, an MOS tube Q5 and an MOS tube Q6 form a geminate transistor to form a full-bridge switch, wherein two bridge arm groups on the diagonal line are alternately conducted, two switch tubes on the same bridge arm are conducted in a complementary manner, the switch tubes are controlled by driving pulses sent by a control unit, and output voltage and current are controlled through pulse width modulation of a high-frequency rectangular pulse wave generating circuit to realize power output regulation;

(4) meanwhile, the switching current of the direct-current bus terminal passes through Q4 and then is subjected to current waveform correction through the amorphous magnetic ring inductor L1, so that the voltage and current waveforms are kept consistent, the switching current waveform is corrected to be a sine waveform, meanwhile, the higher harmonic component is low, and the no-load loss of the magnetic core of the power frequency transformer is reduced;

(5) the secondary side of the power frequency transformer outputs pure sine waves after being filtered by a capacitor, the pure sine waves are sent to the control unit through the output current detection circuit for current detection, and meanwhile, the output current after being connected with the alternating current load is fed back to the control unit through the output current detection circuit to complete conversion of DC-AC energy and then output.

10. The control method according to claim 9, characterized in that the step (1) includes the steps of:

the direct current input anti-reverse-connection circuit is divided by a voltage dividing resistor, filtered by a capacitor and sent to a grid electrode of a P-channel MOS tube, when the P-channel MOS tube is conducted, the voltage of a lithium battery pack passes through the voltage dividing resistor to a voltage stabilizing tube and is clamped to +15V, the voltage of the +15V is used as a driving signal source for conducting or stopping the anti-reverse-connection MOS tube, when the polarity of the lithium battery pack is connected incorrectly, the P-channel MOS tube is always in a stopping state, and the voltage of the +15V does not exist; only when the polarity of the lithium battery pack is correctly connected, the P-channel MOS tube is conducted, and +15V voltage is generated, at the moment, the N-channel MOS tube is conducted, and the lithium battery pack is connected to the direct current input bus end through the N-channel MOS tube.

Technical Field

The invention relates to the technical field of power electronics, in particular to a photovoltaic off-grid inverter with high conversion efficiency and a control method thereof.

Background

The photovoltaic off-grid inverter power supply device is far superior to a high-frequency inverter in terms of load compatibility, so that the photovoltaic off-grid inverter power supply device is very excellent in terms of load compatibility, and is widely applied to various power supply occasions, such as computer equipment, household electrical appliances, lighting places and various industrial power utilization places. Nowadays, with the rapid development of new energy industries, a solar charging controller is combined with a power frequency inverter, and the solar charging controller is widely applied to off-grid photovoltaic systems. The photovoltaic inverter in the current market generally has low inversion efficiency which is far lower than a high-frequency inverter with the conversion efficiency of more than 90%. The reason is that the existing power frequency inverter adopts the design of an isolated magnetic core material, so that the direct current energy generates larger loss on the magnetic core in the process of alternating current energy conversion, and the problem can be solved only by adopting a high-frequency inverter, the existing high-frequency inverter has smaller self loss in the process of alternating current-direct current energy conversion, the overall inversion efficiency is higher, but the existing high-frequency inverter also has the following defects in the use process: 1. the inversion efficiency is low, and the average efficiency is only 80%; 2. the no-load current of a transformer in the existing inverter is large and reaches 3% of the current of a rated direct current end, and in a standby state, no-load power consumption causes great waste of battery energy, the endurance performance of the inverter is reduced, and the subsequent use efficiency is influenced; 3. because the power switch tube has higher junction temperature and large heat productivity during working, a large-area aluminum profile radiator and a large fan are needed for forced air cooling, the volume and the weight of the inverter are increased, and the inverter cannot be installed and used in a portable mode.

Disclosure of Invention

The invention provides a photovoltaic off-grid inverter with high conversion efficiency and a control method thereof, aiming at the defects of the prior art.

The technical scheme adopted by the invention for realizing the purpose is as follows:

a photovoltaic off-grid inverter with high conversion efficiency comprises a lithium battery pack, a direct current input anti-reverse connection circuit, a direct current input voltage sampling circuit, a direct current bus switch current waveform correction circuit, a control unit, a full-bridge framework MOS tube circuit, a high-frequency rectangular pulse wave generation circuit, an output voltage and frequency detection circuit, an alternating current output filter circuit and an output current detection circuit, wherein the direct current input anti-reverse connection circuit, the direct current input voltage sampling circuit, the direct current bus switch current waveform correction circuit, the full-bridge framework MOS tube circuit, the high-frequency rectangular pulse wave generation circuit, the output voltage and frequency detection circuit, the alternating current output filter circuit and the output current detection circuit are all connected with the control unit, the negative electrode of the lithium battery pack is connected with the direct current input anti-reverse connection circuit, and the positive electrode of the lithium battery pack is connected with the direct current input voltage sampling circuit, the direct current bus switch current waveform correction circuit is connected with the direct current input voltage sampling circuit, the full-bridge framework MOS tube circuit is connected with the direct current bus switch current waveform correction circuit, the high-frequency rectangular pulse wave generation circuit is arranged between the control unit and the full-bridge framework MOS tube circuit, and the alternating current output filter circuit is connected with the full-bridge framework MOS tube circuit.

The direct current input voltage sampling circuit is further improved and comprises a resistor R12 and a resistor R13, the resistor R12 and the resistor R13 are connected in series to form a voltage dividing resistor group, the control unit is provided with a plurality of A/D sampling ports, the resistor R13 is connected with one of the A/D sampling ports, the direct current input voltage sampling circuit is clamped by the resistor R12 and the resistor R13 after sampling and then is sent to the A/D sampling port of the control unit, and whether the input voltage is within a rated range or not is judged after analyzing the sampling voltage.

The improved full-bridge structure MOS tube circuit comprises a power frequency transformer, four bridge arms and two groups of switch tube groups, wherein the power frequency transformer comprises a primary side and a secondary side, the primary side and the secondary side are respectively provided with two connectors, the four bridge arms comprise a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm, the first bridge arm and the second bridge arm form a first bridge arm group, the third bridge arm and the second bridge arm are diagonally arranged to form a second bridge arm group, the two groups of switch tube groups are respectively connected between the first bridge arm and the second bridge arm and between the third bridge arm and the fourth bridge arm, the two groups of switch tube groups are respectively formed by two switch tubes, when the first bridge arm group and the second bridge arm group are alternately conducted, the two switch tubes on the same bridge arm group are complementarily conducted, the switch tubes are controlled by driving pulses, and output voltage and current are controlled by pulse width modulation of a high-frequency rectangular, to achieve the purpose of adjusting power output.

The control unit is a single chip microcomputer control unit, the single chip microcomputer control unit is provided with a peripheral connecting circuit, the single chip microcomputer control unit adopts an MC9S08PA32 single chip microcomputer, the control unit is further provided with an MCU oscillation starting rear signal output end, the high-frequency rectangular pulse wave generating circuit is composed of the MCU oscillation starting rear signal output end and a connecting driving waveform converting circuit, the waveform converting circuit is of a circuit structure with four groups of independent waveforms, the single chip microcomputer control unit is provided with high-speed ADC conversion and 16 channels and 12 bits, the wide input voltage of the single chip microcomputer control unit is 2.7V to 5.5VDC, and the highest main frequency is 20 MHZ.

The direct current bus switch current waveform correction circuit is further improved to comprise an inductor L1, the inductor L1 is connected in series at the middle points of the primary side of the power frequency transformer and two bridge arms of an upper half bridge, the inductor L1 is an amorphous magnetic core material inductor, and the direct current bus switch current waveform correction circuit can effectively correct the switch current waveform of a direct current bus end by adjusting the inductance of the inductor L1 under the state of the switching frequency of 20KHZ, so that the switch current waveform is consistent with the switch voltage waveform, a sinusoidal current waveform with small harmonic component and small waveform distortion is generated.

The improved sine wave signal detection circuit is characterized in that the output voltage and frequency detection circuit is composed of an output voltage sampling circuit, a frequency sampling circuit and an operational amplifier, the operational amplifier is connected with the control unit, the output voltage sampling circuit is provided with a voltage detection unit and a first high-resistance resistor, the frequency sampling circuit is provided with a frequency detection unit and a second high-resistance resistor, the first high-resistance resistor is formed by serially connecting a resistor R14 and a resistor R15, the second high-resistance resistor is formed by serially connecting a resistor R16 and a resistor R17, the first high-resistance resistor and the second high-resistance resistor divide voltage and then amplify in equal proportion through the operational amplifier, and an A/D sampling port of the singlechip main control unit measures sine wave signals to be detected.

The power frequency transformer is further improved, the turn ratio between the primary side and the secondary side of the power frequency transformer is 16V:230V, a magnetic core is arranged in the power frequency transformer, the power of the magnetic core is 3000W, a resistor R18 is connected in series between the second bridge arm and the third bridge arm, the first bridge arm comprises an MOS tube Q4, a resistor R4 and a resistor R5, the second bridge arm comprises an MOS tube Q7, a resistor R10 and a resistor 11, the third bridge arm comprises an MOS tube Q5, a resistor R6 and a resistor R7, and the first bridge arm comprises an MOS tube Q6, a resistor R8 and a resistor R9.

The output current detection circuit comprises an output current sampling circuit and a system temperature sampling circuit, the output current sampling circuit is an alternating current transformer T2 serially connected to the output end of the alternating current inverter, the alternating current transformer T2 is provided with a resistor R18, when a certain alternating current flows through the output current detection circuit, induced currents in equal proportion to the induced currents generated at the output end of the transformer T2 are generated and then are subjected to voltage drop through a load resistor, the induced currents are further amplified and then are sent to an A/D sampling port of a single chip microcomputer main control unit, output current feedback is completed, the system temperature sampling circuit is composed of a negative temperature coefficient thermistor, and the system temperature sampling circuit performs voltage division sampling and then sends the signals to the A/D sampling port of the single chip microcomputer for signal measurement.

In a further improvement, a method for controlling an off-grid photovoltaic inverter with high conversion efficiency includes the following steps:

(1) the lithium battery pack is connected through a direct-current input end, the lithium battery pack is conducted after the polarity of the lithium battery pack is detected to be correct through a direct-current input anti-reverse connection circuit, a detection signal is sent to a main control unit of the single chip microcomputer after the direct-current input voltage sampling circuit passes through, and when the direct-current input voltage is detected within a rated input voltage range, the control unit conducts conduction control;

(2) the control unit sequentially sends two paths of high-frequency rectangular pulse wave drives and two paths of low-frequency square wave drives, and the high-frequency rectangular pulse wave signals enable the direct-current input voltage sampling circuit to be conducted to form a direct-current input voltage sampling circuit loop;

(3) the full-bridge framework MOS tube circuit acts simultaneously, an MOS tube Q4 and an MOS tube Q7 in the full-bridge framework MOS tube circuit form a geminate transistor, an MOS tube Q5 and an MOS tube Q6 form a geminate transistor to form a full-bridge switch, wherein two bridge arm groups on the diagonal line are alternately conducted, two switch tubes on the same bridge arm are conducted in a complementary manner, the switch tubes are controlled by driving pulses sent by a control unit, and output voltage and current are controlled through pulse width modulation of a high-frequency rectangular pulse wave generating circuit to realize power output regulation;

(4) meanwhile, the switching current of the direct-current bus terminal passes through Q4 and then is subjected to current waveform correction through the amorphous magnetic ring inductor L1, so that the voltage and current waveforms are kept consistent, the switching current waveform is corrected to be a sine waveform, meanwhile, the higher harmonic component is low, and the no-load loss of the magnetic core of the power frequency transformer is reduced;

(5) the secondary side of the power frequency transformer outputs pure sine waves after being filtered by a capacitor, the pure sine waves are sent to the control unit through the output current detection circuit for current detection, and meanwhile, the output current after being connected with the alternating current load is fed back to the control unit through the output current detection circuit to complete conversion of DC-AC energy and then output.

In a further improvement, the step (1) comprises the following steps:

the direct current input anti-reverse-connection circuit is divided by a voltage dividing resistor, filtered by a capacitor and sent to a grid electrode of a P-channel MOS tube, when the P-channel MOS tube is conducted, the voltage of a lithium battery pack passes through the voltage dividing resistor to a voltage stabilizing tube and is clamped to +15V, the voltage of the +15V is used as a driving signal source for conducting or stopping the anti-reverse-connection MOS tube, when the polarity of the lithium battery pack is connected incorrectly, the P-channel MOS tube is always in a stopping state, and the voltage of the +15V does not exist; only when the polarity of the lithium battery pack is correctly connected, the P-channel MOS tube is conducted, and +15V voltage is generated, at the moment, the N-channel MOS tube is conducted, and the lithium battery pack is connected to the direct current input bus end through the N-channel MOS tube.

The invention has the beneficial effects that: the invention has simple structure, low cost, strong practicability and strong stability; according to the photovoltaic off-grid inverter with high conversion efficiency, the photovoltaic off-grid inverter is provided with the direct current input reverse-connection preventing circuit, the direct current input voltage sampling circuit, the direct current bus switch current waveform correcting circuit, the control unit, the full-bridge framework MOS tube circuit, the high-frequency rectangular pulse wave generating circuit, the output voltage and frequency detecting circuit, the alternating current output filter circuit and the output current detecting circuit, so that the no-load power consumption of the photovoltaic off-grid inverter is reduced to be lower than 1% of the rated input current in the process of DC-AC energy conversion, the conversion rate is improved, the conversion efficiency of the photovoltaic off-grid inverter is enabled to reach 93%, and the volume of an aluminum profile radiator can be effectively reduced; the output voltage and current are controlled by arranging a full-bridge framework MOS tube circuit to be matched with the driving pulse control of the control unit and by the pulse width modulation of the high-frequency rectangular pulse wave generating circuit, so that the purpose of adjusting power output is achieved, and the requirement of high conversion efficiency of the existing electric energy conversion is met; the invention can effectively reduce the self-loss current of the inverter in the no-load state while improving the conversion efficiency of the inverter, reduce the discharge current of the lithium battery pack under the same load condition and prolong the service life of the lithium battery pack.

The invention is further described with reference to the following detailed description and accompanying drawings.

Drawings

Fig. 1 is a schematic diagram of a circuit principle framework of a photovoltaic off-grid inverter with high conversion efficiency according to the present embodiment;

fig. 2 is a schematic circuit diagram of a part of circuit connections in the high conversion efficiency photovoltaic off-grid inverter of the present embodiment.

In the figure: 1. the photovoltaic off-grid inverter comprises a photovoltaic off-grid inverter with high conversion efficiency, 2, a lithium battery pack, 3, a direct current input anti-reverse connection circuit, 4, a direct current input voltage sampling circuit, 5, a direct current bus switch current waveform correction circuit, 6, a control unit, 7, a full-bridge framework MOS (metal oxide semiconductor) tube circuit, 8, a high-frequency rectangular pulse wave generating circuit, 9, an output voltage and frequency detection circuit, 10, an alternating current output filter circuit, 11, an output current detection circuit, 70, a power frequency transformer, 110, an output current sampling circuit and 111, a system temperature sampling circuit.

Detailed Description

The following description is only a preferred embodiment of the present invention, and does not limit the scope of the present invention.

In the embodiment, referring to fig. 1-2, a photovoltaic off-grid inverter 1 with high conversion efficiency comprises a lithium battery pack 2, a dc input reverse-connection preventing circuit 3, a dc input voltage sampling circuit 4, a dc bus switch current waveform correcting circuit 5, a control unit 6, a full-bridge structure MOS transistor circuit 7, a high-frequency rectangular pulse wave generating circuit 8, an output voltage and frequency detecting circuit 9, an ac output filter circuit 10 and an output current detecting circuit 11, wherein the dc input reverse-connection preventing circuit 3, the dc input voltage sampling circuit 4, the dc bus switch current waveform correcting circuit 5, the full-bridge structure MOS transistor circuit 7, the high-frequency rectangular pulse wave generating circuit 8, the output voltage and frequency detecting circuit 9, the ac output filter circuit 10 and the output current detecting circuit 11 are all connected with the control unit 6, a negative electrode of the lithium battery pack 2 is connected with the dc input reverse-connection preventing circuit 3, the positive pole of lithium cell group 2 with direct current input voltage sampling circuit 4 is connected, direct current bus switch current waveform correction circuit 5 with direct current input voltage sampling circuit 4 is connected, full-bridge framework MOS transistor circuit 7 with direct current bus switch current waveform correction circuit 5 is connected, high frequency rectangular pulse wave produces circuit 8 and sets up between control unit 6 and the full-bridge framework MOS transistor circuit 7, exchange output filter circuit 10 with full-bridge framework MOS transistor circuit 7 is connected.

The direct current input voltage sampling circuit 4 comprises a resistor R12 and a resistor R13, the resistor R12 and the resistor R13 are connected in series to form a voltage dividing resistor group, the control unit 6 is provided with a plurality of A/D sampling ports, the resistor R13 is connected with one of the A/D sampling ports, the direct current input voltage sampling circuit 4 is clamped by the resistor R12 and the resistor R13 after sampling and is sent to the A/D sampling port of the control unit 6, and whether the input voltage is within a rated range or not is judged after analyzing the sampling voltage.

The full-bridge framework MOS tube circuit 7 comprises a power frequency transformer 70, four bridge arms and two groups of switch tube groups, wherein the power frequency transformer 70 comprises an original side and a secondary side, the original side and the secondary side are respectively provided with two joints, the four bridge arms 71 comprise a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm, the first bridge arm and the second bridge arm form a first bridge arm group, the third bridge arm and the second bridge arm are diagonally arranged to form a second bridge arm group, the two groups of switch tube groups are respectively connected between the first bridge arm and the second bridge arm and between the third bridge arm and the fourth bridge arm, the two groups of switch tube groups are respectively formed by two switch tubes, when the first bridge arm group and the second bridge arm group are alternately conducted, the two switch tubes on the same bridge arm group are complementarily conducted, the switch tubes are controlled by driving pulses, and output voltage and current are controlled by pulse width modulation of a high, the industrial frequency transformer 70 is wound by an annular magnetic core, has high electrical efficiency, no air gap in the iron core, small magnetic leakage, strong interference resistance and a stacking coefficient of more than 95 percent.

The control unit 6 is a single-chip microcomputer control unit, the single-chip microcomputer control unit I is provided with a peripheral connecting circuit, the single-chip microcomputer control unit adopts an MC9S08PA32 single-chip microcomputer, the control unit 6 is further provided with an MCU oscillation starting rear signal output end, the high-frequency rectangular pulse wave generating circuit 8 is composed of an MCU oscillation starting rear signal output end and a connection driving waveform conversion circuit, the waveform conversion circuit is of a circuit structure with four groups of independent waveforms, the single-chip microcomputer control unit is provided with high-speed ADC conversion and 16 channels and 12 positions, the wide input voltage of the single-chip microcomputer control unit is 2.7V to 5.5VDC, and the highest main frequency is 20 MHZ.

The direct current bus switch current waveform correction circuit 5 comprises an inductor L1, the inductor L1 is connected in series at the primary side of the power frequency transformer 70 and the midpoint of two bridge arms of an upper half bridge, the inductor L1 is an amorphous magnetic core material inductor, and the direct current bus switch current waveform correction circuit 5 can effectively correct the switch current waveform of a direct current bus end by adjusting the inductance of the inductor L1 under the state of the switching frequency of 20KHZ, so that the switch current waveform is kept consistent with the switch voltage waveform, a sinusoidal current waveform with small harmonic component and small waveform distortion is generated, the reactive loss is reduced, and the no-load loss current is reduced.

Output voltage and frequency detection circuit 9 comprises output voltage sampling circuit, frequency sampling circuit and operational amplifier, operational amplifier with the control unit connects, output voltage sampling circuit is equipped with voltage detection unit and high resistance value resistance one, frequency sampling circuit is equipped with frequency detection unit and high resistance value resistance two, high resistance value resistance one is established ties by resistance R14 and resistance R15 and constitutes, high resistance value resistance two is established ties by resistance R16 and resistance R17 and constitutes, carries out the equal proportion through operational amplifier after high resistance value resistance one and high resistance value resistance two partial pressures, and the AD sample connection of singlechip main control unit is surveyed the signal according to the sine wave and is measured.

The turn ratio between the primary side and the secondary side of the power frequency transformer 70 is 16V:230V, a magnetic core is arranged in the power frequency transformer 70, the power of the magnetic core is 3000W, a resistor R18 is connected in series between the second bridge arm and the third bridge arm, the first bridge arm comprises an MOS tube Q4, a resistor R4 and a resistor R5, the second bridge arm comprises an MOS tube Q7, a resistor R10 and a resistor 11, the third bridge arm comprises an MOS tube Q5, a resistor R6 and a resistor R7, and the first bridge arm comprises an MOS tube Q6, a resistor R8 and a resistor R9.

The output current detection circuit 11 comprises an output current sampling circuit 110 and a system temperature sampling circuit 111, wherein the output current sampling circuit 110 is an alternating current transformer T2 serially connected to the output end of the alternating current inverter, the alternating current transformer T2 is provided with a resistor R18, when the output current detection circuit passes through a certain alternating current, an equal proportion of induced electricity generated at the output end of the alternating current transformer T2 flows through a load resistor to generate voltage drop, the voltage drop is further amplified and then sent to an A/D sampling port of a main control unit of the single chip microcomputer to complete output current feedback, the system temperature sampling circuit 111 is composed of a negative temperature coefficient thermistor, and the system temperature sampling circuit 111 performs voltage division sampling and then sends the voltage-sampled voltage to the A/D sampling port of the single chip.

A control method for implementing a photovoltaic off-grid inverter with high conversion efficiency comprises the following steps:

(1) the lithium battery pack is connected through a direct-current input end, the lithium battery pack is conducted after the polarity of the lithium battery pack is detected to be correct through a direct-current input anti-reverse connection circuit, a detection signal is sent to a main control unit of the single chip microcomputer after the direct-current input voltage sampling circuit passes through, and when the direct-current input voltage is detected within a rated input voltage range, the control unit conducts conduction control;

(2) the control unit sequentially sends two paths of high-frequency rectangular pulse wave drives and two paths of low-frequency square wave drives, and the high-frequency rectangular pulse wave signals enable the direct-current input voltage sampling circuit to be conducted to form a direct-current input voltage sampling circuit loop;

(3) the full-bridge framework MOS tube circuit acts simultaneously, an MOS tube Q4 and an MOS tube Q7 in the full-bridge framework MOS tube circuit form a geminate transistor, an MOS tube Q5 and an MOS tube Q6 form a geminate transistor to form a full-bridge switch, wherein two bridge arm groups on the diagonal line are alternately conducted, two switch tubes on the same bridge arm are conducted in a complementary manner, the switch tubes are controlled by driving pulses sent by a control unit, and output voltage and current are controlled through pulse width modulation of a high-frequency rectangular pulse wave generating circuit to realize power output regulation;

(4) meanwhile, the switching current of the direct-current bus terminal passes through Q4 and then is subjected to current waveform correction through the amorphous magnetic ring inductor L1, so that the voltage and current waveforms are kept consistent, the switching current waveform is corrected to be a sine waveform, meanwhile, the higher harmonic component is low, and the no-load loss of the magnetic core of the power frequency transformer is reduced;

(5) the secondary side of the power frequency transformer outputs pure sine waves after being filtered by a capacitor, the pure sine waves are sent to the control unit through the output current detection circuit for current detection, and meanwhile, the output current after being connected with the alternating current load is fed back to the control unit through the output current detection circuit to complete conversion of DC-AC energy and then output.

The step (1) comprises the following steps: the direct current input anti-reverse-connection circuit is divided by a voltage dividing resistor, filtered by a capacitor and sent to a grid electrode of a P-channel MOS tube, when the P-channel MOS tube is conducted, the voltage of a lithium battery pack passes through the voltage dividing resistor to a voltage stabilizing tube and is clamped to +15V, the voltage of the +15V is used as a driving signal source for conducting or stopping the anti-reverse-connection MOS tube, when the polarity of the lithium battery pack is connected incorrectly, the P-channel MOS tube is always in a stopping state, and the voltage of the +15V does not exist; only when the polarity of the lithium battery pack is correctly connected, the P-channel MOS tube is conducted, and +15V voltage is generated, at the moment, the N-channel MOS tube is conducted, and the lithium battery pack is connected to the direct current input bus end through the N-channel MOS tube.

The invention has simple structure, low cost, strong practicability and strong stability; according to the photovoltaic off-grid inverter with high conversion efficiency, the photovoltaic off-grid inverter is provided with the direct current input reverse-connection preventing circuit, the direct current input voltage sampling circuit, the direct current bus switch current waveform correcting circuit, the control unit, the full-bridge framework MOS tube circuit, the high-frequency rectangular pulse wave generating circuit, the output voltage and frequency detecting circuit, the alternating current output filter circuit and the output current detecting circuit, so that the no-load power consumption of the photovoltaic off-grid inverter is reduced to be lower than 1% of the rated input current in the process of DC-AC energy conversion, the conversion rate is improved, the conversion efficiency of the photovoltaic off-grid inverter is enabled to reach 93%, and the volume of an aluminum profile radiator can be effectively reduced; through setting up full-bridge framework MOS pipe circuit cooperation the drive pulse control of control unit, control output voltage and electric current through the pulse width modulation of high frequency rectangular pulse wave generating circuit to reach the purpose of regulation power output, satisfy current electric energy conversion's high conversion efficiency's requirement.

The present invention is not limited to the above embodiments, and other off-grid photovoltaic inverters with high conversion efficiency and control methods thereof, which are obtained by using the same or similar structures, devices, processes or methods as those of the above embodiments of the present invention, are within the protection scope of the present invention.