A protection system for a photovoltaic power generation device and an implementation method thereof

Abstract

The present application discloses a protection system for a photovoltaic power generation device and an implementation method thereof, belonging to the technical field of battery panel protection circuits in photovoltaic power supply. It includes a voltage monitoring unit, a temperature control unit, a forward wiring unit, a reverse wiring unit, and a main circuit unit. The voltage monitoring unit is connected to the temperature control unit, the forward wiring unit, the reverse wiring unit, and the main circuit unit. A diode D2 and a diode D1 are connected in series between the forward wiring unit and the reverse wiring unit. The negative electrode of diode D1 and the positive electrode of diode D2 are connected to the forward wiring unit, and the positive electrode of diode D1 and the negative electrode of diode D2 are connected to the reverse wiring unit. It has the functions of automatically identifying the positive and negative poles of the photovoltaic panel, overvoltage protection, undervoltage protection, overheat protection, and shielding lightning pulse interference. During the wiring process of the photovoltaic panel in the installation process of the photovoltaic power generation device, there is no need to distinguish between the positive and negative poles, and the positive and negative poles of the photovoltaic panel can be automatically switched to adapt to the polarity of the inverter.

Description

Technical Field

[0001] The invention discloses a protection system for a photovoltaic power generation device and an implementation method thereof, belonging to the technical field of battery panel protection circuits in photovoltaic power supply. Background Art

[0002] Solar energy has become the focus of attention due to its unique advantages. The abundant solar radiation is an important energy source, which is inexhaustible, pollution-free, cheap, and freely available to humans. The energy of solar energy reaching the ground every second is as high as 800 megawatt-hours. If 0.1% of the solar energy on the earth's surface is converted into electrical energy, with a conversion rate of 5%, the annual power generation can reach 5.6×1012 kilowatt-hours, which is equivalent to 40 times the world's energy consumption. It is precisely because of these unique advantages of solar energy that after the 1980s, the application scope of photovoltaic power generation systems has become increasingly broad and the market scale has gradually expanded.

[0003] The main components of a photovoltaic power generation system are photovoltaic panels and inverters. Photovoltaic panels generate direct current of a certain power, which is then adjusted in voltage by the inverter and then used directly or incorporated into the national grid.

[0004] When the photovoltaic panels are connected, if the positive and negative poles are connected in reverse, it will cause a short circuit and damage or failure of the inverter. Photovoltaic panels are composed of multiple low-voltage panel units connected in series and parallel. Due to wiring errors and other reasons, the output voltage of the photovoltaic panels may be higher than the rated voltage of the inverter (overvoltage), which will cause damage or failure of the inverter; when the output voltage of the photovoltaic panels is lower than the inverter voltage (undervoltage), long-term operation will cause damage or failure of the inverter.

[0005] Due to reasons such as excessive load current, the internal temperature of the inverter will rise abnormally. Long-term operation will cause the internal circuit components of the inverter to become unreliable and damaged.

[0006] Moreover, photovoltaic panels are installed outdoors, and the electromagnetic interference pulses caused by lightning will interfere with the normal operation of the inverter and pose a safety threat to the user's load.

[0007] In order to protect the stable operation of the photovoltaic power generation system and the safety of equipment, certain protection measures need to be taken, including reverse connection protection, overvoltage protection, undervoltage protection, overheating protection, shielding of lightning pulse interference, etc.

[0008] The protection devices such as reverse connection protection, overvoltage protection, undervoltage protection, etc. of the photovoltaic power generation system in the prior art have the problems of energy consumption, inaccurate protection range, slow response, etc.

[0009] 1. In the prior art, the method for preventing reverse polarity connection is to connect a high-power diode in series in the circuit. By utilizing the unidirectional conduction of the diode, when the polarity is reversed, no current passes through the circuit and the circuit does not work. Since the diode has a forward voltage drop of 0.7V, in a high-power state (such as several hundred amperes of current), the diode itself consumes a large amount of power and generates serious heat. This not only wastes energy, but also in the case of poor heat dissipation, the diode is prone to overheating and burning out.

[0010] 2. In the prior art, overvoltage protection is achieved by an electromagnetic tripping mechanism to monitor the voltage. When the voltage is higher than the rated value, the electromagnetic force increases to drive the armature to mechanically trip and cut off the power supply. The operating voltage range is not precise and the response is slow. It will only operate when the overvoltage exceeds the allowable range by a large margin, and it will trip after several seconds or even more than ten seconds. By this time, certain damage has already been caused to the photovoltaic circuit components.

[0011] 3. In the prior art, undervoltage protection is achieved by an electromagnetic relay to monitor the voltage. When the voltage is lower than the rated value, the suction force of the electromagnetic relay coil becomes smaller, making it impossible to maintain the contact suction, thus cutting off the power supply. The operating voltage range is not precise and the response is slow. In the case of a large voltage drop, it still maintains the suction state and fails to achieve the protection effect.

[0012] 4. In the prior art, overheat protection is achieved by a thermal relay to monitor the load current. When the load current is too large, after a period of time, the thermal relay operates to disconnect and cut off the power supply. There is a time lag. When the overload occurs for more than ten seconds, the thermal relay will operate, which will cause irreversible damage to the inverter.

[0013] 5. In the prior art, only a lightning protection device is installed, and there is no special protection measure against lightning pulse interference, resulting in unstable operation of the inverter during thunderstorms. Summary of the Invention

[0014] The technical problem to be solved by the present invention is to provide a protection system for a photovoltaic power generation device with the functions of automatically identifying the positive and negative poles of photovoltaic panels, overvoltage protection, undervoltage protection, overheat protection, and shielding lightning pulse interference, which can automatically switch the positive and negative poles of the photovoltaic panels to adapt to the polarity of the inverter during the wiring process of the photovoltaic panels in the installation of the photovoltaic power generation device, without the need to distinguish the positive and negative poles.

[0015] To solve the above technical problems, the present invention adopts the following technical solutions:

[0016] A protection system for a photovoltaic power generation device, comprising a voltage monitoring unit, a temperature control unit, a forward connection unit, a reverse connection unit, and a main circuit unit. The voltage monitoring unit is connected to the temperature control unit, the forward connection unit, the reverse connection unit, and the main circuit unit. A diode D2 and a diode D1 are connected in series between the forward connection unit and the reverse connection unit. The negative electrode of diode D1 and the positive electrode of diode D2 are connected to the forward connection unit, and the positive electrode of diode D1 and the negative electrode of diode D2 are connected to the reverse connection unit.

[0017] Further, the voltage monitoring unit includes a voltage monitor. The voltage detector is connected to terminal A and terminal B of the output power supply of the photovoltaic panel. Terminal A is connected to one end of the start button SB1, one end of the auxiliary normally open contact KM1-1 of the 1# contactor, and one end of the auxiliary normally open contact KM1-2 of the 2# contactor. The other end of the start button SB1, the other end of the auxiliary normally open contact KM1-1 of the 1# contactor, and the other end of the auxiliary normally open contact KM1-2 of the 2# contactor are connected to the positive electrode of diode D1. Terminal B is connected to the positive electrode of diode D2.

[0018] Further, the forward connection unit includes a varistor VDR1. One end of the varistor VDR1 is connected to the negative electrode of diode D1. The other end of the varistor VDR1 is connected to one end of a resistor R1. The other end of the resistor R1 is connected to one end of a resistor R2, one end of a capacitor C1, and the K pole of a thyristor SCR1. The G pole of the thyristor SCR1, the other end of the resistor R2, and the other end of the capacitor C1 are connected to the positive electrode of diode D2. The A pole of the thyristor SCR1 is connected to one end of a resistor R4, the positive electrode of a diode D3, and one end of a resistor R3. The other end of the resistor R3 is connected to the negative electrode of diode D1. The other end of the resistor R4 is connected to the positive electrode of diode D2. The negative electrode of the diode D3 is connected to the base of a triode Q1. The collector of the triode Q1 is connected to one end of the 1# contactor coil KM1-0. The other end of the 1# contactor coil KM1-0 is connected to the negative electrode of diode D1. The emitter of the triode Q1 is connected to the positive electrode of diode D2.

[0019] Further, the reverse connection unit includes a varistor VDR2. One end of the varistor VDR2 is connected to the negative electrode of a diode D2. The other end of the varistor VDR2 is connected to one end of a resistor R6. The other end of the resistor R6 is connected to one end of a resistor R5, one end of a capacitor C2, and the K pole of a thyristor SCR2. The G pole of the thyristor SCR2, the other end of the resistor R5, and the other end of the capacitor C2 are connected to the positive electrode of a diode D1. The A pole of the thyristor SCR2 is connected to one end of a resistor R8, the positive electrode of a diode D4, and one end of a resistor R7. The other end of the resistor R8 is connected to the negative electrode of the diode D2. The other end of the resistor R7 is connected to the positive electrode of the diode D1. The negative electrode of the diode D4 is connected to the base of a triode Q2. The collector of the triode Q2 is connected to one end of the 2# contactor coil KM2-0. The other end of the 2# contactor coil KM2-0 is connected to the negative electrode of the diode D2. The emitter of the triode Q2 is connected to the positive electrode of the diode D1.

[0020] Further, the temperature control unit includes a thermistor PTC1 and a thermistor PTC2. One end of the thermistor PTC1 is connected to one end of a resistor R11, one end of a capacitor C3, and the comparison voltage input terminal of an operational amplifier COPOP1. The other end of the resistor R11 is connected to terminal A. The other end of the thermistor PTC1 is connected to one end of the thermistor PTC2. The other end of the thermistor PTC2 and the other end of the capacitor C3 are grounded. The reference voltage input terminal of the operational amplifier COPOP1 is connected to one end of a resistor R9, one end of a resistor R10, and one end of a capacitor C4. The other end of the resistor R9 is connected to terminal A. The other end of the capacitor C and the other end of the resistor R10 are connected to terminal B. The output terminal of the operational amplifier COPOP1 is connected to the G pole of a field effect transistor FET1. The D pole of the field effect transistor FET1 is connected to one end of the coil KM3-0 of the 3# contactor. The other end of the coil KM3-0 of the 3# contactor is connected to one end of the main normally open contact KM3-2 of the 3# contactor and is connected to terminal A. The other end of the main normally open contact KM3-2 of the 3# contactor is connected to the main circuit unit.

[0021] Further, the main circuit unit includes the main normally open contact KM1-2 of the 1# contactor and the main normally open contact KM2-2 of the 2# contactor. One end of the main normally open contact KM1-2 of the 1# contactor and one end of the main normally open contact KM2-2 of the 2# contactor are both connected to the other end of the main normally open contact KM3-2 of the 3# contactor. The other end of the main normally open contact KM1-2 of the 1# contactor is respectively connected to terminal A and terminal B;

[0022] The main circuit unit further includes a capacitor C5. One end of the capacitor C5 is connected to one end of an inductor L1 and the positive extreme point A. The other end of the capacitor C5 is connected to terminal B. The other end of the inductor L1 is connected to one end of a capacitor C6, one end of a resistor R12, and one end of an inverter INV. The other end of the capacitor C6 is connected to terminal B. The other end of the resistor R12 is connected to the negative electrode of a diode D5. The positive electrode of the diode D5 is connected to terminal B. The other end of the inverter INV is connected to terminal B.

[0023] A method for implementing a protection system of a photovoltaic power generation device, including a forward wiring working process and a reverse wiring working process. The forward wiring working process includes the following steps:

[0024] The output power supply of the photovoltaic panel is connected to terminal A and terminal B. When the wiring method of the photovoltaic panel is positive connection, that is, terminal A is the positive pole and terminal B is the negative pole, press the start button SB1, the current flows in through terminal A and out through terminal B. Through the unidirectional conduction of the diode, diode D1 makes the forward wiring unit work; diode D2 makes the reverse connection control unit not work;

[0025] When the voltage between terminal A and terminal B is the rated value, after being divided by resistors R3 and R4, the voltage across resistor R4 provides a bias voltage U for the base and emitter of transistor Q1 through diode D3. At the same time, a base current i is provided for transistor Q1 through resistor R3. Under the condition that the bias voltage U is greater than the conduction voltage of the PN junction of transistor Q1 and the base current i of transistor Q1 reaches the saturation current, transistor Q1 conducts, and the resistance between its collector and emitter approaches zero. The coil KM1-0 of the 1# contactor is energized and attracted, and the auxiliary normally open contact KM1-1 of the 1# contactor closes. The forward wiring unit is self-powered through the auxiliary normally open contact KM1-1. Even if the start button SB1 is released, the forward wiring unit will not lose power;

[0026] When the voltage between terminal A and terminal B is the rated value, the resistance value of varistor VDR1 approaches infinity, the voltage across capacitor C1 is not fully charged and approaches zero, the voltage between the control electrode and the negative pole of thyristor SCR1 approaches zero, and thyristor SCR1 is in the cut-off state; Resistor R2 is connected in parallel across capacitor C1. When the varistor VDR1 leaks a small current to charge capacitor C1, resistor R2 discharges capacitor C1 to ensure that the voltage across capacitor C1 approaches zero; The coil KM1-0 of the 1# contactor is energized and attracted, and the main normally open contact KM1-2 of the 1# contactor closes. The main circuit unit is energized, and the inverter INV is energized, and its voltage direction is positive at the top and negative at the bottom;

[0027] The reverse wiring working process includes the following steps:

[0028] The output power supply of the photovoltaic panel is connected to terminal A and terminal B. When the wiring method of the photovoltaic panel is reverse connection, that is, terminal B is the positive pole and terminal A is the negative pole, press the start button SB1, the current flows in through terminal B and out through terminal A. Through the unidirectional conduction of the diode, diode D2 makes the reverse wiring unit work; diode D1 makes the forward wiring unit not work;

[0029] When the voltage between terminal A and terminal B reaches the rated value, after voltage division by resistor R7 and resistor R8, the voltage across resistor R8 supplies a bias voltage U to the base and emitter of transistor Q2 through diode D4. At the same time, a base current i is supplied to transistor Q2 through resistor R7. Under the condition that the bias voltage U is greater than the conduction voltage of the PN junction of transistor Q2 and the base current i of transistor Q2 reaches the saturation current, transistor Q2 conducts, and the resistance between the collector and emitter of transistor Q2 approaches zero. The coil KM2-0 of the 2# contactor is energized and attracted, and the auxiliary normally open contact KM2-1 of the 2# contactor closes. The forward wiring unit is self-powered through the auxiliary normally open contact KM2-1. Even if the start button SB1 is released, the reverse wiring unit will not lose power;

[0030] When the voltage between terminal A and terminal B reaches the rated value, the resistance value of varistor VDR2 approaches infinity, the voltage across capacitor C2 is close to zero as it cannot be fully charged, the voltage between the control electrode and the cathode of thyristor SCR2 is close to zero, and thyristor SCR2 is in the cut-off state; Resistor R6 is connected in parallel across capacitor C2. When the tiny leakage current of varistor VDR2 charges capacitor C2, resistor R6 discharges capacitor C2 to ensure that the voltage across capacitor C2 is close to zero; Since the coil KM2-0 of the 2# contactor is energized and attracted, the main normally open contact KM2-2 of the 2# contactor closes, the main circuit unit is energized, and the inverter INV is energized, and its voltage direction is also positive at the top and negative at the bottom.

[0031] Furthermore, it also includes an undervoltage and overvoltage protection process, and the undervoltage and overvoltage protection process includes the following steps:

[0032] When the forward wiring unit is working, the undervoltage and overvoltage protection process includes the following steps:

[0033] When the voltage between terminal A and terminal B is lower than the rated value, the voltage across resistor R4 decreases, the voltage between the base and emitter of transistor Q1 is lower than the conduction bias voltage, transistor Q1 does not conduct, the coil KM1-0 of the 1# contactor loses power, and both the auxiliary normally open contact KM1-1 and the main normally open contact KM1-2 of the 1# contactor will open. The main circuit unit loses power, and the inverter INV loses power. Even if the start button SB1 is continuously pressed, the coil KM1-0 of the 1# contactor will not be energized;

[0034] When the voltage between the two terminals of terminal A and terminal B is higher than the rated value, the resistance value of the varistor VDR1 decreases and approaches zero. The capacitor C1 is quickly charged through the resistor R1 and the voltage rises. When the voltage across the capacitor C1 reaches the trigger voltage of the thyristor SCR1, the thyristor SCR1 conducts, the voltage across the resistor R4 is short-circuited to zero, the bias voltage between the base and emitter of the triode Q1 is lost, the triode Q1 is cut off, the coil KM1-0 of the 1# contactor loses power, and the auxiliary normally open contact KM1-1 of the 1# contactor and the main normally open contact KM1-2 of the 1# contactor will both open, the main circuit unit loses power, the inverter INV loses power, and even if the start button SB1 is pressed continuously, the coil KM1-0 of the 1# contactor will not be energized.

[0035] Furthermore, it also includes an overheat protection process, and the overheat protection process includes the following steps:

[0036] The thermistors PTC1 and PTC2 are connected in series and installed at different positions inside the inverter INV to monitor temperature changes. When the temperature inside the inverter INV is normal, the resistance values of the thermistors PTC1 and PTC2 are relatively low, the voltage Vi of the operational amplifier COPOP1 is less than the reference voltage Vref of the operational amplifier COPOP1, the output voltage Vo of the operational amplifier COPOP1 is in phase with the reference voltage Vref of the operational amplifier COPOP1, the output voltage Vo of the operational amplifier COPOP1 is at a high level, the G pole of the field effect transistor FET1 is at a high level, the field effect transistor FET1 conducts, and the state between the D pole and the S pole of the field effect transistor FET1 is in a low-resistance state. The coil KM3-0 of the 3# contactor is attracted, and the main normally open contact KM3-2 of the 3# contactor is in a closed state, and the circuit is conducted;

[0037] When the temperature inside the inverter INV rises abnormally, the resistances of the thermistors PTC1 and PTC2 increase with the increase in temperature, the series resistance value becomes larger, the voltage Vi of the operational amplifier COPOP1 is greater than the reference voltage Vref of the operational amplifier COPOP1, the output voltage Vo of the operational amplifier COPOP1 is inverted and becomes a low level in the opposite phase to the voltage Vi of the operational amplifier COPOP1, the G pole of the field effect transistor FET1 is at a low level, the field effect transistor FET1 is cut off, the state between the D pole and the S pole of the field effect transistor FET1 is in a high-resistance state, the coil KM3-0 of the 3# contactor loses power, and the main normally open contact KM3-2 of the 3# contactor is in an open state, and the circuit is disconnected to cut off the current;

[0038] When the internal temperature of the inverter INV drops to the normal value, the thermistors PTC1 and PTC2 recover to a low resistance value. The voltage Vi of the operational amplifier COPOP1 is less than the reference voltage Vref of the operational amplifier COPOP1. The output voltage Vo of the operational amplifier COPOP1 is in phase with the reference voltage Vref of the operational amplifier COPOP1. The output voltage Vo of the operational amplifier COPOP1 is at a high level. The G pole of the field effect transistor FET1 is at a high level, and the field effect transistor FET1 conducts. The D pole and S pole of the field effect transistor FET1 are in a low-resistance state. The coil KM3-0 of the 3# contactor is attracted, and the main normally open contact KM3-2 of the 3# contactor is in a closed state, and the circuit is re-conducted.

[0039] Furthermore, it also includes a process for shielding lightning pulse interference, and the process for shielding lightning pulse interference includes the following steps:

[0040] The capacitor C5 is a high-frequency filtering capacitor. The capacitor C5 is connected in parallel to the input end of the inverter INV through a reactor L1 with a low resistance value and a capacitor C6 for low-frequency filtering. The capacitance of the capacitor C5 is very small, presenting a low reactance to high-frequency currents. The high-frequency electromagnetic pulse generated by lightning is conducted to the ground through the capacitor C5;

[0041] Due to the self-inductance effect of the reactor L1, it presents a high impedance to medium-frequency electromagnetic pulses and allows direct current and low-frequency currents to pass through; the capacitor C6 has a relatively large capacitance and filters and smooths the low-frequency electromagnetic pulses flowing through the inductor; the resistor R12 is connected in series with the diode D5 and is connected in parallel to the input end of the inverter INV. When a reverse interference pulse is induced by lightning, the resistor R12 can limit the current, and the diode D5 can clip the wave to protect the inverter INV from reverse induced electromotive force interference.

[0042] The present invention adopts the above technical solutions, and compared with the prior art, has the following technical effects:

[0043] 1. It has the functions of automatically identifying the positive and negative poles of photovoltaic panels, overvoltage protection, undervoltage protection, overheat protection, and shielding lightning pulse interference. During the wiring process of photovoltaic panels in the installation of photovoltaic power generation devices, there is no need to distinguish between the positive and negative poles, and it automatically switches the positive and negative poles of the photovoltaic panels to adapt to the polarity of the inverter.

[0044] 3. During the use of the photovoltaic power generation device, if a wiring error causes the input voltage to be higher or lower than the rated voltage, or if the photovoltaic panel monomers are disconnected or short-circuited due to external force or line corrosion, etc., resulting in overvoltage or undervoltage of the photovoltaic panel, the voltage monitoring unit monitors the input voltage, timely cuts off the circuit, disconnects the electrical connection between the photovoltaic panel and the inverter, avoids damage to the photovoltaic module, and protects the inverter from damage.

[0045] 4. During the use of the photovoltaic power generation device, the temperature is monitored through a thermistor. When the inside of the inverter overheats due to overload or other reasons, the circuit is cut off in a timely manner. When the temperature drops, the circuit power supply is automatically restored.

[0046] 5. In thunderstorm weather, for the electromagnetic interference pulses induced in the circuit, the high-frequency electromagnetic interference pulses are filtered through a high-resistance filter capacitor, the low-frequency electromagnetic interference pulses are filtered through a low-resistance filter capacitor, and the surge electromagnetic interference current is suppressed through a low-resistance inductor, making the input voltage of the inverter stable and smooth.

[0047] 6. The problem of inaccurate protection range is solved. Through the voltage sampling circuit, the voltage range is accurately monitored, and the protection range is within ±1V. At the same time, the problem of slow response is solved. When the voltage exceeds the range (overvoltage, undervoltage, overheating), the circuit quickly responds and cuts off the circuit quickly at the millisecond time level. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0049] Figure 1 It is the circuit diagram of the protection system of the photovoltaic power generation device in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] Embodiment, as Figure 1 shown, a protection system for a photovoltaic power generation device includes a voltage monitoring unit, a temperature control unit, a forward connection unit, a reverse connection unit, and a main circuit unit. The voltage monitoring unit is connected to the temperature control unit, the forward connection unit, the reverse connection unit, and the main circuit unit. A diode D2 and a diode D1 are connected in series between the forward connection unit and the reverse connection unit. The negative electrode of the diode D1 and the positive electrode of the diode D2 are connected to the forward connection unit, and the positive electrode of the diode D1 and the negative electrode of the diode D2 are connected to the reverse connection unit.

[0051] The voltage monitoring unit includes a voltage monitor. The voltage detector is connected to terminal A and terminal B of the output power supply of the photovoltaic panel. Terminal A is connected to one end of the start button SB1, one end of the auxiliary normally open contact KM1-1 of the 1# contactor, and one end of the auxiliary normally open contact KM1-2 of the 2# contactor. The other end of the start button SB1, the other end of the auxiliary normally open contact KM1-1 of the 1# contactor, and the other end of the auxiliary normally open contact KM1-2 of the 2# contactor are connected to the positive electrode of the diode D1. Terminal B is connected to the positive electrode of the diode D2.

[0052] The forward wiring unit includes a varistor VDR1. One end of the varistor VDR1 is connected to the negative electrode of a diode D1. The other end of the varistor VDR1 is connected to one end of a resistor R1. The other end of the resistor R1 is connected to one end of a resistor R2, one end of a capacitor C1, and the K pole of a thyristor SCR1. The G pole of the thyristor SCR1, the other end of the resistor R2, and the other end of the capacitor C1 are connected to the positive electrode of a diode D2. The A pole of the thyristor SCR1 is connected to one end of a resistor R4, the positive electrode of a diode D3, and one end of a resistor R3. The other end of the resistor R3 is connected to the negative electrode of the diode D1. The other end of the resistor R4 is connected to the positive electrode of the diode D2. The negative electrode of the diode D3 is connected to the base of a triode Q1. The collector of the triode Q1 is connected to one end of the 1# contactor coil KM1-0. The other end of the 1# contactor coil KM1-0 is connected to the negative electrode of the diode D1. The emitter of the triode Q1 is connected to the positive electrode of the diode D2.

[0053] The reverse wiring unit includes a varistor VDR2. One end of the varistor VDR2 is connected to the negative electrode of a diode D2. The other end of the varistor VDR2 is connected to one end of a resistor R6. The other end of the resistor R6 is connected to one end of a resistor R5, one end of a capacitor C2, and the K pole of a thyristor SCR2. The G pole of the thyristor SCR2, the other end of the resistor R5, and the other end of the capacitor C2 are connected to the positive electrode of a diode D1. The A pole of the thyristor SCR2 is connected to one end of a resistor R8, the positive electrode of a diode D4, and one end of a resistor R7. The other end of the resistor R8 is connected to the negative electrode of the diode D2. The other end of the resistor R7 is connected to the positive electrode of the diode D1. The negative electrode of the diode D4 is connected to the base of a triode Q2. The collector of the triode Q2 is connected to one end of the 2# contactor coil KM2-0. The other end of the 2# contactor coil KM2-0 is connected to the negative electrode of the diode D2. The emitter of the triode Q2 is connected to the positive electrode of the diode D1.

[0054] The temperature control unit includes a thermistor PTC1 and a thermistor PTC2. One end of the thermistor PTC1 is connected to one end of a resistor R11, one end of a capacitor C3, and the comparison voltage input terminal of an operational amplifier COPOP1. The other end of the resistor R11 is connected to terminal A. The other end of the thermistor PTC1 is connected to one end of the thermistor PTC2. The other end of the thermistor PTC2 and the other end of the capacitor C3 are grounded. The reference voltage input terminal of the operational amplifier COPOP1 is connected to one end of a resistor R9, one end of a resistor R10, and one end of a capacitor C4. The other end of the resistor R9 is connected to terminal A. The other end of the capacitor C and the other end of the resistor R10 are connected to terminal B. The output terminal of the operational amplifier COPOP1 is connected to the G pole of a field effect transistor FET1. The D pole of the field effect transistor FET1 is connected to one end of the coil KM3-0 of the 3# contactor. The other end of the coil KM3-0 of the 3# contactor is connected to one end of the main normally open contact KM3-2 of the 3# contactor and is connected to terminal A. The other end of the main normally open contact KM3-2 of the 3# contactor is connected to the main circuit unit.

[0055] The main circuit unit includes the normally open main contact KM1-2 of the 1# contactor and the normally open main contact KM2-2 of the 2# contactor. One end of the normally open main contact KM1-2 of the 1# contactor and one end of the normally open main contact KM2-2 of the 2# contactor are both connected to the other end of the normally open main contact KM3-2 of the 3# contactor. The other end of the normally open main contact KM1-2 of the 1# contactor is respectively connected to terminal A and terminal B.

[0056] The main circuit unit further includes a capacitor C5. One end of the capacitor C5 is connected to one end of a reactor L1 and the positive terminal point A. The other end of the capacitor C5 is connected to terminal B. The other end of the reactor L1 is connected to one end of a capacitor C6, one end of a resistor R12, and one end of an inverter INV. The other end of the capacitor C6 is connected to terminal B. The other end of the resistor R12 is connected to the negative electrode of a diode D5, and the positive electrode of the diode D5 is connected to terminal B. The other end of the inverter INV is connected to terminal B.

[0057] A method for realizing a protection system of a photovoltaic power generation device includes a forward wiring working process, a reverse wiring working process, an under-voltage and over-voltage protection process, an overheat protection process, and a shielding lightning pulse interference process.

[0058] The forward wiring working process includes the following steps:

[0059] The power supply output by the photovoltaic panel is connected to terminal A and terminal B. When the wiring method of the photovoltaic panel is positive connection, that is, terminal A is the positive electrode and terminal B is the negative electrode, press the start button SB1. The current flows in through terminal A and out through terminal B. Through the unidirectional conduction of the diode, the diode D1 enables the forward wiring unit to work; the diode D2 enables the reverse connection control unit not to work;

[0060] When the voltage between terminal A and terminal B is the rated value, after being divided by the resistors R3 and R4, the voltage across the resistor R4 supplies a bias voltage U to the base and emitter of the triode Q1 through the diode D3. At the same time, a base current i is supplied to the triode Q1 through the resistor R3. Under the condition that the bias voltage U is greater than the conduction voltage of the PN junction of the triode Q1 and the base current i of the triode Q1 reaches the saturation current, the triode Q1 conducts, and the resistance between its collector and emitter approaches zero. The coil KM1-0 of the 1# contactor is energized and attracted, and the auxiliary normally open contact KM1-1 of the 1# contactor closes. The forward wiring unit is self-powered through the auxiliary normally open contact KM1-1, that is, even if the start button SB1 is released, the forward wiring unit will not lose power.

[0061] Meanwhile, when the voltage between terminal A and terminal B reaches the rated value, the resistance of varistor VDR1 approaches infinity. Capacitor C1 cannot be fully charged, and the voltage across it approaches zero. The voltage between the control electrode and the cathode of thyristor SCR1 approaches zero, and thyristor SCR1 is in the cut-off state. Resistor R2 is connected in parallel across capacitor C1. When the tiny leakage current of varistor VDR1 charges capacitor C1, resistor R2 discharges capacitor C1 to ensure that the voltage across capacitor C1 approaches zero.

[0062] Preferably, the resistance values of resistor R3 and resistor R4 are reasonably calculated so that under the rated voltage, the voltage across resistor R4 plus the PN junction voltage drop of diode D3 is exactly greater than the bias voltage of triode Q1.

[0063] Since the coil KM1-0 of the 1# contactor is energized and attracted, the main normally open contact KM1-2 of the 1# contactor closes, the main circuit unit is energized, and the inverter INV is energized, with its voltage direction being positive at the top and negative at the bottom.

[0064] The reverse wiring working process includes the following steps:

[0065] The output power of the photovoltaic panel is connected to terminal A and terminal B. When the wiring method of the photovoltaic panel is reverse-connected, that is, terminal B is the positive pole and terminal A is the negative pole, press the start button SB1. The current flows in through terminal B and out through terminal A. Due to the one-way conduction of the diode, diode D2 enables the reverse wiring unit to work; diode D1 enables the forward wiring unit not to work.

[0066] When the voltage between the two terminals of terminal A and terminal B reaches the rated value, after being divided by resistors R7 and R8, the voltage across resistor R8 provides a bias voltage U to the base and emitter of triode Q2 through diode D4. At the same time, resistor R7 provides a base current i to triode Q2. Under the condition that the bias voltage U is greater than the PN junction conduction voltage of triode Q2 and the base current i of triode Q2 reaches the saturation current, triode Q2 conducts, and the resistance between the collector and emitter of triode Q2 approaches zero. The coil KM2-0 of the 2# contactor is energized and attracted, and the auxiliary normally open contact KM2-1 of the 2# contactor closes. The forward wiring unit is self-powered through the auxiliary normally open contact KM2-1. Even if the start button SB1 is released, the reverse wiring unit will not lose power.

[0067] Meanwhile, when the voltage between terminal A and terminal B reaches the rated value, the resistance value of varistor VDR2 approaches infinity. Capacitor C2 cannot be fully charged and the voltage across it approaches zero. The voltage between the control electrode and the cathode of thyristor SCR2 approaches zero, and thyristor SCR2 is in the cut-off state. Resistor R6 is connected in parallel across capacitor C2. When the tiny leakage current of varistor VDR2 charges capacitor C2, resistor R6 discharges capacitor C2 to ensure that the voltage across capacitor C2 approaches zero. Since the coil KM2-0 of the 2# contactor is energized and attracted, the main normally open contact KM2-2 of the 2# contactor closes, the main circuit unit is energized, and the inverter INV is energized, with its voltage direction also being positive at the top and negative at the bottom.

[0068] In summary, regardless of the wiring polarity of terminal A and terminal B, the power supply polarity obtained by inverter INV is positive at the top and negative at the bottom.

[0069] The under-voltage and over-voltage protection processes include the following steps:

[0070] When the forward wiring unit is working, the under-voltage and over-voltage protection processes include the following steps:

[0071] When the voltage between terminal A and terminal B is lower than the rated value (under-voltage), the voltage across resistor R4 decreases. The voltage between the base and the emitter of triode Q1 is lower than the conduction bias voltage, and triode Q1 does not conduct. The coil KM1-0 of the 1# contactor loses power, and both the auxiliary normally open contact KM1-1 and the main normally open contact KM1-2 of the 1# contactor will open. The main circuit unit loses power, and the inverter INV loses power. Even if the start button SB1 is pressed continuously, the coil KM1-0 of the 1# contactor will not be energized.

[0072] When the voltage between terminal A and terminal B is higher than the rated value (over-voltage), the resistance value of varistor VDR1 decreases and approaches zero. Capacitor C1 is quickly charged through resistor R1 and the voltage rises. When the voltage across capacitor C1 reaches the trigger voltage of thyristor SCR1, thyristor SCR1 conducts, the voltage across resistor R4 is short-circuited to zero, the bias voltage between the base and the emitter of triode Q1 is lost, triode Q1 cuts off, the coil KM1-0 of the 1# contactor loses power, and both the auxiliary normally open contact KM1-1 and the main normally open contact KM1-2 of the 1# contactor will open. The main circuit unit loses power, and the inverter INV loses power. Even if the start button SB1 is pressed continuously, the coil KM1-0 of the 1# contactor will not be energized.

[0073] When the reverse wiring unit is working, the under-voltage and over-voltage protection processes include the following steps:

[0074] When the voltage between terminal A and terminal B is lower than the rated value (under-voltage), the voltage across resistor R8 decreases, and the voltage between the base and emitter of triode Q2 is lower than the conduction bias voltage. Triode Q2 does not conduct, and the coil KM2-0 of the 2# contactor loses power. The normally open auxiliary contact KM2-1 of the 2# contactor and the normally open main contact KM2-2 of the 2# contactor disconnect. The main circuit unit loses power, and the inverter INV loses power. Even if the start button SB1 is pressed continuously, the coil KM2-0 of the 2# contactor will not be energized.

[0075] When the voltage between terminal A and terminal B is higher than the rated value (over-voltage), the resistance value of varistor VDR2 decreases and approaches zero. Capacitor C2 is quickly charged through resistor R5 and the voltage rises. When the voltage across capacitor C2 reaches the trigger voltage of thyristor SCR2, thyristor SCR2 conducts, and the two ends of resistor R8 are short-circuited. The bias voltage between the base and emitter of triode Q2 is lost, and triode Q2 cuts off. The coil KM2-0 of the 2# contactor loses power. The normally open auxiliary contact KM2-1 of the 2# contactor and the normally open main contact KM2-2 of the 2# contactor both disconnect. The main circuit unit loses power, and the inverter INV loses power. Even if the start button SB1 is pressed continuously, the coil KM2-0 of the 2# contactor will not be energized.

[0076] Whether during the startup process of the photovoltaic power generation device or during the use process of the photovoltaic power generation device, when under-voltage or over-voltage occurs, the present invention will cut off the power supply in time to protect the photovoltaic modules.

[0077] The overheat protection process includes the following steps:

[0078] Thermistors PTC1 and PTC2 are connected in series and installed at different positions inside the inverter INV to monitor temperature changes. Thermistors PTC1 and PTC2 are positive temperature coefficient thermistors, and their resistance increases with the increase of temperature. The series resistance value of thermistors PTC1 and PTC2 and resistor R11 form a voltage division circuit. When the resistance value of either thermistor PTC1 or PTC2 increases, the voltage Vi at the voltage comparison input terminal of operational amplifier COPOP1 will increase. Capacitor C3 and thermistors PTC1 and PTC2 form a series-parallel circuit to eliminate the parasitic capacitance on thermistors PTC1 and PTC2.

[0079] Resistors R9 and R10 form a voltage division circuit. By adjusting the resistance value ratio of R9 and resistor R10, the reference voltage Vref at the reference voltage input terminal of operational amplifier COPOP1 can be adjusted. Capacitor C4 is connected in parallel with resistor R10 to eliminate the parasitic capacitance generated by resistor R10 during sampling.

[0080] When the internal temperature of the inverter INV is normal, the resistance values of the thermistors PTC1 and PTC2 are relatively low, the voltage Vi is less than the reference voltage Vref, the output voltage Vo of the operational amplifier COPOP1 is in phase with the reference voltage Vref, the output voltage Vo is at a high level, the G pole of the field effect transistor FET1 is at a high level, the field effect transistor FET1 is turned on, and the D pole and S pole of the field effect transistor FET1 are in a low-resistance state. The 3# contactor coil KM3-0 is energized, and the main normally open contact KM3-2 of the 3# contactor is in a closed state, and the circuit is turned on.

[0081] When the internal temperature of the inverter INV rises abnormally, the resistance of the thermistors PTC1 and PTC2 increases with the increase of temperature, the series resistance value becomes larger, the voltage Vi is greater than the reference voltage Vref, the output voltage Vo is inverted and turned into a low level, the G pole of the field effect transistor FET1 is at a low level, the field effect transistor FET1 is turned off, and the D pole and S pole of the field effect transistor FET1 are in a high-resistance state. The 3# contactor coil KM3-0 loses power, and the main normally open contact KM3-2 of the 3# contactor is in an open state, and the circuit is disconnected to cut off the current.

[0082] After a period of time, when the internal temperature of the inverter INV drops to the normal value, the thermistors PTC1 and PTC2 recover to a low resistance value, the voltage Vi is less than the reference voltage Vref, the output voltage Vo of the operational amplifier COPOP1 is in phase with the reference voltage Vref, Vo is at a high level, the G pole of the field effect transistor FET1 is at a high level, the field effect transistor FET1 is turned on, and the D pole and S pole of the field effect transistor FET1 are in a low-resistance state. The 3# contactor coil KM3-0 is energized, and the main normally open contact KM3-2 of the 3# contactor is in a closed state, and the circuit is re-conducted.

[0083] Furthermore, the thermistors are not limited to two. Multiple series-connected thermistors can be installed at the parts of the circuit that are prone to heat generation. If the temperature of any part rises abnormally, the purpose of overheat protection can be achieved.

[0084] At the same time, the adjustment of the reference voltage Vref can be achieved by adjusting the resistance value ratio of R9 and the resistor R10 to adapt to the setting of the total resistance value of multiple series-connected thermistors and the temperature threshold.

[0085] The process of shielding lightning pulse interference includes the following steps:

[0086] The capacitor C5 is a high-frequency filtering capacitor. The capacitor C5 is connected in parallel to the input end of the inverter INV through the reactor L1 with a low resistance value and the capacitor C6 for low-frequency filtering. Because the capacitance of the capacitor C5 is very small, it presents a low reactance to high-frequency current, and the high-frequency electromagnetic pulse generated by lightning is introduced into the ground through the capacitor C5.

[0087] Due to the self-inductance effect, the reactor L1 presents a high impedance to the intermediate-frequency electromagnetic pulse and allows the direct current and low-frequency current to pass through; the capacitor C6 has a large capacitance and filters and smooths the low-frequency electromagnetic pulse flowing through the inductor; the resistor R12 is connected in series with the diode D5 and is connected in parallel at the input end of the inverter INV. When a reverse interference pulse is induced by lightning, the resistor R12 can limit the current, and the diode D5 can clip the wave to protect the inverter INV from the interference of the reverse induced electromotive force.

[0088] The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the disclosed form. Many modifications and variations are obvious to those of ordinary skill in the art. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention and design various embodiments with various modifications suitable for the particular use.

Claims

1. A protection system for a photovoltaic power generation device, characterized in that: It includes a voltage monitoring unit, a temperature control unit, a forward wiring unit, a reverse wiring unit, and a main circuit unit. The voltage monitoring unit is connected to the temperature control unit, the forward wiring unit, the reverse wiring unit, and the main circuit unit. A diode D2 and a diode D1 are connected in series between the forward wiring unit and the reverse wiring unit. The cathode of the diode D1 and the anode of the diode D2 are connected to the forward wiring unit, and the anode of the diode D1 and the cathode of the diode D2 are connected to the reverse wiring unit. The forward wiring unit includes a varistor VDR1, one end of the varistor VDR1 is connected to the cathode of a diode D1, the other end of the varistor VDR1 is connected to one end of a resistor R1, the other end of the resistor R1 is connected to one end of a resistor R2, one end of a capacitor C1 and a K pole of a thyristor SCR1, the G pole of the thyristor SCR1, the other end of the resistor R2 and the other end of the capacitor C1 are connected to the anode of a diode D2, the A pole of the thyristor SCR1 is connected to one end of a resistor R4, the anode of a diode D3 and one end of a resistor R3, the other end of the resistor R3 is connected to the cathode of a diode D1, the other end of the resistor R4 is connected to the anode of a diode D2, the cathode of a diode D3 is connected to the base of a transistor Q1, the collector of the transistor Q1 is connected to one end of a 1# contactor coil KM1-0, the other end of the 1# contactor coil KM1-0 is connected to the cathode of a diode D1, and the emitter of the transistor Q1 is connected to the anode of a diode D2; The reverse wiring unit includes a varistor VDR2, one end of the varistor VDR2 is connected to the cathode of the diode D2, the other end of the varistor VDR2 is connected to one end of a resistor R6, the other end of the resistor R6 is connected to one end of a resistor R5, one end of a capacitor C2 and the K pole of a thyristor SCR2, the G pole of the thyristor SCR2, the other end of the resistor R5 and the other end of the capacitor C2 are connected to the anode of the diode D1, the A pole of the thyristor SCR2 is connected to one end of a resistor R8, the anode of a diode D4 and one end of a resistor R7, the other end of the resistor R8 is connected to the cathode of the diode D2, the other end of the resistor R7 is connected to the anode of the diode D1, the cathode of the diode D4 is connected to the base of the transistor Q2, the collector of the transistor Q2 is connected to one end of the 2# contactor coil KM2-0, the other end of the 2# contactor coil KM2-0 is connected to the cathode of the diode D2, and the emitter of the transistor Q2 is connected to the anode of the diode D1.

2. A protection system for a photovoltaic power generation device as claimed in claim 1, characterized in that: The voltage monitoring unit includes a voltage monitor, which is connected to terminals A and B of the photovoltaic panel output power supply, terminal A is connected to one end of the start button SB1, one end of the auxiliary normally open contact KM1-1 of the 1# contactor and one end of the auxiliary normally open contact KM2-1 of the 2# contactor, the other end of the start button SB1, the other end of the auxiliary normally open contact KM1-1 of the 1# contactor and the other end of the auxiliary normally open contact KM2-1 of the 2# contactor are connected to the positive electrode of the diode D1, and terminal B is connected to the positive electrode of the diode D2.

3. A protection system for a photovoltaic power generation device as claimed in claim 1, characterized in that: The temperature control unit includes a thermistor PTC1 and a thermistor PTC2. One end of the thermistor PTC1 is connected to one end of a resistor R11, one end of a capacitor C3 and a comparison voltage input end of an op amp COPOP1. The other end of the resistor R11 is connected to a terminal A. The other end of the thermistor PTC1 is connected to one end of a thermistor PTC2. The other end of the thermistor PTC2 and the other end of the capacitor C3 are grounded. The reference voltage input end of the op amp COPOP1 is connected to one end of a resistor R9, one end of a resistor R10 and a comparison voltage input end of the op amp COPOP1. One end of capacitor C4 and the other end of resistor R9 are connected to terminal A, the other end of capacitor C and the other end of resistor R10 are connected to terminal B, the output end of op amp COPOP1 is connected to the G pole of field effect transistor FET1, the D pole of field effect transistor FET1 is connected to one end of coil KM3-0 of 3# contactor, the other end of coil KM3-0 of 3# contactor is connected to one end of the main normally open contact KM3-2 of 3# contactor, and connected to terminal A in parallel, and the other end of the main normally open contact KM3-2 of 3# contactor is connected to the main circuit unit.

4. A protection system for a photovoltaic power generation device as claimed in claim 1, characterized in that: The main circuit unit includes a 1# contactor main normally open contact KM1-2 and a 2# contactor main normally open contact KM2-2, one end of the 1# contactor main normally open contact KM1-2 and one end of the 2# contactor main normally open contact KM2-2 are both connected to the other end of the 3# contactor main normally open contact KM3-2, and the other end of the 1# contactor main normally open contact KM1-2 is connected to terminal A and terminal B respectively; The main circuit unit also includes a capacitor C5, one end of which is connected to one end of the inductor L1 and the positive terminal A, and the other end of the capacitor C5 is connected to the terminal B. The other end of the inductor L1 is connected to one end of the capacitor C6, one end of the resistor R12 and one end of the inverter INV, the other end of the capacitor C6 is connected to the terminal B, the other end of the resistor R12 is connected to the cathode of the diode D5, the anode of the diode D5 is connected to the terminal B, and the other end of the inverter INV is connected to the terminal B.

5. A method for implementing a protection system for a photovoltaic power generation device, characterized in that: The implementation method is applied to the photovoltaic power generation device protection system according to any one of claims 1 to 4, including a forward wiring workflow and a reverse wiring workflow, and the forward wiring workflow includes the following steps: The output power of the photovoltaic panel is connected to terminal A and terminal B. When the photovoltaic panel is connected in the positive connection mode, that is, terminal A is the positive pole and terminal B is the negative pole, the start button SB1 is pressed, and the current flows in through terminal A and flows out through terminal B. Through the unidirectional conductive effect of the diode, the diode D1 makes the forward wiring unit work; the diode D2 makes the reverse connection control unit not work; When the voltage between terminal A and terminal B is the rated value, the voltage across resistor R4 is divided by resistors R3 and R4, and a bias voltage U is provided to the base and emitter of transistor Q1 through diode D3. At the same time, a base current i is provided to transistor Q1 through resistor R3. Under the condition that the bias voltage U is greater than the PN junction conduction voltage of transistor Q1, and the base current i of transistor Q1 reaches the saturation current, transistor Q1 is turned on, and the resistance between its collector and emitter is close to zero. The coil KM1-0 of contactor 1# is energized and attracted, and the auxiliary normally open contact KM1-1 of contactor 1# is closed. The forward wiring unit is energized and self-protected through the auxiliary normally open contact KM1-1. Even if the start button SB1 is released, the forward wiring unit will not lose power. When the voltage between terminal A and terminal B is the rated value, the resistance of the varistor VDR1 is close to infinity, the capacitor C1 cannot be fully charged and the voltage at both ends is close to zero, the voltage between the control electrode and the negative electrode of the thyristor SCR1 is close to zero, and the thyristor SCR1 is in the cut-off state; the resistor R2 is connected in parallel to both ends of the capacitor C1, when the small leakage current of the varistor VDR1 charges the capacitor C1, the resistor R2 discharges the capacitor C1 to ensure that the voltage at both ends of the capacitor C1 is close to zero; the coil KM1-0 of the 1# contactor is energized and attracted, the main normally open contact KM1-2 of the 1# contactor is closed, the main circuit unit is energized, the inverter INV is energized, and the voltage direction is positive at the top and negative at the bottom; The reverse wiring workflow includes the following steps: The output power of the photovoltaic panel is connected to terminal A and terminal B. When the photovoltaic panel is connected in reverse, that is, terminal B is the positive pole and terminal A is the negative pole, press the start button SB1, the current flows in through terminal B and flows out of terminal A. Through the unidirectional conductive effect of the diode, the diode D2 makes the reverse wiring unit work; the diode D1 makes the forward wiring unit not work; When the voltage between the two terminals A and B is the rated value, the voltage is divided by resistors R7 and R8, and the voltage across resistor R8 provides a bias voltage U to the base and emitter of transistor Q2 through diode D4, and provides a base current i to transistor Q2 through resistor R7. Under the condition that the bias voltage U is greater than the PN junction conduction voltage of transistor Q2, the base current i of transistor Q2 reaches the saturation current, transistor Q2 is turned on, and the resistance between the collector and emitter of transistor Q2 is close to zero. The coil KM2-0 of the 2# contactor is energized and attracted, and the auxiliary normally open contact KM2-1 of the 2# contactor is closed. The forward wiring unit is energized and self-protected through the auxiliary normally open contact KM2-1. Even if the start button SB1 is released, the reverse wiring unit will not lose power. When the voltage between terminals A and B is the rated value, the resistance of the varistor VDR2 is close to infinity, the capacitor C2 cannot be fully charged and the voltage across the terminals is close to zero, the voltage between the control electrode and the negative electrode of the thyristor SCR2 is close to zero, and the thyristor SCR2 is in the cut-off state; the resistor R6 is connected in parallel across the capacitor C2, when the tiny leakage current of the varistor VDR2 charges the capacitor C2, the resistor R6 discharges the capacitor C2 to ensure that the voltage across the capacitor C2 is close to zero; because the coil KM2-0 of the 2# contactor is energized and attracted, the main normally open contact KM2-2 of the 2# contactor is closed, the main circuit unit is energized, the inverter INV is energized, and the voltage direction is also positive at the top and negative at the bottom.

6. A method for implementing a protection system for a photovoltaic power generation device as claimed in claim 5, characterized in that: It also includes undervoltage and overvoltage protection processes. When the forward wiring unit is working, the undervoltage and overvoltage protection process includes the following steps: When the voltage between terminals A and B is lower than the rated value, the voltage across resistor R4 decreases, the voltage between the base and emitter of transistor Q1 is lower than the conduction bias voltage, transistor Q1 is not conducting, 1# contactor coil KM1-0 loses power, 1# contactor auxiliary normally open contact KM1-1 and 1# contactor main normally open contact KM1-2 are disconnected, the main circuit unit loses power, inverter INV loses power, even if the start button SB1 is pressed continuously, 1# contactor coil KM1-0 will not be energized; When the voltage between terminals A and B is higher than the rated value, the resistance of the varistor VDR1 decreases to near zero, and the voltage of the capacitor C1 rises after being quickly charged by the resistor R1. When the voltage across the capacitor C1 reaches the trigger voltage of the thyristor SCR1, the thyristor SCR1 is turned on, and the short-circuit voltage across the resistor R4 is zero. The bias voltage between the base and emitter of the transistor Q1 is lost, the transistor Q1 is cut off, the 1# contactor coil KM1-0 loses power, the 1# contactor auxiliary normally open contact KM1-1 and the 1# contactor main normally open contact KM1-2 are disconnected, the main circuit unit loses power, and the inverter INV loses power. Even if the start button SB1 is pressed continuously, the 1# contactor coil KM1-0 will not be energized.

7. The method for implementing a protection system for a photovoltaic power generation device according to claim 5, characterized in that: It also includes an overheat protection process, which includes the following steps: Thermistors PTC1 and PTC2 are connected in series and installed at different positions inside the inverter INV to monitor temperature changes. When the temperature inside the inverter INV is normal, the resistance values ​​of thermistors PTC1 and PTC2 are relatively low, the voltage Vi of the op amp COPOP1 is less than the reference voltage Vref of the op amp COPOP1, the output voltage Vo of the op amp COPOP1 is in phase with the reference voltage Vref of the op amp COPOP1, the output voltage Vo of the op amp COPOP1 is high, the G pole of the field effect transistor FET1 is high, the field effect transistor FET1 is turned on, the D pole and the S pole of the field effect transistor FET1 are in a low resistance state, the 3# contactor coil KM3-0 is energized, the 3# contactor main normally open contact KM3-2 is in a closed state, and the circuit is turned on; When the temperature inside the inverter INV rises abnormally, the resistance of thermistors PTC1 and PTC2 increases with the temperature, and their series resistance value increases. The voltage Vi of the operational amplifier COPOP1 is greater than the reference voltage Vref of the operational amplifier COPOP1, and the output voltage Vo of the operational amplifier COPOP1 and the voltage Vi of the operational amplifier COPOP1 are reversed and become low level. The G pole of the field effect transistor FET1 is low level, the field effect transistor FET1 is cut off, and the D pole and S pole of the field effect transistor FET1 are in a high resistance state. The coil KM3-0 of the 3# contactor loses power, and the main normally open contact KM3-2 of the 3# contactor is in a disconnected state. The circuit is disconnected and the current is cut off. When the internal temperature of the inverter INV drops to a normal value, the thermistors PTC1 and PTC2 recover their low resistance values, the voltage Vi of the op amp COPOP1 is less than the reference voltage Vref of the op amp COPOP1, the output voltage Vo of the op amp COPOP1 is in phase with the reference voltage Vref of the op amp COPOP1, the output voltage Vo of the op amp COPOP1 is high, the G pole of the field effect transistor FET1 is high, the field effect transistor FET1 is turned on, the D pole and the S pole of the field effect transistor FET1 are in a low resistance state, the 3# contactor coil KM3-0 is energized, the 3# contactor main normally open contact KM3-2 is in a closed state, and the circuit is turned on again.

8. The method for implementing a protection system for a photovoltaic power generation device according to claim 5, characterized in that: It also includes a lightning pulse interference shielding process, which includes the following steps: Capacitor C5 is a high-frequency filter capacitor. Capacitor C5 is connected in parallel to the input end of the inverter INV through a low-resistance reactor L1 and a low-frequency filter capacitor C6. Capacitor C5 has a very small capacitance and presents a low reactance to high-frequency current. The high-frequency electromagnetic pulse generated by lightning is introduced into the earth through capacitor C5. Due to the self-inductance effect, the reactor L1 presents high impedance to the medium-frequency electromagnetic pulse, but allows the DC and low-frequency current to pass through; the capacitor C6 has a large capacitance and filters and smoothes the low-frequency electromagnetic pulses flowing through the inductor; the resistor R12 is connected in series with the diode D5 and is connected in parallel to the input end of the inverter INV. When the lightning induces an anti-phase interference pulse, the resistor R12 can limit the current and the diode D5 can clip the pulse, thereby protecting the inverter INV from the interference of the anti-phase induced electromotive force.

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