Photovoltaic power relay driving circuit

Abstract

The utility model relates to the technical field of photovoltaic equipment manufacturing, in particular to a photovoltaic power relay driving circuit. The circuit mainly comprises an initial trigger end used for receiving a control signal, a coil used for controlling a power relay to act, an optocoupler circuit connected with the initial trigger end, and a power MOS tube used for overcurrent conduction. The source electrode of the power MOS tube is grounded, the drain electrode of the power MOS tube is connected with the coil, and the grid electrode of the power MOS tube is connected with the optocoupler circuit; a PWM regulator is arranged in the initial trigger end. The photovoltaic relay driving circuit can reduce the accumulation of working heat of each power relay and improve the thermal reliability of a system; interference of interference electric signals on a control signal end can be eliminated, and system stability is improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to photovoltaic equipment manufacturing technical field, specifically relates to a photovoltaic power relay drive circuit. BACKGROUND

[0002] In the field of photovoltaic new energy, the safety requirement of photovoltaic hardware equipment is higher and higher, and in IEC62109-2 safety regulation requirement, non-isolated grid-connected inverter in photovoltaic grid-connected system needs to increase the design of redundancy protection to realize grid connection. Redundancy protection is a kind of design for increasing the reliability of system, and two or more than two sets of same and relatively independent components are used to achieve higher safety level, and relay is the key of redundancy protection, therefore, reasonable and ingenious design and control power relay are particularly important.

[0003] The working principle of non-isolated grid-connected inverter in photovoltaic equipment is similar to that of active inverter, but the two are different, and there is no electrical isolation between the output ac power supply and the public grid. Since the large inverter is mainly three-phase inverter at present, in order to realize redundancy protection, at least two power relays need to be configured for each output phase: one is used for on-off control in normal operation, and the other is used as backup or fault protection. In this way, when one of the power relays fails, the other power relay can still work, ensuring the stable operation of the system. Based on the above consideration, two power relays are needed for each output phase (A phase, B phase and C phase), and a total of 6 power relays are needed. However, in order to further improve the reliability of the system, an additional power relay may also be configured between each output phase and the neutral point (or ground) for cutting off the connection between the phase line and the neutral point in the event of a fault. In this way, at least one relay is added to each output phase.

[0004] In summary, although the use of a large number of power relays ensures high safety based on redundancy protection, the contact coil of the power relay needs a high voltage trigger, and needs to be maintained for a long time after the contact is attracted, so a large amount of heat will be generated, and high temperature will accelerate the aging of the internal plastic and insulating material of the relay, causing the contact to be oxidized and corroded, the technical parameters of the electrical element to decay, and the reliability to decrease. In addition, the power relay is prone to generate interference signals when it acts, and the signals will interfere with the control signal end, affecting the stability of the system. Utility model content

[0005] The utility model aims at providing a photovoltaic power relay drive circuit, which can reduce the accumulation of working heat of each power relay, improve the thermal reliability of the system, and can also eliminate the interference of interference signals on the control signal end, improve the stability of the system.

[0006] In order to achieve the above object, the technical scheme adopted by the utility model is as follows:

[0007] A photovoltaic power relay drive circuit, containing initial trigger end for receiving control signal and coil for controlling power relay action, characterized by, still containing photo-coupler circuit connected with the initial trigger end and power MOS pipe for overcurrent conduction;The source of the power MOS pipe is grounded, the drain of the power MOS pipe is connected with the coil, and the gate of the power MOS pipe is connected with the photo-coupler circuit;The PWM regulator is arranged in the initial trigger end.

[0008] Therefore, the photovoltaic power relay drive circuit in the technical scheme is mainly used for receiving control signals from the DSP control end and controlling the power relay to act, specifically, when the contact of the power relay is attracted, the power output by the photovoltaic panel is formally connected to the power grid;When the contact of the power relay is disconnected, the photovoltaic panel output is cut off.The DSP control end in the prior art can detect the output characteristics of the photovoltaic panel and determine whether the normal working state has been met.When the entire photovoltaic assembly starts to work, its output parameters cannot directly meet the demand of the power grid, and need to be adjusted for a short time to access the power grid to avoid causing power grid fluctuation.After the DSP control end detects and judges, a control signal indicating the start of access is sent.

[0009] The initial trigger end DRV3 is used for receiving control signals, which is connected with the DSP control end, and then the initial trigger end DRV3 can generate a high-level signal;The initial trigger end DRV3 is connected with the photo-coupler circuit, and the photo-coupler circuit can conduct backward after receiving the high-level signal, and transmit the high-level signal to the gate of the power MOS pipe, which is the control electrode;The source of the power MOS pipe is grounded, and the drain is connected with the coil K2 of the power relay;When the power relay is disconnected, the coil K2 is not connected to the path, so the normally open contact is not attracted, and the photovoltaic panel output is disconnected with the power grid;When the control signal is transmitted from the initial trigger end DRV3 and the photo-coupler circuit to the power MOS pipe, that is, the drain of the power MOS pipe receives the high-level signal, the power MOS pipe is turned on, one end of the coil K2 is connected to the trigger voltage end, and the other end is grounded, so as to be turned on, the power relay is attracted, and the photovoltaic panel output is connected to the power grid.

[0010] Because the power relay needs to be attracted for a long time under normal working condition, and according to the inherent characteristics of the relay, the holding voltage is less than the trigger voltage, therefore, in order to reduce the heat quantity, the trigger voltage can be adjusted to the holding voltage. Specifically, a PWM regulator is arranged in the initial trigger end DRV3, the time of turning on of the optocoupler circuit is controlled through the duty ratio adjustment of the PWM regulator, and then the time of turning on of the gate of the power MOS tube is controlled, finally the time of obtaining 12V voltage by the coil K2 in a certain period is realized, through the duty ratio adjustment of the PWM, the voltage across the coil K2 can be controlled to the holding voltage, for example, 7V, under the voltage, the normally open contact of the power relay is in the attracted state, under the lower 7V voltage, the heat accumulation quantity can be reduced.

[0011] In summary, in the utility model, first, the power MOS tube instead of the power optocoupler is applied to control the conduction of the coil K2 of the power relay, because of the excellent performance of the power MOS tube, the heat quantity can be directly reduced, in addition, the PWM regulator is used to adjust the voltage after triggering of the power relay to the lower holding voltage, so that the heat quantity of the whole driving circuit is further reduced, moreover, because the optocoupler circuit is used for isolation, the fluctuation interference of the electric signal when the power relay acts does not affect the relatively precise sensitive DSP control end, the stability of the whole system is ensured. The utility model has the advantages of low system heat quantity and stability, can be applied for a long time, and enhances the redundancy safety of the whole photovoltaic inverter grid-connected system.

[0012] As a preferred embodiment of the utility model, the power MOS tube is an NMOS tube.

[0013] The NMOS tube is an N-type metal-oxide-semiconductor transistor, which is composed of a source, a drain and a gate. It is usually made of two high-doped N+ regions on a P-type silicon substrate with a lower doping concentration, which are used as the source and the drain. A thin silicon dioxide (SiO2) insulating layer is covered on the semiconductor surface between the source and the drain, and a metal electrode is installed on the insulating layer as the gate. Because the channel of the NMOS is composed of electrons, the electron mobility is high, so the on-resistance is relatively small. Because the electron mobility is high and the distance between the source and the drain is usually short, the switching speed of the NMOS tube is fast, so the use of the NMOS tube with the PWM regulation control mode can perfectly meet the working requirements of the driving circuit.

[0014] As a preferred embodiment of the utility model, an RC absorption circuit is arranged between the drain and the source of the power MOS tube, and the RC absorption circuit comprises a first capacitor and a first resistor.

[0015] Specifically, the RC snubber circuit is a circuit structure connected in series by a resistor R and a capacitor C, and connected in parallel with a switch, mainly used for improving the voltage and current waveforms borne by the power electronic device at the opening and closing time. In the RC snubber circuit, if the switch is turned off, the energy accumulated in the parasitic inductance will charge the parasitic capacitor of the switch, and at the same time, it will also charge the snubber capacitor through the snubber resistor. Due to the action of the snubber resistor, the impedance becomes large, and the snubber capacitor also equivalently increases the parallel capacitance capacity of the switch, thereby suppressing the voltage surge when the switch is turned off. In the driving circuit, the RC snubber circuit includes a first capacitor C6 and a first resistor R18, which can limit the voltage rise rate and protect the power MOS tube. When the switch is turned on, the first capacitor C6 will discharge through the switch, and the discharge current is limited by the first resistor R18.

[0016] As a preferred embodiment of the present application, an RC filter circuit is connected in parallel between the drain and the gate of the power MOS tube, and the RC filter circuit includes a second capacitor and a second resistor.

[0017] The RC filter circuit is connected in parallel between the source and the gate of the power MOS tube, and mainly plays a role of filtering and adjusting the switching speed, thereby reducing the switching oscillation and protecting the stability and safety of the power MOS tube in the fast opening and closing state switching.

[0018] As a preferred embodiment of the present application, a pressure-sensitive resistor is arranged between the normally open contacts of the power relay, and the pressure-sensitive resistor is used for filtering the peak voltage.

[0019] In the prior art, the pressure-sensitive resistor is often used as an overvoltage protection element, which can quickly conduct when the voltage exceeds a certain threshold, and limit the voltage within a safe range. The resistance value of the pressure-sensitive resistor R13 changes with the voltage applied across it. When the voltage rises, the resistance value drops sharply, thereby allowing more current to pass through. The known peak voltage that may occur at the inverter or network side, when the peak voltage occurs, the pressure-sensitive resistor R13 will quickly conduct, limiting the voltage across it to a lower level (i.e. clamping voltage).

[0020] As a preferred embodiment of the present application, a freewheeling diode and a third resistor are connected in parallel across the coil.

[0021] Due to the opening of the coil K2 normally open contact, a peak voltage of several hundred volts is generated across the coil K2, which can be discharged through the freewheeling diode D3 and the third resistor R14, thereby ensuring the stability of the 12V power supply and avoiding affecting the service life of the relay, which is conducive to improving the EMC problem.

[0022] As a preferred embodiment of the present application, the power supply voltage of the coil is 12V.

[0023] In summary, the present application has the following advantages:

[0024] 1. Through the application of controllable power MOS tube instead of the traditional power optocoupler to conduct the power relay coil current, due to the excellent performance of the power MOS tube, the heat can be directly reduced.

[0025] 2. Using PWM regulator to regulate the voltage after the power relay trigger to a lower maintenance voltage, so that the heat of the entire drive circuit is further reduced.

[0026] 3. Because of the use of optocoupler circuit for isolation, it is ensured that the electrical signal fluctuation interference when the power relay acts will not affect the more precise sensitive DSP control end, ensuring the stability of the entire system. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The circuit schematic diagram of the present photovoltaic power relay drive circuit. DETAILED DESCRIPTION

[0028] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Anyone can implement the present disclosure in various forms without being limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0029] In this embodiment, the present photovoltaic power relay drive circuit is used to receive the control signal from the DSP control end and control the power relay to act. Specifically, when the contacts of the power relay are attracted, the power output by the photovoltaic panel is formally connected to the power grid; when the contacts of the power relay are disconnected, the output of the photovoltaic panel is cut off. The DSP control end can detect the output characteristics of the photovoltaic panel and determine whether the normal working state has been met in the prior art. When the entire photovoltaic assembly starts to work, its output parameters will not directly meet the demand of the power grid, and need to be adjusted for a short time to connect to the power grid to avoid causing power grid fluctuation. After the DSP control end detects and judges, it will send a control signal indicating the start of connection.

[0030] As shown in Figure 1 The DSP control end is connected with the initial trigger end DRV3, and the initial trigger end DRV3 includes a PWM regulator. When the DSP control end does not send a high-level control signal to the initial trigger end DRV3 or the PWM regulator adjusts the duty cycle to 0, the one end of the light-emitting diode of the optocoupler circuit U2 part is connected to the 3.3V potential point, and the other end is the 0 potential point, so as to turn on the forward current, and the optocoupler circuit is turned on. At this time, the potential of the 4 pin (i.e. the gate G of the NMOS tube Q2) of the optocoupler circuit U2 part is 0V, and the V GS is less than the turn-on voltage V GS(th), the NMOS tube Q2 is turned off, at this time, the potential difference between the source S and the drain D of the NMOS tube Q2 is 12V, the voltage acting on the coil K2 is 0V, the normally open contact of the power relay is disconnected, and the purpose of cutting off is achieved.

[0031] When the DSP control end sends a high-level control signal to the initial trigger end DRV3, and the PWM regulator adjusts the duty cycle to be 100%, the light-emitting diode of the optocoupler circuit U2 part is connected to the 3.3V potential point at one end, and the other end is also a high potential point, so that conduction is not formed, and the optocoupler circuit is disconnected. At this time, the potential of the 4th pin (i.e. the gate G of the NMOS tube Q2) of the optocoupler circuit U2 part is 12V, the V GS greater than the turn-on voltage V GS(th) , the NMOS tube Q2 is turned on, at this time, the potential difference between the source S and the drain D of the NMOS tube Q2 is 0V, the voltage acting on the coil K2 is 12V, and the normally open contact of the power relay is closed.

[0032] When the power relay is successfully attracted and maintained for 200ms, the PWM regulator adjusts the duty cycle to be 60%, so that the optocoupler circuit U2 part is in a 60% time disconnected state, and the NMOS tube Q2 is in a 60% time open state, and the average value of the voltage acting on the coil K2 is adjusted to 12V x 60% = 7.2V. At this time, the voltage is sufficient to meet the power requirement of the coil K2, thereby achieving the purpose of reducing the maintenance voltage under the premise of continuous conduction of the power relay, and thereby reducing the voltage during long-time work.

[0033] In addition, in the driving circuit, an RC absorption circuit is arranged between the drain and the source of the power MOS tube, and the RC absorption circuit comprises a first capacitor C6 and a first resistor R18. The RC absorption circuit comprising the first capacitor C6 and the first resistor R18 can limit the voltage rise rate and protect the power MOS tube. When the switch is turned on, the first capacitor C6 will discharge through the switch, and the discharge current is limited by the first resistor R18.

[0034] An RC filter circuit is connected in parallel between the drain and the gate of the power MOS tube, and the RC filter circuit comprises a second capacitor C7 and a second resistor R19. The RC filter circuit is connected in parallel between the source and the gate of the power MOS tube, and mainly plays a role of filtering and adjusting the switching speed, thereby reducing the switching oscillation and protecting the stability and safety of the power MOS tube in the fast opening and closing state switching.

[0035] In addition, the normally open contact of the power relay is provided with a voltage-dependent resistor R13 for filtering the spike voltage. The resistance value of the voltage-dependent resistor R13 changes with the voltage applied across it. When the voltage rises, the resistance value drops sharply, thus allowing more current to pass through. The spike voltage that may occur on the inverter or the grid side is known, and when the spike voltage occurs, the voltage-dependent resistor R13 will quickly conduct to limit the voltage across it to a lower level (i.e. clamping voltage).

[0036] In addition, the coil K2 is connected in parallel with a freewheeling diode D3 and a third resistor R14. Since a spike voltage of several hundred volts is generated across the coil K2 at the moment when the normally open contact of the coil K2 is opened, it can be discharged through the freewheeling diode D3 and the third resistor R14, thus ensuring the stability of the 12V power supply and avoiding affecting the service life of the relay, which is conducive to improving the EMC problem.

[0037] The above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application; in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. The structural member materials, sizes, shapes, etc. mentioned in the embodiments of the present application are only illustrative descriptions, and do not form strict or absolute limitations. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A photovoltaic power relay drive circuit comprising an initial trigger terminal for receiving a control signal and a coil for controlling the action of a power relay, characterized in that, It also comprises a photo-coupling circuit connected with the initial trigger end and a power MOS tube for over-current conduction; the source of the power MOS tube is grounded, the drain of the power MOS tube is connected with the coil, and the gate of the power MOS tube is connected with the photo-coupling circuit; a PWM regulator is arranged in the initial trigger end.

2. A photovoltaic power relay drive circuit according to claim 1, characterized in that, The power MOS tube is an NMOS tube.

3. A photovoltaic power relay drive circuit according to claim 2, characterized in that, An RC absorption circuit is arranged between the drain and the source of the power MOS tube, and the RC absorption circuit comprises a first capacitor and a first resistor.

4. A photovoltaic power relay drive circuit according to claim 3, characterized in that, An RC filter circuit is connected in parallel between the drain and the gate of the power MOS tube, and the RC filter circuit comprises a second capacitor and a second resistor.

5. A photovoltaic power relay drive circuit according to claim 4, wherein, A pressure-sensitive resistor is arranged between the normally open contacts of the power relay, and the pressure-sensitive resistor is used for filtering sharp voltage.

6. A photovoltaic power relay drive circuit according to claim 5, wherein, A freewheeling diode and a third resistor are connected in parallel at both ends of the coil.

7. A photovoltaic power relay drive circuit according to claim 1, wherein, The power supply voltage of the coil is 12V.

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