Insulation resistance detection circuit for miniature grid-connected inverter

Abstract

The utility model belongs to the technical field of inverters, and discloses an insulation resistance detection circuit used for a miniature grid-connected inverter, a port VCCB is connected with a negative end of a diode D166 and a pin 2 of a relay RLY2, a positive end of the diode D166 and a pin 1 of the relay RLY2 are connected with a collector electrode of a triode Q124, a base electrode of the triode Q124 is connected with one end of a resistor R899 and one end of a resistor R900, the other end of the resistor R899 is connected with a port ISORLY1, and the other end of the resistor R899 is connected with the port ISORLY2. The other end of the R900 and the emitting electrode of the Q124 are connected with a port AGND, the pin 3 of the RLY2 is connected with one end of the R468, the other end of the R468 is connected with one end of the R469, the other end of the R469 is connected with a port CHGND, and the pin 4 of the RLY2 is connected with one end of the R160. The beneficial effects of the utility model are that when the impedance between the photovoltaic assembly and the ground is smaller than a certain value, the micro grid-connected inverter can stop working and disconnect the power grid, thereby protecting the safety of equipment and personnel.

Description

Technical Field

[0001] The utility model relates to the technical field of inverters, in particular to an insulation impedance detection circuit for a micro grid-connected inverter. Background Art

[0002] With the development of new energy, photovoltaic applications are rapidly popularizing in various markets. The rapid growth of microinverters in the European market began in 2021. ENPHASE's status as a global unicorn continues. At the same time, a number of excellent microinverter manufacturers including APSON, Homax, and Deye have doubled their sales. The growth rate of the entire microinverter leads the inverter.

[0003] Compared with household inverters, microinverters have the following obvious advantages: First, they are easy to install. Unlike household products that are subject to labor shortages and have to wait in line for installation for more than half a year, microinverters do not require a professional installation team and are plug-and-play, convenient and fast; second, the system has a lower cost per watt. Microinverters cost more than household inverters at the stand-alone level, but do not require installation costs, so the cost of the entire system is lower; third, microinverters have a wider audience. Microinverters are photovoltaic products that have entered supermarkets. Compared with professional household photovoltaic inverters, they have a broader consumer electronics market. In addition, the popularity of the industry has led to a much higher demand for microinverters than household inverters.

[0004] The insulation impedance detection circuit plays a protective role in the micro-inverter, which is directly related to the safety of the equipment itself or the safety of the equipment user. As time goes by, the quality of the insulation material will deteriorate due to the environment, working conditions or other external forces of the equipment, thereby reducing the resistivity of the insulation material and increasing the leakage current. In severe cases, accidents such as electric shock casualties and equipment damage may occur.

[0005] Therefore, it is necessary to provide an insulation impedance detection circuit for a micro grid-connected inverter. When the impedance between the photovoltaic module and the ground is less than a certain value, the micro grid-connected inverter can stop working and disconnect from the grid to protect equipment and personal safety. Utility Model Content

[0006] The utility model discloses an insulation impedance detection circuit for a micro grid-connected inverter, which relates to the protection of insulation impedance in the grid-connected inverter and can effectively solve the technical problems involved in the background technology.

[0007] To achieve the above purpose, the technical solution of the utility model is:

[0008] An insulation impedance detection circuit for a micro grid-connected inverter, comprising a relay RLY2, a relay RLY4, an operational amplifier U46 and a controller;

[0009] Port VCCB is connected to the negative end of the diode D166 and the pin 2 of the relay RLY2, the positive end of the diode D166 and the pin 1 of the relay RLY2 are connected to the collector of the transistor Q124, the base of the transistor Q124 is connected to one end of the resistor R899 and one end of the resistor R900, the other end of the resistor R899 is connected to the port ISO_RLY1, the other end of the resistor R900 and the emitter of the transistor Q124 are connected to the port AGND, the pin 3 of the relay RLY2 is connected to one end of the resistor R468, the other end of the resistor R468 is connected to one end of the resistor R469, the other end of the resistor R469 is connected to the port CHGND, the pin 4 of the relay RLY2 is connected to one end of the resistor R160, the other end of the resistor R160 is connected to one end of the resistor R161, and the other end of the resistor R161 is connected to the port PV1_INPUT+;

[0010] The port VCCB is connected to the negative end of the diode D26 and the pin 2 of the relay RLY4, the positive end of the diode D26 and the pin 1 of the relay RLY4 are connected to the collector of the transistor Q25, the base of the transistor Q25 is connected to one end of the resistor R381 and one end of the resistor R382, the other end of the resistor R381 is connected to the port ISO_RLY.COM, the other end of the resistor R382 and the emitter of the transistor Q25 are connected to the port AGND, the pin 3 of the relay RLY4 is connected to one end of the resistor R405, the other end of the resistor R405 is connected to one end of the resistor R406, the other end of the resistor R406 is connected to the port AGND, the pin 4 of the relay RLY4 is connected to one end of the resistor R392, the other end of the resistor R392 is connected to one end of the resistor R400, and the other end of the resistor R400 is connected to the port CHGND;

[0011] The port AGND is connected to one end of the resistor R915, the other end of the resistor R915 is connected to one end of the resistor R916, the other end of the resistor R916 is connected to one end of the resistor R917, the other end of the resistor R917 is connected to the port PV.ISO-, the port CHGND is connected to one end of the resistor R919, the other end of the resistor R919 is connected to one end of the resistor R920, the other end of the resistor R920 is connected to one end of the resistor R921, the other end of the resistor R921 is connected to the port PV.ISO+;

[0012] The port PV.ISO- is connected to one end of the resistor R930, the other end of the resistor R930 is connected to pin 3 of the clamping diode D169, one end of the capacitor C485, one end of the resistor R928 and pin 6 of the operational amplifier U46, pin 1 of the clamping diode D169 is connected to port AGND, pin 2 of the clamping diode D169 is connected to port VCCB, the other end of the capacitor C485, the other end of the resistor R928 and pin 7 of the operational amplifier U46 are connected to one end of the resistor R932, the port PV.ISO+ is connected to one end of the resistor R931, the other end of the resistor R931 is connected to pin 3 of the clamping diode D170, one end of the resistor R929, one end of the capacitor C486 and pin 5 of the operational amplifier U46, pin 1 of the clamping diode D170 is connected to port AGND, pin 2 of the clamping diode D170 is connected to port VCCB, the other end of the resistor R929 and the other end of the capacitor C486 are connected to port AGND, the other end of the resistor R932 is connected to one end of capacitor C484, pin 3 of the clamping diode D171 and port ISO.V, the other end of the capacitor C484 is connected to pin 1 of the clamping diode D171 and port AGND, pin 2 of the clamping diode D171 is connected to port SMCU_3.3V, pin 1 of the operational amplifier U46 is connected to pin 2 of the operational amplifier U46, pin 3 of the operational amplifier U46 is connected to port AGND, pin 4 of the operational amplifier U46 is connected to port AGND and one end of capacitor C487, and pin 8 of the operational amplifier U46 is connected to port VCCB and the other end of the capacitor C487;

[0013] The port ISO_RLY1, the port ISO_RLY.COM and the port ISO.V are connected to a controller.

[0014] The technical specifications of photovoltaic grid-connected micro-inverters state that when the impedance between the PV+ and PV- of the photovoltaic module to the ground is greater than 30kΩ, the micro-grid-connected inverter works normally; when the impedance between the PV+ and PV- of the photovoltaic module to the ground is less than 30kΩ, the micro-grid-connected inverter needs to stop working and disconnect the grid and alarm. This circuit uses relays and operational amplifier LM2904BIDR, which has the advantages of simple circuit, good versatility and easy implementation. The circuit consists of two module circuits. The first module is a relay switching to detect the voltage between PV+ and PV- to the ground, and the second module is differential sampling through the operational amplifier LM2904BIDR to transmit to the microcontroller, which is used to detect the impedance between the photovoltaic module and the ground. When the impedance between the PV+ and PV- of the photovoltaic module to the ground is less than 30kΩ, the micro-grid-connected inverter stops working and disconnects the grid and alarms.

[0015] As a preferred improvement of the present utility model: the port VCCB is a power supply port, the port PV1_INPUT+ is connected to the positive end of the inverter input port, the port AGND is connected to the negative end of the inverter input port, the port CHGND is connected to the insulation impedance ground, and the port SMCU_3.3V is connected to a 3.3V power supply.

[0016] As a preferred improvement of the present invention: the controller is a single chip microcomputer, model TMS320F280025PMSR.

[0017] As a preferred improvement of the utility model: the transistor Q124 and the transistor Q25 are of model BC846A-HAF.

[0018] As a preferred improvement of the present utility model: the operational amplifier U46 model is LM2904BIDR.

[0019] As a preferred improvement of the present invention: the clamping diode D170 is of model BAV99.

[0020] The beneficial effects of the utility model are as follows:

[0021] Use relays to switch and detect the voltage between PV+, PV- and ground, and then transmit the voltage to the microcontroller through differential sampling. The microcontroller calculates the sampled voltage to obtain the resistance between PV+, PV- and ground, so as to confirm whether it is protection or normal operation. When the impedance between the photovoltaic module and the ground is less than 30kΩ, the micro grid-connected inverter stops working and disconnects the grid and alarms. Using relays and operational amplifier LM2904BIDR, insulation impedance detection can be achieved through a simple circuit, which has the advantages of simple circuit and good practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0023] Figure 1 It is a schematic diagram of the relay circuit part of the utility model;

[0024] Figure 2 This is the amplification of the relay circuit part of the utility model Figure 1 ;

[0025] Figure 3 This is the amplification of the relay circuit part of the utility model Figure 2 ;

[0026] Figure 4 It is a schematic diagram of the operational amplifier circuit part of the utility model;

[0027] Figure 5 It is an enlarged diagram of the operational amplifier circuit part of the utility model;

[0028] Figure 6 It is a simplified schematic diagram of the working principle of the utility model. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0031] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0032] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0034] See also Figure 1-Figure 2As shown, the utility model provides an insulation impedance detection circuit for a micro grid-connected inverter, including a relay RLY2, a relay RLY4, an operational amplifier U46 and a controller, a port VCCB is connected to the negative end of a diode D166 and a pin 2 of the relay RLY2, a positive end of the diode D166 and a pin 1 of the relay RLY2 are connected to the collector of a transistor Q124, a base of the transistor Q124 is connected to one end of a resistor R899 and one end of a resistor R900, and the other end of the resistor R899 is connected to a port ISO_ RLY1, the other end of the resistor R900 and the emitter of the transistor Q124 are connected to port AGND, pin 3 of the relay RLY2 is connected to one end of the resistor R468, the other end of the resistor R468 is connected to one end of the resistor R469, the other end of the resistor R469 is connected to port CHGND, pin 4 of the relay RLY2 is connected to one end of the resistor R160, the other end of the resistor R160 is connected to one end of the resistor R161, and the other end of the resistor R161 is connected to port PV1_INPUT+.

[0035] See also Figure 3 As shown, the port VCCB is connected to the negative end of the diode D26 and the pin 2 of the relay RLY4, the positive end of the diode D26 and the pin 1 of the relay RLY4 are connected to the collector of the transistor Q25, the base of the transistor Q25 is connected to one end of the resistor R381 and one end of the resistor R382, the other end of the resistor R381 is connected to the port ISO_RLY.COM, the other end of the resistor R382 and the emitter of the transistor Q25 are connected to the port AGND, the pin 3 of the relay RLY4 is connected to one end of the resistor R405, the other end of the resistor R405 is connected to one end of the resistor R406, the other end of the resistor R406 is connected to the port AGND, the pin 4 of the relay RLY4 is connected to one end of the resistor R392, the other end of the resistor R392 is connected to one end of the resistor R400, and the other end of the resistor R400 is connected to the port CHGND.

[0036] See also Figure 4-Figure 5As shown, port AGND is connected to one end of resistor R915, the other end of the resistor R915 is connected to one end of resistor R916, the other end of the resistor R916 is connected to one end of resistor R917, the other end of the resistor R917 is connected to port PV.ISO-, port CHGND is connected to one end of resistor R919, the other end of the resistor R919 is connected to one end of resistor R920, the other end of the resistor R920 is connected to one end of resistor R921, and the other end of the resistor R921 is connected to port PV.ISO+. The port PV.ISO- is connected to one end of the resistor R930, the other end of the resistor R930 is connected to pin 3 of the clamping diode D169, one end of the capacitor C485, one end of the resistor R928 and pin 6 of the operational amplifier U46, pin 1 of the clamping diode D169 is connected to port AGND, pin 2 of the clamping diode D169 is connected to port VCCB, the other end of the capacitor C485, the other end of the resistor R928 and pin 7 of the operational amplifier U46 are connected to one end of the resistor R932, the port PV.ISO+ is connected to one end of the resistor R931, the other end of the resistor R931 is connected to pin 3 of the clamping diode D170, one end of the resistor R929, one end of the capacitor C486 and pin 5 of the operational amplifier U46, pin 1 of the clamping diode D170 is connected to port AGND, pin 2 of the clamping diode D170 is connected to port VCCB, the other end of the resistor R929 and the other end of the capacitor C486 are connected to port AGND, the other end of the resistor R932 is connected to one end of capacitor C484, pin 3 of the clamping diode D171 and port ISO.V, the other end of the capacitor C484 is connected to pin 1 of the clamping diode D171 and port AGND, pin 2 of the clamping diode D171 is connected to port SMCU_3.3V, pin 1 of the op amp U46 is connected to pin 2 of the op amp U46, pin 3 of the op amp U46 is connected to port AGND, pin 4 of the op amp U46 is connected to port AGND and one end of capacitor C487, and pin 8 of the op amp U46 is connected to port VCCB and the other end of the capacitor C487.

[0037] The port VCCB is a power supply port, the port PV1_INPUT+ is connected to the positive end of the inverter input port, the port AGND is connected to the negative end of the inverter input port, the port CHGND is connected to the insulation impedance ground, the port SMCU_3.3V is connected to a 3.3V power supply, and the port ISO_RLY1, the port ISO_RLY.COM and the port ISO.V are connected to a controller.

[0038] As an implementation mode, the controller is a single chip microcomputer, model TMS320F280025PMSR. The transistor Q124 and the transistor Q25 are model BC846A-HAF, the operational amplifier U46 is model LM2904BIDR, and the clamping diode D170 is model BAV99. It should be further explained that the use of other components to achieve the above effects should all fall within the inventive concept of the utility model and should fall within the protection scope of the utility model.

[0039] VCCB is the power supply of the relay, ISO_RLY1 and ISO_RLY.COM are the signal ports for the microcontroller to control the relay. When ISO_RLY1 is high, relay RLY2 is closed, and when ISO_RLY.COM is high, relay RLY4 is closed. PV1_INPUT+ is PV+, AGND is PV-, and CHGND is the insulation impedance ground. The op amp U46 is the LM2904BIDR op amp chip. PV.ISO- and PV.ISO+ sample the voltages at both ends of AGND and CHGND respectively. D169, D170 and D171 are clamping diodes that clamp the voltage below 3.3V. ISO.V is the sampled voltage transmitted to the microcontroller.

[0040] See also Figure 6 As shown, assuming that the voltage between PV+ and PV- is Uo, the voltage between PV- and CHGND (ground) is U1, relay K2 is cut in as U1′, R2′ and R1′ are assumed to be external impedance (if R2′ and R1′ are less than 30k, protection is required), when relay K1 is closed, K2 is disconnected, it can be obtained ( / / indicates parallel connection), when relay K1 and relay K2 are closed, it can be concluded that When the two equations are combined, R1′ and R2′ are obtained. When one of R1′ and R2′ is less than 30kΩ, the micro grid-connected inverter needs to stop working and disconnect from the grid and alarm.

[0041] Embodiment 1

[0042] Assume that the voltage between PV input voltage PV1_INPUT+ and AGND is Uo=45V, when relay RLY2 is disconnected, the voltage between AGND and CHGND is U1, when relay RLY2 is closed, the voltage between AGND and CHGND is U1′, let R160+R161+R468+R469 be R2=199.6kΩ, let R392+R400+R405+R406 be R1=199.6kΩ, let the impedance between PV1_INPUT+ and CHGND be R2′=30kΩ, let the impedance between AGND and CHGND be R1′=30kΩ. When the circuit is working, ISO_RLY.COM is a high-level signal sent by the microcontroller, and relay RLY4 is closed. When ISO_RLY1 is a low-level signal sent by the microcontroller, relay RLY2 is disconnected, and it is obtained According to the formula, the voltage between AGND and CHGND is U1≈20.93V. When ISO_RLY1 is a high level signal sent by the microcontroller, the relay RLY2 is closed, and the result is According to the formula, the voltage between AGND and CHGND is U1′=22.5V. Assuming that the input resistance of op amp U46 is R915+R916+R917+R930 and R919+R920+R921+R931 is R3=1550kΩ, and R928 and R929 are R4=62kΩ, according to the differential formula of op amp, When U=U1, the voltage of the microcontroller receiving port ISO.V is 0.8372V; when U=U1′, the voltage of the microcontroller receiving port ISO.V is 0.9V; when relay RLY4 is closed, relay RLY2 is disconnected and the voltage received by the microcontroller is not greater than 0.8372V; when relay RLY2 is closed and the voltage received by the microcontroller is not greater than 0.9V, the micro grid-connected inverter stops working and disconnects from the grid and alarms.

[0043] Although the implementation scheme of the utility model has been disclosed as above, it is not limited to the applications listed in the specification and the implementation scheme. It can be fully applied to various fields suitable for the utility model. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the utility model is not limited to the specific details and the illustrations shown and described herein.

Claims

1. An insulation impedance detection circuit for a micro grid-connected inverter, characterized in that: It includes relay RLY2, relay RLY4, operational amplifier U46 and controller; Port VCCB is connected to the negative end of the diode D166 and the pin 2 of the relay RLY2, the positive end of the diode D166 and the pin 1 of the relay RLY2 are connected to the collector of the transistor Q124, the base of the transistor Q124 is connected to one end of the resistor R899 and one end of the resistor R900, the other end of the resistor R899 is connected to the port ISO_RLY1, the other end of the resistor R900 and the emitter of the transistor Q124 are connected to the port AGND, the pin 3 of the relay RLY2 is connected to one end of the resistor R468, the other end of the resistor R468 is connected to one end of the resistor R469, the other end of the resistor R469 is connected to the port CHGND, the pin 4 of the relay RLY2 is connected to one end of the resistor R160, the other end of the resistor R160 is connected to one end of the resistor R161, and the other end of the resistor R161 is connected to the port PV1_INPUT+; The port VCCB is connected to the negative end of the diode D26 and the pin 2 of the relay RLY4, the positive end of the diode D26 and the pin 1 of the relay RLY4 are connected to the collector of the transistor Q25, the base of the transistor Q25 is connected to one end of the resistor R381 and one end of the resistor R382, the other end of the resistor R381 is connected to the port ISO_RLY.COM, the other end of the resistor R382 and the emitter of the transistor Q25 are connected to the port AGND, the pin 3 of the relay RLY4 is connected to one end of the resistor R405, the other end of the resistor R405 is connected to one end of the resistor R406, the other end of the resistor R406 is connected to the port AGND, the pin 4 of the relay RLY4 is connected to one end of the resistor R392, the other end of the resistor R392 is connected to one end of the resistor R400, and the other end of the resistor R400 is connected to the port CHGND; The port AGND is connected to one end of the resistor R915, the other end of the resistor R915 is connected to one end of the resistor R916, the other end of the resistor R916 is connected to one end of the resistor R917, the other end of the resistor R917 is connected to the port PV.ISO-, the port CHGND is connected to one end of the resistor R919, the other end of the resistor R919 is connected to one end of the resistor R920, the other end of the resistor R920 is connected to one end of the resistor R921, the other end of the resistor R921 is connected to the port PV.ISO+; The port PV.ISO- is connected to one end of the resistor R930, the other end of the resistor R930 is connected to pin 3 of the clamping diode D169, one end of the capacitor C485, one end of the resistor R928 and pin 6 of the operational amplifier U46, pin 1 of the clamping diode D169 is connected to port AGND, pin 2 of the clamping diode D169 is connected to port VCCB, the other end of the capacitor C485, the other end of the resistor R928 and pin 7 of the operational amplifier U46 are connected to one end of the resistor R932, the port PV.ISO+ is connected to one end of the resistor R931, the other end of the resistor R931 is connected to pin 3 of the clamping diode D170, one end of the resistor R929, one end of the capacitor C486 and pin 5 of the operational amplifier U46, pin 1 of the clamping diode D170 is connected to port AGND, pin 2 of the clamping diode D170 is connected to port VCCB, the other end of the resistor R929 and the other end of the capacitor C486 are connected to port AGND, the other end of the resistor R932 is connected to one end of capacitor C484, pin 3 of the clamping diode D171 and port ISO.V, the other end of the capacitor C484 is connected to pin 1 of the clamping diode D171 and port AGND, pin 2 of the clamping diode D171 is connected to port SMCU_3.3V, pin 1 of the operational amplifier U46 is connected to pin 2 of the operational amplifier U46, pin 3 of the operational amplifier U46 is connected to port AGND, pin 4 of the operational amplifier U46 is connected to port AGND and one end of capacitor C487, and pin 8 of the operational amplifier U46 is connected to port VCCB and the other end of the capacitor C487; The port ISO_RLY1, the port ISO_RLY.COM and the port ISO.V are connected to a controller.

2. The insulation impedance detection circuit for a micro grid-connected inverter according to claim 1, characterized in that: The port VCCB is a power supply port, the port PV1_INPUT+ is connected to the positive terminal of the inverter input port, the port AGND is connected to the negative terminal of the inverter input port, the port CHGND is connected to the insulation impedance ground, and the port SMCU_3.3V is connected to a 3.3V power supply.

3. The insulation impedance detection circuit for a micro grid-connected inverter according to claim 1, characterized in that: The controller is a single chip microcomputer, model TMS320F280025PMSR.

4. The insulation impedance detection circuit for a micro grid-connected inverter according to claim 1, characterized in that: The transistor Q124 and the transistor Q25 are of model BC846A-HAF.

5. The insulation impedance detection circuit for a micro grid-connected inverter according to claim 1, characterized in that: The operational amplifier U46 is of model LM2904BIDR.

6. The insulation impedance detection circuit for a micro grid-connected inverter according to claim 1, characterized in that: The clamping diode D170 is of model BAV99.

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