Relay control circuit and grid-connected inverter control system

Abstract

The invention provides a relay control circuit and a grid-connected inverter control system. The relay control circuit comprises a relay, two switching tubes, an anti-backflow device, two control circuits and two control units, one end of a coil of the relay is connected with a power supply of the relay, and the other end is connected with a first pole of the first switch tube; the second pole and the third pole of the first switch tube are connected with the first pole of the second switch tube; the second pole and the third pole of the second switch tube are connected with system reference ground; the third pole of the first switch tube is also electrically connected with one end of an anti-backflow device, the other end of the anti-backflow device is connected with a first control circuit, and the first control circuit is connected with a first control unit; the third pole of the second switch tube is also connected with the second control circuit; the second control circuit is connected with the second control unit; the first control unit is connected with the second control unit, only one anti-backflow device is added, an additional auxiliary power supply does not need to be introduced, and the cost and the complexity of the circuit can be reduced.

Description

A relay control circuit and a grid-connected inverter control system Technical Field

[0001] This invention relates to the field of grid-connected inverters, and more particularly to a relay control circuit and a grid-connected inverter control system. Background Technology

[0002] In industry and international standards for photovoltaic grid-connected inverters, small photovoltaic grid-connected inverters require electrical control redundancy in the relays at the grid connection port. Generally, to meet regulatory requirements, two relays are added in series at the grid connection port. When the control system fails, the relay system can still perform protective actions. However, this leads to increased product costs and reduced system efficiency. To meet the cost requirements of low-power grid-connected inverters, the industry practice is to use two independent microcontroller units (MCUs) to control a double-pole double-throw relay connected across the live and neutral wires. When one MCU malfunctions or experiences a program error, the other MCU can still control the relay for protection based on signals from its internal communication and detection circuits.

[0003] In this setup with two MCUs, each MCU is connected to a switching transistor and a control circuit. Since the two switching transistors are connected in series, the reference level of the upper transistor changes as the lower transistor is switched on and off. When the lower transistor is turned off, the source potential of the upper transistor becomes VCC (the power supply voltage for a relay is typically 12V), while the relay's control circuit operates at a low voltage of 3.3V or 5V. This can lead to voltage reverse flow, causing control logic failure or device damage.

[0004] Current solutions to the problem of voltage backflow caused by the floating ground of the switching transistor during driving usually require the introduction of an additional auxiliary power supply. Although the control purpose can be achieved, it will increase the cost and the complexity of the circuit. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a relay control circuit and a grid-connected inverter control system, which only requires the addition of an anti-backflow device and does not require the introduction of an additional auxiliary power supply, thereby reducing cost and circuit complexity.

[0006] In a first aspect, embodiments of the present invention provide a relay control circuit, the circuit comprising: a relay, a first switching transistor, an anti-backflow device, a first control circuit, a first control unit, a second switching transistor, a second control circuit, and a second control unit; one end of the coil of the relay is electrically connected to the power supply of the relay, and the other end of the coil is electrically connected to the first pole of the first switching transistor; the second and third poles of the first switching transistor are electrically connected to the first pole of the second switching transistor, and the second and third poles of the second switching transistor are connected to the system reference ground; the third pole of the first switching transistor is also electrically connected to one end of the anti-backflow device, and the other end of the anti-backflow device is electrically connected to the first control circuit, the first control circuit and the first control unit are electrically connected; the third pole of the second switching transistor is also electrically connected to the second control circuit, the second control circuit and the second control unit are electrically connected; the first control unit and the second control unit are electrically connected.

[0007] Optionally, the anti-backflow device is a diode, with the cathode of the diode electrically connected to the third electrode of the first switching transistor, and the anode electrically connected to the first control circuit.

[0008] Optionally, it further includes: a first resistor, a second resistor, a third resistor, and a fourth resistor; the first resistor is located between the third terminal of the first switching transistor and the anti-reverse current device; one end of the second resistor is electrically connected to the third terminal of the first switching transistor and one end of the first resistor, and the other end is electrically connected to the first terminal of the second switching transistor; the third resistor is located between the third terminal of the second switching transistor and the second control circuit; one end of the fourth resistor is electrically connected to the third terminal of the second switching transistor and one end of the third resistor, and the other end is connected to the system reference ground.

[0009] Optionally, the first control unit and the second control control unit communicate and check each other.

[0010] Optionally, the first control unit and the second control unit are used to control the relay to turn on by cooperating with each other according to a preset on-time sequence, and to control the relay to turn off by cooperating with each other according to a preset off-time sequence.

[0011] Optionally, the second control unit is configured to send a conduction signal to the second control circuit to control the second switch to conduct at a first moment after determining that the relay needs to be turned on; the first control unit is configured to send a conduction signal to the first control circuit to control the first switch to conduct at a second moment after determining that the relay needs to be turned on; wherein the second moment is later than the first moment.

[0012] Optionally, the first control unit is configured to send a shutdown signal to the first control circuit to control the first switch to turn off at a third time after determining that the relay needs to be turned off; the second control unit is configured to send a shutdown signal to the second control circuit to control the second switch to turn off at a fourth time after determining that the relay needs to be turned off; wherein the fourth time is later than the third time.

[0013] Optionally, the first switch and the second switch are metal-oxide-semiconductor field-effect transistors or bipolar junction transistors.

[0014] Optionally, the relay is also electrically connected to the grid-connected inverter and the power grid.

[0015] On the other hand, embodiments of the present invention provide a grid-connected inverter control system, including the aforementioned relay control circuit.

[0016] In the technical solution of the relay control circuit and grid-connected inverter control system provided in this invention embodiment, the circuit includes: a relay, a first switching transistor, an anti-backflow device, a first control circuit, a first control unit, a second switching transistor, a second control circuit, and a second control unit; one end of the relay coil is electrically connected to the relay's power supply, and the other end of the coil is electrically connected to the first pole of the first switching transistor; the second and third poles of the first switching transistor are electrically connected to the first pole of the second switching transistor, and the second and third poles of the second switching transistor are connected to the system reference ground; the third pole of the first switching transistor is also electrically connected to one end of the anti-backflow device, and the other end of the anti-backflow device is electrically connected to the first control circuit, and the first control circuit and the first control unit are electrically connected; the third pole of the second switching transistor is also electrically connected to the second control circuit, and the second control circuit and the second control unit are electrically connected; the first control unit and the second control unit are electrically connected. By adding only one anti-backflow device, no additional auxiliary power supply is needed, which reduces cost and circuit complexity. Attached Figure Description

[0017] Figure 1 is a schematic diagram of a relay control circuit provided in an embodiment of the present invention; Figure 2 is a specific schematic diagram of a part of the circuit in Figure 1; Figure 3 is another specific schematic diagram of a part of the circuit in Figure 1; Figure 4 is a schematic diagram of the relay control timing in an embodiment of the present invention; Figure 5 is a structural schematic diagram of a grid-connected inverter control system provided in an embodiment of the present invention. Detailed Implementation

[0018] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0020] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0021] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0022] To solve the floating ground problem of the switching transistor during driving, the conventional solutions are generally as follows: 1. Raise the driving voltage of the control circuit of the upper switching transistor to above VCC, so that the relay power supply VCC cannot flow back to the driving circuit; 2. Use an independent isolated power supply to keep the reference of the upper switching transistor and its connected upper control circuit at the same level, while the voltage of the upper control circuit is always higher than the source voltage of the upper switching transistor, which can also achieve the purpose of preventing the relay power supply VCC from flowing back to the driving circuit.

[0023] The core of both schemes is to introduce an additional auxiliary power supply so that the voltage of the power supply VCC at the reference point of the upper switching transistor is always lower than the reference potential of the upper control circuit, thereby enabling the upper control circuit to control the upper switching transistor at any time.

[0024] While both of the above methods can achieve the goal of control, they will increase costs and circuit complexity.

[0025] To address the aforementioned technical problems, embodiments of the present invention provide a relay control circuit that only requires the addition of an anti-reverse current device, eliminating the need for an additional auxiliary power supply, thereby reducing cost and circuit complexity.

[0026] Figure 1 is a schematic diagram of a relay control circuit provided in an embodiment of the present invention. As shown in Figure 1, the relay control circuit includes: a relay, a first switching transistor, an anti-backflow device, a first control circuit, a first control unit, a second switching transistor, a second control circuit, and a second control unit. One end of the relay coil is electrically connected to the relay power supply VCC, and the other end of the coil is electrically connected to the first pole of the first switching transistor. The second and third poles of the first switching transistor are electrically connected to the first pole of the second switching transistor, and the second and third poles of the second switching transistor are connected to the system reference ground. The third pole of the first switching transistor is also electrically connected to one end of the anti-backflow device, and the other end of the anti-backflow device is electrically connected to the first control circuit. The first control circuit and the first control unit are electrically connected. The third pole of the second switching transistor is also electrically connected to the second control circuit. The second control circuit and the second control unit are electrically connected. The first control unit and the second control unit are electrically connected.

[0027] A relay is an electrical control device that works on the principle of electromagnetics. It can control the switching of a large current circuit with a small current, and plays a role in automatic adjustment, safety protection, and circuit switching in the circuit.

[0028] For example, a relay mainly consists of two parts: an electromagnetic system and a contact system. The electromagnetic system includes a coil, an iron core, an armature, and a return spring. The contact system includes normally open contacts and normally closed contacts. When a rated voltage is applied across the coil, current flows through the coil, generating a magnetic field. The iron core is magnetized, generating a magnetic force that attracts the armature against the spring force, causing the moving contact to close or open with the stationary contact. After the coil is de-energized, the magnetic force disappears, the spring pulls the armature back to its original position, and the contacts return to their initial state. This "energized to engage, de-energized to release" characteristic enables the relay to achieve automatic circuit control.

[0029] For example, the first control unit and the second control unit are MCUs.

[0030] In a relay control circuit provided by this invention, to prevent voltage backflow from the relay's power supply VCC to the first control circuit, an anti-backflow device is added before the first control circuit. The device's withstand voltage is greater than that of the relay's power supply VCC. This invention only adds one anti-backflow device, eliminating the need for an additional auxiliary power supply, thus reducing cost and circuit complexity.

[0031] For example, Figure 2 is a specific schematic diagram of a part of the circuit in Figure 1, and Figure 3 is another specific schematic diagram of a part of the circuit in Figure 1.

[0032] Optionally, as shown in Figures 2 and 3, the anti-reverse current device is a diode D. The cathode of diode D is electrically connected to the third electrode of the first switching transistor Q1, and the anode is electrically connected to the first control circuit.

[0033] Optionally, the first switch Q1 and the second switch Q2 are metal-oxide-semiconductor field-effect transistors (MOSFETs) or bipolar junction transistors (BJTs).

[0034] For example, as shown in Figure 2, the first switch Q1 and the second switch Q2 are metal-oxide-semiconductor field-effect transistors (MOSFETs). A MOSFET is a voltage-controlled semiconductor device and a core component of modern integrated circuits, comprising a gate, source, drain, and substrate. When a positive voltage is applied to the gate, an inversion layer is induced on the semiconductor surface, forming a conductive channel that connects the source and drain. The gate voltage controls the channel width, thereby controlling the drain current. This voltage-controlled characteristic gives MOSFETs the advantages of high input impedance and low drive power.

[0035] When the first switch Q1 and the second switch Q2 are MOSFETs, the first electrode is the drain, the second electrode is the source, and the third electrode is the gate.

[0036] For example, as shown in Figure 3, the first switch Q1 and the second switch Q2 are bipolar junction transistors (BJTs). A BJT is a current-controlled semiconductor device consisting of two PN junctions. It has amplification and switching functions and is a fundamental component in electronic circuits. Compared to MOSFETs, it has advantages such as higher transconductance and better linearity, and still plays an important role in analog circuits and power applications.

[0037] When the first switch Q1 and the second switch Q2 are BJTs, the first electrode is the collector, the second electrode is the emitter, and the third electrode is the base.

[0038] Optionally, as shown in Figures 2 and 3, the relay control circuit further includes: a first resistor, a second resistor, a third resistor, and a fourth resistor; the first resistor Rg1 is located between the third terminal of the first switching transistor Q1 and the anti-reverse current device (the cathode of diode D); one end of the second resistor Rgs1 is electrically connected to the third terminal of the first switching transistor Q1 and one end of the first resistor Rg1, and the other end is located between the first terminal of the second switching transistor Q2; the third resistor Rg2 is located between the third terminal of the second switching transistor Q2 and the second control circuit; one end of the fourth resistor Rgs2 is electrically connected to the third terminal of the second switching transistor Q2 and one end of the third resistor Rg2, and the other end is connected to the system reference ground GND.

[0039] As shown in Figures 2 and 3, the first switching transistor Q1 and the second switching transistor Q2 are connected in series. One end of the coil of relay RY1 is connected to the power supply VCC, and the other end is connected to the first terminal of the first switching transistor Q1. The second terminal of the first switching transistor Q1 is connected to the first terminal of the second switching transistor Q2, and the second terminal of the second switching transistor Q2 is connected to the system reference ground GND. The second resistor Rgs1 and the fourth resistor Rgs2 are connected across the third terminals of the first switching transistor Q1 and the second switching transistor Q2, respectively, to prevent the switching transistors from malfunctioning due to interference. The first resistor Rg1 and the third resistor Rg2 are driving resistors. The third terminal of the first switching transistor Q1 is also connected to one end of the first resistor Rg1, and the other end of the first resistor Rg1 is connected to the cathode of the anti-reverse current device (diode D). The anode of the diode D is connected to the first control circuit. The third terminal of the second switching transistor Q2 is also connected to one end of the third resistor Rg2, and the other end of the third resistor Rg2 is directly connected to the second control circuit.

[0040] Optionally, as shown in Figure 1, the first control unit and the second control control unit communicate and check each other.

[0041] Optionally, the first control unit and the second control unit are used to control the relay to turn on by cooperating with each other according to a preset turn-on sequence, and to control the relay to turn off by cooperating with each other according to a preset turn-off sequence.

[0042] This invention uses two independent control units to issue relay drive control signals. The core of this invention is that the two control units communicate and check each other. Only after the internal self-test is completed is the control unit allowed to issue relay control signals. Furthermore, these two drive signals need to have timing restrictions.

[0043] Optionally, the second control unit is used to send a conduction signal to the second control circuit to control the second switch Q2 to conduct at a first moment after determining that the relay needs to be turned on; the first control unit is used to send a conduction signal to the first control circuit to control the first switch Q1 to conduct at a second moment after determining that the relay needs to be turned on; wherein the second moment is later than the first moment.

[0044] The logic for engaging the relay is that the second control unit sends a signal to open the second switch Q2. Since the second terminal of the first switch Q1 is connected to the reference ground level after the second switch Q2 is opened, the first control unit sends a control signal to open the first switch Q1.

[0045] For example, Figure 4 is a schematic diagram of the relay control timing in an embodiment of the present invention. As shown in Figure 4, when the relay needs to be engaged at time t0, the second control circuit is first controlled to send a high level to the second switch Q2 at time t1. At this time, the second switch Q2 will be turned on, and the reference potential of the second pole of the first switch Q1 will change from 1 / 2 Vcc to GND. Then, at time t2, the first control circuit is controlled to send a high level to the first switch Q1, and the first switch Q1 will also be turned on. VCC will charge the excitation coil of the relay and generate a magnetic force on its iron core, attracting the two contacts and turning on the relay.

[0046] Optionally, the first control unit is used to send a shutdown signal to the first control circuit to control the first switch Q1 to turn off at a third time after determining that the relay needs to be turned off; the second control unit is used to send a shutdown signal to the second control circuit to control the second switch Q2 to turn off at a fourth time after determining that the relay needs to be turned off; wherein the fourth time is later than the third time.

[0047] The logic for turning off the relay is as follows: the first control unit sends a signal to turn off the first switch Q1, and then the second control unit sends a signal to turn off the second switch Q2.

[0048] For example, as shown in Figure 4, when the relay needs to be turned off at time t3, the first control circuit first sends a low level to the first switch Q1 at time t4. At this time, the first switch Q1 will be turned off, and the reference potential of the second terminal of the first switch Q1 is still GND. Then, at time t5, the second control circuit sends a low level to the second switch Q2, and the second switch Q2 will also be turned off. However, after the second switch Q2 is turned off, the reference potential of the second terminal of the first switch Q1 gradually recovers to 1 / 2 Vcc due to the influence of the current between its first and second terminals. Its third terminal voltage will be higher than the voltage at the port of the first control circuit. Therefore, it is blocked by diode D1 to prevent its voltage from affecting the safe operation of the controller. Since both switches Q1 and Q2 have been turned off, the current on the relay coil will gradually decrease to zero, and the magnetic force on the iron core will disappear, and the relay will be turned off.

[0049] Optionally, as shown in Figure 1, the relay is also connected to the grid-connected inverter and the power grid.

[0050] The embodiments of the present invention have a very low cost advantage, and can achieve the purpose of controlling two switching transistors independently without adding an additional separate drive power supply. At the same time, they have inherent control timing to prevent control errors.

[0051] Based on the above-described relay control circuit, this embodiment of the invention provides a control method for the relay control circuit, including: step 1, communication and mutual inspection between the first control unit and the second control control unit.

[0052] Step 2: The second control unit sends a turn-on signal to the second control circuit to control the second switch to turn on immediately after determining that the relay needs to be turned on.

[0053] Step 3: At the second moment after determining that the relay needs to be turned on, the first control unit sends a turn-on signal to the first control circuit to control the first switching transistor to turn on.

[0054] The second moment is later than the first moment.

[0055] Step 4: At the third moment after determining that the relay needs to be turned off, the first control unit sends a turn-off signal to the first control circuit to control the first switching transistor to turn off.

[0056] Step 5: At the fourth moment after determining that the relay needs to be turned off, the second control unit sends a turn-off signal to the second control circuit to control the second switch to turn off.

[0057] The fourth moment is later than the third moment.

[0058] Figure 5 is a schematic diagram of the structure of a grid-connected inverter control system provided in an embodiment of the present invention. As shown in Figure 5, the system includes the relay control circuit in the above embodiment. Since it includes the relay control circuit, it has the same beneficial effects as the relay control circuit.

[0059] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A relay control circuit, characterized in that, The circuit includes: a relay, a first switching transistor, an anti-backflow device, a first control circuit, a first control unit, a second switching transistor, a second control circuit, and a second control unit; one end of the relay coil is electrically connected to the relay's power supply, and the other end of the coil is electrically connected to the first pole of the first switching transistor; the second and third poles of the first switching transistor are electrically connected to the first pole of the second switching transistor, and the second and third poles of the second switching transistor are connected to the system reference ground; the third pole of the first switching transistor is also electrically connected to one end of the anti-backflow device, and the other end of the anti-backflow device is electrically connected to the first control circuit, which is electrically connected to the first control unit; the third pole of the second switching transistor is also electrically connected to the second control circuit, which is electrically connected to the second control unit; the first control unit and the second control unit are electrically connected.

2. The circuit according to claim 1, characterized in that, The anti-backflow device is a diode, with the cathode of the diode electrically connected to the third electrode of the first switching transistor, and the anode electrically connected to the first control circuit.

3. The circuit according to claim 1 or 2, characterized in that, Also includes: A first resistor, a second resistor, a third resistor, and a fourth resistor; the first resistor is located between the third terminal of the first switching transistor and the anti-reverse current device; one end of the second resistor is electrically connected to the third terminal of the first switching transistor and one end of the first resistor, and the other end is electrically connected to the first terminal of the second switching transistor; the third resistor is located between the third terminal of the second switching transistor and the second control circuit; one end of the fourth resistor is electrically connected to the third terminal of the second switching transistor and one end of the third resistor, and the other end is connected to the system reference ground.

4. The circuit according to claim 1, characterized in that, The first control unit and the second control control unit communicate and check each other.

5. The circuit according to claim 4, characterized in that, The first control unit and the second control unit are used to control the relay to turn on according to a preset on sequence and to control the relay to turn off according to a preset off sequence.

6. The circuit according to claim 5, characterized in that, The second control unit is configured to send a conduction signal to the second control circuit to control the second switch to conduct at a first moment after determining that the relay needs to be turned on; the first control unit is configured to send a conduction signal to the first control circuit to control the first switch to conduct at a second moment after determining that the relay needs to be turned on; wherein the second moment is later than the first moment.

7. The circuit according to claim 5, characterized in that, The first control unit is configured to send a shutdown signal to the first control circuit to control the first switch to turn off at a third time after determining that the relay needs to be turned off; the second control unit is configured to send a shutdown signal to the second control circuit to control the second switch to turn off at a fourth time after determining that the relay needs to be turned off; wherein the fourth time is later than the third time.

8. The circuit according to claim 1, characterized in that, The first switch and the second switch are metal-oxide-semiconductor field-effect transistors or bipolar junction transistors.

9. The circuit according to claim 1, characterized in that, The relay is also electrically connected to the grid-connected inverter and the power grid.

10. A grid-connected inverter control system, characterized in that, The relay control circuit includes any one of claims 1 to 9.

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