Switching device, power conversion device, energy storage system and grid-connected control method

Abstract

The application provides a switching device, a power conversion device, an energy storage system and a grid-connected control method. In the switching device, a first end of a coil of a relay is connected to a first power supply voltage, a second end of the coil is connected to ground through a first driving switch tube and a bootstrap resistor connected in series, and the bootstrap resistor is connected to a second power supply voltage through a second driving switch tube. The first driving switch tube is used for being turned on when a driving signal is received. The second driving switch tube is used for being turned on when the second power supply voltage is connected and the first driving switch tube is turned on, so that the voltage of the bootstrap resistor is the second power supply voltage, and the voltage of the bootstrap capacitor relative to the ground can reach the sum of the first power supply voltage and the second power supply voltage, thereby the contact attraction speed can be accelerated, and the relay can be closed at a voltage zero-crossing point.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to a switching device, a power conversion device, an energy storage system, and a grid connection control method. Background Technology

[0002] Relays play a crucial role in energy storage systems, serving as a three-in-one mechanism for safety isolation, energy dispatch, and system protection. Therefore, the requirements for relay efficiency, lifespan, and reliability are increasingly stringent. If the relay's closing time has a large variation, it can easily lead to a relay operating delay, causing the relay to fail to close at the zero-crossing voltage point. In this case, a large voltage difference across the relay contacts will generate a significant inrush current upon closure, potentially triggering a chain reaction of risks such as arcing, contact welding, and a sharp reduction in device lifespan. Summary of the Invention

[0003] In view of this, this application provides a switching device, a power conversion device, an energy storage system, and a grid-connected control method, which is beneficial for realizing the closing of the relay when the voltage crosses zero.

[0004] The first aspect of this application provides a switching device, comprising: a relay, a drive circuit, and a bootstrap circuit; the relay is connected between an inverter circuit and a grid-connected interface for connecting to a power grid; the drive circuit includes a first drive switch and a second drive switch; the bootstrap circuit includes a bootstrap capacitor and a bootstrap resistor; a first terminal of the relay coil is used to connect to a first supply voltage and grounded through a series-connected bootstrap capacitor and bootstrap resistor; a second terminal of the relay coil is grounded through the first drive switch and connected to the bootstrap resistor and a second supply voltage through the second drive switch; the first drive switch is used to turn on when a drive signal is received; the second drive switch is used to turn on when the second supply voltage is connected and the first drive switch is turned on, such that the voltage of the bootstrap resistor is the second supply voltage, and the voltage of the bootstrap capacitor relative to ground can reach the sum of the first supply voltage and the second supply voltage.

[0005] It is understandable that at the instant the second drive switch is turned on, the voltage of the bootstrap capacitor relative to ground can be raised to the sum of the first and second supply voltages. Since the relay coil is connected to the bootstrap circuit, the relay coil can access the voltage of the bootstrap capacitor relative to ground; that is, the relay coil voltage can access the sum of the first and second supply voltages. This increases the strength of the magnetic field generated by the relay, producing a larger electromagnetic signal to drive the relay contacts. Therefore, it can accelerate the closing of the relay contacts, shorten the relay's closing action time, and improve the consistency of the relay's activation time. This reduces the probability of relay action delay, improves the relay's control accuracy, and facilitates the relay closing at the voltage zero-crossing point.

[0006] In one embodiment, the coil of the relay is connected to the voltage of the bootstrap capacitor relative to ground, and generates a first electromagnetic signal when the voltage of the bootstrap capacitor relative to ground is the sum of voltages, and generates a second electromagnetic signal when the bootstrap capacitor discharges to the point where the voltage of the bootstrap capacitor relative to ground is the first supply voltage; wherein, the first electromagnetic signal is used to control the contacts of the relay to start operating; and the second electromagnetic signal is used to control the relay to remain in the closed state.

[0007] In one embodiment, the first driving switch includes an N-type semiconductor switch, and the second driving switch includes a P-type semiconductor switch.

[0008] In one embodiment, the first connection terminal of the first driving switch is connected to the second terminal of the relay coil, the second connection terminal of the first driving switch is grounded, and the control terminal of the first driving switch is connected to the controller and used to receive the driving signal output by the controller; the control terminal of the second driving switch is connected to the first connection terminal of the first driving switch and is connected to the second connection terminal of the second driving switch through a current limiting resistor, the first connection terminal of the second driving switch is connected to a bootstrap resistor, and the second connection terminal of the second driving switch is connected to a power supply.

[0009] In one embodiment, the relay includes a live wire relay and a neutral wire relay. The live wire relay is located between the live wire terminal of the inverter circuit and the live wire terminal of the power grid, and the neutral wire relay is located between the neutral wire terminal of the inverter circuit and the neutral wire terminal of the power grid. The coils of the live wire relay and the neutral wire relay are connected in parallel.

[0010] In one embodiment, the first end of the relay coil is connected to a power supply, and the second end of the relay coil is connected to the power supply through a second drive switch. The first power supply voltage and the second power supply voltage are the power supply voltages output by the power supply.

[0011] The second aspect of this application provides a power conversion device, which includes an inverter circuit, a grid connection interface, and a switching device as described in the first aspect or any embodiment of the first aspect, wherein the switching device is connected between the inverter circuit and the grid connection interface.

[0012] In one embodiment, the power conversion device further includes a controller connected to the first drive switch and the inverter circuit, and used to control the switching state of the first drive switch and the operation of the inverter circuit.

[0013] The third aspect of this application provides an energy storage system, which includes an inverter circuit, a grid connection interface, an energy storage battery, and a switching device as described in the first aspect or any embodiment of the first aspect. The DC terminal of the inverter circuit is connected to the energy storage battery, and the AC terminal of the inverter circuit is connected to the grid connection interface through the switching device.

[0014] A fourth aspect of this application provides a grid-connected control method, which includes: acquiring the phase of the grid voltage and the previous zero-crossing point; acquiring the closing time of the switching device between the inverter circuit and the grid; calculating a first phase from the previous zero-crossing point to the closing time of the switching device based on the closing time of the switching device and the previous zero-crossing point; the first phase representing the phase delay caused by the closing time of the switching device; obtaining a target phase based on the first phase; generating a drive signal based on the target phase; the time corresponding to the target phase representing the output time of the drive signal, and the drive signal being used to drive the first drive switch in the switching device to turn on, so that the switching device closes at the zero-crossing point of the grid voltage.

[0015] It is understood that the grid-connected control method of this application can compensate for the phase delay caused by the closing time of the switching device by calculating the target phase, so as to accurately determine the timing of the early transmission of the drive signal. Therefore, the drive signal generated according to the target phase can control the relay contacts to close precisely at the zero-crossing point of the grid voltage, which greatly reduces the voltage difference across the relay contacts at the moment of contact closure, thereby reducing the inrush current. This effectively reduces the chain risks caused by the inrush current, such as arcing, contact welding, and sudden reduction in device life, improves the safety performance of the switching device and inverter circuit, and helps to extend the service life of the switching device and inverter circuit.

[0016] In one embodiment, obtaining the target phase based on the first phase includes: calculating the difference between the peak phase of the grid voltage and the first phase to obtain the target phase.

[0017] In one embodiment, the grid-connected control method includes: in response to a start command for starting an inverter circuit, performing phase-locked loop control on the AC voltage of the inverter circuit and the grid voltage to obtain the grid voltage phase. Attached Figure Description

[0018] Figure 1 This is a connection diagram of a switching device provided in an embodiment of this application.

[0019] Figure 2 It is a circuit topology diagram of a switching device in related technologies.

[0020] Figure 3 This is a circuit topology diagram of a switching device provided in an embodiment of this application.

[0021] Figure 4 yes Figure 3 The diagram shows a signal waveform of a switching device.

[0022] Figure 5 This is a schematic diagram of an experimental test result for a switching device of related technologies and a switching device according to an embodiment of this application.

[0023] Figure 6 This is a schematic diagram of a power conversion device provided in an embodiment of this application.

[0024] Figure 7 This is a flowchart of a grid connection control method provided in an embodiment of this application.

[0025] Figure 8 This is a detailed flowchart of a grid connection control method provided in an embodiment of this application. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application. Unless otherwise specified, the different embodiments and features described below can be combined with each other.

[0027] Figure 1 This is a schematic diagram of a connection for a switching device provided in an embodiment of this application. Figure 1 As shown, the switching device is connected between the AC terminal of the inverter circuit and the grid connection interface, which is used to connect to the power grid.

[0028] Based on this design, the switching device can function as a grid-connected switch. When the inverter circuit operates in grid-connected mode, the switching device is in the ON state to electrically connect the inverter circuit and the power grid. When the inverter circuit operates in off-grid mode, the switching device is in the OFF state to disconnect the inverter circuit from the power grid.

[0029] The inverter circuit can be selected with appropriate circuit topology according to actual needs. For example, it can use a bidirectional inverter circuit that can achieve both inversion and rectification functions, such as a dual active bridge inverter circuit. Alternatively, it can use a circuit specifically designed for inversion, such as a three-phase full-bridge inverter circuit or a three-phase half-bridge inverter circuit. The DC terminal of the inverter circuit can be electrically connected to a DC power source, such as an energy storage battery, a DC-DC converter circuit, or a DC generator. The inverter circuit can convert the DC voltage provided by the DC power source into AC voltage. When the inverter circuit is connected to the grid, the AC voltage generated by the inverter circuit is in phase with the grid voltage.

[0030] Continue reading Figure 1The inverter circuit 20 and the switching device 10 are electrically connected to the controller 50. The controller 50 can be a general-purpose controller such as a digital signal processor (DSP) or a microcontroller unit (MCU). The switching device 10 includes a relay. The controller 50 is used to control the operating state of the inverter circuit 20 and the on / off state of the relay in the switching device 10.

[0031] It is understood that the relays in the switching device 10 are arranged in groups, with each group consisting of two relays: a live wire relay and a neutral wire relay. The live wire relay is connected between the live wire terminal of the inverter circuit 20 and the live wire terminal of the grid connection interface 30, and the neutral wire relay is connected between the neutral wire terminal of the inverter circuit 20 and the neutral wire terminal of the grid connection interface 30. The relays can be arranged in single or multiple groups. Arranging multiple groups of relays can prevent a single relay from sticking together and causing the switching function of the switching device 10 to fail.

[0032] Figure 2 A circuit diagram of a switching device in the related art is shown. For example... Figure 2 As shown, the switching device includes two sets of relays, namely a first set of relays and a second set of relays. The first set of relays includes relays RY1 and RY3, and the second set of relays includes relays RY2 and RY4. For ease of distinction, relays RY1 and RY2 can also be called live wire relays, and relays RY3 and RY4 can also be called neutral wire relays.

[0033] Contacts K1 and K2 of live wire relays RY1 and RY2 are connected in series between the live wire terminal AC_L of the AC side of inverter circuit 20 and the live wire terminal GRID_L of grid-connected interface 30. Contacts K3 and K4 of neutral wire relays RY3 and RY4 are connected in series between the neutral wire terminal AC_N of the AC side of inverter circuit 20 and the neutral wire terminal GRID_N of grid-connected interface 30. The live wire terminal GRID_L of grid-connected interface 30 is used to connect to the live wire of power grid 40, and the neutral wire terminal GRID_N of grid-connected interface 30 is used to connect to the neutral wire of power grid 40.

[0034] The coil W1 of the live wire relay RY1 and the coil W3 of the neutral wire relay RY3 are connected in parallel, and the coil W2 of the live wire relay RY2 and the coil W4 of the neutral wire relay RY4 are connected in parallel.

[0035] Additionally, please refer to... Figure 2 The switching device also includes drive switching transistors Q1 and Q2. The first ends of coils W1, W2, W3, and W4 are all used to connect to the first power supply voltage V1. The second ends of coils W1 and W3 are grounded through drive switching transistor Q1, and the second ends of coils W2 and W4 are grounded through drive switching transistor Q2.

[0036] For the live wire relay RY1, when the first terminal of coil W1 is connected to the first power supply voltage V1, if the drive switch Q1 is turned on, coil W1 is in a closed circuit, thus generating a magnetic field that attracts and moves the armature of relay RY1. The armature of relay RY1 then pushes the contact K1 to close (or engages) through the insulating push rod of relay RY1. When the first terminal of coil W1 is not connected to the first power supply voltage V1, i.e., coil W1 is de-energized, contact K1 opens. The working process of the neutral wire relay RY3 is the same as or similar to that of the live wire relay RY1, and will not be described further.

[0037] For the live wire relay RY2, when the first terminal of coil W2 is connected to the first power supply voltage V1, if the drive switch Q2 is turned on, coil W2 is in a closed circuit, thus generating a magnetic field that attracts and moves the armature of relay RY2. The armature of relay RY2 then pushes the contact K2 to close via the insulating push rod of relay RY2. When the first terminal of coil W2 is not connected to the first power supply voltage V1, i.e., coil W2 is de-energized, contact K2 opens. The working process of the neutral wire relay RY4 is the same as or similar to that of the live wire relay RY2, and will not be described further.

[0038] When all contacts K1~K4 are closed, that is, when all relays RY1~RY4 are conducting, the live wire terminal AC_L of the AC end of the inverter circuit 20 and the live wire terminal GRID_L of the grid-connected interface 30 are connected, and the neutral wire terminal AC_N of the AC end of the inverter circuit 20 and the neutral wire terminal GRID_N of the grid-connected interface 30 are connected, so the inverter circuit 20 can then operate in grid-connected mode.

[0039] Ideally, relays RY1~RY4 close at the moment the grid voltage crosses zero. This is because the AC voltage generated by the grid-connected inverter circuit 20 is in phase with the grid voltage. When the grid voltage crosses zero, the AC voltage also crosses zero. If the relays are closed at this time, the voltage difference across the relays is essentially zero, which helps ensure the safety of the devices and circuits.

[0040] However, Figure 2 In switching devices, the closing time of relays RY1~RY4 has a large dispersion, which can easily cause relay operation delay. This can result in the relays not closing when the voltage crosses zero. In this case, the voltage difference across the relay contacts will be large, and a large inrush current will be generated at the moment the relay closes, which can lead to a chain of risks such as electric arc, contact welding, and a sudden reduction in device life.

[0041] Therefore, embodiments of this application provide, as follows: Figure 3 The switch device 10 shown can improve the timing dispersion of the closing action of relays RY1~RY4, which is beneficial to realize the closing of the relays when the voltage crosses zero.

[0042] Please see Figure 3 The switching device 10 in this embodiment includes two sets of relays, wherein the first set of relays includes relays RY1 and RY3, and the second set of relays includes relays RY2 and RY4. The contents of relays RY1 to RY4 can be found in [reference needed]. Figure 2 The relevant description will not be repeated here. It should be understood that in other embodiments, the switching device 10 may also be provided with a single set of relays, or three or more sets of relays.

[0043] Continue reading Figure 3 In this embodiment, the switching device 10 further includes a drive circuit 11 and a bootstrap circuit 12. Each group of relays has a corresponding drive circuit 11 and bootstrap circuit 12. The drive circuit 11 is used to drive the relay to conduct, and the bootstrap circuit 12 is used to boost the voltage of the relay to assist in driving the relay to conduct.

[0044] For ease of distinction, in this application embodiment, the driving circuit 11 corresponding to the first group of relays is referred to as the first driving circuit 11A, the bootstrap circuit 12 corresponding to the first group of relays is referred to as the first bootstrap circuit 12A, the driving circuit 11 corresponding to the second group of relays is referred to as the second driving circuit 11B, and the bootstrap circuit 12 corresponding to the second group of relays is referred to as the second bootstrap circuit 12B.

[0045] The first drive circuit 11A includes a first drive switch Q1 and a second drive switch Q3. The first bootstrap circuit 12A includes a bootstrap capacitor C1 and a bootstrap resistor R1. The first terminals of the coils of relays RY1 and RY3 are used to connect to a first supply voltage V1 and are also grounded through the series-connected bootstrap capacitor C1 and bootstrap resistor R1. The second terminals of the coils of relays RY1 and RY3 are grounded through the first drive switch Q1, and are connected to the bootstrap resistor R1 through the second drive switch Q3. The second terminals of the coils of relays RY1 and RY3 are also used to connect to a second supply voltage V2.

[0046] More specifically, both the first driving switch Q1 and the second driving switch Q3 have a first connection terminal, a second connection terminal, and a control terminal. The second terminal of the coils of relays RY1 and RY3 is connected to the first connection terminal of the first driving switch Q1, and the second connection terminal of the first driving switch Q1 is grounded. Based on this, when the connected first driving switch is turned on, the coil of the relay can be connected to the voltage of the bootstrap capacitor relative to ground. The control terminal of the first driving switch Q1 is connected to the controller 50. The control terminal of the second driving switch Q3 is connected to the first connection terminal of the first driving switch Q1, and is also connected to the second connection terminal of the second driving switch Q3 through a current-limiting resistor Rs1. The first connection terminal of the second driving switch Q3 is connected to the bootstrap resistor R1, and the second connection terminal of the second driving switch Q3 is used to connect to the second supply voltage V2.

[0047] The first driving switch Q1 and the second driving switch Q3 can be selected from appropriate types of semiconductor switches according to actual conditions. For example, the first driving switch Q1 may be an N-type semiconductor switch, and the second driving switch Q3 may be a P-type semiconductor switch. The first driving switch Q1 conducts when the voltage between its control terminal and its second connection terminal is greater than the threshold voltage Vth1, and the second driving switch Q3 conducts when the voltage between its control terminal and its second connection terminal is less than the threshold voltage Vth2. For ease of description, Figure 3 The example demonstrates the first driving switch Q1, which includes an N-channel MOSFET (NMOS), and the second driving switch Q3, which includes a P-channel MOSFET (PMOS). The gate of both the N-channel and P-channel MOSFETs is the control terminal, the drain is the first connection terminal, and the source is the second connection terminal.

[0048] The first supply voltage V1 and the second supply voltage V2 are provided by the same power supply. The power supply can be an external auxiliary power supply or a DC power supply connected to the inverter circuit 20; no special limitation is made here. For simplicity, Figure 3 In this document, the first supply voltage V1 and the second supply voltage V2 represent the power supply sources. It should be understood that in other embodiments, the first supply voltage V1 and the second supply voltage V2 may also be provided by different power supply sources.

[0049] The specific values ​​of the first supply voltage V1 and the second supply voltage V2 can be determined according to actual conditions (such as the performance parameters of the relay and switching transistor). V1 and V2 can be the same or different. For ease of description, this application uses V1=V2=+12 volts (V) as an example. It should be understood that the voltage required for the relay contacts to be in the closed state is less than V1 and V2, for example, the voltage required for the relay contacts to be in the closed state is 6V.

[0050] The second driving circuit 11B includes a first driving switch Q2 and a second driving switch Q4, and the second bootstrap circuit 12B includes a bootstrap capacitor C2 and a bootstrap resistor R2. It can be understood that the second driving circuit 11B and the first driving circuit 11A have the same topology, and the second bootstrap circuit 12B and the first bootstrap circuit 12A have the same topology. The control terminal of the second driving switch Q3 and the second connection terminal of the second driving switch Q3 are connected through a current-limiting resistor Rs2. Therefore, the contents of the second driving circuit 11B and the second bootstrap circuit 12B can be referred to the relevant descriptions of the first driving circuit 11A and the second bootstrap circuit 12B, and will not be repeated here.

[0051] Understandably, the switching device 10 can also be equipped with protective elements or circuits as needed to improve safety. For example, such as Figure 3As shown, to prevent current from flowing back to the power supply, the power supply is connected to the first terminal of the coils of relays RY1 and RY3 through anti-reverse diode D1, and to the second terminal of the second drive switch Q3 through anti-reverse diode D2. The power supply is connected to the first terminal of the coils of relays RY2 and RY4 through anti-reverse diode D3, and to the second terminal of the second drive switch Q4 through anti-reverse diode D4.

[0052] For example, such as Figure 3 As shown, the second terminal of coil W1 of relay RY1 is connected to the first terminal of coil W1 via a series-connected Zener diode ZD1 and reverse protection diode D5. Similarly, the second terminal of coil W2 of relay RY2 is connected to the first terminal of coil W2 via a series-connected Zener diode ZD2 and reverse protection diode D6. The second terminal of coil W3 of relay RY3 is connected to the first terminal of coil W3 via a series-connected Zener diode ZD3 and reverse protection diode D7. The second terminal of coil W4 of relay RY4 is connected to the first terminal of coil W4 via a series-connected Zener diode ZD4 and reverse protection diode D8. It can be understood that the Zener diode and reverse protection diode provide an energy discharge path for the reverse electromotive force generated when the coil is de-energized. The Zener diode limits the voltage; therefore, the Zener diode and reverse protection diode prevent damage to the drive circuit and devices connected to the relay coil caused by the reverse electromotive force generated when the coil is de-energized, thus protecting the circuit and devices.

[0053] The following is combined with Figure 4 signal waveform diagram Figure 3 The working principle of the switching device 10 will be explained.

[0054] like Figure 4 As shown, at the beginning, such as the period from time T0 to time T1: The power supply outputs a first supply voltage V1 and a second supply voltage V2 of +12V. Therefore, the first terminal of the coils of relays RY1~RY4 is connected to the first supply voltage V1 of +12V, and the bootstrap capacitors C1 and C2 are also connected to +12V, thus charging. The second terminals of the second drive switches Q3 and Q4 are both connected to the second supply voltage V2 of +12V, and the control terminals of the second drive switches Q3 and Q4 are both connected to the second supply voltage V2 of +12V through current-limiting resistors. The current-limiting resistors limit the current and prevent overcurrent stress on the switches.

[0055] At this time, the first drive switches Q1 and Q2 do not receive a high level output from controller 50. Figure 4The driving signal (represented as "1") causes the voltage Vgs between the control terminal and the second connection terminal of the first driving switch Q1 to be lower than the threshold voltage Vth1 of the first driving switch Q1, and the voltage Vgs between the control terminal and the second connection terminal of the first driving switch Q2 to be lower than the threshold voltage Vth1 of the first driving switch Q2. Therefore, the first driving switches Q1 and Q2 are in the off state.

[0056] When the first drive switching transistors Q1 and Q2 are turned off, the coils W1 to W4 of relays RY1 to RY4 are all open-circuited and cannot be connected to +12V voltage. As a result, no electromagnetic force can be generated to attract the contacts together. Therefore, the coil voltage of relays RY1 to RY4 is 0 at this time, and the contacts K1 to K4 of relays RY1 to RY4 are all in a separated state, and there is a 12V voltage difference across the contacts.

[0057] When the first driving switch Q1 is off and the second driving switch Q3 is connected to the second power supply voltage, the voltage Vgs between the control terminal and the second connection terminal of the second driving switch Q3 reaches a certain magnitude, exceeding the threshold voltage Vth2 of the second driving switch Q3. Therefore, the second driving switch Q3 is also off. Similarly, when the first driving switch Q2 is off, the second driving switch Q4 is also off.

[0058] At time T1: The power supply maintains an output of +12V. The first drive switches Q1 and Q2 receive a high-level drive signal from the controller 50, causing the voltage Vgs between the control terminal and the second connection terminal of the first drive switch Q1 to exceed the threshold voltage Vth1 of the first drive switch Q1, and the voltage Vgs between the control terminal and the second connection terminal of the first drive switch Q2 to exceed the threshold voltage Vth1 of the first drive switch Q2. Therefore, the first drive switches Q1 and Q2 are driven to conduct.

[0059] When the first driving switch Q1 is turned on, the control terminal of the second driving switch Q3 is connected to ground, meaning the voltage level at the control terminal is pulled low. This causes the voltage Vgs between the control terminal and the second connection terminal of the second driving switch Q3 to be lower than the threshold voltage Vth2 of the second driving switch Q3, thus the second driving switch Q3 is also turned on. When the second driving switch Q3 is turned on, the voltage across the bootstrap resistor R1 is the second supply voltage + 12V, causing the voltage of the bootstrap capacitor C1 relative to ground to reach the sum of the voltages across the bootstrap capacitor and the bootstrap resistor. In other words, the voltage of the bootstrap capacitor C1 relative to ground is raised to the sum of the first and second supply voltages, V1 + V2, which is +24 volts (V).

[0060] Similarly, when the first driving switch Q2 is turned on, the second driving switch Q4 is also turned on. When the second driving switch Q4 is turned on, the voltage across the bootstrap resistor R2 is the second supply voltage +12V, which raises the voltage of the bootstrap capacitor C2 relative to ground to +24V.

[0061] When the first drive switch Q1 is turned on, the coils W1-W4 of relays RY1-RY4 are all conductive, allowing the bootstrap capacitor C2 to connect to the +24V voltage relative to ground. This energizes relays RY1-RY4, generating a magnetic field. This produces a first electromagnetic signal (such as a first electromagnetic force) that attracts the armatures of relays RY1-RY4, causing them to move. Driven by the armatures, the insulated push rods of relays RY1-RY4 push contacts K1-K4 to actuate, reducing the contact distance. Since it takes a certain amount of time for the relay contacts to close, at time T1, contacts K1-K4 are not closed, and the voltage difference across the contacts remains at 12V.

[0062] During the period from time T1 to time T3: The power supply maintains an output of +12V, and the first drive switching transistors Q1 and Q2 and the second drive switching transistors Q3 and Q4 remain on. The coils W1 and W4 of relays RY1 to RY4 maintain the voltage relative to ground connected to the bootstrap capacitor C2. Therefore, relays RY1 to RY4 can continuously attract the movement of their armatures, causing the insulating push rods of relays RY1 to RY4 to push the contacts K1 to K4 to continue moving towards the closed state.

[0063] Until time T2, the contacts begin to make contact, meaning they enter a closed state. At this point, it can also be said that the contacts are fully closed. When the relay contacts are in contact, the two ends of the contacts are connected, so the voltage difference across the contacts is 0. From time T2 to time T3, the contacts form a stable contact, meaning they remain in a closed state, and the voltage difference across the contacts remains 0.

[0064] During the closing process of the aforementioned contacts, bootstrap capacitors C1 and C2 gradually discharge, causing their voltage relative to ground to gradually decrease. This means the coil voltages of relays RY1 to RY4 gradually decrease. Until time T3, the voltage of bootstrap capacitors C1 and C2 relative to ground drops to the first supply voltage +12V, meaning the coil voltages of relays RY1 to RY4 drop to 12V. At this point, relays RY1 to RY4 generate a second electromagnetic signal (such as a second electromagnetic force) to keep contacts K1 to K4 of relays RY1 to RY4 in a closed state.

[0065] After time T3 (e.g., the period from T3 to T4): The power supply maintains an output of +12V, the first drive switching transistors Q1 and Q2 and the second drive switching transistors Q3 and Q4 remain on, the contacts K1 and K4 of relays RY1 to RY4 remain closed, the voltage difference across the contacts remains 0, and the voltage of bootstrap capacitors C1 and C2 relative to ground remains +12V.

[0066] When all contacts K1 to K4 of relays RY1 to RY4 are closed, i.e., all relays RY1 to RY4 are conducting, the live wire terminal AC_L of the AC end of inverter circuit 20 and the live wire terminal GRID_L of grid-connected interface 30 are connected, and the neutral wire terminal AC_N of the AC end of inverter circuit 20 and the neutral wire terminal GRID_N of grid-connected interface 30 are connected, so that inverter circuit 20 can operate in grid-connected mode and transmit power with the power grid 40 connected to grid-connected interface 30.

[0067] Understandably, in Figure 2 In the related technologies shown, the coil voltage of relays RY1~RY4 is always the first supply voltage V1. However, in the embodiments of this application, as... Figure 3 and Figure 4 As shown, at the instant the second drive switch is turned on, the coil voltage of relays RY1~RY4 can reach the sum of the first and second supply voltages, V1+V2. That is, the starting voltage for the relay contacts to close can reach the sum of voltages V1+V2. During the gradual closing of the contacts, the coil voltage of relays RY1~RY4 in this embodiment remains higher than V1.

[0068] Because a higher coil voltage results in a stronger magnetic field, a greater electromagnetic force, and thus a faster contact engagement time, the switching device 10 in this embodiment can achieve higher coil voltages for relays RY1 to RY4, thereby accelerating the contact engagement speed and shortening the contact closing time.

[0069] Furthermore, during the contact closure process, the coil voltage in this embodiment drops to the first supply voltage V1, which can reduce the heat generated by the relay while ensuring that the coil voltage is sufficient to maintain the contact closure state, thus helping to extend the service life of the relay.

[0070] Furthermore, a shorter contact closing time indicates a narrower range of contact closing times, meaning the contact closing durations of the relays are more concentrated and consistent. Therefore, by shortening the contact closing time, this embodiment of the application can improve the time dispersion of the closing action of relays RY1~RY4, thereby reducing the probability of relay action delay, improving the control accuracy of the relays, and facilitating the relays to close at the voltage zero crossing point, thus ensuring the safe operation of the device.

[0071] To better understand, related experimental tests were also conducted in the embodiments of this application to verify the improvement effect of the embodiments of this application on the dispersion of relay closing time. This experimental test used 20 relays (sorted by Arabic numerals) from the same batch and with the same model parameters to compare the relay contact closing time of the switching device in the related art and the switching device 10 of the embodiments of this application. The experimental results can be found in [reference needed]. Figure 5 .

[0072] from Figure 5 As can be seen, compared with related technologies, the maximum, minimum, and average values ​​of the relay contact closing time in the embodiments of this application are all smaller, indicating that the switching device 10 of the embodiments of this application can shorten the contact closing time. Moreover, the standard deviation of the relay contact closing time in the embodiments of this application is smaller, indicating that the switching device 10 of the embodiments of this application can improve the dispersion of the contact closing time and make the contact closing time more consistent.

[0073] This is understandable; please refer to [link / reference]. Figure 6 This application also provides a power conversion device 100.

[0074] like Figure 6 As shown, the power conversion device 100 includes an inverter circuit 20, a grid connection interface 30, the aforementioned switching device 10, and a controller 50. The switching device 10 is connected between the inverter circuit 20 and the grid connection interface 30, which is used to connect to the power grid 40. The controller 50 is connected to the first drive switch transistor and the inverter circuit 20. The controller 50 can be used to control the switching state of the first drive switch transistor in the switching device 10 and to control the operation of the inverter circuit 20.

[0075] It should be understood that the inverter circuit 20, grid connection interface 30, switching device 10 and controller 50 can all refer to the relevant descriptions in the foregoing embodiments, and therefore will not be repeated here.

[0076] It should be understood that the relay contact closing time in the switching device 10 of this application embodiment is highly consistent, which helps to improve the relay control accuracy of the power conversion device 100 of this application embodiment. This allows the relay contacts to close when the mains voltage crosses zero, thereby avoiding a chain of risks such as electric arc, contact welding, and sudden reduction in device life caused by the relay not closing when the mains voltage crosses zero. This makes the safety of the devices and circuits in the power conversion device 100 more guaranteed.

[0077] Please continue reading Figure 6 This application also provides an energy storage system 200.

[0078] like Figure 6As shown, the energy storage system 200 includes an inverter circuit 20, a grid connection interface 30, an energy storage battery 60, and a switching device 10. The DC terminal of the inverter circuit 20 is connected to the energy storage battery 60, and the AC terminal of the inverter circuit 20 is connected to the grid connection interface 30 through the switching device 10. The controller 50 is connected to the first drive switch tube and the inverter circuit 20.

[0079] The energy storage battery 60 can serve as a DC power source for the inverter circuit 20. The inverter circuit 20 can convert the DC voltage provided by the energy storage battery 60 into AC voltage and output it through the grid connection interface 30. In some embodiments, when the inverter circuit 20 adopts a bidirectional inverter circuit 20, the energy storage battery 60 can not only serve as a DC power source but also as a load of the inverter circuit 20. The inverter circuit 20 can connect to the grid voltage through the grid connection interface 30 and rectify the grid voltage into DC voltage to charge the energy storage battery 60.

[0080] It should be understood that the inverter circuit 20, grid connection interface 30, switching device 10 and controller 50 can all refer to the relevant descriptions in the foregoing embodiments, and therefore will not be repeated here.

[0081] Furthermore, this application embodiment also provides a grid-connected control method. This grid-connected control method can be applied to the power conversion device 100 or the energy storage system 200 described above, and is executed by the controller 50.

[0082] For details, please refer to Figure 6 The grid connection control method in this application includes the following steps: Step S11: Obtain the phase of the grid voltage and the previous zero crossing point.

[0083] In some embodiments, the controller can use a phase-locked loop (PLL) algorithm or PLL circuit to perform phase-locked control on the AC voltage of the inverter circuit and the grid voltage to track the phase and frequency of the grid voltage in real time, ensuring that the grid voltage is in phase with the AC voltage of the inverter circuit. The controller can obtain the phase of the grid voltage and its zero-crossing points based on the phase-locking process.

[0084] It should be understood that in other embodiments, the controller may also obtain the phase of the grid voltage in other ways, and obtain the previous zero-crossing point in other ways (e.g., using a zero-crossing detection algorithm), and this application does not specifically limit this.

[0085] In one embodiment, the controller can acquire the phase of the grid voltage and the previous zero-crossing point of the grid voltage when the inverter circuit is started. Taking the acquisition of the grid voltage phase as an example, the controller can perform phase-locked loop control on the AC voltage of the inverter circuit and the grid voltage in response to a start command for starting the inverter circuit, so as to acquire the grid voltage phase.

[0086] Step S12: Obtain the closing time of the switching device between the inverter circuit and the power grid.

[0087] It can be understood that the switching device between the inverter circuit and the power grid is... Figure 3 The switching device shown. The closing time (Trly) of the switching device refers to the closing time of the relay contacts in the switching device. For example, in... Figure 4 In this context, the closing time Trly is the time difference between time T3 and time T1. It's understandable that relays of the same model have the same closing time, while relays of different models may have different closing times.

[0088] The closing time Trily can be obtained through hardware circuit testing. In some embodiments, the switching device can also be equipped with a voltage sampling circuit across the contacts of relays RY1~RY4 to detect changes in contact voltage. The closing time Trily is obtained based on the time T1 when the contact voltage reaches V1+V2 and the time T3 when it drops to V1.

[0089] After measuring the closure time Trily, the user can input the closure time Trily through a host computer or user terminal device. The controller obtains the closure time Trily by communicating with the host computer or user terminal device. Alternatively, the closure time Trily can be pre-stored in memory, and the controller can read the memory to obtain the closure time Trily.

[0090] In step S12, the closing time Trily can be an average value. For example, in Figure 5 In the test shown, the average relay contact closing time (Trly) of the switching device was 9.86 milliseconds.

[0091] Step S13: Based on the closing time of the switching device and the previous zero crossing point, calculate the first phase of the closing time of the switching device from the previous zero crossing point.

[0092] In other words, using the previous zero-crossing point of the grid voltage as a reference, the phase corresponding to the closing moment of the switching device is calculated, and this phase is the first phase θ1. The first phase θ1 represents the phase delay caused by the closing time of the relay contacts, that is, the action delay caused by the relay contacts starting to move from the previous zero-crossing point of the grid voltage until they are fully closed.

[0093] In step S13, the controller can convert the closing time Trly into the phase of the previous zero crossing point of the grid voltage using the following formula (1), and the converted phase is the first phase θ1.

[0094] (1).

[0095] Where T is the grid voltage cycle.

[0096] Step S14: Obtain the target phase based on the first phase.

[0097] Here, the time corresponding to the target phase θrly represents the output time of the drive signal, that is, the wave generation time, or the time when the output level is used to turn on the switching device. In step S14, the first phase can be used to perform feedforward compensation on the phase of the AC voltage (that is, the grid voltage) of the inverter circuit. Therefore, the target phase θrly obtained according to the first phase has compensated for the phase delay caused by the relay contact closing time. Based on the target phase θrly, the controller can accurately control the relay to fully close at the zero crossing point.

[0098] In one embodiment, the controller can calculate the difference between the peak phase of the grid voltage and the first phase θ1 to obtain the target phase θrly.

[0099] In other words, using the peak phase as the starting point, the calculation determines how far away from the peak phase is needed, i.e., how much of a phase (or how much time) needs to be delayed before emitting the wave. The moment the target phase θrly is reached corresponds to the wave emission time. It should be understood that the target phase θrly should be limited to one period, i.e., the target phase θrly should not exceed 2π.

[0100] In one embodiment, the peak phase of the grid voltage can be expressed as: , where K is a variable value, K=1,2,3.

[0101] In one embodiment, the controller can calculate the target phase θrly by setting a calculation formula, which is: (2).

[0102] It is understandable that the relay's operating time is variable, making the first phase θ1 variable. Therefore, in practical applications, the value of K needs to be determined based on the actual magnitude of the first phase θ1. When K takes different values, the target phase θrly will also be different.

[0103] Specifically, based on the magnitude of the first phase θ1, there are four possible cases: Case 1: When θ1≤90°, K=1, θrly has the same peak time of the same period. As the starting point benchmark, .

[0104] Case 2: When 90° < θ1 ≤ 270°, K = 2, θrly has the same peak time of the same period. As the starting point benchmark, .

[0105] Case 3: When 270°<θ1≤360°, K=3, θrly has the same peak time of the same period. As the starting point benchmark, .

[0106] Case 4: When θ1 > 360°, K = 1, and θrly is the peak time of the previous cycle. Using this as the starting point, we need to subtract one cycle (i.e., ),get Then recalculate the new θ1 to recalculate. .

[0107] For example, the first phase θ1 calculated by the controller is Then, substituting into the given calculation formula, we get θrly= At this point, it is necessary to use the peak time. As the starting point benchmark, postpone Drive the relay, that is, in The relay contacts are constantly activated, and the relay's operating time is... Therefore, the relay contacts are able to fully engage at the zero-crossing point π, thus entering a closed state.

[0108] In other embodiments, the controller may also use the first phase θ1 to obtain the target phase θrly by other means such as table lookup, curve fitting, or mathematical model. This application does not impose any special limitation on the method of obtaining the target phase based on the first phase.

[0109] Step S15: Output a drive signal according to the target phase. The drive signal is used to drive the first drive switch in the switching device to turn on, so that the switching device closes at the zero crossing point of the grid voltage.

[0110] Specifically, the controller can generate and output drive signals for each first drive switch in the switching device based on the target phase θrly modulation. The debugging method can be selected according to the actual situation, for example, using pulse width modulation (PWM), the generated drive signal is a PWM signal containing both high and low levels. The first drive switch, for example, turns on when it receives a high level and turns off when it receives a low level.

[0111] Continuing with the example in step S14, the controller can operate at peak times. As the starting point benchmark, postpone That is to say, in It outputs a drive signal at all times, and the drive signal is in ~ During the specified time period, the voltage level is high, causing the relay contacts to... ~ The time period is closed, and it ends at zero. The relay is fully engaged and in a closed state at the exact moment of contact. Since the grid voltage is 0 at the zero-crossing point, the AC voltage of the inverter circuit is in phase with the grid voltage and is also 0. Therefore, the voltage difference across the relay contacts is essentially zero, and no large inrush current is generated at the instant the relay closes. This avoids the chain risks of arcing, contact welding, and sudden reduction in device lifespan.

[0112] In related technologies, because the phase feedforward compensation is not performed considering the relay's operating delay, the controller experiences issues at the zero-crossing point. Constantly outputting a drive signal will cause the relay contacts to cross zero. The relay cannot be fully engaged at any given moment, meaning it cannot be in a closed state until after the zero-crossing point. Since the mains voltage is not zero after the zero-crossing point, the voltage difference across the relay contacts is relatively large. At this time, a large inrush current will be generated the moment the relay is fully closed, which will cause a chain of risks such as electric arc, contact welding, and a sudden reduction in the life of the device.

[0113] To better understand, the following will be used as an example. Figure 8 The example flowchart provides a comprehensive explanation of the application process of the entire grid-connected control method.

[0114] like Figure 8 As shown, in cases where the inverter circuit needs to operate in grid-connected mode: First, the controller sends a start command to the inverter circuit to start the inverter circuit, and the inverter circuit starts up and runs when it receives the start command.

[0115] After sending the start command, or in response to the start command, the controller performs phase-locked control on the AC voltage of the inverter circuit and the grid voltage, so that the grid voltage is in phase with the AC voltage of the inverter circuit.

[0116] Then, the controller enters the relay self-test mode to check whether the relay is abnormal.

[0117] If the self-test fails or fails, it indicates that there may be an abnormality in the relay. Therefore, the controller outputs an alarm signal to provide an alarm prompt and controls the inverter circuit to stop.

[0118] If the self-test is successful or passes, it means that the relay is normal and usable. Therefore, the controller executes steps S11 to S13 to calculate the first phase θ1 of the switching device at the closing time of the previous zero crossing point.

[0119] Next, the controller executes step S14, which is to calculate the corresponding target phase θrly based on the first phase θ1.

[0120] Finally, the controller executes step S15, that is, according to the calculated target phase θrly, it outputs a drive signal to the first drive switch in the switching device to drive the first drive switch to conduct, so that the contacts of the relays RY1~RY4 in the switching device close exactly at the current zero crossing point of the mains voltage.

[0121] In summary, the grid-connected control method of this application can compensate for the phase delay caused by the closing time of the switching device by calculating the target phase θrly, so as to accurately determine the timing of the early transmission of the drive signal. Therefore, the drive signal generated according to the target phase θrly can control the relay contacts to close precisely at the zero-crossing point of the grid voltage, which greatly reduces the voltage difference across the relay contacts at the moment of contact closure, thereby reducing the inrush current. This effectively reduces the chain risks caused by the inrush current, such as arcing, contact welding, and sudden reduction in device life, improves the safety performance of the switching device and inverter circuit, and helps to extend the service life of the switching device and inverter circuit.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application.

Claims

1. A switching device, characterized by The switching device includes: a relay, a drive circuit, and a bootstrap circuit; The relay is connected between the inverter circuit and the grid connection interface for connecting to the power grid. The drive circuit includes a first drive switch and a second drive switch. The bootstrap circuit includes a bootstrap capacitor and a bootstrap resistor. The first end of the relay coil is used to connect to a first power supply voltage and to ground through the bootstrap capacitor and the bootstrap resistor connected in series. The second end of the relay coil is grounded through the first driving switch and connected to the bootstrap resistor and to connect to a second power supply voltage through the second driving switch. The first driving switch is turned on when a driving signal is received; the second driving switch is turned on when the second power supply voltage is applied and the first driving switch is turned on, so that the voltage of the bootstrap resistor is the second power supply voltage, and the voltage of the bootstrap capacitor relative to ground can reach the sum of the voltages of the first power supply voltage and the second power supply voltage.

2. The switching device of claim 1, wherein The relay coil is used to connect to the voltage of the bootstrap capacitor relative to ground, and generates a first electromagnetic signal when the voltage of the bootstrap capacitor relative to ground is the sum of the voltages, and generates a second electromagnetic signal when the bootstrap capacitor discharges until the voltage of the bootstrap capacitor relative to ground is the first supply voltage. The first electromagnetic signal is used to control the contacts of the relay to start operating; the second electromagnetic signal is used to control the relay to remain in a closed state.

3. The switching device as described in claim 1, characterized in that, The first driving switch includes an N-type semiconductor switch, and the second driving switch includes a P-type semiconductor switch.

4. The switching device according to any one of claims 1 to 3, characterized in that, The first connection terminal of the first driving switch is connected to the second terminal of the coil of the relay, the second connection terminal of the first driving switch is grounded, and the control terminal of the first driving switch is connected to the controller and used to receive the driving signal output by the controller. The control terminal of the second driving switch is connected to the first connection terminal of the first driving switch, and is connected to the second connection terminal of the second driving switch through a current-limiting resistor. The first connection terminal of the second driving switch is connected to the bootstrap resistor, and the second connection terminal of the second driving switch is connected to the power supply.

5. The switching device according to any one of claims 1 to 4, characterized in that, The relay includes a live wire relay and a neutral wire relay. The live wire relay is located between the live wire terminal of the inverter circuit and the live wire terminal of the power grid, and the neutral wire relay is located between the neutral wire terminal of the inverter circuit and the neutral wire terminal of the power grid. The coils of the live wire relay and the neutral wire relay are connected in parallel.

6. The switching device according to any one of claims 1 to 5, characterized in that, The first end of the relay coil is connected to the power supply, and the second end of the relay coil is connected to the power supply through the second drive switch. The first power supply voltage and the second power supply voltage are the power supply voltages output by the power supply.

7. A power conversion device, characterized in that, The power conversion device includes an inverter circuit, a grid connection interface, and a switching device as described in any one of claims 1 to 6, wherein the switching device is connected between the inverter circuit and the grid connection interface.

8. The power conversion device as described in claim 7, characterized in that, The power conversion device further includes a controller, which is connected to the first drive switch and the inverter circuit, and is used to control the switching state of the first drive switch and the operation of the inverter circuit.

9. An energy storage system, characterized in that, The energy storage system includes an inverter circuit, a grid connection interface, an energy storage battery, and a switching device as described in any one of claims 1 to 6. The DC terminal of the inverter circuit is connected to the energy storage battery, and the AC terminal of the inverter circuit is connected to the grid connection interface through the switching device.

10. A grid-connected control method, characterized in that, The grid connection control method includes: Obtain the phase and the previous zero-crossing point of the grid voltage; Obtain the closing time of the switching device between the inverter circuit and the power grid; Based on the closing time of the switching device and the previous zero-crossing point, calculate the first phase of the closing time of the switching device from the previous zero-crossing point; the first phase represents the phase delay caused by the closing time of the switching device. The target phase is obtained based on the first phase; A drive signal is output according to the target phase; the time corresponding to the target phase represents the output time of the drive signal, and the drive signal is used to drive the first drive switch tube in the switching device to turn on, so that the switching device closes at the zero crossing point of the grid voltage.

11. The grid-connected control method as described in claim 10, characterized in that, Obtaining the target phase based on the first phase includes: The target phase is obtained by calculating the difference between the peak phase of the grid voltage and the first phase.

12. The grid-connected control method as described in claim 10, characterized in that, The grid connection control method includes: In response to a start command for starting the inverter circuit, phase-locked loop control is performed on the AC voltage of the inverter circuit and the grid voltage to obtain the phase of the grid voltage.

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