Grid-connected and off-grid standby power system

Abstract

The utility model relates to a grid-connected and off-grid standby power system, which is characterized in that a frame-type circuit breaker structure is designed to replace the combination of a common circuit breaker and a grid-connected and off-grid contactor in the traditional technology, so that the grid-connected to off-grid capability of the grid-connected and off-grid standby power system can reach the level of the prior art. And even in a high-power use scene, timely switching from a power grid side can be realized, so that the problems that in the prior art, a grid-connected and off-grid contactor is limited by a mechanical structure in the high-power use scene, the release time is gradually increased, and the quick switching requirement of a standby power system cannot be continuously met are solved; in addition, low voltage ride through can be realized through closing control of the control switch, and selection and switching of a user side among different off-grid modes are supported. And in the grid-connected mode, continuous power supply to the coil for keeping the pull-in of the grid-connected and off-grid contactor is not needed any more, so that the energy consumption is lower.

Description

Technical Field

[0001] The utility model relates to the field of power control, in particular to an on-grid and off-grid backup power system. Background Art

[0002] The backup power system based on new energy sources such as photovoltaic storage (solar photovoltaic energy storage) switches and controls the power supply from the traditional power grid and photovoltaic and energy storage to achieve a grid-connected mode and an off-grid mode.

[0003] Due to users' demand for uninterrupted power supply, backup power systems connected to solar-powered energy storage must be able to quickly disconnect from the grid—commonly known as rapid off-grid operation. This prevents external grid failures from affecting the solar-powered energy storage system, causing a sudden voltage drop at the load end and equipment downtime. However, due to the grid's demand for load stability, some power grid companies require backup power systems to have low-voltage ride-through (LVRT) capabilities. Therefore, backup power systems must be able to quickly disconnect from the grid after a temporary drop in grid voltage. This means that LVR capabilities are required.

[0004] like Figure 1 As shown, in order to cope with multiple switching between grid connection and off-grid connection, the traditional backup power system is provided with a grid connection and off-grid contactor on the grid side. After the grid connection and off-grid contactor is energized, the backup power system enters the grid connection mode; after the grid connection and off-grid contactor is disconnected and released, the backup power system switches to the off-grid mode. When the power is relatively low, the release time of the grid connection and off-grid contactor is very fast, and it can basically be disconnected within 20ms, which can realize the function of fast switching to off-grid connection. However, with the continuous increase in power, the backup power system needs to be equipped with grid connection and off-grid contactors of larger size / specification. However, due to the mechanical structure of large-sized grid connection and off-grid contactors, their release time will gradually increase, generally requiring about 70ms, which can no longer meet the requirements of the backup power system for fast disconnection from the grid. This is one of the technical problems that this application aims to solve.

[0005] Furthermore, to meet the requirements of low voltage ride-through (LVRT), the contactor coil will immediately release once power is lost, necessitating a tailored design of its control circuit. For example, Patent Document No. N117713104A (Backup Power Device and Power Converter) proposes a contactor coil control method that meets LVRT requirements. However, while this method allows the contactor coil to remain engaged briefly after a power outage, its control circuit is extremely complex and implementation costs are high. This is another technical problem addressed by this application. Utility Model Content

[0006] A main purpose of the present invention is to overcome at least one of the above-mentioned defects, and to provide an on-grid and off-grid backup power system, which reduces the operating cost of the power system by adjusting the circuit structure, and provides support for users to choose to switch between different on-grid to off-grid modes.

[0007] In order to achieve the above purpose, the technical solution adopted by the utility model is:

[0008] The utility model provides an on-grid and off-grid backup power system, comprising an inverter, a power grid and a power grid circuit breaker. The power grid is connected to the AC output side of the inverter via the power grid circuit breaker to supply power to the load. The power grid circuit breaker is a frame-type circuit breaker, comprising a circuit breaker body, an energy storage module, a shunt release and a control switch. The shunt release is used to control the on / off state of the circuit breaker body, and the control switch is used to control the on / off state of the shunt release.

[0009] The excitation coil and the control switch in the shunt release are connected in series, and the series-connected shunt release and the control switch are further connected to the output side of the energy storage module. The input side of the energy storage module is connected to the power grid or the inverter. The energy storage module draws power from the power grid or the inverter and supplies power for the operation of the shunt release.

[0010] The control signal input end of the control switch is connected to an external control signal and is used to be turned on after receiving the external control signal, so that the shunt release is energized and tripped, thereby disconnecting the circuit breaker body.

[0011] According to one embodiment of the present invention, a rectifier module is included, the input side of the rectifier module is connected to the power grid or the inverter, and the output side of the rectifier module is connected to the energy storage module.

[0012] According to one embodiment of the present invention, the rectifier module is a single-phase rectifier bridge, and two input ends of the single-phase rectifier bridge are respectively connected to two phase lines of the power grid.

[0013] According to one embodiment of the present invention, the energy storage module is an energy storage capacitor, and a loop formed by a shunt release and a control switch connected in series is connected in parallel with the energy storage capacitor.

[0014] According to one embodiment of the present invention, the inverter is connected to the grid connection point after being connected to the inverter circuit breaker, and the grid is also connected to the grid connection point after being connected to the grid circuit breaker, and the load draws power from the grid connection point to operate.

[0015] According to one embodiment of the present invention, the load is connected to the load circuit breaker and then connected to the grid connection point.

[0016] According to one embodiment of the present invention, the control switch is a transistor or a relay.

[0017] In particular, the present invention also provides an on-grid and off-grid backup power system, comprising an inverter, a power grid and a power grid circuit breaker, wherein the power grid is connected to the AC output side of the inverter via the power grid circuit breaker to supply power to the load, and the power grid circuit breaker is a frame-type circuit breaker, comprising a circuit breaker body, a shunt release and a control switch, wherein the shunt release is used to control the on / off state of the circuit breaker body, and the control switch is used to control the on / off state of the shunt release, wherein:

[0018] The excitation coil and the control switch in the shunt release are connected in series, and the series-connected shunt release and the control switch are connected to the output side of the inverter, and are powered by the output side bus of the inverter. The shunt release is an AC-driven shunt release;

[0019] The control signal input end of the control switch is connected to an external control signal and is used to be turned on after receiving the external control signal, so that the shunt release is energized and tripped, thereby disconnecting the circuit breaker body.

[0020] According to one embodiment of the present invention, an undervoltage release with a time delay is included. The undervoltage release with a time delay is used to control the switch state of the grid circuit device body and is connected to the grid to draw power from the grid.

[0021] According to one embodiment of the present invention, the delay value of the undervoltage release with delay exceeds the low voltage ride-through time preset for low voltage ride-through.

[0022] Compared with the existing technology, the advantages and beneficial effects of the grid-connected and off-grid backup power system of the utility model patent application are:

[0023] This application designs a frame-type circuit breaker structure to replace the combination of ordinary circuit breakers + grid-connected and off-grid contactors in traditional technology, so that the grid-connected and off-grid switching capabilities of the grid-connected and off-grid backup power system can reach the existing technical level, and even in high-power usage scenarios, it can achieve timely disconnection from the grid side. It overcomes the problem that the grid-connected and off-grid contactors in traditional technology are limited by mechanical structure in high-power usage scenarios, the release time gradually increases, and they can no longer meet the requirements of rapid grid disconnection of the backup power system. In addition, low voltage crossing can be achieved by controlling the closing of the control switch, supporting the user end to select and switch between different off-grid modes. In the grid-connected mode, it is no longer necessary to continuously power the coil to keep the grid-connected and off-grid contactors attracted, which reduces energy consumption.

[0024] Furthermore, compared with the existing technology with targeted design, the backup power system of the present application requires fewer devices for off-grid operation of the power grid, and the overall structure, layout and wiring are more compact and simple, with more cost advantages, and the control operation is more convenient and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0026] Figure 1 This is the circuit schematic diagram of the existing backup power system;

[0027] Figure 2 This is a circuit schematic diagram of an on-grid and off-grid backup power system according to embodiment 1 of the present invention;

[0028] Figure 3 This is a circuit diagram of an on-grid and off-grid backup power system according to embodiment 2 of the present invention;

[0029] Figure 4 This is a circuit diagram of an on-grid and off-grid backup power system according to embodiment 3 of the present invention;

[0030] Figure 5 This is a standard low voltage ride through (LVRT) grid connection point voltage-time curve. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0032] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example 1:

[0034] Conventional backup power systems are equipped with circuit breakers on the grid side, inverter side, and load side. This embodiment mainly makes improvements on the grid side and designs a frame-type circuit breaker structure to facilitate grid-side on-grid control and off-grid operation.

[0035] like Figure 2As shown, the frame-type circuit breaker structure includes a circuit breaker body installed on the grid side, as well as accessories such as a shunt release, a control switch and an energy storage module.

[0036] The shunt release is used to control the on / off state of the grid circuit device body. In this embodiment, a DC-driven shunt release is used, and its nominal voltage is DC 220V.

[0037] The control switch is connected in series with the shunt release, the excitation coil in the shunt release is connected in series with the control switch, the series-connected shunt release and control switch are further connected to the output side of the energy storage module, the input side of the energy storage module is connected to the power grid or the inverter, the energy storage module draws power from the power grid or the inverter and supplies power to the shunt release, the control switch is used to control the on / off of the shunt release coil current, and the shunt release is used to control the on / off state of the circuit breaker body.

[0038] The control switch receives an external control signal to close or release. The grid-connected and off-grid backup power system, such as the high-power optical backup power system in the prior art, has a mechanism for detecting and feeding back the inverter output voltage, grid voltage, energy storage voltage and even load voltage in the system. Based on the feedback of these voltage detection signals, it can be judged whether the grid-connected and off-grid operation is a fast off-grid operation or a low voltage ride-through operation. The control switch of the backup power system in this embodiment can be closed or released after receiving the external control signal.

[0039] The control switch's control signal input is connected to an external control signal and is configured to conduct upon receiving the external control signal, thereby energizing and tripping the shunt release, thereby disconnecting the circuit breaker. In this embodiment, the control switch is remotely controlled by a host computer. It can be powered by an independent drive power supply or triggered by an input pulse-width modulation signal. The control switch utilizes existing devices, such as transistors or relays, and switches on and off upon receiving an external control signal. Its operating principle is not further described here.

[0040] In order to convert the AC power provided by the grid into DC power suitable for the shunt release, the backup power system of this embodiment is provided with a rectifier module, such as Figure 2 As shown, the rectifier module uses a single-phase rectifier bridge composed of four diodes. The two input ends of the single-phase rectifier bridge are respectively connected to the two phase lines of the power grid, and the two output ends of the single-phase rectifier bridge are respectively connected to the shunt release and the other remaining terminal of the control switch.

[0041] In this embodiment, the energy storage module utilizes a storage capacitor, whose capacitance is selected to activate the shunt release at least once. The storage capacitor is connected in parallel across the series-connected shunt release and control switch, also drawing power from the grid via a single-phase rectifier bridge. The energy storage module is used to reserve energy for the shunt release during a grid power outage.

[0042] The host computer is a computer device that receives user instructions, selects or switches control modes based on preloaded programs and user instructions, and issues operation command signals. In the corresponding control mode, the host computer outputs a corresponding signal to the control switch based on the read grid connection point voltage signal and the current control strategy of the control module to control the on / off state of the control switch.

[0043] The inverter is connected to the grid connection point after being connected to the inverter circuit breaker, and the grid is also connected to the grid connection point after being connected to the grid circuit breaker. The load draws power from the grid connection point. The process of the above backup power system when receiving external control instructions to work is:

[0044] Under normal grid conditions, the grid's single-phase voltage is rectified and then supplied to the shunt release. When disconnection is required, the host computer sends a control signal to close the control switch, energizing the shunt release's excitation coil, which in turn drives the circuit breaker's main contacts to open. Because the shunt release only requires a brief period of power (it has an internal normally closed switch that automatically disconnects power upon actuation), while the actual voltage used in this embodiment is slightly higher than its nominal value, it is still within the withstand voltage range of the shunt release's internal coil and will not cause short-term coil overheating, making it usable. When the grid loses power, although the shunt release cannot be supplied with power, the energy storage capacitor connected in parallel with the rectifier bridge retains some energy. When the control switch is closed, this energy releases energy that can still trigger the shunt release. When low voltage ride-through is required, the control switch can be left open for the required time.

[0045] The operation process of the high-power on-grid and off-grid backup power system will be described below in conjunction with a specific control method.

[0046] The control method for the high-power on-grid and off-grid backup power system comprises the following steps:

[0047] S1. Collect the grid connection point voltage signal, or the grid-side voltage signal, through the detection device and send it to the host computer;

[0048] S2 input user instructions to the host computer, the host computer selects or switches the control module according to the user instruction, the control mode includes a fast off-grid control mode and a low voltage ride-through control mode;

[0049] S21. When the host computer enters the fast off-grid control mode, the control strategy it implements is:

[0050] Read the grid connection point voltage signal and determine whether the grid connection point voltage signal is lower than the first threshold:

[0051] When the grid connection point voltage signal is lower than the first threshold, a control signal is immediately sent to the control switch to control the control switch to close, so that the coil of the shunt release is energized and the circuit breaker body is controlled to disconnect, so that the backup power system enters the off-grid state;

[0052] When the grid connection point voltage signal is not lower than the first threshold, the control switch is maintained in the open state (the internal coil of the shunt release is not energized), and the backup power system is in the grid connection state;

[0053] S22. When the host computer enters the low voltage ride-through mode, the control strategy it implements is:

[0054] Read the grid connection point voltage signal and determine whether the grid connection point voltage signal is lower than the second threshold:

[0055] When the grid connection point voltage signal is not lower than the second threshold, maintaining the control switch in an open state;

[0056] When the grid connection point voltage signal is lower than the second threshold, determining whether the duration for which the grid connection point voltage signal is lower than the second threshold exceeds a preset low voltage ride-through time;

[0057] If the duration does not exceed the preset low voltage ride-through time, the control switch is kept in the open state and the backup power system is in the grid-connected state;

[0058] If the duration exceeds the preset low voltage ride-through time, the host computer immediately sends a control signal to the control switch to control the control switch to close, energize the coil of the shunt release, and control the circuit breaker body to disconnect, so that the backup power system enters the off-grid state.

[0059] In the above steps, the preset low voltage ride-through time is a set value that complies with regulations. According to actual conditions, the first threshold and the second threshold can be the same or different set values ​​that comply with regulations.

[0060] like Figure 5The following graph shows a standard low voltage ride-through (LVRT) grid connection point voltage-time curve. Curve 1 represents the LVRT phase. The minimum LVRT time is generally around 2 seconds. Assuming this embodiment sets the minimum LVRT time to 1.5 seconds, when LVRT is required, the control switch only needs to remain open within the standard 1.5 seconds. For off-grid operation, selecting an existing shunt release based on the specific situation can ensure that the circuit breaker opens within 20 milliseconds.

[0061] Example 2:

[0062] The grid-connected and off-grid backup power system of this embodiment also includes a frame-type circuit breaker structure, which includes a circuit breaker body, a shunt release, and a control switch. The shunt release is used to control the on / off state of the grid circuit breaker body. The control switch's control signal input terminal is connected to a remote external control signal (such as a signal output terminal of a host computer) to control the on / off state of the shunt release coil current.

[0063] This embodiment also uses the host computer's control of the control switch of the on-grid and off-grid backup power system as an example. The host computer receives user instructions and selects or switches the control mode according to the user instructions. In the corresponding control mode, based on the read grid connection point voltage signal and the current control strategy of the control module, it outputs a corresponding signal to the control switch to control the closed state of the control switch.

[0064] Different from Example 1, the high-power on-grid and off-grid backup power system of this embodiment omits the rectifier bridge and energy storage capacitor.

[0065] like Figure 3 As shown, in this embodiment, the shunt release is connected in series with the control switch and then connected to the power output of the backup power system's inverter. The shunt release uses an AC 220V AC drive, with its two ends connected to the inverter output's neutral line and a phase line, respectively, drawing power from the inverter output line.

[0066] Since the inverter side is used to power the shunt release in this embodiment, when the grid loses power, the shunt release can still obtain sufficient power to trip the circuit breaker body.

[0067] The control method of the high-power on-grid and off-grid backup power system in this embodiment includes the following steps:

[0068] S1. Collect the grid connection point voltage signal, or the grid-side voltage signal, through the detection device and send it to the host computer;

[0069] S2 input user instructions to the host computer, the host computer selects or switches the control module according to the user instruction, the control mode includes a fast off-grid control mode and a low voltage ride-through control mode;

[0070] S21. When the host computer enters the fast off-grid control mode, the control strategy it implements is:

[0071] The host computer reads the grid connection point voltage signal and determines whether the grid connection point voltage signal is lower than the third threshold.

[0072] When the grid connection point voltage signal is lower than the third threshold, a control signal is immediately sent to the control switch to control the control switch to close, connect the power supply circuit between the inverter output end and the shunt release, energize the coil of the shunt release, and control the circuit breaker body to disconnect, so that the backup power system enters the off-grid state;

[0073] When the grid connection point voltage signal is not lower than the third threshold, the control switch is kept in the open state, and the backup power system is in the grid connection state;

[0074] S22. When the host computer enters the low voltage ride-through control mode, it reads the grid voltage signal and determines whether the grid voltage signal is lower than the fourth threshold;

[0075] If the grid connection point voltage signal is not lower than the fourth threshold, the control switch is maintained in the open state, and the backup power system is in the grid connection state;

[0076] When the grid connection point voltage signal is lower than the fourth threshold, it is determined whether the duration for which the grid connection point voltage signal is lower than the fourth threshold exceeds a preset low voltage ride-through time:

[0077] If the duration exceeds the preset low voltage ride-through time, the host computer sends a control signal to the control switch to control the control switch to close, connect the power supply circuit between the inverter output end and the shunt release, energize the coil of the shunt release, control the circuit breaker body to disconnect, and put the backup power system into an off-grid state;

[0078] If the duration does not exceed the preset low voltage ride-through time, the control switch is maintained in the open state and the backup power system is in the grid-connected state.

[0079] Similar to Example 1, in the above steps, the preset low voltage ride-through time is a set value that complies with regulations. Depending on the specific situation, the third threshold and the fourth threshold can be the same or different set values.

[0080] Example 3:

[0081] Considering that the backup power system may suffer from the situation of overall power failure, for the sake of safety, the high-power grid-connected and off-grid backup power system of this embodiment adds an undervoltage release with delay on the basis of embodiment 2, such as Figure 4 shown.

[0082] The control method of the backup power system in this embodiment is the same as that in embodiment 2. The undervoltage release automatically operates based on the grid voltage it senses, without the need for a host computer to implement control, and is an auxiliary means to ensure system safety.

[0083] The delayed undervoltage release also controls the on / off state of the grid circuit breaker. Therefore, the undervoltage release's delay value must exceed the preset low-voltage ride-through time to prevent the circuit breaker from accidentally tripping during low-voltage ride-through. Similarly, the undervoltage threshold corresponding to the undervoltage release must not exceed the third or fourth thresholds used to determine whether the grid side is in a low-voltage state to prevent accidental tripping of the circuit breaker.

[0084] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A grid-connected and off-grid backup power system, comprising an inverter, a grid, and a grid circuit breaker, wherein the grid is connected to the AC output side of the inverter via the grid circuit breaker to supply power to a load, characterized in that: The grid circuit breaker is a frame-type circuit breaker, comprising a circuit breaker body, an energy storage module, a shunt release and a control switch. The shunt release is used to control the on / off state of the circuit breaker body, and the control switch is used to control the on / off state of the shunt release. The excitation coil and the control switch in the shunt release are connected in series, and the series-connected shunt release and the control switch are further connected to the output side of the energy storage module. The input side of the energy storage module is connected to the power grid or the inverter. The energy storage module draws power from the power grid or the inverter and supplies power for the operation of the shunt release. The control signal input end of the control switch is connected to an external control signal and is used to be turned on after receiving the external control signal, so that the shunt release is energized and tripped, thereby disconnecting the circuit breaker body.

2. The on-grid and off-grid backup power system according to claim 1, characterized in that: It includes a rectifier module, the input side of which is connected to the power grid or the inverter, and the output side of which is connected to the energy storage module.

3. The on-grid and off-grid backup power system according to claim 2, characterized in that: The rectifier module is a single-phase rectifier bridge, and two input ends of the single-phase rectifier bridge are respectively connected to two phase lines of the power grid.

4. The on-grid and off-grid backup power system according to any one of claims 1 to 3, characterized in that: The energy storage module is an energy storage capacitor, and a loop formed by a shunt release and a control switch connected in series is connected in parallel with the energy storage capacitor.

5. The on-grid and off-grid backup power system according to claim 1, characterized in that: The inverter is connected to the grid connection point after being connected to the inverter circuit breaker, and the grid is also connected to the grid connection point after being connected to the grid circuit breaker. The load draws power from the grid connection point to operate.

6. The on-grid and off-grid backup power system according to claim 5, characterized in that: The load is connected to the load circuit breaker and then to the grid connection point.

7. The on-grid and off-grid backup power system according to claim 1, characterized in that: The control switch is a transistor or a relay.

8. A grid-connected and off-grid backup power system, comprising an inverter, a grid, and a grid circuit breaker, wherein the grid is connected to the AC output side of the inverter via the grid circuit breaker to supply power to a load, characterized in that: The grid circuit breaker is a frame-type circuit breaker, comprising a circuit breaker body, a shunt release and a control switch. The shunt release is used to control the on / off state of the circuit breaker body, and the control switch is used to control the on / off state of the shunt release. The excitation coil and the control switch in the shunt release are connected in series, and the series-connected shunt release and the control switch are connected to the output side of the inverter, and are powered by the output side bus of the inverter. The shunt release is an AC-driven shunt release; The control signal input end of the control switch is connected to an external control signal and is used to be turned on after receiving the external control signal, so that the shunt release is energized and tripped, thereby disconnecting the circuit breaker body.

9. The on-grid and off-grid backup power system according to claim 8, characterized in that: The invention comprises an undervoltage release with a time delay, which is used to control the switch state of the grid circuit device body and is connected to the grid to draw power from the grid.

10. The on-grid and off-grid backup power system according to claim 9, characterized in that: The delay value of the undervoltage release with delay exceeds the low voltage ride-through time preset for low voltage ride-through.

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