A control method of a parallel and off-grid switching switch

Abstract

This invention discloses a control method for a grid-connected / off-grid switching switch, belonging to the field of power electronics technology. In a three-phase four-wire system, each phase is equipped with a hybrid switch consisting of a bidirectional thyristor connected in series with an isolating switch and then connected in parallel with a mechanical switch, while the neutral line is equipped with a mechanical switch. During closing, the neutral line mechanical switch is closed first, followed by the isolating switches of each phase. When a zero-crossing voltage is detected, the bidirectional thyristor is triggered to conduct. After the mechanical switch closes, the thyristor trigger signal is removed. During opening, the bidirectional thyristor is triggered simultaneously, and the mechanical switch is commanded to open. Arc-free commutation is achieved using the inherent delay of the mechanical switch. After confirming successful thyristor freewheeling, the trigger signal is removed, and the isolating switch is opened after the thyristor naturally turns off. This invention allows current to flow through the thyristor only at the moment of switching; the remaining time, current flows through the mechanical switch, combining the advantages of arc-free switching and low loss.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a control method for a grid-connected / off-grid switching switch. Background Technology

[0002] With the development of power electronics technology, large-capacity battery energy storage systems and microgrid solar power generation systems have been widely deployed in the market. To ensure normal power supply to these devices, it is necessary to quickly switch to emergency power supply equipment (such as energy storage converters) during grid failures and then switch back to grid power supply once the grid is restored. Therefore, grid-connected and off-grid transfer switches are key devices for achieving these switching functions.

[0003] Traditional grid-connected and off-grid transfer switch solutions mainly include the following:

[0004] On-off control is achieved using only mechanical switches (such as relays and contactors). This solution has a simple structure and extremely low conduction loss, but mechanical switches are prone to arcing between contacts when disconnecting, leading to contact erosion, shortening switch life, and having a relatively long conduction time.

[0005] This solution uses only solid-state switches such as thyristors for on / off control. It has no mechanical contacts, so there is no arcing during disconnection, and the response speed is fast. However, the thyristors exhibit a conduction voltage drop when in the on state, resulting in significant losses and severe heat generation during continuous current flow, necessitating a large heat dissipation device.

[0006] It consists of a thyristor connected in parallel with a relay (mechanical switch). Its typical control method is as follows: When on, the solid-state switch first turns on to achieve zero-voltage connection, avoiding inrush current. Then, the mechanical switch closes. After detecting the feedback contact signal, the solid-state switch turns off, and the current is transferred to the mechanical switch. When off, the solid-state switch turns on again to prepare for current transfer. A few milliseconds later, the mechanical switch disconnects under near-zero current conditions. After detecting the feedback contact signal, the solid-state switch turns off, completing the final disconnection of the load at the point where the current naturally crosses zero.

[0007] However, the control method of traditional hybrid switches has the following shortcomings: the action time is relatively long; the shutdown process is greatly affected by the actual shutdown delay of the mechanical switch, making it difficult to guarantee shutdown at zero current; and complete electrical isolation cannot be achieved. In addition, traditional hybrid switches lack accurate detection and utilization of the voltage zero-crossing point during the closing process, which can easily generate inrush current to the load.

[0008] In view of this, the present invention provides a control method for a grid-connected / off-grid switching switch to solve the above problems. Summary of the Invention

[0009] In view of the problems existing in the prior art, the present invention provides a control method for a grid-connected switching switch, which is applied to a three-phase four-wire system. The three-phase four-wire system has a set of mixed switches for each of phases A, B, and C. Each set of mixed switches includes a thyristor branch and a mechanical switch. The thyristor branch has a bidirectional thyristor and an isolating switch connected in series with the bidirectional thyristor. The thyristor branch and the mechanical switch are connected in parallel. The neutral wire of the three-phase four-wire system is also equipped with a mechanical switch.

[0010] The following closing and opening control procedures are executed by the control unit:

[0011] Closing control process:

[0012] Step 1: Close the mechanical switch for the neutral wire;

[0013] Step 2: After the mechanical switch for the neutral wire is closed, control the closing of the isolating switches for each phase;

[0014] Step 3: For each phase, when the closing feedback signal of the isolating switch of that phase is received, and the phase voltage of that phase is detected to be zero-crossing according to the phase voltage sampling signal, the bidirectional thyristor of that phase is triggered to conduct, and the conduction status of the bidirectional thyristor of that phase is detected.

[0015] Step 4: After detecting that the bidirectional thyristor of the phase is conducting, control the mechanical switch of the phase to close;

[0016] Step 5: After receiving the closing feedback signal of the mechanical switch of the phase, cancel the trigger signal of the bidirectional thyristor of the phase to complete the conduction process;

[0017] Tripping control process:

[0018] Step Six: The control unit simultaneously sends trigger signals to the bidirectional thyristors of each phase and sends disconnect commands to the mechanical switches of each phase;

[0019] Step 7: For each phase, after receiving the disconnection feedback signal of the mechanical switch of that phase, and after detecting that the bidirectional thyristor is in the freewheeling conduction state based on the voltage sampling signal across the bidirectional thyristor of that phase, cancel the trigger signal of the bidirectional thyristor of that phase.

[0020] Step 8: After detecting that the bidirectional thyristor is turned off based on the voltage sampling signal across the bidirectional thyristor of the phase, control the disconnecting switch of the phase to open, thus completing the turn-off process.

[0021] In a preferred embodiment of the present invention, the closing control process and the opening control process of phases A, B and C are all executed in parallel.

[0022] In a preferred embodiment of the present invention, the control unit is an MCU.

[0023] In a preferred embodiment of the present invention, the closing feedback signal and the opening feedback signal are both auxiliary contact feedback signals of the corresponding mechanical switch.

[0024] In a preferred embodiment of the present invention, in step three, it is determined whether the bidirectional thyristor of the phase is turned on. This is done by detecting that the voltage across the bidirectional thyristor is less than a preset turn-on voltage threshold, or by detecting that the current flowing through the bidirectional thyristor is greater than a preset turn-on current threshold.

[0025] As a preferred embodiment of the present invention, in step three, if the bidirectional thyristor is not detected to be conducting within a preset time, a fault rollback process is executed to control the disconnecting switch of that phase to open and to put the system into a fault state.

[0026] In a preferred embodiment of the present invention, in step seven, the freewheeling conduction state is determined by detecting that the conduction voltage drop across the bidirectional thyristor is greater than a preset minimum conduction threshold and less than a preset maximum conduction threshold.

[0027] As a preferred embodiment of the present invention, the detection of the bidirectional thyristor turn-off in step eight is determined by detecting that the voltage across the bidirectional thyristor is greater than a preset turn-off threshold, or by detecting that the current flowing through the bidirectional thyristor is less than a preset turn-off current threshold.

[0028] As a preferred embodiment of the present invention, after the closing control process is completed, the disconnecting switches of each phase are kept in the closed state so as to provide a switching path for the subsequent opening control process in the disconnecting switch branch.

[0029] The present invention also provides a grid-connected and off-grid switching system, including a control unit, an A-phase mixed switch, a B-phase mixed switch, a C-phase mixed switch, and a neutral wire mechanical switch;

[0030] The A-phase mixed switch, B-phase mixed switch and C-phase mixed switch each include a mechanical switch, a bidirectional thyristor and a disconnecting switch. The bidirectional thyristor and the disconnecting switch are connected in series to form a thyristor branch, and the thyristor branch is connected in parallel with the mechanical switch.

[0031] The neutral wire mechanical switch is connected to the neutral wire of the system;

[0032] The control unit is connected to the control terminals of the mechanical switch, the disconnect switch, the bidirectional thyristor, the feedback signal output terminals of each switch, and the voltage sampling terminal, respectively.

[0033] By adopting the above technical solution, the present invention has the following beneficial effects:

[0034] During the closing process of this invention, the control unit triggers the bidirectional thyristor to conduct when it detects that the phase voltage has crossed zero, thereby achieving zero-voltage connection, avoiding the impact of large current on the load, and protecting the safety of the load equipment.

[0035] During the tripping process, the control unit simultaneously sends a trigger signal to the bidirectional thyristor and a disconnect command to the mechanical switch. By utilizing the inherent action delay of the mechanical switch, the thyristor is turned on before the mechanical switch contacts separate, achieving arc-free transfer of current from the mechanical switch to the thyristor branch. This completely eliminates the arcing phenomenon when the mechanical switch is tripped and extends the service life of the mechanical switch.

[0036] Current flows through the thyristor branch only during the brief switching action of closing and opening; at other times, the current flows entirely through the mechanical switch. Because the mechanical switch has extremely low internal resistance and minimal conduction loss, and the thyristor only conducts during the brief switching process, the heat generation and energy loss problems caused by continuous current flow are avoided, resulting in extremely low overall loss.

[0037] By using disconnecting switches, complete physical and electrical isolation can be achieved after the circuit breaker is tripped, improving system safety. Rigorous detection logic enables precise judgment of the switch status, ensuring the reliability of the control timing. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the topological connection relationship of the hybrid switch single-phase circuit of the present invention;

[0039] Figure 2 This is a schematic diagram of the timing sequence of the opening and closing actions and the timing sequence of the control signals of the hybrid switch of the present invention;

[0040] Figure 3 This is a flowchart for determining the thyristor conduction state during the closing phase of the present invention.

[0041] Figure 4 This is a flowchart illustrating the thyristor conduction (freewheeling) state determination during the tripping phase of this invention.

[0042] Figure 5 This is a flowchart illustrating the thyristor turn-off state determination process during the tripping phase of this invention.

[0043] Figure 6 This is a schematic diagram of the overall state transition and fault rollback logic for the off-grid switching of the present invention.

[0044] Figure 7 This is a schematic diagram of the overall system topology of the present invention applied to a three-phase four-wire system.

[0045] In the picture:

[0046] Q1: Bidirectional thyristor;

[0047] K0, K1, K2: Neutral wire mechanical switch, mechanical switch, disconnector switch;

[0048] t1 to t13: the timing of the opening and closing of the circuit breaker. Detailed Implementation

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0050] Example 1

[0051] like Figures 1 to 7 As shown, a specific embodiment of the control method for a grid-connected / off-grid switching switch according to the present invention includes the following:

[0052] System topology:

[0053] like Figure 7 As shown, this invention is applied to a three-phase four-wire system. In the three-phase four-wire system, phases A, B, and C are each equipped with a set of mixing switches (phase A mixing switch, phase B mixing switch, phase C mixing switch), and the neutral wire N is equipped with a neutral mechanical switch K0.

[0054] like Figure 1 As shown, each set of hybrid switches includes a thyristor branch and a mechanical switch K1. The thyristor branch has a bidirectional thyristor Q1 and an isolating switch K2 connected in series with the bidirectional thyristor Q1, and the thyristor branch and the mechanical switch K1 are connected in parallel.

[0055] The control unit is connected to the control terminals of mechanical switch K1, disconnector switch K2, bidirectional thyristor Q1, feedback signal output terminals of each switch, and voltage sampling terminals. The control unit issues on / off commands to each switch and receives auxiliary contact feedback signals and voltage sampling signals from each switch. The control unit is an MCU (Microcontroller Unit).

[0056] Closing control process (conduction process)

[0057] like Figure 2 As shown, the closing control process includes the following steps:

[0058] Step 1: The MCU sends a command to close the neutral mechanical switch K0, causing the neutral mechanical switch K0 to close.

[0059] Step 2: After the neutral wire mechanical switch K0 is closed, the MCU issues a command to close the isolating switch K2 for each phase (corresponding to...). Figure 2 At time t1). After disconnector switch K2 is closed (corresponding to...) Figure 2 At time t2, the thyristor branch is in standby mode.

[0060] Step 3: The MCU receives the closing feedback signal of the isolating switch K2 for each phase. After confirming that K2 is closed, it detects the zero-crossing point of the phase voltage based on the phase voltage sampling signal. When the phase voltage zero-crossing point is detected (corresponding to...) Figure 2 At time t3, the MCU triggers the bidirectional thyristor Q1 of that phase to turn on (corresponding to...). Figure 2 (At time t4). After the bidirectional thyristor Q1 is triggered to turn on, the MCU detects whether the bidirectional thyristor Q1 of that phase is turned on.

[0061] like Figure 3 As shown, the specific method for detecting whether the bidirectional thyristor Q1 of this phase is conducting is as follows: During the turn-on and closing phase, thyristor conduction detection is performed by activating the conduction detection counter and acquiring the voltage U and loop current I across the bidirectional thyristor Q1. The conduction condition is determined as follows: when U is less than the preset conduction voltage threshold, or I is greater than the preset conduction current threshold (i.e., U < threshold, OR, I > threshold), the bidirectional thyristor Q1 is determined to be normally conducting; if the timer times out and the conduction condition is not met, the bidirectional thyristor Q1 is determined to be faulty.

[0062] Step 4: After detecting that the bidirectional thyristor Q1 of this phase is turned on (corresponding to...) Figure 2 At time t5, the MCU issues a command to close the mechanical switch K1 for that phase. After mechanical switch K1 closes (corresponding to...) Figure 2 At time t6, due to the extremely low internal resistance of mechanical switch K1, the main circuit current instantaneously shifts from the branch of bidirectional thyristor Q1 to the branch of mechanical switch K1. At this time, the current of bidirectional thyristor Q1 drops below the holding current, and bidirectional thyristor Q1 naturally turns off.

[0063] Step 5: The MCU receives the closing feedback signal of the mechanical switch K1 for that phase, and confirms that K1 is closed (corresponding to...). Figure 2 At time t7, the trigger signal of the bidirectional thyristor Q1 of this phase is removed, and the conduction process is completed.

[0064] After the closing control process is completed, keep the isolating switch K2 of each phase closed to keep the thyristor branch connected and provide a switching path for the subsequent opening control process.

[0065] Circuit breaker control process (shutdown process)

[0066] like Figure 2 As shown, the tripping control process includes the following steps:

[0067] Step Six: Upon receiving the trip command, the MCU simultaneously (corresponding to...) Figure 2 At time t8, trigger signals are sent to the bidirectional thyristors Q1 of each phase, and disconnection commands are sent to the mechanical switches K1 of each phase.

[0068] Step 7: Due to the inherent operating delay of mechanical switch K1, when the contacts of mechanical switch K1 actually separate (corresponding to...) Figure 2 At time t9, the bidirectional thyristor Q1 has been turned on. At this time, the current in the circuit is transferred from the contact of mechanical switch K1 to the thyristor branch where the bidirectional thyristor Q1 is located, realizing arc-free commutation.

[0069] The MCU receives the disconnect feedback signal from the mechanical switch K1 of this phase, confirming that K1 has been disconnected. At the same time, it detects whether the bidirectional thyristor Q1 is in the freewheeling conduction state based on the voltage sampling signal across the bidirectional thyristor Q1 of this phase.

[0070] like Figure 4 As shown, the specific method for detecting whether the bidirectional thyristor Q1 is in the freewheeling conduction state is as follows: During the opening phase, thyristor conduction detection is activated, and the conduction detection counter is started to collect the voltage U across the bidirectional thyristor Q1. The conduction condition is determined as follows: when U is greater than the preset minimum conduction threshold and less than the preset maximum conduction threshold (i.e., U < maximum threshold, AND, U > minimum threshold), the bidirectional thyristor Q1 is determined to be in the freewheeling conduction state; if the timer times out and the conduction condition is not met, the bidirectional thyristor Q1 is determined to be in a conduction fault.

[0071] After confirming that mechanical switch K1 is open and bidirectional thyristor Q1 is successfully freewheeling (corresponding to...) Figure 2 At time t10, the MCU cancels the trigger signal of the bidirectional thyristor Q1 of that phase.

[0072] Step 8: After the trigger signal is removed, the bidirectional thyristor Q1 will turn off naturally when the AC current naturally crosses zero (corresponding to...). Figure 2 (At time t11). The MCU detects whether the bidirectional thyristor Q1 is turned off based on the voltage sampling signal across the bidirectional thyristor Q1 in this phase.

[0073] like Figure 5 As shown, the specific method for detecting whether the bidirectional thyristor Q1 is turned off is as follows: During the opening and closing phase, the thyristor turn-off detection is performed by activating the turn-off detection counter and collecting the voltage U and loop current I across the bidirectional thyristor Q1. The turn-off condition is determined as follows: when U is greater than the preset turn-off threshold, or I is less than the preset turn-off current threshold (i.e., U > threshold, OR I < threshold), the bidirectional thyristor Q1 is determined to be normally turned off; if the timer times out and the turn-off condition is not met, the bidirectional thyristor Q1 is determined to be in a turn-off fault.

[0074] After detecting that the bidirectional thyristor Q1 is turned off (corresponding to) Figure 2 At time t12, the MCU issues a command to disconnect the isolating switch K2 for that phase. After the isolating switch K2 is disconnected (corresponding to...), Figure 2 At time t13, the shutdown process is completed.

[0075] Fault rollback process

[0076] like Figure 6 As shown, in step three of the closing control process, if the bidirectional thyristor Q1 is not detected to be conducting within a preset time, the fault rollback process is executed: the isolating switch K2 of the phase is opened, and the mechanical switch K1 remains open, so that the system enters the fault state.

[0077] In this embodiment, the MCU executes the closing control process and the opening control process of phases A, B and C in parallel, that is, the three phases execute steps one to five and steps six to eight at the same time.

[0078] All components mentioned in this article are general standard parts or components known to those skilled in the art. Their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods, so they will not be described in detail here.

[0079] While the specific embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and modifications or variations without creative effort are still within the protection scope of the present invention.

Claims

1. A control method for a grid-connected / off-grid switching switch, applied to a three-phase four-wire system, wherein phases A, B, and C of the three-phase four-wire system are each equipped with a set of hybrid switches, each set of hybrid switches including a thyristor branch and a mechanical switch, wherein the thyristor branch has a bidirectional thyristor and an isolating switch connected in series with the bidirectional thyristor, and the thyristor branch and the mechanical switch are connected in parallel, and the neutral wire of the three-phase four-wire system is also equipped with a mechanical switch, characterized in that... The following closing and opening control procedures are executed by the control unit: Closing control process: Step 1: Close the mechanical switch for the neutral wire; Step 2: After the mechanical switch for the neutral wire is closed, control the closing of the isolating switches for each phase; Step 3: For each phase, when the closing feedback signal of the isolating switch of that phase is received, and the phase voltage of that phase is detected to be zero-crossing according to the phase voltage sampling signal, the bidirectional thyristor of that phase is triggered to conduct, and the conduction status of the bidirectional thyristor of that phase is detected. Step 4: After detecting that the bidirectional thyristor of the phase is conducting, control the mechanical switch of the phase to close; Step 5: After receiving the closing feedback signal of the mechanical switch of the phase, cancel the trigger signal of the bidirectional thyristor of the phase to complete the conduction process; Tripping control process: Step Six: The control unit simultaneously sends trigger signals to the bidirectional thyristors of each phase and sends disconnect commands to the mechanical switches of each phase; Step 7: For each phase, after receiving the disconnection feedback signal of the mechanical switch of that phase, and after detecting that the bidirectional thyristor is in the freewheeling conduction state based on the voltage sampling signal across the bidirectional thyristor of that phase, cancel the trigger signal of the bidirectional thyristor of that phase. Step 8: After detecting that the bidirectional thyristor is turned off based on the voltage sampling signal across the bidirectional thyristor of the phase, control the disconnecting switch of the phase to open, thus completing the turn-off process.

2. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: The closing and opening control processes for phases A, B, and C are all executed in parallel.

3. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: The control unit is an MCU.

4. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: The closing feedback signal and the opening feedback signal are both auxiliary contact feedback signals of the corresponding mechanical switches.

5. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: In step three, it is detected whether the bidirectional thyristor of the phase is turned on. This is determined by detecting that the voltage across the bidirectional thyristor is less than a preset turn-on voltage threshold, or by detecting that the current flowing through the bidirectional thyristor is greater than a preset turn-on current threshold.

6. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: In step three, if the bidirectional thyristor is not detected to be conducting within a preset time, a fault rollback process is executed to control the disconnecting switch of that phase to open and put the system into a fault state.

7. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: In step seven, the freewheeling conduction state is determined by detecting that the conduction voltage drop across the bidirectional thyristor is greater than a preset minimum conduction threshold and less than a preset maximum conduction threshold.

8. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: In step eight, the detection of the bidirectional thyristor turn-off is determined by detecting that the voltage across the bidirectional thyristor is greater than a preset turn-off threshold, or by detecting that the current flowing through the bidirectional thyristor is less than a preset turn-off current threshold.

9. The control method for a grid-connected / off-grid switching switch according to claim 1, characterized in that: After the closing control process is completed, the disconnecting switches of each phase are kept in the closed state so as to provide a switching path for the subsequent opening control process in the disconnecting switch branch.

10. A grid-connected / off-grid switching system, employing the control method as described in any one of claims 1 to 9, characterized in that, This includes a control unit, an A-phase mixing switch, a B-phase mixing switch, a C-phase mixing switch, and a neutral wire mechanical switch; The A-phase mixed switch, B-phase mixed switch and C-phase mixed switch each include a mechanical switch, a bidirectional thyristor and a disconnecting switch. The bidirectional thyristor and the disconnecting switch are connected in series to form a thyristor branch, and the thyristor branch is connected in parallel with the mechanical switch. The neutral wire mechanical switch is connected to the neutral wire of the system; The control unit is connected to the control terminals of the mechanical switch, the disconnect switch, the bidirectional thyristor, the feedback signal output terminals of each switch, and the voltage sampling terminal, respectively.

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