CN114709864A - Off-grid and grid-connected switching control method of energy storage inverter - Google Patents
Off-grid and grid-connected switching control method of energy storage inverter Download PDFInfo
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- CN114709864A CN114709864A CN202210245024.8A CN202210245024A CN114709864A CN 114709864 A CN114709864 A CN 114709864A CN 202210245024 A CN202210245024 A CN 202210245024A CN 114709864 A CN114709864 A CN 114709864A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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Abstract
The invention discloses a grid-off and grid-connected switching control method of an energy storage inverter, which comprises the following steps: A. detecting the closing time of a power grid end relay of the energy storage inverter, and measuring the closing time; B. enabling the energy storage inverter to work in an off-grid running state, detecting the grid frequency when a grid is normal, detecting the zero position of the grid voltage after the output voltage of the energy storage inverter is aligned with the phase amplitude of the grid output voltage, and enabling the energy storage inverter to stop outputting when the grid voltage is zero; C. calculating delay time delta t according to the closing time and the power grid frequency, and disconnecting an inverter end relay of the energy storage inverter and closing a power grid end relay by the delay delta t; D. driving the energy storage inverter to output voltage with the same frequency and phase as the power grid; E. and closing the inverter terminal relay. The invention effectively reduces the current in the closing process of the relay when the off-grid operation state is switched to the grid-connected operation state, so that the energy storage inverter can be switched off and on the grid stably and safely.
Description
Technical Field
The invention belongs to the field of energy storage inverters, and relates to a grid-off and grid-connected switching control method of an energy storage inverter.
Background
When the traditional energy storage inverter is switched from an off-grid operation state to a grid-connected operation state after a call comes, usually, the inverter end relay is directly disconnected, and meanwhile, the grid-connected end relay is closed. In the process of closing the relay at the grid-connected end, because the pressure difference between two ends of the relay is large, the instant large current of the loop is easily caused, the large current can impact the closed relay, the service life of the relay is shortened, and even the relay is adhered and fails; in addition, the large current can also cause the current sensor to detect the large current to report the overcurrent, so that the inverter has a fault shutdown phenomenon, the energy storage inverter stops outputting when being off the grid, and the important load at the off-grid end has a power-off phenomenon; the larger di/dt at the closing moment of the loop relay can also cause interference to weak current signals passing through the loop and nearby, so that the inverter has an interference DSP restart phenomenon, the energy storage inverter is disconnected from the network to stop output, and the important load at the disconnected end has a power failure phenomenon.
Disclosure of Invention
In order to solve the above technical problems, an object of the present invention is to provide a method for controlling off-grid and on-grid switching of an energy storage inverter, which effectively reduces current in a relay closing process when an off-grid operating state is switched to a grid-connected operating state, so that the energy storage inverter can perform off-grid and on-grid switching stably and safely.
A grid-off and grid-connected switching control method of an energy storage inverter comprises the following steps:
A. detecting the closing time of a power grid end relay of the energy storage inverter, and measuring the closing time;
B. enabling the energy storage inverter to work in an off-grid running state, detecting the grid frequency when a grid is normal, detecting the zero position of the grid voltage after the output voltage of the energy storage inverter is aligned with the phase amplitude of the grid output voltage, and enabling the energy storage inverter to stop outputting when the grid voltage is zero;
C. calculating delay time delta t according to the closing time and the power grid frequency, and disconnecting an inverter end relay of the energy storage inverter and closing the power grid end relay by the delay delta t;
D. enabling the driving output of the energy storage inverter to be voltage with the same frequency and phase as the power grid;
E. and closing the inverter terminal relay.
According to a preferred embodiment, said delay time Δ t is calculated according to the following formula:
△t＝1/(2*F)-ton
wherein F represents the grid frequency when the grid is normal, and ton represents the closing time of the grid-side relay.
According to a preferred embodiment, in step D, the grid supplies energy to the load; in step E, the energy storage inverter provides energy for the load.
According to a specific and preferred embodiment, the off-grid and on-grid switching control method is implemented as follows:
s101, when the energy storage inverter is started to carry out relay self-checking, detecting the off-time of an inverter end relay of the energy storage inverter, and measuring the off-time to be toff;
s102, when the energy storage inverter is started to perform relay self-checking, detecting the closing time of a power grid end relay of the energy storage inverter, and measuring the closing time to be ton; when toff is less than ton, the following steps are executed;
s103, enabling the energy storage inverter to work in an off-grid running state, detecting the voltage of a power grid end of the energy storage inverter, detecting that the voltage of the power grid end is normal after the power grid is powered on, detecting that the frequency of the voltage of the power grid is F, carrying out phase comparison on the output voltage of the energy storage inverter according to the voltage of the power grid, and adjusting the phase and amplitude of the output voltage of the energy storage inverter until the phase and amplitude of the output voltage of the energy storage inverter are consistent with the voltage of the power grid;
s104, detecting a voltage zero point of the power grid after the phase amplitudes of the output voltage of the energy storage inverter and the output voltage of the power grid are aligned, and closing the driving PWM wave of the energy storage inverter to stop outputting the energy storage inverter when the voltage of the power grid is zero;
s105, after the driving PWM wave of the energy storage inverter is closed, delaying the time delta t to be 1/(2 x F) -ton, disconnecting the inverter end relay and closing the grid end relay;
s106, the energy storage inverter sends out PWM waves again to enable the energy storage inverter bridge to output voltage with the same frequency and phase as the power grid, and the off-grid load is powered by the power grid at the moment;
and S107, after the energy storage inverter outputs the same-frequency and same-phase voltage with the power grid, the inverter end relay is started to be closed, the energy storage inverter outputs energy for the load, and the grid-connected operation state is switched.
According to a preferred embodiment, step a further detects the turn-off time of the inverter end relay of the energy storage inverter, and measures the turn-off time; and judging whether the opening time is less than the closing time, and executing the steps B to E only when the opening time is less than the closing time.
According to a preferred embodiment, in step a, the closing time is detected when the energy storage inverter performs a startup relay self-test.
According to a preferred embodiment, in step B, the energy storage inverter is operated in an off-grid operation state by closing the inverter side relay and opening the grid side relay.
According to a preferred embodiment, in the step B, the energy storage inverter stops outputting by closing the driving PWM wave of the energy storage inverter; and/or in the step D, the energy storage inverter sends out PWM waves to enable the driving output of the energy storage inverter to be the same frequency and phase voltage with the power grid.
According to a preferred embodiment, the inverter terminal relay comprises a first relay with one end connected to the L output terminal of the inverter circuit and a second relay with one end connected to the N output terminal of the inverter circuit; the power grid end relay comprises a third relay and a fourth relay, wherein one end of the third relay is used for being connected with the L end of the power grid, and one end of the fourth relay is used for being connected with the N end of the power grid; the other end of the first relay is connected to the other end of the third relay, the intermediate node of the third relay and the intermediate node of the third relay are connected with one end of the load, and the other end of the second relay is connected to the other end of the fourth relay, the intermediate node of the fourth relay and the intermediate node of the fourth relay are connected with the other end of the load.
According to a preferred embodiment, a grid-connected end capacitor is connected between the other end of the third relay and the other end of the fourth relay.
According to a preferred embodiment, an off-grid capacitor is connected between two ends of the load, and after the energy storage inverter stops outputting, the voltage at two ends of the off-grid capacitor is zero.
Compared with the prior art, the invention has the following advantages by adopting the scheme:
according to the off-grid and grid-connected switching control method of the energy storage inverter, the driving is closed at the phase zero point, meanwhile, the relay is closed at the phase zero point, when the relay is closed, the two ends almost have no pressure difference, and the current in the closing process of the relay during the off-grid and grid-connected switching is effectively reduced, so that the energy storage inverter can be stably and safely carried out during the on-grid and off-grid switching; the service life of the relay is ensured, and the failure rate is greatly reduced; the relay closing process can not cause unnecessary interference to the whole control system, so that the whole control system can operate safely and stably, the off-grid switching time is effectively guaranteed, and the uninterrupted operation of important loads can be guaranteed.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings required to be used in the description of the embodiments will be briefly introduced below, and it is apparent that the drawings in the description below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
Fig. 1 is a topology diagram of an off-grid switching relay of an energy storage inverter according to an embodiment.
FIG. 2 is a control flow chart of the embodiment;
fig. 3 is a waveform diagram of grid-connected voltage and grid-disconnected voltage when the power grid is powered on in the embodiment.
Fig. 4 is a waveform diagram of the grid-connected voltage and the off-grid voltage after phase alignment in the embodiment.
FIG. 5 is a timing diagram of control signals according to an embodiment.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the invention may be more readily understood by those skilled in the art. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 shows an off-grid and on-grid switching relay topology of an energy storage inverter, wherein a relay group is arranged between an inverter circuit 1 (mainly including an inverter bridge) of the energy storage inverter and a power grid 6, and the relay group is composed of a plurality of relays (hereinafter, also referred to as relays) for switching the energy storage inverter between an off-grid operating state and a grid-connected operating state. The relay group includes an inverter end relay located on one side of the inverter circuit 1 and a grid end relay (also referred to as a grid end relay) located on one side of the grid 6. Specifically, the inverter end relay includes a first relay 2 having one end connected to the L output end of the inverter circuit 1 and a second relay 3 having one end connected to the N output end of the inverter circuit 1; the grid end relay comprises a third relay 4 with one end used for being connected with the L end of a grid 6 and a fourth relay 5 with one end used for being connected with the N end of the grid 6. The other end of the first relay 2 is connected to the other end of the third relay 4, and the intermediate node of the two is connected to one end of the load 7, and the other end of the second relay 3 is connected to the other end of the fourth relay 5, and the intermediate node of the two is connected to the other end of the load 7. And a grid-connected end capacitor 8 is connected between the other end of the third relay 4 and the other end of the fourth relay 5. An off-grid end capacitor 9 is connected between two ends of the load 7, and after the energy storage inverter stops outputting, the voltage at two ends of the off-grid end capacitor 9 is zero. Herein, "inverter terminal" means a terminal closer to the inverter circuit 1, "grid-connected terminal" or "grid terminal" means a terminal closer to the grid 6, and "grid-connected terminal" means a terminal closer to the load 7.
When the energy storage inverter is in an off-grid running state, a first relay 2 and a second relay 3 at an inverting end are closed; the third relay 4 and the fourth relay 5 of the grid side are opened. When the energy storage inverter is in a grid-connected operation state, the first relay 2 and the second relay 3 at the inverting end are closed, and the third relay 4 and the fourth relay 5 at the power grid end are closed.
The process of switching the energy storage inverter from the off-grid operation state to the grid-connected operation state in the embodiment is generally as follows:
firstly, detecting the closing time of a third relay 4 and a fourth relay 5 at a power grid end and the opening time of a first relay 2 and a second relay 3 at an inversion end;
after the power grid 6 is powered on, the inversion output voltage and the power grid 6 voltage are subjected to synchronous and in-phase opposite phase regulation;
detecting a phase zero point and starting to close inversion driving to carry out off-grid and grid-connected switching;
after the driving is closed, the time delay delta t is carried out, the first relay 2 and the second relay 3 on the inversion side are disconnected, and the third relay 4 and the fourth relay 5 on the grid merging side are closed;
the inverter bridge outputs the same-frequency and same-phase voltage, and a first relay 2 and a second relay 3 at the inverter end are closed.
Specifically, referring to fig. 2, the off-grid and on-grid switching control method of the present embodiment specifically includes the following steps:
s101, when the energy storage inverter is started to carry out relay self-checking, detecting the off time of a first relay 2 and a second relay 3 at the inverter end of the energy storage inverter, measuring the off time to be toff, and recording and storing the off time toff of the inverter end relay in a register of a DSP.
S102, when the energy storage inverter is started to carry out relay self-checking, detecting the closing time of a third relay 4 and a fourth relay 5 at the power grid end of the energy storage inverter, and measuring that the closing time is ton; and when toff is less than ton, executing the following steps, and recording and storing the closing time ton of the grid-connected end relay in a register of the DSP.
S103, enabling the energy storage inverter to work in an off-grid running state, and continuously detecting the voltage of the power grid end of the energy storage inverter. After the power grid 6 is powered on, detecting that the voltage of the power grid is normal, detecting that the voltage frequency of the power grid 6 is F, carrying out phase comparison on the output voltage of the energy storage inverter according to the voltage of the power grid 6, and continuously adjusting the phase and amplitude of the output voltage of the energy storage inverter until the phase and amplitude of the output voltage of the energy storage inverter are consistent with the voltage of the power grid 6. The waveforms of the grid-connected voltage (the voltage of the power grid 6) and the off-grid voltage (the inversion voltage) before the phase alignment are shown in fig. 3; after the phase alignment, the waveforms of the grid-connected voltage and the off-grid voltage are substantially overlapped, the phases of the grid-connected voltage and the off-grid voltage are consistent, and the amplitudes of the grid-connected voltage and the off-grid voltage are substantially consistent, as shown in fig. 4.
And S104, after the phase amplitudes of the output voltage of the energy storage inverter and the output voltage of the power grid 6 are aligned, detecting the voltage zero point of the power grid 6, and closing the driving PWM wave of the energy storage inverter to stop the energy storage inverter from outputting when the voltage of the power grid 6 is zero, wherein the voltage at two ends of the capacitor 9 at the off-grid end is almost zero.
And S105, after the inverter outputs a sealed wave to close the driving PWM wave of the energy storage inverter, delaying the time delta t to be 1/(2 x F) -ton, disconnecting the first relay 2 and the second relay 3 at the inverting end, and simultaneously closing the third relay 4 and the fourth relay 5 at the power grid end. Referring to fig. 5, after the ton time, the first relay 2 and the second relay 3 at the inverting terminal are completely opened, the third relay 4 and the fourth relay 5 at the grid-connected end of the inverter are completely closed, and at this time, the time elapsed from the inverter blocking to the closing of the first relay 2 and the second relay 3 is Δ t + ton ═ 1/(2 × F), which is a half cycle of the voltage of the grid 6, so that the time when the third relay 4 and the fourth relay 5 at the grid-connected end are completely closed is still the time when the phase is zero. When the grid-connected end relay is closed, the voltage at two ends is almost zero, so that large current cannot be generated in a loop at the closing moment, the relay cannot be damaged, and the failure of the relay caused by the large current at the closing moment is greatly reduced. The loop has no larger di/dt, so that the interference to a weak signal of a loop accessory is avoided, the phenomena of misoperation and restarting of the inverter are reduced, and the power-off condition of the off-grid important load 7 is avoided.
S106, after the third relay 4 and the fourth relay 5 at the power grid end are closed, the off-grid load 7 is powered by the power grid 6, and the energy storage inverter can start to send out PWM waves again at the moment, so that the inverter circuit 1 of the energy storage inverter bridge outputs voltage with the same frequency and phase as the power grid 6.
And S107, after the energy storage inverter outputs the same-frequency and same-phase voltage with the power grid 6, closing the first relay 2 and the second relay 3 at the inversion end, switching the energy storage inverter output to provide energy for the load 7 into a grid-connected operation state, and finishing off-grid and grid-connection.
The off-grid and grid-connected switching control method can effectively reduce the current in the relay closing process during off-grid and grid-connected switching, so that the energy storage inverter can be stably and safely carried out during on-grid and off-grid switching; the service life of the relay is ensured, and the failure rate is greatly reduced; unnecessary interference to the whole control system can not be caused in the relay closing process, so that the whole control system can safely and stably operate; effectively guarantee and leave the net switching time, guarantee that important load is incessant to be operated.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and are preferred embodiments, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
1. The off-grid and grid-connected switching control method of the energy storage inverter is characterized by comprising the following steps:
A. detecting the closing time of a power grid end relay of the energy storage inverter, and measuring the closing time;
B. enabling the energy storage inverter to work in an off-grid running state, detecting the grid frequency when a grid is normal, detecting the zero position of the grid voltage after the output voltage of the energy storage inverter is aligned with the phase amplitude of the grid output voltage, and enabling the energy storage inverter to stop outputting when the grid voltage is zero;
C. calculating delay time delta t according to the closing time and the power grid frequency, and disconnecting an inverter end relay of the energy storage inverter and closing the power grid end relay by the delay delta t;
D. enabling the driving output of the energy storage inverter to be voltage with the same frequency and phase as the power grid;
E. and closing the inverter terminal relay.
2. The off-grid and grid-connected switching control method according to claim 1, wherein the delay time Δ t is calculated according to the following formula:
△t＝1/(2*F)-ton
wherein F represents the grid frequency when the grid is normal, and ton represents the closing time of the grid-side relay.
3. The grid disconnection and connection switching control method according to claim 1, wherein in the step D, a power grid supplies energy to a load; in step E, the energy storage inverter provides energy for the load.
4. The grid-off and grid-connected switching control method according to claim 1, characterized by being implemented as follows:
s101, when the energy storage inverter is started to carry out relay self-checking, detecting the off-time of an inverter end relay of the energy storage inverter, and measuring the off-time to be toff;
s102, when the energy storage inverter is started to perform relay self-checking, detecting the closing time of a power grid end relay of the energy storage inverter, and measuring the closing time to be ton; when toff is less than ton, the following steps are executed;
s103, enabling the energy storage inverter to work in an off-grid running state, detecting the voltage of a power grid end of the energy storage inverter, detecting that the voltage of the power grid end is normal after the power grid is powered on, detecting that the frequency of the voltage of the power grid is F, carrying out phase comparison on the output voltage of the energy storage inverter according to the voltage of the power grid, and adjusting the phase and amplitude of the output voltage of the energy storage inverter until the phase and amplitude of the output voltage of the energy storage inverter are consistent with the voltage of the power grid;
s104, detecting a voltage zero point of the power grid after the phase amplitudes of the output voltage of the energy storage inverter and the output voltage of the power grid are aligned, and closing the driving PWM wave of the energy storage inverter to stop outputting the energy storage inverter when the voltage of the power grid is zero;
s105, after the driving PWM wave of the energy storage inverter is closed, delaying the time delta t to be 1/(2 x F) -ton, disconnecting the inverter end relay and closing the grid end relay;
s106, the energy storage inverter sends out PWM waves again to enable the energy storage inverter bridge to output voltage with the same frequency and phase as the power grid, and the off-grid load is powered by the power grid at the moment;
and S107, after the energy storage inverter outputs the same-frequency and same-phase voltage with the power grid, the inverter end relay is started to be closed, the energy storage inverter outputs energy for the load, and the grid-connected operation state is switched.
5. The off-grid and grid-connected switching control method according to claim 1, wherein in the step a, the off-time of an inverter end relay of the energy storage inverter is detected, and the off-time is measured; and judging whether the opening time is less than the closing time, and executing the steps B to E only when the opening time is less than the closing time.
6. The grid disconnection and connection switching control method according to claim 1, wherein in the step a, the closing time is detected when the energy storage inverter performs a startup relay self-test.
7. The grid disconnection and connection switching control method according to claim 1, wherein in the step B, the energy storage inverter is operated in an off-grid operation state by closing the inverter side relay and opening the grid side relay.
8. The grid-off and grid-connected switching control method according to claim 1, wherein in step B, the energy storage inverter stops outputting by closing a driving PWM wave of the energy storage inverter; and/or in the step D, the energy storage inverter sends out PWM waves to enable the driving output of the energy storage inverter to be the same frequency and phase voltage with the power grid.
9. The grid disconnection-connection switching control method according to claim 1, wherein the inverter terminal relay includes a first relay having one terminal connected to an L output terminal of the inverter circuit and a second relay having one terminal connected to an N output terminal of the inverter circuit; the power grid end relay comprises a third relay and a fourth relay, wherein one end of the third relay is used for being connected with the L end of the power grid, and one end of the fourth relay is used for being connected with the N end of the power grid; the other end of the first relay is connected to the other end of the third relay, the intermediate node of the third relay and the intermediate node of the third relay are connected with one end of the load, and the other end of the second relay is connected to the other end of the fourth relay, the intermediate node of the fourth relay and the intermediate node of the fourth relay are connected with the other end of the load.
10. The off-grid and grid-connected switching control method according to claim 9, wherein a grid-connected end capacitor is connected between the other end of the third relay and the other end of the fourth relay; and/or an off-grid end capacitor is connected between two ends of the load, and after the energy storage inverter stops outputting, the voltage at two ends of the off-grid end capacitor is zero.
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| CN117116706A (en) * | 2023-09-02 | 2023-11-24 | 广州菲利斯太阳能科技有限公司 | Method and system for preventing large current arc discharge caused by relay closing |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117116706A (en) * | 2023-09-02 | 2023-11-24 | 广州菲利斯太阳能科技有限公司 | Method and system for preventing large current arc discharge caused by relay closing |
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