CN115224724A - Three-phase grid-connected connection method of energy storage system with filter capacitor - Google Patents
Three-phase grid-connected connection method of energy storage system with filter capacitor Download PDFInfo
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- CN115224724A CN115224724A CN202210742171.6A CN202210742171A CN115224724A CN 115224724 A CN115224724 A CN 115224724A CN 202210742171 A CN202210742171 A CN 202210742171A CN 115224724 A CN115224724 A CN 115224724A
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- voltage
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- alternating current
- inverter circuit
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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
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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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/493—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode the static converters being arranged for operation in parallel
-
- 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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Inverter Devices (AREA)
Abstract
The invention belongs to the technical field of power distribution systems, and relates to a three-phase grid-connected connection method of an energy storage system with a filter capacitor, which comprises the following steps: s1, a CPU of an energy storage system controls a direct current relay to be closed, so that an inverter circuit works, and a filter circuit is charged until the peak value of a three-phase filter capacitor reaches the peak value of alternating current voltage; s2, under the condition that the alternating current relay is kept disconnected, continuously acquiring an instantaneous value of the power grid voltage, and acquiring phase angle information of the power grid voltage; s3, when one-phase voltage of the power grid crosses zero, the CPU stops the inverter circuit firstly, and closes the alternating current relay when the one-phase voltage of the power grid crosses zero for one time; s4, after the CPU confirms that the alternating current relay is closed, the inverter circuit is started again to operate along with the network; and S5, the inverter circuit performs charge and discharge control according to the instruction setting of the CPU. The method realizes safe three-phase grid-connected operation by using a simple circuit structure.
Description
Technical Field
The invention relates to the technical field of power distribution systems, in particular to a three-phase grid-connected connection method of an energy storage system with a filter capacitor.
Background
The output filter of the grid-connected energy storage inverter has three conventional types: single L filters, LC filters and LCL filters. The filters of the latter two contain filter capacitors. When the filter capacitor is connected to a power grid, the filter capacitor is equivalent to a short circuit and has no impedance, so that instant high current can be generated, the impact current of the filter capacitor needs to be limited, and the damage of other devices on a line caused by overlarge current is prevented.
One method is to use an auxiliary contactor to add a slow-up resistor, such as CN102522778B. The output loop of the method limits the current output by the inverter by adopting the serially connected resistors, thereby ensuring that the inverter bridge realizes grid-connected operation in a smaller current state; however, the structure is complicated and the cost is high due to the increased resistance, and the space inside the inverter is occupied.
Another method is to adopt a voltage slow-up scheme, such as Chinese patent CN111245277B. The method comprises the steps of firstly controlling the voltage on a filter capacitor to be close to the voltage of a mains supply, and then integrating a main loop alternating current relay; the method needs to increase the voltage sampling of the filter capacitor, but the slow control of the voltage is more complicated.
Therefore, it is necessary to provide a new method to make the circuit structure simple and ensure the safety of the inverter when the inverter is connected to the three-phase grid.
Disclosure of Invention
The invention mainly aims to provide a three-phase grid-connected connection method of an energy storage system with a filter capacitor, which adopts a simple circuit structure and realizes safe three-phase grid-connected connection.
The invention realizes the purpose through the following technical scheme: a three-phase grid-connected connection method of an energy storage system with a filter capacitor comprises the following steps:
s1, a CPU of an energy storage system controls a direct current relay to be closed, so that an inverter circuit works, and a filter circuit is charged until the peak value of a three-phase filter capacitor reaches the peak value of alternating current voltage;
s2, under the condition that the alternating current relay is kept disconnected, continuously acquiring an instantaneous value of the power grid voltage, and acquiring phase angle information of the power grid voltage;
s3, when one-phase voltage of the power grid crosses zero, the CPU stops the inverter circuit firstly, and closes the alternating current relay when the one-phase voltage of the power grid crosses zero for one time;
s4, after the CPU confirms that the alternating current relay is closed, the inverter circuit is started again to operate along with the network;
and S5, the inverter circuit performs charge and discharge control according to the instruction setting of the CPU.
Specifically, in the step S1, when the bus voltage before the dc relay is lower than the voltage value of the ac voltage rectified by the inverter circuit, the CPU starts the DCDC boost circuit first, so that the voltage value of the bus voltage is increased to a maximum voltage value not lower than the ac voltage.
Specifically, the step S3 includes a time Δ t compensation phase difference caused by an on delay of the ac relay, and the ac relay is turned on before the time Δ t at which the grid voltage reaches the phase angle of the maximum voltage value.
The technical scheme of the invention has the beneficial effects that:
according to the method, sampling of a filter capacitor is not needed, the voltage value of the filter capacitor reaches the voltage value during grid connection, then the opening time of the alternating current relay is controlled according to the phase angle of a power grid, the alternating current relay is connected in the shutdown interval of the inverter circuit, and safe grid connection operation is achieved through a simple circuit structure.
Drawings
Fig. 1 is a circuit diagram of an ac-dc conversion portion of an energy storage system including a filter capacitor according to an embodiment.
The labels in the figures indicate:
1-a direct-current relay, wherein,
2-an inverter circuit, which is connected with a power supply,
3-filter circuit, 31 a-filter capacitor a, 31B-filter capacitor B, 31C-filter capacitor C,32 a-filter inductor a, 32B-filter inductor B, 32C-filter inductor C;
4-an alternating current relay;
5-DCDC boost circuit.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
Example (b):
as shown in fig. 1, the three-phase grid-connected connection method of the energy storage system with the filter capacitor of the present invention includes the steps of:
s1, a CPU of the energy storage system controls a direct current relay 1 to be closed, so that an inverter circuit 2 works, and a filter circuit 3 is charged until the peak value of a three-phase filter capacitor reaches the peak value of alternating current voltage. The filter circuit 3 in the embodiment has three filter capacitors (a filter capacitor a 31a, a filter capacitor B31B, and a filter capacitor C31C) and three filter inductors (a filter inductor a 32a, a filter inductor B32B, and a filter inductor C32C), and the three filter capacitors are connected to the energy storage system in a three-phase four-wire manner. Because the phase difference of the three filter capacitors is always 120 degrees, the voltage of one filter capacitor can be monitored to determine the voltage of the other two filter capacitors. Under the condition of symmetrical load, the phase voltage output by the inverter circuit 2, namely the voltage from the output end of the inverter circuit 2 to the neutral point of the direct-current side bus (namely the voltage of the filter capacitor), can be deduced:
(wherein k represents A, B or C, v k Is the switching phase transition speed of the three phases). After charging is completed, the three filter capacitors are all in static voltage values. The inverter circuit 2 adopts an SPWM modulation method, and the modulation ratio M =2U/U dc (U dc Is the voltage value of the dc-side bus of the inverter circuit 2). When the modulation ratio is increased by a value of M =2U d /U dc Rear (U) d Is the positive sequence component of the grid voltage on the D-axis), the filter capacitor voltage may be considered to have approached the grid voltage. The voltage on the filter capacitor does not need to change along with time, and because harmonic waves and the like in the voltage waveform of a real power grid are not fixed, the inverter circuit cannot accurately control the voltage of the filter capacitor to be completely consistent with the voltage of the power grid in real time. In order to achieve the purpose of reducing the impact current, the voltage of the filter capacitor A31 a is only required to be controlled to be close to the voltage of the power grid, and the control difficulty is low. In practical application, the inverter can be adopted by three-phase four-wire, three-phase three-wire or single-phase inverters.
And S2, continuously acquiring the instantaneous value of the power grid voltage under the condition that the alternating current relay 4 is kept disconnected, and acquiring phase angle information of the power grid voltage. At the moment, the alternating current relay 4 is still in a disconnected state, so that the voltage of the power grid and the voltage of the filter capacitor do not affect each otherAnd (6) sounding. The voltage of the power grid is alternating current, so that three-phase voltages of the power grid are in dynamic change, and a trigonometric function relation is compounded. The general expression of the ac voltage is U = U m cos θ (U is phase voltage of AC voltage, U m Maximum voltage value of ac voltage, θ is phase angle), at U m In certain cases, the instantaneous voltage is a function of θ. And acquiring a power grid voltage instantaneous value, and acquiring power grid angle information through a phase-locking algorithm. And obtaining the positive sequence component of the grid voltage on the D axis by using DQ coordinate transformation, namely obtaining the U of the grid voltage m The information of (1).
And S3, when the A-phase voltage of the power grid crosses zero, the CPU stops the inverter circuit 2 firstly, and closes the alternating current relay 4 when the A-phase voltage of the power grid crosses zero once. Because the modulation wave is fixed under the open-loop condition, and direct access to the grid causes overcurrent protection of the inverter circuit 2, the inverter circuit 2 needs to be stopped before the ac relay 4 is closed.
And S4, after confirming that the alternating current relay 4 is closed, the CPU restarts the inverter circuit 2 to enable the inverter circuit to operate along with the network. Because the voltage of the filter capacitor A31 a is close to the maximum voltage value of the power grid, after the alternating current relay 4 is opened, a large impact current cannot be generated on the alternating current relay 4, and after the filter circuit 3 is connected to the power grid, the inverter circuit 2 is started, so that the direct current side can be changed along with the change of the power grid.
And S5, the inverter circuit performs charge and discharge control according to the instruction setting of the CPU.
According to the method, the sampling of a filter capacitor is not needed, the voltage value on the filter capacitor is enabled to reach the voltage value during grid connection, then the opening time of the alternating current relay 4 is controlled according to the phase angle of a power grid, the alternating current relay 4 is switched on within the shutdown interval of the inverter circuit 2, and safe grid connection operation is achieved through a simple circuit structure.
Step S1, when the bus voltage in front of the direct current relay 1 is lower than the voltage value of the alternating current voltage rectified by the inverter circuit 2, the CPU starts the DCDC booster circuit 5 to increase the voltage value of the bus voltage to be not lower than the maximum voltage value of the alternating current voltage. If the voltage value of the dc side is lower than the voltage value of the ac voltage rectified by the inverter circuit 2, the filter voltage converted by the inverter circuit 2 cannot approach the maximum voltage value of the ac voltage in any way, and thus the generation of the inrush current cannot be avoided. It is necessary to first raise the dc bus voltage to a range close to the maximum voltage value of the ac voltage by the DCDC boost circuit 5.
Step S3 includes counting a time Δ t compensation phase difference caused by the start delay of the ac relay 4, and turning on the ac relay 4 before the time Δ t at which the grid voltage reaches the phase angle of the maximum voltage value. The time difference delta t between the time when the AC relay 4 receives the closing signal and the actual action time is normally within 20 ms. In general, the voltage drop is small and can be ignored within 20 ms. This time difference may cause the instantaneous value of the grid voltage to be inconsistent with the voltage value of the filter capacitor a 31a when the inverter circuit 2 is stopped. By adjusting the phase angle followed by the open-loop modulation wave, the phase angle of the filter capacitor voltage when the inverter circuit 2 stops working is consistent with the phase angle of the power grid voltage at the closing action moment of the alternating-current relay 4. I.e. the phase angle theta of the modulated wave C ＝θ PLL +2πΔt/20ms，(θ C Is the phase angle, theta, of the filter capacitor voltage when the inverter circuit 2 stops operating PLL Is the phase angle obtained by the grid phase locking algorithm).
What has been described above are merely some embodiments of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the inventive concept thereof, and these changes and modifications can be made without departing from the spirit and scope of the invention.
Claims (3)
1. A three-phase grid-connected connection method of an energy storage system with a filter capacitor is characterized in that: the method comprises the following steps:
s1, a CPU of an energy storage system controls a direct current relay to be closed, so that an inverter circuit works, and a filter circuit is charged until the peak value of a three-phase filter capacitor reaches the peak value of alternating current voltage;
s2, continuously acquiring an instantaneous value of the power grid voltage under the condition that the alternating current relay is kept disconnected, and acquiring phase angle information of the power grid voltage;
s3, when one-phase voltage of the power grid crosses zero, the CPU stops the inverter circuit firstly, and closes the alternating current relay when the one-phase voltage of the power grid crosses zero for one time;
s4, after the CPU confirms that the alternating current relay is closed, the inverter circuit is started again to operate along with the network;
and S5, the inverter circuit performs charge and discharge control according to the instruction setting of the CPU.
2. The three-phase grid-connected connection method of the energy storage system with the filter capacitor as claimed in claim 1, wherein: in the step S1, when the bus voltage before the dc relay is lower than the voltage value of the ac voltage rectified by the inverter circuit, the CPU starts the DCDC boost circuit first to increase the voltage value of the bus voltage to a maximum voltage value not lower than the ac voltage.
3. The three-phase grid-connected connection method of the energy storage system with the filter capacitor as claimed in claim 1, wherein: and S3, a time delta t compensation phase difference caused by the starting delay of the alternating current relay is counted, and the alternating current relay is opened before the time delta t of the phase angle when the power grid voltage reaches the maximum voltage value.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210742171.6A CN115224724A (en) | 2022-06-27 | 2022-06-27 | Three-phase grid-connected connection method of energy storage system with filter capacitor |
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| CN202210742171.6A CN115224724A (en) | 2022-06-27 | 2022-06-27 | Three-phase grid-connected connection method of energy storage system with filter capacitor |
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| CN202210742171.6A Pending CN115224724A (en) | 2022-06-27 | 2022-06-27 | Three-phase grid-connected connection method of energy storage system with filter capacitor |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115764961A (en) * | 2023-01-10 | 2023-03-07 | 江苏中天科技股份有限公司 | Energy storage system and neutral point potential balance control method and device |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115764961A (en) * | 2023-01-10 | 2023-03-07 | 江苏中天科技股份有限公司 | Energy storage system and neutral point potential balance control method and device |
| CN115764961B (en) * | 2023-01-10 | 2023-05-05 | 江苏中天科技股份有限公司 | Energy storage system and midpoint potential balance control method and device |
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