CN113162207A - Super capacitor pre-charging circuit of grid-connected and off-grid energy storage system and control method - Google Patents
Super capacitor pre-charging circuit of grid-connected and off-grid energy storage system and control method Download PDFInfo
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- CN113162207A CN113162207A CN202110522386.2A CN202110522386A CN113162207A CN 113162207 A CN113162207 A CN 113162207A CN 202110522386 A CN202110522386 A CN 202110522386A CN 113162207 A CN113162207 A CN 113162207A
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
- H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
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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
- 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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A30/00—Adapting or protecting infrastructure or their operation
- Y02A30/60—Planning or developing urban green infrastructure
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention discloses a super capacitor pre-charging circuit of a grid-connected and off-grid energy storage system and a control method, wherein the circuit comprises a fast grid-connected and off-grid switching circuit, a three-phase alternating current circuit breaker, a two-phase LCL alternating current filter circuit, a single-phase full-bridge uncontrolled rectifying circuit, a direct current circuit breaker, a direct current capacitor filter circuit, a direct current pre-charging circuit and a super capacitor bank; the control method comprises the following steps: a super capacitor pre-charging circuit is constructed based on a common grid-connected and off-grid energy storage system, then the original voltage sampling circuit, current sampling circuit, rectifier circuit, thyristor driving circuit and system controller of the system are fully utilized, and the peak-limiting current pre-charging of the super capacitor is realized based on the proposed current-limiting peak value control algorithm. According to the invention, through circuit reconstruction of the original grid-connected and off-grid energy storage system, the circuit structure of the original system is not changed at all, and any component is not added.
Description
Technical Field
The invention relates to a super capacitor pre-charging circuit of a grid-connected and off-grid energy storage system and a control method, and belongs to the field of power electronic technology application.
Background
With the large-scale development of wind power generation and photovoltaic power generation, more and more distributed power systems based on renewable energy sources are gradually connected to an active power distribution network. Because the renewable energy source has strong random fluctuation, the energy storage system, especially the electric energy storage system, is gradually connected into the active power distribution network in a large scale due to flexible control and convenient use so as to stabilize the random fluctuation of the renewable energy source. The electric energy storage system may be generally classified into an energy type energy storage system for storing energy in a large capacity and a power type energy storage system having a fast response characteristic. Generally, a single type of energy storage system has limited applicability and cannot be efficiently used. The hybrid energy storage system can fully utilize the complementarity of different types of energy storage systems in technical characteristics, and can meet the requirements of different loads and the suppression of different energy fluctuations. Based on the method, besides the common lithium battery energy storage system, the power type super capacitor energy storage system and the density type all-vanadium redox flow battery energy storage system are more involved in power regulation of the active power distribution network, operation optimization of the active power distribution network is achieved, and construction of a smart power grid is assisted.
The grid-connected and off-grid energy storage system based on the super capacitor and the grid-connected and off-grid energy storage system based on the vanadium flow battery have the problem that the initial voltage is zero, so that 0V is needed for starting charging and pre-charging. At present, the technical scheme of charging and pre-charging 0V such as a super capacitor in a power electronic system mainly has two realization forms, the first one uses a switching power supply charger to perform constant-current pre-charging on the super capacitor, and the second one is to charge the super capacitor by limiting the current 0V through a resistor after the voltage of a power grid is rectified.
The two solutions described above have the following disadvantages:
1. the super capacitor pre-charging scheme additionally provided with the charger increases the complexity of the system and is low in reliability. In order to perform fast pre-charging in a large-capacity power electronic system, the charger needs to meet not only the charging requirement of a high voltage class, but also the requirement of high-power fast pre-charging. Most of the high-voltage high-power chargers are special chargers, and the high-voltage high-power chargers are few in selection in the market, high in cost and large in size.
2. According to the current-limiting charging scheme based on the pre-charging resistor, in order to achieve rapid pre-charging, a high-power resistor and a corresponding control switch are additionally configured in the system, and although the scheme is simple, the power loss of the system and the heat dissipation design pressure of the system are increased.
Disclosure of Invention
The invention aims to solve the technical problems of how to construct a super capacitor pre-charging circuit by using the existing grid-connected and off-grid energy storage system on the basis of not changing the system structure, and realize the pre-charging of the super capacitor in the grid-connected and off-grid energy storage system by using the original control system, thereby solving the problems of the common super capacitor pre-charging scheme.
In order to solve the technical problem, the technical scheme of the invention is to provide a super capacitor pre-charging circuit of a grid-connected and off-grid energy storage system, which is characterized in that: the system comprises a fast grid-connected and off-grid switching circuit, a pre-charging reconstruction circuit based on a three-phase energy storage converter system and a super capacitor bank;
the fast grid-connected and off-grid switching circuit is composed of a three-phase bidirectional thyristor circuit and comprises a thyristor and a thyristor driving circuit;
the three-phase energy storage converter system mainly comprises: the three-phase alternating current circuit breaker, the direct current circuit breaker, the three-phase LCL alternating current filter circuit, the direct current capacitor filter circuit, the direct current pre-charging circuit and the three-phase full bridge circuit;
the pre-charging reconstruction circuit based on the three-phase energy storage converter system mainly comprises: the system comprises a three-phase alternating current circuit breaker, a direct current circuit breaker, a two-phase LCL alternating current filter circuit, a direct current capacitor filter circuit, a direct current pre-charging circuit and a single-phase full-bridge uncontrolled rectifying circuit;
the super capacitor bank is formed by connecting a plurality of super capacitor modules in series and in parallel, and the super capacitor module is formed by connecting a plurality of super capacitor monomers in series and in parallel.
Furthermore, one end of the fast grid-connection and grid-disconnection switch is connected with a three-phase power grid, and the other end of the fast grid-connection and grid-disconnection switch is connected with an alternating current breaker of a three-phase energy storage converter system;
one end of the three-phase alternating current circuit breaker is connected with the fast grid-connected and off-grid switch, and the other end of the three-phase alternating current circuit breaker is connected with the three-phase LCL alternating current filter circuit;
one end of the three-phase LCL alternating current filter circuit is connected with a three-phase alternating current circuit breaker, and the other end of the three-phase LCL alternating current filter circuit is connected with the middle point of a bridge arm of a three-phase full-bridge circuit;
the middle points of three bridge arms of the three-phase full-bridge circuit are respectively connected with one end of a three-phase LCL alternating current filter circuit;
one end of the direct current filter capacitor is hung at the common anode end of the three-phase full-bridge circuit, and the other end of the direct current filter capacitor is hung at the common cathode end of the three-phase full-bridge circuit;
the capacitance midpoint of the three-phase LCL alternating current filter circuit is connected with the midpoint of the direct current capacitance filter circuit;
the direct current breaker is connected in series between the direct current side of the three-phase energy storage converter and the super capacitor bank;
the DC pre-charge circuit includes: the DC pre-charging circuit is connected in parallel with two ends of the DC breaker.
Further, the technical scheme of the invention provides a super capacitor pre-charging control method based on a common grid-connected and off-grid energy storage system, which is characterized by comprising the following steps:
firstly, closing a direct current pre-charging control switch, and pre-charging the direct current filter capacitor by the super capacitor group through a current-limiting resistor;
sampling the voltage of the super capacitor and the voltage of the direct current filter capacitor, judging whether the pre-charging of the direct current filter capacitor is finished or not, closing the alternating current circuit breaker and the direct current circuit breaker after the pre-charging of the direct current filter capacitor is finished, and disconnecting a control switch of a direct current pre-charging circuit;
starting a constant peak current pre-charging control mode;
automatically entering a variable peak current pre-charging control mode;
judging that the pre-charging work of the super capacitor is finished, and entering a standby mode;
preferably, the specific control method of the constant peak current pre-charge control mode is as follows:
1. detecting the line voltage vab (t) in real time with the sampling frequency fs, and acquiring a corresponding phase angle according to the line voltage vab (t);
2. detecting a super capacitor voltage Vsc (t), a network side inductance current value and a machine side inductance current value IL (t) in real time by using a sampling frequency fs, and storing difference values delta V (t) ═ Vab (t) of the line voltage Vab (t) and the super capacitor voltage Vsc (t) in a phase angle 0-interval in real time, wherein the stored voltage difference data are respectively delta V (0), delta V (1) and delta V (2) · delta V (n), and synchronously storing the machine detection inductance current data IL (0), IL (1) and IL (2) · IL (n);
3. after the data acquisition is completed, filtering and screening the data of the group of data of Δ V (0), Δ V (1) and Δ V (2) · · Δ V (n), screening out data after the second zero crossing, and storing other data as Δ V (0), Δ V (1), Δ V (2) · · Δ V (k) · · Δ V (m), wherein Δ V (0), Δ V (1), Δ V (2) · · Δ V (k-1) are data before the first zero crossing, k is interpolation value when the first zero crossing is crossed, and m is interpolation value when the second zero crossing is crossed;
4. selecting 5 machine side inductance current values IL (m-2), IL (m-1), IL (m +1) and ILs (m +2) before and after the second zero crossing point in the step 3, and then obtaining the maximum machine side inductance current value ILmax by using a bubbling comparison method;
5. after the data screening is finished, performing reverse-order integral calculation according to a formula (1), and obtaining a thyristor trigger angle correlation quantity x according to a set machine side inductance current peak value ILref and combining the formulas (1) and (2), wherein delta IL is an overcurrent adjustment factor, and L is a machine side inductance value;
6. obtaining a trigger angle alpha of a thyristor and a thyristor of b two phases according to a formula alpha being 100 x/fs;
7. the triggering driving of the a-phase thyristor and the b-phase thyristor is completed at the alpha phase angle of the next power frequency period of the line voltage Vab (t);
8. the work in 3, 4, 5, 6, and 7 is then performed periodically.
Preferably, the specific control method of the step four-step peak current pre-charge control mode is as follows: when in use
When the constant is true, the firing angle α of the a, b two-phase thyristor is 100 k/fs.
Preferably, the step five specifically includes: when alpha is 100k/fs ≈/2, namely k ≈ fs/200 is satisfied, judging that the pre-charging work of the super capacitor is completed, disconnecting the alternating current circuit breaker and the direct current circuit breaker, blocking a driving signal of the fast off-grid switch, and entering a standby mode.
Compared with the prior art, the invention has the beneficial effects that:
the invention discloses a super capacitor pre-charging control method of a grid-connected and off-grid energy storage system, which is characterized in that a pre-charging loop is firstly reconstructed on the basis of a common grid-connected and off-grid energy storage system, the pre-charging loop does not make any change on the circuit structure of the complete grid-connected and off-grid energy storage system, the temporary wave control of power frequency voltage is realized by fully utilizing a fast grid-connected and off-grid switch in the original system, the high-frequency filtering and current limiting of charging current are realized by utilizing an LCL alternating current filter in the system, the rectification is realized by utilizing an anti-parallel diode in a three-phase full-bridge circuit, and the current limiting control is realized by utilizing a voltage sampling circuit, a current sampling circuit, a thyristor driving circuit and a system controller of the original system.
According to the super capacitor pre-charging reconstruction circuit and the control method, the super capacitor pre-charging control of the grid-connected and off-grid energy storage system is realized on the basis of not adding any additional component, the pre-charging efficiency of the super capacitor is improved, the system structure is simplified, the system cost is reduced, and the reliability of the system is improved.
Drawings
Fig. 1 is a schematic circuit diagram of a conventional grid-connected and off-grid energy storage system;
FIG. 2 is a schematic diagram of a pre-charge control reconstruction circuit for a super capacitor of a grid-connected and off-grid energy storage system according to the present invention;
fig. 3 is a flow chart of a method for controlling pre-charging of a super capacitor of a grid-connected and off-grid energy storage system according to the present invention;
fig. 4 is a flowchart of an implementation method of a supercapacitor precharge constant peak current control algorithm of a grid-connected and off-grid energy storage system according to the present invention.
Detailed Description
In order to make the invention more comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.
The embodiment firstly provides a super capacitor pre-charging control reconstruction circuit of a grid-connected and off-grid energy storage system.
Fig. 1 is a schematic diagram illustrating a conventional circuit principle of a grid-connected and off-grid energy storage system, and fig. 2 is a schematic diagram illustrating a super capacitor pre-charge control reconfiguration circuit of a grid-connected and off-grid energy storage system according to the present invention, which is provided in fig. 1, and mainly includes: the system comprises a fast grid-connected and off-grid switch circuit, a three-phase alternating current circuit breaker, a two-phase LCL alternating current filter circuit, a single-phase full-bridge uncontrolled rectifier circuit, a direct current circuit breaker, a direct current capacitor filter circuit, a direct current pre-charging circuit and a super capacitor bank.
Compared with the circuit in fig. 1, the reconstructed super capacitor pre-charge control circuit in fig. 2 has the following characteristics: 1. the three-phase fast grid-connected and off-grid switch circuit only uses A, B two phases, the three-phase LCL alternating current filter circuit only uses A, B two phases, and the three-phase full bridge circuit only uses A, B two phases as uncontrolled rectification 2. the voltages of the A, B phase thyristor chopper lines in the fast grid-connected and off-grid switch are controlled in order, so that the pre-charging current of the super capacitor is controlled, and the grid side current amplitude during the switch action is effectively inhibited.
As shown in fig. 2, one end of the fast grid-connected and off-grid switch Sa is connected to the a-phase power grid, and the other end is connected to the a-phase input terminal of the ac circuit breaker DZ 1; one end of the fast grid-connected and off-grid switch Sb is connected with a b-phase power grid, and the other end of the fast grid-connected and off-grid switch Sb is connected with a b-phase input terminal of an alternating current breaker DZ 1; one end of the inductor L1a is connected with the a-phase output terminal of the alternating current breaker DZ1, and the other end is connected with the inductor L2 a; one end of the inductor L1b is connected with a b-phase output terminal of the alternating current breaker DZ1, and the other end is connected with an inductor L2 b; the other end of the inductor L2a is connected to the midpoint of a first bridge arm in the single-phase full-bridge uncontrolled rectifying circuit; the other end of the inductor L2b is connected to the midpoint of a second bridge arm in the single-phase full-bridge uncontrolled rectifying circuit; after the ac filter capacitors Ca and Cb are connected in series, one end is connected to a connection point of L1a and L2a, and the other end is connected to a connection point of L1b and L2 b.
The single-phase full-bridge uncontrolled rectifying circuit comprises the following components: the anode of the anti-parallel diode D1 is connected with the cathode of the anti-parallel diode D2 to form a first bridge arm midpoint, the anode of the anti-parallel diode D3 is connected with the cathode of the anti-parallel diode D4 to form a second bridge arm midpoint, the cathode of the diode D1 and the cathode of the diode D3 are connected in parallel to form the positive end of a direct current bus, and the anode of the diode D2 and the anode of the diode D4 are connected in parallel to form the negative end of the direct current bus.
The direct current capacitor filter circuit is formed by serially connecting capacitors C1 and C2, the anode of the serially connected filter capacitor is connected to the positive end of a direct current bus, the cathode of the serially connected filter capacitor is connected to the negative end of the direct current bus, and the serially connected midpoint of the direct current filter capacitors C1 and C2 is connected with the midpoint of the alternating current filter capacitors Ca and Cb.
The input terminal of the direct current breaker DZ2 is respectively connected with the positive terminal and the negative terminal of a direct current bus, and the output terminal of the direct current breaker DZ2 is respectively connected with the anode and the cathode of a super capacitor bank;
the direct-current pre-charging circuit is composed of direct-current pre-charging resistors R1 and R2 and a direct-current relay Q1, the resistor R1 is connected with a first normally open contact of the direct-current relay Q1 in series and then is connected to the positive end of a direct-current bus and the anode of a super capacitor bank in a hanging mode, and the resistor R2 is connected with a second normally open contact of the direct-current relay Q1 in series and then is connected to the negative end of the direct-current bus and the cathode of the super capacitor bank in a hanging mode.
The embodiment of the invention provides a super capacitor pre-charging control method of a grid-connected and off-grid energy storage system, which comprises the following steps of:
step S01: after the control system issues a direct current pre-charging command, the direct current pre-charging control switch Q1 is closed, and the pre-charging of the super capacitor bank to the direct current filter capacitor is realized through the current limiting resistors R1 and R1; and (3) controlling to close the alternating current circuit breaker DZ1 and the direct current circuit breaker DZ2 and to open the direct current pre-charging circuit control switch when the difference (Vdc-Vsc) between the direct current filter capacitor voltage Vdc and the super capacitor group voltage Vsc is less than 5V, and then entering the step two.
Step S02: starting a constant peak current pre-charging control mode, preferably, the specific control method of the constant peak current pre-charging control mode is as follows:
1. detecting the line voltage vab (t) in real time with the sampling frequency fs, and acquiring a corresponding phase angle according to the line voltage vab (t);
2. detecting a super capacitor voltage Vsc (t), a network side inductance current value and a machine side inductance current value IL (t) in real time by using a sampling frequency fs, and storing difference values delta V (t) ═ Vab (t) of the line voltage Vab (t) and the super capacitor voltage Vsc (t) in a phase angle 0-interval in real time, wherein the stored voltage difference data are respectively delta V (0), delta V (1) and delta V (2) · delta V (n), and synchronously storing the machine detection inductance current data IL (0), IL (1) and IL (2) · IL (n);
3. after the data acquisition is completed, filtering and screening the data of the group of data of Δ V (0), Δ V (1) and Δ V (2) · · Δ V (n), screening out data after the second zero crossing, and storing other data as Δ V (0), Δ V (1), Δ V (2) · · Δ V (k) · · Δ V (m), wherein Δ V (0), Δ V (1), Δ V (2) · · Δ V (k-1) are data before the first zero crossing, k is interpolation value when the first zero crossing is crossed, and m is interpolation value when the second zero crossing is crossed;
4. selecting 5 machine side inductance current values IL (m-2), IL (m-1), IL (m +1) and ILs (m +2) before and after the second zero crossing point in the step 3, and then obtaining the maximum machine side inductance current value ILmax by using a bubbling comparison method;
5. after the data screening is finished, performing reverse-order integral calculation according to a formula (1), and obtaining a thyristor trigger angle correlation quantity x according to a set machine side inductance current peak value ILref and combining the formulas (1) and (2), wherein delta IL is an overcurrent adjustment factor, and L is a machine side inductance value;
6. obtaining a trigger angle alpha of a thyristor and a thyristor of b two phases according to a formula alpha being 100 x/fs;
7. the triggering driving of the a-phase thyristor and the b-phase thyristor is completed at the alpha phase angle of the next power frequency period of the line voltage Vab (t);
8. the work in 3, 4, 5, 6, and 7 is then performed periodically.
The method for acquiring the thyristor trigger angle correlation quantity x in the 7-phase converter is detailed in that when ILmax is less than or equal to ILref, the pre-charging current peak value is smaller than the set machine side inductance current peak value ILref, and the counter-sequence integration is based
And is
Obtaining a thyristor firing angle correlation quantity x; when ILmax>ILref, indicating that the peak value of the pre-charge current is greater than the set peak value ILref of the machine side inductor current, at this time, a positive over-current adjustment factor Δ IL needs to be added, and then the correlation quantity of the trigger angle of the thyristor is obtained by integration and comparison so as to reduce the peak value of the pre-charge current.
Step S03: entering a variable peak current pre-charging control mode, preferably, the specific control method of the variable peak current pre-charging control mode is as follows: when in use
When the constant is true, the firing angle α of the a, b two-phase thyristor is 100 k/fs.
Step S04: and judging that the pre-charging work of the super capacitor is finished, entering a standby mode, preferably when alpha is equal to 100k/fs and is equal to 2, namely k is equal to fs/200, the charging current of the super capacitor is close to zero, judging that the pre-charging work of the super capacitor is finished, then disconnecting the alternating current circuit breaker and the direct current circuit breaker, and blocking a driving signal of the fast off-grid switch.
The present invention is not limited to the above-described embodiments, and those skilled in the art can implement various embodiments in accordance with the present disclosure. It should be understood that the above-described embodiments are illustrative only and are not limiting upon the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereto that may occur to those skilled in the art upon reading the present disclosure.
Claims (6)
1. A super capacitor pre-charging circuit of a grid-connected and off-grid energy storage system is characterized by comprising a fast grid-connected and off-grid switch circuit, a three-phase alternating current circuit breaker, a two-phase LCL alternating current filter circuit, a single-phase full-bridge uncontrolled rectifying circuit, a direct current circuit breaker, a direct current capacitor filter circuit, a direct current pre-charging circuit and a super capacitor bank;
one end of the fast grid-connected and off-grid switch is connected with a three-phase power grid, and the other end of the fast grid-connected and off-grid switch is connected with a three-phase alternating current breaker;
one end of the three-phase alternating current circuit breaker is connected with the fast grid-connected and off-grid switch, and the other end of the three-phase alternating current circuit breaker is connected with the two-phase LCL alternating current filter circuit;
one end of the two-phase LCL alternating current filter circuit is connected with a three-phase alternating current circuit breaker, and the other end of the two-phase LCL alternating current filter circuit is connected with the middle point of a bridge arm of the single-phase full-bridge uncontrolled rectifying circuit;
one end of the direct current capacitor filter circuit is hung at the common anode end of the single-phase full-bridge uncontrolled rectifying circuit, and the other end of the direct current capacitor filter circuit is hung at the common cathode end of the single-phase full-bridge uncontrolled rectifying circuit;
the capacitance midpoint of the two-phase LCL alternating current filter circuit is connected with the midpoint of the direct current capacitance filter circuit;
the direct current breaker is connected in series between the direct current side of the single-phase full-bridge uncontrolled rectifying circuit and the super capacitor bank;
the DC pre-charge circuit includes: the DC pre-charging circuit is connected in parallel with two ends of the DC breaker.
The super capacitor bank is formed by connecting a plurality of super capacitor modules in series and in parallel, and the super capacitor module is formed by connecting a plurality of super capacitor monomers in series and in parallel.
2. A super capacitor pre-charging control method of a grid-connected and off-grid energy storage system is characterized by being applied to the pre-charging circuit of claim 1 to perform the following steps:
step S01: the supercapacitor group precharges the direct current filter capacitor;
step S02: starting a constant peak current pre-charging control mode;
step S03: entering a variable peak current pre-charging control mode;
step S04: and after the pre-charging is finished, entering a standby mode.
3. The method for controlling pre-charging of super capacitor in grid-connected and off-grid energy storage system as claimed in claim 2, wherein said step S01 is to control a dc pre-charging switch to pre-charge the dc filter capacitor with the super capacitor group through a current limiting resistor.
4. The method for controlling the pre-charging of the super capacitor of the grid-connected and off-grid energy storage system according to claim 3, wherein the step S02 is specifically the following step:
a) detecting the line voltage vab (t) in real time with the sampling frequency fs, and acquiring a corresponding phase angle according to the line voltage vab (t);
b) detecting a super capacitor voltage Vsc (t), a network side inductance current value and a machine side inductance current value IL (t) in real time by using a sampling frequency fs, and storing difference values delta V (t) ═ Vab (t) of the line voltage Vab (t) and the super capacitor voltage Vsc (t) in a phase angle 0-interval in real time, wherein the stored voltage difference data are respectively delta V (0), delta V (1) and delta V (2) · delta V (n), and synchronously storing the machine detection inductance current data IL (0), IL (1) and IL (2) · IL (n);
c) after the data acquisition is completed, filtering and screening the data of the group of data of Δ V (0), Δ V (1) and Δ V (2) · · Δ V (n), screening out data after the second zero crossing, and storing other data as Δ V (0), Δ V (1), Δ V (2) · · Δ V (k) · · Δ V (m), wherein Δ V (0), Δ V (1), Δ V (2) · · Δ V (k-1) are data before the first zero crossing, k is interpolation value when the first zero crossing is crossed, and m is interpolation value when the second zero crossing is crossed;
d) selecting 5 machine side inductance current values IL (m-2), IL (m-1), IL (m +1) and ILs (m +2) before and after the second zero crossing point in the step 3, and then obtaining the maximum machine side inductance current value ILmax by using a bubbling comparison method;
e) after the data screening is finished, performing reverse-order integral calculation according to a formula (1), and obtaining a thyristor trigger angle correlation quantity x according to a set machine side inductance current peak value ILref and combining the formulas (1) and (2), wherein delta IL is an overcurrent adjustment factor, and L is a machine side inductance value;
f) obtaining a trigger angle alpha of a thyristor and a thyristor of b two phases according to a formula alpha being 100 x/fs;
g) the triggering driving of the a-phase thyristor and the b-phase thyristor is completed at the alpha phase angle of the next power frequency period of the line voltage Vab (t);
h) the work in c, d, e, f, and g is then performed periodically.
5. The method for controlling the pre-charging of the super capacitor of the grid-connected and off-grid energy storage system as claimed in claim 4, wherein the specific control method in the step S03 is as follows: when in use
When the constant is true, the firing angle α of the a, b two-phase thyristor is 100 k/fs.
6. The method for controlling the pre-charging of the super-capacitor of the grid-connected and off-grid energy storage system according to claim 5, wherein the step S04 is specifically that when α ═ 100k/fs ≈/2, that is, k ≈ fs/200 is established, the charging current of the super-capacitor is close to zero, it is determined that the pre-charging operation of the super-capacitor is completed, and then the ac circuit breaker and the dc circuit breaker are opened, and the driving signal of the fast grid-connected and off-grid switch is blocked.
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