CN114094624A - Low-voltage ride through coordination control method for wave power generation system - Google Patents
Low-voltage ride through coordination control method for wave power generation system Download PDFInfo
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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
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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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
- H02J3/46—Controlling of the sharing of output between the 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
- 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
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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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
Abstract
The invention relates to a coordination control method for low voltage ride through of a wave power generation system, which coordinates and controls a network side controller, a machine side controller and a super capacitor energy storage device according to the power of each link during a fault period, and comprises the following steps: the network side controller adopts voltage outer loop current inner loop control based on the voltage orientation of the power grid; when a low-voltage fault occurs in a power grid, the machine side controller works in a rotor energy storage mode, and a rotor rotating speed reference value is obtained by a direct-current bus voltage outer ring; when the machine side controller works in a rotor limit rotating speed mode, a rotor rotating speed reference value is given as a rotating speed limit value; the super-capacitor energy storage device is controlled by a power outer ring current inner ring, the power outer ring is used for maintaining power balance at two ends of a direct current bus, and the current inner ring is used for realizing rapid tracking control; the machine side controller, the network side controller and the super capacitor energy storage device have different running states under different conditions.
Description
Technical Field
The invention relates to the technical field of wave power generation grid-connected system control, in particular to a low-voltage fault ride-through coordination control system of a float type permanent magnet synchronous wave power generation grid-connected system.
Background
Wave energy is a clean renewable energy source, and with the continuous development and maturity of wave power generation technology and the rapid large-scale and commercial development, the permeability of a wave power generation system is continuously improved, and the reliability and the stability of a grid-connected system are reduced. The drop of the power grid voltage is a common problem, and the drop of the power grid voltage brings a series of transient processes to the wave power generation system, endangers the normal operation of the system, and can cause the aggravation of faults and even the disconnection of the system when the system is serious. Therefore, when a power grid fault occurs, as a loop of a new energy grid-connected power generation system, the low voltage ride through capability of the wave energy power generation system is a necessary condition for uninterrupted grid-connected operation.
According to the grid-connected operation standard of wind power generation in China, when a low-voltage fault of a power grid occurs, a grid-connected system is required to send certain reactive power to the power grid to help the voltage of the power grid to recover. Normally, the grid-side inverter is controlled to operate in a reactive compensation state, and under the condition of meeting the requirement of generating reactive power, as much active power as possible is generated. For more severe faults, however, relying on a single grid-side reactive compensation control is not sufficient to consume unbalanced power on the dc side. Therefore, when a more severe fault occurs, in order to reduce the input active power, the power input by the wave energy capturing device is usually temporarily stored in the rotor of the electric machine, so that the power balance between the two ends of the direct current side is realized. Due to the rotation speed limit of the motor rotor, for more serious low-voltage faults, redundant unbalanced power on the direct current side can be consumed in a mode of externally connecting an unloading resistor, but redundant energy is consumed in a form of heat energy. Therefore, replacing the unloading resistor with the super capacitor is more beneficial to energy utilization.
Disclosure of Invention
The invention aims to provide a low-voltage ride-through coordination control strategy for a wave power generation system. According to the invention, low-voltage faults with different severity degrees can be passed through by coordinating the controller on the controller side, the controller of the super-capacitor energy storage device and the grid-side inverter under the condition of meeting the reactive compensation requirement of new energy grid-connected operation. Compared with the traditional low-voltage ride-through method based on an external hardware circuit, the method can fully utilize the unbalanced power during the fault period, reduce the switching times of the super capacitor and prolong the service life of the super capacitor energy storage device. The technical scheme is as follows:
a low voltage ride through coordination control method for a wave power generation system coordinates and controls a network side controller, a machine side controller and a super capacitor energy storage device according to the power of each link during a fault period, and comprises the following steps:
(1) the grid side controller is based on grid voltage orientation, adopts voltage outer loop current inner loop control, and under the normal operation condition of the power grid, the grid side controller operates under the unit power factor mode, and q axle current reference value is 0, and d axle current reference value is given through the voltage outer loop to maintain the stability of direct current bus voltage, and when the power grid has low voltage fault, in order to satisfy the requirement of output reactive power, q axle current reference value is calculated by the following formula:
igqref2≥1.5(0.9-eg[p.u.])IN
wherein eg[p.u.]Is the per unit value of the fault voltage at the grid-connected point, INThe rated current value is the grid side inverter.
The d-axis current reference value cannot be larger than considering the current clipping of the grid-side inverter
Wherein ImaxFor the grid-side inverter current amplitude, typically 1.5IN。
Therefore, the actual d-axis current reference is shown as follows
igdref＝min{igdref1,igdref2}
Wherein igdref1Is a d-axis current reference value obtained by a voltage outer loop.
(2) The d-axis reference value of the machine side controller is set to be 0, the q-axis current reference value is obtained by maximum wave energy capture control under the condition that a power grid normally operates, when the power grid has a low-voltage fault, the machine side controller works in a rotor energy storage mode, and the rotor rotating speed reference value is obtained by a direct-current bus voltage outer ring; when the machine-side controller operates in the rotor limit speed mode, the rotor speed reference is given as a speed limit value.
(3) The super-capacitor energy storage device is controlled by a power outer ring current inner ring, the power outer ring is used for maintaining power balance at two ends of a direct current bus, and the current inner ring is used for realizing rapid tracking control. When a low-voltage fault occurs, the bidirectional buck/boost converter works under the buck circuit, and the direct-current bus charges the super capacitor; when the fault is eliminated, the bidirectional buck/boost converter works under the boost circuit, and the super capacitor is discharged.
The super capacitor capacity should be designed to meet the most serious low-voltage fault of the power grid under the coordination control of low-voltage ride through, and when the power grid has a low-voltage fault of 0.2pu, the active power output by the grid-side inverter is represented as:
wherein igqref_scIs the q-axis current of the grid-side inverter when a 0.2pu fault occurs.
The energy absorbed by the supercapacitor energy storage device during a fault is expressed as
Esc＝0.625ΔP-Er_max＝0.625(Ps_rate-Pg_sc)-Er_max
Wherein P iss_rateIndicating the rated power of the output of the machine-side controller, Er_maxRepresenting the stored energy of the motor rotor rising from the nominal speed to the limit speed.
The super capacitor capacity is expressed as
Wherein U issc_rateAnd Usc_initThe rated voltage and the initial voltage of the super capacitor energy storage device are shown, and when the super capacitor energy storage device is charged, the voltage is from Usc_initRises to Usc_rate，wmaxIs the generator rotor limit speed value, wNIs the rated speed value of the generator rotor igqref_scD-axis current of the grid-side inverter when 0.2pu fault occurs, egIs the fault voltage at the grid-connected point.
The design of the filter inductor of the super-capacitor energy storage device needs to meet the working requirement of the bidirectional buck/boost converter, the maximum impact current in the charging and discharging process can be passed through, and the filter inductor is calculated according to the following formula
Wherein IscpRepresents the rated current amplitude, delta I, of the super capacitor working in buck modescpRepresenting the maximum allowable ripple current, fsIndicating the switching frequency, U, of the buck/boost circuitdcIs the supercapacitor side dc voltage.
(4) The low voltage ride through coordination control method comprises the following steps:
active power P input into power grid by grid-side invertergrefCalculated by the following formula
Maximum storage power P of motor rotor under corresponding low-voltage faultω_maxCalculated by the following formula
Wherein ω ismaxAs limit value of the rotational speed of the rotor of the motor, omegaNRated value, t, for the speed of the rotor of the machineFThe power generation system is allowed to access for a maximum time for a corresponding low voltage.
The control strategy is divided into four modes according to the relation of the power values of all links in the fault period, so that the machine side controller, the network side controller and the super capacitor energy storage device have different running states under different conditions:
when P is presentgref≥PsWhen the system works, a low voltage ride through coordination control strategy works in a mode 1, a time side controller works in a maximum wave energy capture mode, a network side controller works in a reactive compensation mode, and a super capacitor energy storage device does not need to participate in control; when P is presents>Pgref≥Ps-Pω_maxWhen the control strategy is in the mode 2, the opportunity side controller works in the motor rotor energy storage mode, the network side controller works in the reactive compensation mode, and the super capacitor energy storage device does not need to participate in control; when P is presents-Pω_max>PgrefDuring the operation, the low voltage ride through coordination control strategy works in a mode 3, the machine side controller works in a motor rotating speed limit value state, the network side controller works in a reactive compensation mode, the bidirectional buck/boost converter of the super-capacitor energy storage device works in a buck circuit, and the direct-current bus starts to charge the super-capacitor. When the fault detector detects that the low-voltage fault of the power grid is cleared, the low-voltage ride-through control strategy is switched to a mode 4, the controller at the time side recovers the maximum wave energy capture control strategy, the controller at the time side recovers the unit power factor operation, the bidirectional buck/boost converter of the super-capacitor energy storage device works under the boost circuit, and the super-capacitor discharges. And switching out the energy storage device until the voltage of the super capacitor recovers to the initial value, and finishing the low-voltage ride through process.
According to the low voltage ride through coordination control strategy of the wave power generation system based on the super-capacitor energy storage device, low voltage faults of different severity degrees can be ride through by the coordination control machine side controller, the super-capacitor energy storage device controller and the grid side inverter under the condition that reactive compensation required by new energy grid-connected operation is met. Compared with the traditional low-voltage ride-through method based on an external hardware circuit, the method can fully utilize the unbalanced power during the fault period, reduce the switching times of the super capacitor and prolong the service life of the super capacitor energy storage device.
The invention has the following beneficial effects:
1) the control strategy can meet the reactive compensation standard of the low-voltage fault of the distributed energy grid-connected system.
2) The control strategy can realize ride-through of the grid-connected system in low-voltage faults of different degrees.
3) The control strategy can reduce the design capacity of the super capacitor, reduce the light-on times of the super capacitor and prolong the service life.
4) The control strategy is simple in structure, easy to realize software and hardware, convenient to maintain and capable of effectively improving the reliability and commercial feasibility of the wave power generation system.
5) The control strategy can also be applied to inverter control systems of wind power generation, solar power generation and the like.
Drawings
Fig. 1 is a low voltage ride through curve.
Fig. 2 is a block diagram of a wave power grid-connected system.
Fig. 3 is a machine side controller.
Fig. 4 is a network side controller.
FIG. 5 is a supercapacitor controller.
Fig. 6 is a control logic block diagram.
Detailed Description
The present invention will be further explained with reference to the detailed description of the drawings so that those skilled in the art can more fully understand the present invention and can practice it, and the examples given are only for the purpose of illustration and are not intended to limit the scope of the present invention.
Referring to the wind power generation grid-connected operation standard in China, as shown in figure 1, a power generation system is required to be in a grid-connected state without being disconnected in an area above a grid voltage drop curve, and the power generation system is allowed to be switched out in an area below the curve. Meanwhile, during the low-voltage fault of the power grid, the power generation system is required to be capable of outputting corresponding reactive power to the power grid to help the voltage of the power grid to recover.
The wave power generation grid-connected system comprises a float type wave energy capturing device, a permanent magnet synchronous generator, a machine side rectifier, a direct current side filter capacitor, a super capacitor energy storage device, a grid side inverter, a filter reactor, a transformer and a corresponding controller, wherein the controller is controlled by the proposed low voltage ride through coordination control strategy.
The network side control block diagram is shown in fig. 3, the network side controller adopts voltage outer loop current inner loop control based on network voltage orientation, under the condition of normal operation of a power network, the network side controller operates in a unit power factor mode, a q-axis current reference value is 0, and a d-axis current reference value is given through a voltage outer loop so as to maintain the stability of the direct-current bus voltage. When the power grid has a low-voltage fault, in order to meet the requirement of outputting reactive power, the q-axis current reference value is calculated by the following formula:
igqref2≥1.5(0.9-eg[p.u.])IN
wherein eg[p.u.]Is the per unit value of the fault voltage at the grid-connected point, INThe rated current value is the grid side inverter.
The d-axis current reference value cannot be larger than considering the current clipping of the grid-side inverter
Wherein ImaxFor the grid-side inverter current amplitude, typically 1.5IN。
Thus, the actual d-axis current reference is shown as follows:
igdref＝min{igdref1,igdref2}
wherein igdref1For d-axis current reference values obtained by voltage outer-loop
The machine side controller as shown in fig. 4, the d-axis reference value of the machine side converter is set to 0, and the q-axis current reference value is given by the coordinated control strategy. Under the condition of normal operation of the power grid, the q-axis current reference value is obtained by maximum wave energy capture control. When a low-voltage fault occurs in a power grid, the machine side controller works in a rotor energy storage mode, and a rotor rotating speed reference value is obtained by a direct-current bus voltage outer ring; when the machine-side controller operates in the rotor limit speed mode, the rotor speed reference is given as a speed limit value.
The super capacitor energy storage device controller adopts power outer loop current inner loop control as shown in fig. 5. The power outer ring is used for maintaining power balance at two ends of the direct current bus, and the current inner ring is used for realizing rapid tracking control. When a serious low-voltage fault occurs, the bidirectional buck/boost converter works under the buck circuit, and the direct-current bus charges the super capacitor; when the fault is eliminated, the bidirectional buck/boost converter works under the boost circuit, and the super capacitor is discharged.
Specifically, the super capacitor capacity should be designed to meet the most serious low-voltage fault of the power grid under the coordination control of low-voltage ride-through, and when the power grid has a low-voltage fault of 0.2pu, the active power output by the grid-side inverter can be represented as
Wherein igqref_scIs the q-axis current of the grid-side inverter when a 0.2pu fault occurs.
During a fault, the energy absorbed by the supercapacitor energy storage device may be expressed as:
Esc＝0.625ΔP-Er_max＝0.625(Ps_rate-Pg_sc)-Er_max
wherein P iss_rateIndicating the rated power of the output of the machine-side controller, Er_maxRepresenting the stored energy of the motor rotor rising from the nominal speed to the limit speed.
The super capacitor capacity can be expressed as
Wherein U issc_rateAnd Usc_initThe rated voltage and the initial voltage of the super capacitor energy storage device are shown, and when the super capacitor energy storage device is charged, the voltage is from Usc_initRises to Usc_rate。
The design of the filter inductor of the super-capacitor energy storage device needs to meet the working requirement of the bidirectional buck/boost converter, and the filter inductor can pass through the maximum impact current in the charging and discharging processes, so that the filter inductor can be calculated by the following formula
Wherein IscpRepresents the rated current amplitude, delta I, of the super capacitor working in buck modescpRepresenting the maximum allowable ripple current, fsRepresenting the switching frequency of the buck/boost circuit.
The control block diagram of the low voltage ride through coordination control strategy is shown in fig. 6, and the specific control steps are explained as follows
Step one, detecting the voltage and current amplitude of a grid-connected point through a fault detector, and judging whether a low-voltage fault occurs in a power grid.
And step two, if the power grid normally operates, the wave power generation system machine side controller operates in a maximum wave energy capturing state, and the grid side controller operates in a unit power factor state.
Step three, when detecting that the power grid has low voltage fault, calculating and comparing active power P generated by the permanent magnet synchronous generator when the fault occurssActive power P input to the grid by the grid-side invertergrefAnd the maximum stored power P of the motor rotor under corresponding low-voltage faultω_max。
Wherein P isgrefCan be calculated by the following formula:
Pω_maxcan be calculated by the following formula
Wherein ω ismaxAs limit value of the rotational speed of the rotor of the motor, omegaNRated value, t, for the speed of the rotor of the machineFThe power generation system is allowed to access for a maximum time for a corresponding low voltage.
When P is presentgref≥PsWhen the system works, a low voltage ride through coordination control strategy works in a mode 1, a time side controller works in a maximum wave energy capture mode, a network side controller works in a reactive compensation mode, and a super capacitor energy storage device does not need to participate in control; when P is presents>Pgref≥Ps-Pω_maxWhen the control strategy is in the mode 2, the opportunity side controller works in the motor rotor energy storage mode, the network side controller works in the reactive compensation mode, and the super capacitor energy storage device does not need to participate in control; when P is presents-Pω_max>PgrefDuring the operation, the low voltage ride through coordination control strategy works in a mode 3, the machine side controller works in a motor rotating speed limit value state, the network side controller works in a reactive compensation mode, the bidirectional buck/boost converter of the super-capacitor energy storage device works in a buck circuit, and the direct-current bus starts to charge the super-capacitor.
And step four, when the fault detector detects that the low-voltage fault of the power grid is cleared, the low-voltage ride-through control strategy is switched to a mode 4, the controller at the time side recovers the maximum wave energy capture control strategy, the controller at the network side recovers the unit power factor operation, the bidirectional buck/boost converter of the super-capacitor energy storage device works under the boost circuit, and the super-capacitor discharges. And switching out the energy storage device until the voltage of the super capacitor recovers to the initial value, and finishing the low-voltage ride through process.
In a word, the control strategy is divided into four modes according to the relation of the power values of all links in the fault period, so that the machine side controller, the network side controller and the super capacitor energy storage device have different running states under different conditions:
the specific explanation for the above table is: when P is presentgref≥PsIn the time, the low voltage ride through coordination control strategy works in a mode 1, the time side controller works in a maximum wave energy capture mode, and the network side controller works in a non-zero stateUnder the power compensation mode, the super-capacitor energy storage device does not need to participate in control; when P is presents>Pgref≥Ps-Pω_maxWhen the control strategy is in the mode 2, the opportunity side controller works in the motor rotor energy storage mode, the network side controller works in the reactive compensation mode, and the super capacitor energy storage device does not need to participate in control; when P is presents-Pω_max>PgrefDuring the operation, the low voltage ride through coordination control strategy works in a mode 3, the machine side controller works in a motor rotating speed limit value state, the network side controller works in a reactive compensation mode, the bidirectional buck/boost converter of the super-capacitor energy storage device works in a buck circuit, and the direct-current bus starts to charge the super-capacitor. When the fault detector detects that the low-voltage fault of the power grid is cleared, the low-voltage ride-through control strategy is switched to a mode 4, the controller at the time side recovers the maximum wave energy capture control strategy, the controller at the time side recovers the unit power factor operation, the bidirectional buck/boost converter of the super-capacitor energy storage device works under the boost circuit, and the super-capacitor discharges. And switching out the energy storage device until the voltage of the super capacitor recovers to the initial value, and finishing the low-voltage ride through process.
Claims (1)
1. A low voltage ride through coordination control method for a wave power generation system coordinates and controls a network side controller, a machine side controller and a super capacitor energy storage device according to the power of each link during a fault period, and comprises the following steps:
(1) the grid side controller is based on grid voltage orientation, adopts voltage outer loop current inner loop control, and under the normal operation condition of the power grid, the grid side controller operates under the unit power factor mode, and q axle current reference value is 0, and d axle current reference value is given through the voltage outer loop to maintain the stability of direct current bus voltage, and when the power grid has low voltage fault, in order to satisfy the requirement of output reactive power, q axle current reference value is calculated by the following formula:
igqref2≥1.5(0.9-eg[p.u.])IN
wherein eg[p.u.]Is the per unit value of the fault voltage at the grid-connected point, INRated current value of the grid side inverter;
the d-axis current reference value cannot be larger than considering the current clipping of the grid-side inverter
Wherein ImaxFor the grid-side inverter current amplitude, typically 1.5IN；
Therefore, the actual d-axis current reference is shown as follows
igdref＝min{igdref1,igdref2}
Wherein igdref1The d-axis current reference value is obtained through a voltage outer ring;
(2) the d-axis reference value of the machine side controller is set to be 0, the q-axis current reference value is obtained by maximum wave energy capture control under the condition that a power grid normally operates, when the power grid has a low-voltage fault, the machine side controller works in a rotor energy storage mode, and the rotor rotating speed reference value is obtained by a direct-current bus voltage outer ring; when the machine side controller works in a rotor limit rotating speed mode, a rotor rotating speed reference value is given as a rotating speed limit value;
(3) the super-capacitor energy storage device is controlled by a power outer ring current inner ring, the power outer ring is used for maintaining power balance at two ends of a direct current bus, and the current inner ring is used for realizing rapid tracking control; when a low-voltage fault occurs, the bidirectional buck/boost converter works under the buck circuit, and the direct-current bus charges the super capacitor; when the fault is eliminated, the bidirectional buck/boost converter works under the boost circuit, and the super capacitor discharges;
the super capacitor capacity should be designed to meet the most serious low-voltage fault of the power grid under the coordination control of low-voltage ride through, and when the power grid has a low-voltage fault of 0.2pu, the active power output by the grid-side inverter is represented as:
wherein igqref_scQ-axis current of the grid-side inverter when a fault occurs;
the energy absorbed by the supercapacitor energy storage device during a fault is expressed as
Esc＝0.625ΔP-Er_max＝0.625(Ps_rate-Pg_sc)-Er_max
Wherein P iss_rateIndicating the rated power of the output of the machine-side controller, Er_maxRepresenting the stored energy of the motor rotor rising from the rated speed to the limit speed;
the super capacitor capacity is expressed as
Wherein U issc_rateAnd Usc_initThe rated voltage and the initial voltage of the super capacitor energy storage device are shown, and when the super capacitor energy storage device is charged, the voltage is from Usc_initRises to Usc_rate，wmaxIs the generator rotor limit speed value, wNIs the rated speed value of the generator rotor igqref_scD-axis current of the grid-side inverter when 0.2pu fault occurs, egThe fault voltage is the fault voltage at the grid-connected point;
the design of the filter inductor of the super-capacitor energy storage device needs to meet the working requirement of the bidirectional buck/boost converter, the maximum impact current in the charging and discharging process can be passed through, and the filter inductor is calculated according to the following formula
Wherein IscpRepresents the rated current amplitude, delta I, of the super capacitor working in buck modescpRepresenting the maximum allowable ripple current, fsIndicating the switching frequency, U, of the buck/boost circuitdcIs the super capacitor side dc voltage;
(4) the low voltage ride through coordination control method comprises the following steps:
net sideActive power P input by inverter to power gridgrefCalculated by the following formula
Maximum storage power P of motor rotor under corresponding low-voltage faultω_maxCalculated by the following formula
Wherein ω ismaxAs limit value of the rotational speed of the rotor of the motor, omegaNRated value, t, for the speed of the rotor of the machineFAllowing the power generation system to access for a maximum time for the corresponding low voltage;
the control strategy is divided into four modes according to the relation of the power values of all links in the fault period, so that the machine side controller, the network side controller and the super capacitor energy storage device have different running states under different conditions:
when P is presentgref≥PsWhen the system works, a low voltage ride through coordination control strategy works in a mode 1, a time side controller works in a maximum wave energy capture mode, a network side controller works in a reactive compensation mode, and a super capacitor energy storage device does not need to participate in control; when P is presents>Pgref≥Ps-Pω_maxWhen the control strategy is in the mode 2, the opportunity side controller works in the motor rotor energy storage mode, the network side controller works in the reactive compensation mode, and the super capacitor energy storage device does not need to participate in control; when P is presents-Pω_max>PgrefWhen the low-voltage ride-through coordination control strategy works in a mode 3, the machine side controller works in a state of the limit value of the rotating speed of the motor, the network side controller works in a reactive compensation mode, the bidirectional buck/boost converter of the super-capacitor energy storage device works in a buck circuit, and the direct-current bus starts to charge the super-capacitor; low voltage ride through control strategy when fault detector detects clearing of grid low voltage faultSwitching to a mode 4, recovering a maximum wave energy capture control strategy by the time side controller, recovering the network side controller to operate with a unit power factor, operating the bidirectional buck/boost converter of the super-capacitor energy storage device under a boost circuit, and discharging the super-capacitor; and switching out the energy storage device until the voltage of the super capacitor recovers to the initial value, and finishing the low-voltage ride through process.
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