CN113765146B - Double-fed induction fan fault ride-through system and method under direct-current commutation failure - Google Patents
Double-fed induction fan fault ride-through system and method under direct-current commutation failure 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
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- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/12—Circuit arrangements for AC mains or AC distribution networks for adjusting voltage in AC networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for AC mains or AC distribution networks for adjusting voltage in AC networks by changing a characteristic of the network load by adjustment of reactive power
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- H—ELECTRICITY
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- 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
- H02J3/36—Arrangements for transfer of electric power between AC networks via a high-tension DC link
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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
- H02J3/50—Controlling the sharing of the out-of-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/14—Estimation or adaptation of machine parameters, e.g. flux, current or voltage
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/24—Vector control not involving the use of rotor position or rotor speed sensors
- H02P21/28—Stator flux based control
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- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/007—Control circuits for doubly fed generators
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- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
- H02P9/102—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for limiting effects of transients
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- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
- H02P9/105—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for increasing the stability
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- 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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- H02P2101/00—Special adaptation of control arrangements for generators
- H02P2101/15—Special adaptation of control arrangements for generators for wind-driven turbines
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- H02P2103/00—Controlling arrangements characterised by the type of generator
- H02P2103/10—Controlling arrangements characterised by the type of generator of the asynchronous type
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Abstract
The invention discloses a double-fed induction fan fault ride-through system and a ride-through method under direct-current commutation failure
A transformer and a power grid. The fault ride-through system of the doubly-fed induction fan under the direct-current commutation failure limits the rotor overcurrent caused by continuous faults, limits the rotor overvoltage through the direct-current unloading circuit, designs the improved control strategy of the rotor-side converter, can absorb or send inductive reactive current, can accelerate transient magnetic flux linkage attenuation by using the rotor-side converter, and improves the low-voltage and high-voltage continuous fault ride-through capability of the doubly-fed induction fan.
Description
Technical Field
The invention belongs to the technical field of double-fed induction fan equipment, and particularly relates to a fault ride-through system and a ride-through method of a double-fed induction fan under the condition of direct-current commutation failure.
Background
In the technical field of Doubly-fed induction wind turbine equipment, a Doubly-fed induction generator (DFIG) is still and continuously used as a main flow machine type of a wind power plant in an HVDC (high voltage direct current) transmission end alternating current system. However, when a commutation failure occurs in an inverter station of an HVDC system, a low-then-high continuous fault may be caused to a transmitting wind farm bus. Direct connection of the DFIG to the stator results in a high susceptibility of the DFIG to voltage faults. Under the background of large-scale wind power integration, the fan needs to be ensured to be capable of passing through low and high voltage continuous faults, and the stability of a power system is prevented from being seriously reduced.
Fault-ride-through studies of DFIGs by researchers have typically been conducted for low and high voltages, respectively. Only the fan strategy is optimized, and although the DFIG can cross a slight fault, the limited rated capacity of the converter of the DFIG causes that the optimized control strategy can not cross a serious fault. Therefore, the introduction of the hardware device protection DFIG is a common method, and among various methods, the series impedance circuit has the advantages of low cost and easy realization. However, if impedances are connected in series on the stator side, the terminal voltage may rise further during high voltage faults, which are low and high voltage continuous faults, jeopardizing safe operation of the DFIG stator and rotor windings and sensing equipment, etc.
Therefore, the direct current unloading resistor (DC-Chopper) is connected in parallel at the position where the impedance circuit is connected in series at the rotor side of the DFIG and the direct current bus, and corresponding improved control is provided, so that the rotor is ensured not to be over-current and the voltage of the direct current bus is not over-voltage, the attenuation of the transient process is accelerated, reactive support is provided, and the low-high voltage continuous fault ride-through capability of the DFIG is improved.
Disclosure of Invention
The invention aims to solve the problems that the existing doubly-fed induction fan fault ride-through research only considers single low-voltage fault or high-voltage fault, a low-voltage and high-voltage continuous fault protection scheme is lacked, and the existing doubly-fed induction fan reactive power control scheme cannot timely output dynamic reactive current required by fan grid-connected standard due to continuous voltage change in a short time, and provides a doubly-fed induction fan fault ride-through system and a ride-through method under direct-current commutation failure.
The technical scheme of the invention is as follows: the double-fed induction fan fault ride-through system under the condition of direct-current commutation failure comprises a double-fed induction fan, a current-limiting impedance, a first thyristor control switch, a second thyristor control switch, a rotor-side converter, a direct-current unloading circuit, a grid-side converter and an inductor
A transformer and a power grid;
the stator side of the double-fed induction fan is connected with a power grid through a transformer, and the rotor side of the double-fed induction fan sequentially passes through a current-limiting impedance, a rotor-side converter, a direct-current unloading circuit, a grid-side converter and an inductor
The transformer is connected with a power grid; the two ends of the first thyristor control switch are connected with the two ends of the current-limiting impedance in a one-to-one correspondence mode, and the two ends of the second thyristor control switch are connected with the two ends of the current-limiting impedance in a one-to-one correspondence mode.
The invention has the beneficial effects that: the fault ride-through system of the doubly-fed induction fan under the direct-current commutation failure limits the rotor overcurrent caused by continuous faults, limits the rotor overvoltage through the direct-current unloading circuit, designs the improved control strategy of the rotor-side converter, can absorb or send inductive reactive current, can accelerate transient magnetic flux linkage attenuation by using the rotor-side converter, and improves the low-voltage and high-voltage continuous fault ride-through capability of the doubly-fed induction fan.
Based on the system, the invention also provides a double-fed induction fan fault ride-through method under the condition of direct-current commutation failure, which comprises the following steps:
s1: when the voltage of a public connection point between the transformer and the power grid is lower than 0.9pu or more than 1.1pu, a first thyristor control switch and a second thyristor control switch are turned on, and a rotor-side converter adopts an improved control strategy and emits or absorbs reactive positive sequence current according to the voltage of the power grid;
s2: setting the reference value of the active positive sequence current and the reference value of the reactive positive sequence current of the rotor-side converter to be 0 within a preset time;
s3: and when the reference value of the active positive sequence current and the reference value of the reactive positive sequence current of the rotor-side converter are kept to be 0, the first thyristor control switch and the second thyristor control switch are closed within a preset time, and the current-limiting impedance is withdrawn, so that the doubly-fed induction fan can be recovered to operate in a normal state.
Further, in step S1, the control strategy of the rotor-side converter is specifically: transient flux linkage attenuation is accelerated by outputting demagnetizing current, a rotor current peak value is restrained by current-limiting impedance, and in the period that the voltage of a public connection point is lower than 0.9pu, a doubly-fed induction fan is controlled to improve the voltage of a power grid by outputting reactive positive sequence current, and the reference value of active positive sequence current of a rotor-side converter is reduced according to a set proportion according to stator voltage deviation; and when the voltage of the public connection point is more than 1.1pu, controlling the doubly-fed induction fan to improve the voltage of the power grid by absorbing the reactive positive sequence current, and keeping the reference value of the active positive sequence current at the moment as the reference value of the active positive sequence current before the fault.
Further, in step S1, the reference value of the reactive positive sequence current is output
The calculation formula of (2) is as follows:
wherein,
the inductance value of the stator inductance is represented,
the inductance value of the current-limiting impedance is represented,
the inductance value of the exciting inductor is represented,
represents the reactive current coefficient required by grid-tie standards during low voltage faults,
represents the reactive current coefficient required by grid-tie standards during high voltage faults,
the terminal voltages of the stator are indicated,
representing the absolute value of the difference between the actual voltage and the nominal voltage,
representing the grid angular frequency;
reference value of active positive sequence current
The calculation formula of (2) is as follows:
wherein,
representing the positive sequence reference value of the active current before the fault.
Demagnetization current
The calculation formula of (2) is as follows:
wherein,
，
，
，
the angular frequency of the stator is represented,
representing the stator transient flux linkage caused by a voltage fault,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the resistance of the rotor is represented by,
a resistance representing the impedance of the current limit,
the number of the imaginary numbers is represented,
representing the transient inductance of the rotor after the triggering of the current-limiting impedance,
the leakage inductance coefficient is represented by the value of,
indicating rotorThe inductance of the inductor is set to be,
the demagnetization factor is represented by the ratio of the magnetic flux,
the inductance representing the current limiting impedance.
Peak value of rotor current
The calculation formula of (2) is as follows:
wherein,
，
it is shown that,
the stator coupling coefficient is represented by the equation,
the terminal voltages of the stator are indicated,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the slip ratio is represented as a function of,
the angular frequency of the stator is represented,
the stator coupling coefficient is represented by the equation,
which represents the magnitude of the low voltage drop,
which represents the magnitude of the rise in the high voltage,
the initial value of the current before the fault is shown,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the power frequency period of the power grid is represented,
represents the maximum output voltage of the rotor-side converter,
representing the stator resistance.
The invention has the beneficial effects that: according to the fault ride-through method of the doubly-fed induction fan under the direct-current commutation failure, after the fault occurs, the current-limiting impedance is connected in series in the rotor loop, the rotor overcurrent peak value is restrained, and the rotor side transformer is matched
The current device is improved and controlled to send out inductive reactive current during low-voltage fault, absorb inductive reactive current during high-voltage fault, output demagnetizing current to accelerate transient flux linkage attenuation, and enhance the low-voltage and high-voltage continuous fault ride-through capability of the doubly-fed induction fan.
Drawings
Fig. 1 is a structural diagram of a doubly-fed induction fan fault ride-through system under the condition of direct-current commutation failure;
FIG. 2 is a flow chart of a doubly-fed induction fan fault ride-through method under the condition of direct-current commutation failure;
fig. 3 is a voltage waveform diagram of a low-high voltage continuous fault caused by a commutation failure of an inverter station of the high-voltage direct-current transmission system;
fig. 4 is a control block diagram of the rotor-side converter.
Detailed Description
The embodiments of the present invention will be further described with reference to the accompanying drawings.
As shown in FIG. 1, the invention provides a double-fed induction fan fault ride-through system under direct-current commutation failure, which comprises a double-fed induction fan, a current-limiting impedance, a first thyristor control switch, a second thyristor control switch, a rotor-side converter, a direct-current unloading circuit, a grid-side converter, an inductor
A transformer and a power grid;
the stator side of the double-fed induction fan is connected with a power grid through a transformer, and the rotor side of the double-fed induction fan sequentially passes through a current-limiting impedance, a rotor-side converter, a direct-current unloading circuit, a grid-side converter and an inductor
The transformer is connected with a power grid; the two ends of the first thyristor control switch are connected with the two ends of the current-limiting impedance in a one-to-one correspondence mode, and the two ends of the second thyristor control switch are connected with the two ends of the current-limiting impedance in a one-to-one correspondence mode.
Based on the above system, the present invention further provides a method for fault ride-through of a doubly-fed induction wind turbine under direct-current commutation failure, as shown in fig. 2, including the following steps:
s1: when the voltage of a public connection point between the transformer and the power grid is lower than 0.9pu or more than 1.1pu, a first thyristor control switch and a second thyristor control switch are turned on, and a rotor-side converter adopts an improved control strategy and emits or absorbs reactive positive sequence current according to the voltage of the power grid; the reactive current is used for supporting the voltage recovery of the power grid, and the step can confirm continuous fault clearing;
s2: setting the reference value of the active positive sequence current and the reference value of the reactive positive sequence current of the rotor-side converter to be 0 within a preset time;
s3: and when the reference value of the active positive sequence current and the reference value of the reactive positive sequence current of the rotor-side converter are kept to be 0, the first thyristor control switch and the second thyristor control switch are closed within a preset time, and the current-limiting impedance is withdrawn, so that the doubly-fed induction fan can be recovered to operate in a normal state.
In the embodiment of the present invention, in step S1, the control strategy of the rotor-side converter is specifically: transient flux linkage attenuation is accelerated by outputting demagnetizing current, a rotor current peak value is restrained by current-limiting impedance, and in the period that the voltage of a public connection point is lower than 0.9pu, a doubly-fed induction fan is controlled to improve the voltage of a power grid by outputting reactive positive sequence current, and the reference value of active positive sequence current of a rotor-side converter is reduced according to a set proportion according to stator voltage deviation; and when the voltage of the public connection point is more than 1.1pu, controlling the doubly-fed induction fan to improve the voltage of the power grid by absorbing the reactive positive sequence current, and keeping the reference value of the active positive sequence current at the moment as the reference value of the active positive sequence current before the fault.
In the embodiment of the invention, in step S1, the reference value of the reactive positive sequence current is output
The calculation formula of (2) is as follows:
wherein,
the inductance value of the stator inductance is represented,
the inductance value of the current-limiting impedance is represented,
the inductance value of the exciting inductor is represented,
reactive power representing grid-tie specification requirements during low voltage faultsThe current coefficient of the current is measured,
represents the reactive current coefficient required by grid-tie standards during high voltage faults,
the terminal voltages of the stator are indicated,
representing the absolute value of the difference between the actual voltage and the nominal voltage,
representing the grid angular frequency;
reference value of active positive sequence current
The calculation formula of (2) is as follows:
wherein,
representing the positive sequence reference value of the active current before the fault;
the reactive positive sequence current reference value and the active current positive sequence reference value satisfy the following formula:
wherein,
representing a continuous current threshold of the rotor-side converter;
demagnetization current
The calculation formula of (2) is as follows:
wherein,
，
，
，
the angular frequency of the stator is represented,
representing the stator transient flux linkage caused by a voltage fault,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the resistance of the rotor is represented by,
a resistance representing the impedance of the current limit,
the number of the imaginary numbers is represented,
representing the transient inductance of the rotor after the triggering of the current-limiting impedance,
the leakage inductance coefficient is represented by the value of,
the inductance of the rotor is represented by,
the demagnetization factor is represented by the ratio of the magnetic flux,
the inductance representing the current limiting impedance.
During steady-state operation, the RSC control strategy is a traditional double-ring control structure of a power outer ring and a current inner ring. Active power reference signal
And a reactive power reference signal
Respectively with actual values of active power of the stator
And actual value of reactive power
Making difference, obtaining rotor active current reference value by PI controller
And a reactive current reference value
. Reference and actual values of rotor current
、
The error between the two is input into a PI controller, and a coupling compensation term is added to obtain a rotor voltage reference value
、
. When a continuous fault occurs, the power outer loop is disconnected, and only the power inner loop is operated to improve the current response speed during the transient state. At this time, RSC performs the proposed current coordination control.
Peak value of rotor current
The calculation formula of (2) is as follows:
wherein,
，
it is shown that,
the stator coupling coefficient is represented by the equation,
the terminal voltages of the stator are indicated,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the slip ratio is represented as a function of,
the angular frequency of the stator is represented,
the stator coupling coefficient is represented by the equation,
which represents the magnitude of the low voltage drop,
which represents the magnitude of the rise in the high voltage,
the initial value of the current before the fault is shown,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the power frequency period of the power grid is represented,
represents the maximum output voltage of the rotor-side converter,
representing the stator resistance.
In the embodiment of the invention, as shown in fig. 3, a typical low-high voltage continuous fault caused by a commutation failure of an inverter station of a high-voltage direct-current power transmission system is shown. Fig. 3 (a) shows a three-phase stator voltage waveform, and fig. 3 (b) shows a stator voltage effective value.
A time of day fault occurs, the voltage is
Down to at all times
Multiple nominal value, up to
At the moment the stator voltage rises to
Multiple nominal value, up to
The time of day. And finally, the voltage is recovered to the value before the fault.
The improved control strategy of the rotor side provided by the invention specifically comprises the following steps:
during steady-state operation, the control strategy of the rotor-side converter is a double-ring control structure of a traditional power outer ring and a traditional current inner ring. Active power reference signal
And a reactive power reference signal
Respectively with actual values of active power of the stator
And actual value of reactive power
Making difference, obtaining rotor active current reference value by PI controller
And a reactive current reference value
. Reference and actual values of rotor current
、
The error between the two is input into a PI controller, and a coupling compensation term is added to obtain a rotor voltage reference value
、
. When a continuous fault occurs, the power outer loop is disconnected, and only the power inner loop is operated to improve the current response speed during the transient state. At this time, the rotor side current changes
The device performs the proposed current coordination control. Low and high voltage periods are additional when a continuous fault has been entered
The reference value of the output rotor reactive positive sequence current is
According to the formula, the double-fed induction fan outputs inductive reactive current to improve the voltage of a power grid during a low voltage period, and absorbs the inductive reactive current to reduce the voltage of the power grid during a high voltage period. The provided strategy still considers the active output of the double-fed induction fan under slight low-voltage fault and high-voltage fault, and prevents rotor overspeed and electric power
The system stability decreases. Adopting a reactive current priority control target, and setting an active current positive sequence reference value to be reduced in an equal proportion according to stator voltage deviation because voltage reduction is not beneficial to transmitting active power to a power grid during low voltage; during high voltage, which is favorable for power delivery, the active current positive sequence reference value remains at the pre-fault value. The positive sequence reference value of the active current is
The root mean square value of the reactive and active positive sequence current should not exceed the continuous current threshold value of RSC
Need to satisfy
。
Because the stator voltage continuously changes in a short time and the rotor current reference value also continuously changes, in order to realize the effect of the current coordination control strategy, a hysteresis comparator is adopted in a current loop during a fault period.
The remaining available capacity of the rotor-side converter current is used to accelerate transient flux linkage decay. As shown in fig. 4, stator voltage
Minus stator current
And stator resistance
The product of (a) to obtain the stator flux linkage differential
And then integrating to obtain the stator flux linkage
。
Obtaining stator flux linkage through coordinate changedqAn axial component. Due to the adoption ofdAxial voltage orientation control, stator flux linkageqAxial component
Subtracting the steady-state component to obtain the stator flux linkageqAxial transient component
. Stator flux linkagedAxial transient component
Namely the stator flux linkagedAn axial component. Multiplying the two by a demagnetization coefficient to obtain rotor demagnetization currentdqAxial component
、
. After the current-limiting impedance is triggered, the equivalent transient impedance of the rotor changes. At this time, the demagnetization current is
The current limiting impedance provided by the invention specifically comprises the following components: as shown in fig. 1, the current-limiting impedance is arranged on the rotor side of the doubly-fed induction wind turbine and is connected in parallel with two anti-parallel thyristor controlled switches. When the motor runs normally, the thyristor controls the switch to be closed, and the current circulation of the rotor is not influenced. When a fault is detected, the parallel switch is turned off, the current-limiting impedance is input to the rotor side, the transient impedance of the rotor is equivalently increased, the overcurrent peak value of the rotor is limited, and redundant energy is consumed. The choice of the impedance parameters should be considered according to the more severe case. In a typical low-high voltage continuous fault, the most severe case is that the transient flux linkage caused by the low-voltage fault is in the same direction as the transient flux linkage caused by the high-voltage fault. In addition, since the magnitude of the transient magnetic flux generated by the step type voltage fault is larger than that of the voltage fault having a certain change time, it can be considered that both the low voltage fault and the high voltage fault are the step type faults. In a shorter time, neglecting the decay of the transient flux linkage, a low voltage fault and a subsequent high voltage fault can be equated to a voltage fault. At this time, the series impedance is inserted into the rotor circuit. Can calculate the peak value of the rotor current to meet
. The impedance value of the required current limiting impedance can be selected according to the above formula.
The working principle and the process of the invention are as follows: the invention provides a low-high voltage continuous fault ride-through scheme of a doubly-fed induction fan based on rotor side series impedance and improved control. The current-limiting impedance is connected in series at the rotor side of the doubly-fed induction wind turbine, and the control strategy comprises a control strategy of a rotor-side converter of the DFIG. When no voltage fault occurs, the current-limiting impedance is bypassed by the parallel thyristor control switch, and the rotor impedance is not changed. When a fault is detected, the switch of the current-limiting impedance is switched off, the current-limiting impedance is connected in series with the rotor loop, the equivalent impedance of the rotor of the double-fed induction fan is increased,
rotor fault current peaks are suppressed while RSC provides dynamic reactive support to the grid with improved control. In order to prevent overvoltage of a direct-current bus of the doubly-fed induction fan caused by overmodulation of a grid-side converter due to high voltage in a low-high voltage continuous fault process, a direct-current unloading circuit is connected in parallel with the direct-current bus, when the direct-current voltage rises to an upper limit threshold, the direct-current unloading circuit is started, and when the direct-current voltage is lower than a lower limit threshold, the direct-current unloading circuit is withdrawn. Therefore, the double-fed induction fan can pass through continuous faults.
The invention has the beneficial effects that:
(1) the fault ride-through system of the doubly-fed induction fan under the direct-current commutation failure limits the rotor overcurrent caused by continuous faults, limits the rotor overvoltage through the direct-current unloading circuit, designs the improved control strategy of the rotor-side converter, can absorb or send inductive reactive current, can accelerate transient magnetic flux linkage attenuation by using the rotor-side converter, and improves the low-voltage and high-voltage continuous fault ride-through capability of the doubly-fed induction fan.
(2) According to the fault ride-through method of the doubly-fed induction fan under the direct-current commutation failure, after the fault occurs, current-limiting impedance is connected in series in a rotor loop, the overcurrent peak value of a rotor is restrained, the rotor-side converter is matched for improved control, inductive reactive current is sent out during the low-voltage fault, the inductive reactive current is absorbed during the high-voltage fault, demagnetizing current is output, transient magnetic linkage attenuation is accelerated, and the low-voltage and high-voltage continuous fault ride-through capacity of the doubly-fed induction fan is enhanced.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.
Claims (3)
1. The method is applied to a double-fed induction fan fault ride-through system under the direct-current commutation failure, and the system comprises a double-fed induction fan, a current-limiting impedance, a first thyristor control switch, a second thyristor control switch, a rotor-side converter, a direct-current unloading circuit, a grid-side converter and an inductance inductor
The stator side of the double-fed induction fan is connected with the power grid through a transformer; the current-limiting impedance, the first thyristor control switch and the second thyristor control switch are connected in parallel, wherein the first thyristor control switch and the second thyristor control switch are connected in parallel in a reverse direction, one parallel end of the first thyristor control switch and the second thyristor control switch is connected with the rotor side of the doubly-fed induction fan, and the other parallel end of the first thyristor control switch and the second thyristor control switch is connected with one end of the rotor-side converter; the other end of the rotor side converter is sequentially connected with a direct current unloading circuit, a network side converter and an inductor in series
Then the power grid is connected with a power grid through a transformer; the method comprises the following steps:
s1: when the voltage of a public connection point between the transformer and the power grid is lower than 0.9pu or more than 1.1pu, a first thyristor control switch and a second thyristor control switch are turned on, and a rotor-side converter adopts an improved control strategy and emits or absorbs reactive positive sequence current according to the voltage of the power grid;
s2: setting the reference value of the active positive sequence current and the reference value of the reactive positive sequence current of the rotor-side converter to be 0 within a preset time;
s3: when the reference value of the active positive sequence current and the reference value of the reactive positive sequence current of the rotor-side converter are kept to be 0, the first thyristor control switch and the second thyristor control switch are closed within a preset time, and the current-limiting impedance is withdrawn, so that the doubly-fed induction fan can be recovered to operate in a normal state;
in step S1, the control strategy of the rotor-side converter is specifically: transient flux linkage attenuation is accelerated by outputting demagnetizing current, a rotor current peak value is restrained by current-limiting impedance, and in the period that the voltage of a public connection point is lower than 0.9pu, a doubly-fed induction fan is controlled to improve the voltage of a power grid by outputting reactive positive sequence current, and the reference value of active positive sequence current of a rotor-side converter is reduced according to a set proportion according to stator voltage deviation; and when the voltage of the public connection point is more than 1.1pu, controlling the doubly-fed induction fan to improve the voltage of the power grid by absorbing the reactive positive sequence current, and keeping the reference value of the active positive sequence current at the moment as the reference value of the active positive sequence current before the fault.
2. The method for fault ride-through of the doubly-fed induction fan under the condition of direct-current commutation failure according to claim 1, wherein in the step S1, a reference value of reactive positive sequence current is output
The calculation formula of (2) is as follows:
wherein,
the inductance value of the stator inductance is represented,
the inductance value of the current-limiting impedance is represented,
the inductance value of the exciting inductor is represented,
represents the reactive current coefficient required by grid-tie standards during low voltage faults,
represents the reactive current coefficient required by grid-tie standards during high voltage faults,
the terminal voltages of the stator are indicated,
representing the absolute value of the difference between the actual voltage and the nominal voltage,
representing the grid angular frequency;
reference value of the active positive sequence current
The calculation formula of (2) is as follows:
wherein,
representing the positive sequence reference value of the active current before the fault;
the demagnetization current
The calculation formula of (2) is as follows:
wherein,
，
，
，
the angular frequency of the stator is represented,
representing the stator transient flux linkage caused by a voltage fault,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the resistance of the rotor is represented by,
a resistance representing the impedance of the current limit,
the number of the imaginary numbers is represented,
representing the transient inductance of the rotor after the triggering of the current-limiting impedance,
the leakage inductance coefficient is represented by the value of,
the inductance of the rotor is represented by,
the demagnetization factor is represented by the ratio of the magnetic flux,
the inductance representing the current limiting impedance.
3. The method for fault ride-through of the doubly-fed induction wind turbine under the condition of direct-current commutation failure according to claim 1, wherein in the step S1, the peak value of the rotor current is
The calculation formula of (2) is as follows:
wherein,
，
the stator coupling coefficient is represented by the equation,
the terminal voltages of the stator are indicated,
represents the transient resistance of the rotor after the triggering of the current limiting impedance,
the slip ratio is represented as a function of,
the angular frequency of the stator is represented,
which represents the magnitude of the low voltage drop,
which represents the magnitude of the rise in the high voltage,
the initial value of the current before the fault is shown,
the power frequency period of the power grid is represented,
represents the maximum output voltage of the rotor-side converter,
representing the stator resistance.
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