CN108847676B - Low voltage ride through control method based on Boost circuit - Google Patents

Low voltage ride through control method based on Boost circuit Download PDF

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CN108847676B
CN108847676B CN201810559075.1A CN201810559075A CN108847676B CN 108847676 B CN108847676 B CN 108847676B CN 201810559075 A CN201810559075 A CN 201810559075A CN 108847676 B CN108847676 B CN 108847676B
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current
voltage
reactive
sequence component
active
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CN108847676A (en
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甘德树
裴星宇
程旭
赵晓燕
林桂辉
吴海雄
廖石江
林敏洪
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Guangdong Power Grid Co Ltd
Zhuhai Power Supply Bureau of Guangdong Power Grid Co Ltd
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Guangdong Power Grid Co Ltd
Zhuhai Power Supply Bureau of Guangdong Power Grid Co Ltd
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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
    • H02J3/12—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
    • H02J3/383—
    • 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
    • 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 the technical field of photovoltaic inverters, in particular to a low-voltage ride-through control method based on a Boost circuit, which comprises the steps of stabilizing the voltage of a direct-current side bus through a Boost control system, carrying out coordinate transformation on a sampled current value to obtain an active current component and a reactive current component, and carrying out positive-negative sequence separation phase locking on the sampled voltage value to obtain an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the voltage of a power grid side; and then the pulse signal for controlling the switch of the inverter is obtained through the current control module to control the inverter, so that the low-voltage ride through of the system is realized. The method combines the mode of giving the active and reactive current reference values, and can provide reactive power support for the power grid while ensuring the current quality during the fault period; controlling the voltage of the direct current bus in a safe range during the low voltage ride through; and the hardware structure of the existing two-stage inverter is not required to be changed, and the method has excellent adaptability.

Description

Low voltage ride through control method based on Boost circuit
Technical Field
The invention relates to the technical field of photovoltaic inverters, in particular to a low-voltage ride-through control method based on a Boost circuit.
Background
As the proportion of photovoltaic power generation in an electric power system is gradually increased, the photovoltaic power generation brings new influence and challenge to the safe and stable operation of the electric power system. The related standards require that the photovoltaic inverter has a certain low voltage ride through capability. At present, the low voltage ride through research on the photovoltaic inverter in China is under development, and the common photovoltaic inverter can be divided into a unipolar type and a bipolar type. However, most of the existing methods can achieve better effects, but are designed for a single-stage photovoltaic inverter, and are not suitable for a two-stage photovoltaic inverter. In order to realize low voltage ride through of a two-stage photovoltaic inverter, the conventional method has a vector control strategy based on positive sequence voltage orientation of a power grid, and the stable operation of the photovoltaic inverter is ensured when various asymmetric faults occur in the power grid by combining a direct current side unloading circuit; the super capacitor is controlled to absorb active power, the direct-current bus voltage is stabilized, and the power injected into the inverter by the photovoltaic array is reduced, so that low-voltage ride through is realized; the low voltage ride through of the two-stage photovoltaic inverter and the like are realized through an additional hardware auxiliary circuit. However, these low voltage ride through control methods require modification of the hardware structure of the existing two-stage inverter, and are not suitable.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a low-voltage ride-through control method based on a Boost circuit, which does not change the hardware structure of the conventional two-stage inverter and provides reactive power support for a power grid while ensuring the current quality during the fault period.
In order to solve the technical problems, the invention adopts the technical scheme that:
the low voltage ride through control method based on the Boost circuit is used for low voltage ride through of a two-stage photovoltaic inverter; the two-stage photovoltaic inverter consists of a Boost circuit and a DC/AC inverter circuit, wherein the DC/AC inverter circuit is connected to a power grid through a three-phase circuit, and the three-phase circuit is connected with a voltage detection module and a current detection module which are used for collecting the voltage and the current values of the power grid; the DC/AC inverter circuit comprises an inverter and an inverter switching tube which are electrically connected; the Boost circuit is connected with a Boost control system, the voltage detection module is connected with a positive and negative sequence separation phase locking module based on an SOGI, the DC/AC inverter circuit is connected with a current control module, and the current detection module is connected with a coordinate transformation module; the method comprises the following steps:
s1, introducing a voltage U based on the maximum power point before faultmaxThe bus voltage of feedforward controls the outer loop PI, changes the voltage control mode of the Boost circuit part, and stabilizes the DC bus voltage UdcAs a control target;
s2, when a three-phase asymmetric fault occurs, processing the voltage value acquired by the voltage detection module through the SOGI-based positive and negative sequence separation phase locking module to obtain an active positive sequence component
Figure BDA0001682720310000021
Positive reactive sequence component
Figure BDA0001682720310000022
Positive and negative sequence component
Figure BDA0001682720310000023
And a reactive negative sequence component
Figure BDA0001682720310000024
S3, when a three-phase asymmetric fault occurs, coordinate transformation is carried out on the current value acquired by the current acquisition module through the coordinate transformation module to acquire a current active component idAnd a reactive component of current iq；
S4, inputting the active positive sequence component obtained in the step S2 into a current control module
Figure BDA0001682720310000025
Positive reactive sequence component
Figure BDA0001682720310000026
Positive and negative sequence component
Figure BDA0001682720310000027
Negative reactive sequence component
Figure BDA0001682720310000028
And the current active component i obtained in step S3dCurrent reactive component iqAnd the pulse signal for controlling the switching tube of the inverter is output to control the inverter, so that low voltage ride through is realized.
The invention relates to a low voltage ride through control method based on a Boost circuit, which comprises the steps of stabilizing the voltage of a direct current side bus through a Boost control system, sampling a power grid current value and a power grid voltage value through a current detection module and a voltage detection module on an alternating current side respectively, carrying out coordinate transformation on the sampled current value to obtain a current active component and a current reactive component, and carrying out positive and negative sequence separation phase locking on the sampled voltage value to obtain an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the power grid side voltage; and then the pulse signal for controlling the switch of the inverter is obtained through the current control module to control the inverter, so that the low-voltage ride through of the system is realized. The invention can complete low voltage ride through without changing the hardware structure of the existing two-stage inverter and has good adaptability.
Preferably, in step S1, the voltage control outer loop PI is controlled at the dc bus voltage UdcOutputting positive control quantity to raise output voltage U of photovoltaic array during risingpcAt a DC bus voltage UdcOutputting negative control quantity to reduce output voltage U of photovoltaic array when voltage is reducedpc. The voltage control outer ring PI is arranged to ensure that the voltage of the direct current bus is controlled within a safe range during low voltage ride through.
Preferably, in step S2, the processing steps of the SOGI-based positive-negative order separation phase-locking module to the three-phase asymmetric voltage are as follows:
s21, obtaining the three-phase asymmetric voltage according to a symmetric component method:
Figure BDA0001682720310000029
Figure BDA00016827203100000210
in the formulae (1) and (2), q is a 90 DEG phase lag factor, eαβαβ is the grid voltage in the stationary frame,
Figure BDA0001682720310000031
is the positive sequence component of the grid voltage,
Figure BDA0001682720310000032
is the negative sequence component of the grid voltage;
s22. the transfer function of the sogi is:
Figure BDA0001682720310000033
Figure BDA0001682720310000034
in the equations (3) and (4), v is the input sinusoidal signal, ω' is the filter center frequency, k is the damping coefficient, often taken as
Figure BDA0001682720310000035
When the center frequency of the SOGI is the same as the frequency of the input signal, then the output signals v 'and v have the same amplitude and phase, qv' and v being the same amplitude, but the phase lags by 90 °. The SOGI can realize orthogonal processing of input signals and realize positive and negative sequence separation.
Preferably, the coordinate transformation module in step S3 processes the three-phase asymmetric current as follows:
s31, an alternating current side mathematical model of the photovoltaic inverter can be established according to a symmetric component method:
Figure BDA0001682720310000036
in the formula (5), ed P、eq P、ed N、eq NRespectively an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the voltage of the power grid; u. ofd P、uq P、ud N、uq NRespectively outputting an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of voltage for the inverter; i.e. id P、iq P、id N、id NRespectively an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the current; r is a load resistor, and L is a filter inductor;
s32. define K ═ Ud_fault P/UNWherein, Ud_fault PIs a fault-time positive sequence voltage, UNThe grid connection point rated voltage is obtained, and K is the voltage drop depth;
s33, under the premise of no overcurrent, outputting the maximum reactive current:
id_fault *＝imax-iR(t-t1)(id_fault *≥Kimax) (6)
Figure BDA0001682720310000037
in the formula iRGiven values, typically 8000, imax＝IN，INRated current for grid-connected point, iq_fault *For at a given current command id _ fault*Reactive current of time, id_fault *For at a given current command id _ fault*The active current of time.
Preferably, in step S4, the current control module includes a first control loop PI1, a second control loop PI2 and an SVPWM module, and the first control loop PI1 and the second control loop PI2 are electrically connected to the SVPWM module respectively. Wherein the first control loop PI1 is used to control the active current and the second control loop PI2 is used to control the reactive current.
Preferably, in step S4, the step of controlling the inverter by the current control module includes:
s41, according to the reactive current i calculated in the step S33q_fault *And an active current id_fault *Calculating active current modulation signals
Figure BDA0001682720310000041
Figure BDA0001682720310000042
In the formula (8), KP1、KI1Proportional and integral coefficients, respectively, of the first control loop PI 1;
s42, calculating according to a formula (9) to obtain a reactive current modulation signal
Figure BDA0001682720310000043
Figure BDA0001682720310000044
In the formula (9), KP2、KI2Proportional and integral coefficients, respectively, of the second control loop PI 2;
s43, the active current modulation signal obtained by the calculation in the step S41 is used
Figure BDA0001682720310000045
Reactive current modulation signal calculated in step S42
Figure BDA0001682720310000046
And sending the signal into an SVPWM module for operation to obtain a switching tube control signal of the DC/AC inverter circuit.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention designs a current control strategy based on network side negative sequence voltage feedforward, and combines a mode of giving active and reactive current reference values, thereby ensuring the current quality during the fault period and providing reactive power support for the power grid.
(2) The invention designs a Boost bus voltage control loop based on maximum power point voltage feedforward before fault, and can control the direct current bus voltage in a safety range during low voltage ride through.
(3) The control method designed by the invention does not change the hardware structure of the existing two-stage inverter and has excellent adaptability.
Drawings
Fig. 1 is a general control block diagram of a Boost circuit-based low voltage ride through control method of the present invention.
Fig. 2 is a schematic structural diagram of the Boost control system of the present invention.
Fig. 3 is a schematic diagram of the power variation of the photovoltaic array of the present invention.
FIG. 4 is a diagram of a current command id _ fault according to an embodiment*The waveform curve of (2).
Detailed Description
The present invention will be further described with reference to the following embodiments. Wherein the showings are for the purpose of illustration only and are shown by way of illustration only and not in actual form, and are not to be construed as limiting the present patent; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. based on the orientation or positional relationship shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but it is not intended to indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and are not to be construed as limiting the present patent, and the specific meaning of the terms may be understood by those skilled in the art according to specific circumstances.
Example one
Fig. 1 shows a first embodiment of the Boost circuit-based low voltage ride through control method of the present invention, which is used for low voltage ride through of a two-stage photovoltaic inverter; the two-stage photovoltaic inverter consists of a Boost circuit and a DC/AC inverter circuit, wherein the DC/AC inverter circuit is connected to a power grid through a three-phase circuit, and the three-phase circuit is connected with a voltage detection module and a current detection module which are used for collecting the voltage and the current values of the power grid; the DC/AC inverter circuit comprises an inverter and an inverter switching tube which are electrically connected; the system is characterized in that the Boost booster circuit is connected with a Boost control system, the voltage detection module is connected with a positive and negative sequence separation phase locking module based on an SOGI, the DC/AC inverter circuit is connected with a current control module, and the current detection module is connected with a coordinate transformation module; the method comprises the following steps:
s1, introducing a voltage U based on the maximum power point before faultmaxThe bus voltage of feedforward controls outer loop PI, as shown in FIG. 2, the voltage control mode of Boost circuit part is changed, and the DC bus voltage U is stabilizeddcAs a control target;
s2, when a three-phase asymmetric fault occurs, processing the voltage value acquired by the voltage detection module through the SOGI-based positive and negative sequence separation phase locking module to obtain an active positive sequence component
Figure BDA0001682720310000061
Positive reactive sequence component
Figure BDA0001682720310000062
Positive and negative sequence component
Figure BDA0001682720310000063
And a reactive negative sequence component
Figure BDA0001682720310000064
S3, when a three-phase asymmetric fault occurs, coordinate transformation is carried out on the current value acquired by the current acquisition module through the coordinate transformation module to acquire a current active component idAnd a reactive component of current iq；
S4, inputting the active positive sequence component obtained in the step S2 into a current control module
Figure BDA0001682720310000065
Positive reactive sequence component
Figure BDA0001682720310000066
Positive and negative sequence component
Figure BDA0001682720310000067
Negative reactive sequence component
Figure BDA0001682720310000068
And the current active component i obtained in step S3dCurrent reactive component iqAnd the pulse signal for controlling the switching tube of the inverter is output to control the inverter, so that low voltage ride through is realized.
When the method is implemented, the voltage of a direct-current side bus is stabilized through a Boost control system, a current value and a voltage value of a power grid are obtained by sampling the voltage value of an alternating-current side through a current detection module and a voltage detection module respectively, the sampled current value is subjected to coordinate transformation to obtain a current active component and a current reactive component, and the sampled voltage value is subjected to positive and negative sequence separation phase locking to obtain an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the voltage of the power grid; and then the pulse signal for controlling the switch of the inverter is obtained through the current control module to control the inverter, so that the low-voltage ride through of the system is realized.
Specifically, in step S1, the voltage control outer loop PI is controlled at the dc bus voltage UdcOutputting positive control quantity to raise output voltage U of photovoltaic array during risingpcAt a DC bus voltage UdcOutputting negative control quantity to reduce output voltage U of photovoltaic array when voltage is reducedpc. The voltage control outer ring PI is arranged to ensure that the voltage of the direct current bus is controlled within a safe range during low voltage ride through.
As shown in FIG. 2, UdcIs a DC bus voltage, UmaxAnd obtaining a photovoltaic array maximum power point voltage reference value by adopting an MPPT algorithm (maximum power point tracking algorithm) before the fault occurs. When the voltage drops, the DC bus voltage UdcThe rising voltage in the dotted line frame controls the output of the outer ring PI to positive control quantity which is superposed to UmaxThis can shift the operating point of the photovoltaic array to the right of the maximum power point. For a photovoltaic array, the power change when the actual operating voltage deviates from the maximum power point voltage to the left and right, respectively, is shown in fig. 3. According to the P-U characteristic of the photovoltaic array, the maximum power point voltage UmaxGenerally at the position of 0.8 times of the open circuit voltage, therefore, the average rate of change of the output power to the voltage on the right side of the maximum power point voltage of the photovoltaic array is larger than that on the left side, and when Δ U1 is equal to Δ U2 in fig. 3, the relationship P existsleft>Pright. In summary, when the voltage drops, the output voltage U of the photovoltaic array can be quickly raised by the control mode of the voltage feedforward of the maximum power point before the fault shown in fig. 2 and matching with appropriate controller parameterspvTo reduce the output power thereof, thereby controlling the voltage of the direct current bus within a safe range.
In step S2, the processing steps of the SOGI-based positive-negative sequence separation phase-locking module on the three-phase asymmetric voltage are as follows:
s21, obtaining the three-phase asymmetric voltage according to a symmetric component method:
Figure BDA0001682720310000071
Figure BDA0001682720310000072
in the formulae (1) and (2), q is a 90 DEG phase lag factor, eαβIn the static coordinate system of αβThe voltage of the power grid is measured,
Figure BDA0001682720310000073
is the positive sequence component of the grid voltage,
Figure BDA0001682720310000074
is the negative sequence component of the grid voltage;
s22. the transfer function of the sogi is:
Figure BDA0001682720310000075
Figure BDA0001682720310000076
in the equations (3) and (4), v is the input sinusoidal signal, ω' is the filter center frequency, k is the damping coefficient, often taken as
Figure BDA0001682720310000077
When the center frequency of the SOGI is the same as the frequency of the input signal, then the output signals v 'and v have the same amplitude and phase, qv' and v being the same amplitude, but the phase lags by 90 °. The SOGI can realize orthogonal processing of input signals and realize positive and negative sequence separation.
The processing steps of the coordinate transformation module to the three-phase asymmetric current in the step S3 are as follows:
s31, an alternating current side mathematical model of the photovoltaic inverter can be established according to a symmetric component method:
Figure BDA0001682720310000078
in the formula (5), ed P、eq P、ed N、eq NRespectively an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the voltage of the power grid; u. ofd P、uq P、ud N、uq NActive positive sequence of output voltage of inverterComponent, reactive positive sequence component, active negative sequence component, reactive negative sequence component; i.e. idP、iq P、id N、id NRespectively an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the current; r is a load resistor, and L is a filter inductor;
s32. define K ═ Ud_fault P/UNWherein, Ud_fault PIs a fault-time positive sequence voltage, UNThe grid connection point rated voltage is obtained, and K is the voltage drop depth; in order to realize reactive support of the power grid, the method adopted by the embodiment gives the current instruction id _ fault according to the voltage drop depth*As shown in fig. 4. In FIG. 4, t0To detect voltage failure (i.e. K)<0.9) time, t1To t2For the current regulation process, t3The moment when the fault starts to recover; wherein id_fault *Is maintained as imaxIs set to 5 ms.
S33, under the premise of no overcurrent, outputting the maximum reactive current:
id_fault *＝imax-iR(t-t1)(id_fault *≥Kimax) (6)
Figure BDA0001682720310000081
in the formula iRGiven values, typically 8000, imax＝IN，INRated current for grid-connected point, iq_fault *For at a given current command id _ fault*Reactive current of time, id_fault *For at a given current command id _ fault*The active current of time.
In step S4, the current control module includes a first control loop PI1, a second control loop PI2, and an SVPWM module, and the first control loop PI1 and the second control loop PI2 are electrically connected to the SVPWM module, respectively. Wherein the first control loop PI1 is used to control the active current and the second control loop PI2 is used to control the reactive current.
The step of controlling the inverter by the current control module comprises the following steps:
s41, according to the reactive current i calculated in the step S33q_fault *And an active current id_fault *Calculating active current modulation signals
Figure BDA0001682720310000082
Figure BDA0001682720310000083
In the formula (8), KP1、KI1Proportional and integral coefficients, respectively, of the first control loop PI 1;
s42, calculating according to a formula (9) to obtain a reactive current modulation signal
Figure BDA0001682720310000084
Figure BDA0001682720310000085
In the formula (9), KP2、KI2Proportional and integral coefficients, respectively, of the second control loop PI 2;
s43, the active current modulation signal obtained by the calculation in the step S41 is used
Figure BDA0001682720310000086
Reactive current modulation signal calculated in step S42
Figure BDA0001682720310000087
And sending the signal into an SVPWM module for operation to obtain a switching tube control signal of the DC/AC inverter circuit.
Through the steps, the method combines the mode of giving the active and reactive current reference values, and can provide reactive power support for the power grid while ensuring the current quality during the fault period; controlling the voltage of the direct current bus in a safe range during the low voltage ride through; the low-voltage ride through can be realized without changing the hardware structure of the existing two-stage inverter, and the low-voltage ride through has excellent adaptability.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims (1)

1. A low voltage ride through control method based on a Boost circuit is used for low voltage ride through of a two-stage photovoltaic inverter; the two-stage photovoltaic inverter consists of a Boost circuit and a DC/AC inverter circuit, wherein the DC/AC inverter circuit is connected to a power grid through a three-phase circuit, and the three-phase circuit is connected with a voltage detection module and a current detection module which are used for collecting the voltage and the current values of the power grid; the DC/AC inverter circuit comprises an inverter and an inverter switching tube which are electrically connected; the system is characterized in that the Boost booster circuit is connected with a Boost control system, the voltage detection module is connected with a positive and negative sequence separation phase locking module based on an SOGI, the DC/AC inverter circuit is connected with a current control module, and the current detection module is connected with a coordinate transformation module; the method comprises the following steps:
s1, introducing a voltage U based on the maximum power point before faultmaxThe bus voltage of feedforward controls the outer loop PI, changes the voltage control mode of the Boost circuit part, and stabilizes the DC bus voltage UdcAs a control target;
s2, when a three-phase asymmetric fault occurs, processing the voltage value acquired by the voltage detection module through the SOGI-based positive and negative sequence separation phase locking module to obtain an active positive sequence component
Figure FDA0002511929250000013
Positive reactive sequence component
Figure FDA0002511929250000014
Positive and negative sequence component
Figure FDA0002511929250000019
And a reactive negative sequence component
Figure FDA0002511929250000015
S3, when a three-phase asymmetric fault occurs, coordinate transformation is carried out on the current value acquired by the current acquisition module through the coordinate transformation module to acquire a current active component idAnd a reactive component of current iq；
S4, inputting the active positive sequence component obtained in the step S2 into a current control module
Figure FDA0002511929250000016
Positive reactive sequence component
Figure FDA00025119292500000110
Positive and negative sequence component
Figure FDA0002511929250000018
Negative reactive sequence component
Figure FDA0002511929250000017
And the current active component i obtained in step S3dCurrent reactive component iqThe pulse signal for controlling the switching tube of the inverter is output to control the inverter, so that low voltage ride through is realized;
in step S1, the voltage control outer loop PI is set to the dc bus voltage UdcOutputting positive control quantity to raise output voltage U of photovoltaic array during risingpcAt a DC bus voltage UdcOutputting negative control quantity to reduce output voltage U of photovoltaic array when voltage is reducedpc；
In step S2, the processing steps of the SOGI-based positive-negative sequence separation phase-locking module on the three-phase asymmetric voltage are as follows:
s21, obtaining the three-phase asymmetric voltage according to a symmetric component method:
Figure FDA0002511929250000011
Figure FDA0002511929250000012
in the formulae (1) and (2), q is a 90 DEG phase lag factor, eαβαβ is the grid voltage in the stationary frame,
Figure FDA0002511929250000025
is the positive sequence component of the grid voltage,
Figure FDA0002511929250000026
is the negative sequence component of the grid voltage;
s22. the transfer function of the sogi is:
Figure FDA0002511929250000021
Figure FDA0002511929250000022
in the equations (3) and (4), v is the input sinusoidal signal, ω' is the filter center frequency, k is the damping coefficient, often taken as
Figure FDA0002511929250000027
When the center frequency of the SOGI is the same as the frequency of the input signal, then the output signals v 'and v have the same amplitude and phase, qv' and v are the same amplitude, but the phase lags by 90 °;
the processing steps of the coordinate transformation module to the three-phase asymmetric current in the step S3 are as follows:
s31, an alternating current side mathematical model of the photovoltaic inverter can be established according to a symmetric component method:
Figure FDA0002511929250000023
in the formula (5), ed P、eq P、ed N、eq NRespectively an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the voltage of the power grid; u. ofd P、uq P、ud N、uq NRespectively outputting an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of voltage for the inverter; i.e. id P、iq P、id N、id NRespectively an active positive sequence component, a reactive positive sequence component, an active negative sequence component and a reactive negative sequence component of the current; r is a load resistor, and L is a filter inductor;
s32. define K ═ Ud_fault P/UNWherein, Ud_fault PIs a fault-time positive sequence voltage, UNThe grid connection point rated voltage is obtained, and K is the voltage drop depth;
s33, under the premise of no overcurrent, outputting the maximum reactive current:
id_fault *＝imax-iR(t-t1)(id_fault *≥Kimax) (6)
Figure FDA0002511929250000024
in the formula iRGiven values, typically 8000, imax＝IN，INRated current for grid-connected point, iq_fault *For the reactive current at a given current command id _ fault, id_fault *Is the active current at a given current command id _ fault;
in step S4, the current control module includes a first control loop PI1, a second control loop PI2, and an SVPWM module, and the first control loop PI1 and the second control loop PI2 are electrically connected to the SVPWM module respectively;
in step S4, the step of controlling the inverter by the current control module includes:
s41, according to the reactive current i calculated in the step S33q_fault *And an active current id_fault *Calculating active current modulation signals
Figure FDA0002511929250000033
Figure FDA0002511929250000031
In the formula (8), KP1、KI1Proportional and integral coefficients, respectively, of the first control loop PI 1;
s42, calculating according to a formula (9) to obtain a reactive current modulation signal
Figure FDA0002511929250000034
Figure FDA0002511929250000032
In the formula (9), KP2、KI2Proportional and integral coefficients, respectively, of the second control loop PI 2;
s43, the active current modulation signal obtained by the calculation in the step S41 is used
Figure FDA0002511929250000035
Reactive current modulation signal calculated in step S42
Figure FDA0002511929250000036
And sending the signal into an SVPWM module for operation to obtain a switching tube control signal of the DC/AC inverter circuit.
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