CN113036810A - Phase-locked control method and device for zero voltage ride through of photovoltaic grid-connected inverter - Google Patents

Phase-locked control method and device for zero voltage ride through of photovoltaic grid-connected inverter Download PDF

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CN113036810A
CN113036810A CN202110466724.5A CN202110466724A CN113036810A CN 113036810 A CN113036810 A CN 113036810A CN 202110466724 A CN202110466724 A CN 202110466724A CN 113036810 A CN113036810 A CN 113036810A
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voltage
phase
angular frequency
grid
power grid
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CN113036810B (en
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袁锦华
叶玉霆
曹圆林
李进贤
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Qinghai Weihang Beichuang New Energy Technology 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The invention discloses a phase-locked control method and a phase-locked control device for zero voltage ride through of a photovoltaic grid-connected inverter. When the positive sequence voltage amplitude is lower than 0.9 times of rated voltage, starting to latch the power grid angular frequency value of the previous phase-locked loop operation period, and when the positive sequence voltage amplitude is lower than 0.1 times of rated voltage, executing a zero-voltage phase-locking control process, and performing phase-locking control by taking the latched reference angular frequency value as a zero-voltage reference angular frequency signal; when the positive sequence voltage amplitude is lower than 0.1 time of rated voltage, the latched power grid angular frequency value is used as a reference value of an integral term of a phase-locked loop PI regulator, and after the positive sequence voltage amplitude is higher than 0.1 time of rated voltage, the phase-locked loop PI calculation is enabled, the output current impact of an inverter in the transient recovery process of a power grid is restrained, and the continuity of the angular frequency before and after zero voltage faults is ensured.

Description

Phase-locked control method and device for zero voltage ride through of photovoltaic grid-connected inverter
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a phase-locked control method and device for zero voltage ride through of a photovoltaic grid-connected inverter.
Background
The voltage transient drop caused by the grid fault is one of common faults of an electric power system, the national standard GB/T19964-2012 'technical Specification for connecting a photovoltaic power station to a grid' specifies that a photovoltaic grid-connected power station has certain fault voltage ride-through capability, namely, the photovoltaic power generation system is required to have the capability of continuously maintaining operation without leaving from the grid under the condition that the terminal voltage is reduced to a certain value, and the repeated grid-connected times of the power generation system during the fault are greatly reduced by avoiding the protection action time, so that the impact on the grid is reduced.
According to the national standard GB/T19964 and 2012' technical Specification for connecting photovoltaic power stations to power grids, the low voltage ride through requirements which should be met by the photovoltaic power stations include: when the voltage of a grid-connected point of the photovoltaic power station drops to 0, the photovoltaic power station can continuously run for 0.15s without disconnecting from the grid; when the voltage of the grid-connected point of the photovoltaic power station drops below the curve 1, the photovoltaic power station can be cut out from the power grid. With the continuous improvement of the permeability of new energy photovoltaic power generation, zero voltage ride through is taken as a key grid-connected technology and a difficult technology, and becomes a problem to be solved urgently by a photovoltaic power station. Different from conventional low voltage ride through, when the voltage of a power grid drops to zero, the conventional inverter phase-locked loop control cannot obtain a phase angle controlled by the output current of the inverter due to the loss of a reference voltage signal, so that the output current is easy to be disordered, and the off-grid phenomenon is easy to occur.
The invention discloses a zero voltage ride-through phase-locked control method of a photovoltaic grid-connected inverter in the prior art, which is a Chinese invention patent with the patent application number of 201510336191.3. Through simple processing of phase-locked loop PI integral, the phase of the output current of the inverter is continuous before and after zero voltage fault, current disorder and impact caused by loss of reference voltage are avoided, the method is simple and effective, and the requirement of the standard on zero voltage ride through of the inverter can be met; when the positive sequence component of the power grid voltage is detected to be lower than 10%, the zero voltage phase locking processing flow is started, the PI integral of a phase locking loop is stopped, and the synchronous angular frequency is fixed, namely, the power grid angular frequency which enters a previous calculation period of 10% voltage point is kept to perform current control during zero voltage ride through, but the fixed power grid angular frequency value is calculated in the transient process of the rapid drop of the power grid voltage, the transient drop time is short, the deep drop moment is turbulent in voltage waveform, and the phase locking error is large; in the process of restoring the voltage of the power grid, due to the discontinuity between the fixed angular frequency and the calculated angular frequency at the moment of restoring the power grid, the problems of larger current impact and even grid disconnection are easily caused.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a phase-locked control method for zero voltage ride through of a photovoltaic grid-connected inverter, which can ensure the continuity of the output current phase of the inverter before and after zero voltage fault and is suitable for single-stage or multi-stage grid-connected photovoltaic inverters with different power levels.
In order to realize the purpose of the invention, the invention adopts the following technical scheme:
a phase-locked control method for zero voltage ride through of a photovoltaic grid-connected inverter comprises the following steps:
s0: sampling three-phase power grid voltage value ua，ub，uc；
S1: respectively obtaining positive sequence voltage components under two-phase static coordinates and two-phase synchronous rotating coordinates through a positive and negative sequence separation algorithm
Figure BDA0003042941680000021
S2: calculating the positive sequence voltage u of the power grid+And the value is used as the judgment basis for whether the power grid voltage drops and zero voltage drop;
s3: positive sequence voltage u+The amplitude is more than or equal to 90 percent uNJudging conditions;
s4: if u+≥90％uNIf the condition is satisfied, the voltage range is normal, the latch unit continuously reads the current grid angular frequency value and stores the current grid angular frequency value in the variable omega1Performing the following steps; if the voltage of the power grid drops, when u is detected+＜90％uNOtherwise, the process S4 is not executed, and the grid angular frequency value (within the normal voltage range) corresponding to the previous latch cycle of the latch unit is stored in the variable ω1And at a positive sequence voltage u+Amplitude < (R) >90％uNUnder the condition of variable ω1The value remains unchanged;
s5: positive sequence voltage u+The amplitude is more than or equal to 10 percent uNCondition judgment, uNIs the rated grid voltage;
s6: if u+≥10％uNThe condition is satisfied, and the q-axis component of the positive sequence voltage of the power grid
Figure BDA0003042941680000031
As phase locked loop PI regulator input signal e (k);
s7: calculating by a phase-locked loop PI regulator, and outputting a calculated value of the angular frequency of the power grid;
s8: positive sequence voltage u+Amplitude of less than 10% uNWhen the conditions are met, executing a zero voltage ride through control process, and reading the power grid angular frequency value omega latched by the process S41A reference angular frequency signal as a zero voltage interval;
s9: will refer to angular frequency omega1As a reference value for the phase-locked loop PI regulator integral variable in process S7;
s10: an angular frequency integration step according to u in the process S5+≥10％uNAnd (4) judging the condition, selecting the PI operation angular frequency of the S7 process or the reference angular frequency signal of the branch of the S8 process, integrating and outputting a phase angle theta.
S11: and the periodic value of the phase angle theta is 2 pi, so that the phase-locked control on the voltage of the power grid is completed.
Preferably, the process of performing the phase locking control of the grid voltage by the phase angle θ in step S11 is,
using phase angle theta in vector control of grid-connected inverter, three-phase inverter module outputs current ia,ib,icThree-phase mains voltage ua，ub，ucAfter coordinate transformation, respectively obtaining current components i under a two-phase dq synchronous rotating coordinate systemd,iqAnd a voltage component vd,vqWherein i isd,iqAs feedback signals for active and reactive current control, vd，vqA feedforward voltage as a vector control dq axis;
Figure BDA0003042941680000041
active and reactive current commands;
Figure BDA0003042941680000042
for control commands of the DC bus voltage of the inverter, omega0For the initial power frequency angular frequency, L is the total filter inductance value (L) of the inverter1+L2)，
Figure BDA0003042941680000043
As a voltage command of SVPWM, output Sa,Sb,ScThe switching signals are switching signals of a power switching tube of the three-phase inverter.
Preferably, the operation process of the PI regulator in step S7 is: ω (k) ═ kPe(k)+uI(k)；
Wherein the integral term: u. ofI(k)＝uI(k-1)+kITse(k)kPFor proportional control parameters, kIFor integrating the control parameter, TsThe operation period is controlled by the phase lock.
Preferably, the angular frequency integration process is θ ═ u (k) ═ u (k-1) + Tsω (k) and set ω0The phase locking speed is accelerated for the initial power frequency angular frequency.
Preferably, a phase-lock control device using the phase-lock control method includes:
switch control unit, connecting switch k1For controlling whether to latch the q-axis component of the positive sequence voltage from the current grid
Figure BDA0003042941680000044
The angular frequency omega is obtained through a PI regulator;
a latch unit for latching the q-axis component of the current grid positive sequence voltage
Figure BDA0003042941680000045
The angular frequency omega obtained by the PI regulator is locked in omega1Performing the following steps;
switching control unit, connecting switch k2For switching between channel one and channel two, using the positive sequence voltage q-axis component of the network when switching to channel one
Figure BDA0003042941680000046
Obtaining angular frequency omega as reference angular frequency through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta; power grid angular frequency value omega latched by latch unit when switching to channel two1And the reference angular frequency is used, and integral operation is carried out, so that a power grid voltage phase angle theta is obtained.
Preferably, the specific control method of the phase-locked control device is as follows:
1) positive sequence voltage u+The amplitude is more than or equal to 90 percent uNNormal voltage range, control switch k1Closing, continuously reading the current grid angular frequency value by the latch unit, and switching the switch k2Grid positive sequence voltage q-axis component connected to channel one
Figure BDA0003042941680000051
Obtaining angular frequency omega through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta;
2)10％uNless than or equal to positive sequence voltage u+Amplitude of less than 90% uNLow voltage range, control switch k1When the power grid is disconnected, the latch unit latches the power grid angular frequency value of the previous phase-locked loop operation period and stores the power grid angular frequency value in the variable omega1And at a positive sequence voltage u+Amplitude of less than 90% uNHolding the latched angular frequency signal omega under conditions1And (4) fixing. Change-over switch k2Keeping at channel one, and adopting the q-axis component of the positive sequence voltage of the power grid
Figure BDA0003042941680000052
Obtaining angular frequency omega through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta;
3)0％uNless than or equal to positive sequence voltage u+Amplitude of less than 10% uNZero voltage range, control switch k1Keep off state, switch k is switched2HandoverTo a channel II, a power grid angular frequency value omega latched by a latch unit1And performing integral operation as a reference angular frequency to obtain a power grid voltage phase angle theta in a zero voltage range.
Compared with the prior art, the invention has the following beneficial effects:
1) the method can ensure that the photovoltaic grid-connected inverter can stably realize zero voltage ride through, and improve the stability of power grid operation. The invention latches the normal power grid angular frequency before the power grid voltage drops as the reference angular frequency of the zero voltage interval and performs phase-locked control, thereby providing continuous phase for the output current of the inverter. The problem that when the voltage of a power grid drops to zero, the inverter phase-locked control loses the reference voltage and current output is easy to be disordered is solved.
2) The invention adopts the angular frequency signal before the grid voltage drop as the zero voltage reference angular frequency, can provide continuous phase for the output current of the inverter, and avoids the problems that the phase angle before the zero voltage is directly adopted as the reference angular frequency to carry out phase-locked control, and the transient state drop time of the grid voltage is very short, the voltage waveform is disordered at the moment of deep drop, the phase-locked error is large, and the output current is easy to cause impact.
3) When the positive sequence voltage amplitude is lower than 0.1 time of rated voltage, the latched reference angle frequency value is used as the reference value of the integral term of the phase-locked loop PI regulator, so that the output current impact of the inverter in the transient recovery process of a power grid can be restrained, and the continuity of the angular frequency before and after zero voltage fault is ensured.
Drawings
FIG. 1 is a flow chart of a phase-locked control method for zero voltage ride through of a photovoltaic grid-connected inverter according to the invention;
FIG. 2 is a structural diagram of a phase-locked control device for zero voltage ride through of a photovoltaic grid-connected inverter according to the present invention;
FIG. 3 is a grid-connected inverter vector control block diagram of a phase-locked control method for zero voltage ride through of a photovoltaic grid-connected inverter according to the present invention;
fig. 4 is a topological structure diagram of a main circuit of the photovoltaic grid-connected inverter adopted in the phase-locked control method for zero voltage ride through of the photovoltaic grid-connected inverter according to the invention.
Detailed Description
The drawings in the embodiments of the invention will be combined; the technical scheme in the embodiment of the invention is clearly and completely described as follows:
as shown in fig. 1, in an embodiment of the present invention, a phase-locked control method for zero-voltage ride through of a photovoltaic grid-connected inverter includes the following steps:
s0: sampling three-phase power grid voltage value ua，ub，uc；
S1: respectively obtaining positive sequence voltage components under two-phase static coordinates and two-phase synchronous rotating coordinates through a positive and negative sequence separation algorithm
Figure BDA0003042941680000061
S2: calculating the positive sequence voltage u of the power grid+And the value is used as the judgment basis for whether the power grid voltage drops and zero voltage drop;
s3: positive sequence voltage u+The amplitude is more than or equal to 90 percent uNJudging conditions;
s4: if u+≥90％uNIf the condition is satisfied, the voltage range is normal, the latch unit continuously reads the current grid angular frequency value and stores the current grid angular frequency value in the variable omega1Performing the following steps; if the voltage of the power grid drops, when u is detected+＜90％uNOtherwise, the process S4 is not executed, and the grid angular frequency value (within the normal voltage range) corresponding to the previous latch cycle of the latch unit is stored in the variable ω1And at a positive sequence voltage u+Amplitude of less than 90% uNUnder the condition of variable ω1The value remains unchanged;
s5: positive sequence voltage u+The amplitude is more than or equal to 10 percent uNCondition judgment, uNIs the rated grid voltage;
s6: if u+≥10％uNThe condition is satisfied, and the q-axis component of the positive sequence voltage of the power grid
Figure BDA0003042941680000071
As locksPhase loop PI regulator input signal e (k);
s7: calculating by a phase-locked loop PI regulator, and outputting a calculated value of the angular frequency of the power grid;
s8: positive sequence voltage u+Amplitude of less than 10% uNAnd because the voltage amplitude is low, the sampling precision is insufficient, and the phase-locked error is large. The invention judges u+＜10％uNWhen the conditions are met, executing a zero voltage ride through control process, and reading the power grid angular frequency value omega latched by the process S41A reference angular frequency signal as a zero voltage interval;
s9: will refer to angular frequency omega1The main effect of the reference value as the integral variable of the phase-locked loop PI regulator in the process S7 is that u is recovered when the grid voltage is restored+≥10％uNAfter the condition is satisfied, the angular frequency of the phase-locking power grid is switched from the latched reference angular frequency value to the output signal of the PI regulator, so that the reference angular frequency omega is switched in a zero-voltage interval1As the reference value of the integral variable of the phase-locked loop PI regulator in the process S7, the continuity of the angular frequency before and after the zero-voltage fault can be ensured, so that the continuity of the output current phase of the inverter is ensured, and the inverter can smoothly realize zero-voltage ride through.
S10: an angular frequency integration step according to u in the process S5+≥10％uNAnd (4) judging the condition, selecting the PI operation angular frequency of the S7 process or the reference angular frequency signal of the branch of the S8 process, integrating and outputting a phase angle theta.
S11: and the periodic value of the phase angle theta is 2 pi, so that the phase-locked control on the voltage of the power grid is completed.
Specifically, the operation process of the PI regulator in step S7 is as follows: ω (k) ═ kPe(k)+uI(k)；
Wherein the integral term: u. ofI(k)＝uI(k-1)+kITse(k)；kPFor proportional control parameters, kIFor integrating the control parameter, TsThe operation period is controlled by the phase lock.
Specifically, the angular frequency integration process is θ ═ u (k) ═ u (k-1) + Tsω (k) and set ω0The phase locking speed is accelerated for the initial power frequency angular frequency.
As shown in fig. 2, a phase-locked control device for zero voltage ride through of a photovoltaic grid-connected inverter includes:
switch control unit 1, connecting switch k1For controlling whether to latch the q-axis component of the positive sequence voltage from the current grid
Figure BDA0003042941680000081
The angular frequency omega is obtained through a PI regulator;
a latch unit 2 for latching the q-axis component of the current grid positive sequence voltage
Figure BDA0003042941680000082
The angular frequency omega obtained by the PI regulator is locked in omega1Performing the following steps;
switching control unit 3, connecting switch k2For switching between channel one and channel two, using the positive sequence voltage q-axis component of the network when switching to channel one
Figure BDA0003042941680000083
Obtaining angular frequency omega as reference angular frequency through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta; power grid angular frequency value omega latched by latch unit when switching to channel two1And the reference angular frequency is used, and integral operation is carried out, so that a power grid voltage phase angle theta is obtained.
As shown in fig. 2, the specific control logic is:
1) switch control unit 1 controls switch k1The action logic is as follows: when the positive sequence voltage u of the power grid+The amplitude is more than or equal to 90 percent uN，k1Switch closed, positive sequence voltage u of the grid+Amplitude of less than 90% uN，k1The switch is turned off;
2) switching control unit 2 controls switch k2The action logic is as follows: when the positive sequence voltage u of the power grid+The amplitude is more than or equal to 10 percent uN，k2The switch is switched to the channel I when the positive sequence voltage u of the power grid+Amplitude of less than 10% uN，k2The switch is switched to channel two.
With reference to the phase-lock control method shown in fig. 1, the specific control method of the phase-lock control device is as follows:
1) positive sequence voltage u+The amplitude is more than or equal to 90 percent uNNormal voltage range, control switch k1When the circuit is closed, the latch unit 2 continuously reads the current power grid angular frequency value and switches the switch k2Grid positive sequence voltage q-axis component connected to channel one
Figure BDA0003042941680000091
Obtaining angular frequency omega through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta;
2)10％uNless than or equal to positive sequence voltage u+Amplitude of less than 90% uNLow voltage range, control switch k1When the power grid is disconnected, the latch unit 2 latches the power grid angular frequency value of the previous phase-locked loop operation period and stores the power grid angular frequency value in the variable omega1And at a positive sequence voltage u+Amplitude of less than 90% uNHolding the latched angular frequency signal omega under conditions1And (4) fixing. Change-over switch k2Keeping at channel one, and adopting the q-axis component of the positive sequence voltage of the power grid
Figure BDA0003042941680000092
Obtaining angular frequency omega through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta;
3)0％uNless than or equal to positive sequence voltage u+Amplitude of less than 10% uNZero voltage range, control switch k1Keep off state, switch k is switched2Switching to a second channel, and adopting the power grid angular frequency value omega latched by the latch unit 21And performing integral operation as a reference angular frequency to obtain a power grid voltage phase angle theta in a zero voltage range.
In specific implementation, the obtained grid voltage phase angle θ is used in the grid-connected inverter vector control shown in fig. 3, and the main circuit topology of the grid-connected inverter is shown in fig. 4, wherein udcIs a DC bus voltage udcFor a direct input current, C1Supporting capacitors for DC buses, V1～V6For 6 IGBT work of inverter bridgeRate switching tube, L1Is a filter inductor at the side of the inverter module, L2Is a network side filter inductor, CfAC is a filter capacitor, ia,ib,icFor the output current of the three-phase inverter module ua,ub,ucFor three-phase mains voltage, ea,eb,ecIs three-phase grid electromotive force. Three-phase inverter module output current ia,ib,icThree-phase mains voltage ua,ub,ucAfter coordinate transformation, respectively obtaining current components i under a two-phase dq synchronous rotating coordinate systemd,iqAnd a voltage component vd,vq；
Wherein id,iqAs feedback signals for active and reactive current control, vd，vqA feedforward voltage as a vector control dq axis;
Figure BDA0003042941680000101
active and reactive current commands;
Figure BDA0003042941680000102
for control commands of the DC bus voltage of the inverter, omega0For the initial power frequency angular frequency, L is the total filter inductance value (L) of the inverter1+L2)，
Figure BDA0003042941680000103
As a voltage command of SVPWM, output Sa,Sb,ScThe switching signals are switching signals of a power switching tube of the three-phase inverter.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical scope of the present invention by equivalent replacement or change according to the technical solution and the modified concept of the present invention within the technical scope of the present invention.

Claims (6)

1. A phase-locked control method for zero voltage ride through of a photovoltaic grid-connected inverter is characterized by comprising the following steps: the method comprises the following steps:
s0: sampling three-phase power grid voltage value ua，ub，uc；
S1: respectively obtaining positive sequence voltage components under two-phase static coordinates and two-phase synchronous rotating coordinates through a positive and negative sequence separation algorithm
Figure FDA0003042941670000011
S2: calculating the positive sequence voltage u of the power grid+And the value is used as the judgment basis for whether the power grid voltage drops and zero voltage drop;
s3: positive sequence voltage u+The amplitude is more than or equal to 90 percent uNJudging conditions;
s4: if u+≥90％uNIf the condition is satisfied, the voltage range is normal, the latch unit continuously reads the current grid angular frequency value and stores the current grid angular frequency value in the variable omega1Performing the following steps; if the voltage of the power grid drops, when u is detected+＜90％uNOtherwise, the process S4 is not executed, which is equivalent to the latch unit latching the grid angular frequency value of the previous phase-locked loop operation cycle, and storing the grid angular frequency value in the variable ω1And at a positive sequence voltage u+Amplitude of less than 90% uNUnder the condition of variable ω1The value remains unchanged;
s5: positive sequence voltage u+The amplitude is more than or equal to 10 percent uNCondition judgment, uNIs the rated grid voltage;
s6: if u+≥10％uNThe condition is satisfied, and the q-axis component of the positive sequence voltage of the power grid
Figure FDA0003042941670000012
As phase locked loop PI regulator input signal e (k);
s7: calculating by a phase-locked loop PI regulator, and outputting a calculated value of the angular frequency of the power grid;
s8: positive sequence voltage u+Amplitude of less than 10% uNWhen the conditions are met, executing a zero voltage ride through control process, and reading the power grid angular frequency value omega latched by the process S41A reference angular frequency signal as a zero voltage interval;
s9: will refer to angular frequency omega1As a reference value for the phase-locked loop PI regulator integral variable in process S7;
s10: an angular frequency integration step according to u in the process S5+≥10％uNAnd (4) judging the condition, selecting the PI operation angular frequency of the S7 process or the reference angular frequency signal of the branch of the S8 process, integrating and outputting a phase angle theta.
S11: and the periodic value of the phase angle theta is 2 pi, so that the phase-locked control on the voltage of the power grid is completed.
2. The phase-locked control method for zero voltage ride through of the photovoltaic grid-connected inverter according to claim 1, characterized in that:
the process of performing the phase lock control of the grid voltage by the phase angle theta in step S11 is,
using phase angle theta in vector control of grid-connected inverter, three-phase inverter module outputs current ia,ib,icThree-phase mains voltage ua，ub，ucAfter coordinate transformation, respectively obtaining current components i under a two-phase dq synchronous rotating coordinate systemd,iqAnd a voltage component vd,vqWherein i isd,iqAs feedback signals for active and reactive current control, vd，vqA feedforward voltage as a vector control dq axis;
Figure FDA0003042941670000021
active and reactive current commands;
Figure FDA0003042941670000022
for control commands of the DC bus voltage of the inverter, omega0For the initial power frequency angular frequency, L is the total filter inductance value (L) of the inverter1+L2)，
Figure FDA0003042941670000023
As a voltage command of SVPWM, output Sa,Sb,ScIs a three-phase inverterAnd switching signals of the power switching tube.
3. The phase-locked control method for zero voltage ride through of the photovoltaic grid-connected inverter according to claim 1, characterized in that:
the operation process of the PI regulator in step S7 is as follows: ω (k) ═ kPe(k)+uI(k)；
Wherein the integral term: u. ofI(k)＝uI(k-1)+kITse(k)；kPFor proportional control parameters, kIFor integrating the control parameter, TsThe operation period is controlled by the phase lock.
4. The phase-locked control method for zero voltage ride through of the photovoltaic grid-connected inverter according to claim 1, characterized in that:
the angular frequency integration process is theta ═ u (k) ═ u (k-1) + Tsω (k); and set omega0Is the initial power frequency angular frequency.
5. A control apparatus using the phase-lock control method according to any one of claims 1 to 4, characterized in that: the method comprises the following steps:
switch control unit, connecting switch k1For controlling whether to latch the q-axis component of the positive sequence voltage from the current grid
Figure FDA0003042941670000031
The angular frequency omega is obtained through a PI regulator;
a latch unit for latching the q-axis component of the current grid positive sequence voltage
Figure FDA0003042941670000032
The angular frequency omega obtained by the PI regulator is locked in omega1Performing the following steps;
switching control unit, connecting switch k2For switching between channel one and channel two, using the positive sequence voltage q-axis component of the network when switching to channel one
Figure FDA0003042941670000033
Obtaining angular frequency omega as reference angular frequency through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta; power grid angular frequency value omega latched by latch unit when switching to channel two1And the reference angular frequency is used, and integral operation is carried out, so that a power grid voltage phase angle theta is obtained.
6. The phase-lock control method of the control device according to claim 5, characterized in that: the method comprises the following steps:
1) positive sequence voltage u+The amplitude is more than or equal to 90 percent uNNormal voltage range, control switch k1Closing, continuously reading the current grid angular frequency value by the latch unit, and switching the switch k2Grid positive sequence voltage q-axis component connected to channel one
Figure FDA0003042941670000034
Obtaining angular frequency omega through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta;
2)10％uNless than or equal to positive sequence voltage u+Amplitude of less than 90% uNLow voltage range, control switch k1When the power grid is disconnected, the latch unit latches the power grid angular frequency value of the previous phase-locked loop operation period and stores the power grid angular frequency value in the variable omega1And at a positive sequence voltage u+Amplitude of less than 90% uNHolding the latched angular frequency signal omega under conditions1And (4) fixing. Change-over switch k2Keeping at channel one, and adopting the q-axis component of the positive sequence voltage of the power grid
Figure FDA0003042941670000041
Obtaining angular frequency omega through a PI regulator, and performing integral operation to obtain a power grid voltage phase angle theta;
3)0％uNless than or equal to positive sequence voltage u+Amplitude of less than 10% uNZero voltage range, control switch k1Keep off state, switch k is switched2Switching to a second channel, and adopting the power grid angular frequency value omega latched by the latch unit1And performing integral operation as a reference angular frequency to obtain a power grid voltage phase angle theta in a zero voltage range.
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