CN110676874A - Direct-drive fan subsynchronous oscillation electrical quantity analysis method considering frequency coupling effect - Google Patents

Direct-drive fan subsynchronous oscillation electrical quantity analysis method considering frequency coupling effect Download PDF

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CN110676874A
CN110676874A CN201910955662.7A CN201910955662A CN110676874A CN 110676874 A CN110676874 A CN 110676874A CN 201910955662 A CN201910955662 A CN 201910955662A CN 110676874 A CN110676874 A CN 110676874A
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direct
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drive fan
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CN110676874B (en
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舒进
袁赛军
都劲松
杨俊�
牛坤
蒋昊
马晋辉
蒋成文
燕振元
乔越
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Xian Thermal Power Research Institute Co Ltd
Huaneng Group Technology Innovation Center Co Ltd
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Huaneng Group Technology Innovation Center Co Ltd
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Abstract

The invention discloses a direct-drive fan subsynchronous oscillation electrical quantity analysis method considering frequency coupling effect, which comprises the steps of firstly, inputting parameters of a direct-drive fan to be analyzed, and establishing a simplified model of the direct-drive fan; secondly, establishing an external impedance analytical model of the direct-drive fan based on a harmonic linearization method, wherein the establishing process mainly accounts for the frequency coupling effect of the output harmonic current of the direct-drive fan under the single-frequency harmonic voltage disturbance; then, applying single frequency f to the direct-drive fan grid-connected pointpDisturbing harmonic voltage, calculating f in output currentpAnd 2f1‑fpHarmonic components, which give an analytical expression of the frequency coupling relation of the output current, and comprehensively analyze the subsynchronous oscillation response characteristic of the direct-drive fan; the invention discloses a subsynchronous oscillation electrical quantity coupling response mechanism of the direct-drive fan under harmonic voltage disturbance quantitatively, and the quantitative relation among the subsynchronous oscillation electrical quantity coupling response mechanism, the subsynchronous oscillation electrical quantity coupling response mechanism and the direct-drive fan can be given only by inputting parameters of the direct-drive fan.

Description

Direct-drive fan subsynchronous oscillation electrical quantity analysis method considering frequency coupling effect
Technical Field
The invention belongs to the field of power systems, relates to the field of stability analysis of direct-drive fans, and particularly relates to a direct-drive fan subsynchronous oscillation electrical quantity analysis method considering a frequency coupling effect.
Background
The proportion of new energy electric energy access systems is gradually increased, and new challenges are brought to the safe and stable operation of the power system, wherein the new challenges include stability problems such as subsynchronous oscillation and the like. Meanwhile, the specific gravity of the direct-drive wind turbine generator in the fan type is also improved year by year, and the direct-drive wind turbine generator brings a brand-new subsynchronous oscillation challenge after being connected to a power grid. On the premise that the back-to-back double PWM converters isolate the machine network side and do not carry out series compensation and external transmission, subsynchronous oscillation still occurs after the direct-drive wind turbine generator is connected into the system. The novel subsynchronous oscillation is obviously different from subsynchronous oscillation of a traditional thermal power steam turbine unit and a double-fed wind turbine unit in the aspects of mechanism and suppression measures. With the construction of large-scale wind power bases in China, the modeling, analysis and suppression measures of subsynchronous oscillation induced by direct-drive wind power integration become problems to be solved urgently. The method for researching the subsynchronous oscillation problem of the grid connection of the direct-drive wind turbine generator has important significance for determining and perfecting the subsynchronous oscillation mechanism of the fan, making a corresponding inhibition strategy, improving the grid connection performance of the direct-drive fan and ensuring the safety and stability of a power system.
The impedance method is an analysis method for researching the grid-connected stability of the direct-drive fan, which is emerging in recent years, and is based on a small signal disturbance method, impedance models of the direct-drive fan and an alternating current power grid are respectively established, and the stability of the grid-connected direct-drive fan is judged by utilizing a Nyquist stability criterion.
Disclosure of Invention
In order to solve the problem of the sub-synchronous oscillation of the grid-connected direct-drive wind field, the invention aims to provide a method for analyzing the sub-synchronous oscillation electrical quantity of a direct-drive fan considering the frequency coupling effect.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a direct-drive fan subsynchronous oscillation electrical quantity analysis method considering frequency coupling effect is characterized by comprising the following steps: establishing a direct-drive fan small-signal impedance analytical model considering a frequency coupling effect, and giving a frequency coupling quantitative relation of output harmonic current of the direct-drive fan under single-frequency harmonic voltage disturbance; the method is characterized in that: the method comprises the following steps:
step 1: inputting direct-drive fan parameters
The following parameters of the direct drive fan are obtained: fan grid-connected voltage V1The current output power frequency current I of the fan1Angle of power factor
Figure BDA0002227204610000021
Phase-locked loop PI parameter Kp，KiCurrent inner loop PI parameter Kpi，KiiThe filter inductor L at the outlet of the inverter;
step 2: establishing simplified model of direct-drive fan
According to the structure of the direct-drive fan and the time scale characteristics of a control link, simplifying the direct-drive fan into a grid-connected inverter model: the wind turbine, the generator and the machine side converter are replaced by a direct current voltage source; power outer loop control of the grid-side converter is omitted; parameters required by the simplified model are obtained in the step 1;
and step 3: establishing external impedance analytical model of direct-drive fan
The method is characterized in that a direct-drive fan external impedance analytical model is established based on a harmonic linearization method, and the establishment process mainly accounts for the frequency coupling effect of the output harmonic current of the direct-drive fan under the single-frequency harmonic voltage disturbance:
practical simulation shows that omega exists when the voltage of the power grid side existspWhen harmonic wave exists, the output current of the inverter can simultaneously exist omegapAnd 2 omega1-ωpThe harmonic current of the frequency, the inverter output current time domain expression is as follows:
Figure BDA0002227204610000022
in the formula ia(t) is instantaneous value of phase current A, I1、Ip、Ip2The amplitude of the power frequency current, the amplitude of the output current with the same frequency as the disturbance voltage and the amplitude of the complementary frequency output current are respectively; omega1、ωp、2ω1-ωpThe angular frequency of the power frequency current, the angular frequency which is the same as the disturbance voltage in frequency and the angular frequency of the output current with complementary frequency are respectively;
Figure BDA0002227204610000023
the initial phase of the power frequency current, the initial phase of the output current with the same frequency as the disturbance voltage and the initial phase of the complementary frequency output current are respectively;
similar to the definition of phasor in the circuit science, the frequency domain expressions of the output current with the same frequency as the disturbance voltage and the complementary frequency output current in the formula (3) are respectively as follows:
Figure BDA0002227204610000031
Ipis w at the same frequency as the disturbance voltagepA frequency output current frequency domain expression; i isp2Angular frequency 2w of output current being complementary frequency1-wpThe output current frequency domain expression of (1);
and taking the frequency coupling effect into account, and obtaining a frequency domain expression of the input A-phase reference voltage of the pulse width modulator of the converter as follows:
Figure BDA0002227204610000032
Figure BDA0002227204610000033
in the formula: varef[wp]And Varef[2w1-wp]Are respectively wpAnd 2w1-wpA phase a reference voltage frequency domain expression of frequency; wherein: s and j are the fundamental variables of complex operations in mathematics;
Figure BDA0002227204610000034
performing exponential operation; hi(s-jw1)＝Kpi+Kii/(s-jw1) Is the transfer function of the current inner loop PI regulator;
Figure BDA0002227204610000035
wherein
Figure BDA0002227204610000036
Is the transfer function of the phase locked loop;
Figure BDA0002227204610000037
is the frequency domain expression V of the positive sequence disturbance voltagepConjugation of (1);
the converter using an averaging model, i.e. the output voltage Vga[wp]Is equal to the reference voltage Varef[wp](ii) a Because only one filter inductor exists between the output voltage of the converter and the voltage of the grid-connected point, the three satisfy the following conditions:
sLIp＝Vga[wp]-Va[wp](12)
substituting formula (8) for formula (12) and connecting to external impedance Z of direct-drive fanp(s)＝-Vp/IpThe analytical expression of (a) is:
and 4, step 4: calculating the output current of the direct-drive fan under the single-frequency voltage disturbance
For wpAs can be seen from equation (13), the disturbance voltage at a frequency corresponds to an output current at the frequency:
Figure BDA0002227204610000041
in the formula: vpIs a frequency domain expression of positive sequence disturbance voltage, Zp(jwp) Is that the direct-drive fan is at an angular frequency w with the same frequency as the disturbance voltagepImpedance calculated according to the following equation (13), IpIs w at the same frequency as the disturbance voltagepA frequency output current frequency domain expression;
because the fan grid-connected point only contains wpVoltage of frequency, so angular frequency 2w of output current for complementary frequency1-wpSatisfies the following conditions:
Varef[2w1-wp]＝Vga[2w1-wp]＝j(2w1-wp)LIp2(15)
substituting formula (9) and eliminating V by formula (13)p(s), there can be obtained:
the above formula reveals a single frequency omegapUnder voltage disturbance, the inverter outputs omegapAnd 2 omega1-ωpA quantitative relationship of the coupled current components; i ispIs w at the same frequency as the disturbance voltagepA frequency output current frequency domain expression; i isp2Angular frequency 2w of output current being complementary frequency1-wpThe output current frequency domain expression of (1); when V ispAfter the determination, the output currents of the two coupling frequencies can be calculated according to the equations (14) and (16), respectively.
Compared with the prior art, the invention has the following advantages:
the invention discloses a direct-drive fan subsynchronous oscillation electrical quantity analysis method considering a frequency coupling effect. Firstly, inputting parameters of a direct-drive fan to be analyzed, and establishing a simplified model of the direct-drive fan; secondly, the direct-drive fan external impedance analytical model is established based on a harmonic linearization method, and the main innovation point of the direct-drive fan external impedance analytical model is that the frequency coupling effect of the output harmonic current of the direct-drive fan under the single-frequency harmonic voltage disturbance is considered; finally, based on the analysis expression of the output current frequency coupling relation, the subsynchronous oscillation response characteristic of the direct-drive fan is comprehensively analyzed, and a theoretical basis is provided for researching the subsynchronous oscillation and supersynchronous oscillation coupling relation of the direct-drive fan.
Drawings
FIG. 1 is a flow chart of the present patent.
Fig. 2 is a schematic diagram of a direct-drive fan grid-connected simplified topological structure.
Fig. 3 is a graph of output current relationship under harmonic voltage disturbance, wherein fig. 3a is a comparison of amplitude relationship and fig. 3b is a comparison of phase relationship.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
As shown in fig. 1, the invention discloses a method for analyzing subsynchronous oscillation electrical quantity of a direct-drive fan considering frequency coupling effect, which comprises the following steps:
step 1: inputting direct drive fan parameters
The following parameters of the direct-drive fan are obtained: fan grid-connected voltage V1The current output power frequency current I of the fan1Angle of power factor
Figure BDA0002227204610000051
Phase-locked loop PI parameter Kp，KiCurrent inner loop PI parameter Kpi，KiiAnd an inverter outlet filter inductor L.
Step 2: establishing simplified simulation model of direct-drive fan
The permanent magnet direct drive type fan stator side is generally connected to a power grid through a topology structure of back-to-back double PWM converters, so that the machine side is isolated from the grid side. The permanent magnet direct-drive fan injects large-capacity power into the power grid side, but the inertia of a power system is not remarkably improved, so that the problem of unstable unit operation is easily caused. When the secondary and super-synchronous oscillation of the direct-drive type fan is analyzed, if the simplified direct-drive wind power system is directly subjected to mathematical modeling, the complexity is high and is not necessary.
Therefore, by combining the above two points, a simplified model of the direct-drive blower suitable for the subsynchronous oscillation analysis is shown in fig. 2. v. ofa,vb,vcIs a grid connection point three-phase voltage ia,ib,icThe three-phase current output by the fan is a time domain expression. The phase-locked loop PLL provides a reference angle for coordinate changes so that control of the fan can be performed in the dq coordinate system. As can be seen from the figure, the simplified wind turbine topology only includes the grid-side inverter GSC and the current inner loop control in the dq coordinate system. Due to power decoupling, Idref,IqrefThe reference values of the active power and the reactive power can be respectively calculated. Actual output current i after coordinate transformationd,iqThe deviation from the reference value is compensated by a current controller (PI control) and current feedforward to obtain the reference value v of the output voltagedref,vqref. The latter is transformed into a voltage reference value under a three-phase static coordinate system through coordinate inverse transformation, and provides a modulation wave signal for the inverter PWM modulation technology.
And step 3: establishing external impedance analytical model of direct-drive fan
The voltage of a fan grid-connected point contains angular frequency omegapPositive sequence voltage of (d):
Figure BDA0002227204610000065
in the formula, va(t) is the A phase instantaneous voltage; v1Is the amplitude of the fundamental component, VpIs the amplitude of the disturbance component, ω1Is the angular frequency, omega, of the power frequency voltagepIs the disturbance voltage angular frequency;
Figure BDA0002227204610000061
is the initial phase of the perturbation voltage;
according to the definition of phasor in the circuit, the frequency domain expression of two voltages in equation (1) is: fundamental component V1＝V1Positive sequence disturbance voltage
Figure BDA0002227204610000062
Omega exists in park transformation due to frequency coupling effectpAnd 2 omega1-ωpError in frequency:
Figure BDA0002227204610000063
in the formula: cos θpll[wp]And cos θpll[2w1-wp]Is the phase-locked angle thetapllOmega in (1)pAnd 2 omega1-ωpA frequency component;
Figure BDA0002227204610000064
is the transfer function of the phase-locked loop, s and j are basic variables of complex operation in mathematics, Kp and Ki are proportional and integral constants of the phase-locked loop respectively,
Figure BDA0002227204610000071
is the frequency domain expression V of the positive sequence disturbance voltagepConjugation of (1).
Practical simulation shows that omega exists when the voltage of the power grid side existspWhen harmonic wave exists, the output current of the inverter can simultaneously exist omegapAnd 2 omega1-ωpThe harmonic current of the frequency, the inverter output current time domain expression is as follows:
Figure BDA0002227204610000072
in the formula ia(t) is instantaneous value of phase current A, I1、Ip、Ip2The amplitude of the power frequency current, the amplitude of the output current with the same frequency as the disturbance voltage and the amplitude of the complementary frequency output current are respectively; omega1、ωpThe angular frequency of the power frequency current and the angular frequency of the output current with the same frequency as the disturbance voltage are respectively;
Figure BDA0002227204610000073
the initial phase of the power frequency current, the initial phase of the output current with the same frequency as the disturbance voltage and the initial phase of the complementary frequency output current are respectively.
Similar to the definition of phasor in the circuit science, the frequency domain expressions of the output current with the same frequency as the disturbance voltage and the complementary frequency output current in the formula (3) are respectively as follows:
Figure BDA0002227204610000074
Ipis w at the same frequency as the disturbance voltagepA frequency output current frequency domain expression; i isp2Angular frequency (2 w) of output current being complementary frequency1-wp) Output current frequency domain expression of
And (3) convolving the equation (3) with the equation (2), and neglecting a quadratic small term to obtain a park transformed current dq axis frequency domain expression:
Figure BDA0002227204610000075
Id[wp-w1]and Iq[wp-w1]Respectively, the frequency of the dq-axis current is wp-w1Of the frequency component, Tp(jwp) Is Tp(s) wherein s is jwpThus, the compound was obtained.
According to a direct drive type fan current inner loop PI decoupling control strategy, a dq axis reference voltage expression is as follows:
Figure BDA0002227204610000081
in the formula: vdrefAnd VqrefReference voltages, H, for d-and q-axes, respectivelyi(s)＝Kpi+KiiIs the transfer function of the current inner loop PI regulator, KpiAnd KiiRespectively, the proportional and integral constants of the current inner loop regulator.
Considering that under a steady-state working point, the direct current component of the dq-axis current is equal to a reference value thereof; further, when formula (4) is substituted for formula (5), VdrefAnd VqrefAlso contains a frequency wp-w1The frequency component of (a). DC component sum wp-w1The expressions of the frequency components are shown in equations (6) and (7), respectively:
Figure BDA0002227204610000082
Figure BDA0002227204610000083
the three-phase voltage reference value is obtained by inverse coordinate transformation of a dq axis voltage reference value, and the frequency domain expression of the input A-phase reference voltage of the converter pulse width modulator obtained by convolution is as follows:
Figure BDA0002227204610000084
Figure BDA0002227204610000085
in the formula: varef[wp]And Varef[2w1-wp]Are respectively wpAnd 2w1-wpPhase a reference voltage frequency domain representation of frequency.
The PWM inverter adopts a simplified model, ignores the dynamic error of a switch, and can consider that the output voltage is equal to the reference voltage.
Figure BDA0002227204610000086
In the formula: vga[wp]And Vga[2w1-wp]Are respectively wpAnd 2w1-wpAnd the A phase of the frequency outputs a voltage frequency domain expression.
And the output voltage of an inverter of the direct-drive fan is connected with the PCC after passing through the filter inductor. The instantaneous value v of the output voltage of the inverter can be easily obtained according to the circuit lawga、vgb、vgcOutput current ia、ib、icAnd PCC point voltage va、vb、vcSatisfies the following conditions:
Figure BDA0002227204610000091
as shown in the formula (1), the PCC point voltage contains only the angular frequency wpAt a frequency wpThe frequency domain expression of equation (11) is as follows:
sLIp＝Vga[wp]-Va[wp](12)
equations (4), (8) and (10) are substituted into equation (12), and the direct-drive fan external impedance is defined as Zp(s)＝-Vp(s)/Ip(s), the expression of an external impedance analytical model of the grid-connected direct-drive type fan can be deduced as follows:
Figure BDA0002227204610000092
in the formula: hi(s-jw1)＝Kpi+Kii/(s-jw1) Is the aforementioned Hi(s) displacement transformation.
And 4, step 4: calculating the output current of the fan under the single-frequency voltage disturbance
For wpAs can be seen from equation (13), the disturbance voltage at a frequency corresponds to an output current at the frequency:
Figure BDA0002227204610000093
in the formula: vpIs a frequency domain expression of positive sequence disturbance voltage, Zp(jwp) Is the direct-drive fan at and disturbance voltageAngular frequency w of the same frequencypImpedance calculated according to the following equation (13), IpIs w at the same frequency as the disturbance voltagepAnd outputting a current frequency domain expression by frequency.
Because the fan grid-connected point only contains wpVoltage of frequency, so angular frequency 2w of output current for complementary frequency1-wpSatisfies the following conditions:
Varef[2w1-wp]＝Vga[2w1-wp]＝j(2w1-wp)LIp2(15)
in the formula Ip2Angular frequency 2w of output current being complementary frequency1-wpThe output current frequency domain expression of (1).
Substituting formula (9) and eliminating V by formula (13)p(s), there can be obtained:
Figure BDA0002227204610000101
Ip2angular frequency 2w of output current being complementary frequency1-wpThe output current frequency domain expression of (1).
It can be seen that the above formula reveals a single frequency ωpUnder voltage disturbance, the inverter outputs omegapAnd 2 omega1-ωpQuantitative relationship of the coupled current components. When the amplitude and the frequency of the disturbance voltage are determined, the output currents of the two coupling frequencies can be calculated according to the formula (14) and the formula (16), respectively.
Examples
In order to verify the correctness of the above formula, simulation verification is performed according to the following parameters: 50Hz fundamental voltage amplitude V1566V, perturbation voltage:
Figure BDA0002227204610000102
disturbance frequency: 20Hz, current inner loop PI parameter Kp＝0.25，Ki355; phase-locked loop control parameters: kp＝0.085，Ki32; current reference value Idref＝1847,Iqref0; outlet filter inductor of inverterThe parameter L is 0.15 e-3H.
The parameters are substituted into the formula (14), and the 20Hz output current with the same frequency as the disturbance voltage can be calculated as follows:
Ip＝45∠2.75 A (17)
the output current at a coupling frequency of 80Hz can be calculated from equation (16) as:
Ip2＝0.7754×45∠(3.063-2.75)＝35∠0.256 A (18)
the simulation result is shown in fig. 3, when 20Hz disturbance voltage exists at the fan grid-connected point, it can be seen that the output current of the fan grid-connected point also simultaneously has 20/80Hz harmonic component in addition to 50Hz power frequency component, and the amplitude and phase are respectively shown in fig. 3a and fig. 3 b. Note that the fundamental component amplitude in FIG. 3a is outside the vertical axis range, and the actual output current follows the d-axis current reference Idref(ii) a For clarity, the phases of the components of FIG. 3b other than 20/50/80Hz have been filtered out. It can be seen that the amplitude and phase of the 20/80Hz current are consistent with the calculation results of the equations (17) and (18), and the correctness of the equations (14) and (16) is verified.
In summary, for a direct-drive fan with determined parameters, a single frequency ω exists at a machine-end grid-connected pointpWhen the harmonic voltage is disturbed, the output current of the inverter can simultaneously exist omegapAnd 2 omega1-ωpThe harmonic currents of the frequencies can be calculated according to equations (14) and (16), respectively.

Claims (1)

1. A direct-drive fan subsynchronous oscillation electrical quantity analysis method considering frequency coupling effect is characterized by comprising the following steps: establishing a direct-drive fan small-signal impedance analytical model considering a frequency coupling effect, and giving a frequency coupling quantitative relation of output harmonic current of the direct-drive fan under single-frequency harmonic voltage disturbance; the method is characterized in that: the method comprises the following steps:
step 1: inputting direct-drive fan parameters
The following parameters of the direct drive fan are obtained: fan grid-connected voltage V1The current output power frequency current I of the fan1Angle of power factorPhase-locked loop PI parameter Kp，KiCurrent inner loop PI parameter Kpi，KiiThe filter inductor L at the outlet of the inverter;
step 2: establishing simplified model of direct-drive fan
According to the structure of the direct-drive fan and the time scale characteristics of a control link, simplifying the direct-drive fan into a grid-connected inverter model: the wind turbine, the generator and the machine side converter are replaced by a direct current voltage source; power outer loop control of the grid-side converter is omitted; parameters required by the simplified model are obtained in the step 1;
and step 3: establishing external impedance analytical model of direct-drive fan
The method is characterized in that a direct-drive fan external impedance analytical model is established based on a harmonic linearization method, and the establishment process mainly accounts for the frequency coupling effect of the output harmonic current of the direct-drive fan under the single-frequency harmonic voltage disturbance:
practical simulation shows that omega exists when the voltage of the power grid side existspWhen harmonic wave exists, the output current of the inverter can simultaneously exist omegapAnd 2 omega1-ωpThe harmonic current of the frequency, the inverter output current time domain expression is as follows:
in the formula ia(t) is instantaneous value of phase current A, I1、Ip、Ip2The amplitude of the power frequency current, the amplitude of the output current with the same frequency as the disturbance voltage and the amplitude of the complementary frequency output current are respectively; omega1、ωp、2ω1-ωpThe angular frequency of the power frequency current, the angular frequency which is the same as the disturbance voltage in frequency and the angular frequency of the output current with complementary frequency are respectively;
Figure FDA0002227204600000021
the initial phase of the power frequency current and the initial phase of the output current with the same frequency as the disturbance voltageThe initial phase of the bit, complementary frequency output current;
similar to the definition of phasor in the circuit science, the frequency domain expressions of the output current with the same frequency as the disturbance voltage and the complementary frequency output current in the formula (3) are respectively as follows:Ipis w at the same frequency as the disturbance voltagepA frequency output current frequency domain expression; i isp2Angular frequency 2w of output current being complementary frequency1-wpThe output current frequency domain expression of (1);
and taking the frequency coupling effect into account, and obtaining a frequency domain expression of the input A-phase reference voltage of the pulse width modulator of the converter as follows:
Figure FDA0002227204600000023
in the formula: varef[wp]And Varef[2w1-wp]Are respectively wpAnd 2w1-wpA phase a reference voltage frequency domain expression of frequency; wherein: s and j are the fundamental variables of complex operations in mathematics;
Figure FDA0002227204600000025
performing exponential operation; hi(s-jw1)＝Kpi+Kii/(s-jw1) Is the transfer function of the current inner loop PI regulator;
Figure FDA0002227204600000026
wherein
Figure FDA0002227204600000027
Is the transfer function of the phase locked loop;
Figure FDA0002227204600000028
is the frequency domain expression V of the positive sequence disturbance voltagepConjugation of (1);
the converter using an averaging model, i.e. the output voltage Vga[wp]Is equal to the reference voltage Varef[wp](ii) a Because only one filter inductor exists between the output voltage of the converter and the voltage of the grid-connected point, the three satisfy the following conditions:
sLIp＝Vga[wp]-Va[wp](12)
substituting formula (8) for formula (12) and connecting to external impedance Z of direct-drive fanp(s)＝-Vp/IpThe analytical expression of (a) is:
Figure FDA0002227204600000031
and 4, step 4: calculating the output current of the direct-drive fan under the single-frequency voltage disturbance
For wpAs can be seen from equation (13), the disturbance voltage at a frequency corresponds to an output current at the frequency:
in the formula: vpIs a frequency domain expression of positive sequence disturbance voltage, Zp(jwp) Is that the direct-drive fan is at an angular frequency w with the same frequency as the disturbance voltagepImpedance calculated according to the following equation (13), IpIs w at the same frequency as the disturbance voltagepA frequency output current frequency domain expression;
because the fan grid-connected point only contains wpVoltage of frequency, so angular frequency 2w of output current for complementary frequency1-wpSatisfies the following conditions:
Varef[2w1-wp]＝Vga[2w1-wp]＝j(2w1-wp)LIp2(15)
substituting formula (9) and eliminating V by formula (13)p(s)The following can be obtained:
Figure FDA0002227204600000033
the above formula reveals a single frequency omegapUnder voltage disturbance, the inverter outputs omegapAnd 2 omega1-ωpA quantitative relationship of the coupled current components; i ispIs w at the same frequency as the disturbance voltagepA frequency output current frequency domain expression; i isp2Angular frequency 2w of output current being complementary frequency1-wpThe output current frequency domain expression of (1); when V ispAfter the determination, the output currents of the two coupling frequencies can be calculated according to the equations (14) and (16), respectively.
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CN111525611A (en) * 2020-04-26 2020-08-11 西安热工研究院有限公司 Frequency coupling effect-considering doubly-fed grid-connected system subsynchronous oscillation analysis method
CN111641229A (en) * 2020-06-16 2020-09-08 山东大学 Wind power generation system output monitoring method and system based on extended harmonic domain model
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CN112217203A (en) * 2020-09-28 2021-01-12 西安热工研究院有限公司 Direct-drive wind power plant subsynchronous oscillation equivalence method capable of keeping model structure
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CN111525611A (en) * 2020-04-26 2020-08-11 西安热工研究院有限公司 Frequency coupling effect-considering doubly-fed grid-connected system subsynchronous oscillation analysis method
CN111525611B (en) * 2020-04-26 2023-07-21 西安热工研究院有限公司 Subsynchronous oscillation analysis method of doubly-fed grid-connected system considering frequency coupling effect
CN111641229A (en) * 2020-06-16 2020-09-08 山东大学 Wind power generation system output monitoring method and system based on extended harmonic domain model
CN111641229B (en) * 2020-06-16 2022-07-01 山东大学 Wind power generation system output monitoring method and system based on extended harmonic domain model
CN112186759A (en) * 2020-09-28 2021-01-05 西安热工研究院有限公司 Doubly-fed wind power plant subsynchronous oscillation suppression method for adaptively capturing frequency points
CN112217203A (en) * 2020-09-28 2021-01-12 西安热工研究院有限公司 Direct-drive wind power plant subsynchronous oscillation equivalence method capable of keeping model structure
CN112186759B (en) * 2020-09-28 2022-11-15 西安热工研究院有限公司 Doubly-fed wind power plant subsynchronous oscillation suppression method for adaptively capturing frequency points
CN112217203B (en) * 2020-09-28 2022-11-25 西安热工研究院有限公司 Direct-drive wind power plant subsynchronous oscillation equivalence method capable of keeping model structure
CN114374208A (en) * 2022-01-13 2022-04-19 广东电网有限责任公司 Subsynchronous oscillation prejudging method and subsynchronous oscillation prejudging device for direct-drive fan
CN114374208B (en) * 2022-01-13 2023-06-13 广东电网有限责任公司 Method and device for prejudging subsynchronous oscillation of direct-drive fan

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