CN112290590B - PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation - Google Patents

PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation Download PDF

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CN112290590B
CN112290590B CN202011127334.7A CN202011127334A CN112290590B CN 112290590 B CN112290590 B CN 112290590B CN 202011127334 A CN202011127334 A CN 202011127334A CN 112290590 B CN112290590 B CN 112290590B
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frequency modulation
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super capacitor
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virtual inertia
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CN112290590A (en
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曾雪洋
***
张纯
陈玉敏
张华�
张华杰
苏学能
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Electric Power Research Institute of State Grid Sichuan Electric Power 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • 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
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • H02J2207/00—Indexing scheme relating to details of circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J2207/50—Charging of capacitors, supercapacitors, ultra-capacitors or double layer capacitors
    • 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
    • H02J2300/28—The renewable source being wind energy
    • 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
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction
    • 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
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

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Abstract

The invention discloses a PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation, which relates to the technical field of wind power generation, and adopts the technical scheme that: simulating the inertia response and primary frequency modulation of the power grid by using the dynamic power of a super capacitor directly connected into a fan back-to-back converter, and calculating a coupling mathematical relation between direct current voltage and alternating current frequency in the power grid; designing and arranging a virtual capacitor and a short-term primary frequency modulation controller of a PMSG fan access super capacitor according to a coupling mathematical relation; measuring frequency information in a power grid through a phase-locked loop, and calculating a virtual inertia coefficient provided by a fan super capacitor according to a coupling mathematical relational expression; the frequency modulation controller outputs a new direct current voltage reference value under the condition that the super capacitor provides virtual inertia and short-term primary frequency modulation after calculation; and controlling the frequency modulation of the PMSG fan by the fixed direct-current voltage of the GSC according to the direct-current voltage reference value. The invention can effectively restrain the slope of frequency change, reduce the deviation amount of transient frequency and improve the dynamic characteristic of frequency.

Description

PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation
Technical Field
The invention relates to the technical field of wind power generation, in particular to a PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation.
Background
In recent years, the installed capacity of wind power is increasing in proportion to the power grid. Unlike a synchronous generator, a permanent magnet direct drive (PMSG) fan is connected to a power grid through a power electronic converter, in order to capture maximum wind energy, power output by the fan is generally controlled by Maximum Power Point Tracking (MPPT), which causes the rotation speed of the fan and the frequency of the power grid to present a decoupled state, and the rotational inertia of a fan rotor is hidden.
With the continuous increase of the wind power access proportion, the inertia of the power system will be reduced, which brings serious challenges to the frequency stabilization and control of the power system. The rotational kinetic energy of the fan rotor can provide frequency support, but can cause the fan to operate off the MPPT point and can cause a secondary frequency drop during rotor speed recovery. The load reduction control can enable the fan to deviate from the MPPT point during normal operation, and the operation economy is reduced. At present, super capacitors are applied to wind turbines, but are mainly used for smoothing output power and improving transient fault ride-through capability, and most of the super capacitors are connected through a bidirectional DC/DC converter. In fact, the super capacitor can be directly connected to the PMSG back-to-back converter, and a DC/DC converter can be omitted.
However, the prior research is not related to whether the wind turbine is connected with the super capacitor to provide virtual inertia and short-term primary frequency modulation under the topology, and the research on the situation that the super capacitor provides primary frequency modulation control has great significance. Therefore, how to research and design a PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation is a problem which is urgently needed to be solved at present.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide the PMSG fan control method based on the super-capacitor virtual inertia and the short-term primary frequency modulation, the frequency modulation performance of the PMSG fan control method is not influenced by the wind speed, and the fan is not required to carry out load shedding control.
The technical purpose of the invention is realized by the following technical scheme: the PMSG fan control method based on the super capacitor virtual inertia and the short-term primary frequency modulation comprises the following steps:
s101: simulating the inertia response and primary frequency modulation of the power grid by using the dynamic power of a super capacitor directly connected into a fan back-to-back converter, and calculating a coupling mathematical relation between direct current voltage and alternating current frequency in the power grid;
s102: designing and arranging a virtual capacitor and a short-term primary frequency modulation controller of a PMSG fan access super capacitor according to a coupling mathematical relation;
s103: measuring frequency information in a power grid through a phase-locked loop, calculating a virtual inertia coefficient provided by a fan super capacitor according to a coupling mathematical relation, and inputting the frequency information and the virtual inertia coefficient into a frequency modulation controller;
s104: the frequency modulation controller outputs a new direct current voltage reference value under the condition that the super capacitor provides virtual inertia and short-term primary frequency modulation after calculation;
s105: and controlling the frequency modulation of the PMSG fan by the fixed direct-current voltage of the grid-side converter GSC according to the direct-current voltage reference value.
Further, the frequency modulation controller comprises virtual inertia control and short-term primary frequency modulation; wherein the content of the first and second substances,
the virtual inertia control is used for simulating the inertia response of the synchronous generator, inhibiting the change slope of the frequency and preventing the rapid falling of the frequency;
and the short-term primary frequency modulation is used for reducing the maximum deviation of the frequency in the transient process so as to provide stronger frequency support for the fan in a short time and improve the dynamic characteristic of the frequency.
Further, the mathematical coupling relation is specifically as follows:
Figure BDA0002734047700000021
in the formula, a first term under a root sign represents that the super capacitor provides virtual inertia, and a second term under the root sign represents that the super capacitor provides primary frequency modulation; v* dcIs a reference value of DC voltage, HdcVirtual inertia coefficient, S, provided for a blower supercapacitorWTRated power of the fan, f0For nominal frequency, f for measured frequency information, KdcDroop coefficient, V, providing primary frequency modulation for super capacitordc0Is the direct current voltage of normal operation, and C is the capacity of the super capacitor.
Further, the method for solving the coupling mathematical relation specifically includes:
the inertial response of the generator is used for preventing the slope of the frequency change in the initial stage of the disturbance, and the output additional power of the generator is in proportion to the slope of the frequency change, specifically:
Figure BDA0002734047700000022
the response speed of the primary frequency modulation is slower than that of the inertial response, and the output additional power is in direct proportion to the frequency deviation, specifically:
Figure BDA0002734047700000023
in the formulae (5) and (6), HgIs the inertia time constant of the generator, f0Is the nominal frequency, f is the measured frequency information, Δ f is the frequency deviation, KPIs the droop coefficient of the generator;
the dynamic behavior of the power system frequency is represented as:
Figure BDA0002734047700000024
in the formula, H is the equivalent inertia time constant of the alternating current system, D is the damping coefficient of the system, and PGTotal power of the generator, PLFor total load power, Δ PSThe power released or stored after the super capacitor is adopted for the fan;
combining formula (1) and formula (2), Δ PSCan be expressed as:
Figure BDA0002734047700000025
in the formula, HdcVirtual inertia coefficient, K, for a blower supercapacitordcProviding a droop coefficient of primary frequency modulation for the super capacitor;
substituting formula (5) into (3) yields:
Figure BDA0002734047700000031
according to the formula (5), after the super capacitor of the fan provides virtual inertia and primary frequency modulation control, the inertia and damping inertia characteristics of the power system are increased;
the energy in the super capacitor can be released by changing the size of the direct-current voltage through the direct-current voltage control of the grid-side converter GSC, and the dynamic electromagnetic power of the direct-current capacitor is as follows:
Figure BDA0002734047700000032
in the formula, VdIs a direct voltage, SWTRated power of the fan, PinFor input of power into the super-capacitor, PoutTo output the power of the super capacitor, Δ PCElectromagnetic power released or stored for the super capacitor;
let Delta PSAnd Δ PCEquality, we can get:
Figure BDA0002734047700000033
Figure BDA0002734047700000034
Figure BDA0002734047700000035
Figure BDA0002734047700000036
in formulae (7) to (8), f1For quasi-steady-state frequency values after disturbance, Vdc1Is a disturbed quasi-steady-state DC voltage value, Vdc0Is a direct current voltage for normal operation. Δ f is the frequency deviation (Δ f ═ f)1-f0)，ΔVdcIs a direct current voltage deviation (Δ V)dc＝Vdc1-Vdc0)。
Further, the short-term primary frequency modulation adopts a washout link to separate a direct current part in the quasi-steady-state frequency deviation.
Further, the time constant T in the washout link1Is 8 s.
Further, the virtual inertia coefficient is specifically:
assuming that only the supercapacitor is considered to provide virtual inertia, the virtual inertia provided by the supercapacitor is:
Figure BDA0002734047700000037
Figure BDA0002734047700000038
Figure BDA0002734047700000039
in the formula,. DELTA.VmaxIs the maximum allowable DC voltage deviation (Δ V)dc＝Vdcmax-Vdc0Or Δ Vdc＝Vdc0-Vdcmin)，ΔfVThe frequency deviation of the overlay is controlled for virtual inertia.
Further, the capacity of the super capacitor is specifically selected as follows:
under normal DC voltage operation, the super capacitor is used for frequency adjustment and can store energy Delta EsComprises the following steps:
Figure BDA0002734047700000041
in the formula, EmaxTo be at the maximum allowable DC voltage VdcmaxEnergy stored in the lower super capacitor, E0For a normal operating voltage VdcoptEnergy stored by the lower super capacitor;
at the same time, under normal operating voltage, the super capacitor is used for frequency modulation of releasable energy delta ErComprises the following steps:
Figure BDA0002734047700000042
in the formula, EminTo a minimum allowable DC voltage VdcminLower stored energy;
assuming that the capacitance value remains unchanged in the charging and discharging process of the super capacitor, the direct current operating voltage under normal conditions is as follows:
ΔEs＝ΔEr (16)
Figure BDA0002734047700000043
Figure BDA0002734047700000044
when the frequency is reduced, the fan increases the active power output according to the primary frequency modulation curve, and when the increased active power reaches 10% of rated power, the increased active power can not be increased any more; therefore, the relationship between the magnitudes of the dc capacitors is:
ΔEr≥Pst＝0.1PN (19)
Figure BDA0002734047700000045
Figure BDA0002734047700000046
further, the primary frequency modulation duration is not more than 30 s.
Further, the direct-current voltage reference value is subjected to voltage value amplitude limiting by an amplitude limiter and then is input to the grid-side converter GSC.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a virtual inertia and short-term primary frequency modulation control method for a PMSG fan by adopting a super capacitor. The virtual inertia control is positioned to simulate the inertial response of the synchronous generator to suppress the changing slope of the frequency and prevent the rapid drop of the frequency. The short-term primary frequency modulation of the direct current capacitor can effectively reduce the maximum deviation of the frequency in the transient process, and can provide stronger frequency support for the fan in a short time, thereby improving the dynamic characteristic of the frequency. The PMSG fan adopts the virtual inertia of a super capacitor and a short-term primary frequency modulation control method, the MPPT control of the fan cannot be influenced, the load shedding control of the fan is not needed, and the running economy of the fan is improved. After the fan adopts the control method, the slope of frequency change can be effectively restrained, the transient frequency deviation amount can be reduced, and the dynamic characteristic of frequency can be improved. The method has important engineering meaning for a future 'low inertia' power system with high-proportion wind power access.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a topology structure diagram of a PMSG direct-drive fan model accessed to a power grid in the prior art;
FIG. 2 is a topological diagram of a PMSG fan connected to a super capacitor (Supercapactor) in the embodiment of the invention;
FIG. 3 is a control block diagram of a super capacitor providing virtual inertia and short term primary frequency modulation in an embodiment of the present invention;
FIG. 4 is a diagram of a simulation example structure according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating comparative analysis results of different control strategies according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the following examples and accompanying fig. 1-5, wherein the exemplary embodiments and descriptions of the present invention are only used for explaining the present invention and are not to be construed as limiting the present invention.
Example (b): PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation
As shown in fig. 1, the PMSG fan is connected to a low inertia ac grid system. The PMSG fan is connected to a power grid through a back-to-back converter. A Stator Side Converter (SSC) controls active power and reactive power output by the fan. Grid Side Converters (GSC) control the dc voltage and the ac voltage amplitude.
As shown in fig. 2, a topology diagram of a PMSG fan connected to a super capacitor (super capacitor) can be divided into two types, one type is that the super capacitor is connected to a back-to-back converter of the fan through a bidirectional DC/DC converter, and the other type is that the super capacitor is directly connected to the back-to-back converter of the fan. The first access mode needs to add a DC/DC converter, in this way, the variable DC voltage range of the super capacitor is large, but in the power conversion stage, the DC/DC converter will generate extra loss, the power efficiency is reduced, the control system is complex, and the overall coordination and reliability of the wind turbine will also be weakened. Compared with the first scheme, the second scheme can omit a DC/DC converter, reduce power loss, and has simple control and high reliability. The present invention thus employs a second access scheme.
As shown in fig. 3, firstly, the inertia response and the primary frequency modulation of the power grid are simulated by the dynamic power of the super capacitor directly connected to the back-to-back converter of the fan, and the coupling mathematical relation between the direct current voltage and the alternating current frequency in the power grid is calculated. And then designing and arranging a virtual capacitor and a short-term primary frequency modulation controller of the PMSG fan access super capacitor according to a coupling mathematical relation. And then, measuring frequency information in the power grid through a phase-locked loop, calculating a virtual inertia coefficient provided by the super capacitor of the fan according to a coupling mathematical relation, and inputting the frequency information and the virtual inertia coefficient into a frequency modulation controller. And then, the frequency modulation controller outputs a new direct current voltage reference value under the condition that the super capacitor provides virtual inertia and short-term primary frequency modulation after calculation. And finally, controlling the frequency modulation of the PMSG fan by the fixed direct-current voltage of the grid-side converter GSC according to the direct-current voltage reference value.
Mathematical relation of coupling between DC voltage and AC frequency
The inertial response of the generator is used for preventing the slope of the frequency change in the initial stage of the disturbance, and the output additional power of the generator is in proportion to the slope of the frequency change, specifically:
Figure BDA0002734047700000061
the response speed of the primary frequency modulation is slower than that of the inertial response, and the output additional power is in direct proportion to the frequency deviation, specifically:
Figure BDA0002734047700000062
in the formulae (9) and (10), HgIs the inertia time constant of the generator, f0Is the nominal frequency, f is the measured frequency information, Δ f is the frequency deviation, KPIs the droop coefficient of the generator;
the dynamic behavior of the power system frequency is represented as:
Figure BDA0002734047700000063
in the formula, H is the equivalent inertia time constant of the alternating current system, D is the damping coefficient of the system, and PGTotal power of the generator, PLFor total load power, Δ PSThe power released or stored after the super capacitor is adopted for the fan;
combining formula (1) and formula (2), Δ PSCan be expressed as:
Figure BDA0002734047700000064
in the formula, HdcVirtual inertia coefficient, K, for a blower supercapacitordcProviding a droop coefficient of primary frequency modulation for the super capacitor;
substituting formula (5) into (3) yields:
Figure BDA0002734047700000065
according to the formula (5), after the super capacitor of the fan provides virtual inertia and primary frequency modulation control, the inertia and damping inertia characteristics of the power system are increased;
the energy in the super capacitor can be released by changing the size of the direct-current voltage through the direct-current voltage control of the grid-side converter GSC, and the dynamic electromagnetic power of the direct-current capacitor is as follows:
Figure BDA0002734047700000066
in the formula, VdIs a direct voltage, SWTRated power of the fan, PinFor input of power into the super-capacitor, PoutTo output the power of the super capacitor, Δ PCElectromagnetic power released or stored for the super capacitor;
let Delta PSAnd Δ PCEquality, we can get:
Figure BDA0002734047700000067
Figure BDA0002734047700000068
Figure BDA0002734047700000069
Figure BDA0002734047700000071
in formulae (11) to (12), f1For quasi-steady-state frequency values after disturbance, Vdc1Is a disturbed quasi-steady-state DC voltage value, Vdc0Is a normally operating dc voltage. Δ f is the frequency deviation (Δ f ═ f)1-f0)，ΔVdcIs a direct current voltage deviation (Δ V)dc＝Vdc1-Vdc0)。
According to the formula (10), a new direct-current voltage reference value V of GSC constant direct-current voltage control under virtual inertia and short-term primary frequency modulation provided by the super capacitor can be deduced* dcThe direct-current voltage reference value is input to a grid-side converter GSC after being subjected to voltage value amplitude limiting by adopting an amplitude limiter, and the method specifically comprises the following steps of:
Figure BDA0002734047700000072
in the formula, a first term under a root sign represents that the super capacitor provides virtual inertia, and a second term under the root sign represents that the super capacitor provides primary frequency modulation; v* dcIs a reference value of DC voltage, HdcVirtual inertia coefficient, S, provided for a blower supercapacitorWTRated power of the fan, f0For nominal frequency, f for measured frequency information, KdcDroop coefficient, V, providing primary frequency modulation for super capacitordc0Is the direct current voltage of normal operation, and C is the capacity of the super capacitor.
The frequency modulation controller comprises virtual inertia control and short-term primary frequency modulation; the virtual inertia control is used for simulating the inertia response of the synchronous generator, inhibiting the change slope of the frequency and preventing the rapid falling of the frequency; and the short-term primary frequency modulation is used for reducing the maximum deviation of the frequency in the transient process so as to provide stronger frequency support for the fan in a short time and improve the dynamic characteristic of the frequency. And the short-term primary frequency modulation adopts a washout link to separate and remove a direct current part in the quasi-steady-state frequency deviation. Time constant T in the washout link1Is 8 s.
(II) calculating the virtual inertia coefficient, specifically:
assuming that only the supercapacitor is considered to provide virtual inertia, the virtual inertia provided by the supercapacitor is:
Figure BDA0002734047700000073
Figure BDA0002734047700000074
Figure BDA0002734047700000075
in the formula,. DELTA.VmaxIs the maximum allowable DC voltage deviation (Δ V)dc＝Vdcmax-Vdc0Or Δ Vdc＝Vdc0-Vdcmin)，ΔfVThe frequency deviation of the overlay is controlled for virtual inertia.
(III) selecting the capacity of the super capacitor, specifically:
under normal DC voltage operation, the super capacitor is used for frequency adjustment and can store energy Delta EsComprises the following steps:
Figure BDA0002734047700000076
in the formula, EmaxTo be at the maximum allowable DC voltage VdcmaxEnergy stored in the lower super capacitor, E0For a normal operating voltage VdcoptEnergy stored by the lower super capacitor;
at the same time, under normal operating voltage, the super capacitor is used for frequency modulation of releasable energy delta ErComprises the following steps:
Figure BDA0002734047700000081
in the formula, EminTo a minimum allowable DC voltage VdcminLower stored energy;
assuming that the capacitance value remains unchanged in the charging and discharging process of the super capacitor, the direct current operating voltage under normal conditions is as follows:
ΔEs＝ΔEr (16)
Figure BDA0002734047700000082
Figure BDA0002734047700000083
when the frequency is reduced, the fan increases the active power output according to the primary frequency modulation curve, and when the increased active power reaches 10% of rated power, the increased active power can not be increased any more; therefore, the relationship between the magnitudes of the dc capacitors is:
ΔEr≥Pst＝0.1PN (19)
Figure BDA0002734047700000084
Figure BDA0002734047700000085
wherein the primary frequency modulation duration does not exceed 30 s.
(IV) verification of accuracy
In order to verify the accuracy of the virtual inertia of the super capacitor and the short-term primary frequency modulation control method adopted by the PMSG fan, a system of accessing the PMSG fan into a low-inertia alternating current power grid as shown in figure 4 is built in the PSCAD/EMTDC. The weak AC power network consists of fixed load and cut load. PMSG fan parameters are shown in table 1. The synchronous generator employs a seven-order model with the parameters shown in table 2. The fixed load was 3MW +0.3Mvar and the variable load was 0.15MW +0.015 Mvar. Hdc＝Hg＝3.2s， Kdc＝10，Vmin＝0.7pu。Vdc0＝1pu，Vdcmin0.7 pu. The supercapacitor according to equation (21) should be greater than or equal to 2.61F, with the supercapacitor chosen to be 2.7F in the present invention. Wind speed 10m/s, variable load was put in 10s to create frequency disturbances. Fig. 5 is a comparative simulation result of the blower without additional control, the supercapacitor virtual inertia control only, the supercapacitor short-term primary frequency modulation control only, and the supercapacitor virtual inertia and short-term primary frequency modulation control.
Table 1 PMSG fan main parameters
Figure BDA0002734047700000086
Figure BDA0002734047700000091
TABLE 2 main parameters of synchronous generator
Figure BDA0002734047700000092
As can be seen from FIG. 5, when the fan is not additionally controlled, the fan does not respond to the frequency, and the lowest frequency point fnadir49.13Hz, the maximum frequency deviation reaches 0.87Hz, the maximum slope of the frequency change | ROOF-max0.3692Hz/s are achieved. After the fan adopts the super capacitor, only virtual inertia control is carried out, and mostThe large frequency deviation is improved to 0.74Hz, the relative non-additional control is improved by 14.9 percent, | ROOF |maxThe frequency is improved to 0.2599Hz/s, which is improved by 29.6 percent relative to the frequency without additional control. When only short-term primary frequency modulation is carried out, the maximum frequency deviation is improved to 0.36Hz, the maximum frequency deviation is improved by 58.6 percent relative to no additional control, | ROOF |maxThe frequency is improved to 0.3196Hz/s, which is improved by 13.4 percent compared with no additional control. When the fan adopts virtual inertia and short-term primary frequency modulation control, the maximum frequency deviation is improved to 0.35Hz, and is improved by 59.8 percent relative to no additional control, | ROOF |maxThe frequency is improved to 0.2420Hz/s, which is improved by 34.5 percent relative to no additional control. Therefore, the virtual inertia control can effectively slow down the slope of frequency change, and the short-term primary frequency modulation control can effectively reduce the frequency deviation in the transient process and improve the dynamic characteristic of the frequency. After the fan simultaneously adopts virtual inertia control and short-term primary frequency modulation control, the maximum slope | ROOF-maxAnd lowest point f of lifting frequencynadirAnd the fan can provide stronger frequency support in a short time, and the dynamic characteristic of the frequency is improved, so that the method has important significance for a power system accessed by high-proportion wind power.
The working principle is as follows: the invention provides a virtual inertia and short-term primary frequency modulation control method for a PMSG fan by adopting a super capacitor. The virtual inertia control is positioned to simulate the inertial response of the synchronous generator to suppress the changing slope of the frequency and prevent the rapid drop of the frequency. The direct current capacitor short-term primary frequency modulation can effectively reduce the maximum deviation of the frequency in the transient process, can provide stronger frequency support for the fan in a short time, and improves the dynamic characteristic of the frequency. The PMSG fan adopts the virtual inertia of a super capacitor and a short-term primary frequency modulation control method, the MPPT control of the fan cannot be influenced, the fan load shedding control is not needed, and the running economy of the fan is favorably improved. After the fan adopts the control method, the slope of frequency change can be effectively restrained, the transient frequency deviation amount can be reduced, and the dynamic characteristic of frequency can be improved. The method has important engineering significance for a low-inertia power system with a high-proportion wind power access in the future.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. The PMSG fan control method based on the super-capacitor virtual inertia and the short-term primary frequency modulation is characterized by comprising the following steps of:
s101: simulating the inertia response and primary frequency modulation of the power grid by using the dynamic power of a super capacitor directly connected into a fan back-to-back converter, and calculating a coupling mathematical relation between direct current voltage and alternating current frequency in the power grid;
s102: designing and arranging a virtual capacitor and a short-term primary frequency modulation controller of a PMSG fan access super capacitor according to a coupling mathematical relation;
s103: measuring frequency information in a power grid through a phase-locked loop, calculating a virtual inertia coefficient provided by a fan super capacitor according to a coupling mathematical relation, and inputting the frequency information and the virtual inertia coefficient into a frequency modulation controller;
s104: the frequency modulation controller outputs a new direct current voltage reference value under the condition that the super capacitor provides virtual inertia and short-term primary frequency modulation after calculation;
s105: controlling the frequency modulation of a PMSG fan by the fixed direct-current voltage of the grid-side converter GSC according to a direct-current voltage reference value;
the coupling mathematical relation is specifically as follows:
Figure FDA0003557886710000011
in the formula, a first term under a root sign represents that the super capacitor provides virtual inertia, and a second term under the root sign represents that the super capacitor provides primary frequency modulation; v* dcIs a reference value of DC voltage, HdcVirtual inertia coefficient provided for fan super capacitor，SWTRated power of the fan, f0For nominal frequency, f for measured frequency information, KdcDroop coefficient, V, providing primary frequency modulation for super capacitordc0The voltage is a direct current voltage for normal operation, and C is the capacity of the super capacitor.
2. The PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation of claim 1, wherein the frequency modulation controller comprises virtual inertia control and short-term primary frequency modulation; wherein the content of the first and second substances,
the virtual inertia control is used for simulating the inertia response of the synchronous generator, inhibiting the change slope of the frequency and preventing the rapid falling of the frequency;
and the short-term primary frequency modulation is used for reducing the maximum deviation of the frequency in the transient process so as to provide stronger frequency support for the fan in a short time and improve the dynamic characteristic of the frequency.
3. The PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation according to claim 1, wherein the coupled mathematical relational expression solving method specifically comprises:
the inertial response of the generator is used for preventing the slope of the frequency change in the initial stage of the disturbance, and the output additional power of the generator is proportional to the slope of the frequency change, specifically:
Figure FDA0003557886710000012
the response speed of the primary frequency modulation is slower than that of the inertial response, and the output additional power is in direct proportion to the frequency deviation, specifically:
Figure FDA0003557886710000021
in the formulae (1) and (2), HgIs the inertia time constant of the generator, f0For nominal frequency, f is measured frequency informationΔ f is the frequency deviation, KPIs the droop coefficient of the generator;
the dynamic behavior of the power system frequency is represented as:
Figure FDA0003557886710000022
in the formula, H is the equivalent inertia time constant of the alternating current system, D is the damping coefficient of the system, and PGTotal power of the generator, PLFor total load power, Δ PSThe power released or stored after the super capacitor is adopted for the fan;
combining formula (1) and formula (2), Δ PSCan be expressed as:
Figure FDA0003557886710000023
in the formula, HdcVirtual inertia coefficient, K, for a blower supercapacitordcProviding a droop coefficient of primary frequency modulation for the super capacitor;
substituting formula (4) into (3) yields:
Figure FDA0003557886710000024
according to the formula (5), after the super capacitor of the fan provides virtual inertia and primary frequency modulation control, the inertia and damping inertia characteristics of the power system are increased;
the energy in the super capacitor is released by changing the size of the direct current voltage through the direct current voltage control of the grid-side converter GSC, and the dynamic electromagnetic power of the direct current capacitor is as follows:
Figure FDA0003557886710000025
in the formula, VdcIs a direct voltage, SWTRated power of the fan, PinFor input of power into the super-capacitor, PoutTo output the power of the super-capacitor, Δ PCElectromagnetic power released or stored for the super capacitor;
let Delta PSAnd Δ PCEquality, we can get:
Figure FDA0003557886710000026
Figure FDA0003557886710000027
Figure FDA0003557886710000028
Figure FDA0003557886710000029
in formulae (3) to (4), f1For quasi-steady-state frequency values after disturbance, Vdc1Is a disturbed quasi-steady-state DC voltage value, Vdc0The voltage is a direct current voltage for normal operation; Δ f is the frequency deviation, Δ f ═ f1-f0，ΔVdcIs a DC voltage deviation, Δ Vdc＝Vdc1-Vdc0。
4. The PMSG fan control method based on super capacitor virtual inertia and short-term primary frequency modulation of claim 1, wherein the short-term primary frequency modulation adopts a washout link to separate a direct current part in a quasi-steady-state frequency deviation.
5. The PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation of claim 4, wherein a time constant T in the washout link1Is 8 s.
6. The PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation according to claim 1, wherein the virtual inertia coefficients are specifically:
assuming that only the supercapacitor is considered to provide virtual inertia, the virtual inertia provided by the supercapacitor is:
Figure FDA0003557886710000031
Figure FDA0003557886710000032
Figure FDA0003557886710000033
in the formula,. DELTA.VmaxFor maximum permissible DC voltage deviation, Δ Vdc＝Vdcmax-Vdc0Or Δ Vdc＝Vdc0-Vdcmin，ΔfVThe frequency deviation of the overlay is controlled for virtual inertia.
7. The PMSG fan control method based on super capacitor virtual inertia and short-term primary frequency modulation according to claim 1, wherein the capacity of the super capacitor is selected as follows:
under normal DC voltage operation, the super capacitor is used for frequency adjustment and can store energy Delta EsComprises the following steps:
Figure FDA0003557886710000034
in the formula, EmaxTo be at the maximum allowable DC voltage VdcmaxEnergy stored in the lower super capacitor, E0Energy stored for the super capacitor at normal operating voltage;
at the same time as this is done,under normal operating voltage, the super capacitor is used for frequency modulation releasable energy Delta ErComprises the following steps:
Figure FDA0003557886710000035
in the formula, EminTo a minimum allowable DC voltage VdcminLower stored energy;
assuming that the capacitance value remains unchanged in the charging and discharging process of the super capacitor, the direct current operating voltage under normal conditions is as follows:
ΔEs＝ΔEr (16)
Figure FDA0003557886710000036
Figure FDA0003557886710000037
when the frequency is reduced, the fan increases the active power output according to the primary frequency modulation curve, and when the increased active power reaches 10% of rated power, the increased active power is not increased; therefore, the relationship between the magnitudes of the dc capacitors is:
ΔEr≥Pst＝0.1PN (19)
Figure FDA0003557886710000041
Figure FDA0003557886710000042
8. the PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation of claim 7, wherein the primary frequency modulation duration is not more than 30 s.
9. The PMSG fan control method based on super-capacitor virtual inertia and short-term primary frequency modulation of claim 1, wherein the direct-current voltage reference value is input to a grid-side converter GSC after being subjected to voltage value amplitude limiting by an amplitude limiter.
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