CN111313469B - Pre-synchronization control method of virtual synchronous machine without phase-locked loop - Google Patents
Pre-synchronization control method of virtual synchronous machine without phase-locked loop Download PDFInfo
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- CN111313469B CN111313469B CN202010210974.8A CN202010210974A CN111313469B CN 111313469 B CN111313469 B CN 111313469B CN 202010210974 A CN202010210974 A CN 202010210974A CN 111313469 B CN111313469 B CN 111313469B
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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
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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
- H02J3/40—Synchronising a generator for connection to a network or to another generator
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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
- H02J3/40—Synchronising a generator for connection to a network or to another generator
- H02J3/42—Synchronising a generator for connection to a network or to another generator with automatic parallel connection when synchronisation is achieved
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
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Abstract
The invention relates to a grid-connected inverter control method of an energy storage system and a power grid interface, in particular to a virtual synchronous machine pre-synchronization control method without a phase-locked loop, which is characterized in that three-phase voltage of a power grid and output three-phase voltage of a virtual synchronous machine are collected before grid connection, a sine value of the phase difference and a voltage amplitude difference delta U are obtained according to a 3/2 coordinate transformation formula and then sent to a PI controller, when the control is stable, an input steady-state error is 0, namely sin delta theta and delta U are 0, at the moment, the output voltage of the virtual synchronous machine has a voltage amplitude value and a phase which are consistent with the voltage of the power grid, and a grid-connected switch is closed to complete grid connection switching of the virtual synchronous machine. The invention has the advantages that: the method can effectively avoid the influence of phase difference symbol jumping on the control process of the PI controller, saves the design of a phase-locked loop, simplifies the presynchronization control process, and improves the control precision and the control speed.
Description
Technical Field
The invention relates to a grid-connected inverter control method of an energy storage system and a power grid interface, in particular to a virtual synchronous machine pre-synchronization control method without a phase-locked loop.
Background
The distributed energy storage system is mainly connected to a power grid through a grid-connected inverter, along with the continuous increase of the total capacity of the energy storage system, a large number of grid-connected inverters affect the stable operation of the power grid, and the control modes of the traditional inverter mainly include constant power control (PQ control), constant voltage and constant frequency control (VF control), droop control (drop control) and the like. The droop control simulates some external characteristics of the synchronous generator for the first time, so that the grid-connected inverter can participate in the primary frequency modulation and primary voltage regulation processes of the power system. Under the condition, the virtual synchronous machine can simulate the rotational inertia and the droop characteristic of the synchronous generator, and adjust the active power and the reactive power output by the virtual synchronous machine according to the change of the frequency and the amplitude of the voltage of the power grid, so that the virtual synchronous machine has the advantage of providing voltage and frequency support for the power grid.
In practical application, if the virtual synchronous machine output voltage and the power grid voltage have different amplitudes and phases at the moment of grid connection, great power impact is generated, and therefore pre-synchronization control is required before grid connection. The traditional presynchronization control mode is that a phase difference delta theta between the output voltage of the virtual synchronous machine and the voltage of a power grid and a voltage amplitude difference delta U are obtained through a phase-locked loop, and then the virtual synchronous machine has the voltage amplitude U and the phase theta which are consistent with the voltage of the power grid before grid connection is realized through phase presynchronization control and voltage amplitude presynchronization control, so that power impact at the moment of grid connection is avoided. However, since the voltage phase is changed in the range of 0-2 PI, when a certain voltage phase reaches 2 PI, the voltage phase is stepped to 0, so that the value of the phase difference Δ θ obtained by the conventional phase-locked loop has a process of continuous jump, and if the phase difference is sent to the PI link, the control accuracy and the time length of the PI controller are affected, so that the problems of insufficient control accuracy, long control time and the like are caused.
Disclosure of Invention
The invention aims to provide a presynchronization control method of a virtual synchronous machine without a phase-locked loop, which improves the control precision and the control speed according to the defects of the prior art.
The purpose of the invention is realized by the following ways:
the presynchronization control method of the virtual synchronous machine without the phase-locked loop is characterized by comprising the following steps of:
1) the virtual synchronous machine operates with local active load before grid connection and acquires three-phase voltage u of a power gridpA、upB、upCAnd the virtual synchronous machine outputs three-phase voltage uoA、uoB、uoCAnd if the three-phase voltage is symmetrical, then:
upA+upB+upC＝0
uoA+uoB+uoC＝0
2) according to the 3/2 coordinate transformation formula, obtaining the expression of the alpha-beta axis component of the output voltage of the virtual synchronous machine and the alpha-beta axis component of the power grid voltage under an alpha-beta coordinate system as follows:
alpha-axis component u of output voltage of virtual synchronous machineoα：uoα＝Uomcosθo
Beta-axis component u of output voltage of virtual synchronous machineoβ：uoβ＝Uomsinθo
Alpha-component u of the mains voltagepα：upα＝Upmcosθp
Beta-axis component u of the mains voltagepβ：upβ＝Upmsinθp
In the formula of UpmTo the grid voltage amplitude, UomFor outputting a voltage amplitude, θ, to the virtual synchronous machine0For the phase of the output voltage of the virtual synchronous machine, thetapIs the phase of the grid voltage; further, the method can be obtained as follows:
Upm＝upα 2+upβ 2
Uom＝uoα 2+uoβ 2
ΔU＝Upm-Uom
3) and providing a PI controller, sending the sine value sin delta theta and the voltage amplitude difference delta U of the phase difference into the PI controller, superposing an output error signal of the PI controller on a frequency given value of the power frequency controller and a voltage given value of the excitation controller to perform closed-loop control, inputting a steady-state error of 0 when the control is stable, namely the sin delta theta and the delta U are 0, closing a grid-connected switch when the output voltage of the virtual synchronous machine has a voltage amplitude and a phase which are consistent with the voltage of a power grid, and completing grid-connected switching of the virtual synchronous machine.
The invention is based on the following analysis: the phase difference delta theta obtained by the traditional phase-locked loop has a continuous jumping process, but when the delta theta is very small, sin delta theta is approximately equal to delta theta, sin (delta theta +/-2 k pi) is equal to sin delta theta, wherein k is equal to 0,1,2 and 3. Therefore, the phase difference delta theta is replaced by sin delta theta and sent to the PI link for phase pre-synchronization control, the influence of phase difference symbol jumping on the control process of the PI controller can be avoided, the sine value sin delta theta of the phase difference and the voltage amplitude difference delta U are directly calculated under an alpha beta coordinate system, the design of a phase-locked loop is omitted, the pre-synchronization control process is simplified, and the control precision and the control speed are improved.
Drawings
Fig. 1 is a schematic diagram of a main circuit topology of a virtual synchronous machine according to the present invention.
Fig. 2 is a schematic diagram of a power frequency controller of the virtual synchronous machine according to the present invention.
Fig. 3 is a schematic structural diagram of an excitation controller of the virtual synchronous machine according to the present invention.
Fig. 4 is a waveform diagram of the phase difference Δ θ according to the present invention.
Fig. 5 is a waveform diagram of the sine value sin Δ θ of the phase difference Δ θ according to the present invention.
Fig. 6 is a matlab simulation waveform of the a-phase voltage output by the virtual synchronous machine and the a-phase voltage of the power grid in the pre-synchronization process.
Fig. 7 is a matlab simulation waveform of the sine value sin Δ θ of the phase difference during the pre-synchronization process.
The present invention will be further described with reference to the following examples.
Detailed Description
The best embodiment is as follows:
referring to the attached figure 1, the invention is described by taking a 12KW grid-connected virtual synchronous machine as an object. Referring to the drawings, the embodiment of the present invention is described in detail below, as shown in fig. 1, before the virtual synchronous machine is connected to the grid, the virtual synchronous machine operates with a local active load, and the output voltage frequency of the virtual synchronous machine is determined by the power frequency controller shown in fig. 2, and the specific equation is as follows:
Pref-Pm＝-Kp(ωref-ω)
in the formula PrefAs an active power command, PmAs virtual mechanical power, ωrefFor voltage angular frequency command, KpThe active droop coefficient, omega, the virtual synchronous machine output voltage frequency, J, the virtual moment of inertia, D, the virtual damping coefficient, and omegaNIs the nominal angular frequency.
The output voltage amplitude is determined by the excitation controller shown in fig. 3, and the specific control equation is as follows:
Emmodulating the amplitude, Q, of the wave for three phasesrefFor reactive power command, QeFor the actual output of reactive power, KqIs a reactive sag factor, UNFor rated output voltage amplitude, UomExporting for a virtual synchronous machineAmplitude of voltage, MfThe method is used for simulating the mutual inductance value of the stator winding and the rotor winding of the synchronous motor.
On the basis, the presynchronization control method of the virtual synchronous machine without the phase-locked loop comprises the following steps:
1) the virtual synchronous machine operates with local active load before grid connection and acquires three-phase voltage u of a power gridpA、upB、upCAnd the virtual synchronous machine outputs three-phase voltage uoA、uoB、uoCAnd if the three-phase voltage is symmetrical, then:
upA+upB+upC＝0
uoA+uoB+uoC＝0
2) according to 3/2 coordinate transformation:
the expressions of obtaining the alpha beta axis component of the output voltage of the virtual synchronous machine and the alpha beta axis component of the grid voltage under the alpha beta coordinate system are respectively as follows:
uoα＝Uomcosθo；uoβ＝Uomsinθo
upα＝Upmcosθp；upβ＝Upmsinθp
in the formula of UpmTo the grid voltage amplitude, UomFor outputting a voltage amplitude, θ, to the virtual synchronous machine0For the phase of the output voltage of the virtual synchronous machine, thetapIs the phase of the grid voltage; further, the method can be obtained as follows:
Upm＝upα 2+upβ 2；Uom＝uoα 2+uoβ 2
thereby: Δ U ═ Upm-Uom
3) And providing a PI controller, sending the sine value sin delta theta and the voltage amplitude difference delta U of the phase difference to the PI controller, superposing an output error signal of the PI controller on a frequency given value of the power frequency controller and a voltage given value of the excitation controller to perform closed-loop control, inputting a steady-state error of 0 when the control is stable, namely the sin delta theta and the delta U are 0, closing a grid-connected switch when the output voltage of the virtual synchronous machine has a voltage amplitude and a phase which are consistent with the voltage of a power grid, and completing the grid-connected switching of the virtual synchronous machine.
Because the value of the phase difference delta theta obtained by the traditional phase-locked loop has a continuous jumping process, as shown in figure 4, when the delta theta is very small, sin delta theta is approximately equal to the delta theta, and the sin delta theta does not have a jumping process and is always a continuous curve, as shown in figure 5, the sin delta theta obtained under an alpha beta coordinate system is adopted to replace the phase difference delta theta and is sent to a PI link for phase presynchronization control, the influence of the phase difference delta theta symbol jumping process on the presynchronization control process can be avoided, the design of the phase-locked loop is omitted, the presynchronization control process is simplified, the control precision is improved, and the control speed is improved.
Fig. 6 shows waveforms of a phase voltage a output by the virtual synchronous machine and a phase voltage a of a power grid during a virtual synchronous machine presynchronization control simulation under MATLAB/simulink, and fig. 7 shows a waveform of a sine value sin Δ θ of a phase difference between the two waveforms. As shown in the figure, the pre-synchronization control switch is opened at 0.2s, then the output voltage phase of the virtual synchronous machine tracks the voltage phase of the power grid, and the consistency is realized at 0.26s, so that the pre-synchronization control process is completed. The method has the advantages that the experimental waveform can be obtained, the phase and the amplitude of the output voltage of the virtual synchronous machine accurately track the phase and the amplitude of the voltage of the power grid after the presynchronization is started, the grid-connected switch is closed after the presynchronization is completed, the off/grid-connected switching of the virtual synchronous machine is realized, obvious grid-connected instant power impact does not occur, the presynchronization control is cut off after grid connection, and the grid-connected current of the virtual synchronous machine rises to enable the output power to reach a power set value and stably work.
The parts of the invention not described are the same as the prior art.
Claims (1)
1. The presynchronization control method of the virtual synchronous machine without the phase-locked loop is characterized by comprising the following steps of:
1) the virtual synchronous machine operates with local active load before grid connection and acquires three-phase voltage u of a power gridpA、upB、upCAnd the virtual synchronous machine outputs three-phase voltage uoA、uoB、uoCAnd if the three-phase voltage is symmetrical, then:
upA+upB+upC＝0
uoA+uoB+uoC＝0
2) according to the 3/2 coordinate transformation formula, obtaining the expression of the alpha-beta axis component of the output voltage of the virtual synchronous machine and the alpha-beta axis component of the power grid voltage under an alpha-beta coordinate system as follows:
alpha-axis component u of output voltage of virtual synchronous machineoα：uoα＝Uomcosθo
Beta-axis component u of output voltage of virtual synchronous machineoβ：uoβ＝Uomsinθo
Alpha-component u of the mains voltagepα：upα＝Upmcosθp
Beta-axis component u of the network voltagepβ：upβ＝Upmsinθp
In the formula of UpmFor the amplitude of the mains voltage, UomFor outputting a voltage amplitude, θ, to the virtual synchronous machine0For the phase of the output voltage of the virtual synchronous machine, thetapIs the phase of the grid voltage; further, the method can be obtained as follows:
Upm＝upα 2+upβ 2
Uom＝uoα 2+uoβ 2
ΔU＝Upm-Uom
3) and providing a PI controller, sending the sine value sin delta theta and the voltage amplitude difference delta U of the phase difference to the PI controller, superposing an output error signal of the PI controller on a frequency given value of the power frequency controller and a voltage given value of the excitation controller to perform closed-loop control, inputting a steady-state error of 0 when the control is stable, namely the sin delta theta and the delta U are 0, closing a grid-connected switch when the output voltage of the virtual synchronous machine has a voltage amplitude and a phase which are consistent with the voltage of a power grid, and completing the grid-connected switching of the virtual synchronous machine.
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