CN114744675A - Low voltage ride through control method and device for virtual synchronous generator - Google Patents

Low voltage ride through control method and device for virtual synchronous generator Download PDF

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Publication number
CN114744675A
CN114744675A CN202210395667.0A CN202210395667A CN114744675A CN 114744675 A CN114744675 A CN 114744675A CN 202210395667 A CN202210395667 A CN 202210395667A CN 114744675 A CN114744675 A CN 114744675A
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grid
power
voltage
synchronous generator
fault
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靳江江
王振福
王世权
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Huaneng Dingbian New Energy Electricity Generating Co ltd
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Huaneng Dingbian New Energy Electricity Generating Co ltd
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Priority to AU2022291654A priority patent/AU2022291654A1/en
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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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/14—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
    • 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The embodiment of the specification provides a virtual synchronous generator low voltage ride through control method and device, wherein the method comprises the following steps: the virtual synchronous generator runs a VSG-based grid-connected inverter control algorithm, runs a grid-connected pre-synchronization algorithm after entering a first stable state, executes automatic grid connection after synchronizing with a power grid, and cuts off the grid-connected pre-synchronization algorithm; inputting grid-connected active power and reactive power after grid connection, so that the virtual synchronous generator is increased to a given value by a slope curve and enters a second stable state; when a power grid fault is detected, the type of the fault and the drop depth cut-in virtual resistance are determined through a fault detection module, grid-connected active power output is adjusted, the control capacity of VSG on current is increased through an additional current loop, and the running characteristic of the simulated SG underexcited state is kept; when the grid fault is recovered, the output omega of the active loop and the output E of the reactive loop of the virtual synchronous generator are recovered to a normal operation state after delaying for a plurality of cycles. When solving the grid voltage trouble, improve VSG control system's stability.

Description

Low voltage ride through control method and device for virtual synchronous generator
Technical Field
The present invention relates to the field of virtual synchronous generators, and in particular, to a low voltage ride through control method and apparatus for a virtual synchronous generator.
Background
In recent years, energy and environmental problems become a great challenge for the development of the human society, new energy is widely used, and more distributed power supplies start to be connected to a power grid. With the enlargement of the capacity and the scale of the distributed power supply access power grid, the occupation ratio of the synchronous generator in the power grid is lower and lower, but the advantages of the synchronous generator in the power grid are prominent: firstly, the motion inertia of the rotor enables the rotor to have stronger robustness, and the damping existing between machines limits the rapid change of the state of the rotor; and secondly, the synchronous generator can directly participate in voltage regulation and frequency modulation of the power grid. The occupancy of the synchronous generator is reduced, inertia and damping characteristics provided for the power grid are reduced, the distributed power supply needs to be connected to the power grid through a power electronic device, and the power electronic device is long at a high switching speed, so that the grid-connected inverter does not have inertia and damping characteristics and cannot provide corresponding frequency voltage support for the power grid, and the stability of the power system is reduced. To solve this problem, Virtual Synchronous Generator (VSG) technology has been developed. The VSG controlled grid-connected inverter simulates the mechanical characteristics and the electrical characteristics of SG and can participate in voltage regulation and frequency modulation of a power grid like SG, so that the external characteristics of the grid-connected inverter adopting a VSG control algorithm are approximately consistent with the SG, and the problem of large-scale new energy power generation grid connection is solved by the VSG technology. However, when the voltage of the power grid drops, the output current is out of limit due to a traditional VSG control strategy based on active-frequency control, so that power electronic devices are damaged, and the inverter is disconnected; in addition, even if the VSG is not off-grid when the voltage of the power grid drops, the traditional VSG cannot provide reactive support for the power grid during low voltage ride through, and is not beneficial to the recovery of the voltage of the power grid. Moreover, when the power grid fails, the conventional VSG also has the problems of power angle oscillation, instability, slow recovery process and the like. Therefore, the research on the low voltage ride through control of the VSG is of great significance.
A 'virtual synchronous generator low voltage ride through control method based on mode smooth switching' published in 'power grid technology' in 2016 and 5 months on the first-class, the old proposes a control strategy of VSG and traditional LVRT smooth switching, and can avoid transient current impact caused by sudden change of a control mode during fault recovery and realize low voltage ride through of the VSG under different working conditions. However, the method changes the essential attribute of VSG control, does not carry out deep analysis on switching stability, and does not carry out analysis on the switching transient process. And it is not demonstrated whether the direct current control strategy is more advantageous than the virtual synchronous machine control strategy during a grid voltage sag.
In the 'virtual synchronous generator low voltage ride through control strategy based on all-pass filter' published in 'power automation equipment' in 5.2019, Lufang boat and the like, it is proposed that damping torque is added into VSG to ensure the stability of rotor motion and a power grid voltage deviation feedback current loop is combined to ensure the stable transition of output current to realize low voltage ride through. However, the scheme has the defects in the VSG system stability analysis research under the asymmetric fault.
The 'virtual synchronous generator low voltage ride through control strategy based on underexcited state operation' published by Schaku et al in 3 months 'power system automation' in 2018 provides a new LVRT control method based on VSG operated in an underexcited state. The droop characteristic, the reactive ring and the active ring are respectively improved without changing the original VSG control structure, so that the transient impact of the power grid fault on the VSG is restrained, and the conversion process of the excitation state is accelerated. And an additional current loop is improved on the basis of keeping the original VSG characteristics, a new orientation method is applied, the operation of the system in an underexcited state is assisted, and fault ride-through is realized. The method does not need a switching control algorithm or a state smooth switching strategy, and can simultaneously solve the problems of LVRT and power grid asymmetric drop. However, the control scheme still has an over-current condition during the low voltage ride through process, and the transient current peak value is large, and meanwhile, the virtual resistor at the VSG output terminal increases the impedance of the filter and the transmission network when the VSG is in normal operation, and changing the impedance characteristics of the filter and the transmission network will have the following effects: 1) the output impedance of the VSG is increased, so that the synchronous power of the VSG is reduced, and the VSG is not beneficial to stabilization; 2) the coupling relation between active power and reactive power and the phase-amplitude value of the potential in the VSG is changed; 3) the voltage drop across the virtual resistor for the normal operating current of the VSG can affect the performance of the VSG under normal grid conditions. The voltage drop on the virtual resistor is different at different operating points.
Disclosure of Invention
One or more embodiments of the present specification provide a virtual synchronous generator low voltage ride through control method, including:
s1, the virtual synchronous generator runs a VSG-based grid-connected inverter control algorithm, runs a grid-connected pre-synchronization algorithm after entering a first stable state, executes automatic grid connection after being synchronized with a power grid, and cuts off the grid-connected pre-synchronization algorithm;
s2, inputting grid-connected active power and reactive power after the virtual synchronous generator is connected to the grid, so that the virtual synchronous generator is increased to a given value by a slope curve and enters a second stable state;
s3, when the virtual synchronous generator detects that a power grid fault occurs, the type and the falling depth of the fault are determined through the fault detection module, a fault flag bit is output, a cut-in virtual resistor is controlled according to the fault flag bit, grid-connected active power output is adjusted according to the falling depth, a reactive loop is shielded, meanwhile, the VSG control capacity on current is increased through an additional current loop, and the running characteristics of the SG underexcited state are kept simulated;
and S4, when the virtual synchronous generator detects that the grid fault is recovered, recovering the output omega of the active loop and the output E of the reactive loop of the virtual synchronous generator to a normal operation state after delaying for a plurality of cycles, and removing the virtual resistor.
One or more embodiments of the present specification provide a virtual synchronous generator low voltage ride through control device, including:
the virtual synchronous generator runs a VSG-based grid-connected inverter control algorithm, runs a grid-connected pre-synchronization algorithm after entering a first stable state, executes automatic grid connection after being synchronized with a power grid, and cuts off the grid-connected pre-synchronization algorithm;
the virtual synchronous generator is connected with the grid and then inputs grid-connected active power and reactive power, so that the virtual synchronous generator is increased to a given value by a slope curve and enters a second stable state;
the low-voltage ride-through module is used for determining the type and the falling depth of a fault through the fault detection module when the virtual synchronous generator detects that a power grid fault occurs, outputting a fault zone bit, controlling a cut-in virtual resistor according to the fault zone bit, adjusting grid-connected active power output according to the falling depth, shielding a reactive loop, increasing the control capability of VSG on current through an additional current loop, and keeping the running characteristic of the simulated SG underexcited state;
and when the virtual synchronous generator detects that the power grid fault is recovered, the output omega of the active ring and the output E of the reactive ring of the virtual synchronous generator are recovered to a normal operation state after delaying for a plurality of cycles, and the virtual resistor is cut off at the same time.
One or more embodiments of the present specification provide an electronic device including:
a processor; and the number of the first and second groups,
a memory arranged to store computer executable instructions that, when executed, cause the processor to implement the steps of the virtual synchronous generator low voltage ride through control method as described above.
One or more embodiments of the present specification provide a storage medium for storing computer-executable instructions that, when executed, implement the steps of the virtual synchronous generator low voltage ride through control method as described above.
The method improves the operation state of the VSG algorithm to be kept at the value before the fault occurs when the power grid fault is detected by the virtual synchronous generator low-voltage ride through control strategy based on underexcitation state operation; when the recovery of the grid fault is detected, the low voltage ride through strategy of the VSG algorithm is recovered after the system delays for a plurality of weeks, and from another angle, the operation state of the virtual synchronous generator is controlled aiming at different faults by analyzing the type and the depth of the grid voltage drop, so that the low voltage ride through of the VSG is realized.
Drawings
In order to more clearly illustrate one or more embodiments or prior art solutions of the present specification, the drawings that are needed in the description of the embodiments or prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present specification, and that other drawings can be obtained by those skilled in the art without inventive exercise.
Fig. 1 is a flowchart of a low voltage ride through control method of a virtual synchronous generator according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a grid-connected inverter based on virtual synchronous generator control according to an embodiment of the present invention;
FIG. 3 is a timing diagram of a low voltage ride through of a grid tied inverter of an embodiment of the present invention;
FIG. 4 is a schematic diagram of a low voltage ride through control method of a grid-tied inverter control algorithm operating at a VSG in accordance with an embodiment of the present invention;
FIG. 5 is a block diagram of pre-synchronization grid-connection strategy control according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of an inverter voltage angle and a grid voltage angle in a pre-synchronization grid-connection process of a dual PLL grid-connection pre-synchronization strategy according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of an A-phase voltage and a grid A-phase voltage in a pre-synchronization grid connection process of a dual PLL grid connection pre-synchronization strategy according to an embodiment of the present invention;
fig. 8 is a schematic voltage diagram of a grid-connected point of a low voltage ride through when the three phases of the grid voltage drop to 0.2pu of the virtual synchronous generator according to the embodiment of the present invention;
fig. 9 is a schematic voltage diagram of a grid-connected point of a low voltage ride through when the three phases of the grid voltage drop to 0.5pu of the virtual synchronous generator according to the embodiment of the present invention;
fig. 10 is a schematic diagram of grid-connected current of the virtual synchronous generator according to the embodiment of the present invention when the three phases of the grid voltage drop to 0.2pu, and the low voltage passes through;
fig. 11 is a schematic diagram of active power of a virtual synchronous generator according to an embodiment of the present invention when the three phases of the grid voltage drop to 0.2pu, and the low voltage passes through;
fig. 12 is a schematic diagram of reactive power of a virtual synchronous generator according to an embodiment of the present invention when the three phases of the grid voltage drop to 0.2pu for low voltage ride through;
fig. 13 is a schematic diagram of grid-connected current of the virtual synchronous generator according to the embodiment of the present invention when the three phases of the grid voltage drop to 0.5pu for low voltage ride through;
fig. 14 is a schematic diagram of active power of a virtual synchronous generator according to an embodiment of the present invention when the three phases of the grid voltage drop to 0.5pu for low voltage ride through;
fig. 15 is a schematic diagram of reactive power of a virtual synchronous generator according to an embodiment of the present invention when the three phases of the grid voltage drop to 0.5pu for low voltage ride through;
fig. 16 is a schematic diagram of grid-connected current of the virtual synchronous generator according to the embodiment of the present invention when the grid voltage drops to 0.2pu in a single phase manner and the voltage passes through the low voltage;
fig. 17 is a schematic diagram of a virtual synchronous generator low voltage ride through control apparatus according to an embodiment of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solutions in one or more embodiments of the present disclosure, the technical solutions in one or more embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in one or more embodiments of the present disclosure, and it is obvious that the described embodiments are only a part of the embodiments of the present disclosure, and not all embodiments. All other embodiments that can be derived by a person skilled in the art from one or more of the embodiments described herein without making any inventive step shall fall within the scope of protection of this document.
Method embodiment
According to an embodiment of the present invention, a method for controlling a low voltage ride through of a virtual synchronous generator is provided, fig. 1 is a flowchart of the method for controlling a low voltage ride through of a virtual synchronous generator according to an embodiment of the present invention, and as shown in fig. 1, the method for controlling a low voltage ride through of a virtual synchronous generator according to an embodiment of the present invention specifically includes:
step S101, the virtual synchronous generator runs a grid-connected inverter control algorithm based on VSG, runs a grid-connected pre-synchronization algorithm after entering a first stable state, executes automatic grid connection after being synchronized with a power grid, and cuts off the grid-connected pre-synchronization algorithm;
step S102, inputting grid-connected active power and reactive power after the virtual synchronous generator is connected to the grid, so that the virtual synchronous generator is increased to a given value by a slope curve and enters a second stable state;
s103, when the virtual synchronous generator detects that a power grid fault occurs, determining the type and the falling depth of the fault through a fault detection module, outputting a fault zone bit, controlling a cut-in virtual resistor according to the fault zone bit, adjusting grid-connected active power output according to the falling depth, shielding a reactive loop, increasing the control capacity of VSG on current through an additional current loop, and keeping the running characteristic of the simulated SG underexcited state;
and S104, when the virtual synchronous generator detects that the grid fault is recovered, recovering the output omega of the active loop and the output E of the reactive loop of the virtual synchronous generator to a normal operation state after delaying for a plurality of cycles, and simultaneously cutting off the virtual resistor.
The virtual synchronous generator low voltage ride through control method further comprises the following steps: the virtual synchronous generator enables the VSG system to run approximately with a unit power factor when the power grid is normal and fluctuated, and the normal excitation state running characteristic and the droop characteristic of the synchronous generator are simulated.
Referring to fig. 2 to 16, a virtual synchronous generator low voltage ride through control method is specifically described, fig. 2 is a schematic diagram of a grid-connected inverter structure based on virtual synchronous generator control according to an embodiment of the present invention, a new energy power generation device is connected to an inductor 30 of a three-phase LC filter through a power converter 20, where the inductor 30 is a three-phase inductor L in fig. 2f(ii) a The inductor 30 is connected to the output current sensor 52 via the capacitor 31 of the three-phase LC filter, and the capacitor 31 is the three-phase capacitor C in fig. 2fThe output current sensor 52 includes three current sensors I in fig. 2a、Ib、IcWherein the capacitor 31 of the three-phase LC filter adopts star connection, and the two ends of the capacitor 31 are connected with the capacitance voltage sensor 40 of the LC filter, and the capacitance voltage sensor 40 comprises three in figure 2Voltage sensor ua、ub、uc(ii) a The output current sensor 52 is connected to a three-phase grid-connected contactor 60, the three-phase grid-connected contactor 60 being a three-phase contactor PCC in fig. 2, the three-phase grid-connected contactor 60 being connected to a three-phase grid 71 via a grid line impedance 70, the grid line impedance 70 comprising a three-phase resistor R in fig. 2gThree-phase reactance Lg；
The output end of a capacitance voltage sensor 40 of the LC filter is simultaneously connected with the input end of an instantaneous power calculation module 82 output by the grid-connected inverter and the input end of a first 3s/2r conversion module 81, and the output end of an output current sensor 52 is simultaneously connected with the input end of the instantaneous power calculation module 82 and the input end of a synthetic vector module 83 of output current of the grid-connected inverter;
output signal P of instantaneous power calculation module 82eThe output signal Q of the instantaneous power calculation module 82 is connected to the power feedback input end of the virtual exciter 100;
two output signals u of a first 3s/2r conversion module 81d、uqThe input end of a voltage amplitude calculation module 90 which is provided by the invention and used for switching the output of the inverter when the voltage of the power grid fails is connected;
output signal u of voltage amplitude calculation module 90 output by invertermThe output signal I of the resultant vector module 83 of the output current of the grid-connected inverter, which is connected to the voltage amplitude feedback terminal of the virtual exciter 100&The input end of the stator electrical equation module 120 is accessed;
the invention provides an output P of an active power given value calculation module 92 according to the type of the power grid fault and the voltage drop depth of the power grid*The virtual speed regulator 91 is connected, the output f of the grid voltage positive and negative sequence separation module 150 is connected to the virtual speed regulator 91, and the output u of the grid voltage positive and negative sequence separation module 150dq +And udq -The output signal P of the power grid fault detection module 180 and the virtual speed regulator 91 is connectedmThe power giving end of the rotor mechanical equation module 101 is accessed;
the output signal theta of the rotor mechanical equation module 101 is simultaneously coupled to the output signal E of the virtual exciter 100An input for a three-phase voltage 110; synthesizing the output signals of the three-phase voltage 110, i.e. E in FIG. 2a、Eb、EcAnd the output signal of the dummy resistance module 120, i.e., Δ u in FIG. 2a、Δub、ΔucMeanwhile, the input end of the output voltage calculation module 130 of the virtual synchronous generator is accessed;
the output signal of the output voltage calculation module 130, i.e. u in FIG. 2a *、ub *、uc *The input end of the second 3s/2r conversion module 140 is connected with the PLL, and the angle theta of the output voltage of the PLL is connected with the input end of the second 3s/2r conversion module 140; the output signal of the second 3s/2r transform module 140, i.e. u in FIG. 2α *、uβ *The input end of the grid-connected inverter current loop amplitude limiting module 160 is accessed;
the output signal of the clipping module 150, i.e. i in fig. 2Lα *、iLβ *The grid voltage is accessed to the input end of a PI controller of a current loop of the grid-connected inverter after operation;
the inductive current sensor 50 is connected to the input of a first 3s/2r transform module 81, the output signal of the first 3s/2r transform module 81, i.e. i in fig. 2d、iqAnd is connected to the feedback end of the grid-connected inverter current loop module 160;
the output signal of the grid-connected inverter current loop module 160 is connected to the input end of the 2s/3s conversion module 170, the output signal of the 2s/3s conversion module 170, namely U in FIG. 2, is connected to the input end of the SPWM modulation module 180, the output signal of the SPWM modulation module 180 is used as the driving signal of the power converter 20, and the switching action of a power device is controlled so as to realize the electric energy conversion;
fig. 3 is a low voltage ride through timing diagram of a grid-connected inverter according to an embodiment of the present invention, fig. 4 is a schematic diagram of a low voltage ride through control method of a grid-connected inverter control algorithm operating on a VSG according to an embodiment of the present invention, and according to the hardware configuration shown in fig. 1 and shown in fig. 4, the virtual synchronous generator low voltage ride through control method is implemented according to the following steps:
step 1, operating a VSG-based grid-connected inverter control algorithm, operating a grid-connected pre-synchronization algorithm after entering a steady state, automatically and synchronously connecting with a power grid, and removing the pre-synchronization algorithm at the moment of grid connection;
the embodiment of the invention adopts a double PLL grid-connected presynchronization strategy proposed by Yangliang of China mining university and the control block diagram of the strategy is shown in figure 5, the phase angle theta output by a VSG active power loop is compensated after the phase angle of grid voltage and the phase angle of output voltage of a grid-connected inverter are subjected to difference through a PI controller, and the output phase angle of the inverter can be the same as the grid voltage. The method comprises the following specific steps: firstly, converting a voltage reference value of a virtual excitation controller into an amplitude value of a power grid voltage, and converting a droop coefficient D of the excitation controllerqAn integration link is added to enable the inverter voltage amplitude to have no static error and track the grid voltage amplitude, and a specific control block diagram of the system is shown in reference to fig. 4. After the pre-synchronization is started, the switch 1 and the switch 2 are closed, and the switch 4 and the switch 5 are respectively closed at omegag，ugThe inverter frequency and the voltage reference value are converted to the power grid side, and the output voltage amplitude and the frequency of the inverter are adjusted without static difference. When the output frequency of the inverter is the same as the grid frequency, the switch 3 is closed, so that the inverter phase does not have a static error to track the grid phase. And when the output voltage of the inverter is coincided with the voltage of the power grid, closing the grid-connected contactor PCC. Opening switch 1, switch 2 and switch 3 exits the quiet regulation of phase, amplitude and frequency. Switch 4 and switch 5 are closed at omega respectivelynAnd unAnd enabling the inverter to have frequency modulation and voltage regulation characteristics, and completing inverter grid connection.
Step 2, inputting grid-connected active power and reactive power after the grid is accessed, increasing the grid-connected active power and reactive power to a given value by a slope curve and entering a steady state;
step 3, enabling the VSG system to operate approximately to a unit power factor when the power grid is normal and fluctuates, and simulating the normal excitation state operation characteristic and droop characteristic of the SG;
when the voltage drop amplitude of the power grid is too small, the system judges that the power grid is in power grid disturbance instead of power grid fault at the moment, and V is calculated according to the double synchronous PLLpabcDirectly triggering the original droop response. At this time, the given reactive value is Q*And Q is taken by reactive feedback. The system operation state is as shown in FIG. 3Showing the original VSG response characteristics.
And 4, when the power grid fault is detected to happen instantly, the fault detection module determines the type of the fault and the falling depth through calculation, then outputs a fault zone bit, and simultaneously calculates the power output of the VSG active loop and the output voltage amplitude of the reactive loop to complete the transition from the normal excitation state to the underexcitation state. And switching in the virtual resistor to reduce fault current, adjusting grid-connected active power output according to the voltage drop degree of the power grid, providing reactive support for the power grid, and simultaneously increasing the control capability of VSG on current through an additional current loop.
Specifically, as shown in a block diagram 4, positive and negative sequence components of the grid voltage are extracted through a decoupling phase-locked loop under a double-synchronous coordinate system, when the grid voltage fault is judged, a fault signal S is output to be 1 by a fault detection module, and at the moment, a switch S is switched on1Switching to make the given value and feedback value of reactive power offset the droop characteristic of the shielding reactive loop to make the feedback value of voltage amplitude equal to the given value, S2The switch is closed to cut into the virtual resistance module, the real-time positive sequence component of the grid voltage under a d-q coordinate system is calculated, and the calculated positive sequence component of the grid voltage d-q axis is sent to a given power calculation module of an active loop, wherein the specific calculation formula is as follows:
Figure BDA0003597236310000101
wherein, PrefGiven active power, V, for normal grid-connected operationampIs the amplitude, V, of the mains voltaged +And Vq +Is a d-q axis positive sequence voltage component, P, of the power grid*Real-time active power is given after the voltage of the power grid falls, N is an intermediate variable representing the voltage falling degree and is defined as the ratio of the actual voltage amplitude of the power grid to the rated voltage value of the power grid, and VNIs the grid voltage rating.
Virtual resistance RvIncreases the equivalent impedance of the VSG at fault ride-through, which is expressed by the following equation:
Figure BDA0003597236310000111
in addition, the limiting current loop is shown as 160 in FIG. 2, and the current loop adopts VSG algorithm reactive loop output phase theta under a rotating coordinate systeminFor current loop positioning, taking the positive sequence component of the grid voltage as the feedback quantity and UinCalculating a given current through a PI link, limiting (the current is not limited when a fault signal is 0) through a P link to enable the current to be within 1.3pu, and then adding reactive compensation to calculate delta I after calculating the q-axis given currentq *，ΔIq *The specific calculation process is as follows:
the reactive power expression under the d-q rotating coordinate system is as follows:
Figure BDA0003597236310000112
wherein Q is reactive power under d-Q rotating coordinate system, VdAnd VqIs a voltage component under d-q rotating coordinate system, IdAnd IqThe current component in the coordinate system is rotated for d-q.
Since the VSG outputs an active power rating while the fault current of the VSG is limited to within 1.3pu during a grid fault, in order to provide the maximum reactive support for the grid at this time, the following formula can be obtained:
Figure BDA0003597236310000113
in the formula VmabcIs the amplitude of the positive sequence grid voltage, I*For amplitude of the grid-connected current, kiFor the current overload multiple during fault to be equal to ki＝1.3，SmaxIn order to ensure the maximum value of the apparent power when the fault current is within 1.3pu, P is the grid-connected active power.
The reactive power compensation current brought into the available reactive power compensation current is as follows:
Figure BDA0003597236310000114
wherein, Delta IqCompensating the current for the reactive power of the network, VmabcTo the amplitude of the positive-sequence grid voltage, I*For amplitude of the grid-connected current, kiThe current overload multiple during the fault period is shown, and P is grid-connected active power.
Step 5, outputting omega of the active loop at the moment of detecting the recovery of the power grid faultmAnd output E of the reactive loopmAnd after delaying for a plurality of periods, the VSG control state is restored to a normal VSG control state, so that the current impact caused by the sudden change of the state is buffered, and the virtual resistor is cut off from the system, namely.
To illustrate the effectiveness of the embodiments of the present invention, simulation verification was performed in MATLAB, and the verification results and data analysis were as follows:
the simulated working condition (1) is as follows: and starting grid connection presynchronization at 0.2s, starting grid connection at 0.5s, cutting off a presynchronization algorithm, increasing the power in a slope mode at 0.6s, enabling the system to stably run at about 1.2s, and enabling the three-phase voltage to drop at 2s for 0.625 s.
The simulation working condition (2) is as follows: and starting grid connection presynchronization at 0.2s, starting grid connection at 0.5s, cutting off a presynchronization algorithm, increasing the power in a slope mode at 0.6s, enabling the system to stably operate at about 1.2s, and enabling the single-phase voltage to drop to 0.2pu at 2s for 0.625 s.
FIG. 6 is a graph of inverter voltage angle and grid voltage angle during pre-synchronization of a dual PLL grid-tie pre-synchronization strategy;
FIG. 7 is a diagram of dual PLL grid-connection pre-synchronization strategy pre-synchronization grid-connection process A phase voltage and grid A phase voltage;
FIG. 8 shows the grid-connected point voltage of the low voltage ride through when the three phases of the grid voltage drop to 0.2pu for the virtual synchronous generator according to the method of the present invention;
FIG. 9 shows the grid-connected point voltage of the low voltage ride through when the three phases of the grid voltage drop to 0.5pu for the virtual synchronous generator according to the method of the present invention;
fig. 10 shows the grid-connected current of the virtual synchronous generator in the low-voltage ride through when the three-phase voltage of the power grid drops to 0.2pu, and it can be seen from fig. 10 that the maximum amplitude of the inrush current generated in the low-voltage ride through process by the method of the present invention is 33.61 a.
Fig. 11 and 12 show the active power and reactive power of the virtual synchronous generator with low voltage ride through when the three phases of the grid voltage drop to 0.2pu according to the method of the present invention, and it can be seen that the solution of the present invention can provide 643var of reactive support during the fault period, and the peak value of active power fluctuation is 3253W.
Fig. 13 shows the grid-connected current of the virtual synchronous generator of the present invention during the low voltage ride through when the three-phase of the grid voltage drops to 0.5pu, and it can be seen from fig. 14 that the maximum surge current amplitude generated during the fault ride through by the present invention is about 27.02A.
Fig. 15 and 16 show the active power and reactive power of the virtual synchronous generator in the method of the present invention when the three phases of the grid voltage drop to 0.2pu, and it can be seen that the solution of the present invention can provide 450var of reactive support during the fault period, and the peak value of the active power fluctuation is 3140W.
Fig. 16 shows the grid-connected current of the virtual synchronous generator with low voltage ride through when the grid voltage drops to 0.2pu in a single phase, and it can be seen from fig. 10 that the amplitude of the impulse current generated by the method of the present invention at 2.0s and 2.625s is about 21.61A.
Through the simulation verification and comparison, the control method can ensure that the grid-connected inverter controlled by the VSG passes through at low voltage under the condition of no large overcurrent, provides certain reactive support for a power grid, and can uniformly process symmetrical and asymmetrical faults.
Apparatus embodiment one
According to an embodiment of the present invention, a virtual synchronous generator low voltage ride through control device is provided, fig. 17 is a schematic diagram of the virtual synchronous generator low voltage ride through control device according to the embodiment of the present invention, and as shown in fig. 17, the virtual synchronous generator low voltage ride through control device according to the embodiment of the present invention specifically includes:
the island operation module 171 is used for operating a VSG-based grid-connected inverter control algorithm by the virtual synchronous generator, operating a grid-connected pre-synchronization algorithm after entering a first stable state, executing automatic grid connection by the virtual synchronous generator after synchronizing with a power grid, and cutting off the grid-connected pre-synchronization algorithm;
the grid connection module 172 inputs grid connection active power and reactive power after the virtual synchronous generator is connected to the grid, so that the virtual synchronous generator is increased to a given value by a slope curve and enters a second stable state;
the low-voltage ride-through module 173 determines the type and the drop depth of a fault through the fault detection module when the virtual synchronous generator detects that a power grid fault occurs, outputs a fault zone bit, controls the cut-in of a virtual resistor according to the fault zone bit, adjusts the grid-connected active power output according to the drop depth, shields a reactive loop, increases the control capability of VSG on current through an additional current loop, and keeps the running characteristic of a simulated SG underexcited state;
and in the recovery module 174, when the virtual synchronous generator detects that the grid fault is recovered, the output ω of the active loop and the output E of the reactive loop of the virtual synchronous generator are recovered to a normal operation state after delaying for a plurality of cycles, and the virtual resistor is removed.
The virtual synchronous generator low voltage ride through control device further comprises: and the normal operation module is used for enabling the VSG system to operate at a similar unit power factor when the power grid is normal and fluctuates and simulating the normal excitation state operation characteristic and the droop characteristic of the synchronous generator.
Device embodiment II
An embodiment of the present invention provides an electronic device, including:
a processor; and (c) a second step of,
a memory arranged to store computer executable instructions which, when executed, cause the processor to carry out the steps as described in the above method embodiments.
Example III of the device
Embodiments of the present invention provide a storage medium for storing computer-executable instructions that, when executed, implement the steps as described in the above-described method embodiments.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A virtual synchronous generator low voltage ride through control method is characterized by comprising the following steps:
s1, the virtual synchronous generator runs a VSG-based grid-connected inverter control algorithm, runs a grid-connected pre-synchronization algorithm after entering a first stable state, executes automatic grid connection after being synchronized with a power grid, and cuts off the grid-connected pre-synchronization algorithm;
s2, inputting grid-connected active power and reactive power after the virtual synchronous generator is connected to the grid, and enabling the virtual synchronous generator to increase to a given value in a slope curve and enter a second stable state;
s3, when the virtual synchronous generator detects that a power grid fault occurs, the type and the falling depth of the fault are determined through a fault detection module, a fault flag bit is output, a cut-in virtual resistor is controlled according to the fault flag bit, grid-connected active power output is adjusted according to the falling depth, a reactive loop is shielded, meanwhile, the VSG current control capacity is increased through an additional current loop, and the running characteristic of a simulated SG underexcited state is kept;
and S4, when the virtual synchronous generator detects that the grid fault is recovered, recovering the output omega of the active loop and the output E of the reactive loop of the virtual synchronous generator to a normal operation state after delaying for a plurality of cycles, and simultaneously cutting off the virtual resistor.
2. The method of claim 1, wherein the virtual synchronous generator low voltage ride through control method further comprises: the virtual synchronous generator enables the VSG system to operate approximately with a unit power factor when the power grid is normal and fluctuates, and the normal excitation state operation characteristic and the droop characteristic of the synchronous generator are simulated.
3. The method according to claim 1, wherein in step S3, controlling a cut-in virtual resistance according to the fault flag, and adjusting a grid-connected active power output according to the drop depth specifically comprises:
obtaining the virtual resistance R by equation 1v；
Figure FDA0003597236300000011
Wherein R isvIs a virtual resistance value, S is a fault flag bit;
extracting positive and negative sequence components of the power grid voltage through a decoupling phase-locked loop under a double-synchronous coordinate system, outputting a fault signal by a fault detection module when the power grid voltage is judged to be in fault, and switching through a switch S1Switching to make the given value and feedback value of reactive power offset the droop characteristic of the shielding reactive loop to make the feedback value of voltage amplitude equal to the given value, and switching by using switch S2The method comprises the steps of switching in a virtual resistance module, calculating a positive sequence component of real-time power grid voltage under a d-q coordinate system, sending the calculated positive sequence component of a d-q axis of the power grid voltage to a given power calculation module of an active ring, and obtaining real-time given active power after the power grid voltage drops through a formula 2;
Figure FDA0003597236300000021
wherein, PrefGiven active power, V, for normal grid-connected operationampIs the amplitude, V, of the mains voltaged +And Vq +Is a d-q axis positive sequence voltage component, P, of the power grid*Real-time active power is given after the voltage of the power grid drops, N is an intermediate variable representing the voltage drop degree and is defined as the ratio of the actual voltage amplitude of the power grid to the rated voltage value of the power grid, and VNIs the grid voltage rating.
4. The method of claim 1, wherein the increasing the current control capability of the VSG through the additional current loop, the maintaining the simulated SG under-excited state operating characteristics specifically comprises:
the additional current loop adopts VSG algorithm reactive loop output phase theta under a rotating coordinate systeminFor the positioning of the additional current loop, the positive sequence component of the network voltage is taken as the feedback quantity and UinAnd calculating a given current through a PI link, controlling the given current within a specific value, and calculating reactive power compensation current by adding reactive compensation after calculating the q-axis given current.
5. The method according to claim 4, the calculating a reactive power compensation current comprising in particular:
obtaining a reactive power expression under a d-q coordinate system through a formula 3;
Figure FDA0003597236300000022
wherein Q is reactive power in a d-Q rotating coordinate system, VdAnd VqIs a voltage component under d-q rotating coordinate system, IdAnd IqThe current component under a d-q rotating coordinate system is adopted;
acquiring reactive power compensation current of the power grid through a formula 4;
Figure FDA0003597236300000031
wherein, Delta IqCompensating the current for the reactive power of the network, VmabcIs the amplitude of the positive sequence grid voltage, I*For amplitude of the grid-connected current, kiThe current overload multiple during the fault period is shown, and P is grid-connected active power.
6. A virtual synchronous generator low voltage ride through control apparatus, comprising:
the virtual synchronous generator runs a VSG-based grid-connected inverter control algorithm, runs a grid-connected pre-synchronization algorithm after entering a first stable state, executes automatic grid connection after being synchronized with a power grid, and cuts off the grid-connected pre-synchronization algorithm;
the virtual synchronous generator is connected with the grid and then inputs grid-connected active power and reactive power, so that the virtual synchronous generator is increased to a given value by a slope curve and enters a second stable state;
the virtual synchronous generator comprises a low-voltage ride-through module, a fault detection module, a fault flag bit, a cut-in virtual resistor, a grid-connected active power output, a reactive ring, an additional current ring and a control module, wherein when the virtual synchronous generator detects that a power grid fault occurs, the type and the fall depth of the fault are determined through the fault detection module, the fault flag bit is output, the cut-in virtual resistor is controlled according to the fault flag bit, the grid-connected active power output is regulated according to the fall depth, the reactive ring is shielded, the VSG control capability on current is increased through the additional current ring, and the running characteristic of a simulated SG underexcited state is kept;
and when the virtual synchronous generator detects that the power grid fault is recovered, the output omega of the active ring and the output E of the reactive ring of the virtual synchronous generator recover to a normal operation state after delaying for a plurality of periods, and the virtual resistor is cut off at the same time.
7. The apparatus of claim 6, wherein the virtual synchronous generator low voltage ride through control apparatus further comprises: and the normal operation module is used for enabling the VSG system to operate at a similar unit power factor when the power grid is normal and fluctuates and simulating the normal excitation state operation characteristic and the droop characteristic of the synchronous generator.
8. The apparatus of claim 6, wherein the low voltage ride through module is specifically configured to:
obtaining the virtual resistance R by equation 1v；
Figure FDA0003597236300000041
Wherein R isvIs a virtual resistance value, S is a fault flag bit;
extracting positive and negative sequence components of the power grid voltage through a decoupling phase-locked loop under a double-synchronous coordinate system, outputting a fault signal by a fault detection module when the power grid voltage is judged to be in fault, and switching through a switch S1Switching to make the given value and feedback value of reactive power offset the droop characteristic of the shielding reactive loop, making the feedback value of voltage amplitude equal to the given value, and switching by switch S2Switching in a virtual resistance module, simultaneously calculating a positive sequence component of the real-time power grid voltage under a d-q coordinate system, transmitting the calculated positive sequence component of the d-q axis of the power grid voltage to a given power calculation module of an active loop, and acquiring real-time given active power after the power grid voltage drops through a formula 2;
Figure FDA0003597236300000042
wherein, PrefGiven active power, V, for normal grid-connected operationampIs the amplitude, V, of the mains voltaged +And Vq +Is a d-q axis positive sequence voltage component, P, of the power grid*Real-time active power is given after the voltage of the power grid falls, N is an intermediate variable representing the voltage falling degree and is defined as the ratio of the actual voltage amplitude of the power grid to the rated voltage value of the power grid, and VNIs the grid voltage rating;
the additional current loop adopts VSG algorithm reactive loop output phase theta under a rotating coordinate systeminFor the positioning of the additional current loop, the positive sequence component of the network voltage is taken as the feedback quantity and UinCalculating a given current through a PI link, controlling the given current within a specific value, and calculating reactive power compensation current by adding reactive power compensation after the q-axis given current is calculated;
obtaining a reactive power expression under a d-q coordinate system through a formula 3;
Figure FDA0003597236300000043
wherein Q is reactive power under d-Q rotating coordinate system, VdAnd VqFor the voltage component in the d-q rotating coordinate system, IdAnd IqThe current component under a d-q rotating coordinate system is adopted;
acquiring reactive power compensation current of the power grid through a formula 4;
Figure FDA0003597236300000051
wherein, Delta IqCompensating the current for the reactive power of the network, VmabcIs the amplitude of the positive sequence grid voltage, I*For amplitude of the grid-connected current, kiThe current overload multiple during the fault period is shown, and P is grid-connected active power.
9. An electronic device, comprising:
a processor; and the number of the first and second groups,
a memory arranged to store computer executable instructions that when executed cause the processor to implement the steps of the virtual synchronous generator low voltage ride through control method of any one of claims 1 to 5.
10. A storage medium storing computer executable instructions which, when executed, implement the steps of a virtual synchronous generator low voltage ride through control method as claimed in any one of claims 1 to 5.
CN202210395667.0A 2022-04-14 2022-04-14 Low voltage ride through control method and device for virtual synchronous generator Pending CN114744675A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116154850A (en) * 2023-01-11 2023-05-23 华北电力大学 Low-voltage ride through method and system for internal potential amplitude limiting and rotating virtual synchronous generator
CN117411098A (en) * 2023-10-16 2024-01-16 湖北工业大学 Self-adaptive virtual admittance current limiting method based on voltage drop dynamic

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116154850A (en) * 2023-01-11 2023-05-23 华北电力大学 Low-voltage ride through method and system for internal potential amplitude limiting and rotating virtual synchronous generator
CN116154850B (en) * 2023-01-11 2023-11-03 华北电力大学 Low-voltage ride through method and system for internal potential amplitude limiting and rotating virtual synchronous generator
CN117411098A (en) * 2023-10-16 2024-01-16 湖北工业大学 Self-adaptive virtual admittance current limiting method based on voltage drop dynamic
CN117411098B (en) * 2023-10-16 2024-04-19 湖北工业大学 Self-adaptive virtual admittance current limiting method based on voltage drop dynamic

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