CN111725833A - Virtual synchronous generator rotational inertia dynamic interval calculation method and system - Google Patents
Virtual synchronous generator rotational inertia dynamic interval calculation method and system Download PDFInfo
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Abstract
The invention relates to a method and a system for calculating a dynamic interval of rotational inertia of a virtual synchronous generator, wherein the method comprises the following steps: determining an upper limit value of a virtual synchronous generator rotational inertia dynamic interval according to corresponding rotational inertia of the virtual synchronous generator in different operating environments; determining a lower limit value of a dynamic interval of the rotational inertia of the virtual synchronous generator according to a difference value between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value; the calculation method provided by the invention considers that the rotational inertia of the virtual synchronous generator is influenced by a battery charge and discharge limit value, a damping ratio and a frequency improvement coefficient, and accurately calculates the dynamic interval of the rotational inertia of the virtual synchronous generator in a power grid; in practical application, the value of the rotational inertia of the virtual synchronous generator of the power grid is controlled to be within a dynamic range, so that the power oscillation frequency of the system can be effectively reduced, and the steady-state performance of the power grid is improved.
Description
Technical Field
The invention relates to the field of inverter control, in particular to a method and a system for calculating a dynamic interval of rotational inertia of a virtual synchronous generator.
Background
In recent years, with the continuous use of traditional fossil energy, the problems of energy crisis, environmental pollution, climate change and the like become more serious, and thus the scale of the distributed power generation mode such as renewable pollution-free wind energy, solar energy and the like is continuously enlarged. As a typical distributed power generation mode, the installation scale of a photovoltaic power generation system is continuously increased in nearly 20 years.
The inverter is used as the core of energy conversion and control in the distributed power generation system and an interface with a power distribution network, and the performance of the inverter directly influences and determines the quality of the whole grid-connected system. In order to better absorb new energy with an inverter as a core device, related researchers have proposed the concept of an ac microgrid capable of realizing "off/on grid" operation. However, the lack of support by the rotor inertia makes the frequency and voltage of the microgrid difficult to stabilize, bringing stability problems into the large grid when participating in the regulation of the latter. Therefore, how to make the inverter incorporated into the micro grid or the large grid to show the operation characteristics of the traditional synchronous generator is a research hotspot of domestic and foreign scholars. A Virtual Synchronous Generator (VSG) control strategy is introduced by taking the mechanical motion and the electromagnetic equation of the rotor of the traditional synchronous generator as reference, and the inertia and the damping characteristic of the synchronous generator can be simulated.
The power frequency transient process of the virtual synchronous generator is analyzed in a document 'improved rotary inertia adaptive control of the virtual synchronous generator in a multi-micro-source independent micro-grid' (Chinese motor engineering reports of Song Qiong, Zhang, Sun Ka, and the like, 2017, 37 (02): 412 and 424.), a virtual inertia adaptive VSG control scheme is provided, and a small J is provided to avoid dynamic power oscillation when the VSG is put into the micro-grid; when the frequency change rate is in zero crossing reversal, J takes a small value to realize rapid recovery of frequency, but the scheme uses the system frequency change rate as a feedback quantity and does not consider the influence of battery charge and discharge limitation on the selection of the inertia of the inverter.
The document 'cascading photovoltaic power generation system with synchronous motor characteristics' (Turkish singing, Lanzhen, Xiaofan, etc., China Motor engineering reports, 2017, 37 (02): 433-.
The literature 'a power grid-friendly light storage distributed power control strategy' (temperature and light, yogh, bidamen, and the like, the Chinese Motor engineering bulletin, 2017, 37 (02): 464-.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a method for accurately calculating a dynamic interval of the rotational inertia of a virtual synchronous generator, and provides a scientific basis for setting the rotational inertia of the virtual synchronous generator in the running process of a power grid.
The purpose of the invention is realized by adopting the following technical scheme:
the invention provides a method for calculating a dynamic interval of rotational inertia of a virtual synchronous generator, which is improved in that the method comprises the following steps:
determining an upper limit value of a virtual synchronous generator rotational inertia dynamic interval according to corresponding rotational inertia of the virtual synchronous generator in different operating environments;
and determining the lower limit value of the dynamic range of the rotational inertia of the virtual synchronous generator according to the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value.
Preferably, the determining the upper limit value of the virtual synchronous generator rotational inertia dynamic interval according to the corresponding rotational inertia of the virtual synchronous generator in different operating environments includes:
determining an upper limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamax：
Jmax＝min{J1,J2,J3}
In the formula, J1The maximum value of the corresponding moment of inertia is the maximum value when the virtual synchronous generator is in an over-damping or critical damping operation environment; j. the design is a square2The maximum value of the corresponding rotational inertia is obtained when a storage battery of a power grid to which the virtual synchronous generator belongs is in a maximum charging power operation environment; j. the design is a square3The maximum value of the corresponding rotational inertia is obtained when the storage battery of the power grid to which the virtual synchronous generator belongs is in the operating environment with the maximum discharge power.
Further, the maximum value J of the corresponding moment of inertia when the virtual synchronous generator is in the over-damping or critical damping operation environment is determined according to the following formula1：
In the formula, D is the damping coefficient of the virtual synchronous generator; x is the circuit equivalent reactance of the virtual synchronous generator;
is the damping ratio of the virtual synchronous generator; w is a0Is the rated angular frequency of the virtual synchronous generator; e is a virtual identityThe outlet voltage effective value of the step generator; u is the effective value of the voltage of the power grid;
wherein, when the virtual synchronous generator works in an over-damping state, then
Greater than 1; when the virtual synchronous generator works in the critical damping state, then
Equal to 1;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum charging power operation environment according to the following formula2：
In the formula, Pc△ P as the maximum output power value corresponding to the maximum charging power operation environment of the storage battery of the power grid to which the virtual synchronous generator belongseThe load fluctuation quantity amplitude; pi is the circumference ratio;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum discharge power operation environment according to the following formula3：
In the formula, PfThe output power is the maximum corresponding to the maximum discharge power of the storage battery of the power grid to which the virtual synchronous generator belongs in the maximum discharge power operation environment;
preferably, the determining a lower limit value of a dynamic range of a rotational inertia of the virtual synchronous generator according to a difference between a system frequency value corresponding to a power grid where the virtual synchronous generator is located when the load fluctuation is over and a system frequency steady-state value includes:
determining the lower limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamin：
In the formula, D is the damping coefficient of the virtual synchronous generator; k is the active droop coefficient of the virtual synchronous generator; t duration of load fluctuation; w is a0△ f, the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value;
determining a difference value delta f between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value according to the following formula:
△f＝αmin(f0-f1)
in the formula (f)0The system frequency value of the power grid where the virtual synchronous generator is located when the load fluctuation is finished; f. of1α for the steady state value of the system frequency of the power grid where the virtual synchronous generator is located at the end of the load fluctuationminIs a preset minimum value of the frequency improvement coefficient;
determining the steady state value f of the system frequency at the end moment of the load fluctuation according to the following formula1：
In the formula, △ Pe *The amplitude of the load fluctuation amount is represented by pi, which is the circumferential rate.
Further, after determining the lower limit value of the virtual synchronous generator rotational inertia dynamic interval according to the difference between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is over and the system frequency steady-state value, the method further includes:
and controlling the value of the rotational inertia of the virtual synchronous generator to be positioned in the dynamic range of the rotational inertia of the virtual synchronous generator.
The invention provides a computing system of a virtual synchronous generator rotational inertia dynamic interval, which is characterized by comprising the following components:
a first determination module: the virtual synchronous generator moment of inertia dynamic interval upper limit value is determined according to the corresponding moment of inertia in different running environments of the virtual synchronous generator;
a second determination module: and the lower limit value of the virtual synchronous generator rotational inertia dynamic interval is determined according to the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value.
Preferably, the first determining module is configured to:
determining an upper limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamax：
Jmax＝min{J1,J2,J3}
In the formula, J1The maximum value of the corresponding moment of inertia is the maximum value when the virtual synchronous generator is in an over-damping or critical damping operation environment; j. the design is a square2The maximum value of the corresponding rotational inertia is obtained when a storage battery of a power grid to which the virtual synchronous generator belongs is in a maximum charging power operation environment; j. the design is a square3The maximum value of the corresponding rotational inertia is obtained when the storage battery of the power grid to which the virtual synchronous generator belongs is in the operating environment with the maximum discharge power.
Further, the maximum value J of the corresponding moment of inertia when the virtual synchronous generator is in the over-damping or critical damping operation environment is determined according to the following formula1：
In the formula, D is the damping coefficient of the virtual synchronous generator; x is the circuit equivalent reactance of the virtual synchronous generator;
is the damping ratio of the virtual synchronous generator; w is a0Is the rated angular frequency of the virtual synchronous generator; e is an effective value of outlet voltage of the virtual synchronous generator; u is the effective value of the voltage of the power grid;
wherein when the virtual synchronous generator is operatedIn the damping state, then
Greater than 1; when the virtual synchronous generator works in the critical damping state, then
Equal to 1;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum charging power operation environment according to the following formula2：
In the formula, Pc△ P as the maximum output power value corresponding to the maximum charging power operation environment of the storage battery of the power grid to which the virtual synchronous generator belongseThe load fluctuation quantity amplitude; pi is the circumference ratio;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum discharge power operation environment according to the following formula3：
In the formula, PfThe output power is the maximum corresponding to the maximum discharge power of the storage battery of the power grid to which the virtual synchronous generator belongs in the maximum discharge power operation environment;
preferably, the second determining module is configured to:
determining the lower limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamin：
In the formula, D is the damping coefficient of the virtual synchronous generator; k is the active droop coefficient of the virtual synchronous generator; t duration of load fluctuation; w is a0Is a virtual△ f, calculating the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is over and the system frequency steady-state value;
determining a difference value delta f between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value according to the following formula:
△f＝αmin(f0-f1)
in the formula (f)0The system frequency value of the power grid where the virtual synchronous generator is located when the load fluctuation is finished; f. of1α for the steady state value of the system frequency of the power grid where the virtual synchronous generator is located at the end of the load fluctuationminIs a preset minimum value of the frequency improvement coefficient;
determining the steady state value f of the system frequency at the end moment of the load fluctuation according to the following formula1：
In the formula, △ Pe *The amplitude of the load fluctuation amount is represented by pi, which is the circumferential rate.
Further, after determining the lower limit value of the virtual synchronous generator rotational inertia dynamic interval according to the difference between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is over and the system frequency steady-state value, the method further includes:
and controlling the value of the rotational inertia of the virtual synchronous generator to be positioned in the dynamic range of the rotational inertia of the virtual synchronous generator.
Compared with the closest prior art, the invention has the following beneficial effects:
according to the technical scheme provided by the invention, the upper limit value of the dynamic interval of the rotational inertia of the virtual synchronous generator is determined according to the corresponding rotational inertia of the virtual synchronous generator in different operating environments; determining a lower limit value of a dynamic interval of the rotational inertia of the virtual synchronous generator according to a difference value between a system frequency value corresponding to a power grid where the virtual synchronous generator is located when load fluctuation is finished and a system frequency steady-state value, and accurately calculating the dynamic interval of the rotational inertia of the virtual synchronous generator in the power grid based on the influence of a battery charging and discharging limit value, a damping ratio and a frequency improvement coefficient on the rotational inertia of the virtual synchronous generator;
in practical application, the value of the rotational inertia of the virtual synchronous generator of the power grid is controlled to be within a dynamic range, so that the power oscillation frequency of the system can be effectively reduced, and the steady-state performance of the power grid is improved.
Drawings
FIG. 1 is a flow chart of a method for calculating a dynamic range of a rotational inertia of a virtual synchronous generator;
FIG. 2 is a control diagram of the output power of a virtual synchronous generator in an embodiment of the present invention;
FIG. 3 is a graph of grid output power under different rotational inertia conditions;
FIG. 4 is a graph of system frequency change after grid load change;
FIG. 5 is a steady-state graph of system frequency value and system frequency corresponding to the power grid at the end of a load fluctuation;
fig. 6 is a flow chart of a computing system for a dynamic range of rotational inertia of a virtual synchronous generator.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
When the load or photovoltaic output of the micro-grid is changed, the energy storage device (storage battery) provides inertia power and active power distributed by the speed regulator to maintain the frequency stability of the system; a typical virtual synchronous generator uses a control mode of constant rotational inertia, however, an energy storage device providing inertial power has a limitation of a state of charge, and a reasonable value interval needs to be set for the rotational inertia of the virtual synchronous generator in order to protect a normal state of an energy storage battery and prolong the service life of the energy storage battery;
the invention provides a method for calculating a dynamic interval of rotational inertia of a virtual synchronous generator, which comprises the following steps of:
step 101, determining an upper limit value of a virtual synchronous generator rotational inertia dynamic interval according to corresponding rotational inertia of the virtual synchronous generator in different operating environments;
and 102, determining a lower limit value of a dynamic range of the rotational inertia of the virtual synchronous generator according to a difference value between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value.
Specifically, the step 101 includes: determining an upper limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamax：
Jmax＝min{J1,J2,J3}
In the formula, J1The maximum value of the corresponding moment of inertia is the maximum value when the virtual synchronous generator is in an over-damping or critical damping operation environment; j. the design is a square2The maximum value of the corresponding rotational inertia is obtained when a storage battery of a power grid to which the virtual synchronous generator belongs is in a maximum charging power operation environment; j. the design is a square3The maximum value of the corresponding rotational inertia is obtained when the storage battery of the power grid to which the virtual synchronous generator belongs is in the operating environment with the maximum discharge power.
Specifically, the maximum value J of the corresponding moment of inertia when the virtual synchronous generator is in the over-damping or critical damping operation environment is determined according to the following formula1：
In the formula, D is the damping coefficient of the virtual synchronous generator; x is the circuit equivalent reactance of the virtual synchronous generator;
is the damping ratio of the virtual synchronous generator; w is a0Is the rated angular frequency of the virtual synchronous generator; e is an effective value of outlet voltage of the virtual synchronous generator; u is the effective value of the voltage of the power grid;
wherein, when the virtual synchronous generator works in an over-damping state, then
Greater than 1; when the virtual synchronous generator works in the critical damping state, then
Equal to 1;
for example: in the preferred embodiment of the present invention, the process of obtaining the maximum value of the corresponding moment of inertia when the virtual synchronous generator is in the over-damped or critical-damped operating environment may be:
determining a rotor motion model of the virtual synchronous generator according to the following formula:
in the formula: j is a virtual moment of inertia; d is a virtual damping coefficient; e is the effective value of the outlet voltage of the virtual synchronous generator; u is the effective value of the voltage of the power grid; x is the equivalent reactance of the virtual synchronous generator circuit; w is the system angular frequency; w is a0Is the rated angular frequency; outputting a power angle for a system virtual synchronous generator; p is a radical ofmReference power for the load; peOutputting power for the virtual synchronous machine;
as can be seen from the above equation of motion of the rotor of the virtual synchronous generator and the output power control diagram of the virtual synchronous generator shown in fig. 2, the transfer function between the output power of the virtual synchronous generator and the load reference power is:
the undamped natural oscillation angular frequency and the damping ratio of the power grid system are respectively as follows according to the transfer function:
in the formula, wnUndamped natural oscillation angular frequency is adopted for a power grid system; and zeta is the damping ratio of the power grid system.
At this time, the inertia moment of the virtual synchronous generator is:
from the above formula, when D is fixed, the larger J, the smaller ω and ζ; as shown in fig. 3, when J is larger, the active oscillation is more severe, so that the occurrence of power oscillation should be avoided as much as possible when selecting the moment of inertia, that is, the virtual synchronous generator is made to operate in an over-damped or critical-damped operating environment as much as possible;
therefore, the maximum value of the corresponding moment of inertia when the virtual synchronous generator is in an over-damping or critical damping operation environment is as follows:
wherein, when the virtual synchronous generator works in an over-damping state, then
Greater than 1; when the virtual synchronous generator works in the critical damping state, then
Equal to 1;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum charging power operation environment according to the following formula2：
In the formula, PcThe maximum output power value corresponding to the maximum charging power operation environment of the storage battery of the power grid to which the virtual synchronous generator belongs can be judged according to the real-time state detected by a battery management system in the actual engineering △ PeThe load fluctuation quantity amplitude; pi is the circumference ratio;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum discharge power operation environment according to the following formula3：
In the formula, PfThe output power is the maximum corresponding to the maximum discharge power of the storage battery of the power grid to which the virtual synchronous generator belongs in the maximum discharge power operation environment; the real-time state can be judged according to the real-time state detected by a battery management system in actual engineering;
as shown in fig. 4, when the virtual synchronous generator is operated off-grid, the load changes, and the system performs transient adjustment; the rotational inertia of the virtual synchronous generator does not affect the final system frequency value, but only affects the speed of transient adjustment, and the larger the rotational inertia is, the longer the time for reaching the steady state is; therefore, a minimum rotation inertia value of the virtual synchronous generator needs to be determined, so that the system adjustment time is shortest;
further, as shown in fig. 5, the step 102 includes: determining the lower limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamin：
In the formula, D is the damping coefficient of the virtual synchronous generator; k is the active droop coefficient of the virtual synchronous generator; t duration of load fluctuation; w is a0△ f, the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value;
determining a difference value delta f between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value according to the following formula:
△f＝αmin(f0-f1)
in the formula (f)0The system frequency value of the power grid where the virtual synchronous generator is located when the load fluctuation is finished; f. of1α for the steady state value of the system frequency of the power grid where the virtual synchronous generator is located at the end of the load fluctuationminThe frequency improvement coefficient is a preset minimum value and is determined by the actual engineering situation;
determining the steady state value f of the system frequency at the end moment of the load fluctuation according to the following formula1：
In the formula, △ Pe *The amplitude of the load fluctuation amount is represented by pi, which is the circumferential rate.
Further, after determining the lower limit value of the virtual synchronous generator rotational inertia dynamic interval according to the difference between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is over and the system frequency steady-state value, the method further includes:
and controlling the value of the rotational inertia of the virtual synchronous generator to be positioned in the dynamic range of the rotational inertia of the virtual synchronous generator.
When the same load fluctuation is responded, the system storage battery with larger rotational inertia absorbs or releases more energy, the storage battery has larger electric quantity change after the adjustment is finished, and the storage battery is only charged and not discharged when the electric quantity is smaller than the minimum one-way inertia support limit value according to the performance characteristics of the battery; similarly, when the electric quantity is larger than the maximum one-way inertial support limit value, only discharging is carried out, and charging is not carried out; therefore, a proper rotational inertia interval can be set, so that the electric quantity of the storage battery can work within the bidirectional inertia support limit value as much as possible, the phenomenon of over-charge or over-discharge of the electric quantity is avoided, and the service life of the storage battery is prolonged.
The invention provides a computing system for a virtual synchronous generator rotational inertia dynamic interval, as shown in fig. 6, the system comprises:
a first determination module: the virtual synchronous generator moment of inertia dynamic interval upper limit value is determined according to the corresponding moment of inertia in different running environments of the virtual synchronous generator;
a second determination module: and the lower limit value of the virtual synchronous generator rotational inertia dynamic interval is determined according to the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value.
Specifically, the first determining module is configured to:
determining an upper limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamax：
Jmax＝min{J1,J2,J3}
In the formula, J1The maximum value of the corresponding moment of inertia is the maximum value when the virtual synchronous generator is in an over-damping or critical damping operation environment; j. the design is a square2The maximum value of the corresponding rotational inertia is obtained when a storage battery of a power grid to which the virtual synchronous generator belongs is in a maximum charging power operation environment; j. the design is a square3The maximum value of the corresponding rotational inertia is obtained when the storage battery of the power grid to which the virtual synchronous generator belongs is in the operating environment with the maximum discharge power.
Specifically, the maximum value J of the corresponding moment of inertia when the virtual synchronous generator is in the over-damping or critical damping operation environment is determined according to the following formula1：
In the formula, D is the damping coefficient of the virtual synchronous generator; x is the circuit equivalent reactance of the virtual synchronous generator;
is the damping ratio of the virtual synchronous generator; w is a0Is the rated angular frequency of the virtual synchronous generator; e is the effective value of the outlet voltage of the virtual synchronous generator(ii) a U is the effective value of the voltage of the power grid;
wherein, when the virtual synchronous generator works in an over-damping state, then
Greater than 1; when the virtual synchronous generator works in the critical damping state, then
Equal to 1;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum charging power operation environment according to the following formula2：
In the formula, Pc△ P as the maximum output power value corresponding to the maximum charging power operation environment of the storage battery of the power grid to which the virtual synchronous generator belongseThe load fluctuation quantity amplitude; pi is the circumference ratio;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum discharge power operation environment according to the following formula3：
In the formula, PfThe output power is the maximum corresponding to the maximum discharge power of the storage battery of the power grid to which the virtual synchronous generator belongs in the maximum discharge power operation environment;
specifically, the second determining module is configured to:
determining the lower limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamin：
Wherein D is virtual synchronous power generationDamping coefficient of the machine; k is the active droop coefficient of the virtual synchronous generator; t duration of load fluctuation; w is a0△ f, the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value;
determining a difference value delta f between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value according to the following formula:
△f＝αmin(f0-f1)
in the formula (f)0The system frequency value of the power grid where the virtual synchronous generator is located when the load fluctuation is finished; f. of1α for the steady state value of the system frequency of the power grid where the virtual synchronous generator is located at the end of the load fluctuationminIs a preset minimum value of the frequency improvement coefficient;
determining the steady state value f of the system frequency at the end moment of the load fluctuation according to the following formula1：
In the formula, △ Pe *The amplitude of the load fluctuation amount is represented by pi, which is the circumferential rate.
Further, after determining the lower limit value of the virtual synchronous generator rotational inertia dynamic interval according to the difference between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is over and the system frequency steady-state value, the method further includes:
and controlling the value of the rotational inertia of the virtual synchronous generator to be positioned in the dynamic range of the rotational inertia of the virtual synchronous generator.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (10)
1. A method for calculating a dynamic range of rotational inertia of a virtual synchronous generator is characterized by comprising the following steps:
determining an upper limit value of a virtual synchronous generator rotational inertia dynamic interval according to corresponding rotational inertia of the virtual synchronous generator in different operating environments;
and determining the lower limit value of the dynamic range of the rotational inertia of the virtual synchronous generator according to the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value.
2. The method of claim 1, wherein the determining the upper limit value of the dynamic range of the rotational inertia of the virtual synchronous generator according to the corresponding rotational inertia of the virtual synchronous generator in different operating environments comprises:
determining an upper limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamax：
Jmax＝min{J1,J2,J3}
In the formula, J1The maximum value of the corresponding moment of inertia is the maximum value when the virtual synchronous generator is in an over-damping or critical damping operation environment; j. the design is a square2The maximum value of the corresponding rotational inertia is obtained when a storage battery of a power grid to which the virtual synchronous generator belongs is in a maximum charging power operation environment; j. the design is a square3The maximum value of the corresponding rotational inertia is obtained when the storage battery of the power grid to which the virtual synchronous generator belongs is in the operating environment with the maximum discharge power.
3. The method of claim 2, wherein the maximum value J of the moment of inertia corresponding to the virtual synchronous generator in an over-damped or critically-damped operating environment is determined according to the following equation1：
In the formula, D is the damping coefficient of the virtual synchronous generator; x is the circuit equivalent reactance of the virtual synchronous generator;
is the damping ratio of the virtual synchronous generator; w is a0Is the rated angular frequency of the virtual synchronous generator; e is an effective value of outlet voltage of the virtual synchronous generator; u is the effective value of the voltage of the power grid;
wherein, when the virtual synchronous generator works in an over-damping state, then
Greater than 1; when the virtual synchronous generator works in the critical damping state, then
Equal to 1;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum charging power operation environment according to the following formula2：
In the formula, Pc△ P as the maximum output power value corresponding to the maximum charging power operation environment of the storage battery of the power grid to which the virtual synchronous generator belongseThe load fluctuation quantity amplitude; pi is the circumference ratio;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum discharge power operation environment according to the following formula3：
In the formula, PfFor discharging power of storage battery of power grid to which virtual synchronous generator belongsMaximum output power corresponding to maximum operation environment.
4. The method of claim 1, wherein the determining a lower limit value of the dynamic range of the rotational inertia of the virtual synchronous generator according to the difference between the system frequency value corresponding to the grid where the virtual synchronous generator is located at the end of the load fluctuation and the steady-state value of the system frequency comprises:
determining the lower limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamin：
In the formula, D is the damping coefficient of the virtual synchronous generator; k is the active droop coefficient of the virtual synchronous generator; t duration of load fluctuation; w is a0△ f, the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value;
determining a difference value delta f between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value according to the following formula:
△f＝αmin(f0-f1)
in the formula (f)0The system frequency value of the power grid where the virtual synchronous generator is located when the load fluctuation is finished; f. of1α for the steady state value of the system frequency of the power grid where the virtual synchronous generator is located at the end of the load fluctuationminIs a preset minimum value of the frequency improvement coefficient;
determining the steady state value f of the system frequency at the end moment of the load fluctuation according to the following formula1：
In the formula, △ Pe *The amplitude of the load fluctuation amount is represented by pi, which is the circumferential rate.
5. The method of claim 4, wherein after determining the lower limit value of the dynamic range of the rotational inertia of the virtual synchronous generator according to the difference between the system frequency value corresponding to the grid where the virtual synchronous generator is located at the end of the load fluctuation and the steady-state value of the system frequency, the method further comprises:
and controlling the value of the rotational inertia of the virtual synchronous generator to be positioned in the dynamic range of the rotational inertia of the virtual synchronous generator.
6. A system for computing a dynamic range of rotational inertia of a virtual synchronous generator, the system comprising:
a first determination module: the virtual synchronous generator moment of inertia dynamic interval upper limit value is determined according to the corresponding moment of inertia in different running environments of the virtual synchronous generator;
a second determination module: and the lower limit value of the virtual synchronous generator rotational inertia dynamic interval is determined according to the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value.
7. The system of claim 6, wherein the first determination module is to:
determining an upper limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamax：
Jmax＝min{J1,J2,J3}
In the formula, J1The maximum value of the corresponding moment of inertia is the maximum value when the virtual synchronous generator is in an over-damping or critical damping operation environment; j. the design is a square2The maximum value of the corresponding rotational inertia is obtained when a storage battery of a power grid to which the virtual synchronous generator belongs is in a maximum charging power operation environment; j. the design is a square3The maximum value of the corresponding rotational inertia is obtained when the storage battery of the power grid to which the virtual synchronous generator belongs is in the operating environment with the maximum discharge power.
8. The method of claim 7The system is characterized in that the maximum value J of the corresponding moment of inertia when the virtual synchronous generator is in an over-damping or critical damping operation environment is determined according to the following formula1：
In the formula, D is the damping coefficient of the virtual synchronous generator; x is the circuit equivalent reactance of the virtual synchronous generator;
is the damping ratio of the virtual synchronous generator; w is a0Is the rated angular frequency of the virtual synchronous generator; e is an effective value of outlet voltage of the virtual synchronous generator; u is the effective value of the voltage of the power grid;
wherein, when the virtual synchronous generator works in an over-damping state, then
Greater than 1; when the virtual synchronous generator works in the critical damping state, then
Equal to 1;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum charging power operation environment according to the following formula2：
In the formula, Pc△ P as the maximum output power value corresponding to the maximum charging power operation environment of the storage battery of the power grid to which the virtual synchronous generator belongseThe load fluctuation quantity amplitude; pi is the circumference ratio;
determining the maximum value J of the corresponding moment of inertia when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum discharge power operation environment according to the following formula3：
In the formula, PfThe maximum output power value is the corresponding maximum output power value when the storage battery of the power grid to which the virtual synchronous generator belongs is in the maximum discharge power operation environment.
9. The system of claim 6, wherein the second determination module is to:
determining the lower limit value J of the virtual synchronous generator rotational inertia dynamic interval according to the following formulamin：
In the formula, D is the damping coefficient of the virtual synchronous generator; k is the active droop coefficient of the virtual synchronous generator; t duration of load fluctuation; w is a0△ f, the difference value between the system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and the system frequency steady-state value;
determining a difference value delta f between a system frequency value corresponding to the power grid where the virtual synchronous generator is located when the load fluctuation is finished and a system frequency steady-state value according to the following formula:
△f＝αmin(f0-f1)
in the formula (f)0The system frequency value of the power grid where the virtual synchronous generator is located when the load fluctuation is finished; f. of1α for the steady state value of the system frequency of the power grid where the virtual synchronous generator is located at the end of the load fluctuationminIs a preset minimum value of the frequency improvement coefficient;
determining the steady state value f of the system frequency at the end moment of the load fluctuation according to the following formula1：
In the formula, △ Pe *The amplitude of the load fluctuation amount is represented by pi, which is the circumferential rate.
10. The method of claim 9, wherein after determining the lower limit value of the dynamic range of the rotational inertia of the virtual synchronous generator according to the difference between the system frequency value corresponding to the grid where the virtual synchronous generator is located at the end of the load fluctuation and the steady-state value of the system frequency, the method further comprises:
and controlling the value of the rotational inertia of the virtual synchronous generator to be positioned in the dynamic range of the rotational inertia of the virtual synchronous generator.
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