An improved virtual inertia control method for asynchronous condensers based on fuzzy control

Abstract

The application relates to an improved virtual inertia control method of an asynchronous phase modifier based on fuzzy control, and relates to the field of motor excitation control.The application is used to solve the problem of inertia reduction of a high-proportion new energy system.The application comprises the following steps: obtaining inertia output P through fuzzy logic control of system frequency deviation Delta f;obtaining power reference value P through the inertia output P;obtaining traditional generator set output power P according to the power reference value P;obtaining prime mover output power P through primary frequency modulation of the system frequency deviation Delta f and frequency change rate; and obtaining the system frequency deviation Delta f according to the traditional generator set output power P and the prime mover output power P. inertia ref ref G w G w The application is helpful for solving the problem of inertia reduction of a high-proportion new energy system, and further improves system frequency stability.​​​​​​

Description

TECHNICAL FIELD

[0001] The present application relates to the field of motor excitation control, in particular to an improved virtual inertia control method of asynchronous phase modifier based on fuzzy control. BACKGROUND

[0002] In recent years, the proportion of new energy power generation in China has been increasing, which makes the inertia of the power system gradually decrease, weakening the inertia support and frequency regulation capability of the system under active impact. As synchronous machines, phase modifiers have inertia response, which can effectively increase the inertia of the system and provide short-term frequency support for the system. The asynchronous phase modifier adopts AC excitation, and the rotor is a multi-phase symmetrical winding. When operating normally, the rotor is supplied with multi-phase symmetrical AC excitation. Compared with the traditional synchronous phase modifier, in addition to being able to adjust the amplitude of the excitation current, the frequency and phase of the excitation current can also be adjusted, increasing the degree of freedom of the excitation control. In the process of excitation system of the asynchronous phase modifier, if the traditional inertia control strategy is adopted, when the system is in shock, the df / dt control link will produce a negative damping effect, which is not conducive to the design of the excitation controller parameters and the stable operation of the system. SUMMARY

[0003] The present application provides an improved virtual inertia control method of asynchronous phase modifier based on fuzzy control, comprising:

[0004] S1, the system frequency deviation Δf is obtained through fuzzy logic control to obtain the inertia output P inertia , and then the power reference value P ref is obtained;

[0005] S2, the traditional generator set output power P ref is obtained according to the power reference value P G , the prime mover output power P w is obtained through primary frequency regulation according to the system frequency deviation Δf, and the system frequency deviation Δf is obtained according to the traditional generator set output power P G and the prime mover output power P w .

[0006] Further, step S1 comprises:

[0007] S11, the system frequency change rate after high-pass filtering and the hysteresis control system frequency deviation Δf are input into the fuzzy logic controller to obtain the inertia output P inertia ;

[0008] S12, the rotor speed w is multiplied by the damping constant Kw, and then combined with the inertia output P inertia , and the combined signal is superimposed with the rotor speed change value Δw after low-pass filtering;

[0009] S13, the superimposed signal obtained in step S12 is input into a limiter to obtain a power reference value P ref .

[0010] Further, step S2 comprises:

[0011] S21, the rate reference value P ref and the output power change value ΔP of the conventional generator set G are compared to obtain the output power P of the conventional generator set G ;

[0012] S22, the system frequency deviation Δf is input into a primary frequency modulation device to obtain the output power change value ΔP of the prime mover w , the rate reference value P ref and the output power change value ΔP of the prime mover w are compared to obtain the output power P of the prime mover w ;

[0013] S23, the output power P of the prime mover w is combined with the output power P of the conventional generator set G , and the combined signal is input into a speed regulator to obtain the system frequency deviation Δf.

[0014] Further, the output power change value ΔP of the conventional generator set G is obtained from the system frequency deviation Δf by frequency regulation of the conventional generator set.

[0015] Further, the primary frequency modulation process comprises:

[0016] the system frequency deviation Δf is multiplied by an inertia control coefficient K p , and the multiplied signal is combined with the system frequency change rate multiplied by a frequency modulation control coefficient K d .

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] The control strategy of the present application replaces the df / dt control link with the dΔf / dt control link, thereby making up for the negative damping defect of the conventional inertia control strategy. In addition, since the dΔf / dt and Δf control structure is adopted, not only the steady-state frequency deviation existing in the Δf single closed-loop control can be eliminated, but also the rapid tracking of the rotational speed can be realized.

[0019] The concept, specific structure and generated technical effects of the present application will be further described below with reference to the accompanying drawings, so as to fully understand the purpose, features and effects of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1An asynchronous alternator system structure principle diagram for a specific embodiment of the present application;

[0021] Figure 2 A flow chart of improved virtual inertia control of an asynchronous alternator based on fuzzy control for a specific embodiment of the present application;

[0022] Figure 3 A power grid dynamic comprehensive frequency response model for a specific embodiment of the present application;

[0023] Figure 4 A traditional unit frequency regulation model for a specific embodiment. DETAILED DESCRIPTION

[0024] The present application is described and explained more fully with specific reference being made to the following figure(s). The following detailed description is made in connection with the preferred embodiments illustrated in the figures.

[0025] It is to be understood that the figures included are merely schematic and that actual implementations can differ from those of the figures. It is further understood that the present application might include more steps and / or steps performed in a different order.

[0026] Some example embodiments of the present application are described for illustrative purposes, and it is to be understood that the present application can be implemented in other ways not specifically shown in the figures.

[0027] The present application provides an improved virtual inertia control method of an asynchronous alternator based on fuzzy control, and the asynchronous alternator system structure is as shown in Figure 1

[0028] As shown in Figure 1 The asynchronous alternator system structure diagram is as shown in the figure, the stator winding of the asynchronous alternator is directly connected to the power grid, and the rotor winding is connected to the AC excitation current. The excitation system includes a grid-side converter and a rotor-side converter, wherein the control target of the grid-side converter is mainly to ensure the constant voltage of the DC bus, and the control target of the rotor-side converter is to regulate the active and reactive power output by the stator of the alternator, and the two are decoupled through the DC link and are relatively independent.

[0029] ​For the convenience of analysis, the reference direction is selected, and the stator and rotor are both in the motor convention, i.e. the voltage drop direction is consistent with the current direction, and the current and the flux direction comply with the right-hand screw rule. At the same time, the following assumptions are made:

[0030] (1) The three-phase windings of the stator and rotor are symmetrical, the magnetic motive force is distributed in space according to the sine rule, and only the harmonic components are ignored;

[0031] (2) The magnetic circuit is linear, saturation is not considered, and the self-inductance and mutual inductance of the winding are constant;

[0032] (3) The core loss, eddy current loss and hysteresis loss are ignored;

[0033] (4) The influence of temperature and frequency changes on the resistance of the winding is ignored;

[0034] The voltage equation of the asynchronousized phase modifier in the dq coordinate system is:

[0035]

[0036]

[0037] wherein u sd , u sq , u rd , u rq are the d, q axis voltage components of the stator and rotor respectively;

[0038] i sd , i sq , i rd , i rq are the d, q axis current components of the stator and rotor respectively;

[0039] ψ sd , ψ sq , ψ rd , ψ rq are the d, q axis flux components of the stator and rotor respectively.

[0040] The flux equation of the asynchronousized phase modifier in the dq coordinate system is:

[0041]

[0042]

[0043] wherein L m is the mutual inductance between the equivalent coaxial windings of the stator and rotor in the dq coordinate system (since the two-phase winding is used to equivalent the three-phase winding, L i.e. the equivalent mutual inductance is 1.5 times the maximum mutual inductance of any two phases in the original three-phase winding); L s = L m + Lls L is the equivalent self-inductance of the stator winding r = L m + L rs L is the equivalent self-inductance of the rotor winding.

[0044] The motion equation of the asynchronous exciter in the dq coordinate system is as follows:

[0045]

[0046] In the formula, J is the moment of inertia, w r is the rotor angular velocity.

[0047] The excitation system of the asynchronous exciter comprises a grid-side converter and a rotor-side converter, wherein the control target of the grid-side converter is mainly to ensure the voltage of the DC bus to be constant, and the control target of the rotor-side converter is to regulate the active and reactive power output by the stator of the exciter, and the two are decoupled through the DC link and are relatively independent.

[0048] The output P M of the prime mover, the rotor angular velocity w r and the power angle δ of the synchronous generator continuously oscillate with the angular velocity w h , and specifically satisfy the following relationship:

[0049]

[0050]

[0051]

[0052] The inertial response of the power system is as follows:

[0053]

[0054] In the formula, M is the inertia constant, K D is the damping coefficient, K S is the synchronization coefficient, P M0 is the initial output of the prime mover in the system, is the active power output by the generator, w0 is the initial angular velocity of the rotor of the synchronous generator, is the mechanical angular velocity of the synchronous generator, δ0 is the initial power angle of the synchronous generator, is the generator damping, Δw r is the change amount of the rotor angular velocity of the synchronous generator.

[0055] The improved virtual inertia control method of the embodiment comprises:

[0056] S1, the inertia output P inertia of the system frequency deviation Δf is obtained through fuzzy logic control, and then the power reference value Pref ;

[0057] As shown in Figure 2 , specifically comprising:

[0058] S11, the system frequency rate of change after high-pass filter link processing and the system frequency deviation Δf after hysteresis control link are input into the fuzzy logic controller to obtain the inertia output P inertia ;

[0059] In this embodiment, the hysteresis upper limit comparison value and the hysteresis lower limit comparison value are set for the input signal of the replacement control link. When the input signal is higher than the hysteresis upper limit comparison value, the corresponding action of the input signal being too high is executed; when the input signal is lower than the hysteresis lower limit comparison value, the corresponding action of the input signal being too low is executed; and when the input signal is between the hysteresis upper limit comparison value and the hysteresis lower limit comparison value, no action is executed. The hysteresis upper limit comparison value is greater than the hysteresis lower limit comparison value, and the difference between the hysteresis upper limit comparison value and the hysteresis lower limit comparison value is called the hysteresis width. The hysteresis control set in this application can realize hysteresis judgment of the input signal and overcome the problem of frequent changes of the output signal caused by small range fluctuations of the input signal between the hysteresis upper limit comparison value and the hysteresis lower limit comparison value.

[0060] The frequency change of the power grid under disturbance fault is closely related to the system inertia level. When the system frequency drops, increasing the equivalent inertia of the system can reduce the frequency drop amplitude. In this embodiment, the fuzzy controller is used to flexibly adjust the respective coefficients K1 and K2 of Δf, .

[0061] The inertia output P inertia is obtained by the following formula:

[0062]

[0063] The coefficients K1 and K2 are the proportional coefficient and the differential coefficient corresponding to the process of generating the inertia output P inertia from the proportional-differential control of the frequency deviation Δf in the control strategy. By adjusting the coefficients K1 and K2, the dynamic adjustment of the equivalent inertia of the system and the frequency modulation control parameters is realized, and the purpose of improving the frequency characteristics of the power grid is further achieved.

[0064] In a specific embodiment, the fuzzy rules of the fuzzy logic controller include the coefficient K1 fuzzy control rule and the coefficient K2 fuzzy control rule, as shown in Tables 1 and 2:

[0065] Table 1 Fuzzy rules of coefficient K1

[0066]

[0067] Table 2 Fuzzy rules of coefficient K2

[0068]

[0069] S12, rotor angular velocity variation Δw r Synthesis of ΔP after differentiation, low-pass filter and integral element M and the inertial output P inertia Superimposed, the rotor speed deviation after low-pass filter is added to the controller as an auxiliary signal, so that the rotor speed of the asynchronous phase modifier is kept at the synchronous speed, and the rotor speed of the asynchronous phase modifier is kept at the synchronous speed through the damping coefficient K D The rotor speed of the asynchronous phase modifier can be kept within the allowable range, and the allowable range is 1.0±0.15[p.u.];

[0070] S13, the superimposed signal obtained in step S12 is subjected to a limiter to obtain a power reference value P ref , the limiter prevents the active reference value from exceeding 1.0[p.u.].

[0071] S2, according to the power reference value P ref , the output power P of the traditional generator set is obtained G , the system frequency deviation Δf and the frequency change rate The prime mover output power P is obtained through primary frequency modulation w , according to the traditional generator set output power P G and the prime mover output power P w , the system frequency deviation Δf is obtained.

[0072] As Figure 3 shown, step S2 includes:

[0073] S21, the rate reference value P ref and the traditional generator set output power variation ΔP a are synthesized to obtain the output power P of the traditional generator set G ;

[0074] The traditional generator set output power variation ΔP a is obtained by the system frequency deviation Δf through the traditional unit frequency regulation link. The frequency regulation model of the traditional generator set of the embodiment is as shown in Figure 4 , and the system state equation is:

[0075]

[0076] Wherein, H is the inertia constant; η DC-in is the direct current input ratio; η W is the wind power ratio; Δf is the frequency deviation; P step is the power disturbance; T RSynchronization unit regulating electromagnetic power time constant; ΔP m Synchronization unit electromagnetic power change; R is the regulating coefficient; K m Synchronization unit standby coefficient; K L Load frequency factor; ΔP L Load change; ΔP a Synchronization unit output active change; ΔP d System prime mover output power change.

[0077] S22, system frequency deviation Δf is obtained by primary frequency modulation wind turbine output power change value ΔP w , power reference value P ref And prime mover output power change ΔP w Synthesis of wind turbine output power P w ;

[0078] The primary frequency modulation process in the embodiment includes:

[0079] System frequency deviation Δf and inertia control coefficient K p The signal after multiplication and system frequency change rate And frequency modulation control coefficient K d The signal after multiplication is superimposed.

[0080] S23, the wind turbine output power P w And the output power P G After superimposing the conventional generator set, the speed regulator obtains the system frequency deviation Δf.

[0081] The common power supply in the system includes thermal power, hydropower, gas, nuclear power unit, the above power supply is connected to the grid through the synchronous generator, and in the frequency analysis, the active-frequency response characteristics of the above power supply can adopt the simplified active-frequency response dynamic model, that is, only the active regulating link of the generator set governor, the prime mover power output link, and the asynchronous phase modifier are considered. The virtual inertia control coefficient and the frequency modulation control coefficient are used for participating in system frequency modulation.

[0082] The above embodiment only exemplarily illustrates the principle of the present application and its effect, and is not used to limit the present application. Any person skilled in the art can modify or change the above embodiment without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A method for improving virtual inertia control of an asynchronous phase modifier based on fuzzy control, characterized in that Comprising: S1, system frequency deviation inertial output through fuzzy logic control , and then power reference value ; S2, according to the power reference value get the output power of the traditional generator set , the system frequency deviation and the frequency change rate get the output power of the prime mover through the first frequency modulation , according to the output power of the traditional generator set and the output power of the prime mover get the system frequency deviation , specifically comprising: S21, the rate reference value and the output power change value of the conventional generator set the output power of the conventional generator set is synthesized ; S22, system frequency deviation obtaining the output power change value of the prime mover by once frequency modulation , the rate reference value and the output power change value of the prime mover comparing to obtain the output power of the prime mover ; S23, the prime mover output power Combining the fan transfer function with the output power of the conventional generator set After superposition, the system frequency deviation is obtained through the governor .

2. The improved virtual inertia control method for an asynchronous condenser based on fuzzy control according to claim 1, characterized in that, Step S1 comprises: S11, the system frequency change rate after high-pass filtering processing and the system frequency deviation after the dead zone link As the input of fuzzy control, the inertia output is obtained ; S12, rotor angular velocity variation synthesized after differentiation, low-pass filter, and integration with the inertial output superimposed; S13, clipping the superimposed signal obtained in step S12 to obtain a power reference value .

3. The improved virtual inertia control method for an asynchronous alternator based on fuzzy control according to claim 2, characterized in that, Step S11 comprises: Establishing the adjustment frequency deviation with the proportional coefficient K1 and the adjustment frequency change rate with the fuzzy rule of the differential coefficient K2, according to the frequency deviation and the frequency change rate output the proportional coefficient K1 and the differential coefficient K2; The inertial output is obtained according to the following formula : 。 4. The improved virtual inertia control method for an asynchronous condenser based on fuzzy control according to claim 1, characterized in that, The conventional generator set output power change value From the system frequency deviation The conventional generator set frequency regulation is obtained, and the conventional generator set frequency regulation model is: ； H is an inertia constant; is a direct current input proportion; is a wind power proportion; is a frequency deviation; is a power disturbance amount; R is a synchronous unit regulating electromagnetic power time constant; is a synchronous unit electromagnetic power change amount; is a regulation difference coefficient; is a synchronous unit reserve coefficient; is a load frequency factor; is a load change amount; is a synchronous unit output active change amount; is a system prime mover output power change amount.

5. The improved virtual inertia control method for an asynchronous alternator based on fuzzy control according to claim 1, wherein The first frequency modulation process comprises: System frequency deviation multiplied by the frequency control coefficient K p multiplied by the frequency control coefficient K multiplied by the frequency control coefficient K d multiplied by the frequency control coefficient K

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