CN114374206B - Grid-connected point voltage adjusting method and system of fused salt energy storage and conversion device for thermal power - Google Patents

Abstract

The application provides a grid-connected point voltage adjusting method and a grid-connected point voltage adjusting system of a fused salt energy storage and conversion device for thermal power, wherein the method comprises the following steps: determining a voltage equivalent equation of the fused salt thermal power energy storage and conversion device and a VSG reactive power-voltage regulation equation of the fused salt thermal power energy storage and conversion device; acquiring a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device of the thermal power containing virtual impedance, and determining the amplitude of the virtual impedance; determining the voltage of a grid connection point required for supporting the thermal power molten salt energy storage device to operate when the power system of the thermal power plant generates a ground fault according to the amplitude of the virtual impedance; and adjusting the voltage of the grid-connected point based on the voltage of the grid-connected point. According to the technical scheme provided by the invention, the virtual impedance is introduced into the VSG reactive-voltage control, the reference signal of the voltage closed loop link is changed, the voltage supporting function during the fault period is achieved, the fused salt energy storage and heating device is ensured to be always in the running state, and the equipment halt caused by the over-low voltage is prevented.

Description

Grid-connected point voltage adjusting method and system of fused salt energy storage and conversion device for thermal power

Technical Field

The application relates to the technical field of voltage regulation, in particular to a grid-connected point voltage regulation method and a grid-connected point voltage regulation system of a fused salt energy storage and conversion device for thermal power.

Background

In recent years, with the development of the energy storage industry, various novel energy storage technologies are broken through continuously, and demonstration applications are realized in more and more scenes, wherein the novel energy storage technologies mainly include a heat storage technology, a hydrogen energy storage technology, an electromagnetic energy storage technology, a flywheel energy storage technology and the like. The heat storage technology belongs to an energy type energy storage technology, has high energy density, low cost, long service life, various utilization modes and high comprehensive heat utilization efficiency, and can play a great role in the fields of renewable energy consumption, clean heating and application of energy storage systems of solar photo-thermal power stations. In recent years, the heat storage technologies that have attracted much attention mainly include molten salt heat storage technologies and high-temperature phase change heat storage technologies. The molten salt heat storage technology has the main advantages of large scale, convenient use by matching with a conventional gas engine and is mainly applied to a large-scale tower type photo-thermal power generation system and a groove type photo-thermal power generation system.

The molten salt energy storage heating device is connected with an electricity system of a thermal power plant through a converter device by adopting a direct current coil, and the power regulation of the molten salt energy storage heating device can be realized by adopting a Virtual Synchronous Generator (VSG) control strategy in the converter device of the thermal power molten salt energy storage heater, so that the frequency support of the thermal power plant is realized. However, the conventional VSG has no voltage supporting capability, and the molten salt energy storage and heating device needs to be operated all the time in order to keep the molten salt in a liquid state, so that the equipment cannot be shut down due to symmetric and asymmetric short circuits of the connected lines.

Disclosure of Invention

The application provides a grid-connected point voltage adjusting method and a grid-connected point voltage adjusting system for a fused salt energy storage and conversion device for fire power, and aims to at least solve the technical problem that equipment of a fused salt energy storage and heating device is shut down due to the fact that VSG in the related art does not have voltage supporting capacity.

An embodiment of the first aspect of the application provides a grid-connected point voltage adjusting method for a fused salt energy storage and conversion device for thermal power generation, where the method includes:

establishing an equation of the absorption active power and reactive power of the thermal power molten salt energy storage and conversion device and simplifying the equation;

respectively determining a voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power and a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device of the thermal power based on the simplified equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device of the thermal power;

determining the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device of the thermal power by using the voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power;

substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device containing virtual impedance, and determining the amplitude of the virtual impedance;

determining the voltage of a grid connection point required for supporting the thermal power molten salt energy storage device to operate when the electrical system of the thermal power plant generates a ground fault according to the amplitude of the virtual impedance;

and carrying out grid-connected point voltage regulation on the grid-connected point voltage required by supporting the operation of the fused salt thermal power energy storage device when the electrical system of the thermal power plant generates a ground fault.

An embodiment of a second aspect of the present application provides a grid-connected point voltage regulation system of a fused salt energy storage and conversion device for thermal power, where the system includes:

the establishing module is used for establishing an equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device for thermal power and simplifying the equation;

the first determining module is used for respectively determining a voltage equivalent equation of the fused salt thermal power storage converting device and a VSG reactive-voltage regulating equation of the fused salt thermal power storage converting device based on the simplified active and reactive power equations absorbed by the fused salt thermal power storage converting device;

the second determining module is used for determining voltage compensation voltage drop of a grid-connected point voltage of the fused salt energy storage and conversion device by using the voltage equivalent equation of the fused salt energy storage and conversion device;

the third determining module is used for substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device containing virtual impedance and determining the amplitude of the virtual impedance;

the fourth determining module is used for determining the voltage of a grid connection point required by the thermal power molten salt energy storage device to support operation when the electrical system of the thermal power plant generates a ground fault according to the amplitude of the virtual impedance;

and the adjusting module is used for supporting the grid-connected point voltage required by the operation of the thermal power fused salt energy storage device to adjust the grid-connected point voltage based on the ground fault generated by the power system of the thermal power plant.

The technical scheme provided by the embodiment of the application at least has the following beneficial effects:

the application provides a grid-connected point voltage adjusting method and a grid-connected point voltage adjusting system of a fused salt energy storage and conversion device for thermal power, wherein the method comprises the following steps: establishing an equation of the absorption active power and reactive power of the fused salt energy storage and conversion device for thermal power and simplifying the equation; respectively determining a voltage equivalent equation of the thermal molten salt energy storage and conversion device and a VSG (voltage source generator) reactive power-voltage regulation equation of the thermal molten salt energy storage and conversion device based on the simplified active power and reactive power absorption equation of the thermal molten salt energy storage and conversion device; determining the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device of the thermal power by using the voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power; substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device containing virtual impedance, and determining the amplitude of the virtual impedance; determining the voltage of a grid connection point required for supporting the thermal power molten salt energy storage device to operate when the electrical system of the thermal power plant generates a ground fault according to the amplitude of the virtual impedance; and carrying out grid-connected point voltage regulation on the grid-connected point voltage required by supporting the operation of the fused salt thermal power energy storage device when the electrical system of the thermal power plant generates a ground fault. According to the technical scheme provided by the invention, the virtual impedance is introduced into the VSG reactive-voltage control, the reference signal of the voltage closed loop link is changed, the voltage supporting function during the fault period is achieved, the fused salt energy storage and heating device is ensured to be always in the running state, and the equipment halt caused by the over-low voltage is prevented.

Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.

Drawings

The foregoing and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a flowchart of a grid-connected point voltage regulation method of a fused salt energy storage and conversion device for fossil power according to an embodiment of the present application;

FIG. 2 is a topological diagram of a fused salt energy storage and heating device and a converter device for fossil power provided according to an embodiment of the application;

FIG. 3 is a VSG reactive-voltage control block diagram for a fused salt energy storage converter device with virtual impedance fire power according to one embodiment of the application

FIG. 4 is a diagram of a positive sequence model architecture provided in accordance with one embodiment of the present application;

FIG. 5 is a diagram of a negative sequence model architecture provided in accordance with one embodiment of the present application;

fig. 6 is an equivalent fault network diagram of an asymmetric short-circuit fault occurring after the fused salt thermal power storage is connected to a plant power system according to an embodiment of the present application;

fig. 7 is an equivalent fault network diagram of a symmetrical short-circuit fault occurring after the thermal power molten salt energy storage is connected to the service electrical system according to an embodiment of the present application;

fig. 8 is a structural diagram of a grid-connected point voltage regulation system of a fused salt energy storage and conversion device for fossil power according to an embodiment of the present application.

Detailed Description

Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary and intended to be used for explaining the present application and should not be construed as limiting the present application.

The application provides a grid-connected point voltage adjusting method and system for a fused salt energy storage and conversion device for thermal power, wherein the method comprises the following steps: establishing an equation of the absorption active power and reactive power of the thermal power molten salt energy storage and conversion device and simplifying the equation; respectively determining a voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power and a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device of the thermal power based on the simplified equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device of the thermal power; determining the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device of the thermal power by using the voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power; substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device containing virtual impedance, and determining the amplitude of the virtual impedance; determining the voltage of a grid connection point required for supporting the thermal power molten salt energy storage device to operate when the electrical system of the thermal power plant generates a ground fault according to the amplitude of the virtual impedance; and carrying out grid-connected point voltage regulation on the grid-connected point voltage required by supporting the operation of the fused salt thermal power energy storage device when the electrical system of the thermal power plant generates a ground fault. According to the technical scheme provided by the invention, the virtual impedance is introduced into the VSG reactive-voltage control, the reference signal of the voltage closed loop link is changed, the voltage supporting function during the fault period is achieved, the fused salt energy storage and heating device is ensured to be always in the running state, and the equipment halt caused by the over-low voltage is prevented.

The method and the system for adjusting the grid-connected point voltage of the fused salt energy storage and conversion device for thermal power according to the embodiment of the application are described below with reference to the accompanying drawings.

Example one

Fig. 1 is a flowchart of a grid-connected point voltage adjusting method of a fused salt energy storage and conversion device for fossil power according to an embodiment of the present application, and as shown in fig. 1, the method may include:

step 1: establishing an equation of the absorption active power and reactive power of the fused salt energy storage and conversion device for thermal power and simplifying the equation;

in the disclosed embodiment, the establishing an equation of active power and reactive power absorbed by the thermal molten salt energy storage and conversion device and simplifying the equation includes:

the calculation formula of the established equation of the absorbed active power and the reactive power of the fused salt energy storage and conversion device for thermal power is

Because the inductive reactance Xg is far greater than the impedance Rg and the thermal power fused salt energy storage grid-connected condition, the reactive angle difference between the grid-connected point voltage of the converter device and the voltage of the power transmission line for the thermal power plant is as follows: sin for medical useδ≈δ，cosδIs approximately equal to 0, and the simplified equation of the absorbed active power and reactive power of the thermal power molten salt energy storage and conversion device can be obtained

Xg is transmission power for connected thermal power plantInductance corresponding to the line inductance Lg; u is the amplitude of the alternating current three-phase bridge arm voltage of the converter device, E is the amplitude of the grid-connected point three-phase voltage of the converter device, and delta is a power angle; it should be noted that the thermal molten salt energy storage and conversion device absorbs active power and has a linear relationship with a power angle, and reactive power and the voltage amplitude of a grid connection point of the thermal molten salt energy storage and conversion device have a linear relationship, so that power decoupling control can be realized.

Wherein, as shown in figure 2, the molten salt energy storage and heating device and the converter device for fossil power are topological diagrams,C _dcis a direct current side filtering flashlight;R _f、L _f、C _fforming a filter circuit;u _abc、i _abcalternating current three-phase bridge arm voltage and current for the converter device;e _abcgrid-connected point three-phase voltage for the converter device;L _g、R _gconstituting the line impedance.

And 2, step: respectively determining a voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power and a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device of the thermal power based on the simplified equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device of the thermal power;

in the embodiment of the disclosure, determining the voltage equivalent equation of the fused salt thermal power energy storage converter device based on the simplified equation of the absorbed active power and reactive power of the fused salt thermal power energy storage converter device includes:

obtaining a voltage equivalent equation of the fused salt energy storage and conversion device for thermal power based on the topological graph, the kirchhoff voltage law and the simplified equation of the active power and the reactive power absorbed by the fused salt energy storage and conversion device for thermal power in figure 2:

wherein L is equivalent inductance (L=L _f+L _g) R is equivalent resistance: (R=R _f+R _g），i_abcIs an alternating three-phase bridge arm current u_abcIs an AC three-phase bridge arm voltage, e_abcIs a grid-connected point three-phase voltage.

In the embodiment of the disclosure, determining the VSG reactive-voltage regulation equation of the fused salt thermal power energy storage converter device based on the simplified equation of the absorbed active power and reactive power of the fused salt thermal power energy storage converter device includes:

obtaining a VSG rotor mechanical equation of the fused salt thermal power energy storage and conversion device based on the simplified equation of the real power and reactive power absorbed by the fused salt thermal power energy storage and conversion device:

wherein:Jfor the purpose of virtual moment of inertia for the VSG,Din order to be a damping coefficient of the VSG,T _min order to be a mechanical torque, the torque,T _ein order to be an electromagnetic torque,T _din order to damp the torque, the torque is,

for the purpose of the nominal virtual angular velocity,

is the virtual electrical angular velocity. It is noted that the nature of the VSG active power is to introduce virtual inertia moment on the basis of active-frequency droop controlJHas the rotation inertia of the synchronous generator and introduces the damping coefficientDThe VSG can also simulate a synchronous generator excitation current control mode to realize voltage amplitude adjustment, has excitation adjustment inertia, and is similar to a VSG rotor mechanical equation of a thermal power molten salt energy storage and conversion device, so that a reactive-voltage adjustment equation can be obtained:

wherein: k_uIs the reactive equivalent inertia coefficient, Delta U is the reactive-voltage regulating quantity, Q_refAbsorbing reactive power target value, Q, of fused salt energy storage and conversion device for thermal power_eAbsorbing actual output value of reactive power, K, for fused salt energy storage and conversion device of thermal power_QFor a reactive-voltage regulation factor, u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_VdVirtual internal potentials for d-axis VSG in dq coordinate system.

And step 3: determining the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device of the thermal power by using the voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power;

in this disclosed embodiment, the determining, by using the equivalent voltage equation of the fused salt energy storage and conversion device, the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device includes:

step 3-1: based on Park transformation matrix T_abc→dq0Converting alternating current three-phase bridge arm voltage, current and grid-connected point three-phase voltage in the fused salt energy storage and conversion device for thermal power generation into a mathematical model under a dq two-phase coordinate system;

wherein, defineT _dqabc→0Is composed ofParkConverting the matrix to obtain the AC three-phase bridge arm voltage and current of the fused salt energy storage and conversion device for thermal power generation、The grid-connected point three-phase voltage can be converted into:

then substituting the converted formula into a voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power to obtain the fused salt energy storage and conversion device of the thermal powerdqThe mathematical model under the two-phase coordinate system is as follows:

in the formula u_aIs a phase bridge arm voltage, u_bIs b-phase bridge arm voltage, u_cFor the c-phase bridge arm voltage, the bridge arm voltage is,i _athe current of the bridge arm of the phase a,i _bthe phase of the bridge arm current is b phase bridge arm current,i _cis c-phase bridge arm current, e_aFor the grid-connected point a phase voltage, e_bTo the grid-connected point b phase voltage, e_cIs the grid-connected point c phase voltage.

Step 3-2: determining a transfer function under current closed-loop regulation according to a mathematical model under the dq two-phase coordinate system;

wherein the transfer function is expressed by

In the formula u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_qIs the effective value of bridge arm voltage, K, of the q-axis thermal power molten salt energy storage and conversion device under the dq coordinate system_PControlling the proportional regulation coefficient, K, for the current PI_IThe integral adjustment coefficient is controlled for the current PI,i _d ^*is a bridge arm current target value of the d-axis thermal power molten salt energy storage and conversion device under a dq coordinate system,i _q ^*is an effective current target value of a bridge arm current of a q-axis thermal power molten salt energy storage and conversion device under a dq coordinate system,i _dis the effective value of the bridge arm current of the d-axis fused salt energy storage and conversion device of the thermal power under the dq coordinate system,i _qis the effective value of bridge arm current of a q-axis fused salt energy storage and conversion device of thermal power under a dq coordinate system,

as a virtual electrical angular velocity, e_dThe grid-connected point voltage e of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_qThe grid-connected point voltage of the q-axis fused salt thermal power energy storage and conversion device under the dq coordinate system, L is equivalent inductance, and it needs to be explained that the current closed-loop regulation adopts a PI control mode.

Step 3-3: when the ground fault of a thermal power plant system is determined according to a transfer function under current closed loop regulation, the voltage variation expression of the grid-connected point of the thermal power fused salt energy storage and conversion device is determined, namely when the single-phase, two-phase or three-phase short circuit ground fault occurs, the equivalent impedance of a power transmission line is rapidly reduced, and the voltage transient state is reduced, so that the voltage variation of the grid-connected point of the thermal power fused salt energy storage and conversion device is generated.

Wherein, the voltage variation expression of the grid-connected point is

In the formula,. DELTA.u_dIs the voltage variation quantity delta of the grid-connected point of the d-axis fused salt energy storage and conversion device of the d-axis thermal power under the dq coordinate systemu _q For the voltage variation of the grid-connected point of the q-axis thermal power molten salt energy storage and conversion device under the dq coordinate system,u _d ^*bridge arm of d-axis thermal power fused salt energy storage and conversion device under dq coordinate systemThe target value of the voltage is set,u _q ^*a bridge arm voltage target value u of the q-axis thermal power molten salt energy storage and conversion device under a dq coordinate system_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_qThe effective value of the bridge arm voltage of the q-axis fused salt thermal power energy storage and conversion device under the dq coordinate system.

Step 3-4: constructing a virtual impedance equation and substituting the virtual impedance equation into the voltage variation expression of the grid-connected point of the thermal power molten salt energy storage and conversion device to obtain the voltage compensation voltage drop of the grid-connected point of the thermal power molten salt energy storage and conversion device when the thermal power plant system has a ground fault;

it should be noted that, in order to increase the voltage supporting capability of the VSG control system of the thermal molten salt energy storage and conversion device, the voltage variation of the grid-connected point of the thermal molten salt energy storage and conversion device is compensated, and a virtual impedance equation is constructed:

wherein:R _Xin order to be a virtual resistance, the resistance,L _Xis a virtual inductor. The invention compensates for delta using virtual impedanceu _d 、Δu _q And the voltage supporting capability of a VSG control system of the fused salt energy storage and conversion device for thermal power is improved.

Wherein the calculation formula of the compensation pressure drop is as follows:

in the formula,. DELTA.u_dIs the voltage variation quantity delta of the grid-connected point of the d-axis fused salt energy storage and conversion device of the d-axis thermal power under the dq coordinate systemu _q For the voltage variation of the grid-connected point of the q-axis thermal power molten salt energy storage and conversion device under the dq coordinate system,L _Xas a virtual inductor, the inductance of the inductor,R _Xis a virtual impedance, i_dIs the effective value of the bridge arm current i of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_qIs the effective value of bridge arm current of a q-axis fused salt energy storage and conversion device of thermal power under a dq coordinate system,

is the virtual electrical angular velocity.

And 4, step 4: substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device containing virtual impedance, and determining the amplitude of the virtual impedance;

in the embodiment of the disclosure, the calculation formula of the VSG reactive power-voltage regulation equation of the thermal molten salt energy storage converter device containing the virtual impedance is

In the formula, K_uIs a reactive equivalent inertia coefficient, Delta U is a reactive-voltage regulating variable, K_QFor the reactive-voltage regulation factor, u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power molten salt energy storage and conversion device under the dq coordinate system_VdIs d-axis VSG virtual internal potential, Q, under dq coordinate system_refAbsorbing reactive power target value, Q, of fused salt energy storage and conversion device for thermal power_eAbsorbing actual output value of reactive power, delta u, for fused salt energy storage and conversion device of thermal power_dVoltage variation of grid-connected points of the d-axis fused salt thermal power energy storage and conversion device under the dq coordinate system; it should be noted that the virtual impedance essentially introduces a current feedback link in voltage control, and continuously corrects a voltage target value by using the voltage drop of the current on the virtual impedance to improve the transient voltage, so that when the power system of the thermal power plant has a ground fault, the power transmission line has a side short circuit or an asymmetric short circuit, and a voltage supporting effect is achieved. As shown in fig. 3, the VSG reactive-voltage control block diagram is a VSG reactive-voltage control block diagram including a virtual impedance thermal molten salt energy storage and conversion device, and voltage and current closed-loop control is performed on voltage variation of a grid-connected point of a q-axis thermal molten salt energy storage and conversion device and a d-axis thermal salt energy storage and conversion device in a dq coordinate system obtained based on virtual impedance in a VSG reactive-voltage control strategy.

It should be noted that the ground fault includes: symmetric shorts and asymmetric shorts.

When an asymmetric short circuit occurs, the positive sequence current at the time of ground fault occursFlow component and negative sequence current component expression, and establishing i in voltage compensation voltage drop of grid-connected point of fused salt energy storage converter for thermal power generation when asymmetric short circuit occurs_d、i_qThe expression of a negative sequence double oscillation component is superposed:

wherein, I_f1Is a positive sequence currenti _f1Amplitude of (D), I_f2Is a negative sequence currenti _f2The amplitude of (c).

According to obtainingi _d 、i _q The negative sequence double oscillation component expression is superposed to obtain the virtual impedanceZ _XThe amplitude expression:

wherein:u _f1is a positive-sequence voltage, and is,u _f2is a negative-sequence voltage, and is,ufor the grid-connected point voltage of the fused salt energy storage and conversion device of the thermal power,I _limfor the current vector clipping radius, play the limit value effect to arbitrary phase current under the short circuit condition, avoid short-circuit current to exceed the vector clipping circle, positive sequence, negative sequence current amplitude satisfies:

。

and 5: determining the voltage of a grid connection point required for supporting the thermal power molten salt energy storage device to operate when the electrical system of the thermal power plant generates a ground fault according to the amplitude of the virtual impedance;

in this disclosed embodiment, the determining, according to the amplitude of the virtual impedance, a grid-connected point voltage required for supporting the operation of the fused salt thermal power energy storage device when the electrical system of the thermal power plant generates a ground fault includes:

step 5-1: acquiring a positive sequence current component and a negative sequence current component when a thermal power plant system has a ground fault;

it should be noted that the ground fault of the power transmission line for the thermal power plant can be divided into a symmetric short circuit and an asymmetric short circuit. Symmetrical short-circuit, i.e. three-phase earth short-circuit, fault network pairAt this time, the voltage of the grid-connected point of the fused salt energy storage and conversion device of the thermal power only has a positive sequence component; the asymmetric short circuit can be divided into a single-phase grounding short circuit and a two-phase grounding short circuit, the voltage of a grid-connected point of the fused salt energy storage and conversion device for thermal power is asymmetric due to the fact that symmetric current passes through a fault line, a power transmission line for thermal power plants adopts a neutral point ungrounded mode, and at the moment, the voltage of the grid-connected point not only has a positive sequence component but also has a negative sequence component. The positive sequence model when the thermal power plant system has the ground fault is shown in figure 4, the negative sequence model is shown in figure 5, based on the models, the thermal power molten salt energy storage system is equivalent to a constant voltage electric load, and the expression of the positive sequence current component when the thermal power plant system has the ground fault is obtained

Obtaining the expression of the negative sequence current component when the thermal power plant system has the ground fault as

，u _f1Is a positive-sequence voltage, and is,u _f2is negative sequence voltage, u is the voltage of the grid-connected point of the fused salt energy storage and conversion device of the thermal power,i _f1is a positive-sequence current, and is,i _f2is a negative sequence current, Z_XAs a result of the virtual impedance,Cis a parallel capacitor.

Step 5-2: determining the relationship between the virtual resistance and the virtual inductance when the thermal power plant system has the ground fault according to the positive sequence current component and the negative sequence current component when the thermal power plant system has the ground fault;

it should be noted that, in order to suppress three-phase voltage imbalance caused by negative sequence voltage during an asymmetric short circuit, and at the same time, the VSG control system provides maximum voltage support, according to a grid-connected point voltage expression of the fused salt energy storage and conversion device for thermal power, when an asymmetric short circuit occurs, a virtual impedance-to-inductance ratio is set to be the same as a fault point line impedance-to-inductance ratio, and a virtual resistance-to-inductance relational expression is obtained:

。

need to make sure thatIn order to realize the voltage support of the VSG control system of the thermal molten salt energy storage converter device when a symmetric short-circuit fault occurs, the maximum positive sequence current command needs to be kept, namelyi _f1=I _limAt this time, the virtual impedanceZ _XThe impedance-inductance ratio is 1, the amplitudes of the real part and the imaginary part are equal, and further a relation formula of the virtual resistance and the virtual inductance is obtained:

。

step 5-3: determining the voltage of a grid-connected point required for supporting the operation of the fused salt energy storage device of the thermal power plant when the electrical system of the thermal power plant generates the ground fault according to the relation between the virtual resistor and the virtual inductor when the electrical system of the thermal power plant generates the ground fault and the amplitude of the virtual impedance;

it should be noted that fig. 6 is an equivalent fault network diagram of an asymmetric short circuit fault occurring after the fused salt energy storage of thermal power is connected to the plant power system, and further, when the asymmetric short circuit occurs, according to the situation that the asymmetric short circuit occursi _d 、i _q The negative sequence double-oscillation component expression is superposed, when the asymmetric short circuit occurs, the positive sequence impedance and the negative sequence impedance are equal, the fault point line impedance is equal, and at the moment, the positive sequence current isi _f1And negative sequence currenti _f2And (3) obtaining a grid-connected point voltage expression of the fused salt energy storage and conversion device for thermal power, wherein the grid-connected point voltage expression comprises the following steps:

，i _f1、i _f2andZ _g1、Z _xthe proportion relation is that,

it should be noted that, as shown in fig. 7, an equivalent fault network diagram of a symmetric short-circuit fault after the fused salt thermal power storage is connected to the plant power system is shown, that is, when the symmetric short-circuit fault occurs, because there is no negative sequence component, according to the positive sequence current component expression and fig. 7 when the ground fault occurs, the grid-connected point voltage expression of the fused salt thermal power storage converter is obtained:

wherein:Z _g1the line impedance of a grid-connected point of a fused salt energy storage and conversion device for thermal power plant from a short circuit point of a power transmission line,u _Fis the fault point to ground voltage drop.

Step 6: and carrying out voltage regulation on a grid connection point based on the grid connection point voltage required by supporting the operation of the thermal power molten salt energy storage device when the electrical system of the thermal power plant generates a ground fault.

In summary, according to the method for adjusting the voltage of the grid-connected point of the fused salt energy storage converter device for thermal power, provided by the invention, the VSG control strategy is adopted in the converter device for the fused salt energy storage heater for thermal power, so that the fused salt energy storage for thermal power has virtual inertia, damping and virtual excitation regulation characteristics, meanwhile, virtual impedance is introduced into VSG reactive-voltage control, the reference signal of a voltage closed loop link is changed, the voltage support effect during the fault period is achieved, the fused salt energy storage heater device is ensured to be always in the running state, and the equipment halt caused by too low voltage is prevented.

Example two

Fig. 8 is a grid-connected point voltage regulating system of a fused salt energy storage and conversion device for fossil power according to an embodiment of the present application, as shown in fig. 8, the grid-connected point voltage regulating system may include:

the establishing module 100 is used for establishing an equation of the absorption active power and reactive power of the thermal power molten salt energy storage and conversion device and simplifying the equation;

the first determining module 200 is configured to respectively determine a voltage equivalent equation of the fused salt thermal energy storage converter device and a VSG reactive-voltage regulating equation of the fused salt thermal energy storage converter device based on the simplified absorbed active and reactive power equations of the fused salt thermal energy storage converter device;

the second determining module 300 is configured to determine voltage compensation voltage drop of a grid-connected point of the fused salt energy storage and conversion device by using the voltage equivalent equation of the fused salt energy storage and conversion device;

the third determining module 400 is configured to substitute the voltage compensation voltage drop at the grid-connected point of the fused salt thermal energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt thermal energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt thermal energy storage and conversion device containing a virtual impedance, and determine an amplitude of the virtual impedance;

a fourth determining module 500, configured to determine, according to the amplitude of the virtual impedance, a grid-connected point voltage required for supporting the operation of the fused salt thermal power energy storage device when the power system of the thermal power plant generates a ground fault;

and the adjusting module 600 is used for supporting the grid-connected point voltage required by the operation of the thermal power molten salt energy storage device to adjust the grid-connected point voltage when the electrical system of the thermal power plant generates the ground fault.

In an embodiment of the present disclosure, the establishing module 100 is specifically configured to:

the calculation formula of the established equation of the absorbed active power and the reactive power of the fused salt energy storage and conversion device for thermal power is

Because the inductive reactance Xg is far greater than the impedance Rg and the thermal power fused salt energy storage grid-connected condition, the reactive angle difference between the grid-connected point voltage of the converter device and the voltage of the power transmission line for the thermal power plant is as follows: sin for medical useδ≈δ，cosδIs approximately equal to 0, and the simplified equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device for thermal power can be obtained

Xg is the inductive reactance corresponding to the inductance Lg of the power transmission line for the connected thermal power plant; u is the amplitude of the AC three-phase bridge arm voltage of the converter device, E is the amplitude of the three-phase voltage of the grid-connected point of the converter device, and delta is the power angle.

In an embodiment of the present disclosure, the first determining module 200 is specifically configured to:

the calculation formula of the equivalent voltage equation of the fused salt energy storage converter for thermal power is as follows:

wherein L is equivalent inductance, R is equivalent resistance, i_abcIs an alternating three-phase bridge arm current u_abcIs an AC three-phase bridge arm voltage, e_abcThree-phase voltage of a grid connection point;

the calculation formula of the VSG reactive power-voltage regulation equation of the thermal molten salt energy storage and conversion device is as follows:

in the formula, K_uIs a reactive equivalent inertia coefficient, Delta U is a reactive-voltage regulating quantity, Q_refAbsorbing reactive power target value, Q, of fused salt energy storage and conversion device for thermal power_eAbsorbing actual output value of reactive power, K, for thermal power molten salt energy storage converter_QFor a reactive-voltage regulation factor, u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_VdVirtual internal potentials are d-axis VSG in dq coordinate system.

In an embodiment of the present disclosure, the second determining module 300 includes:

a conversion unit 301 for transforming the matrix T based on Park_abc→dq0Converting alternating current three-phase bridge arm voltage, current and grid-connected point three-phase voltage in the fused salt energy storage and conversion device for thermal power generation into a mathematical model under a dq two-phase coordinate system;

a first determining unit 302, configured to determine a transfer function under current closed-loop adjustment according to a mathematical model in the dq two-phase coordinate system;

the second determining unit 303 is configured to determine, according to the transfer function under the current closed-loop regulation, an expression of a grid-connected point voltage variation of the fused salt energy storage and conversion device for thermal power plant during a ground fault of the thermal power plant system;

the obtaining unit 304 is configured to construct a virtual impedance equation and substitute the virtual impedance equation into the voltage variation expression of the grid-connected point of the thermal molten salt energy storage and conversion device, so as to obtain a voltage compensation voltage drop of the grid-connected point of the thermal molten salt energy storage and conversion device when a ground fault occurs in a thermal power plant system;

and the current closed-loop regulation adopts a PI control mode.

It should be noted that the calculation formula of the transfer function under the current closed-loop regulation is as follows:

in the formula u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power molten salt energy storage and conversion device under the dq coordinate system_qIs the effective value of the bridge arm voltage, K, of the q-axis thermal power molten salt energy storage and conversion device under the dq coordinate system_PControlling the proportional regulation coefficient, K, for the current PI_IThe integral adjustment coefficient is controlled for the current PI,i _d ^*is a bridge arm current target value of the d-axis thermal power molten salt energy storage and conversion device under a dq coordinate system,i _q ^*the target value of the effective current of the bridge arm current of the q-axis fused salt energy storage and conversion device under the dq coordinate system,i _dis the effective value of the bridge arm current of the d-axis fused salt energy storage and conversion device of the thermal power under the dq coordinate system,i _qis the effective value of bridge arm current of a q-axis fused salt energy storage and conversion device of thermal power under a dq coordinate system,

as a virtual electrical angular velocity, e_dIs the grid-connected point voltage e of the d-axis fused salt energy storage and conversion device of the d-axis thermal power under the dq coordinate system_qAnd the grid-connected point voltage of the q-axis thermal power molten salt energy storage and conversion device under the dq coordinate system, wherein L is equivalent inductance.

It should be noted that, when the thermal power plant system has a ground fault, the expression of the grid-connected point voltage variation of the thermal molten salt energy storage converter device is as follows:

in the formula,. DELTA.u_dVoltage variation quantity delta of grid-connected point of d-axis thermal power fused salt energy storage and conversion device under dq coordinate systemu _q The voltage variation of the grid-connected point of the q-axis fused salt energy storage and conversion device under the dq coordinate system,u _d ^*is a bridge arm voltage target value of the d-axis thermal power molten salt energy storage and conversion device under a dq coordinate system,u _q ^*is a bridge arm voltage target value u of a q-axis thermal power molten salt energy storage and conversion device under a dq coordinate system_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_qThe effective value of the bridge arm voltage of the q-axis fused salt thermal power energy storage and conversion device under the dq coordinate system.

Specifically, when the thermal power plant system has a ground fault, the calculation formula of the grid-connected point voltage compensation voltage drop of the thermal power molten salt energy storage and conversion device is as follows:

in the formula,. DELTA.u_dIs the voltage variation quantity delta of the grid-connected point of the d-axis fused salt energy storage and conversion device of the d-axis thermal power under the dq coordinate systemu _q The voltage variation of the grid-connected point of the q-axis fused salt energy storage and conversion device under the dq coordinate system,L _Xas a virtual inductor, the inductance of the inductor,R _Xas a result of the virtual impedance,i _dis the effective value of the bridge arm current of the d-axis fused salt energy storage and conversion device of the thermal power under the dq coordinate system,i _qis the effective value of bridge arm current of a q-axis fused salt energy storage and conversion device of thermal power under a dq coordinate system,

is the virtual electrical angular velocity.

In an embodiment of the present disclosure, the third determining module 400 is specifically configured to:

the calculation formula of the VSG reactive-voltage regulation equation of the thermal power molten salt energy storage and conversion device containing the virtual impedance is as follows:

in the formula, K_uIs a reactive equivalent inertia coefficient, Delta U is a reactive-voltage regulating variable, K_QIs a reactive-voltage regulation coefficient,u_dis the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_VdIs d-axis VSG virtual internal potential, Q, under dq coordinate system_refAbsorbing reactive power target value, Q, of fused salt energy storage and conversion device for thermal power_eAbsorbing actual output value of reactive power, delta u, for fused salt energy storage and conversion device of thermal power_dThe grid-connected point voltage variation of the d-axis fused salt thermal power energy storage and conversion device under the dq coordinate system.

In an embodiment of the present disclosure, the fourth determining module 500 includes:

the acquiring unit 501 is configured to acquire a positive sequence current component and a negative sequence current component when a ground fault occurs in a thermal power plant system;

a third determining unit 502, configured to determine a relationship between a virtual resistance and a virtual inductance when the thermal power plant system has an earth fault according to the positive sequence current component and the negative sequence current component when the thermal power plant system has an earth fault;

a fourth determining unit 503, configured to determine, according to the relationship between the virtual resistor and the virtual inductor when the thermal power plant system has a ground fault and the amplitude of the virtual impedance, a grid-connected point voltage required for supporting the thermal power molten salt energy storage device to operate when the thermal power plant electric system has a ground fault.

In summary, the grid-connected point voltage regulation system of the fused salt energy storage and conversion device for thermal power provided by the invention adopts a VSG control strategy in the conversion device of the fused salt energy storage heater for thermal power, so that the fused salt energy storage for thermal power has virtual inertia, damping and virtual excitation regulation characteristics, and meanwhile, virtual impedance is introduced into VSG reactive-voltage control to change a reference signal of a voltage closed loop link, so that a voltage support effect during a fault is achieved, the fused salt energy storage and heating device is ensured to be always in a running state, and equipment shutdown caused by too low voltage is prevented.

In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing steps of a custom logic function or process, and alternate implementations are included within the scope of the preferred embodiment of the present application in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present application.

Although embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present application, and that variations, modifications, substitutions and alterations may be made to the above embodiments by those of ordinary skill in the art within the scope of the present application.

Claims (8)

1. A grid-connected point voltage adjusting method of a fused salt energy storage and conversion device for thermal power is characterized by comprising the following steps:

establishing an equation of the absorption active power and reactive power of the fused salt energy storage and conversion device for thermal power and simplifying the equation;

respectively determining a voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power and a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device of the thermal power based on the simplified equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device of the thermal power;

determining the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device of the thermal power by using the voltage equivalent equation of the fused salt energy storage and conversion device of the thermal power;

substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device containing virtual impedance, and determining the amplitude of the virtual impedance;

determining the voltage of a grid connection point required for supporting the thermal power molten salt energy storage device to operate when the electrical system of the thermal power plant generates a ground fault according to the amplitude of the virtual impedance;

carrying out grid-connected point voltage regulation on the basis of the grid-connected point voltage required for supporting the thermal power molten salt energy storage device to operate when the electrical system of the thermal power plant generates a ground fault;

substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device with virtual impedance, and the method comprises the following steps:

the calculation formula of the VSG reactive-voltage regulation equation of the thermal power molten salt energy storage and conversion device containing the virtual impedance is as follows:

in the formula, K_uIs a reactive equivalent inertia coefficient, Delta U is a reactive-voltage regulating variable, K_QFor a reactive-voltage regulation factor, u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_VdIs d-axis VSG virtual internal potential, Q, under dq coordinate system_refAbsorbing reactive power target value Q for thermal power molten salt energy storage converter_eAbsorbing actual output value of reactive power, delta u, for fused salt energy storage and conversion device of thermal power_dThe method is the voltage variation of a grid-connected point of a d-axis fused salt energy storage and conversion device under a dq coordinate system, wherein the expression of the amplitude of the virtual impedance is

；

Wherein:u _f1is a positive-sequence voltage, and is,u _f2is a negative-sequence voltage, and is,ufor the grid-connected point voltage of the thermal power fused salt energy storage and conversion device,I _limfor the current vector clipping radius, play the limit value effect to arbitrary phase current under the short circuit condition, avoid short-circuit current to exceed the vector clipping circle, positive sequence, negative sequence current amplitude satisfies:

wherein, I_f1Is a positive sequence currenti _f1Amplitude of (1)_f2Is a negative sequence currenti _f2The amplitude of (d);

the grid-connected point voltage required for supporting the operation of the fused salt energy storage device of the thermal power plant when the electrical system of the thermal power plant generates the ground fault is determined according to the amplitude of the virtual impedance, and the method comprises the following steps:

acquiring a positive sequence current component and a negative sequence current component when a thermal power plant system has a ground fault;

determining the relationship between the virtual resistance and the virtual inductance when the thermal power plant system has the ground fault according to the positive sequence current component and the negative sequence current component when the thermal power plant system has the ground fault;

determining the voltage of a grid-connected point required for supporting the operation of the fused salt energy storage device of the thermal power plant when the electrical system of the thermal power plant generates the ground fault according to the relation between the virtual resistor and the virtual inductor when the system of the thermal power plant generates the ground fault and the amplitude of the virtual impedance, wherein the ground fault comprises a symmetrical short circuit and an asymmetrical short circuit, and the positive sequence current component expression when the system of the thermal power plant generates the ground fault is

，

The negative sequence current component expression when the thermal power plant system has ground fault is

，

u _f1Is a positive-sequence voltage, and is,u _f2is negative sequence voltage, u is the voltage of the grid-connected point of the fused salt energy storage and conversion device of the thermal power,i _f1is a positive-sequence current, and is,i _f2is a negative sequence current, Z_XIs a virtual impedance.

2. The method of claim 1, wherein the establishing the equation of real and reactive power absorbed by the fused salt energy storage converter device and simplifying the equation comprises:

the calculation formula of the established equation of the absorbed active power and the reactive power of the fused salt energy storage and conversion device for thermal power is

Because the inductive reactance Xg is far greater than the impedance Rg and the thermal power fused salt energy storage grid-connected condition, the reactive angle difference between the grid-connected point voltage of the converter device and the voltage of the power transmission line for the thermal power plant is as follows: sin for medical useδ≈δ，cosδIs approximately equal to 0, and the simplified equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device for thermal power can be obtained

Xg is the inductive reactance corresponding to the inductance Lg of the power transmission line for the connected thermal power plant; u is the amplitude of the alternating current three-phase bridge arm voltage of the converter device, E is the amplitude of the three-phase voltage of the grid-connected point of the converter device, and delta is the power angle.

3. The method of claim 1, wherein the determining the voltage equivalent equation of the molten salt energy storage converter device and the VSG reactive-voltage regulation equation of the molten salt energy storage converter device respectively based on the simplified absorbed active and reactive power equations of the molten salt energy storage converter device comprises:

the calculation formula of the equivalent voltage equation of the fused salt energy storage converter for thermal power is as follows:

wherein L is equivalent inductance, R is equivalent resistance, i_abcIs an alternating three-phase bridge arm current u_abcIs an AC three-phase bridge arm voltage, e_abcThree-phase voltage of a grid connection point;

the calculation formula of the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device for thermal power generation is as follows:

in the formula, K_uIs a reactive equivalent inertia coefficient, Delta U is a reactive-voltage regulating quantity, Q_refAbsorbing reactive power target value, Q, of fused salt energy storage and conversion device for thermal power_eAbsorbing actual output value of reactive power, K, for fused salt energy storage and conversion device of thermal power_QFor a reactive-voltage regulation factor, u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_VdVirtual internal potentials for d-axis VSG in dq coordinate system.

4. The method of claim 1, wherein the determining a grid-connected point voltage compensation voltage drop of the thermal molten salt energy storage converter device by using the thermal molten salt energy storage converter device voltage equivalent equation comprises:

based on Park transformation matrix T_abc→dq0Converting alternating current three-phase bridge arm voltage, current and grid-connected point three-phase voltage in the thermal power molten salt energy storage and conversion device voltage equivalent equation into a mathematical model under a dq two-phase coordinate system;

determining a transfer function under current closed-loop regulation according to a mathematical model under the dq two-phase coordinate system;

determining a grid-connected point voltage variation expression of the fused salt energy storage and conversion device of the thermal power plant when the system of the thermal power plant is in ground fault according to the transfer function under the current closed loop regulation;

constructing a virtual impedance equation and substituting the virtual impedance equation into the grid-connected point voltage variation expression of the fused salt energy storage and conversion device of the thermal power plant to obtain the grid-connected point voltage compensation voltage drop of the fused salt energy storage and conversion device of the thermal power plant when a ground fault occurs to a system of the thermal power plant;

and the current closed-loop regulation adopts a PI control mode.

5. The method of claim 4, wherein the transfer function under closed loop regulation of current is calculated as follows:

in the formula u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_qIs the effective value of bridge arm voltage, K, of the q-axis thermal power molten salt energy storage and conversion device under the dq coordinate system_PControl of the proportional regulating coefficient, K, for the current PI_IThe integral adjustment coefficient is controlled for the current PI,i _d ^*is a bridge arm current target value of the d-axis thermal power molten salt energy storage and conversion device under a dq coordinate system,i _q ^*the target value of the effective current of the bridge arm current of the q-axis fused salt energy storage and conversion device under the dq coordinate system,i _dis the effective value of the bridge arm current of the d-axis fused salt energy storage and conversion device of the thermal power under the dq coordinate system,i _qis the effective value of bridge arm current of a q-axis fused salt energy storage and conversion device of thermal power under a dq coordinate system,

as a virtual electrical angular velocity, e_dIs the grid-connected point voltage e of the d-axis fused salt energy storage and conversion device of the d-axis thermal power under the dq coordinate system_qThe grid-connected point voltage of the q-axis fused salt thermal power energy storage and conversion device under the dq coordinate system is shown, and L is equivalent inductance.

6. The method according to claim 4, wherein the grid-connected point voltage change quantity expression of the thermal molten salt energy storage converter device when the thermal power plant system has a ground fault is as follows:

in the formula,. DELTA.u_dVoltage variation quantity delta of grid-connected point of d-axis thermal power fused salt energy storage and conversion device under dq coordinate systemu _q The voltage variation of the grid-connected point of the q-axis fused salt energy storage and conversion device under the dq coordinate system,u _d ^*is a bridge arm voltage target value of the d-axis thermal power molten salt energy storage and conversion device under a dq coordinate system,u _q ^*is a bridge arm voltage target value u of a q-axis thermal power molten salt energy storage and conversion device under a dq coordinate system_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_qThe effective value of the bridge arm voltage of the q-axis fused salt thermal power energy storage and conversion device under the dq coordinate system.

7. The method according to claim 4, wherein when the thermal power plant system has an earth fault, the voltage drop compensation of the grid-connected point voltage of the thermal molten salt energy storage and conversion device is calculated according to the following formula:

in the formula,. DELTA.u_dIs the voltage variation quantity delta of the grid-connected point of the d-axis fused salt energy storage and conversion device of the d-axis thermal power under the dq coordinate systemu _q The voltage variation of the grid-connected point of the q-axis fused salt energy storage and conversion device under the dq coordinate system,L _Xas a virtual inductor, the inductance of the inductor,R _Xas a result of the virtual impedance,i _dis the effective value of the bridge arm current of the d-axis thermal power molten salt energy storage and conversion device under the dq coordinate system,i _qbridge arm current of q-axis thermal power molten salt energy storage and conversion device under dq coordinate systemThe effective value of the effective value is,

is the virtual electrical angular velocity.

8. A grid-connected point voltage regulation system of a fused salt energy storage and conversion device for thermal power is characterized by comprising:

the establishing module is used for establishing an equation of the absorbed active power and reactive power of the fused salt energy storage and conversion device for thermal power and simplifying the equation;

the first determining module is used for respectively determining a voltage equivalent equation of the fused salt thermal power storage converting device and a VSG reactive-voltage regulating equation of the fused salt thermal power storage converting device based on the simplified active and reactive power equations absorbed by the fused salt thermal power storage converting device;

the second determining module is used for determining voltage compensation voltage drop of a grid-connected point voltage of the fused salt energy storage and conversion device by using the voltage equivalent equation of the fused salt energy storage and conversion device;

the third determining module is used for substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device containing virtual impedance and determining the amplitude of the virtual impedance,

substituting the voltage compensation voltage drop of the grid-connected point of the fused salt energy storage and conversion device into a VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device to obtain the VSG reactive-voltage regulation equation of the fused salt energy storage and conversion device with virtual impedance, and the method comprises the following steps:

the calculation formula of the VSG reactive-voltage regulation equation of the thermal power molten salt energy storage and conversion device containing the virtual impedance is as follows:

in the formula (I), the compound is shown in the specification,K_uis a reactive equivalent inertia coefficient, Delta U is a reactive-voltage regulating variable, K_QFor a reactive-voltage regulation factor, u_dIs the effective value of the bridge arm voltage u of the d-axis thermal power fused salt energy storage and conversion device under the dq coordinate system_VdIs d-axis VSG virtual internal potential, Q, under dq coordinate system_refAbsorbing reactive power target value, Q, of fused salt energy storage and conversion device for thermal power_eAbsorbing actual output value of reactive power, delta u, for fused salt energy storage and conversion device of thermal power_dThe method is the voltage variation of a grid-connected point of a d-axis fused salt energy storage and conversion device under a dq coordinate system, wherein the expression of the amplitude of the virtual impedance is

；

Wherein:u _f1is a positive-sequence voltage, and is,u _f2is a negative-sequence voltage, and is,ufor the grid-connected point voltage of the fused salt energy storage and conversion device of the thermal power,I _limfor the current vector clipping radius, play the limit value effect to arbitrary phase current under the short circuit condition, avoid short-circuit current to exceed the vector clipping circle, positive sequence, negative sequence current amplitude satisfies:

wherein, I_f1Is a positive sequence currenti _f1Amplitude of (1)_f2Is a negative sequence currenti _f2The amplitude of (d);

a fourth determining module, configured to determine, according to the amplitude of the virtual impedance, a grid-connected point voltage required for supporting operation of the fused salt thermal power energy storage device when the power system of the thermal power plant generates a ground fault,

the grid-connected point voltage required for supporting the operation of the fused salt energy storage device of the thermal power plant when the electrical system of the thermal power plant generates the ground fault is determined according to the amplitude of the virtual impedance, and the method comprises the following steps:

acquiring a positive sequence current component and a negative sequence current component when a thermal power plant system has a ground fault;

determining the relationship between the virtual resistance and the virtual inductance when the thermal power plant system has the ground fault according to the positive sequence current component and the negative sequence current component when the thermal power plant system has the ground fault;

determining the voltage of a grid-connected point required for supporting the fused salt energy storage device to operate when the electrical system of the thermal power plant generates the ground fault according to the relation between the virtual resistor and the virtual inductor when the electrical system of the thermal power plant generates the ground fault and the amplitude of the virtual impedance, wherein the ground fault comprises a symmetrical short circuit and an asymmetrical short circuit, and the positive sequence current component expression when the electrical system of the thermal power plant generates the ground fault is

，

The negative sequence current component expression when the thermal power plant system has ground fault is

，

u _f1Is a positive-sequence voltage, and is,u _f2is negative sequence voltage, u is the voltage of the grid-connected point of the fused salt energy storage and conversion device of the thermal power,i _f1is a positive-sequence current, and is,i _f2is a negative sequence current, Z_XIs a virtual impedance;

and the adjusting module is used for supporting the grid-connected point voltage required by the operation of the thermal power fused salt energy storage device to adjust the grid-connected point voltage based on the ground fault generated by the power system of the thermal power plant.

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