A method and system for supporting grid inertia based on dual-axis excitation phase shifters.

Abstract

This invention relates to the field of inertia support technology for new energy power systems, specifically disclosing a grid inertia support method and system based on a dual-axis excitation synchronous condenser. The method includes: acquiring the frequency and voltage of key nodes in the power grid through a phase-locked loop; determining transient frequency stability assessment indicators based on the grid's rated power, the frequency of key nodes, the longest duration of the frequency in each frequency band, and weighting coefficients; determining the system frequency status based on the frequency of key nodes and the transient frequency stability assessment indicators; when the system frequency status is unstable, controlling the dual-axis excitation synchronous condenser to send or absorb active power to the grid until the system frequency status stabilizes, then absorbing or sending active power from the grid through the frequency dual-axis excitation synchronous condenser to restore the motor speed to synchronous speed; when the system frequency status is stable, controlling the dual-axis excitation synchronous condenser to send or absorb reactive power to the grid.

Description

Technical Field

[0001] This invention relates to the field of inertia support technology for new energy power systems, specifically to a grid inertia support method and system based on a dual-axis excitation synchronous condenser. Background Technology

[0002] With the energy transition, new energy sources, primarily photovoltaic and wind power, are gradually becoming the mainstay of electricity supply. By the end of 2022, my country's cumulative installed capacity of new energy reached 760 million kilowatts, with an average annual increase of 120 million kilowatts over the past three years. It is projected to reach 1.1 billion kilowatts in 2025 and 1.8 billion kilowatts in 2030, accounting for nearly 50% of total installed capacity. Considering the low inertia and weak disturbance rejection characteristics of power electronic devices, and with the increasing penetration rate of power electronics, current new power systems face challenges such as insufficient system inertia and frequency regulation capabilities, as well as low frequency stability. There is an urgent need for an economical and effective new method to support the inertia of power systems. Summary of the Invention

[0003] To address the aforementioned problems, the purpose of this invention is to provide a power grid inertia support method and system based on a dual-axis excitation synchronous condenser, which provides reliable inertia support for the power system and reduces the frequency regulation pressure of traditional generators.

[0004] This invention provides a method for supporting the inertia of a power grid based on a dual-axis excitation phase modulator, comprising:

[0005] Step S1: Obtain the frequency and voltage of key nodes in the power grid through a phase-locked loop;

[0006] Step S2: Determine the transient frequency stability assessment index based on the rated power of the power grid, the frequency of the key node, the longest duration of the frequency in each frequency band, and the weighting coefficient.

[0007] Step S3: Determine the system frequency status based on the frequency and transient frequency stability evaluation index of the key nodes;

[0008] Step S4: When the system frequency is unstable, calculate the active power of the dual-axis excitation synchronous condenser based on the frequency, and calculate the required d-axis excitation voltage and q-axis excitation voltage based on the active power.

[0009] Step S5: Control the dual-axis excitation phase converter to send or absorb the active power to the grid according to the d-axis excitation voltage and q-axis excitation voltage until the system frequency condition stabilizes. Then, absorb or send the active power from the grid through the frequency dual-axis excitation phase converter so that the motor speed returns to synchronous speed.

[0010] Step S6: When the system frequency is stable, calculate the reactive power of the dual-axis excitation phase converter based on the voltage of the key node, and control the dual-axis excitation phase converter to send or absorb the reactive power to the grid.

[0011] In one possible implementation, S2 includes:

[0012] Calculate the weighting coefficient K using the following formula. j :

[0013] F = K j |f N -f(t i )|t j,max =1

[0014] In the formula, F is the transient frequency stability evaluation index, f(t) i ) for t i The frequency of the voltage or branch current at a critical node at a given time, f N For the rated frequency, K j Let t be the weighting coefficient for the j-th frequency interval. j,max The longest duration of frequency within the j-th frequency band.

[0015] In one possible implementation, S3 includes:

[0016] The system frequency status H[f(t] is determined based on the frequency of the key nodes and the transient frequency stability evaluation index. i The formula is as follows:

[0017]

[0018]

[0019] In the formula, F is the transient frequency stability evaluation index, f(t) i ) for t i The frequency of the voltage or branch current at the critical node at time m, where m is the total number of time points and n is the total number of frequency intervals, H[f(t)] i )] represents the system frequency status, K j f is the weighting coefficient for the j-th frequency interval. N The frequency is the rated frequency, dt is the time interval, and f is the frequency. j-1 f is the lower limit of the j-th frequency interval. j This represents the upper limit of the j-th frequency range.

[0020] In one possible implementation, S4 includes:

[0021] The active power P supplied to the grid by the dual-axis excitation synchronous condenser during the speed reduction process is determined by the following formula:

[0022]

[0023] In the formula, J is the moment of inertia of the camera, Ω1 is the rotor mechanical angular velocity at time t1, Ω0 is the rotor mechanical angular velocity at time t0, and dt is the time interval.

[0024] In one possible implementation, S4 includes:

[0025] The required d-axis excitation voltage and q-axis excitation voltage are calculated based on the aforementioned active power, using the following formulas:

[0026]

[0027]

[0028]

[0029] In the formula, u f1 and u f2 The excitation voltage component before coordinate transformation, u fd U is the d-axis excitation voltage. fq K is the q-axis excitation voltage. Pp K is the active power ratio coefficient. Qp K is the reactive power proportionality coefficient. Pi K is the active integral coefficient. Qi K is the reactive power integral coefficient. Pd K represents the active differential coefficient. Qd θ is the reactive power differential coefficient, P is the active power, Q is the reactive power, dt is the time interval, and θ is the reactive power differential coefficient. U Let P be the phase angle of the stator voltage in the dq coordinate system. ref Q is the active power reference signal. ref This is the reactive power reference signal.

[0030] In one possible implementation, S4 further includes:

[0031] The motor speed of the dual-axis excitation phase shifter is input into a neural network adaptive PID controller to obtain the active power reference signal P. ref The formula is as follows:

[0032]

[0033] In the formula, Ω N Ω represents the synchronous mechanical angular velocity, K represents the actual rotor mechanical angular velocity, and K represents the synchronous mechanical angular velocity. fp K is the speed proportional coefficient. fi K is the integral coefficient of rotational speed. fd dt is the differential coefficient of rotational speed, and dt is the time interval.

[0034] In one possible implementation, S4 further includes:

[0035] The parameters of the neural network adaptive PID controller are adjusted according to the following formula:

[0036] X (i) (n)=X (i) (n-1)+ΔX (i) (n)

[0037]

[0038] In the formula, i represents the position of the control parameter; i=1 represents the hidden layer in the neural network, and i=2 represents the output layer; n is the number of simulation steps; X is the control parameter; ΔX is the change in the control parameter; η is the learning rate; and P... ref Q is the active power reference signal. ref This is the reactive power reference signal.

[0039] One possible implementation also includes:

[0040] When the system is under maximum load, the dual-axis excitation synchronous condenser operates under overexcitation. The compensation capacity of the dual-axis excitation synchronous condenser is determined according to the following formula:

[0041]

[0042] In the formula, Q c For the rated capacity of the undetermined dual-axis excitation phase converter, x ij U' is the total reactance between busbars i and j, k is the transformer turns ratio, and U' is the total reactance between busbars i and j. jCmin To compensate for the voltage on the low-voltage side of bus J under maximum load, U jmax To compensate for the voltage on the high-voltage side of busbar J under maximum load,

[0043] When the excitation system is underloaded, the dual-axis excitation synchronous condenser operates underexcited. The compensation capacity of the dual-axis excitation synchronous condenser is determined according to the following formula:

[0044]

[0045] In the formula, U' jCmin The voltage on the low-voltage side of bus J after compensation under minimum load; U jmin To compensate for the voltage on the high-voltage side of busbar J before minimum load;

[0046] The rated capacity Q of the dual-axis excitation phase shifter is calculated using the following formula. c ':

[0047]

[0048] In the formula, k real This represents the actual turns ratio of the transformer.

[0049] One possible implementation also includes:

[0050] The moment of inertia J of the dual-axis excitation camera is determined according to the following formula:

[0051]

[0052] In the formula, P mean To set the average power output of the synchronous condenser, T is the average time for the synchronous condenser to output power, Ω min For the minimum mechanical speed, Ω N To synchronize mechanical angular velocity.

[0053] The present invention also provides a power grid inertia support system based on a dual-axis excitation phase modulator, which applies any of the above-mentioned power grid inertia support methods and includes: a dual-axis excitation phase modulator, an excitation system, an inertia support controller, and a transformer;

[0054] The dual-axis excitation synchronous condenser has excitation windings on both the d-axis and q-axis of the rotor.

[0055] The d-axis and q-axis excitation windings of the dual-axis excitation phase converter, and the inertia support controller are respectively connected to the excitation system; the step-up transformer is connected to the dual-axis excitation phase converter.

[0056] The inertia controller obtains the required excitation voltage for the d-axis and the required excitation voltage for the q-axis through key electrical quantities of the system.

[0057] The excitation system applies an excitation voltage to the excitation winding and controls the rotational speed by adjusting the angle between the combined excitation magnetic field of the d-axis and q-axis and the synchronous magnetic field.

[0058] The transformer raises the voltage of the excitation synchronous condenser to the line voltage for grid connection of the dual-axis excitation synchronous condenser, providing inertial support for the power system.

[0059] This invention provides a grid inertia support method and system based on a dual-axis excitation synchronous condenser, connecting the dual-axis excitation synchronous condenser to the power grid via a transformer. The dual-axis excitation motor can actively control its rotor speed by adjusting the angle between the combined magnetic field of the d-axis and q-axis excitation and the synchronous magnetic field, thereby changing the electromagnetic torque. When the system frequency is too low, the synchronous condenser speed is reduced to generate inertial power; when the system frequency is too high, the synchronous condenser speed is increased to absorb inertial power. After the system frequency stabilizes through a series of frequency regulation measures using the synchronous motor, the synchronous condenser absorbs or generates power, returning the motor speed to the synchronous speed. The transient frequency stability index is used to evaluate the system frequency status, directly demonstrating the inertia support effect of the dual-axis excitation synchronous condenser. Control parameter optimization using a neural network adaptive PID algorithm improves control response speed and reduces steady-state error. Based on this, the capacity of the dual-axis excitation synchronous condenser is selected according to system requirements, offering advantages such as low cost and good economic efficiency. This provides reliable inertia support for the power system and reduces the frequency regulation pressure on traditional generators. Attached Figure Description

[0060] Figure 1 A flowchart illustrating the power grid inertia support method provided in an embodiment of the present invention;

[0061] Figure 2 Electrical wiring diagram provided for embodiments of the present invention;

[0062] Figure 3 This is a decoupling control topology diagram of a dual-axis excitation motor provided in an embodiment of the present invention;

[0063] Figure 4 The diagram shows the inertia support effect of the dual-axis excitation camera provided in an embodiment of the present invention. Detailed Implementation

[0064] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. That is, the present invention is not limited to the described preferred embodiments, and the scope of the present invention is defined by the claims.

[0065] In the description of this invention, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance; those skilled in the art can understand the specific meaning of the above terms in this invention as appropriate.

[0066] Figure 1 This is a flowchart illustrating the power grid inertia support method provided in an embodiment of the present invention, as shown below. Figure 1As shown, this invention provides a method for supporting the inertia of a power grid based on a dual-axis excitation phase shifter, comprising:

[0067] Step S1: Obtain the frequency and voltage of key nodes in the power grid through a phase-locked loop;

[0068] Step S2: Determine the transient frequency stability assessment index based on the rated power of the power grid, the frequency of key nodes, the longest duration of the frequency in each frequency band, and the weighting coefficient.

[0069] Based on the frequency stability requirements of actual power grid operation, frequency f is divided into five frequency bands according to the severity of frequency fluctuations: f < 48.8Hz, 48.8Hz ≤ f < 49.5Hz, 49.5Hz ≤ f < 50.5Hz, 50.5Hz ≤ f < 51.2Hz, and f ≥ 51.2Hz, with weighting coefficients K1, K2, K3, K4, and K5 respectively. Among these, 49.5Hz ≤ f < 50.5Hz is considered normal frequency fluctuation, therefore weighting coefficient K3 = 0. The other weighting coefficients are calculated using the following formula. j :

[0070] F = K j |f N -f(t i )|t j,max =1

[0071] In the formula, F is the transient frequency stability evaluation index, f(t) i ) for t i The frequency of the voltage or branch current at a critical node at a given time, f N For the rated frequency, K j Let t be the weighting coefficient for the j-th frequency interval. j,max The longest duration of frequency within the j-th frequency band.

[0072] Step S3: Determine the system frequency status based on the frequency of key nodes and transient frequency stability evaluation indicators;

[0073] In one possible implementation, S3 includes:

[0074] The system frequency status H[f(t] is determined based on the frequency and transient frequency stability evaluation indicators of key nodes. i The formula is as follows:

[0075]

[0076] In the formula, F is the transient frequency stability evaluation index, f(t) i ) for t i The frequency of the voltage or branch current at the critical node at time m, where m is the total number of time points and n is the total number of frequency intervals, H[f(t)]i )] represents the system frequency status, K j f is the weighting coefficient for the j-th frequency interval. N The frequency is the rated frequency, dt is the time interval, and f is the frequency. j-1 f is the lower limit of the j-th frequency interval. j This represents the upper limit of the j-th frequency range.

[0077] The closer the transient frequency stability evaluation index is to 0, the better the frequency stability; the closer the index is to 1, the worse the frequency stability. It can intuitively reflect whether the frequency of the current node voltage or branch current meets the frequency stability requirements.

[0078] Step S4: When the system frequency is unstable, calculate the active power of the dual-axis excitation synchronous condenser based on the frequency, and calculate the required d-axis excitation voltage and q-axis excitation voltage based on the active power.

[0079] In one possible implementation, S4 includes:

[0080] The active power P supplied to the grid by the dual-axis excitation synchronous condenser during the speed reduction process is determined by the following formula:

[0081]

[0082] In the formula, J is the moment of inertia of the camera, Ω1 is the rotor mechanical angular velocity at time t1, Ω0 is the rotor mechanical angular velocity at time t0, and dt is the time interval.

[0083] The effect of the active power generated by the dual-axis synchronous condenser on the frequency of the power grid is shown in the following formula:

[0084]

[0085] In the formula, J sys Let f be the equivalent inertia of the power system, f be the system frequency, and p be the differential operator.

[0086] In one possible implementation, S4 includes:

[0087] In this invention, it is assumed that the d-axis and q-axis parameters of the dual-axis excitation phase condenser are the same. The relationship between the active power P and reactive power Q generated by the phase condenser and the d-axis excitation current and q-axis excitation current is as follows:

[0088]

[0089]

[0090] In the formula, u d u q These are the d-axis and q-axis stator voltages, respectively, i d iq These are the d-axis and q-axis stator currents, respectively, X ad X is the d-axis armature reaction reactance. d For the d-axis synchronous reactance, ω r i represents the motor speed. fd i fq These are the d-axis and q-axis excitation currents, respectively, and θ U Let U be the phase angle of the stator voltage in the dq coordinate system, and U be the amplitude of the stator voltage.

[0091] The formulas for calculating the required d-axis excitation voltage and q-axis excitation voltage based on the active power are as follows:

[0092]

[0093]

[0094]

[0095] In the formula, u f1 and u f2 The excitation voltage component before coordinate transformation, u fd U is the d-axis excitation voltage. fq K is the q-axis excitation voltage. Pp K is the active power ratio coefficient. Qp K is the reactive power proportionality coefficient. Pi K is the active integral coefficient. Qi K is the reactive power integral coefficient. Pd K represents the active differential coefficient. Qd θ is the reactive power differential coefficient, P is the active power, Q is the reactive power, dt is the time interval, and θ is the reactive power differential coefficient. U Let P be the phase angle of the stator voltage in the dq coordinate system. ref Q is the active power reference signal. ref This is the reactive power reference signal.

[0096] In one possible implementation, S4 also includes:

[0097] The motor speed of the dual-axis excitation phase shifter is input into a neural network adaptive PID controller to obtain the active power reference signal P. ref The formula is as follows:

[0098]

[0099] In the formula, Ω N Ω represents the synchronous mechanical angular velocity, K represents the actual rotor mechanical angular velocity, and K represents the synchronous mechanical angular velocity. fp K is the speed proportional coefficient. fi K is the integral coefficient of rotational speed. fd dt is the differential coefficient of rotational speed, and dt is the time interval.

[0100] Active power reference signal P ref Its size and duration can be adjusted as needed. The larger the active power reference signal and the longer its duration, the greater the active power generated by the dual-axis excitation synchronous condenser, and the more significant the decrease in the speed of the dual-axis excitation synchronous condenser.

[0101] In one possible implementation, the inertia support has multiple transient processes, including releasing inertial power, maintaining asynchronous operation, and absorbing active power to return to synchronous speed. In each process, a neural network adaptive PID controller is used to realize online automatic adjustment of PID parameters, improve the control response speed, and reduce errors.

[0102] The parameters of the neural network adaptive PID controller are adjusted according to the following formula:

[0103] X (i) (n)=X (i) (n-1)+ΔX (i) (n)

[0104]

[0105] In the formula, i represents the position of the control parameter; i=1 represents the hidden layer in the neural network, and i=2 represents the output layer; n is the number of simulation steps; X is the control parameter; ΔX is the change in the control parameter; η is the learning rate; and P... ref Q is the active power reference signal. ref This is the reactive power reference signal.

[0106] Step S5: Control the dual-axis excitation synchronous condenser to send or absorb active power to the grid according to the d-axis excitation voltage and q-axis excitation voltage until the system frequency condition stabilizes. Then, absorb or send active power from the grid through the frequency dual-axis excitation synchronous condenser so that the motor speed returns to synchronous speed.

[0107] A dual-axis excitation synchronous condenser, with excitation windings on both the d and q axes, is connected to the power grid via a transformer. Decoupled control of active and reactive power is achieved by adjusting the excitation voltages of the d and q axes. When the grid frequency decreases, the excitation voltage is controlled to reduce the speed of the dual-axis excitation synchronous condenser, releasing rotor kinetic energy and generating active power, thus providing inertial support for the grid. To avoid secondary frequency drops, the dual-axis excitation synchronous condenser maintains asynchronous operation for a period of time. After the grid frequency stabilizes, the synchronous condenser absorbs active power, bringing the motor speed back to synchronous speed. When the grid frequency increases, the excitation voltage is controlled to increase the speed of the dual-axis excitation synchronous condenser, absorbing rotor kinetic energy and active power, thus providing inertial support for the grid. To avoid secondary frequency rises, the dual-axis excitation synchronous condenser maintains asynchronous operation for a period of time. After the grid frequency stabilizes, the synchronous condenser absorbs active power, bringing the motor speed back to synchronous speed.

[0108] This invention provides inertial support to the power system by integrating a dual-axis excitation synchronous condenser into the power grid, effectively reducing the frequency regulation pressure on synchronous generators. Based on this, key parameters such as the equipment capacity and moment of inertia of the dual-axis excitation synchronous condenser, as well as control parameters, were determined, and a specific control method was proposed, which features good economy and rapid adjustment.

[0109] Step S6: When the system frequency is stable, calculate the reactive power of the dual-axis excitation synchronous condenser based on the voltage of the key nodes, and control the dual-axis excitation synchronous condenser to send or absorb reactive power to the grid.

[0110] In one possible implementation, the dual-axis excitation synchronous condenser satisfies the operating conditions of generating reactive power during overexcitation and absorbing reactive power during underexcitation, while also providing sufficient inertia support for the power system. Its equipment capacity and rotational inertia are selected according to the following formula.

[0111] When the system is under maximum load, the dual-axis synchronous condenser operates under overexcitation. The compensation capacity of the dual-axis synchronous condenser is determined according to the following formula:

[0112]

[0113] In the formula, Q c For the rated capacity of the undetermined dual-axis excitation phase converter, x ij U' is the total reactance between busbars i and j, k is the transformer turns ratio, and U' is the total reactance between busbars i and j. jCmin To compensate for the voltage on the low-voltage side of bus J under maximum load, U jmax To compensate for the voltage on the high-voltage side of busbar J under maximum load,

[0114] When the excitation system is underloaded, the dual-axis synchronous condenser operates underexcited. The compensation capacity of the dual-axis synchronous condenser is determined according to the following formula:

[0115]

[0116] In the formula, U' jCmin The voltage on the low-voltage side of bus J after compensation under minimum load; U jmin To compensate for the voltage on the high-voltage side of busbar J before minimum load;

[0117] The rated capacity Q of the dual-axis excitation phase shifter is calculated using the following formula. c ':

[0118]

[0119] In the formula, k real This represents the actual turns ratio of the transformer.

[0120] One possible implementation also includes:

[0121] The moment of inertia J of the dual-axis excitation camera is determined according to the following formula:

[0122]

[0123] In the formula, P mean To set the average power output of the synchronous condenser, T is the average time for the synchronous condenser to output power, Ω min For the minimum mechanical speed, Ω N To synchronize mechanical angular velocity.

[0124] Example 1

[0125] Figure 2 The electrical wiring diagram provided for the embodiments of the present invention is as follows: Figure 2 As shown, the left side of the power system represents new energy power generation, primarily composed of photovoltaic (PV) panels, while the right side uses synchronous generators to represent a small power grid. The PV power station is connected to the small power grid via a step-up transformer and power lines, supplying power to the system load. The control strategy is as follows: Figure 1 As shown, control box Figure 3 As shown. Figure 3 The decoupling control topology diagram of the dual-axis excitation motor provided in this embodiment of the invention is shown in Table 1 below. The main parameters of the power system are as follows:

[0126] Table 1

[0127]

[0128] First, determine the key parameters such as the capacity and moment of inertia of the parallel dual-axis excitation synchronous condenser. For ease of calculation, the transformer is assumed to be at its rated tap, with a turns ratio k of 230kV / 20kV. After maximum load compensation, the voltage on the low-voltage side of the busbar is the rated voltage, i.e., U'jCmax = 20kV. Before compensation at maximum load, the voltage on the high-voltage side of the busbar is 0.9 times the rated voltage, i.e., Ujmax = 207kV. The calculated capacity of the dual-axis excitation synchronous condenser is Qc = 83.36MVar, as shown in the following formula:

[0129]

[0130] The required average power output of the dual-axis excitation phase shifter is Pmean = 50MW, the duration is T = 5s, and the minimum permissible mechanical angular velocity is Ωmin = 0.9 * 100π = 282.7433 rad / s. The moment of inertia J can be calculated as J = 7916 kg·m², and the corresponding inertial time constant Tj is 9.37s, as shown in the following formula:

[0131]

[0132]

[0133] Building such Figure 1 The power system shown in the simulation consists of two small systems, each with a capacity of 50 MVA, connected by transformers and transmission lines to supply power to a 100 MW load. At t = 10 s, the system load suddenly increases by 130 MW, and the system frequency suddenly decreases. The grid inertia support method based on dual-axis excitation synchronous condensers described in this invention is used to support the system's inertia. During the sudden load increase, the magnitude and duration of the synchronous condenser's reference active power (Pref) are changed, as shown in Table 2.

[0134] Table 2

[0135] plan Active power / pu Duration / s 1 0.2 10 2 0.4 10 3 0.2 20

[0136] Comparing the systems using dual-axis excitation phase shifters for inertia support (Schemes 1 to 3) with those not using dual-axis excitation phase shifters (Scheme 4), the system frequency curves are as follows: Figure 4 As shown. Figure 4 The diagram shows the inertia support effect of the dual-axis excitation camera provided in an embodiment of the present invention.

[0137] Depend on Figure 4 It can be seen that without the use of a dual-axis excitation synchronous condenser (Scheme 4), the system frequency drops due to the increased load, reaching a minimum of 49.10Hz. Subsequently, due to the primary frequency regulation of the generator, the frequency gradually recovers to 50Hz. This shows that relying solely on the primary frequency regulation of the generator results in significant system frequency fluctuations and poor frequency stability; therefore, a dual-axis excitation synchronous condenser is needed to provide inertial support for the system. When a dual-axis excitation synchronous condenser is used, the frequency fluctuation amplitude decreases. Using Schemes 1, 2, and 3, the minimum frequencies are 49.22Hz, 49.29Hz, and 49.26Hz respectively, indicating that the dual-axis excitation synchronous condenser can provide inertial support for the system. Simultaneously, the synchronous condenser's speed decreases due to the release of kinetic energy, and it maintains asynchronous operation for a period of time. At t = 80s, the primary frequency regulation of the synchronous generator ends, and the dual-axis excitation synchronous condenser absorbs power from the system, causing its speed to return to synchronous speed. At this point, the frequency fluctuation is within the range of 50±0.5Hz, resulting in minimal disturbance to the system frequency.

[0138] To quantify the system frequency stability using different schemes, transient frequency indices need to be calculated. The maximum allowable time for different frequency ranges is shown in Table 3, where 49.5Hz ≤ f < 50.5Hz represents the normal frequency fluctuation range. The transient frequency indices for different schemes are calculated, and a comparison of these indices is shown in Table 4.

[0139] Table 3

[0140]

[0141] Table 4

[0142]

[0143] As shown in Table 4, without using a dual-axis excitation synchronous condenser (Scheme 4), the transient frequency index is 0.0455. With a dual-axis excitation synchronous condenser, the index for Scheme 1 is 0.0455. After increasing the active power reference signal (Scheme 2) and extending the inertia support time (Scheme 3), the transient frequency indices are 0.0427 and 0.0370, respectively. This indicates that the greater the power output of the synchronous condenser and the longer the power output duration, the better the system inertia support effect.

[0144] The present invention also provides a power grid inertia support system based on a dual-axis excitation phase modulator, which applies any of the above-mentioned power grid inertia support methods and includes: a dual-axis excitation phase modulator, an excitation system, an inertia support controller, and a transformer;

[0145] The dual-axis excitation synchronous condenser has excitation windings on both the d-axis and q-axis of the rotor;

[0146] The d-axis and q-axis excitation windings and the inertia support controller of the dual-axis excitation synchronous condenser are connected to the excitation system, respectively; the step-up transformer is connected to the dual-axis excitation synchronous condenser.

[0147] The inertia controller obtains the required excitation voltage for the d-axis and q-axis through key electrical quantities of the system.

[0148] The excitation system applies an excitation voltage to the excitation winding and controls the speed by adjusting the angle between the combined excitation magnetic field of the d-axis and q-axis and the synchronous magnetic field to change the electromagnetic torque.

[0149] The transformer raises the voltage of the excitation synchronous condenser to the line voltage for grid connection of the dual-axis excitation synchronous condenser, providing inertial support for the power system.

[0150] This invention provides a grid inertia support method and system based on a dual-axis excitation synchronous condenser, connecting the dual-axis excitation synchronous condenser to the power grid via a transformer. The dual-axis excitation motor can actively control its rotor speed by adjusting the angle between the combined magnetic field of the d-axis and q-axis excitation and the synchronous magnetic field, thereby changing the electromagnetic torque. When the system frequency is too low, the synchronous condenser speed is reduced to generate inertial power; when the system frequency is too high, the synchronous condenser speed is increased to absorb inertial power. After the system frequency stabilizes through a series of frequency regulation measures using the synchronous motor, the synchronous condenser absorbs or generates power, returning the motor speed to the synchronous speed. The transient frequency stability index is used to evaluate the system frequency status, directly demonstrating the inertia support effect of the dual-axis excitation synchronous condenser. Control parameter optimization using a neural network adaptive PID algorithm improves control response speed and reduces steady-state error. Based on this, the capacity of the dual-axis excitation synchronous condenser is selected according to system requirements, offering advantages such as low cost and good economic efficiency. This provides reliable inertia support for the power system and reduces the frequency regulation pressure on traditional generators.

[0151] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for supporting the inertia of a power grid based on a dual-axis excitation phase-regulator, characterized in that, include: Step S1: Obtain the frequency and voltage of key nodes in the power grid through a phase-locked loop; Step S2: Determine the transient frequency stability assessment index based on the rated power of the power grid, the frequency of the key node, the longest duration of the frequency in each frequency band, and the weighting coefficient. Step S3: Determine the system frequency status based on the frequency and transient frequency stability evaluation index of the key nodes; Step S4: When the system frequency is unstable, calculate the active power of the dual-axis excitation synchronous condenser based on the frequency, and calculate the required d-axis excitation voltage and q-axis excitation voltage based on the active power. Step S5: Control the dual-axis excitation phase converter to send or absorb the active power to the grid according to the d-axis excitation voltage and q-axis excitation voltage until the system frequency condition stabilizes. Then, absorb or send the active power from the grid through the frequency dual-axis excitation phase converter so that the motor speed returns to synchronous speed. Step S6: When the system frequency is stable, calculate the reactive power of the dual-axis excitation phase converter based on the voltage of the key node, and control the dual-axis excitation phase converter to send or absorb the reactive power to the grid. S4 includes: The required d-axis excitation voltage and q-axis excitation voltage are calculated based on the active power, using the following formulas: In the formula, u f1 and u f2 The excitation voltage component before coordinate transformation, u fd U is the d-axis excitation voltage. fq K is the q-axis excitation voltage. Pp K is the active power ratio coefficient. Qp K is the reactive power proportionality coefficient. Pi K is the active integral coefficient. Qi K is the reactive power integral coefficient. Pd K represents the active differential coefficient. Qd θ is the reactive power differential coefficient, P is the active power, Q is the reactive power, dt is the time interval, and θ is the reactive power differential coefficient. U Let P be the phase angle of the stator voltage in the dq coordinate system. ref Q is the active power reference signal. ref This is the reactive power reference signal; The motor speed of the dual-axis excitation phase shifter is input into a neural network adaptive PID controller to obtain the active power reference signal P. ref The formula is as follows: In the formula, Ω N Ω represents the synchronous mechanical angular velocity, K represents the actual rotor mechanical angular velocity, and K represents the synchronous mechanical angular velocity. fp K is the speed proportional coefficient. fi K is the integral coefficient of rotational speed. fd Here, dt is the differential coefficient of rotational speed; The parameters of the neural network adaptive PID controller are adjusted according to the following formula: X (i) (n)=X (i) (n-1)+ΔX (i) (n) In the formula, i represents the position of the control parameter; i=1 represents the hidden layer in the neural network, and i=2 represents the output layer; n is the number of simulation steps; X is the control parameter; ΔX is the change in the control parameter; η is the learning rate; and P... ref Q is the active power reference signal. ref This is the reactive power reference signal.

2. The power grid inertia support method according to claim 1, characterized in that, S2 includes: Calculate the weighting coefficient K using the following formula. j : F=K j |f N -f(t i )|t j,max =1 In the formula, F is the transient frequency stability evaluation index, f(t) i ) for t i The frequency of the voltage or branch current at a critical node at a given time, f N For the rated frequency, K j Let t be the weighting coefficient for the j-th frequency interval. j,max The longest duration of frequency within the j-th frequency band.

3. The power grid inertia support method according to claim 1, characterized in that, S3 includes: The system frequency status H[f(t] is determined based on the frequency of the key nodes and the transient frequency stability evaluation index. i The formula is as follows: In the formula, F is the transient frequency stability evaluation index, f(t) i ) for t i The frequency of the voltage or branch current at the critical node at time m, where m is the total number of time points and n is the total number of frequency intervals, H[f(t)] i )] represents the system frequency status, K j f is the weighting coefficient for the j-th frequency interval. N The frequency is the rated frequency, dt is the time interval, and f is the frequency. j-1 f is the lower limit of the j-th frequency interval. j This represents the upper limit of the j-th frequency range.

4. The power grid inertia support method according to claim 1, characterized in that, S4 includes: The active power P supplied to the grid by the dual-axis excitation synchronous condenser during the speed reduction process is determined by the following formula: In the formula, J is the moment of inertia of the camera, Ω1 is the rotor mechanical angular velocity at time t1, Ω0 is the rotor mechanical angular velocity at time t0, and dt is the time interval.

5. The power grid inertia support method according to claim 1, characterized in that, Also includes: When the system is under maximum load, the dual-axis excitation synchronous condenser operates under overexcitation. The compensation capacity of the dual-axis excitation synchronous condenser is determined according to the following formula: In the formula, Q c For the rated capacity of the undetermined dual-axis excitation phase converter, x ij U' is the total reactance between busbars i and j, k is the transformer turns ratio, and U' is the total reactance between busbars i and j. jCmin To compensate for the voltage on the low-voltage side of bus J under maximum load, U jmax To compensate for the voltage on the high-voltage side of busbar J under maximum load, When the excitation system is underloaded, the dual-axis excitation synchronous condenser operates underexcited. The compensation capacity of the dual-axis excitation synchronous condenser is determined according to the following formula: In the formula, U' jCmin The voltage on the low-voltage side of bus J after compensation under minimum load; U jmin To compensate for the voltage on the high-voltage side of busbar J before minimum load; The rated capacity Q of the dual-axis excitation phase shifter is calculated using the following formula. c ': In the formula, k real This represents the actual turns ratio of the transformer.

6. The power grid inertia support method according to claim 4, characterized in that, Also includes: The moment of inertia J of the dual-axis excitation camera is determined according to the following formula: In the formula, P mean To set the average power output of the synchronous condenser, T is the average time for the synchronous condenser to output power, Ω min For the minimum mechanical speed, Ω N To synchronize mechanical angular velocity.

7. A power grid inertia support system based on a dual-axis excitation phase shifter, employing the power grid inertia support method according to any one of claims 1-6, characterized in that, include: Dual-axis synchronous condenser, excitation system, inertia support controller, transformer; The dual-axis excitation synchronous condenser has excitation windings on both the d-axis and q-axis of the rotor. The d-axis and q-axis excitation windings of the dual-axis excitation phase converter, and the inertia support controller are respectively connected to the excitation system; the step-up transformer is connected to the dual-axis excitation phase converter. The inertia controller obtains the required excitation voltage for the d-axis and the required excitation voltage for the q-axis through key electrical quantities of the system. The excitation system applies an excitation voltage to the excitation winding and controls the rotational speed by adjusting the angle between the combined excitation magnetic field of the d-axis and q-axis and the synchronous magnetic field. The transformer raises the voltage of the excitation synchronous condenser to the line voltage for grid connection of the dual-axis excitation synchronous condenser, providing inertial support for the power system. The inertia controller is used for: The required d-axis excitation voltage and q-axis excitation voltage are calculated based on the active power, using the following formulas: In the formula, u f1 and u f2 The excitation voltage component before coordinate transformation, u fd U is the d-axis excitation voltage. fq K is the q-axis excitation voltage. Pp K is the active power ratio coefficient. Qp K is the reactive power proportionality coefficient. Pi K is the active integral coefficient. Qi K is the reactive power integral coefficient. Pd K represents the active differential coefficient. Qd θ is the reactive power differential coefficient, P is the active power, Q is the reactive power, dt is the time interval, and θ is the reactive power differential coefficient. U Let P be the phase angle of the stator voltage in the dq coordinate system. ref Q is the active power reference signal. ref This is the reactive power reference signal; The motor speed of the dual-axis excitation phase shifter is input into a neural network adaptive PID controller to obtain the active power reference signal P. ref The formula is as follows: In the formula, Ω N Ω represents the synchronous mechanical angular velocity, K represents the actual rotor mechanical angular velocity, and K represents the synchronous mechanical angular velocity. fp K is the speed proportional coefficient. fi K is the integral coefficient of rotational speed. fd Here, dt is the differential coefficient of rotational speed; The parameters of the neural network adaptive PID controller are adjusted according to the following formula: X (i) (n)=X (i) (n-1)+ΔX (i) (n) In the formula, i represents the position of the control parameter; i=1 represents the hidden layer in the neural network, and i=2 represents the output layer; n is the number of simulation steps; X is the control parameter; ΔX is the change in the control parameter; η is the learning rate; and P... ref Q is the active power reference signal. ref This is the reactive power reference signal.

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