Power grid inertia supporting method and system based on double-shaft excitation phase modifier

Abstract

The invention relates to the technical field of inertia support of a new energy power system, and particularly discloses a power grid inertia support method and system based on a double-shaft excitation phase modifier, and the method comprises the steps: obtaining the frequency and voltage of a key node of a power grid through a phase-locked loop; determining a transient frequency stability evaluation index according to 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 weight coefficient; determining a system frequency condition according to the frequency of the key node and a transient frequency stability evaluation index; when the frequency condition of the system is unstable, controlling the double-shaft excitation phase modifier to emit or absorb active power to the power grid until the frequency condition of the system is stable, and absorbing or emitting the active power from the power grid through the frequency double-shaft excitation phase modifier, so that the rotating speed of the motor is recovered to the synchronous speed; and when the system frequency condition is stable, the double-shaft excitation phase modifier is controlled to send reactive power to the power grid or absorb reactive power.

Description

Technical Field

[0001] The present invention relates to the technical field of inertia support for a new energy power system, and in particular to a power grid inertia support method and system based on a dual-axis excitation phase regulator. Background Art

[0002] With the energy transformation, new energy sources, mainly photovoltaic and wind power, have gradually become the main power supply. By the end of 2022, my country's cumulative installed capacity of new energy will reach 760 million kilowatts, with an average annual increase of 120 million kilowatts in the past three years. It is expected to reach 1.1 billion kilowatts in 2025 and 1.8 billion kilowatts in 2030, accounting for nearly 50% of the installed capacity. Taking into account the low inertia and weak anti-interference characteristics of power electronic devices, as the penetration rate of power electronics continues to increase, the current new power system has problems such as insufficient system inertia and frequency regulation capabilities, and low frequency stability. At present, there is an urgent need for an economical and effective means of inertia support for new power systems. Summary of the invention

[0003] In view of the above problems, the purpose of the present invention is to provide a grid inertia support method and system based on a dual-axis excitation phase shifter, which provides reliable inertia support for the power system and reduces the frequency regulation pressure of traditional generators.

[0004] The present invention provides a power grid inertia support method based on a dual-axis excitation phase shifter, comprising:

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

[0006] Step S2, determining a transient frequency stability evaluation index according to the rated power of the power grid, the frequency of the key node, the longest duration of the frequency in each frequency band, and a weight coefficient;

[0007] Step S3, determining the system frequency status according to the frequency of the key node and the transient frequency stability evaluation index;

[0008] Step S4, when the system frequency condition is unstable, the active power of the dual-axis excitation phase shifter is calculated according to the frequency, and the required d-axis excitation voltage and q-axis excitation voltage are calculated according to the active power;

[0009] Step S5, controlling the dual-axis excitation phase shifter to send or absorb the active power to the power grid according to the d-axis excitation voltage and the q-axis excitation voltage, until the system frequency condition is stable, and absorbing or sending the active power from the power grid through the frequency dual-axis excitation phase shifter, so that the motor speed returns to the synchronous speed;

[0010] Step S6, when the system frequency condition is stable, the reactive power of the dual-axis excitation phase shifter is calculated according to the voltage of the key node, and the dual-axis excitation phase shifter is controlled to emit or absorb the reactive power to the power grid.

[0011] In a possible implementation, the S2 includes:

[0012] The weight coefficient K is calculated according to the following formula j :

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

[0014] Where F is the transient frequency stability evaluation index, f(t i ) is t i The voltage at the critical node or the frequency of the branch current at that moment, f N is the rated frequency, K j is the weight coefficient of the jth frequency interval, t j,max is the maximum duration of a frequency in the jth frequency band.

[0015] In a possible implementation, S3 includes:

[0016] Determine the system frequency status H[f(t i )], the formula is as follows:

[0017]

[0018]

[0019] Where F is the transient frequency stability evaluation index, f(t i ) is t i The voltage or branch current frequency of the key node at the moment, m is the total number of moments, n is the total number of frequency intervals, H[f(t i )] represents the system frequency status, K j is the weight coefficient of the jth frequency interval, f N is the rated frequency, dt is the time interval, f j-1 is the lower limit of the jth frequency interval, f j is the upper limit of the jth frequency interval.

[0020] In a possible implementation, the S4 includes:

[0021] The active power P emitted by the dual-axis excitation phase regulator to the power grid during the speed reduction process is determined according to the following formula:

[0022]

[0023] Where, J is the moment of inertia of the phase regulator, Ω 1 t 1 The rotor mechanical angular velocity at the moment, Ω 0 t 0 The rotor mechanical angular velocity at the moment, dt is the time interval.

[0024] In a possible implementation, the S4 includes:

[0025] The required d-axis excitation voltage and q-axis excitation voltage are calculated according to the active power, and the formula is also as follows:

[0026]

[0027]

[0028]

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

[0030] In a possible implementation, the S4 further includes:

[0031] The motor speed of the dual-axis excitation phase regulator is input into the 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 is the synchronous mechanical angular velocity, Ω is the actual rotor mechanical angular velocity, K fp is the speed proportional coefficient, Kfi is the speed integral coefficient, K fd is the speed differential coefficient, and dt is the time interval.

[0034] In a possible implementation, the 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] Where i represents the position of the control parameter, i = 1 is the hidden layer in the neural network, i = 2 is the output layer in the neural network, 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, P ref is the active power reference signal, Q ref is the reactive power reference signal.

[0039] In a possible implementation, the method further includes:

[0040] When the system is at maximum load, the dual-axis excitation phase regulator is overexcited and the compensation capacity of the dual-axis excitation phase regulator of the dual-axis excitation phase regulator is determined according to the following formula:

[0041]

[0042] In the formula, Q c is the rated capacity of the dual-axis excitation phase regulator to be determined, x ij is the total reactance between busbars i and j, k is the transformer ratio, U' jCmin is the voltage of busbar j on the low voltage side after compensation at maximum load, U jmax is the voltage of the j busbar on the high voltage side before compensation at maximum load,

[0043] When the excitation system is at minimum load, the dual-axis excitation phase regulator is under-excited, and the compensation capacity of the dual-axis excitation phase regulator of the dual-axis excitation phase regulator is determined according to the following formula:

[0044]

[0045] In the formula, U' jCmin is the voltage of busbar j on the low voltage side after compensation at minimum load; U jmin The voltage of the j busbar on the high voltage side before compensation at the minimum load;

[0046] Calculate the rated capacity Q of the dual-axis excitation phase regulator according to the following formula c ':

[0047]

[0048] In the formula, k real is the actual transformation ratio of the transformer.

[0049] In a possible implementation, the method further includes:

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

[0051]

[0052] Where P mean is the average power output by the phase regulator, T is the average time for the phase regulator to output power, Ω min is the minimum mechanical speed, Ω N is the synchronous mechanical angular velocity.

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

[0054] The dual-axis excitation phase regulator is provided with excitation windings on both the d-axis and the q-axis of the rotor;

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

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

[0057] The excitation system applies an excitation voltage to the excitation winding, and changes the electromagnetic torque by adjusting the angle between the d-axis and q-axis excitation composite magnetic field and the synchronous magnetic field to control the rotation speed;

[0058] The transformer increases the voltage of the excitation phase regulator to the line voltage for connecting the dual-axis excitation phase regulator to the grid and providing inertial support for the power system.

[0059] The invention provides a method and system for supporting the inertia of a power grid based on a dual-axis excitation phase condenser, and connects the dual-axis excitation phase condenser to the power grid in parallel through a transformer. The dual-axis excitation motor can change the electromagnetic torque by adjusting the angle between the d-axis and q-axis excitation composite magnetic fields and the synchronous magnetic field to realize active control of the rotor speed. When the system frequency is too low, the phase condenser speed is controlled to decrease and emit inertial power; when the system frequency is too high, the phase condenser speed is controlled to increase and absorb inertial power. After the system frequency is stabilized through a series of frequency modulation measures of the synchronous motor, the phase condenser is controlled to absorb or emit power to return the motor speed to the synchronous speed. The system frequency condition is judged by the transient frequency stability index, which intuitively reflects the inertia support effect of the dual-axis excitation phase condenser. The control parameters are optimized by the neural network adaptive PID algorithm, which improves the control response speed and reduces the steady-state error. On this basis, the capacity of the dual-axis excitation phase condenser is selected according to the system requirements, which has the advantages of low cost and good economy, provides reliable inertial support for the power system, and reduces the frequency modulation pressure of traditional generators. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 A schematic diagram of a flow chart of a power grid inertia support method provided by an embodiment of the present invention;

[0061] Figure 2 An electrical wiring diagram provided for an embodiment of the present invention;

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

[0063] Figure 4 This is a diagram showing the inertial support effect of the dual-axis excitation phase shifter provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0064] The following detailed description of the embodiments of the present invention is further described in detail in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the preferred embodiments described, and the scope of the present invention is defined by the claims.

[0065] In the description of the present invention, it should be noted that, unless otherwise specified, “plurality” means two or more than two; the terms “first”, “second”, etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0066] Figure 1 A schematic diagram of a flow chart of a grid inertia support method provided by an embodiment of the present invention, such as Figure 1As shown, the present invention provides a power grid inertia support method based on a dual-axis excitation phase shifter, comprising:

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

[0068] Step S2, determining a transient frequency stability evaluation index according to the rated power of the power grid, the frequency of the key node, the maximum duration of the frequency in each frequency band, and the weight coefficient;

[0069] According to the demand for frequency stability in the actual operation of the power grid, the frequency f is divided into the following five frequency bands according to the severity of frequency fluctuation: f<48.8Hz, 48.8Hz≤f<49.5Hz, 49.5Hz≤f<50.5Hz, 50.5Hz≤f<51.2Hz, f≥51.2Hz, and the weight coefficients are K1, K2, K3, K4, and K5. Among them, 49.5Hz≤f<50.5Hz belongs to normal frequency fluctuation, so the weight coefficient K3=0, and the other weight coefficients are calculated according to the following formula: j :

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

[0071] Where F is the transient frequency stability evaluation index, f(t i ) is t i The voltage at the critical node or the frequency of the branch current at that moment, f N is the rated frequency, K j is the weight coefficient of the jth frequency interval, t j,max is the maximum duration of a frequency in the jth frequency band.

[0072] Step S3, determining the system frequency status according to the frequency of the key node and the transient frequency stability evaluation index;

[0073] In a possible implementation, S3 includes:

[0074] Determine the system frequency status H[f(t i )], the formula is as follows:

[0075]

[0076] Where F is the transient frequency stability evaluation index, f(t i ) is t i The voltage or branch current frequency of the key node at the moment, m is the total number of moments, n is the total number of frequency intervals, H[f(ti )] represents the system frequency status, K j is the weight coefficient of the jth frequency interval, f N is the rated frequency, dt is the time interval, f j-1 is the lower limit of the jth frequency interval, f j is the upper limit of the jth frequency interval.

[0077] The closer the transient frequency stability evaluation index is to 0, the better the frequency stability is; the closer the index is to 1, the worse the frequency stability is. 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 condition is unstable, the active power of the dual-axis excitation phase shifter is calculated according to the frequency, and the required d-axis excitation voltage and q-axis excitation voltage are calculated according to the active power;

[0079] In a possible implementation, S4 includes:

[0080] The active power P emitted by the dual-axis excitation phase regulator to the power grid during the speed reduction process is determined according to the following formula:

[0081]

[0082] Where, J is the moment of inertia of the phase regulator, Ω 1 t 1 The rotor mechanical angular velocity at the moment, Ω 0 t 0 The rotor mechanical angular velocity at the moment, dt is the time interval.

[0083] The influence of the active power generated by the dual-axis excitation phase regulator on the frequency of the power grid is as follows:

[0084]

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

[0086] In a possible implementation, S4 includes:

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

[0088]

[0089]

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

[0091] According to the active power, the required d-axis excitation voltage and q-axis excitation voltage are calculated, and the formula is as follows:

[0092]

[0093]

[0094]

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

[0096] In a possible implementation, S4 further includes:

[0097] The motor speed of the dual-axis excitation phase regulator is input into the 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 is the synchronous mechanical angular velocity, Ω is the actual rotor mechanical angular velocity, K fp is the speed proportional coefficient, K fiis the speed integral coefficient, K fd is the speed differential coefficient, and dt is the time interval.

[0100] Active power reference signal P ref Its size and duration can be changed according to demand. The larger the active power reference signal is and the longer the duration is, the greater the active power emitted by the dual-axis excitation phase shifter is, and the more significant the speed drop of the dual-axis excitation phase shifter is.

[0101] In one possible implementation, the inertial 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] Where i represents the position of the control parameter, i = 1 is the hidden layer in the neural network, i = 2 is the output layer in the neural network, 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, P ref is the active power reference signal, Q ref is the reactive power reference signal.

[0106] Step S5, controlling the dual-axis excitation phase shifter to send or absorb active power to the grid according to the d-axis excitation voltage and the q-axis excitation voltage, until the system frequency condition is stable, and absorbing or sending active power from the grid through the frequency dual-axis excitation phase shifter, so that the motor speed returns to the synchronous speed;

[0107] The dual-axis excitation phase condenser with excitation windings on both the d and q axes is connected to the power grid through a transformer. The decoupling control of active and reactive power is achieved by adjusting the excitation voltages of the d and q axes. When the grid frequency drops, the excitation voltage is controlled to reduce the speed of the dual-axis excitation phase condenser, release the rotor kinetic energy, and generate active power, thereby providing inertia support for the grid. To avoid secondary frequency drops, the dual-axis excitation phase condenser maintains an asynchronous operation state for a period of time. After the grid frequency stabilizes, the phase condenser is controlled to absorb active power to return the motor speed to the synchronous speed. When the grid frequency rises, the excitation voltage is controlled to increase the speed of the dual-axis excitation phase condenser, absorb the rotor kinetic energy, and absorb active power, thereby providing inertia support for the grid. To avoid secondary frequency increases, the dual-axis excitation phase condenser maintains an asynchronous operation state for a period of time. After the grid frequency stabilizes, the phase condenser is controlled to absorb active power to return the motor speed to the synchronous speed.

[0108] The present invention provides inertial support for the power system by connecting the dual-axis excitation phase condenser to the power grid, effectively reducing the frequency regulation pressure of the synchronous generator. On this basis, the key parameters such as equipment capacity, moment of inertia and control parameters of the dual-axis excitation phase condenser are determined, and a specific control method is proposed, which has the characteristics of good economy and rapid regulation.

[0109] Step S6, when the system frequency condition is stable, the reactive power of the dual-axis excitation phase shifter is calculated according to the voltage of the key node, and the dual-axis excitation phase shifter is controlled to emit or absorb reactive power to the power grid.

[0110] In a possible implementation, the dual-axis excitation phase regulator can meet the operating conditions of emitting reactive power in over-excitation operation and absorbing reactive power in under-excitation operation, and at the same time can provide 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 at maximum load, the dual-axis excitation phase regulator is overexcited. The compensation capacity of the dual-axis excitation phase regulator is determined according to the following formula:

[0112]

[0113] In the formula, Q c is the rated capacity of the dual-axis excitation phase regulator to be determined, x ij is the total reactance between busbars i and j, k is the transformer ratio, U' jCmin is the voltage of busbar j on the low voltage side after compensation at maximum load, U jmax is the voltage of the j busbar on the high voltage side before compensation at maximum load,

[0114] When the excitation system is at minimum load, the dual-axis excitation phase regulator is under-excited. The compensation capacity of the dual-axis excitation phase regulator is determined according to the following formula:

[0115]

[0116] In the formula, U' jCmin is the voltage of busbar j on the low voltage side after compensation at minimum load; U jmin The voltage of the j busbar on the high voltage side before compensation at the minimum load;

[0117] Calculate the rated capacity Q of the dual-axis excitation phase regulator according to the following formula c ':

[0118]

[0119] In the formula, k real is the actual transformation ratio of the transformer.

[0120] In a possible implementation, the method further includes:

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

[0122]

[0123] Where P mean is the average power output by the phase regulator, T is the average time for the phase regulator to output power, Ω min is the minimum mechanical speed, Ω N is the synchronous mechanical angular velocity.

[0124] Example 1

[0125] Figure 2 The electrical wiring diagram provided by the embodiment of the present invention is as follows: Figure 2 As shown in the figure, the left side of the power system is the new energy power generation represented by photovoltaics, which is composed of photovoltaic panels, and the right side is represented by a synchronous generator to represent a small power grid. The photovoltaic power station is connected to the small power grid through a step-up transformer and power lines, and supplies power to the system load. The control strategy is as follows Figure 1 As shown, the control box Figure 3 shown. Figure 3 The decoupling control topology diagram of the dual-axis excitation motor provided by the embodiment of the present invention. The main parameters of the power system are shown in Table 1:

[0126] Table 1

[0127]

[0128] First, determine the key parameters such as the capacity and moment of inertia of the parallel dual-axis excitation phase regulator. For the convenience of calculation, the transformer is considered to be in rated gear and the transformation ratio k is 230kV / 20kV. The voltage of the busbar on the low-voltage side after maximum load compensation is the rated voltage, that is, U'jCmax=20kV. The voltage of the busbar on the high-voltage side before compensation at maximum load is 0.9 times the rated voltage, that is, Ujmax=207kV. The capacity of the dual-axis excitation phase regulator Qc=83.36MVar is calculated as follows:

[0129]

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

[0131]

[0132]

[0133] Build as Figure 1 The power system shown in the figure is simulated. Both the left and right sides are small systems of 50MVA, which are connected through transformers and transmission lines to supply power to a 100MW power load. At t=10s, the system load suddenly increases by 130MW. The system frequency suddenly decreases. The grid inertia support method based on the dual-axis excitation phase regulator of the present invention is used to support the system inertia. During the period of sudden increase in system load, the magnitude and duration of the phase regulator reference active power Pref are changed respectively. The magnitude and duration of the active reference power are shown in Table 2.

[0134] Table 2

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

[0136] Comparing the use of dual-axis excitation phase shifter for inertial support (Schemes 1 to 3) and not using dual-axis excitation phase shifter (Scheme 4), the system frequency curve is as follows Figure 4 shown. Figure 4 This is a diagram showing the inertial support effect of the dual-axis excitation phase shifter provided in an embodiment of the present invention.

[0137] Depend on Figure 4It can be seen that when the dual-axis excitation phase condenser (Scheme 4) is not used, the system frequency drops due to the increase in load, and the minimum is 49.10Hz. After that, due to the primary frequency modulation of the generator, the frequency gradually recovers to 50Hz. It can be seen that relying only on the primary frequency modulation of the generator, the system frequency fluctuation amplitude is large and the frequency stability is poor. Therefore, a dual-axis excitation phase condenser is needed to provide inertia support for the system. When the dual-axis excitation phase condenser is used, the frequency fluctuation amplitude is weakened. When schemes 1, 2, and 3 are used, the minimum frequencies are 49.22Hz, 49.29Hz, and 49.26Hz, respectively, indicating that the dual-axis excitation phase condenser can provide inertia support for the system. At the same time, due to the release of kinetic energy, the speed of the phase condenser will decrease and maintain asynchronous operation for a period of time. At t=80s, the primary frequency modulation of the synchronous generator ends, and the dual-axis excitation phase condenser absorbs power from the system to return the speed to the synchronous speed. At this time, the frequency fluctuation is within the range of 50±0.5Hz, and the disturbance to the system frequency is small.

[0138] In order to quantify the system frequency stability using different schemes, it is necessary to calculate the transient frequency index. The maximum allowable time for different frequency ranges is shown in Table 3, where 49.5Hz≤f<50.5Hz is the normal frequency fluctuation range. The transient frequency index of different schemes is calculated, and the comparison of transient frequency index is shown in Table 4.

[0139] Table 3

[0140]

[0141] Table 4

[0142]

[0143] It can be seen from Table 4 that without using the dual-axis excitation phase condenser (Scheme 4), the transient frequency index is 0.0455; after using the dual-axis excitation phase condenser, the index of Scheme 1 is 0.0455. After increasing the active reference signal size (Scheme 2) and extending the inertia support time (Scheme 3), the transient frequency indexes are 0.0427 and 0.0370 respectively, indicating that the greater the power output of the phase 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 shifter, applying any of the above-mentioned power grid inertia support methods, comprising: a dual-axis excitation phase shifter, an excitation system, an inertia support controller, and a transformer;

[0145] The dual-axis excitation phase regulator is provided with excitation windings on both the d-axis and the q-axis of the rotor;

[0146] The d-axis excitation winding and q-axis excitation winding of the dual-axis excitation phase regulator and the inertia support controller are respectively connected to the excitation system; the step-up transformer is connected to the dual-axis excitation phase regulator;

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

[0148] The excitation system applies excitation voltage to the excitation winding, and changes the electromagnetic torque and controls the speed by adjusting the angle between the d-axis and q-axis excitation composite magnetic field and the synchronous magnetic field;

[0149] The transformer increases the voltage of the excitation phase regulator to the line voltage for connecting the dual-axis excitation phase regulator to the grid and providing inertial support for the power system.

[0150] The invention provides a method and system for supporting the inertia of a power grid based on a dual-axis excitation phase condenser, and connects the dual-axis excitation phase condenser to the power grid in parallel through a transformer. The dual-axis excitation motor can change the electromagnetic torque by adjusting the angle between the d-axis and q-axis excitation composite magnetic fields and the synchronous magnetic field to realize active control of the rotor speed. When the system frequency is too low, the phase condenser speed is controlled to decrease and emit inertial power; when the system frequency is too high, the phase condenser speed is controlled to increase and absorb inertial power. After the system frequency is stabilized through a series of frequency modulation measures of the synchronous motor, the phase condenser is controlled to absorb or emit power to return the motor speed to the synchronous speed. The system frequency condition is judged by the transient frequency stability index, which intuitively reflects the inertia support effect of the dual-axis excitation phase condenser. The control parameters are optimized by the neural network adaptive PID algorithm, which improves the control response speed and reduces the steady-state error. On this basis, the capacity of the dual-axis excitation phase condenser is selected according to the system requirements, which has the advantages of low cost and good economy, provides reliable inertial support for the power system, and reduces the frequency modulation pressure of traditional generators.

[0151] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for supporting the inertia of a power grid based on a dual-axis excitation phase shifter, characterized in that: include: Step S1, obtaining the frequency and voltage of key nodes of the power grid through a phase-locked loop; Step S2, determining a transient frequency stability evaluation index according to the rated power of the power grid, the frequency of the key node, the longest duration of the frequency in each frequency band, and a weight coefficient; Step S3, determining the system frequency status according to the frequency of the key node and the transient frequency stability evaluation index; Step S4, when the system frequency condition is unstable, the active power of the dual-axis excitation phase shifter is calculated according to the frequency, and the required d-axis excitation voltage and q-axis excitation voltage are calculated according to the active power; Step S5, controlling the dual-axis excitation phase shifter to send or absorb the active power to the power grid according to the d-axis excitation voltage and the q-axis excitation voltage, until the system frequency condition is stable, and absorbing or sending the active power from the power grid through the frequency dual-axis excitation phase shifter, so that the motor speed returns to the synchronous speed; Step S6, when the system frequency condition is stable, the reactive power of the dual-axis excitation phase shifter is calculated according to the voltage of the key node, and the dual-axis excitation phase shifter is controlled to emit or absorb the reactive power to the power grid.

2. The grid inertia support method according to claim 1, characterized in that: The S2 includes: The weight coefficient K is calculated according to the following formula j : F=K j |f N -f(t i )|t j,max =1 Where F is the transient frequency stability evaluation index, f(t i ) is t i The voltage at the critical node or the frequency of the branch current at that moment, f N is the rated frequency, K j is the weight coefficient of the jth frequency interval, t j,max is the maximum duration of a frequency in the jth frequency band.

3. The grid inertia support method according to claim 1, characterized in that: The S3 includes: Determine the system frequency status H[f(t i )], the formula is as follows: Where F is the transient frequency stability evaluation index, f(t i ) is t i The voltage or branch current frequency of the key node at the moment, m is the total number of moments, n is the total number of frequency intervals, H[f(t i )] represents the system frequency status, K j is the weight coefficient of the jth frequency interval, f N is the rated frequency, dt is the time interval, f j-1 is the lower limit of the jth frequency interval, f j is the upper limit of the jth frequency interval.

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

5. The grid inertia support method according to claim 1, characterized in that: The S4 includes: The required d-axis excitation voltage and q-axis excitation voltage are calculated according to the active power, and the formula is also as follows: In the formula, u f1 and u f2 is the excitation voltage component before coordinate transformation, u fd is the d-axis excitation voltage, u fq is the q-axis excitation voltage, K Pp is the active proportional coefficient, K Qp is the reactive power proportional coefficient, K Pi is the active integral coefficient, K Qi is the reactive power integral coefficient, K Pd is the active differential coefficient, K Qd is the reactive differential coefficient, P is the active power, Q is the reactive power, dt is the time interval, θ U is the phase angle of the stator voltage in the dq coordinate system, P ref is the active power reference signal, Q ref is the reactive power reference signal.

6. The grid inertia support method according to claim 5, characterized in that: The S4 further comprises: The motor speed of the dual-axis excitation phase regulator is input into the neural network adaptive PID controller to obtain the active power reference signal P ref , the formula is as follows: In the formula, Ω N is the synchronous mechanical angular velocity, Ω is the actual rotor mechanical angular velocity, K fp is the speed proportional coefficient, K fi is the speed integral coefficient, K fd is the speed differential coefficient, and dt is the time interval.

7. The grid inertia support method according to claim 6, characterized in that: The S4 further comprises: 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) Where i represents the position of the control parameter, i = 1 is the hidden layer in the neural network, i = 2 is the output layer in the neural network, 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, P ref is the active power reference signal, Q ref is the reactive power reference signal.

8. The grid inertia support method according to claim 7, characterized in that: Also includes: When the system is at maximum load, the dual-axis excitation phase regulator is overexcited and the compensation capacity of the dual-axis excitation phase regulator of the dual-axis excitation phase regulator is determined according to the following formula: In the formula, Q c is the rated capacity of the dual-axis excitation phase regulator to be determined, x ij is the total reactance between busbars i and j, k is the transformer ratio, U' jCmin is the voltage of busbar j on the low voltage side after compensation at maximum load, U jmax is the voltage of the j busbar on the high voltage side before compensation at maximum load, When the excitation system is at minimum load, the dual-axis excitation phase regulator is under-excited, and the compensation capacity of the dual-axis excitation phase regulator of the dual-axis excitation phase regulator is determined according to the following formula: In the formula, U' jCmin is the voltage of busbar j on the low voltage side after compensation at minimum load; U jmin The voltage of the j busbar on the high voltage side before compensation at the minimum load; Calculate the rated capacity Q of the dual-axis excitation phase regulator according to the following formula c ': In the formula, k real is the actual transformation ratio of the transformer.

9. The grid inertia support method according to claim 7, characterized in that: Also includes: The moment of inertia J of the dual-axis excitation condenser of the dual-axis excitation condenser is determined according to the following formula: Where P mean is the average power output by the phase regulator, T is the average time for the phase regulator to output power, Ω min is the minimum mechanical speed, Ω N is the synchronous mechanical angular velocity.

10. A power grid inertia support system based on a dual-axis excitation phase shifter, using the power grid inertia support method according to any one of claims 1 to 9, characterized in that: include: Dual-axis excitation phase condenser, excitation system, inertial support controller, transformer; The dual-axis excitation phase regulator is provided with excitation windings on both the d-axis and the q-axis of the rotor; The d-axis excitation winding and q-axis excitation winding of the dual-axis excitation phase regulator and the inertia support controller are respectively connected to the excitation system; the step-up transformer is connected to the dual-axis excitation phase regulator; The inertia controller obtains the excitation voltage required for the d-axis and the excitation voltage required for the q-axis through the key electrical quantities of the system; The excitation system applies an excitation voltage to the excitation winding, and changes the electromagnetic torque by adjusting the angle between the d-axis and q-axis excitation composite magnetic field and the synchronous magnetic field to control the rotation speed; The transformer increases the voltage of the excitation phase regulator to the line voltage for connecting the dual-axis excitation phase regulator to the grid and providing inertial support for the power system.

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