Frequency voltage support control method and system for energy storage power station facing weak power grid

Abstract

The invention provides a frequency voltage support control method and system of an energy storage power station facing a weak power grid, and is applied to the technical field of energy storage control. The method comprises the steps of determining current positive and negative sequence active power and positive and negative sequence reactive power of an energy storage power station and a deviation value of current positive and negative sequence voltage amplitudes and a deviation value of current positive and negative sequence frequencies of the energy storage power station based on three-phase voltage and three-phase current of a common connection point alternating current side of a weak power grid; with safe operation of the energy storage power station as a constraint condition, droop control is carried out based on current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and a deviation value of current positive and negative sequence voltage amplitudes and a deviation value of positive and negative sequence frequencies of the energy storage power station; and controlling active power and reactive power output by the energy storage power station based on the output of the droop control so as to support the frequency and voltage of the main power grid during the power system fault through the energy storage power station. According to the invention, the problem of poor safety and stability of the operation of the weak power grid with the coexistence of frequency and voltage transient disturbance is solved.

Description

Technical Field

[0001] The present invention relates to the field of energy storage control technology, and in particular to a frequency and voltage support control method and system for an energy storage power station for a weak power grid. Background Art

[0002] At present, the power system is facing challenges and opportunities brought by the rapid growth of new energy installed capacity. With the rapid development of the scale of grid-connected new energy such as wind power and photovoltaic power, the power supply structure of my country's power system has gradually shifted from conventional power sources to new energy sources. The frequency and voltage resistance of new energy are weaker than those of traditional units, resulting in a significant decline in the overall regulation capacity of the power grid. Especially in the voltage ride-through and recovery stage of new energy, the active and reactive power output switching characteristics and the control method mainly to ensure equipment safety make the active and reactive unbalanced power of the power grid deeply coupled, and the transient frequency and voltage of the system under AC and DC faults show coupling characteristics. For example, new energy bases such as the Haixi region of the Northwest Power Grid are typical scenarios where a high proportion of new energy is connected to the main grid through weak interconnection channels. The unbalanced power caused by the fault is significantly affected by the system voltage. The system frequency characteristics are not only related to the active exchange level before the fault, but also closely related to the voltage level after the disturbance. After the system fault, there will be a scene where frequency and voltage transient disturbances coexist, which brings severe challenges to the safe and stable control of the power grid. Traditional control methods based on the frequency-active power relationship face many problems. Due to the difficulty in matching the control object and timing, conventional control measures such as machine cutting and load shedding face the problems of overly conservative control and huge control volume. They are unable to cope with the frequency-voltage coupling challenges brought by new energy, nor can they ensure the continuous safe and stable operation of the power grid.

[0003] Energy storage power stations can store excess electricity output by renewable energy and release it when needed to ensure the normal operation of the power system, thereby improving the operational stability of the power grid. At present, energy storage still participates in the control of the power grid based on the traditional frequency-active power relationship, which cannot solve the problem of poor operational safety and stability of weak power grids with coexistence of frequency and voltage transient disturbances. Summary of the invention

[0004] In order to overcome the problem of poor safety and stability in the operation of a weak power grid with coexisting frequency and voltage transient disturbances, the present invention provides a frequency and voltage support control method and system for an energy storage power station for a weak power grid.

[0005] In one aspect, the present invention provides a frequency and voltage support control method for an energy storage power station for a weak power grid, the method comprising:

[0006] Based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, determine the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station;

[0007] Taking the safe operation of the energy storage power station as a constraint condition, droop control is performed based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station;

[0008] Active power and reactive power output by the energy storage power station are controlled based on the output of the droop control, so as to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station.

[0009] Optionally, based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, determining the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station includes:

[0010] Based on the conversion results of the three-phase voltage and the three-phase current in the two-phase stationary coordinate system, positive and negative sequence separation is performed respectively to obtain the positive and negative sequence components of the current voltage and current;

[0011] Power calculation is performed based on the transformation result of the rotating coordinate system of the positive and negative sequence components of the current voltage and current to obtain the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station.

[0012] Optionally, based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, determining the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station includes:

[0013] Based on the positive and negative sequence components of the current voltage and current, determining the current positive and negative sequence voltage amplitude and the positive and negative sequence frequency;

[0014] Based on the current positive and negative sequence voltage amplitude and the reference voltage amplitude of the energy storage power station, the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station is determined; based on the current positive and negative sequence frequency and the reference frequency of the energy storage power station, the deviation value of the current positive and negative sequence frequency of the energy storage power station is determined.

[0015] Optionally, the safe operation constraints of the energy storage power station include the output active power amplitude constraint of the energy storage power station, the current amplitude constraint of the converter output of the energy storage power station, the output capacity constraint of the energy storage power station and the reference power constraint of the energy storage power station.

[0016] Optionally, the reference power constraint of the energy storage power station is to determine upper and lower limits of the reference power of the energy storage power station based on the state of charge of the energy storage power station.

[0017] Optionally, the expression for the current amplitude constraint output by the converter of the energy storage power station is:

[0018] max(I a ,I b ,I c )≤I lim ;

[0019] In the formula, I a ,I b ,I c are the amplitude components of the three phases of the three-phase current output by the converter of the energy storage power station, I lim is the maximum allowable output current of the energy storage power station;

[0020] The expression of the reference power constraint of the energy storage power station is:

[0021]

[0022] In the formula, SOC is the state of charge of the energy storage power station, SOC max , SOC min They are the maximum and minimum limits of the state of charge of the energy storage power station; SOC high , SOC low are the expected large and small values ​​of the state of charge of the energy storage power station respectively; k a is the adaptive factor; P0 is the nominal discharge power of the energy storage power station; They are positive and negative sequence active power reference values ​​respectively;

[0023] The output active power amplitude of the energy storage power station is constrained to not exceed a preset safety threshold;

[0024] The output capacity constraint of the energy storage power station is that the output capacity of the energy storage power station does not exceed the rated capacity of the converter of the energy storage power station.

[0025] Optionally, the droop control is performed based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station, taking the safe operation of the energy storage power station as a constraint condition, and includes:

[0026] Adjusting the active power-frequency droop coefficient based on the deviation value of the current positive and negative sequence frequency of the energy storage power station to obtain an adjusted positive and negative sequence active power-frequency droop coefficient;

[0027] Adjusting the reactive power-voltage droop coefficient based on the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station to obtain an adjusted positive and negative sequence reactive power-voltage droop coefficient;

[0028] Taking the safe operation of the energy storage power station as a constraint condition, performing active power-frequency droop control based on the adjusted positive and negative sequence active power-frequency droop coefficient and the current positive and negative sequence active power of the energy storage power station, and obtaining the positive and negative sequence frequency output by the droop control;

[0029] Taking the safe operation of the energy storage power station as a constraint condition, reactive-voltage droop control is performed based on the adjusted positive-negative sequence reactive-voltage droop coefficient and the current positive-negative sequence reactive power of the energy storage power station to obtain the positive-negative sequence voltage amplitude output by the droop control.

[0030] Optionally, the calculation formulas for the positive and negative sequence frequencies and the positive and negative sequence voltage amplitudes output by the droop control are:

[0031]

[0032] Where P + / - , Q + / - are the current positive and negative sequence active power and positive and negative sequence reactive power respectively; They are respectively the positive and negative sequence active power reference values ​​and the positive and negative sequence reactive power reference values; is the positive and negative sequence reference frequency of droop control, is the positive and negative sequence reference voltage amplitude for droop control; is the positive and negative sequence frequency of the droop control output, is the positive and negative sequence voltage amplitude of the droop control output; m + / - is the adjusted positive and negative sequence active power-frequency droop coefficient, n + / - is the adjusted positive and negative sequence reactive power-voltage droop coefficient;

[0033] The calculation formulas for the adjusted positive and negative sequence active power-frequency droop coefficient and the adjusted positive and negative sequence reactive power-voltage droop coefficient are as follows:

[0034]

[0035] In the formula, is the positive and negative sequence active power-frequency droop coefficient during normal operation of the power system, is the positive and negative sequence reactive power-voltage droop coefficient during normal operation of the power system, f + / - is the current positive and negative sequence frequency, V + / - is the current positive and negative sequence voltage amplitude, k p , k r ,ω o are the proportional gain, resonant gain and resonant frequency of the PR controller respectively, and s is the Laplace operator.

[0036] Optionally, the output based on the droop control controls the active power and reactive power output by the energy storage power station to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station, including:

[0037] Taking the safe operation of the energy storage power station as a constraint condition, the voltage outer loop and current inner loop control are performed based on the positive and negative sequence frequencies and positive and negative sequence voltage amplitudes output by the droop control to generate corresponding positive and negative sequence reference currents;

[0038] Generate a pulse width modulation wave based on the positive and negative sequence reference current and the current positive and negative sequence frequency control;

[0039] Based on the pulse width modulation wave, the converter of the energy storage power station is controlled to adjust the active power and reactive power output by the energy storage power station, so as to support the frequency and voltage of the main power grid during power system fault through the energy storage power station.

[0040] Optionally, the performing active power-frequency droop control based on the adjusted positive-negative sequence active power-frequency droop coefficient and the current positive-negative sequence active power of the energy storage power station to obtain the positive-negative sequence frequency output by the droop control includes:

[0041] Based on the adjusted positive and negative sequence active power-frequency droop coefficient and the difference between the current positive and negative sequence active power of the energy storage power station and the active power reference value, an active power-frequency droop control is performed to obtain the positive and negative sequence frequency output by the droop control;

[0042] The reactive-voltage droop control is performed based on the adjusted positive-negative sequence reactive-voltage droop coefficient and the current positive-negative sequence reactive power of the energy storage power station to obtain the positive-negative sequence voltage amplitude output by the droop control, including:

[0043] Based on the adjusted positive and negative sequence reactive-voltage droop coefficient and the difference between the current positive and negative sequence reactive power of the energy storage power station and the reactive power reference value, reactive-voltage droop control is performed to obtain the positive and negative sequence voltage amplitude output by the droop control;

[0044] The active power reference value and the reactive power reference value are determined based on the received power control instructions respectively.

[0045] On the other hand, the present invention also provides a frequency voltage support control system for an energy storage power station for a weak power grid, comprising:

[0046] A power and deviation determination module, used to determine the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid;

[0047] A droop control module, used to perform droop control based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station, with the safe operation of the energy storage power station as a constraint condition;

[0048] A support control module is used to control the active power and reactive power output by the energy storage power station based on the output of the droop control, so as to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station.

[0049] On the other hand, the present invention also provides an electronic device, comprising: at least one processor and a memory; the memory and the processor are connected via a bus;

[0050] The memory is used to store one or more programs;

[0051] When the one or more programs are executed by the at least one processor, any one of the above-mentioned frequency and voltage support control methods for the energy storage power station for the weak power grid is implemented.

[0052] On the other hand, the present invention also provides a readable storage medium having an execution program stored thereon, and when the execution program is executed, the frequency and voltage support control method for the energy storage power station for the weak power grid described in any one of the above items is implemented.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] The present invention provides a frequency and voltage support control method and system for an energy storage power station for a weak power grid. On the one hand, for a weak power grid with coexisting frequency and voltage transient disturbances, the active power and reactive power output by the energy storage power station are decoupled and controlled so that the active power and reactive power can be provided to the main power grid simultaneously with positive and negative sequence voltage and frequency support during a power system fault, thereby ensuring the stable operation of the power system during the fault. On the other hand, based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station are determined; with the safe operation of the energy storage power station as a constraint condition, droop control is performed based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station, which can realize adaptive dynamic droop control based on the current voltage and frequency deviation, so that the energy storage power station can provide faster tracking of the power grid, and then realize the energy storage power station to support the power grid quickly and accurately, and improve the stability of the power grid during faults; and in the droop control process, the safe operation of the energy storage power station is used as a constraint condition, which ensures the safety of the energy storage power station during power grid faults and avoids excessive support. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a flow chart of a frequency and voltage support control method for a weak power grid energy storage power station of the present invention;

[0056] Figure 2 A schematic diagram of a topological structure of energy storage connected to a power grid and an energy storage support control structure according to an example of the present invention;

[0057] Figure 3 A schematic diagram of a control process of a droop control module according to an example of the present invention;

[0058] Figure 4 This is a comparison diagram of the effects of the control method of the present invention before and after supporting the energy storage power station when a voltage sag occurs in the power grid in an example of the present invention;

[0059] Figure 5 This is a comparison diagram of the effects of the control method of the present invention before and after supporting the energy storage power station when a voltage surge occurs in the power grid in an example of the present invention;

[0060] Figure 6 This is a comparison diagram of the effects of the control method of the present invention before and after supporting the energy storage power station when the power grid frequency temporarily drops in an example of the present invention;

[0061] Figure 7 This is a comparison diagram of the effects of the control method of the present invention before and after supporting the energy storage power station when the power grid frequency temporarily rises in an example of the present invention;

[0062] Figure 8 It is a schematic structural diagram of the electronic device of the present invention. DETAILED DESCRIPTION

[0063] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0064] Embodiment 1:

[0065] The present invention provides a frequency and voltage support control method for a weak power grid energy storage power station, as shown in the schematic diagram Figure 1 As shown, including:

[0066] Step S110, based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, determine the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station;

[0067] Step S120, taking the safe operation of the energy storage power station as a constraint condition, performing droop control based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station;

[0068] Step S130 , controlling the active power and reactive power output by the energy storage power station based on the output of the droop control, so as to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station.

[0069] In this example implementation, a weak grid refers to a grid where frequency and voltage transient disturbances coexist after a power system failure. The energy storage power station is connected to the weak grid to improve the stability of the grid. The weak grid connected to the energy storage power station may include new energy nodes, energy storage nodes, and the main grid. The specific network topology is as follows: Figure 2 As shown in the figure, the grid-connected converter of the energy storage power station is connected to the point of common coupling (PCC) in parallel through the LC filter through the 0.38 / 35kV transformer T1, and then connected to the main grid through the transformer T2. The line impedance from the PCC point to the main grid is R g +j′X g , R g represents the real part of the line impedance from the PCC point to the main grid, X g Represents the imaginary part of the line impedance from the PCC point to the main grid, j′ is the imaginary number sign, and the frequency and voltage of the main grid are supported by controlling the grid-connected converter of the energy storage power station. Renewable energy nodes such as photovoltaic and wind power are connected to the system through the PCC point. By detecting the voltage and current of the PCC point, that is, the three-phase voltage v abc and three-phase current i abc (i.e., the output current of the energy storage power station), determine the deviation of the current active and reactive power of the energy storage power station and the current voltage amplitude and frequency relative to the corresponding reference value, and perform droop control based on the deviation to adjust the active and reactive power output of the energy storage power station to support the frequency and voltage of the main power grid during the fault, and ensure the stability of the main power grid during the fault. When an asymmetric fault occurs in the power grid or the three-phase load is unbalanced, a negative sequence component will be generated in the grid current and voltage. For this reason, the present invention controls the positive sequence and negative sequence separately. The present invention is aimed at weak power grids with coexisting frequency and voltage transient disturbances, and decouples the active and reactive power output of the energy storage power station so that it can provide positive and negative sequence voltage and frequency support at the same time while meeting the safety constraints of the energy storage power station itself, so as to ensure the stable operation of the power grid.

[0070] In order to achieve stable support for the voltage and frequency of the weak power grid, the frequency and voltage response mechanism of the weak power grid can be studied before formulating the control strategy, as follows:

[0071] For a power system with n nodes, the power injected into the system by any node i can be expressed as:

[0072] S i =P i +jQ i (1)

[0073] Among them, S i , P i , Q i are the complex power, active power and reactive power injected into the grid via node i, respectively, and:

[0074]

[0075] Where P ij , Q ij are respectively the active power and reactive power of the line between node i and node j; U i , U j are the voltage amplitudes of nodes i and j respectively; G ij , B ij is the conductance and susceptance of the line between nodes i and j; θ ij is the phase angle difference of the node voltage between nodes i and j, and n is the number of nodes in the power system.

[0076] From formula (2), it can be seen that the power flow between nodes in the power system is mainly affected by the node voltage (amplitude, phase angle). Considering that in the dynamic operation of the power grid, the power injected into the grid by the node and the amplitude and phase angle of the node voltage are dynamic quantities that change with time, the derivatives of the active power and reactive power injected into the grid by node i in formula (2) at time t are calculated respectively, and the composite derivation rule is used to obtain:

[0077]

[0078] Observe the symmetric characteristics of the trigonometric functions of active and reactive power in equation (3), and assume that the intermediate variables α and β are:

[0079]

[0080] Substituting (4) into (3) we can obtain:

[0081]

[0082] It can be seen from the concise and intuitive form of formula (5) that in the dynamic process of the power system, the change rate of active and reactive power injected into the grid by the node is directly related to the change rate of the node voltage amplitude and the voltage phase angle between nodes. The node frequency defined in the international standard IEC / IEEE60255-118-1 is as follows:

[0083]

[0084] In the formula, f i is the frequency of node i, f0 is the rated frequency of the system, θ i is the phase angle of the voltage at node i. Different from the traditional power system where a large amount of rotational inertia is stored in the rotor of the synchronous generator set, with the gradual withdrawal of thermal power units from the grid and the continuous increase in the installed capacity of new energy sources in the new power system, the system rotational inertia continues to decrease, and the spatial distribution of inertia becomes more and more uneven. When the scale of the power grid and the transmission distance remain unchanged, the frequencies of different nodes in the new power system will show significant differences. The formation and law of this difference have been studied. Based on this, it is assumed that large-scale energy storage is connected to the grid via node i. After a fault event occurs, the energy storage adjusts the frequency of node i through rapid frequency control. Therefore, it can be assumed that θ ij The rate of change is:

[0085]

[0086] In the formula, is θ ij The rate of change, f j is the frequency of node j, Δf i is the difference between the frequency of node i and the rated frequency of the system. Substituting equation (7) into equation (5), we can get:

[0087]

[0088] It can be seen from formula (8) that the node power change rate has a direct mathematical relationship with the frequency deviation and the node voltage change rate, that is, the active power, reactive power, frequency and voltage are interrelated and coupled in the dynamic response process of the system, so energy storage is required to provide positive and negative sequence voltage and frequency support at the same time. Based on the above analysis, the present invention designs a positive and negative sequence voltage and frequency support control method with reactive and active power decoupling of energy storage.

[0089] In an example implementation, determining the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid in S110 includes the following processes:

[0090] Based on the conversion results of the three-phase voltage and the three-phase current in the two-phase stationary coordinate system, positive and negative sequence separation is performed respectively to obtain the positive and negative sequence components of the current voltage and current;

[0091] Power calculation is performed based on the transformation result of the rotating coordinate system of the positive and negative sequence components of the current voltage and current to obtain the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station.

[0092] In this exemplary implementation, the current active and reactive power of the energy storage power station is obtained by performing coordinate transformation and power calculation on the three-phase voltage and three-phase current detected on the AC side of the PCC point. Figure 2 As shown, coordinate conversion, positive and negative sequence separation and power calculation can be performed by a coordinate transformation module, a positive and negative sequence separation module and a power calculation module. Specifically, the coordinate transformation module (T 2r / 3s ) The three-phase voltage v detected by PCC point abc and three-phase current i abc Transformed into the voltage u in the two-phase stationary coordinate system αβ (t) and current i αβ (t). The positive and negative sequences are then separated from the conversion results in the two-phase stationary coordinate system. The positive and negative sequence separation based on the delayed phase cancellation method can be adopted. The delayed signal cancellation (DSC) method is based on the combination of positive and negative sequence component vectors, allowing accurate information of the sequence components to be obtained under a time delay of one quarter cycle (5 ms when the grid frequency is 50 Hz).

[0093] In the general case of an asymmetric grid, the voltage vector u in the two-phase stationary coordinate system is αβ (t) can be expressed as:

[0094]

[0095] Among them, u αβ-P (t),u αβ-N (t) are the positive and negative sequence voltage components in the stationary coordinate system; U P , U N are the amplitudes of the positive and negative phase sequence voltage vectors respectively; is the phase displacement of the positive and negative phase sequence voltage vectors; ω g is the angular frequency. The DSC method applied to the two-phase stationary coordinate system is expressed by equations (10) and (11):

[0096]

[0097] In the formula, are the estimated positive and negative phase sequence voltage components, T g is the grid voltage cycle, u αβ (tT g / 4) is T g The voltage vector in the two-phase stationary coordinate system under the time delay of / 4. Substituting equation (9) into equation (10) and equation (11), the estimated positive and negative phase sequence voltage components can be obtained, as shown in equation (12) and equation (13):

[0098]

[0099] Similarly, the above method can be used to calculate the current i abc The positive and negative phase sequence components of the voltage and current in the stationary coordinate system are obtained, that is, the positive and negative sequence components of the current voltage and current. Finally, the positive and negative sequence components of the voltage and current in the stationary coordinate system are converted to the rotating coordinate system to obtain the positive and negative sequence components of the voltage and current in the rotating coordinate system, including the positive and negative sequence components of the voltage in the rotating coordinate system. and the positive and negative sequence components of the current in, and are respectively the positive and negative sequence components of the voltage d-axis in the rotating coordinate system, and are respectively the positive and negative sequence components of the voltage q axis in the rotating coordinate system, and are respectively the positive and negative sequence components of the current d-axis in the rotating coordinate system, and They are respectively the positive and negative sequence components of the current q axis in the rotating coordinate system. The obtained positive and negative sequence components of the voltage and current in the rotating coordinate system are output to the power calculation module. The power calculation module calculates the active and reactive power output power of the energy storage power station after passing through the first-order low-pass filter. Its calculation expression is shown in formula (16):

[0100]

[0101] Where P i + , P i - are respectively the current positive and negative sequence active power of the energy storage power station, Q i + , Q i - are respectively the current positive and negative sequence reactive power of the energy storage power station, ω c is the cutoff frequency of the first-order low-pass filter, and s is the Laplace operator. The calculation result is output to the droop control module. The output of the positive and negative sequence separation module enters the phase-locked loop through another path, and the positive and negative sequence frequencies f output by the phase-locked loop are + 、f - Then enter the coordinate conversion module to form a loop.

[0102] In an example implementation, determining the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid in S110 includes the following process:

[0103] Based on the positive and negative sequence components of the current voltage and current, determining the current positive and negative sequence voltage amplitude and the positive and negative sequence frequency;

[0104] Based on the current positive and negative sequence voltage amplitude and the reference voltage amplitude of the energy storage power station, the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station is determined; based on the current positive and negative sequence frequency and the reference frequency of the energy storage power station, the deviation value of the current positive and negative sequence frequency of the energy storage power station is determined.

[0105] In this example implementation, the droop control is essentially that the energy storage power station sets a fixed proportional coefficient. When a frequency-voltage deviation is detected, active and reactive power proportional to the frequency-voltage deviation is transmitted to the main grid through the energy storage converter based on the fixed proportional coefficient, so as to respond to changes in the system frequency and voltage. However, when the system frequency is too large, the active power provided by the energy storage power station according to the fixed proportional coefficient cannot fully meet the safety requirements of the system frequency. Based on this problem, this example performs adaptive dynamic droop control based on the deviation values ​​of voltage and frequency. Therefore, it is necessary to obtain the deviation values ​​of voltage and frequency. This example determines the current positive and negative sequence voltage amplitude and positive and negative sequence frequency based on the positive and negative sequence components of the current voltage and current, and then prepares for subsequent droop control based on the deviation value between the current positive and negative sequence voltage amplitude and the system's reference voltage amplitude, and the deviation value between the positive and negative sequence frequency and the system's reference frequency.

[0106] In an example implementation, the safe operation of the energy storage power station is used as a constraint condition in S120, and droop control is performed based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station, including the following process:

[0107] Adjusting the active power-frequency droop coefficient based on the deviation value of the current positive and negative sequence frequency of the energy storage power station to obtain an adjusted positive and negative sequence active power-frequency droop coefficient;

[0108] Adjusting the reactive power-voltage droop coefficient based on the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station to obtain an adjusted positive and negative sequence reactive power-voltage droop coefficient;

[0109] Taking the safe operation of the energy storage power station as a constraint condition, performing active power-frequency droop control based on the adjusted positive and negative sequence active power-frequency droop coefficient and the current positive and negative sequence active power of the energy storage power station, and obtaining the positive and negative sequence frequency output by the droop control;

[0110] Taking the safe operation of the energy storage power station as a constraint condition, reactive-voltage droop control is performed based on the adjusted positive-negative sequence reactive-voltage droop coefficient and the current positive-negative sequence reactive power of the energy storage power station to obtain the positive-negative sequence voltage amplitude output by the droop control.

[0111] In this example implementation, when an asymmetric fault or unbalanced three-phase load occurs in the power grid, negative sequence components will be generated in the power grid current and voltage, and control is performed in the positive sequence and negative sequence respectively. This example performs adaptive dynamic droop control based on the deviation value of the current voltage and frequency, specifically, it can be achieved through Figure 2 The droop control module adjusts the droop coefficient according to the deviation value of the current voltage and frequency, as shown in formula (15).

[0112]

[0113] In the formula, is the positive and negative sequence active power-frequency droop coefficient during normal operation of the power system, is the positive and negative sequence reactive power-voltage droop coefficient during normal operation of the power system, f + / - is the current positive and negative sequence frequency, V + / - is the current positive and negative sequence voltage amplitude, is the positive and negative sequence reference frequency of droop control, is the positive and negative sequence reference voltage amplitude of droop control, k p , k r ,ω o are the proportional gain, resonant gain, and resonant frequency of the PR controller, respectively, and s is the Laplace operator. It can be seen from formula (15) that when the voltage amplitude and frequency deviation become larger, the droop coefficient will increase, the droop curve will become steeper, and the output active and reactive power will change faster, so that the energy storage power station can provide faster tracking of the power grid, so that the energy storage power station can quickly and accurately support the power grid.

[0114] like Figure 2 As shown, the reference frequency and reference voltage amplitude in the droop control process can be calculated by the reference power calculation module, which can be calculated according to the following formula, as shown in (16).

[0115]

[0116] Where P ref + , P ref - are respectively the positive and negative sequence reference active power of the energy storage power station, Q ref + , Q ref - are respectively the positive and negative sequence reference reactive power of the energy storage power station, and are the positive and negative sequence components of the reference voltage d-axis in the rotating coordinate system, and are the positive and negative sequence components of the reference voltage q axis in the rotating coordinate system, and are the positive and negative sequence components of the reference current d-axis in the rotating coordinate system, and They are respectively the positive and negative sequence components of the reference current q axis in the rotating coordinate system.

[0117] After obtaining the adjusted positive and negative sequence active power-frequency droop coefficient and the adjusted positive and negative sequence reactive power-voltage droop coefficient, active power-frequency droop control and reactive power-voltage droop control are performed. Figure 3 As shown, in the droop control module, the positive and negative sequence output active power P output by the power calculation module is received + / - And positive and negative sequence output reactive power Q + / - After filtering by a first-order low-pass filter, the positive and negative sequence active power reference values ​​output by the reference power calculation module are combined and positive and negative sequence reactive power reference values Frequency deviation And voltage amplitude deviation value After reactive power regulation, the signal is processed by the PR (proportional resonance) controller, combined with the positive and negative sequence active power-frequency droop coefficient during normal operation of the power system. Positive and negative sequence reactive power-voltage droop coefficients during normal operation of power system and reference frequency Reference voltage amplitude Adjust the frequency and voltage amplitude, and output the adjusted positive and negative sequence active power-frequency droop coefficient m + / - and the adjusted positive and negative sequence reactive power-voltage droop coefficient n + / - .

[0118] Exemplarily, active power-frequency droop control and reactive power-voltage droop control are performed according to the following formula, as specifically shown in formula (17).

[0119]

[0120] Where P + / - , Q + / - are the current positive and negative sequence active power and positive and negative sequence reactive power respectively; They are respectively the positive and negative sequence active power reference values ​​and the positive and negative sequence reactive power reference values; is the positive and negative sequence reference frequency of droop control, is the positive and negative sequence reference voltage amplitude for droop control; is the positive and negative sequence frequency of the droop control output, is the positive and negative sequence voltage amplitude of the droop control output; m + / - is the adjusted positive and negative sequence active power-frequency droop coefficient, n + / - is the adjusted positive and negative sequence reactive power-voltage droop coefficient.

[0121] Exemplarily, the positive and negative sequence active power reference values ​​and the positive and negative sequence reactive power reference values ​​in the above-mentioned droop control process can also be determined by receiving power control instructions from the remote control party. That is to say, when the system is operating normally, the system allows the energy storage power station to receive active and reactive power reference values ​​sent by the remote control party (such as the dispatching center) and obey the command of the dispatching center. In this case, active-frequency droop control can be performed based on the adjusted positive and negative sequence active-frequency droop coefficient and the difference between the current positive and negative sequence active power of the energy storage power station and the active power reference value to obtain the positive and negative sequence frequency output by the droop control; reactive-voltage droop control can be performed based on the adjusted positive and negative sequence reactive-voltage droop coefficient and the difference between the current positive and negative sequence reactive power of the energy storage power station and the reactive power reference value to obtain the positive and negative sequence voltage amplitude output by the droop control; wherein the active power reference value and the reactive power reference value are respectively determined based on the received power control instructions. As Figure 2 As shown, the power control instruction of the dispatching center can be received by the remote control instruction receiving module, and the power control instruction can include an active power reference value and a reactive power reference value.

[0122] It should be noted that in order to ensure the safe operation of the energy storage power station and avoid over-support, the safe operation of the energy storage power station needs to be used as a constraint condition in the above-mentioned droop control process, that is, the safe operation of the energy storage power station needs to be used as a constraint condition in the above-mentioned droop control process. The safe operation constraints of the energy storage power station include the output active power amplitude constraint of the energy storage power station, the current amplitude constraint of the converter output of the energy storage power station, the output capacity constraint of the energy storage power station and the reference power constraint of the energy storage power station. Exemplarily, the reference power constraint of the energy storage power station is to determine the upper and lower limits of the reference power of the energy storage power station based on the charge state of the energy storage power station. The specific analysis of this constraint condition is as follows:

[0123] (1) Output active power amplitude constraints of energy storage power stations

[0124] During an asymmetric fault, the double frequency oscillation of the output active power can cause overvoltage of the DC bus capacitor, affecting its service life and even equipment safety. Therefore, this example controls the output active power amplitude of the energy storage power station Do not exceed the safety threshold As shown in formula (18):

[0125]

[0126] Where V + 、V - are the positive and negative sequence voltage amplitudes, respectively, are the positive and negative sequence components of the d-axis current in the rotating coordinate system, They are respectively the q-axis positive and negative sequence components of the current in the rotating coordinate system.

[0127] (2) Current amplitude constraints of the converter output of the energy storage power station

[0128] Considering the limited overcurrent capacity of power devices, the amplitude of the three-phase current needs to be limited to a safe range. The three-phase current amplitude of the grid-connected converter can be expressed as:

[0129]

[0130] In the formula, I abc is the amplitude of the three-phase current, A1 is the intermediate quantity corresponding to the active current, and A2 is the intermediate quantity corresponding to the reactive current; δ is γ, is the positive and negative sequence phase of the three-phase current, δ and γ are the intermediate variables of the phase respectively; are the amplitudes of the positive and negative sequence active current components, respectively. are the amplitudes of the positive and negative sequence reactive current components respectively. To ensure the safety of the equipment, the current of the phase with the largest amplitude among the three-phase currents should meet the following conditions:

[0131] max(I a ,I b ,I c )≤I lim ; (twenty two)

[0132] The above formula is the expression of the current amplitude constraint of the converter output of the energy storage power station, where I a ,I b ,I c are the amplitude components of the three phases of the three-phase current output by the converter of the energy storage power station, I lim It is the maximum allowable output current of the energy storage power station, which is generally 1 to 2 times the rated current.

[0133] (3) Reference power constraints of energy storage power stations

[0134] This example considers the adaptive output constraint of the real-time state of the energy storage SOC (State of Charge). The maintenance of the energy storage SOC is the key to the efficient use of its power. In order to prevent a greater impact on the grid frequency due to the saturation or exhaustion of the energy storage SOC and maintain the long-term stable operation of the energy storage power station, this example performs adaptive output control based on the real-time state of the energy storage SOC, that is, the reference power limit is adjusted according to the change of SOC, as shown in formula (23).

[0135]

[0136] In the formula, SOC is the state of charge of the energy storage power station, SOC max , SOCmin They are the maximum and minimum limits of the state of charge of the energy storage power station; SOC high , SOC low They are respectively the expected larger and smaller values ​​of the state of charge of the energy storage power station, which can be selected independently according to the needs; k a is an adaptive factor that determines the shape of the limit power-SOC curve; P0 is the nominal discharge power of the energy storage power station; are the positive and negative sequence active power reference values ​​respectively. From formula (23), it can be seen that when 0<SOC<SOC min When SOC is , the energy storage station is not allowed to discharge, and the charging limit increases as the SOC decreases; when SOC min <SOC<SOC max When SOC>SOC, the discharge limit of the energy storage power station increases with the increase of SOC, and the charging limit decreases with the increase of SOC; max When the SOC decreases, the energy storage power station is not allowed to charge, and the discharge limit decreases as the SOC decreases. This example adaptively adjusts the output of the energy storage power station according to the real-time state of the energy storage SOC, so that its power limit is adjusted according to the change of SOC, achieving accurate support for the power grid while ensuring the safe and stable operation of the energy storage power station itself.

[0137] (4) Output capacity constraints of energy storage power stations

[0138] In order to prevent the grid-connected converter from over-operating and affecting its service life, this example limits the output capacity of the energy storage power station, as shown in formula (24):

[0139]

[0140] In the formula, S is the capacity required for the energy storage power station to output reference power, S ref is the rated capacity of the converter of the energy storage power station.

[0141] The above constraints are Figure 2 The safety constraint module in is applied to the corresponding control process. By constraining the output active amplitude, phase current, active power and capacity of the energy storage power station, the safe operation of the energy storage power station during the droop control process during system failure is guaranteed, avoiding over-support.

[0142] In some example embodiments, the step S130 of controlling the active power and reactive power output by the energy storage power station based on the output of the droop control to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station includes the following process:

[0143] Taking the safe operation of the energy storage power station as a constraint condition, the voltage outer loop and current inner loop control are performed based on the positive and negative sequence frequencies and positive and negative sequence voltage amplitudes output by the droop control to generate corresponding positive and negative sequence reference currents;

[0144] Generate a pulse width modulation wave based on the positive and negative sequence reference current and the current positive and negative sequence frequency control;

[0145] Based on the pulse width modulation wave, the converter of the energy storage power station is controlled to adjust the active power and reactive power output by the energy storage power station, so as to support the frequency and voltage of the main power grid during power system fault through the energy storage power station.

[0146] In this exemplary implementation, the positive and negative sequence frequencies and positive and negative sequence voltage amplitudes output by the droop control are controlled by the voltage and current dual loops to generate pulse width modulation waves to adjust the active and reactive power output by the converter. Figure 2 As shown, the droop control module outputs After entering the current and voltage dual-loop control module to perform voltage outer loop control to generate a reference voltage, the reference voltage is then subjected to current inner loop control to generate a reference current. and In the voltage and current dual-loop control process, the safety constraint module is used to perform safety constraints; the reference current is converted by the coordinate conversion module (i.e., T 2r / 3s ) converts the reference current in the two-phase rotating coordinate system into a three-phase reference current and outputs it to PWM (Pulse Width Modulation). PWM generates a pulse width modulation wave based on the three-phase reference current output and acts on the grid-connected converter to adjust the active and reactive power output of the energy storage power station, thereby supporting the frequency and voltage of the main grid during power system faults through the energy storage power station.

[0147] The present invention solves the outstanding problems caused by the structural changes of power supply by making full use of the energy storage resources with decoupled active and reactive control, and by coordinating multiple types of control resources, effectively responding to the frequency and voltage coupling challenges brought by new energy, and ensuring the continuous safe and stable operation of the power grid. The present invention utilizes the fast decoupling control capability of active and reactive power of energy storage. Compared with wind power and photovoltaic resources, it still has considerable active and reactive control capabilities during the voltage crossing process, and provides good control resources for the operation control of weak power grids with coexisting frequency and voltage transient disturbances. In the face of energy storage participating in the emergency control of the power grid, the reactive control capability of energy storage and the support capability in the transient process are still not considered. Energy storage is only used as an excellent active control resource with fast response speed and less impact on the power grid. The active and reactive support capabilities of energy storage in the transient process are not brought into play, and the problem of being unable to effectively control the fault form of the power grid with frequency and voltage coupling cannot be solved. Aiming at the scenario where transient disturbances of system frequency and voltage coexist, the present invention performs positive and negative sequence active and reactive decoupling control on the energy storage power station, so that it can simultaneously provide positive and negative sequence voltage and frequency support to ensure the stable operation of the power grid.

[0148] The present invention enables the energy storage power station to give full play to the voltage and frequency regulation decoupling control capabilities, while taking into account the safety of the energy storage power station itself, providing emergency support when transient disturbances occur in both the system frequency and voltage, thereby ensuring the stable operation of the weak power grid.

[0149] Experimental verification

[0150] By building a transient simulation model of energy storage, the transient response capability of energy storage under the control strategy of the present invention is further analyzed. In terms of scene setting, by setting a fault in the 1.2s-1.6s time period, the voltage rise / drop scene is simulated; by setting a sudden increase / drop in load at 1.5s, the frequency rise / drop scene is simulated. The effect diagram of the energy storage power station support before and after the control method of the present invention is used in various scenes is as follows: Figure 4-Figure 7 shown.

[0151] Figure 4 and Figure 5 The following are the comparison diagrams of the effects of the energy storage power station before and after the main grid voltage drops / rises. Figure 4 It can be seen that during the voltage sag period, the voltage of the PCC fault section is maintained at 0.98pu under the support strategy of the present invention, which has a better recovery effect compared with the grid voltage of 0.62pu. Figure 5 It can be seen that during the voltage surge period, the voltage at the PCC can be restored to 1.02 pu, which verifies the superior performance of the control strategy of the present invention.

[0152] Figure 6 and 7 The frequency comparison diagrams before and after the energy storage power station supports the main grid when the frequency temporarily drops / rises are shown respectively. Figure 6It can be seen that when the load suddenly increases, the system frequency drops temporarily. Compared with the frequency before support, the maximum frequency deviation after energy storage support is reduced from 0.22Hz to 0.04Hz, the peak time is reduced from 0.022s to 0.014s, the overshoot is 28.6%, the response time is 0.052s, the adjustment time is 0.081s, and the steady-state error is 0. Figure 7 It can be seen that in the case of a sudden load drop, the system frequency rises temporarily. Compared with the frequency before support, the maximum frequency deviation after energy storage support is reduced from 0.24Hz to 0.06Hz, the peak time is reduced from 0.023s to 0.016s, the overshoot is 37.8%, the response time is 0.024s, the adjustment time is 0.057s, and the steady-state error is 0. The simulation results verify that the control strategy of the present invention has a good support effect under both temporary rise and fall of the grid frequency.

[0153] The present invention aims at the scenario where transient disturbances of system frequency and voltage coexist. By decoupling the positive and negative sequence active and reactive power of the energy storage power station, the energy storage power station can provide positive and negative sequence voltage and frequency support at the same time to ensure the stable operation of the power grid. The present invention adaptively changes the droop coefficient according to the positive and negative voltage frequency deviation of the PCC point, thereby realizing the rapid and accurate support of the energy storage power station to the power grid. The present invention ensures the safe operation of the energy storage power station and avoids excessive support by constraining the output active amplitude, phase current, active power and capacity of the energy storage power station.

[0154] The present invention also adaptively adjusts the output of the energy storage power station according to the real-time state of the energy storage SOC, so that its power limit is adjusted according to the change of SOC, thereby achieving accurate support for the power grid while ensuring the safe and stable operation of the energy storage power station itself.

[0155] Embodiment 2:

[0156] Based on the same inventive concept, the present invention also provides a frequency voltage support control system for an energy storage power station for a weak power grid, the system comprising:

[0157] A power and deviation determination module, used to determine the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid;

[0158] A droop control module, used to perform droop control based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station, with the safe operation of the energy storage power station as a constraint condition;

[0159] A support control module is used to control the active power and reactive power output by the energy storage power station based on the output of the droop control, so as to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station.

[0160] In a possible implementation manner, the power and deviation determination module includes:

[0161] A positive-negative sequence separation submodule, configured to perform positive-negative sequence separation based on the conversion results of the three-phase voltage and the three-phase current in a two-phase stationary coordinate system, to obtain positive-negative sequence components of the current voltage and current;

[0162] The power calculation submodule is used to perform power calculation based on the transformation results of the rotating coordinate system of the positive and negative sequence components of the current voltage and current, and obtain the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station.

[0163] In a possible implementation manner, the power and deviation determination module further includes a deviation determination submodule, and the deviation determination submodule is used to:

[0164] Based on the positive and negative sequence components of the current voltage and current, determining the current positive and negative sequence voltage amplitude and the positive and negative sequence frequency;

[0165] Based on the current positive and negative sequence voltage amplitude and the reference voltage amplitude of the energy storage power station, the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station is determined; based on the current positive and negative sequence frequency and the reference frequency of the energy storage power station, the deviation value of the current positive and negative sequence frequency of the energy storage power station is determined.

[0166] In a possible implementation, the safe operation constraints of the energy storage power station include the output active power amplitude constraint of the energy storage power station, the current amplitude constraint of the converter output of the energy storage power station, the output capacity constraint of the energy storage power station and the reference power constraint of the energy storage power station.

[0167] In a possible implementation manner, the reference power constraint of the energy storage power station is to determine the upper and lower limits of the reference power of the energy storage power station based on the state of charge of the energy storage power station.

[0168] In a possible implementation manner, the expression for the current amplitude constraint output by the converter of the energy storage power station is:

[0169] max(I a ,I b ,I c )≤I lim ;

[0170] In the formula, I a ,I b ,I care the amplitude components of the three phases of the three-phase current output by the converter of the energy storage power station, I lim is the maximum allowable output current of the energy storage power station;

[0171] The expression of the reference power constraint of the energy storage power station is:

[0172]

[0173] In the formula, SOC is the state of charge of the energy storage power station, SOC max , SOC min They are the maximum and minimum limits of the state of charge of the energy storage power station; SOC high , SOC low are the expected large and small values ​​of the state of charge of the energy storage power station respectively; k a is the adaptive factor; P0 is the nominal discharge power of the energy storage power station; They are positive and negative sequence active power reference values ​​respectively;

[0174] The output active power amplitude of the energy storage power station is constrained to not exceed a preset safety threshold;

[0175] The output capacity constraint of the energy storage power station is that the output capacity of the energy storage power station does not exceed the rated capacity of the converter of the energy storage power station.

[0176] In a possible implementation, the droop control module includes:

[0177] A droop coefficient adjustment submodule, for adjusting the active-frequency droop coefficient based on the deviation value of the current positive and negative sequence frequency of the energy storage power station to obtain the adjusted positive and negative sequence active-frequency droop coefficient; adjusting the reactive-voltage droop coefficient based on the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station to obtain the adjusted positive and negative sequence reactive-voltage droop coefficient;

[0178] The droop control submodule is used to perform active-frequency droop control based on the adjusted positive-negative sequence active-frequency droop coefficient and the current positive-negative sequence active power of the energy storage station with the safe operation of the energy storage station as a constraint condition, so as to obtain the positive-negative sequence frequency output by the droop control; and perform reactive-voltage droop control based on the adjusted positive-negative sequence reactive-voltage droop coefficient and the current positive-negative sequence reactive power of the energy storage station with the safe operation of the energy storage station as a constraint condition, so as to obtain the positive-negative sequence voltage amplitude output by the droop control.

[0179] In a possible implementation manner, the calculation formulas for the positive and negative sequence frequencies and the positive and negative sequence voltage amplitudes output by the droop control are:

[0180]

[0181] Where P + / - , Q + / - are the current positive and negative sequence active power and positive and negative sequence reactive power respectively; They are respectively the positive and negative sequence active power reference values ​​and the positive and negative sequence reactive power reference values; is the positive and negative sequence reference frequency of droop control, is the positive and negative sequence reference voltage amplitude for droop control; is the positive and negative sequence frequency of the droop control output, is the positive and negative sequence voltage amplitude of the droop control output; m + / - is the adjusted positive and negative sequence active power-frequency droop coefficient, n + / - is the adjusted positive and negative sequence reactive power-voltage droop coefficient;

[0182] The calculation formulas for the adjusted positive and negative sequence active power-frequency droop coefficient and the adjusted positive and negative sequence reactive power-voltage droop coefficient are as follows:

[0183]

[0184] In the formula, is the positive and negative sequence active power-frequency droop coefficient during normal operation of the power system, is the positive and negative sequence reactive power-voltage droop coefficient during normal operation of the power system, f + / - is the current positive and negative sequence frequency, V + / - is the current positive and negative sequence voltage amplitude, k p , k r ,ω o are the proportional gain, resonant gain and resonant frequency of the PR controller control process respectively, and s is the Laplace operator.

[0185] In a possible implementation, the support control module includes:

[0186] A dual-loop control submodule, for taking the safe operation of the energy storage power station as a constraint condition, performing voltage outer loop and current inner loop control based on the positive and negative sequence frequencies and positive and negative sequence voltage amplitudes output by the droop control, and generating corresponding positive and negative sequence reference currents;

[0187] A pulse modulation submodule, used for generating a pulse width modulation wave based on the positive and negative sequence reference current and the current positive and negative sequence frequency control;

[0188] The support control submodule is used to control the converter of the energy storage power station based on the pulse width modulation wave to adjust the active power and reactive power output by the energy storage power station, so as to support the frequency and voltage of the main power grid during power system failure through the energy storage power station.

[0189] In a possible implementation manner, the droop control submodule is specifically used for:

[0190] Based on the adjusted positive and negative sequence active power-frequency droop coefficient and the difference between the current positive and negative sequence active power of the energy storage power station and the active power reference value, an active power-frequency droop control is performed to obtain the positive and negative sequence frequency output by the droop control;

[0191] Based on the adjusted positive and negative sequence reactive-voltage droop coefficient and the difference between the current positive and negative sequence reactive power of the energy storage power station and the reactive power reference value, reactive-voltage droop control is performed to obtain the positive and negative sequence voltage amplitude output by the droop control;

[0192] The active power reference value and the reactive power reference value are determined based on the received power control instructions respectively.

[0193] Embodiment 3:

[0194] like Figure 8 As shown, the present invention also provides an electronic device, which may be a computer device, a single-chip device, an intelligent mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, the processor, and the transceiver component are connected via a bus; the memory may be used to store an execution program, and an exemplary execution program may include instructions; the processor is used to execute the instructions stored in the memory. The memory may also be used to store data, which may be called and / or modified when the instructions are executed.

[0195] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in a storage medium to implement the corresponding method flow or corresponding functions, so as to implement the steps of a frequency and voltage support control method for a weak power grid energy storage power station in the above embodiment.

[0196] Example 4

[0197] Based on the same inventive concept, the present invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory), which is a memory device in an electronic device for storing programs and data. It can be understood that the storage medium here can include both built-in storage media in electronic devices and, of course, extended storage media supported by electronic devices. The storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more execution programs (including program codes). It should be noted that the storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor loads and executes one or more instructions stored in the storage medium, which can implement the steps of a frequency and voltage support control method for a weak power grid energy storage power station in the above embodiment.

[0198] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0199] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0200] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1A function specified in one or more boxes.

[0201] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit its protection scope. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that after reading the present invention, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims to be approved.

Claims

1. A frequency and voltage support control method for a weak power grid energy storage power station, characterized in that: The method comprises: Based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, determine the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station; Taking the safe operation of the energy storage power station as a constraint condition, droop control is performed based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station; Active power and reactive power output by the energy storage power station are controlled based on the output of the droop control, so as to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station.

2. The method according to claim 1, characterized in that Based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station are determined, including: Based on the conversion results of the three-phase voltage and the three-phase current in the two-phase stationary coordinate system, positive and negative sequence separation is performed respectively to obtain the positive and negative sequence components of the current voltage and current; Power calculation is performed based on the transformation result of the rotating coordinate system of the positive and negative sequence components of the current voltage and current to obtain the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station.

3. The method according to claim 2, characterized in that Based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid, the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station are determined, including: Based on the positive and negative sequence components of the current voltage and current, determining the current positive and negative sequence voltage amplitude and the positive and negative sequence frequency; Based on the current positive and negative sequence voltage amplitude and the reference voltage amplitude of the energy storage power station, the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station is determined; based on the current positive and negative sequence frequency and the reference frequency of the energy storage power station, the deviation value of the current positive and negative sequence frequency of the energy storage power station is determined.

4. The method according to claim 1, characterized in that: The safe operation constraints of the energy storage power station include the output active power amplitude constraint of the energy storage power station, the current amplitude constraint of the converter output of the energy storage power station, the output capacity constraint of the energy storage power station and the reference power constraint of the energy storage power station.

5. The method according to claim 4, characterized in that The reference power constraint of the energy storage power station is to determine the upper and lower limits of the reference power of the energy storage power station based on the state of charge of the energy storage power station.

6. The method according to claim 5, characterized in that The expression for the current amplitude constraint output by the converter of the energy storage power station is: max(I a ,I b ,I c )≤I lim ; In the formula, I a ,I b ,I c are the amplitude components of the three phases of the three-phase current output by the converter of the energy storage power station, I lim is the maximum allowable output current of the energy storage power station; The expression of the reference power constraint of the energy storage power station is: In the formula, SOC is the state of charge of the energy storage power station, SOC max , SOC min They are the maximum and minimum limits of the state of charge of the energy storage power station; SOC high , SOC low are the expected large and small values ​​of the state of charge of the energy storage power station respectively; k a is the adaptive factor; P0 is the nominal discharge power of the energy storage power station; They are positive and negative sequence active power reference values ​​respectively; The output active power amplitude of the energy storage power station is constrained to not exceed a preset safety threshold; The output capacity constraint of the energy storage power station is that the output capacity of the energy storage power station does not exceed the rated capacity of the converter of the energy storage power station.

7. The method according to claim 6, characterized in that The droop control is performed based on the safe operation of the energy storage power station as a constraint condition and the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station, including: Adjusting the active power-frequency droop coefficient based on the deviation value of the current positive and negative sequence frequency of the energy storage power station to obtain an adjusted positive and negative sequence active power-frequency droop coefficient; Adjusting the reactive power-voltage droop coefficient based on the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station to obtain an adjusted positive and negative sequence reactive power-voltage droop coefficient; Taking the safe operation of the energy storage power station as a constraint condition, performing active power-frequency droop control based on the adjusted positive and negative sequence active power-frequency droop coefficient and the current positive and negative sequence active power of the energy storage power station, and obtaining the positive and negative sequence frequency output by the droop control; Taking the safe operation of the energy storage power station as a constraint condition, reactive-voltage droop control is performed based on the adjusted positive-negative sequence reactive-voltage droop coefficient and the current positive-negative sequence reactive power of the energy storage power station to obtain the positive-negative sequence voltage amplitude output by the droop control.

8. The method according to claim 7, characterized in that The calculation formulas for the positive and negative sequence frequencies and the positive and negative sequence voltage amplitudes of the droop control output are as follows: Where P + / - , Q + / - are the current positive and negative sequence active power and positive and negative sequence reactive power respectively; They are respectively the positive and negative sequence active power reference values ​​and the positive and negative sequence reactive power reference values; is the positive and negative sequence reference frequency of droop control, is the positive and negative sequence reference voltage amplitude for droop control; is the positive and negative sequence frequency of the droop control output, is the positive and negative sequence voltage amplitude of the droop control output; m + / - is the adjusted positive and negative sequence active power-frequency droop coefficient, n + / - is the adjusted positive and negative sequence reactive power-voltage droop coefficient; The calculation formulas for the adjusted positive and negative sequence active power-frequency droop coefficient and the adjusted positive and negative sequence reactive power-voltage droop coefficient are as follows: In the formula, is the positive and negative sequence active power-frequency droop coefficient during normal operation of the power system, is the positive and negative sequence reactive power-voltage droop coefficient during normal operation of the power system, f + / - is the current positive and negative sequence frequency, V + / - is the current positive and negative sequence voltage amplitude, k p , k r ,ω o are the proportional gain, resonant gain and resonant frequency of the PR controller respectively, and s is the Laplace operator.

9. The method according to claim 7 or 8, characterized in that: The active power and reactive power output by the energy storage power station are controlled based on the output of the droop control so as to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station, including: Taking the safe operation of the energy storage power station as a constraint condition, the voltage outer loop and current inner loop control are performed based on the positive and negative sequence frequencies and positive and negative sequence voltage amplitudes output by the droop control to generate corresponding positive and negative sequence reference currents; Generate a pulse width modulation wave based on the positive and negative sequence reference current and the current positive and negative sequence frequency control; Based on the pulse width modulation wave, the converter of the energy storage power station is controlled to adjust the active power and reactive power output by the energy storage power station, so as to support the frequency and voltage of the main power grid during power system fault through the energy storage power station.

10. The method according to claim 7 or 8, characterized in that: The active-frequency droop control is performed based on the adjusted positive-negative sequence active-frequency droop coefficient and the current positive-negative sequence active power of the energy storage power station to obtain the positive-negative sequence frequency output by the droop control, including: Based on the adjusted positive and negative sequence active power-frequency droop coefficient and the difference between the current positive and negative sequence active power of the energy storage power station and the active power reference value, an active power-frequency droop control is performed to obtain the positive and negative sequence frequency output by the droop control; The reactive-voltage droop control is performed based on the adjusted positive-negative sequence reactive-voltage droop coefficient and the current positive-negative sequence reactive power of the energy storage power station to obtain the positive-negative sequence voltage amplitude output by the droop control, including: Based on the adjusted positive and negative sequence reactive-voltage droop coefficient and the difference between the current positive and negative sequence reactive power of the energy storage power station and the reactive power reference value, reactive-voltage droop control is performed to obtain the positive and negative sequence voltage amplitude output by the droop control; The active power reference value and the reactive power reference value are determined based on the received power control instructions respectively.

11. A frequency voltage support control system for a weak power grid energy storage power station, characterized in that: include: A power and deviation determination module, used to determine the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station based on the detected three-phase voltage and three-phase current on the AC side of the common connection point of the weak power grid; A droop control module, used to perform droop control based on the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station and the deviation value of the current positive and negative sequence voltage amplitude and the deviation value of the positive and negative sequence frequency of the energy storage power station, with the safe operation of the energy storage power station as a constraint condition; A support control module is used to control the active power and reactive power output by the energy storage power station based on the output of the droop control, so as to support the frequency and voltage of the main power grid during a power system fault through the energy storage power station.

12. The system according to claim 11, characterized in that The power and deviation determination module comprises: A positive-negative sequence separation submodule, configured to perform positive-negative sequence separation based on the conversion results of the three-phase voltage and the three-phase current in a two-phase stationary coordinate system, to obtain positive-negative sequence components of the current voltage and current; The power calculation submodule is used to perform power calculation based on the transformation results of the rotating coordinate system of the positive and negative sequence components of the current voltage and current, and obtain the current positive and negative sequence active power and positive and negative sequence reactive power of the energy storage power station.

13. The system according to claim 12, characterized in that The power and deviation determination module further includes a deviation determination submodule, wherein the deviation determination submodule is used to: Based on the positive and negative sequence components of the current voltage and current, determining the current positive and negative sequence voltage amplitude and the positive and negative sequence frequency; Based on the current positive and negative sequence voltage amplitude and the reference voltage amplitude of the energy storage power station, the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station is determined; based on the current positive and negative sequence frequency and the reference frequency of the energy storage power station, the deviation value of the current positive and negative sequence frequency of the energy storage power station is determined.

14. The system according to claim 11, characterized in that The safe operation constraints of the energy storage power station include the output active power amplitude constraint of the energy storage power station, the current amplitude constraint of the converter output of the energy storage power station, the output capacity constraint of the energy storage power station and the reference power constraint of the energy storage power station.

15. The system according to claim 14, characterized in that The reference power constraint of the energy storage power station is to determine the upper and lower limits of the reference power of the energy storage power station based on the state of charge of the energy storage power station.

16. The system according to claim 15, characterized in that The expression for the current amplitude constraint output by the converter of the energy storage power station is: max(I a ,I b ,I c )≤I lim ; In the formula, I a ,I b ,I c are the amplitude components of the three phases of the three-phase current output by the converter of the energy storage power station, I lim is the maximum allowable output current of the energy storage power station; The expression of the reference power constraint of the energy storage power station is: In the formula, SOC is the state of charge of the energy storage power station, SOC max , SOC min They are the maximum and minimum limits of the state of charge of the energy storage power station; SOC high , SOC low are the expected large and small values ​​of the state of charge of the energy storage power station respectively; k a is the adaptive factor; P0 is the nominal discharge power of the energy storage power station; They are positive and negative sequence active power reference values ​​respectively; The output active power amplitude of the energy storage power station is constrained to not exceed a preset safety threshold; The output capacity constraint of the energy storage power station is that the output capacity of the energy storage power station does not exceed the rated capacity of the converter of the energy storage power station.

17. The system according to claim 16, characterized in that The droop control module comprises: A droop coefficient adjustment submodule, for adjusting the active-frequency droop coefficient based on the deviation value of the current positive and negative sequence frequency of the energy storage power station to obtain the adjusted positive and negative sequence active-frequency droop coefficient; adjusting the reactive-voltage droop coefficient based on the deviation value of the current positive and negative sequence voltage amplitude of the energy storage power station to obtain the adjusted positive and negative sequence reactive-voltage droop coefficient; The droop control submodule is used to perform active-frequency droop control based on the adjusted positive-negative sequence active-frequency droop coefficient and the current positive-negative sequence active power of the energy storage station with the safe operation of the energy storage station as a constraint condition, so as to obtain the positive-negative sequence frequency output by the droop control; and perform reactive-voltage droop control based on the adjusted positive-negative sequence reactive-voltage droop coefficient and the current positive-negative sequence reactive power of the energy storage station with the safe operation of the energy storage station as a constraint condition, so as to obtain the positive-negative sequence voltage amplitude output by the droop control.

18. The system according to claim 17, characterized in that The calculation formulas for the positive and negative sequence frequencies and the positive and negative sequence voltage amplitudes of the droop control output are as follows: Where P + / - , Q + / - are the current positive and negative sequence active power and positive and negative sequence reactive power respectively; They are respectively the positive and negative sequence active power reference values ​​and the positive and negative sequence reactive power reference values; is the positive and negative sequence reference frequency of droop control, is the positive and negative sequence reference voltage amplitude for droop control; is the positive and negative sequence frequency of the droop control output, is the positive and negative sequence voltage amplitude of the droop control output; m + / - is the adjusted positive and negative sequence active power-frequency droop coefficient, n + / - is the adjusted positive and negative sequence reactive power-voltage droop coefficient; The calculation formulas for the adjusted positive and negative sequence active power-frequency droop coefficient and the adjusted positive and negative sequence reactive power-voltage droop coefficient are as follows: In the formula, is the positive and negative sequence active power-frequency droop coefficient during normal operation of the power system, is the positive and negative sequence reactive power-voltage droop coefficient during normal operation of the power system, f + / - is the current positive and negative sequence frequency, V + / - is the current positive and negative sequence voltage amplitude, k p , k r ,ω o are the proportional gain, resonant gain and resonant frequency of the PR controller control process respectively, and s is the Laplace operator.

19. The system according to claim 17 or 18, characterized in that The support control module comprises: A dual-loop control submodule, for taking the safe operation of the energy storage power station as a constraint condition, performing voltage outer loop and current inner loop control based on the positive and negative sequence frequencies and positive and negative sequence voltage amplitudes output by the droop control, and generating corresponding positive and negative sequence reference currents; A pulse modulation submodule, used for generating a pulse width modulation wave based on the positive and negative sequence reference current and the current positive and negative sequence frequency control; The support control submodule is used to control the converter of the energy storage power station based on the pulse width modulation wave to adjust the active power and reactive power output by the energy storage power station, so as to support the frequency and voltage of the main power grid during power system failure through the energy storage power station.

20. The system according to claim 17 or 18, characterized in that The droop control submodule is specifically used for: Based on the adjusted positive and negative sequence active power-frequency droop coefficient and the difference between the current positive and negative sequence active power of the energy storage power station and the active power reference value, an active power-frequency droop control is performed to obtain the positive and negative sequence frequency output by the droop control; Based on the adjusted positive and negative sequence reactive-voltage droop coefficient and the difference between the current positive and negative sequence reactive power of the energy storage power station and the reactive power reference value, reactive-voltage droop control is performed to obtain the positive and negative sequence voltage amplitude output by the droop control; The active power reference value and the reactive power reference value are determined based on the received power control instructions respectively.

21. An electronic device, characterized in that: include: at least one processor and memory; The memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, the frequency and voltage support control method for the energy storage power station for a weak power grid as described in any one of claims 1 to 10 is implemented.

22. A readable storage medium, characterized in that: An execution program is stored thereon, and when the execution program is executed, the frequency and voltage support control method for the energy storage power station for the weak power grid as described in any one of claims 1 to 10 is implemented.

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