CN114629144A - Energy storage power station black start method and system based on virtual synchronous machine - Google Patents

Abstract

The invention relates to a virtual synchronous machine-based energy storage power station black start method and system, aiming at overcoming the problems that the capacity of a traditional black start micro source is limited and is distributed unevenly, the maximum value of the magnetic flux of an iron core of a distribution transformer is obtained by setting the voltage of the primary side of the distribution transformer and calculating under the condition of neglecting the attenuation of the transient component of the magnetic flux, and the time of zero-voltage soft start of an energy storage power station is obtained under the condition of ensuring the quick black start of the energy storage power station and the unsaturated state of the iron core of the transformer in the whole start process; determining a control strategy of a single energy storage unit and a pre-synchronization control strategy among a plurality of energy storage units based on the virtual synchronous machine; and determining a cooperative control strategy of the plurality of energy storage units according to the charge states of different energy storage units in the energy storage power station. The method abandons the traditional hydroelectric power, thermal power and the like which are directly used as black start power sources, fully exerts the advantages of the energy storage battery and uses the energy storage battery as a black start micro-source, and provides a new scheme for the rapid recovery of the power grid after the power failure.

Description

A method and system for black start of energy storage power station based on virtual synchronous machine

technical field

The invention belongs to the technical field of black start of energy storage power stations, and in particular relates to a method and system for black start of energy storage power stations based on virtual synchronous machines.

Background technique

Electric energy plays a very important role in human life. When the power grid is completely paralyzed due to the influence of external factors or misoperation, a blackout accident will have a greater negative impact on national production and life. In order to reduce losses, when there is no temporary power provided by external grids, the power grid can only rely on micro-sources with self-starting capability inside the system to respond quickly, and restore loads at all levels in the power grid in a stable and orderly manner, so as to achieve a comprehensive and rapid power grid. recover. Black start means that after the power grid goes out of operation due to external or internal faults and enters a completely black state, without relying on the help of the power grid, only the black start micro sources in the power grid drive other micro sources without black start capability in the power grid, and gradually expand the recovery scope of the system , and finally realize the restart of the entire grid.

Black start is the first and key stage of power grid restoration. As a traditional black start power source, hydropower has the advantages of less power consumption and quick start. The research on black start based on pumped storage is quite mature. However, in areas lacking hydropower units and weak local power grids, it is often difficult to use hydropower units to participate in the black start of the power grid, while the energy storage power station responds quickly, the output power is flexible and controllable, and the installation position is not limited. On the basis of the black-start characteristics of power stations, a black-start method and system for energy storage power stations based on virtual synchronous machines are proposed to solve the problems of limited capacity and uneven distribution of traditional black-start micro-sources.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a black-start method and system for an energy storage power station based on a virtual synchronous machine, so as to solve the problems of limited capacity and uneven distribution of traditional black-start micro-sources.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A black-start method for an energy storage power station based on a virtual synchronous machine, comprising the following steps:

S1, establish the zero-voltage soft-start control strategy of the energy storage unit in the energy storage power station:

S1.1, set the voltage of the primary side of the distribution transformer during the zero-voltage soft-start process of the energy storage power station;

S1.2, based on the voltage of the primary side of the distribution transformer set in step S1.1, according to the voltage equation of the primary circuit of the transformer, and under the condition of ignoring the attenuation of the transient component of the magnetic flux, calculate the total magnetic flux of the distribution transformer. maximum value;

S1.3, based on the maximum value of the total magnetic flux of the distribution transformer obtained in step S1.2, to ensure the fast black start of the energy storage power station and the iron core magnetic flux of the distribution transformer is always not saturated during the entire zero-voltage soft start process Under the condition of , get the time of zero-voltage soft start of the energy storage power station;

S2, based on the virtual synchronous machine, determine a control strategy of a single energy storage unit and a pre-synchronization control strategy between multiple energy storage units;

S3, according to the state of charge of different energy storage units in the energy storage power station, determine a coordinated control strategy of multiple energy storage units.

Traditional black-start micro-sources usually choose hydroelectric units, gas-fired units and other power generation equipment. However, due to the limitation of geographical resources, there are few hydropower stations in the northwest region, and it is unlikely to choose hydro-electric units as black-start micro-sources. Therefore, energy storage power stations are used as black-start micro-sources. Starting the micro-source provides another idea for quick recovery after a power grid failure. In this application, by establishing a zero-voltage soft-start control strategy for the energy storage unit in the energy storage power station, the fast black start of the energy storage power station can be realized. The pre-synchronization control strategy of the energy storage unit is adopted, and the cooperative control strategy of the energy storage unit is determined by considering the difference of the state of charge of different energy storage units, so as to overcome the problems of limited capacity and uneven distribution of traditional black-start micro-sources.

Further, in step S1.1, set the voltage u ( t ) on the primary side of the distribution transformer during the zero-voltage soft-start process of the energy storage power station, which satisfies:

（1）

(1)

Among them, U _m is the voltage amplitude of the primary side; TE is the time for the output power station of the energy storage power station to increase from zero to the no-load potential; _ω is the angular velocity, t is the time, and α is the initial phase angle of the voltage.

Further, in step S1.2, the voltage equation of the primary circuit of the transformer is:

（2）

(2)

为通过一次绕组的总磁通，即配电变压器的总磁通；Among them, N ₁ is the number of turns of the primary winding; R ₁ and L ₁ are the resistance and self-inductance of the primary winding, respectively;

is the total magnetic flux passing through the primary winding, that is, the total magnetic flux of the distribution transformer;

为：In the process of zero-voltage soft start, set L ₁ as a fixed value, substitute formula (1) into formula (2) and solve it in sections to obtain the total magnetic flux of the distribution transformer

for:

（3）

(3)

；

；in,

;

;

；

;

为稳态时磁通幅值；A ₁、A ₂分别为[0，T _E )和[T _E ，+∞)时间区间的磁通暂态分量的幅值，两者由合闸时刻的铁芯剩磁

决定。The main magnetic flux of the iron core is formed by the addition of two parts, namely the steady-state component and the transient component. The transient component is a decay exponential function, and the decay speed is determined by the time constant T ( T = R ₁ /L ₁ ). Decide;

is the magnetic flux amplitude at steady state; A ₁ , A ₂ are the amplitudes of the transient components of the magnetic flux in the [0, T _E ) and [ T _E , +∞) time intervals, respectively, and the two are determined by the iron at the closing time. core remanence

Decide.

=0，则配电变压器的总磁通

变换为：In order to suppress the magnetizing inrush current of the transformer, the initial voltage phase angle α = π is set, and under the condition of ignoring the attenuation of the transient component of the magnetic flux, that is, R ₁ ≈0, the remanence of the iron core at the time of closing

=0, then the total magnetic flux of the distribution transformer

Transform to:

（4）

(4)

：When sinωt =-1, that is, ωt = (4 k -1) π /2, the maximum value of the total magnetic flux of the distribution transformer is obtained

:

（5）

(5)

where k =1,2,3,….

Further, in step _S1.3 , in the time period t ∈ [0, TE ), in order to ensure that the magnetic flux of the transformer will not be saturated in this time period, it should be ensured that:

（6）

(6)

Can launch:

（7）

(7)

，考虑到铁芯的饱和磁通约等于1.2-1.4倍的

，应保证：In the time period t _∈ [ TE , +∞), since the maximum magnetic flux of the iron core may be greater than

, considering that the saturation flux of the iron core is approximately equal to 1.2-1.4 times the

, should guarantee:

（8）

(8)

Thus it can be deduced that:

（9）

(9)

Under the condition that the fast black start of the energy storage power station is guaranteed and the magnetic flux of the transformer will not be saturated during this time period, the time TE of the zero voltage soft start of the energy storage power _station should meet:

（10）。

(10).

Further, in step S2, the specific process is:

S2.1, the active power control link is constructed according to the mechanical equation of the virtual synchronous machine, and the phase between the rotor angular speed of the virtual synchronous machine and the reference back EMF can be obtained. In the active power control link of the virtual synchronous machine, the closed-loop rotor speed is added, and the rotor speed The reference value is set to the rated angular velocity of the grid voltage, so that the frequency support effect of the virtual synchronous machine on the grid can be realized; according to the excitation regulation principle of the synchronous generator, the reactive power control link can be constructed, the excitation current can be obtained, and the reference back EMF can be further obtained. Amplitude, in the reactive power control link of the virtual synchronous machine, the closed-loop control of the grid voltage amplitude is added, so that the voltage support effect of the virtual synchronous machine on the power grid can be realized; the phase sum of the reference back EMF obtained by the active power control link The amplitude of the reference back EMF obtained in the reactive power control link is calculated to obtain the reference back EMF, and the switching signal is obtained by modulating the SVPWM module, thereby realizing the virtual synchronous machine control of the energy storage converter, that is, determining the control strategy of a single energy storage unit.

To make the output characteristics of the energy storage converter have the characteristics of a synchronous generator, it is embodied in the control that the back EMF of the energy storage converter is adjusted to the electromotive force of the synchronous generator, which is the virtual synchronous motor electromotive force. Therefore, it is necessary to explore the expression form of the virtual synchronous electromotive force first. The flux linkage equation of the virtual synchronous machine is expressed as follows:

（11）

(11)

、

、

分别为a相、b相、c相的磁链，i _ga 、i _gb 、i _gc 分别为a相、b相、c相的电流，i _f 为励磁电流，θ _r 为参考反电势的相位，即励磁磁链与定子a相绕组的夹角。where L is the self-inductance of the stator winding, M is the mutual inductance between the stator windings, M _f is the mutual inductance between the excitation winding and the stator winding,

,

,

are the flux linkages of phase a, phase b, and phase c, respectively, i _ga , i _gb , and i _gc are the currents of phase a, phase b, and phase c, respectively, i _f is the excitation current, θ _r is the phase of the reference back EMF, That is, the angle between the excitation flux linkage and the stator a phase winding.

The stator voltage equation for a synchronous generator can be written as:

（12）

(12)

In the formula, u _ga , u _gb , and u _gc are the voltages of the a-phase, b-phase, and c-phase of the stator, respectively, R _s is the stator resistance, and the positive direction of the current is from the grid side to the converter side;

Substituting equation (11) into equation (12), we can get:

（13）

(13)

In the formula, ω _r is the rotor angular velocity.

In the virtual synchronous machine, the excitation current is considered as a controlled current source, so the last term in equation (13) can be ignored, and the virtual synchronous machine electromotive force can be expressed as follows:

（14）

(14)

where e _a , e _b , and e _c are the electromotive forces of phase a, phase b, and phase c of the virtual synchronous machine, respectively; E is the amplitude of the reference back-EMF;

In a virtual synchronous machine, the rotor angular velocity ω _r is determined by its mechanical equation, which is expressed as:

（15）

(15)

In the formula, J is the moment of inertia of the rotor, D _p is the droop coefficient of the discharge during the black start of the energy storage unit; T _m is the input mechanical torque; T _e is the output electromagnetic torque.

In order to further establish the relationship between the rotor angular velocity and power, it can be considered that the product of the input mechanical torque T _m and the grid voltage rated angular velocity ω _n is the reference active power P _ref of the virtual synchronous machine, namely:

（16）

(16)

where P _ref is the reference active power of the virtual synchronous machine, ω _n is the grid voltage rated angular velocity;

The output active power and reactive power of the virtual synchronous machine are defined as the power of the converter side, so the output active power and reactive power of the virtual synchronous machine are calculated as follows:

（17）

(17)

In the formula, P _e is the output active power of the virtual synchronous machine; Q _e is the output reactive power of the virtual synchronous machine.

In the virtual synchronous machine, the excitation current i _f is determined by its reactive power control link, and the expression is as follows:

（18）

(18)

In the formula, K is the reactive power regulation coefficient, s is the Laplace operator; Q _ref is the reference reactive power of the virtual synchronous machine, D _q is the voltage droop control coefficient, U _ref is the voltage reference value, and U is the voltage feedback value.

S2.2, construct the virtual inductance and virtual resistance on the virtual synchronous machine, and calculate the virtual current and virtual power according to the back EMF on the energy storage converter side, the grid voltage, and the virtual inductance and virtual resistance, so that the virtual synchronous machine enters the self-synchronizing work. mode, that is, the power reference value is given as zero, and the power feedback value is selected as virtual power, so as to realize the self-synchronization of the virtual synchronous machine and grid connection; make the virtual synchronous machine switch to the normal working mode, that is, the power reference value is given according to the demand, and the power feedback The value is selected as the actual power;

Among them, the virtual current is calculated as follows:

（19）

(19)

The virtual power is calculated as follows:

（20）

(20)

Among them, i _vabc is the three-phase virtual current; L _v is the virtual inductance, R _v is the virtual resistance, s is the Laplace operator; e _abc is the back EMF on the energy storage converter side, that is, the virtual synchronous machine electromotive force; u _gabc is the grid voltage; P _v is the virtual power.

S2.3, after the current energy storage unit completes the black start process and establishes a stable terminal voltage, its terminal voltage is used as the grid voltage in step S2.2, and the voltage established when the next energy storage unit starts is used as the voltage in step S2.2. The back EMF on the side of the energy storage converter is used to establish the pre-synchronization control of different energy storage units in the energy storage power station.

The traditional synchronous generator can realize self-synchronization grid connection due to its own power angle synchronization characteristics; therefore, the virtual synchronous machine control strategy can also learn from the self-synchronization principle of synchronous machine to realize self-synchronization grid connection control. The main reason why the traditional virtual synchronous machine cannot be self-synchronized and connected to the grid is that the output current before the grid connection is zero, so it cannot achieve self-synchronization through its own power angle synchronization characteristics; therefore, it is necessary to construct a set of The virtual impedance is used to simulate the impedance of the line when connected to the grid. The virtual current is calculated by the grid voltage, the back EMF of the energy storage converter and the virtual impedance, and the virtual power is further calculated to realize the self-synchronization of the virtual synchronous machine.

The virtual synchronous machine works in the self-synchronizing working mode before grid connection, its power reference value is given as zero, and the power feedback value is selected as virtual power. In this way, when the virtual power follows the reference value and is adjusted to zero, the value of the virtual current is also zero, indicating that the back EMF on the energy storage converter side has been accurately synchronized with the grid voltage at this time, and the grid-connected operation can be performed. After the virtual synchronous machine is successfully connected to the grid, it switches to the normal working mode, the power reference value is given according to the demand, and the power feedback value is selected as the actual power.

Further, step S3 is specifically:

The SOC of the energy storage system is divided into 3 intervals, D _m is the droop coefficient of the energy storage power station, the minimum value ( Q _{SOC_min} ) is set to 0.1, and the lower value ( Q _{SOC_low} ) is 0.2; Therefore, the linear piecewise function is used to set the droop control coefficient D _p of the discharge during the black start process according to the state of charge of the energy storage unit, which can not only achieve smooth output, but also avoid the control problems caused by complex functions, which is more conducive to The practical application of the project, the linear piecewise function is obtained as follows:

（21）

(twenty one)

Among them, D _p is the droop coefficient of the discharge during the black start of the energy storage unit, and the larger the value, the greater the discharge power of the energy storage unit; D _m is the sag coefficient of the energy storage power station, and Q _SOC represents the charge of the energy storage unit The state, whose value range is 0~1, indicates the state of the energy storage unit from no power to full power.

State-of-charge feedback is a basic and very important control strategy, which can make the energy storage system compensate for power fluctuations while ensuring that its state of charge does not exceed a predetermined range. Due to the limited capacity of the energy storage system configured in the new energy power station, if the maximum coefficient is used for charging and discharging, the state of charge (SOC) of the energy storage is easy to cross the line. To avoid this problem, dynamically adjust the charge-discharge coefficient when the SOC of the energy storage system is too high (charging) or too low (discharging), which can reduce the output of the energy storage. It can not only effectively avoid the overcharge and discharge problem of energy storage, improve the service life, but also reduce the adverse impact on the power grid system when the SOC exceeds the limit.

The present invention also provides a black-start control system for an energy storage power station based on a virtual synchronous machine, comprising:

The voltage setting module is used to set the voltage of the primary side of the distribution transformer during the zero-voltage soft-start process of the energy storage power station;

The magnetic flux calculation module is used to calculate the maximum value of the total magnetic flux of the distribution transformer according to the voltage of the primary side of the distribution transformer set by the setting module, under the condition of ignoring the attenuation of the transient component of the magnetic flux;

The zero-voltage soft-start time calculation module is used to ensure the fast black start of the energy storage power station and the iron core magnetic flux of the distribution transformer is not saturated during the entire zero-voltage soft-start process according to the calculation results of the magnetic flux calculation module. , calculate the time of zero pressure soft start;

The energy storage unit control module is used to establish single energy storage unit control based on virtual synchronous machine and pre-synchronization control between multiple energy storage units;

The optimization control module is used to determine the cooperative control strategy of multiple energy storage units according to the state of charge of different energy storage units in the energy storage power station.

Technical effects of the present invention: The present invention is a method and system for black start of an energy storage power station based on a virtual synchronous machine, which abandons the use of traditional hydropower, thermal power, etc. directly as micro sources for black start of the power grid, and gives full play to the flexibility of the output power of the energy storage power station. With the characteristics of controllability and unlimited installation location, the energy storage power station is used as a micro-source for black start of the power grid. By establishing a zero-voltage soft start control strategy for the energy storage unit in the energy storage power station, the fast black start of the energy storage power station can be realized. The synchronous machine determines the pre-synchronization control strategy of the energy storage unit, and determines the cooperative control strategy of the energy storage unit by considering the difference of the state of charge of different energy storage units, to overcome the problems of limited capacity and uneven distribution of traditional black-start micro-sources, which is a major power outage. The rapid restoration of the post-grid grid provides a new solution.

Description of drawings

1 is a flowchart of a method for controlling a black start of an energy storage power station based on a virtual synchronous machine according to Embodiment 1;

2 is a block diagram of a pre-synchronization control between energy storage units according to Embodiment 1;

3 is a diagram showing the relationship between the unit regulated power and SOC of the energy storage power station in Embodiment 1;

Fig. 4 is the SOC change diagram of the energy storage power station of Example 1;

FIG. 5 is a graph showing the simulation result of measuring point 6 in Example 1. FIG.

Detailed ways

In order to make those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only Embodiments are part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "comprising" and "having" in the description and claims of the present invention and the above-mentioned drawings, as well as any variations thereof, are intended to cover non-exclusive inclusion, for example, including a series of steps or units The processes, methods, systems, products or devices are not necessarily limited to those steps or units expressly listed, but may include other steps or units not expressly listed or inherent to such processes, methods, products or devices.

According to an embodiment of the present invention, an embodiment of a black-start control method for an energy storage power station based on a virtual synchronous machine is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in, for example, a set of computer-executable instructions. and, although a logical order is shown in the flowcharts, in some cases the steps shown or described may be performed in an order different from that herein.

Example 1

A black-start method for an energy storage power station based on a virtual synchronous machine, as shown in Figure 1, includes the following steps:

S1, establish the zero-voltage soft-start control strategy of the energy storage unit in the energy storage power station:

S1.1, set the voltage u ( t ) on the primary side of the distribution transformer during the zero-voltage soft-start process of the energy storage power station to satisfy:

（1）

(1)

Among them, U _m is the voltage amplitude of the primary side; TE is the _time for the output power station of the energy storage power station to increase from zero to the no-load potential; α is the initial phase angle of the voltage; t is the time; ω is the angular velocity.

S1.2, based on the voltage of the primary side of the distribution transformer set in step S1.1, according to the voltage equation of the primary circuit of the transformer, and under the condition of ignoring the attenuation of the transient component of the magnetic flux, calculate the total magnetic flux of the distribution transformer. maximum value;

The voltage equation of the primary circuit of the transformer is:

（2）

(2)

为通过一次绕组的总磁通，即配电变压器的总磁通；Among them, N ₁ is the number of turns of the primary winding; R ₁ and L ₁ are the resistance and self-inductance of the primary winding, respectively;

is the total magnetic flux passing through the primary winding, that is, the total magnetic flux of the distribution transformer;

为：In the process of zero-voltage soft start, set L ₁ as a fixed value, substitute formula (1) into formula (2) and solve it in sections to obtain the total magnetic flux of the distribution transformer

for:

（3）

(3)

；

；in,

;

;

；

;

为稳态时磁通幅值；A ₁、A ₂分别为[0，T _E )和[T _E ，+∞)时间区间的磁通暂态分量的幅值，两者由合闸时刻的铁芯剩磁

决定。The main magnetic flux of the iron core is formed by the addition of two parts, namely the steady-state component and the transient component. The transient component is a decay exponential function, and the decay speed is determined by the time constant T ( T = R ₁ /L ₁ ). Decide;

is the magnetic flux amplitude at steady state; A ₁ , A ₂ are the amplitudes of the transient components of the magnetic flux in the [0, T _E ) and [ T _E , +∞) time intervals, respectively, and the two are determined by the iron at the closing time. core remanence

Decide.

=0，则配电变压器的总磁通

变换为：In order to suppress the magnetizing inrush current of the transformer, the initial voltage phase angle α = π is set, and under the condition of ignoring the attenuation of the transient component of the magnetic flux, that is, R ₁ ≈0, the remanence of the iron core at the time of closing

=0, then the total magnetic flux of the distribution transformer

Transform to:

（4）

(4)

：When sinωt =-1, that is, ωt = (4 k -1) π /2, the maximum value of the total magnetic flux of the distribution transformer is obtained

:

（5）

(5)

Among them, k=1,2,3,….

S1.3, based on the maximum value of the total magnetic flux of the distribution transformer obtained in step S1.2, to ensure that the energy storage power station can quickly zero-voltage soft start and the core magnetic flux of the distribution transformer during the entire zero-voltage soft start process Under the condition of not being saturated all the time, the time of zero-voltage soft start of the energy storage power station is obtained:

In the time period of t _∈ [0, TE ), in order to ensure that the magnetic flux of the transformer will not be saturated in this time period, it should be ensured that:

（6）

(6)

Thus it can be deduced that:

（7）

(7)

，考虑到铁芯的饱和磁通约等于1.2-1.4倍的

，应保证：In the time period t _∈ [ TE , +∞), since the maximum magnetic flux of the iron core may be greater than

, considering that the saturation flux of the iron core is approximately equal to 1.2-1.4 times the

, should guarantee:

（8）

(8)

Thus it can be deduced that:

（9）

(9)

On the condition that the fast black start of the energy storage power station and the magnetic flux of the transformer will not be saturated during this time period, the time TE of the zero voltage soft start of the energy storage power _station should satisfy:

（10）。

(10).

S2, based on the virtual synchronous machine, determine a control strategy of a single energy storage unit and a pre-synchronization control strategy between multiple energy storage units;

S2.1, the active power control link is constructed according to the mechanical equation of the virtual synchronous machine, the rotor angular velocity ω _r of the virtual synchronous machine and the phase θ _r of the reference back EMF can be obtained. In the active power control link of the virtual synchronous machine, a closed-loop rotor speed is added. , the rotor speed reference value is set as the grid voltage rated angular velocity ω _n , so that the frequency support effect of the virtual synchronous machine on the grid can be realized; the reactive power control link is constructed according to the excitation regulation principle of the synchronous generator, and the excitation current i _f can be obtained, and further The amplitude of the reference back EMF can be obtained. In the reactive power control link of the virtual synchronous machine, the closed-loop control of the grid voltage amplitude can be added, so that the voltage support effect of the virtual synchronous machine on the power grid can be realized; obtained from the active power control link The phase of the reference back EMF and the amplitude of the reference back EMF obtained from the reactive power control link are calculated to obtain the reference back EMF, and the switching signal is obtained by modulating the SVPWM module, so as to realize the virtual synchronous machine control of the energy storage converter, that is, to determine a single The control strategy of the energy storage unit.

To make the output characteristics of the energy storage converter have the characteristics of a synchronous generator, it is embodied in the control that the back EMF of the energy storage converter is adjusted to the electromotive force of the synchronous generator, which is the virtual synchronous motor electromotive force. Therefore, it is necessary to explore the expression form of the virtual synchronous electromotive force first. The flux linkage equation of the virtual synchronous machine is expressed as follows:

（11）

(11)

、

、

分别为a相、b相、c相的磁链，i _ga 、i _gb 、i _gc 分别为a相、b相、c相的电流，i _f 为励磁电流，θ _r 为参考反电势的相位，即励磁磁链与定子a相绕组的夹角。where L is the self-inductance of the stator winding, M is the mutual inductance between the stator windings, M _f is the mutual inductance between the excitation winding and the stator winding,

,

,

are the flux linkages of phase a, phase b, and phase c, respectively, i _ga , i _gb , and i _gc are the currents of phase a, phase b, and phase c, respectively, i _f is the excitation current, θ _r is the phase of the reference back EMF, That is, the angle between the excitation flux linkage and the stator a phase winding.

The stator voltage equation of a synchronous generator can be written in the following form,

（12）

(12)

In the formula, u _ga , u _gb , and u _gc are the voltages of the a-phase, b-phase, and c-phase of the stator, respectively, R _s is the stator resistance, and the positive direction of the current is from the grid side to the converter side;

Substituting equation (11) into equation (12), we can get:

（13）

(13)

In the formula, ω _r is the rotor angular velocity.

In the virtual synchronous machine, the excitation current is considered as a controlled current source, so the last term in equation (13) can be ignored, and the virtual synchronous machine electromotive force can be expressed as follows:

（14）

(14)

where e _a , e _b , and e _c are the electromotive forces of phase a, phase b, and phase c of the virtual synchronous machine, respectively; E is the amplitude of the reference back-EMF;

In a synchronous generator, the rotor angular velocity ω _r is determined by its mechanical equation, which is expressed as:

（15）

(15)

In the formula, J is the moment of inertia of the rotor, D _p is the droop coefficient of the discharge during the black start of the energy storage unit; T _m is the input mechanical torque; T _e is the output electromagnetic torque.

The product of mutual inductance and excitation current can be determined by the demand for reactive power. When the system needs inductive reactive power, increase the excitation current, and when the system needs capacitive reactive power, reduce the excitation current.

In order to further establish the relationship between the rotor angular velocity and power, it can be considered that the product of the input mechanical torque T _m and the grid voltage rated angular velocity ω _n is the reference active power P _ref of the virtual synchronous machine, namely:

（16）

(16)

In the formula, P _ref is the reference active power of the virtual synchronous machine, and ω _n is the rated angular velocity of the grid voltage.

The output active power and reactive power of the virtual synchronous machine are defined as the power of the converter side, so the output active power and reactive power of the virtual synchronous machine are calculated as follows:

（17）

(17)

In the formula, P _e is the output active power of the virtual synchronous machine; Q _e is the output reactive power of the virtual synchronous machine;

In the virtual synchronous machine, the excitation current i _f is determined by its reactive power control link, and the expression is as follows:

（18）

(18)

In the formula, K is the reactive power regulation coefficient, s is the Laplace operator; Q _ref is the reference reactive power of the virtual synchronous machine, D _q is the voltage droop control coefficient, U _ref is the voltage reference value, and U is the voltage feedback value;

According to the above analysis, the control block diagram of the virtual synchronous machine can be obtained as shown in Figure 2.

S2.2, construct the virtual inductance and virtual resistance on the virtual synchronous machine, and calculate the virtual current and virtual power according to the back EMF on the energy storage converter side, the grid voltage, and the virtual inductance and virtual resistance, so that the virtual synchronous machine enters the self-synchronizing work. mode to realize the self-synchronization grid connection of the virtual synchronization machine;

Among them, the virtual current is calculated as follows:

（19）

(19)

The virtual power is calculated as follows:

（20）

(20)

Among them, i _vabc is the three-phase virtual current; L _v is the virtual inductance, R _v is the virtual resistance, s is the Laplace operator; e _abc is the back EMF on the energy storage converter side, that is, the virtual synchronous machine electromotive force; u _gabc is the grid voltage; P _v is the virtual power.

The traditional synchronous generator can realize self-synchronization grid connection due to its own power angle synchronization characteristics; therefore, the virtual synchronous machine control strategy can also learn from the self-synchronization principle of synchronous machine to realize self-synchronization grid connection control. The main reason why the traditional virtual synchronous machine cannot be self-synchronized and connected to the grid is that the output current before the grid connection is zero, so it cannot achieve self-synchronization through its own power angle synchronization characteristics; therefore, it is necessary to construct a set of The virtual impedance is used to simulate the impedance of the line when connected to the grid. The virtual current is calculated by the grid voltage, the back EMF of the energy storage converter and the virtual impedance, and the virtual power is further calculated to realize the self-synchronization of the virtual synchronous machine.

The virtual synchronous machine works in the self-synchronizing working mode before grid connection, its power reference value is given as zero, and the power feedback value is selected as virtual power. In this way, when the virtual power follows the reference value and is adjusted to zero, the value of the virtual current is also zero, indicating that the back EMF on the energy storage converter side has been accurately synchronized with the grid voltage at this time, and the grid-connected operation can be performed. After the virtual synchronous machine is successfully connected to the grid, it switches to the normal working mode, the power reference value is given according to the demand, and the power feedback value is selected as the actual power.

S2.3, after the current energy storage unit completes the black start process and establishes a stable terminal voltage, its terminal voltage is used as the grid voltage in step S2.2, and the voltage established when the next energy storage unit starts is used as the voltage in step S2.2. The back EMF on the side of the energy storage converter is used to establish the pre-synchronization control of different energy storage units in the energy storage power station. Each energy storage unit in the energy storage power station adopts virtual synchronous control. After the first energy storage unit completes the black start process and establishes a stable terminal voltage, the grid voltage in S2.2 can be simulated. When the subsequent energy storage units start The established voltage can simulate the back EMF on the energy storage converter side in S2.2, so the above method can be used to complete the pre-synchronization control between different energy storage units in the energy storage power station.

S3, according to the state of charge of the energy storage unit in the energy storage power station, determine the cooperative control strategy of the energy storage unit, specifically:

The SOC of the energy storage system is divided into 3 intervals, D _m is the droop coefficient of the energy storage power station, the minimum value ( Q _{SOC_min} ) is set to 0.1, and the lower value ( Q _{SOC_low} ) is 0.2; Therefore, the linear piecewise function is used to set the droop control coefficient D _p in the black start process according to the state of charge of the energy storage unit, which can not only achieve smooth output, but also avoid the control problems caused by complex functions, which is more conducive to engineering The practical application of , the linear piecewise function is obtained as follows, as shown in Figure 3:

（21）

(twenty one)

Among them, D _p is the droop coefficient of the discharge during the black start of the energy storage unit, and the larger the value, the greater the discharge power of the energy storage unit; D _m is the droop coefficient of the energy storage power station; Q _SOC represents the charge of the energy storage unit The state, whose value range is 0~1, indicates the state of the energy storage unit from no power to full power.

When the energy storage power station is used for the black start of the power grid, since the initial state of charge of each energy storage unit is different, if the output of each energy storage unit during the black start process is consistent, the overall life of the energy storage power station will be reduced. . Therefore, it is necessary to introduce the state of charge feedback control strategy to optimize the control strategy of the energy storage power station, that is, the energy storage unit with a higher initial state of charge maintains a higher output during the black start process, while the energy storage unit with a lower initial state of charge maintains a higher output. The output of the energy storage unit is maintained at a low level.

In order to verify the correctness of the proposed control strategy, a simulation model is built in the PSCAD simulation platform. The energy storage power station in this model includes six energy storage units, in which each energy storage unit is replaced by a 2MW energy storage converter, and another 7.5MW load is connected. , the voltage level of 10kV is connected to the load side.

Figure 4 is a graph of the SOC change of the energy storage power station. Under the condition of continuous discharge, the initial SOC of the energy storage power station is set to 20%. It can be seen from Figure 4 that the black start control regardless of the SOC state, when the time t is 60s, the SOC reaches the lower limit of 10%. The SOC of the energy storage power station is better maintained under the improved control method considering the difference of different states of charge, which is 3.2% higher than the SOC of the above control.

Table 1

Table 1 shows the voltage, active power and reactive power values of 6 measuring points in the lines of different voltage levels between the energy storage power station and the load side during the black start process of the energy storage power station. It can be seen from Table 1 that the proposed black start control strategy of the energy storage power station can effectively restore the power grid after the fault, and the voltage at each point on the line is relatively stable during the black start process, and there will be no obvious overvoltage phenomenon, which is beneficial to the power grid. Safe and stable operation. Figure 5 is the simulation result of measuring point 6 in Table 1. Figure 5 shows the voltage and power values at the measuring point 6. It can be seen that the proposed control strategy can better complete the black start process of the energy storage power station, and there will be no overvoltage on the line.

Example 2

This embodiment provides a black-start control system for an energy storage power station based on a virtual synchronous machine, which includes:

The voltage setting module is used to set the voltage of the primary side of the distribution transformer during the zero-voltage soft-start process of the energy storage power station;

The magnetic flux calculation module is used to calculate the maximum value of the total magnetic flux of the distribution transformer according to the voltage of the primary side of the distribution transformer set by the setting module, under the condition of ignoring the attenuation of the transient component of the magnetic flux;

The zero-voltage soft-start time calculation module is used to ensure the fast black start of the energy storage power station and the iron core magnetic flux of the distribution transformer is not saturated during the entire zero-voltage soft-start process according to the calculation results of the magnetic flux calculation module. , calculate the time of zero pressure soft start;

The energy storage unit control module is used to establish single energy storage unit control based on virtual synchronous machine and pre-synchronization control between multiple energy storage units;

The optimization control module is used to determine the cooperative control strategy of multiple energy storage units according to the state of charge of different energy storage units in the energy storage power station.

In the embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments. In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The method embodiments described above are only illustrative, for example, the division of the units may be a logical function division, and there may be other division methods in actual implementation, for example, multiple units or components may be combined or Integration into another system, or some features can be ignored, or not implemented. On the other hand, the shown or discussed mutual coupling or direct coupling or communication connection may be through some interfaces, indirect coupling or communication connection of units or modules, and may be in electrical or other forms.

The units described as separate components may or may not be physically separated, and components shown as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution in this embodiment. In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically alone, or two or more units may be integrated into one unit. The above-mentioned integrated units may be implemented in the form of hardware, or may be implemented in the form of software functional units. The integrated unit, if implemented as a software functional unit and sold or used as a stand-alone product, may be stored in a computer-readable storage medium.

Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium , including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes .

The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications to the above-described embodiments can be readily made, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made to the present invention by those skilled in the art according to the disclosure of the present invention should all fall within the protection scope of the present invention.

Claims (7)

1. A virtual synchronous machine-based black start method for an energy storage power station is characterized by comprising the following steps:

s1, establishing a zero-pressure soft start control strategy of an energy storage unit in the energy storage power station:

s1.1, setting the voltage of a primary side of a distribution transformer in the zero-voltage soft start process of an energy storage power station;

s1.2, based on the voltage of the primary side of the distribution transformer set in the step S1.1, calculating to obtain the maximum value of the total magnetic flux of the distribution transformer under the condition of neglecting the attenuation of the transient component of the magnetic flux according to a voltage equation of a primary loop of the transformer;

s1.3, based on the maximum value of the total magnetic flux of the distribution transformer obtained in the step S1.2, obtaining the zero-voltage soft start time of the energy storage power station under the condition that the quick black start of the energy storage power station and the iron core magnetic flux of the distribution transformer are always unsaturated in the whole zero-voltage soft start process;

s2, determining a control strategy of a single energy storage unit and a pre-synchronization control strategy among a plurality of energy storage units based on the virtual synchronous machine;

and S3, determining a cooperative control strategy of the energy storage units according to the charge states of different energy storage units in the energy storage power station.

2. The energy storage power station black-start method based on the virtual synchronous machine as claimed in claim 1, wherein step S1.1 is to set the voltage of the primary side of the distribution transformer during the zero-voltage soft start of the energy storage power stationu（t) So that it satisfies:

（1）

wherein,U _m is the primary side voltage amplitude;T _E outputting the time for increasing the power station from zero to the no-load potential for the energy storage power station;ωin order to be the angular velocity of the object,tas a matter of time, the time is,αis the initial phase angle of the voltage.

3. The energy storage power station black start method based on the virtual synchronous machine as claimed in claim 2, wherein in step S1.2, the voltage equation of the primary loop of the transformer is:

（2）

wherein,N ₁the number of turns of the primary winding;R ₁、L ₁resistance and self-inductance of the primary winding respectively;

is the total magnetic flux through the primary winding, i.e. the total magnetic flux of the distribution transformer;

during zero pressure soft start, settingL ₁Substituting the formula (1) into the formula (2) for constant value and solving in sections to obtain the total magnetic flux of the distribution transformer

Comprises the following steps:

（3）

wherein,

；

；

；

the magnetic flux amplitude at steady state;A ₁、A ₂are each a group of [0 ],T _E ) And 2T _E , + ∞) time interval of the amplitude of the magnetic flux transient component, which is determined by the residual magnetism of the core at the moment of closing

Determining;

in order to restrain the magnetizing inrush current of the transformer, the initial phase angle of the voltage is setα=πUnder conditions where attenuation of the transient component of the magnetic flux is neglected, i.e.R ₁0, residual magnetism of iron core at closing time

=0, total magnetic flux of distribution transformer

The transformation is:

（4）

order tosinωt=1, i.e.ωt=（4k-1）πAt/2, obtaining the maximum value of the total magnetic flux of the distribution transformer

：

（5）

Wherein,k=1,2,3,…。

4. the virtual synchronous machine-based energy storage power station black-start method according to claim 3, characterized in that in step S1.3,

in thatt∈[0，T _E ) In order to ensure that the magnetic flux of the transformer does not saturate during this time period, it is ensured that:

（6）

it can be deduced that:

（7）

in thatt∈[T _E Time period, + ∞) should ensure that:

（8）

so that it is possible to deduce:

（9）

under the conditions of ensuring the quick black start of the energy storage power station and ensuring that the magnetic flux of the transformer cannot be saturated in the time period, the zero-pressure soft start time of the energy storage power stationT _E It should satisfy:

（10）。

5. the energy storage power station black-start method based on the virtual synchronous machine as claimed in claim 1, wherein in step S2, the specific process is as follows:

s2.1, constructing an active power control link according to a mechanical equation of the virtual synchronous machine, and obtaining the phase of the rotor angular speed and the reference back emf of the virtual synchronous machine; constructing a reactive power control link according to the excitation regulation principle of the synchronous generator, so that excitation current can be obtained, and the amplitude of the reference counter potential can be further obtained; calculating the phase of the reference back emf obtained by the active power control link and the amplitude of the reference back emf obtained by the reactive power control link to obtain the reference back emf, and modulating by the SVPWM module to obtain a switching signal, so that virtual synchronous machine control of the energy storage converter is realized, namely a control strategy of a single energy storage unit is determined;

s2.2, constructing a virtual inductor and a virtual resistor on the virtual synchronous machine, and calculating to obtain virtual current and virtual power according to the side counter potential of the energy storage converter, the grid voltage, the virtual inductor and the virtual resistor, so that the virtual synchronous machine enters a self-synchronous working mode, namely a power reference value is set to be zero, a power feedback value is selected as the virtual power, and self-synchronous grid connection of the virtual synchronous machine is realized; switching the virtual synchronous machine into a normal working mode, namely setting a power reference value as required and selecting a power feedback value as actual power;

wherein the virtual current is calculated as follows:

（19）

wherein, the virtual power is calculated as follows:

（20）

wherein,i _vabc is a three-phase virtual current;L _v as a virtual inductor, the inductance of the inductor,R _v is a virtual resistance, s is a laplace operator;e _abc the method comprises the following steps of (1) providing a back electromotive force on the side of an energy storage converter, namely an electromotive force of a virtual synchronous machine;u _gabc is the grid voltage;P _v is the virtual power;

and S2.3, after the previous energy storage unit completes the black start process to establish a stable end voltage, taking the end voltage as the power grid voltage in the step S2.2, and taking the voltage established when the next energy storage unit is started as the side back electromotive force of the energy storage converter in the step S2.2, so as to establish the pre-synchronization control of different energy storage units in the energy storage power station.

6. The energy storage power station black-start method based on the virtual synchronous machine as claimed in claim 1, wherein step S3 is to divide the energy storage system SOC into 3 intervals, and then to set the black-start process of different energy storage units according to the energy storage unit SOCSag factor of medium dischargeD _p A linear piecewise function is obtained as follows:

（21）

wherein,D _p is the droop coefficient of the discharge during the black start of the energy storage unit,D _m for the sag factor of the energy storage power station,Q _SOC the charging state of the energy storage unit is represented, the value range of the charging state is 0-1, and the state of the energy storage unit from no electricity to full electricity is represented.

7. A system for black start of an energy storage power station based on a virtual synchronous machine comprises:

the voltage setting module is used for setting the voltage of the primary side of the distribution transformer in the zero-voltage soft start process of the energy storage power station;

the magnetic flux calculation module is used for calculating the maximum value of the total magnetic flux of the distribution transformer under the condition of neglecting the attenuation of the transient component of the magnetic flux according to the voltage of the primary side of the distribution transformer set by the setting module;

the zero-voltage soft start time calculation module is used for calculating the zero-voltage soft start time under the condition that the quick black start of the energy storage power station and the iron core magnetic flux of the distribution transformer are always unsaturated in the whole zero-voltage soft start process according to the calculation result of the magnetic flux calculation module;

the energy storage unit control module is used for controlling a single energy storage unit and controlling pre-synchronization among a plurality of energy storage units based on the virtual synchronous machine;

and the optimization control module is used for determining a cooperative control strategy of the plurality of energy storage units according to the charge states of different energy storage units in the energy storage power station.

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