Black start method based on bus capacitor voltage

Abstract

The invention discloses a black start method based on bus capacitor voltage, the method is applied to a doubly-fed wind generating set, the doubly-fed wind generating set comprises a doubly-fed wind generator, a grid-side converter, a machine-side converter and a bus capacitor, and the method comprises the following steps: disconnecting a connection switch between the doubly-fed wind generating set and a power grid; starting a yaw variable pitch system of the doubly-fed wind generator, enabling the rotating speed of a fan to reach a given rotating speed, starting a machine-side converter, controlling the machine-side converter to operate in a grid following mode, and charging a bus capacitor by utilizing the voltage of the bus capacitor in a self-excitation mode; controlling a machine-side converter to switch from a network following mode to a network construction mode for operation, and constructing a stator-side voltage; and when the stator-side voltage is stable, starting the grid-side converter and controlling the grid-side converter to operate in a grid following mode so as to stabilize the bus capacitor voltage, and meanwhile, outputting energy outwards to participate in recovery after power failure of the power grid. According to the invention, black start can be realized based on the doubly-fed wind generating set, and the realization cost of black start is reduced at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of wind power generation, and in particular to a black start method based on bus capacitor voltage. Background Art

[0002] As the penetration rate of renewable energy in the power system continues to increase, the risk factor of regional power outages in the power system continues to increase. In the current power system fault power outage recovery plan, most users usually choose hydropower plants or thermal power plants as the power source for the black start of the power grid. However, due to factors such as regional resources, the black start power supply of the power system has problems such as uneven distribution and insufficient quantity. These problems will greatly affect the recovery speed and efficiency of the power system after the fault power outage. With a large proportion of wind power connected to the power system, if the potential functions of wind turbines can be explored and used as black start power sources for the power grid, it will play an important role in improving the speed of power system fault recovery and reducing the economic losses and social impacts caused by power outages. In this regard, studying the control method of wind turbines with black start capability is of great significance for the rapid restoration of power supply in power systems in areas with limited regional resources.

[0003] At present, there are two control modes for wind turbines: grid-following control and grid-building control. Most of them adopt the first control mode. The control variable of the grid-following control mode is current. Grid-following control is a current closed-loop control that relies on the phase angle of the grid voltage provided by the phase-locked loop as a reference. It is externally manifested as a controlled current source characteristic, does not have the ability to independently build a network, and cannot independently serve as a black start power supply for power system recovery. The control variables of the grid-building control mode are voltage phase angle and amplitude. The grid-building control introduces the virtual synchronous generator rotor motion equation in the control link, so that it has the characteristics of a synchronous generator, can independently establish a stable voltage, and is externally manifested as a controlled voltage source characteristic, and has the ability to independently serve as a black start power supply for the power system.

[0004] However, since the grid-following control mode cannot be networked independently, a black start solution has been developed in which diesel generator sets or energy storage devices are used as the starting power supply for wind turbines to provide power support after the wind turbines are started. However, when the system scale is large, if the starting power supply cannot meet the starting of the wind turbines, the black start process will inevitably fail. At the same time, increasing the capacity of diesel generator sets and energy storage devices will also greatly increase the cost of black start. Although the grid-building control mode has the ability to independently build a power grid, it is suitable as a black start power supply for power system restoration. However, the existing solution requires first connecting an additional power supply to the bus capacitor side to charge the bus capacitor, and then starting the rotor-side converter using the grid-building control mode to build the stator-side voltage of the doubly fed generator set, which will also increase the cost of black start and make the black start operation more complicated. Summary of the invention

[0005] The embodiment of the present invention provides a black start method based on bus capacitor voltage, aiming to reduce the overall implementation cost of the black start while realizing the black start based on a doubly-fed wind turbine generator set.

[0006] In a first aspect, an embodiment of the present invention provides a black start method based on bus capacitor voltage, which is applied to a doubly-fed wind turbine generator set, wherein the doubly-fed wind turbine generator set includes a doubly-fed wind turbine generator, a grid-side converter, a machine-side converter and a bus capacitor, and the black start method includes:

[0007] Disconnect the connection switch between the doubly-fed wind turbine generator set and the power grid, and control the yaw and pitch control system of the doubly-fed wind turbine generator set to start, so that the wind turbine speed of the yaw and pitch control system reaches a given speed;

[0008] Turn on the generator-side converter and control it to operate in the grid-following mode, and use the bus capacitor voltage to charge the bus capacitor in a self-excitation manner;

[0009] After the bus capacitor is fully charged, the generator-side converter is controlled to switch from the grid-following mode to the grid-building mode, and the stator-side voltage is built;

[0010] When the stator side voltage is stable, the grid-side converter is turned on and controlled to operate in the grid-following mode to stabilize the bus capacitor voltage, while outputting energy to the outside and participating in the recovery after a power outage caused by a grid fault.

[0011] Furthermore, the control model of the machine-side converter when operating in the grid-following mode is as follows:

[0012]

[0013] Where: U sd , U sq are the d-axis and q-axis components of the grid voltage, U dref , U qref are the d-axis and q-axis components of the virtual grid voltage, I rdref ,I rqref are the d-axis and q-axis components of the rotor current, respectively, and K up , K ui They are the proportional coefficient and integral coefficient of the voltage outer loop respectively.

[0014] Furthermore, the control model of the machine-side converter when operating in the grid-building mode is as follows:

[0015]

[0016] Where J is the virtual moment of inertia of network control, ω is the actual angular velocity output by network control, and ω n is the rated angular velocity, P mis the input power of network control, P fb is the feedback power of network control, D is the damping coefficient, and t is the time.

[0017] Furthermore, the input power P of the network control is calculated m The formula is as follows:

[0018] P m =P ref +K ω (ω n -ω fb )

[0019] Where P ref is the active power command, K ω is the active power droop coefficient, ω fb Real-time feedback of angular frequency.

[0020] Furthermore, the model of stator side voltage constructed when the machine-side converter operates in the grid-building mode is as follows:

[0021]

[0022] Where U s_ref is the virtual electromotive force, K qp , K qi are the proportional coefficient and integral coefficient of the reactive power loop, U ref is the given voltage command, Q ref is the given reactive power command, Q fb is the reactive power feedback, D q is the reactive power droop coefficient.

[0023] Furthermore, the control model of the grid-side converter when operating in the grid-following mode is as follows:

[0024]

[0025] Where: K dcp , K dci are the proportional coefficient and integral coefficient of the bus voltage loop, V ref is the bus voltage given instruction, V dc is the bus voltage, I dref ,I qref They are the grid-side inner loop d and q axis current instructions respectively;

[0026]

[0027] Where: K recp , K reci are the proportional coefficient and integral coefficient of the inner current loop, I recd ,I recqare the d-axis and q-axis components of the grid-side current, u pwmd 、u pwmq are the grid-side wave voltages respectively.

[0028] Furthermore, the doubly-fed wind turbine generator set also includes a first switch, a second switch and a third switch, the first switch and the second switch are connected in series between one end of the grid-side converter and the stator side of the doubly-fed wind turbine generator, and the first switch is arranged close to the grid-side converter, the second switch is arranged close to the stator side, and one end of the third switch is connected to the grid, and the other end is connected between the first switch and the second switch.

[0029] Furthermore, the doubly-fed wind turbine generator set further comprises a first transformer and a second transformer, wherein the first transformer is connected between the first switch and the second switch, one end of the second transformer is connected to the third switch, and the other end of the second transformer is connected between the first transformer and the second switch.

[0030] Furthermore, the doubly-fed wind turbine generator set also includes a first switch and a second switch, the first switch is connected between one end of the grid-side converter and the stator side of the doubly-fed wind turbine generator, and the first switch is arranged close to the stator side, one end of the second switch is connected to the grid, and the other end is connected between the first switch and one end of the grid-side converter.

[0031] In a second aspect, an embodiment of the present invention further provides a doubly-fed wind turbine generator set, the doubly-fed wind turbine generator set comprising a controller, the controller comprising a memory and a processor, the memory being configured to store a computer program, and the processor, when executing the computer program, implements the black start method based on bus capacitor voltage in the first aspect of the embodiment of the present invention and any one of the implementation methods of the first aspect.

[0032] The present invention provides a black start method based on bus capacitor voltage. When performing a black start, first, the connection between the doubly fed wind generator set and the power grid is disconnected, then the switch on the loop of the doubly fed wind generator set is closed, and the machine-side converter controlled by the grid-following mode is turned on, and then the residual voltage of the bus capacitor is used to excite the doubly fed motor, that is, the voltage is excited from the stator side, and the DC bus capacitor is charged through the grid-side converter. After the bus is fully charged, the machine-side converter switches from the grid-following mode to the grid-building model to construct the stator voltage of the doubly fed wind generator set. After the stator voltage is stable, the grid-side converter is turned on, and the DC bus capacitor voltage is stabilized by the grid-following mode control method. As a result, the entire black start process depends on its own system, and the doubly fed wind generator set is used as a black start power supply, and no additional power supply is required to charge the bus capacitor, which greatly reduces the overall implementation cost of the black start solution of the doubly fed wind generator set based on the grid-building control mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0034] Figure 1 A schematic flow chart of a black start method based on bus capacitor voltage provided by an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of a first topology of a doubly-fed wind turbine generator set in a black start method based on bus capacitor voltage provided by an embodiment of the present invention;

[0036] Figure 3 Another schematic flow chart of a black start method based on bus capacitor voltage provided by an embodiment of the present invention;

[0037] Figure 4 A schematic diagram of a second topology of a doubly-fed wind turbine generator set in a black start method based on bus capacitor voltage provided by an embodiment of the present invention;

[0038] Figure 5 A schematic diagram of a third topology of a doubly-fed wind turbine generator set in a black start method based on bus capacitor voltage provided by an embodiment of the present invention;

[0039] Figure 6 A control schematic diagram of a grid-following control mode in a black start method based on bus capacitor voltage provided by an embodiment of the present invention;

[0040] Figure 7 A control schematic diagram of a network control mode in a black start method based on bus capacitor voltage provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0043] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0044] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0045] See below Figure 1 An embodiment of the present invention provides a black start method based on bus capacitor voltage, which is applied to a doubly fed wind generator set. The doubly fed wind generator set is connected to a power grid. The doubly fed wind generator set includes a doubly fed wind generator, a grid-side converter, a machine-side converter and a bus capacitor. One end of the grid-side converter is connected to the stator side of the doubly fed wind generator, one end of the machine-side converter is connected to the rotor side of the doubly fed wind generator, and the bus capacitor is connected between the other end of the grid-side converter and the other end of the machine-side converter. The black start method includes: steps S101 to S104.

[0046] Step S101, disconnecting the connection switch between the doubly-fed wind turbine generator set and the power grid, and controlling the yaw and pitch control system of the doubly-fed wind turbine generator set to start, so that the wind turbine speed of the yaw and pitch control system reaches a given speed;

[0047] The yaw and pitch system is the core part of the wind turbine generator set for controlling the efficiency of wind energy conversion. By adjusting the angle of the blades, it can achieve the maximum capture of wind energy and the stable output of power generation. The system consists of a yaw system and a pitch system, each with different functions and operating mechanisms. Among them, the function of the yaw system mainly includes controlling the deflection of the wind rotor so that it can follow the change of wind direction and maintain the best windward angle, thereby improving the utilization rate of wind energy. In addition, the yaw system can also reduce the load of the wind rotor in strong winds or storms to protect the safety of the wind turbine. The functions of the pitch system mainly include: power control, that is, adjusting the blade angle according to the grid demand and system operation status to achieve stable control of power generation and ensure the safety and stability of the grid; maximum wind energy capture, that is, automatically adjusting the blade angle so that the wind turbine is always in the best windward state and maximizes the capture of wind energy; load control, that is, by adjusting the blade angle, reducing the load of the wind turbine in extreme weather and protecting the equipment from damage.

[0048] Step S102, start the generator-side converter and control the generator-side converter to operate in a grid-following mode, and use the bus capacitor voltage to charge the bus capacitor in a self-excitation manner;

[0049] Step S103: After the bus capacitor is fully charged, the generator-side converter is controlled to switch from the grid-following mode to the grid-building mode, and the stator-side voltage is established;

[0050] Step S104: When the stator side voltage is stable, the grid-side converter is turned on and controlled to operate in the grid-following mode to stabilize the bus capacitor voltage and output energy to the outside to participate in the recovery after the power outage caused by the grid fault.

[0051] In this embodiment, when performing a black start, the connection switch between the doubly-fed wind turbine generator set and the power grid is first disconnected to prevent the power grid from suddenly receiving power, which may cause overcurrent due to the inconsistency between the voltage of the subsequent doubly-fed wind turbine generator set and the voltage of the power grid. Then, the switch on the loop of the doubly-fed wind turbine generator set is closed, and the machine-side converter controlled by the grid-following mode is turned on, and the residual voltage of the bus capacitor is used to excite the doubly-fed motor, that is, the voltage is excited from the stator side, and the DC bus capacitor is charged through the grid-side converter. After the bus is fully charged, the machine-side converter switches from the grid-following mode to the grid-building model to build the stator voltage of the doubly-fed wind turbine generator set. After the stator voltage is stable, the grid-side converter is turned on, and the DC bus capacitor voltage is stabilized by the grid-following mode control method. As a result, the entire black start process depends on its own system. The doubly-fed wind turbine generator set is used as a black start power supply, and no additional power supply is required to charge the bus capacitor, which greatly reduces the overall implementation cost of the black start solution of the doubly-fed wind turbine generator set based on the grid-building control mode.

[0052] In a specific embodiment, the control model of the machine-side converter when operating in the grid-following mode is as follows:

[0053]

[0054] Where: U sd , U sq are the d-axis and q-axis components of the grid voltage, U dref , U qref are the d-axis and q-axis components of the virtual grid voltage, I rdref ,I rqref are the d-axis and q-axis components of the rotor current, respectively, and K up , K ui They are the proportional coefficient and integral coefficient of the voltage outer loop respectively.

[0055] Furthermore, the control model of the machine-side converter when operating in the grid-building mode is as follows:

[0056]

[0057] Where J is the virtual moment of inertia of network control, ω is the actual angular velocity output by network control, and ω n is the rated angular velocity, P m is the input power of network control, Pfb is the feedback power of network control, D is the damping coefficient, and t is the time.

[0058] Furthermore, the input power P of the network control is calculated m The formula is as follows:

[0059] P m =P ref +K ω (ω n -ω fb )

[0060] Where P ref is the active power command, K ω is the active power droop coefficient, ω fb Real-time feedback of angular frequency.

[0061] Furthermore, the model of the stator side voltage constructed when the machine-side converter operates in the grid-building mode is as follows:

[0062]

[0063] Where U s_ref is the virtual electromotive force, K qp , K qi are the proportional coefficient and integral coefficient of the reactive power loop, U ref is the given voltage command, Q ref is the given reactive power command, Q fb is the reactive power feedback, D q is the reactive power droop coefficient.

[0064] Furthermore, the control model of the grid-side converter when operating in the grid-following mode is as follows:

[0065]

[0066] Where: K dcp , K dci are the proportional coefficient and integral coefficient of the bus voltage loop, V ref is the bus voltage given instruction, V dc is the bus voltage, I dref ,I qref They are the grid-side inner loop d and q axis current instructions respectively;

[0067]

[0068] Where: K recp , K reci are the proportional coefficient and integral coefficient of the inner current loop, I recd ,I recq are the d-axis and q-axis components of the grid-side current, upwmd 、u pwmq are the grid-side wave voltages respectively.

[0069] In an actual application scenario, the doubly-fed wind turbine generator set also includes a first switch, a second switch and a third switch, wherein the first switch and the second switch are connected in series between one end of the grid-side converter and the stator side of the doubly-fed wind turbine generator, and the first switch is arranged close to the grid-side converter, the second switch is arranged close to the stator side, and one end of the third switch is connected to the power grid, and the other end is connected between the first switch and the second switch.

[0070] Furthermore, the doubly-fed wind turbine generator set further comprises a first transformer and a second transformer, wherein the first transformer is connected between the first switch and the second switch, one end of the second transformer is connected to the third switch, and the other end of the second transformer is connected between the first transformer and the second switch.

[0071] Furthermore, the doubly-fed wind turbine generator set also includes a first switch and a second switch, wherein the first switch is connected between one end of the grid-side converter and the stator side of the doubly-fed wind turbine generator, and the first switch is arranged close to the stator side, and one end of the second switch is connected to the grid, and the other end is connected between the first switch and one end of the grid-side converter.

[0072] Several embodiments are provided below for illustration:

[0073] Embodiment 1:

[0074] The topology structure of the doubly-fed wind turbine generator (DFIG) is set as follows: Figure 2 As shown, switches are set on the lines of the stator side and grid side converter of the DFIG. When a power failure occurs in the power system, the doubly fed wind turbine generator set is needed as the black start power supply of the power system. The machine side converter is turned on, and the grid control model is used to build the terminal voltage of the doubly fed generator set; the grid side converter is turned on, and the DC bus capacitor voltage is stabilized using the grid control mode. Figure 3 The specific execution process is: disconnect the grid-side switch, turn on the yaw and pitch control system of the doubly fed unit, make the wind turbine speed reach the given speed, close the grid-side converter switch and the doubly fed generator stator switch, so that the stator side and the grid-side converter form a path. Turn on the machine-side converter and operate in the voltage and current double closed-loop grid control mode to charge the bus. The virtual voltage provides voltage reference information for the grid control mode, and uses the residual voltage of the bus capacitor to charge the bus capacitor through self-excitation. After the bus is charged, the machine-side converter switches from the root grid mode to the grid-building mode to build the stator side voltage of the doubly fed unit. After the stator voltage is stable, turn on the grid-side converter and use the grid-building mode control method to stabilize the DC bus capacitor voltage. Finally, participate in the recovery after the power system failure.

[0075] The machine-side converter follows the grid control mode. The specific model is as follows:

[0076]

[0077] Where: U sd , U sq are the d-axis and q-axis components of the grid voltage, U dref , U qref are the d-axis and q-axis components of the virtual grid voltage, I rdref ,I rqref are the d-axis and q-axis components of the rotor current, respectively, and K up , K ui are the proportional coefficient and integral coefficient of the voltage outer loop respectively. The control block diagram is shown in Figure 6 After the bus voltage is charged, it switches to the grid control mode.

[0078] The grid control mode of the machine-side converter is as follows:

[0079]

[0080] Where J is the virtual moment of inertia of network control, ω is the actual angular velocity output by network control, and ω n is the rated angular velocity, P m is the input power of network control, P fb is the feedback power of network control, and D is the damping coefficient.

[0081] The input power includes active power command and frequency droop control regulation power, namely:

[0082] P m =P ref +K ω (ω n -ω fb )

[0083] Where P ref is the active power command, K ω is the active power droop coefficient, ω fb Real-time feedback of angular frequency.

[0084] The grid control mode stabilizes the terminal voltage of the doubly-fed generator set by controlling the reactive power. The specific model is as follows:

[0085]

[0086] Where U s_ref is the virtual electromotive force, K qp , K qi are the proportional coefficient and integral coefficient of the reactive power loop, Uref is the given voltage command, Q ref is the given reactive power command, Q fb is the reactive power feedback, D q is the reactive power droop coefficient. The control block diagram of the network control mode is as follows: Figure 7 shown.

[0087] Embodiment 2:

[0088] The topology structure of the doubly-fed wind turbine generator (DFIG) is set as follows: Figure 4 As shown in the figure, switches are only set on the line on the stator side of the DFIG. When the power grid fails and the power is cut off, the doubly fed wind turbine generator set is started as a black start power supply after the power grid fails and the power is cut off. The specific execution process is: disconnect the grid side switch, start the wind turbine yaw and pitch control system, raise the wind turbine speed to a given speed, and close the stator side switch of the doubly fed wind turbine generator; start the machine side converter using the grid-following control mode, and the virtual voltage provides voltage reference information for the grid-following control mode; use the residual voltage of the bus capacitor to excite the doubly fed motor, and the stator side excitation voltage is charged to the DC bus capacitor through the grid side converter; after the bus charging is completed, the control mode of the machine side converter is switched to the grid-forming control mode to form the stator side voltage of the doubly fed unit. After the stator side voltage is stable, start the grid side converter controlled by the root grid mode to maintain the stability of the DC bus capacitor voltage. Finally, the doubly fed wind turbine generator set is used as a black start power supply after the power grid fails and the power is cut off.

[0089] The machine-side converter follows the grid control mode. The specific model is as follows:

[0090]

[0091] Where: U sd , U sq are the d-axis and q-axis components of the grid voltage, U dref , U qref are the d-axis and q-axis components of the virtual grid voltage, I rdref ,I rqref are the d-axis and q-axis components of the rotor current, respectively, and K up , K ui are the proportional coefficient and integral coefficient of the voltage outer loop respectively. The control block diagram is shown in Figure 6 After the bus voltage is charged, it switches to the grid control mode.

[0092] The grid control mode of the machine-side converter is as follows:

[0093]

[0094] Where J is the virtual moment of inertia of network control, ω is the actual angular velocity output by network control, and ω nis the rated angular velocity, P m is the input power of network control, P fb is the feedback power of network control, and D is the damping coefficient.

[0095] The input power includes active power command and frequency droop control regulation power, namely:

[0096] P m =P ref +K ω (ω n -ω fb )

[0097] Where P ref is the active power command, K ω is the active power droop coefficient, ω fb Real-time feedback of angular frequency.

[0098] The grid control mode stabilizes the stator voltage of the doubly-fed generator set by controlling the reactive power. The specific model is as follows:

[0099]

[0100] Where U s_ref is the virtual electromotive force, K qp , K qi are the proportional coefficient and integral coefficient of the reactive power loop, U ref is the given voltage command, Q ref is the given reactive power command, Q fb is the reactive power feedback, D q is the reactive power droop coefficient. The control block diagram of the network control mode is as follows: Figure 7 shown.

[0101] Embodiment three:

[0102] The topology structure of the doubly-fed wind turbine generator (DFIG) is set as follows: Figure 5As shown, switches are set on the stator side and grid-side converter lines of the DFIG, and a motor with a stator rated voltage of 10.5Kv is added, and a 1140V converter is added to the grid-side converter line. When a power failure occurs in the power system, the yaw and pitch control system of the double-fed unit is started, the machine-side converter is started, and the grid-side converter is started. The specific execution process is: disconnect the grid-side switch, start the pitch and pitch control system to make the wind turbine speed reach a given speed, close the switch at the 1140V end of the grid-side converter and close the stator 10.5kV side switch; start the machine-side converter, use the residual voltage of the bus capacitor to charge the bus capacitor through self-excitation, and the machine-side converter adopts a voltage and current double closed-loop grid control mode, and the synchronized voltage is a virtual voltage; after the bus capacitor is charged, the machine-side converter switches to the grid control mode, so that the stator side of the double-fed wind turbine generator outputs a stable voltage; the grid-side converter is started to maintain the bus capacitor voltage stable. Finally, the doubly-fed wind turbine generator set is used as a black start power source for recovery after a power outage caused by a grid fault.

[0103] The machine-side converter follows the grid control mode. The specific model is as follows:

[0104]

[0105] Where: U sd , U sq are the d-axis and q-axis components of the grid voltage, U dref , U qref are the d-axis and q-axis components of the virtual grid voltage, I rdref ,I rqref are the d-axis and q-axis components of the rotor current, respectively, and K up , K ui are the proportional coefficient and integral coefficient of the voltage outer loop respectively. The control block diagram is shown in Figure 6 After the bus voltage is charged, it switches to the grid control mode.

[0106] The grid control mode of the machine-side converter is as follows:

[0107]

[0108] Where J is the virtual moment of inertia of network control, ω is the actual angular velocity output by network control, and ω n is the rated angular velocity, P m is the input power of network control, P fb is the feedback power of network control, and D is the damping coefficient.

[0109] The input power includes active power command and frequency droop control regulation power, namely:

[0110] P m =P ref +Kω (ω n -ω fb )

[0111] Where P ref is the active power command, K ω is the active power droop coefficient, ω fb Real-time feedback of angular frequency.

[0112] The grid control mode stabilizes the terminal voltage of the doubly-fed generator set by controlling the reactive power. The specific model is as follows:

[0113]

[0114] Where U s_ref is the virtual electromotive force, K qp , K qi are the proportional coefficient and integral coefficient of the reactive power loop, U ref is the given voltage command, Q ref is the given reactive power command, Q fb is the reactive power feedback, D q is the reactive power droop coefficient. The control block diagram of the network control mode is as follows: Figure 7 shown.

[0115] An embodiment of the present invention further provides a doubly-fed wind turbine generator set, which also includes a controller. The controller includes a memory and a processor. The memory is configured to store a computer program. When the processor executes the computer program, it implements the black start method based on bus capacitor voltage provided in the embodiment of the present invention.

[0116] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of this application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of this application.

[0117] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

Claims

1. A black start method based on bus capacitor voltage, characterized in that: Applied to a doubly-fed wind turbine generator set, the doubly-fed wind turbine generator set includes a doubly-fed wind turbine generator, a grid-side converter, a machine-side converter and a bus capacitor, and the black start method includes: Disconnecting the connection switch between the doubly-fed wind turbine generator set and the power grid, and controlling the yaw and pitch control system of the doubly-fed wind turbine generator set to start, so that the wind turbine speed of the yaw and pitch control system reaches a given speed; Turn on the generator-side converter and control it to operate in the grid-following mode, and use the bus capacitor voltage to charge the bus capacitor in a self-excitation manner; After the bus capacitor is fully charged, the generator-side converter is controlled to switch from the grid-following mode to the grid-building mode, and the stator-side voltage is built; When the stator side voltage is stable, the grid-side converter is turned on and controlled to operate in the grid-following mode to stabilize the bus capacitor voltage, while outputting energy to the outside and participating in the recovery after a power outage caused by a grid fault.

2. The black start method according to claim 1, characterized in that: The control model of the machine-side converter when operating in the grid-following mode is as follows: Where: U sd , U sq are the d-axis and q-axis components of the grid voltage, U dref , U qref are the d-axis and q-axis components of the virtual grid voltage, I rdref ,I rqref are the d-axis and q-axis components of the rotor current, respectively, and K up , K ui They are the proportional coefficient and integral coefficient of the voltage outer loop respectively.

3. The black start method according to claim 1, characterized in that: The control model of the machine-side converter when operating in the grid-building mode is as follows: Where J is the virtual moment of inertia of network control, ω is the actual angular velocity output by network control, and ω n is the rated angular velocity, P m is the input power of network control, P fb is the feedback power of network control, D is the damping coefficient, and t is the time.

4. The black start method according to claim 3, characterized in that: Calculate the input power P of the network control m The formula is as follows: P m =P ref +K ω (oh n -oh fb ) Where P ref is the active power command, K ω is the active power droop coefficient, ω fb Real-time feedback of angular frequency.

5. The black start method according to claim 1, characterized in that: The model for constructing the stator side voltage when the machine-side converter operates in the grid-building mode is as follows: Where U s_ref is the virtual electromotive force, K qp , K qi are the proportional coefficient and integral coefficient of the reactive power loop, U ref is the given voltage command, Q ref is the given reactive power command, Q fb is the reactive power feedback, D q is the reactive power droop coefficient.

6. The black start method according to claim 1, characterized in that: The control model of the grid-side converter when operating in the grid-following mode is as follows: Where: K dcp , K dci are the proportional coefficient and integral coefficient of the bus voltage loop, V ref is the bus voltage given instruction, V dc is the bus voltage, I dref ,I qref They are the grid-side inner loop d and q axis current instructions respectively; Where: K recp , K reci are the proportional coefficient and integral coefficient of the inner current loop, I recd ,I recq are the d-axis and q-axis components of the grid-side current, u pwmd 、u pwmq are the grid-side wave voltages respectively.

7. The black start method according to claim 1, characterized in that: The doubly-fed wind turbine generator set also includes a first switch, a second switch and a third switch, wherein the first switch and the second switch are connected in series between one end of the grid-side converter and the stator side of the doubly-fed wind turbine generator, and the first switch is arranged close to the grid-side converter, the second switch is arranged close to the stator side, and one end of the third switch is connected to the grid, and the other end is connected between the first switch and the second switch.

8. The black start method according to claim 7, characterized in that: The doubly-fed wind turbine generator set further includes a first transformer and a second transformer, wherein the first transformer is connected between the first switch and the second switch, one end of the second transformer is connected to the third switch, and the other end of the second transformer is connected between the first transformer and the second switch.

9. The black start method according to claim 1, characterized in that: The doubly-fed wind turbine generator set also includes a first switch and a second switch, wherein the first switch is connected between one end of the grid-side converter and the stator side of the doubly-fed wind turbine generator, and the first switch is arranged close to the stator side, and one end of the second switch is connected to the grid, and the other end is connected between the first switch and one end of the grid-side converter.

10. A doubly-fed wind turbine generator set, characterized in that: The doubly-fed wind turbine generator set includes a controller, the controller includes a memory and a processor, the memory is configured to store a computer program, and the processor implements the black start method based on bus capacitor voltage as described in any one of claims 1-9 when executing the computer program.

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