Direct vector control method for stable operation of new energy power generation in power-easily-fluctuating power grid

Abstract

The invention provides a direct vector control method for stable operation of new energy power generation in a power-fluctuation-prone power grid, and the method comprises the steps: constructing a new energy power generation system, and carrying out the non-impact current grid connection of the new energy power generation system; performing reactive power control and active power control on the new energy power generation system after the non-impact current grid connection; in reactive active power control of a new energy power generation system, a low-frequency oscillation fault of a power grid is eliminated in principle; when the active power of the new energy power generation system is controlled by the constructed phase control function, the inherent virtual rotational inertia characteristic of the phase control function can suppress the power fluctuation of the power grid; and direct vector control of stable operation of the new energy power generation system is realized by synchronously tracking the voltage frequency and phase of the power grid to control active power and reactive power. According to the invention, the problems that the existing grid-connected operation control realization technology is easy to cause low-frequency oscillation of a power grid and the introduction of virtual rotational inertia causes complex control system model and difficult parameter setting can be solved in principle.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation technology, and in particular relates to a direct vector control method for the stable operation of new energy power generation in power grids with fluctuating power. Background Technology

[0002] The power system is a complex system that converts mechanical energy, electrical energy, and magnetic energy. Its power fluctuations, which are prone to causing faults, are mainly divided into electromechanical oscillations and electromagnetic oscillations. Currently, the application of grid-connected power converters and the operation of AC / DC hybrid transmission have weakened the AC coupling between power grids to some extent, reducing the electromechanical oscillations between synchronous generator sets. However, the electromagnetic oscillation problem caused by power electronic equipment is becoming increasingly prominent.

[0003] Renewable energy power generation, also known as new energy power generation, mainly includes hydropower, photovoltaic power generation, and wind power generation. Hydropower can be classified as traditional power generation. The traditional power grid composed of these systems has been developed for a century and is safe and reliable in operation. However, with the increasing penetration rate of new energy power generation systems connected to the traditional power grid, the risk of grid failure caused by new energy power generation systems controlled by existing technologies has increased. Since the factors that cause grid instability are still under research, while the development of new energy power generation is rapid and the annual increase in grid-connected capacity is significant, the technology for ensuring the stable operation of the power system to ensure the grid connection of new energy power generation systems is lagging behind. Therefore, the direct vector control algorithm obtained from the research on the stable operation of power systems composed of typical power generation systems prone to power fluctuations is of great significance for the grid connection operation control of new energy power generation systems.

[0004] A typical power grid containing renewable energy generation systems, consisting of diesel generator sets, doubly-fed induction generator (DFIG) wind power systems, and photovoltaic (PV) power systems, is prone to power fluctuations. Diesel generator sets are susceptible to speed and voltage fluctuations, with output voltage and frequency fluctuations exceeding those of traditional power grids. DFIG wind power generators are also prone to speed fluctuations. While PV power output voltage and frequency are relatively stable, grid-connected generation using phase-locked loop (PLL) technology is prone to frequency and phase fluctuations. All three factors contribute to grid power fluctuations. In fact, DFIG wind power also experiences power fluctuations due to PLL technology during grid-connected control. Therefore, these three typical power systems containing renewable energy generation are difficult to control stably using existing technologies. Grid-connected control of PV power is similar to that of direct-drive wind power, except that the rotational inertia of a direct-drive wind power system is greater than that of a PV system. Before the introduction of virtual rotational inertia algorithms, PV systems have virtually no rotational inertia. However, using direct vector control algorithms, the rotational inertia of the generator can be simulated by controlling the power angle. If the power angle remains constant under all circumstances, its rotational inertia can be considered nearly infinite.

[0005] In summary, traditional electromagnetic oscillations caused by resonant circuits in power systems are often localized oscillations of a single oscillation mode. However, broadband oscillations in "high-energy-density" power systems involve multiple regions, multiple generating units, and multiple electrical devices, and the oscillation frequency varies with the topology of the power electronic equipment, exhibiting multimodal characteristics. For modes with lower oscillation frequencies, the oscillation energy is large, and the impact range is wide. A "high-energy-density" power system refers to an organic whole containing a high proportion of new energy generation and a high proportion of power electronic equipment, supplying power to users via a hybrid AC / DC transmission method. The grid-connected control algorithm for power generation systems containing power converters in this invention adapts to frequency and voltage fluctuations in the grid voltage, and possesses controllable virtual rotational inertia. It can fundamentally solve the problems of low-frequency grid oscillations easily caused by existing grid-connected operation control technologies and the complexity of control system models and difficulty in parameter tuning due to the introduction of virtual rotational inertia. Summary of the Invention

[0006] The purpose of this invention is to propose a direct vector control method for the stable operation of new energy power generation in power grids with fluctuating power output. This method addresses the dynamic errors in existing generator grid connection and operation control tracking of grid voltage, frequency, and phase, as well as the further impact of grid voltage and frequency fluctuations on tracking errors, leading to grid power fluctuations caused by frequency and voltage fluctuations during the operation of the new energy power generation system. Maintaining a constant power angle provides the necessary active power support during faults. Since diesel generators can stably operate in a power grid, the grid connection control method involved in this invention offers greater stability when operating on traditional power grids.

[0007] To achieve the above objectives, this invention provides a direct vector control method for the stable operation of new energy power generation in a power grid prone to power fluctuations, comprising:

[0008] A new energy power generation system is constructed, and the new energy power generation system is connected to the grid without inrush current; wherein, the new energy power generation system uses diesel generators as the main grid structure;

[0009] Reactive power control and active power control are performed on the new energy power generation system after grid connection without inrush current.

[0010] In the reactive power control and active power control of the new energy power generation system, the low-frequency oscillation fault of the power grid can be eliminated in principle.

[0011] Controlling the output voltage of each power converter can control reactive power. The constructed phase control function controls the active power output of the wind turbine, the grid-connected active power of the photovoltaic power generation, and the active power on the excitation input side of the wind turbine. Adjusting the phase control function parameters can control the virtual rotational inertia of the power converter of the new energy power generation system, thereby suppressing power fluctuations in the power grid and completing the direct vector control for the stable operation of the new energy power generation system.

[0012] Optionally, grid connection of the new energy power generation system without inrush current includes:

[0013] The diesel generator voltage is collected as the modulation signal for the input-side power converter of the photovoltaic power generation power converter and the doubly fed generator excitation system. The amplitude of the modulation signal is controlled so that the output voltage amplitude of the photovoltaic power generation and excitation system input-side power converter is the same as the grid voltage amplitude, thus achieving grid connection without inrush current.

[0014] The system detects the rotational speed of the generator driven by the doubly-fed induction generator (DFIG) wind power generation system and monitors the grid voltage. The frequency of the excitation voltage is composed of the generator speed and the grid voltage frequency. The phase and amplitude of the voltage of the power converter on the input side of the excitation system are controlled to ensure that the phase sequence, frequency, phase, and amplitude of the generator output voltage are consistent with the grid voltage. Under the condition of meeting the minimum grid connection speed, the system controls the generator to achieve grid connection without inrush current. After grid connection, the excitation of the DFIG generator is disconnected.

[0015] The excitation winding voltage of the doubly fed generator after grid connection is detected. The excitation winding voltage is used as the excitation voltage modulation signal of the generator. The amplitude of the output voltage of the power converter is controlled to be the same as the amplitude of the induced voltage of the excitation winding to connect the generator excitation, so as to realize that the power converter on the output side of the excitation system is connected without inrush current.

[0016] Optionally, reactive power control of the new energy power generation system includes:

[0017] By controlling the amplitude of the voltage modulation signal of the photovoltaic power converter, reactive power control can be achieved.

[0018] The amplitude of the excitation voltage of the doubly-fed generator is controlled to control the generator output voltage, thereby achieving reactive power control.

[0019] Optionally, active power control of the new energy power generation system includes:

[0020] Based on the first preset formula, the phase of the voltage modulation signal of the photovoltaic power converter is controlled to lead, thereby realizing the active power control of the grid-connected power generation input to the grid. Based on the second preset formula, the phase is controlled to lag, thereby realizing the controllable rectification control during grid-connected power generation, that is, the active power is input from the grid to the power converter.

[0021] Based on the first preset formula, the phase of the voltage modulation signal of the power converter on the input side of the doubly fed generator excitation system is advanced to realize the active power control of the grid-connected generator input to the grid. Based on the second preset formula, the phase is delayed to realize the controllable rectification control during grid-connected generation, that is, the active power is input from the grid to the power converter.

[0022] Based on the first preset formula or the second preset formula, the excitation voltage phase of the doubly-fed generator is controlled to control the generator output voltage phase, thereby realizing the active power control of the new energy power generation system.

[0023] Optionally, the first preset formula is:

[0024]

[0025] Among them, u o (s) is the output voltage signal of the phase control function, u i (s) is the input signal of the phase control function, s is the frequency domain operator, and R is introduced. C The parameter K is a virtual parameter, which determines the parameter K. δC τ is the gain compensation coefficient for the advance angle control signal. RC is the time constant.

[0026] Optionally, the second preset formula is:

[0027]

[0028] Where RL is the introduced virtual parameter, and K δL τ is the gain compensation coefficient for the lag angle control signal. RL is the time constant.

[0029] The present invention has the following beneficial effects:

[0030] The grid-connected control method for a power generation system containing a power converter of the present invention has the characteristics of adapting to frequency fluctuations and voltage fluctuations of the grid voltage, as well as the controllable characteristics of virtual rotational inertia. It can solve in principle the problems of existing new energy power generation grid-connected operation control technology, which is prone to low-frequency grid oscillation and the problems of complex control system model and difficult parameter tuning caused by the introduction of virtual rotational inertia. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0032] Figure 1 This is a block diagram of a new energy power generation system with easily fluctuating power and a stable operation control structure according to an embodiment of the present invention;

[0033] Figure 2 This is a diagram showing the grid-connected operation of the power converter according to an embodiment of the present invention;

[0034] Figure 3 The above diagram shows the voltage waveform of the grid-connected A-phase after filtering and the grid voltage waveform according to an embodiment of the present invention.

[0035] Figure 4 This is a diagram showing the three-phase current waveforms of the power converter when it is connected to the grid according to an embodiment of the present invention.

[0036] Figure 5 This is a control principle diagram of the power grid converter directly connected to the power grid according to an embodiment of the present invention;

[0037] Figure 6 This is a control principle diagram of a doubly-fed wind turbine generator system according to an embodiment of the present invention;

[0038] Figure 7 This is a schematic diagram illustrating the principle of generator output leading reactive current in an embodiment of the present invention.

[0039] Figure 8 This is a schematic diagram illustrating the principle of generator output delayed reactive current in an embodiment of the present invention.

[0040] Figure 9 The phase control function in this embodiment of the invention controls the output modulated signal voltage phase to lead the input voltage phase diagram;

[0041] Figure 10 The phase control function in this embodiment controls the output modulated signal voltage phase to lag behind the input voltage phase diagram. Detailed Implementation

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present application will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0044] This embodiment proposes a direct vector control method for the stable operation of new energy power generation in a power grid prone to power fluctuations. Figure 1 The diagram shows the principle block diagram for grid connection and stable operation control of a new energy power generation system with easily fluctuating power. It includes various links such as grid connection and operation control of photovoltaic power generation, grid connection and operation control of the power converter on the input side of the doubly-fed generator excitation system, starting of the doubly-fed generator, connection of the power converter on the output side of the doubly-fed generator excitation system to the generator excitation winding, and operation control. Figure 2 This embodiment is a diagram showing the parallel operation of the input-side power converter of the photovoltaic power generation and doubly-fed generator excitation system directly connected to the power grid. Figure 5The diagram shown is a schematic of the power converter on the input side of the photovoltaic power generation and doubly-fed generator excitation system directly connected to the power grid in this embodiment, including grid voltage and current detection, and power converter voltage and current detection; Figure 6 The diagram shown is a schematic of the doubly fed generator system in this embodiment, including generator output voltage and current detection, excitation winding voltage and current detection, and grid voltage detection. Figure 5 and Figure 6 Commonly used reactive and active current calculation units for input grid current; reactive current closed-loop control unit and active current closed-loop control unit.

[0045] The direct vector control method for stable operation of new energy power generation in a power grid prone to fluctuations, proposed in this embodiment, includes:

[0046] Construct a new energy power generation system and connect it to the grid without inrush current; the new energy power generation system uses diesel generators as the main grid structure.

[0047] Reactive power control and active power control are implemented for new energy power generation systems connected to the grid without inrush current.

[0048] In the reactive power control and active power control of new energy power generation systems, the low-frequency oscillation fault of the power grid can be eliminated in principle.

[0049] While controlling the active power of the new energy power generation system by the constructed phase control function, the inherent virtual rotational inertia characteristic of the phase control function can suppress grid power fluctuations. Direct vector control can be used to achieve stable operation of the new energy power generation system by synchronously tracking the grid voltage frequency and controlling the active and reactive power.

[0050] Furthermore, grid connection of new energy power generation systems without inrush current includes:

[0051] The diesel generator voltage is collected as the modulation signal for the input-side power converter of the photovoltaic power generation power converter and the doubly fed generator excitation system. The amplitude of the modulation signal is controlled so that the output voltage amplitude of the photovoltaic power generation and excitation system input-side power converter is the same as the grid voltage amplitude, thus achieving grid connection without inrush current.

[0052] The system detects the rotational speed of the generator driven by the doubly-fed induction generator (DFIG) wind power generation system and monitors the grid voltage. The frequency of the excitation voltage is composed of the generator speed and the grid voltage frequency. The phase and amplitude of the voltage of the power converter on the input side of the excitation system are controlled to ensure that the phase sequence, frequency, phase, and amplitude of the generator output voltage are consistent with the grid voltage. Under the condition of meeting the minimum grid connection speed, the system controls the generator to achieve grid connection without inrush current. After grid connection, the excitation of the DFIG generator is disconnected.

[0053] The excitation winding voltage of the doubly fed generator after grid connection is detected. The excitation winding voltage is used as the excitation voltage modulation signal of the generator. The amplitude of the output voltage of the power converter is controlled to be the same as the amplitude of the induced voltage of the excitation winding to connect the generator excitation, so as to realize that the power converter on the output side of the excitation system is connected without inrush current.

[0054] Specifically, in this embodiment, Figure 1 This is a diagram of the power grid structure. The principle of power grid construction is to detect the generator voltage as the modulation signal for controlling the input voltage of the power converter of the photovoltaic power generation and doubly-fed generator excitation system, and to detect the induced voltage of the excitation winding after the doubly-fed generator is connected to the grid without excitation as the modulation signal for controlling the voltage of the power converter. The voltage to be connected is used as the modulation signal for controlling the output voltage of the power converter. It has the characteristic of being synchronized with the grid voltage or the induced voltage of the excitation winding in frequency and phase. The modulation ratio of the modulation signal is set so that the output voltage of the power converter has the same amplitude as the voltage to be connected. In this way, the output voltage of each power converter has the same phase sequence, same amplitude, same frequency and same phase as the voltage connected in parallel with it. Thus, the power converter achieves inrush current-free connection.

[0055] Photovoltaic power generation Figure 2 The principle behind parallel connection without inrush current is as follows:

[0056] Converter output voltage equation:

[0057] u ca =Ku dc sin(ω c t-δ)

[0058]

[0059]

[0060] Among them, u c The output voltage of the converter is represented by K, which is the modulation coefficient of the DC bus voltage, and u is the output voltage of the converter. dc δ is the DC bus voltage, and δ is the controllable converter voltage output phase angle.

[0061] Grid voltage equation:

[0062] u sa =U sm sin(ω s t)

[0063]

[0064]

[0065] Where u s U represents the grid voltage.sm This represents the amplitude of the grid voltage.

[0066] Ignoring the effect of the filter capacitor, the voltage dynamic equation of the grid-connected circuit is as follows:

[0067]

[0068]

[0069]

[0070] Where the total filter inductance L = L1 + L2, R is the total resistance of the filter inductance, and i a,b,c Current in each phase.

[0071] Substituting equations 1 and 2 into equation 3, we get:

[0072]

[0073]

[0074]

[0075] By applying Equation 2, the grid voltage is used as the modulation signal for the converter output voltage to obtain an output voltage with the same frequency and phase as the grid voltage.

[0076] Order: Ku dc =U sm Determine the SPWM modulation ratio so that the output voltage amplitude of the converter is equal to the grid voltage amplitude, and set δ = 0 in Equation 4, ignoring the loop resistance, as shown in Equation 5.

[0077]

[0078]

[0079]

[0080] Where ΔU=Ku dc -U sm .

[0081] That is, when ΔU=0, the converter output voltage amplitude can achieve grid connection without inrush current and no-load operation.

[0082] The methods for grid connection without inrush current are the same for photovoltaic power converters and doubly-fed wind power excitation systems. Grid connection of wind turbines includes starting, connecting the excitation system output-side power converter to the generator excitation winding output without inrush current, and controlling the generator output voltage with the excitation system output-side power converter voltage to achieve grid connection without inrush current. The specific methods are as follows:

[0083] (1) The diesel generator voltage is collected as the modulation signal for the input-side power converter of the photovoltaic power generation and doubly-fed generator excitation system. It has automatic phase sequence identification function and automatic tracking of the grid voltage frequency and phase characteristics. By controlling the amplitude of the modulation signal so that the output voltage amplitude of the photovoltaic power generation and excitation system input-side power converter is the same as the grid voltage amplitude, grid connection without inrush current can be achieved. Figure 3 The waveforms of the power converter output voltage after filtering and the grid voltage waveform are shown. Figure 4 This is the current waveform after grid connection;

[0084] (2) Doubly fed generator starting and grid connection method: The rotational speed of the generator driven by the doubly fed wind power system and the grid voltage are detected. The frequency of the excitation voltage, composed of the generator speed and the grid voltage frequency, is determined. The phase and amplitude of the voltage of the power converter on the input side of the excitation system are controlled to ensure that the frequency, phase, amplitude, and phase sequence of the generator output voltage are consistent with the grid voltage. Under the condition of meeting the minimum grid connection speed, the generator is controlled to achieve grid connection without inrush current. After grid connection, the doubly fed generator excitation is disconnected.

[0085] (3) Detect the excitation winding voltage after the doubly fed generator is connected to the grid, and use this voltage as the excitation voltage modulation signal of the generator to control the amplitude of the output voltage of the power converter to be the same as the amplitude of the induced voltage of the excitation winding. Turn on the generator to excite and realize that the power converter on the output side of the excitation system is connected without impact current.

[0086] In this embodiment, the power control principle after networking is as follows:

[0087] Figure 5 and Figure 6 This document presents power control schematics for the input-side power converters in photovoltaic power generation and excitation systems, as well as for the doubly-fed generator. Since the direct vector control principle strictly tracks the frequency and phase of the grid voltage, the only parameter that can control the output voltage of each power converter is the amplitude of the modulation signal. Controlling the amplitude of the output voltage of each power converter can control the reactive power of the grid-connected power generation system. A phase control function is constructed to adjust the phase of the output voltage of the power converters, thereby controlling the phase difference between the output voltage of each power converter and the grid voltage, and ultimately controlling the active power of the grid-connected power generation system, thus achieving power angle control.

[0088] Furthermore, reactive power control of new energy power generation systems includes:

[0089] By controlling the amplitude of the voltage modulation signal of the photovoltaic power converter, reactive power control can be achieved.

[0090] The amplitude of the excitation voltage of the doubly-fed generator is controlled to control the generator output voltage, thereby achieving reactive power control.

[0091] Specifically, the reactive power control proposed in this embodiment after grid connection is a method for controlling reactive power after the new energy power generation system is connected to the grid without inrush current. Essentially, reactive power is determined by reactive current, which in turn is determined by the voltage difference between the grid-connected power generation system and the grid. Therefore, controlling the voltage amplitude of the power generation system can control the reactive power when the power generation system is connected to the grid. The specific method is as follows:

[0092] As shown in Equation 4, reactive power control can be achieved during grid-connected operation of the converter by controlling the modulation ratio of the grid voltage signal.

[0093] (1) Reactive power control is achieved by controlling the amplitude of the voltage modulation signal of the photovoltaic power converter;

[0094] (2) Control the excitation voltage amplitude of the doubly fed generator to control the generator output voltage and achieve reactive power control.

[0095] When ΔU>0, the converter outputs capacitive reactive power for grid-connected operation, such as... Figure 7 As shown;

[0096] When ΔU<0, the converter outputs inductive reactive power for grid-connected operation, such as... Figure 8 As shown.

[0097] Furthermore, active power control of new energy power generation systems includes:

[0098] Based on the first preset formula, the phase of the voltage modulation signal of the photovoltaic power converter is controlled to lead, thereby realizing the active power control of the grid-connected power generation input to the grid. Based on the second preset formula, the phase is controlled to lag, thereby realizing the controllable rectification control during grid-connected power generation, that is, the active power is input from the grid to the power converter.

[0099] Based on the first preset formula, the phase of the voltage modulation signal of the power converter on the input side of the doubly fed generator excitation system is advanced to realize the active power control of the grid-connected generator input to the grid. Based on the second preset formula, the phase is delayed to realize the controllable rectification control during grid-connected generation, that is, the active power is input from the grid to the power converter.

[0100] The excitation voltage phase of the doubly-fed generator is controlled based on the first or second preset formula to control the generator output voltage phase and realize the active power control of the new energy power generation system.

[0101] Specifically, the active power control after grid connection in this embodiment is as follows: Active power control method after grid connection of the new energy power generation system without inrush current. Essentially, active power is determined by active current, which in turn is determined by the phase difference between the grid-connected power generation system and the grid voltage. Therefore, controlling the voltage phase of the power generation system can control the active power when the power generation system is connected to the grid. The specific method is as follows:

[0102] (1) The active power input to the grid is controlled by the phase advance of the voltage modulation signal of the photovoltaic power converter controlled by Equation 6, and the controllable rectification control is achieved by the phase lag of Equation 10 when the grid is connected to the power converter. That is, the active power is input from the grid to the power converter, which is to charge the energy storage link or DC bus.

[0103] (2) The phase of the voltage modulation signal of the power converter on the input side of the doubly fed generator excitation system is advanced by Equation 6 to realize the active power control of the grid-connected generator input to the grid. The phase of the phase is delayed by Equation 10 to realize the controllable rectification control when the grid is connected to the grid. That is, the grid inputs active power to the power converter, which is DC bus charging to control the bus voltage to be constant.

[0104] (3) The phase of the excitation voltage of the doubly fed generator can be controlled by Equation 6 or Equation 10 to control the phase of the generator output voltage and achieve active power control.

[0105] The principle of active power control is illustrated by the active current control of a doubly-fed wind turbine connected to the grid.

[0106] After the generator is connected to the grid, by Figure 6 The active current given i in the system with active current closed-loop control unit Pref The active current i is calculated by detecting the generator output current. P1 The phase of the output excitation voltage δ is compared with that calculated by the active current controller. f Active current control is achieved by controlling the phase of the generator output voltage, which leads the phase of the grid voltage. The phase control function is constructed to adjust the excitation voltage phase to lead or lag, thereby controlling the generator output voltage phase and thus regulating the active current.

[0107] The specific function for increasing the output voltage phase of the power converter to lead the grid voltage phase is constructed as shown in Equation 6. By introducing an integral element, the following control function for power angle lead is constructed. The purpose is to reduce the unit speed n.

[0108]

[0109] Among them, R c and C p It is a virtual parameter, K δC Defined as the gain compensation coefficient for the advance power angle control signal.

[0110] τ RC =R c C p (7)

[0111]

[0112] Figure 9The curve showing the phase relationship between the output voltage and the input signal voltage, controlled by the phase control function in Equation 6, is shown. The lead angle is determined by Equation 9.

[0113]

[0114] The specific function for reducing the output voltage phase of the power converter from leading the grid voltage phase is constructed as shown in Equation 10. Introducing a lag inertial element, the following power angle lag control function is constructed. The aim is to increase the unit speed n.

[0115]

[0116] Among them, R l and L p It is a virtual parameter, K δL Defined as the gain compensation coefficient for the lag angle control signal.

[0117]

[0118]

[0119] Figure 10 The phase control function in Equation 10 creates a phase lag relationship curve between the output voltage and the input signal voltage, and the power angle is determined by Equation 13.

[0120]

[0121] Specifically, in this embodiment, the principle for eliminating low-frequency power oscillations caused by dynamic errors in existing technologies for tracking grid voltage frequency is as follows:

[0122] The implemented method for controlling active and reactive power of a new energy power generation system after grid connection without inrush current features strict consistency between the grid connection voltage frequency and the grid voltage frequency. During grid connection, the output voltage phase of the power generation system automatically tracks the grid voltage phase. This avoids low-frequency power fluctuations caused by frequency fluctuations resulting from the use of phase-locked loop (PLL) technology to track the grid voltage frequency, thus fundamentally eliminating the cause of low-frequency grid oscillation faults due to PLL technology in new energy power generation.

[0123] Specifically, this embodiment introduces a virtual moment of inertia, which essentially simulates the rotational inertia of the rotating mechanical parts of a traditional generator system. Under load disturbances and dynamic adjustments to the input mechanical power, the rotating parts absorb and release rotational mechanical energy to suppress power fluctuations caused by changes in power angle due to speed variations, thus acting as a damper for disturbances. New energy power generation systems with power converters have the advantage of rapid adjustment but lack this damping effect. Furthermore, the application of phase-locked loop (PLL) technology in their dynamic control process to track the dynamic adjustment of grid voltage and frequency is a contributing factor to increased power fluctuations.

[0124] The method for achieving grid-connected active power of a new energy power generation system without inrush current is based on controlling the phase difference between the output voltage of the power generation system and the grid voltage using a constructed phase control function. This essentially controls the power angle between the power generation system and the grid. Since the power angle is adjustable, the inherent generator inertia of the new energy power generation system allows for dynamic adjustment of the power angle based on disturbances, absorbing and releasing power to compensate for power disturbances. Under the condition of a constant power angle, the virtual inertia of the new energy power generation system is infinite. This avoids the problems of increased control algorithm complexity and difficulty in model parameter tuning caused by introducing virtual inertia in existing technologies.

[0125] This embodiment uses diesel generators, whose frequency and voltage are easily fluctuated due to load disturbances, as the main structure of the power grid. The system structure includes high-penetration renewable energy photovoltaic power generation and doubly-fed wind power generation systems. This forms a power transmission structure that applies direct vector control (DVC) to achieve stable operation of new renewable energy power generation in a power system with fluctuating power, thus eliminating the low-frequency oscillation problem caused by phase-locked loop (PLL) technology during grid-connected operation of power converters. The DVC algorithm detects the diesel generator voltage information to obtain a modulation signal containing all its voltage information, enabling the output voltage of each power converter to automatically follow the diesel generator voltage. Controlling the output voltage amplitude of the power converter controls the reactive and active power base values ​​of the converter output; controlling the phase angle between the converter output voltage and the grid voltage controls the active power output of the converter. Therefore, the grid-connected renewable energy power generation system architecture has a weak coupling relationship with the traditional power grid, fundamentally eliminating the risk of low-frequency oscillation faults that existing renewable energy power generation systems bring to the traditional power grid.

[0126] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A direct vector control method for stable operation of new energy power generation in a power grid prone to power fluctuations, characterized in that, include: A new energy power generation system is constructed, and the new energy power generation system is connected to the grid without inrush current; wherein, the new energy power generation system uses a diesel generator as the main grid structure, and the new energy power generation system includes photovoltaic grid connection, wind power generation excitation input side grid connection and wind power generator grid connection; Reactive power control and active power control are performed on the new energy power generation system after grid connection without inrush current. In the reactive power control and active power control of the new energy power generation system, frequency and phase synchronization error-free tracking is used to eliminate low-frequency oscillation faults in the power grid. By controlling the output voltage of each power converter to control reactive power, and by using a constructed phase control function to control the output active power of the wind turbine, the grid-connected active power of the photovoltaic power generation, and the active power on the excitation input side of the wind turbine, the virtual rotational inertia of the power converter of the new energy power generation system is controlled by adjusting the phase control function parameters, thereby suppressing the power fluctuation of the power grid and completing the direct vector control for the stable operation of the new energy power generation system.

2. The direct vector control method for stable operation of new energy power generation in a power grid prone to fluctuations, as described in claim 1, is characterized in that... The grid connection of the new energy power generation system without inrush current includes: The diesel generator voltage is collected as the modulation signal for the input-side power converter of the photovoltaic power generation power converter and the doubly fed generator excitation system. The amplitude of the modulation signal is controlled so that the output voltage amplitude of the input-side power converter of the photovoltaic power generation and excitation system is the same as the grid voltage amplitude, so as to realize grid connection of the power converter of the input side of the photovoltaic power generation and excitation system without inrush current. The system detects the rotational speed of the generator driven by the doubly-fed induction generator (DFIG) wind power generation system and monitors the grid voltage. The frequency of the excitation voltage is composed of the generator speed and the grid voltage frequency. The phase and amplitude of the voltage of the power converter on the output side of the excitation system are controlled to ensure that the phase sequence, frequency, phase, and amplitude of the generator output voltage are consistent with the grid voltage. Under the condition of meeting the minimum grid connection speed, the system controls the generator to achieve grid connection without inrush current. After the generator is connected to the grid, the excitation of the DFIG generator is disconnected. The excitation winding voltage of the doubly fed generator after grid connection is detected. The excitation winding voltage is used as the excitation voltage modulation signal of the generator to control the amplitude of the output voltage of the power converter on the output side of the excitation system to be the same as the amplitude of the induced voltage of the excitation winding, so as to connect the generator excitation and realize the power converter on the output side of the excitation system without inrush current.

3. The direct vector control method for stable operation of new energy power generation in a power grid with fluctuating power, as described in claim 1, is characterized in that... Reactive power control of the aforementioned new energy power generation system includes: By controlling the amplitude of the voltage modulation signal of the photovoltaic power converter, reactive power control can be achieved. The amplitude of the excitation voltage of the doubly-fed generator is controlled to control the generator output voltage, thereby achieving reactive power control.

4. The direct vector control method for stable operation of new energy power generation in a power grid prone to fluctuations, as described in claim 1, is characterized in that... Active power control of the aforementioned new energy power generation system includes: Based on the first preset formula, the phase of the voltage modulation signal of the photovoltaic power converter is controlled to advance to realize the active power control of the grid-connected power generation input to the grid. Based on the second preset formula, the phase is controlled to lag to realize the controllable rectification control when the grid is connected to the power converter, that is, the active power is input from the grid to the power converter. Based on the first preset formula, the phase of the voltage modulation signal of the power converter on the input side of the doubly fed generator excitation system is advanced to realize the active power control of the grid-connected generator input to the grid. Based on the second preset formula, the phase is delayed to realize the controllable rectification control during grid-connected generation, that is, the active power is input from the grid to the power converter. Based on the first preset formula or the second preset formula, the excitation voltage phase of the doubly-fed generator is controlled to control the generator output voltage phase, thereby realizing the active power control of the new energy power generation system.

5. The direct vector control method for stable operation of new energy power generation in a power grid with fluctuating power, as described in claim 4, is characterized in that... The first preset formula is: Among them, u o (s) is the output voltage signal of the phase control function, u i (s) is the input voltage signal for the phase control function, s is the frequency domain operator, and R C For the introduced virtual parameter, K δC τ is the gain compensation coefficient for the advance angle control signal. RC is the time constant.

6. The direct vector control method for stable operation of new energy power generation in a power grid prone to fluctuations, as described in claim 5, is characterized in that... The second preset formula is: Where RL is the introduced virtual parameter, and K δL τ is the gain compensation coefficient for the lag angle control signal. RL is the time constant.

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