A system and method for suppressing the impact of subsynchronous oscillation of photovoltaic power station on power grid

Abstract

The present invention is a system and method for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid, and belongs to the field of subsynchronous oscillation suppression. Its technical solution is that it includes a signal acquisition device, the other end of the signal acquisition device is connected to a signal processing device, the system also includes an energy storage converter, the energy storage converter is connected to an energy storage unit, the signal processing device is connected to the energy storage converter for transmitting the screened oscillation component signal, and the energy storage unit is connected for outputting or absorbing power at the photovoltaic power station grid connection point. Through the signal processing device and energy storage converter, the collected subsynchronous oscillation signal is processed by electrical signal and power is offset, and the energy storage converter can achieve a low-cost power suppression effect, which is beneficial to improving the stability of the power grid operation and the stability of the power grid output power, without the need to adopt a damping control technology with a complex calculation process, and improves the suppression rate of the system.

Description

Technical Field

[0001] The present invention belongs to the field of subsynchronous oscillation suppression, and in particular relates to a system and method for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid. Background Art

[0002] Subsynchronous oscillation (SSO) is a very common and harmful low-frequency oscillation in power systems. With the vigorous development of new energy and the widespread application of power electronics technology, large-scale new energy bases have subsynchronous oscillations with time-varying frequencies through series compensation or DC transmission systems.

[0003] With the access of a large number of new energy power generation systems to the power grid, the original power grid with thermal power turbine units as the main power generation system has weakened and gradually developed towards a weak power grid. When a photovoltaic power station is connected to a weak power grid, it is easy to cause subsynchronous oscillation failure in the photovoltaic power station. In severe cases, it will damage the nearby thermal power units, cause an impact on the power grid, and cause a large-scale power outage. In order to suppress the impact of subsynchronous oscillation on the power grid caused by the photovoltaic power station when it is connected to a weak power grid, the prior art usually adopts a damping control strategy such as reactive compensation to suppress the subsynchronous oscillation of the photovoltaic power station. The damping control strategy is a method of suppressing subsynchronous oscillation by adjusting the system damping. By introducing appropriate damping in the power system, the stability of the system can be increased, thereby reducing the risk of subsynchronous oscillation.

[0004] In the actual photovoltaic subsynchronous oscillation process, the frequency range is wide, and damping usually only works on a specific frequency. This operation method is technically complex and requires a lot of mathematical calculations and derivations. The photovoltaic power station is a nonlinear, high-dimensional system, and the mathematical modeling process is usually not precise enough, which also leads to inaccurate design of the damping control strategy, which in turn leads to poor suppression of subsynchronous oscillations in photovoltaic power stations and unavoidable impact on the power grid. Summary of the invention

[0005] In view of the problems in the prior art, the present invention provides a system and method for suppressing the impact of subsynchronous oscillation of photovoltaic power stations on the power grid, which solves the problems of high technical complexity and poor suppression effect in the existing subsynchronous oscillation suppression methods.

[0006] The technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present application provides a system for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid, comprising a voltage transformer and a first current transformer, wherein the voltage transformer and the first current transformer are both arranged at a grid connection point, and are used to collect a voltage signal and a first current signal at a grid connection point between a photovoltaic system and an external power grid circuit, respectively, and further comprising a second current transformer, a signal processing device, an energy storage converter, and an energy storage battery;

[0008] The voltage signal outputs the electrical angular velocity of the grid voltage vector, the phase of the grid voltage vector, the component of the grid voltage vector under the d-axis of the two-phase rotating coordinate system, and the component of the grid voltage vector under the q-axis of the two-phase rotating coordinate system through a phase-locked loop;

[0009] The voltage transformer, the first current transformer, the second current transformer, and the energy storage converter are all connected to the signal processing device;

[0010] The energy storage converter is connected to the signal processing device, the filter, and the energy storage battery respectively; the filter of the energy storage converter is connected to the external power grid;

[0011] The second current transformer is arranged at the AC side of the filter outlet of the energy storage converter, and is used to collect the second current signal at the grid connection point between the AC side of the energy storage converter and the external power grid circuit;

[0012] The signal processing device includes a first power calculation module, a second power calculation module and a quasi-resonance control module; the first power calculation module receives a voltage signal and a first current signal, and outputs the active power and reactive power of the photovoltaic power station after calculation; the resonance control module receives the active power and reactive power output by the first power calculation module, and outputs an active power reference signal and a reactive power reference signal; the second power calculation module receives a second current signal and a voltage signal, and outputs an actual active power signal and an actual reactive power signal of the energy storage converter after calculation;

[0013] The energy storage converter receives the active power reference signal, reactive power reference signal, actual active power signal, and actual reactive power signal generated by the signal processor, processes them, and then outputs a control signal to the energy storage unit;

[0014] The energy storage unit outputs or absorbs power at the grid connection point according to the control signal.

[0015] Furthermore, the quasi-resonant control module includes a quasi-resonant controller and a proportional-integral controller, the quasi-resonant controller is used to filter out the AC component signal that deviates from the resonant angular frequency in the power signal through the AC component signal in the power signal at its resonant angular frequency, and the proportional-integral controller is used to adjust the resonant angular frequency of the quasi-resonant controller;

[0016] The transfer function of the quasi-resonant control module is:

[0017]

[0018] in , s is the Laplace operator, are the amplitude gain, cutoff angular frequency and resonant angular frequency of the quasi-resonant controller respectively.

[0019] Furthermore, the signal processing device also includes a judgment module, which is used to receive the first current signal collected by the first current transformer and perform a fast Fourier transform to obtain the content of the AC component at different frequencies, and then compare the ratio of the content of the 4Hz-46Hz component to the content of the industrial frequency 50Hz component to determine whether sub-synchronous oscillation occurs in the photovoltaic power station.

[0020] Further, the first power calculation module includes a first coordinate transformation unit and a first power calculation unit;

[0021] The first coordinate transformation unit receives the phase of the grid voltage vector and the first current signal to perform Park transformation, calculates and outputs the component of the three-phase grid-connected current output by the photovoltaic system under the d-axis and the q-axis of the two-phase rotating coordinate system, and then outputs the active grid-connected power and reactive grid-connected power of the photovoltaic power station after passing through the first power calculation unit with the component of the grid voltage vector under the dq-axis of the two-phase rotating coordinate system;

[0022] The second coordinate transformation unit receives the phase of the grid voltage vector and the second current signal to perform Park transformation, calculates and outputs the component of the three-phase grid-connected current output by the energy storage system under the d-axis and the q-axis of the two-phase rotating coordinate system, and then outputs the actual active power signal and the actual reactive power signal of the energy storage inverter after passing through the second power calculation unit with the component of the grid voltage vector under the dq-axis of the two-phase rotating coordinate system.

[0023] Furthermore, the first power calculation module also includes an inversion unit, which is used to receive the active power and reactive power output by the photovoltaic system output by the first power calculation unit and invert them to output an active power reference signal and a reactive power reference signal of the energy storage inverter.

[0024] Furthermore, the energy storage converter includes a power outer loop module and a current inner loop module, the input end of the power outer loop module is connected to the signal processing device, the output end of the power outer loop module is connected to the input end of the current inner loop module, and the output end of the current inner loop module is connected to the energy storage unit;

[0025] The power outer loop module receives the active power reference signal, reactive power reference signal, actual active power signal, and actual reactive power signal generated by the signal processing device, and performs difference processing on the active power reference signal and the actual active power signal, and the reactive power reference signal and the actual reactive power signal, respectively, to use them as the active current reference value and the reactive current reference value of the current inner loop module. After receiving the active current reference value and the reactive current reference value, the current inner loop module performs difference processing on the components of the second current signal in the dq coordinate system to use them as the control signal of the energy storage unit.

[0026] Furthermore, the energy storage unit includes a plurality of energy storage batteries connected in series.

[0027] In a second aspect, an embodiment of the present application further provides a method for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid, which is implemented by the subsynchronous oscillation suppression system described in the first aspect, and includes the following steps:

[0028] S1, a signal acquisition device acquires a voltage signal, a first current signal, and a second current signal at a grid connection point;

[0029] S2. Perform fast Fourier transform on the collected first current signal to obtain the content of the AC component at different frequencies, compare the ratio of the content of the 4Hz-46Hz component to the content of the power frequency 50Hz component, and determine whether subsynchronous oscillation occurs in the photovoltaic power station:

[0030] If the ratio is greater than or equal to the threshold, the system is considered to have subsynchronous oscillation and enters S3;

[0031] If the ratio is less than the threshold, return to step S1;

[0032] S3, performing Park transformation on the collected voltage signal, the first current signal, and the second current signal, and calculating the actual active power signal, the actual reactive power signal, the active grid-connected power, and the reactive grid-connected power through the power calculation formula in the dq coordinate system;

[0033] S4, using the active grid-connected power and the reactive grid-connected power as signal inputs of the quasi-resonant control module, and the quasi-resonant control module screens out the signal of the oscillation component in the output power of the photovoltaic power station;

[0034] S5, invert the oscillation component signal screened out by the signal processing device, and collect the second current signal on the input end of the energy storage converter at the same time, calculate it with the voltage signal in step S1, obtain the actual power value on the input end of the energy storage converter, and make a difference between the inverted oscillation component signal and the actual power value, and use the difference as the input value of the power outer loop module;

[0035] S6, the power outer loop module outputs a current reference value, the current reference value is subtracted from the actual current value at the input end of the energy storage converter, and the difference is used as the input value of the current inner loop module;

[0036] S7. The output end of the current inner loop module controls the output or absorption of power by the energy storage converter at the photovoltaic power station grid connection point.

[0037] Further, step S7 includes the following method:

[0038] S7-1, the output of the current inner loop module is used as the input signal of space vector pulse width modulation;

[0039] S7-2, the output signal of the space vector pulse width modulation is used as the input signal of the insulated gate bipolar transistor in the energy storage converter;

[0040] S7-3. The output signal of the insulated gate bipolar transistor in the energy storage converter controls the output or absorption of power at the grid connection point by the energy storage converter.

[0041] Furthermore, in step S2, the threshold is preferably 5%.

[0042] It can be seen from the above technical scheme that the present invention has the following advantages: through the signal processing device and energy storage converter, the collected subsynchronous oscillation signal can be directly processed and the power offset can be performed, and the energy storage converter can achieve low-cost power suppression effect, which is conducive to improving the stability of power grid operation and the stability of power grid output, without the need for complex mathematical calculations to achieve oscillation suppression. At the same time, by using the subsynchronous oscillation suppression method provided in this scheme, there is no need for complex calculations such as phase shifting, and the overall processing speed of the circuit is faster and the response is faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the description will be briefly introduced below. Obviously, the accompanying drawings in the following description are only 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 creative work.

[0044] Figure 1 It is a schematic diagram of a photovoltaic power station grid-connected system in a specific implementation example of the present invention.

[0045] Figure 2 It is a waveform diagram of the grid-connected point power when subsynchronous oscillation occurs in the photovoltaic power station in the embodiment of the specific implementation mode of the present invention.

[0046] Figure 3 It is the Bode diagram of the quasi-resonant controller in the specific implementation example of the present invention.

[0047] Figure 4 It is a principle block diagram of a quasi-resonant controller in a specific implementation example of the present invention.

[0048] Figure 5 It is a principle block diagram of a proportional-integral controller and a quasi-resonant controller in a specific implementation example of the present invention.

[0049] Figure 6 It is a control effect diagram of the proportional-integral controller and the quasi-resonant controller in the specific implementation example of the present invention, wherein Figure 6 (a) is the control effect diagram of the proportional-integral controller and the quasi-resonant controller when the input signal has a sudden change in amplitude; Figure 6 (b) is the control effect diagram of the proportional-integral controller and the quasi-resonant controller when the input signal undergoes a frequency mutation; Figure 6 (c) is the control effect diagram of the proportional-integral controller and the quasi-resonant controller when the input signal undergoes a sudden phase change; Figure 6 (d) is the control effect diagram of the proportional-integral controller and the quasi-resonant controller when the input signal contains a DC component.

[0050] Figure 7 It is a schematic diagram of a specific implementation example of the present invention for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid based on an energy storage system.

[0051] Figure 8 It is a signal processing diagram of a signal processing device in an embodiment of a specific implementation manner of the present invention.

[0052] Fig. 9 It is a signal flow chart of the judgment module in the specific implementation example of the present invention.

[0053] Fig.10 It is a signal processing diagram of the energy storage converter in the specific implementation example of the present invention.

[0054] Fig.11 It is a flow chart of the method in the specific implementation example of the present invention. DETAILED DESCRIPTION

[0055] In the detailed description below, various embodiments of the present disclosure will be described more fully. The present disclosure may have various embodiments, and adjustments and changes may be made therein. However, it should be understood that there is no intention to limit the various embodiments of the present disclosure to the specific embodiments disclosed herein, but rather the present disclosure should be understood to cover all adjustments, equivalents and / or alternatives that fall within the spirit and scope of the various embodiments of the present disclosure.

[0056] In order to clearly describe the technical solutions of the embodiments of the present application, some terms and technologies involved in the embodiments of the present application are briefly introduced below:

[0057] 1. The proportional integral controller (PI controller) is an advanced controller that combines proportional and integral control functions. It is widely used in control systems such as liquid level, pressure, and flow in industrial production. Its core working principle is to compare the deviation between the set value and the actual output value, use proportional control to quickly respond to the deviation change, and introduce integral control to gradually eliminate the deviation to achieve a zero-error control effect.

[0058] 2. The power storage converter (PCS) is a power electronic device whose core function is to realize the bidirectional flow and optimized management of electric energy, especially in new energy power stations, microgrids, smart grids and other fields. The device can convert electric energy into storage form through built-in energy storage elements (such as capacitors or battery packs) and converters, and convert it back to usable electric energy when needed. In this process, the controller plays a vital role. It is responsible for monitoring and controlling the working status of the energy storage converter, ensuring the safe operation of the battery, and realizing the precise regulation of the active power and reactive power of the power grid.

[0059] 3. Quasi-resonant controller is an advanced power electronic device controller. It realizes zero-static error control by introducing a resonant link and utilizing the characteristic of infinite gain of the controller at the resonance point in the control loop. This controller has a complex frequency response curve and can achieve high-precision control effect. In small and medium power three-phase rectifiers, quasi-resonant controllers are often used in combination with three-phase dq transformation to convert three-phase AC quantities into DC quantities in a synchronous rotating coordinate system for control. In addition, quasi-resonant controllers also have a variety of protection functions, such as overcurrent protection and short-circuit protection, to ensure the stable operation of the power supply system. With the development of digital control technology, quasi-resonant controllers have also been widely used in fields such as single-phase rectifiers and inverters, and have become one of the important technologies in the field of power electronic device control.

[0060] 4. Space Vector Pulse Width Modulation (SVPWM) is an efficient power electronic modulation technology, mainly used in inverters and motor drive systems. This technology improves conversion efficiency and output voltage quality while reducing harmonics by controlling the three-phase voltage vector to be close to the ideal DC voltage. The core idea is to regard the three-phase inverter as a vector source that can generate various space vectors. By switching the switching devices reasonably, a voltage vector of a specific size and direction can be synthesized within a switching cycle. These synthesized vectors are arranged in a specific order on the complex plane to form a hexagonal or circular vector trajectory, thereby generating a smooth rotating magnetic field in the motor and realizing precise control of the motor. Compared with traditional pulse width modulation (PWM) technology, SVPWM technology has higher DC external grid voltage utilization, lower harmonic distortion, and better dynamic response and stability. It is an indispensable advanced modulation technology in modern motor drives and power electronic equipment.

[0061] 5. Insulated Gate Bipolar Transistor (IGBT) is a high-performance semiconductor switching device that combines the advantages of bipolar transistors and field effect transistors. IGBT has an insulated gate. By controlling the voltage of the gate, the on and off states of the transistor can be controlled. In the on state, IGBT has a low on-state voltage drop and conduction loss, can withstand high voltage and current loads, and has a relatively fast switching speed. These characteristics make IGBT an ideal choice for power electronics applications and are widely used in power electronic devices such as inverters, converters, and power supplies. In addition, IGBT also has the advantages of simple driving and easy parallel connection, which makes it widely used in industrial motors, civilian small-capacity motors, converters, induction heating and other fields. At the same time, the structural design of IGBT gives it good thermal stability and high reliability, and it can work reliably in high temperature environments, further expanding its application areas. In summary, the insulated gate bipolar transistor is an important power semiconductor device that plays an important role in the field of power electronics.

[0062] 6. Potential Transformer (PT) is an instrument used to transform voltage. It is mainly composed of primary and secondary coils, iron core and insulation, and has two windings, namely primary winding and secondary winding. The main function of the voltage transformer is to convert high voltage into low voltage in proportion, usually into a standard secondary voltage of 100V for metering, instrumentation and relay protection. At the same time, it can also isolate high voltage from electrical workers to ensure the safety of equipment and personnel.

[0063] 7. Current Transformer (CT) is an instrument that converts a large primary current into a small secondary current for measurement based on the principle of electromagnetic induction. Its primary winding has fewer turns and is connected in series in the circuit of the current to be measured; while the secondary winding has more turns and is connected in series in the measuring instrument and protection circuit. The main function of the current transformer is to convert a large primary current into a small secondary current through a certain transformation ratio for protection, measurement and other purposes.

[0064] like Figure 1 As shown, for example, subsynchronous oscillation (SSO) is a very common and harmful low-frequency oscillation in power systems. With the vigorous development of new energy and the widespread application of power electronics technology, large-scale new energy bases have subsynchronous oscillations with time-varying frequencies in series compensation or DC transmission systems.

[0065] When a photovoltaic power station is connected to a weak power grid, it is easy to cause subsynchronous oscillation failure in the photovoltaic power station. In serious cases, it will damage the nearby thermal power units, cause an impact on the power grid, and cause a large-scale power outage.

[0066] In an ideal state, when the photovoltaic power station does not have subsynchronous oscillation, the power waveform at the grid connection point is a non-oscillating waveform. When the photovoltaic power station has subsynchronous oscillation, the power waveform at the grid connection point is Figure 2 As shown, is the active power output of the photovoltaic power station, is the unit of active power; is the reactive power output by the photovoltaic power station, is the unit of reactive power; t / s is the unit of time.

[0067] In view of the above problems, the present embodiment provides a subsynchronous oscillation suppression system and method, which solves the problems of high technical complexity and poor suppression effect in the prior art.

[0068] Hereinafter, the terms "include" or "may include" used in various embodiments of the present disclosure indicate the presence of disclosed functions, operations, or elements, and do not limit the addition of one or more functions, operations, or elements. In addition, as used in various embodiments of the present disclosure, the terms "include", "have", and their cognates are intended only to indicate specific features, numbers, steps, operations, elements, components, or a combination of the foregoing, and should not be understood as first excluding the presence of one or more other features, numbers, steps, operations, elements, components, or a combination of the foregoing or the possibility of adding one or more features, numbers, steps, operations, elements, components, or a combination of the foregoing.

[0069] In various embodiments of the present disclosure, the expression "or" or "at least one of A or / and B" includes any combination or all combinations of the words listed at the same time. For example, the expression "A or B" or "at least one of A or / and B" may include A, may include B, or may include both A and B.

[0070] The expressions (such as "first", "second", etc.) used in the various embodiments of the present disclosure may modify the various constituent elements in the various embodiments, but may not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing one element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of the various embodiments of the present disclosure, the first element may be referred to as the second element, and similarly, the second element may also be referred to as the first element.

[0071] It should be noted that if it is described that one component element is “connected” to another component element, the first component element may be directly connected to the second component element, and a third component element may be “connected” between the first component element and the second component element. Conversely, when one component element is “directly connected” to another component element, it can be understood that there is no third component element between the first component element and the second component element.

[0072] 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 only 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.

[0073] The signal acquisition device is one or more of a voltage transformer, a current transformer or a power transformer. According to an embodiment of the present application, the signal acquisition device is a voltage transformer and a current transformer.

[0074] like Figure 7 As shown, this embodiment provides a system for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid, including a voltage transformer and a first current transformer, both of which are arranged at a grid connection point, and are used to collect a voltage signal and a first current signal at a grid connection point between a photovoltaic system and an external power grid circuit, respectively, and also includes a second current transformer, a signal processing device, an energy storage converter and an energy storage battery;

[0075] The voltage signal outputs the electrical angular velocity of the grid voltage vector, the phase of the grid voltage vector, the component of the grid voltage vector under the d-axis of the two-phase rotating coordinate system, and the component of the grid voltage vector under the q-axis of the two-phase rotating coordinate system through a phase-locked loop;

[0076] The voltage transformer, the first current transformer, the second current transformer, and the energy storage converter are all connected to the signal processing device;

[0077] The energy storage converter is connected to the signal processing device, the filter, and the energy storage battery respectively; the filter of the energy storage converter is connected to the external power grid;

[0078] The second current transformer is arranged at the AC side of the filter outlet of the energy storage converter, and is used to collect the second current signal at the grid connection point between the AC side of the energy storage converter and the external power grid circuit;

[0079] The signal processing device includes a first power calculation module, a second power calculation module and a quasi-resonance control module; the first power calculation module receives a voltage signal and a first current signal, and outputs active power and reactive power of the photovoltaic power station after calculation; the resonance control module receives the active power and reactive power output by the first power calculation module, and outputs an active power reference signal and a reactive power reference signal; the second power calculation module receives a second current signal and a voltage signal, and outputs an actual active power signal and an actual reactive power signal after calculation;

[0080] The energy storage converter receives the active power reference signal, reactive power reference signal, actual active power signal, and actual reactive power signal generated by the signal processor, processes them, and then outputs a control signal to the energy storage unit;

[0081] The energy storage unit outputs or absorbs power at the grid connection point according to the control signal. As an example, the energy storage unit includes a plurality of energy storage batteries connected in series.

[0082] In this embodiment, the first power calculation module includes a first coordinate transformation unit and a first power calculation unit;

[0083] The first coordinate transformation unit receives the phase of the grid voltage vector and the first current signal to perform Park transformation, calculates and outputs the components of the three-phase grid-connected current output by the photovoltaic system under the dq axis of the two-phase rotating coordinate system, and then outputs the active grid-connected power and reactive grid-connected power of the photovoltaic power station after passing through the first power calculation unit with the components of the grid voltage vector under the dq axis of the two-phase rotating coordinate system;

[0084] The second coordinate transformation unit receives the phase of the grid voltage vector and the second current signal for Parker transformation, calculates and outputs the components of the three-phase grid-connected current output by the energy storage system under the dq axis of the two-phase rotating coordinate system, and then outputs the actual active power signal and the actual reactive power signal of the energy storage inverter after passing through the second power calculation unit with the components of the grid voltage vector under the dq axis of the two-phase rotating coordinate system.

[0085] The first power calculation module also includes an inversion unit, which is used to receive the active power and reactive power output by the photovoltaic system output by the first power calculation unit and invert them to output an active power reference signal and a reactive power reference signal.

[0086] According to an embodiment of the present application, the signal processing device is a quasi-resonant controller, which is used to filter out the AC component signal that deviates from its resonant angular frequency through the AC component signal at its resonant angular frequency, such as Figure 3 and Figure 4 As shown in the figure, they are the Bode diagram and principle block diagram when the quasi-resonant controller is used alone, where Figure 3Here, dB is the unit of amplitude; deg is the unit of phase; rad / s is the unit of frequency.

[0087] Figure 4 In this equation, s is the Laplace operator; are the amplitude gain, cutoff angular frequency, and resonant angular frequency of the quasi-resonant controller respectively. The transfer function of the quasi-resonant controller is:

[0088]

[0089] In order to understand the characteristics of the quasi-resonant controller, the resonant frequency is designed is 20Hz, which is the resonant angular frequency It is 2*π*20rad / s. =1, =5rad / s. Based on the above parameters, we can draw the following Figure 3 Bode plot of the quasi-resonant controller shown.

[0090] according to Figure 3 It can be seen that the quasi-resonant controller can allow the AC component at its resonant angular frequency to pass through and filter out the AC component that deviates greatly from its resonant angular frequency.

[0091] Since the subsynchronous oscillation frequency range of the photovoltaic power station is relatively wide, 4Hz-46Hz. At the same time, according to the Bode diagram of the quasi-resonant controller, it can be seen that the quasi-resonant controller only works within a certain frequency range. It can be understood that the resonant angular frequency is only related to the parameter value N. Therefore, by updating the N value in real time, it is possible to ensure the real-time extraction of the subsynchronous oscillation component of the photovoltaic power station. For this reason, the quasi-resonant controller is also connected to a proportional-integral controller, which is used to adjust the resonant angular frequency of the quasi-resonant controller, such as Figure 5 As shown, the input and output of the quasi-resonant controller are subtracted to obtain a deviation signal between the two, which is transmitted to the proportional-integral controller. The output of the proportional-integral controller updates the N value in real time, thereby achieving the purpose of adaptive resonant angular frequency. Adding a proportional-integral controller can ensure real-time extraction of the subsynchronous oscillation component of the photovoltaic power station and send it to the control algorithm of the energy storage system, thereby suppressing the subsynchronous oscillation of the photovoltaic power station in real time.

[0092] After transforming the quasi-resonant controller, the transfer function is:

[0093]

[0094] like Figure 6As shown in the figure, in order to further verify the control effect of the designed proportional-integral controller and quasi-resonant controller, the models of the proportional-integral controller and the quasi-resonant controller were built using simulation software. The input signal was made to undergo amplitude mutation, frequency mutation, phase mutation, and contain a DC component at 0.3s, a total of four forms, to observe the extraction effect of the proportional-integral controller and the quasi-resonant controller on the AC component.

[0095] It can be understood that before the input signal has a sudden change in amplitude, frequency, or phase, the input signal and the output signal are in a coincident state. When the input signal has a sudden change in amplitude, frequency, or phase, the proportional-integral controller and the quasi-resonant controller can still quickly track the input signal. Figure 6 (a) Figure 6 (b) Figure 6 In (c), the input signal and the output signal coincide. At the same time, when the input signal contains a DC component, it can prevent the DC component from passing through and only allow the AC component to pass through. Figure 6 (d) Therefore, the proportional-integral controller and the quasi-resonant controller can track the subsynchronous oscillation components of a wide range of photovoltaic power plants and extract them in real time.

[0096] It should be further explained that the energy storage converter includes a power outer loop module and a current inner loop module, the input end of the power outer loop module is connected to the signal processing device, the output end of the power outer loop module is connected to the input end of the current inner loop module, and the output end of the current inner loop module is connected to the energy storage unit;

[0097] The power outer loop module receives the active power reference signal, reactive power reference signal, actual active power signal, and actual reactive power signal generated by the signal processing device, and performs difference processing on the active power reference signal and the actual active power signal, and the reactive power reference signal and the actual reactive power signal, respectively, to use them as the active current reference value and the reactive current reference value of the current inner loop module. After receiving the active current reference value and the reactive current reference value, the current inner loop module performs difference processing on the components of the second current signal in the dq coordinate system to use them as the control signal of the energy storage unit.

[0098] By setting up the signal processing device and the energy storage inverter, the collected subsynchronous oscillation signal can be directly processed with electrical signals and power offset, and the set energy storage inverter can achieve low-cost power suppression effect, which is beneficial to improving the stability of the grid operation and the stability of the grid output power.

[0099] Further, such as Figure 7-Figure 11As shown, as a refinement and expansion of the specific implementation of the above embodiment, in order to fully illustrate the specific implementation process in this embodiment, a method for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid is provided, which is implemented by the subsynchronous oscillation suppression system mentioned in the above embodiment, including the following steps:

[0100] S1. The signal collection device collects the signal at the photovoltaic power station grid connection point:

[0101] u abc : voltage signal;

[0102] i pvabc : first current signal;

[0103] i abc : The second current signal;

[0104] where u abc After processing through the phase-locked loop, we get:

[0105] ω1: electrical angular velocity of the grid voltage vector;

[0106] θ1: phase of the grid voltage vector;

[0107] u d : The component of the grid voltage vector under the d-axis of the two-phase rotating coordinate system;

[0108] u q : The component of the grid voltage vector under the q-axis of the two-phase rotating coordinate system;

[0109] S2. Perform fast Fourier transform on the collected first current signal to obtain the content of AC components at different frequencies, compare the ratio of the content of 4 Hz-46 Hz component to the content of the power frequency 50 Hz component, and determine whether subsynchronous oscillation occurs in the photovoltaic power station;

[0110] For fast Fourier transform, suppose there is a discrete current signal x[n] of length N, where n is an integer from 0 to N-1. The discrete Fourier transform formula is:

[0111]

[0112] where X[k] is the frequency domain representation of the signal x[n], and j is an imaginary unit (satisfying =−1).

[0113] If the ratio is greater than or equal to the threshold, it is considered that the system has subsynchronous oscillation and enters s3; the threshold is preferably 5%.

[0114] If the ratio is less than the threshold, return to step S1;

[0115] S3, the collected current ipvabc 、i abc Perform Parker transformation to get i pvd ,i pvq 、i d ,i q , the grid-connected power P of the photovoltaic power station is calculated by the power calculation formula in the dq coordinate system pv , Q pv ;

[0116] where i pvd is the component of the three-phase grid-connected current output by the photovoltaic system under the d-axis of the two-phase rotating coordinate system, i pvq is the component of the three-phase grid-connected current output by the photovoltaic system under the q-axis of the two-phase rotating coordinate system, i d is the component of the three-phase grid-connected current output by the energy storage system under the d-axis of the two-phase rotating coordinate system, i q is the component of the three-phase grid-connected current output by the energy storage system under the q-axis of the two-phase rotating coordinate system; P pv is the active power output of the photovoltaic system, Q pv Reactive power output by the photovoltaic system;

[0117] S4, the grid-connected power P pv , Q pv As a signal input to the signal processing device, the signal processing device screens out a signal of an oscillating component in the output power of the photovoltaic power station;

[0118] S5, the oscillation component signal screened out by the signal processing device is inverted to obtain the reference value P of the power outer loop module of the energy storage converter ESSref , Q ESSref At the same time, the actual current value i on the filter input side of the energy storage converter is collected d 、i q , and compare it with the voltage u in step S1 d 、u q The actual power value on the input side of the energy storage converter is calculated. P ESS , Q ESS , the difference between the inverted oscillation component signal and the actual power value is taken as the input value of the power outer loop module;

[0119] Where P ESSOef is the active power reference signal of the energy storage converter, Q ESSOef is the reactive power reference signal of the energy storage converter, P ESS is the actual active power signal, Q ESS is the actual reactive power signal;

[0120] S6, the output current reference value of the power outer ring module, the current reference value and the actual current value i on the input side of the energy storage converter d 、i q Make a difference, and the difference is used as the input value of the current inner loop module;

[0121] S7, the output end of the current inner loop module controls the output or absorption of power by the energy storage converter at the photovoltaic power station grid connection point;

[0122] It should be further explained that step S7 includes the following method:

[0123] S7-1, the output of the current inner loop module is used as the input signal of space vector pulse width modulation;

[0124] S7-2, the output signal of the space vector pulse width modulation is used as the input signal of the insulated gate bipolar transistor in the energy storage converter;

[0125] S7-3. The output signal of the insulated gate bipolar transistor in the energy storage converter controls the output or absorption of power at the grid connection point by the energy storage converter.

[0126] By using the subsynchronous oscillation suppression method provided in this embodiment, there is no need for phase shifting and other steps with complex calculations, and the overall processing speed of the circuit is faster and the response is more rapid.

[0127] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid, comprising a voltage transformer and a first current transformer, wherein the voltage transformer and the first current transformer are both arranged at a grid connection point, and are used to collect a voltage signal and a first current signal at a grid connection point between a photovoltaic system and an external power grid circuit, respectively, and characterized in that: It also includes a second current transformer, a signal processing device, an energy storage converter and an energy storage battery; The voltage signal outputs the electrical angular velocity of the grid voltage vector, the phase of the grid voltage vector, the component of the grid voltage vector under the d-axis of the two-phase rotating coordinate system, and the component of the grid voltage vector under the q-axis of the two-phase rotating coordinate system through a phase-locked loop; The voltage transformer, the first current transformer, the second current transformer, and the energy storage converter are all connected to the signal processing device; The energy storage converter is connected to the signal processing device, the filter, and the energy storage battery respectively; the filter of the energy storage converter is connected to the external power grid; The second current transformer is arranged at the AC side of the filter outlet of the energy storage converter, and is used to collect the second current signal at the grid connection point between the AC side of the energy storage converter and the external power grid circuit; The signal processing device includes a first power calculation module, a second power calculation module and a quasi-resonance control module; the first power calculation module receives a voltage signal and a first current signal, and outputs active power and reactive power of the photovoltaic power station after calculation; the resonance control module receives the active power and reactive power output by the first power calculation module, and outputs an active power reference signal and a reactive power reference signal; the second power calculation module receives a second current signal and a voltage signal, and outputs an actual active power signal and an actual reactive power signal of the energy storage converter after calculation; The energy storage converter receives the active power reference signal, reactive power reference signal, actual active power signal, and actual reactive power signal generated by the signal processor, processes them, and then outputs a control signal to the energy storage unit; The energy storage unit outputs or absorbs power at the grid connection point according to the control signal; The quasi-resonant control module includes a quasi-resonant controller and a proportional-integral controller, wherein the quasi-resonant controller is used to filter out the AC component signal that deviates from the resonant angular frequency in the power signal through the AC component signal in the power signal at its resonant angular frequency, and the proportional-integral controller is used to adjust the resonant angular frequency of the quasi-resonant controller; The transfer function of the quasi-resonant control module is: in , s is the Laplace operator, are the amplitude gain, cutoff angular frequency, and resonant angular frequency of the quasi-resonant controller respectively; The first power calculation module includes a first coordinate transformation unit and a first power calculation unit; The first coordinate transformation unit receives the phase of the grid voltage vector and the first current signal to perform Park transformation, calculates and outputs the component of the three-phase grid-connected current output by the photovoltaic system under the d-axis and the q-axis of the two-phase rotating coordinate system, and then outputs the active grid-connected power and reactive grid-connected power of the photovoltaic power station after passing through the first power calculation unit with the component of the grid voltage vector under the dq-axis of the two-phase rotating coordinate system; The second coordinate transformation unit receives the phase of the grid voltage vector and the second current signal to perform Park transformation, calculates and outputs the component of the three-phase grid-connected current output by the energy storage system under the d-axis and the q-axis of the two-phase rotating coordinate system, and then outputs the actual active power signal and the actual reactive power signal of the energy storage converter after passing through the second power calculation unit with the component of the grid voltage vector under the dq-axis of the two-phase rotating coordinate system; The first power calculation module also includes an inversion unit, which is used to receive the active power and reactive power output by the photovoltaic system output by the first power calculation unit and invert them to output an active power reference signal and a reactive power reference signal; The energy storage converter includes a power outer loop module and a current inner loop module, the input end of the power outer loop module is connected to the signal processing device, the output end of the power outer loop module is connected to the input end of the current inner loop module, and the output end of the current inner loop module is connected to the energy storage unit; The power outer loop module receives the active power reference signal, reactive power reference signal, actual active power signal, and actual reactive power signal generated by the signal processing device, and performs difference processing on the active power reference signal and the actual active power signal, and the reactive power reference signal and the actual reactive power signal, respectively, to use them as the active current reference value and the reactive current reference value of the current inner loop module. After receiving the active current reference value and the reactive current reference value, the current inner loop module performs difference processing on the components of the second current signal in the dq coordinate system to use them as the control signal of the energy storage unit.

2. The system for suppressing the impact of subsynchronous oscillation of photovoltaic power station on power grid according to claim 1 is characterized in that: The signal processing device also includes a judgment module, which is used to receive the first current signal collected by the first current transformer and perform a fast Fourier transform to obtain the content of the AC component at different frequencies, and then compare the ratio of the content of the 4Hz-46Hz component to the content of the industrial frequency 50Hz component to determine whether sub-synchronous oscillation occurs in the photovoltaic power station.

3. The system for suppressing the impact of subsynchronous oscillation of photovoltaic power station on power grid according to claim 1 is characterized in that: The energy storage unit includes a plurality of energy storage batteries connected in series.

4. A method for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid, using a system for suppressing the impact of subsynchronous oscillation of a photovoltaic power station on a power grid as claimed in claim 2, characterized in that: The following steps are involved: S1, a signal acquisition device acquires a voltage signal, a first current signal, and a second current signal at a grid connection point; S2. Perform fast Fourier transform on the collected first current signal to obtain the content of the AC component at different frequencies, compare the ratio of the content of the 4Hz-46Hz component to the content of the power frequency 50Hz component, and determine whether subsynchronous oscillation occurs in the photovoltaic power station: If the ratio is greater than or equal to the threshold, the system is considered to have subsynchronous oscillation and enters S3; If the ratio is less than the threshold, return to step S1; S3, performing Park transformation on the collected voltage signal, the first current signal, and the second current signal, and calculating the actual active power signal, the actual reactive power signal, the active grid-connected power, and the reactive grid-connected power through the power calculation formula in the dq coordinate system; S4, using the active grid-connected power and the reactive grid-connected power as signal inputs of the quasi-resonant control module, and the quasi-resonant control module screens out the signal of the oscillation component in the output power of the photovoltaic power station; S5, invert the oscillation component signal screened out by the signal processing device, and collect the second current signal on the input end of the energy storage converter at the same time, calculate it with the voltage signal in step S1, obtain the actual power value on the input end of the energy storage converter, and make a difference between the inverted oscillation component signal and the actual power value, and use the difference as the input value of the power outer loop module; S6, the power outer loop module outputs a current reference value, the current reference value is subtracted from the actual current value at the input end of the energy storage converter, and the difference is used as the input value of the current inner loop module; S7. The output end of the current inner loop module controls the output or absorption of power by the energy storage converter at the photovoltaic power station grid connection point.

5. The method for suppressing the impact of subsynchronous oscillation of photovoltaic power station on power grid according to claim 4 is characterized in that: Step S7 includes the following method: S7-1, the output of the current inner loop module is used as the input signal of space vector pulse width modulation; S7-2, the output signal of the space vector pulse width modulation is used as the input signal of the insulated gate bipolar transistor in the energy storage converter; S7-3. The output signal of the insulated gate bipolar transistor in the energy storage converter controls the output or absorption of power at the grid connection point by the energy storage converter.

6. The method for suppressing the impact of subsynchronous oscillation of photovoltaic power station on power grid according to claim 4, characterized in that: In step S2 the threshold value is 5%.

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