Power grid broadband oscillation damping suppression system

Abstract

The application discloses a power grid broadband oscillation damping suppression system, and relates to the technical field of electric power, wherein the power grid broadband oscillation damping suppression system is connected between a power grid and a new energy power generation unit or between the power grid and a load, and comprises a power frequency series resonance circuit composed of a reactor, a capacitor and a resistor, a zinc oxide lightning arrester, a bypass circuit breaker, a power current transformer and a thyristor conduction circuit; the capacitor is connected in parallel with the resistor after being connected in series with the reactor; the zinc oxide lightning arrester is connected in parallel with the capacitor; the power current transformer is connected in parallel with the bypass circuit breaker after being connected in series with the power frequency series resonance circuit; and the thyristor conduction circuit is connected in parallel with one of the capacitor and the resistor. The application can provide positive damping for power grid broadband oscillation, has the effect of suppressing power grid broadband oscillation, and guarantees reliable and stable operation of the power grid.

Description

Technical Field

[0001] This invention relates to the field of power technology, and more particularly to a damping suppression technology, especially a power grid broadband oscillation damping suppression system. Background Technology

[0002] With the large-scale integration of new energy sources such as photovoltaics and wind power into the power grid, the proportion of high-capacity power electronic equipment such as energy storage converters, photovoltaic inverters, and wind turbine converters in the power grid is constantly increasing. The interaction between power electronic equipment and the power grid in these new power systems, which induces broadband oscillations, has become one of the important issues affecting the safe and stable operation of the power grid.

[0003] Wideband oscillation refers to the dynamic process in which electrical quantities (such as voltage, current, power, etc.) in a power system fluctuate periodically over time due to the interaction between electrical equipment, power electronic equipment and the power grid, and the oscillation frequency varies within a wide range (0.1Hz~7kHz).

[0004] Compared with the oscillations of traditional power systems, broadband oscillations typically exhibit characteristics such as complexity, randomness, dispersion, coupling, and wide-area propagation. Their formation mechanisms are complex and varied, and the combinations of oscillation scenarios are numerous, posing severe challenges to their mechanism modeling, quantitative analysis, risk warning, and active suppression.

[0005] The existence of broadband oscillations seriously threatens the safe and stable operation of the power system. On the one hand, the numerous power quality problems caused by broadband oscillations may increase the overcurrent stress of power electronic equipment, causing power equipment failure or damage, thereby affecting the service life of power equipment. On the other hand, the grid voltage and current exceeding the limit and the torsional vibration problem of rotating equipment in the grid caused by broadband oscillations may cause the power system protection device to operate, thereby causing large-scale power outage accidents.

[0006] Existing research has clearly shown that broadband oscillations that occur during normal system operation can be essentially explained as reciprocating energy exchanges that are excited by specific control factors outside the operating frequency, either mechanically, electromagnetically, or through their coupling. By changing the impedance characteristics of the system or device, the excitation conditions of broadband oscillations can be disrupted, and broadband oscillations can be effectively suppressed.

[0007] Currently, commonly used broadband oscillation suppression measures mainly target fixed risk points with a single oscillation mode, employing different control measures from both the source and grid sides to achieve oscillation suppression. Source-side suppression addresses the performance of the broadband oscillation excitation source itself, modifying equipment dynamic performance by improving equipment topology, optimizing control parameters, and adding additional control strategies to increase the equipment's damping level for broadband oscillations, thus suppressing them. Grid-side suppression involves installing suppression equipment such as series and parallel FACTS (Flexible AC Transmission Systems) devices (e.g., SVC, SVG) in the system network, or using a monitoring + stability control tripping method, sacrificing load loss to suppress broadband oscillations. Currently, all broadband oscillation suppression solutions are costly, requiring significant initial investment, and their suppression effects are not ideal. Summary of the Invention

[0008] The purpose of this invention is to provide a power grid broadband oscillation damping and suppression system to suppress the broadband oscillation phenomenon of the power grid and ensure the reliable and stable operation of the power grid.

[0009] The above-mentioned objectives of the present invention are mainly achieved by the following technical solutions.

[0010] This invention provides a power grid broadband oscillation damping suppression system. This system is connected between the power grid and a new energy power generation unit or between the power grid and a load. The system includes: a power frequency series resonant circuit composed of a reactor, a capacitor, and a resistor; a zinc oxide surge arrester; a bypass circuit breaker; an energy-harvesting current transformer; and a thyristor conduction circuit. The capacitor is connected in series with the reactor and then in parallel with the resistor. The zinc oxide surge arrester is connected in parallel with the capacitor. The energy-harvesting current transformer is connected in series with the power frequency series resonant circuit and then in parallel with the bypass circuit breaker. The thyristor conduction circuit is connected in parallel with one of the capacitor and the resistor.

[0011] Furthermore, the thyristor conduction circuit includes a series-connected anti-parallel pair of thyristors and a current-limiting reactor.

[0012] Furthermore, the thyristor conduction circuit is connected in parallel with the capacitor.

[0013] Furthermore, the thyristor conduction circuit is connected in parallel with the resistor.

[0014] Furthermore, when the power grid operates normally at its rated operating frequency (50Hz), the power frequency reactance of the reactor is equal to the power frequency capacitive reactance of the capacitor, the total power frequency impedance of the power frequency series resonant circuit is zero, and the operating voltage across the power grid is zero when the power grid is operating at the power frequency.

[0015] Furthermore, when a wideband oscillation occurs within a preset range, the output impedance of the power frequency series resonant circuit increases with the increase of the oscillation frequency, and the resistance value is positive.

[0016] Furthermore, when a short-circuit fault occurs in the power grid, the zinc oxide surge arrester rapidly limits the overvoltage through its nonlinear characteristics.

[0017] Furthermore, when a short-circuit fault occurs in the power grid, the anti-parallel thyristor pair is rapidly triggered to conduct through the overvoltage breakdown characteristic of the overturning diode, transferring the short-circuit current from the capacitor to the anti-parallel thyristor pair; the current-limiting reactor suppresses the rate of current rise at the moment of conduction; and the bypass circuit breaker obtains operating power through the energy-harvesting current transformer to achieve closure.

[0018] Furthermore, the bypass circuit breaker disconnects after the power grid short-circuit fault is cleared.

[0019] Furthermore, the power grid broadband oscillation damping suppression system is connected in series with the transmission line, or in series with the collector line of the photovoltaic and wind power generation unit.

[0020] The power grid broadband oscillation damping and suppression system provided in this embodiment of the invention, consisting of a power frequency series resonant circuit composed of reactors, capacitors, and resistors, can dampen the occurrence of broadband oscillations when they occur in the medium and high frequency ranges of the power grid, thereby suppressing the occurrence of broadband oscillations and ensuring the reliable and stable operation of the power grid. When the power grid is operating at the power frequency (50Hz) without broadband oscillations, the total impedance of the power grid broadband oscillation damping and suppression system is zero, and the operating voltage at both ends is also zero, so it does not generate active or reactive power and does not affect the operation of the power grid. When a single-phase grounding or phase-to-phase short-circuit fault occurs in the power grid, the zinc oxide surge arrester can limit the overvoltage caused by the short-circuit fault at both ends of the capacitor. The series-connected anti-parallel thyristor pair and current-limiting reactor can be quickly triggered to conduct, transferring the short-circuit current and protecting the capacitor from damage due to overvoltage. The energy-harvesting current transformer provides the operating power to the bypass circuit breaker, causing the bypass circuit breaker to close. After the bypass circuit breaker closes, the entire power grid broadband oscillation damping and suppression system can be taken out of operation, thereby realizing the short-circuit fault ride-through function of the power grid and achieving the purpose of protecting the circuit. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1This is a schematic diagram of the power frequency series resonant circuit of the power grid broadband oscillation damping and suppression system according to an embodiment of the present invention; Figure 2 The circuit diagram of the power grid broadband oscillation damping and suppression system is shown in the embodiment of the present invention. Figure 1 ; Figure 3 The circuit diagram of the power grid broadband oscillation damping and suppression system is shown in the embodiment of the present invention. Figure 2 ; Figure 4 This is an example diagram showing the installation location of the power grid broadband oscillation damping and suppression system according to an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0023] To suppress broadband oscillations, current common suppression measures primarily target fixed risk points within a single oscillation mode, employing different control measures from both the source and grid sides. Source-side suppression addresses the performance of the broadband oscillation excitation source itself, modifying equipment dynamics by improving equipment topology, optimizing control parameters, and adding additional control strategies to increase the equipment's damping level for broadband oscillations. Grid-side suppression involves installing series and parallel FACTS (Flexible AC Transmission Systems) devices (such as SVCs and SVG) in the system network, or using a monitoring + stability control tripping approach, sacrificing load losses to suppress broadband oscillations. Currently, all broadband oscillation suppression solutions are costly, require significant initial investment, and their suppression effectiveness is not ideal.

[0024] The broadband oscillations under small-disturbance stability (self-excited oscillation problem) in power systems can be described as follows: the impedances of active devices (power electronic converters, generators, etc.) and passive devices (transformers, lines, etc.) in the power system form an RLC resonant network. At specific frequency bands, the active devices exhibit negative resistance characteristics at the resonant frequency, leading to oscillations. In new energy power systems, the grid-connected operation of power electronic equipment relies on a flexible control system (voltage, current, phase-locked loop, and power loop, etc.), causing its output impedance (small-signal impedance transfer function) to exhibit complex frequency domain characteristics. The equivalent impedance of the AC transmission network and the passive impedance of the equipment easily form an LC resonant circuit. Due to the feedback control system, the active devices exhibit negative resistance characteristics over a wider frequency band. Compared to traditional power systems, new energy power systems are more likely to meet the conditions required for oscillation, thus making broadband oscillations more likely. Therefore, a large part of the reason for broadband oscillations is that the passive network LC impedance in the power grid resonates in the mid-to-high frequency bands beyond 50Hz, while the active network exhibits negative resistance characteristics in the mid-to-high frequency bands, causing broadband oscillations in the power grid at these frequencies.

[0025] Based on this, this application provides a power grid broadband oscillation damping and suppression system. This invention constructs a 50Hz resonant circuit using an RLC passive network. When the power grid operates at 50Hz, this resonant circuit is connected in series within the grid, with a total impedance of zero, and will not affect grid operation. The conditions for LC resonance to occur in the mid-to-high frequency bands outside 50Hz are greatly reduced, and the resistance value becomes positive. After this passive network is connected to the power grid, it greatly reduces the probability of LC resonance occurring in the mid-to-high frequency bands and greatly increases the damping (increased positive resistance) after LC oscillation occurs, thereby suppressing the occurrence of broadband oscillations. The meanings of the attached figures are as follows: Figure 1 This is a schematic diagram of the power frequency series resonant circuit of the power grid broadband oscillation damping and suppression system according to an embodiment of the present invention. Figure 2 and Figure 3 The following are circuit diagrams of the power grid broadband oscillation damping and suppression system of the present invention. Figure 4 This is an example diagram showing the installation location of the power grid broadband oscillation damping and suppression system according to an embodiment of the present invention.

[0026] The broadband oscillation damping and suppression system of this invention is connected between the power grid and the new energy power generation unit or between the power grid and the load. For example... Figure 1 , Figure 2 and Figure 3 As shown, the power grid broadband oscillation damping suppression system 10 includes: a power frequency series resonant circuit composed of a reactor 1, a capacitor 2 and a resistor 3, a zinc oxide surge arrester 4, a bypass circuit breaker 7, an energy harvesting current transformer 8 and a thyristor conduction circuit 9. The capacitor 2 is connected in series with the reactor 1 and then in parallel with the resistor 3; The zinc oxide surge arrester 4 is connected in parallel with the capacitor 2; The energy harvesting current transformer 8 is connected in series with the power frequency series resonant circuit and then in parallel with the bypass circuit breaker 7. The thyristor conduction circuit 9 is connected in parallel with one of the capacitor 2 and the resistor 3.

[0027] In the power grid broadband oscillation damping suppression system 10 of the present invention, the power frequency series resonant circuit composed of reactor 1, capacitor 2, and resistor 3 will not have any impact on the power grid at the power frequency of 50Hz. It provides positive damping when the power grid experiences mid- to high-frequency oscillations, thus suppressing broadband oscillations and ensuring the reliable and stable operation of the power grid. If the power grid broadband oscillation damping suppression system 10 based on the power frequency series resonant circuit is installed on a large scale on the collection lines of wind power / photovoltaic and other new energy power plants, and on the feeder lines of large-capacity power electronic loads such as data centers, it can effectively suppress broadband oscillations caused by a high proportion of power electronic devices in the power grid, ensuring the reliable and stable operation of the power grid.

[0028] In practical implementation, the power frequency series resonant circuit is a circuit based on the RLC power frequency series resonant structure, such as... Figure 1 As shown, this power frequency series resonant circuit is installed between the power grid and the load, or between the power grid and the new energy power generation unit. Wherein: The inductive reactance X of reactor 1 L satisfy: X L = ωL (1) The capacitive reactance X of capacitor 2 C satisfy: X C = 1 / ωC (2) Where, ω= 2πf ; f For the power grid operating frequency, f It can be 50Hz.

[0029] By configuring the parameters of the reactance value L of reactor 1 and the capacitance value C of capacitor 2, X can be made... L = -X C The resistance value of resistor 3 is R = 1~10Ω.

[0030] When this power frequency series resonant circuit is connected in series to the power grid, since the power grid's operating frequency is 50Hz, reactor 1 and capacitor 2 resonate in series at the 50Hz frequency, resulting in zero power frequency voltage across them. Regardless of the resistance value of resistor 3, no power frequency current flows through it. That is, this power frequency series resonant circuit does not generate active or reactive power at the 50Hz power grid frequency, and has no impact on the grid's operation at that frequency. However, when the power grid experiences broadband oscillations, currents containing medium and high frequencies flow through this power frequency series resonant circuit. The inductive reactance of reactor 1 increases with frequency, while the capacitive reactance of capacitor 2 decreases with frequency. The total reactance of its LC series circuit increases sharply with frequency, exhibiting reactive characteristics, which can dampen medium and high frequency harmonic currents. Since the resistance value of resistor 3, connected in parallel with the LC series circuit, does not change with frequency, it can dissipate the active power of the medium and high frequency oscillating currents, thus providing damping.

[0031] Since the power frequency series resonant circuit does not have any impact on the power grid at the power frequency of 50Hz, when the power grid oscillates in the medium and high frequency range, its output impedance value is not zero but increases with the increase of the oscillation frequency, and the resistance value is positive. It can consume the power of the medium and high frequency oscillation and play a positive damping effect. Therefore, the power frequency series resonant circuit plays a damping and suppression role for the medium and high frequency active power oscillation between the power supply and the load.

[0032] In some embodiments, such as Figure 2 and Figure 3 The thyristor conduction circuit 9 includes 5 pairs of anti-parallel thyristors connected in series and a current-limiting reactor 6.

[0033] The anti-parallel thyristor pair 5 is triggered to conduct quickly by the overvoltage breakdown characteristic of the overturning diode (BOD), transferring the short-circuit current from capacitor 2 to the anti-parallel thyristor pair 5. The current-limiting reactor 6 connected in series with the anti-parallel thyristor pair 5 can suppress the rate of current rise at the moment the anti-parallel thyristor pair 5 is triggered to conduct.

[0034] In some embodiments, such as Figure 2 The thyristor conduction circuit 9 is connected in parallel with the capacitor 2.

[0035] In some embodiments, such as Figure 3 The thyristor conduction circuit 9 is connected in parallel with the resistor 3, that is, the thyristor conduction circuit 9 is connected in parallel across the reactor 1 and the capacitor 2.

[0036] When a short-circuit fault occurs in the power grid, the short-circuit current flows into capacitor 2, causing a sharp increase in voltage across its terminals. The zinc oxide surge arrester (MOV) 4, with its nonlinear characteristics, can quickly limit the overvoltage. However, due to its limited energy capacity, the MOV 4's overvoltage limiting time is relatively short. As the voltage across capacitor 2 increases, the thyristor anti-parallel pair 5 is rapidly triggered to conduct through the overvoltage breakdown characteristic of the overturning diode (BOD), transferring the short-circuit current from capacitor 2 to the thyristor anti-parallel pair 5. The current-limiting reactor 6, connected in series with the thyristor anti-parallel pair 5, suppresses the rate of current rise at the moment of triggering conduction. The bypass circuit breaker 7 obtains its operating power from the energy-harvesting current transformer 8. Simultaneously with the triggering conduction of the thyristor anti-parallel pair 5, the bypass circuit breaker 7 closes, causing the entire system to shut down, thus providing rapid protection for capacitor 2 and enabling short-circuit fault ride-through.

[0037] In some embodiments, such as Figure 2 and Figure 3 If the power frequency of the power frequency series resonant circuit is equal to the rated operating frequency of the power grid (50Hz), the power frequency reactance of the reactor is equal to the power frequency capacitive reactance of the capacitor, and the power frequency reactance of reactor 1 is equal to the power frequency capacitive reactance of capacitor 2.

[0038] In some embodiments, such as Figure 2 and Figure 3 When the power grid experiences a wide-frequency oscillation within a preset range, the output impedance of the power frequency series resonant circuit increases with the increase of the oscillation frequency, and the resistance value is positive.

[0039] In specific implementation, the above-mentioned preset range is 10Hz~7000Hz, but the present invention is not limited thereto.

[0040] In some embodiments, such as Figure 2 and Figure 3 When the power grid short-circuit fault is cleared, the bypass circuit breaker 7 is disconnected.

[0041] When the short-circuit fault in the power grid is cleared, the power supply provided by the current transformer 8 to the bypass circuit breaker 7 disappears, the bypass circuit breaker 7 opens, and the entire system is put into operation, restoring the operation of the power grid broadband oscillation damping suppression system 10.

[0042] In practical implementation, an example diagram of the installation location of the power grid broadband oscillation damping suppression system 10 in photovoltaic power plants and transmission lines is shown below. Figure 4 As shown.

[0043] The power grid broadband oscillation damping suppression system 10 of the present invention uses primary electrical equipment directly used for the production and use of electrical energy, which is connected to the power grid in series, without secondary automatic control equipment for monitoring, measuring, controlling, regulating and protecting the primary electrical equipment.

[0044] In a 50Hz power grid frequency environment, the broadband oscillation damping and suppression system 10 is connected in series between the photovoltaic or wind power source and the load in the new energy power grid. Specifically, it can be connected in series with a 110kV or 220kV transmission line, or with the 35kV collector line of the photovoltaic or wind power generation unit. Figure 4 As shown, in a typical power supply line where a 35kV collector line of a new energy photovoltaic power generation station is stepped up to 110kV to supply power to the load, the grid broadband oscillation damping suppression system 10 of the present invention can be installed in series on the 35kV collector line of the photovoltaic power generation unit, or in series on the 110kV power supply line with stepped-up output, so as to suppress the medium and high frequency broadband oscillations that may occur between the photovoltaic power station and the load.

[0045] When a single-phase grounding or phase-to-phase short-circuit fault occurs in the power grid, a huge circuit current will flow through the power frequency series resonant circuit, and the voltage U across capacitor 2 will increase. C = I X C A huge short-circuit current will cause U C Exceeding the rated voltage of capacitor 2 can cause insulation breakdown and damage to capacitor 2. The zinc oxide surge arrester 4, bypass circuit breaker 7, energy extraction current transformer 8, and thyristor conduction circuit 9 of the power grid broadband oscillation damping suppression system 10 can prevent this phenomenon from occurring and ensure the power grid short-circuit fault ride-through capability of the power frequency series resonant circuit.

[0046] The present invention provides a power grid broadband oscillation damping suppression system based on a power frequency series resonant circuit, which can achieve positive damping of power transmission power oscillation in the medium and high frequency bands of the power grid caused by a high proportion of power electronic devices in the new energy power grid, effectively suppress the broadband oscillation phenomenon of the power grid, and ensure the reliable and stable operation of the power grid.

[0047] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A broadband power grid oscillation damping and suppression system, characterized in that, The broadband oscillation damping and suppression system for grid connection between the grid and the new energy power generation unit or between the grid and the load includes: a power frequency series resonant circuit composed of reactors, capacitors and resistors, a zinc oxide surge arrester, a bypass circuit breaker, an energy extraction current transformer and a thyristor conduction circuit. The capacitor is connected in series with the reactor and then in parallel with the resistor; The zinc oxide surge arrester is connected in parallel with the capacitor; The energy harvesting current transformer is connected in series with the power frequency series resonant circuit and then in parallel with the bypass circuit breaker. The thyristor conduction circuit is connected in parallel with one of the capacitors and the resistor.

2. The power grid broadband oscillation damping and suppression system according to claim 1, characterized in that, The thyristor conduction circuit includes a series-connected anti-parallel pair of thyristors and a current-limiting reactor.

3. The power grid broadband oscillation damping and suppression system according to claim 1 or 2, characterized in that, The thyristor conduction circuit is connected in parallel with the capacitor.

4. The power grid broadband oscillation damping and suppression system according to claim 1 or 2, characterized in that, The thyristor conduction circuit is connected in parallel with the resistor.

5. The power grid broadband oscillation damping and suppression system as described in claim 1, characterized in that: If the resonant frequency of the power frequency series resonant circuit is equal to the 50Hz rated operating frequency of the power grid, the power frequency reactance of the reactor is equal to the power frequency capacitive reactance of the capacitor, the total power frequency impedance of the power frequency series resonant circuit is zero, and the operating voltage across the power grid is zero when the power grid is running at the power frequency.

6. The power grid broadband oscillation damping and suppression system as described in claim 1, characterized in that: When the power grid experiences a wide-frequency oscillation within a preset range, the output impedance of the power frequency series resonant circuit increases with the increase of the oscillation frequency, and the resistance value is positive.

7. The power grid broadband oscillation damping and suppression system as described in claim 2, characterized in that: When a short-circuit fault occurs in the power grid, the zinc oxide surge arrester quickly limits the overvoltage through its nonlinear characteristics.

8. The power grid broadband oscillation damping and suppression system as described in claim 7, characterized in that: The anti-parallel thyristor pair is rapidly triggered to conduct by the overvoltage breakdown characteristic of the overturning diode, transferring the short-circuit current from the capacitor to the anti-parallel thyristor pair; the current-limiting reactor suppresses the rate of current rise at the moment of conduction; the bypass circuit breaker obtains its operating power through the energy-harvesting current transformer to achieve closure.

9. The power grid broadband oscillation damping and suppression system as described in claim 8, characterized in that: Once the power grid short-circuit fault is cleared, the bypass circuit breaker disconnects.

10. The power grid broadband oscillation damping and suppression system according to claim 1, characterized in that, The broadband oscillation damping suppression system is connected in series with the transmission line or in series with the collector line of the photovoltaic and wind power generation unit.

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