Rlc damping device and method for suppressing non-power frequency oscillations of a power system

Abstract

The application discloses an RLC damping circuit and device for inhibiting non-power frequency oscillation of a power system, which is characterized in that a power frequency series circuit is composed of a reactor L and a capacitor C in series, and a damping resistor R is connected in parallel to the power frequency series circuit composed of the reactor L and the capacitor C. The RLC damping circuit and device are connected in series in a transmission channel in which non-power frequency resonance occurs, so as to damp and inhibit non-power frequency oscillation.

Description

Technical Field

[0001] This application relates to the electrical engineering field, specifically the power system sub-discipline, and particularly to techniques for suppressing non-power frequency oscillations in power systems. Background Technology

[0002] With the increasing penetration of new energy sources and the widespread application of new power electronic devices, non-power frequency oscillations in power systems are becoming more frequent: low-frequency oscillations near the power frequency and wide-frequency oscillations between 100Hz and 10000Hz frequently occur in power grids at all levels. These oscillations are characterized by sudden onset and cover the entire frequency band except for the power frequency, with the oscillation frequency also drifting during the oscillation process. How to suppress non-power frequency oscillations in power systems has become a global problem, and there is still no effective solution.

[0003] Non-power frequency oscillations in new power systems pose serious safety hazards to the power system: they can ultimately lead to the disconnection of new energy power generation devices from the grid, abnormal operation of power electronic application equipment leading to a decline in product quality or scrapping, and in severe cases, power system collapse, affecting social security.

[0004] There are two main ways to suppress non-power frequency oscillations: (1) Non-power frequency oscillations caused by integer harmonics can be suppressed by installing parallel filters at the source of the harmonics. Various passive power filter circuits are widely used. However, in filter design, the lower the harmonic order, the higher the design difficulty and the larger the filter installation capacity. For low-frequency interharmonics such as 25Hz or 75Hz that are close to the power frequency, it is not possible to suppress them by designing and installing parallel filters. (2) Install damping devices. Theoretically, a resistor device can be connected in series in the power transmission channel for damping, but the series connection of the damping resistor will consume a large amount of power frequency active power, which is not feasible in practice. Summary of the Invention

[0005] This application addresses various non-power frequency oscillations induced by high-proportion renewable energy device integration into the power system and high-proportion power electronic device applications, proposing a method... Figure 1 The RLC damping circuit and device shown are configured to connect the RLC damping device in series in a power transmission channel where non-power frequency oscillations occur, thereby damping and suppressing these oscillations. The specific details of the invention are as follows:

[0006] 1. An RLC damping device and method for suppressing non-power frequency oscillations in a power system, characterized by using a reactor L and a capacitor C connected in series to form a power frequency resonant circuit, i.e., designing the LC series resonant frequency to be the power frequency, and connecting a damping resistor R in parallel across the series power frequency resonant circuit formed by the reactor L and the capacitor C to form an RLC damping device; connecting the RLC damping device in series in a power transmission circuit where non-power frequency oscillations occur to dampen the non-power frequency oscillations.

[0007] 2. The RLC damping device and method according to the present invention is characterized in that: in order to compensate for the parameter drift of inductance L and capacitance C caused by temperature effects during operation, which causes the LC resonant circuit to deviate from the power frequency resonant frequency, a reactor with adjustable inductance L is designed and selected; by detecting the power frequency voltage across the LC resonant circuit or the power frequency current of the resistor R branch, the inductance L of the reactor is automatically adjusted so that the LC resonant frequency is dynamically maintained at the power frequency.

[0008] In this application, the inductance L and capacitance C must satisfy the following conditions.

[0009]

[0010] Where f s The power frequency is: Therefore, the advantages of this RLC damping device are: (1) At the power frequency, its equivalent impedance is theoretically zero, which can minimize the power frequency loss of the device. At non-power frequency, it can effectively exhibit resistance characteristics, realize the consumption of non-power frequency energy, and thus dampen and suppress non-power frequency oscillations. (2) It can dampen non-power frequency oscillations across the entire frequency band and effectively suppress frequency drift oscillations.

[0011] Factors such as heat generation in the reactor and capacitor during operation, as well as ambient temperature, can cause drift in the parameters of inductance L and capacitance C, leading to a deviation of the LC resonant frequency from the power frequency and increasing device losses. Therefore, in design and use, reactors with adjustable inductance L can be selected; the power frequency voltage U across the LC resonant circuit can be monitored. LC，50Hz Or the power frequency current I flowing through the resistor R，50hz Once U LC，50 or I R，50hz A deviation from the minimum value indicates a drift in inductance L and capacitance C. In this case, the inductance L can be fine-tuned to dynamically maintain the LC resonant frequency at the power frequency. This is to prevent the power frequency loss of the parallel resistor R from increasing after the LC resonant frequency deviates from the power frequency.

[0012] The theoretical minimum power frequency voltage across the LC circuit is:

[0013]

[0014] The minimum power frequency current of the parallel resistor R is:

[0015]

[0016] In formulas (2) and (3):

[0017] I is the power frequency current in the power transmission channel;

[0018] r L It is the internal resistance of the reactor;

[0019] r o It is the internal resistance of the capacitor;

[0020] R is the resistance value of the resistor. Attached Figure Description

[0021] Figure 1 It is a circuit that dampens and suppresses non-power frequency oscillations;

[0022] Figure 2 This is an example of damping non-power frequency oscillations in the transmission channel of a photovoltaic power station. Detailed Implementation

[0023] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the technical principles of this application will be further explained in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Taking a power system with a power frequency of 50Hz as an example, in the attached Figure 1 In this design, the reactor L and capacitor C are connected in series, and the inductance L and capacitance C are selected to meet the following conditions:

[0025]

[0026] The damping resistor R is attached as follows. Figure 1 The circuit shown is connected in parallel across the two ends of the LC series circuit to form an RLC damping circuit. The parameters R, L, C and their capacity can be designed and selected according to the non-power frequency oscillation frequency and current magnitude under the constraint conditions (formula (4)). The specific values ​​can be determined by analyzing the negative damping characteristic parameters of the internal components of the power electronic device and confirmed by simulation calculation. The rated voltage and rated current of the device's R, L, and C can be determined according to the specific engineering design.

[0027] Taking the suppression of non-power frequency oscillations in the output channel of a photovoltaic power plant as an example, (see attached) Figure 1 The RLC damping device shown is attached Figure 2 By connecting the photovoltaic power station and the system in series to the AC transmission line shown, the non-power frequency oscillations between the photovoltaic power station and the system can be damped and suppressed.

[0028] Example 1 of parameter selection:

[0029] The design parameters are L = 200mH, C = 50.66μF, and R = 100Ω. According to... Figure 1 The circuit has an equivalent impedance of 0 at 50Hz; an equivalent impedance of 47.04-j49.91Ω at 25Hz; an equivalent impedance of 21.52+j41.1Ω at 75Hz; and an equivalent resistance greater than 90Ω and an equivalent reactance less than 30Ω in the frequency band above 250Hz.

[0030] Example 2 of parameter selection:

[0031] The design parameters are L = 300mH, C = 33.77373μF, and R = 100Ω. According to... Figure 1 The circuit has an equivalent impedance of 0 at 50Hz; an equivalent impedance of 66.65-j47.15Ω at 25Hz; an equivalent impedance of 38.15+j48.58Ω at 75Hz; and an equivalent resistance greater than 95Ω and an equivalent reactance less than 21Ω in the frequency band above 250Hz.

[0032] This RLC damping device can be used to suppress non-power frequency oscillations occurring in wind power generation, energy storage, and power electronic applications, as described in this embodiment. It can also be used to suppress low-frequency oscillations occurring in traditional power systems.

Claims

1. An RLC damping device and method for suppressing non-power frequency oscillations in a power system, characterized by using electricity The reactor L and capacitor C are connected in series to form a power frequency resonant circuit. The design makes the LC series resonant frequency the power frequency, and a damping resistor R is connected in parallel across the series power frequency resonant circuit formed by the reactor L and capacitor C to form an RLC damping device. The RLC damping device is connected in series in the power transmission circuit where non-power frequency oscillation occurs to dampen the non-power frequency oscillation.

2. The RLC damping device and method according to claim 1, characterized in that: To compensate for the parameter drift of inductance L and capacitance C caused by temperature effects during operation, which causes the LC resonant circuit to deviate from the power frequency resonant frequency, an adjustable inductance L reactor is designed and selected. By detecting the power frequency voltage across the LC resonant circuit or the power frequency current in the resistor R branch, the inductance L of the reactor is automatically adjusted so that the LC resonant frequency is dynamically maintained at the power frequency.

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