Harmonic control method and control device of power system and storage medium

Abstract

The embodiment of the invention provides a harmonic control method and device of an electric power system and a storage medium, the electric power system comprises a converter for converting direct current into alternating current, and the method comprises the following steps: determining a frequency range of a resonance point of the electric power system; under the condition that the switching frequency of the converter falls into the frequency range, determining a target resonant frequency of the resonant point; determining the type and electrical parameters of a nonlinear device needing to be added by taking the target resonant frequency as an optimization target; and setting the non-linear device in the power system. According to the method, a relatively serious resonance point in a power system is identified, and the vibration frequency of the resonance point of the power system is changed in a mode of increasing a nonlinear device, so that the frequency point of an original resonance source in a circuit is avoided, and the harmonic problem in a specific scene is solved in a low-cost mode; and long-term stable operation of a power system can be ensured.

Description

Harmonic control methods, control devices and storage media for power systems Technical Field

[0001] This invention relates to the field of energy storage power generation, and more specifically to a harmonic control method, control device, and storage medium for a power system. Background Technology

[0002] Power system lines typically contain parasitic inductance and capacitance. These stray parameters interact with the loads in the AC control circuit and the leakage inductance of the transformer, eventually forming a resonant frequency point that is primarily nonlinear. This resonant frequency point interacts with the resonant frequency in the circuit, causing oscillations in the power grid under the same distribution, significantly increasing the amplitude of existing harmonics. Harmonics have a significant impact on the stable operation of devices on the line, especially components with weak harmonic immunity. Prolonged operation in a power grid containing such high harmonic levels can easily lead to failure or even damage.

[0003] To address these challenges, relevant technical solutions (especially in residential or small-scale commercial and industrial distribution networks) tend to employ active power filters (APFs). While this approach offers some harmonic suppression, it suffers from inherent drawbacks such as high cost, large size, and high operating losses. Its widespread adoption faces significant obstacles in practical engineering applications, particularly in cost- and efficiency-sensitive commercial and industrial energy storage scenarios. Therefore, there is an urgent need to develop a low-cost, high-efficiency, and easily implemented harmonic suppression technology. Summary of the Invention

[0004] The purpose of this invention is to provide a harmonic control method, control device, and storage medium for power systems. This method can solve harmonic problems in specific scenarios at low cost and efficiently reduce harmonics in power systems.

[0005] To achieve the above objectives, embodiments of the present invention provide a harmonic control method for a power system, the power system including a converter that converts direct current to alternating current. The method includes: determining the frequency range of the resonant point of the power system; determining a target resonant frequency of the resonant point when the switching frequency of the converter falls within the frequency range; determining the type and electrical parameters of the nonlinear device to be added based on the target resonant frequency as an optimization target; and installing the nonlinear device in the power system.

[0006] On the other hand, this application also proposes a harmonic control device for a power system, the power system including a converter that converts direct current to alternating current, the harmonic control device comprising: a first processing module for determining the frequency range of the resonant point of the power system; a second processing module for determining the target resonant frequency of the resonant point when the switching frequency of the converter falls within the frequency range; an optimization module for determining the type and electrical parameters of the nonlinear device to be added, with the target resonant frequency as the optimization target; and a third processing module for setting the nonlinear device in the power system.

[0007] On the other hand, this application also proposes a machine-readable storage medium storing instructions that, when executed by a processor, configure the processor to perform the aforementioned harmonic control method for the power system.

[0008] This invention provides a harmonic control method for power systems. By identifying severe resonant points in the power system and changing the vibration frequency of these resonant points by adding nonlinear devices, the method avoids the frequency points of the original resonant sources in the circuit. This solves the harmonic problem in a specific scenario at low cost and ensures the long-term stable operation of the power system.

[0009] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0010] The accompanying drawings are provided to further illustrate the embodiments of the present invention and constitute a part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the drawings: Figure 1 is a schematic flowchart of a harmonic control method for a power system according to the present invention; Figure 2 is a schematic flowchart of the overall technical route of the harmonic control method of the present invention; Figure 3 is a schematic diagram of the voltage waveform of the power system before optimization according to the present invention; Figure 4 is a schematic diagram of the harmonic content analysis of the power system before optimization according to the present invention; Figure 5 is a schematic diagram of adding capacitor positions to the power system according to the present invention; Figure 6 is a schematic diagram of adding capacitor and inductor positions to the power system according to the present invention; Figure 7 is a schematic diagram of the voltage waveform of the power system after optimization according to the present invention; Figure 8 is a schematic diagram of the harmonic content analysis of the power system after optimization according to the present invention; Figure 9 is a schematic diagram of the structure of a harmonic control device for a power system according to the present invention. Detailed Implementation

[0011] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0012] It should be noted that the acquisition, transmission, storage, use, and processing of data in the technical solution of this application all comply with relevant laws and regulations. In the embodiments of this application, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this application, and do not imply that the applicant has already used or necessarily used such solutions.

[0013] The applicant has observed that the commonly used solution in the industry for harmonic resonance problems in power systems is to add active power filters. While this solution can suppress harmonics, it has significant inherent drawbacks: high equipment procurement costs, large physical size, and considerable power loss during operation, leading to a reduction in overall system energy efficiency. Especially in user-side or small-scale industrial and commercial power distribution scenarios, cost and space constraints pose numerous challenges to the promotion and application of this solution. Therefore, this invention aims to provide a more cost-effective and engineering-feasible harmonic suppression solution. This method does not rely on general-purpose active filtering equipment, but rather, based on field-measured resonance data, selectively adds passive nonlinear devices (such as capacitors and inductors) at key nodes of the power grid (such as the 400V side) to construct an LC (inductor-capacitor) filter network. The core function of this network is to actively reconstruct the original resonant frequency of the system, safely migrating it from the dangerous frequency band that is harmful to equipment to a preset stable operating range.

[0014] Figure 1 is a schematic flowchart of a harmonic control method 100 for a power system according to the present invention. The power system includes a converter (PCS) that converts DC to AC. The switching frequency of the converter, which turns the power system on and off rapidly, may resonate with the resonant point of the power system and damage the components.

[0015] For example, the power system in this embodiment can be an energy storage power generation system. The following description will focus on a commercial or industrial energy storage power generation system as a specific application scenario. An energy storage power generation system is an important implementation of a power system, typically comprising a primary system and a secondary system. The primary system mainly consists of a DC-side energy storage system and an AC-side grid connection (i.e., the AC grid), with the converter, as the core power conversion device, located between the energy storage system and the AC grid. The secondary system can be equipped with a cooling system to maintain a suitable operating temperature for the batteries and a fire suppression system to prevent thermal runaway-induced deflagration accidents.

[0016] Furthermore, in terms of power structure, commercial and industrial energy storage power generation systems generally operate using direct AC grid connection. For example, when the grid connection circuit also includes residential electricity consumption, the energy storage power generation system needs to operate in parallel with various household appliances (such as televisions and refrigerators). In industrial park scenarios, it often shares the same power line with industrial electrical equipment such as frequency converters, UPS (Uninterruptible Power Supply), welding machines, and motors, typically without additional electrical isolation devices. To improve the current limiting capability of the power system during short-circuit faults, commercial and industrial energy storage systems usually select grid connection transformers with high leakage inductance. This design objectively increases the inductive reactance in the control circuit. This inductive reactance, together with the distributed capacitance in the power system, becomes a key factor affecting the inherent resonant frequency of the control device.

[0017] In terms of energy conversion, the DC power output from the battery needs to be converted into AC power by a converter for grid connection. The converter uses the high-speed switching action of its internal power semiconductor devices to chop the DC power into a pulse-width modulation (PWM) waveform, which is then processed by a filter circuit to become AC power at the power frequency that meets grid connection requirements. However, the rapid switching of the semiconductor devices during the conversion process interacts with the inherent resonant frequency of the downstream filter circuit, resulting in the superposition of high-frequency harmonic components in the output AC waveform. Especially when multiple converters are connected to the same grid connection point, under the influence of parameters such as the distributed capacitance to ground of the power system, circulating currents and oscillations are easily generated in the frequency band below the switching frequency, posing a potential threat to the power quality of the grid.

[0018] In response, the harmonic control method 100 of the present invention can solve the harmonic problem in the above-mentioned scenario at low cost and efficiently reduce the harmonics of the power system. As shown in FIG1, the harmonic control method 100 may include the following steps S110-S140: Step S110, determining the frequency range of the resonant point of the power system.

[0019] Referring to the technical roadmap shown in Figure 2, in engineering practice, a certain energy storage power station frequently experienced control circuit component burnout faults. Disassembly and analysis revealed that the damaged components were concentrated in the front-end filter circuit. To investigate the fault mechanism, this solution will employ a closed-loop method of "test-analysis-design-verification".

[0020] Specifically, converters typically employ high-frequency switching devices, such as IGBTs (Insulated Gate Bipolar Transistors), to achieve DC-AC conversion. Their switching action generates broadband harmonic currents. When these harmonic components resonate with the parasitic parameters of the lines in the energy storage and power generation system (including distributed parasitic inductance and capacitance), they cause abnormal amplification of voltage / current. As shown in Figure 3, the yellow waveform represents the measured voltage waveform in the energy storage and power generation system. It can be seen that the fundamental wave is not smooth but rather jagged, indicating that significant distortion components are superimposed on it. Furthermore, the spectrum diagram shown in Figure 4, obtained through professional spectrum analysis software, clearly identifies the main frequency range of the power system's resonant point as being in the 2.3-3.1 kHz band.

[0021] Step S120: If the switching frequency of the converter falls within the frequency range of the resonant point, determine the target resonant frequency of the resonant point.

[0022] This step requires determining whether the converter's switching frequency falls within the identified resonant frequency range, which is a prerequisite for initiating subsequent harmonic control optimization procedures. In this embodiment, after determining through step S110 that the power system's resonant points are distributed in the 2.3-3.1kHz frequency band, it is necessary to further determine the target resonant frequency for harmonic optimization.

[0023] In the energy storage power station described in this embodiment, the measured switching frequency of the converter is 2.7kHz, which falls precisely within the aforementioned resonant danger range of 2.3-3.1kHz. Spectrum analysis data shows that under this operating condition, the harmonic content in some frequency bands exceeds 20% of the baseline level, leading to a severe deterioration in the stability of the power system and directly causing overheating and burnout of filter circuit components, necessitating the introduction of corresponding optimization methods. Therefore, when the converter switching frequency falls within the resonant frequency range, step S120 determines that harmonic optimization must be performed to suppress resonance and reduce overall harmonic distortion. The determination of the target resonant frequency needs to be carried out within a predefined safe range.

[0024] Specifically, the upper and lower limits of the safe range can be obtained by the following steps S121-S123: Step S121, determine the upper limit of the target resonant frequency based on the switching frequency of the converter.

[0025] The upper limit is set to avoid direct excitation of resonance by the converter switching operation. It should be strongly correlated with the converter's own switching frequency, specifically set as a first set ratio of the switching frequency. In this patent solution, the first set ratio can be determined by the frequency domain avoidance relationship between the switching frequency and the dominant resonant frequency of the power system. The core basis is that the fundamental frequency and its lower harmonic components of the switching frequency must maintain sufficient spacing in the spectrum from the inherent frequency of the LC / LCL resonant circuit to prevent energy coupling and oscillation amplification. Preferably, the first set ratio is preferably in the range of 1 / 3 to 1 / 2, placing it between the fundamental frequency and the second harmonic, forming a natural spectral isolation band. For example, a value of 1 / 2 can balance efficiency and robustness; while a value of 1 / 3 is suitable for high-damping systems, allowing for greater tolerance. Given a switching frequency of 2.7kHz, the upper limit of the target resonant frequency can be set to 1350Hz.

[0026] Step S122: Determine the lower limit of the target resonant frequency based on the reference frequency of the AC power grid.

[0027] The lower limit is set to ensure that the target frequency is far from the power grid frequency and its main low-order harmonics, avoiding interaction with the power grid background harmonics. Its calculation is based on the reference frequency of the AC power grid (usually 50Hz or 60Hz), which can be multiplied by a second set ratio. This second set ratio can be determined by the relationship between the background harmonic spectrum distribution of the AC power grid and the safe frequency band for filter design. It aims to construct a frequency domain isolation band to avoid resonance or amplification effects caused by coupling with the power grid background harmonic energy. Considering the engineering balance between the concentrated harmonic energy area and the system's immunity, its preferred range is 8 to 12. For example, if the ratio is 10, then for a 50Hz power grid, the lower limit is 500Hz.

[0028] Step S123: Determine the target resonant frequency between the lower limit and the upper limit.

[0029] Between the calculated lower limit (e.g., 500Hz) and upper limit (e.g., 1350Hz), a specific frequency value is selected as the final target resonant frequency. This frequency will be the optimization target for subsequent design of nonlinear devices (capacitors or inductors). In this embodiment, based on engineering experience and preliminary calculations, the target resonant frequency can be preferentially set to 1kHz, which is within the aforementioned safe range.

[0030] It is important to note that the initial selection of the target resonant frequency is not static. It serves as a design input for subsequent calculations of the parameters of any additional nonlinear components such as capacitors and inductors. If, during subsequent component selection or system verification, the initially set frequency (e.g., 1kHz) is found to cause unrealistic component parameters or unsatisfactory filtering effects, fine-tuning is permitted within this safe range, for example, adjusting it to 0.9kHz or 1.1kHz. After adjustment, step S120 and subsequent calculations must be repeated until a target resonant frequency that best balances system performance and engineering feasibility is found.

[0031] Step S130: Using the target resonant frequency as the optimization target, determine the type and electrical parameters of the nonlinear devices that need to be added.

[0032] After setting the target resonant frequency, this scheme enters the crucial optimization step. This step aims to translate the theoretical goal into a concrete hardware solution by determining the type of nonlinear device and suitable electrical parameters, providing a quantitative basis for subsequent installation and commissioning.

[0033] Among these, capacitors are the preferred nonlinear devices, with key parameters including capacitance, connection type, rated current, and rated voltage. To improve engineering practicality, this scheme adopts a simplified calculation model, and some parameters can be directly referenced from typical engineering experience data. The design process is as follows: assess the parasitic inductance of the power system lines; estimate the capacitance of the required nonlinear devices; estimate the reactive current that will be generated in the nonlinear devices to select the rated current of the nonlinear devices; select the rated voltage of the nonlinear devices based on the system voltage; and install the selected nonlinear device samples in the unit for testing.

[0034] Specifically, step S130 includes the following steps S131-S133: Step S131, determining the line parasitic inductance value of the power system.

[0035] The applicant discovered that the inherent resonance in the power system's control loop primarily originates from the parasitic inductance of the AC-side transformer in the energy storage system (referring to the inherent, non-ideal, and non-negligible inductance component formed by the current path in the physical structures of the power system, such as conductors, busbars, and connectors; also known as equivalent inductance or leakage inductance). This parameter is an inherent characteristic of the energy storage system and cannot be adjusted. In contrast, since the copper loss at this power level is relatively small compared to the iron loss, the cable inductance, according to manual calculations, is much smaller than the parasitic inductance of the transformer and can therefore be ignored in engineering calculations. Based on this, the capacitance calculation of nonlinear devices can be derived using the parasitic inductance as the basic parameter, combined with the resonant frequency of the original power system's resonance point. In other words, the required capacitance of nonlinear devices can be calculated by multiplying the parasitic inductance by a set coefficient.

[0036] The parasitic inductance of a transformer can be calculated using the following steps 1)-3): 1) Determine the equivalent inductive impedance of each phase of the transformer based on the secondary phase voltage and rated secondary current. The secondary phase voltage refers to the effective voltage across each phase winding on the secondary side (output side) of the transformer. In a three-phase system, this is the line voltage divided by the square root of three (star connection) or equal to the line voltage (delta connection). The rated secondary current refers to the maximum effective current that can continuously flow through the secondary side of the transformer under rated capacity, rated voltage, and specified temperature rise conditions.

[0037] Taking the parameters of a certain power system as an example: the transformer power is 52kVA, and the method adopts a primary side 690V delta connection and a secondary side 400V star connection, with a structure of Dy / n11. Its rated current on the 400V side is 75A, and the short-circuit impedance is 6%. Calculate the equivalent inductive impedance of each phase of the transformer as follows:

[0038] in, For transformer phase reactance; The secondary phase voltage of the transformer is 230V; This is the rated current of the transformer secondary side.

[0039] 2) Determine the total inductive reactance of the power system based on the equivalent inductive impedance of each phase of the transformer and the set coefficient.

[0040] In one specific implementation, the total inductive reactance of the power system lines and the inductive reactance of the components are incorporated into the transformer's inductive reactance multiplied by a predetermined coefficient. Preferably, this predetermined coefficient is determined by the total inductive reactance of the power system lines and the inductive reactance of the components; more preferably, the predetermined coefficient is 1.05-1.15. Here, based on experience, the predetermined coefficient can be set to 1.1 times, thus representing the total inductive reactance of the power system. for: .

[0041] 3) Based on the maximum resonant response frequency of the power system ( =2.7kHz) and total inductive reactance of the system Determine the line parasitic inductance value of the power system. .

[0042] Therefore, in practical implementation, the single-phase inductive reactance can first be calculated based on the transformer's nameplate parameters (such as secondary voltage, rated current, and short-circuit impedance percentage). Then, by introducing an empirical coefficient (usually preferably in the range of 1.05 to 1.15), the distributed inductance of the line and the inductive reactance of other components are taken into consideration, thus obtaining the total inductive reactance of the power system. Finally, by combining this with the highest resonant frequency measured in the power system, the accurate parasitic inductance of the line can be calculated, serving as the basis for subsequent capacitance calculations.

[0043] Step S132: Determine the calculated capacitance value based on the target resonant frequency and the parasitic inductance of the line.

[0044] After obtaining the line parasitic inductance value, the design objective is to shift the inherent resonant point of the power system from the original high-frequency dangerous range to a pre-set, safe low-frequency target value. This process can be based on the LC resonance principle, matching the target resonant frequency with the line parasitic inductance value. Substituting the values ​​into the formula, the theoretically required filter capacitor value can be calculated. Specifically, the highest resonant frequency of the original power system is 2.7kHz, and the target resonant frequency is... Since the frequency is 1kHz, we can temporarily only add a capacitor. We can decide whether to add an inductor later based on the calculation results. Then, according to the following formula... Calculate the required increase in computing capacity. .

[0045] Step S133: If the calculated capacitance value is within the set range of a standard capacitor, then the standard capacitor is determined as the target capacitor.

[0046] After calculating the theoretical capacitance, the design process requires determining and selecting the target capacitor. The core here is to determine the degree of matching between the calculated capacitance and the standard capacitor series by setting a range. This range is typically defined as a combination of industry standard series and reasonable engineering margin, using internationally recognized standard capacitance values ​​as a reference. To balance technical specifications and economic costs, the solution also introduces the concept of "engineering margin," an allowable parameter fluctuation range to address the idealization of theoretical calculations and the discrepancies in actual device parameters. For example, it allows for a ±5% or ±5% difference between the calculated capacitance and the standard value. The deviation.

[0047] For example, suppose the calculated capacitance value is: Although it's not a standard capacitance value, it is within the standard capacitance range. ±5 Within this tolerance range, the standard capacitor can be used directly. In other words, if the calculated capacitance value falls within this allowable tolerance band, the standard capacitor can be directly selected as the target capacitor. This is the preferred option because it is the simplest and most direct, and therefore the target capacitor can be directly set as... However, if this margin is exceeded, the design will consider increasing the inductance to keep the circuit resonant frequency near the set value.

[0048] In addition, electrical parameters may also include rated current and rated voltage. The rated current of the target capacitor can be determined based on the reactive current of the target capacitor under the power frequency voltage of the power system (also known as the effective value of the power frequency voltage) and the reactive current under harmonic voltage (also known as the effective value of the harmonic voltage or the effective value of the resonant voltage). That is, this reactive current mainly consists of two parts: the reactive current generated under the power frequency voltage and the reactive current generated by the harmonic voltage. Adding these two together yields the total reactive current for increasing the capacitor. Since the reactive current in other frequency bands is relatively small, it can be ignored here.

[0049] In this embodiment, the effective value of the reactive current generated by the power frequency voltage across the added capacitor is: .in, The power frequency voltage frequency; To increase the capacitance value; This is the effective value of the power frequency voltage. When calculating the reactive current generated by the resonant voltage in the example, the effective value of the resonant voltage needs to be measured. The harmonic voltage can be tested on-site using an oscilloscope, and the effective value of the resonant voltage can be determined using the oscilloscope's RMS calculation function. On-site testing showed that the maximum effective value was 30V. The effective value of the reactive current generated by the resonant voltage across the added capacitor is: .in, The resonant voltage frequency is 2.7kHz, which is chosen here. To increase the capacitance value; Let's consider the effective value of the resonant voltage (over a larger area). Then, the calculated total reactive current from the added capacitor is: This method selects a capacitor with a rated current of 55A (the minimum rated current greater than 39.2A among standard capacitor components), which can support an operating ambient temperature of 60℃. The rated voltage of the target capacitor is determined based on the rated reference voltage of the power system, superimposed harmonics, and overvoltages. For example, if the line voltage of the power system is around 400V, considering the superposition of harmonics and system overvoltages, and the possibility of delta connection to the system, a capacitor with a rated voltage of 690V RMS can be selected. The operating temperature range is -40℃ to 85℃, the allowable overvoltage is 1.2 times the rated voltage for 1 minute, the peak current is 1900A, and the internal resistance is 1mΩ.

[0050] Additionally, if the calculated capacitance value differs from all standard values ​​beyond the margin range, an alternative strategy needs to be activated, i.e., a standard capacitor with a smaller but similar capacitance value is used as the target capacitor. Step S130 may further include the following steps S134-S135: Step S134: If the calculated capacitance value is not within the set range of any standard capacitor, select the nearest standard capacitor with a lower calculated capacitance value as the target capacitor.

[0051] In other words, when the deviation between the theoretically calculated capacitance value and all standard capacitance values ​​exceeds the preset engineering margin (such as ±5% or ±5%)... If the target capacitor cannot be achieved through direct replacement, the decision-making process switches to the LC combination mode. In this mode, the nearest neighbor standard capacitor with a capacitance value lower than the calculated capacitance value is selected as the target capacitor. This preference for a slightly lower capacitance value aims to reserve adjustment space for subsequent series inductors and avoid power system detuning.

[0052] For example, suppose the calculated capacitance value is: And it's not a standard capacitance value. However, the nearest standard capacitor is 50. and 80 Both of these options exceeded the allowable range; therefore, the selected capacitor value was... Simultaneously, another nonlinear device—an inductor—needs to be added to the circuit, together forming an LC filter network. The resonant frequency of this LC combination can be precisely calibrated by adjusting the inductor value, ensuring it ultimately falls near the target value. Alternatively, if simply adding a capacitor fails to achieve the desired reduction in resonance, or if a suitable capacitor is unavailable, a combined LC suppression strategy can be employed, which involves connecting an inductor in series with the circuit.

[0053] Step S135: Determine the inductance value of the inductor based on the target resonant frequency and the capacitance value of the target capacitor.

[0054] After determining the target capacitor, the precise value of the required series inductor can be calculated in reverse using the LC resonance formula, based on the preset target resonant frequency and the actual capacitance value of the target capacitor. The principle is that by adjusting the inductor value, the deviation between the standard capacitor value and the theoretical value can be compensated, thereby precisely calibrating the resonant frequency of the entire LC circuit near the set value, thus ensuring the final filtering effect. For example, it can be based on the target resonant frequency... (e.g., 1kHz), according to the formula It can be calculated The inductance is 0.507mH, since the original circuit inductance is Calculate the required increase in inductance value. That is, the inductor that needs to be added here. It is 0.135mH.

[0055] Additionally, it's important to note that a larger inductance value results in greater heat generation and higher power consumption; therefore, the required increase in inductance should generally not exceed 0.5mH. Since the inductance value is inversely proportional to the square of the resonant frequency, when the calculated inductance value is large, the set resonant frequency in the above formula can be changed. (For example, changing from 1kHz to 1.2kHz), increasing this frequency will decrease the inductance value. Conversely, if you want to increase the inductance value, you need to lower the resonant frequency (for example, from 1kHz to 0.9kHz), and the required increase in inductance value will be... This will be increased accordingly. This mechanism gives the design scheme the ability to flexibly balance performance and feasibility.

[0056] Step S140: Install nonlinear devices in the power system.

[0057] This step involves the specific deployment of the selected nonlinear devices. Its main task is to add nonlinear devices such as capacitors and / or inductors at designated nodes in the power system (generally nodes with severe resonance), according to the determined types and electrical parameters. The core objective is to efficiently and stably shift the resonant points, which exist in the high-frequency danger zone (e.g., 2.3kHz-3.1kHz), to a preset low-frequency safety zone (e.g., 1kHz) by changing the system's impedance-frequency characteristics. Standardized physical connections are necessary to ensure that all previous architectural designs and numerical calculations can achieve their maximum value.

[0058] For example, the power system may include a three-phase circuit, as shown in Figures 5-6. The three-phase circuit is located between the energy storage system and the AC grid, and the converter T can convert the DC power of the energy storage system into AC power for transmission to the AC grid. Then step S140 may include a sub-step S141 of connecting a capacitor and, preferably, a sub-step S142 of connecting an inductor.

[0059] Step S141: Connect the capacitor in the nonlinear device to the three-phase circuit via a star connection.

[0060] In a three-phase circuit, capacitors typically need to be connected in parallel across all three phases, usually in star or delta configurations. In a star connection, each terminal of the three capacitors is connected to each phase of the three-phase circuit, with the other ends of each capacitor connected together. In a delta connection, the two ends of each capacitor are daisy-chained, and the daisy-chain junctions are then connected to each phase of the three-phase circuit.

[0061] In one specific implementation, this solution preferentially recommends a star connection for the capacitor components, as shown in Figure 5: three capacitors are set, each consisting of a capacitor C and a parallel resistor R, along with a three-phase switch QF. One end of each of the three capacitors needs to be connected to a phase line of the three-phase circuit, and the other ends of each capacitor are connected together to effectively suppress common-mode and differential-mode harmonics in the three-phase circuit. The core advantage of this connection method lies in its voltage equalization characteristic: the voltage across each capacitor is the system phase voltage. Compared to the delta connection method (which withstands line voltage), the rated voltage requirement for the capacitors is lower, helping to reduce costs and improve safety. Simultaneously, this connection method can effectively filter out specific harmonics in the three-phase circuit and balance unbalanced currents between the three phases.

[0062] Step S142: The inductor in the nonlinear device is connected to the three-phase circuit in series.

[0063] Furthermore, when employing a combined LC suppression strategy, an inductor needs to be added to the power system. The inductor value can be determined based on the capacitance value and the circuit harmonic frequency, which will not be elaborated here. Specifically, the location for adding the inductor is shown in Figure 6, that is, in each phase of the three-phase circuit, a certain node of that phase is disconnected, and the two ends of the inductor are connected to the two disconnected endpoints respectively. The main function of the series inductor includes tuning, that is, together with the capacitor, determining the final resonant frequency of the system. By adding appropriate inductive reactance, the deviation between the standard capacitor value and the theoretically calculated value can be compensated, ensuring that the resonant frequency of the LC combination can reach the preset optimization target.

[0064] In another embodiment, after the initial installation of the nonlinear devices is completed, the scheme can also enter a closed-loop stage of verification, feedback, and optimization. Then, after step S140, the harmonic control method 100 of the present invention may further include: step S151, performing harmonic testing on the power system.

[0065] The core of this stage lies in calibrating the preliminary design using measured data to ensure a high degree of consistency between the theoretical model and the actual system, ultimately achieving the goal of long-term, stable, and economical harmonic suppression. The testing process and key indicators include electrical parameter monitoring, thermal stability testing, and harmonic spectrum analysis. Electrical parameter monitoring can monitor the steady-state current and transient inrush current of the capacitor in real time during operation; thermal stability testing can run the capacitor continuously for more than 2 hours under two typical operating conditions—charging and discharging—under full load conditions of the power system, while simultaneously recording the long-term operating temperature of the capacitor; harmonic spectrum analysis uses specialized software to perform Fourier transform on the voltage / current waveforms of the power system (as shown in Figure 7), generating the spectrum diagram shown in Figure 8 for comparison before and after.

[0066] The actual test results met the design expectations. Electrical parameter monitoring showed that the reactive current during stable operation of the capacitor was approximately 30A, which is lower than the theoretically calculated value. The inventors believe this is because, to ensure the robustness of the design, the theoretical calculation used the maximum harmonic voltage under the most extreme operating conditions as the input. The harmonic voltage during normal operation of the power system is lower than this extreme value, which fully demonstrates that the design has reserved sufficient safety margin. Thermal test data showed that the long-term stable operating temperature of the capacitor body was approximately 40℃. Under the condition that the ambient temperature inside the cabinet was 34℃, its temperature rise was only 6℃, demonstrating excellent thermal management efficiency. Furthermore, as can be seen from the yellow voltage waveform of the power system in Figure 7, the sawtooth shape has been significantly eliminated, indicating that the resonance of the power system has been essentially eliminated. Harmonic spectrum analysis in Figure 8 shows that after the capacitor was connected to the system, high-frequency harmonics were significantly reduced. While the low-frequency harmonics near the system's natural frequency (1kHz) increased slightly after adding the capacitor, the overall resonance was significantly reduced.

[0067] However, if the harmonic test fails, meaning the harmonic content of the power system fails to be reduced below the allowable standard, it indicates a deviation in the initial model. Therefore, referring to the technical roadmap in Figure 2, this solution also provides the following two strategies for iterative optimization: step S152 and / or step S153, one or a combination thereof can be selected based on the actual situation.

[0068] Step S152: Adjust the setting coefficient, and based on the adjusted setting coefficient, determine the calculated capacitance value of the capacitor accordingly and set the capacitor in the power system.

[0069] This strategy corrects the parasitic inductance value of the line in step S131, focusing on correcting the estimated leakage inductance of the power system. As mentioned earlier, the total inductive reactance of the power system is determined based on the equivalent inductive impedance of each phase of the transformer and a set factor. If the initial set factor is not chosen appropriately, it will lead to deviations in the subsequent capacitance calculations. Therefore, the set factor needs to be adjusted appropriately. For example, it can be fine-tuned within the set factor range (1.05-1.15). For example, the set factor can be lowered from 1.1 to 1.05. After adjustment, the total inductive reactance of the system needs to be recalculated, and then the calculated capacitance value needs to be updated. This process is equivalent to recalibrating and optimizing the software parameters of the power system without changing any physical wiring. Subsequently, the capacitors in the power system need to be reselected and replaced based on the new calculated capacitance value.

[0070] Step S153: Adjust the target resonant frequency between the lower and upper limits based on the adjustment coefficient, and determine the type and electrical parameters of the nonlinear device to be added accordingly based on the adjusted target resonant frequency, and set the nonlinear device in the power system.

[0071] This strategy directly optimizes the target resonant frequency in step S123, specifically within a preset upper and lower limit range (500-1350 Hz), by introducing an adjustment coefficient to fine-tune the target resonant frequency. This adjustment coefficient is determined through the dynamic matching relationship between the linear response range of the nonlinear device and the resonant frequency of the power system. Its core purpose is to ensure that the system operating point avoids the saturation region, threshold nonlinear region, or impedance abrupt change region of the nonlinear device, thereby ensuring that the device maintains stable and controllable absorption or clamping capability under resonant energy impact. Preferably, the adjustment coefficient ranges from 0.9 to 1.1. Subsequently, based on this new, adjusted target resonant frequency, step S130 is re-executed to determine the type and electrical parameters of the nonlinear device to be added, and then it is reinstalled. For example, in the above example, the resonant frequency is set at 1 kHz, and the switching frequency is 2.7 kHz. If the calculated nonlinear device is unsuitable, the resonant frequency can be appropriately adjusted to 0.9 kHz or 1.1 kHz. The added nonlinear device is then recalculated according to the above scheme.

[0072] In practical engineering, these two strategies often form an efficient debugging loop. For example, strategy S152 can be tried first. If the effect is still not ideal, strategy S153 can be activated, or both parameters can be adjusted simultaneously to quickly converge to the optimal solution. This invention does not limit this.

[0073] In summary, this invention provides a method for suppressing high-frequency resonance in power systems. By identifying severe resonance points in the power system and altering their vibration frequencies by adding nonlinear devices, it avoids the original resonant source frequencies in the circuit, solving harmonic problems in specific scenarios at low cost and ensuring the long-term stable operation of the power system. Its core lies in constructing a closed-loop technical framework encompassing problem diagnosis, target setting, parameter design, and verification optimization. The core innovation of this harmonic control scheme lies in its "closed-loop adaptive" capability. It continuously optimizes system performance through an iterative cycle of "design-deployment-testing-adjustment." This scheme effectively balances the four core requirements of "suppression effect," "modification cost," "operating losses," and "long-term stability," making it particularly suitable for application in cost-sensitive, high-reliability large-scale industrial scenarios.

[0074] The applicant discovered that while there are general-purpose active power filters with adaptive capabilities on the market, they are expensive and consume a lot of energy, typically only suitable for special scenarios with complex and variable harmonics and where cost is not a major concern. In contrast, this invention achieves the same objective in a more economical and reliable manner through a targeted resonant point reconstruction strategy. In other words, the beneficial effect of this solution is to achieve an optimal balance between technical performance and economy, specifically including: 1. This application reduces grid resonance content at a lower cost by using nonlinear devices such as passive capacitors and inductors to construct the filter network, and prioritizing the use of standard industrial products, thereby achieving effective harmonic suppression while keeping costs far below those of active filtering solutions.

[0075] 2. While solving the resonance problem, this application can also minimize power consumption. This is because the nonlinear device in this application does not generate significant active power loss, which helps to reduce the overall energy consumption of the power system.

[0076] 3. This application ensures that the system can operate stably for a long time after the modification, and the installation and maintenance process is simple, which significantly improves the engineering applicability and promotion value of the solution.

[0077] On the other hand, Figure 9 is a schematic diagram of a harmonic control device for a power system according to the present invention. The harmonic control device 200 for a power system according to the present invention includes: a first processing module 210, used to determine the frequency range of the resonant point of the power system; a second processing module 220, used to determine the target resonant frequency of the resonant point when the switching frequency of the converter falls within the frequency range; an optimization module 230, used to determine the type and electrical parameters of the nonlinear device to be added with the target resonant frequency as the optimization target; and a third processing module 240, used to set the nonlinear device in the power system.

[0078] The harmonic control device of the present invention identifies the more severe resonance points in the power system and changes the vibration frequency of the resonance points by adding nonlinear devices, thereby avoiding the frequency points of the original resonance sources in the circuit. It solves the harmonic problem in a specific scenario in a low-cost manner and can ensure the long-term stable operation of the power system.

[0079] Other beneficial effects of the harmonic control device 200 for the power system of the present invention can be found in the above description of the harmonic control method 100 for the power system, and will not be repeated here.

[0080] This invention also provides a machine-readable storage medium storing instructions for causing a machine to execute: the harmonic control method 100 for a power system as described above.

[0081] This invention provides a processor for running a program, wherein the program is executed to perform: the harmonic control method 100 for a power system as described above.

[0082] The harmonic control device 200 of the power system includes a processor and a memory. Each module in the device 200 is stored in the memory as a program unit, and the processor executes the program units stored in the memory to realize the corresponding functions.

[0083] The processor contains a core, which retrieves the corresponding program units from memory. One or more cores can be configured, and adjusting core parameters effectively reduces power harmonics.

[0084] The memory may include non-permanent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0085] This invention provides a device including a processor, a memory, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the various steps of the harmonic control method 100. The device described herein may be a server, PC, PAD, mobile phone, etc.

[0086] This application also provides a computer program product that, when executed on a data processing device, is adapted to perform a program that initializes various steps such as those of the harmonic control method 100.

[0087] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0088] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more flowchart illustrations and / or one or more block diagrams.

[0089] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0090] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0091] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0092] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0093] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0094] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0095] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A harmonic control method for a power system, characterized in that, The power system includes a converter that converts direct current to alternating current. The harmonic control method includes: determining the frequency range of the resonant point of the power system; determining a target resonant frequency for the resonant point when the switching frequency of the converter falls within the frequency range; determining the type and electrical parameters of the nonlinear device to be added based on the target resonant frequency as an optimization target; and installing the nonlinear device in the power system.

2. The harmonic control method according to claim 1, characterized in that, The nonlinear device includes a capacitor, and the electrical parameters include capacitance value and connection type. Determining the type and electrical parameters of the nonlinear device to be added includes: determining the line parasitic inductance value of the power system; determining the calculated capacitance value of the capacitor based on the target resonant frequency and the line parasitic inductance value; and determining the standard capacitor as the target capacitor if the calculated capacitance value is within a set range of a standard capacitor.

3. The harmonic control method according to claim 2, characterized in that, The nonlinear device also includes an inductor. Determining the type and electrical parameters of the nonlinear device to be added includes: selecting the nearest standard capacitor with a lower calculated capacitance value as the target capacitor when the calculated capacitance value is not within the set range of any standard capacitor; and determining the inductance value of the inductor based on the target resonant frequency and the capacitance value of the target capacitor.

4. The harmonic control method according to claim 2 or 3, characterized in that, The electrical parameters also include rated current and rated voltage. The rated current of the target capacitor is determined based on the reactive current of the target capacitor under the power frequency voltage and the reactive current under the harmonic voltage of the power system. The rated voltage of the target capacitor is determined based on the rated reference voltage of the power system, superimposed harmonics, and overvoltage.

5. The harmonic control method according to claim 2, characterized in that, The determination of the parasitic line inductance value of the power system includes: determining the equivalent inductive impedance of each phase of the transformer based on the secondary phase voltage and secondary rated current of the transformer in the power system; determining the total inductive reactance of the power system based on the equivalent inductive impedance of each phase of the transformer and a set coefficient, preferably the set coefficient is determined by the total line inductance of the power system and the inductive reactance of the components, more preferably the set coefficient is 1.05-1.15; and determining the parasitic line inductance value of the power system based on the maximum resonant response frequency of the power system and the total system inductance.

6. The harmonic control method according to claim 5, characterized in that, After the nonlinear device is installed in the power system, the harmonic control method further includes: performing a harmonic test on the power system; adjusting the set coefficient if the harmonic test fails; and determining the calculated capacitance value of the capacitor based on the adjusted set coefficient and installing the capacitor in the power system accordingly.

7. The harmonic control method according to claim 1, characterized in that, The power system is an energy storage power generation system, including a DC-side energy storage system and an AC-side AC grid. The converter is located between the energy storage system and the AC grid. Determining the target resonant frequency of the resonant point includes: determining an upper limit of the target resonant frequency based on the switching frequency of the converter; determining a lower limit of the target resonant frequency based on the reference frequency of the AC grid; and determining the target resonant frequency between the lower limit and the upper limit. The upper limit is a first set ratio of the switching frequency of the converter, and the lower limit is a second set ratio of the reference frequency of the AC grid. Preferably, the first set ratio is determined by the frequency domain avoidance relationship between the switching frequency and the dominant resonant frequency of the power system, and the second set ratio is determined by the avoidance relationship between the background harmonic spectrum distribution of the AC grid and the safe frequency band of the filter design. More preferably, the first set ratio is 1 / 3-1 / 2, and the second set ratio is 8-12.

8. The harmonic control method according to claim 7, characterized in that, After the nonlinear device is installed in the power system, the harmonic control method further includes: performing a harmonic test on the power system; if the harmonic test fails, adjusting the target resonant frequency between the lower limit and the upper limit based on an adjustment coefficient, preferably the adjustment coefficient is determined by the dynamic matching relationship between the linear response range of the nonlinear device and the resonant frequency of the power system; more preferably the adjustment coefficient is 0.9-1.1; and based on the adjusted target resonant frequency, determining the type and electrical parameters of the nonlinear device to be added accordingly and installing the nonlinear device in the power system.

9. The harmonic control method according to claim 1, characterized in that, The power system includes a three-phase circuit. The step of setting the nonlinear device in the power system includes: connecting the capacitors of the nonlinear device to the three-phase circuit in a star connection manner, including: connecting one end of each of the three capacitors to the phase line of the three-phase circuit respectively, and connecting the other end of each capacitor to each other. Preferably, the step of setting the nonlinear device in the power system further includes: connecting the inductors of the nonlinear device to the three-phase circuit in a series connection manner.

10. A harmonic control device for a power system, the power system comprising a converter that converts direct current to alternating current, characterized in that, The harmonic control device includes: a first processing module for determining the frequency range of the resonant point of the power system; a second processing module for determining the target resonant frequency of the resonant point when the switching frequency of the converter falls within the frequency range; an optimization module for determining the type and electrical parameters of the nonlinear device to be added, with the target resonant frequency as the optimization target; and a third processing module for setting the nonlinear device in the power system.

11. A machine-readable storage medium storing instructions thereon, characterized in that, When executed by a processor, the instruction causes the processor to be configured to perform the harmonic control method for the power system as described in any one of claims 1 to 9.

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