A hybrid power filtering method

Abstract

The application relates to a hybrid power filtering method, belonging to the filtering field. The existing scheme combining a passive filter and an active filter is prone to causing damage to the passive filter and the active filter. Load current and grid-side current in a power system are collected simultaneously to extract harmonic components; each harmonic current is obtained, compensation current and total harmonic current distortion rate are obtained according to the each harmonic current; the temperature or voltage of the active filter is detected in real time; when the temperature of the active filter is less than or equal to a preset temperature threshold or the voltage is less than or equal to a preset voltage threshold, the active filter is controlled to be connected to the power system; when the temperature of the active filter is greater than the preset temperature threshold or the voltage is greater than the preset voltage threshold, the total harmonic current distortion rate is compared with each harmonic set threshold, and the passive filter branch corresponding to the harmonic with the total harmonic current distortion rate greater than the set threshold is controlled to be connected to the power system. The application is used for hybrid filtering.

Description

Technical Field

[0001] This invention relates to the field of filtering. Background Technology

[0002] With the widespread application of nonlinear loads (such as frequency converters, rectifiers, and electric arc furnaces) in power systems, the problem of power grid harmonic pollution is becoming increasingly serious. Harmonics not only cause voltage distortion and power quality degradation in the power grid, but also trigger a series of problems such as overheating of electrical equipment, malfunction of relay protection, and communication interference, seriously affecting the safe and stable operation of the power system.

[0003] Currently, common harmonic mitigation devices mainly fall into two categories: passive filters and active filters.

[0004] Passive filters: They have a simple structure and low cost, but their filtering effect is greatly affected by the power grid impedance, and they can only filter out specific harmonics, which can easily cause resonance problems and have poor flexibility.

[0005] Active power filters can dynamically compensate for harmonics, have a fast response speed and strong adaptability, but they are expensive, complex to control, and their reliability still faces challenges in large-capacity applications. Once a fault occurs, the filtering function will completely fail.

[0006] In existing technologies, although there are hybrid governance schemes that combine active and passive filters, most of them are simple parallel connections and lack intelligent collaborative control logic. When the active filter fails, the passive filter adopts a full switching method, which not only easily causes resonance and overcompensation, but also generates overvoltage and overcurrent, directly burning out capacitors and reactors and shortening the life of passive equipment. Therefore, it is easy to damage both passive and active filters. Summary of the Invention

[0007] The purpose of this invention is to solve the problem that existing solutions combining passive and active filters are prone to damage to both passive and active filters, and to propose a hybrid power filtering method.

[0008] A hybrid power filtering method, the method comprising the following:

[0009] Step 1: Simultaneously collect the load current and grid-side current in the power system, and use the Fourier transform method or low-pass filter to extract the harmonic components in the load current and the grid-side current, respectively as the load harmonic components and grid harmonic components.

[0010] Step 2: Obtain the harmonic currents of each order based on the load harmonic components and the grid harmonic components, and obtain the compensation current and the total harmonic current distortion rate based on the harmonic currents.

[0011] Step 3: Real-time detection of the temperature or voltage of the active filter. When the temperature of the active filter is less than or equal to the preset temperature threshold or the voltage is less than or equal to the preset voltage threshold, the active filter is determined to be fault-free. The first contactor coil on the line where the active filter is located is controlled to be energized. The energization of the first contactor coil causes the normally open contact of the first contactor to close, so that the active filter is connected to the power system. The active filter is controlled to generate the compensation current to suppress the load harmonic components and the grid harmonic components. When the temperature of the active filter is greater than the preset temperature threshold or the voltage is greater than the preset voltage threshold, the active filter is determined to be faulty, and step 4 is executed.

[0012] Step 4: Compare the total harmonic current distortion rate with the set threshold for each harmonic, and control the passive filter branch corresponding to the harmonic whose total harmonic current distortion rate is greater than the set threshold to connect to the power system. Use the corresponding resonant frequency of the passive filter to suppress the load harmonic components and the grid harmonic components.

[0013] Preferably, a low-pass filter is used to extract the harmonic components in the load current. The specific process is as follows:

[0014] A low-pass filter is used to extract the fundamental component of the load current. The fundamental component is then subtracted from the load current signal or the grid current signal to obtain the load harmonic component or the grid harmonic component.

[0015] Preferably, the compensation current Represented as:

[0016] ,

[0017] In the formula, Main compensation coefficient, For load harmonic components, The damping coefficient is... These are the harmonic components of the power grid.

[0018] Preferably, the total harmonic current distortion rate is expressed as:

[0019] ,

[0020] In the formula, The total harmonic current distortion rate is . For the first Secondary harmonic current.

[0021] Preferably, each passive filter includes inductors L1-L2, capacitors C1-C2, and a damping reactor L2.

[0022] One end of the parallel connection between inductor L1 and capacitor C1 is connected to one end of inductor L2, and the other end is connected to one end of capacitor C2. The other end of inductor L2 is connected to the moving contact of the normally open contact. The stationary contact of the normally open contact is connected to one end of the second contactor coil. The other end of the second contactor coil is connected to the power system. The other end of capacitor C2 is connected to the power ground. The active filter is connected to the second moving contact of the single-pole double-throw switch. The stationary contact of the single-pole double-throw switch is connected to the power grid.

[0023] Each passive filter has different values ​​for inductor L1 and capacitors C1-C2, resulting in different output resonant frequencies.

[0024] Preferably, the resonant frequency is expressed as:

[0025] ,

[0026] In the formula, For the first The resonant frequency of a passive filter, The value of inductor L1, The value of inductor L2, This is the value of capacitor C1.

[0027] Preferably, the active filter is implemented using IGBTs.

[0028] Preferably, two current transformers are used to collect the load current and grid-side current in the power system, respectively.

[0029] Preferably, a temperature sensor and a voltage sensor are used to collect the temperature and voltage of the active filter, respectively.

[0030] The beneficial effects of this invention are:

[0031] This invention, by incorporating a contactor and fault detection mechanism, allows the system to automatically switch to passive filter operation when the active filter fails, ensuring uninterrupted filtering and improving the system's continuous operational reliability. Furthermore, it only activates the corresponding passive filter branch for harmonic orders exceeding a set threshold, avoiding the activation of unnecessary branches, thus reducing unnecessary heat generation and aging, and avoiding the risks of overcompensation and reactive power backfeed, effectively protecting both the active and passive filters.

[0032] This invention uses either Fourier transform or low-pass filter to extract load and power grid harmonic components. The appropriate method can be selected according to actual needs, thereby improving the accuracy and adaptability of harmonic detection.

[0033] The system tuning filter of this invention adopts an LC structure, and the active filter can be implemented using common power devices such as IGBTs. The overall structure is clear and easy to implement, and the manufacturing cost is controlled while ensuring performance.

[0034] This invention is applicable to load-side harmonic mechanisms and can also be used for comprehensive management of grid-side harmonics, making it highly practical for engineering applications and worthy of widespread adoption. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the principle of a hybrid power filtering method. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0038] Example:

[0039] A hybrid power filtering method, the method comprising the following:

[0040] Step 1: Simultaneously collect the load current and grid-side current in the power system, and use the Fourier transform method or low-pass filter to extract the harmonic components in the load current and the grid-side current, respectively as the load harmonic components and grid harmonic components.

[0041] Step 2: Obtain the harmonic currents of each order based on the load harmonic components and the grid harmonic components, and obtain the compensation current and the total harmonic current distortion rate based on the harmonic currents.

[0042] Step 3: Real-time detection of the temperature or voltage of the active filter. When the temperature of the active filter is less than or equal to the preset temperature threshold or the voltage is less than or equal to the preset voltage threshold, the active filter is determined to be fault-free. The first contactor coil on the line where the active filter is located is controlled to be energized. The energization of the first contactor coil causes the normally open contact of the first contactor to close, so that the active filter is connected to the power system. The active filter is controlled to generate the compensation current to suppress the load harmonic components and the grid harmonic components. When the temperature of the active filter is greater than the preset temperature threshold or the voltage is greater than the preset voltage threshold, the active filter is determined to be faulty, and step 4 is executed.

[0043] Step 4: Compare the total harmonic current distortion rate with the set threshold for each harmonic, and control the passive filter branch corresponding to the harmonic whose total harmonic current distortion rate is greater than the set threshold to connect to the power system. Use the corresponding resonant frequency of the passive filter to suppress the load harmonic components and the grid harmonic components.

[0044] Specifically, the control unit can determine whether the active filter is faulty based on parameters such as the DC side voltage, output current, and IGBT temperature of the active filter. The judgment conditions may include: DC voltage exceeding the set range, continuous overload of output current interruption, IGBT temperature exceeding the safety threshold, communication abnormality, or loss of control signal.

[0045] Further specifying the method, a low-pass filter is used to extract the harmonic components in the load current. The specific process is as follows:

[0046] A low-pass filter is used to extract the fundamental component of the load current. The fundamental component is then subtracted from the load current signal or the grid current signal to obtain the load harmonic component or the grid harmonic component.

[0047] Further restrictions, compensation current Represented as:

[0048] ,

[0049] In the formula, Main compensation coefficient, For load harmonic components, The damping coefficient is... These are the harmonic components of the power grid.

[0050] Specifically, the compensation current is the same in magnitude as the harmonic current resulting from the sum of the load harmonic components and the grid harmonic components, but in opposite phase.

[0051] Further defining the total harmonic current distortion rate, we express it as:

[0052] ,

[0053] In the formula, The total harmonic current distortion rate is . For the first Secondary harmonic current.

[0054] Further specifying, each tuned filter includes inductors L1-L2, capacitors C1-C2, and a damping reactor L2.

[0055] One end of the parallel connection between inductor L1 and capacitor C1 is connected to one end of inductor L2, and the other end is connected to one end of capacitor C2. The other end of inductor L2 is connected to the moving contact of the normally open contact. The stationary contact of the normally open contact is connected to one end of the second contactor coil. The other end of the second contactor coil is connected to the power system. The other end of capacitor C2 is connected to the power ground. The active filter is connected to the second moving contact of the single-pole double-throw switch. The stationary contact of the single-pole double-throw switch is connected to the power grid.

[0056] Each passive filter has different values ​​for inductor L1 and capacitors C1-C2, resulting in different output resonant frequencies.

[0057] Further specifying, the resonant frequency is expressed as:

[0058] ,

[0059] In the formula, For the first The resonant frequency of a passive filter, The value of inductor L1, The value of inductor L2, This is the value of capacitor C1.

[0060] Further specifying, the active filter is implemented using IGBTs.

[0061] Further specifying, the active filter is implemented using IGBTs.

[0062] To further limit this, two current transformers are used to collect the load current and grid-side current in the power system, respectively.

[0063] Further, temperature and voltage sensors are used to collect the temperature and voltage of the active filter, respectively.

[0064] Experimental verification:

[0065] Taking a 380V / 50Hz power grid in an industrial site as an example:

[0066] The main harmonics of the load are the 5th, 7th, and 11th harmonics;

[0067] The active filter capacity is set to 100A;

[0068] Each passive filter is designed for each harmonic. The passive filter designed for the 5th harmonic has L1=2mH, L2=5mH, C1=100uF, and C2=200uF.

[0069] After the system was put into operation, the total harmonic distortion rate of the grid current dropped from 25% to below 4%. Moreover, when simulating an active filter failure, the system can seamlessly switch to the passive filter of the corresponding branch, and the harmonic distortion rate is maintained within 8%, meeting the requirements for continuous operation on site.

[0070] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A hybrid power filtering method, characterized in that, The method includes the following: Step 1: Simultaneously collect the load current and grid-side current in the power system, and use the Fourier transform method or low-pass filter to extract the harmonic components in the load current and the grid-side current, respectively as the load harmonic components and grid harmonic components. Step 2: Obtain the harmonic currents of each order based on the load harmonic components and the grid harmonic components, and obtain the compensation current and the total harmonic current distortion rate based on the harmonic currents. Step 3: Real-time detection of the temperature or voltage of the active filter. When the temperature of the active filter is less than or equal to the preset temperature threshold or the voltage is less than or equal to the preset voltage threshold, the active filter is determined to be fault-free. The first contactor coil on the line where the active filter is located is controlled to be energized. The energization of the first contactor coil causes the normally open contact of the first contactor to close, so that the active filter is connected to the power system. The active filter is controlled to generate the compensation current to suppress the load harmonic components and the grid harmonic components. When the temperature of the active filter is greater than the preset temperature threshold or the voltage is greater than the preset voltage threshold, the active filter is determined to be faulty, and step 4 is executed. Step 4: Compare the total harmonic current distortion rate with the set threshold for each harmonic, and control the passive filter branch corresponding to the harmonic whose total harmonic current distortion rate is greater than the set threshold to connect to the power system. Use the corresponding resonant frequency of the passive filter to suppress the load harmonic components and the grid harmonic components.

2. The hybrid power filtering method according to claim 1, characterized in that, The harmonic components in the load current are extracted using a low-pass filter. The specific process is as follows: A low-pass filter is used to extract the fundamental component of the load current. The fundamental component is then subtracted from the load current signal or the grid current signal to obtain the load harmonic component or the grid harmonic component.

3. The hybrid power filtering method according to claim 1, characterized in that, Compensation current Represented as: ， In the formula, Main compensation coefficient, For load harmonic components, The damping coefficient is... These are the harmonic components of the power grid.

4. The hybrid power filtering method according to claim 1, characterized in that, The total harmonic current distortion rate is expressed as: ， In the formula, The total harmonic current distortion rate is . For the first Secondary harmonic current.

5. The hybrid power filtering method according to claim 1, characterized in that, Each passive filter includes inductors L1-L2, capacitors C1-C2, and inductor L2. One end of the parallel connection between inductor L1 and capacitor C1 is connected to one end of inductor L2, and the other end is connected to one end of capacitor C2. The other end of inductor L2 is connected to the moving contact of the normally open contact. The stationary contact of the normally open contact is connected to one end of the second contactor coil. The other end of the second contactor coil is connected to the power system. The other end of capacitor C2 is connected to the power ground. The active filter is connected to the second moving contact of the single-pole double-throw switch. The stationary contact of the single-pole double-throw switch is connected to the power grid. Each passive filter has different values ​​for inductor L1 and capacitors C1-C2, resulting in different output resonant frequencies.

6. The hybrid power filtering method according to claim 5, characterized in that, The resonant frequency is expressed as: ， In the formula, For the first The resonant frequency of a passive filter, The value of inductor L1, The value of inductor L2, This is the value of capacitor C1.

7. The hybrid power filtering method according to claim 1, characterized in that, The active filter is implemented using IGBTs.

8. A hybrid power filtering system according to claim 1, characterized in that, Two current transformers are used to collect the load current and grid-side current in the power system, respectively.

9. A hybrid power filtering system according to claim 1, characterized in that, Temperature and voltage sensors are used to collect the temperature and voltage of the active filter, respectively.

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