Simplified THD calculation device, active harmonic filter device including the same, simplified THD calculation method and active harmonic filtering method including the same

Abstract

The present invention relates to a simplified THD calculation device and method. The problem to be solved is to reduce the cost required for the device necessary for conventional THD calculation by operating with a simplified algorithm capable of performing power conversion and calculating a desired order of THD simultaneously on a single Digital Signal Processor (DSP). For example, a simplified THD calculation device and method are disclosed, comprising: a notch filter unit that outputs a digital output signal with specific harmonics removed by blocking a specific frequency of a selected order with respect to a digital input signal; and a signal subtraction unit that outputs a specific harmonic of the selected order by subtracting the digital output signal from the digital input signal.

Description

Technology Field

[0001] Embodiments of the present invention relate to a simplified Total Harmonic Distortion (THD) calculation device, an active harmonic filter device including the same, a simplified THD calculation method, and an active harmonic filtering method including the same. Background Technology

[0002] Although AC voltage and AC current are inherently sinusoidal waves, the input current of rectifiers, inverters, etc., cannot become a sinusoidal wave due to non-linear characteristic loads such as iron cores and becomes a distorted wave. Such a distorted wave becomes a waveform in which frequency components that are integer multiples of a sinusoidal wave with a fundamental frequency of 50 Hz or 60 Hz are superimposed.

[0003] Generally, parasitic frequency components such as 5 times and 7 times the fundamental frequency are superimposed. High-frequency components superimposed on the fundamental frequency waveform are called harmonics, and the frequency component 5 times the fundamental frequency is referred to as the 5th harmonic (5th order), and the one 7 times is referred to as the 7th harmonic, etc.

[0004] THD (Total Harmonic Distortion) refers to 'total harmonic distortion.' Specifically, it is a value representing the proportion of all harmonic components other than the fundamental frequency (usually 60 Hz) in voltage or current signals. In other words, it serves as an indicator to measure how distorted a signal is.

[0005] This THD plays an important role in evaluating signal distortion in power systems and analyzing the effects of harmonics.

[0006] Generally, calculating THD of various orders requires complex formulas and corresponding complex processing steps, and implementing these complex formulas and processing steps requires expensive, high-performance DSPs (Digital Signal Processors). Prior art literature

[0007] Published Patent Application No. 10-2018-0114274 (Publication Date: October 18, 2018) Registered Patent Application No. 10-1417962 (Registration Date: July 3, 2014) The problem to be solved

[0008] Embodiments of the present invention provide a simplified THD calculation device capable of reducing the cost required for conventional THD calculation devices by operating with a simplified algorithm that can perform power conversion and calculate a desired order of THD simultaneously in a single Digital Signal Processor (DSP); an active harmonic filter device including the same; a simplified THD calculation method; and an active harmonic filtering method including the same. means of solving the problem

[0009] A simplified Total Harmonic Distortion (THD) calculation device according to one embodiment of the present invention includes: a notch filter unit that outputs a digital output signal in which specific harmonics are removed by blocking a specific frequency of a selected order from a digital input signal; and a signal subtraction unit that outputs a specific harmonic of the selected order by subtracting the digital output signal from the digital input signal.

[0010] In addition, it may further include a harmonic order selection unit that receives the order of a specific harmonic and selects the notch filter unit according to the input order.

[0011] In addition, it may further include an analog-to-digital converter that converts an analog signal containing harmonic components generated from a nonlinear load into a digital signal and outputs it to the notch filter unit.

[0012] An active harmonic filter device according to another embodiment of the present invention includes: a Total Harmonic Distortion (THD) calculation unit that outputs a digital output signal with the specific harmonic removed by blocking a specific frequency of a selected order from a digital input signal, and outputs a specific harmonic of the selected order by subtracting the digital output signal from the digital input signal; and an active filter unit that performs harmonic filtering by supplying a frequency with a phase 180 degrees opposite to the specific frequency of the order calculated through the THD calculation unit to a line of a power supply system.

[0013] A simplified Total Harmonic Distortion (THD) calculation method according to another embodiment of the present invention comprises: a harmonic filtering step in which a notch filter unit blocks a specific frequency of a selected order from a digital input signal to output a digital output signal in which a specific harmonic is removed; and a harmonic output step in which a signal subtraction unit subtracts the digital output signal from the digital input signal to output a specific harmonic of the selected order.

[0014] Additionally, the harmonic order selection unit may further include a harmonic order selection step in which the order of a specific harmonic is input and the notch filter unit according to the input order is selected.

[0015] Additionally, the analog-to-digital converter may further include an analog-to-digital conversion step that converts an analog signal containing harmonic components generated from a non-linear load into a digital signal and provides it for the notch filter step.

[0016] Another active harmonic filtering method in another embodiment of the present invention comprises: a THD (Total Harmonic Distortion) calculation unit that outputs a digital output signal in which specific harmonics are removed by blocking a specific frequency of a selected order from a digital input signal, and outputs a specific harmonic of the selected order by subtracting the digital output signal from the digital input signal; and an active filtering unit that performs harmonic filtering by supplying a frequency with a phase 180 degrees opposite to the specific frequency of the order output through the THD calculation step to a line of a power supply system. Effects of the invention

[0017] According to the present invention, a simplified THD calculation device that can reduce the cost required for conventional THD calculation devices by operating with a simplified algorithm capable of calculating a desired order of THD while simultaneously performing power conversion in a single Digital Signal Processor (DSP), an active harmonic filter device including the same, a simplified THD calculation method, and an active harmonic filtering method including the same can be provided. Brief explanation of the drawing

[0018] FIG. 1 is a block diagram showing the overall configuration of a simplified THD calculation device according to one embodiment of the present invention. Figure 2 is a graph exemplarily showing signal A (digital input signal) shown in Figure 1 and signal B (digital output signal with harmonics removed) which is the result of performing a notch filter. FIG. 3 is a conceptual diagram illustrating a method for outputting (calculating) only a harmonic signal of a selected order according to one embodiment of the present invention. FIG. 4 is a conceptual diagram illustrating a method for outputting (calculating) multiple order harmonic signals selected from a Digital Signal Processor (DSP) according to one embodiment of the present invention. FIG. 5 is a diagram showing the configuration of an active harmonic filter device according to another embodiment of the present invention. Figure 6 is a diagram showing the active filter section of Figure 5 as a 3-level inverter (3-phase) topology. Figure 7 is a circuit diagram showing the detailed configuration of the active filter section of Figure 5. FIG. 8 is a flowchart showing the overall configuration of a simplified THD calculation method according to another embodiment of the present invention. FIG. 9 is a flowchart showing the configuration of an active harmonic filtering method according to another embodiment of the present invention. Specific details for implementing the invention

[0019] The terms used in this specification will be briefly explained, and the invention will be described in detail.

[0020] The terms used in this invention have been selected based on currently widely used general terms, taking into account their functions within the invention; however, these terms may vary depending on the intent of those skilled in the art, case law, the emergence of new technologies, etc. Additionally, in specific cases, terms have been arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, the terms used in this invention should be defined not merely by their names, but based on their meanings and the overall content of the invention.

[0021] When a part of a specification is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, terms such as "...part" or "module" as used in the specification refer to a unit that processes at least one function or operation, and this may be implemented in hardware or software, or as a combination of hardware and software.

[0022] Embodiments of the present invention are described below with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification are denoted by similar reference numerals.

[0023] FIG. 1 is a block diagram showing the overall configuration of a simplified THD calculation device according to an embodiment of the present invention, FIG. 2 is a graph exemplarily showing signal A (digital input signal) shown in FIG. 1 and signal B (digital output signal with harmonics removed) which is the result of performing a notch filter, FIG. 3 is a conceptual diagram showing a method of outputting (calculating) only a selected order harmonic signal according to an embodiment of the present invention, and FIG. 4 is a conceptual diagram showing a method of outputting (calculating) multiple selected order harmonic signals from a single DSP (Digital Signal Processor) according to an embodiment of the present invention.

[0024] Referring to FIG. 1, a simplified THD calculation device (1000) according to one embodiment of the present invention may include at least one of a harmonic order selection unit (100), an analog-to-digital conversion unit (200), a notch filter unit (300), and a signal subtraction unit (400).

[0025] The above harmonic order selection unit (100) receives the order (n-th order) of a specific harmonic and can select or set a notch filter (n-th order) that matches the selected order among a plurality of notch filters included in the notch filter unit (300) according to the input order.

[0026] The above analog-to-digital converter (200) can convert an analog signal containing harmonic components generated from a non-linear load into a digital signal and output it to a notch filter (300).

[0027] The analog-to-digital converter (200) according to one embodiment of the present invention may be equipped with a delta-sigma modulation ADC, an axial comparison type ADC, a parallel structure ADC, etc., but it is preferable to use a delta-sigma modulation ADC, which has the highest accuracy and is mainly used in measurement systems with 24-bit resolution, but the analog-to-digital converter (200) is not limited to only such an ADC.

[0028] The above notch filter unit (300) can output a digital output signal (B) with specific harmonics removed by performing a filtering operation to block a specific frequency of the order (n-th order) selected by the harmonic order selection unit (100) for a digital input signal input from the analog-to-digital converter unit (200). Accordingly, a digital input signal (A) having an n-th harmonic and a digital output signal (B) with the n-th harmonic removed can be obtained, respectively.

[0029] A notch filter section (300) according to one embodiment of the present invention may be equipped with a plurality of notch filters according to the harmonic order. A notch filter is a filter that attenuates a frequency of a specific range to a very low level, and in this regard, the transfer function of THD can be defined as Equation 1 below.

[0030] [Formula 1]

[0031]

[0032] In the THD transfer function of Equation 1, 'freq' represents the notch frequency, 'gmin' represents the gain at the notch frequency, and 'damp' represents the damping ratio of the filter poles. More specifically, freq (notch frequency) is the value of the notch frequency, specified in units of rad / s, and gmin (gain at notch frequency) is the gain value at the notch frequency expressed in absolute units, which controls the notch depth; the notch filter has unity gain at low or high frequencies. In this case, the gain is lowest at the notch frequency (i.e., the value provided to the freq port). damp (damping ratio of the filter poles) is specified as a positive scalar value to control the notch width, and the closer it is to 0, the steeper the notch characteristic. As illustrated in graph 'B' of Fig. 2, these parameters control the notch depth and frequency of the continuous-time freq (notch frequency), and damp (damping ratio of the filter poles) controls the notch width ( It adjusts ), and the larger the damp (attenuation ratio of filter poles), the wider the notch ( ) also increases. In a program that processes the THD transfer function, the order value selected through the harmonic order selection unit (100) is set as a variable and can be used to process the THD calculation result for the corresponding order.

[0033] Meanwhile, the notch filter section (300) may be equipped with a signal subtraction section (400) that subtracts the digital input signal (A) and the digital output signal (B) for each filter, along with notch filters according to each order as described above, but may also be equipped with one signal subtraction section (400) for a plurality of notch filters according to design specifications.

[0034] The above signal subtraction unit (400) can output a specific harmonic signal of a selected order (n-th order) by subtracting (AB) the digital output signal (B) output through the notch filter unit (300) from the digital input signal (A) input from the analog-to-digital converter unit (200).

[0035] That is, the signal subtraction unit (400) subtracts the digital output signal (B) from which the corresponding n-th harmonic has been removed from the digital input signal (A) having the n-th harmonic, so that only the n-th harmonic component remains. By outputting this signal, the desired order of harmonics (THDn=AB) can be calculated through a processor composed of relatively simple hardware and software means without going through the complex calculation process for calculating the existing THD.

[0036] As described above, when various harmonic components need to be calculated, if a desired order among 1st to nth order notch filters is selected (e.g., 1st order selected) as shown in FIG. 4, the notch filter of the corresponding order operates accordingly. A digital input signal (A) having a 1st order harmonic is received and a digital output signal (B) with the 1st order harmonic removed is output. A corresponding signal subtraction unit (400) can subtract the digital output signal (B) with the 1st order harmonic removed from the digital input signal (A) having the 1st order harmonic to output the 1st order harmonic calculation result. Alternatively, a digital input signal (A) having an nth order harmonic is received and a digital output signal (B) with the nth order harmonic removed is output. A corresponding signal subtraction unit (400) can subtract the digital output signal (B) with the nth order harmonic removed from the digital input signal (A) having the nth order harmonic to output the nth order harmonic calculation result. Each n-th harmonic calculation result can be applied to the original signal and used for harmonic removal.

[0037] To this end, at least one notch filter or notch filter section (300) and signal subtraction section (400) configured by order may be implemented as a single DSP or can be implemented in a single DSP.

[0038] FIG. 5 is a diagram showing the configuration of an active harmonic filter device according to another embodiment of the present invention, FIG. 6 is a diagram showing the active filter section of FIG. 5 as a 3-level inverter (3-phase) topology, and FIG. 7 is a circuit diagram showing the detailed configuration of the active filter section of FIG. 5.

[0039] Referring to FIG. 5, an active harmonic filter device (10) according to another embodiment of the present invention includes a Total Harmonic Distortion (THD) calculation unit (11) that outputs a digital output signal with specific harmonics removed by blocking a specific frequency of a selected order from a digital input signal and outputs a specific harmonic of a selected order by subtracting the digital output signal from the digital input signal, and an active filter unit (12) that performs harmonic filtering by supplying a frequency with a phase opposite by 180 degrees to the specific frequency of the order calculated through the THD calculation unit (11) to a line of a power supply system (Grid).

[0040] Since the above THD calculation unit (11) is identical to the configuration of the THD calculation device (1000) described above through one embodiment, a detailed description thereof is omitted.

[0041] The active filter unit (12) can perform a filtering function to prevent harmonics from entering by supplying a frequency signal with a phase 180 degrees opposite to the harmonics calculated by the THD calculation unit (11) to the line of the power supply system (Grid), thereby canceling out and removing the corresponding harmonics. This active filter unit (12) can be implemented by applying a 3-level inverter (3-phase) as shown in FIG. 6.

[0042] FIG. 8 is a flowchart showing the overall configuration of a simplified THD calculation method according to another embodiment of the present invention.

[0043] Referring to FIG. 8, a simplified THD calculation device (1000) according to another embodiment of the present invention may include at least one of a harmonic order selection step (S100), an analog-to-digital conversion step (S200), a harmonic filtering step (S300), and a harmonic output step (S400).

[0044] The above harmonic order selection step (S100) receives the order (n-th order) of a specific harmonic and can select or set a notch filter (n-th order) that matches the selected order among a plurality of notch filters included in the harmonic filtering step (S300) according to the input order so that it can operate.

[0045] The above analog-to-digital conversion step (S200) can convert an analog signal containing harmonic components generated from a non-linear load into a digital signal and output it to a harmonic filtering step (S300).

[0046] In the analog-to-digital conversion step (S200) according to another embodiment of the present invention, a delta-sigma modulation ADC (Analog Digital Converter), an axial comparison type ADC, a parallel structure ADC, etc., may be applied, but among these, it is preferable to apply a delta-sigma modulation ADC, which has the highest accuracy and is mainly used in measurement systems with 24-bit resolution, but the analog-to-digital conversion step (S200) is not limited only to such an ADC.

[0047] The above harmonic filtering step (S300) can output a digital output signal (B) with specific harmonics removed by performing a filtering operation to block a specific frequency of the order (n-th order) selected in the harmonic order selection step (S100) for a digital input signal input from the analog-to-digital conversion step (S200). Accordingly, a digital input signal (A) having an n-th harmonic and a digital output signal (B) with the corresponding n-th harmonic removed can be obtained, respectively.

[0048] A harmonic filtering step (S300) according to another embodiment of the present invention may include a plurality of notch filters according to the harmonic order. A notch filter is a filter that attenuates a frequency of a specific range to a very low level, and in this regard, the transfer function of THD can be defined as Equation 2 below.

[0049] [Equation 2]

[0050]

[0051] In the THD transfer function of Equation 2, 'freq' represents the notch frequency, 'gmin' represents the gain at the notch frequency, and 'damp' represents the damping ratio of the filter poles. More specifically, freq (notch frequency) is the value of the notch frequency, specified in units of rad / s, and gmin (gain at notch frequency) is the gain value at the notch frequency expressed in absolute units, which controls the notch depth; the notch filter has unity gain at low or high frequencies. In this case, the gain is lowest at the notch frequency (i.e., the value provided to the freq port). damp (damping ratio of the filter poles) is specified as a positive scalar value to control the notch width, and the closer it is to 0, the steeper the notch characteristic. As illustrated in graph 'B' of Fig. 2, these parameters control the notch depth and frequency of the continuous-time freq (notch frequency), and damp (damping ratio of the filter poles) controls the notch width ( It adjusts ), and the larger the damp (attenuation ratio of filter poles), the wider the notch ( ) also increases. In a program that processes the THD transfer function, the order value selected through the harmonic order selection step (S100) is set as a variable and can be used to process the THD calculation result for that order.

[0052] Meanwhile, the harmonic filtering step (S300) may include a harmonic output step (S400) that subtracts the digital input signal (A) and the digital output signal (B) for each filter, along with notch filters according to each order as described above, but may also include one harmonic output step (S400) for multiple notch filters depending on the design specifications.

[0053] The above harmonic output step (S400) can output a specific harmonic signal of a selected order (n-th order) by subtracting (AB) the digital output signal (B) output through the harmonic filtering step (S300) from the digital input signal (A) input from the analog-to-digital conversion step (S200).

[0054] That is, the harmonic output step (S400) subtracts the digital output signal (B) from which the corresponding n-th harmonic has been removed from the digital input signal (A) having the n-th harmonic, so that only the n-th harmonic component remains. By outputting this signal, the desired order of harmonics (THDn=AB) can be calculated through a processor composed of relatively simple hardware and software means without going through the complex calculation process for calculating the existing THD.

[0055] As described above, when various harmonic components need to be calculated, if a desired order among 1st to nth order notch filters is selected (e.g., 1st order selected) as shown in FIG. 4, the notch filter of the corresponding order operates accordingly. A digital input signal (A) having a 1st harmonic is received and a digital output signal (B) with the 1st harmonic removed is output. A corresponding harmonic output step (S400) can then subtract the digital output signal (B) with the 1st harmonic removed from the digital input signal (A) having the 1st harmonic to output the 1st harmonic calculation result. Alternatively, a digital input signal (A) having an nth harmonic is received and a digital output signal (B) with the nth harmonic removed is output. A corresponding harmonic output step (S400) can then subtract the digital output signal (B) with the nth harmonic removed from the digital input signal (A) having the nth harmonic to output the nth harmonic calculation result. It can be output. The calculation result of each n-th harmonic can be applied to the original signal and used for harmonic removal.

[0056] FIG. 9 is a flowchart showing the configuration of an active harmonic filtering method according to another embodiment of the present invention.

[0057] Referring to FIG. 9, an active harmonic filtering method (S10) according to another embodiment of the present invention includes a THD calculation step (S11) that outputs a digital output signal with the specific harmonic removed by blocking a specific frequency of a selected order from a digital input signal and outputs a specific harmonic of a selected order by subtracting the digital output signal from the digital input signal; and an active filtering step (S12) that performs harmonic filtering by supplying a frequency with a phase 180 degrees opposite to the specific frequency of the order output through the THD calculation step (S11) to a line of a power supply system.

[0058] Since the above THD calculation step (S11) is identical to the configuration of the THD calculation method (S1000) described above through one embodiment, a detailed description thereof is omitted.

[0059] The active filtering step (S12) can perform a filtering function to prevent harmonics from entering by supplying a frequency signal with a phase 180 degrees opposite to the harmonics calculated in the THD calculation step (S11) to the line of the power supply system (Grid), thereby canceling out and removing the corresponding harmonics.

[0060] According to the present embodiment, a simplified algorithm capable of performing power conversion and simultaneously calculating a desired order of Total Harmonic Distortion (THD) in a single Digital Signal Processor (DSP) can be operated, thereby reducing the cost required for the device necessary for conventional THD calculation.

[0061] The above description is merely one embodiment for implementing a simplified THD calculation device according to the present invention, an active harmonic filter device including the same, a simplified THD calculation method, and an active harmonic filtering method including the same. The present invention is not limited to the above embodiment, and the technical spirit of the present invention extends to the scope in which various modifications can be made by anyone with ordinary knowledge in the field to which the invention belongs, without departing from the gist of the invention as claimed in the following claims. Explanation of the symbols

[0062] 1000: Simplified THD Calculator 100: Harmonic order selector 200: Analog-to-Digital Converter 300: Notch filter section 400: Signal subtraction unit 10: Active harmonic filter device 11: THD Calculation Unit 12: Active filter section S1000: Simplified THD Calculation Method S100: Harmonic order selection step S200: Analog-to-digital conversion step S300: Harmonic filtering stage S400: Harmonic output stage S10: Active harmonic filtering method S11: THD calculation step S12: Active filtering step

Claims

Claim 1 A simplified Total Harmonic Distortion (THD) calculation device comprising: a harmonic order selection unit that receives the order of a specific harmonic and selects a notch filter according to the input order; an analog-to-digital converter that converts an analog signal containing harmonic components generated from a nonlinear load into a digital input signal and outputs it to a notch filter selected by the harmonic order selection unit; a notch filter unit that blocks a specific frequency of the selected order for the digital input signal and outputs a digital output signal from which the specific harmonic has been removed; and a signal subtraction unit that performs a subtraction operation of the digital output signal from the digital input signal to output a specific harmonic of the selected order, wherein the notch filter unit and the signal subtraction unit are characterized by real-time updating and switching parameters of multiple order-specific notch filters within a single Digital Signal Processor (DSP), generating a digital output signal corresponding to each order, and then calculating the Total Harmonic Distortion (THD) in real-time through an operation of subtracting the digital output signal from the digital input signal. Claim 2 delete Claim 3 delete Claim 4 An active harmonic filter device comprising: a Total Harmonic Distortion (THD) calculation unit that receives the order of a specific harmonic, selects a notch filter according to the input order, converts an analog signal containing harmonic components generated from a nonlinear load into a digital input signal, outputs it to the selected notch filter, outputs a digital output signal with the specific harmonic removed by blocking a specific frequency of the selected order from the digital input signal, and outputs the specific harmonic of the selected order by subtracting the digital output signal from the digital input signal; and an active filter unit that performs harmonic filtering by supplying a frequency with a phase 180 degrees opposite to the specific frequency of the order calculated through the THD calculation unit to a line of a power supply system, wherein the THD calculation unit updates and switches parameters of multiple notch filters for each order in real time within a single Digital Signal Processor (DSP), generates a digital output signal corresponding to each order, and calculates the THD in real time through an operation of subtracting the digital output signal from the digital input signal. Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete

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