CN114200213A - Capacitance online monitoring method and device of low-frequency power transmission matrix converter - Google Patents

Abstract

The invention provides a capacitance online monitoring method and device of a low-frequency power transmission matrix converter, which comprises the following steps: collecting the current voltage of a capacitor to be monitored, and collecting voltage signals and current signals at two ends of a current conversion chain where the capacitor to be monitored is located; respectively inputting the voltage signal and the current signal into a wave trap to obtain a first alternating voltage, a first alternating current, a second alternating voltage and a second alternating current; acquiring a first power factor angle according to the first alternating voltage and the first alternating current, acquiring a second power factor angle according to the second alternating voltage and the second alternating current, and acquiring a phase angle difference between the first alternating voltage and the second alternating voltage; determining a real-time capacitance value according to a calculation formula by combining the voltage average value of the capacitor to be monitored in a preset time period; and when the real-time capacitance value is reduced to a preset limit value, judging that the capacitor to be monitored is aged. The capacitance value is calculated on line based on the circuit structure relationship of the M3C converter, and the normal operation and control of the M3C converter are not influenced.

Description

Capacitance online monitoring method and device of low-frequency power transmission matrix converter

Technical Field

The invention belongs to the technical field of matrix converters, and particularly relates to a capacitance online monitoring method and device of a low-frequency power transmission matrix converter.

Background

The low-frequency power transmission reduces the power transmission frequency, and is beneficial to improving the problems of system reactive power and distributed parameters, thereby realizing certain long-distance power transmission. The converter is used as an indispensable device in the low-frequency power transmission process and is used for power frequency and low-frequency voltage conversion. At present, a common mature converter is a Modular Multilevel Converter (MMC), and because the MMC works in an environment with large harmonic waves and high temperature for a long time, the capacitor is easy to age, and the service life of the M3C converter is further influenced. Therefore, based on the circuit structure of the MMC current converter, the variation of the capacitance value is monitored by using the relationship between the voltage, the current and the capacitance, so as to realize the online monitoring of the aging degree of the capacitance.

As a novel AC/AC conversion device, a modular multilevel matrix converter (M3C) has better low-frequency characteristics compared with an MMC converter, and thus is more suitable for low-frequency power transmission application compared with the MMC converter, and generally includes at least one converter chain, each converter chain is formed by connecting a plurality of AC/dc conversion modules in series, and is similar to a conventional MMC converter, and a capacitor is also used in the AC/dc conversion module. Most of the existing monitoring methods are directed at calculating capacitance values of a circuit structure of an MMC current converter, and since a converter chain topology structure of an M3C current converter is changed compared with that of the MMC current converter, the existing monitoring methods cannot be applied to the M3C current converter, and a capacitance online monitoring method for the M3C current converter is urgently needed.

Disclosure of Invention

In order to solve the defects in the prior art, the invention provides an online capacitance monitoring method for a low-frequency power transmission matrix converter, which comprises the following steps:

collecting the current voltage of a capacitor to be monitored, and collecting voltage signals and current signals at two ends of a current conversion chain where the capacitor to be monitored is located;

respectively inputting the voltage signal and the current signal into a first wave trap and a second wave trap with different trap frequencies to obtain a first alternating voltage and a first alternating current of the output signal of the first wave trap and a second alternating voltage and a second alternating current of the output signal of the second wave trap;

acquiring a first power factor angle according to the first alternating voltage and the first alternating current, acquiring a second power factor angle according to the second alternating voltage and the second alternating current, and acquiring a phase angle difference between the first alternating voltage and the second alternating voltage;

combining the voltage average value of the capacitor to be monitored in a preset time period before the acquisition time, constructing a calculation formula of the capacitance value, and determining the real-time capacitance value of the capacitor to be monitored according to the calculation formula;

and when the real-time capacitance value is reduced to a preset limit value, judging that the capacitor to be monitored is aged.

Optionally, the capacitance value is calculated by the following formula:

wherein, C_iFor the real-time capacitance value of the ith capacitor to be monitored in an on-line monitoring mode, N is the total number of all capacitors to be monitored on a current conversion chain, and U_ciFor the present voltage of the ith capacitor to be monitored, U_{ci_av}The voltage average value of the ith capacitor to be monitored in a preset time period, t is the acquisition time, S₁₁Is the product of the first AC voltage and the first AC current, S₁₂Is the product of the first alternating voltage and the second alternating current, S₂₁Is the product of the second alternating voltage and the first alternating current,S₂₂is the product of the second alternating voltage and the second alternating current, alpha is the first power factor angle, beta is the second power factor angle,

is the phase angle difference, ω, between the first AC voltage and the second AC voltage₁Angular frequency, ω, of the trap frequency of the first trap₂Is the angular frequency of the notch frequency of the second trap.

Optionally, the low-frequency power transmission matrix converter includes at least one converter chain, each converter chain includes at least one ac/dc conversion module, the ac/dc conversion module includes a full-bridge circuit formed by four fully-controlled switching devices, and a capacitor to be monitored connected in parallel with the full-bridge circuit.

Optionally, the trap frequency of the first trap is greater than the trap frequency of the second trap.

Optionally, the first ac voltage U of the output signal of the first wave trap is obtained₁And a first alternating current I₁Second AC voltage U of output signal of second wave trap₂And a second alternating current I₂Before, still include: and respectively filtering the output signal of the first wave trap and the output signal of the second wave trap through a low-pass filter.

Optionally, a cut-off frequency of a low-pass filter through which the first trap output signal passes is greater than a notch frequency of the first trap, and a cut-off frequency of a low-pass filter through which the second trap output signal passes is greater than a notch frequency of the second trap.

Optionally, the determining the preset time period before the acquisition time according to the trap frequencies of the first trap and the second trap includes:

and determining common divisor of the trap frequencies of the first trap and the second trap, and taking integral multiple of reciprocal of the common divisor as the duration of the preset time period.

The invention also provides an online capacitance monitoring device of the low-frequency power transmission matrix converter based on the same idea, which comprises the following components:

a collecting unit: the current voltage acquisition module is used for acquiring the current voltage of the capacitor to be monitored and acquiring a voltage signal and a current signal at two ends of a current conversion chain where the capacitor to be monitored is located;

a notch unit: the first wave trap and the second wave trap are used for respectively inputting voltage signals and current signals into the first wave trap and the second wave trap with different trap frequencies, so that first alternating voltage and first alternating current of signals output by the first wave trap are obtained, and second alternating voltage and second alternating current of signals output by the second wave trap are obtained;

phase angle unit: the power factor correction circuit is used for acquiring a first power factor angle according to the first alternating voltage and the first alternating current, acquiring a second power factor angle according to the second alternating voltage and the second alternating current, and acquiring a phase angle difference between the first alternating voltage and the second alternating voltage;

a calculation unit: the method comprises the steps of establishing a calculation formula of a capacitance value by combining the voltage average value of the capacitor to be monitored in a preset time period before the acquisition time, and determining the real-time capacitance value of the capacitor to be monitored according to the calculation formula;

a determination unit: and the aging detection circuit is used for judging the aging of the capacitor to be monitored when the real-time capacitance value is reduced to a preset limit value.

Optionally, the capacitance value is calculated by the following formula:

wherein, C_iFor the real-time capacitance value of the ith capacitor to be monitored in an on-line monitoring mode, N is the total number of all capacitors to be monitored on a current conversion chain, and U_ciFor the present voltage of the ith capacitor to be monitored, U_{ci_av}The voltage average value of the ith capacitor to be monitored in a preset time period, t is the acquisition time, S₁₁Is the product of the first AC voltage and the first AC current, S₁₂Is the product of the first alternating voltage and the second alternating current, S₂₁Is the product of the second AC voltage and the first AC current, S₂₂Is the product of the second alternating voltage and the second alternating current, alpha is the first power factor angle, beta is the second power factor angle,

is the phase angle difference, ω, between the first AC voltage and the second AC voltage₁Angular frequency, ω, of the trap frequency of the first trap₂Is the angular frequency of the notch frequency of the second trap.

The technical scheme provided by the invention has the beneficial effects that:

the capacitance online monitoring method provided by the invention can be used for online calculation of the capacitance value based on the circuit structure relationship of the M3C converter, and the normal operation and control of the M3C converter are not influenced in the calculation process. In addition, the invention is provided with the wave trap during the capacitance value calculation, and can perform online monitoring and analysis on the harmonic conditions of different frequencies of the M3C converter.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

Fig. 1 is a schematic flow chart of a capacitance online monitoring method for a low-frequency power transmission matrix converter according to an embodiment of the present invention;

fig. 2 is a full-bridge circuit diagram of an ac/dc conversion module in the M3C matrix converter;

fig. 3 is a block diagram of a capacitance online monitoring device of a low-frequency power transmission matrix converter according to another embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The terms "first," "second," "third," "fourth," and the like in the description and in the claims, as well as in the drawings, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein.

It should be understood that, in various embodiments of the present invention, the sequence numbers of the processes do not mean the execution sequence, and the execution sequence of the processes should be determined by the functions and the internal logic of the processes, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

It should be understood that in the present application, "comprising" and "having" and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

It should be understood that, in the present invention, "a plurality" means two or more. "and/or" is merely an association describing an associated object, meaning that three relationships may exist, for example, and/or B, may mean: a exists alone, A and B exist simultaneously, and B exists alone. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "comprises A, B and C" and "comprises A, B, C" means that all three of A, B, C comprise, "comprises A, B or C" means that one of A, B, C comprises, "comprises A, B and/or C" means that any 1 or any 2 or 3 of A, B, C comprises.

It should be understood that in the present invention, "B corresponding to a", "a corresponds to B", or "B corresponds to a" means that B is associated with a, and B can be determined from a. Determining B from a does not mean determining B from a alone, but may be determined from a and/or other information. And the matching of A and B means that the similarity of A and B is greater than or equal to a preset threshold value.

As used herein, "if" may be interpreted as "at … …" or "when … …" or "in response to a determination" or "in response to a detection", depending on the context.

The technical solution of the present invention will be described in detail below with specific examples. The following several specific embodiments may be combined with each other, and details of the same or similar concepts or processes may not be repeated in some embodiments.

Example one

As shown in fig. 1, this embodiment provides an online capacitance monitoring method for a low-frequency power transmission matrix converter, including:

s1: collecting the current voltage of a capacitor to be monitored, and collecting voltage signals and current signals at two ends of a current conversion chain where the capacitor to be monitored is located;

s2: respectively inputting the voltage signal and the current signal into a first wave trap and a second wave trap with different trap frequencies to obtain a first alternating voltage and a first alternating current of the output signal of the first wave trap and a second alternating voltage and a second alternating current of the output signal of the second wave trap;

s3: acquiring a first power factor angle according to the first alternating voltage and the first alternating current, acquiring a second power factor angle according to the second alternating voltage and the second alternating current, and acquiring a phase angle difference between the first alternating voltage and the second alternating voltage;

s4: combining the voltage average value of the capacitor to be monitored in a preset time period before the acquisition time, constructing a calculation formula of the capacitance value, and determining the real-time capacitance value of the capacitor to be monitored according to the calculation formula;

s5: and when the real-time capacitance value is reduced to a preset limit value, judging that the capacitor to be monitored is aged.

In this embodiment, the low-frequency power transmission matrix converter is an M3C converter, capacitance values in the ac/dc conversion modules can be directly calculated on line through the above processes, and normal operation and control of the M3C converter are not affected in the calculation process through a signal sampling mode.

The low-frequency power transmission matrix converter in the embodiment comprises at least one converter chain, each converter chain comprises at least one alternating current-direct current conversion module, and each alternating current-direct current conversion module comprises a full-bridge circuit formed by four fully-controlled switch devices and a capacitor to be monitored, wherein the capacitor to be monitored is connected with the full-bridge circuit in parallel. The full-bridge circuit is shown in fig. 2 and comprises four full-control switching devices connected in series in pairs, and the full-control switching devices connected in series in pairs are connected in parallel and then connected in parallel with a capacitor. And finally, the alternating current measurement of the alternating current-direct current conversion module is sequentially connected in series to form a current conversion chain, one end of the current conversion chain is connected with the first alternating current system, and the other end of the current conversion chain is connected with the second alternating current system, so that the functions of electric energy conversion and electric energy transmission from the first alternating current system to the second alternating current system can be realized.

Based on the circuit topology structure of the M3C converter, first, the present embodiment determines the starting point and the time of sampling by using the phase-locking function, and collects the current voltage U of the ith capacitor to be detected based on a certain frequency from the starting point and the time_ciAnd simultaneously determining a current conversion chain where the alternating current-direct current conversion module containing the capacitor to be monitored is positioned, and collecting a voltage signal U and a current signal I at two ends of the current conversion chain. And respectively passing the voltage signal U and the current signal I through a first trap with a trap frequency of F1 and a second trap with a trap frequency of F2, wherein the trap frequency F1 of the first trap is greater than the trap frequency F2 of the second trap. The first alternating voltage U can be obtained according to the output signal of the voltage signal U and the current signal I passing through the first wave trap₁And a first alternating current I₁According to the voltage signal U and the current signal I, a second alternating voltage U can be obtained through an output signal of the second wave trap₂And a second alternating current I₂。

In the above process, according to the first AC voltage U₁And a first alternating current I₁The capacitance state of the capacitor to be monitored at the notch frequency F2 can be obtained according to the second alternating voltage U₂And a second alternating current I₂The capacitance state of the capacitor to be monitored at the notch frequency F1 can be obtained, and in the embodiment, F1 and F2 are low-frequency power transmission respectivelyTwo main harmonic frequencies of matrix converter, it can be seen from this that this embodiment can split the mixing of transverter to the capacitance value state of waiting to monitor electric capacity under different harmonic frequencies is monitored respectively, compares in the defect that traditional monitoring methods can only monitor electric capacity operating condition under the mixing condition, and this embodiment can further accurately know the operating condition that the electric capacity of waiting to detect receives different harmonic influences through setting up the trapper.

In this embodiment, in order to improve the accuracy of the capacitance value of the capacitor to be monitored, low pass filters are further respectively disposed behind the first wave trap and the second wave trap, and the output signal of the first wave trap and the output signal of the second wave trap are respectively filtered by the low pass filters. Wherein the cut-off frequency of the low pass filter through which the first trap output signal passes is greater than the trap frequency F1 of the first trap, and the cut-off frequency of the low pass filter through which the second trap output signal passes is greater than the trap frequency F2 of the second trap. Interference signals of other frequencies can be filtered through the low-pass filter, and then subsequent phase difference analysis is carried out, so that the capacitance value of the capacitor to be detected can be calculated more accurately in the subsequent process according to the voltage signal and the current signal processed by the wave trap.

To construct a calculation formula of the capacitance value, the present embodiment is based on the first ac voltage U₁And a first alternating current I₁Obtaining a first power factor angle alpha, U₁And I₁By calculating the phase difference between U₁And I₁The ratio of (d) determines the phase difference. In the same way, according to the second alternating voltage U₂And a second alternating current I₂A second power factor angle beta is obtained. At the same time, a first alternating voltage U is obtained₁And a second alternating voltage U₂Phase angle difference of

This embodiment still needs to acquire the voltage average value of the capacitance to be monitored in the preset period before the acquisition time, and the preset period before the acquisition time is determined according to the notch frequency of the first notch filter and the second notch filter, including: and determining a common divisor of the trap frequencies of the first trap and the second trap, and taking an integral multiple of the reciprocal of the common divisor as the duration of a preset time period, namely backing the duration forward from the acquisition time as the preset time period.

After the acquisition of the parameters is completed, deducing based on ripple analysis of the capacitor to be monitored so as to perform real-time online calculation on the capacitance value of the ith capacitor to be detected according to the calculation formula of the capacitance value,

wherein, C_iFor the real-time capacitance value of the ith capacitor to be monitored in an on-line monitoring mode, N is the total number of all capacitors to be monitored on a current conversion chain, and U_ciFor the present voltage of the ith capacitor to be monitored, U_{ci_av}The voltage average value of the ith capacitor to be monitored in a preset time period, t is the acquisition time, S₁₁Is the product of the first AC voltage and the first AC current, i.e. S₁₁＝U₁I₁，S₁₂Is the product of the first AC voltage and the second AC current, i.e. S₁₂＝U₁I₂，S₂₁Is the product of the second AC voltage and the first AC current, i.e. S₂₁＝U₂I₁，S₂₂Is the product of the second AC voltage and the second AC current, i.e. S₂₂＝U₂I₂Where α is a first power factor angle, β is a second power factor angle,

is the phase angle difference, ω, between the first AC voltage and the second AC voltage₁Angular frequency being the trap frequency of the first trap, i.e. having ω₁＝2π×F1，ω₂Angular frequency being the trap frequency of the second trap, i.e. having ω₂2 pi × F2. In this embodiment, there is a special case that if the first ac voltage and the second ac voltage have the same amplitude, the first power factor angle α and the second power factor angle β are complementary angles, so the above formula has cos α ═ cos β, so that α and β in the above calculation formula of the capacitance value can be replaced with each other, simplifying the calculation formula.

In this embodiment, the preset limit may be set to a certain limit of 80% -95% of the factory-leaving capacitance value, for example, the preset limit is 95% of the factory-leaving capacitance value, which means that if the real-time capacitance value decreases by 5% from the factory-leaving capacitance value, the capacitor is considered to be aged, and replacement or maintenance is prompted, and meanwhile, reference may be made to the capacitance values at two notch frequencies F1 and F2 obtained in S2, so as to provide reference for analyzing the influence degree of different harmonics on capacitor aging.

Example two

As shown in fig. 3, the present embodiment provides an online capacitance monitoring device 6 for a low-frequency power transmission matrix converter, including:

the acquisition unit 61: the current voltage acquisition module is used for acquiring the current voltage of the capacitor to be monitored and acquiring a voltage signal and a current signal at two ends of a current conversion chain where the capacitor to be monitored is located;

notch section 62: the first wave trap and the second wave trap are used for respectively inputting voltage signals and current signals into the first wave trap and the second wave trap with different trap frequencies, so that first alternating voltage and first alternating current of signals output by the first wave trap are obtained, and second alternating voltage and second alternating current of signals output by the second wave trap are obtained;

phase angle unit 63: the power factor correction circuit is used for acquiring a first power factor angle according to the first alternating voltage and the first alternating current, acquiring a second power factor angle according to the second alternating voltage and the second alternating current, and acquiring a phase angle difference between the first alternating voltage and the second alternating voltage;

the calculation unit 64: the method comprises the steps of establishing a calculation formula of a capacitance value by combining the voltage average value of the capacitor to be monitored in a preset time period before the acquisition time, and determining the real-time capacitance value of the capacitor to be monitored according to the calculation formula;

the determination unit 65: and the aging detection circuit is used for judging the aging of the capacitor to be monitored when the real-time capacitance value is reduced to a preset limit value.

Through the process, the capacitance values in the alternating current-direct current conversion modules can be directly calculated on line, and normal operation and control of the M3C converter are not influenced in the calculation process through a signal sampling mode.

In this embodiment, the low-frequency power transmission matrix converter, that is, the M3C converter includes at least one converter chain, and each converter chain includes at least one ac/dc conversion module, the ac/dc conversion module includes a full-bridge circuit formed by four fully-controlled switching devices, and a capacitor to be monitored connected in parallel with the full-bridge circuit. The full-bridge circuit is shown in fig. 2 and comprises four full-control switching devices connected in series in pairs, and the full-control switching devices connected in series in pairs are connected in parallel and then connected in parallel with a capacitor. And finally, the alternating current measurement of the alternating current-direct current conversion module is sequentially connected in series to form a current conversion chain, one end of the current conversion chain is connected with the first alternating current system, and the other end of the current conversion chain is connected with the second alternating current system, so that the functions of electric energy conversion and electric energy transmission from the first alternating current system to the second alternating current system can be realized.

Based on the above circuit topology structure of the M3C converter, first, the collecting unit 61 of this embodiment determines the starting point and the time of sampling by using the phase-locking function, and collects the current voltage U of the ith capacitor to be detected based on a certain frequency from the starting point and the time_ciAnd simultaneously determining a current conversion chain where the alternating current-direct current conversion module containing the capacitor to be monitored is positioned, and collecting a voltage signal U and a current signal I at two ends of the current conversion chain. The trap unit 62 further passes the voltage signal U and the current signal I through a first trap with a trap frequency F1 and a second trap with a trap frequency F2, respectively, wherein the trap frequency F1 of the first trap is greater than the trap frequency F2 of the second trap. The first alternating voltage U can be obtained according to the output signal of the voltage signal U and the current signal I passing through the first wave trap₁And a first alternating current I₁According to the voltage signal U and the current signal I, a second alternating voltage U can be obtained through an output signal of the second wave trap₂And a second alternating current I₂。

In the above process, according to the first AC voltage U₁And a first alternating current I₁Can obtain the capacitance to be monitoredThe state of the capacitor at the notch frequency F2 is based on the second AC voltage U₂And a second alternating current I₂The capacitance state of the capacitor to be monitored at the notch frequency F1 can be obtained, wherein F1 and F2 are two main harmonic frequencies of the low-frequency power transmission matrix converter in the embodiment, and therefore the embodiment can be implemented when S2 is implemented. Therefore, the frequency mixing of the current converter can be split, the capacitance states of the capacitor to be monitored under different harmonic frequencies can be monitored respectively, the defect that the working state of the capacitor can be monitored only under the frequency mixing condition in the traditional monitoring method is compared, and the working state of the capacitor to be monitored under the influence of different harmonics can be further accurately known by arranging the wave trap.

In this embodiment, in order to improve the accuracy of the capacitance value of the capacitor to be monitored, low pass filters are further respectively disposed behind the first wave trap and the second wave trap, and the output signal of the first wave trap and the output signal of the second wave trap are respectively filtered by the low pass filters. Wherein the cut-off frequency of the low pass filter through which the first trap output signal passes is greater than the trap frequency F1 of the first trap, and the cut-off frequency of the low pass filter through which the second trap output signal passes is greater than the trap frequency F2 of the second trap. Interference signals of other frequencies can be filtered through the low-pass filter, and then subsequent phase difference analysis is carried out, so that the capacitance value of the capacitor to be detected can be calculated more accurately in the subsequent process according to the voltage signal and the current signal processed by the wave trap.

In order to construct a calculation formula of the capacitance value, the phase angle unit 63 in this embodiment is based on the first ac voltage U₁And a first alternating current I₁Obtaining a first power factor angle alpha, U₁And I₁By calculating the phase difference between U₁And I₁The ratio of (d) determines the phase difference. In the same way, according to the second alternating voltage U₂And a second alternating current I₂A second power factor angle beta is obtained. At the same time, a first alternating voltage U is obtained₁And a second alternating voltage U₂Phase angle difference of

This embodiment still needs to acquire the voltage average value of the capacitance to be monitored in the preset period before the acquisition time, and the preset period before the acquisition time is determined according to the notch frequency of the first notch filter and the second notch filter, including: and determining a common divisor of the trap frequencies of the first trap and the second trap, and taking an integral multiple of the reciprocal of the common divisor as the duration of a preset time period, namely backing the duration forward from the acquisition time as the preset time period.

After the acquisition of the above parameters is completed, the calculating unit 64 deduces based on the ripple analysis of the capacitor to be monitored, so as to perform real-time online calculation on the capacitance value of the ith capacitor to be detected according to the following capacitance value calculation formula,

wherein, C_iFor the real-time capacitance value of the ith capacitor to be monitored in an on-line monitoring mode, N is the total number of all capacitors to be monitored on a current conversion chain, and U_ciFor the present voltage of the ith capacitor to be monitored, U_{ci_av}The voltage average value of the ith capacitor to be monitored in a preset time period, t is the acquisition time, S₁₁Is the product of the first AC voltage and the first AC current, i.e. S₁₁＝U₁I₁，S₁₂Is the product of the first AC voltage and the second AC current, i.e. S₁₂＝U₁I₂，S₂₁Is the product of the second AC voltage and the first AC current, i.e. S₂₁＝U₂I₁，S₂₂Is the product of the second AC voltage and the second AC current, i.e. S₂₂＝U₂I₂Where α is a first power factor angle, β is a second power factor angle,

is the phase angle difference, ω, between the first AC voltage and the second AC voltage₁Angular frequency being the trap frequency of the first trap, i.e. having ω₁＝2π×F1，ω₂Angular frequency being the trap frequency of the second trap, i.e. having ω₂2 pi × F2. In this embodiment, if the first ac voltage and the second ac voltage have the same amplitude, the first power factor angle α and the second power factor angle β are complementary angles, so that the above-mentioned calculation formula has cos α ═ cos β, and α and β in the above-mentioned calculation formula of the capacitance value can be replaced with each other, thereby simplifying the calculation formula.

The determining unit 65 obtains the real-time capacitance value of the ith capacitor to be monitored according to the above calculation formula, and compares the real-time capacitance value with the factory capacitance value of the capacitor, in this embodiment, the preset limit may be set to a certain limit in 80% -95% of the factory capacitance value, for example, the preset limit is 95% of the factory capacitance value, which means that if the real-time capacitance value decreases by 5% from the factory capacitance value, the capacitor is considered to be aged, and replacement or maintenance is prompted, and meanwhile, reference may be made to the capacitance values at two notch frequencies F1 and F2 obtained in S2, so as to provide reference for analyzing the influence degree of different harmonics on capacitor aging.

The sequence numbers in the above embodiments are merely for description, and do not represent the sequence of the assembly or the use of the components.

The above description is only exemplary of the present invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A capacitance online monitoring method of a low-frequency power transmission matrix converter is characterized by comprising the following steps:

collecting the current voltage of a capacitor to be monitored, and collecting voltage signals and current signals at two ends of a current conversion chain where the capacitor to be monitored is located;

respectively inputting the voltage signal and the current signal into a first wave trap and a second wave trap with different trap frequencies to obtain a first alternating voltage and a first alternating current of the output signal of the first wave trap and a second alternating voltage and a second alternating current of the output signal of the second wave trap;

acquiring a first power factor angle according to the first alternating voltage and the first alternating current, acquiring a second power factor angle according to the second alternating voltage and the second alternating current, and acquiring a phase angle difference between the first alternating voltage and the second alternating voltage;

combining the voltage average value of the capacitor to be monitored in a preset time period before the acquisition time, constructing a calculation formula of the capacitance value, and determining the real-time capacitance value of the capacitor to be monitored according to the calculation formula;

and when the real-time capacitance value is reduced to a preset limit value, judging that the capacitor to be monitored is aged.

2. The method according to claim 1, wherein the capacitance value is calculated by the formula:

wherein, C_iFor the real-time capacitance value of the ith capacitor to be monitored in an on-line monitoring mode, N is the total number of all capacitors to be monitored on a current conversion chain, and U_ciFor the present voltage of the ith capacitor to be monitored, U_{ci_av}The voltage average value of the ith capacitor to be monitored in a preset time period, t is the acquisition time, S₁₁Is the product of the first AC voltage and the first AC current, S₁₂Is the product of the first alternating voltage and the second alternating current, S₂₁Is the product of the second AC voltage and the first AC current, S₂₂Is the product of the second alternating voltage and the second alternating current, alpha is the first power factor angle, beta is the second power factor angle,

is the phase angle difference, ω, between the first AC voltage and the second AC voltage₁Angular frequency, ω, of the trap frequency of the first trap₂Is the angular frequency of the notch frequency of the second trap.

3. The method according to claim 1, wherein the low-frequency transmission matrix converter comprises at least one converter chain, each converter chain comprises at least one ac/dc conversion module, the ac/dc conversion module comprises a full-bridge circuit formed by four fully-controlled switching devices, and a capacitor to be monitored is connected in parallel with the full-bridge circuit.

4. The method according to claim 1, wherein the trap frequency of the first trap is greater than the trap frequency of the second trap.

5. The on-line capacitance monitoring method for the low-frequency transmission matrix converter according to claim 1, wherein the first alternating voltage U for obtaining the output signal of the first wave trap is obtained₁And a first alternating current I₁Second AC voltage U of output signal of second wave trap₂And a second alternating current I₂Before, still include: and respectively filtering the output signal of the first wave trap and the output signal of the second wave trap through a low-pass filter.

6. The on-line capacitance monitoring method for the low-frequency transmission matrix converter according to claim 5, wherein a cut-off frequency of a low-pass filter passed by the first trap output signal is greater than a notch frequency of the first trap, and a cut-off frequency of a low-pass filter passed by the second trap output signal is greater than a notch frequency of the second trap.

7. The method for online monitoring the capacitance of the low-frequency transmission matrix converter according to claim 1, wherein the preset time period before the acquisition time is determined according to the trap frequencies of the first trap and the second trap, and the method comprises the following steps:

and determining common divisor of the trap frequencies of the first trap and the second trap, and taking integral multiple of reciprocal of the common divisor as the duration of the preset time period.

8. An on-line capacitance monitoring device for a low-frequency power transmission matrix converter, the on-line capacitance monitoring device comprising:

a collecting unit: the current voltage acquisition module is used for acquiring the current voltage of the capacitor to be monitored and acquiring a voltage signal and a current signal at two ends of a current conversion chain where the capacitor to be monitored is located;

a notch unit: the first wave trap and the second wave trap are used for respectively inputting voltage signals and current signals into the first wave trap and the second wave trap with different trap frequencies, so that first alternating voltage and first alternating current of signals output by the first wave trap are obtained, and second alternating voltage and second alternating current of signals output by the second wave trap are obtained;

phase angle unit: the power factor correction circuit is used for acquiring a first power factor angle according to the first alternating voltage and the first alternating current, acquiring a second power factor angle according to the second alternating voltage and the second alternating current, and acquiring a phase angle difference between the first alternating voltage and the second alternating voltage;

a calculation unit: the method comprises the steps of establishing a calculation formula of a capacitance value by combining the voltage average value of the capacitor to be monitored in a preset time period before the acquisition time, and determining the real-time capacitance value of the capacitor to be monitored according to the calculation formula;

a determination unit: and the aging detection circuit is used for judging the aging of the capacitor to be monitored when the real-time capacitance value is reduced to a preset limit value.

9. The device according to claim 8, wherein the capacitance value is calculated by the formula:

wherein, C_iFor the real-time capacitance value of the ith capacitor to be monitored in an on-line monitoring mode, N is the total number of all capacitors to be monitored on a current conversion chain, and U_ciFor the present voltage of the ith capacitor to be monitored, U_{ci_av}The voltage average value of the ith capacitor to be monitored in a preset time period, t is the acquisition time, S₁₁Is the product of the first AC voltage and the first AC current, S₁₂Is the product of the first alternating voltage and the second alternating current, S₂₁Is the product of the second AC voltage and the first AC current, S₂₂Is the product of the second alternating voltage and the second alternating current, alpha is the first power factor angle, beta is the second power factor angle,

is the phase angle difference, ω, between the first AC voltage and the second AC voltage₁Angular frequency, ω, of the trap frequency of the first trap₂Is the angular frequency of the notch frequency of the second trap.

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