Distributed power quality monitoring system and method

Abstract

The invention belongs to the technical field of electric energy detection, and particularly relates to a distributed electric energy quality monitoring system and method. Comprising a voltage transformer, a low-pass filter, an analog-to-digital conversion module and a DSP chip. The distributed power quality monitoring method uses data stored in an RAM of the DSP chip for calculation, and comprises the following steps: S1, judging a disturbance starting moment; s2, judging a disturbance termination moment; s3, the disturbance type is judged; s4, storing, displaying and transmitting; a distributed electric energy quality monitoring system is used as a basic module for distributed electric power monitoring of an active station area, a distributed voltage signal passes through a voltage transformer and a conditioning circuit, is subjected to AD conversion and then is collected and calculated by a DSP processor, and a transient signal is extracted and identified through a voltage transient algorithm, so that a voltage transient event can be accurately monitored and a waveform can be recorded; through monitoring and analysis of the transient state of the photovoltaic voltage, management personnel are helped to carry out monitoring, operation management is facilitated, and risks are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric energy detection, and in particular relates to a distributed electric energy quality monitoring system and method. Background Art

[0002] With the large-scale access of non-traditional loads such as distributed photovoltaics and charging piles to distribution stations, the power quality and power balance issues in active stations are becoming increasingly prominent. Since distributed photovoltaics are easily affected by weather and have the characteristics of randomness and volatility, these characteristics have brought certain impacts on the power quality of the stations, especially the voltage quality, threatening the steady-state and transient voltage quality of the distribution network.

[0003] There is a significant difference between voltage transient disturbance and voltage fluctuation. Voltage transient disturbance is a large change in voltage in a very short period of time, which may directly or indirectly cause a variety of accidents, including motor shutdown, inverter voltage protection, computer storage data loss, etc. In distributed photovoltaic power generation systems, since a large number of household photovoltaic power generation systems are connected to the distribution area in a decentralized manner, voltage transient events will cause the voltage drop at the photovoltaic inverter port, resulting in a surge in the inverter's current injected into the grid, which in turn causes grid fluctuations and failures, bringing risks to the normal operation and management of the grid. Therefore, it is necessary to attach great importance to the monitoring and analysis of photovoltaic voltage transients, and for this purpose, a power quality monitoring system is needed. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a distributed power quality monitoring system and method to accurately monitor voltage transient events and record waveforms. By monitoring and analyzing photovoltaic voltage transients, it helps management personnel to monitor and facilitate operation management, thereby reducing risks.

[0005] The object of the present invention is achieved as follows: a distributed power quality monitoring system, which includes a voltage transformer, a low-pass filter, an analog-to-digital conversion module and a DSP chip;

[0006] The voltage transformer is connected to the low-pass filter, the analog-to-digital conversion module and the DSP chip in sequence;

[0007] The DSP chip is provided with a display interface for connecting to a display and a communication interface for connecting to a communication module;

[0008] The input signal of the distributed power quality monitoring system is the three-phase voltage of the monitoring point A / B / C. After being converted into a small voltage signal by the voltage transformer, the high-frequency components in the signal are filtered out by the low-pass filter, and then input into the analog-to-digital conversion module for analog-to-digital conversion. The DSP chip transmits the sampling pulse signal to 16BIT sampling according to the set sampling frequency, and the analog-to-digital conversion module performs synchronous sampling. When the sampling of the analog-to-digital conversion module is completed, the AD_busy signal is output. When the DSP chip detects that the state of the analog-to-digital conversion module has turned to idle, the sampling data is immediately read out from the analog-to-digital conversion module, stored in the RAM provided in the DSP chip itself for calculation, and then displayed and transmitted through the display interface and the communication interface.

[0009] A distributed power quality monitoring method, using the distributed power quality monitoring system and using the data stored in the RAM of the DSP chip for calculation, comprises the following steps:

[0010] S1. Determine the starting time of the disturbance;

[0011] S2, determining the disturbance termination time;

[0012] S3, identify the disturbance type;

[0013] S4. Store, display and transmit.

[0014] The step S1 of determining the disturbance starting time includes:

[0015] By detecting the difference signal between the voltage signal of the current cycle and the signal of the previous cycle, the discretized voltage sampling difference digital signal is expressed as:

[0016] Δu k =|u (k+n+1) -u (k+n) |>k d u max (1)

[0017] where u (k+n+1) Refers to the sampling value of the kth point in the n+1th cycle, u (k+n) Refers to the sampling value of the kth point in the nth cycle, k d is the sensitivity coefficient, generally taken as 0.05, u max The digital value corresponding to the maximum voltage

[0018] When Δu k =0, no disturbance occurs, otherwise there is disturbance. Since the actual signal will have a small fluctuation even if there is no disturbance, Δu is set kIt is compared with its threshold value. When it is greater than the threshold value, it is considered that disturbance has occurred. The threshold value is set to 0.05 times the maximum amplitude voltage of the signal.

[0019] The step S1 of determining the disturbance starting time includes:

[0020] According to the method of judging that the voltage deviation is greater than the set disturbance constant value; let δ = 2u ki α+ε, forming an adaptive linear threshold decision formula based on the sampling signal, that is,

[0021] ξ>2k k |u ki+1 |α+ε (2)

[0022] Where ξ is the voltage deviation, u ki is the voltage at the kth sampling point in the ith cycle, u ki+1 Refers to the voltage at the k+1th sampling point in the ith cycle; 2u ki+1 α is called the valuation coefficient, Indicates the sampling interval angle;

[0023] k k ≥1, is the reliability coefficient, 0<ε<1, considering the special case where the sampling signal is zero;

[0024] When the extracted disturbance signal is greater than δ, it is determined that a disturbance occurs.

[0025] When Δu k If the value is greater than the threshold or the extracted disturbance signal is greater than δ, it is determined that a disturbance has occurred, a disturbance start signal is issued, and timing begins.

[0026] The step S2 determines the disturbance termination time, including:

[0027] After receiving a disturbance signal that transitions to another state to start pulsation, the sampling point is compared with the previous sampling point and the next sampling point, and the reverse method is used to determine whether the deviation voltage meets the following conditions:

[0028] ξ<2k k |u ki+1 |α+ε (3)

[0029] When the extracted disturbance signal is less than δ, the termination condition is met and a termination pulse is issued;

[0030] After the above formula (3) is satisfied, the data of the same period before the disturbance is compared to see if it has been reset, that is, whether the five consecutive points satisfy the following formula:

[0031] Δu k =|u (k+n) -u(k+n-i) |<k d u max (4)

[0032] If satisfied, it is recorded as the end of disturbance;

[0033] Or after satisfying the above formula (3), the effective value calculated for 5 consecutive adjacent 3-point sampling values ​​is:

[0034]

[0035] Among them U 1m ,U 2m ,U 3m ,U 4m ,U 5m They are the effective values ​​of three points calculated five times in a row, and u1, u2, and u3 refer to the sampling values ​​of three consecutive points in each calculation;

[0036] When U 1m ,U 2m ,U 3m ,U 4m ,U 5m When the relative error between the two does not exceed 1% to 3%, it is recorded as the end of disturbance;

[0037] When the sampling value satisfies the conditions of formula (3) and formula (4) or formula (3) and formula (5), the disturbance is considered to be over and the termination time is recorded. If none of the above conditions are met, the disturbance will be automatically terminated and recorded after a certain set time.

[0038] The S3 determines the disturbance type including:

[0039] When u k satisfy

[0040]

[0041] That is, within half a cycle (10ms), the absolute value of the average value of the sampled voltage value is greater than 110% of the average value of the absolute value of the sinusoidal quantity, and the duration T d >20ms, N is the number of sampling points, then it is recorded as a temporary overvoltage event;

[0042] When there are at least 5 consecutive sampling points voltage u k satisfy

[0043] |u k |>k d |u max | (7)

[0044] That is, the absolute value of the voltage at the sampling point is greater than k dtimes the maximum value of the voltage, and the duration is 0.3ms<T d <20ms, recorded as a transient overvoltage event, where k d Refers to the reliability coefficient, which is 1.3-1.5;

[0045] When u k satisfy

[0046]

[0047] That is, the average value of the absolute value of the voltage sampled within half a cycle is less than 90% of the average value of the sinusoidal quantity 90%×0.637u max , and the duration is 10ms<T d <3s, N refers to the number of sampling points, then it is recorded as a voltage sag event;

[0048] When there are at least 20 consecutive sampling points u k satisfy

[0049] 0<|u k |<10%|u max | (9)

[0050] That is, when the absolute value of the voltage value sampled at 20 points is greater than 0 and less than 10% of the maximum voltage value 0<u k <10%|u max |, and the duration is 2ms<T d If the interruption time is less than 1min, it will be recorded as a short interruption event;

[0051] When a disturbance occurs but does not meet the conditions of instantaneous overvoltage, temporary overvoltage, voltage sag, or short interruption, it is recorded as a general disturbance event.

[0052] The average value of the absolute value of the sinusoidal quantity is 0.637 times its maximum value.

[0053] Beneficial effects of the present invention: A distributed power quality monitoring system of the present invention comprises a voltage transformer, a low-pass filter, an analog-to-digital conversion module and a DSP chip; the voltage transformer is sequentially connected to the low-pass filter, the analog-to-digital conversion module and the DSP chip; a distributed power quality monitoring method uses the distributed power quality monitoring system and uses the data stored in the RAM of the DSP chip for calculation, comprising the steps of: S1, determining the start time of the disturbance; S2, determining the end time of the disturbance; S3, distinguishing the type of disturbance; S4, storing and displaying and transmitting; the distributed power quality monitoring system is used as the basic module for distributed power monitoring in active areas, and the distributed voltage signal is passed through the voltage transformer and the conditioning circuit, and after AD conversion, it is provided to the DSP processor for collection and calculation; the transient signal is extracted and identified through the voltage transient algorithm, and the voltage transient event can be accurately monitored and the waveform can be recorded. By monitoring and analyzing the photovoltaic voltage transient, it helps the management personnel to monitor and facilitate the operation management, thereby reducing the risk. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0055] Figure 1 A schematic diagram of the structure of a distributed power quality monitoring system according to an embodiment of the present invention;

[0056] Figure 2 A schematic diagram of a flow chart of a voltage transient monitoring algorithm according to an embodiment of the present invention;

[0057] Figure 3 A schematic diagram of the band shape of a voltage transient monitoring indicator in an embodiment of the present invention;

[0058] Figure 4 Schematic diagram of the connection detection device in an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described below in conjunction with the accompanying drawings.

[0060] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0061] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] It should be noted that all directional indications in the embodiments of the present invention (such as up-down-left-right-front-back...) are only used to explain the relative position relationship - movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly. The connection can be a direct connection or an indirect connection.

[0063] like Figure 1-4 As shown, a distributed power quality monitoring system of the present invention includes a voltage transformer, a low-pass filter, an analog-to-digital conversion module and a DSP chip;

[0064] The voltage transformer is connected to the low-pass filter, the analog-to-digital conversion module and the DSP chip in sequence;

[0065] The DSP chip is provided with a display interface for connecting to a display and a communication interface for connecting to a communication module;

[0066] The input signal of the distributed power quality monitoring system is the three-phase voltage of the monitoring point A / B / C. After being converted into a small voltage signal by the voltage transformer, the high-frequency components in the signal are filtered out by the low-pass filter, and then input into the analog-to-digital conversion module for analog-to-digital conversion. The DSP chip transmits the sampling pulse signal to 16BIT sampling according to the set sampling frequency, and the analog-to-digital conversion module performs synchronous sampling. When the sampling of the analog-to-digital conversion module is completed, the AD_busy signal is output. When the DSP chip detects that the state of the analog-to-digital conversion module has turned to idle, the sampling data is immediately read out from the analog-to-digital conversion module, stored in the RAM provided in the DSP chip itself for calculation, and then displayed and transmitted through the display interface and the communication interface.

[0067] Further, in one embodiment, the DSP chip adopts the TMS320F28335 chip of TI company, which has 150MIPS, 512KB flash memory, EMIF, C2000 with 12-bit ADC. TM The 32-bit MCU includes a single-precision (32-bit) IEEE754 floating-point unit (FPU) and is programmed in floating-point mode to meet the needs of multi-data processing capabilities and high-precision processing tasks.

[0068] Furthermore, in one embodiment, the analog-to-digital conversion module uses the AD7606 chip, which is an 8-channel 16-bit AD with an input range of positive and negative 10V, a single 5V power supply, an input impedance of 1MΩ, and a maximum sampling rate of 200KSPS. It has built-in analog input clamp protection, a second-order anti-aliasing filter, a sample-and-hold amplifier, a 16-bit charge redistribution successive approximation analog-to-digital converter (ADC), a flexible digital filter, a 2.5V reference voltage source, a reference voltage buffer, and a high-speed serial and parallel interface.

[0069] A distributed power quality monitoring method, using the distributed power quality monitoring system and using the data stored in the RAM of the DSP chip for calculation, comprises the following steps:

[0070] S1. Determine the starting time of the disturbance;

[0071] S2, determining the disturbance termination time;

[0072] S3, identify the disturbance type;

[0073] S4. Store, display and transmit.

[0074] Voltage transient monitoring indicators include: instantaneous overvoltage events, temporary overvoltage events, voltage sag events, short-term interruption events and general disturbance events.

[0075] The voltage transient monitoring algorithm specifically determines the start and end time of the disturbance, records it, and classifies it according to the conditions it meets to determine the type of event. Its data source is the discrete sampling data of the DSP chip, which samples 200 points per cycle and performs continuous sampling.

[0076] There are two methods for determining the starting time of disturbance. The first method is:

[0077] By detecting the difference signal between the voltage signal of the current cycle and the signal of the previous cycle, the discretized voltage sampling difference digital signal is expressed as:

[0078] Δu k =|u (k+n+1) -u (k+n) |>k d u max (1)

[0079] where u (k+n+1) Refers to the sampling value of the kth point in the n+1th cycle, u (k+n) Refers to the sampling value of the kth point in the nth cycle, k d is the sensitivity coefficient, generally taken as 0.05, u max The digital value corresponding to the maximum voltage

[0080] When Δu k =0, no disturbance occurs, otherwise there is disturbance. Since the actual signal will have a small fluctuation even if there is no disturbance, Δu is set k It is compared with its threshold value. When it is greater than the threshold value, it is considered that disturbance has occurred. The threshold value is set to 0.05 times the maximum amplitude voltage of the signal.

[0081] The second method is:

[0082] According to the method of judging that the voltage deviation is greater than the set disturbance value, the size of the sampling value reliability coefficient δ is directly related to its detection sensitivity and reliability. Considering the fixed threshold, the linearity detection effect of the relative sampling value amplitude is not good. Let δ = 2u ki α+ε, forming an adaptive linear threshold decision formula based on the sampling signal, that is,

[0083] ξ>2k k |u ki+1 |α+ε (2)

[0084] Where ξ is the voltage deviation, u ki is the voltage at the kth sampling point in the ith cycle, u ki+1 Refers to the voltage at the k+1th sampling point in the ith cycle; 2u ki+1 α is called the valuation coefficient, Indicates the sampling interval angle;

[0085] k k ≥1, is the reliability coefficient, 0<ε<1, considering the special case where the sampling signal is zero;

[0086] When the extracted disturbance signal is greater than δ, it is determined that a disturbance occurs.

[0087] According to the above two methods, when Δu k If the value is greater than the threshold or the extracted disturbance signal is greater than δ, it is determined that a disturbance has occurred, a disturbance start signal is issued, and timing begins.

[0088] The step S2 determines the disturbance termination time, including:

[0089] After receiving a disturbance signal that transitions to another state to start pulsation, the sampling point is compared with the previous sampling point and the next sampling point, and the reverse method is used to determine whether the deviation voltage meets the following conditions:

[0090] ξ<2k k |u ki+1 α+ε (3)

[0091] When the extracted disturbance signal is less than δ, the termination condition is met and a termination pulse is issued;

[0092] After the above formula (3) is satisfied, the data of the same period before the disturbance is compared to see if it has been reset, that is, whether the five consecutive points satisfy the following formula:

[0093] Δu k =|u (k+n) -u (k+n-i) |<k d u max (4)

[0094] If satisfied, it is recorded as the end of disturbance;

[0095] Or after satisfying the above formula (3), the effective value calculated for 5 consecutive adjacent 3-point sampling values ​​is:

[0096]

[0097] Among them U 1m ,U 2m ,U 3m ,U 4m ,U 5m They are the effective values ​​of three points calculated five times in a row, and u1, u2, and u3 refer to the sampling values ​​of three consecutive points in each calculation;

[0098] When U 1m ,U 2m ,U 3m ,U 4m ,U 5m When the relative error between the two does not exceed 1% to 3%, it is recorded as the end of disturbance;

[0099] When the sampling value satisfies the conditions of formula (3) and formula (4) or formula (3) and formula (5), the disturbance is considered to be over and the termination time is recorded. If none of the above conditions are met, the disturbance will be automatically terminated and recorded after a certain set time.

[0100] The S3 determines the disturbance type including:

[0101] The sensitivity of smooth mutation points and harmonic quantities can be further corrected by using the average value method. Under normal circumstances, the average value of the absolute value of the sine quantity is 0.637 times its maximum value.

[0102] When u k satisfy

[0103]

[0104] That is, within half a cycle (10ms), the absolute value of the average value of the sampled voltage value is greater than 110% of the average value of the absolute value of the sinusoidal quantity, and the duration T d >20ms, N is the number of sampling points, then it is recorded as a temporary overvoltage event;

[0105] When there are at least 5 consecutive sampling points voltage u k satisfy

[0106] |u k |>k d |u max | (7)

[0107] That is, the absolute value of the voltage at the sampling point is greater than k d times the maximum value of the voltage, and the duration is 0.3ms<T d <20ms, recorded as a transient overvoltage event, where k d Refers to the reliability coefficient, which is 1.3-1.5;

[0108] When u k satisfy

[0109]

[0110] That is, the average value of the absolute value of the voltage sampled within half a cycle is less than 90% of the average value of the sinusoidal quantity 90%×0.637u max , and the duration is 10ms<T d <3s, N refers to the number of sampling points, then it is recorded as a voltage sag event;

[0111] When there are at least 20 consecutive sampling points u k satisfy

[0112] 0<|u k |<10%|u max | (9)

[0113] That is, when the absolute value of the voltage value sampled at 20 points is greater than 0 and less than 10% of the maximum voltage value 0<u k <10%|u max |, and the duration is 2ms<T d If the interruption time is less than 1min, it will be recorded as a short interruption event;

[0114] When a disturbance occurs but does not meet the conditions of instantaneous overvoltage, temporary overvoltage, voltage sag, or short interruption, it is recorded as a general disturbance event.

[0115] like Figure 4As shown in the figure, in the transient voltage monitoring process, it is necessary to distinguish between the steady-state characteristic voltage fluctuation during normal operation and the voltage transient disturbance during fault. Voltage fluctuation is a series of voltage (RMS value) changes or continuous changes in a certain period of time. The voltage fluctuation value is the difference between the two extreme values ​​(maximum value) and (minimum value) of adjacent RMS values. The percentage value relative to the nominal voltage can be expressed as:

[0116]

[0117] Voltage transient disturbances are generated randomly in power systems and last for a short time. Their signals are time-varying. The evaluation of transient voltage quality, especially voltage sag and voltage swell, is usually described by the degree of sag (swell) and duration. Transient indicators include: instantaneous overvoltage, temporary overvoltage, voltage sag and short-term interruption events.

[0118] For this purpose, transient indicators include: instantaneous overvoltage, temporary overvoltage, voltage sag and short interruption events, among which the instantaneous overvoltage is oscillatory or non-oscillatory, usually decays very quickly, lasts for only a few milliseconds and has a slow wave front (such as operating overvoltage) or tens of microseconds and has a fast wave front (such as lightning overvoltage). Temporary overvoltage refers to an overvoltage whose frequency is the power frequency or a certain harmonic frequency, and has no decay or slow decay within its duration. Voltage sag refers to the sudden drop in voltage at a certain point in the power system, which returns to normal after a short duration of half a cycle to a few seconds. Short-term voltage interruption refers to the disappearance of the power supply voltage for a period of time, generally not more than one minute. The short interruption can be considered as a voltage sag with an amplitude of 100%. Its waveform is as follows Figure 3 shown.

[0119] like Figure 4 The connection detection device shown is tested by a three-phase programmable voltage signal source to verify the correctness of the voltage transient monitoring device, and the waveform is recorded and drawn and the event identification is displayed through a display. The voltage swell, voltage sag and voltage terminal signals are applied to the three-phase voltage through the programmable voltage signal source, and all of them can be accurately identified and the waveforms recorded. The present invention accumulates, counts, mines and analyzes the correlation of data through the establishment of a distributed voltage transient monitoring system, and can subsequently conduct in-depth research on the attribution positioning, risk prediction and decision-making support of distributed power quality and other intelligent analysis functions.

[0120] In summary, a distributed power quality monitoring system of the present invention includes a voltage transformer, a low-pass filter, an analog-to-digital conversion module and a DSP chip; the voltage transformer is connected to the low-pass filter, the analog-to-digital conversion module and the DSP chip in sequence; a distributed power quality monitoring method uses the distributed power quality monitoring system and uses the data stored in the RAM of the DSP chip for calculation, including the steps of: S1, determining the start time of the disturbance; S2, determining the end time of the disturbance; S3, distinguishing the type of disturbance; S4, storing and displaying and transmitting; the distributed power quality monitoring system is used as the basic module for distributed power monitoring in active areas, and the distributed voltage signal is passed through the voltage transformer and the conditioning circuit, and after AD conversion, it is provided to the DSP processor for collection and calculation. Through the voltage transient algorithm, the transient signal is extracted and identified, and the voltage transient event can be accurately monitored and the waveform can be recorded. By monitoring and analyzing the photovoltaic voltage transient, it helps management personnel to monitor and facilitate operation management, thereby reducing risks.

[0121] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0122] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A distributed power quality monitoring system, characterized in that: Including voltage transformer, low-pass filter, analog-to-digital conversion module and DSP chip; The voltage transformer is connected to the low-pass filter, the analog-to-digital conversion module and the DSP chip in sequence; The DSP chip is provided with a display interface for connecting to a display and a communication interface for connecting to a communication module; The input signal of the distributed power quality monitoring system is the three-phase voltage of the monitoring point A / B / C. After being converted into a small voltage signal by the voltage transformer, the high-frequency components in the signal are filtered out by the low-pass filter, and then input into the analog-to-digital conversion module for analog-to-digital conversion. The DSP chip transmits the sampling pulse signal to 16BIT sampling according to the set sampling frequency, and the analog-to-digital conversion module performs synchronous sampling. When the sampling of the analog-to-digital conversion module is completed, the AD_busy signal is output. When the DSP chip detects that the state of the analog-to-digital conversion module has turned to idle, the sampling data is immediately read out from the analog-to-digital conversion module, stored in the RAM provided in the DSP chip itself for calculation, and then displayed and transmitted through the display interface and the communication interface.

2. A distributed power quality monitoring method, using a distributed power quality monitoring system as claimed in claim 1, and using the data stored in the RAM of the DSP chip for calculation, characterized in that: The following steps are involved: S1. Determine the starting time of the disturbance; S2, determining the disturbance termination time; S3, identify the disturbance type; S4. Store, display and transmit.

3. A distributed power quality monitoring method as claimed in claim 2, characterized in that: The step S1 of determining the disturbance starting time includes: By detecting the difference signal between the voltage signal of the current cycle and the signal of the previous cycle, the discretized voltage sampling difference digital signal is expressed as: Δu k =|u (k+n+1) -u (k+n) |>k d u max (1) where u (k+n+1) Refers to the sampling value of the kth point in the n+1th cycle, u (k+n) Refers to the sampling value of the kth point in the nth cycle, k d is the sensitivity coefficient, generally taken as 0.05, u max The digital value corresponding to the maximum voltage When Δu k =0, no disturbance occurs, otherwise there is disturbance. Since the actual signal will have a small fluctuation even if there is no disturbance, Δu is set k It is compared with its threshold value. When it is greater than the threshold value, it is considered that disturbance has occurred. The threshold value is set to 0.05 times the maximum amplitude voltage of the signal.

4. A distributed power quality monitoring method as claimed in claim 2, characterized in that: The step S1 of determining the disturbance starting time includes: According to the method of judging that the voltage deviation is greater than the set disturbance constant value; let δ = 2u ki α+ε, forming an adaptive linear threshold decision formula based on the sampling signal, that is, ξ>2k k |u ki+1 |a+e (2) Where ξ is the voltage deviation, u ki is the voltage at the kth sampling point in the ith cycle, u ki+1 Refers to the voltage at the k+1th sampling point in the ith cycle; 2u ki+1 α is called the valuation coefficient, Indicates the sampling interval angle; k k ≥1, is the reliability coefficient, 0<ε<1, considering the special case where the sampling signal is zero; When the extracted disturbance signal is greater than δ, it is determined that a disturbance occurs.

5. A distributed power quality monitoring method as claimed in claim 3 or 4, characterized in that: When Δu k If the value is greater than the threshold or the extracted disturbance signal is greater than δ, it is determined that a disturbance has occurred, a disturbance start signal is issued, and timing begins.

6. A distributed power quality monitoring method as claimed in claim 5, characterized in that: The step S2 determines the disturbance termination time, including: After receiving a disturbance signal that transitions to another state to start pulsation, the sampling point is compared with the previous sampling point and the next sampling point, and the reverse method is used to determine whether the deviation voltage meets the following conditions: ξ<2k k |u ki+1 a+e (3) When the extracted disturbance signal is less than δ, the termination condition is met and a termination pulse is issued; After the above formula (3) is satisfied, the data of the same period before the disturbance is compared to see if it has been reset, that is, whether the five consecutive points satisfy the following formula: Δu k =|u (k+n) -u (k+n-i) |<k d u max (4) If satisfied, the disturbance is recorded as ended; Or after satisfying the above formula (3), the effective value calculated for 5 consecutive adjacent 3-point sampling values ​​is: Among them U 1m ,U 2m ,U 3m ,U 4m ,U 5m They are the effective values ​​of three points calculated five times in a row, and u1, u2, and u3 refer to the sampling values ​​of three consecutive points in each calculation; When U 1m ,U 2m ,U 3m ,U 4m ,U 5m When the relative error between the two does not exceed 1% to 3%, it is recorded as the end of disturbance; When the sampling value satisfies the conditions of formula (3) and formula (4) or formula (3) and formula (5), the disturbance is considered to be over and the termination time is recorded. If none of the above conditions are met, the disturbance will be automatically terminated and recorded after a certain set time.

7. A distributed power quality monitoring method as claimed in claim 6, characterized in that: The S3 determines the disturbance type including: When u k satisfy That is, within half a cycle (10ms), the absolute value of the average value of the sampled voltage value is greater than 110% of the average value of the absolute value of the sinusoidal quantity, and the duration T d >20ms, N is the number of sampling points, then it is recorded as a temporary overvoltage event; When there are at least 5 consecutive sampling points voltage u k satisfy in k |>k d |in max | (7) That is, the absolute value of the voltage at the sampling point is greater than k d times the maximum value of the voltage, and the duration is 0.3ms<T d <20ms, recorded as a transient overvoltage event, where k d Refers to the reliability coefficient, which is 1.3-1.5; When u k satisfy That is, the average value of the absolute value of the voltage sampled within half a cycle is less than 90% of the average value of the sinusoidal quantity 90%×0.637u max , and the duration is 10ms<T d <3s, N refers to the number of sampling points, then it is recorded as a voltage sag event; When there are at least 20 consecutive sampling points u k satisfy 0<|u k |<10%|in max | (9) That is, when the absolute value of the voltage value sampled at 20 points is greater than 0 and less than 10% of the maximum voltage value 0<u k <10%|u max |, and the duration is 2ms<T d If the interruption time is less than 1min, it will be recorded as a short interruption event; When a disturbance occurs but does not meet the conditions of instantaneous overvoltage, temporary overvoltage, voltage sag, or short interruption, it is recorded as a general disturbance event.

8. A distributed power quality monitoring method as claimed in claim 7, characterized in that: The average value of the absolute value of the sinusoidal quantity is 0.637 times its maximum value.

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