A portable power distribution system dynamic harmonic detection device and method

Abstract

The present invention relates to a portable dynamic harmonic detection device and method for a power distribution system. The device includes a sampling module, a harmonic calculation module, a harmonic generation module, and a background analysis and calculation module. The sampling module, harmonic calculation module, and background analysis and calculation module are connected in sequence, and the background analysis and calculation module is connected to the harmonic generation module. The sampling module is connected to a measurement point PCC. After the detection device is activated, the harmonic generation module actively adds harmonic currents. The sampling module collects all power quality parameters before and after the measurement point PCC and sends them to the harmonic calculation module. The harmonic calculation module sends the calculated data to the background analysis and calculation module. The background analysis and calculation module combines the frequency and amplitude of the harmonic currents added by the harmonic generation module to analyze the power distribution system's anti-interference ability against harmonic currents of different frequencies under different operating environments. Compared with the existing technology, the present invention has the advantages of small size and light weight.

Description

Technical Field

[0001] The present invention relates to a dynamic harmonic detection technology for a power distribution system, and in particular to a portable dynamic harmonic detection device and method for a power distribution system. Background Art

[0002] Electricity development is based on balancing energy supply and demand. However, the load structure of modern power grids has undergone a fundamental shift compared to traditional grids. While the widespread use of power electronics has greatly facilitated people's lives and production, it has also severely impacted grid power quality, leading to frequent occurrences of harmonic interference, voltage and frequency fluctuations, and three-phase imbalance. To address these issues, a wide range of power quality optimization and control devices have emerged in recent years, including AC filters, static VAR compensators (SVCs, TCRs, MCRs, TSCs, TSFs), active power filters (APFs), static VAR generators (SVGs, STATCOMs), unified power quality compensators (UPQCs), solid-state transfer switches (SSTSs), power electronic transformers (PETs), and dynamic voltage restorers (DVRs). The selection of control equipment for engineering projects is crucial, and is based on measured data.

[0003] In existing technologies, simulation and actual measurement are crucial for understanding power quality issues. Due to the presence of numerous random uncertainties, simulation is primarily used during the planning phases for power grids and users. Once the grid is operational or users are connected, actual measurement is the most effective way to understand the true power quality situation. Currently, power quality measurement methods primarily include continuous monitoring, scheduled patrol monitoring, and specialized testing. Corresponding power quality monitoring equipment includes remote power quality detectors, portable multi-function power quality analyzers, and handheld harmonic analyzers. The above monitoring devices can obtain all electrical parameters of the power grid. The advantages of remote power quality detectors are that they form a regional or local power grid monitoring network based on multi-point monitoring, allowing for power flow analysis of the entire region. However, their disadvantage is that they can only measure at fixed monitoring points. The advantages of portable multi-functional power quality analyzers are their large storage capacity, portability, and extensive software analysis platforms. However, their disadvantage is that they are not suitable for continuous remote monitoring or multi-point monitoring. The advantages of handheld harmonic analyzers are their portability, ability to store partial waveforms, communication interfaces, and extensive background analysis systems. However, their disadvantages are that they store little data, record single-phase voltage and current parameters, and are only suitable for regular on-site inspections and on-site commissioning of nonlinear equipment. Currently, these types of power quality monitoring devices share common characteristics: a rich variety of detection data, high sampling accuracy, fast multi-point data acquisition and calculation speed, and multiple data processing methods. By entering the collected data into a simulation system, the actual operation of the distribution system can be almost completely restored. The above measurement data are all based on instantaneous data at steady-state system levels. While these data can be used to analyze the current system operation, they cannot directly analyze the system's operation after adding control equipment. This is because power quality control equipment is primary equipment, and connecting primary equipment to the grid will inevitably change some parameters of the overall grid. As the grid transitions from steady-state to transient and then back to steady-state, how can we detect and determine the operating trend of the distribution system after actively adding some transient interference (such as third-order harmonic current, fifth-order harmonic current, etc.)? Can the purpose of power quality optimization be achieved after adding compensation devices? This requires the provision of a new detection device and method to solve the above technical problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a portable power distribution system dynamic harmonic detection device and method in order to overcome the above-mentioned defects in the prior art.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] According to one aspect of the present invention, a portable dynamic harmonic detection device for a power distribution system is provided, the device comprising a sampling module, a harmonic calculation module, a harmonic generation module, and a background analysis and calculation module, wherein the sampling module, the harmonic calculation module, and the background analysis and calculation module are connected in sequence, and the background analysis and calculation module is connected to the harmonic generation module;

[0007] The sampling module is connected to the measuring point PCC. After the detection device is started, the harmonic generation module actively adds harmonic current. The sampling module collects all the power quality parameters before and after the measuring point PCC and sends them to the harmonic calculation module. The harmonic calculation module sends the calculated data to the background analysis and calculation module. The background analysis and calculation module combines the frequency and amplitude of the harmonic current added by the harmonic generation module to analyze the anti-interference ability of the distribution system to harmonic currents of different frequencies under different operating environments. Finally, the change data of the system impedance and load impedance after the external interference is added are screened out. The corresponding harmonic control equipment and capacity size at the measuring PCC are evaluated through this data.

[0008] As a preferred technical solution, the sampling module includes a set of voltage sampling circuits and two sets of flexible current sampling loops, wherein the two sets of flexible current sampling loops include a PCC front-end current sampling loop and a PCC back-end current sampling loop.

[0009] As a preferred technical solution, the four-phase voltage lines of the set of voltage sampling circuits are connected to the measurement point PCC through crocodile clamps; the PCC front-end current sampling loop is located at the front end of the measurement point PCC close to the transformer side, and the PCC rear-end current sampling loop is located at the rear end of the measurement point PCC close to the load device side.

[0010] As a preferred technical solution, the harmonic calculation module includes a preprocessor, a sampling frequency generator, a sampling conversion circuit, a discrete Fourier transform DFT unit, a grouping combination module and a smoothing module. The sampling conversion circuit is connected to the preprocessor, the sampling frequency generator and the discrete Fourier transform DFT unit respectively, and the discrete Fourier transform DFT unit, the grouping combination module and the smoothing module are connected in sequence.

[0011] As a preferred technical solution, the harmonic generation module includes an LCL filter module, a three-level power module, a logic processing module, a core control module and a first display module; the LCL filter module is connected to the logic processing module, the logic processing module is connected to the three-level power module, and the LCL filter module, three-level power module, logic processing module and first display module are respectively connected to the core control module.

[0012] As a preferred technical solution, the background analysis and calculation module includes a protocol conversion module, a background system receiving module and a second display module connected in sequence.

[0013] As a preferred technical solution, the sampling module collects the PCC point voltage, PCC front-end current IS, PCC rear-end current IL, and extracts the voltage and current angle through the sampling frequency generator phase lock. calculate and

[0014] The above-mentioned data is sent to the harmonic calculation module for sampling conversion, and discrete Fourier transform DFT is performed on the front-end current IS of the PCC point and the rear-end current IL of the PCC point respectively to extract the reactive component and harmonic component, and the effective value of each component is calculated by gain;

[0015] At the same time, the harmonic generation module locks the and According to the set harmonic amplitude, combined with and Generate harmonic generation instructions; the harmonic components extracted by the discrete Fourier transform (DFT) unit are compared with the frequency of the harmonic generation instructions to screen out the harmonic components with the same frequency as the harmonic generation instructions. Then, the same-frequency harmonic components of the front-end current IS of the PCC point are compared with the same-frequency components of the rear-end current IL of the PCC point. The sampling data and comparison results are sent to the background analysis and calculation module for secondary analysis. At the same time, the sampling results and comparison analysis results are output and displayed.

[0016] As a preferred technical solution, the harmonic generation instruction can be set to output a single harmonic current or output multiple times simultaneously.

[0017] According to another aspect of the present invention, a method for detecting dynamic harmonics in a portable power distribution system is provided, comprising the following steps:

[0018] Step 1: Determine the PCC point and install a set of voltage lines UA, UB, and UC of a portable dynamic harmonic detection device, as well as two sets of flexible current sampling loops. The current sampling loops are for the PCC front-end currents ISa, ISb, ISc, and ISn, and the PCC back-end currents ILa, ILb, ILc, and ILn.

[0019] Step 2: Start the portable dynamic harmonic detection device, in which the harmonic generation module only calculates the set subharmonic command current, clears the data in the verification comparator, and saves the collected and calculated specified subharmonic data into the verification comparator;

[0020] Step 3: The harmonic generation module calculates the set subharmonic command current and actively injects the set subharmonic current into the power grid system, and saves the collected and calculated specified subharmonic data into the verification comparator;

[0021] Step 4: Compare the two sets of data in the check comparator. If the difference between the effective value of the PCC front-end current IS_hn' and the effective value of the PCC front-end current IS_hn is greater than or equal to the effective value of the device output harmonic current IB_hn, it can be determined that the distribution system has no amplification effect on the specified harmonic at that moment;

[0022] If the difference between the effective value of the PCC front-end current IS_hn' and the effective value of the PCC front-end current IS_hn is greater than zero and less than the effective value of the device output harmonic current IB_hn, then it can be determined that the distribution system has an amplification effect on the specified harmonic at that moment;

[0023] If the difference between the effective value of the PCC front-end current IS_hn' and the effective value of the PCC front-end current IS_hn is less than zero, then it can be determined that the power distribution system has a significant amplification effect on the specified harmonic at that moment;

[0024] Step 5: During the dynamic harmonic detection process, the portable dynamic harmonic detection device generates harmonic currents of the 2nd, 3rd, ..., 50th order of the set amplitude through the harmonic generation module in the device, injects them into the distribution system, and records the stability data of the distribution system before and when the specified harmonic is generated. The data is uploaded to the background analysis and calculation module through the communication module to generate a full electrical parameter and dynamic harmonic measurement and detection report.

[0025] As a preferred technical solution, the described no amplification effect means that the PCC front-end impedance is smaller than the PCC rear-end impedance; the described amplification effect PCC means that the front-end impedance is close to the PCC rear-end impedance, and the system has a risk of series resonance; the described obvious amplification effect means that the PCC front-end impedance is greater than the PCC rear-end impedance, and the system is capacitive, which has a risk of oscillation.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. The portable dynamic harmonic detection device of the present invention is small in size and light in weight, with a design weight of less than 10 kg, and can be easily carried;

[0028] 2. The portable dynamic harmonic detection device of the present invention is different from traditional power quality analyzers. It can not only passively detect various harmonic-related parameters of the system in real time, but also actively output or collectively output the set subharmonic current in a timely manner, and monitor the changes in the subharmonic current before and during the injection of the set subharmonic current, and before and after PCC.

[0029] 3. The portable dynamic harmonic detection device of the present invention can set the duration of the output subharmonic to be no more than 10ms; the output amplitude can be set; the output time interval can be set; if the output of the same subharmonic is determined to be harmonic amplification, the subharmonic will no longer be actively output;

[0030] 4. The portable dynamic harmonic detection device of the present invention outputs a test harmonic current phase that is sampled and phase-locked by the PCC point voltage. The generated test command harmonic current phase is identical to the PCC point phase but opposite in amplitude, thus preventing harmonic pollution to the system and triggering system oscillation.

[0031] 5. The portable dynamic harmonic detection device of the present invention has one set of voltage sampling interfaces and two sets of current sampling interfaces. The current of each phase of the two sets of current sampling is consistent with the phase of the corresponding voltage (for example, ISa and ILa can both calculate the voltage and current phase angle based on the phase of Ua). It can simultaneously monitor the changes in the system full-wave power factor PF and fundamental power factor DPF before and after the PCC point;

[0032] 6. The sampling time interval of the data compared with each other in the comparator of the portable dynamic harmonic detection device of the present invention is no more than 20ms (one cycle). The sampling interval is short and the comparison calculation accuracy is high. It is also applicable to some power distribution systems with fast load changes.

[0033] 7. The portable dynamic harmonic detection device of the present invention can upload the monitoring data to the background analysis system through the communication module, and can perform secondary analysis on the amplification phenomenon of specific subharmonic currents. It can summarize the amplification data of harmonic currents with the same output frequency and different amplitudes, and estimate the amplification amplitude of the subharmonic when adding harmonic source load or compensation device according to the amplification factor at different amplitudes, and generate a dynamic harmonic detection report. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the primary wiring diagram of the portable dynamic harmonic monitoring device of the present invention;

[0035] Figure 2 This is a basic structural diagram of the harmonic measurement of the power quality detection device of the present invention;

[0036] Figure 3 This is a basic structural diagram of the portable dynamic harmonic monitoring device of the present invention;

[0037] Figure 4 This is a schematic diagram of the portable dynamic harmonic detection device of the present invention;

[0038] Figure 5 This is a flow chart of measurement information calculation and analysis of the portable dynamic harmonic detection device of the present invention. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0040] The present invention discloses a portable power distribution system dynamic harmonic detection device and method. The device is compact and portable, and can be installed at the detection point without power outage. During the detection process, it can actively and periodically add some transient interference to collect changes in system parameters before and after the interference is added. The method is applied to dynamic harmonic detection and data analysis at points requiring power quality management in a low-voltage 0.4KV power distribution system. First, a low-voltage 0.4KV measurement point (common connection point PCC) is selected, and the four-phase voltage lines (phase A, phase B, phase C, phase N) of the detection device are connected to the measurement point (PCC) via alligator clamps. The device's two sets of flexible current loops (ISa, ISb, ISc, ISn, ILa, ILb, ILc, ILn) are installed: one set is placed at the front end of the PCC near the transformer side (ISa, ISb, ISc, ISn), and the other set is placed at the rear end of the PCC near the load device side (ILa, ILb, ILc, ILn). The detection device is then activated, locking the system frequency in real time and proactively injecting instantaneous 2nd, 3rd, 4th, and 50th harmonic currents in sequence. The detection device simultaneously records all power quality parameters before and after PCC operation. Combined with the frequency and amplitude of the harmonic currents injected by the detection device itself, it analyzes the distribution system's ability to resist interference from harmonic currents of varying frequencies under different operating conditions. Finally, data on changes in system and load impedance after the external interference is filtered out. This data can be used to assess the appropriate harmonic control equipment and capacity at that point (PCC), thereby achieving more accurate dynamic harmonic detection.

[0041] The grid operation parameters include

[0042] PCC point voltage frequency f,

[0043] PCC point phase voltage UA, UB, UC,

[0044] The front end of the PCC is close to the transformer side current ISa, ISb, ISc, ISn,

[0045] The current ILa, ILb, ILc, and ILn are close to the load equipment side of the PCC rear end.

[0046] Detect equipment output current IBa, IBb, IBc, IBn;

[0047] The primary wiring of the portable dynamic harmonic monitoring device is shown in Figure 1, where PCC is the common electrical connection point; IS is the sampling current at the front end of PCC; IL is the sampling current at the back end of PCC; IB is the output current of the detection device;

[0048] According to the actual collected current and voltage before and after the PCC point, calculate

[0049] PCC front-end active power PS, PSa, PSb, PSc,

[0050] PCC back-end active power PL, PLa, PLb, PLc,

[0051] PCC front-end reactive power QS, QSa, QSb, QSc,

[0052] PCC back-end reactive power QL, QLa, QLb, QLc,

[0053] PCC front-end apparent power SS, SSa, SSb, SSc,

[0054] PCC back-end apparent power SL, SLa, SLb, SLc,

[0055] PCC front-end fundamental power factor DPF_s, DPF_sa, DPF_sb, DPF_sc,

[0056] PCC rear end fundamental power factor DPF_1, DPF_1a, DPF_1b, DPF_1c,

[0057] PCC front-end full-wave power factor PF_s, PF_sa, PF_sb, PF_sc,

[0058] PCC back-end full-wave power factors PF_1, PF_1a, PF_1b, PF_1c;

[0059] And through the discrete Fourier transform DFT to extract the effective value and proportion of each harmonic of voltage and current, calculate

[0060] Total harmonic distortion rate of PCC point voltage THDu, THDu_A, THDu_B, THDu_C,

[0061] Effective value of each voltage harmonic UA_h1...UA_hn (n=1...50), UB_h1...UB_hn (n=1...50), UC_h1...UC_hn (n=1...50),

[0062] Voltage harmonic content UA_thd1...UA_thdn (n=1...50), UB_thd1...UB_thdn (n=1...50), UC_thd1...UC_thdn (n=1...50),

[0063] PCC front-end current total harmonic distortion rate THDi_S, THDi_SA, THDi_SB, THDi_SC,

[0064] Total harmonic distortion rate of the PCC rear-end current THDi_L, THDi_LA, THDi_LB, THDi_LC,

[0065] The effective values ​​of the current harmonics at the front end of the PCC are ISa_h1...ISa_hn (n=1...50), ISb_h1...ISb_hn (n=1...50), and ISc_h1...ISc_hn (n=1...50).

[0066] The effective values ​​of the current harmonics at the rear end of the PCC are ILa_h1...ILa_hn (n=1...50), ILb_h1...ILb_hn (n=1...50), and ILc_h1...ILc_hn (n=1...50).

[0067] The harmonic contents of the current at the front end of the PCC are ISa_thd1...ISa_thdn (n=1...50), ISb_thd1...ISb_thdn (n=1...50), and ISc_thd1...ISc_thdn (n=1...50).

[0068] The effective values ​​of the current harmonics at the rear end of the PCC are ILa_thd1...ILa_thdn (n=1...50), ILb_thd1...ILb_thdn (n=1...50), and ILc_thd1...ILc_thdn (n=1...50).

[0069] The accuracy and calculation formula of each indicator of the testing equipment are shown in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] Where u is the actual measured value of voltage, u N is the given value of u; f is the actual test value of frequency, f N is the given value of f; ε uis the actual test value of voltage imbalance, ε uN is ε u The given value of ε i is the actual test value of current imbalance, ε iN is ε i The given value of u(i) h is the actual test value of the hth harmonic voltage (current), u(i) hN for u(i) h Given value; P st is the short-time flicker test value, P stN P st Given value; δ u is the voltage fluctuation test value, δ uN is δ u The given value of .

[0074] IEC and national standards stipulate that harmonic measurement should adopt Fourier analysis method. The power grid harmonic measurement adopts Fourier transform with strict synchronization sampling with the power grid fundamental wave period and rectangular window. The basic time window width of harmonic measurement is stipulated as 10 cycles. The basic structure of harmonic measurement for power grid power quality detection device is shown in Figure 2 , where the voltage input is the phase voltage at the system PCC point; the current input is the front-end current at the system PCC point; output 1 is the DFT analysis result; output 2 is the harmonic and interharmonic subgroups; output 3 is the harmonic group and interharmonic group; output 4 is the compliance of the measurement result according to the limit value test of the relevant standards.

[0075] The portable dynamic harmonic monitoring device is mainly composed of four parts: sampling part, harmonic calculation part, harmonic generation part, and background analysis and calculation part. Among them, the sampling part is composed of a group of voltage sampling (UA, UB, UC) and two groups of flexible current sampling loops (PCC front-end current ISa, ISb, ISc, ISn and PCC back-end current ILa, ILb, ILc, ILn); the harmonic calculation part is composed of a preprocessor, a sampling frequency generator, a sampling conversion, a discrete Fourier series DFT, a group combination module, a flat wave module, etc.; the harmonic generation part is composed of an LCL filter module, a three-level power module, a logic module, a core control module, a display module, etc.; the background analysis and calculation part is composed of a protocol conversion module, a background system receiving module, a display module, etc. The basic structure of the portable dynamic harmonic monitoring device is as follows: Figure 3 , where the voltage input is the phase voltage at the system PCC point; current input 1 is the front-end current IS at the system PCC point; current input 2 is the rear-end current IL at the system PCC point; and the output is the comparative analysis results and various parameter displays.

[0076] The control principle diagram of the sampling part, harmonic calculation part and harmonic generation part of the portable dynamic harmonic detection device is as follows: Figure 4, where the voltage input is the phase voltage at the system PCC point; current input 1 is the front-end current IS at the system PCC point; current input 2 is the rear-end current IL at the system PCC point; and the output is the comparative analysis results and various parameter displays.

[0077] The portable dynamic harmonic detection device collects the PCC point voltage, PCC front-end current IS, PCC back-end current IL, and extracts the voltage and current angle through the sampling frequency generator phase lock (PLL) calculate and The above sampling data is sent to the IC controller for sampling conversion, and the front-end current IS of the PCC point and the rear-end current IL of the PCC point are subjected to discrete Fourier transform DFT respectively, and the reactive component and harmonic component are extracted respectively, and the effective value of each component is calculated by gain; at the same time, the harmonic generation module locks the harmonics according to the calculation result of the sampling frequency generator. and According to the harmonic amplitude set by the harmonic generator, combined with and Generate a harmonic generation instruction, which can be set to a single harmonic current output or multiple simultaneous outputs; the harmonic components extracted by DFT are compared with the frequency of the harmonic generation instruction to screen out the harmonic components with the same frequency as the harmonic generation instruction, and then compare the same-frequency harmonic components of the front-end current IS of the PCC point with the same-frequency components of the rear-end current IL of the PCC point. The sampling data and comparison results are sent to the verification comparator for secondary analysis, and the sampling results and comparison analysis results are output and displayed at the same time.

[0078] like Figure 5 The figure shows the flow chart of the measurement information calculation and analysis of the portable dynamic harmonic detection device, where

[0079] U is the three-phase voltage UA, UB, UC;

[0080] IS is the current ISa, ISb, ISc, and ISn at the front end of the PCC close to the transformer side;

[0081] IL is the current ILa, ILb, ILc, ILn at the back end of the PCC close to the load equipment side;

[0082] IS_hn (n=2...50th) is the effective value of each harmonic of the current at the front end of the PCC when the detection device output IB=0: ISa_h1...ISa_hn (n=1...50th), ISb_h1...ISb_hn (n=1...50th), ISc_h1...ISc_hn (n=1...50th);

[0083] IL_hn (n=2...50) is the effective value of the current harmonics ILa_h1...ILa_hn (n=1...50), ILb_h1...ILb_hn (n=1...50), and ILc_h1...ILc_hn (n=1...50) at the back end of the PCC when the detection device output IB=0;

[0084] IS_hn' (n = 2...50th) is the effective value of each harmonic current at the front end of the PCC when the detection device outputs IB = the set value: ISa_h1'...ISa_hn' (n = 1...50th), ISb_h1'...ISb_hn' (n = 1...50th), ISc_h1'...ISc_hn' (n = 1...50th);

[0085] IL_hn' (n = 2...50) is the effective value of each harmonic current ILa_h1'...ILa_hn' (n = 1...50), ILb_h1'...ILb_hn' (n = 1...50), ILc_h1'...ILc_hn' (n = 1...50) at the back end of the PCC when the detection device output IB = the set value;

[0086] IS_hk' is the effective value of the kth harmonic current in the PCC front-end harmonic current that is screened out with the same frequency as the harmonic generator and when IB = 0;

[0087] IS_hk is the effective value of the kth harmonic current in the PCC front-end harmonic current when the harmonic generator has the same frequency as the selected one and IB = the set value;

[0088] IL_hk' is the effective value of the kth harmonic current in the harmonic current at the back end of the PCC, which is the same frequency as the harmonic generator and when IB = 0;

[0089] IL_hk is the effective value of the kth harmonic current in the harmonic current at the back end of the PCC when the harmonic current is filtered out and has the same frequency as the harmonic generator and IB = the set value;

[0090] IB_hk is the effective value of the kth harmonic current output by the harmonic generator according to the set value;

[0091] The detection method of the portable dynamic harmonic detection device is as follows:

[0092] Step 1: Determine the PCC point, according to Figure 1-1 A set of voltage lines (UA, UB, UC) of a portable dynamic harmonic detection device and two sets of flexible current sampling loops (PCC front-end current ISa, ISb, ISc, ISn and PCC back-end current ILa, ILb, ILc, ILn) are installed in the wiring mode.

[0093] Step 2: Start the portable dynamic harmonic detection device. The harmonic generation module of the device only calculates the set harmonic command current and does not actually generate the output harmonic effective value. The data in the verification comparator is cleared and the collected and calculated specified harmonic data (IS_hn' (n = 1...50 set harmonic order) and IL_hn' (n = 1...50 set harmonic order)) are saved in the verification comparator.

[0094] Step 3: The harmonic generation module of the device calculates the set subharmonic command current and actively injects the set subharmonic current into the power grid system. The collected and calculated specified subharmonic data (IS_hn (n=1...50 set harmonic order) and IL_hn (n=1...50 set harmonic order)) are saved in the verification comparator;

[0095] Step 4: Compare the two sets of data in the check comparator. If the difference between the effective value of the PCC front-end current IS_hn' (n = 1...50 set harmonic order) and the effective value of the PCC front-end current IS_hn (n = 1...50 set harmonic order) is greater than the effective value of the device output harmonic current IB_hn (n = 1...50 set harmonic order), then it can be determined that the distribution system has no amplification effect on the specified harmonic at that moment, that is, the PCC front-end impedance is smaller than the PCC back-end impedance; if the difference between the effective value of the PCC front-end current IS_hn' (n = 1...50 set harmonic order) and the effective value of the PCC front-end current IS_hn (n = 1...50 set harmonic order) is equal to the effective value of the device output harmonic current IB_hn (n = 1...50 set harmonic order), then it can be determined that the distribution system has no amplification effect on the specified harmonic at that moment, that is, the PCC front-end impedance is smaller than the PCC back-end impedance. Impedance; If the difference between the effective value of the PCC front-end current IS_hn' (n = 1...50, set harmonic order) and the effective value of the PCC front-end current IS_hn (n = 1...50, set harmonic order) is greater than zero and less than the effective value of the device output harmonic current IB_hn (n = 1...50, set harmonic order), then it can be determined that the distribution system has an amplification effect on the specified harmonic at that moment, that is, the PCC front-end impedance is close to the PCC back-end impedance, and the system has a risk of series resonance; If the difference between the effective value of the PCC front-end current IS_hn' (n = 1...50, set harmonic order) and the effective value of the PCC front-end current IS_hn (n = 1...50, set harmonic order) is less than zero, then it can be determined that the distribution system has an amplification effect on the specified harmonic at that moment, that is, the PCC front-end impedance is greater than the PCC back-end impedance, the system is capacitive for this harmonic, and the system has a risk of oscillation. The verification and comparison are shown in Table 2.

[0096] Table 2

[0097]

[0098] IS_hn' is the effective value of the specified harmonic current at the front end of the PCC when the device does not generate the specified harmonic current;

[0099] IS_hn is the effective value of the specified harmonic current at the front end of the PCC when the device generates a specified harmonic current;

[0100] IB_hn is the effective value of the specified harmonic current output by the device;

[0101] In the presence of nth harmonics, the impedance of the inductive load in the distribution system is:

[0102] X L(n) =2πf(n)L(1)........................①

[0103] In the presence of nth harmonic, the impedance of the capacitive load of the distribution system is:

[0104]

[0105] When there are high-order harmonics, the increase of f(n) leads to X L(n) Increase, and X C(n) This further causes the subharmonic current to flow in the direction of smaller impedance.

[0106] Step 5: During the dynamic harmonic detection process, the portable dynamic harmonic detection device generates harmonic currents of the 2nd, 3rd, ..., 50th order of the set amplitude through the harmonic generation module in the device, injects them into the distribution system, and records the stability data of the distribution system before and during the generation of the specified harmonic. This data is uploaded to the background analysis system through the communication module, and a full electrical parameter and dynamic harmonic measurement and detection report is generated. This report can be used as a basis for professionals to select reactive power compensation or harmonic control for the distribution system. Specific embodiments

[0108] In a petrochemical industrial park, a medium-voltage 10 kV incoming line and a 0.4 kV transformer with a capacity of 1600 kVA were used. The load primarily consisted of variable-frequency fans, variable-frequency transmission belts, and variable-frequency air conditioners. The actual operating current was 1000 A RMS, with a full-wave power factor of 0.85 and a fundamental power factor of 0.94. The on-site voltage harmonic distortion rate was 7.2%, and the current harmonic distortion rate was 45%. The third harmonic current was 120 A, the fifth harmonic was 350 A, and the seventh harmonic was 100 A (other harmonics were omitted). This distribution system required power quality testing and assessment, as well as a comprehensive harmonic control solution.

[0109] Traditional power quality analyzers can only measure and obtain the current system electrical parameters, such as a voltage harmonic distortion rate of 7.2% and a current harmonic distortion rate of 45%, including 3rd harmonic current of 120A, 5th harmonic current of 350A, and 7th harmonic current of 100A. These analyzers cannot fully assess the impact of changes in individual harmonics on the system.

[0110] Use a portable dynamic harmonic detection device to detect harmonics in the system. The wiring is as follows: Figure 1 As shown, the detection device is started. The main harmonic currents in the system are the 3rd harmonic, the 5th harmonic, and the 7th harmonic. The system runs stably and the current fluctuation is within 5%. Therefore, the detection device is set to output harmonic duration of 10ms, the output amplitude of 10A, the output frequency of 3rd, 5th, and 7th harmonics, and the three phases are outputted single-time. The time interval between each output is 100ms. If the output of the same frequency harmonic is judged as harmonic amplification for 100 consecutive times, it will no longer be output. At the same time, it is judged that the harmonic current of this order has the phenomenon of harmonic amplification for the system.

[0111] For example, a preliminary analysis of the 7th harmonic current of the system is performed:

[0112] The traditional power quality analyzer detects that there is 7th harmonic 100A in the distribution system. Figure 1 As shown in the figure, IS_h7=IL_h7=100A, IB_h7=0A. If a harmonic compensation device is selected, a 7th harmonic filter with a 100A output is required to completely filter out the 7th harmonic current in the system. However, in the actual compensation process, due to the influence of factors such as system background voltage harmonics and changes in system impedance Z, the following three situations may occur, as shown in Table 3;

[0113] Table 3

[0114]

[0115]

[0116] Use a portable dynamic harmonic detection device to detect the harmonics of this system. Through the first step of wiring and setting the detection device, enter the second step of starting the detection device. When the detection device does not output the set sub-harmonics, record the voltage and current harmonic parameters of each order before and after the PCC of the distribution system. Through the discrete Fourier transform (DFT), separate the harmonic parameters of each order and store them in the register. For example, data such as IS_h3’ = IL_h3’ = 120A, IS_h5’ = IL_h5’ = 350A, IS_h7’ = IL_h7’ = 100A, etc.; in the third step, on the detection device, sequentially output IB_h3 = 10A, IB_h5 = 10A, IB_h7 = 10A, etc. according to the set values, and at the same time record data such as IS_h3, IL_h3, IS_h5, IL_h5, IS_h7, IL_h7, etc., and store this data in the register; in the fourth step, the values stored in the register are triggered by the harmonic generator to screen out the corresponding values such as IS_hk’ (k = set order), IL_hk’ (k = set order), IS_hk (k = set order), IL_hk (k = set order), etc., and store them in the comparison comparator for comparison. For example, IS_h3 = 115A, IS_h5 = 340A, IS_h7 = 90A, etc. The comparison judgment conditions are shown in Table 2. It is judged that there is no amplification phenomenon for the 5th, 7th, etc. harmonics at this time (IS_h5’ - IS_h5 = IB_h5, IS_h7’ - IS_h7 = IB_h7), and there is an amplification phenomenon for the 3rd harmonic (0 < IS_h3’ - IS_h3 < IB_h3). The abnormal harmonic continuous counter counts the 3rd harmonic; in the fifth step, repeat steps two to four to repeatedly detect the 3rd harmonic. If it is detected that there is no amplification phenomenon for the 3rd harmonic, the count of the abnormal harmonic continuous counter is cleared. Otherwise, if the continuous count reaches 100 times (set value), it is finally determined that the system has an amplification phenomenon for the 3rd harmonic, and at the same time, the detection device is terminated from actively outputting the 3rd harmonic current; the detection device continues to detect the harmonics of other frequencies, and outputs and displays the data stored in the register and the harmonic amplification judgment data above. At the same time, the data is uploaded to the background system through the communication module for big data statistics and secondary data analysis.

[0117] In engineering projects, there are many uncertain factors such as various types of equipment power consumption and rapid changes in utilization rate, which lead to frequent changes in the impedance Z(s) of the distribution system and the load impedance Z(L), and there are many system harmonic frequencies. Therefore, the distribution system data obtained through the portable dynamic harmonic detection device is of great reference significance to power quality optimization technicians.

[0118] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for detecting dynamic harmonics in a portable power distribution system, characterized in that: The device includes a sampling module, a harmonic calculation module, a harmonic generation module and a background analysis and calculation module, wherein the sampling module, the harmonic calculation module and the background analysis and calculation module are connected in sequence, and the background analysis and calculation module is connected to the harmonic generation module; The sampling module is connected to the measurement point PCC. After the detection device is started, the harmonic generation module actively adds harmonic current. The sampling module collects all power quality parameters before and after the measurement point PCC and sends them to the harmonic calculation module. The harmonic calculation module sends the calculated data to the background analysis and calculation module. The background analysis and calculation module combines the frequency and amplitude of the harmonic current added by the harmonic generation module to analyze the anti-interference ability of the distribution system to harmonic currents of different frequencies under different operating environments. Finally, the change data of the system impedance and load impedance after the addition of external interference are screened out. The corresponding harmonic control equipment and capacity size at the measurement point PCC are evaluated based on this data. The method comprises the following steps: Step 1: Determine the PCC point and install a set of voltage lines UA, UB, and UC of a portable dynamic harmonic detection device, as well as two sets of flexible current sampling loops. The current sampling loops are for the PCC front-end currents ISa, ISb, ISc, and ISn, and the PCC back-end currents ILa, ILb, ILc, and ILn. Step 2: Start the portable dynamic harmonic detection device, in which the harmonic generation module only calculates the set subharmonic command current, clears the data in the verification comparator, and saves the collected and calculated specified subharmonic data into the verification comparator; Step 3: The harmonic generation module calculates the set subharmonic command current and actively injects the set subharmonic current into the power grid system, and saves the collected and calculated specified subharmonic data into the verification comparator; Step 4: Compare the two sets of data in the check comparator. If the difference between the effective value of the PCC front-end current IS_hn' and the effective value of the PCC front-end current IS_hn is greater than or equal to the effective value of the device output harmonic current IB_hn, it can be determined that the distribution system has no amplification effect on the specified harmonic at that moment; If the difference between the effective value of the PCC front-end current IS_hn' and the effective value of the PCC front-end current IS_hn is greater than zero and less than the effective value of the device output harmonic current IB_hn, then it can be determined that the distribution system has an amplification effect on the specified harmonic at that moment; If the difference between the effective value of the PCC front-end current IS_hn' and the effective value of the PCC front-end current IS_hn is less than zero, then it can be determined that the power distribution system has a significant amplification effect on the specified harmonic at that moment; Step 5: During the dynamic harmonic detection process, the portable dynamic harmonic detection device generates harmonic currents of the 2nd, 3rd, ..., 50th order of the set amplitude through the harmonic generation module in the device, injects them into the distribution system, and records the stability data of the distribution system before and when the specified harmonic is generated. The data is uploaded to the background analysis and calculation module through the communication module to generate a full electrical parameter and dynamic harmonic measurement and detection report.

2. The method according to claim 1, characterized in that The sampling module includes a set of voltage sampling circuits and two sets of flexible current sampling loops, wherein the two sets of flexible current sampling loops include a PCC front-end current sampling loop and a PCC back-end current sampling loop.

3. The method according to claim 2, characterized in that The four-phase voltage lines of the set of voltage sampling circuits are connected to the measurement point PCC through crocodile clamps; the PCC front-end current sampling loop is placed at the front end of the measurement point PCC close to the transformer side, and the PCC rear-end current sampling loop is placed at the rear end of the measurement point PCC close to the load device side.

4. The method according to claim 1, wherein The harmonic calculation module includes a preprocessor, a sampling frequency generator, a sampling conversion circuit, a discrete Fourier transform DFT unit, a grouping combination module and a smoothing module. The sampling conversion circuit is connected to the preprocessor, the sampling frequency generator and the discrete Fourier transform DFT unit respectively, and the discrete Fourier transform DFT unit, the grouping combination module and the smoothing module are connected in sequence.

5. The method according to claim 1, wherein The harmonic generation module includes an LCL filter module, a three-level power module, a logic processing module, a core control module and a first display module; the LCL filter module is connected to the logic processing module, the logic processing module is connected to the three-level power module, and the LCL filter module, the three-level power module, the logic processing module and the first display module are respectively connected to the core control module.

6. The method according to claim 1, characterized in that The background analysis and calculation module includes a protocol conversion module, a background system receiving module and a second display module which are connected in sequence.

7. The method according to claim 2, characterized in that The sampling module collects the PCC point voltage, PCC front-end current IS, and PCC rear-end current IL, and at the same time extracts the voltage and current angle φ through phase-locking of the sampling frequency generator, and calculates cosφ and sinφ; The above-mentioned data is sent to the harmonic calculation module for sampling conversion, and discrete Fourier transform DFT is performed on the front-end current IS of the PCC point and the rear-end current IL of the PCC point respectively to extract the reactive component and harmonic component, and the effective value of each component is calculated by gain; At the same time, the harmonic generation module locks sinφ and cosφ according to the calculation results of the sampling frequency generator, and generates harmonic generation instructions based on the set harmonic generation amplitude by combining sinφ and cosφ; The harmonic components extracted by the discrete Fourier transform (DFT) unit are compared with the frequency of the harmonic generation instruction to screen out the harmonic components with the same frequency as the harmonic generation instruction. Then, the same-frequency harmonic components of the front-end current IS of the PCC point are compared with the same-frequency components of the rear-end current IL of the PCC point. The sampling data and comparison results are sent to the background analysis and calculation module for secondary analysis. At the same time, the sampling results and comparison analysis results are output and displayed.

8. The method according to claim 7, characterized in that The harmonic generation instruction can be set to output a single harmonic current or multiple harmonic currents simultaneously.

9. The method according to claim 1, characterized in that The aforementioned no amplification effect means that the PCC front-end impedance is smaller than the PCC rear-end impedance; the aforementioned amplification effect means that the PCC front-end impedance is close to the PCC rear-end impedance, and the system has the risk of series resonance; the aforementioned obvious amplification effect means that the PCC front-end impedance is greater than the PCC rear-end impedance, and the system is capacitive, which has the risk of oscillation.

Images