CN107884654A - A kind of transformer station's multiple spot equipment for monitoring power quality and method - Google Patents

Abstract

The invention belongs to the technical field of substation equipment, and discloses a substation multi-point power quality monitoring device and method. The monitoring method uses a voltage and current detection and conditioning circuit, and completes the acquisition of three-phase voltage and current signals by means of the AD conversion port of the DSP itself. Through the internal algorithm processing, each voltage and current harmonic data is obtained, and the power quality parameters of voltage and current symmetry, power factor, and total harmonic content are analyzed; the power quality calculation results are continuously written into the designated storage unit, and then through MODBUS The RTU protocol is sent to the upper computer for analysis and processing. The invention arranges a multi-point power quality monitoring device, uses the MODBUS protocol to complete the transmission of multi-point power quality detection data and centralized information management, and analyzes the power quality status of each node of the substation; and can alarm each state to analyze potential pollution sources of power quality , to provide support for substation operation and maintenance.

Description

A substation multi-point power quality monitoring device and method

technical field

The invention belongs to the technical field of substation equipment, and in particular relates to a substation multi-point power quality monitoring device and method.

Background technique

With the increase of non-linear load users in the power system and more users putting forward higher and higher requirements for power quality, the power quality monitoring of the distribution network where the substation is located is widely valued in the power system. The power grid department uses this as a basis to ensure the reliable operation of the power grid, and at the same time monitors the pollution emitted by users to the power grid; some power quality-sensitive enterprises can use this to understand the power supply quality of the power grid and judge its impact on sensitive equipment; enterprises with large pollution to the power grid can monitor Its pollutant discharge to the power grid is up to standard, and it can be tested whether its compensation equipment is effective; at the same time, the objective data saved by the equipment can also be used as a basis for judging when a dispute occurs between the power grid and customers.

In summary, the problems in the prior art are:

Most of the existing power quality monitoring tasks in substations are single-point task detection, which is usually used to detect key equipment, with little attention to the source of power quality, and to locate potential power quality problems, and the function is relatively single. Existing power quality testing equipment often operates independently, and there is no unnecessary connection between the collected data, and there is a lack of centralized management and analysis of multi-point power quality testing data. If a distributed multi-point power quality detection device based on a specific network protocol can be established, and through centralized detection and management of the power quality data of each node, the correlation relationship between each power quality data can be analyzed, and the power quality of each power quality can be determined through a specific algorithm. status, predict and alarm the data with serious faults in power quality; and can complete the location of some power quality pollution sources according to the correlation of each data, and have particularly active guidance for the commissioning, operation, maintenance and repair of substations It can provide important reference data for predicting possible faults in advance, detecting grid pollution, evaluating the effectiveness of power quality compensation equipment, evaluating the pollution status of power-consuming enterprises and assigning responsibilities.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a substation multi-point power quality monitoring device and method.

The present invention is achieved in this way, a multi-point power quality monitoring method of a substation, the multi-point power quality monitoring method of a substation completes the three-phase voltage and current signal by means of the AD conversion port of the DSP itself through the voltage and current detection and conditioning circuit Acquisition, through the internal algorithm processing, get the voltage and current harmonic data of each order, and analyze the power quality parameters of voltage and current symmetry, power factor and total harmonic content; continuously write the power quality calculation results into the designated storage unit, and then It is sent to the host computer for analysis and processing through the MODBUS RTU protocol.

Further, the substation multi-point power quality monitoring method specifically includes:

With DSP28335 as the control core, through the voltage and current conditioning circuit, the three-phase voltage and current signals are transformed into a low-voltage unipolar DC form that meets the AD port level requirements of the DSP;

With the help of the algorithm programming inside the AD conversion port of DSP, according to the collected three-phase voltage and current values, calculate the harmonic content of the three-phase voltage and current below the 25th order in a specified cycle, and calculate the three-phase voltage and current balance. The power factor is stored in the internal memory according to the specified data format;

Follow the MODBUS RTU communication protocol, and use the master to call the slave to complete the master-slave multi-machine communication;

The upper computer uses the power control configuration software to write the control interface, and extracts, quantifies, and converts the power quality parameters;

Write the software algorithm of the host computer, adjust the alarm threshold of power quality parameters, and give color and sound alarm prompts for the threshold exceeding parameters in the power quality parameters;

During multi-point measurement, the direction distribution of potential pollution sources of power quality problems can be predicted according to the value of power quality parameters.

Another object of the present invention is to provide a substation multi-point power quality monitoring device comprising:

DSP28335 controller, used for substation multi-point power quality monitoring and control operation program;

The conditioning circuit first converts the high-voltage and high-current analog signal into a low-voltage and low-current AC signal, and then converts it into a digital quantity through the AD conversion device for calculation; use DSP with its own 12-bit AD conversion port;

Multi-point communication interface: used to complete remote information collection of multiple monitoring terminals;

Power quality parameter calculation module,

Used to calculate the harmonic content of voltage and current;

The power grid synchronous signal acquisition module obtains the phase information of the power grid with the help of the three-phase software phase-locking principle; according to the principle of coordinate transformation, when the size of the three-phase voltage synthesis vector u _s remains unchanged, the q-axis component u of u _s in the synchronous rotating coordinate system _sq reflects the phase relationship between the d-axis and the grid voltage u _s ; when u _sq =0, the grid voltage u _s and the d-axis are in phase; by controlling u _sq =0 it is used to realize the same phase of the two; the zero and u _sq After doing the difference, ω _err is obtained through the PI regulator, compared with the reference frequency ω _N , and integrated to obtain the phase lock phase angle θ;

MODBUS software protocol module, using RS485 network to establish a master-slave multi-machine communication system, the master calls the slave, and the slave responds to communicate;

The multi-point detection and harmonic source location module is used to locate the harmonic source and divide the harmonic responsibility; and determine the direction of the harmonic source based on the direction of the harmonic power flow.

Another object of the present invention is to provide a method for calculating power quality parameters comprising:

Using the recursive discrete FFT algorithm,

A periodic signal X(t) whose period is T and angular frequency is ω, if discrete sampling is performed, the number of sampling points per cycle is N, and the sampling period is τ, then the periodic signal is expressed as:

In the formula, n is the multiple relationship between the decomposed signal and the fundamental signal, An and Bn are the amplitudes of the periodic signal at n times the fundamental frequency; m is the sampling point sequence number, k is any one of the N sampling points, x(kτ ) is the value at the kth sampling point.

In the calculation process of a period, start from the fixed starting point m=0, and then participate in the calculation of the subsequent N-1 data at the same time; similarly, if the N sampling values before the current sampling i are known, the above sampling period is the same Expressed as:

In the above formula, m=i-N+1 is the initial data signal of N sampling values before sampling point i, and there are N data between sampling point i; the meanings of other symbols are consistent with the previous description.

Perform recursion, combined with the characteristics of the signal period:

In this way, if the monitoring signal is a periodic signal, if An(i) represents the spectrum analysis result of this calculation, and if the result An(i-1) of the last spectrum analysis is already known, the periodic signal can be combined in this time The sampling value X(iτ) of X(iτ) and its sampling value X[(i-N)τ] before a complete cycle are substituted into the above formula to obtain the spectrum analysis result An(i) of this time. In the same way, Bn(i) can be obtained this time according to the last analysis result.

Compared with direct calculation using FFT algorithm, the calculation amount of this formula is smaller and the calculation speed is faster.

Another object of the present invention is to provide a multi-point detection and harmonic source location method including:

The harmonic source of the power quality detection unit PQU is divided into forward and backward; Zs is the forward equivalent impedance of PQU, Zc is the backward equivalent impedance; harmonic impedance Z=Zs+Zc=jX, X is the total harmonic Wave reactance; then the harmonic power backward of PQU is:

P=U _s Icos θ=U _s U _c sin δ/X;

Among them, θ is the phase of U _s leading current I, and δ is the phase difference between the system side and the user side harmonic source; when P has a positive or negative value, the harmonics come from different sides.

Advantage of the present invention and positive effect are:

The present invention arranges multi-point power quality monitoring devices for the key positions of each node in the substation, uses the MODBUS protocol to complete multi-point power quality detection and information centralized management, and analyzes the power quality status of each node in the substation; the present invention utilizes the periodic characteristics of power grid signals , to improve the basic algorithm of harmonic calculation, the corresponding results can be obtained only by using the last result, the sampling data of this time and the corresponding sampling data of the previous cycle, because there is no need to use the traditional method of N times of data collection and cumulative calculation, so The time required is shorter, and the algorithm execution efficiency is increased by more than 50%. In the present invention, the MODBUS protocol is used to transmit and collect data, and the power quality data of each node is distinguished through the address code, which has good scalability. With the help of the RS485 network, up to 256 sub-node power collection devices can be expanded to form a distributed data collection network. . The software system developed by the configuration software of the upper computer can collect and collect information on the power quality of the equipment at each monitoring point in a centralized manner. Through the set alarm threshold, the alarm data exceeding the safety threshold can be alarmed by color, sound, etc., to assist Relevant personnel perform maintenance, analysis, testing, etc. The host computer software has a certain power quality positioning and detection function, combined with the distribution topology of each node, by calculating the forward and backward impedance of each PQU power quality node detection unit, and then combining the impedance of adjacent nodes for comparison and calculation, to determine the harmonic Potential locations of power quality such as waves, guide staff to find the distribution of main harmonic pollution sources of the power grid, and provide technical support for subsequent power management and responsibility division.

Description of drawings

Fig. 1 is a schematic diagram of a substation multi-point power quality monitoring device provided by an embodiment of the present invention.

Fig. 2 is a circuit diagram of voltage transmission and conditioning provided by the embodiment of the present invention.

Fig. 3 is a diagram of a multi-machine communication interface provided by an embodiment of the present invention.

Fig. 4 is a calculation diagram of a power grid synchronization signal provided by an embodiment of the present invention.

Fig. 5 is a schematic diagram of harmonic power direction positioning provided by an embodiment of the present invention.

Fig. 6 is a flowchart of a method for locating a harmonic source based on harmonic power calculation provided by an embodiment of the present invention.

Fig. 7 is a detection diagram of a power grid synchronization signal provided by an embodiment of the present invention.

Fig. 8 is a diagram of a sampling sequence of a periodic signal provided by an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The existing multi-point power quality monitoring devices in substations do not use the MODBUS protocol to complete multi-point power quality detection and information centralized management, and analyze the power quality status of each node in the substation; and they cannot alarm each state; they cannot simultaneously compare the power of each node. Quality data, analyze potential pollution sources of power quality, and provide support for substation operation and maintenance.

The application principle of the present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 1, the substation multi-point power quality detection device provided by the embodiment of the present invention includes:

DSP28335 controller, used for substation multi-point power quality monitoring and control operation program;

The conditioning circuit first converts the high-voltage and high-current analog signal into a low-voltage and low-current AC signal, and then converts it into a digital quantity through the AD conversion device for calculation; use DSP with its own 12-bit AD conversion port;

Multi-point communication interface: used to complete remote information collection of multiple monitoring terminals;

Power quality parameter calculation module,

Used to calculate the harmonic content of voltage and current;

The power grid synchronous signal acquisition module obtains the phase information of the power grid with the help of the three-phase software phase-locking principle; according to the principle of coordinate transformation, when the size of the three-phase voltage synthesis vector u _s remains unchanged, the q-axis component u of u _s in the synchronous rotating coordinate system _sq reflects the phase relationship between the d-axis and the grid voltage u _s ; when u _sq =0, the grid voltage u _s and the d-axis are in phase; by controlling u _sq =0 to achieve the same phase of the two; zero and u _sq After doing the difference, ω _err is obtained through the PI regulator, compared with the reference frequency ω _N , and integrated to obtain the phase lock phase angle θ;

MODBUS software protocol module, using RS485 network to establish a master-slave multi-machine communication system, the master calls the slave, and the slave responds to communicate;

The multi-point detection and harmonic source location module is used to locate the harmonic source and divide the harmonic responsibility; and determine the direction of the harmonic source based on the direction of the harmonic power flow.

The present invention will be further described below in conjunction with specific analysis.

The substation multi-point power quality detection method provided by the embodiment of the present invention uses DSP28335 as the core to design the controller, and through the designed voltage and current conditioning circuit, the three-phase voltage and current signals are transformed into a low voltage that meets the level requirements of the DSP AD port. Unipolar DC form.

Internally through algorithm programming, according to the collected three-phase voltage and current values, calculate the harmonic content of the three-phase voltage and current below the 25th order in a specified cycle, calculate the three-phase voltage and current balance, power factor, and data format to store it in the internal memory;

Follow the MODBUS RTU communication protocol, and use the master-slave mode to complete the master-slave multi-machine communication; the host computer uses the force control configuration software to write the control interface to realize the extraction, quantification, and unit conversion of power quality parameters;

Write the software algorithm of the host computer, which can adjust the alarm threshold of power quality parameters, and give color and sound alarm prompts for parameters exceeding the threshold in power quality parameters;

During multi-point measurement, the direction distribution of potential pollution sources of power quality problems can be predicted according to the value of power quality parameters.

The substation multi-point power quality detection device provided by the embodiment of the present invention is mainly composed of power quality detection hardware and evaluation and positioning software. The hardware uses DSP28335 as the core control unit, and uses voltage transformers and current transformers to obtain the voltage and current information of key nodes in the substation; after the voltage and current size and polarity conditioning circuit, it is sent to the AD port of DSP itself for three-phase analog voltage and quantification of analog current signals. DSP internally designs software algorithms, calculates each harmonic component and content, analyzes and obtains main power quality parameters such as voltage, current symmetry, and power factor. The hardware is installed in the main node of the main wiring of the substation in a modular form to form a multi-point layout; each module is equipped with an RS485 communication interface to form an RS485 communication network. The host and the slave use the MODBUS RTU protocol for communication, and RS485 realizes the matching of USB and 485 bus levels through SP481 and FT232R chips. The upper computer interface is developed by force control configuration software, which has the display of power quality parameters such as voltage and current harmonic components, three-phase waveform symmetry, etc., and the alarm threshold can be set. When the corresponding parameters exceed the standard, a corresponding alarm will be issued; In the multi-point acquisition mode, by comparing the magnitude and direction of the main power quality parameters, the potential position of the power quality is initially indicated, which is convenient for the staff to grasp the power quality status of the power grid, and assists the operation and maintenance of the power grid.

The application principle of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

1. Power quality monitoring method,

In order to facilitate the needs of multi-point measurement, the scheme adopts a modular design idea, uses DSP28335 as the control core, designs voltage and current detection and conditioning circuits, and completes the acquisition of three-phase voltage and current signals by means of the AD conversion port of DSP itself. Algorithm processing, get the voltage and current harmonic data, and analyze typical power quality parameters such as voltage and current symmetry, power factor, total harmonic content, etc. The power quality calculation results are continuously written into the designated storage unit, and then sent to the host computer for analysis and processing through the MODBUS RTU protocol.

2. Hardware circuit:

In the hardware circuit design of the power quality tester, the multi-channel AC voltage and current conversion and conditioning circuit design is the most critical.

2.1 Conditioning circuit:

For the detection of AC analog voltage and current, the high-voltage and high-current analog signals are converted into low-voltage and small-current AC signals, and then converted into digital quantities by the AD conversion device for calculation. From the perspective of simplifying the hardware circuit, the 12-bit AD conversion port of the DSP is directly used, but because it can only accept unipolar voltage signals, it is necessary to design a conditioning circuit to convert bipolar signals into unipolar signals, as shown in Figure 2 .

In Figure 2, the input voltage signal is converted into a mA-level current signal through the resistor RA1, and converted into a low-voltage analog signal through the sampling resistor RA2 on the secondary side of the voltage transformer (5mA: 5mA). In the conditioning circuit, in order to suppress common-mode interference, the output of the voltage transformer is output to the post-stage amplifier in a differential manner, and then converted to the allowable range of the AD converter. At this time, the relationship between the output of the first stage Ua1 and the input voltage is:

2.2 Multi-point communication interface:

Considering the requirements of multi-point power quality collection, the power quality collection of each point should be uploaded to the host computer through the multi-computer communication system. The present invention designs an RS485 interface circuit, which can complete remote information collection of multiple monitoring terminals, as shown in FIG. 3 .

The upper computer communicates with the computer through USB, FT232R can convert the USB to TTL level, and then convert it to RS485 level by SP481 for multiple lower computer connections. Among them, FT232R has an internal programmable UART controller, and the baud rate is adjustable from 18bps to 3Mbps. In this circuit, the CBUS3 and CBUS4 pins of the programmable IO are configured as the data transmission (TXDEN#) and reception (PWREN#) enable pins of SP481. CBUS0 and CBUS1 are configured as data sending and receiving status ports, and an external LED is used to indicate the data sending and receiving status.

3. Software design

3.1 Calculation of power quality parameters

The power quality index in the substation mainly includes the main harmonic content in voltage and current, voltage balance degree, current balance degree, power factor, phase relationship, etc. One of the most critical is to calculate the harmonic content of each order.

The invention adopts the FFT algorithm to calculate the fundamental wave and the main harmonic content below the 21st order. Considering that the fast FFT calculation requires a complete full-cycle calculation of the signal, in order to improve the real-time performance of the calculation and reduce the calculation amount of the discrete FFT, the recursive discrete FFT algorithm is adopted. The core of the algorithm is to use the latest sampling value for calculation every time.

A periodic signal X(t) whose period is T and angular frequency is ω, if it is discretely sampled, the number of sampling points per cycle is N, and the sampling period is τ, then the periodic signal can be expressed as:

The sampling sequence of periodic signal sampling is stored in memory as shown in Fig. 8 Sampling sequence diagram of periodic signal.

In a cycle calculation process, the above calculation process starts from the fixed starting point m=0, and then participates in the calculation of the subsequent N-1 data at the same time, so the real-time performance of instantaneous harmonic analysis is slightly poor. If the N sample values before the current sample i are known, then:

It is recursively combined with the characteristics of the signal period to get:

It can be seen from the above formula that when FFT calculates the harmonic content, it only needs to calculate the current sampling point instead of N sampling points. Data is updated according to the position of the sampling value in each sampling period, thereby reducing the workload of FFT calculation.

3.2 Power Grid Synchronization Signal Acquisition

The acquisition of power grid synchronous signal is the basis of power quality analysis. In this paper, the phase information of the power grid is obtained by means of the principle of three-phase software phase-locking. According to the principle of coordinate transformation, when the magnitude of the three-phase voltage synthesis vector u _s is constant, the q-axis component u _sq of u _s in the synchronous rotating coordinate system can reflect the phase relationship between the d-axis and the grid voltage u _s . When u _sq =0, grid voltage u _s and d axis are in phase. The same phase of both can be realized by controlling u _sq =0. After making a difference between zero and u _sq , ω _err is obtained through the PI regulator, compared with the reference frequency ω _N , and integrated to obtain the phase lock phase angle θ. Its realization principle is shown in Fig. 4 .

3.3 MODBUS software protocol

The hardware of the present invention adopts the RS485 network to establish a master-slave multi-machine communication system, calls the slave machine through the master machine, and communicates in the slave machine answering mode. In order to facilitate communication with configuration software such as force control, each module of the lower computer adopts the MODBUS RTU communication protocol. The format agreed in the communication agreement is as follows:

Table 1 MODBUS RTU communication protocol format

.

The MODBUS protocol defines the master-slave device identification method and the prescribed message format. Considering the accuracy of the calculated power quality parameters, the data generally adopts 2 bytes, and the starting address of each power quality parameter should be specified in the communication protocol. In order to prevent communication errors, apply CRC16 checksum.

3.4 Multi-point detection and harmonic source location method

One of the purposes of power quality testing is to locate harmonic sources and divide harmonic responsibilities. The invention determines the orientation of the harmonic source based on the direction of the harmonic power flow. Take Figure 5 as an example.

The black block in Figure 5 is the power quality detection unit PQU, and its harmonic sources can be divided into forward and backward; then in Figure 5 (b), Zs is the forward (power side) equivalent impedance of a PQU, Zc It is the backward (user side) equivalent impedance; therefore the system harmonic impedance Z=Zs+Zc=jX in Figure 5(c), X is the total harmonic reactance; then the backward harmonic of PQU in Figure 5(c) The wave power is:

P=U _s Icos θ=U _s U _c sin δ/X (5);

Among them, θ is the phase of U _s leading current I, and δ is the phase difference between the system side and the user-measured harmonic source. When P has positive and negative values, it means that the harmonics come from different sides.

After determining the harmonic direction, the direction of each harmonic source can be further determined by comparing the magnitude of the harmonic content in the multi-point power quality. Still taking Figure 5(a) as an example, first determine the direction of the harmonic source by calculating the positive and negative values of the harmonic power at PQU ①; if the harmonic source is determined to be backward, then proceed to the next step by calculating the subsequent harmonic power at PQU ② Extrapolated until the last level of PQU. Then further compare the harmonic content of each PQU to determine the main distribution of each harmonic.

The flowchart of the harmonic source location method based on harmonic power calculation is shown in Figure 6.

The present invention will be further described below in conjunction with result verification.

1 Synchronization signal detection result

Fig. 7 shows the result of calculating the power grid synchronization signal by this device. Among them, U _sa is the phase A voltage of the grid, ω is the phase angle, and U _a is the fundamental signal of item A of the grid calculated according to ω. It can be seen that the accurate tracking of the grid phase can be realized.

2. Host computer configuration monitoring software

In order to be able to monitor the power quality information of each key node in the substation in real time on the host computer, the present invention establishes a three-phase diode uncontrolled DC experiment platform to produce specific harmonic pollution for verifying the monitoring effect.

The main power quality parameters measured by this device can set parameter thresholds to give alarm indications for parameters that exceed the range. With the help of the analysis of multi-node parameters, the main power quality pollution sources can also be effectively located.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (5)

1. A kind of 1. transformer station's multiple spot electric energy quality monitoring method, it is characterised in that transformer station's multiple spot electric energy quality monitoring side Method is detected by voltage and current and modulate circuit, and three-phase voltage and current signal are completed by DSP itself AD conversion port Collection, handled through internal algorithm, obtain each secondary voltage and current harmonic data, and analysis voltage, current-symmetrical degree, power because Element, the power quality parameter of total harmonic distortion；Quality of power supply result of calculation is continuously written into designated memory cell, then passed through MODBUS rtu protocols are sent to host computer analyzing and processing.
2. 2. transformer station's multiple spot electric energy quality monitoring method as claimed in claim 1, it is characterised in that transformer station's multiple spot electricity Energy quality monitoring method specifically includes：

   Using DSP28335 as control core, by voltage and current modulate circuit, by three-phase voltage and current signal pick-up into symbol Close the low voltage single-pole DC form of DSP AD port levels requirement；

   By the arithmetic programming inside DSP AD conversion port, according to the three-phase voltage current numerical value of collection, with defined week Phase, calculate less than 25 times each harmonic contents of three-phase voltage and electric current, calculate three-phase voltage and current balance type degree, power because Number, and be stored in by defined data format in internal storage；

   MODBUS RTU communications protocol is followed, the multi computer communication of master-slave mode is completed using main frame calling slave mode；

   Host computer writes operation and control interface using ForceControl configuration software, carries out the extraction of power quality parameter, quantifies, identity transformation；

   Upper computer software algorithm is write, power quality parameter alarm threshold value is adjusted, to the exceeded parameter of threshold value in power quality parameter Carry out color, audible alarm prompting；

   During multimetering, according to power quality parameter numerical values recited, the directional spreding of prediction power quality problem potential pollution source.
3. A kind of 3. transformer station's multiple spot electric energy quality monitoring dress of transformer station's multiple spot electric energy quality monitoring method as claimed in claim 1 Put, it is characterised in that transformer station's multiple spot equipment for monitoring power quality includes：

   DSP28335 controllers, for transformer station's multiple spot electric energy quality monitoring and control operation program；

   Modulate circuit, high-voltage great-current analog signal is first converted into low pressure low current AC signal, then turned through a/d conversion device Digital quantity is turned to be calculated；12 AD conversion ports are carried using DSP；

   Multi-point communication interface, for completing the remote information gathering of multiple monitoring terminals；

   Power quality parameter computing module, for calculating each harmonic content in voltage and current；

   Synchronized signal acquisition module, grid phase information is obtained by three-phase software phlase locking principle；According to coordinate transform Principle, three-phase voltage resultant vector u_sSize it is constant when, the u under synchronous rotating frame_sQ axis components u_sqReflect d axles With line voltage u_sPhase relation；Work as u_sqWhen=0, line voltage u_sWith the same phase of d axles；By controlling u_sq=0 is used to realize two The same-phase of person；By zero and u_sqAfter making the difference, ω is obtained through pi regulator_err, with reference frequency ω_NAfter comparing, by integration, obtain To pll phase angle θ；

   MODBUS software protocol modules, master-slave mode multi computer communication system is established using RS485 networks, slave is called by main frame, Slave response mode is communicated；

   Multiple spot detects and harmonic source location module, for positioning harmonic source and division harmonic contributions；And based on harmonic power tide Stream direction determines harmonic source orientation.
4. 4. a kind of power quality parameter computational methods of transformer station's multiple spot equipment for monitoring power quality as claimed in claim 3, its It is characterised by, the power quality parameter computational methods use the discrete fft algorithm of recurrence, including：

   A cycle is T, and angular frequency is ω periodic signal X (t), if carrying out discrete sampling, each periodic sampling points are N, Sampling period is τ, then periodic signal is expressed as：

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   N is the multiple proportion of the signal and fundamental signal decomposed in formula, and An and Bn are amplitude of the periodic signal in n times of fundamental frequency；M is Sampled point sequence number, k are any one in N number of sampled point, and x (k τ) is the numerical value on k-th of sampled point；

   In a cycle calculating process, since fixed starting point m=0, then computing is simultaneously participated in N-1 data thereafter； If N number of sampled value before known present sample i, sampling period are then expressed as：

   <mrow> <mtable> <mtr> <mtd> <mrow> <msub> <mi>A</mi> <mi>n</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>2</mn> <mi>N</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>m</mi> <mo>=</mo> <mi>i</mi> <mo>-</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> </mrow> <mi>i</mi> </munderover> <mi>X</mi> <mrow> <mo>(</mo> <mi>m</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> <mi>cos</mi> <mrow> <mo>(</mo> <mi>n</mi> <mi>&amp;omega;</mi> <mi>m</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>B</mi> <mi>n</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>2</mn> <mi>N</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>m</mi> <mo>=</mo> <mi>i</mi> <mo>-</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> </mrow> <mi>i</mi> </munderover> <mi>X</mi> <mrow> <mo>(</mo> <mi>m</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> <mi>sin</mi> <mrow> <mo>(</mo> <mi>n</mi> <mi>&amp;omega;</mi> <mi>m</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> <mo>;</mo> </mrow>

   The initial data signal of N sampled value before m=i-N+1 is sampled point i in above formula, to there is N number of number between sampled point i According to；

   Recurrence is carried out, the characteristic in binding signal cycle obtains：

   <mrow> <mtable> <mtr> <mtd> <mrow> <msub> <mi>A</mi> <mi>n</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>A</mi> <mi>n</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <mn>2</mn> <mo>&amp;lsqb;</mo> <mi>X</mi> <mrow> <mo>(</mo> <mi>i</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> <mo>-</mo> <mi>X</mi> <mrow> <mo>(</mo> <mi>i</mi> <mo>-</mo> <mi>N</mi> <mo>)</mo> </mrow> <mi>&amp;tau;</mi> <mo>&amp;rsqb;</mo> <mi>cos</mi> <mrow> <mo>(</mo> <mi>n</mi> <mi>&amp;omega;</mi> <mi>i</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> </mrow> <mi>N</mi> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>B</mi> <mi>n</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>B</mi> <mi>n</mi> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <mn>2</mn> <mo>&amp;lsqb;</mo> <mi>X</mi> <mrow> <mo>(</mo> <mi>i</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> <mo>-</mo> <mi>X</mi> <mrow> <mo>(</mo> <mi>i</mi> <mo>-</mo> <mi>N</mi> <mo>)</mo> </mrow> <mi>&amp;tau;</mi> <mo>&amp;rsqb;</mo> <mi>s</mi> <mi>i</mi> <mi>n</mi> <mrow> <mo>(</mo> <mi>n</mi> <mi>&amp;omega;</mi> <mi>i</mi> <mi>&amp;tau;</mi> <mo>)</mo> </mrow> </mrow> <mi>N</mi> </mfrac> </mrow> </mtd> </mtr> </mtable> <mo>;</mo> </mrow>

   If monitoring signals are periodic signal, if An (i) represents the result of spectrum analysis of this calculating, if having known last time frequency spectrum The result An (i-1) of analysis, with reference to this to periodic signal this sampled value X (i τ) and at it before a complete cycle Sampled value X [(i-N) τ], then substitute into carry out recurrence, after the formula that the characteristic in binding signal cycle obtains, obtain this frequency Compose analysis result An (i)；This Bn (i) is obtained according to last time result of spectrum analysis.
5. 5. multiple spot detection and the harmonic source location side of a kind of transformer station's multiple spot equipment for monitoring power quality as claimed in claim 3 Method, it is characterised in that the multiple spot detection includes with harmonic source location method：

   Power Quality Detection unit PQU harmonic source is divided into forward and backward；Zs is PQU forward direction equiva lent impedance, and Zc is backward Equiva lent impedance；Harmonic impedance Z=Zs+Zc=jX, X are total harmonic wave reactance；Then harmonic power backward PQU is：

   P=U_sIcos θ=U_sU_csinδ/X；

   Wherein θ is U_sLeading current I phase, δ are system side and user-side harmonic source phase difference；It is humorous when positive and negative values occurs in P Ripple is from not homonymy.