CN102571518B - Electronic transformer data transmission method based on field bus - Google Patents

Abstract

The invention discloses a data transmission method for an electronic transformer based on a field bus, comprising: a CAN bus-based master-slave unit connection method, a transmission data encoding method, a master-slave unit data sampling synchronization method, and a data transmission method of a time trigger mechanism. The invention adopts data lossless coding realized based on feedback self-adaptive quantization algorithm and differential pulse coding algorithm. The one-master multi-slave system connection method divided by power supply intervals ensures the real-time sampling point data transmission and sharing of three-phase system voltage and current AC signals at a lower transmission rate, and the number of intervals has nothing to do with the transmission rate. Each slave unit accurately tracks the start time of the data frame of the master station to realize the synchronization of each unit in the system, and ensures the synchronization and phase relationship of the system-level AC signal sampling without the need for a hardware synchronization line.

Description

A data transmission method of electronic transformer based on field bus

【Technical field】

The invention relates to an electronic transformer data transmission method, in particular to a field bus-based electronic transformer data transmission method.

【Background technique】

The modern power system is increasingly developing towards high voltage level and large capacity, and the degree of automation of its operation is constantly improving. The traditional electromagnetic transformer with iron core is increasingly unable to meet the requirements of the power system due to its own structural limitations.

In recent years, electronic current/voltage transformers (ECT/EVT) based on the principles of optics and electronics have many advantages such as anti-electromagnetic interference, good insulation performance, large transient response range, wide frequency response range, and no saturation phenomenon. The ideal substitute products for traditional electromagnetic transformers and new equipment for future power transmission and distribution systems have received widespread attention from researchers at home and abroad.

In order to promote the practical application of electronic transformers, the International Electrotechnical Commission has formulated a series of international standards such as IEC60044-7/8 and IEC61850-9-1. These standards repeatedly involve the interface component between electronic transformers and secondary equipment - the merging unit (MU, Merging Unit).

The currently proposed merging unit is defined for electronic transformers with digital output. Its main function is to collect three-phase current and voltage information synchronously, and summarize and output them to the secondary side protection measurement and control equipment according to a certain format. The merging unit defined in IEC61850-9-1 largely refers to IEC60044-7/8, including the synchronization method of the merging unit. The interface between the merging unit and the secondary protection measurement and control equipment is a serial one-way multi-channel point-to-point connection. The content of the message sent by the merging unit to the protection and measurement and control equipment mainly includes the current, voltage and validity flag of each channel, in addition, some binary input information and time label information reflecting the switch state are added. In the communication network with the secondary protection and control equipment, the Ethernet transmission system currently occupying the mainstream position is adopted.

The above-mentioned traditional transmission method based on the merging unit mainly has the following disadvantages: the hardware needs a synchronization line to realize the synchronization of data acquisition of each unit, the system wiring is complicated, and the hardware cost is high; at a certain signal transmission rate, the data transmission efficiency is low.

【Content of invention】

The purpose of the present invention is to provide a field bus-based electronic transformer data transmission method, which realizes the synchronization of master-slave unit data acquisition without the need of hardware synchronization lines, reduces system cost and wiring complexity, and improves data transmission. transmission efficiency.

In order to achieve the above object, the present invention adopts the following technical solutions:

A fieldbus-based electronic transformer data transmission method, comprising the following steps:

Step 1. Master-slave unit connection method based on CAN bus: Connect a group of electronic voltage transformers to the main unit module MU, which is used to collect voltage signals, send system synchronization frames and sample data; the main unit module MU is connected to multiple slave unit modules SU through the CAN bus, and the slave unit modules SU are distributed in each power supply interval and connected to a group of electronic current transformers ECT;

Step 2. Transmission data encoding method:

First, calculate the difference value x'(n) for adjacent sampling data x(n) and x(n-1) and judge whether it exceeds 7bit quantization. If not, send the difference value x'(n) directly once, And set all the logarithmic coding flags and incremental coding flags to 0; if the primary differential value x′(n) exceeds 7bit quantization, then calculate the secondary differential value x″(n), and judge the secondary differential value x″( n) Whether it exceeds 7bit quantization, if not, send the second difference value x"(n), the logarithmic encoding flag position is 0, and the incremental encoding flag position is 1;

Among them: the nth sampled data is x(n), the n-1th sampled data is x(n-1),

x′(n) is the primary difference value, and x″(n) is the secondary difference value:

x′(n)=x(n)-x(n-1) (1)

x″(n)=x′(n)-x′(n-1) (2)

If the secondary difference value exceeds 7bit quantization, the logarithmic encoding method is adopted, that is, the primary difference value x'(n) and the secondary difference value x"(n) are respectively processed to sticky bits and then shifted to the right by 4 bits; then calculate and judge the first difference Whether the value x'(n) exceeds 7bit quantization, if not, the encoded data is a primary differential value x'(n), the logarithmic encoding flag position is 1, and the incremental encoding flag position is 0; if the primary differential value x'(n ) exceeds 7bit quantization, calculate again to judge whether the secondary difference value x″(n) exceeds 7bit quantization, if not, the encoded data is the secondary difference value x″(n), logarithmic coding flag, incremental coding flag All bits are set to 1; if the secondary differential value x″(n) exceeds 7bit quantization, overflow processing will be performed on the secondary differential value.

Described a kind of electronic transformer data transmission method based on field bus also comprises the following steps:

Step 3: Master-slave unit module data sampling synchronization method: first, the master unit module sends a synchronization frame to make the first sampling time of the master unit module and each slave unit module the same, that is, first check and accept the CAN module of the master and slave unit modules The filter is set to only receive the synchronous frame and the data frame of the main unit module, and is set to receive the interrupt mode; then the main unit module sends the synchronous frame, and at time t0, the main unit module and the slave unit module receive the synchronous frame and generate a reception interrupt at the same time , start the A/D conversion to sample at this time, so as to realize the synchronization of the first sampling of each unit, and the above-mentioned time synchronization method will be adopted for each transmission cycle TB in the future; among them, the system virtual time is used in the synchronization process, that is, the main unit The count value of the first timing counter in the module is used as the time reference for synchronization of each slave unit module, and the count value of the timing counter of each unit module is corrected according to the difference between the count value and the machine cycle of each module;

A further improvement of the present invention is that: the field bus-based electronic transformer data transmission method also includes the following steps:

Step 4: Data transmission method using a time mechanism: First, use a synchronous sampling timing counter to divide the 10ms basic transmission cycle TB into 16 time slices, each time slice is 0.625ms; then divide the 16 time slices into four data transmissions Window: the synchronization frame sending window, the master unit module data sending window, the slave unit module data sending window, and the window to be expanded;

The synchronous frame sending window occupies the 16th time slice, which is used for frame sending time and time synchronization;

The data sending window of the main unit module includes the 1st-4th time slice, which is used to send the sampling data of 4 voltage transformers EVT;

The data sending window of the slave unit module includes the 5th-11th time slice, which is used to send the sampling data of 7 current transformers ECT;

The window to be extended includes 12th to 15th four time slices, which are used for the extension of the transmission data frame, the sending of the data frame of the slave unit module or the retransmission of the data of the slave unit module.

The further improvement of the present invention lies in that the number of slave unit modules SU is the same as the number of power supply intervals of the substation.

The further improvement of the present invention lies in: point-to-point serial communication between the master unit module MU and the slave unit SU and the receiving end.

The further improvement of the present invention lies in: adopting 16-bit overall quantization, and compressing 16-bit data information into 9-bit transmission data through data lossless coding.

The further improvement of the present invention is that: the logarithmic encoding flag is 1 to indicate that the encoded data has been compressed by logarithmic encoding, and 0 indicates that it has not been compressed by logarithmic encoding; the incremental encoding flag is 1 to indicate that the encoded data adopts a secondary difference value, which is 0 indicates that the encoded data uses the general incremental method.

The further improvement of the present invention is: the method for correcting the timing counter count value of each unit module in step 3 is:

The main unit module counts the time count value NT _m1 of its first timer counter as NT _m1 = NT ₁ -NT _Δt , where NT ₁ is the count value corresponding to 10ms, NT _Δt is the count value corresponding to Δt, and Δt is the synchronization The time interval between frame sending and receiving; Send synchronous frame after it produces interruption, the counting value NT _m2 of the second timing counter that comprises this moment main unit module in the synchronous frame; After each slave unit module receives the synchronous frame, will The count value NT _m2 of the second timing counter of the main unit module is compared with the count value NT _s2 of the second timing counter in each slave unit module minus the corresponding count value NT _Δt of Δt, then using formula (3) and formula (4 ) Calculate the count values of the first timer counter and the second timer counter in the slave unit module corresponding to the system virtual time 0.625ms, 10ms, and revise their respective count values to new values NT _s1 ', NT _s2 ':

NT _s2 ′NT _m2 +NT _Δt (3)

NT _s1 ′NT _s2 ′/16 (4)

In the formula: NT _s1 ' is the count value of the first timing counter in the slave unit module;

NT _s2 ' is the count value of the second timing counter in the slave unit module;

NT _Δt is the count value corresponding to Δt;

NT _m2 is the count value of the second timer counter in the main unit module.

The further improvement of the present invention is that each slave unit accurately tracks the start time of the data frame of the master station, thereby realizing the synchronization of data sampling of each unit in the system, and ensuring the synchronization and synchronization of system-level AC signal sampling without the need for a hardware synchronization line. Phase relationship, and on this basis, the time-sharing and combined transmission of master-slave unit data is realized.

The system division of one master and multiple slaves in the present invention makes the system only need to collect a group of voltage signals, which reduces the amount of information collection and hardware cost.

Compared with the prior art, the present invention has the following advantages: the present invention improves the efficiency of data transmission by performing lossless encoding on the transmission data, divides the system connection structure of one master and multiple slaves with power supply intervals, and at a lower transmission rate The data transmission and sharing of the sampling points of the three-phase voltage and current AC signals are guaranteed.

Because various microprocessors all have CAN interface at present, thus can obtain CAN bus resource more conveniently; The solution is easier to implement; and the CAN bus can also be connected by optical fiber, which improves the anti-interference and stability of the system, and has technical effects in the following aspects:

1. The CAN bus is used to connect the intervals of the interval layer, and the main unit module samples the voltage signal and realizes the voltage sampling data sharing at the bus level;

2. Using the transmission data encoding method increases the amount of transmitted data and improves the efficiency of data transmission under a certain signal transmission rate;

3. The synchronization method used saves the hardware synchronization transmission line, which reduces the cost and wiring complexity of the system.

【Description of drawings】

Fig. 1 is a system hardware schematic diagram of a field bus-based electronic transformer data transmission method according to the present invention. Among them, ECT is a current transformer, EVT is a voltage transformer, n is a natural number, n=1, 2, 3.....

Fig. 2 is a data encoding flow chart of a field bus-based electronic transformer data transmission method according to the present invention. Among them: x(n) is the nth sampling data; x(n-1) is the n-1th sampling data; x′(n) is the first difference; x″(n) is the second difference; LFlag is the pair Number coding flag; DFlag is difference incremental coding flag; SendData is coded data;

Fig. 3 is a kind of schematic diagram of the virtual time axis of the electronic transformer data transmission method data transmission system based on the field bus of the present invention; Wherein TB is that the basic cycle of system data transmission is 10ms, Ts is the sampling time interval, Δt is the transmission of the synchronous frame Time, t0, t16 is the time when the synchronization frame is received, t0, t1, t2...t16 is the time of synchronous sampling of each unit module, t _x is the time when the synchronization frame is sent;

Fig. 4 is a schematic diagram of dividing the transmission window of the data encoding transmission system of the electronic transformer data transmission method based on the field bus of the present invention;

Fig. 5 is a schematic diagram of data transmission in a data encoding transmission system based on a field bus-based electronic transformer data transmission method according to the present invention.

【Detailed ways】

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

The present invention is a field bus-based electronic transformer data transmission method, comprising: a CAN bus-based master-slave unit connection method, a transmission data encoding method, a master-slave unit data sampling synchronization method, and a data transmission method of a time trigger mechanism;

This embodiment is carried out for sampling at 32 points of the power frequency cycle;

1. Master-slave unit connection method based on CAN bus:

As shown in Figure 1, the present invention connects a group of voltage transformers EVT to the main unit module MU, and each receiving end can share the collected data of the EVT, thereby reducing the number of electronic voltage transformers used. Connect the current transformers of each interval to the slave unit module SU. The master unit module MU is connected to each slave unit module SU through a CAN bus. There is point-to-point serial communication between the master unit module MU, the slave unit module SU, and the receiving unit.

The main unit module MU is used for voltage data acquisition, sending system synchronization frame and sampling data. The master unit module MU is connected to multiple slave unit modules SU, and can only accept the data sent by itself to generate the reception interrupt of the synchronization frame, so as to perform better synchronization. The main unit module MU cannot perform monitoring arbitration transmission, and can only send blindly. Each slave unit module SU accurately follows the start time of the synchronization frame sent by the master unit module MU, so as to realize the synchronization of each unit in the system, and ensures the synchronization and phase relationship of the system and AC signal sampling without the need for hardware synchronization lines .

2. Transmission data encoding method:

In order to make more effective use of bus resources, we first compress and encode the real-time sampling data and then transmit it. We mainly use the feedback adaptive quantization algorithm and the differential pulse encoding algorithm to achieve lossless encoding.

In order to meet the needs of general relay protection, the default sampling system is 32 points per power frequency cycle, and 16-bit overall quantization is used to ensure measurement accuracy and protection accuracy. The 16-bit data information is represented by 9-bit transmission data through data encoding.

A total of 9 bits of data are transmitted in each phase, and the transmission format is as follows:

Among them, the first two bits are flag bits, the first bit is the logarithmic encoding flag bit and is represented by LFlag, the LFlag bit is 1, indicating that the encoded data has been compressed by logarithmic encoding, and 0, indicating that it has not been compressed by logarithmic encoding; the second bit is the increase Quantity encoding flag is expressed by DFlag, DFlag bit is 1, which means that the coded data adopts the second difference value, and is 0, which means that the coded data adopts the general incremental method.

Since the data domain of the CAN bus changes in units of bytes, we use DFlag to occupy one of the 11-bit identifiers of the CAN bus. Since each module in the system needs to send three sets of data, the data field adopts 3 bytes in length and occupies the lower three bits of the 11-bit identifier of the CAN bus to transmit the LFlag of the three sets of data.

Note that the nth sampled data is x(n), and the n-1th sampled data is x(n-1);

x'(n) is the first difference value; x"(n) is the second difference value.

x'(n)=x(n)-x(n-1) (1)

x″(n)=x′(n)-x′(n-1) (2)

As shown in Figure 2: first calculate the differential value x'(n) once and judge whether it exceeds 7bit quantization (that is, whether it is less than or equal to 7bit). If not, set LFLag and DFlag to 0, and send the differential value x'( n); if it exceeds, calculate the secondary differential value x"(n) and judge whether it exceeds 7bit quantization, if it does not exceed 7bit quantization, then LFlag is set to 0, DFlag is set to 1, and the encoded data is the secondary differential value x"(n ).

If the secondary difference exceeds x″(n) and is quantized by 7 bits, the logarithmic encoding method is used, and the primary difference value x′(n) and the secondary difference value x″(n) are processed with sticky bits and then shifted to the right by 4 bits . Then calculate and judge whether the value of the primary difference x'(n) exceeds 7bit quantization, if not, the encoded data is the primary difference value x'(n), LFlag is set to 1, and DFlag is set to 0; if the primary difference value x'( n) More than 7bit quantization, recalculate and judge that the secondary difference value x"(n) is enough to exceed 7bit quantization, if not, the encoded data is the secondary difference value x"(n), LFlag and DFLag are both set to 1; if If the secondary differential value x"(n) exceeds 7-bit quantization, overflow processing is performed on the secondary differential value x"(n).

In the transmission data encoding processing method of the present invention, the feedback adaptive quantization algorithm and the differential pulse encoding algorithm are used; the adaptive quantization is mainly reflected in enlarging the quantization unit and reducing the amount of data transmission when the transmission protection data meets the protection accuracy requirements. Differential pulse coding is reflected in the fact that the transmitted data is the primary difference value and the secondary difference value of the original data, which can not only reduce the number of data quantization bits to compress the data but also effectively filter out the DC component. The 16-bit data information is compressed into 9-bit transmission data through the encoding algorithm, and the first bit is the logarithmic encoding flag LFlag, indicating whether to use logarithmic encoding compression; the second bit is the incremental encoding flag DFLag, indicating that the binary encoding is used The secondary differential value is still a general increment, and the last seven bits are encoded data. By judging the quantized digits of the primary and secondary differential values, it is decided whether to use logarithmic encoding to send the primary differential value x′(n) or the secondary differential value The value x"(n) achieves the purpose of data encoding.

3. Master-slave unit data sampling synchronization method:

First, the master unit module sends a synchronization frame to make the first sampling time of the master unit module and each slave unit module the same. First, set the acceptance filter in the CAN module of the master and slave unit modules to only receive synchronous frames and data frames of the master unit module, and set it to receive interrupt mode. Then the master unit module sends a synchronization frame, as shown in Figure 3, at time t0, the master and slave unit modules receive the synchronization frame and generate a reception interrupt at the same time, and start A/D conversion at this time for sampling. This ensures the synchronization of the first sampling of each unit. The above-mentioned time synchronization method will be adopted for each transmission cycle TB in the future.

In order to cooperate with the transmission period TB=10ms of sampling data, we adopt to send a synchronization frame every 10ms. However, this will inevitably lead to an increase in synchronization error. In order to reduce synchronization errors, we introduce the concept of system virtual time (as shown in Figure 3). The system virtual time is the time of system synchronization, which is the count value of the first timing counter in the master unit module, and the time of each slave module is based on it. In order to make the time of each slave unit module consistent with the system virtual time, it is necessary to change the count value of the timer counter of each unit module according to the difference between the count value of the first timer counter in the master unit module and the machine cycle of each module.

The correction method of the count value of the timing counter of each unit module is as follows:

Since 10ms/0.625ms=16, there are 16 sampling moments between two synchronous frames, that is, within 10ms, that is, 16 timing counter interruptions. Figure 3 is the system virtual time axis, which only describes the 10ms time axis between two synchronization frames. Among them, Δt is the time interval between sending and receiving the synchronous frame, and the counting value of the timing counter can be calculated according to the CAN bus baud rate and the main frequency of the processor.

At time t0, the master and slave unit modules receive the synchronous frame, start A/D conversion to realize synchronous sampling, and start two timing counters (including the first timing counter and the second timing counter) inside the master and slave unit modules at the same time , the first timing counter is used for timing 0.625ms, and the corresponding written count value is NT ₁ , the second timing counter is used for timing 10ms, and the corresponding written count value is NT ₂ , and the corresponding count value of Δt is set to NT _Δt . At time t1, the first timer counter in each module generates an interrupt, restarts the first timer counter of each module and starts A/D conversion, and repeats this until A/D conversion is started at time t15. Then the main unit module counts the time count value NT _m1 of its first timing counter as NT _m1 = NT ₁ -NT _Δt , which is the count value corresponding to 0.625-Δtms, and sends a synchronization frame when it generates an interrupt, which contains At this time, the count value NT _m2 of the second timing counter of the main unit module is counted as the count value corresponding to 10-Δtms.

The synchronous frame format adopts the standard frame format of CAN bus containing 11-bit identifier, and the data field is 8B as follows:

The count value NT _m2 of the second timing counter of the main unit module The number of data frames to be sent 16bit 0～7

After each slave unit module receives the synchronization frame, the count value NT _m2 of the second timing counter of the master unit module is then calculated by formula (3) and formula (4) in the slave unit module corresponding to the system virtual time 0.625ms and 10ms The count values of the first timer counter and the second timer counter are modified to new values NT _s1 ′, NT _s2 ′ respectively.

NT _s2 ′=NT _m2 +NT _Δt (3)

NT _s1 '=NT _s2 '/16 (4)

In the formula: NT _s1 ′ is the count value of the first timing counter in the slave unit module; NT _s2 ′ is the count value of the second timer counter in the slave unit module; NT _Δt is the count value corresponding to Δt; NT _m2 is the main The counting value of the second timing counter of the unit module; and the main unit module uses the counting value of its first timing counter and the given value corresponding to 10ms to compare and modify the corresponding value of Δt, thus realizing the synchronization between each unit module and the virtual time of the system .

4. Data transmission method of time-triggered mechanism:

For the transmission of sampling data, the system of the present invention adopts a data transmission method of an event trigger mechanism. In each sending cycle TB, 4 frames of EVT data frames are sent by the master unit module in a collision domain, and 7 frames of ECT data frames are sent by the slave unit module, a total of 11 frames and a total of 12 frames of data plus synchronization frames.

As shown in Figure 3, firstly, the 10ms basic transmission cycle TB is divided into 16 time slices by using the timing counter in the main unit module of synchronous sampling, and each time slice is 0.625ms. This can meet the requirement of sending 12 frames of data per basic sending cycle, and there are 4 time slices to expand the number of sending frames. As shown in Figure 4, 16 time slices are divided into four data sending windows: synchronous frame sending window; main unit module data (EVT data) sending window; slave unit module data (ECT data) sending window; not shown).

1. Synchronous frame sending window

This window only occupies the 16th time slice. The specific frame sending time and time synchronization method are the master-slave unit data transmission synchronization method described in Title 3.

2. Main unit module data (EVT data) sending window

This window includes time slices 1-4, which are used for the main unit module to send 4 EVT sampling data. The specific transmission method is shown in Figure 4. At time t0, the master and slave unit modules receive a synchronization frame and generate a reception interrupt. In this interrupt, the main unit module starts A/D conversion sampling, starts its two timing counters, and at the same time starts sending the first frame of data; while the slave unit module only starts A/D conversion sampling and its timing counters, Receive the sending data frame of the main unit module, but only record the number. When the first timing counter of each unit module is interrupted, that is, the t1 moment (although each unit module uses a respective timing counter, it can be considered that each module arrives at the t1 moment at the same time due to the use of the above synchronization method.), each unit module restarts the first Timing counter, start A/D conversion. At this time, the master unit module sends the second frame of data, and the slave unit module does not send data. Repeat this until the 4th time slice, when the main unit module finishes sending the EVT sampling data. That is to say, the master unit module sends data at t0, t1, t2, and t3, while the slave unit module does not send data and only records the number of data frames sent by the master unit module and is about to send with the master unit module received in the synchronization frame. The number of data frames to compare. At the same time, each slave unit module performs sampling and timing operations.

3. Slave unit module data (ECT data) sending window

This window includes time slices 5-11, which are used to send 7 ECT sampling data from the unit module.

The specific transmission method is shown in FIG. 4. When the first timing counter of each unit module generates a timing interrupt at time t4, restart their first timing counters and start A/D conversion. And the number of data frames sent by the main unit module recorded at this time is equal to the number of data frames to be sent by the main unit module received in the synchronization frame. At this time, the slave unit module sends the first frame of data, and the main unit module does not send data. Repeat this until the 11th time slot t10, the slave unit module sends ECT sampling data, and the master unit module does not send data. That is to say, the slave unit module sends data at t4, t5, t6, t7, t8, t9, t10, t11, while the master unit module does not send data. But they all perform sampling and timing operations.

What needs to be supplemented here is that when sending data, the slave unit module adopts a monitoring and sending method different from the master unit module, and the data frame priority of the master unit module is high. Therefore, if there is a network failure such as failure to receive the synchronization time, the clocks of the master and slave modules are seriously out of sync, the slave module can still use its own timer to complete the tasks of data sampling and data transmission, and the slave module is recording After the main unit module sends 4 data frames, it will not affect the data transmission of the main unit module. But its data frame sending time may be delayed.

4. The window to be expanded

This window contains a total of 4 time slices from 12th to 15th, and has two purposes:

1) Extension for transmitting data frames. When a module adds a sampling sensor, it needs to increase the transmission data frame accordingly, but this expansion is limited.

2) Due to the transmission of non-periodic signals. When there is a failure in the data frame transmission of the slave unit module, it can be used for the transmission of the data frame of the slave unit module, or the retransmission of the data of the slave unit module.

Finally, the receiving end can judge whether the master-slave unit modules are synchronized according to the time when the data frames of the master unit module and the slave unit module are sent, so as to facilitate the application of secondary equipment.

Claims (6)

1. a Fieldbus Based electronic mutual inductor data transmission method, is characterized in that, comprises the following steps:

Step one, the master-slave unit method of attachment based on CAN: one group of electronic type voltage transformer is connected on master unit module MU; Master unit module MU is connected to multiple from unit module SU by CAN, each from the corresponding supply cell of unit module SU, is connected to one group of electronic current mutual inductor ECT;

Step 2, transmission data encoding processing method: adopt the data lossless coding based on feedback adaptive quantization algorithm and differential pulse coding algorithm realization:

First, first difference score value x'(n is calculated to neighbouring sample data x (n-1), x (n)) and judge whether it quantizes more than 7bit, if do not exceeded, direct transmission first difference score value x'(n), and logarithm coding maker position and incremental encoding flag bit are all set to 0; If first difference score value x'(n) quantize more than 7bit, calculate second difference score value x again " (n); " whether (n) quantizes more than 7bit to judge second difference score value x, if do not exceed, send second difference score value x " (n); logarithm coding maker position 0, incremental encoding mark position 1;

Wherein: x (n) is n-th sampled data, x (n-1) is (n-1)th sampled data, x'(n) be first difference score value, x " (n) is second difference score value:

x'(n)＝x(n)-x(n-1) (1)

x"(n)＝x'(n)-x'(n-1) (2)

If second difference score value x " (n) quantizes more than 7bit, adopts logarithm coding method, by first difference score value x'(n), " (n's second difference score value x) moves to right after processing sticky bit respectively 4; And then calculating judges first difference score value x'(n) whether quantize more than 7bit, if do not exceeded, then send first difference score value x'(n), logarithm coding maker position 1, incremental encoding mark position 0; If first difference score value x'(n) quantize more than 7bit, again calculate and judge second difference score value x " whether (n) quantizes more than 7bit; if do not exceed, then send second difference score value x " (n), logarithm coding maker position, incremental encoding flag bit all put 1; If second difference score value x, " (n) quantizes more than 7bit, carries out Overflow handling to second difference score value;

Wherein first is logarithm coding maker position LFlag, represents whether adopt logarithm compression coding; Second is incremental encoding flag bit DFLag, represent and adopt second difference score value or general increment, latter seven is coded data, by the judgement of the quantization digit to first and second difference value, determine whether adopt number encoder, send first difference score value x'(n) or second difference score value x " (n) reaches the object of data encoding.

2. Fieldbus Based electronic mutual inductor data transmission method according to claim 1, is characterized in that, the Fieldbus Based electronic mutual inductor data transmission method of described one is further comprising the steps of:

Step 3, master-slave unit data sampling synchronous method: first master unit module MU transmission synchronization frame makes master unit module with respectively identical from the moment of unit module SU first time sampling, namely first the acceptance fitration in the CAN module of master and slave unit module is arranged to the form receiving only synchronization frame and master unit module data frame, and is configured to receive interrupt mode; Then master unit module sends synchronization frame, when the t0 moment, master and slave unit module receives synchronization frame and produces receive interruption simultaneously, now starts A/D conversion and samples, thus realizing the synchronous of each unit first time sampling, later each transmission cycle TB adopts above-mentioned sampling synchronization method; Wherein, the system virtualization time is adopted in synchronizing process, also namely using the count value of the first timer conter in master unit module MU as each time reference synchronous from unit module SU, and by this count value and the difference of each module machine cycle, each unit module timer conter count value is corrected.

3. Fieldbus Based electronic mutual inductor data transmission method according to claim 2, is characterized in that, the Fieldbus Based electronic mutual inductor data transmission method of described one is further comprising the steps of:

Step 4, adopts the data transmission method of time triggered mechanism: first utilize the timer conter of synchronized sampling that the basic transmission cycle T B of 10ms is divided into 16 timeslices, each timeslice is 0.625ms; Then 16 timeslices are divided into four data transmission windows: be respectively synchronization frame send window, master unit module data send window, from unit module data transmission window, treat extended window;

Described synchronization frame send window takies the 16th timeslice, for frame transmitting time and time synchronized;

Described master unit module data send window comprises the timeslice of 1-4, for sending the sampled data of 4 voltage transformer EVT;

The described timeslice comprising 5-11 from unit module SU data transmission window, for sending the sampled data of 7 current transformer ECT;

Described treats that extended window comprises 12-15 totally 4 timeslices, the expansion for transmitting data frame, the transmission from unit module Frame or the repeating transmission from unit module data.

4. Fieldbus Based electronic mutual inductor data transmission method as claimed in claim 1, is characterized in that, described master unit module MU and from being point-to-point serial communication between unit module SU, receiving terminal.

5. Fieldbus Based electronic mutual inductor data transmission method according to claim 1, is characterized in that, adopts 16 overall quantifications, by data encoding by the data message boil down to 9 of 16 transmission data.

6. Fieldbus Based electronic mutual inductor data transmission method as claimed in claim 2, is characterized in that, in step 3 to the method that the timer conter count value of each unit module corrects is:

Master unit module MU is by the time counting value NT of its first timer conter _m1count NT _m1=NT ₁-NT _{Δ t}, wherein NT ₁for the count value that 10ms is corresponding, NT _{Δ t}for the count value corresponding to Δ t, Δ t is the time interval between synchronization frame sends and receives; When transmission synchronization frame of having no progeny in its generation, in synchronization frame, comprise the count value NT of second timer conter of now master unit module MU _m2; After respectively receiving synchronization frame from unit module, by the count value NT of master unit module MU second timer conter _m2with each count value NT from the second timer conter unit module SU _s2deduct the count value NT that Δ t is corresponding _{Δ t}compare, then utilize formula (3) and formula (4) to calculate the count value of the first timer conter and the second timer conter from unit module SU corresponding to system virtualization time 0.625ms, 10ms, and revise their respective count values for be newly worth NT _s1', NT _s2':

NT _s2'＝NT _m2+NT _Δt (3)

NT _s1'＝NT _s2'/16 (4)

In formula: NT _s1' be count value from the first timer conter unit module SU;

NT _s2' be count value from the second timer conter unit module SU;

NT _{Δ t}for the count value that Δ t is corresponding;

NT _m2for the count value of the second timer conter in master unit module MU.