Characteristics and application of the most popula

2022-07-24
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Characteristics and applications of ansenmey semiconductor power line carrier chip

I. distribution line communication

medium and low voltage AC distribution lines are used for power transmission, and can also be used as transmission media to realize data communication. Power line carrier communication (PLC) technology is a technology that transmits analog or digital signals on the distribution line at high speed by carrier. The power line is used as the data transmission medium, and the existing power distribution network is used for communication without rewiring. The signal will not be attenuated or even shielded because it passes through the building wall. The relatively low cost makes this technology popular in many fields, such as automatic meter reading system and light control

Figure 1 is a typical application case of PLC technology - the schematic diagram of remote automatic meter reading system

the meter exchanges data with the concentrator through the power line. The concentrator is usually located near the transformer and is the core manager of the network. It is responsible for network management, centralized data collection, command transmission, etc; At the same time, it also carries out data exchange and information transmission with the master station through the uplink (PSTN or RF, etc.). A concentrator can manage dozens to hundreds of meters

in this system, the concentrator will read the operation data of each electric meter according to the set time interval and transmit the data to the master station to realize automatic remote centralized meter reading

it cannot be doubted that 1.1 EDF project

nowadays, many countries in the world have adopted or will deploy smart meter system and adopt automatic remote centralized reading mode. At present, the LINKY electricity meter project of ERDF in France has attracted much attention

ERDF, a subsidiary of EDF, the largest power distribution operator in the EU, has launched a project involving a total of 35million electricity meters. From 2012 to 2017, the project will replace the traditional meters in France with the new LINKY smart meters. Power line carrier (PLC) technology is adopted for smart meter communication

the main technical requirements of the project for PLC are as follows:

physical layer: IEC and en

modulation mode: s-fsk

communication carrier frequency: FM (signal frequency):63.3khz; FS (empty number frequency):74khz

communication rate: 2400 baud

synchronization between physical layer and power line 50Hz

application layer: IEC and IEC

1.2 communication between ansenmey semiconductor and PLC

ansmey semiconductor has developed S-FSK PLC modem for low/medium voltage power line data communication, which has been successfully applied in the industrial field for more than 8 years. Modem is a narrow-band PLC transceiver using S-FSK modulation. It is the only device that has been verified in the market for many years

the product has developed from the early amis-30585 to the second generation amis-49587

amis-49587 fully meets the technical requirements of ERDF and has been selected by LINKY smart meter supplier as the core device of PLC communication

in the following, the characteristics of amis-49587 are introduced in combination with the requirements of EDF LINKY electricity meter project

II. Transceiver covering phy and MAC layer

2.1 OSI layer reference model of LINKY meter:

linky project adopts 3-layer network structure:

- phy of physical layer adopts IEC standard

- the data link layer DLL (including Mac and LLC sublayers) adopts IEC/IEC standard

- the application layer adopts IEC/IEC standard

amis-49587. The most prominent feature is that as a PLC transceiver, it not only completes the transceiver, modulation and demodulation of S-FSK signals in the physical layer, but also includes the processing of MAC sublayer. This feature enables users to focus more on the development of the application layer. Through amis-49587, the LLC layer data packets are exchanged, and the bottom frame header, frame verification, etc. will be automatically added. This greatly reduces the workload of customer software development

2.2 the optimized s-fsk

power distribution line used in the physical layer is not specially designed for signal transmission, its impedance is changing at any time, and it is also very easy to introduce various external electromagnetic interference. The selection of modulation mode strives to make it have a good communication effect for the special situation of power line under the condition of low cost

fsk (frequency shift keying) is a classical frequency modulation method with low cost: two independent carrier frequencies are used to transmit binary 0 and 1. S-FSK (spread FSK) is to keep the two frequencies as far away as possible (>10khz) so that the transmission quality of the two frequencies is relatively independent, so as to better deal with the impact of common narrowband interference in electricity

in Figure 3, we can see that under the broadband interference with average noise energy, the signal-to-noise ratio of the received signals of the two carrier frequencies is similar. The receiver filters out other frequencies and generates two demodulation signals - DS and DM at F0 (empty signal frequency) and F1 (signal transmission frequency). If ds>dm, it is considered that the data "0" is received; Otherwise, it is considered as data "1", in which case the receiver operates in FSK mode; If the signal-to-noise ratio of one carrier frequency is very poor due to narrowband interference, the receiver will ignore this channel and compare the demodulation signal of another better channel with an internal threshold T to determine whether to receive "1" or "0". At this time, the receiver operates in ask mode of amplitude shift keying

in addition, the demodulation algorithm of modem internal processor is particularly important. It has a great influence on the receiving sensitivity. LINKY project requires that the receiver can normally identify within 2mV to 2V of the effective value of S-FSK signal

the flexible modulation and demodulation mode and advanced and reliable demodulation algorithm make amis-49587 have excellent performance against power line interference

2.3 physical layer frame format

amis-49587 transmits data according to IEC physical frame format

physical frames are sent at intervals of time slices (or time slots). The starting point of the frame is called the slot indicator, which corresponds to the zero crossing point of the power line voltage 50Hz. The client (that is, the host) must start sending physical frames at the zero crossing point. It is very important to understand that the whole IEC system is based on time slice synchronization

taking the 2400bps rate as an example, it takes 150ms to transmit one time slice or physical frame

a physical frame consists of a preamble preamble, a start subframe delimiter, a Mac subframe (data), and a pause field pause

the physical frame always starts from an integer multiple of the basic time slice, which is called the time slice indicator. After time slice synchronization, the physical layer of each device can independently track the time slice indicator through its internal clock

preamble and start subframe delimiters (Aaaah and 54c7h) are of great significance. The receiver can:

1) adjust and determine the reception gain

2) measure the signal-to-noise ratio

3) determine the demodulation method FSK or ask

4) check whether it is the start of a legal physical frame

5) adjust the synchronization between the server (that is, the slave) and the client (client)

2.4 MAC frame and physical frame

as shown in Figure 5: the physical frame "packs" the MAC frame and sends it. A physical frame has 38 byte data fields, and one MAC subframe can be sent at a time. A long MAC frame can consist of up to seven MAC subframes. Long MAC frames with multiple MAC subframes will be split into several subframes and sent sequentially by the corresponding number of physical frames. After receiving all of them, the receiver will integrate them

The

mac frame header consists of the number of sub frames, the initial trusted value IC, the current trusted value CC, the difference trusted value DC, the source address, the destination address, and the padding length pad length. The use of trusted values will be described in detail in the following relay chapter. LLC frames are included in MAC frames as data

III. ansenmey semiconductor PLC solution

solution is mainly composed of PLC modem, amis-49587, drive amplifier ncs5650 and coupling transformer

plc signal transmission path (red arrow): the S-FSK signal modulated by amis-49587 is amplified by ncs5650 and coupled to the power line through transformer. The transformer realizes voltage transformation and impedance matching, and is also used for strong and weak current isolation. In addition to the power amplification of the ncs5650 signal, the structure of its two-stage operational amplifier also constitutes a fourth-order low-pass filter with steep attenuation characteristics. In Europe, where there are strict restrictions on power line access equipment, only adding similar filters can ensure that the high-frequency interference injection of the system to the power line meets the requirements of EN 50065 specification

the blue arrow indicates the receiving path: the signal coupled from the power line by the transformer passes through the low-pass filter composed of amis-49587 built-in amplifier to perform FSK demodulation analysis in the internal arm

the black arrow in Figure 6 is a 50Hz zero crossing detection signal pin. The system relies on this signal for synchronous timing

only trustworthy manufacturers can use the blue dotted box in the figure to show the application processor in the meter, which is responsible for the processing and measurement of the communication application layer. Its interface with PLC modem is a simple SCI serial port

the power supply of the scheme is very simple: one 12V supply line amplifier is used to drive the PLC signal coupling transformer; One circuit of 3.3V supplies power to amis-49587

3.1 amis-49587 functional block diagram

let's learn more about the internal structure of amis-49587

The core of amis-49587 is a 32-bit ARM processor, which completes the processing of physical layer and MAC layer, runs S-FSK modulation and demodulation algorithm, and also manages the communication with external MCU. The embedded software is stored in the on-chip ROM

on the left side of the chip is the analog part: FSK signal synthesis output, reception demodulation, system clock and 50Hz phase locked loop

the chip includes all analog and digital parts such as S-FSK signal processing and MCU interface management. The transformer drive becomes the heat source on the transceiver board because it is the power amplification part. In order to prevent high heat from affecting the system accuracy, amis-49587 does not include the power drive of the signal into this IC, but adopts an external scheme

3.2 unique system relay scheme

in network communication, long-distance information transmission needs relay. Amis-49587 of Anson semiconductor supports relay with credit algorithm. In this relay scheme, the system does not need a preset repeater. Its core idea is that each server (i.e. electricity meter) can be a repeater of other servers to help transfer information or commands. Even if the destination address of the received frame does not match, if it needs to be forwarded, the server will forward it. The forwarding adopts the mode of time slice and chorus, which depends on the unified synchronization of the whole system with the time slice

repetition with credit relay algorithm adopts a method called trusted value management. The trusted value is divided into 7 levels and managed by the client (concentrator). The system stipulates that if the server is configured as a repeater, if the current trusted value of the received MAC frame is greater than 0, the server will repeatedly forward the frame when the next time slice arrives, and the current trusted value will be reduced by one. The process of frame repetition is terminated until the current trust value is 0. Under this mechanism, at the same time, many servers may repeat forwarding at the same time, which is harmony

the following (see Figure 8) takes the forwarding process of a single MAC frame as an example to illustrate the repetition with credit mechanism

1) the concentrator sends a frame to the meter 5 in time slice K and sets the initial trust value as 2 in the MAC frame header. The meter (module PLC) 1 and 2 correctly received this frame in time slice K due to their close distance

2) due to the confidence value (CR) of this frame

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