A Single Prepaid Electricity Meter with LoRa Communication

Module

Dong Yan

, Kai Zhang

College of Automation, Chongqing University of Posts and Telecommunications, Chongwen Road, Chongqing City, China

College of media and art, Chongqing University of Posts and Telecommunications, Chongwen Road, Chongqing City,

China

Keywords: Single Phase Watt Hour Meter; LoRa; Prepayment; Energy Metering

Abstract: In order to achieve the goal of long-distance communication, low power consumption and lowcost of single-

phase prepaid energy meter, this paper presents a single-phase prepaid energy meter with LoRa

communication module based on the analysis of the existing energy meter communication methods.The

LoRa communication module uses the SX1278 chip, which is briefly introduced in this article.The single-

phase prepaid energy meter added to the LoRa communication module is powerful and has broad

application prospects.

1 INTRODUCTION

With the development of Smart Grid, the Prepaid

electric energy meter is promote and popularize

widely. At present, the main recording way of wire

communication includes power line carrier

communication and RS485 communication. The

subsistent power grid could utilize Power line carrier

communication to finish, which do not need extra

investment of layout and in low price. Otherwise,

there are several shortcomings about it, such as loud

intermittent noise (Starting and stopping or working

time of electric appliance), fast signal attenuation,

circuit fluctuation and impedance etc. RS485

communication system is easily to operation to

ammeter record. However, great workload and high

priced maintaining, frequent circuit burn-in and

damage are big problems. GPRS and ZigBee is

major communication for power information

acquisition。GPRS could spread over great distance

with super security and stability as wireless

constructed through telecom operator. Construction

of base station is a precondition of GPRS. Building a

base station require a big sum of funds and should

pay high maintain cost. So we could know this

technology is not adaptive used in remote and rural

area because there are not strong signal. Although

we could decrease the cost of base station

construction depend on ZigBee wireless

communication, short-distance communication limit

the function of the technology. It is not suit to spread.

Thus we should find a new way to deal with

meter record, it must keep in low cost and energy

consumption meantime, can finish long-distance

communication. LoRa possess these characters, it is

a new wireless communication technology with low

energy consumption and cost, moreover has

extremely well network Extensibility and

communication ability. LoRa be used in free

frequency that is non-authorized band, include

433MHz、868MHz、915MHz etc. Because of the

minimum receive current about 10mA and sleep

current less than 200nA, we could utilize advanced

Spread spectrum modulation technology and coding

way to enhance Anti-jamming performance and

increase link budget. LoRa could enhance the

stability of Deep fading and Doppler shift, it can

received the communication distance up from 15km.

So we could know the LoRa communication

technology have so extremely excellent performance

that meter could be promote widely.

2 LORA COMMUNICATION

ELECTRIC CIRCUIT

LoRa communication chip be product by

Semtechcompany in USA. The chip and transceiver

circuitconstitute the module of Wireless transceiver.

The main disposal system of SX1278transceiver is

LoRaRemote modem, it could be used in long-

distance spread spectrum communication with

strong anti-interference performance and reduce

current consumption. Depend on LoRatechnology,

SX1278 in the low price crystal and material have

more higher sensitivity than 148dBm. It is become

the best choice of long distance communication and

high-tech applications.

LoRa modem technology have remarkable

advantage in diffraction, it tackle the problem of

long distance, weak anti-interference ability and

large energy consumption. Compared with similar

products, SX1278 not only reduce electric current

consumption also optimize the function of phase

noise、 Selectivity, receiver linearity, 3order input

interception(IIP3), as fig.1 and fig.2.

Fig.1 SX1278 pin.

Fig.2LoRa wireless module.

2.1 SX1278 Receive and Transmission

Switch Circuit

The fig.3 show the operating principle of SX1278

reception and transmission switch current. It is half

duplex communication chip, so it must work in one

alternative pattern of data reception or transmission.

The behalf of radio switch, it could work in data

reception or transmission pattern through control the

level of CTRL pin and VDD pin.

Fig.3 Radio switch circuit.

2.2 SX1278 Receive Circuit

The fig.4 illustrates the construction of SX1278

reception current. L1, L2, C3, C4 are components of

filter. Base on the really communicational frequency,

these parts could choose suitable parameter. Because

different electrical applicants be used in there, the

actual wireless communicational environment is

complex-the radio signals of various frequencies

could be received through antenna. This situation

will impact the distance of communication. In this

picture, U1 is SAW filter that be used for filter the

frequency signal of outside could make Specific

frequency signal through. If there are not SAW

Filter, external signal can interfere the work of

SX1278.

Fig.4 SX1278 receive circuit.

2.3 SX1278 Transmission Circuit

The content of fig.5 about SX1278 transmit circuit,

which consist of several filters. L3 and C11

constitute the series resonance current. C16, L5 and

C17, L6 construct two group of Parallel resonance

current. The equipment could choose suitable device

parameter according to different communication

frequency.

Fig.5 SX1278 transmission circuit.

3 OVERALL DESIGN SCHEME

In this paper, a sort of Monophasic prepaid electric

energy meter with LoRa communicational module

be accepted, which include micro-processor, basic

module, Electric energy metering module, relay

controlled module, power module, pay-in advance

module, LoRa communicational module. The way of

connection showed like fig.6.The function of

different modules as follows:

Fig.6Design scheme.

3.1 MCU Module

Micro-Control Unitis the key device of meter, it

could connect other modules as a uniform system

through powerful compute ability. In this process,

Electric energy meter, data display, relay control and

prepayment control of electric energy meter and

wireless communication function could be finished.

3.2 Basic Module

The basic module include LCD unit, clock unit,

memory unit，direction unit, pulse output unit. The

LCD unit used for display the data of different fee

ratio in Accumulative energy and total data of

Accumulative energy, moreover, including The

maximum demand. The direction, date, term,

Accumulative energy ， the information of relay

communication signal, pay-in advanced information,

address etc.

Clock unit consist of Built-in hardware clock

circuit with temperature compensation function that

can transfer the date and time automatically. The

outputting frequency of inner clock port is 1Hz

(among the temperature range about-25℃～+60℃),

and the accuracy rating of clock ≤±3s/d (under the

23℃，the accuracy rating of clock≤±1s/d).

Store unit used EEPROM that can erasure

1million again. It can Save power, area code,

numbering, and other data and states so that these

data cannot lose after power cut.

Direction unit used LED as instructional light, in

there, the pulse direction light is red, it does not

blink in normal time, but blinking on the time of

measurement of active power. Alarming light also is

red, it will blinking only in alarming time. Trip

instruction light is yellow, it blinking in the time of

Load switch.

3.3 Electric Energy Module

The electric energy metering module includes

Current sampling, voltage sampling and energy

metering chip. The main duty of current sampling is

sampling of neutral wire and live wire. Voltage

sampling gathers the sample of voltage between

neutral wire and live wire. Electric energy metering

chip could collect voltage and current signal through

the process of enlargement of gain amplifier. And

then it will transfer analogue signal into digital

signal through AD converter. After filter the result of

active power could be get through the way of current

statistics multiply by voltage statistics. This

information will be submitted to micro-processor in

the form of high pulse.

3.4 Relay Control Module

Relay control module include relay and control

which main function about control the circulation

turn on or off. The microprocessor will give

disconnect command, when it receive the signal

submitted by upper computer about delinquent fee.

After MCU sent disconnect signal, relay control

reception instruction and then it execute the order to

interrupt the supply of power.

3.5 Power Module

Power module could be support by power line

supply and Li batter supply, in general condition,

power module supply electricity to meter through

power line. When power cut due to line fault, the Li

batter could support current to meter for keep work

of meter.

3.6 Prepayment Module

This part could fulfill prepayment function through

insert IC card. The main functions include:

Intelligent control: IC meter calculate energy

used of customer through pulse counter

automatically.

Pre-alarm function: If remaining power in the

record of IC card less than alarming quality, warning

signal will be sent. The user could purchase power

as soon as possible.

Load control function: when load continually

exceed the setting value of meter, the load switch

will disconnect automatically, which could protect

the circuit and facilities against destroy. When load

be limited in controlling range, meter switches off

automatically. It is convenient to customer.

Energy call-backs function: IC card will record

the data of remaining amount again for supporting

inquiry of manage system, when user insert IC card

in machine every time.Please remember that all the

papers must be in English and without orthographic

errors.

Security protection function: it use memory cards,

encryption cards, CPU cards as a power purchase

card, key security authentication in the IC card and

meter, which has a high degree of security. In this

way, a household only has one card and each

purchase card only valid once.

Replacement card function: When the electric

card lost, the clerk can replenish the electricity

generation card for the user through the electricity

sales network.

Inspection function: The electricity sales network

can issue inspection cards and regularly check the

operation of the user's IC card and meter.

Electricity-freezing function: The power sales

department have right to freeze the amount of

electricity generated through the order of IC card,

then the frozen electricity data will write back to the

line loss statistics, meantime, electricity billing will

be computed.

Load statistics function: The power sales

department can issue a conduction of load freezing

to the IC card power meter through the data

communication channel. The IC card power meter

can calculate the user's power at a certain moment

according to the instruction，and then it can freeze

the information that transmit it to the power sales

department for resident power load analysis.

3.7 Lora Module

According to the analysis above, Lora module adopt

SX1278 chip product by Semtech Company in USA.

This chip and external transceiver circuit compose

LoRa wireless transceiver module. It could use in

data transmission meter send upper computer in

electric sale. Meantime, it could receive the data

coming from the power sales department. In this

process, the remote control of meter could be

finished.

4 CONCLUSIONS

In this paper, we analysed the advantage and

disadvantage of limited communication and wireless

communication, we could know that the most of

meter communication ways are not meet the

requirement of remote communication that must

have low power consumption, low-cost, long-

distance. So a sort of Single-phase prepayment

meter with LoRa communication module is inferred.

After brief introduction of a signal prepayment

meter with LoRa wireless communication module

(SPM-LWM), we generate a design schedule of

SPM-LWM，and introduce the function in different

module briefly. With the development of smart

power grid, this power meter has great applicability

in future.

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