Abstract: This article introduced the ADE7758 electrical energy measurement chip’s in African GPRS network electrical energy table application, elaborated the apparent electrical energy measurement and the calibration method with emphasis, the ADE7758 digit soft dial gauge flow and the algorithm, as well as ADE7758 phase calibration algorithm.
Key word: Apparent electrical energy calibration; Digital soft dial gauge; Algorithm; Phase calibration;
1. introduction
At present the domestic GPRS network electrical energy table mostly has the measurement to be active, the idle work, the voltage, the electric current, must measure, functions and so on voltage depreciation. The author when makes an Africa’s GPRS electrical energy table at present the customer proposed that must measure the apparent electrical energy, domestic very little has this kind of demand, in the market also very little can see that has this function electrical energy table. After inspects in every way, the author decided that uses American ADI Corporation’s ADE7758 three-phase multi-purpose electrical energy measurement chip.
ADE7758 is the three-phase high accuracy multi-purpose electrical energy measurement chip which American ADI Corporation promotes. The ADE7758 voltage channel is 16bit ∑-△ ADC, the dynamirange is 20:1; The electric current channel is 24bit ∑-△ ADC, the dynamirange is 500:1. ADE7758 can measure the active electrical energy, the idle work electrical energy, the apparent electrical energy, the voltage effective value, the electric current effective value, can the profile sampling, be able the measurement voltage cycle, the frequency and so on. ADE7758 the miss distance is smaller than 0.1% in 1000:1 dynamirange. ADE7758 has two group pulse outputs, a group for active electrical energy pulse, another group for idle work/apparent multiplying pulse output. ADE7758 active, the idle work, the apparent electrical energy may distinguish the independent control, may design the different pulse constant.
2.ADE7758 periphery hardware circuit design
The ADE7758 voltage electric current channel input signal scope for ±0.5V, the recommendation adds when rated voltage Un the voltage channel input signal is about 250mV, adds when maximum current Imax the electric current channel input signal is about 300mV. Author this design’s electric instrument rated voltage Un=240V, the voltage channel with 5 200ΚΩ resistances and a 1ΚΩ resistance differential pressure, adds when rated voltage Un the input signal is 240mV; The current transformer changes compares 300:1, the sample resistance is 2 7.5Ω resistances, adds when maximum current Imax the input signal is 300mV. Figure 1 is the ADE7758 periphery circuit diagram.
Figure 1 ADE7758 circuit diagram
3. apparent electrical energy measurement
Apparent electrical energy the gauging device has two kinds:①Arithmetic method:
,②Vector method: S=
. Regarding a pure sine system two method measurement result is the same. Uses what in ADE7758 is the arithmetic method. ADE7758 active/idle work which accumulation pattern measures in LINE under the CYCLE in identical cycle, therefore the vector method is very easy in exterior MCU to realize. This time when makes the electrical energy measurement with ADE7758, the active electrical energy measurement is through MCU gathers ADE7758 active pulse output base pin APCF, then MCU summation pulse number; The idle work electrical energy measurement is through establishes ADE7758 to let the idle work/apparent multiplying pulse output idle work signal impulse, the gauging device be the same with the active electrical energy measurement. Because ADE7758 can only output two group signal impulses, but idle work/apparent multiplying pulse output hypothesis for idle work pulse output, therefore the apparent electrical energy measurement was unable to use the accumulation pulse the method. In this design overall evaluation MCU duty and procedure code space limit, we decided that uses ADE7758 the arithmetic method measurement apparent electrical energy. The attention apparent electrical energy always, did not consider that active and the idle work direction, the voltage effective value and the electric current effective value multiplication has the apparent electrical energy.
4.ADE7758 calibration flow.
The ADE7758 calibration has two methods to be possible to supply the choice:①Calibrates ADE7758 using ADE7758 dial gauge pulse output APCF/VARCF through dial gauge Taiwan, this way is most commonly used, the Manufacturer also meets these requirements, but this way’s shortcoming is the efficiency is low.②Uses the precise datum source, establishes the ADE7758 work in the line cycle accumulation pattern. This kind of pattern’s merit is the efficiency is high, the calibration is quite quick.
Because of the ADE7758 voltage gain, the current gain can be influential to the following active/idle work/apparent energy, therefore ADE7758 must the calibrating voltage increase first, the current gain, the ADE7758 calibration must calibrate the three-phase voltage to increase, the three-phase current increases, the three-phase active gain, the three-phase idle work increases, three-phase phase calibration, apparent electrical energy threshold’s calibration. The ADE7758 calibration flow must strictly the flow according to shown in Figure 2 to carry on:
Figure 2 ADE7758 dial gauge flow chart
5. calibrates ADE7758 the algorithm
a 5.1 voltage electric current calibration
May make up through the regulation voltage electric current’s gain as a result of the periphery hardware circuit’s error causes the computation the voltage current error to be big.
Because the ADE7758 voltage electric current channel’s linearity is very good, very easy to satisfy the system to the voltage electric current precision request, therefore we have used a calibration method, raises the dial gauge efficiency. Realizes the method to be as follows specifically:
⑴ Joins A VN=240V, electric current Ib=1.5A, PH=1, establishes good dial gauge Taiwan;
⑵ Resets voltage gain AVRMSGAIN with PDA, current gain register IGAIN;
⑶ Reads with PDA saves voltage effective value AVRMS;
⑷ PDA according to formula: 
=
, extracts the voltage gain to read in ADE7758;⑸ Reads electric current effective value AIRMS with PDA;
⑹ PDA according to formula: 
, extracts the current gain to read in ADE7758.
5.2 calibrate the active/idle work electrical energy gradually
In order to control the electric instrument the error to meet the electrical energy table precision class requirements which in the stipulation scope GB code stipulated that we hoped that can approach gradually reduces the electric instrument the error, but ADE7758 provides using the handbook the method is a step calibration, is unable to approach gradually, this rechecks to the electric instrument is not very good, if the electric instrument rechecks the error not to satisfy the request not to be able to revise in the original foundation by approaches gradually, for could realize approaches gradually reduces the error we to use the following method:
⑴ Joins A VN=220V, electric current Ib=1.5A, PH=1, establishes good dial gauge Taiwan;
⑵ With PDA through infrared read active gain register starting value AWG0 value;
⑶ Input PDA the dial gauge Taiwan demonstration’s erroneous ER% values;
⑷ PDA according to formula: 
, extracts increases AWG active the value, reads in ADE7758.
⑸ The transform current, confirms each error. (the controllable error range is: - 33% <Er%< 100%, when the error surpasses the scope must adjust the periphery hardware circuit to solve. )
Each time revises ADE7758 the gain is carries on the computation in the original foundation according to present’s error, can therefore approach gradually reduces the error. The BC calibration with A, the idle work calibration is similar with the active calibration, here no longer repeats.
5.3 calibration apparent electrical energy
Was opposite calibrates the apparent electrical energy with the calibration active/idle work electrical energy to be complex, because the active/idle work electrical energy might carry on the calibration through active/idle work pulse output APCF/VARCF through the dial gauge Taiwan demonstration error. But because the ADE7758 idle work/apparent base pin is the multiplying. What this design choice output is the idle work pulse output, therefore the apparent electrical energy’s calibration could not calibrate through the dial gauge Taiwan’s method. ADE7758 has provided one kind of measurement pattern: The line cycle accumulation pattern, this kind of pattern is through establishes ADE7758 to cause an its accumulation integer half-wave the energy, the hypothesis half-wave number at the appointed time, the ADE7758 condition register corresponding interrupt flag bit will set will be 1. If the interrupt mask register permits this interrupt, the IRQ base pin will have jump a from high to low to inform the MCU half-wave cycle already, the energy register data will complete the renewal. When this time develops the African network electrical energy table, we establish LINCYC=100, like this to the 50HZ power frequency electrical network is 100 half-waves, is also 50 cycles, namely 1 second electric quantity, has established LCYCMODE=0C, namely LVA=1 causes the ADE7758 apparent electrical energy measurement by the line cycle accumulation pattern.
When calibration apparent electrical energy adds the precise datum source: Establishes the ADE7758 work in the line cycle accumulation pattern, corrects looks at each other in threshold S_GATE, saves in EEPOM. Realizes the method specifically:
⑴ Joins ABC rated voltage VN, ABC nominal current Ib, PH=1, establishes good dial gauge Taiwan;
⑵ PDA reads A, B, C to look at each other in the electrical energy AVAHR(07H), BVAHR(08H), CVAHR(09H);
⑶ PDA according to formula:
, extracts 0.01KVAH the equivalent value to issue MCU;
⑷ MCU according to PDA transmission 0.01KVAH equivalent numerical calculus apparent electrical energy.
5.4 calibrate the phase gradually
When ADE7758 uses ADI Corporation to provide the typical circuit which designs 1 level of electric instruments the phase not to need the calibration then to satisfy the precision class request generally, otherwise but when designs 0.5S with ADE7758 or the high accuracy rank electric instrument must calibrate the phase not to satisfy the error to request. Author when calibration formula which provides with ADI Corporation discovered that cannot the very good calibration electric instrument, the author see has many about the ADE778 calibration phase’s formula, but confirmation one has not been correct. Discovers after author dwell upon ADE7758 material contains errors, final author infer the correct formula, is very good after the actual movement effect, the inferential reasoning process no longer repeats, calibrates the process as follows specifically (take A as example):
⑴ Joins A VN=220V, electric current Ib=1.5A, PH=0.5, establishes good dial gauge Taiwan;
⑵ Reads phase register APHCAL0 with PDA the value;
⑶ Inputs PDA the dial gauge Taiwan magnitude of error (attention basis error’s positive and negative choice formula);
⑷ PDA according to magnitude of error basis formula:
Extracts the phase to calibrate APHCAL the value, reads in ADE7758.
⑸ The transform current, confirms each error. (the controllable error range is: - 8% <Er%< 4%, when the error surpasses the scope must adjust the periphery hardware circuit to solve. )
6. concluding remark
This article innovation spot is: Through caused its work to the ADE7758 register’s nimble disposition to realize the apparent electrical energy calibration in the LINCYC pattern, simultaneously designed the calibration method which approached gradually to further increase the measuring accuracy. The author inferred the phase calibration formula according to handbook, the practice has proven in the ordinary circumstances only to need two steps then calibrates the phase. Used ADE7758 completely to complete this task of design. This system already in the African scene movement, the practice indicated that electrical energy table movement stable reliable, the apparent electrical energy electric quantity computation is precise, satisfies the customer completely the request, obtained user’s consistent high praise.
Reference:
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