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Data Sheet

ADE9178

THEORY OF OPERATION

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Rev. A | 39 of 122

To check how to calculate the energy register value, see the

Worked Examples section.

Total Active Energy

For each phase, there are three types of active

energy outputs available: positive energy, negative ener-

gy and signed energy. The registers available for ac-

tive energy are xWATTHR_SIGNED_HI and xWATTHR_SIGN-

ED_LO, xWATTHR_POS_HI and xWATTHR_POS_LO, and

xWATTHR_NEG_HI and xWATTHR_NEG_LO to store signed, posi-

tive and negative energy outputs, respectively.

Total Apparent Energy

For each phase, there is one positively accumulated apparent

energy output (xVAHR_HI and xVAHR_LO) exists.

No Load Detection

No load detection prevents energy accumulation due to noise

when the input currents are below a given meter start current. To

determine if a no load condition is present, the ADE9178 evaluates

if the accumulated energy is below a user-defined threshold over

a user-defined time period, which is done on a per phase and per

energy channel basis. The NOLOAD_TMR[2:0] bits in the EP_CFG

64 samples to 4096 samples, 64/4 ksps = 16 ms to 1024 ms,

as shown in Table 19 . No load detection is enabled by default,

over the minimum time of 64/4 ksps = 16 ms. No load detection

is disabled when the NOLOAD_TMR[2:0] bits in the EP_CFG are

equal to 111 (binary). No load accumulation is always done in

absolute accumulation mode. For more details, see Figure 53.

Note, for more details on a known bug with no load feature, see

Table 30.

Table 19. No Load Detection Table

NOLOAD_TMR

Samples to Evaluate in

No Load Condition

Time That No Load

Detection is Evaluated

(ms)

128

256

512

128

1024

256

2048

512

4096

1024

No load disabled

The user-defined no load thresholds can be written into the

ACT_NL_LVL and APP_NL_LVL registers to sets the no load

threshold for the total active energy and total apparent energy,

respectively. The configured threshold is directly compared against

the accumulated power to decide no load detection. For example,

to configure a no load threshold of 0.1% of full-scale active power

accumulated for 64 samples, ACT_NL_LVL must be configured to

(POWFS_CODES × 0.001 × 64).

No load status of active and apparent energy are indicated by

using the bits WATTNLOAD and VANLOAD of STATUS0/STATUS1

when the no load status changes, either going into or out of no

load. The PHNOLOAD register indicates whether each phase of

energy is in no load.

Figure 55 shows what happens when the xWATT, low-pass filtered

active power value goes above the user-configured no load thresh-

old and then back down below it again. The same concept applies

to apparent energy values as well.

Figure 55. No Load Behavior

Power Factor (PF) Calculation

The total active power and total apparent power are accumulated

over 1 sec. Then, the power factor on each phase is calculated by

the following equation:

xPF

= xWATT accumulated over 1 sec

xVA

accumulated over 1 sec

(22)

The accumulation is a signed accumulation. The sign of the xPF

calculation follows the sign of xWATT. The PF results is stored in

5.27 fixed point format. The highest PF value is 0x07FF_FFFF,

which corresponds to a PF of 1. The PF of −1 is stored as

0xF800_0000. To determine the PF from the xPF register value,

use this equation:

Power

Factor (PF) = xPF × 2−27

(23)

Note that the value in xPF register should be treated as a 2's

complement number.

To determine if the PF is leading or lagging, find the angle between

voltage and current (ANGL_xV_xI) by using the Angle Calculation

shown in the Full-Scale Codes And Conversion Equations section.

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