MCP39F521 datasheet(24/52 Pages) MICROCHIP

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MCP39F521

DS20005442A-page 24

 2015 Microchip Technology Inc.

5.6

Energy Accumulation

Energy accumulation for all four energy registers

(import/export, active/reactive) occurs at the end of

each computation cycle, if the energy accumulation

has been turned on. See Section 6.3, System Status

the

Energy

Control

no-load threshold test is done to make sure the

measured energy is not below the no-load threshold; if

it is above the no-load threshold, the accumulation

occurs with a default energy resolution of 1mWh for all

of the energy registers.

5.6.1

NO-LOAD THRESHOLD

The no-load threshold is set by modifying the value in

the No-Load Threshold register. The unit for this

default value is 100 or 1.00W. Any power that is below

1W will not be accumulated into any of the energy

registers.

5.7

Apparent Power (S)

This 32-bit register is the output register for the final

apparent power indication. It is the product of RMS

current and RMS voltage as shown in Equation 5-2.

EQUATION 5-2:

APPARENT POWER (S)

For scaling of the apparent power indication, the

calculation engine uses the register Apparent Power

Divisor. This is described in the following register

operations, per Equation 5-3.

EQUATION 5-3:

APPARENT POWER (S)

5.8

Active Power (P)

The MCP39F521 has two simultaneous sampling A/D

converters. For the active power calculation, the

instantaneous current and instantaneous voltages are

multiplied together to create instantaneous power.

This instantaneous power is then converted to active

power by averaging or calculating the DC component.

Equation 5-4 controls the number of samples used in

this accumulation prior to updating the Active Power

output register.

Please note that although this register is unsigned, the

direction of the active power (import or export) can be

determined by the Active Power Sign bit (SIGN_PA)

located in the System Status register (Register 6-1).

EQUATION 5-4:

ACTIVE POWER

FIGURE 5-4:

Active Power Calculation Signal Flow.

RMS



CurrentRMS

VoltageRMS



ApparentPowerDivisor

---------------------------------------------------------------------

-------V



–





OffsetActivePower:s32

ActivePower:u32

GainActivePower:u16

Range:b32



ACCU

-1

÷ 2N

÷2RANGE

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