MAXQ3180-RAN+ datasheet(36/48 Pages) MAXIM

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Highpass Filter (HPF)

A simple first-order highpass filter (HPF) is used.The fil-

ter formula is:

Yn = (1 - hpf_b0f/216) x (Yn-1 + Xn - Xn-1)

The filter coefficient (hpf_b0f) is a signed 16-bit value

and can be configured by the master.

Integrator

The digital integrator block can be engaged separately

for each current phase (IA, IB, IC) and for neutral cur-

rent (IN) by setting configuration bits INTGA, INTGB,

INTGC, and INTGN in the CONNCT register. When

enabled, the digital integrator block calculates the inte-

gral of the input current signal (i.e., sum of samples)

and then feeds this integral into the processing path

instead of the current sample. This sum can produce a

DC offset that must be removed by an additional HPF

stage. The HPF can be combined with the integrator in

a single formula:

Yn = (1 - hpf_b0f/216) x (Yn-1 + Xn)

where hpf_b0f is the same coefficient used in the

stand-alone HPF stage. The integrator increases the

amplitude of accumulation by approximately (NS/2

π),

where NS is the number of samples per line cycle (fac-

tor approximately 16 for 50Hz signal and 200μs sam-

pling rate). The output of the integrator is scaled down

by factor 16 in the MAXQ3180.

The HPF, when combined with the digital integrator,

introduces an additional phase shift into the current

channel. To compensate for this, the second HPF stage

is automatically engaged in the voltage processing

path when the current integrator is active.

Fundamental and Harmonics Modes

The power calculation engine can work in one of three

modes: full, fundamental, and harmonics. The mode of

operation is selected by the HRM configuration bits.

• HRM = 00b—Full mode. Neither the bandpass or the

bandstop filters are applied.

• HRM = 01b—Fundamental mode. The voltage chan-

nel signal is put through the bandpass filter (BPF).

This BPF is centered on the fundamental frequency,

so only fundamental power is measured.

• HRM = 10b—Harmonics mode. The voltage channel

signal is put through the bandstop filter (BSF). That

BSF is centered on the fundamental frequency, so

fundamental power is removed and only harmonics

power is measured.

Both filters, the BPF and BSF, are second-order filters and

use the same set of coefficients. The filter formulas are:

BPF:

Yn = 2Yn-1 - Yn-2 + (bpf_b0f/220) x (2Yn-2 + Xn - Xn-2) -

(bpf_a1f/220) x Yn-1

BSF:

Yn = 2Yn-1 - Yn-2 + Xn - 2Xn-1 - Xn-2 + (bpf_b0f/220) x

(2Yn-2 - Xn - Xn-2) + (bpf_a1f/220) x (Xn-1 - Yn-1)

Low-Power, Multifunction, Polyphase AFE

______________________________________________________________________________________

INTEGRATOR

+ HPF

PHASE ANGLE COMPENSATION

GAIN, OFFSET, AND

LINEARITY CALIBRATION

SI2

I2_RMS

V2_RMS

P.V2

ACTIVE

REACTIVE

HPF

SV2

HPF

BPF

BSF

P.R

P.A

P.I2

Figure 8. DSP Flow

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