ade7953 Analog Devices, Inc., ade7953 Datasheet - Page 28

• Manufacturer Part Number: ade7953
• Description: Single Phase, Multifunction Metering Ic With Neutral Current Measurement Ade7953
• Manufacturer: Analog Devices, Inc.

ADE7953
REACTIVE ENERGY CALCULATION
The ADE7953 achieves the integration of the reactive power
signal in two stages. In the first stage, the reactive power signals
are accumulated in an internal 48-bit register every 143 μs
(6.99 kHz) until an internal fixed threshold is reached. When
this threshold is reached, a pulse is generated and is accumu-
lated in 24-bit, user-accessible accumulation registers. The
internal threshold results in a maximum accumulation rate
of approximately 210 kHz with full-scale inputs. This process
occurs simultaneously on Current Channel A and Current
Channel B, and the resulting readings can be read in the 24-bit
RENERGYA (Address 0x220 and Address 0x320) and
RENERGYB (Address 0x221 and Address 0x321) registers.
Both stages of the accumulation are signed and, therefore,
negative energy is subtracted from positive energy.
Note that the reactive energy register contents roll over to full-
scale negative (0x800000) and continue to increase in value
when the power or energy flow is positive. Conversely, if the
power is negative, the energy register underflows to full-scale
positive (0x7FFFFF) and continues to decrease in value.
RENERGYA and RENERGYB are read-with-reset registers
by default. This means that the contents of these registers are
reset to 0 after a read operation. This feature can be disabled
by clearing Bit 6 (RSTREAD) of the LCYCMODE register
(Address 0x004).
The ADE7953 includes two sets of interrupts that are triggered
when the reactive energy register is half full (positive or negative)
or when an overflow or underflow condition occurs. The first set
of interrupts is associated with the Current Channel A reactive
energy, and the second set of interrupts is associated with the
Current Channel B reactive energy. These interrupts are disabled
by default and can be enabled by setting the VAREHFA and
VAREOFA bits in the IRQENA register (Address 0x22C and
Address 0x32C) for Current Channel A, and the VAREHFB and
VAREOFB bits in the IRQENB register (Address 0x22F and
Address 0x32F) for Current Channel B.
VOLTAGE CHANNEL
OUTPUT FROM
OUTPUT FROM
LPF2
ADC
LPF1
Figure 52. Reactive Energy Line Cycle Accumulation
xVARGAIN
ZERO-CROSSING
DETECTION
Rev. 0 | Page 28 of 68
xVAROS
+
+
15
48
FIXED INTERNAL
ACCUMULATION
CALIBRATION
Reactive Energy Integration Time Under Steady Load
The discrete time sample period (T) for the accumulation registers
is 4.76 μs (1/210 kHz). With full-scale sinusoidal signals on the
analog inputs and a phase shift of 90°, a pulse is generated and
added to the RENERGYA and RENERGYB registers every 4.76 μs,
assuming that the AVARGAIN and BVARGAIN registers are set
to 0x00. The maximum positive value that can be stored in the
24-bit RENERGYA and RENERGYB registers is 0x7FFFFF before
the register overflows. The integration time under these condi-
tions can be calculated as follows:
Reactive Energy Line Cycle Accumulation Mode
In reactive energy line cycle accumulation mode, the energy
accumulation of the ADE7953 is synchronized to the voltage
channel zero crossing so that the reactive energy on Current
Channel A and Current Channel B can be accumulated over
an integral number of half line cycles. Line cycle accumulation
mode is disabled by default and can be enabled on Current
Channel A and Current Channel B by setting the ALVAR and
BLVAR bits to 1 in the LCYCMODE register (Address 0x004).
The accumulation time should be written to the LINECYC
register (Address 0x101) in the unit of number of half line cycles.
The number of half line cycles written to the LINECYC register
is used for both the Current Channel A and Current Channel B
accumulation periods. The ADE7953 can accumulate reactive
energy for up to 65,535 half line cycles. This equates to an accu-
mulation period of approximately 655 sec with 50 Hz inputs
and 546 sec with 60 Hz inputs.
At the end of a line cycle accumulation cycle, the RENERGYA and
RENERGYB registers are updated, and the CYCEND flag in the
IRQSTATA register (Address 0x22D and Address 0x32D) is set.
If the CYCEND bit in the IRQENA register is set, an external
interrupt is issued on the IRQ pin. In this way, the IRQ pin can
also be used to signal the completion of the line cycle accumula-
tion. Another accumulation cycle begins immediately as long as the
ALVAR and BLVAR bits in the LCYCMODE register remain set.
THRESHOLD
INTERNAL
CONTROL
LINECYC
Time = 0x7FFFFF × 4.76 μs = 39.9 sec
0
0
23
RENERGYx
0
(22)