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ADE7758 Datasheet(PDF) 34 Page - Analog Devices |
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ADE7758 Datasheet(HTML) 34 Page - Analog Devices |
34 / 72 page ADE7758 Data Sheet Rev. E | Page 34 of 72 (see the Active Power Calculation section). Equation 14 gives an expression for the instantaneous power signal. This is filtered by LPF2, which has a magnitude response given by Equation 23. () 2 2 8 1 1 H f f + = (23) – E(t) t Vlt VI ×cos(4π ×f1 ×t) 4π ×f1 1 + 2 2f1 8 The active power signal (output of the LPF2) can be rewritten as () () ( t f f IRMS VRMS IRMS VRMS t p 1 2 2 1 4 cos 8 2 1 π × ⎥ ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎢ ⎣ ⎡ + × − × = ) (24) Figure 70. Output Frequency Ripple where f1 is the line frequency, for example, 60 Hz. Line Cycle Active Energy Accumulation Mode From Equation 24, E(t) equals The ADE7758 is designed with a special energy accumulation mode that simplifies the calibration process. By using the on- chip, zero-crossing detection, the ADE7758 updates the watt-hr accumulation registers after an integer number of zero crossings (see Figure 71). The line-active energy accumulation mode for watt-hr accumulation is activated by setting the LWATT bit (Bit 0) of the LCYCMODE register. The total energy accumu- lated over an integer number of half-line cycles is written to the watt-hr accumulation registers after the LINECYC number of zero crossings is detected. When using the line cycle accumulation mode, the RSTREAD bit (Bit 6) of the LCYCMODE register should be set to Logic 0. () ) 4 cos( 8 2 1 4 – 1 2 2 1 1 t f f f IRMS VRMS t IRMS VRMS π π × ⎥ ⎥ ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣ ⎡ + × × × (25) From Equation 25, it can be seen that there is a small ripple in the energy calculation due to the sin(2ωt) component (see Figure 70). The ripple gets larger with larger loads. Choosing a lower output frequency for APCF during calibration by using a large APCFDEN value and keeping APCFNUM relatively small can significantly reduce the ripple. Averaging the output frequency over a longer period achieves the same results. ZXSEL01 ZERO-CROSSING DETECTION (PHASE A) ZXSEL11 ZERO-CROSSING DETECTION (PHASE B) ZXSEL21 ZERO-CROSSING DETECTION (PHASE C) 1ZXSEL[0:2] AREBITS3 TO 5 IN THELCYCMODEREGISTER CALIBRATION CONTROL LINECYC[15:0] WATTOS[11:0] WG[11:0] WDIV[7:0] + + % + + WATTHR[15:0] ACCUMULATE ACTIVE POWER FOR LINECYC NUMBER OF ZERO-CROSSINGS; WATT-HR ACCUMULATION REGISTERS ARE UPDATED ONCE EVERY LINECYC NUMBER OF ZERO-CROSSINGS ACTIVE POWER 15 0 40 0 Figure 71. ADE7758 Line Cycle Active Energy Accumulation Mode |
Similar Part No. - ADE7758_15 |
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Similar Description - ADE7758_15 |
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