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ADE7752B Datasheet(PDF) 21 Page - Analog Devices |
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ADE7752B Datasheet(HTML) 21 Page - Analog Devices |
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21 / 24 page  ADE7752B Rev. 0 | Page 21 of 24 Example 2 In this example, the ADE7752B is connected to a 3-phase, 3-wire delta service as shown in Figure 17. The total active energy calculation processed in the ADE7752B can be expressed as Total Active Power = (VA – VC) × IA + (VB – VC) × IB where: VA, VB, and VC represent the voltage on Phase A, Phase B, and Phase C, respectively. IA and IB represent the current on Phase A and Phase B, respectively. With respect to the voltage and current inputs in Equation 7 and Equation 8, the total active power (P) is () ( ) ( ) ( ) () () ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω × × × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω × × − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω × × + ω × × × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω × × − ω × × = − × − + − − = 3 2 cos 2 3 4 cos 2 3 2 cos 2 cos 2 3 4 cos 2 cos 2 t I t V v t V t I t V t V P I I V V I I V V P l B l C l B l A l C l A BN BP C B AN AP C A (15) For simplification, assume that ΦA = ΦB = ΦC = 0 and VA = VB = VC = V. The preceding equation becomes () () ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω × π + ω × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π × × × + ω × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π × × × = 3 2 cos sin 3 sin 2 cos 3 2 sin 3 2 sin 2 t t I V t t I V P l l B l l A (16) P then becomes ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π × × + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π × × = 3 2 sin 3 sin 3 2 2 sin 3 2 sin t I V t I V P l B BN l A AN (17) where: VAN = V × sin(2π/3) VBN = V × sin(π/3) As the LPF on each channel eliminates the 2ωl component of the equation, the active power measured by the ADE7752B is 2 3 2 3 × × + × × = B BN A AN I V I V P (18) If full-scale ac voltage of ±500 mV peak is applied to the voltage channels and current channels, the expected output frequency is calculated as follows: value reference nominal V 4 . 2 0 rms V 2 5 . 0 ac peak V m 500 1 , Hz 56 . 0 = = = = = = = = = = = = = REF C CN C B A BN AN 7 to 1 V I V I I I V V S1 S0 SCF f (19) Note that if the on-chip reference is used, actual output frequencies can vary from device to device due to a reference tolerance of ±8%. Hz 133 . 0 2 3 4 . 2 2 2 56 . 0 5 . 0 5 . 0 313 . 6 2 2 = × × × × × × × = Freq (20) Table 6 shows a complete listing of all maximum output frequencies when using all three channel inputs. Table 6. Maximum Output Frequency on F1 and F2 SCF S1 S0 Maximum Frequency for AC Inputs (Hz) 0 0 0 0.92 1 0 1 1.84 0 0 1 0.46 1 0 1 1.84 0 1 0 2.09 1 1 0 0.46 0 1 1 0.23 1 1 1 0.23 FREQUENCY OUTPUT CF The pulse output calibration frequency (CF) is intended for use during calibration. The output pulse rate on CF can be up to 64× the pulse rate on F1 and F2. Table 7 shows how the two frequencies are related, depending on the states of the logic inputs S0, S1, and SCF. Because of its relatively high pulse rate, the frequency at this logic output is proportional to the instantane- ous active power. As is the case with F1 and F2, the frequency is derived from the output of the low-pass filter after multiplication. However, because the output frequency is high, this active power information is accumulated over a much shorter time. Thus, less averaging is carried out in the digital-to-frequency conversion. The CF output is much more responsive to power fluctuations with much less averaging of the active power signal (see Figure 11). Table 7. Maximum Output Frequency on CF SCF S1 S0 f1 to 7 (Hz) CF Maximum for AC Signals (Hz) 0 0 0 2.24 16 × F1, F2 = 14.76 1 0 0 4.49 8 × F1, F2 = 14.76 0 0 1 1.12 32 × F1, F2 = 14.76 1 0 1 4.49 16 × F1, F2 = 29.51 0 1 0 5.09 160 × F1, F2 = 334 1 1 0 1.12 16 × F1, F2 = 7.38 0 1 1 0.56 32 × F1, F2 = 7.38 1 1 1 0.56 16 × F1, F2 = 3.69 |
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