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ADE7569 数据表(PDF) 63 Page - Analog Devices |
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ADE7569 数据表(HTML) 63 Page - Analog Devices |
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63 / 144 page  ADE7566/ADE7569/ADE7166/ADE7169 Rev. A | Page 63 of 144 When a new half-line cycle is written in the LINCYC register, the LWATTHR register is reset, and a new accumulation starts at the next zero crossing. The number of half-line cycles is then counted until LINCYC is reached. This implementation provides a valid measurement at the first CYCEND interrupt after writing to the LINCYC register (see ) sin( 2 ) ( θ t V t v + ω = (21) ) sin( 2 ) ( t I t i ω = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω = ′ 2 sin 2 ) ( t I t i (22) Figure 70). The line active energy accumulation uses the same signal path as the active energy accumulation. The LSB size of these two registers is equivalent. where: θ is the phase difference between the voltage and current channel. v is the rms voltage. i is the rms current. LINCYC VALUE CYCEND IRQ LWATTHR REGISTER q (t) = v(t) × i’(t) (23) q (t) = VI sin (θ) + VI sin ) 2 ( θ + ωt The average reactive power over an integral number of lines (n) is given in Equation 24. ∫ θ = = nT VI dt t q nT Q 0 ) sin( ) ( 1 (24) Figure 70. Energy Accumulation When LINCYC Changes where: T is the line cycle period. q is referred to as the reactive power. From the information in Equation 10 and Equation 11, () ()dt ft f VI dt VI t E nT nT π ⎪ ⎪ ⎭ ⎪ ⎪ ⎬ ⎫ ⎪ ⎪ ⎩ ⎪ ⎪ ⎨ ⎧ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + − = ∫ ∫ 2 cos 9 . 8 1 0 2 0 (18) Note that the reactive power is equal to the dc component of the instantaneous reactive power signal q(t) in Equation 23. The instantaneous reactive power signal q(t) is generated by multiplying the voltage and current channels. In this case, the phase of the current channel is shifted by 90°. The dc component of the instantaneous reactive power signal is then extracted by a low-pass filter to obtain the reactive power information (see where: n is an integer. T is the line cycle period. Because the sinusoidal component is integrated over an integer number of line cycles, its value is always 0. Therefore, Figure 71). 0 0 + = ∫ nT VIdt E (19) E (t) = VInT (20) In addition, the phase-shifting filter has a non-unity magnitude response. Because the phase-shifted filter has a large attenuation at high frequency, the reactive power is primarily for calculation at line frequency. The effect of harmonics is largely ignored in the reactive power calculation. Note that, because of the magnitude characteristic of the phase shifting filter, the weight of the reactive power is slightly different from the active power calculation (see the Note that in this mode, the 16-bit LINCYC register can hold a maximum value of 65,535. In other words, the line energy accumulation mode can be used to accumulate active energy for a maximum duration of over 65,535 half-line cycles. At a 60 Hz line frequency, it translates to a total duration of 65,535/120 Hz = 546 sec. Energy Register Scaling section). The frequency response of the LPF in the reactive signal path is identical to the one used for LPF2 in the average active power calculation. Because LPF2 does not have an ideal brick wall frequency response (see REACTIVE POWER CALCULATION FOR THE ADE7569/ADE7169 Figure 64), the reactive power signal has some ripple due to the instantaneous reactive power signal. This ripple is sinusoidal and has a frequency equal to twice the line frequency. Because the ripple is sinusoidal in nature, it is removed when the reactive power signal is integrated to calculate energy. Reactive power, a function available for the ADE7569/ADE7169 but not for the ADE7566/ADE7166, is defined as the product of the voltage and current waveforms when one of these signals is phase-shifted by 90°. The resulting waveform is called the instantaneous reactive power signal. Equation 23 gives an expression for the instantaneous reactive power signal in an ac system when the phase of the current channel is shifted by 90°. The reactive power signal can be read from the waveform register by setting the WAVMODE register (0x0D) and the WFSM bit in the Interrupt Enable 3 SFR (MIRQENH, 0xDB). Like the current and voltage channels waveform sampling modes, the waveform data is available at sample rates of 25.6 kSPS, 12.8 kSPS, 6.4 kSPS, or 3.2 kSPS. |
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