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ADE5166 数据表(PDF) 59 Page - Analog Devices |
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ADE5166 数据表(HTML) 59 Page - Analog Devices |
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59 / 148 page  Preliminary Technical Data ADE5166/ADE5169/ADE5566/ADE5569 Rev. PrB | Page 59 of 148 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 Figure 49). The line active energy accumulation uses the same signal path as the active energy accumulation. The LSB size of these two registers is equivalent. LINCYC VALUE CYCEND IRQ LWATTHR REGISTER Figure 49. Energy Accumulation When LINCYC Changes From the information in Equation 8 and Equation 9, () ()dt ft f VI dt VI t E nT nT π ⎪ ⎪ ⎭ ⎪ ⎪ ⎬ ⎫ ⎪ ⎪ ⎩ ⎪ ⎪ ⎨ ⎧ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + − = ∫ ∫ 2 cos 9 . 8 1 0 2 0 (16) 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, 0 0 + = ∫ nT VIdt E (17) E(t) = VInT (18) 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. REACTIVE POWER CALCULATION FOR THE ADE5569/ADE5169 Reactive power, a function available for the ADE5569/ADE5169 but not for the ADE5566/ADE5166, 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 21 gives an expression for the instantaneous reactive power signal in an ac system when the phase of the current channel is shifted by 90°. ) sin( 2 ) ( θ t V t v + ω = (19) ) sin( 2 ) ( t I t i ω = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π + ω = ′ 2 sin 2 ) ( t I t i (20) where: θ is the phase difference between the voltage and current channel. v is the rms voltage. i is the rms current. q(t) = v(t) × i’(t) (21) q(t) = VI sin (θ) + VI sin(2ωt + θ) The average reactive power over an integral number of lines (n) is given in Equation 22. ∫ θ = = nT VI dt t q nT Q 0 ) sin( ) ( 1 (22) where: T is the line cycle period. q is referred to as the reactive power. Note that the reactive power is equal to the dc component of the instantaneous reactive power signal q(t) in Equation 21. 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 Figure 50). In addition, the phase-shifting filter has a nonunity 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 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 Figure 43), 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. 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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