I have a MCU equipped with a single ADC and a single S&H (Sample and Hold) circuit. The board where the MCU is placed has several inputs (let's say 3 x currents, 3 x voltages). The MCU is programmed to sample each input at 1 kS/s. Since it has a single ADC, the ADC sampling frequency is at least 6 kS/s (due to the fact we have 6 inputs), and the ADC input is multiplexed on the various input signals sequentially.

I wish to calculate active power (single-phase and/or three-phases), but unfortunately the ADC has a single S/H, and hence the sample of the voltage and the sample of the current are not taken at the same time.
The best solution would be to use an MCU with several ADCs sampling simultaneously, or an MCU with one ADC but several S&H circuits.
Nevertheless is there some way to calculate active power accurately (multiplying the instantaneous voltage and current samples) with single ADC and single S&H, for instance through linear interpolation (to align the current and voltage samples to the same instant)?

[![enter image description here](https://i.stack.imgur.com/a6yFt.png)](https://i.stack.imgur.com/a6yFt.png)

[![enter image description here](https://i.stack.imgur.com/tmfB4.png)](https://i.stack.imgur.com/tmfB4.png)