[FEATURE] Support decouple current measurement in state estimation

[TonyXiang8787]

Background

Currently the state estimation supports two types of sensors: voltage_sensor and power_sensor. Their meaning is self explanatory. In distribution grids, we have also many current measurements. Supporting current magnitude measurement is difficult since we do not know the direction of active/reactive power. To decouple the current, we need the voltage as a reference, with which we can calculate power. Therefore, we only support power measurements as this moment.

Decoupled current

Sometimes we have both voltage and current measurements in practice. However, certain voltage magnitude measurement has prohibitable high error margin which makes the calculated power value useless. Meanwhile, the phase angle between the voltage and current is actually accurately measured. In this case, we can use the current magnitude and angle to decouple current magnitude to active/reactive current. This can give significant information for the power flow in the grid.

Feature request

This issue proposes to support decoupled current measurement into PGM state estimation. Concretely, the following tasks:

• Define new component sym_current_sensor and asym_current_sensor.
  • They should have the attributes i_p_measured and i_q_measured, representing the active and reactive current.
  • The reference direction should be the same as the measured object, similar to power_sensor.
  • Also define relevant sigmas.
• In the observability check, treat the current sensor the same as power sensor. They both contribute to observability.
• In iterative linear solver, the implementation is straightforward, as the measured value in linear solver is already current phasor. We just need to shift the current phase angle with the node voltage phase angle.
• In Newton-Raphson solver, we need to refine the mathematics of current sensor and implement them.