[FEATURE] Support 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.

Current measurement with relative phase angle to the local voltage

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 have current magnitude + relative phase angle measurement.

Current measurement using PMU with global phase angle

If we install PMU current measurement in the grid, we can measure the current magnitude and the global phase angle with regarding the reference angle in the HV/MV substation. In this way we measure the current phasor.

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_measured and i_angle_measured, representing the current magnitude and angle.
  • [ ] They should have the attributes angle_measurement_type which is an enumeration of local and global.
    • [ ] In case of local, this is a relative angle to the local voltage.
    • [ ] In case of global, this is a PMU current phasor with the global angle to the reference angle in the HV/MV substation.
  • [ ] 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. In case of a local angle, 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.

[petersalemink95]

@TonyXiang8787 you mention that a sym/asym current_sensor should have i_p_measured and i_q_measured, which means the decoupling lies at the end-user. Wouldn't we in this case want to have i_measured and i_angle_measured, i.e. the current magnitude and angle, where we would do the decoupling? From a user perspective it would be beneficial if they can just provide the measured values, instead of calculating i_p_measured and i_q_measured themselves

[TonyXiang8787]

@TonyXiang8787 you mention that a sym/asym current_sensor should have i_p_measured and i_q_measured, which means the decoupling lies at the end-user. Wouldn't we in this case want to have i_measured and i_angle_measured, i.e. the current magnitude and angle, where we would do the decoupling? From a user perspective it would be beneficial if they can just provide the measured values, instead of calculating i_p_measured and i_q_measured themselves

I agree with you and will adjust the issue. Also we might want to support current phasors, and this interface can be re-used.