Benefits of using STPMxx with Rogowski coil-based sensors

AN3306

12/21

Doc ID 18182 Rev 1

Equation 6

The final result is:

Equation 7

This makes the use of STPMxx devices with Rogowski coil-based current sensors, such as

the Pulse current sensor, advantageous. When a Rogowski coil-based sensor is used, a

very high degree of accuracy is obtained by design due to the following:

●

DC offset cancellation and the power calculation algorithm produces a DC component,

proportional to the active power, without any offset or AC ripple.

●

Ripple-free power calculation, so integration of power over the line period is avoided,

and thus energy accumulation is not affected by fluctuation of the line frequency.

●

The architecture makes the STPMxx devices ready for Rogowski coil-based sensors

without the need for an additional integration block, which would increase system

complexity and overall application cost.

5.2

Mutual current compensation

For poly-phase systems, where galvanic isolation between phases is a must, and immunity

to DC magnetic fields is becoming a requirement in international standards, a Rogowski

coil-based sensor offers an interesting and inexpensive solution.

The drawback of this approach is cross influence between current channels.

The STPMC1, a dedicated device for poly-phase measurement, features embedded

functionality which allows error compensation from mutual currents.

For single-phase systems, two correction factors,

α (alpha) and β (beta), produce a ±3.1%

correction factor in 512 steps. Asymmetrical compensation is implemented by multiplying

the phase current with

α and neutral current with β, and these values are then subtracted

from neutral and phase currents, respectively, as shown in Table 3 and Equation 8 and

Equation 9.

Equation 8

Table 3.

Mutual current compensation matrix for single-phase systems

Phase

S

T

S

−β

T

α−