andes.core.service.NumRepeat

class andes.core.service.NumRepeat(u, ref, **kwargs)

A helper Service type which repeats a v-provider's value based on the shape from a BackRef

Examples

NumRepeat was originally designed for computing the inertia-weighted average rotor speed (center of inertia speed). COI speed is computed with

\[\omega_{COI} = \frac{ \sum{M_i * \omega_i} } {\sum{M_i}}\]

The numerator can be calculated with a mix of BackRef, ExtParam and ExtState. The denominator needs to be calculated with NumReduce and Service Repeat. That is, use NumReduce to calculate the sum, and use NumRepeat to repeat the summed value for each device.

In the COI class, one would have

class COIModel(...):
    def __init__(...):
        ...
        self.SynGen = BackRef()
        self.SynGenIdx = RefFlatten(ref=self.SynGen)
        self.M = ExtParam(model='SynGen',
                          src='M',
                          indexer=self.SynGenIdx)

        self.wgen = ExtState(model='SynGen',
                             src='omega',
                             indexer=self.SynGenIdx)

        self.Mt = NumReduce(u=self.M,
                                 fun=np.sum,
                                 ref=self.SynGen)

        self.Mtr = NumRepeat(u=self.Mt,
                               ref=self.SynGen)

        self.pidx = IdxRepeat(u=self.idx,ref=self.SynGen)

Finally, one would define the center of inertia speed as

self.wcoi = Algeb(v_str='1', e_str='-wcoi')

self.wcoi_sub = ExtAlgeb(model='COI',
                         src='wcoi',
                         e_str='M * wgen / Mtr',
                         v_str='M / Mtr',
                         indexer=self.pidx,
                         )

It is very worth noting that the implementation uses a trick to separate the average weighted sum into n sub-equations, each calculating the \((M_i * \omega_i) / (\sum{M_i})\). Since all the variables are preserved in the sub-equation, the derivatives can be calculated correctly.

__init__(u, ref, **kwargs)

Methods

assign_memory(n)	Assign memory for self.v and set the array to zero.
get_names()	Return name in a list

Attributes

class_name	Return the class name
n	Return the count of values in self.v.
v	Return the values of the repeated values in a sequential 1-D array