Working Point (P/Sn, Pf, U, N) – Motor or Generator op. mode

Positioning and objective

Through this test, the user can also verify whether the desired operating point is compatible with the machine. Additionally, the user can identify the appropriate reference values for the field current and the control angle needed to achieve this operating point.

Working point – Sine wave – Motor – P, Pf, U, N” - Overview

The results of this test give an overview of the electromagnetic analysis of the machine, considering its topology.

The general data of the machine, like the machine constant and power balance, are computed and displayed. The user can choose between motor and generator conventions to build the model.

The magnetic flux density is also computed in every region of the machine’s magnetic circuit to evaluate the design.

It also gives the capability to make comparisons between the results obtained from the measurements and those obtained with FluxMotor.

User inputs

The main user input parameters are the choice of the convention and the operating mode, then the output power/apparent power, the power factor (lead/lag), the speed and the line-line voltage. In addition, the windings temperatures must be set.

Main outputs

Test results are illustrated with data, graphs, and tables.

Main results

Machine performance at the base speed point (General data, Machine constants, Power balance, Flux in airgap, Flux density in iron)

Ripple mechanical torque at the working point

Main principles of computation

Introduction

The aim of this test in motor / generator convention is to give a good overview of the electromagnetic potential of the machine by characterizing the working point according to the output power / apparent power, power factor, speed and voltage set by the user.

In addition, ripple torque at the working point is also computed.

To achieve such an objective, in the back end of FluxMotor, an automatic search is performed to identify the line current I, the field current If and control angle ψ providing the performance defined by the user.

Generator operating mode

In the generator operating mode, the line current can be deduced directly from the user input (output power / apparent power, power factor and line-line voltage). The research zone comprises thus two dimensions: field current and control angle. It is defined by the maximum field current, the number of computations along the field current axis and the control angle axis, all of which can be adjusted by the user in the inputs of the test.

Research zone of the P-Pf-U-N for the generator operating mode defined by maximum field current and number of computations along the field current axis and control angle axis

Within the research zone, the If-I-Psi-N test will be executed at all points (If, ψ) to determine the performance response surfaces of the machine. Then an optimizer is used to search for the point (If, ψ) providing the match with the targeted performance.

Performance of the machine in generator operating mode within the research zone in terms of voltage, active power and reactive power and the point (If, ψ) providing the targeted performance

Motor operating mode

In the motor operating mode, the line current cannot be deduced directly from the user input (output power, power factor and line-line voltage) as the output power is related to on-shaft mechanical power without any knowledge of efficiency. The research zone comprises thus three dimensions: field current, armature current and control angle, or field current, d-axis armature current and q-axis armature current. It is defined by the maximum field current, the number of computations along the field current axis and the number of computations along the d-axis and q-axis of the armature current, all of which can be adjusted by the user in the inputs of the test.

Research zone of the P-Pf-U-N for the motor operating mode

Within the research zone, the If-I-Psi-N test will be executed at all points (If, Id, Iq) to determine the performance response surfaces of the machine. Then an optimizer is used to search for the point (If, Id, Iq) providing the match with the targeted performance.

Performance of the machine in generator operating mode within the research zone in terms of voltage, output power and phase angle and the point (If, Id, Iq) providing the targeted performance

Feasibility diagram and color meaning of outputs in the working point table

In this test, one can set any combination of power, power factor, voltage, and speed. However, not all the combinations are feasible for a given synchronous machine. To help users detect unfeasible operating points, a powerful tool called the Feasibility Diagram is provided.

The concept is like the P-Q diagram used by generator designers. In the P-Q plane, curves corresponding to different field current (If) values are plotted. Each point on these curves represents a combination of field current, armature current magnitude, and control angle. The curves range from If = 0 to Ifmax, and while the armature current remains constant (determined by the apparent power and voltage targets), each point on a curve corresponds to a different control angle.

The Feasibility output in the working point table will display "Yes" if the target point is feasible or "No" if it is not, based on the position of the working point relative to the feasible area.

Feasibility diagram, the operating point is accessible

Feasibility diagram, operating point not accessible

Even if the working point is not feasible, the optimizer in the backend of FluxMotor still provides a combination of field current, armature current, and control angle. This combination allows the machine to operate, but the resulting power, power factor, and voltage might be close to the target values—or far from them. We provide these results regardless, as they might still be helpful to the user.

Color-coding system allowing to detect if a working point is accessible and how to achieve it by modifying test inputs