Synchronous generator parameter identification

Synchronous machine identification and parameter determination can be performed either during normal operation (i.e. on-line), or during specially designed identification experiments (i.e. off-line) [90]. Each approach has advantages as well as disadvantages. For example, in the on-line case the measured input-output data reflect the actual operating conditions. A disadvantage is that it is not possible to manipulate the input signals arbitrarily in order to obtain the best identification results. This implies that the influence of the operating conditions on the (accuracy of the) identified parameters has to be carefully analysed. Off-line tests, on the other hand, require that the machine under test has to be taken out of regular operation, an action that might be inappropriate or even impossible.

Off-line identification experiments have been used for decades to identify electrical machine parameters. Two concepts are commonly used: running machine, or standstill. Standstill tests are very attractive from a practical viewpoint - if it is permissible to take the machine out of operation - because driving the machine often creates serious complications of the measurement set-up [301]. Furthermore, the measured signals will have good signal-to-noise ratios due to the absence of disturbance signals (electromagnetic interference). All standstill tests reported in literature are variations on the same concept, they mainly differ in the kind of excitation signal applied (i.e. step, ramp, sinusoidal, or random excitation).

The standstill test concept is preferred because there is no interaction between the direct- and the quadrature axis. Observe that the block diagram of Fig. 3.26 reduces to that of Fig. 4.22 for the standstill case (i.e. = 0). Using this observation, it can be concluded that the parameter identification for both axes may be carried out separately. In practice, zero generator speed can be enforced by mechanically locking the rotor during the experiments.


Figure 4.22: Block diagram of an ideal synchronous machine at standstill.

In addition, there are a few important practical demands in selecting a technique for the identification and parameter determination of the Lagerwey LW-50/750 generator considering the fact that the generator has already been installed in the nacelle at about 50 meter above the ground level. First of all, the measurements should have low power consumption. Secondly, the test equipment should be compact, and finally, the measurement time should be limited (i.e. < 1 day).

Before selecting the most appropriate standstill test, we will first highlight the most important aspects of both the quadrature-axis and the direct-axis identification.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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