No abstract

A simplified sensorless vector control system is derived by using the extended electromotive force (EMF) model. By using a steady-state voltage equation approximately, the rotor speed and position are computed from the output voltage of a γ-axis proportional plus integral (PI) current controller with decoupling control. A linear model is proposed for the small perturbation around a steady-state operating point. The system stability is discussed in terms of the trajectories of the system matrix eigenvalues for speed estimation and control parameters. The comparison between the simulation results obtained using a nonlinear model and the experimental results validates the derived system.

We have proposed a current observer-based speed sensorless vector control system taking into account both iron loss and stator resistance identification. The method is constructed in a synchronously rotating reference frame. The effectiveness of the proposed system has been investigated by digital simulation and experimentation. Furthermore important control parameters such as stator resistance, observer gain and filter of speed estimation are studied by comparing the computed result with experimental one.

-As a distributed generation system increases, a stable power supply becomes difficult. Thus control of power leveling (PL) unit is required to maintain the balance of power flow for irregular power generation. The unit is required to respond to change of voltage and bidirectional power flow. So the bidirectional buck/boost DC/DC converter is applied for the control of PL unit in this research. The PL unit with Super Capacitor (SC) is able to absorb change of power, and it is examined whether the stable power supply is possible. The output current of PL unit is controlled so as to keep power balance and DC bus voltage. The effectiveness of the proposed control is proved in simulation.

The line current detection type AF is attractive to compensate using only one current sensor and only one AF compensates all harmonics. However, it is difficult to compensate harmonics completely due to stability and a resonance problem. We propose a new method using the repetitive control for the line current detection type active filter. Aiming at a periodicity of the harmonics, the repetitive control is applied to the AF control. The line current harmonics is detected and memorized at every sampling time during the fundamental cycle. The memorized data are given to a reference of the AF after a fundamental period. The AF output current reference is optimized and the deviation in the line current harmonics gradually decreases by repeating the method. Good simulation results of the harmonics compensation by the proposed method are presented.