ABSTRACT A novel strategy of current regulation of a field-oriented
controlled induction motor using a gate turn-off thyristor (GTO)
inverter is proposed which is based on multivariable state feedback
control with an integrator. The controller is designed by the pole
placement technique of multivariable system regulation theory.
Feedforward control is included in the control laws to improve transient
responses. For the full state feedback control, the rotor flux is
estimated with a reduced-order state observer. A good steady-state
performance is obtained by means of an integral compensation, and fast
transient response is also feasible since the required voltage is
directly calculated from the feedforward control. Space voltage vector
pulse width modulation is adopted as a switching strategy. A variable
modulation scheme is presented which is changed from three-phase to
two-phase modulation in the high modulation range, which gives lower
current ripple over the whole operating range
[Show abstract][Hide abstract] ABSTRACT: The paper discusses the problem of flux estimation for the induction motor (IM) drive and presents a sensorless observer. The objective is to estimate the fluxes of the IM in the stationary reference frame and to obtain the magnitude and the angle of the rotor flux. In a typical sensorless IM scheme, both these estimates are needed. The paper first presents an alternative state-space model of the IM. Using this, a Sliding Mode (SM) observer is designed. The paper first assumes that the speed of the motor is measured and develops a sensored observer; this is later transformed into a sensorless observer by feeding it with a speed estimate. This approach eliminates the need to measure the speed; instead, the speed estimate is an input of the SM observer. The paper studies the behavior of the observer under these conditions, finds a favorable tuning and shows that the resulting estimates are quite insensitive to the speed mismatch. The proposed design allows accurate estimation of the magnitude and angle of the flux. Previous observers developed under the same conditions based on the traditional IM model were capable of estimating only the angle of the flux (but not the magnitude). The advantage of this method is that it also yields an accurate flux magnitude. The equilibrium point of the observer with improper speed input is studied and conclusions are drawn. The theoretical developments and observations are supported by the simulations.
2014 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM 2014); 06/2014
[Show abstract][Hide abstract] ABSTRACT: The paper discusses the problem of speed and rotor flux magnitude estimation for the induction motor (IM) drive and presents a sliding mode observer (SMO) that is constructed based on the IM model in the synchronous reference frame. To implement the control scheme of the IM drive, generally, the speed and the flux magnitude are needed. In a control scheme with speed and flux regulation, they are used for d and q axis feedback. If the current control scheme uses a decoupling compensator, the flux and speed are needed to compute the decoupling voltages. The paper develops a SM observer for the flux magnitude based on the synchronous reference frame model of the IM. The method assumes that the d-q voltages and currents are available. The observer requires knowledge of the motor speed - instead, the SMO is fed with a speed estimate (assumed inaccurate). Using a specific gain design, the SMO is made insensitive to the input speed inaccuracy. Using the equivalent controls of the observer, the initial speed estimate is corrected to obtain two secondary speed estimates. A weighted average speed estimate that combines the secondary estimates is also shown. The theoretical findings are supported with simulations.
2014 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM 2014); 06/2014
[Show abstract][Hide abstract] ABSTRACT: The paper discusses the problem of flux estimation for the induction motor (IM) drive and presents a sensorless observer. The intention is to estimate the IM fluxes in the stationary reference frame in order to obtain both the magnitude and the angle of the rotor flux. The flux magnitude is typically used for d axis feedback; the flux angle is needed for field orientation. The paper presents an alternative state-space model of the IM. Based on this, a Lyapunov-type nonlinear state observer with continuous feedback is designed. The paper first assumes that the speed is known and develops a sensored observer; then, this is transformed into a sensorless observer by feeding it with a speed estimate (assumed inaccurate). This method eliminates the speed measurement. The paper shows that, despite the improper speed input, the design yields a partially accurate estimate of the state vector that is sufficient for obtaining the magnitude and angle of the flux. Previous observers developed under the same conditions based on the traditional IM model were only capable of estimating the angle of the flux (but not the magnitude). The novelty is that this method also yields an accurate flux magnitude. It is shown that the equilibrium point of the observer is influenced by the design gains; with high enough gain, the observer converges. The theoretical developments are supported by simulations.
7th IET International Conference on Power Electronics, Machines and Drives (PEMD 2014); 01/2014
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