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Inverter dead-time, which is meant for safe commutation of devices is known to induce sub-harmonic oscillations in lightly-loaded induction motor drives operating in open-loop. This paper presents an experimental procedure to determine whether a given motor drive would exhibit such oscillations, and if yes, the region of such oscillatory behaviour. In particular, this paper presents case studies on...
Volts-per-hertz (V/f) controlled induction motor drives could exhibit small-signal instability in the low and medium speed ranges, and particularly under light-load conditions. This results in sustained sub-harmonic oscillations in motor current, torque and speed. This instability is accentuated on account of inverter dead-time. This paper examines improving the stability by connecting an external...
We discuss the theory and implementation of phased array receivers in the focal plane of a telescope as applied to the mm-wave band. Simulated performance and construction details are given for a 64 element, 70–95 GHz array receiver for use on the Green Bank Telescope (GBT).
Space vector modulated voltage-source inverters require an overmodulation algorithm for continuous control of line-side voltage during overmodulation and for a smooth transition from PWM to six-step mode. Overmodulation increases the dc bus utilisation of a voltage source inverter, but requires significantly higher computational effort than linear modulation. This paper proposes a novel single-zone...
Dead-time is introduced between the gating signals to the top and bottom switches in a voltage source inverter (VSI) leg, to prevent shoot through fault due to the finite turn-off times of IGBTs. The dead-time results in a delay when the incoming device is an IGBT, resulting in error voltage pulses in the inverter output voltage. This paper presents the design, fabrication and testing of an advanced...
This paper demonstrates light-load instability in open-loop induction motor drives on account of inverter dead-time. The dynamic equations of an inverter fed induction motor, incorporating the effect of dead-time, are considered. A procedure to derive the small-signal model of the motor, including the effect of inverter dead-time, is presented. Further, stability analysis is carried out on a 100-kW,...
In traction applications, power electronic converters experience wide variation in DC link voltage during operation. The purpose of this paper is to study the variations in turn-on and turn-off switching energy losses in the IGBTs with the DC link voltage. The IGBT switching characteristics are measured at various operating conditions, and turn-on and turn-off switching energy losses are determined...
Acoustic noise is one of the undesirable consequences of the harmonic currents fed into an induction motor by a voltage source inverter. If the inverter is modulated at a fixed switching frequency, the resulting current harmonic components are located in narrow bands around integral multiples of the switching frequency. This causes discrete tonal noise which is unpleasant to human ear. This paper...
Low-order harmonic pulsating torque is a major concern in high-power drives, high-speed drives and motor drives operating in over-modulation region. This paper considers the specific case of eliminating or minimizing the sixth-harmonic torque (τ6) with a PWM waveform having only two switching angles per quarter. A method for evaluation of harmonic torques in the synchronously revolving dq reference...
Proportional Integral (PI) controller based current control is widely employed in differenct motor drives. However, in case of switched reluctance motor (SRM), the non-linearity and double wsaliency of the motor make the modelling and controller design challenging. This paper attempts linearisation of the flux linkage characteristic of the SRM at different operating points. The models include saturation...
Gallium nitride (GaN) based high-electron-mobility transistor (HEMT) is becoming popular as fast switching devices for power electronic applications. This paper presents a comparative study of the critical parameters such as on-state resistance, reverse conduction drop, leakage current, maximum junction temperature, threshold voltage, gate charge requirement and device capacitances of commercially...
Real-time simulation of photovoltaic (PV) panel can be used for research on power electronic converter topologies and control for PV applications. This paper presents real-time simulation of PV panel using a miniature full spectrum simulator (mini-FSS), developed for educational purposes. A mathematical model of the PV panel is solved using Newton Raphson method on the real-time simulator. This can...
PWM waveforms with positive voltage transition at the positive zero crossing of the fundamental voltage (type-A) are generally considered for PWM waveform with even number of switching angles per quarter whereas, waveforms with negative voltage transition at the positive zero crossing (type-B) are considered for odd number of switching angles per quarter. Optimal PWM, for minimization of total harmonic...
Aim of this paper is to study the variations in turn-on and turn-off switching energy losses in the IGBTs with device current at different DC link voltages and junction temperatures. The IGBT switching characteristics are obtained experimentally at various operating conditions, and turn-on and turn-off switching energy losses are determined. The relationship between the switching energy losses and...
Inverter dead-time, which is meant to prevent shoot-through fault, causes harmonic distortion and change in the fundamental voltage in the inverter output. Typical dead-time compensation schemes ensure that the amplitude of the fundamental output current is as desired, and also improve the current waveform quality significantly. However, even with compensation, the motor line current waveform is observed...
The acoustic noise emitted by an induction motor, powered by a voltage source inverter, is an environmental issue. Harmonics present in the stator current are the main reason for the increased acoustic noise in motor drives. The pulse-width modulation technique used to modulate the inverter is the key factor determining the magnitude of current harmonics. Bus-clamping pulse-width modulation (BCPWM)...
Half-wave symmetry (HWS) and quarter-wave symmetry (QWS) are traditionally associated with high waveform quality of the inverter output voltage, particularly when the ratio of switching frequency to the modulating frequency (i.e. pulse number, P) is quite low. This paper investigates and establishes the possibility of high-quality pulse-width modulated waveforms with HWS, but without QWS, for P =...
Special switching sequences involving division of active state time are used in space-vector-based generation of pulse width modulation (PWM) waveforms. This paper proposes a hybrid PWM technique which is a combination of the conventional and special switching sequences. The proposed hybrid PWM technique reduces the peak-to-peak torque ripple at high speeds of an induction motor drive. Supporting...
Usually the top and bottom IGBT devices in an inverter leg are of the same make (i.e. from same manufacturer). At low power level, these two devices even may be contained in the same module. However at high power levels the top and bottom devices are in separate modules. Sometimes, in the event of device failure, device of particular make may be replaced by one of another make, but of same ratings...
Insulated gate bipolar transistors (IGBTs) are used in high-power voltage-source converters rated up to hundreds of kilowatts or even a few megawatts. Knowledge of device switching characteristics is required for reliable design and operation of the converters. Switching characteristics are studied widely at high current levels, and corresponding data are available in datasheets. But the devices in...
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