This paper presents a pulsewidth modulation (PWM) algorithm for a three-phase ac-dc rectifier, where the third and fifth harmonics are indicated in the input phase voltages. A mathematical analysis, which includes this voltage harmonic's components, shows that the unity input displacement factor (IDF) can be reached by appropriate evaluation of duty-cycle functions. A PWM algorithm is proposed based on this developed theoretical achievement. This approach enables current sensorless unity IDF rectification. The PWM algorithmis investigated theoretically and verified by simulations and experiment.
COBISS.SI-ID: 15236630
Generally, AT-cut quartz crystals have a limited scope of use when it comes to high-precision measurement of very small impedance changes due to their nonlinear frequency-temperature characteristics in the range between 0 °C and 50 °C. The new method improving quartz oscillator frequency-temperature characteristic compensation is switching between two impedance loads. By modifying the oscillator circuit with two logic switches and two impedance loads, the oscillator can switch oscillation between two resonance frequencies. The difference in resonance frequencies compensates the frequency-temperature characteristics influence as well as the influence of of fset and quartz crystal ageing. The experimental results show that the new approach using the switching method highly improves second-to-second frequency stability from +/-0.125 Hz to +/-0.00001 Hz and minute-to-minute frequency stability from 0.1 Hz to 0.0001 Hz, which makes the high-precision measurement of aF and fH changes possible.
COBISS.SI-ID: 14953750
This paper presents a discrete-event switching control of DC-DC converters which belong to a particular class of hybrid systems. Taking advantage of the energetical properties of these converters, Lyapunov function is proposed. This function, which is systematically deduced from the physical model, allows the creation of various stabilizing switching sequences. From a theoretical point of view, asymptotic stability can be obtained. The digital control is implemented by FPGA system, with additional A/D peripherals. Experimental results for digitally controlled synchronous buck converter show the effectiveness of the proposed approach.
COBISS.SI-ID: 14924310