Semiconductor Losses Calculation of a Quasi-Z-Source Inverter with Dead-Time

A quasi-Z-source inverter (qZSI) belongs to the group of single-stage boost inverters. The input dc voltage is boosted by utilizing an impedance network and so called shoot-through (ST) states. In pulse-width modulations utilized for the qZSI, the dead-time is commonly omitted. However, unintended ST states inevitably occur as a result of this action, due to the non-ideality of the switching devices, causing the unintended voltage boost of the inverter and an increase in the switching losses. Hence, the implementation of the dead-time is desirable with regard to both the controllability and efficiency of the qZSI. This paper deals with the calculation of semiconductor losses of the three- phase qZSI with implemented dead time. An algorithm available in the literature was utilized for that purpose. The algorithm in question was originally proposed and applied for the qZSI with omitted dead-time, where the occurrence of unintended, undetected ST states combined with the errors in the switching energy characteristics of the insulated gate bipolar transistor (IGBT) provided by a manufacturer led to errors in the obtained results. However, these errors were unjustifiably ascribed solely to the errors in the switching energy characteristics of the IGBT. In this paper, a new, corrected multiplication factor is experimentally determined and applied to the manufacturer-provided IGBT switching energies. The newly-determined multiplication factor is expectedly lower than the one obtained in the case of omitted dead time. The loss- calculation algorithm with the new multiplication factor was experimentally evaluated for different values of the qZSI input voltage, the duty cycle, and the switching frequency

Akustička analiza glasa transrodne žene uslijed vokalne terapije − prikaz slučaja

U ovome je radu prikazana akustička analiza glasa transrodne žene u tranziciji, prije i poslije vokalne terapije. VHI i TWVQ upitnicima klijentica je procijenila vlastiti glas, a rezultati su uputili na težak oblik vokalne disforije. Usporedbom parametara fundamentalne frekvencije i formanata pokazalo se da je vokalnom terapijom glas transrodne žene postao statistički značajno viši (p < 0,05), a intonacija razvedenija. Naučenom impostacijom usvojena je prednja dikcija koja se očitovala povišenim vrijednostima formanata. Rezultati ukazuju na promjenu kategorizacije iz muškoga u androgeni glas. Perceptivnom analizom te analizom dugotrajnoga prosječnoga spektra govora također je potvrđena timbralna promjena koja se ogleda u postizanju svjetlijega i ženstvenijega glasa. S druge pak strane, rezultati samoprocjene glasa pokazali su da klijentica i dalje osjeća tešku vokalnu disforiju te da joj ostvareni značajni pomaci u visini i boji glasa te intonaciji nisu bili dovoljni. S obzirom na navedeno, sa svrhom poboljšanja kvalitete života klijentice, preporučuje se nastavak vokalne terapije i daljnja obrada kod fonokirurga

Dynamic model of a self-excited induction generator with fundamental stray load and iron losses

This paper considers a dynamic model of a self-excited induction generator that takes into account the fundamental stray load and iron losses. The model is de¬scribed with the same number of differential equations as the conventional induc¬tion machine model. Determination of the stray load and iron losses resistances does not involve any tests other than those imposed by the international standards nor does it require any details about induction machine materials or geometry. The dynamic analysis has been carried out for the case of a wind turbine-driven self-excited induction generator. The steady-state analysis, on the other hand, has been carried out for the case of a load-independent prime mover. The considered advanced model, aside from being compared with the conventional model, has been experimentally validated for two different-efficiency induction machines, both rated 1.5 kW

Hybrid Wind-Solar Power System with a Battery-Assisted Quasi-Z-Source Inverter: Optimal Power Generation by Deploying Minimum Sensors

This paper presents a hybrid renewable energy system (RES) including wind and photovoltaic (PV) power sources. The wind energy subsystem (WES) consists of a squirrel-cage induction generator (SCIG) driven by a variable-speed wind turbine (WT) and corresponding power electronic converter, by means of which a speed-sensorless indirect-rotor-field-oriented control of the SCIG is implemented. The outputs of both the WES and PV power source rated 1.5 kW and 3.5 kW, respectively, are connected to the DC bus, with the quasi-Z-source inverter (qZSI) acting as an interlinking converter between the DC bus and the AC grid/load. An advanced pulse-width-modulation scheme is applied to reduce the qZSI switching losses. The considered RES can operate both in grid-tie and island operation, whereas the battery storage system&mdash;integrated within the qZSI impedance network&mdash;enables more efficient energy management. The proposed control scheme includes successively executed algorithms for the optimization of the WES and PV power outputs under varying atmospheric conditions. A perturb-and-observe PV optimization algorithm is executed first due to the significantly faster dynamics and higher-rated power of the PV source compared to the WES. The WES optimization algorithm includes two distinct fuzzy logic optimizations: one for extraction of the maximum wind power and the other for minimization of the SCIG losses. To reduce the number of the required sensors, all three MPPT algorithms utilize the same input variable&mdash;the qZSI&rsquo;s input power&mdash;thus increasing the system&rsquo;s reliability and reducing the cost of implementation. The performance of the proposed hybrid RES was experimentally evaluated over wide ranges of simulated atmospheric conditions in both the island and grid-tie operation

Photovoltaic System with a Battery-Assisted Quasi-Z-Source Inverter: Improved Control System Design Based on a Novel Small-Signal Model

This paper deals with a photovoltaic (PV) system containing a quasi-Z-source inverter (qZSI) and batteries connected in parallel with the qZSI&rsquo;s lower-voltage capacitor. The control system design is based on knowledge of three transfer functions which are obtained from the novel small-signal model of the considered system. The transfer function from the d-axis grid current to the battery current has been identified for the first time in this study for the considered system configuration and has been utilized for the design of the battery current control loop for the grid-tied operation. The transfer function from the duty cycle to the PV source voltage has been utilized for the design of the PV source voltage control loop. The PV source voltage is controlled so as to ensure the desired power production of the PV source. For the maximum power point tracking, a perturb-and-observe algorithm is utilized that does not require the measurement of the PV source current, but it instead utilizes the battery current during the stand-alone operation and the d-axis reference current during the grid-tied operation. The corresponding tracking period was determined by using the transfer function from the duty cycle to the battery current and in accordance with the longest settling time noted in the corresponding step response. The proposed control algorithm also has integrated protection against battery overcharging during the stand-alone operation. The considered system has been experimentally tested over wide ranges of irradiance and PV panel temperature

Experimental Investigation of a Standalone Wind Energy System with a Battery-Assisted Quasi-Z-Source Inverter

This paper presents a wind energy conversion system (WECS) for grid-isolated areas. The system includes a squirrel-cage induction generator (SCIG) and a battery-assisted quasi-Z source inverter (qZSI). The batteries ensure reliable and stable operation of the WECS in spite of the wind power oscillations. The maximum power is captured from both the wind turbine (WT) and the SCIG through adjustment of the WT speed and the SCIG operating flux, respectively. The utilized maximum power point tracking (MPPT) algorithms belong to the group of fuzzy logic (FL) search-based algorithms. The battery state of charge (SOC) is tracked online and controlled. When it reaches the minimum allowed level, the load is automatically disconnected; conversely, when it reaches the maximum allowed level, the battery charging is stopped via WT speed control. The load voltage root-mean-square (RMS) value and frequency are at all times controlled at grid-level values. The performance of the proposed system was experimentally validated, in steady state and during transients, achieving wide ranges of wind speed, load power, SOC, and alternating current/direct current (AC/DC) voltage levels. The system startup and low-wind operation were also analyzed. The control algorithms were executed in real time by means of the DS1103 and MicroLabBox controller boards (dSpace)

Calculation of Semiconductor Power Losses of a Three-Phase Quasi-Z-Source Inverter

This paper presents two novel algorithms for the calculation of semiconductor losses of a three-phase quasi-Z-source inverter (qZSI). The conduction and switching losses are calculated based on the output current-voltage characteristics and switching characteristics, respectively, which are provided by the semiconductor device manufacturer. The considered inverter has been operated in a stand-alone operation mode, whereby the sinusoidal pulse width modulation (SPWM) with injected 3rd harmonic has been implemented. The proposed algorithms calculate the losses of the insulated gate bipolar transistors (IGBTs) and the free-wheeling diodes in the inverter bridge, as well as the losses of the impedance network diode. The first considered algorithm requires the mean value of the inverter input voltage, the mean value of the impedance network inductor current, the peak value of the phase current, the modulation index, the duty cycle, and the phase angle between the fundamental output phase current and voltage. Its implementation is feasible only for the Z-source-related topologies with the SPWM. The second considered algorithm requires the instantaneous values of the inverter input voltage, the impedance network diode current, the impedance network inductor current, the phase current, and the duty cycle. However, it does not impose any limitations regarding the inverter topology or switching modulation strategy. The semiconductor losses calculated by the proposed algorithms were compared with the experimentally determined losses. Based on the comparison, the correction factor for the IGBT switching energies was determined so the errors of both the algorithms were reduced to less than 12%

Photovoltaic System with a Battery-Assisted Quasi-Z-Source Inverter: Improved Control System Design Based on a Novel Small-Signal Model

This paper deals with a photovoltaic (PV) system containing a quasi-Z-source inverter (qZSI) and batteries connected in parallel with the qZSI’s lower-voltage capacitor. The control system design is based on knowledge of three transfer functions which are obtained from the novel small-signal model of the considered system. The transfer function from the d-axis grid current to the battery current has been identified for the first time in this study for the considered system configuration and has been utilized for the design of the battery current control loop for the grid-tied operation. The transfer function from the duty cycle to the PV source voltage has been utilized for the design of the PV source voltage control loop. The PV source voltage is controlled so as to ensure the desired power production of the PV source. For the maximum power point tracking, a perturb-and-observe algorithm is utilized that does not require the measurement of the PV source current, but it instead utilizes the battery current during the stand-alone operation and the d-axis reference current during the grid-tied operation. The corresponding tracking period was determined by using the transfer function from the duty cycle to the battery current and in accordance with the longest settling time noted in the corresponding step response. The proposed control algorithm also has integrated protection against battery overcharging during the stand-alone operation. The considered system has been experimentally tested over wide ranges of irradiance and PV panel temperature