High Power and High Frequency Class-DE Inverters

This thesis investigates the various aspects of the theory. design and construction of a Class-DE type inverter and how these affect the power and frequency limits over which a Class-DE inverter can feasibly be used to produce AC (or RF) power. To this extent. an analysis of Class-DE operation in a half-bridge inverter is performed. A similar approach to Hamill [61 is adopted but a different time reference was used. This allows the concept of a conduction angle to b1: introduced and hence enables a more intuitive understanding of the. equations thereafter. Equations to calculate circuit element values LCR ne1wor'k are developed. The amount above the resonant frequency of the LCR network that the switching frequency must be in order to obtain the correct phase lag of the load current is shown. The effect of a non-linear output capacitance is studied, and equations are modified lo take this effect into account. It was found that a Class-DE topology offers a theoretical power advantage over a Clalls-E topology. However, this power advantage decreases with increasing frequency and is dependent on the output capacitance of the active switching devices. Using currently available MOSFETs, a Class-OE topology has a theoretical power advantage over a Class-E topology up to approximately 10MHz. However, the prac1ical problems of implementing a Class-DE invener lO work into the HF band are formidable. These practical problems and the extent to which they ltml! !he operating frequency and power of a Class-DE type inverter are investigated Guidelines to solving these practical problems are discussed and some novel soluuons are developed that considerably extend the feasible operating frequency and power of a Class-DE inverter. These solutions enabled a brc,adband design of the control circuitry. communication-link and gate-drive to be developed. Using these des[gns, a prototype broadband half-bridge inverter was developed which was capable of switching from 50k.Hz through to 6MHz. When operated in the Class-DE mode, the inverter was found to be capable of delivering a power output of over J kW from SOk.l-lz to 5Mllz with an efficiency of over 91 %. The waveforms obtained from the inverter clearly show Class-OE operation. The results of this thesis prove that a Class-DE series resonant inverter can produce. RF power up to a frequency of 5MHz with a higher combination of power and efficiency than any other present topology. The pracucal problems of even higher operaun& frequencies are discussed and some possible solutions suggested. The mismatched load tolerance of a Class-DE type inverter is briefly investigated. A Class-DE Lype inverter could be used for any applications requiring RF power in the HF band, such as AM or SW rransmirters, induction neating and plasma generators. The information presented in this thesis will be useful 10 designers wishing lo implement such an impeller. In add1non a Class-DE inverter could form the first stage of a highly efficient and high frequency DC-DC converter and the 1nformat1on presented here is directly applicable to such an applicatio

A NEW REDUCED SWITCH ZVS-PWM THREE-PHASE INVERTER

Dc-ac inverters convert a dc input voltage into a desired ac output voltage and are widely used in many industrial applications, including utility grid interfaces, motor drives, and wind energy systems. Because of their widespread use, there has been considerable interest to try to make them more efficient to conserve energy. One way of doing so is to reduce the losses that are generated by the switching of the inverter devices as they help convert the dc input voltage into an ac output. As a result, there has been considerable research into implementing inverters with so-called soft-switching - zero-voltage and zero-current switching techniques that make either the voltage across a switch or the current through it zero at the time of a switching transition (from on to off or off to on). Since the power dissipated in a switch is related to the amount of overlap of voltage and current during a switching transition, making either the switch voltage or switch current zero at this time can result in a significant reduction in switching losses. A new, reduced switch, zero-voltage switching (ZVS), three-phase dc-ac inverter is proposed in this thesis. The proposed inverter does not have the drawbacks that other previously proposed ZVS-PWM inverters have such as cost, increased conduction losses, the appearance of distortion in the output waveforms, and the lack of bidirectional operation capability. In the thesis, an extensive literature review of previously proposed soft-switched inverters is performed. The new inverter is then presented and its operation is explained in detail. The steady-state operation of the new inverter is analyzed and the results of the analysis are used to determine the converter\u27s steady-state characteristics. Based on these characteristics, a procedure for the design of the inverter is developed and then demonstrated with an example. Finally, the feasibility of the proposed converter and the validity of the analysis are confirmed with simulation results obtained from PSIM, a widely used, commercially available software simulation package for power electronic

Power Quality in Electrified Transportation Systems

"Power Quality in Electrified Transportation Systems" has covered interesting horizontal topics over diversified transportation technologies, ranging from railways to electric vehicles and ships. Although the attention is chiefly focused on typical railway issues such as harmonics, resonances and reactive power flow compensation, the integration of electric vehicles plays a significant role. The book is completed by some additional significant contributions, focusing on the interpretation of Power Quality phenomena propagation in railways using the fundamentals of electromagnetic theory and on electric ships in the light of the latest standardization efforts

Power factor-corrected transformerless three-phase PWM converter for UPS applications

This thesis describes the research of a new transformerless three phase PWM converter for uninterruptible power supplies (UPS) applications. The removal of the bulky three phase transformer in larger power UPS can provide a significant saving in weight and cost of the overall system. The converter consists of a new four-wire rectifier coupled with a four-wire inverter via a dc bus. The supply and load neutral may be connected together without any neutral current flowing into the utility regardless of the load on the inverter. This allows the load to be at the same potential as the utility. The rectifier, inverter and complete UPS and control system are described in detail and simulation results are used extensively to back up the theory. An experimental prototype of the four-wire rectifier provides further confirmation of the principles. A further proposal to digitize the system is given. This would reduce the size of the required control circuit and simplify the hardware requirements

Soft switching techniques for multilevel inverters

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica

Analog Single Sideband-Pulse Width Modulation Processor for Parametric Acoustic Arrays

Parametric acoustic arrays are ultrasonic-based loudspeakers that produce highly directive audio. The audio must first be preprocessed and modulated into an ultrasonic carrier before being emitted into the air, where it will self-demodulate in the far field. The resulting audio wave is proportional to the double time-derivative of the square of the modulation envelope. This thesis presents a fully analog processor which encodes the audio into two Pulse Width Modulated (PWM) signals in quadrature phase and sums them together to produce a Single Sideband (SSB) spectrum around the fundamental frequency of the PWM signals. The two signals are modulated between 8% and 24% duty cycle to maintain a quasi-linear relationship between the duty cycle and the output signal level. This also allows the signals to sum without overlapping each other, maintaining a two-level output. The system drives a network of narrowband transducers with a center frequency equal to the PWM fundamental. Because the transducers are voltage driven, they have a bandpass frequency response which behaves as a first-order integrator on the SSB signal, eliminating the need for two integrators in the processor. Results show that the “SSB-PWM” output wave has a consistent 20-30dB difference in magnitude between the upper sideband and lower sideband. In simulation, a single tone test shows higher total harmonic distortion for lower frequencies and higher modulation depth. A two-tone test creates a 2nd order intermodulation term that increases with the frequencies of the input signals