Phase-shifted Inverter Research Articles

A High-Power, Medium-Voltage, Series-Resonant Converter for DC Wind Turbines

A new modulation scheme is introduced for a single-phase series-resonant converter, which permits continuous regulation of power from nominal level to zero, in presence of variable input and output dc voltage levels. Rearranging the circuit to locate the resonant LC tank on the rectifier side of the high turns-ratio transformer combined with frequency control and phase-shifted inverter modulation keep transformer flux constant from nominal frequency down to dc, always in subresonant continuous or discontinuous conduction mode. This overcomes the principal deficit of series-resonant converters, and the resulting compact and efficient transformer, and soft-commutated inverter, present particular advantages in high-power, high-voltage applications, such as dc offshore wind turbines. With transformer excitation frequency in hundreds of Hz range, line-frequency diodes can be employed in the high-voltage rectifier valve. Circuit operation and conduction modes, governing equations, and sample waveforms are presented, together with experiments from a scaled demonstrator.

Development and Testing of a New Instrument for Researching on Cancer Treatment Technologies Based on Magnetic Hyperthermia

A power electronics circuit allows the generation of high-frequency magnetic field that can be used to increase the temperature of cancer cells previously invaded with the magnetic nanoparticles. The circuit designed for this purpose is a high-frequency phase-shift inverter implemented with SiC devices and natural zero voltage switching. The inductive load has been optimized to increase as much as possible the magnetic field at the center of it considering the physical restrictions. Into this inductor, an adiabatic probe filled with nanoparticles is placed being the main objective to increase its temperature. The control of the inverter has been designed in such a way that it is easy to try waveforms different from the classical sine waves to see its effect on the temperature of the sample. Although the research is in one of the early stages, the first conclusions about the optimal frequency and field have been obtained showing that this technique could be a real option in the future.

Application of Piezoelectric-Transformer-Based Resonant Circuits for AC LED Lighting-Driven Systems With Frequency-Tracking Techniques

This paper proposes an application of piezoelectric transformer (PT) based inverters for alternating current (ac) light-emitting diode (LED) lighting-driven systems with a new resonant topology and frequency-tracking technique. This proposed architecture comprises a full-bridge phase-shift inverter with a PT-based C-L-C series resonant circuit, piezoelectric ceramic transformers, and a microwinding resonant transformer to extend the range of operation frequency, hence achieving a two-terminal alternating voltage to drive ac LED arrays while stabilizing the resonant characteristics. In this system design, a frequency-tracking mechanism is also integrated into the field-programmable gate array controller to improve operation efficiency. Since only the secondary current of the resonant transformer is required for the controller, the circuit implementation is simple and additional sensor devices can be largely saved. Moreover, by considering that the frequency-gain characteristics of PTs may be affected due to temperature changes; the controller is designed to adjust the operation frequency swiftly in order to restrict the temperature effect. This proposed method has been verified on modular ac LED lighting systems. Test results confirm the feasibility of the method for lighting system applications.

Enhancing Luminance of CCFL-Based Lighting Systems Using Low-Frequency Driving Techniques

This paper proposes the luminance enhancement with low-frequency driving techniques for cold cathode fluorescent lamp (FL) (CCFL)-based lighting systems. The driver architecture features a full-bridge phase-shift inverter with a resonant tank and a three-winding step-up transformer to reduce leakage current, remove parasitic capacitance, enhance optical efficiency, balance and increase lamp uniformity, and achieve two-terminal high-voltage low-frequency driving of CCFLs. The low-frequency control of the driving technique is implemented in a field-programmable gate array controller to achieve luminance enhancement. The control strategy starts igniting the lamp with a high frequency and then reduces to low frequency in order to facilitate the linear increment of lamp brightness. Through the employment of this proposed approach, since the primary current of the transformers is only required, the circuit implementation can be completed with ease. Experimental results show that the proposed technique and control strategy help enhance luminance efficiency and reduce leakage current, demonstrating the practicality for the application considered.

Improving the Reliability of Series Resonant Inverters for Induction Heating Applications

This paper analyzes a high-power (100-kW) high-frequency (50-kHz) voltage-fed inverter with a series resonant load circuit for industrial induction heating applications which is characterized by a full-bridge inverter composed of isolated-gate bipolar transistors and a new power control based on phase-shift (PS) control. This power control circuit incorporates a load-adaptive variable-frequency controller and automated blanking time management in order to allow the inverter to work in zero-voltage switching for all output power levels and load conditions. An important improvement of the inverter reliability is achieved by choosing an appropriate and novel switching sequence for the PS inverter. The results are verified experimentally using a prototype for induction hardening applications. A comparative study between the proposed and standard PS power control will be made.

A Method of Single Phase High Frequency Inverter Based on Tracking Control to Load Resonant Frequency

In this paper, we propose a new control method of the inverter frequency and the inverter output power with load resonant frequency adjusting phase shift inverter. The proposed control method is applicable to stet the phase-shift inverter with only one output current sensor. When the proposed method is employed, the fundamental waveform signal of inverter output voltage is obtained because the output voltage of a phase-shift inverter is a pulse waveform. Unity power factor and a high efficiency are achieved by adopting the proposed method involving the tracking control of load resonant frequency. In the proposed method, the fundamental waveform signal of inverter output voltage coincides with the detected inverter output current waveform. Moreover, as the inverter output power is regulated by controlling the phase angle of inverter leg in this proposed method, soft-switching control can be realized. In study, the validity of the proposed method is confirmed on the basis of experimental results.

Analysis of Circuit Operation under ZVS and NON-ZVS Conditions in Phase-Shift Inverter for Induction Heating

This paper presents a detailed analysis of circuit operation under ZVS and NON-ZVS conditions in a full-bridge high-frequency phase-shift control series resonant MOSFET inverter with the load of induction heating. Various modes of circuit operation both under ZVS and NON-ZVS conditions are first analyzed in details. The voltage and current equations of these circuits are then obtained and used for calculation of the waveforms by MATLAB program. The calculated results can lead to the consideration of various circuit parameters that determine ZVS or NON-ZVS operating conditions. The theoretical results are also verified by experimental ones, using a prototype test set rated at 3kW.