Impedance Control Resonant Converter

Technology

This invention proposes a new resonant power converter architecture that operates at a fixed frequency, yet achieves simultaneous zero voltage switching (ZVS) and near zero current switching (ZCS) of the transistors across a wide operating range. An impedance control resonant power converter operated at a fixed switching frequency includes an impedance control network (ICN) coupled between two or more inverters operated at a fixed duty ratio with a phase shift between them and one or more rectifiers. The proposed approach uses inverter stacking techniques to reduce the voltages of individual devices. The inverters are coupled to the converter input and the rectifier(s) is coupled to the converter output. The phase shift is used to control output power or compensate for variations in input or output voltage. Implementation of fixed duty ratio of individual switches allows the increase of switching frequency (hence reducing size and mass) while achieving very high efficiency, and/or to scale designs at conventional frequencies for extreme high-efficiency operation. This technique also enables effect resonant gating. The combination of ZVS/near-ZCS with resonant gating changes the loss tradeoffs encountered in conventional soft switching designs, and enables design scaling into new areas providing better combinations of size and loss.  

Problem Addressed

To achieve high efficiencies at high power densities, power converters must operate at a  high switching frequency, using soft-switching techniques such as zero voltage switching (ZVS) and zero current switching (ZCS) (where the switch voltage and current are zero at the switching transition). However, soft-switching only provides high efficiency operations under specific operating conditions, and performance tends to degrade greatly when considering requirements of operation across varying input voltage, output voltage, and power levels. This challenge in maintaining high efficiency is tied to both the circuit design and the control methodology. One common way of controlling resonant soft-switched inverters (e.g., series, parallel, series parallel converters, etc.) is frequency control, in which the output voltage is regulated in the face of load and voltage variations by modulating the converter switching frequency. Because of the inductive loading requirements to achieve ZVS switching, power is reduced in such converters by increasing the switching frequency, thereby exacerbating switching loss. Another method of control that can be applied to bridge converters at fixed frequency is phase-shift control. In this method, multiple inverter legs are phase-shifted from each other to counteract variations in input voltage and maintain output power. Unfortunately, as the inverters are phase shifted from each other, it is possible for asymmetric current waveforms to arise. This can increase conduction loss as well as a loss of ZVS. A third technique for enabling soft-switching is through the use of an auxiliary circuit that can divert current or voltage from the main power switches in order to shape the waveforms necessary for ZCS or ZVS. These circuits inherently add component and control complexity, and may not always lead to an increase in efficiency across the full operating range. There is an evident need for converter designs and associated controls that can provide reduced loss when operating over wide voltage and power ranges. This invention especially focuses on operation over wide input voltage and power ranges.  

Advantages

• Enhances achievable performance for wide input voltage and power range operation
• ICN combines power from the inverters such that as the phase angle among inverters is adjusted, low-loss switching of the inverter circuits is maintained
• ICR converter can also be designed as an inverter (dc/ac converter) for synthesizing an ac output component at frequencies far below the switching frequency