K.M. Smith

A comparison of voltage-mode soft-switching methods for PWM converters

A comparison study was conducted to characterize the loss mechanisms, component stresses, and overall efficiencies of a group of voltage-mode soft-switching pulse width modulation (PWM) methods, including two methods developed by the authors. All soft-switching methods in the selected group allow zero voltage turn-on and turn-off of the main switch and utilize a single auxiliary switch with some resonant components. Advantages and disadvantages are identified for each method. Experimental verification for each soft-switching method is provided. It was found that only those methods that softly switch the auxiliary switch, minimize redirection current, and recover the auxiliary circuit energy improve efficiency over most of the load range.

Properties and synthesis of passive lossless soft-switching PWM converters

This paper derives general topological and electrical properties common to all lossless passive soft-switching power converters with defined characteristics, and proposes a synthesis procedure for the creation of new power converters. The synthesis procedure uses the properties to determine all possible locations for the resonant inductors and capacitors added to achieve soft switching. A set of circuit cells is then used to recover the energy stored in these resonant elements. This paper also explains the operation of the circuit cells and the many new passive lossless soft-switching power converters. A family of soft-switching boost converters is given as an example of the synthesis procedure. Experimental waveforms are also shown for a new soft-switching Cuk converter.

Engineering design of lossless passive soft switching methods for PWM converters. II. With nonminimum voltage stress circuit cells

This paper proposes the analysis and design methodology of lossless, passive soft switching methods for PWM converters. The emphasis of the design and analysis is for PWM converters that use nonminimum voltage stress (non-MVS) circuit cells to provide soft switching. PWM converters with non-MVS circuit cells have several distinct advantages over converters that use minimum voltage stress (MVS) cells. With the same relative size of the inductor and capacitor added for soft switching, the non-MVS cells have a substantially larger duty ratio range where soft switching is guaranteed. In addition, the overcurrent stress of the main switch, under most conditions, will be lower and an optimum value of inductor and capacitor added for soft switching can be used. Therefore, with proper design, the non-MVS cells provide higher efficiency. These advantages are obtained with the price of higher switching voltage stress and one additional inductor. The loss model for a MOSFET and optimum capacitor and inductor values are utilized in the design procedure. Examples of the design procedure are given for PFC and DC-DC applications. Experimental results backup the claim of higher efficiency.

A new PWM controller with one-cycle response

This paper proposes a new nonlinear control technique that has one-cycle response, does not need a resetable integrator in the control path, and has nearly constant switching frequency. It obtains one-cycle response by forcing the error between the switched variable and the control reference to zero each cycle, while the on and off pulses of the controller are adjusted each cycle to ensure near constant switching frequency. The small switching frequency variation due to changes in the reference signal and supply voltage and delays in the circuit are quantified. Using double-edge modulation, the switching frequency variation is further reduced, thus, the associated signal distortion is minimized. An experimental 0-20 kHz bandwidth 95 W RMS power audio amplifier using the control method demonstrates the applicability of this control technique for high-fidelity audio applications. The amplifier has a power supply ripple rejection (PSRR) of 63 dB at 120 Hz. Additionally, the total harmonic distortion plus noise (THD+N) is less than 0.07% measured with a power supply ripple of 15%.

A comparison of voltage mode soft switching methods for PWM converters

A comparison study was conducted to characterize the loss mechanisms, component stresses, and overall efficiencies of a group of voltage mode soft switching PWM methods including two improvement circuits developed at UCI. All soft switching methods in the selected group allow zero voltage turn-on and turn-off of the main switch and utilize a single auxiliary switch with some resonant components. Advantages and disadvantages were identified for each method. Experimental verification for each soft switching method were provided.

Lossless, passive soft switching methods for inverters and amplifiers

This paper proposes lossless passive soft-switching methods for inverters developed from a synthesis procedure applicable to all pulsewidth modulation (PWM) converters. The lossless passive soft-switching converter properties and synthesis procedure are derived for inverters. Promising full-bridge and half-bridge soft-switching inverter examples are shown from the synthesis results. These include a new soft turn-on full bridge that contains only six components and a new soft turn-on and turn-off half bridge that contains 12 components. The voltage stress across the active switches can be easily maintained below 125% of V/sub bus/. Additionally, no transformers are used for energy recovery, eliminating their associated diode stress and leakage inductance problems. The theoretical and experimental waveforms and analysis are given.

A comparison of active and passive soft switching methods for PWM converters

This paper performs a comparison of the efficiencies of active and passive soft switching methods for PWM converters. The losses in both methods were theoretically itemized and experimentally measured. The values of the resonant elements were experimentally optimized so that both methods were compared on their best conditions. A boost converter was built and tested under the static and dynamic PFC operation condition as well as DC-DC operation condition. Studies show that the passive method has better efficiency in the high power operation region, while the active method outperforms the passive method in the low power region.

A new PWM controller with one cycle response

This paper proposes a new nonlinear control technique that has one cycle response, does not need a resettable integrator in the control path, and has nearly constant switching frequency. It obtains one cycle response by forcing the error between the switched-variable and the control reference to zero, each cycle. The on-pulse of the controller is adjusted each cycle by a simple circuit to ensure almost constant switching frequency. The small switching frequency variation due to variations in the reference signal and supply voltage and delays in the circuit are quantified. An additional improvement is achieved by using double edge modulation. An experimental 10 kHz bandwidth 100 Watt RMS power audio amplifier using the control method shows THD+N less than 0.62% and power supply ripple rejection (PSRR) of 56 dB demonstrating the applicability of this control technique for high fidelity audio applications.

Realization of a digital PWM power amplifier using noise and ripple shaping

A digital pulse width modulation technique featuring noise and ripple shaping (NRS) for audio power amplification is realized. The sampled and extrapolated power source amplitude signal is used to shape the interpolated input digital signal. This shaped signal is fed to a noise shaper to produce a reduced bit digital signal fully representing the original signal. The output power signal is not affected by the requantization error or the power source ripple. Therefore, DC power regulators can be eliminated without sacrificing the signal to noise ratio. A digital signal processor controlled full bridge power amplifier was built with close to 5 kHz bandwidth and 40 dB ripple rejection improvement at 60 Hz over conventional PWM power amplifiers.<<ETX>>

Intelligent magnetic-amplifier-controlled soft-switching method for amplifiers and inverters

This paper proposes a simple efficient soft-switching method for switching power converters, inverters and amplifiers. Soft switching of a DC/AC H-bridge power converter is realized by paralleling two auxiliary switches and a magnetic amplifier with the load. The auxiliary switches are turned on at a predetermined time before the commutation of the main switches. The magnetic amplifier then automatically determines the necessary amount of redirection current to ensure soft switching of all switches under any load conditions. This method requires no expensive sensors or complex control circuitry. It is ideal for class-D audio power amplifiers, where the load current is widely changing. Further applications include DC/DC power converters, motor drivers, uninterruptible power supplies (UPS), communication and space power applications, where high efficiency, low electromagnetic interference (EMI) and small size are crucial.