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1. One-Cycle Control of switching circuits
One-Cycle Control is a nonlinear large-signal pulse-width-modulation method. The duty-ratio of a switch is
controlled such that in each cycle the average value of a switched variable of the switching circuit is exactly equal
to or proportional to the control reference in steady state and in the transient. One-Cycle Control effectively
rejects power source perturbations, precisely forces the average value of the switched variable follows the
dynamic reference, and automatically corrects switching errors, all this in one switching cycle. Switching circuits
with One-Cycle Control process the signal and the power in one stage, thus the efficiency is higher and complexity
of the circuit is lower. Switching circuits with One Cycle Control exhibit high linearity, large dynamic range,
excellent disturbance rejection, and robust performance. This control method is very general and applicable to all
types of pulse-width-modulated, resonant-based, or soft-switched switching converters for either voltage or
current control in continuous or discontinuous conduction mode. Furthermore, One-Cycle Control can be used to
control any physical variable or abstract signal that is in the form of a switched variable or can be converted to
the form of a switched variable.
Related Publications:
K. Smedley and S. Cuk, "One-Cycle Control of Switching Converters," 22nd Annual IEEE Power Electronics
Specialists Conference (Cat. No.91CH3008-0), Cambridge, MA, 1991. pp. 888-96. See also US patent 5,278,490
and IEEE Transactions on Power Electronics, Nov. 1995, Vol. 10, No. 6, P625-633.
K. Smedley and Slobodan Cuk "Dynamics of One-Cycle Controlled Cuk Converters", IEEE Transactions on Power
Electronics, Nov. 1995, Vol. 10, No. 6, P634-639.
K. Smedley: ìOne-Cycle Controlled Switching Circuitî US Patent # 5,278,490, Jan, 1994.
2. High fidelity Class-D power amplifiers.
The basic One-Cycle Control method is extended to control bipolar switching converters. The immediate
application is found in the switching power amplification. Switching circuits for audio power amplifiers still remain
one of the most challenging research topic in the field of Power Electronics, due to the low distortion and high
bandwidth requirements. One-Cycle Control fit into this application naturally. One-Cycle Control precisely follows
the control reference in one switching cycle, this guarantees that a wide bandwidth can be achieved; One-Cycle
Control effectively rejects the power source ripple and processes power and signal in one stage, therefore, no
precision dc power source is necessary, as a matter of fact, a rectified but unregulated power source with small
capacitor can be used as its dc power source. One-Cycle Control automatically correct the power switch transient
error and conduction error, as a result, no switching component matching is necessary, the output has no cross
over distortion, high linearity is achievable. Currently, we have implemented a new One-Cycle Response class-D
power amplifier featuring continuous integration without reset, nearly constant switching frequency, and double
edge modulation. It obtains one cycle response by forcing the error between the switched-variable and the control
reference to zero each cycle, while the on-pulse of the controller is adjusted each cycle to ensure near constant
switching frequency. An experimental 0-20kHz bandwidth, 95 Watt 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 63dB at 120Hz. The total harmonic distortion plus noise (THD+N)
is less than 0.07% measured with a power supply ripple of 15%. With this technology, the weight of your audio
amplifier can be reduced about one order of magnitude, yet with top quality sound. This technology is current
being commercialized by Power Physics, Inc.
Related Publications:
Z. Lai and K. Smedley "A New Extension of One-Cycle Control and its Application to dc-ac converters," IEEE
Transactions on Power Electronics, Jan. 1996, Vol. 11, No.1, P99-104.
M. Smith and K. Smedley, "A New PWM Controller with One-Cycle Response", IEEE Transactions on Power
Electronics. Jan. 1999.
M. Smith and K. Smedley, ìPWM Controller with One-Cycle Response,î US Patent 6,084,450, July 4, 2000.
3. Digital-PWM Class-D Amplifiers
The noise and ripple shaping technique will lead to a total digital switching power amplification with high fidelity.
These configurations eliminate the need for a dc power regulator and reduces the size and volume of the lowpass
filter, thus further reduces the overall size and weight without sacrificing the signal to noise ratio. The noise and
ripple shaping (NRS) digital-PWM power amplification technique combines both power and signal processing
within the digital domain to eliminate the need for highly regulated power supplies and a high speed PWM clock.
The technique works by using a sampled and extrapolated power source signal to shape an interpolated input
signal. The ripple shaped input signal is then fed to the noise shaper to produce a reduced bit digital signal
representing the original signal. This lower bit digital signal is loaded into a digital-PWM circuit that generates the
trigger signals for the output full bridge. The output power signal from the full bridge is not affected by the
requantization error or the power-source ripple. A proof concept circuit of full-bridge power amplifier controlled
by the Analog Devices ADSP-21020 DSP was built achieving close to 5kHz bandwidth and 60dB ripple rejection at
60Hz. The PWM output circuit uses 8 bits and a 33Mhz clock frequency while theoretically maintaining 16 bits of
resolution. We are currently optimizing the ADSP-21020 algorithm by replacing c code with assembly, this system
should be able to operate at close to 20kHz bandwidth.
Related Publications:
K. Smedley: ìDigital Pulse Width Modulation Audio Amplifier with Noise and Ripple Shapingî US Patent 5,559,467,
Sep. 1996.
4. General Pulse-Width Modulation and Single-Phase Power Factor Correction.
Two resettable integrators suffice to implement most of the PWM functions for most converters, such as regular
PWM, current-mode control with linear or nonlinear ramp, feed-forward control, power factor correction for
continuous current mode and discontinuous current mode, and perhaps other control functions that do not
currently exist. As application examples, a family of controllers for unity-power-factor rectifiers at continuous or
discontinuous conduction mode are derived Some controllers in this family are first time discovered and are very
simple yet with high performance. For example, we can realize CCM mode power factor correction for boost,
flyback, cuk converters by ONE-INTEGRATOR WITH RESET. This circuit can be integrated into a multi-purpose
control chip that may immediately replace many single purpose control chips on the market.
Related Publications:
Z. Lai, K. Smedley, and Y. Ma, "Time Quality One Cycle Control for Power Factor Correction," IEEE Transactions on
Power Electronics, March 1997, vol.12, (no.2):369-75.
Z. Lai and K. Smedley, "A General PWM Modulator and Its Applications ," IEEE Transactions on Circuits and
Systems I: Fundamental Theory and Applications, April 1998, vol.45, (no.4):386-96.
Z. Lai and K. Smedley, "A Family of Power-Factor-Correction Controllers Based on the General PWM Modulator,"
IEEE Transactions on Power Electronics, May 1998, vol.13, (no.3):501-10.
5. Active Soft Switching Methods for Switching Converters and Inverters
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 newly developed methods. 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 are provided. We found that not all the existing
methods improved efficiency over most of the load range, but only those methods that softly switch the auxiliary
switch, minimize redirection current, and recover the auxiliary circuit energy. We developed a simple, efficient
soft-switching method for switching power converters, inverters, and amplifiers. Soft switching of a DC/AC H-
Bridge 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 converters, motor drivers, UPS, communication, and space applications where high
efficiency, low EMI, and small size are crucial.
Related Publications:
M. Smith and K. Smedley, "A Comparison of Voltage Mode Soft Switching Methods for PWM Converters" (PDF
format), IEEE Transactions on Power Electronics, March 1997, vol.12, (no.2):376-86.
M. Smith and K. Smedley, "Intelligent Magnetic Amplifier Controlled Softswitching Method for Inverters and
Amplifiers," IEEE Transactions on Power Electronics, Jan. 1998, vol.13, (no.1):84-92.
C. Qiao and K. Smedley, "An Isolated Full Bridge Boost Converter with Active Soft Switching" IEEE Power
Electronics Specialists Conference, June 2001.
6. Passive Lossless Soft Switching Methods for Switching Converters and Inverters
We have had significant achievement in passive lossless softswitching. Very recently, A unified synthesis method
was introduced to design lossless snubbers for dc-dc converters, see paper "Properties and Synthesis of Passive,
Lossless Soft-Switching PWM Converters," and for dc-ac inverters, see paper "Lossless Passive Soft Switching
Methods for Inverters and Amplifiers." Rules for zero current turn-on, zero voltage turn-off, and lossless energy
recovery were derived in these papers. With these rules, all possible locations in the circuit can be found to insert
snubber components. Furthermore, some snubber cells were devised that conveniently slide into these locations to
realize lossless snubber functions for any switching converter. The theory is general and the applications are
limitless. Use our general method, suitable lossless soft switching circuit can be derived for any applications. For
example, one of our derived lossless snubber circuit for zero current turn-on of all switches in an H-bridge
inverter uses six passive components, while previously reported circuits use 12 passive components or more for
the same function.
Related Publications:
M. Smith and K. Smedley, "Properties and Synthesis of Passive, Lossless Soft-Switching PWM Converters" (PDF
format), EPMC97, Israel, Also IEEE Tansactions on Power Electronics, Sep. 1999.
M. Smith and K. Smedley, "Lossless Passive Soft Switching Methods for Inverters and Amplifiers" (PDF format),
IEEE Power Electronics Specialists Conference, 1997. IEEE Transactions on Power Electronics, Jan 2000.
M. Smith and K. Smedley, "Engineering Design of Lossless Passive Soft Switching Converters, Part I. Minimum
Stress Cells," IEEE Applied Power Electronics Conference, 1998.
M. Smith and K. Smedley, "Engineering Design of Lossless Passive Soft Switching Converters, Part II.
Nonminimum Stress Cells," INTELEC, 1999.
I. Matsuura, M. Smith and K. Smedley, "A Comparison of Active and Passive Soft Switching Methods," IEEE Power
Electronics Specialist Conference 1998.
7. Flyback converter magnetic analysis and design for improved efficiency and cross-regulation.
An analytical model of cross regulation is derived that reveals the crucial factors that affect cross regulation in
flyback converters. Among them, the most influential factor is the clamp voltage. We found that the cross
regulation in the multiple windings of a flyback converter can be significantly improved by lowering the clamp
voltage to slightly above the reflected output voltage. We investigated various ways to lower the clamp voltage.
To lower the clamp voltage of a conventional RC leads to higher clamp loss. A new energy-regenerative clamp is
proposed that enables the clamp voltage to be much lower than that of the RC clamp and recovers leakage energy
from the transformer. In contrast to the conventional RC clamp, the clamp voltage of the energy-regenerative
clamp does not vary in response to load conditions. A significant efficiency improvement is achieved for the entire
universal input-voltage range. The best cross regulation is resulted in the low line input-voltage range. This
proposed clamp uses the same number of components as the RC clamp and its clamp winding shares the same
core with the transformer. Therefore, the proposed energy-regenerative clamp is a cost-effective approach to
improve both efficiency and cross regulation in multiple output flyback converters.
Related Publications:
C. Ji and K. Smedley, "Cross Regulation in Flyback Converters, Part I: Analytical Model" IEEE Power Electronics
Specialists Conference, June 1999.
C. Ji and K. Smedley, "Cross Regulation in Flyback Converters, Part II: Solusions" IEEE Industrial Electronics
Conference (IECON), Nov. 1999.
8. Magnetic Analysis and Design Engine (MADE)
A piece of software "Magnetic Analysis and Design Engine" was developed that provides a unique tool for
designing flyback transformers and calculating the core loss, copper loss, and leakage inductance under both DCM
and CCM operating conditions.
9. Unified controller for three-phase power factor correction
We have developed a unified and simple controller to realize unity power factor for most existing three-phase
rectifier topologies. Most of currently available three-phase boost rectifier topologies can be de-coupled to dual-
boost sub-topologies either in parallel or series configuration. Based on these sub-topologies, a general constant
frequency power-factor correction (PFC) controller based on One-Cycle Control is proposed for three phase boost
derived rectifiers. This controller is comprised of an integrator with reset, two flip-flops, and some logic circuits.
No multiplies is required. It is simple and general, therefore it represents the state-of-the-art. This controller can
be applied to most currently available rectifiers with a few changes in the logic connections. With this controller,
not only unity-power-factor and low input current distortion are achieved, but the switching losses are reduced
because only two high frequency switches are controller during each 60ƒ of the line cycle. The proposed
controller is ready to be integrated into a three-phase PFC control chip.
Related Publications:
K. Smedley and C. Qiao, ìUnified Constant-frequency Integration Control of Three-Phase Rectifiers, Inverters, and
Active Power Filters for Unity Power Factorî US Patent application filed 9/98 and approved 2001.
C. Qiao and K. Smedley, "A general Three-Phase PFC Controller for Rectifiers with a Parallel Connected Dual
Boost Topology," IEEE Industry Applications Conference Annual Meeting, October 2-7, 1999.
C. Qiao and K. Smedley, "A general Three-Phase PFC Controller for Rectifiers with a Sedries Connected Dual
Boost Topology," IEEE Industry Applications Conference Annual Meeting, October 2-7, 1999.
C. Qiao and K. Smedley, "Unified Constant-frequency Integration Control of Three-phase Standard Bridge Boost
Rectifier" CIEP 2000, Mexico.
C. Qiao and K. Smedley, "Three-phase Unity-Power-Factor VIENNA Rectifier with Unified Constant-frequency
Integration Control" CIEP 2000, Mexico.
10. Unified Controller for Single-Phase and Three-Phase Active Power Filters.
An active power filter (APF) is a device that is connected in parallel to and cancels the reactive and harmonic
currents from a group of nonlinear loads so that the resulting total current drawn from the ac main is sinusoidal.
This paper presents a Unified Constant-frequency Integration (UCI) APF control method based on one-cycle
control. This method employs an integrator with reset as its core component to control the pulse width of an ac-dc
converter so that its current draw is precisely opposite to the reactive and harmonic current draw of the nonlinear
loads. In contrast to previously proposed methods, there is no need to generate a current reference for the control
of the converter current, thus no need for a multiplier and no need to sense the ac line voltage, the APF current, or
the nonlinear load current. Only one current sensor and one voltage sensor are used to sense the ac main current
and the dc capacitor voltage. The control method features carrier free, constant switching frequency operation,
minimum reactive and harmonic current generation, and simple analog circuitry. It provides a low cost and high
performance solution for power quality control. Detailed analysis and design were conducted using a two-level ac-
dc boost topology. A prototype was developed to demonstrate the performance of the proposed APF. This control
method is generalized to control a family of converters that are suitable for APF applications.
Related Publications:
K. Smedley and L. Zhou, "Unified Constant-frequency Integration Control of Single Phase Active Power Filter,"
US Patent 6,249,108, June 19, 2001.
K. Smedley and C. Qiao, ìUnified Constant-frequency Integration Control of Three-Phase Rectifiers, Inverters, and
Active Power Filters for Unity Power Factorî US Patent application filed 9/98 and approved 2001.
L. Zhou and K. Smedley, "Unified Constant-frequency Integration Control of Single Phase Active Power Filter,"
IEEE Applied Power Electronics Conference, 2000.
C. Qiao and K. Smedley, "Three-phase Active Power Filters with Unified Constant-frequency Integration
Control" International Power Electronics and Motion Control Conference, 2000, Beijing China.
C. Qiao, T. Jin, and K. Smedley, ìUnified Constant-frequency Integration Control of Three-phase Active-Power-
Filter with Vector Operationî IEEE Power Electronics Specialists Conference, June 2001.
C. Qiao and K. Smedley, ìA Comprehensive Analysis and Design of a Single Phase Active Power Filter with
Unified Constant-frequency Integration Controlî IEEE Power Electronics Specialists Conference, June 2001.
T. Jin, C. Qiao and K. Smedley, ìOperation of Unified Constant-frequency Integration Controlled Three-phase
Active Power Filter in Unbalanced System" IEEE Industry Electronics Conference, Nov. 2001.
S. Serena, C. Qiao and K. Smedley, ìA Single-Phase Active Power Filter with Integration Control" IEEE Industry
Electronics Conference, Nov. 2001.
11: Single-Switch, Single-Stage Power Factor Correction.
A topological review of the single stage power factor correctted (PFC) rectifiers is presented in this paper. Most of
reported single-stage PFC rectifiers cascade a boost-type converter with a forward or a flyback dc-dc converter
so that input current shaping, isolation, and fast output voltage regulation are performed in one single stage. The
cost and performance of a single-stage PFC converters depend greatly on how its input current shaper (ICS) and
the dc-dc converter are integrated together. For the cascade connected single-stage PFC rectifiers, the energy
storage capacitor is found in either series or parallel path of energy flow. The second group appears to represents
the main stream. Therefore, the focus of this paper is on these group. It is found that many of these topologies can
be implemented by combining a 2-terminal or 3-terminal boost ICS cell with dc-dc converter along with an energy
storage capacitor in between. A general rule is observed that translates a 3-terminal ICS cell to a 2-terminal ICS
cell using an additional winding from the transformer and vice versa. According to the translation rule, many of
reported single-stage PFC topologies can be viewed as electrically equivalent to one another. Several new PFC
converters were derived from some existing topologies using the translation rule.
Related Publications:
C. Qiao and K. Smedley, "A Topology Survey of Single-Stage Power Factor Corrector with Boost Type Input-
Current-Shaper Cell" IEEE Applied Power Electronics Conference, 2000.
C. Qiao and K. Smedley, ìA Single-Stage Power Factor Corrected Converter with Continuous Conduction Mode
Operation and Regenerative Clampingî IEEE INTELEC, Sep. 2000.
C. Qiao and K. Smedley, "A Universal Input Single-Phase Single-Stage Power Supply with Power Factor
Correction and Automatic Voltage Clamping" IEEE Power Electronics Specialists Conference, June 2001.
12: Single-Phase Passive Power Factor Correction.
A new passive Power Factor Corrector (PFC) based on Valley Fill (VF) is proposed for an off-line Flyback
converter. By adding an extra winding which is magnetically coupled to the Flyback transformer and electrically
coupled to the VF, higher Power Factor (PF) and lower Total Harmonic Distortion (THD) can be achieved. The
proposed circuit uses a high frequency inductor, low voltage capacitors that operate at a voltage slightly higher
then the half of the peak line voltage, and a low stress switch for DC/DC conversion. Since it is passive an active
switch for PFC functions is not necessary. The paper describes the proposed circuit in detail followed by
experimental results.
Related publications:
P. Parto and K. Smedley, "PASSIVE PFC FOR FLYBACK CONVERTORS." International Power Conversion and
Intelligent Motion Conference (PCIM 99), Chicago.
13. Unity Power Factor Grid-Connected Inverters for Alternative Energy Sources.
A unified approach is taking to realize grid-connected sinusoidal current inversion for a group of alternative
energy sources such as fuel cells, solar cells, micro turbines, fusion reactors, wind power, etc.
Related publications:
K. Smedley and C. Qiao, ìUnified Constant-frequency Integration Control of Three-Phase Rectifiers, Inverters, and
Active Power Filters for Unity Power Factorî US Patent application filed 9/98 and approved 2001.
C. Qiao and K. Smedley, "Unified Constant-frequency Control of Grid Connected Inverters" IEEE Industry
Application Society Annual Meeting, Oct. 2001.
14: Low Voltage High Current Voltage Regulators.
15: Resonant Converters.
16: Direct Fusion Energy Extractor
All our findings are supported by rigid experimental evidences.
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