Self-oscillating Resonant Converter Research Articles

Hybrid Control of Self-Oscillating Resonant Converters

We describe parallel and series resonant converters (PRC and SRC) via a unified set of input-dependent coordinates whose dynamics are intrinsically hybrid. We then propose hybrid feedback showing a self-oscillating behavior whose amplitude and frequency can be adjusted by a reference input ranging from zero to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> . For any reference value in that range, we give a Lyapunov function certifying the existence of a unique nontrivial hybrid limit cycle whose basin of attraction is global except for the origin. Our results are confirmed by experimental results on an SRC prototype.

Hybrid Control of Self-Oscillating Resonant Converters With Three-Level Input

We propose a hybrid feedback law inducing self-oscillating behavior in second-order resonant converters. With our controller, the converter switches at the resonant frequency of its tank, without the need of external oscillators. In addition, the output amplitude can be adjusted by a reference signal ranging from zero to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\scriptstyle {}^{\scriptstyle \pi }}\hspace {-0.224em}/\hspace {-0.112em}{\scriptstyle 2}$ </tex-math></inline-formula> . The amplitude modulation is then performed while maintaining an approximately constant switching frequency. Theoretical results show uniqueness and almost global asymptotic stability of a nontrivial hybrid limit cycle. Experimental results show that a circuit implementing the new controller successfully matches the desirable simulated behavior.

A Control Actuation Concept for Self-Oscillating Resonant Converters

This article presents a concept of controller actuation mechanism for self-oscillating resonant converters (SORCs). Simplicity, robustness, and cost-effectiveness are among the main features of this type of converter. Described as a self-oscillating system with an intrinsic positive-type feedback switching network, also known as the self-oscillating command circuit (SOCC), it performs its own gate drive with self-sustained frequency, designed around an equilibrium point. Designers often disregard this converter as an explicit solution for closed-loop applications, especially those that require extra layers of control, due to its inherent inability to operate under pulse frequency modulation without extra circuitry. Thus, in this article, a robust, efficient, and simple way of controlling the SORC through frequency modulation is proposed. The idea consists of varying the self-oscillating frequency through the equivalent magnetizing inductance of the SOCC, using a mechanism called variable current transformer. Thus, through the injection of a small controllable dc current, it is possible to modulate the frequency of resonant converters. This allows the self-oscillating system to follow a reference current signal, operating in closed-loop over a wide range of input voltage and load variation.

Results on hybrid control of self-oscillating resonant converters

Abstract A unified set of input-dependent coordinates is proposed for the description of parallel and series resonant converters. The description naturally leads to a hybrid feedback control strategy for self-oscillating behavior. We show through a hybrid representation that the ensuing dynamics admits a unique almost globally attractive hybrid limit cycle. A tuning parameter, the switching angle, is then numerically shown to lead to monotonic variation of the peak output current/voltage and of the self-induced switching frequency. Numerical simulations with high-accuracy software illustrate the desirable behavior of the self-oscillating scheme, and it robustness to unmodeled phenomena.

Analysis and Design of Self-Oscillating Resonant Converters with Loss-Free Resistor Characteristics

A general approach for the analysis and design of self-oscillating resonant converters is presented in this paper, for a particular class of circuits in which the change of input voltage polarity is caused by the zero-crossings of the input inductor current. The key features of the method are an analytical description in the time-domain of a spiral that eventually converges into an ellipse, and a frequency–domain analysis that explains the behavior of the ellipse as a limit cycle. On a theoretical basis, this class of circuits behaves as loss-free resistors (LFR) because in steady-state the input inductor current is in phase with the first harmonic of the input voltage. The proposed analytical procedure predicts accurately the amplitude and frequency of the limit cycle and justifies the stability of its generation. This accuracy is reflected in the close agreement between the theoretical expressions and the corresponding simulated and measured waveforms. Third and fourth order resonant converters are designed following simple guidelines derived from the theoretical analysis.

Design Approach for a Self-Oscillating Resonant Converter Operating in High Frequency for LED Applications

In this paper, a design approach for the self-oscillating command circuit (SOCC) as a driver for a resonant converter operating in high frequency for LED applications is proposed. This proposal, conceived from the proposed methodologies, contemplates the influence of the Cascode gallium nitride (GaN) FET input and output capacitances, making it relevant to higher switching frequencies, where such parasitic elements lead to increased errors. In conjunction with higher efficiency levels, series resonant inverters like the zero-voltage switching half-bridge are known to have potentially reduced size on its reactive components when operated at higher frequencies, resulting in smaller and lighter systems. Combined to the ‘simplicity and low cost of the SOCC, these advantages translate into a simple and cost-effective high-power-density application. The self-oscillating resonant converter (SORC) accurate design is based upon the describing function method as a linearization tool and the extended Nyquist stability criterion that evaluates whether or not the system can oscillate around given predicted frequency. Practical input capacitance measurement data for different silicon MOSFETs and a Cascode GaN FET are compared and considered in order to obtain a high-frequency design approach for an SORC. Simulation and experimental results for an SORC with Cascode GaN FET operating at 1 MHz for a 10-W LED are shown based on the design procedure described.

Dynamic Modeling and Control of Self-Oscillating Parallel Resonant Converters Based on a Variable Structure Systems Approach

This paper describes a novel modeling approach for self-oscillating resonant power converters operating under a control method based on the variable structure of the system (VSS). Using a fundamental harmonic approximation, the link between control and switching frequency in steady state is found to be accurately described by an affine function that depends on the load. Besides, this link has been extended in order to characterize the control-to-switching frequency dynamics, resulting in a novel small-signal continuous-time model. The resulting control-to-switching frequency transfer function can be appended to the well-known models for frequency modulation, in order to obtain a complete control-to-output system. The new model exposes that the dynamics of the converter under the VSS-based control approach presents advantages with respect to the conventional methods as frequency modulation: 1) reduced dc gain variation for uncertain loads and 2) improved phase margin at high frequencies. The dynamic modeling is complemented with the design of a controller for regulating the output voltage of a parallel resonant converter, whose performance and robustness are compared with the standard frequency modulation. Numerical simulations and experimental results confirm and verify the analytical derivations.

A practical soft switching power supply with self-oscillating circuit and resonant converter using a cross transformer

Recently, soft switching power supplies using resonant converters have been attracting notice owing to their high efficiency and low noise characteristics. Conventional resonant-type converters have a complex control circuit, and we solved this problem by using a cross transformer. Various types of switching power supplies which have a simple structure can be realized by a combination of a self-oscillating driving circuit and a resonant converter. This paper presents our development process and describes the latest technology of soft switching power supplies making use of super-small-sized cross transformers. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(1): 60–69, 1997