This paper proposes a novel synchronous rectifier (SR) driving scheme for resonant converters. It is very suitable for high-frequency, high-efficiency, and high-power-density dc-dc resonant converters with SRs. In this paper, an LLC resonant converter with the proposed synchronous rectification is designed and analyzed. With the proposed driving scheme, the SR body diode conduction is reduced to almost zero. The driving scheme eliminates the reverse-recovery problem of SRs. Both current and voltage stresses are greatly decreased, and the conduction loss and switching loss of SRs are also reduced considerably. The experimental results show that the proposed LLC resonant converter with SRs can achieve low stress, high efficiency, and high power density.

A Novel Driving Scheme for Synchronous Rectifiers in LLC Resonant Converters

The matrix converter stands as an alternative in power conversion. It has no energy storage devices, performing the energy conversion by directly connecting input with output phases through bidirectional switches based on power semiconductors, allowing high-frequency operation. For this reason, it is known as the all-silicon power converter, featuring reduced size and weight. Forced commutations of the high number of semiconductors cause switching losses that reduce the efficiency of the system and imply the use of large heat sinks. This paper presents a novel method to reduce switching losses based on predictive control. The idea is to predict switching losses for every valid switching state of the converter, if applied during the next sampling time, and then, select the optimum state based on an evaluation criterion. The proposed strategy was experimentally tested on an 18-kVA matrix converter driving an 11-kW induction machine, reducing energy losses and increasing efficiency up to 3% compared to the basic strategy. As a consequence, the converter misuses less energy and requires smaller heat sinks.

Predictive Approach to Increase Efficiency and Reduce Switching Losses on Matrix Converters

The piecewise linear model has traditionally been used to calculate switching losses in switching mode power supplies due to its simplicity and good performance. However, the use of the latest low voltage power MOSFET generations and the continuously increasing range of switching frequencies have made it necessary to review this model to account for the parasitic inductances that it does not include. This paper presents a complete analytical switching loss model for power MOSFETs in low voltage switching converters that includes the most relevant parasitic elements. It clarifies the switching process, providing information about how these parasitics, especially the inductances, determine switching losses and hence the final converter efficiency. The analysis presented in this paper yields two different types of possible switching situations: capacitance-limited switching and inductance-limited switching. This paper shows that, while the piecewise linear model may be applied in the former, the proposed model is more accurate for the latter. Carefully-obtained experimental results, described in detail, support the analytical results presented.

An Insight into the Switching Process of Power MOSFETs: An Improved Analytical Losses Model

In this paper, a review of switching loss mechanisms for synchronous buck voltage regulators (VRs) is presented. Following the review, a new simple and accurate analytical switching loss model is proposed for synchronous buck VRs. The model includes the impact of common source inductance and switch parasitic inductances on switching loss. The proposed model uses simple equations to calculate the rise and fall times and piecewise linear approximations of the high-side MOSFET voltage and current waveforms to allow quick and accurate calculation of switching loss in a synchronous buck VR. A simulation program with integrated circuit emphasis (Spice) simulations are used to demonstrate the accuracy of the voltage source driver model operating in a 1-MHz synchronous buck VR at 12-V input, 1.3-V output. Switching loss was estimated with the proposed model and compared to Spice measurements. Experimental results are presented to demonstrate the accuracy of the proposed model.

A Practical Switching Loss Model for Buck Voltage Regulators

In this article, based on the LLC resonant converter fundamental harmonic analysis model, the modulation strategies for LLC resonant converter can be categorized into the following three groups: 1) input voltage fundamental harmonic modulation; 2) resonant tank elements modulation; and 3) secondary equivalent impedance modulation. Operational principles and control diagrams for different modulation strategies are given. Comprehensive comparisons between these modulation strategies in terms of topology complexity, control complexity, and voltage gain range are presented with respect to the same system specifications. The advantages and disadvantages for each modulation strategy are summarized to provide guidance for engineers when analyzing and designing an LLC resonant converter. The hybrid modulation strategies are categorized into different groups based on the specific applications. Brief introductions of these hybrid modulation strategies are presented. Future trends regarding the modulation strategies of LLC resonant converters are presented.

Overview of Modulation Strategies for LLC Resonant Converter

This paper proposes a new resonant gate drive circuit for driving both the control metal oxide semiconductor field effect transistor (MOSFET) and synchronous MOSFET in a synchronous buck converter. The circuit can recover more than 70% of the conventional gate drive loss. More importantly, the driving circuit can also reduce the switching loss. It charges and discharges the gate of MOSFET at a constant current during switching interval. Other advantages of the proposed circuit include better noise immunity for dv/dt turn on, less sensitive to parasitic track inductance. The experimental prototype shows that the loss reduction is 10% of the output power for 12 V input, 1.5 V/15 A output with switching frequency of 1 MHz.

A New Resonant Gate Drive Circuit for Synchronous Buck Converter

In this paper, a new common inductor current sharing method is proposed for a multiphase LLC resonant converter for high-power applications. Automatic current sharing is achieved by using a common resonant inductor connecting the resonant inductors in each LLC phase in parallel. The current sharing performance of the proposed method is evaluated under first harmonic approximation (FHA) assumption. The proposed method can automatically share the primary resonant current and the load current for all phases without any additional circuit and control strategy. A 600-W two-phase LLC converter prototype based on the proposed method is built to verify the feasibility. Excellent current sharing performance (less than 0.5% current sharing error at full load) has been achieved.

A Passive Current Sharing Method With Common Inductor Multiphase LLC Resonant Converter

At high-frequency applications, the gate drive loss of the power metal oxide semiconductor field-effect transistor (MOSFET) becomes quite significant. A new dual-channel low side resonant gate drive circuit is proposed in this paper. The proposed drive circuit can provide two symmetrical drive signals for driving two MOSFETs. It charges and discharges the MOSFET gate capacitor with a constant current source. Both gate drive loss and, more importantly, switching loss can be reduced significantly. The proposed resonant gate drive circuit can be used to drive the synchronous MOSFETs in a current doubler or full-wave rectifier configuration. It can also be used to drive the primary MOSFETs in push-pull converters. Analysis, computer simulation, and experimental results show that significant power loss reduction is achieved by the proposed circuit.

A New Dual-Channel Resonant Gate Drive Circuit for Low Gate Drive Loss and Low Switching Loss

This paper first starts with reviewing several commonly practiced PWM schemes for the three-phase isolated buck matrix-type rectifier. Then, an optimal six-segment PWM scheme (“Type A”) is proposed. The analysis shows “Type A” PWM scheme has lower duty-cycle loss, maximum output inductor current ripple, and minimum switching loss comparing with other PWM schemes when the mosfet devices are employed. In addition, a low input current total harmonic distortion (THD) can be achieved with duty-cycle compensation. Finally, the steady-state analysis of duty-cycle loss, inductor current ripple, and THD are all compared and verified by the experimental results for “Type A” PWM and eight-segment PWM (“Type E”).

The Optimal PWM Modulation and Commutation Scheme for a Three-Phase Isolated Buck Matrix-Type Rectifier

At high frequency applications, the gate drive loss of the power MOSFET becomes quite significant. A new dual channel low side resonant gate drive circuit is proposed in this paper. The proposed drive circuit can provide two symmetrical drive signals for driving two MOSFETs. It can recover most of the driving energy and clamp the gate and source voltage of the driven MOSFETs to either drive voltage or ground via a low impedance path. The circuit can also alleviate the dv/dt issue. The proposed circuit consists of four switches and a single winding inductor. The proposed resonant gate drive circuit can be used to drive the synchronous MOSFETs in a current doubler or full-wave rectifier. It can also be used to drive the primary MOSFETs in push-pull converters.

Zhihua Yang

Papers

A New Resonant Gate Drive Circuit for Synchronous Buck Converter

A Passive Current Sharing Method With Common Inductor Multiphase LLC Resonant Converter

A New Dual-Channel Resonant Gate Drive Circuit for Low Gate Drive Loss and Low Switching Loss

The Optimal PWM Modulation and Commutation Scheme for a Three-Phase Isolated Buck Matrix-Type Rectifier

A New Dual Channel Resonant Gate Drive Circuit for