With the rapid development of modern energy applications such as renewable energy, PV systems, electric vehicles, and smart grids, DC-DC converters have become the key component to meet strict industrial demands. More advanced converters are effective in minimizing switching losses and providing an efficient energy conversion; nonetheless, the main challenge is to provide a single converter that has all the required features to deliver efficient energy for different types of modern energy systems and energy storage system integrations. This paper reviews multilevel, bidirectional, and resonant converters with respect to their constructions, classifications, merits, demerits, combined topologies, applications, and challenges; practical recommendations were also made to deliver clear ideas of the recent challenges and limited capabilities of these three converters to guide society on improving and providing a new, efficient, and economic converter that meets the strict demands of modern energy system integrations. The needs of other industrial applications, as well as the number of used elements for size and weight reduction, were also considered to achieve a power circuit that can effectively address the identified limitations. In brief, integrated bidirectional resonant DC-DC converters and multilevel inverters are expected to be well suited and highly demanded in various applications in the near future. Due to their highlighted merits, more studies are necessary for achieving a perfect level of reducing losses and components.

A Review on State-of-the-Art Power Converters: Bidirectional, Resonant, Multilevel Converters and Their Derivatives

A new nonisolated bidirectional dc–dc converter with low voltage and current stresses across the semiconductor devices is presented in this article. The proposed converter is a combination of a dual-stacked bidirectional boost converter. The converter presents different operations modes, such as: synchronous and asynchronous. These modes can reduce the current ripple of the voltage source. Besides that, in this article, the modeling and control of the proposed converter are done. To validate the theoretical evaluations of the proposed converter, a 1-kW, 144-V/400-V prototype was built to verify its performance where the peak efficiency is 96.33% and 96.87% for step-up and step-down modes, respectively.

Dual-Stacked Bidirectional Boost/Buck DC–DC Converter

Boost and full-bridge integrated converter for wide input-voltage range application

This article proposes a highly efficient current-fed half-bridge resonant converter over a wide range of the output voltages. By adding a bidirectional switch across center nodes of the voltage doubler and applying corresponding switching modulation, the converter accomplishes almost zero-voltage switching at the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> instant under the wide output voltage variations. Moreover, the circuit experiences very little instantaneous reactive current even when the output voltage varies widely. Primary-side duty cycle fixed at 0.5 balances the voltages across the capacitors at the primary side and at the secondary side each irrespective of the output voltage variation; it also limits the voltage stress at the active power components. Therefore, the proposed converter delivers high efficiency and compact component size. We fabricated a 400-W experimental prototype to validate the superior properties of the proposed converter. 

Highly Efficient Current-Fed Half-Bridge Resonant Converter for Pulse Power Applications

A new isolated zero-voltage switching (ZVS)/zero-current switching (ZCS) push–pull (PP) DC/DC converter is presented. One auxiliary switch S3 and a clamping capacitor Cc are introduced at the primary of the conventional push–pull converter and a voltage doubler-rectifier is adopted on the secondary side. This proposed converter has the features: (1) Switching losses are reduced significantly owing to zero-voltage switching of primary switches and zero-current switching of secondary diodes over a wide load range variation. (2) The voltage spike across all of the power devices can be clamped that enable the use of low-voltage, low-performance, and lower-cost devices. (3) The energy stored in the transformer leakage inductance is used for the soft-switching action and no additional resonant inductor is required. (4) A voltage doubler-rectifier is employed to remove the problem of the diode reverse-recovery effect and reduce the duty cycle loss that provides a much higher voltage conversion ratio. These merits make this simple converter provide an attractive solution for a distributed power system, uninterruptible power system, or battery charge/discharge system. The detailed operation, analysis, design, comparative study, and experimental results for the proposed converter are presented and a 600 W prototype was developed to verify the discussed theoretical analysis. 

Analysis and design of a wide range ZVS/ZCS push–pull DC/DC converter with voltage clamped

This article presents a bidirectional soft-switching push–pull resonant converter that is highly efficient over a wide range of battery voltages. It is derived by integrating a current-fed push–pull circuit and an active voltage doubler circuit with a bidirectional switch. The converter operates as a pulsewidth modulation (PWM) current-fed push–pull resonant-boost converter in the forward direction, but as a PWM half-bridge resonant converter in the backward direction. The most attractive feature of the proposed converter is that, by employing the bidirectional switch and corresponding switching modulation, it can achieve almost ZVS at turn- off instants under wide variations of battery voltages. Therefore, the proposed converter achieves high efficiency even during high-frequency operation. Moreover, no instantaneous reactive current flows through the circuit under wide variations of battery voltages and loads. Furthermore, the proposed bidirectional resonant converter has a high conversion ratio in both power flow directions without using a transformer that has high turns-ratio. The operating principles and characteristics of the proposed bidirectional resonant converter are presented in detail. Experimental results using a 1-kW prototype verified the feasibility and efficiency of the proposed converter.

Bidirectional Soft Switching Push–Pull Resonant Converter Over Wide Range of Battery Voltages

This article proposes a high step-up quasi-resonant converter that minimizes switching loss over a wide range of input voltages. By employing a bidirectional switch and corresponding switching modulation, the proposed converter achieves the main switch with almost zero voltage, and therefore incurs very little switching loss at all active switches. Moreover, no instantaneous reactive current flows through the circuit under wide variations of input voltages and loads. The duty cycle of primary-side switches is fixed to 0.5; then, the input and clamp capacitor voltages become identical, and thereby the following resonant capacitor voltages remain in balance. As a consequence, the proposed converter becomes compact and achieves high boost-ratio and high efficiency over a wide range of input voltages. The operating principle of the converter is presented along with its design procedure. 400-W/380-V prototype of the proposed converter has been implemented and tested at 40–60 V to verify its effectiveness.

High Step-Up Quasi-Resonant Converter Featuring Minimized Switching Loss Over Wide Input Voltage Range

This article proposes a highly efficient quasi-single-stage ac–dc converter that incorporates a bidirectional switch at the secondary side of the circuit. Its attractiveness is that the proposed ac–dc converter achieves almost ZVS turn-off at high instantaneous power and low-voltage turn-off at low instantaneous power. Moreover, the secondary-side switching reduces the loss at the main switch, and thereby more than offsets the losses that occur at the main switch and the clamp switch in a conventional ac–dc converter. An additional benefit of this converter is that the voltages across the primary-side capacitors and secondary-side capacitors are well balanced because the duty cycle at the primary-side switch is fixed at 0.5. Experimental results show that the proposed ac–dc converter is effective and more efficient than a conventional solution.

Highly Efficient Quasi-Single-Stage AC-DC Converter Employing Bidirectional Switch

The use of renewable energy is on the rise and is expanding ever so greatly in this modern age of technology. However, it comes with a new set of challenges to properly integrate these renewable energy-based power plants thus forming a virtual power plant safely and reliably into the power grid in which a smart grid plays an effective role. The main focus of this paper is to review the functions a modern-day smart grid plays in the integration of distributed energy resources to the grid to form a virtual power plant including cybersecurity measures. It also addresses a basic example of the detection of a cyber-attack caused into the grid assuming it to be manipulated by a hacker together with a novel solution and later validated by performing simulation. 

Jamil Hassan

Papers

Bidirectional Soft Switching Push–Pull Resonant Converter Over Wide Range of Battery Voltages

High Step-Up Quasi-Resonant Converter Featuring Minimized Switching Loss Over Wide Input Voltage Range

Highly Efficient Quasi-Single-Stage AC-DC Converter Employing Bidirectional Switch

An Overview of the Functions of Smart Grids Associated with Virtual Power Plants Including Cybersecurity Measures