Isolated Power Converter Research Articles

A Fully Isolated Delta-Sigma ADC for Shunt Based Current Sensing

This paper presents the world’s first reported chip-level 5 kVrms isolated delta-sigma ADC architecture which realizes isolation in both the power and signal domains. The compact IC package contains an integrated isolated power converter which includes an on-chip transformer, oscillator and rectifier, three delta–sigma analog-to-digital converters, a voltage reference, a temperature transducer, on-chip data transformers, and a controller/communication chip. Because it includes all of the isolation units within the same package, no PCB level isolation components are needed. This solution displaces the need for isolation using opto-couplers or costly, bulky and frequency dependent current transformers, and enables lower cost shunt resistor based current sensing applications such as domestic and industrial energy monitoring. It also enables new portable current sensing applications where high voltage isolation is required. The system-in-package (SIP) draws 12.5 mA from a 3.3 V supply and achieves 74.4 dBFS SNDR and 80.8 dBFS SFDR in a bandwidth of 3.3 kHz. It achieves an insulation voltage rating of 400 Vrms continuous and 5 kVrms over a 1 minute duration.

Equivalent Noise Source: An Effective Method for Analyzing Common-Mode Noise in Isolated Power Converters

The interwinding capacitance of the transformer and the primary-side circuit nodes to ground capacitance are critical coupling path for common-mode (CM) noise in isolated power converters. In order to analyze the CM noise, the transformer interwinding capacitance is usually equivalent to lumped capacitance. In this paper, a generalized lumped capacitance model for constructing the CM noise equivalent circuit that is valid at low frequencies is derived. By simplifying the CM noise equivalent circuit based on Thevenin’s theorem, the equivalent noise source (ENS) for CM noise is proposed. The ENS is expressed by a linear combination of voltages in the converter, where the coefficients of these voltages are determined by transformer winding structure and the circuit configuration. With the help of ENS, the CM noise of the converter under different circuit configuration can be systematically analyzed and conveniently compared, which develops an effective reference for selecting a proper circuit configuration. Finally, the lumped capacitance model and the ENS for CM noise are verified by the experimental results.

Novel Isolated Multilevel DC–DC Power Converter

An isolated multilevel dc–dc power converter is proposed in this paper. The proposed isolated multilevel dc–dc power converter consists of an isolated power converter, a series/parallel switching circuit, and an output L–C filter. The isolated power converter is composed of a half-bridge inverter, a three-winding transformer, and two full-bridge rectifiers. The half-bridge inverter is switched in constant duty to generate two output dc voltages through two secondary windings of the three-winding transformer and two full-bridge rectifiers, respectively. The series/parallel switching circuit is used to control the two output dc voltages of the isolated power converter connected in series or in parallel, to control the output voltage of isolated multilevel dc–dc power converter. To verify the performance of the proposed isolated multilevel dc–dc power converter, a prototype is developed and tested. The experimental results show that the proposed isolated multilevel dc–dc power converter has the expected performance.

A Gate Driver with Integrated Dead-Time Controller

Deadtimes are required to avoid simultaneous conduction of high-side and low-side power transistors in half-bridge power converters. During these secure times, free-wheeling current flow generates extra power losses. Very short deadtimes are desired but they cannot be safely set in conventional isolated power converters because of a digital input propagation delay mismatch. A specific deadtime management is introduced in this paper to ensure proper operation of a high-voltage synchronous power converter. A controller integrated in each isolated gate driver secures synchronous switching by detecting the opposite switch turn-off before turn-on. With such a selfswitching technique, very short but safe nonoverlap times can be set. A gate driver has been implemented in a 0.35 μm 20-V CMOS process. The monolithically integrated controller consumes only 140 μA and 0.22 mm2 of silicon area. The proposed local deadtime management has been validated in two synchronous buck converters without external free-wheeling diodes: a 500-W 250-V to 55-V converter based on SiC JFETs and a 30-W 45-V to 10-V converter based on eGaN FETs. In either case, the proposed controller allows a higher efficiency from 10% of the rated load with resulting deadtimes as short as 15 ns.

High Efficiency on Si-Integrated Microtransformers for Isolated Power Conversion Applications

This paper details the design, fabrication, and characterization of silicon-integrated microtransformers for isolated bias supplies. Racetrack-shaped microtransformers were designed and fabricated using the advanced double-layer metal (DLM) microfabrication process. The DLM devices have high inductance density of more than 80 nH/mm2 with an efficiency of approximately 78.2% at 20 MHz at 0.5-W output. This is the highest efficiency and power density reported for an integrated transformer in the literature. The inductance drop is less than 20% with a bias current of 0.35 A with up to 6-kV dc breakdown voltage achieved.

Effective Test Bed of 380-V DC Distribution System Using Isolated Power Converters

This paper proposes an effective test bed for a 380-V dc distribution system using isolated power converters. The proposed test-bed system is composed of a grid-interactive ac–dc converter for regulating the dc-bus voltage, a bidirectional converter for the battery power interface, a renewable energy simulator, dc home appliances modified from conventional ac components, a dc distribution panel board, and its monitoring system. This paper discusses three isolated power converters, i.e., a bidirectional ac–dc converter, a bidirectional dc–dc converter, and a unidirectional dc–dc converter for the effective power interface of a dc bus. These isolated power converters are designed using a dual-active-bridge converter and the resonant topologies of $CLLC$ and $LLC$ . The proposed test-bed system was implemented using a 5-kW bidirectional ac–dc prototype converter, a 3-kW bidirectional dc–dc prototype converter, and a 3-kW unidirectional dc–dc prototype converter. Finally, the performance of the test-bed system has been verified using practical experiments of load variations and bidirectional power flow, employing the prototype converters.

A Generalized Common-Mode Current Cancelation Approach for Power Converters

The interwinding parasitic capacitance of transformers and the parasitic capacitance between semiconductor switches and the ground are two major contributors to the common-mode (CM) noise currents in switched mode power converters. In this paper, a generalized CM current cancelation approach is proposed for the reduction of CM noise in isolated power converters. The approach is demonstrated in a forward converter. In this approach, the total effect of the two parasitic capacitances on CM noise is represented with an equivalent parasitic capacitance (EPC) at low frequencies. With this EPC, different CM current cancelation techniques can be efficiently organized to simultaneously cancel the low-frequency CM noise caused by these two parasitic capacitances. Furthermore, the EPC can be used to evaluate and quantify the performance of CM noise reduction techniques. Both theoretical analysis and experimental results show that the proposed approach is easy to implement and can significantly attenuate low frequency CM noise and therefore greatly reduce CM filter size and cost.

Shielding-Cancelation Technique for Suppressing Common-Mode EMI in Isolated Power Converters

In an isolated power converter, the interwinding capacitance of the transformer is the critical coupling path for the generating of common-mode (CM) noise. The shielding technique, for the purpose of blocking the electric coupling between the adjacent windings, has been widely used to deal with the CM noise. For the transformer with a single shielding layer, the displacement current that flows between the shielding layer and its adjacent windings still causes CM noise. In this paper, the shielding-cancelation (SC) technique is proposed by combining the shielding technique and the winding cancelation method together: The shielding layer is adjusted to have the same turns number and winding direction with its adjacent windings. In this way, the $dv/dt$ on the interwinding capacitance is always zero; thus, the CM noise can be effectively suppressed. A flyback converter prototype is built in the laboratory, and the performance of the SC technique on suppressing the CM noise is verified by experiments.

Design‐oriented model and critical inductance method for long life isolated power converters

For moderate-to-high power converters, electrolytic capacitor is an indispensable component. Life of electrolytic capacitor is critical compared with its semi-conductor counterparts. This study proposes a new model to analyse the converter life and to design the circuit to lower the current ripple in the electrolytic capacitor in order to reach for longer converter life. Two-stage power converter (a power factor correction converter followed by a DC–DC converter) is the typical practice for AC–DC converter. Forward converter and Flyback converters are the common choices for the downstream converter for this power range. Comparison between two modes of operation, discontinuous conduction mode and continuous conduction mode (CCM), for the two converter topologies shows a typical CCM Forward converter to have almost 300 times longer life than a CCM Flyback converter. Another focus of the work is to analyse the effect of circuit parameters on the converter life. A critical inductance is established to guide the design for long life converters.

The Study of Isolated Multi-Input Converter for Green Energy Application

To increase the development and popularization of the Green Energy Generation System (GEGS), this paper aims to develop a multi-input isolated power converter, which could be coordinated on a green-energy-based DC bus. The proposed converter is integrated with commercial grid and batteries, to achieve the grid energy supplement and battery-based emergency backup power supply, respectively. The operational principle of proposed converter is presented, there are three operation mode and its simulation result are illustrated as well.

Classification and comparison of interfacing schemes for connecting fuel cells to a single-phase utility line

Based on a systematic classification of dc source to utility interfacing schemes, this paper presents six major interfacing schemes for connecting fuel cells to a single-phase utility line using high-frequency transformer isolated power converters. The operation, advantages and disadvantages are discussed for each scheme with examples and operating waveforms. Several features e.g., utility line power factor, line current THD, size, ease of connection to utility line and simplicity of control, are compared. Based on their performance and fuel cell characteristics, a suitable scheme is selected. The selected scheme (#4) uses a dc/dc converter followed by a current controlled voltage source inverter. Details of the power conditioning unit (PCU) based on the selected scheme are given with some PSIM simulation results.

Global Loss Evaluation Methods for Nonsinusoidally Fed Medium-Frequency Power Transformers

Medium-voltage conversion systems, such as traction and grid-connected converters, are continuously evolving toward higher power densities. Consequently, volume, weight, and material reductions are becoming major design issues, which lead the research focus toward high-/medium-frequency isolated power conversion systems. An optimized design of these conversion systems requires a detailed transformer-loss evaluation considering both copper and core losses. This paper presents a simple and flexible methodology to analyze global medium-frequency transformer losses in an isolated DC-DC converter fed by general nonsinusoidal waveforms. Various loss evaluation approaches are considered, pointing out their validity and limitations by means of finite-element simulations and experimental tests.