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Bidirectional Converter Fed DC-Drive System with fly back snubber
Abstract
A Bidirectional Converter Fed Dc-Drive System with fly back Snubber has efficient conversion ratio, high output power, and smooth start-up. A clamping capacitor is used to reduce the voltage spikes caused by the current difference between the low voltage side inductor and leakage inductance of the isolation transformer. A diode and fly back snubber is used as protection circuit. It can reduce the current flowing through the active switches at the current-fed side. A model of 1.5-kW power with low voltage side of 48 V and high voltage side of 360 V has been implemented.
... In [29]- [30] a regenerative Flyback converter replaces the resistor in an RCD snubber circuit thus recovering part of the energy. Additionally, this Flyback provides isolation and enables soft-start capability of the proposed bidirectional converter in [29]. ...
... In [29]- [30] a regenerative Flyback converter replaces the resistor in an RCD snubber circuit thus recovering part of the energy. Additionally, this Flyback provides isolation and enables soft-start capability of the proposed bidirectional converter in [29]. The active regenerative snubber concept can be extended to other isolated or non-isolated topologies. ...
... This makes it difficult to estimate the related losses in a real application. The worst possible scenario can be estimated by (29). ...
The requirements for the blocking voltage of the rectification devices on the secondary side of Phase Shift Full Bridge DCDC converter topology are, by nature, higher than for other quasi-resonant or fully resonant topologies (DAB, LLC). This is especially aggravated in wide range operation converters and further increased by the rectifiers' drain voltage overshoot. Unlike other resonant topologies, the inductor at the output of the PSFB effectively decouples the capacitor bank from the rectification stage, which otherwise acts as a strong lossless snubber. Higher blocking voltage requirements for the rectification devices worsen their Figure of Merit, increasing their related losses and decreasing the overall efficiency of the converter. In this paper the main causes of the rectifiers drain voltage overshoots in PSFB are analyzed. Design guidelines for the mitigation of the different causes are introduced, as well as a novel modulation scheme for the overshoot reduction while the output filter operates in DCM, without penalties in performance, complexity or cost. A prototype of PSFB DCDC converter of 3300 W, with 400 V input to 54.5 V output nominal voltages, was designed and built to test the proposed solutions achieving a peak efficiency of 98.12 % at 50 % of load.
MOTIVATION AND OBJECTIVES
The power supplies or power converters are required in many applications to convert between the AC of the distribution grid to AC or DC at different voltage and current levels required by the electric loads. Each applica-tion may include different conversion steps and at different voltage levels. In every conversion step part of the energy is lost and dissipated in the form of unwanted heat. The conversion efficiency in every step is the result of dividing the utilized output power by the total input power in the converter. The total efficiency of the system is the result of multiplying the individual efficiencies of the stages, and will always be necessarily lower than the minimum of the individual efficiencies in the conversion chain.
Traditional linear power supplies have been extensively replaced by the more efficient and smaller Switched Mode Power Supplies (SMPS). SMPS makes use of semiconductor switches commutating at a relatively high frequency and reactive circuit elements (inductors and capacitors) to perform the power conversion. The semi-conductor switches in SMPS alternate between their on state, where their voltage drop is minimal, and their off state, where they don’t conduct current. However, during the switches turn-on transition and turn-off transition, there is certain overlap of voltage and current which causes switching losses.
For the currently available semiconductor power switching devices the resonant and quasi-resonant convert-ers are the most attractive options for achieving high efficiency, high power density or a combination of both at a reasonable cost. The key advantage of the resonant and quasi-resonant converters is the reduction of the switching losses. The switching losses can be reduced achieving Zero Voltage Switching (ZVS) for the turn-on transition and Zero Current Switching (ZCS) for the turn-off transition.
Among the isolated, resonant and quasi-resonant DCDC converter topologies, the most common ones in medium-high power and high-voltage applications are the series-parallel resonant converter (LLC), the Phase Shifted Full Bridge (PSFB) and the Dual Active Bridge (DAB) due to their simplicity and high efficiencies. Among those topologies each one has its own advantages and disadvantages, which makes each of them best suited for different applications, power and voltage ranges.
This thesis is focused in the study of the LLC and the PSFB. Both of this topologies are very promising and well suited for any of the available power switch semiconductor technologies in the market, and more specifi-cally for Si Super Junction (SJ) MOSFETs, which are the most mature devices and the most competitive in cost currently and in the foreseeable future. The general objective of this thesis is the optimization, improved reliabil-ity and functionality of the LLC and the PSFB converters maintaining as much as possible the simplicity of the standard circuit configuration.
Therefore, this thesis comprises the design and construction of several DCDC converters with similar specifi-cations and similar magnetic structures to study the achievable performance of the two main topologies objec-tive of this work: LLC and PSFB. More specifically, the fundamental research objectives of this thesis include:
• The development of very high-efficiency DCDC converters for server applications, including the design optimization of quasi-resonant converters experimentally demonstrated with a 1.4 kW PSFB converter from 400 V to 12 V.
• The development of very high-efficiency DCDC converters for telecommunitation applications, including the design optimization of quasi-resonant converters, experimentally demonstrated with a 3.3 kW PSFB converter from 380 V to 54.5 V, and the design optimization of resonant converters, experimentally de-mostrated with a 3.3 kW half-bridge LLC converter from 400 V to 52 V.
• The development of bidirectional DCDC converters for Electrical Energy Storage (EES) applications, includ-ing the bidirectional operation of traditionally considered non-bidirectional PSFB converters, experimentally demonstrated with a 3.3 kW bidirectional PSFB from 380 V to 54 V and from 50 V to 400 V.
• The integration of a very high-efficiency DCDC converter in a complete two-stage off-line Power Supply Unit (PSU) for server applications, experimentally demonstrated with a 3 kW totem-pole ACDC converter followed by a 3 kW half-bridge LLC DCDC converter from 400 V to 50 V.
Once the objectives have been outlined and after the previous brief theoretical background, in the following we summarize the several contributions of this thesis together with the most relevant results obtained and the conclusions that could be derived from them.
RESULTS AND CONCLUSIONS
It has been found that, although PSFB can achieve higher efficiencies than what is commonly expected thanks to the newest devices and the newly proposed control techniques, the LLC is still potentially superior and capable of higher efficiencies with less components at a lesser cost. However, in bidirectional applications the large signal gain range of the PSFB makes it arguably superior to the LLC.
A 3300 W bidirectional PSFB DCDC converter from 380 V to 54 V has been designed and built achieving 98 % efficiency in forward or buck mode and 97% in reverse or boost mode. The achieved power density is in the range of 4.34 W/cm³ (71.19 W/in³), which is enabled by the use of Surface Mount Device (SMD) packages, the innovative stacked magnetic construction and the innovative cooling solution. This DCDC converter proves the feasibility of PSFB topology as a high efficiency topology at the level of fully resonant topologies when com-bined with the latest SJ MOSFET technologies. This DCDC converter proves as well that the PSFB topology can be used as a bidirectional DCDC stage without changes in the standard design or construction of a traditional and well known topology, but only through innovations in control techniques powered by digital control.
A 3300 W LLC DCDC converter from 400 V to 51.5 V has been designed and built achieving 98.1 % peak of efficiency. The achieved power density is in the range of 4 W/cm³ (66 W/in³). The optimized layout and an optimized driving circuitry achieves benchmark performance with minimum stress on the devices, enabled also by the innovative cooling concepts presented in this converter. This DCDC converter proves the feasibility of the half-bridge LLC as a high-efficiency topology for a 3300 W converter, at the level of full-bridge LLC or a dual stage LLC. This DCDC converter also proves that digital control is not only capable of controlling the LLC topology but the most effective way to overcome its difficulties and pitfalls. Moreover, the included protections mechanisms and control schemes further boost the reliability and performance of the converter achieving the best possible efficiency.
A 1400 W PSFB DCDC converter from 400 V to 12 V has been designed and built achieving 97 % peak effi-ciency. The achieved power density is in the range of 3.70 W/cm³ (60.78 W/in³) thanks to the full SMD solution. This DCDC converter proves that an analytical optimum design procedure can further boost the performance of the PSFB near fully resonant topologies for low voltage outputs.
Finally, a complete 3 kW two stage off-line PSU for server applications has been designed and built achieving 97.5 % peak efficiency. The overall outer dimensions of the PSU are 73.5 mm x 520 mm x 40 mm, which yields a power density in the range of 32 W/inch³ (1.95 W/cm³). Due to the outer dimension limits, a planar transformer with reduced height and volume was preferred for this design.
In the next paragraphs the described contributions correspond to the published works that constitute this the-sis by compendium of publications.
In the first contribution, a novel modulation scheme is proposed for the bidirectional operation of the PSFB DCDC converter reducing the secondary side rectifiers overshoot without requiring additional circuitry or lossy snubbering techniques. The novel modulation scheme is experimentally demonstrated in a 3.3 kW PSFB DCDC converter with nominal 380 V input and nominal 54.5 V output.
M. Escudero, D. Meneses, N. Rodriguez and D. P. Morales, "Modulation Scheme for the Bidirectional Opera-tion of the Phase-Shift Full-Bridge Power Converter," in IEEE Transactions on Power Electronics, vol. 35, no. 2, pp. 1377-1391, Feb. 2020.
In the second contribution, a novel modulation scheme is proposed for the reduction of the overshoot in the secondary side rectifiers in PSFB DCDC converters operating in Discontinuous Conduction Mode (DCM). Fur-thermore, other secondary side rectifiers overshoot causes are analyzed and solutions proposed for each of the scenarios. The novel modulation scheme and the design principles are experimentally demonstrated in a 3.3 kW PSFB DCDC converter with nominal 380 V input and nominal 54.5 V output.
M. Escudero, M. Kutschak, D. Meneses, D. P. Morales and N. Rodriguez, "Synchronous Rectifiers Drain Volt-age Overshoot Reduction in PSFB Converters," in IEEE Transactions on Power Electronics, vol. 35, no. 7, pp. 7419-7433, July 2020.
In the third contribution, a detailed set of design criteria for PSFB DCDC converters is proposed. The design optimization procedure is experimentally demonstrated with the design of a new 1.4 kW PSFB DCDC converter further exceeding the efficiency and power density of a previous 1.4 kW PSFB DCDC converter with similar specifications, input voltage (400 V) and output voltage (12 V).
Escudero, M.; Kutschak, M.-A.; Meneses, D.; Rodriguez, N.; Morales, D.P. A Practical Approach to the De-sign of a Highly Efficient PSFB DC-DC Converter for Server Applications. Energies 2019, 12, 3723.
In the fourth contribution the impact in the performance and the design of resonant ZVS converters of the non-linear distribution of charge in the capacitances of semiconductor devices is analyzed. A Si SJ device is compared to a SiC device of equivalent Coss(tr), and to a GaN device of equivalent Coss(er), in single device topol-ogies and half-bridge based topologies, in full ZVS and in partial or full hard-switching. A prototype of 3300 W resonant LLC DCDC converter, with nominal 400 V input to 52 V output, was designed and built to demon-strate the validity of the analysis.
M. Escudero, M. Kutschak, N. Fontana, N. Rodriguez and D. P. Morales, "Non-Linear Capacitance of Si SJ MOSFETs in Resonant Zero Voltage Switching Applications," in IEEE Access, vol. 8, pp. 116117-116131, 2020.
In the fifth contribution the design of a new complete power supply for server applications is discussed. The main constraints of the new solution are the very high peak efficiency, the long hold-up time and the maximum outer dimension. The PSU is comprised of a front-end ACDC bridgeless totem-pole PFC and a back-end DCDC half-bridge LLC. Due to the extended hold-up time, the PSU requires large intermediate energy storage and an extended gain range for the LLC. Due to the outer dimension limits, a planar transformer with reduced height and volume is preferred. Finally, the very high efficiency target requires a careful design based on the accurate modeling of the overall losses of the converter. The analysis is demonstrated experimentally with a 3 kW PSU achieving 97.47 % of efficiency at 230 VAC.
M. Escudero, M. -A. Kutschak, D. Meneses, N. Rodriguez and D. P. Morales, "High Efficiency, Narrow Output Range and Extended Hold-Up Time Power Supply with Planar and Integrated Magnetics for Server Applica-tions," PCIM Europe digital days 2021; International Exhibition and Conference for Power Electronics, Intel-ligent Motion, Renewable Energy and Energy Management, 2021, pp. 1-8.
Hybrid vehicles need a high voltage DC bus to supply power to the motor. Architectures of these vehicles usually include a DC-DC bi-directional converter between this voltage bus and the conventional battery. When the DC bus is held by a big capacitor, the selection and design of the aforementioned converter has an additional difficulty since the converter has to work with an output voltage ranging from 0 to 420 V in steady-state conditions. A bi-directional DC-DC converter for a hybrid vehicle is proposed in this paper. It can be used in the case that a big capacitor holds the voltage in the high side. The application forces three different operation modes being the converter able to operate in those conditions. Experimental results of a 1500 W prototype are included in the paper
The newly developed phase-shift controlled bidirectional DC-DC
converter has the conventional features of phase-shifted converters,
including zero-voltage switching (ZVS) and constant switching frequency.
However, it has been improved by developing a bi-directional power flow
capability and applying synchronous rectification, hence the on-state
voltage drop of the active device is small
This paper outlines a soft-switching mechanism based on zero-voltage-zero-current-switching (ZVZCS) principle for the front-end isolated DC/DC converter of an isolated three-phase rectifier-type high-frequency-link bidirectional power converter. In conjunction with a back-end DC/AC converter operating with a novel patent-filed hybrid modulation scheme outlined in , , and that reduces the number of hard-switched commutation per switching cycle, the proposed ZVZCS scheme can lead to less overall switching losses than other conventional switching schemes. The proposed ZVZCS scheme is effective for various load conditions, operates seamlessly with a simple active-clamp circuit, and is suitable for applications where low-voltage dc to high-voltage three-phase ac power conversion is required.
Driven by worldwide demand for renewable sources, the photovoltaic market saw in the last years a considerable amount of innovations regarding the construction and operation of inverters connected to the grid. One significant advance, among some that will be here discussed is, for example, the abolition of the galvanic isolation in inverters installed in Germany. There, transformerless topologies, like the H5 and Heric, can reach very high levels of efficiency and allow the best cost-benefit ratio for low-power grid-tied systems. This paper will follow this direction and propose a single-phase transformerless inverter circuit being composed of the association of two step-down converters. Each one modulates a half-wave of the output current, as the correct polarity of the connection to the grid is provided by low-frequency switches. Due to its straightforward design, reduced amount of semiconductors, and simple operation, it is possible to achieve a high level of efficiency and reliability. These and some other characteristics will be benchmarked against other existing circuits, being followed by a theoretical analysis on the properties of the proposed solution. The project of a laboratory prototype will be presented, along with a discussion about the obtained experimental results.
Multi-port DC-DC converters have attracted special interest in applications where multiple energy sources are used. In this paper, a current-fed bi-directional three-port converter is proposed. Steady state and dynamic analysis of the converter is presented along with simulation results. The converter has the advantages of reduced current ripple at the input due to the presence of input inductor, high voltage step up ratios and no bulk input capacitors. One of the applications of such a converter is in fuel-cell hybrid systems with energy storage for use in telecommunication sub-stations.
In this paper two bi-directional DC-DC converters for a 1MW next-generation BTB system of a distribution system, as it is applied in Japan, are presented and compared with respect to design, efficiency and power density. One DC-DC converter applies commercially available Si-devices and the other one high voltage SiC switch, which consists of a SiC JFET cascode (MOSFET+1 JFET) in series with five SiC JFETs. In the comparison also the high frequency, high voltage transformer, which ensures galvanic isolation and which is a core element of the DC-DC converter, is examined in detail by analytic calculations and FEM simulations. For validating the analytical considerations a 20kW SiC DC-DC converter has been designed in detail. Measurement results for the switching and conduction losses have been acquired from the SiC and also for a Si system for calculating the losses of the scaled 1MW system.
This paper proposes a zero-current and zero-voltage switching (ZCZVS) PWM boost full-bridge (FB) converter. The leading switches can realize ZCS under wide load range using the energy of the output capacitor. With the use of the parasitic capacitors of the lagging switches and auxiliary inductance paralleled with primary winding of the transformer, the lagging switches can realize ZVS under any load. Compared with ZCS PWM boost FB converter, the proposed converter has no current duty cycle loss. The operation principle and parameters design are analyzed in detail. Experimental results are presented to verify the effectiveness of the proposed converter.
This paper proposes a new soft switching technique for the phase-shift controlled bi-directional DC-DC converter. The described converter employs a low profile high frequency transformer and two active full-bridge converters for bidirectional power flow capability. A new soft switching technique is proposed, which guarantees soft switching over wide range (no load to full load) without any additional circuit components. In the proposed switching scheme, the switch pairs in the diagonal position of the converter each are turned on/off simultaneously by the switching signals with a variable duty ratio depending on the phase shift amount, and the converter is operated without freewheeling interval. The load range for soft switching is analyzed mathematically and verified by experiments.
The isolated full-bridge boost power converter is attractive in
applications such as single-stage power factor correction (PFC) with
isolation requirement, or bi-directional DC-DC power converters. It
features several merits such as multiple-output capability with one
shared choke, single-stage energy processing and good input current
shaping ability. But its major disadvantage is that the transformer
leakage inductance causes high transient voltage across the bridge
switches, which increases the switching rating and decreases the
reliability. In this paper, an active soft switching circuit is proposed
for the isolated full-bridge boost converter. The proposed soft
switching circuit clamps the voltage across the full bridge, transfers
the energy in the leakage inductance to the load, and provides zero
voltage turn-off for all the main switches. Furthermore, the auxiliary
switch features zero current turn-on and zero voltage turn-off.
Therefore, the efficiency is improved. The analysis is verified by
experimental results
A new bi-directional dual full-bridge DC/DC converter with a
unified soft-switching scheme and soft-start capability is proposed in
this paper. A simple voltage clamp branch is used to limit transient
voltage across the current-fed bridge and realize zero-voltage-switching
(ZVS) in boost mode operation, while achieving hybrid
zero-voltage/zero-current switching (ZVZCS) for the voltage-fed bridge
in buck mode operation. The theory of operations including soft-start-up
process is discussed in this paper
A new full-bridge, active-clamp boost converter is proposed for
single-phase high power PFC applications and applications requiring
transformer isolation. The active-clamp network serves to limit bridge
switch turn-off voltage overshoot and enable the energy stored in the
transformer leakage inductance to be used for zero-voltage switching.
PWM phase-shift control of the bridge switches is utilized to obtain
zero-current switching for two of the four bridge switches. Simulation
results are presented which verify the principle of operation
A soft-commutating method and control scheme for an isolated boost full bridge converter is proposed in this paper to implement dual operation of the well-known soft-switching full bridge dc/dc buck converter for bidirectional high power applications. It provides a unique commutation logic to minimize a mismatch between current in the current-fed inductor and current in the leakage inductance of the transformer when commutation takes place, significantly reducing the power rating for a voltage clamping snubber and enabling use of a simple passive clamped snubber. To minimize the mismatch, the method and control scheme utilizes the resonant tank and freewheeling path in the existing full bridge inverter at the voltage-fed side to preset the current in the leakage inductance of the transformer in a resonant manner. Zero-voltage-switching is also achieved for all the switches at the voltage-fed side inverter in boost mode operation. The proposed soft-commutating method is verified through boost mode operation of a 3-kW bidirectional isolated full bridge dc/dc converter developed for fuel cell electric vehicle applications. The tested result verified the isolated boost converter can operate at an input voltage of 8.5–15V and an output voltage of 250–420V with a peak efficiency of 93% and an average efficiency of 88% at 55-kHz switching frequency with 72 C automotive coolant.
A current-fed three-port bi-directional OC-OC converterA soft-switching scheme for an isolated OC/OC converter with pulsating OC output for a three-phase high frequency-link PWM converterHighly Efficient Single-Phase Transformer less Inverters for Grid-Connected Photovoltaic Systems
- H Zhu
- N Krishnaswami
- Mohan
Zhu, "A novel soft-commutating isolated boost full-bridge ZVS-PWM OC-OC converter for bidirectional high power applications," IEEE Trans. Power Electron., vol. 21, no. 2, pp. 422-429, Mar. 2006 H. Krishnaswami and N. Mohan, "A current-fed three-port bi-directional OC-OC converter," in Proc. Telecommun. Energy Conf., 2007, pp. 523-526 R. Huang and S. K. Mazumder, "A soft-switching scheme for an isolated OC/OC converter with pulsating OC output for a three-phase high frequency-link PWM converter," IEEE Trans. Power Electron., vol. 24, no. 10, pp. 2276-2288, Oct. 2009. Samuel Vasconcelos Araujo, Student Member, IEEE, Peter Zacharias, Member, IEEE, and Regine Mallwitz, Member, IEEE,"Highly Efficient Single-Phase Transformer less Inverters for Grid-Connected Photovoltaic Systems", IEEE transactions on industrial electronics, vol. 57, no. 9, September 2010.