Moreover, the CG characteristics of the quadratic boost converter can effectively reduce additional EMI in the vehicle powertrain. According to Principle 1, two capacitors can be utilized to store and release more energy, obtaining the SC structure. This structure optimizes the topology with regards to the voltage conversion ratio, as shown in Fig. After modifying the SC Fig. This topology could significantly improve the output voltage and possessed smooth input current and output voltage.
The SI structure could effectively improve the VG and is accompanied by the advantages of simple control and easy implementation. However, the input and output of the SC structure do not have CGs. According to Principle 2, a VM can be obtained by transferring energy between two capacitors to multiply the output voltage [ 66 , 67 ]. The single-stage VM is shown in Fig. The novel topologies designed in Refs. The Dickson VM used in the post-stage of the converter proposed in [ 69 ] was improved upon in Ref.
However, VSs of components increase with the number of stages in the VM, which, in turn, increases the possibility of component defects and decreases the reliability of the entire FCV powertrain. In addition, the high VS results in the converter requiring components with high rated powers, which increases the cost and power loss in the powertrain. New energy systems were selected as the research background, and the boost topology was combined with a modified VM in Ref.
However, when the modified VM is cascaded, VSs of the post-stage components increases. Prior to applying the modified VM structure to FCVs, a new topology should be designed from the perspective of reducing VSs to reduce the cost and power loss in the powertrain. The Z-source structure can be obtained by transferring the SC structure according to Principle 3, as shown in Fig.
The power source, L1, and L2 supply power to the load [ 76 ]. A steady-state analysis of a Z-source step-up topology operating in the continuous conduction mode CCM was conducted in Ref. Moreover, the application prospect in FCV was discussed. The Z-source structure was integrated with the quasi-Z-source one in Ref. This converter exhibited good step-up capability.
The Z-source structure can provide a high gain under the non-limit duty cycle, which can effectively match the low output voltage of FCs with the high bus voltage.
However, using the Z-source structure in the FCV powertrain would generate a pulsating current in the FC, affecting its life. In addition, the input and output of the Z-source structure do not have a CG. The two points above restrict the application of Z-source structures in the FCV powertrain. To overcome the disadvantage of the Z-source structure not having a CG, a quasi-Z-source can be obtained from the impedance transformation of the Z-source structure, as shown in Fig. The operating principles of the quasi-Z-and Z-source structures are similar.
In addition, the efficiency of this converter reached Based on the investigations conducted in Ref. The quasi-Z-source converter was subsequently tested under the worldwide harmonized light-duty test cycle. A high voltage boost DC-DC converter composed of a quasi-Z-source converter and a quadratic boost converter was proposed in Ref. A high VG quasi-Z-source topology for new energy sources was proposed in Ref. The VGs of the quasi-Z-source and Z-source structures were equal.
When the duty ratio is nearly 0. Moreover, the CIC of the quasi-Z-source structure is beneficial to FCs, low VSs of the devices are conducive to reducing the cost of the powertrain, and the CG characteristics can effectively reduce the additional EMI in the powertrain. Therefore, this structure is suitable for FCV systems. On this basis, a feedforward control strategy for these topologies was proposed. A TL topology was implemented in Refs [ 85 ] and [ 86 ] as the post stage of the step-up converter for an FCV, effectively reducing VSs of the components.
For the FC composite energy storage system, the VS on the switch of the TL topology presented in Ref [ 87 ] equaled to only half of the output voltage, and the dynamic response of the converter was significantly improved.
However, the disadvantages of high control accuracy and a large number of switches necessitates extensive research on developing an optimization scheme to reduce the cost and power loss of the powertrain.
According to Principle 1, a voltage lifting VL circuit can be obtained by using an inductor and a capacitor to store and release more energy, as shown in Fig. Based on the basic boost topology, positive and negative VL circuits, first proposed in Refs [ 88 ] and [ 89 ], respectively, effectively improved the step-up ratio. However, the input and output sides did not have a CG.
The VL circuit can significantly improve the step-up ratio, and its input and output have a CG. The flexible structure can be easily designed. However, this circuit has a pulsating input current, which is unfavorable for the FC stack. A hybrid structure can be obtained by replacing a functional unit of the basic topology with one or multiple topologies or a part of the topology.
Hybrid topology can optimize the performance of the topology according to specific requirements, which is a common method of designing DC-DC converters for FCVs. The schematic diagram of hybrid topology construction is shown in Fig. Moreover, Boost, Cuk, and sepic circuits have CIC, which is appropriate for the basic topology of the hybrid structure.
The characteristics of a few DC-DC boost converters constructed using the hybrid structure are listed in Table 1. Using a hybrid structure constitutes an important method of generating novel boost converters for FCVs by introducing functional units to optimize the performance of the topology. Alternatively, high VG topology can be used as the hybrid unit to effectively match the low output voltage of FCs and the high bus voltage. To reduce the power loss of components and improve the reliability of the powertrain, reducing the VSs of components is necessary.
However, there are many devices in the hybrid topology, which would increase the cost of the powertrain and decrease the efficiency. Cascading more than two topologies the duplicate part can be shared can generate a cascaded structure, as shown in Fig.
The 1st converter utilizes the FC as its power source, and the subsequent converter, in turn, uses the output voltage of the former one as the power source. Thus, a cascade relationship is formed. The n th converter provides energy to the load. The cascaded structure exhibits the advantages of variety and simple implementation.
Many studies have been conducted on utilizing cascaded structures to construct new boost topologies for FCVs. A few configurations and advantages of the cascaded structure are listed in Table 2. The cascaded structure can flexibly combine sub-topologies, according to the requirements of the particular application, to obtain a new topology.
This new topology, thus, inherits the advantages of each sub-topology. To ensure the suitability of the cascaded topology for the FCV powertrain, a topology with low ICR can be used in the front-stage of the cascaded topology, ensuring the low current ripple characteristics of FCs.
The cascaded topology can use a high gain structure as an intermediate link to maintain the bus voltage under different FC output powers, and thus, adapt to different driving conditions. To reduce the cost of the powertrain and improve reliability, the TL structure can be used as the end-stage of the cascade topology. However, the efficiency of the cascaded topology is the product of the efficiency at each stage, resulting in reductions in the entire efficiency of the vehicle powertrain [ ].
To synopsize, Table 3 systematically summarizes the advantages and disadvantages of typical impedance networks and provides suggestions for constructing DC-DC boost converters for FCVs. Existing evaluation indexes for DC-DC boost converters mainly consider the performance of DC-DC converters, while the proposed evaluation indexes also take the requirements of connection with FC into consideration. The evaluation indexes of the DC-DC boost converter constitute the standard based on which the merits and demerits of the topology are assessed.
The universal requirements for a DC-DC boost converter include voltage and current stress, conversion efficiency, power density, number of components, the slope of step-up ratio, and presence of CG. VG of the converter is defined as the ratio of the output voltage to the input voltage. The strength of the step-up capability of the topology increases with the step-up ratio.
Figure 17 compares the VGs of 13 topologies. During the high-frequency switching of DC-DC boost converters, the internal energy storage components are also charged and discharged at high frequencies. This would, in turn, generate current ripples at the input side of the converter.
Therefore, reducing the ICR is imperative [ ]. Although the current ripple can be filtered using filters, the input current of the DC-DC boost converter for FCV should not be pulsating considering the limited vehicle space.
The output power of the FC varies with the road conditions. The DC bus voltage is power battery voltage; therefore, its variation range is small, and the output current of the FC would significantly change. The output voltage of the FC would noticeably drop for increasing output current. In addition, a higher VG of the topology partly implies a wider voltage range that can be inputted.
VS constitutes the maximum reverse voltage born by the component when it is switched off. Current stress constitutes the maximum current flowing through the component. The significant increase in the component stress, in turn, increases the possibility of component defects, leading to low reliability of the entire converter.
In addition, the voltage and current stresses determine the rated parameters of power electronic components. Generally, the higher the voltage and current stress the component can withstand, the more expensive and the larger the size.
To reduce the cost and size, the power electronic components in the DC-DC boost converter for FCV should have low voltage and current stresses. The ratio of the rated power to the volume of the step-up converter is defined as the power density.
Owing to the limited space in FCVs, the converter is required to process high power at a small size. Utilizing appropriate circuit models and analysis methods to accurately calculate the parameters of inductors, capacitors, switches, and other components in the topology is a common method for improving the power density.
Miniaturization and the use of a high-frequency converter constitute the most effective methods of increasing the power density. However, with increasing operating frequencies of the component, severe EMI issues begin to arise. The complex DC-DC topology can generally improve the performance in one or several aspect s. However, the disadvantages of having many components are evident, especially in the cascaded and hybrid structures.
A large number of components increase the cost of the DC-DC boost converter and reduce the power density. The number of components should be reduced as much as possible to meeting the requirements of FCVs. Owing to the parasitic parameters and the frequent switching on and off of the switches, DC-DC converter losses include conduction and switching losses. This not only results in an output power lower than the input power but also raises the temperature of the converter.
The conversion efficiency of the DC-DC converter is defined as the ratio of output power to input power. Moreover, high efficiency is the objective behind developing DC-DC topologies. The conduction loss increases with the current.
The switching loss of the converter, however, increases with the operating frequency. Soft-switching technology can be used to reduce switching loss. Implementing soft-switching technology, designing filters, parasitic parameter optimization, designing shield structure, and adding a CG are effective measures to suppress EMI [ ]. The slope of the step-up ratio is an index that describes the change in the step-up ratio with the duty cycle.
A high step-up ratio slope implies that the step-up ratio increases rapidly with a slight increase in the duty cycle. The designers of the DC-DC boost converter tend to favor a gentle slope of the step-up ratio because it indicates that the control requirement of the topology is easy to achieve. In this section, DC-DC boost converters based on impedance network are compared in terms of eight aspects: the technology used, VG, ICR, duty cycle range, voltage and current stresses, number of components, CG, and maximum efficiency.
The power density and conversion efficiency of the topology are affected by many factors, such as the operating frequency, rated power, and the number of components. The distribution of indexes for several existing topologies are summarized in Table 4. The maximum efficiency in Table 4 is the value obtained in the corresponding paper.
Two points are to be explained: first, the advantages and disadvantages of the indicators of topology are relative. The topologies evaluated in Fig. Secondly, no topology is excellent in all aspects. Certain performances of the topology should be optimized from the perspective of an application when designing the topology. Date of Publication: 20 November DOI: Need Help?
Together they form a unique fingerprint. View full fingerprint. Institute of Electrical and Electronics Engineers Inc.. The impedance matching network has been designed for 1GHz but through testing the receiver with a signal generator followed by an antenna, it has been found that the signal frequency of MHz yields optimal energy capture at the tested received power levels of 0dBm, 3dBm, and 6dBm. The signal is produced from a signal generator which sends power to the transmitting antenna, then wirelessly to the receiving antenna that is connected to the wireless power receiver, and the voltage boosted to charge the energy storage supercapacitor.
With the optimal settings in place the system would be able to substitute for the wires powering low-voltage devices on aircraft, reducing the weight on board and allowing for these devices to be powered with radio frequency RF signals. This would save fuel and reduce carbon emission, thereby helping to slow climate change.
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