- Introduction
1.1 Background
Transport systems have gradually become electric, which poses a threat to the growth of car manufacturing industries as EVs form the key solution to curbing carbon emission and the use of fossil products. This change has led to the need for efficient, compact and reliable power electronics system that meets energy needs of the new generation EVs. Of these, onboard battery chargers form an important component to facilitate convenient and efficient charging directly from the electrical grid.
Onboard chargers provide electric vehicle users with flexibility and independence by integrating all the charging infrastructures on board, so that they are independent of any external charging equipment. These chargers provide the proper DC voltage levels to the vehicle batteries from the grid AC power, allowing safe and effective transfer of energy.
This design involves an onboard charger with a dual-voltage output, such that it supplies high-voltage traction batteries for propulsion and low-voltage auxiliary systems for vehicle electronics. The successful implementation of this design should provide smooth running and complete operations of the vehicle by meeting the two different power requirements. Such designs may also decrease the energy consumption and eliminate the requirement of other additional converters for increasing the efficiency as well as the miniaturization of the entire system comprehensively.
Onboard charger technology developments will need to keep pace with growing EV adoption, consumer expectations for fast charging, safety, and reliability while adhering to the demands of industry standards and regulatory requirements. Contribute to this evolving landscape with the best onboard charger performance in an economically feasible proposition, growing the demand for sustainable, smart power electronics solutions.
1.2 Problem Statement
Designing onboard charger demands more challenges in terms of high efficiency, less loss, and obtaining specific safety or EMI regulations. Also, the charger should be capable to face load transient or grid fluctuation, and it has to be compact and cost-effective.
1.3 Objectives
Design and Simulate a High-Efficiency Onboard Battery Charger using MATLAB/Simulink.
- To reach a power factor as close to unity as possible through PFC techniques.
2. Designing a DC-DC conversion stage for dual outputs (400V DC and 48V DC).
3. Regarding output stability feedback on regulations, using regulatory feedback as a measure of stability feedback.
4. Enhancement of thermal conditions and resources for the presented system.
- Literature Review
2.1 Onboard Chargers: Overview
They also refer to systems incorporated in an EV converting AC from the power supply to charge onboard batteries from the grid.
These systems enable electric vehicles to charge in an effective and flexible manner by connecting directly to a standard power grid without additional equipment. The efficiency and design of onboard chargers can make a difference in terms of charging time, overall energy consumption, and even long-term performance of vehicle battery systems.
As EVs increase in the market, there has been an increasing need to develop onboard chargers that strike a balance between compactness, efficiency, and cost. Onboard chargers should provide high power quality while maintaining safety and reliability according to industrial standards. Especially in recent years, the advancing trend for fast charging solutions has necessitated the need for new onboard charger solutions, which require high power density, efficient thermal management, and a diverse approach to control schemes.
2.2 Power factor Correction Techniques
Low power factors produce energy losses, heat production, and disturbance of other appliances connected to the power supply.
Power factor correction will become one of the main features of onboard chargers as it upgrades the quality of power, minimizing harmonic distortion and allowing the input current waveform to be in phase with the voltage waveform.
Boost PFC converters are widely used owing to simplicity, efficiency, and effectiveness at high power level. They are ideal for applications in systems that need high voltage output and serve as the foundation stage in most onboard charger designs.
Interleaved PFC techniques operate the converters in parallel for high-power applications. This has the effect of reducing the ripple in input currents and results in higher overall efficiency. It makes this technology ideal for EV chargers dealing with higher power demands.
2.3 Dual-Voltage Outputs in Onboard Chargers
The on-board charger integration with the option for two voltages has become an important need of modern EVs. High voltage outputs-say, 300 to 400 V DC-charge the traction batteries used in powering the propulsion system, whereas the low voltage outputs, such as 48 V DC, are used in auxiliary systems, including lighting, infotainment, and climate control.
The approach of dual output further minimizes additional DC-DC converters within the vehicle, allowing further enhancements in overall system compactness and operational efficiencies. It also makes it possible for manufacturers to simplify the power distribution architecture of the vehicle for better energy usage and lower component costs.
2.4 Thermal control in power electronics
Power electronics design as a discipline cannot underestimate thermal management, especially in onboard chargers running at fairly high-power levels. Ineffective cooling results in performance decline, shortening of component durability, as well as system crashes.
Reversible cooling methodologies that are effective in low to mediums power systems include heat sinks and thermal pads. The foundation for all those solutions is the fact conductivity of certain materials enables them to draw the heat away from the critical system components and transfer it to the surroundings.
High power applications tend to utilize liquid cooled system and other active cooling methods Integral. In such systems, there is a cooling fluid to improve the heat transfer rate to minimize fluctuations in performance when subjected to conditions that are unfavourable.
2.5 Advances in Control Systems
Owing to the fluctuating nature of EV charging processes, there is a need to develop an innovative control system that would address issues of output voltage and various load states. Advanced algorithms are increasingly used to provide reliable operation and optimize energy transfer in modern onboard chargers.
Proportional-Integral-Derivative controllers were widely used due to the simplicity and effectiveness of the management of the system dynamics. Voltage and current levels are regulated by these types of controllers to minimize the deviation from a set point, hence providing stability during charging.
It is also observed that, because of the very reasons mentioned above, there is an increased application of fuzzy logic control systems in the literature. In these systems, onboard chargers can adapt to a variety of operational scenarios with improved robustness and performance across a wide range of conditions.
These are developments making state-of-the-art technologies in onboard chargers: advancements in PFC techniques, dual-voltage design, thermal management, and control systems. In fact, it is the integration of these features that enables manufacturers to provide such chargers, meeting requirements for fast charging, compact form factors, and high reliability of modern EVs.
3. Methodology
3.1 Topology Selection
The choice of the Onboard Charger system as the best possible topology was made in regard to its suitability to achieve the best possible AC-DC conversion with PFC and dual voltage. The proposed topology is an integrated boost PFC converter in series with a buck converter. Thus, it has minimum loss for converting the energy to feed the output voltage for both high voltage traction batteries and low voltage electric vehicle auxiliaries.
PFC Boost Converter: The PFC stage is aimed at enhancing the power factor of the AC input and enhancing the input voltage in order to give out a higher DC bus voltage of not less than 400V DC. This step minimises the harmonic distortion as well as provides an input current wave form corresponding to the voltage waveform in the charging process.
Buck Converter: This is after charging PFC and reduces the 400V DC to 48V DC powering the low voltage auxiliary systems in a vehicle. A buck converter plays an essential role in voltage regulation at low energy losses.
The PFC boost converter and the buck converter together permit the onboard charger to handle both the high-power needs of the traction battery and the lower-power needs of the vehicle’s auxiliary systems. This is the basis for a design approach using dual outputs and eliminates the need for multiple separate converters, assuring a more compact, efficient system.
Objective 1: The first objective is to design an onboard charger that efficiently manages the high-voltage traction batteries and the low-voltage auxiliary systems with its dual voltage output architecture. This would be used since it provides both high-voltage and low-voltage outputs with minimal components, which would ensure greater system efficiency and less overall size in the system.
3.2 Design Calculations
3.2.1 PFC Boost Converter
The stage of the PFC boosts or modulates the DC output voltage, improving the power factor. It increases the input AC voltage of 120V to a stable 400V DC bus voltage to be used for charging the high voltage battery. Some important equations used to find the performance of the PFC boost converter are:
Output Voltage Calculation:
Vout = Vm/1-D
Where Vout is the output voltage,Vin is the input voltage, and D is the duty cycle. The duty cycle is adjusted to maintain 400V DC output voltage irrespective of input voltage variations.
Inductor Ripple Current Calculation:
iL = vnD/fsL
Where il is the ripple current in the inductor, is the input voltage, D is the duty cycle, is the switching frequency, and L is the Inductance.The inductor is selected based on these calculations in order to minimize current ripple, which helps maintain a steady voltage output.
3.2.2 Buck Converter
This is once again stepped down to 48V DC for the low-voltage systems by a buck converter. Output voltage and ripple voltage are some of the major parameters that need to be controlled for efficient operation.
Calculation of Output Voltage:
V = D .AV
Where is the output voltage, D is the duty cycle, is the input voltage. Vin is the input voltage from the PFC stage. The duty cycle is tightly controlled to maintain the output voltage at 48V DC.
Output Ripple Voltage Calculation:
Where;
deltaVL is the ripple voltage at the output capacitor, deltaiLis the ripple current, fs is the switching frequency, and C-capacitance of the output capacitor. Since ripple voltage is at its minimum after optimization of these parameters, smooth and stable operation of those auxiliary systems is guaranteed.
Objective 2: Minimization of ripple in the voltage output at both the PFC boost converter and buck converter stages will ensure maximum power conversion efficiency. Calculations are performed for minimum ripple in voltage outputs along with high efficiency in both AC-DC and DC-DC conversion processes in the case of converters such as PFC boost and buck converters.
3.3 Component Selection
Selecting the appropriate components is very important for the onboard charger performance and reliability. The component selection can be done by the capability of managing required power with minimum energy losses.
Inductors: These inductors are planned to bear high current with low ripple current. In fact, this is one of the key features required for a voltage output to be stable. A proper selection of inductance values and rating of current ensures efficient operation of the inductor at the PFC boost converter and buck converter.
Capacitors: The reason for the choice of electrolytic capacitors is their high energy density, necessary in filtering voltage ripple at both the PFC stage output and buck converter. Those selected can handle the energy stored in and released at every cycle of charging.
Semiconductors (MOSFETs): The selected components are MOSFETs with low on-resistance (RDS (on)) is chosen to minimize losses resulting from switching and conduction. These MOSFETs chosen are suitable for high-frequency applications, considering the huge current demands that may be engaged from the system; thus, this contributes to the efficiency of the charger. Small values of RDS (on) reduce the heat developed during switching, reducing the loss of power.
Objective 3: Choose and integrate the inductors, capacitors, and semiconductors capable of meeting the onboard charger requirements of power handling and energy efficiency. Due to the careful choice of the components, onboard chargers can operate under dissimilar load conditions with high efficiency and minimum energy loss together with minimal thermal challenges.
3.4 Control System Design
Such a control system should be able to work out the duty cycles for both the PFC boost converter and the buck converter so that stability is maintained with minimum losses at variable input and load conditions. A voltage/current sensor-based PI controller acts there to perform the duty cycle control.
PI Controller for PFC Boost Converter: The PI controller controls the duty cycle of the PFC boost converter in order to hold the desired 400V DC while providing a power factor optimized. The controller will constantly tune up based on the feedback received from the voltage and current sensors so that the whole system remains within stable and efficient parameters.
PI Controller for Buck Converter: A PI controller in a buck converter works on duty cycle regulation to step down 400V DC to 48V DC for the auxiliary systems. The feedback mechanism ensure that 48 V output voltage is maintained constant irrespective of the fluctuation of the load from the auxiliary systems.
PI controller has been fine-tuned in a way it changes proportional to the dynamic load and input, and has ensured charge process with highly efficient and good stability voltage regulation.
Objective 4: The advanced control system is utilized to stabilize the output voltages against changes in load and input conditions for optimum performance at both high-voltage and low-voltage systems. Application of the PI controller enables the onboard charger to act upon variations in both the load and input conditions as it stabilizes the output voltages at a constant level on both systems.
3.5 Thermal Management
The thermal management of the onboard charger is highly necessary to maintain both its performance and longevity. Semiconductors produce heat during the time in which they are operational because of power conversion, and there needs to be effective thermal management to keep operating the system within safe temperature limits.
Heat Sinks and Thermal Pads: The heat sinks increase the heat dissipation surface area, enabling the components to remain within acceptable temperature limits. Thermal pads present interfaces between semiconductors and heat sinks with the purpose of increasing heat transfer efficiency. To put it simply, these components have been designed in such a way that they maximize the cooling potential by keeping in mind the compact nature of the charger system.
Thermal simulation: This allows the development of forecasting of the temperature distribution within the onboard charger, which will ensure the system operates safely. These simulations assume a number of operating conditions, including fluctuations in the input voltage and changes in the load, to identify any hotspots that may be present. By employing these simulations, there is an ability to optimisation in the cooling solution, refraining from overheating for right operations.
Active Cooling: Depending on the power involved, active cooling methods such as liquid cooling may be applied. In high-power converters, liquid cooling is efficient compared to air cooling because it provides a greater heat dissipation capacity, hence allowing the system to keep lower operating temperatures even in conditions of heavy loads.
Simulation Results and Discussion
Simulation Setup
The system was modeled in MATLAB/Simulink. The key parameters included:
Figure 2: Output of AC-DC converter
Figure 3: Output of DC-DC boost converter
AC-DC Converter Output:
The current waveform of the ACDC converter has an output that is a smoothened sine wave with a great reduction in harmonic distortion.
The voltage waveform settles around 360V DC. Ripple is observed as shown in Figure 2
DC-DC Boost Converter Output:
The boost converter successfully boosts the DC voltage into 400V without any instability. Besides, the output voltage is with low ripple and reaches the design target as shown in Figure 3.
Efficiency:
The general system reaches an acceptable level of conversion efficiency during the appropriate design of PFC stage and switching controls of the boost converter.
Power Factor:
The input current waveform to the AC-DC converter is in close proximity to the input voltage waveform, thus, nearly unity power factor.
Discussion
The results from simulation support the performance of the proposed design for achieving the following stated objectives;
1. AC-DC Converter Performance:
PFC stage successfully performs the function of rectification, along with shaping the current for lesser harmonic distortion. The input current waveform is almost sinusoidal; hence, it ensures better power quality.
The minor ripple in the DC voltage is because of the inefficiency of the filtering stage. Further reduction can be achieved with increased size of the output capacitor.
2. Performance of DC-DC Boost Converter:
The boost converter yields the required voltage of 400V DC, which would be apt for its high voltage application in battery charging of an electric vehicle. Also, PWM control helps regulate the output effectively for different variations in load.
The ripple in the output voltage is minimal since the size of the inductor and capacitor is appropriate.
3. System Efficiency:
The efficiency of the system is high due to the optimized switching operation of both AC-DC and DC-DC stages. Thermal loss is also very less, which contributes to overall energy efficiency.
4. Limitations and Challenges:
The ripple in the AC-DC stage may also slightly impact the input stability of the boost converter. Performance might be improved by possibly adding active filtering mechanisms or improving the design of the PFC controller.
Conclusion
An onboard dual-output charger design may be efficient and reliable for its performance in electric vehicle application. Additionally, the AC-DC converter can successfully rectify 120V AC into DC supply, implementing power factor correction which improves quality and standard of grid power. The DC-DC boost converter has successfully boosted the high voltage to 400 V DC with low ripple that is going to meet the requirements at the point of EV battery charging. Simulation results prove the system maintains stable output voltages against a wide range of operating input and load conditions. In fact, the power factor at the input stage goes to near unity, pointing out the success of PFC design by reducing harmonic distortion and increasing the overall system efficiency.
Among the features that have been integrated into this design are sophisticated control strategies and thermal management techniques that ensure stable operation and prolong component life expectancy. However, the limitations of minor ripple at the AC-DC stage further point toward areas of further improvement. Some of the future works could include enhancements in the filtering stage, integration of active thermal control systems, and real-world prototyping based on obtained simulation results. This research proved that onboard chargers with dual output feasibility are one of the most enabling technologies for power systems in EVs, which thus fulfills a higher demand for efficiency, compactness, and versatility. The contribution of this work to the broader effort of further development of EV technology and promotion of sustainable transportation systems globally is highlighted.
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