패턴 서치 알고리즘을 이용한 병렬형 하이브리드 전기 상용차의 동력원 용량 및 제어 전략 최적화

Abstract

세계적으로 온실가스 감축을 위해 많은 노력을 하고 있으며, 이에 따라 수송 분야에서도 지속해서 연비 배기 규제가 강화되고 있다. 강화되는 연비 규제에 대응하기 위해서 대형 상용차 분야에서는 수소와 전기 에너지를 이용하는 친환경 수송 시스템에 대한 연구가 활발히 진행되고 있다. 특히 수소 시스템은 에너지 밀도가 높고 충전 시간이 비교적 짧아 화물수송용 대형 상용차에 적용하기 용이하다. 따라서 대형 상용차의 연비 배기 문제를 해결하기 위한 유력한 대안 중 하나로 떠오르고 있다. 하지만 수소 충전 인프라 보급의 지연으로 대형 수소 상용차의 대중화가 지연되고 있는 상황이며 당장에 강화되는 연비 규제에 대안으로 활용하기 어렵다. 하이브리드 전기 시스템은 이러한 과도기적인 상황에서 당면한 문제를 효율적으로 해결할 수 있는 방안 중 하나로 활용할 수 있으며 이에 따라 하이브리드 전기 시스템의 효용성을 검토해 볼 필요가 있다. 본 연구에서는 시뮬레이션 기반으로 하이브리드 전기 시스템 적용 대형 상용차의 연비 성능을 평가하였다. 차량 시뮬레이션 툴 Autonomie를 이용하여 변속기 입력축에 모터를 병렬로 연결한 병렬형 하이브리드 구조 갖는 차량 모델을 개발하였다. 이때 모터의 용량을 20kW에서 250kW까지 적용하여 유럽 대형차 온실가스 측정 모드인 WHVC(World Harmonized Vehicle Cycle) 주행 결과값을 통해 연비 개선도를 평가하였다. 하이브리드 시스템의 동력 분배 제어 방식은 실차에 적용할 수 있는 규칙 기반(Rule-based) 제어기를 통해 이루어진다. 하이브리드 자동차 시장에서 활용되고 있는 동력 분배 제어 전략을 분석하고 이를 바탕으로 구성하였다. 이때 모터의 용량에 따라 이상적인 제어 규칙값이 다르기 때문에 공정한 제어 성능 비교를 위해 패턴 서치 알고리즘을 이용하여 모터 용량별 제어기의 제어 규칙 파라미터를 최적화하고 그 결과를 비교하였다. 최적화 결과, 병렬형 하이브리드 시스템의 연비 개선도는 모터 용량이 증가함에 따라 증가하다가 200kW의 모터 적용 하이브리드 시스템에서 수렴하며, 최대 21.1%의 연비 개선도를 보인다. 이때, 엔진의 작동점이 개선되어 평균 엔진 효율이 기존 내연기관 대비 1.8%p 향상되는 것을 확인하였다. 또한 60kW의 모터 적용 하이브리드 시스템 사용시, 단위 시스템 비용당 최대 연비 개선도를 보임을 확인하였다. 본 연구의 결과물로, MATLAB 스크립트 기반의 파라미터 최적화 프로세스를 구축하였으며, 이를 통해 하이브리드 시스템뿐만 아니라 다양한 모델 기반 파라미터 최적화 연구에 범용적으로 사용할 수 있는 프로세스를 갖추어 다양한 최적화 연구에 기여할 수 있을 것으로 예상된다.|Many efforts are being made to reduce greenhouse gas emissions worldwide, and as a result, regulations on fuel consumption in the transportation are continuously being strengthened. In order to meet stricter fuel economy regulations, research on eco-friendly systems for Commercial heavy-duty vehicles using hydrogen and electricity is being actively conducted. In particular, the hydrogen system has a high energy density and a relatively short charging time, which is advantageous to apply to a commercial heavy-duty vehicle, which is one of the potential alternatives to solve the fuel consumption problem. However, due to the delay in the supply of hydrogen-filled infrastructure, the popularization of large hydrogen commercial vehicles is being delayed, and it is difficult to use it as an alternative to the regulation of fuel efficiency which is tightened at the moment. Hybrid electric system can be used as one of the ways to efficiently solve the problems faced in this transitional situation, and therefore, it is necessary to examine the utility of hybrid electric systems. In this study, we evaluated the fuel economy performance of a commercial heavy-duty vehicle using a hybrid electric system on a simulation basis. The vehicle simulation tool Autonomie was used to develop a vehicle model with a parallel hybrid structure in which a motor was connected in parallel to the transmission input shaft. At this time, the capacity of the motor was applied from 20kW to 250kW, and the fuel economy improvement rate was evaluated through the results of driving the World Harmonized Vehicle Cycle (WHVC), which is a European greenhouse gas measurement mode. The power distribution control method of the hybrid system is achieved through a rule-based controller applicable to the actual vehicle. The power distribution control used in the hybrid vehicle market is analyzed and based on this. At this time, since the ideal control rule value varies according to the capacity of the motor, the control rule parameter of the controller for each motor capacity is optimized using the pattern search algorithm to compare the control performance. As a result of the optimization, as the motor capacity increases, the fuel economy improvement rate of the vehicle increases, but converges in the 200 kW motor-applied hybrid system, and improves the fuel economy by up to 21.1%. In addition, when using a 60kW motor-applied hybrid system, the maximum fuel economy was improved per unit system cost. In general, as the motor capacity is increased, the operating point of the engine is improved, thereby improving the average engine efficiency and reducing the regenerative braking efficiency. In addition, as a result of this study, we established a parameter optimization process based on MATLAB script, and it is expected to contribute to various optimization studies by preparing a process that can be used universally for various model-based parameter optimization studies as well as hybrid system.; Many efforts are being made to reduce greenhouse gas emissions worldwide, and as a result, regulations on fuel consumption in the transportation are continuously being strengthened. In order to meet stricter fuel economy regulations, research on eco-friendly systems for Commercial heavy-duty vehicles using hydrogen and electricity is being actively conducted. In particular, the hydrogen system has a high energy density and a relatively short charging time, which is advantageous to apply to a commercial heavy-duty vehicle, which is one of the potential alternatives to solve the fuel consumption problem. However, due to the delay in the supply of hydrogen-filled infrastructure, the popularization of large hydrogen commercial vehicles is being delayed, and it is difficult to use it as an alternative to the regulation of fuel efficiency which is tightened at the moment. Hybrid electric system can be used as one of the ways to efficiently solve the problems faced in this transitional situation, and therefore, it is necessary to examine the utility of hybrid electric systems. In this study, we evaluated the fuel economy performance of a commercial heavy-duty vehicle using a hybrid electric system on a simulation basis. The vehicle simulation tool Autonomie was used to develop a vehicle model with a parallel hybrid structure in which a motor was connected in parallel to the transmission input shaft. At this time, the capacity of the motor was applied from 20kW to 250kW, and the fuel economy improvement rate was evaluated through the results of driving the World Harmonized Vehicle Cycle (WHVC), which is a European greenhouse gas measurement mode. The power distribution control method of the hybrid system is achieved through a rule-based controller applicable to the actual vehicle. The power distribution control used in the hybrid vehicle market is analyzed and based on this. At this time, since the ideal control rule value varies according to the capacity of the motor, the control rule parameter of the controller for each motor capacity is optimized using the pattern search algorithm to compare the control performance. As a result of the optimization, as the motor capacity increases, the fuel economy improvement rate of the vehicle increases, but converges in the 200 kW motor-applied hybrid system, and improves the fuel economy by up to 21.1%. In addition, when using a 60kW motor-applied hybrid system, the maximum fuel economy was improved per unit system cost. In general, as the motor capacity is increased, the operating point of the engine is improved, thereby improving the average engine efficiency and reducing the regenerative braking efficiency. In addition, as a result of this study, we established a parameter optimization process based on MATLAB script, and it is expected to contribute to various optimization studies by preparing a process that can be used universally for various model-based parameter optimization studies as well as hybrid system.