| الوصف: |
Baterijska električna vozila imaju značajno smanjen domet u ekstremno toplim i hladnim okolišnim uvjetima zbog visoke potrošnje električne energije od strane sustava grijanja i hlađenja putničkog prostora (HVAC sustavi). Stoga se električna vozila opremaju novim, energetski učinkovitim, integriranim HVAC sustavima, koji se trebaju optimalno upravljati radi postizanja maksimalne energetske učinkovitosti uz zadržavanje visokog stupnja toplinske ugode. U radu se prvo prikazuje novi koncept HVAC sustava temeljen na principu dizalice topline koji osim hlađenja omogućava i grijanje putničkog prostora. Za modelski zasnovano optimiranje i upravljanje postavljaju se upravljanju-orijentirani modeli predmetnog HVAC sustava koji se parametriraju na temelju detaljnog fizikalnog simulacijskog modela. Zatim se provodi numeričko optimiranje upravljačkih varijabli, koje se temelji na dinamičkom programiranju te daje uvide u optimalno ponašanje sustava u zimskim i ljetnim okolišnim uvjetima, kao i temeljne smjernice za sintezu sustava upravljanja. Prvi predloženi sustav upravljanja uključuje kaskadnu regulaciju temperature zraka u putničkom prostoru vozila uz optimalnu alokaciju upravljačkih ulaza i podređenu regulaciju HVAC sustava. Mape optimalne alokacije formiraju se van realnog vremena primjenom višekriterijskog optimiranja na temelju genetskog algoritma i detaljnog fizikalnog modela, pri čemu se u prvom problemu optimiranja maksimizira koeficijent učinkovitosti HVAC sustava, a u drugom problemu minimizira potrošnja električne energije i indeks toplinske ugode. Drugi predloženi sustav upravljanja uključuje nelinearno modelsko prediktivno upravljanje (NMPC), koje zadaje reference podređenim regulacijskim krugovima HVAC sustava. NMPC minimizira potrošnju električne energije i indeks toplinske ugode, uzimajući u obzir dinamiku i ograničenja sustava te postojanje informacije o poremećajnim varijablama na pomičnom vremenskom horizontu u budućnosti. Projektirani upravljački sustavi podrobno su ispitani u simulacijskom okruženju. K tome, sustav kaskadne regulacije s optimalnom alokacijom upravljačkih ulaza implementiran je na eksperimentalnom električnom vozilu B klase i ispitan u laboratorijskim uvjetima. Consumer acceptance of electric vehicles is increasing strongly, with the trend bound to continue in the future due to beneficial regulations, government incentives, and consumer's awareness and willingness to shift towards sustainable mobility. Although the innovation in automotive industry is accelerating and the declared range of current battery electric vehicles (BEVs) is increasing, their mass market share is still hindered due to long and widely unavailable charging and end-users’ perception of lacking BEVs range. The already restricted driving range of BEVs is significantly reduced in extremely hot and cold ambient conditions due to high energy consumption of the heating, ventilation and air-conditioning (HVAC) system. To overcome the BEV range reduction in extreme weather conditions, new energyefficient HVAC systems have been developed recently for improved cabin heating and cooling efficiency. These are typically vapor-compression cycle-based heat pump systems with integrated cabin, battery, and powertrain thermal management, and they support operation in both heating and cooling mode. The advanced BEV HVAC systems are characterized by an increased number of actuators, which makes the energy management and control system design more challenging. To minimize the power consumption at a favourable level of thermal comfort, it is necessary to develop new control systems that can optimally coordinate multiple and often redundant actuators of the HVAC system, and which utilize optimisation-based control methods, such as control allocation or model predictive control. The thesis first presents modelling of an advanced heat pump-based BEV HVAC system and a cabin thermal dynamics system, which paves the road for model-based optimal control system design. Next, dynamic programming-based offline control trajectory optimization is carried out to gain insight into the optimal control actions for various operating conditions and obtain guidelines for the design of online control systems. Finally, a cascade control strategy based on the optimal control allocation and a nonlinear model predictive control strategy are designed for the considered HVAC system. Both control systems are verified in simulation environments, while the cascade control strategy is also implemented in a B-segment BEV and experimentally examined in hot and cold weather conditions. The main aim of the thesis is to design optimal control systems for a passenger cabin heating and cooling system of an electric vehicle, which coordinate multiple redundant actuators, accounts for the dynamics and constraints of the overall system and utilizes predictive information such as vehicle's driving cycle and ambient conditions, in order to improve energy efficiency and maintain high level of thermal comfort in extremely cold and hot weather conditions. The thesis is organized in nine chapters, whose content is summarized in what follows. Chapter 1: Introduction. Outlines the motivation for the presented research and gives a literature review of the three main topics of the thesis, which are modelling, optimization, and control of BEV HVAC systems. Finally, it states the main hypothesis and overviews the thesis. Chapter 2: Functional description of passenger cabin heating and air-conditioning system. Presents the considered heat pump-based BEV HVAC system. The chapter first describes the working principle of two main operating modes: heating and cooling. Next, the main feedback control loops are defined, and the control system design requirements are described, including the considered thermal comfort index. Finally, two control system concepts, which are designed in the rest of the thesis, are proposed. The first concept is based on cascade control structure, in which the superimposed cabin air temperature controller commands the heating/cooling power to optimal control input allocation algorithm, which transforms the power demand into references for low-level feedback controllers and auxiliary open-loop control inputs. The second concept is based on nonlinear model predictive control (NMPC) that regulates the cabin air temperature and replaces the superimposed cabin air temperature controller and optimal allocation, while directly setting the references for low-level controllers. Chapter 3: Modelling of passenger cabin heating and cooling system. Outlines several simulation models used in the thesis. Detailed physics-based HVAC system model, developed within a wider project team and implemented in Dymola environment, is used for the purpose of control system simulation verification, multi-objective optimisation-based control input allocation design, and low-order models' parametrization. The low-order control-oriented models are used for the low-level HVAC control system design, control trajectory optimization and NMPC system design. The low-level HVAC feedback control system design is based on a linear autoregressive model with exogenous inputs, which describes the cabin inlet air and superheat temperature transients with respect to compressor speed and electronic expansion valve control inputs. Next, nonlinear HVAC system models of first and second order are presented, which describe the low-level controlled cabin inlet air temperature dynamics including the superheat temperature control loop. Model parameters (time constants and damping ratio) are determined by means of numerical identification procedure, which is based on detailed physics-based simulation model responses for a large set of operating points. The obtained model parameter maps are fitted by appropriate analytical functions. Next, nonlinear regression models of HVAC system power consumption and PMV thermal comfort index are presented, which are needed for the sake of cost function formulation. Finally, nonlinear singlezone cabin models of first and second order are presented. The first-order nonlinear cabin model describes the cabin air temperature transient process, and it is used in control trajectory optimization, whereas the second-order model additionally describes the cabin body temperature transient process, and it is used in NMPC system design. Chapter 4: Control trajectory optimization. Proposes a dynamic programming-based (DP) method for optimization of HVAC system control trajectories. The HVAC system and cabin dynamics are represented by the first-order nonlinear models, and the DP algorithm is implemented in C++ programming language to enhance the computational efficiency. The cost function reflects the following two conflicting criteria: PMV-based thermal comfort index and HVAC system energy efficiency. Two approaches of accounting for the energy efficiency are considered: (i) through maximization of HVAC system coefficient of performance (COP) and (ii) via minimization of HVAC system electric power consumption. Minimization of the DP cost function is subject to hard constraints on control variables, as well as constraints that reflect a limited HVAC operating range. Control trajectory optimization is carried out for winter and summer ambient conditions, and different cost function setups, thus yielding Pareto optimal frontiers. The optimization results are analysed with the aim of gaining insights into the optimal control performance and obtaining guidelines for control system design. Chapter 5: Optimal control input allocation. Proposes an offline multi-objective genetic algorithm-based optimization method for generating control input allocation maps. According to the cascade control concept, the inputs to optimal control allocation are the cooling or heating power demand, and the cabin air state determined by temperature and relative humidity. The optimization method relies on detailed physics-based HVAC simulation model, while cabin model is omitted as cabin air state is reflected by an operating point for which the optimization is conducted. Firstly, the COP is maximized in both operating modes to obtain optimal control inputs, which include cabin inlet air temperature reference, blower fan air mass flow, secondary coolant loop pumps’ speeds and main radiator fan power level. The obtained optimal control input allocation maps are fitted by proper analytical functions to facilitate implementation and calibration. Additionally, multi-objective optimization is carried out with the aim of simultaneously minimizing the HVAC power consumption and the thermal comfort index. In this case, infrared heating panels' (IRP) control inputs are considered, as well. The multiobjective optimization yields Pareto optimal frontiers, which are analysed with the aim of gaining insight into potential thermal comfort improvement when utilizing infrared heating panels and providing guidelines for online thermal comfort control system design. Chapter 6: Hierarchical control strategy design. The optimal control input allocation maps, obtained in Chapter 5, are incorporated into a proper cascade control strategy. This chapter first outlines the design of a superimposed cabin air temperature feedback controller and a PMVbased feedback controller acting through IRPs. Next, the design of low-level feedback controllers is presented, including optimization-based design of gain-scheduling maps. The cascade control system performance is verified through simulations in heat-up and cool-down scenarios, which start from ambient conditions and last until the thermal comfort is reached. The impact of various superimposed controller and control allocation setups on energy consumption and thermal comfort metrics is analysed. Finally, steady-state simulations are carried out to analyse the extent to which the cabin air temperature reference can be lowered for reduced power consumption, where the thermal comfort degradation is compensated for by applying IRPs. Chapter 7: Nonlinear model predictive control (NMPC). Presents the design of NMPC-based HVAC system control strategy. First, the optimal control problem is formulated, and it includes optimization of cabin inlet air temperature and mass flow trajectories on a receding horizon, which simultaneously minimizes the thermal comfort index and the HVAC system electric energy consumption. NMPC accounts for the HVAC system and cabin dynamics, a limited HVAC operating range and predictive information about disturbances, such as vehicle velocity and ambient air temperature. Next, transformation of the optimal control problem into a nonlinear program based on the direct multiple shooting method is presented. Finally, the NMPC system is verified in winter and summer ambient conditions for different cost function settings, and it is compared with cascade control strategy. Chapter 8: Experimental verification of cascade control strategy. Presents implementation of the cascade control strategy, designed in Chapter 6, within an experimental B-segment battery electric vehicle (BEV). The chapter first describes the experimental vehicle and its control hardware system, consisting of the main computer, which is used for HVAC system control and human-machine interface communication, and an electronic control unit, which communicates with actuators and sensors and contains safety features. Then, details of cascade control strategy implementation within the control hardware are presented, including implementation of practical modifications, such as safety-related refrigerant pressure controllers and robust HVAC system start-up procedure. Results of initial commissioning of the control strategy are presented, which are the basis for additional control strategy calibration. The modified control strategy is experimentally validated in a climate chamber in hot and cold ambient conditions, and the obtained performance metrics are analysed. Chapter 9: Conclusion. Gives the concluding remarks, outlines the possible future work directions, and states the following main contributions of the doctoral thesis: (i) dynamic programming-based control trajectory optimization algorithm for a passenger cabin heating and cooling system of an electric vehicle, which minimizes the electric energy consumption and provides a high level of passenger thermal comfort; (ii) a cascade control strategy of passenger cabin heating and cooling system based on a superimposed cabin air temperature controller and optimal allocation of references for low-level controllers; (iii) an optimal control strategy of passenger cabin heating and cooling system based on model predictive control, which coordinates multiple actuators with the aim of increasing vehicle driving range while maintaining high level of passenger thermal comfort. |
