The steady rise in oil prices and environmental issues now force the automotive design and production industry to take electric vehicles and electric trucks seriously. However, the specific design challenges caused by electric vehicles and hybrid vehicles far exceed traditional power vehicles. A new electrical architecture design that is not referenced in previous industrial records brings new risks. Therefore, it is necessary to reduce the risk as much as possible and evaluate the virtual test environment of the design choice before the car is launched.
Battery performance is critical to the success of electric vehicles and hybrid vehicles. The three major elements of battery performance include battery energy density (in kilowatt hours (kWh)), battery life, and cost. Only when these three major factors have been significantly improved, hybrid cars can be widely popularized.
Cars should choose the right battery type. For pure electric vehicles like Tesla, batteries tend to be larger and more powerful. These batteries are often exhausted and then recharged. Since there is no alternative source of power for this type of vehicle, it is important to calculate the amount of electricity near the "depletion" point. The voltage of these batteries is often greater than 300 volts (V) and the capacity is up to 60 kWh.
In comparison, the battery power of hybrid vehicles is lower. The battery of a hybrid vehicle may only go through 1,000 deep cycles during its lifetime, but the shallow cycle may be as high as 1 million times, and it will never really reach the full discharge state, and often cannot reach the full charge state. The voltage of a hybrid car battery is generally greater than 144 V, and the capacity is up to 10 kWh-far lower than the electric car battery, because the hybrid car is equipped with alternative power sources.
Power management of electric vehicle or hybrid vehicle batteries will become a key issue in the future. One of the main points of power management is to control charging and power generation; for example, when a car brakes, it must control the regenerative power that is fed back into the battery pack. The in-vehicle communication network must be further strengthened to control these systems and provide car charging status information to drivers who are driving or not in the car. In addition, such information also needs to be fed back to the dealer to understand the health of the battery pack.
Auxiliary facilities such as cabin temperature, steering, and entertainment, which are often overlooked by traditional heat engines, will need batteries to provide power and therefore also need to be managed. It may also include an improved navigation system for calculating the most effective route to manage power, help the driver find the nearest charging station, or calculate the distance to the destination to ensure that the vehicle has sufficient power. Driven by these needs, electric vehicles and hybrid vehicles will strengthen the design of electrical engineering content and the calculation of road traffic conditions.
Customers hope that short-term original equipment manufacturers (OEMs) will be able to provide "extended range" hybrid vehicles and plug-in hybrid vehicles. These types of vehicles combine traditional engines and electric motors, but are more complicated in terms of electronic construction than traditional cars that will be replaced.
Key design challenges
A major challenge for design engineers is to overcome mileage concerns, which means that they need to simulate driving cycles to maximize the mileage and performance of vehicles using existing power sources.
Another design challenge is the need to reduce electromagnetic interference and to be able to simulate and prevent the effects of high current and voltage switching.
Safety is a top priority for design engineers. They must be able to ensure the safety of people in all environments, including high currents and voltages, especially in the event of failures and collisions.
Increasing electrical complexity puts forward more requirements for structurally optimizing vehicle layout design. Designers are therefore under pressure to reduce vehicle costs and weight across the board.
Eventually, the increase in vehicle electrical design content will create more demand for the vehicle network, so it is increasingly important to reduce costs and ensure that the network can perform effective functions as required.
Electronic design automation tools can be used to solve these challenges. Mentor ’s Capital Tools Suite (Capital®) provides a comprehensive solution for power distribution system (EDS) design, covering system requirements, features and functions, as well as upstream processes such as logical and physical architecture, and downstream processes such as manufacturing and service (Figure 1).
Figure 1: Distribution system design tools such as Capital cover the entire vehicle production process from concept to customer service
Run multiple driving cycles
Design engineers need to be able to simulate the effects of vehicle electricity and charging. Usually this involves acceleration and braking when going up or downhill. They also need to be able to manage high-power auxiliary equipment; if it is a hybrid car, it may require traditional engine starting, of course, heating and air conditioning equipment in the car, and it must be able to provide a system that used the traditional heat engine to provide power. Such as power steering and brake assist systems, power seats and windows, lights and wipers. Low-power systems also need simulation, which may include navigation and entertainment, parking assistance systems, radar and telephones.
The first step in the simulation is to create a data book containing many optional battery types for vehicles, including lithium-ion batteries and nickel-metal hydride batteries. These batteries can be simulated in tools such as Capital with a high degree of complexity; for example, the effect of temperature on the battery can be simulated.
The second step is to design the vehicle circuit, and then build and attach the simulation model to the equipment in the system.
The third step is to integrate multiple systems representing various parts of the vehicle. Depending on the complexity of the customer's matching options, it may be necessary to build a variety of systems that are suitable for "extremely complex" vehicle configurations.
The fourth step is to build a demand model for any system that needs to be simulated. For example, Capital supports simulation scripts, so it can run multiple driving cycles and automatically run in various situations. The battery condition can be monitored and reported throughout the driving cycle simulation.
The fifth step is to analyze the data results, and then make a correct judgment to select the battery that meets the requirements for the vehicle.
Reduce electromagnetic interference
In electric vehicles and hybrid vehicles, the combination of high voltage and current switching combined with low-level network signals will bring a higher risk of cross-coupling between signals, which can cause various problems, such as the emergence of individual components or the overall system malfunction. The design goal is to minimize interior and radiated interference. Design engineers must also meet the strict standards put forward by various institutions, such as the International Organization for Standardization (InternaTIonal OrganizaTIon for StandardizaTIon, referred to as ISO) and the Society of AutomoTIve Engineers (SAE).
When the "energy radiator" (energy source) finds a "path" to a "receiver" that reacts in some unexpected way, electromagnetic interference problems arise. In general, designers can only control the path, because the energy source and receiver specifications are generally fixed to meet performance, weight, and cost requirements.
The layout and spacing of energy source and receiver devices can affect electromagnetic interference behavior. At the beginning of the architecture creation phase at the beginning of the design cycle, design engineers can use electrical design tools to create custom spacing limits based on the spacing rules for specific devices.
Software such as Capital has multiple functions that can help mitigate these effects; most of these functions focus on the coupling path between the energy source and the receiver or devices affected by electromagnetic interference. Reasonable layout is an effective way to control the influence of electromagnetic interference. A recent report issued by the Automotive Industry Research Association (MIRA) recommends that the distance between electronic drive components and the motors they control be as close as possible. The ideal grounding design can also effectively control electromagnetic interference. Capital software provides automation functions that support rule-based equipment and grounding layouts, ensuring the best solution for all vehicle designs.
Signal routing can also be used to control electromagnetic interference. Sometimes, the signal must be far away from the noisy area or sent through a separate wiring harness in order to prevent cross coupling between high and low voltage. At the beginning of the architecture development stage, Capital can provide support for rule-based signal routing; and as the physical design continues to improve, it can also support signal separation and encoding output to 3D MCAD tools. Many of these functions were initially used in aeronautical design and are currently used by many leading companies. Electrical data can also be exported from one tool to another tool for electromagnetic interference estimation and simulation.
Sometimes it needs to be shielded. Although shielding is an effective method of controlling electromagnetic interference, its cost is high; however, electrical design tools such as Capital can accurately estimate costs, allowing design engineers to conduct a series of comparative studies before selecting the best method.
Ensure a safe environment in all situations
The high voltage and current of electric vehicles and hybrid vehicles can pose a devastating risk of electric shock. Exposure to direct current higher than 80V can be fatal. Since some electric vehicles and hybrid vehicles can reach 600V DC, all possible safety conditions must be considered and designed for.
Tools such as Capital can accurately simulate the power impact caused by a fault. For example, collisions cause the grounding system to fail, and because of the coupling with the DC voltage, some of the vehicle bodies have a very dangerous energization situation. Incorrect design or unexpected circuit behavior may cause electric shock. Failure mode and impact analysis (FMEA) can be used to accurately determine and prioritize potential failure modes. Failure modes and impact analysis are generally time-consuming, but now they can be automated through some electrical design tools. Based on the results of the failure mode and impact analysis, you can better understand the most important design issues and provide the necessary feedback so that the design engineer can correct them by modifying the design.
Simulation also allows designers to predict the electrical impact of design errors, such as latent circuits, switches, and loads in some way that can lead to unexpected operation or failure of an electrical function, resulting in a series of consequences-from the driver's helpless More serious consequences such as the failure of important safety-related functions such as lights.
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