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48伏特起动发电机
本篇我们首先测验考试了解为什么使用48伏特系统,然后介绍48伏特起动发电机的不同安装选项。

 2018-10-24

48伏特起动发电机

2017年,整个汽车行业都实现了显著增长–从汽车OEM到小型器件制造商。汽车电气化成为备受瞩目的热门话题,特殊是48伏特架构。事实上,在任何搜索引擎中搜索“48伏特”这个术语,您城市搜索到大量成果,这注解面向汽车系统的这个工程解决方案已在市场上占据了一席之地。

在前一篇“48伏特轻度混合动力系统的呈现”中,我简要介绍了新型48伏特汽车架构及其与现有12伏特系统的不同。在这篇我们的话题将触及确定新电压程度背后的原因,并深入探讨它的主要应用之一——48伏特起动发电机。

为什么是48伏特?
显而易见的首要问题是:“为什么偏偏是48伏特?”。这是一个非常主要的问题,要记住,在上世纪90年代,人们提出了42伏特电功率尺度来取代12伏特尺度。虽然这个尺度没有得到成长,但其意图是解决我们当今面临的一些不异问题,例如更大功率的电驱动配件及更轻的线束。选择48伏特作为尺度有两个主要原因 –安全性和效率。  

在提高电压时,涉及的一个主要问题是它可能危及人身安全。虽然有人仍在争论48伏特是否足够安全,但这个电压程度提供了我们需要的更高功率而没有进入“高电压”范围。图1显示了48伏特电池在不同电压程度下的工作情况。正如ZVEI的文档“电动出行的电压等级”所述,60伏特(直流)是安全上限最大值,高于它的电池电压都被视为过于危险。在“正常工作”范围内,电池能够达到最佳性能,但汽车内部的电子器件应该能够耐受最坏情况的高电压条件。

Figure 1: Safety voltage margins

As I’ve previously stated, the current 12-volt system is unable to cope with the growing demand for electrical power within conventional vehicles. However the 42-volt proposal was a complete replacement of the 12-volt electrical architecture while 48-volt complements it. The 48-volt battery simply adds an additional power source for new applications which also contribute to a smoother driving experience. Furthermore, the size and cost of wiring and components is significantly reduced due to the higher voltage of the 48-volt battery.

A closer look at the 48-volt starter generator options

Having a similar appearance as the car alternator (Figure 2a) but slightly bigger in size, the 48-volt starter generator’s initial topology position is at the engine’s belt. The belt-driven starter generator (BSG), also known as P0 architecture (Figure 2b) is a cost-effective solution which can provide up to a 15% reduction in CO2. Looking at some boost recuperation systems (such as Bosch’s), the maximum power ratings are around 10 kW for mechanical output in boost mode and 12 kW for electrical output during recuperation – both at 48-volts. While these numbers are rated for short periods of time, the BSG’s continuous power can reach up to 5 kW with maximum efficiency of 85%.

Figure 2a and 2b: Car alternator and P0 starter generator topology

However with tightening emission regulations, automotive Tier 1 suppliers have developed different starter generator topologies to further reduce the CO2 footprint of 48-volt mild hybrid vehicles. In ascending order, these configurations offer better emission reduction but become increasingly complex and costly.

Figure 3: 48-volt mild hybrid starter generator topologies

Crankshaft mounted starter generator (P1)

As the name suggests this solution has the starter generator mounted directly on the crankshaft (which converts the linear motion of pistons into rotary motion). This provides higher torque than the P0 architecture due to the absence of a belt drive, and with no belt losses there is greater efficiency. The maximum power required is 10 kW but the efficiency goes up to 94%. However one significant limitation of this solution is that torque requirements can be demanding, due to no torque/speed ratio between the crankshaft and the starter generator. An example of this topology is the 2010 Mercedes-Benz S400 BlueHybrid.

Shaft mounted machine (P2/P3)

Both P0 and P1 architectures are mounted on the engine, but there are other mounting options such as having the 48-volt electrical machine on the gearbox’s input/output shaft (P2/P3 respectively). By providing a mechanical disconnect, this translates to improved energy flow efficiency and allows for the provision of hybrid functions (e.g. e-drive).

 

The P2 architecture is ether integrated into the transmission on the input shaft or attached on the side, and results in increased energy recuperation and electrical drive capabilities. Mounting  the solution on the output shaft (P3), provides the highest level of the above-mentioned benefits. The obvious disadvantage of the shaft mounted electrical machine is the cost of integration.

Rear axle mounted electrical machine (P4)

The ultimate architecture at this time involves mounting at the rear axle drive (P4). This provides the vehicle with 4-wheel drive capabilities, with the combustion engine at the front and the electrical machine at the back. Maximum power requirement of the P2-P4 architectures can reach up to 21 kW with an efficiency of 95%. Moving the starter generator closer to the rear axle also provides more hybrid functionality to the vehicle. The new 48-volt machine is able to reduce the CO2 emissions by up to 21% in urban driving environment depending on its architecture.

What is more, this high-power application requires a significant portion of electronics to drive it. Naturally power MOSFETs play a key role in these electronic modules, but they need to be capable of withstanding worst case scenarios such as excessive currents and thermal leakages. Hence, the topic of my next blog will be to delve into the semiconductor content inside 48-volt applications such as the starter generator. Stay tuned!

作者:安世半导体 技术营销工程师 Ivan Petrov

Ivan近期获得曼彻斯特大学电气和电子工程专业工程学学士(荣誉)学位,其于2016年9月插手安世半导体担任技术营销工程师一职,并在短短的一年后晋 升为研究生营销工程师。他负责功率半导体业务的市场阐发。在过去的一年里,他颁发了几篇深受好评的传统动力系统陈述,并最先致力于汽车电气化这一迅速成长 的领域。Ivan对电动车(xEV)系统的了解来自于其静态研究、参与的众多xEV会议和全球客户拜访。在工作之余,他是一名活跃的网球选手,他的比赛风 格和外表曾被人拿来与罗杰·费德勒和格里戈尔·季米特洛夫比力。