I. Introduction Touch screen technology enables direct interaction with devices through touch. Using either capacitive or resistive methods, these screens detect user input, translating it into commands. Widely used in smartphones, tablets, and kiosks, touch screens offer intuitive navigation, eliminating the need for physical buttons and enhancing user experience across various applications. Understanding how touch screens work is crucial for users and developers alike. It enhances user experience by ensuring effective interaction, informs choices in device selection, and guides troubleshooting. For developers, knowledge of touch technology is vital for creating intuitive applications and improving interface design, ultimately leading to greater user satisfaction. This blog aims to explore why touch screens predominantly respond to fingers, delving into the science behind touch sensitivity. By examining the principles of capacitive and resistive technology, we will uncover the
Introduction:
The growth of urban sprawl and
pollution in big cities is raising public awareness to a more stable mobility
solution, which means more efficient use of energy, reduction in pollutants and
continued driving development of electric vehicles (EVs). With a view to
achieving 100 million EVs on international roads by 2020 (IEA and EVI, 2013),
the automotive industry has set the bar high for the public bookings about
electromobility so as the battery technology is in high demand. Next to the
development of chemical and technological advances in mobile battery
technology, battery management system (BMS) is the main protector of the EVs
battery system, tasked with verification reliable and safe operation of connected
battery cells to deliver high currents at high voltage (HV) levels (the term
“battery management system” has no universal meaning and is generally understood to refer to any system responsible
for monitoring, control, and protection of battery cells, either individually
or connected to make battery systems).
Definition
Battery
management system (BMS) is a technology that provides effective monitoring of
the battery cells and optimizes battery performance. BMS helps us in monitoring
the following parameters:
1. SOH:
State of health
Why is BMS needed?
1. To increase safety and reliability of battery systems.
2. To protect individual cells and battery systems from damage.
3. To improve battery energy usage efficiency (i.e., increased driving range).
4. To prolong battery lifetime.
What does
BMS do?
BMS is mainly responsible to monitor and execute all
the tasks that are required for the safety and efficient use of battery pack.
They are depicted below.
As the basis for the extensive processing and
management of BMS data, accurate measurement of external battery parameters is
very important. Next to the cell voltage and current, the maximum temperature
in the hot or cold areas inside the pack should be measured and measured with
additional parameters or additional sensor values (e.g., humidity sensor,
coolant temperature sensor) inside the battery pack or other application
parameters. (e.g., speed, power, environmental conditions, and EV location
data) should be obtained using analog or digital I / O. Depending on the
application, shorter sample times in 10−3 s may be required to allow accurate
measurement.
2. Data processing and data storage
The power in the battery
pack depends largely on battery status parameters to be calculated from input
values for pre-installation or the use of complex algorithms or models, eg,
limiting battery power (charging status, or SoC) or battery depletion level
(health status, or -SoH). In addition, BMS can store cell / package usage
history (e.g., SoC and SoH history, cycle calculations, temperature profiles)
to allow high-level measurement algorithms based on previous usage data.
3. Electrical management
To
prolong battery life and increase efficiency, the electrical management is
responsible for controlling the charge and discharge processes, by limiting
the discharge current and controlling the charging current and voltage based
on the calculated battery states (e.g., SoC, SoH) and the input parameters. In
addition, the unavoidable charge imbalances between the individual cells in a
multicell system have to be equalized by the electrical management.
4. Thermal management
Most high-performance
battery applications require a thermal control system assigned to the function
of temperature measurement between cells, cooling batteries to prolong life and
prevent heat dissipation, as well as battery damage by excessive heat and
chemical reaction of batteries. The cooling system may be air-based or
water-based. Cold cooling makes it difficult to withstand the heat of the
electrolyte and plastic components in the cell, which limits the heat transfer
to the surface of the cells. Depending on the environment, cells may need to be
heated to bring the temperature into the operating window.
5. Safety management
As
mentioned, batteries are very sensitive to high and low power and overcurrents
and temperatures outside the specified operating window, so the main task of
managing safety is the monitoring of these variables and the protection of
batteries against these conditions. Safety management also includes battery
pack safety and corresponding trigger mechanism of fire extinguishing equipment.
6. Communication
Another
important function of the BMS is to communicate with other embedded control
systems of the vehicle or application, both on board and inside. Transfer
information may include battery status information (e.g., SoC, SoH) or
predictions (e.g., available power), while the vehicle may provide additional
BMS parameters (environmental conditions, power requirements, location data).
Special care should be taken to ensure the separation of the HV present in the
battery system at the low-voltage (LV) communication channels used by the
vehicle to ensure the safety of the user and the system. Internal diagnostic
services should be provided by BMS to allow for the storage of a battery pack.
Depending on the application, different systems are used for data exchange
(e.g., local area network control (CAN) / FlexRay for system connection between
analog and digital, digital input output or pulse frequency change signals in
sensors).
What is BMS in lithium batteries?
Lithium-ion batteries, the energy
storage technology of choice in the automotive industry for the use in EVs at
the moment and in the foreseeable future, are very susceptible to
overtemperatures, overvoltages (overcharge), undervoltages (deep discharge),
and overcurrents and can be damaged or can fail if exposed to these conditions.
Additionally, lithium-ion batteries have a reduced efficiency at low
temperatures, display a capacity fading effect, and an increase in internal
resistance with use over time. Even though the terminal voltage of individual
lithium-ion cells is higher than for other chemistries such as NiMH, multiple
batteries have to be connected in series to achieve the required higher
voltages for use in an EV electric drivetrain and may need to be parallelized
to increase the available capacity. There is no common nomenclature for
multicell battery systems: In this chapter, the term “battery module” or
“module” is used to describe a unit of up to 12 series connected cells with a
total voltage of maximum 60 V, and the term “battery pack” or “pack” is
employed to describe a unit of multiple modules connected to form an HV battery
system with up to 600 V total voltage.
The stringent operating conditions of lithium-ion batteries (which, in large part, applies to other battery chemistries as well) together with the aforementioned objectives lead to a group of requirements that have to be met by the BMS.
How does BMS work?
The whole BMS is divided into
three categories, cell monitoring unit (CMU), module management unit (MMU) and
pack management unit(PMU).
CMU: One CMU is connected with
each cell which measures temperature, voltage, SOH of each cells.
MMU: A group of CMU is controlled
by MMU, usually between 8 to 12 cells. It also helps in intercellular
balancing.
PMU: It controls all the MMUs and
communicates with the external systems and also monitors the pack voltage, current
and takes suitable actions for safety aspects.
There are four different ways in
which battery management system work. They are narrated one by one as below.
1. 2. Modular:
A few controllers, each handling certain number of cells with communication
between the cells.
2.
3. Distributed:
A BMS board is installed at each cells, with only communication cable between
battery & controller.
3. 4. Master-Slave: One master controller is connected to the slaves and the saves are connected to cells.
Battery management system works in four different modes as
below.
Idle mode: BMS performs all the functions except allowing
current.
Charge mode: BMS performs all the functions and allows
current from Charger to the battery Pack.
Discharge mode: BMS performs all the functions and allows
current from the battery Pack to the Load.
Error Mode: BMS performs all the functions except allowing
current and doesn’t allow entering into Charge or Discharge mode unless all the
Errors in the system are resolved.
What sensors are used in battery management system?
For thermal management in BMS, Thermistors is widely
used due to its versatility, lower cost, and easy implementation. A voltage
divider is normally used to bias it. To rail high voltage, op-amp (popularly OPA4197)
is used. The current sensors like ACS712 can be used but preferably Smart BMS
SOC Indicator are employed.
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