In-vehicle power management: In-vehicle power control and power design standards

Today, fleet management innovation has made great progress. Whether trucks, buses, taxis or other means of transportation, they all use wireless satellite positioning systems, which allows dispatchers to understand the location, status and fuel consumption of all vehicles, thereby greatly improving the control and management of the fleet. Passengers are also better served. Display screens can provide a variety of entertainment content, as well as practical, real-time information, such as departure and arrival times, weather bars and emergency notifications.

The above-mentioned in-vehicle systems require a complex power management solution. The new Advantech ARK-1388 embedded industrial computer designed for in-vehicle applications can provide different customers with very flexible and safe startup and shutdown time settings through microcontroller-based hardware and software. The startup and shutdown process is directly controlled by the vehicle battery status and ignition status. In addition, the ARK-1388 can support both 12 V and 24 V vehicle battery systems. This new power management system is mainly suitable for taxis, trucks, mining cars and buses.

Challenges of Power Management Systems

Regardless of the operating conditions, the electrical systems of motor vehicles must meet demanding power requirements, such as load dump, cold start, and low power consumption in standby mode . How can we avoid load dump caused by disconnecting the battery cable when charging the switch? How can we protect the electrical system, such as the built-in car air conditioner, when the voltage is suddenly too high or too low? How can we ensure the stability and safety of the vehicle equipment? The following will explain.

General limitations of automotive power supply design

For example, the voltage transient range (VIN) of a 12 V battery power line is very wide, ranging from 6 V to 87 V. Typical vehicle power systems often operate in the 9 V to 16 V range. The normal nominal voltage of the battery is 12 V when the engine is off and 14.4 V when it is started. However, this range can easily expand to more than 80 V peak during transient conditions.

Figure 1: Analog input voltage

As the number of electronic control units (ECUS) in vehicles increases dramatically, the total current of the vehicle battery also increases, which affects the quiescent (IQ) and shutdown (ISD) current budgets. When the engine is off, some electrical system units are still running, which also consumes the battery. To control the quiescent (IQ) current budget, most users set the maximum value of the IQ of a single ECU. Devices such as CAN transceivers, real-time clocks, and microcontrollers can consume most of the IQ budget of the ECU, so the IQ budget of the power supply can be minimized. ARK-1388 monitors the status of the vehicle power supply through the microcontroller, so the power consumption in sleep mode can be less than 10 mA.

To solve these problems, designers have had to use separate vehicle power modules to connect electronic devices to the vehicle power system. These external modules, which are mostly customized, are easily damaged when subjected to shock and vibration, thus weakening the stability of the vehicle system.

This additional module also brings additional expenses to manufacturers and takes up space in the vehicle. Advantech products use an integrated solution with hardware power protection and software intelligent monitoring functions to ensure safe startup and shutdown.

Tested and certified according to ISO 7637

The ISO-7637-2:2004 standard specifies the testing of the compatibility of equipment in passenger cars and commercial vehicles with 12 V or 24 V electrical systems with electrical transients. Levels of immunity to transient failures are also defined. The standard applies to all road vehicles with electrical systems, regardless of propulsion mode.

Annex 2 of the ISO-7637 standard describes how to distinguish the functional states of vehicle electronic equipment. Different test conditions describe the possible system operating environments. The functional states are divided into several categories, and the corresponding failure mechanisms are also different. The selected test level and test time can be defined according to the agreement between Advantech and the vehicle manufacturer.

The ARK-1388 embedded computer has been tested for 12 V and 24 V battery systems. One test is a transient simulation when the inductive load is disconnected from the power supply . One test is a simulation of the sudden interruption of the current in the test device parallel to the device due to the inductance of the connected wiring . Another test is a transient simulation when the DC engine acts as the power source after the ignition is turned off. The results of the simulated conversion process show that transients can occur and are affected by the distributed capacitance and the inductance of the connected wiring.

If no specific value is defined, it is recommended to use the levels in columns I to IV. ARK-1388 passes test level III for 12 V and 24 V systems; please refer to ISO-7637-2 certification for detailed specifications of each test pulse.

Figure 2: Test levels in ISO-7637-2 for 12 V / 24 V systems

Advantech Hardware Power Design

The on-board power protection mechanism can check and monitor various system conditions and issue fault alarms.

The power protection mechanism prevents the device from possible damage caused by reverse polarity. This mechanism allows the DC-powered device to operate normally even if the battery is installed upside down or the DC power supply is connected reversely.

The equipment is also equipped with a surge protector to protect it from damage caused by voltage spikes. This mechanism regulates the voltage to the electrical equipment by suppressing or shorting the voltage to ground if the voltage exceeds a safe value.

Cold cranking is a prominent problem in automotive environmental applications. When a vehicle engine is cold or frozen for a period of time, the oil becomes very viscous, requiring the engine to increase output torque, which in turn increases the battery current. This high current load can drop the battery voltage to 6 V at ignition and then return to the rated voltage of 13.8 V (typical). However, some subsystems require a constant voltage of 5 V throughout the cold crank process, which is when problems arise. This includes applications such as ECUs, environmental and emergency system microprocessors, which are closely related to vehicle safety and performance.

Advantech's ideal power solution also supports load dump. Load dump occurs when the switch is charging while the battery cable is disconnected and there are other current loads on the circuit . The battery may be disconnected while the engine is running due to cable corrosion, unstable connection or intentional disconnection. If the battery is suddenly disconnected while the switch is charging, the instantaneous voltage peak can be as high as 80 V. Most computer systems may crash in this situation. The load dump amplitude depends on the switch speed and the current collection when the battery is disconnected. The load dump pulse duration mainly depends on the duration and pulse amplitude of the current collection circuit. The load dump amplitude of most new switches is limited by the additional limiting diode .

Advantech Software Power Design

In addition to the hardware Power Management function, Advantech products also feature software intelligent monitoring. The installed microcontroller stabilizes the onboard power system. The user-friendly utility interface allows users to set the timing and voltage by themselves. For example, multiple power groups with delay time can be set through the utility and hardware jumpers. An alarm will be issued when the setting is overwritten.

The user can set the power supply to "vehicle mode" or "ATX mode" via a jumper. When set to "vehicle mode", the microcontroller-based PIC software checks the vehicle's ignition and battery status. Before the system starts, the software automatically determines the battery type and checks whether the threshold voltage is 12 V or 24 V. If the battery voltage is sufficient to start the system, the software checks the ignition status. The ignition voltage set in the utility is high, such as more than 8 V. The software ensures that the computing system does not automatically start before the ignition is turned on. When switching the ignition on and off, the system power starts smoothly. The timing state for stabilizing the voltage can be set to the default value, such as after 10 s. If the voltage does not stabilize after the set value, the system automatically shuts down.

When the system is running, the PIC software will continuously monitor the battery voltage status. If the battery is low, the driver will be notified and the system will automatically shut down within the set time.

The PIC software also checks the ignition status. When the vehicle ignition is turned off, the operating system will delay shutting down and completely shut down after the data is saved. The delay time is 30 seconds (power-off delay) to 180 seconds (hard power-off delay), depending on the software settings. If the system cannot be shut down smoothly for some reason, the hard power-off delay setting will ensure that the data is automatically forced into standby mode to avoid the battery being exhausted and the car being unable to start.

Advantech Embedded Computer Manager provides a user-friendly interface for XP/XPe environments; displays power supply voltage level, ignition, and battery status as needed; adjusts minimum voltage based on battery status; delays startup/shutdown timing based on application purpose; and can send alerts to the server via UI messages or emails.

System functions of embedded industrial computers

Advantech Power Management The solution is based on a powerful and flexible embedded industrial computer product line, which is particularly suitable for diverse and demanding in-vehicle environment applications. The main advantages of embedded industrial computers are compact structure, high reliability, passive cooling and effective heat dissipation. According to the IMS survey report, the best market for embedded industrial computers in the next few years is in the transportation and infrastructure fields. Embedded rugged embedded industrial computers make this trend clearer with their practicality, vibration resistance and suitability for harsh environment applications. Digital signage and customer information systems are currently popular applications for embedded industrial computers.

Advantech embedded industrial computers are compact, rugged computers that run embedded operating systems such as Windows? CE, Windows? XPe, or Linux Embedded.

Embedded industrial computers greatly improve the performance of harsh environment applications. Industrial computers do not integrate hard disks or rotating components, so they are more resistant to shock and vibration. The fanless IPC design, aluminum housing, and limited internal wiring ensure high reliability in multiple applications. Due to its good heat dissipation performance, industrial computers are dedicated to outdoor and automotive applications. Advantech provides ARK embedded industrial computers with scalable computing and I/O performance and full-featured functions.

The new ARK-1388 embedded industrial computer belongs to the ultra-compact ARK-1300 series and is particularly suitable for space-constrained applications. The low-power computer solution integrates an Intel? Celeron M ULV 423 or Intel? CoreTM 2 Duo U7500 processor (with 1.06 GHZ clock frequency), Intel? 82945GM chipset , and onboard 2 GB DDR 2 memory.

The embedded industrial computer provides flexible installation space for GSM/GPRS/EDGE or UMTS/HSDPA modules and features a 50-channel GPS function for easy integration of special navigation modules. The product complies with 802.11 b/g WLAN specifications for wireless LAN communication. The front panel also features VGA and 18/36-bit LVDS interfaces for easy connection of a display or touch screen. The ARK-1388 supports dual independent displays, one for the driver and one for the passenger. In addition, the device features 4 USB 2.0 interfaces, 4 serial ports, 4 isolated digital inputs and 2 digital outputs with relays . For entertainment and customer information, the ARK-1388 audio outputs are connected via a 6 W stereo left and right channel amplifier to help overcome noise issues. Data storage is up to 8 GB via a CF card.

Advantech's embedded industrial computer ARK-1388 can operate normally in a wide temperature range of -20°C ~ 60°C (Intel? Celeron M processor), or up to 55°C (Intel? Core 2 Duo CPU), and supports a wide power input range of 9 V ~ 32 V.

For in-vehicle applications, ARK-1388 can control media and information systems and download data via UMTS/HSDPA or GSM/GPRS/EDGE. The industrial computer also integrates a power control mechanism that can monitor the vehicle engine and battery status. The startup/shutdown delay sequence can be quickly set through the utility.

Figure 3: ARK-1388 vehicle-mounted embedded industrial computer

in conclusion

Advantech's integrated solution replaces the external power management module and ensures the stability of in-vehicle applications. The compact ARK-1388 embedded industrial computer system not only saves space, but also avoids additional expenses. Its industrial computer specifications support wide temperature operation and are shock and vibration resistant, making it an ideal choice for in-vehicle applications.

The on-board power supply design has hardware power protection and software intelligent monitoring functions to ensure safe startup and shutdown.