Teknomadix BMS has higher functions such as monitoring battery internal and ambient temperature, controlling the charge rate of a connected battery charger, monitoring and recording usage data, and remote diagnostics. The BMS works as a guard, in a cooperation with other in vehicle systems that provide battery protection, generate status signals, warnings, or disconnect the battery from the load or charge source should any of the parameters the BMS is monitoring become out of the set bounds.
It is necessary to understand what needs to be controlled by the BMS and why it needs controlling. This requires a deeper understanding of the fundamental cell chemistries, performance characteristics and battery failure modes particularly Lithium battery failures. The battery can not simply be treated as a black box.
Automotive batteries require the most demanding management from a BMS. It has to interface with a number of other on board systems, and it has to work in real time in rapidly changing charging and discharging conditions.
As a vehicle accelerates and brakes frequently, it operates through harsh and uncontrolled environments. This is in stark contrast to a home solar battery bank or an emergency backup battery system such as in a hospital or computer data center.
A proper BMS in a battery powered electric vehicle has a lot of responsibility:
Teknomadix BMS design incorporates a lot more functions than simply managing the batteries charge. It can determine the vehicle's location, desired operating mode, whether it is accelerating, braking, idling or stopped, and implement remote cellular controls over the power management system.
Automated Cell Protection
The prime function of our BMS is to provide the necessary monitoring and controls to protect the battery cells from out of tolerance ambient or operating conditions. This is of particular importance in automotive applications because of the harsh working environment. As well as individual cell protection, the automotive system must be designed to respond to external fault conditions by isolating the battery as well as providing a service technician information for addressing and repairing the cause of the fault. For example cooling systems can be turned on if the battery approaches an overheat state. If the overheating becomes excessive then the battery can be remotely disabled.
Multi Level System
The BMS is part of a multi level system with the following general safety objectives and safeguards;
BMS Hardware - Fail safe back-up
Battery Monitoring Unit (BMU), the Battery Control Unit (BCU) and the CAN bus vehicle communications network interface with the rest of the vehicle energy management systems.
The BMS is also coupled to other vehicle systems which communicate with the BMS via the CAN bus vehicle network such as the Thermal Management System and anti theft or lockout devices which physically disconnect the traction battery.
Battery Monitoring Unit
The Battery Monitoring Unit is a microprocessor based unit incorporating three functions or sub-modules. These sub-modules are not necessarily separate physical units but are described separately for clarity.
The Battery Model characterizes the behavior of the battery in response to various external and internal conditions in a software algorithm. The model can utilize these inputs to estimate with a high accuracy level (98%) the status of the battery at any instant in time.
The SOC is determined by integrating the current flow over time, modified to take account of the many factors stored in the battery log which affect the performance of the cells, then subtracting the result from the known capacity of the fully charged battery. This is described in detail here SOC.
The battery model uses a log of past history for maintenance purposes or to predict how many miles the vehicle may run before the battery needs recharging. The remaining range, based on recent driving or usage patterns, is calculated from the current SOC and the energy consumed and the distance covered since the previous charge (or alternatively from a previous long term average). The distance traveled is derived from data provided by other sensors on the CAN bus
The accuracy of the range calculation is more important for EVs whose only source of power a single daily charge.
To reduce costs, instead of monitoring each cell in parallel, the BMS incorporates a multiplexing architecture which switches the voltage from each cell (input pairs) in turn to a single digital output line for sampling and comparison. Major cost savings are realized by reducing the number of control and sampling circuits keeping the overall system component count to a minimum.
The BMU also provides the inputs for estimating the SOH ( State of Health, or Cycle Count) of the battery.
The Performance Module, like the Battery Model contains a reference data set with all the tolerances and limits relevant to the various parameters monitored by the Battery Model. The Performance Module also takes instructions from the CAN bus such as commands from the Inverter Controller via the BMS to accept a regenerative braking charge or from other autonomous vehicle systems or directly from the vehicle operator. This unit is also used to set and to monitor the vehicle operating mode parameters.
The Performance Module allows the operator to program the system, with custom settings specific to the customer's application, and preferred driving style. The user may configure lower limits, to conserve energy and extend range. Raise limits to increase stopping torque from regenerative braking, or to increase acceleration and top speed.
The Performance module compares the status of the measured battery parameters from the Battery Model with the customized settings from the Performance Module. Logic circuits provide control to initiate cell protection actions or to be used in the various BMS feedback loops which drive the system to its desired operating point or isolate the battery in the case of unsafe conditions. These error messages provide the input signals for the Battery Control Unit.
Teknomadix BMS uses the CAN bus which was designed for communications between various internal functional systems in a vehicle. It also interfaces with external IOT systems for monitoring and control functions. The implementation of an always on or intermittent wireless Internet connection makes remote maintenance and service management for systems & equipment warranty especially ideal for OEM and after-market retailers. As well as providing a rich aggregate dataset that presents many unique opportunities for analysis.
The system also includes standard automotive On Board Diagnostics (OBD) with Diagnostic Trouble Codes (DTC) made available to the service technician. This connection allows technicians to identify any external causes of battery failure.
Battery Control Unit
The Battery Control Unit contains all the BMS power electronics circuitry. It takes control signals from the Battery Monitoring Unit to control the battery charging process and to switch the power connections to individual cells.
In its simplest form, the BMS provides a "binary" ON/OFF response to a fault or an out of tolerance condition such as an overload, merely isolating the battery completely by opening the main contactor switch. Progressive control provides more finite systems controls in the case of an out of bounds condition by utilizing the communications bus to modulate the demand on the battery pack to within acceptable tolerances.
Cell balancing is an essential function of the Teknomadix BMS. As noted above it is required to compensate for weaknesses in individual cells which could eventually cause the failure of the combined traction battery.
Master and Slaves
The master and slaves, organizes the cells into series parallel arrays with one slave managing each module.
©2020 Teknomadix Electric Innovations llc