Electrifying Auxiliaries: A flexible system approach for multiple auxiliaries

Sponsored by KEB

Traditionally, a combustion engine provides more than just traction power to the wheels for commercial vehicles. It powers smaller auxiliary loads from the drive belt such as the power steering pump, air compressor for brakes and suspension, HVAC compressor, and coolant pump. And for body equipment, an engine provides power via PTO to larger loads such as hydraulic pumps. But electric vehicles with a propulsion motor that are not constantly running means the auxiliaries must be independently controlled.   

Whether it is a delivery van, bus, heavy-duty truck, or mobile machinery, all of these vehicle types will likely have multiple auxiliaries. Additionally, vehicles could have variable configurations of equipment. KEB offers a flexible system approach to electrify multiple auxiliaries with the T6 Auxiliary Inverter. This paper examines each product feature and showcases the value it has for designers and system integrators.

Scalable and Modular Hardware

To support multiple auxiliaries, the T6 Auxiliary Inverter is designed to be a scalable and modular “system” solution. The system consists of multiple inverter output stages contained within a single housing. This means that one high voltage DC input supply to the system, one set of coolant plumbing connections, and one set of low voltage control connections. From a scalability standpoint, the T6 system can be scaled from a single inverter output to a maximum of six independent AC motor control outputs. And from a modularity standpoint, each inverter module has a power rating option of 7.5kW (16.5A), 15kW (33A) or 30kW (60A). Thus, there are 83 possible hardware system configurations.  

For multi-axis systems, there are several benefits to consider:

Reduced components – Compared with individually distributed inverters units for each auxiliary, a multi-axis system solution reduces redundant components such as DC cables, DC fuses, coolant plumbing, and low voltage wiring harnesses. A reduction in the number of components leads to a cleaner layout, a smaller footprint, less weight, fewer potential points of failure, lower maintenance, and a simplified installation process. 

Reduced cost – In addition to reducing the total systems cost by eliminating redundant components, a multi-axis unit itself becomes increasingly cost-efficient as the number of output modules increases. That is, the marginal cost to add additional power modules to a system goes down. Thus, a multi-axis inverter becomes a particularly attractive investment when controlling more than two auxiliaries. 

Flexible installation – The T6 Auxiliary Inverter does NOT need to be installed near the auxiliary motor. This flexibility is important where space is limited. Motor cable lengths up to 30 meters have been tested and approved, allowing the inverter to be remote mounted from the auxiliary motor. This is possible since electromagnetic compatibility (EMC) was given consideration in the design phases, such as integrated DC choke filters to mitigate electromagnetic interference, connector shielding and clamping, and shifted IGBT switching. Additionally, the T6 housing is IP67-rated for environmental conditions and therefore suitable for external mounting, such as the chassis frame or elsewhere on the vehicle.  

Flexible Motor Control Solutions

Since auxiliary motors come in different types, the T6 Auxiliary Inverter provides flexible options to control all types of AC motors with robust control and easy start-up. The supported motor types include induction motors, permanent magnet synchronous or servo motors, and synchronous reluctance motors which can be operated in speed, torque, or positioning control modes. All of these motor types and control modes can operate with sensorless motor control.

Sensorless control eliminates the need for a motor encoder (or resolver) by utilizing a model of the motor characteristics with current and voltage as feedback to provide closed-loop performance and has several benefits.  

Reduced cost, increased reliability – Eliminating the motor encoder and cable reduces system costs and eliminates a potential point of failure. It increases system reliability against factors to which an encoder may be susceptible, such as electrical noise, vibration, or temperature

Increased efficiency – Sensorless control is field-oriented or vector control which optimizes output voltage, therefore increasing power efficiency based on the actual operating load conditions.

Increased performance – KEB’s sensorless control algorithms are best-in-class, providing a highly dynamic speed control response and accurate torque control. This results in fast turn-on times for power-on-demand equipment recovering from energy-saving standby operation. It increases performance and productivity with tight regulation in response to load steps and faster operating cycle times. It also increases fault protection by mitigating current overshoot and has programmable current limits.   

Lastly, characterizing a motor for sensorless operation is easy with the T6 Auxiliary Inverter. The characterization algorithms are robust and compatible with nearly all AC motors, regardless of the manufacturer (this is a frequently asked question from first-time users who have struggled with this on other products). KEB’s free Combivis program has easy-to-use setup wizards that walk the user through the basic motor nameplate data (e.g. current, voltage, speed, frequency, power) entry. The characterization itself is an automated learn process that only takes a few minutes. When the characteristics have been acquired, the settings can be saved to quickly commission subsequent motors.  

System Management and CAN Communications

For system control and diagnostics with the vehicle ECU, the T6 Auxiliary Inverter utilizes an embedded controller which acts as a CAN J1939 communications hub and gateway.  

Each auxiliary motor control stage can have configurable transmit and receive process data telegrams and SPN mappings as well as configurable PGN addresses. The benefit of this arrangement is that there is one 2-wire CAN connection and one Controller ID for controlling and managing multiple auxiliary nodes. This enables the user to determine what data they want to be communicated over the CAN bus for each inverter node and how to arrange the assignment and addressing. Alternatively, there is the option to utilize pre-installed embedded control programs with pre-configured communication and inverter settings (e.g. Torque/Speed Control) for quick setup of any node(s). 

Startup Tools and Support

KEB is known for its reliable products and customer support.  

KEB’s free Combivis program is a powerful tool to assist in startup and adjustment with easy-to-use wizards, useful diagnostics and troubleshooting features such as a digital oscilloscope, and TeamViewer is integrated for remote support. The program can save project files and parameter lists for quick setup of subsequent systems (these files can also be used to pre-configure the T6 system from the factory). 

Another key feature is the automated motor learn wizard. It is used to characterize motors for sensorless operation. Only basic motor nameplate data is generally needed, and the automated process takes 3 – 5 minutes.  

In addition to software tools, KEB has dedicated eMobility teams for local support. These teams are regionally based in North America and Europe.  KEB helps at every stage of the project – design concept, system sizing and selection, startup and commissioning (including onsite support, as permitted), series production preparation, and technical and after-sales troubleshooting and support.

If there are auxiliary electrification applications you’d like to discuss, please reach out to us at sales@kebamerica.com.

Sponsored by KEB