ISOMETER® iso165C – the insulation monitoring device (IMD) for unearthed DC drive sytems (IT sytems) in electrical vehicles

The ISOMETER® iso165C monitors the insulation resistance between the active high-voltage (HV) components of an electrical drive system (Un = DC 0 V…600 V) and the reference earth (chassis ground). The patented measurement technology is used to monitor the condition of the insulation on the DC side as well as on the AC motor side of the electrical drive system. The ISOMETER® iso165C is assembled with three connectors. To achieve internal galvanic separation, connector 1 is connected to low-voltage (LV) areas and connectors 2 and 3 are connected to the HV battery in the car environment. Due to its space saving design and optimized measurement technology, the device is optimized for use in hybrid or fully electric vehicles. The device meets the increased automotive requirements with regard to environmental conditions (e.g. temperatures and vibration, EMC). The iso165C CAN interface allows it to integrate seamlessly into an existing CAN environment.

The iso165C consists of two main components, the Vehicle Interface Controller (VIFC) and the Insulation Monitoring Controller (IMC). The VIFC consists of a microcontroller with a UART communication interface that translates and forwards requests from the HS-CAN bus transparently to the IMC. The corresponding IMC responses are returned to the requesting instance via the HS-CAN bus. The VIFC supervises the running state of the IMC via a signal known as "Alive", and internally and cyclically requests the insulation value and the running state of the IMC. The results are cyclically sent as an informal message via the HS-CAN bus. The IMC consists of the HV connectors with HV coupling relays, the measurement circuit and a microcontroller to analyse the measurement results. It generates internal alarm information from the measurement results, which is coded to produce the "Alive" signal mentioned previously. This signal is transmitted in parallel with the measurements and status information to the VIFC and from there over the HS-CAN bus. The IMC is galvanically separated from the car environment.

On initial power up, the iso165C does not carry out any measurements until communication between the VIFC and IMC has been established. In addition, the HV coupling relays of the HV1 voltage path are, by default, open and therefore no valid measurement of voltage HV1 and the insulation resistance is possible until these relays are closed by an external command. Once communication has been established between the VIFC and IMC and the HV1 path relays closed, the iso165C can immediately start measuring voltages HV1, HV2 and the insulation resistance.

The ISOMETER® iso165C generates a pulsed measuring voltage that is superimposed on the IT system by the terminals T_31_E/KE (chassis). Because the connection between the terminals E/KE and the chassis ground (T_31) is continuously monitored, it is necessary to install two separated conductors from terminals T_31_E/KE to chassis ground.