Parallel String Settings

Parallel String Settings

These settings deal with options specific to theparallel string control logic present on Orion BMS product lines. When 2 or more equal voltage strings need to be combined together to form a higher capacity DC bus, parallel string functionality is used to ensure that the strings are engaged safely and consistently together, and that the overall stack metrics are being communicated properly to the end application.

When multiple nodes are configured in parallel, one of the Orion BMS controlled strings will be configured as the ?master? node while the remaining parallel strings (each with their own BMS installed) are configured as ?slave? nodes. Each of the slave BMS nodes are responsible for directly monitoring the pack they are connected to, but also for sending relevant information about the battery pack to the master node.

The master node is responsible both for monitoring the local pack information that it is directly connected to, but also for receiving information from the available slave nodes. Based on this information, the master node is able to compute and provide the following values:

In addition to calculating the above values / parameters, the master node is also responsible for interfacing with the main application. It can do this by a number of ways:

The master node is able to transmit the combined (cumulative) parameters listed above via CANBUS to applications that support such communication using the existing built-in custom CANBUS message capabilities. The master node can also interface with the application by using the three primary relay enable outputs (Charge Enable, Charger Safety and Discharge Enable). When configured as a master node, these relay enable outputs are reflective of the entire combined battery stack as a whole (meaning if the Charge Enable relay output switches off on any one string the master Charge Enable will also switch off).

Besides just calculating specific information and controlling the application, the master node is also responsible for determining when / if slave string nodes are permitted to connect (engage) with the DC bus by looking for a number of criteria.

These criteria include the following conditions: Verifying that the slave pack voltage is close to the active DC bus voltage to prevent large inrush current if the slave node were to be engaged (the exact maximum range it is looking for is programmable). Verifying that the slave pack is free from critical errors or faults that could compromise behavior or function.

The slave node itself will also validate that the above criteria are satisfied before requesting permission from the master node to join the DC bus. Both the slave node itself and the master node must agree in order for the slave node to engage. Once the negotiation is successfully completed, the slave will engage its contactor to join the DC bus.

APPLICATION NOTE: In applications where a shunt-trip breaker style connection is used instead of a traditional contactor, the negotiation must complete before the shunt trip breaker is manually engaged. If the breaker is manually switched on before permission is granted, the BMS will immediately terminate the breaker and remove itself from the DC bus.

During operation, if either the master or the slave node itself detects a problem (such as significant deviation in voltage from the main DC stack or some other critical fault code) the node will be immediately disconnected and removed from all cumulative calculated values. Only actively engaged (paralleled) strings are included in cumulative parameters (such as combined SOC, current limits, average current, etc).

In order to meet application specific requirements for power output or runtime capacity, the master node can be configured to require a specific number of active strings in order to engage the application. If used, this means that the master would prevent the application from activating until a minimum number of strings are brought online (paralleled). Additionally, if too many strings disconnect during normal operation it will also terminate the application (all three primary relay outputs on the master are switched off and the cumulative current limits are both held at 0A). This feature can be disabled (meaning that as long as at least 1 string is present then the application can be used).

Parallel Specific Settings

CRITICAL NOTE: In applications that use shunt trip breakers instead of contactors, the BMS units themselves CANNOT actually prevent the strings from initially engaging. They can cause the strings to immediately disconnect after the breaker is flipped on, but since shunt trip breakers are manually activated switches, once the operator engages the breaker the BMS itself cannot prevent the string from connecting to the main DC bus (besides tripping off again immediately, but by that point there may have already been extensive current transfer). Because of this, the operator must first manually verify that conditions are safe to engage before engaging the shunt breaker switch. Data provided by the BMS can be used in this decision process.