Abstract
The Eclipse provides the ability to control remote equipment in the form of a DER inverter. DER refers to Distributed Energy Resources and is used to describe various decentralized sources of power generation and energy storage systems. Examples include solar arrays, wind farms, backup generators and batteries. These types of resources are now being integrated into the management of the grid to better accommodate peak demand. The DER sources of power are typically DC voltage utilizing an inverter to create the required AC power. The Eclipse can be used to remotely control the inverter and monitor its output.
Usage
The Eclipse is an all-in-one control and monitoring solution for DER inverters. Its primary purpose is to remotely manage the state of power from a DER inverter. The Eclipse is designed for DER implementations up to 1,000 kW and avoids the need for expensive equipment normally utilized in larger DER deployments. The Eclipse is quick and easy to deploy and requires minimal configuration and setup.
Due to the Eclipse’s small size and rugged construction, it can be installed in or near the inverter cabinet itself. The Eclipse is housed in a completely weatherproof NEMA-4X enclosure so outdoor installation is never a problem. An optional, magnetic mounting bracket is available to secure the unit in place. The Eclipse is line powered via any available connection to 70V-300V. It features two independent, dry contact, form C relays that are controllable via its built-in LTE cellular modem. There are also two voltage sense digital inputs (60V-150V) that can be monitored for presence or absence of voltage through the same remote connection. The inverter’s status outputs (or AC outputs) get connected to the Eclipse’s voltage sense inputs. The Eclipse dry contact outputs get connected to the inverter control inputs. This setup allows for remote monitoring of the inverter’s status and for remote control of the inverter itself.
SCADA Interface
The Eclipse has a DNP3 based SCADA interface accessible through the cellular modem. The modem can be provisioned with the cellular provider for public or private accessibility. Private provisioning allows it to appear within a utility’s private network for enhanced security. Once the modem is provisioned it can be used by a SCADA master to monitor the inverter output and control its state.
The Eclipse voltage sense digital inputs are represented by DNP3 binary input points 20 and 21 of group 1. These binary inputs are ‘read only’ values that are updated in the Eclipse once per second. The Eclipse relays are represented by DNP3 binary output points 20 and 21 of groups 10 and 12. There are two different groups for the relays due to the multiple methods of control in the DNP3 protocol. In addition to the direct access points for the relay outputs and voltage inputs, there are also counters that increment with each change in state. The specific binary counters are DNP3 group 20 with the digital input and relay points being 24 through 27 respectively.
Relays
The relays are implemented as a “Complementary Latch Model” per the DNP3 specification. This means that each relay represents a physical output that remains in the state given by the last command and that the output states are complementary actions (on/off, enable/disable, etc.). It is important to note that these are not latching relays and in the event of a power failure the relay outputs will return to their default state. Since these are Form C relays the default state in use can be either normally open or normally closed. Even though the relays are outputs from the perspective of the SCADA master, they still have an active state associated with them. The active state of a relay can be read via the group 10 points. The state can be changed by writing to the group 10 points.
This type of output control method is only applicable to points using the “Complementary Latch Model” as described above. It is the method of choice for the Eclipse since it uses electromechanical relays that maintain their state for a meaningful period of time (i.e. seconds or longer). The group 12 points can be used to implement other control models for binary outputs but the Eclipse is only using the “Complementary Latch Model.” Group 12 access to the relays is available via the ‘select and operate controls’ utilizing the “latch on” and “latch off” methods.
The Eclipse does not require the select operation but it will process it and return a valid status. The operate function is used to change the state of the relays but the additional on-time and off-time parameters of the operate function are not used by the Eclipse. However, there is a count parameter that must be set to 1 in order for the relay output to change. If the count is set to zero then the command is processed without actually changing the output of the relays. This is useful for testing the setup of the SCADA master. Each time a relay changes state due to a DNP3 command its associated binary counter (point 26 or 27) in group 20 is incremented.
Digital Inputs
The digital voltage inputs monitor the presence or absence of voltage. Being digital inputs, they do not give a numerical reading of the voltage present. Instead, they merely indicate that voltage in the range of 60V-150V is present. The logical state of the input is maintained as a separate item within the Eclipse. The physical input is polled 60 times per second where 30 consecutive reads must be identical before the logical state is changed. The logical state is the value returned to the SCADA master and represents the “debounced” value of the input, filtering out any single cycle variances of the actual AC voltage connected to the input. Each time the logical state of an input changes, its associated binary counter (point 24 or 25) in group 20 is incremented. In addition to the counters, the Eclipse will also generate DNP3 binary events for state changes of the digital inputs. These binary events can be retrieved by the SCADA master via polling or they can be set up to initiate an event message for near real-time updates to the SCADA system.
Alerting and Monitoring
A feature of the Eclipse is the option to monitor 3-phase voltage and current with appropriate leads attached. This allows the Eclipse to be fully supported in Canvass with all associated alerting capabilities. The Canvass interface also allows for monitoring and control of the Eclipse relays and inputs. Since the Eclipse has outputs that can be remotely controlled, only a single external source can be allowed to change the outputs. Therefore, if DNP3 is enabled on the Eclipse, the Canvass interface will not be able to change the state of the relay outputs but will still be able to read the currently active states. Canvass will get alert messages for any changes in state for both the relays and the digital inputs. This allows Canvass email alerts to be set up to supply near real-time updates on the status of the controlled device. This capability sets up a useful complementary arrangement allowing for a SCADA system to control the relays and Canvass sending the appropriate notifications of the state changes.
Conclusion
The Eclipse is a unique and low-cost option to remotely monitor and control DER inverters. It features both status inputs and controllable outputs for intelligent management of the remote device. The Eclipse can be accessed via standardized DNP3 messaging using a SCADA system, PMI’s Canvass cloud system or a combination of the two.
