ARDA DC Microgrid Platform

Microgrid Control

ARDA DC Microgrid Platform's proprietary Controls use DC bus Voltage as the communication means.
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​Energy Storage is the sole Microgrid Manager. It simultaneously performs the Power and Energy Management Control functions through fast responding ARDA Battery DC-DC Converters.

​The Microgrid Control has a distributed character whereby Sources and Loads respond independently from each other and from the Microgrid Manager with their own internal algorithms. This functionality is provided by slave controllers that are either embedded in the Sources and Loads or provided as add-ons.
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The AC Grid and the interfacing grid tie inverter do not play any Management role, they are simply another Source/Load.
ARDA Power has deployed versions of the Microgrid Controls at a 60MW Solar plant in Ontario, at ARDA Power’s main office, and in Burlington Project.

Control with NO wired or wireless Communications

1st Control Layer

REGULATING Function: Maintain DC bus Voltage at a set point

The Energy Storage system maintains DC bus Voltage set point using very fast responses to variances in DC bus voltage.
Note: DC bus signaling (droop) control methods are not used by the Platform for Regulating Function.
Regulating Function of ARDA DC Microgrid Platform's control
click to enlarge
WHO: exclusively Energy Storage
If a Load or a Source suddenly changes, creating a power imbalance (uncontrolled deviation from the DC bus Voltage set point) on the DC bus, ​only the Energy Storage elements respond in a fast and coordinated manner.
Sources and Loads do not respond to fast transients in the DC bus and are not involved in the instantaneous power management (Regulating Function) of the Microgrid.
​​​The system’s exclusive use of Energy Storage for the Regulating Function (without assistance form other components including the grid-tie converter) provides for a single mode of operation in both grid-tied and off-grid operation. This simplifies system design and operation and improves reliability and resiliency.
The grid tie DC-AC converter regulates the DC bus only in the case of failure of the Energy Storage, representing an abnormal bypass operation mode.
HOW: fast
The Microgrid Control's Regulating Function simplifies system stability and the commissioning effort, but requires a fast response.
PLUG-and-PLAY enabler
The Regulating function of the ARDA DC Microgrid Platform's Control is one of the Plug-and-Play capability enablers.

2nd Control Layer

​SUSTAINING Function: Energy Balance through Battery Management

The Energy Storage system is also responsible for the Control's Sustaining Function. The Sustaining Function provides for the Energy Balance between Power Production and Power Consumption through Battery Management. In this sense, the Energy Storage system is ​the Energy Manager of the Microgrid.
Energy Storage is the Microgrid's Energy Manager
The Sustaining Function (unlike Regulating Function) uses so called DC bus signaling:
STEP 1: The Energy Manager "blindly" commands Sources and Loads using slow changes in the DC bus Voltage set point.

STEP 2: Sources and Loads use average measured DC bus voltage​ (rather than instantaneous bus voltage) to "blindly" understand and respond to the Energy Manager's command following individual internal algorithms.​
WHO: Energy Storage "blindly" Commands, other Elements "blindly" Respond
Here "Blindness" is a benefit, not a handicap. In STEP 1 the Energy Storage does not communicate with Sources or Loads since it knows that these elements will fulfill its "expectations". In STEP 2 Loads and Sources automatically respond to a change in DC bus Voltage without communicating with the Microgrid Manager and with each other.
The Energy Manager does not need to know anything about Sources or Loads on the bus - it simply changes the average measured DC bus Voltage, knowing that other elements will react to the changes to achieve the goal.
As a result, Sources and Loads can be added or removed from the Microgrid without effecting the system operation and without requiring any retuning or reprogramming.
Balanced Microgrid - State of Charge remains within the Preferred Boundaries 
The Energy Manager balances the Energy (or average Power) of the Microgrid amongst Sources and Loads by taking action when the Energy Storage system's State of Charge goes beyond the Preferred Boundaries. 

​The Manager ensures that the components are not pushed to extreme operating conditions where they cannot respond to changes in demand or generation.​
The Energy Storage system is the best place to locate the Sustaining Function, as it knows about both:
  • ​the Battery's State of Charge, 
  • ​the Microgrid's Power Balance.
Algorithm Example:
​Energy Storage changes the DC voltage set point
​when its State of Charge goes  beyond
​Preferred Boundaries SL1 - SH1.
Algoritms example: DC signaling based on Energy Storage state of charge
click to enlarge
HOW: slow via DC bus signaling
Since the Sustaining functions are slow by nature, with the exception of the Energy Storage system, fast response to power demand changes from Microgrid components is not important to the Microgrid stability.
​In fact, the components should react slowly to remove any effect of transient voltage changes in the DC bus and to give the energy manager time to evaluate if the response has been sufficient.
PLUG-and-PLAY enabler
The Sustaining function of the ARDA DC Microgrid Platform's Control is one of the Plug-and-Play capability enablers.

Self Calibration

A self calibration algorithm executed by the Energy Storage uses a known DC voltage to calibrate all the other components connected to the bus.

​With this self calibration, aging and tolerance in voltage measurements are less critical to the optimum operation of the Microgrid.

​click to go to
ARDA Battery DC-DC Converter

ARDA Battery DC-DC Converter

Both Regulatory (fast) and Sustaining (slow) tasks have to be done simultaneously:

- DC bus Voltage control with fast responses
- DC bus Voltage change with slow dynamics
​

The Microgrid Control's Regulating Function requires fast response and full power range for the Energy Storage.

​ ARDA Battery DC-DC Converters in tandem with a capable Storage Technology successfully handle all these tasks.

​3rd Control Layer

OPTIMIZING Functions: Optimize Operating Cost and Performance

The 3rd Microgrid Control's layer is represented by individual optimization Algorithms (patterns) of the Microgrid's components like Sources, Loads and AC Grid in their power responses to the Energy Manager's commands. These Algorithms optimize such things as:
  • Microgrid Operating Cost
  • Lifetime of Components
  • Energy Consumption
WHO: individual Source or Load
The Microgrid components will have different Cost and Performance requirements. Each one will have its own Algorithm with varying responses to the DC bus Voltage change initiated by the Energy Manager:
  • linear
  • non-linear (quadratic, exponential, steps, etc.)
  • discontinuities
  • season driven
  • market driven
  • weather driven
  • time of day driven
Microgrid Example:
Loads and Sources with individual Algorithms
Examples of Optimization Algorithms in ARDA DC Microgrid Platform
click to enlarge
HOW: (re)program a Source or Load with no change effect on the Microgrid
Any changes to to the individual Algorithms, addition or removal of a Component, do not effect the rest of the Microgrid because:
  • individual Microgrid Components don't take any part in the Regulating Function,
  • in the Sustaining Function, their responses are "blind" - using the average measured DC bus voltage​.

Source and Loads Converters

Power converters used for Sources and Loads only need to be provided with the capability to adjust their production/consumption based on a control signal.

The control signal can be embedded in the power converter or provided by an add-on controller.

​This would make any power converter capable of following a power reference compatible with the ARDA Microgrid Platform.

Third-party Energy Management

Customers may also want to employ third party management systems that use price, weather and other external data to optimize system performance including real time decisions on the import and export of energy to and from the external AC Grid.

​The ARDA DC Microgrid Platform will provide interfaces to accommodate such third party energy management systems.

Master and Response Controllers

The Microgrid's Virtual Master Controller and Response Controllers both have a distributed architecture.

They are either embedded in the power converters or supplied as add-ons.

AC Grid - just another Source or Load

In the ARDA DC Microgrid Platform, the AC Grid and its interfacing grid tie DC-AC converter play NO Management role. Instead the AC Grid is simply a bidirectional device that can operate as a Source or a Load on our Platform.

​The Microgrid's Mode of Operation and Controls are the same in On grid or Off grid operation. This decouples the Microgrid from the AC Grid and eliminates the risk that a large disturbance on the Grid can affect the Microgrid or result in loss of power.

The DC Microgrid removes the requirement to follow frequency and phase angles and eliminates reactive power flows making operation of a microgrid much simpler.