John Butkowski

Beckett Energy Systems

IEEE EnergyTech 2012 Suggested Test Protocol for Distributed Energy Storage

Systems at “The Edge of the Grid”

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Distributed Energy Storage at the Grid Edge

• Scalable and Modular• In 25kW/25kWh

increments• For 2 – 8 Homes• Utility Initiated

Communications and Control

• Grid Tied – Bidirectional

• True Islanding Capability and Synchronous return

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Test Protocol Objective

• Develop a universal test protocol to ensure that a Distributed Energy Storage System (DESS) consisting of a Power Conversion and Battery System and can safely perform applications and grid compatibility functions required for “edge of grid” operation.

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Test Protocol

• Five “Basic” Tests - ensure the DESS is safe to connect to the power grid. The DESS SHOULD NOT be connected to the power grid until these tests are complete. These tests are performed using an isolated source such as a generator, MG set, and/or a programmable supply.

• Seven “Power Quality” Tests – characterize the power quality of the DESS.

• “Use Case” Tests - assess functions of the DESS that are not common to all systems but provide value to the utilities.

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Basic Test Overview

Hardware/Software Review Basic Command Review Performance Review Unintentional Islanding Abnormal Voltage and Frequency

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Test 1 - Hardware and Software Review

• Document hardware / software received

• Review workmanship and internal topology

• Review system documentation/training from the manufacturer

Basic Tests

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Basic Tests

• Verify the DESS will turn on and off properly when it receives the charge and discharge commands

• Confirm the function of any safety disconnects or Emergency Power Off features

Test 2 - Basic Command Review

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Basic Tests

• Record the utility bus AC waveforms with the DESS connected

• Record the DC waveforms of the battery charge/discharge functions

• Verify the ability of the system to charge and discharge at various range of power levels

Test 3 - Performance Review

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Basic Tests

• Verify that the DESS disconnects from the grid within two seconds of an islanding condition. This test ensures that power will not be fed back into the grid in the event of a grid outage. (Note that this test does not address any downstream islanding capabilities, only loss of grid power.)

Test 4 - Grid Compatibility: Unintentional Islanding

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Test 5 - Grid Compatibility: Abnormal Voltage & Frequency

• Verify that the DESS must disconnect when

presented with abnormal voltage and frequency. These tests will be performed while the DESS is discharging 100% rated power into the utility bus

Basic Tests

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Power Quality Tests

DC Current Measurement Inrush Current Transfer Profile Reconnect Following Abnormal Condition

Disconnect Harmonics Flicker Efficiency / Parasitic Losses

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• Verify that an inverter that connects to the grid complies with the DC injection limit specified in IEEE Std 1547 (DC current injection is less than 0.5% of the full rated output current)

Power Quality Tests

Test 6 - DC Current Measurement

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Power Quality Tests

• Measure the potential for inrush current when a DESS is energized. The result is particularly important for systems containing a transformer or certain types of input filters since the inrush can be significantly higher than the full load operating current.

Test 7 - Inrush Current

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Power Quality Tests

• Characterize the DESS specific response for connecting and synchronizing to the grid during initiation of charge and discharge cycles.

• During this test the voltage level before and after connection will be evaluated to ensure the system does not exceed the IEEE std. 1547 allowance of 5% voltage fluctuation.

Test 8 - Transfer Profile

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Test 9 - Reconnect Following Abnormal Condition Disconnect

• To evaluate the performance of the DESS reconnect timer which delays the reconnection to the utility bus following a trip event. Test is conducted at full rated output power.

Extended Power Quality Tests

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Power Quality Tests

• This test measures the Total Harmonic Distortion (THD) present at the DESS input/output during charge and discharge at 100% of full rated discharge.

Test 10 - Harmonics

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Test 11 - Flicker

• Characterize the flicker parameters (voltage fluctuations resulting in perceptible light flicker) associated with the DESS during start-up.

Power Quality Tests

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Power Quality Tests

• Characterize round trip efficiency through a full charge/discharge cycle at unity power factor.

• Measure the no-load losses of the DESS when it is not charging or discharging. This information can be used along with the round-trip efficiency data to estimate total losses based on use profiles.

Test 12 – Efficiency / Parasitic Losses

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Use Case Tests

Watt and VAR Support Downstream Step Load Downstream Overload Downstream Island Initiation Resynchronization Following Downstream

Islanding Downstream Voltage Total Harmonic

Distortion

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Test 13 - Watt and VAR Support

• This test is designed for DESS’s that are capable of sourcing and sinking reactive power on command. This functionality is important to utilities since they can use DES systems with this capability to provide reactive power compensation to the grid as needed. This test will determine the limits of the DESS’s ability to transmit and receive power in all four quadrants (sourcing and sinking both watts and VARs).

Use Case Tests

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Test 14 - Downstream Step Load

• This test assesses the system’s ability to regulate output voltage during step load changes. It should only be performed on DESS’s with downstream islanding capability, and should be performed during a downstream islanding condition. For a DESS system that is grid connected, a step load should not be a significant issue since the grid typically has much lower source impedance than the DESS inverter.

Use Case Tests

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Test 15 - Downstream Overload

• This test profiles the DESS inverter’s overload capability during an intentional islanding event and only applies to DESS’s with downstream islanding capability. This test is intended to verify the system can meet its overload rating. Test points (overload magnitude and time) should be chosen based on each system’s specifications, overload protection and anticipated use.

Use Case Tests

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Test 16 - Downstream Island Initiation

During unfavorable line conditions (outage, over- or under-voltage, frequency deviations, etc.), the system should disconnect from the utility bus. Systems with islanding functionality will continue to supply a downstream load with power until the stored energy runs out. This test records the PQ profile of this transfer to island mode. This should not be confused with the unintentional islanding test. In island mode, the DESS system has a separate island bus from the utility bus which it can keep energized during outages on the power grid. This test should only be performed on systems with islanding functionality.

Use Case Tests

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Test 17 - Resynchronization Following Downstream Islanding

• Verify that after favorable line conditions return, DESS will resync the island bus to the utility bus and return downstream load to utility power following a 5 minute minimum time out. This test only applies to DESS’s with downstream islanding capability.

Use Case Tests

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Test 18 - Downstream Voltage Total Harmonic Distortion (THD)

• During an islanding condition, the DESS inverter serves as the source for downstream loads. This test determines the voltage THD of the DESS inverter. The measured THD will be compared with the recommended limits found in IEEE Std. 519.

Use Case Tests

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Energy Storage

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