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Battery energy storage System (BESS) is a technology that enables power system operators and utilities to store energy for later use. A BESS is an electrochemical device connected to a DC-AC inverter which that interfaces with an AC network. The battery can charge (i.e., consume energy) from the grid and then later discharge the stored energy to provide power to the grid when needed.
The diagram below illustrates the basic concept of the BESS. It is comprised of a battery used for energy storage, a smoothing capacitor across its outputs, and a Voltage-Source Converter (VSC) that provides the required DC/AC conversion for connecting the DC battery outputs with an external AC - bus.
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Mask and Parameters
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Controller Tab
Controller subsection
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Name | Unit | Description |
|---|---|---|
Prioritiy | The user is able to define whether the controller should prioritize active or reactive power via the usage of this parameter. | |
Nominal power Pn | VA | Nominal power of the converter in VA. Default is 60000. |
Nominal frequency fn | Hz | This parameter allows the user to specify the nominal frequency in hertz. Default is 50. |
Q regulator gain Kp | This parameter allows the user to specify the reactive regulator gain Kp. Default is 1. | |
Q regulator gain Ki | This parameter allows the user to specify the reactive regulator gain Ki. Default is 25. | |
P regulator gain Kp | This parameter allows the user to specify the active regulator gain Kp. Default is 1. | |
P regulator gain Ki | This parameter allows the user to specify the active regulator gain Ki. Default is 25. | |
Current regulator gain Kp | This parameter allows the user to specify the current regulator gain Kp. Default is 1. | |
Current regulator gain Ki | This parameter allows the user to specify the current regulator gain Ki. Default is 50. | |
Islanded mode voltage regulator gain Kp | This parameter allows the user to specify the islanded mode voltage regulator gain Kp. Default is 3. | |
Islanded mode voltage regulator gain Ki | This parameter allows the user to specify the islanded mode voltage regulator gain Ki. Default is 40. | |
DC voltage regulator enable | This parameter allows the user to specify the DC voltage regulator enable. Default is unchecked. | |
DC link voltage regulator Kp | This parameter allows the user to specify the DC link voltage regulator Kp. Default is 1. | |
DC link voltage regulator Ki | This parameter allows the user to specify the DC link voltage regulator Ki. Default is 50. | |
Current limit | This parameter allows the user to specify the current limit. Default is 1.2. | |
Sample time | s | This parameter allows the user to specify the block sample time in seconds. Default is 50e-6. |
Proportional gain | This parameter enables the user to select the proportional gain for the PI controller in PV mode and grid-connected mode. Default is 1. | |
Integral gain | This parameter enables the user to select the integral gain for the PI controller in PV mode and grid-connected mode. Default is 5. | |
Upper limit | This parameter enables the user to select the upper limit for the PI controller in PV mode and grid-connected mode. Default is 1. | |
Lower limit | This parameter enables the user to select the lower limit for the PI controller in PV mode and grid-connected mode. Default is -1. | |
Antiwinup gain | This parameter enables the user to select the antiwinup gain for the PI controller in PV mode and grid-connected mode. Default is 1. |
Measurement Filters subsection
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Name | Unit | Description |
|---|---|---|
Filter type | Specify the type of filter for voltage measurements: Lowpass (default), Highpass, Bandpass , or Bandstop (notch). | |
Nominal frequency fn | Hz | Specify the natural frequency of the filter for voltage measurements, in hertz. This value must be a scalar or a vector. Default is 1000. |
Damping ratio Zeta (Q = 1/(2*Zeta)) | Specify the damping ratio of the filter. The damping ratio is typically a value between 0 and 1. Default is 0.707. | |
Filter type | Specify the type of filter for current measurements: Lowpass (default), Highpass, Bandpass , or Bandstop (notch). | |
Nominal frequency fn | Hz | Specify the natural frequency of the filter for current measurements, in hertz. This value must be a scalar or a vector. Default is 1000. |
Damping ratio Zeta (Q = 1/(2*Zeta)) | Specify the damping ratio of the filter for current measurements. The damping ratio is typically a value between 0 and 1. Default is 0.707. |
Battery and DC link Tab
Battery parameters subsection
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Name | Unit | Description |
|---|---|---|
Type | Specify the battery model: Lithium-Ion (default), Lead-Acid, Nickel-Cadmium, Nickel-Metal-Hydride. | |
Nominal voltage | V | Specify the nominal voltage, Vnom, of the battery, in V. Default is 1200. |
Rated capacity | Ah | Specify the rated capacity, Qrated, of the battery, in Ah. The rated capacity is the minimum effective capacity of the battery. Default is 166.67. |
Initial state-of-charge | % | Specify of the state-of-charge (SOC) of the battery, expressed as a percentage of the maximum potential charge, at the beginning of simulation. An SOC of 100% indicates a fully charged battery and 0% indicates an empty battery. Default is 60. |
Battery response time | s | Specify the response time of the battery, in s, at 95% of the final value. This value represents the voltage dynamics and can be observed when a current step is applied. Default is 0.5. |
Discharge parameters subsection
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Name | Unit | Description |
|---|---|---|
Determined from the nominal parameters of the battery | Select to have the block determine the parameters in the Discharge settings based on the values specified for the parameters in the Parameters settings: on (default), off. Dependencies: Selecting this parameter disables the parameters in the Discharge settings. | |
Maximum capacity | Ah | Maximum theoretical capacity, Q, when a discontinuity occurs in the battery voltage, in Ah. This value is generally equal to 105% of the rated capacity. Dependencies: To enable this parameter, in the Parameters settings, set Use a preset battery to no. |
Cut-off Voltage | V | Maximum theoretical capacity, Q, when a discontinuity occurs in the battery voltage, in Ah. This value is generally equal to 105% of the rated capacity. Dependencies: To enable this parameter, in the Parameters settings, set Use a preset battery to no. |
Fully charged voltage | V | Fully charged voltage, Vfull, for a given discharge current. The fully charged voltage is not the no-load voltage. Dependencies: To enable this parameter, in the Parameters settings, set Use a preset battery to no. |
Nominal discharge current | A | Nominal discharge current, in A, for which the discharge curve is measured. Dependencies: To enable this parameter, in the Parameters settings, set Use a preset battery to no. |
Internal resistance | Ohms | Internal resistance of the battery, in ohms. When a preset model is used, a generic value is loaded that corresponds to 1% of the nominal power (nominal voltage multiplied by the battery rated capacity). The resistance is constant during the charge and the discharge cycles and does not vary with the amplitude of the current. Dependencies: To enable this parameter, in the Parameters settings, set Use a preset battery to no. |
Capacity | Ah | Amp-hour capacity at nominal voltage. Capacity, Qnom, extracted from the battery until the voltage drops under the nominal voltage. Dependencies: To enable this parameter, in the Parameters settings, set Use a preset battery to no. |
Exponential zone | [Voltage (V), | Voltage, Vexp, and the capacity, Qexp, that correspond to the end of the exponential zone. The voltage should be between Vnom and Vfull. The capacity should be between 0 and Qnom. Dependencies: To enable this parameter, in the Parameters settings, set Use a preset battery to no. |
DC link parameters subsection
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Name | Unit | Description |
|---|---|---|
Capacitance | F | The shunt capacitance, in farads (F). Default is 0.0120. |
Set the initial capacitor voltage | If selected, the initial capacitor voltage is defined by the Capacitor initial voltage parameter. If cleared, the software calculates the initial capacitor voltage in order to start the simulation in steady-state. Default is selected. | |
Capacitor initial voltage | V | The initial capacitor voltage used at the start of the simulation. The Capacitor initial voltage parameter is not visible and has no effect on the block if the Set the initial capacitor voltage parameter is not selected. |
Resistance | Ohms | The shunt branch resistance, in ohms (Ω). Default is 1e12. |
Voltage Source Converter Tab
Two-level converter subsection
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Name | Unit | Description |
|---|---|---|
Model type | Average model (Uref-controlled) is the only type of converter model. | |
Diode on-state resistance | Ohms | Internal resistance of the diodes, in ohms. The default value is 1e-3. |
Diode snubber resistance | Ohms | The snubber resistance, in ohms. Set the snubber resistance to inf to eliminate the snubbers. The default value is 1000. |
Diode snubber capacitance | F | The snubber capacitance in farads. Set the snubber capacitance to 0 to eliminate the snubbers. The default value is 1e-6. |
Diode forward voltage | V | Forward voltage, in volts, across the diode when it is conducting. The default value is 1e-3. |
Current source snubber resistance | Ohms | The snubber resistance across the two current sources, in ohms. Set the snubber resistance to inf to eliminate the snubbers. The default value is inf. |
Rated voltage | V | The rated voltage of the BESS (Battery Energy Storage System). |
Series RL branch subsection
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Name | Unit | Description |
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Branch type | Series RL branch. | |
Resistance R | Ohms | The series branch resistances (chocke resistance), in ohms (Ω). Default is 0.01. |
Inductance L | H | The series branch inductances (chocke inductance), in henries (H). Default is 0.0041. |
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Measurements Tab
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Name | Unit | Description |
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Winding 1 connection (Gride-side)
The winding connectors for winding 1 on the gride side. Choices are Y, Yn, Yg (default), Delta (D1), and Delta (D3). Default is Yg.
Winding 2 connection (Converter-side)
The winding connectors for winding 1 on the Converter side. Choices are Y, Yn, Yg (default), Delta (D1), and Delta (D3). Default is Delta (D1).
Type
Select Three single-phase transformers (default) to implement a three-phase transformer using three single-phase transformer models. You can use this core type to represent very large power transformers found in utility grids (hundreds of MW).
Select Three-limb core (core-type) to implement a three-limb core three-phase transformer. In most applications, three-phase transformers use a three-limb core (core-type transformer). This type of core produces accurate results during an asymmetrical fault for both linear and nonlinear models (including saturation). During asymmetrical voltage conditions, the zero-sequence flux of a core-type transformer returns outside the core, through an air gap, structural steel, and a tank. Thus, the natural zero-sequence inductance L0 (without delta winding) of such a core-type transformer is usually very low (typically 0.5 pu < L0 < 2 pu) compared with a three-phase transformer using three single-phase units (L0 > 100 pu). This low L0 value affects voltages, currents, and flux unbalances during linear and saturated operation.
Select Five-limb core (shell-type) to implement a five-limb core three-phase transformer. On rare occasions, very large transformers are built with a five-leg core (three phase legs and two external legs). This core configuration, also known as shell type, is chosen mainly to reduce the height of the transformer and make transportation easier. During unbalanced voltage conditions, as opposed to the three-limb transformer, the zero-sequence flux of the five-limb transformer stays inside the steel core and returns through the two external limbs. The natural zero-sequence inductance (without delta) is therefore very high (L0 > 100 pu). Except for small current unbalances due to core asymmetry, the behavior of the five-limb shell-type transformer is similar to that of a three-phase transformer built with three single-phase units.
Units
Specify the units used to enter the parameters of this block. Select pu to use per unit. Select SI to use SI units. Changing the Units parameter from pu to SI, or from SI to pu, automatically converts the parameters displayed in the mask of the block. The per unit conversion is based on the transformer rated power Pn in VA, nominal frequency fn in Hz, and nominal voltage Vn, in Vrms, of the windings. Default is pu.
Nominal power Pn
VA
The nominal power rating , in volt-amperes (VA), of the transformer. The nominal parameters have no impact on the transformer model when the Units parameter is set to SI. Typically, its value is 1.2 times the Nominal Power Pn (VA) of the controller indicated in the controller Tab. Default is 72000.
Winding 1 (Grid-side) parameters
The phase-to-phase nominal voltage in volts RMS, resistance, and leakage inductance in pu for winding 1. Default is [ 6600 , 0.004 , 0.04 ] when the Units parameter is pu and [7.35e+05 4.3218 0.45856] when the Units parameter is SI.
Winding 2 (Converter-side) parameters
The phase-to-phase nominal voltage in volts RMS, resistance, and leakage inductance in pu for winding 2. Default is [480, 0.004 , 0.04 ] when the Units parameter is pu and [3.15e+05 0.7938 0.084225] when the Units parameter is SI.
Magnetization resistance Rm
The magnetization resistance Rm in pu or SI depends on the Units parameter. Default is 500 when the Units parameter is pu and 1.0805e+06 when the Units parameter is SI.
Magnetization inductance Lm
The magnetization inductance Lm, in pu, for a nonsaturable core. Default is 500 when the Units parameter is pu and 2866 when the Units parameter is SI.
Inductance L0 of zero-sequence flux path return
The Inductance L0 of zero-sequence flux path return, in pu, for the three-limb core transformer type. This parameter is visible only if the Type parameter is set to Three-limb core (core type). Default is 0.5 when the Units parameter is pu and 2.866 when the Units parameter is SI.
Inductance L0 of zero-sequence flux path return
The Inductance L0 of zero-sequence flux path return, in pu, for the three-limb core transformer type. This parameter is visible only if the Type parameter is set to Three-limb core (core type). Default is 0.5 when the Units parameter is pu and 2.866 when the Units parameter is SI.
Measurements Tab
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Name
Unit
Description
Time contant
s
Time contant | s | Low pass filter time constant for power measurements, in seconds. Default value is 0.05. |
Cut-off frequency | Hz | Low pass filter cut-off frequency for voltage and current measurements, in hertz. Default is 10. |
Nominal power of network | W | Nominal power of network, in watts. Default is 12e3. |
Time constant for power measurement filter | Power measurement filter time constant for signal conditioning, in seconds. Default value is 0.05. | |
Time constant for voltage measurement filter | Voltage measurement filter time constant for signal conditioning, in seconds. Default value is 0.1. |
Inputs, Outputs, and Signals Available for Monitoring
Inputs
Name | Unit | Description |
|---|---|---|
P ref | pu | Specify the active power reference of the Battery Energy Storage System. |
Q ref | pu | Specify the reactive power reference of the Battery Energy Storage System. |
V ref | pu | Specify the voltage reference of the Battery Energy Storage System. |
GC Mode | Specify the status of the Battery Energy Storage System whether it is in grid connected mode (1) or grid forming mode (0). | |
BESS mode | Specify the mode of Battery Energy Storage System. | |
status | Whether or not connected to the microgrid (1: connected, 0: disconnected). |
Outputs
Name | Unit | Description |
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Measurements | kW, kVAr, kV, A, pu | With this port, the user can view the model's power measurements for six signals: |
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2- Vgrid: grid-side voltage or the voltage after the transformer and breaker that connect the BESS to the external grid, in volt
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3- Igrid: grid-side current or the current after the transformer and breaker that connect the BESS to the external grid, in amper. To have it in pu, it must be devied by the nominal current of grid side.
4- Q (kW): the reactive power of BESS in kVAR.
5- Vbess: the local voltage of the BESS or the point before to connecting the BESS to the external grid
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A | The actual circuit connection of BESS, Phase A. | |
B | The actual circuit connection of BESS, Phase B. | |
C | The actual circuit connection of BESS, Phase C. |