SOC Estimator (Coulomb Counting)

State of charge estimator with Coulomb counting

Since R2022b

• 

Libraries:
Simscape / Battery / BMS / Estimators

Description

The SOC Estimator (Coulomb Counting) block implements an estimator that calculates the state of charge (SOC) of a battery by using the Coulomb counting method.

The SOC is the ratio of the released capacity C_releasable to the rated capacity C_rated. Manufacturers provide the value of the rated capacity of each battery, which represents the maximum amount of charge in the battery:

$$SOC=\frac{C_{\text{releasable}}}{C_{\text{rated}}}.$$

This block supports single-precision and double-precision floating-point simulation.

Note

To enable inherited single-precision floating-point simulation, the data type of all inputs and parameters, except for the Sample time (-1 for inherited) parameter, must be single.

You can switch between continuous and discrete implementations of the block by using the Sample time (-1 for inherited) parameter. To configure the block for continuous time, set the Sample time (-1 for inherited) parameter to 0. To configure the block for discrete time, set the Sample time (-1 for inherited) parameter to a positive, nonzero value, or to -1 to inherit the sample time from an upstream block.

Note

Continuous-time implementation of this block works only in a double-precision floating-point simulation. If you provide single-precision floating-point parameters and inputs, this block casts them to double-precision floating-point values to prevent errors.

This diagram shows the structure of the block:

Equations

To compute the SOC of the battery, the SOC Estimator (Coulomb Counting) block counts the Ampere hour and current integration:

$$SOC=SOC\left(t_0\right)+\frac{1}{C_{\text{rated}}}{\displaystyle \underset{t_0}{\overset{t_0+\tau }{\int }}{I}_{\text{batt}}},$$

where C_rated is the nominal battery capacity and I_batt is the battery current.

Examples

Explore Techniques to Estimate Battery State of Charge

Explores different techniques to estimate the state of charge (SOC) of a battery, including the Kalman filter algorithm and the Coulomb counting method. The Kalman filter is an estimation algorithm that infers the state of a linear dynamic system from incomplete and noisy measurements. This example illustrates the effectiveness of the Kalman filter in dynamically estimating the SOC of a battery, even when starting with inaccurate initial conditions and when the measurements are noisy. The SOC of a battery measures the current capacity of the battery in relation to its maximum capacity.

• Since R2024b
• Open Live Script

Estimate State of Charge of Lithium Iron Phosphate Battery

Estimate the state of charge (SOC) of lithium iron phosphate (LFP) batteries by using the Coulomb Counting method with error correction. The Coulomb counting method is implemented at 1 second sample time. To correct the estimate of the Coulomb counting method, the example implements an extended Kalman filter with a sampling time of 10 seconds. The initial SOC of the battery is equal to 0.4. The estimator uses an initial condition for the SOC equal to 0.6. The LFP battery keeps charging and discharging for six hours. The estimator converges to the real value of the SOC in approximately half an hour and then follows the real SOC value.

• Since R2024b
• Open Model

Assumptions and Limitations

The nominal capacity of the battery does not consider aging.

Ports

Input

Current — Battery current, A

scalar | vector

Battery current, in ampere, specified as a scalar for a single cell or a vector for multiple cells. To specify this input as a vector of cell currents, select the Specify Current input as cell current(s) parameter.

InitialSOC — Initial state of charge, unitless

scalar | vector

Initial state of charge, specified as a scalar or vector of entries in the range [0, 1]. The size of this input port must be equal to the size of the Current input port.

Output

SOC — Battery state of charge

scalar | vector

State of charge of the battery, returned as a scalar or a vector. The size of this output port is equal to the size of the Current and InitialSOC input ports.

Parameters

Specify Current input as cell current(s) — Option to specify current input port as vector

on (default) | off

Since R2023b

Option to specify the value of the Current input port as a vector of cell currents. If you select this parameter, the value at the Current input port can be a scalar or a vector of size equal to the size of the block inputs.

Cell capacity, AH (A*Hr) — Battery capacity when fully charged

27 (default) | nonnegative scalar

Cell capacity of the battery, in ampere-hour. The block calculates the state of charge by dividing the accumulated charge by this value. The block calculates accumulated charge by integrating the battery current.

Sample time (-1 for inherited) — Block sample time

1 (default) | 0 | -1 | integer

Time between consecutive block executions. During execution, the block produces outputs and, if appropriate, updates its internal state. For more information, see What Is Sample Time? and Specify Sample Time.

For inherited discrete-time operation, specify this parameter as -1. For discrete-time operation, specify this parameter as a positive integer. For continuous-time operation, specify this parameter as 0.

If this block is in a masked subsystem or a variant subsystem that supports switching between continuous operation and discrete operation, promote the sample time parameter. Promoting the sample time parameter ensures correct switching between the continuous and discrete implementations of the block. For more information, see Promote Block Parameters on a Mask.

Algorithm data type — Option to choose data type for block algorithm

Inherit: auto (default) | double | single | <data type expression>

Since R2025a

Option to choose the data type for the block algorithm, specified as one of these values:

• Inherit: auto — You can simulate the block in both single and double precision. You must explicitly provide the inputs and parameters as either single or double.

• double — The block algorithm casts all inputs and parameters to double data type.

• single — The block algorithm casts all inputs and parameters to single data type.

• <data type expression> — The block algorithm casts all inputs and parameters to the data type object you specify.

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the data type attributes. For more information, see Specify Data Types Using Data Type Assistant and Control Data Types of Signals.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2022b

R2025a: Switch between single-precision and double-precision floating-point simulation using Algorithm data type parameter

You can now easily switch between single-precision and double-precision floating-point simulation of the block algorithm by using the Algorithm data type parameter.

R2023b: Specify the value of the Current input as a vector of cell currents

You can now specify the value of the Current input port as a vector of cell currents.

To enable a vectorized input, select the Specify Current input as cell current(s) parameter. If you select this parameter, the Current input port must have the same size as the other inputs and represents individual cell currents.