I wanted to share circuit schematic of a 3.7V Li-Ion battery simulation model for simulation.
The 3.7V Li-ion battery model implemented as a hierarchical subcircuit shown above uses a clever combination of analog behavioral sources, a specialized capacitor, and switches to dynamically mimic the charge, discharge, and terminal voltage characteristics of a real lithium-ion cell.
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Watch the following video that operation of the Li-Ion battery circuit model in action.
Here is a breakdown of how the key components inside the subcircuit work together:
1. Energy Storage & Capacity (C1)
- Component: [C1] (Capacitor valued at 1F with model ACTVCAP and attribute VMAX="3.7").
- Function: In this model, capacitance represents electrical charge (Ampere-hours or Coulombs) rather than standard electrostatic capacitance. The voltage across this capacitor corresponds directly to the state-of-charge (SoC) / open-circuit voltage of the battery.
2. State-of-Charge & Current Integration (ACS1 & AVS1)
- Components: [ACS1] (Current Source) and [AVS1] (Voltage Source) configured with algebraic expressions.
- Function: These controlled sources act as an integrator/translator network. ACS1 senses the terminal current and injects/extracts equivalent charge into the charge-storage capacitor [C1] based on the capacity scaling attributes (such as the SDR / discharge rate parameters passed from the parent sheet).
3. Internal Resistance (R1)
- Component: [R1] (Resistor valued at 0.7mΩ).
- Function: Represents the internal equivalent series resistance (ESR) of the battery. When current flows into or out of the battery, this resistor causes the instantaneous voltage sag or charge-overvoltage observed at the terminals [B1:+] / [B1:-].
4. Voltage Protection / Limits (S1, D1, D2, V2)
- Components: Voltage-controlled switch [S1], diodes [D1], [D2], and pulse/bias source [V2].
- Function: This circuitry handles boundary conditions—such as cutting off discharge when the cell voltage drops too low or regulating behavior near full charge limits (4.2V max / 2.5V / 3.0V cutoffs)—preventing the behavioral capacitor from unphysically over-charging or over-discharging.
Summary
In short, instead of representing a battery as a simple ideal DC voltage source with a series resistor, this Li-Ion subcircuit models the nonlinear discharge curve and charge capacity of a real chemistry cell dynamically as you draw current from or feed current into it in the root schematic.
See also the spice version or spice model of Li-Ion Battery:3.7V Li-Ion Battery Spice Model | Download Free
