org.usfirst.frc.team1736.lib.BatteryParam

Class BatteryParamEstimator

java.lang.Object

org.usfirst.frc.team1736.lib.BatteryParam.BatteryParamEstimator

public class BatteryParamEstimator
extends java.lang.Object

DESCRIPTION:
Battery parameter estimator - calculates an estimate for a battery's open circuit voltage (Voc) and equivilant series resistance (ESR) based on a windows of system current/voltage measurements. Ensures enough spread in the measurement window to ensure confidence in the estimate. Based on a whitepaper detailing an algorithm developed for the 2016 FRC season by FRC1736 RobotCasserole.
The constants for the initial parameter estimate were tuned assuming a freshly charged, relatively new MK ES17-12 battery (from andymark). It should self-adjust to whatever battery you put in. However, if you seen a giant jump at the start of each match, you may wish to update the "*init" constants to more accurately represent your "nominal" initial system state.

Whitepaper link: Current Estimation.

USAGE:

1. Instantiate Class
2. Once per periodic loop, call the updateEstimate() method to calculate a new paramater estimate
3. After updateEstimate(), call the other getters to utilize the estimated parameters.

Constructor Summary

Constructors

Constructor and Description
BatteryParamEstimator(int length) Initalizes all internal variables for using the class.

Method Summary

Modifier and Type	Method and Description
boolean	getConfidence() Getter for Confidence condition met boolean.
double	getEstESR() Getter for ESR.
double	getEstVoc() Getter for Voc.
double	getEstVsys(double Idraw_A) Given a system current draw, estimate the resulting system voltage given the latest estimated battery parameters.
double	getMaxIdraw(double VsysMin_V) Given a minimum system voltage allowable, estimate the maximum current which may be drawn from the battery at the present time.
void	setConfidenceThresh(double Thresh_A)
void	updateEstimate(double measSysVoltage_V, double measSysCurrent_A) Update the internal estimates with a new measured system voltage and current.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BatteryParamEstimator

public BatteryParamEstimator(int length)

Initalizes all internal variables for using the class.

Parameters:

length - Window size to consider for estimation. 100 is usually a good start. Smaller windows make the estimator react faster to rapid changes in the electrical system, but larger windows make it more immune to noise. Engineering tradeoff, you pick!

Method Detail

setConfidenceThresh

public void setConfidenceThresh(double Thresh_A)

updateEstimate

public void updateEstimate(double measSysVoltage_V,
                           double measSysCurrent_A)

Update the internal estimates with a new measured system voltage and current. Should be called once per control loop.

Parameters:

measSysVoltage_V - Battery voltage as measured by PDB

measSysCurrent_A - Current draw as measured by PDB

getEstESR

public double getEstESR()

Getter for ESR. Must be called after estimator is run.

Returns:

the most recent calculated equivalent series resistance

getEstVoc

public double getEstVoc()

Getter for Voc. Must be called after estimator is run.

Returns:

the most recent calculated open circuit voltage

getConfidence

public boolean getConfidence()

Getter for Confidence condition met boolean. Must be called after estimator is run.

Returns:

True if the most recent window had enough spread in I_draw for a reasonable estimate, false if not.

getEstVsys

public double getEstVsys(double Idraw_A)

Given a system current draw, estimate the resulting system voltage given the latest estimated battery parameters.

Parameters:

Idraw_A - estimated system current draw in Amps

Returns:

Estimated Vsys in Volts

getMaxIdraw

public double getMaxIdraw(double VsysMin_V)

Given a minimum system voltage allowable, estimate the maximum current which may be drawn from the battery at the present time.

Parameters:

VsysMin_V - minimum desirable system voltage

Returns:

The maximum current which the robot may pull in amps.