State of charge estimation device and method of estimating state of charge

A state of charge estimation device for estimating a state of charge of an electric storage device, the state of charge estimation device comprising:

• a voltage measurement component configured to measure a voltage across the electric storage device;
• a current measurement component configured to measure a current flowing through the electric storage device;
• and
• a controller component configured to:
• when estimation of state of charge of the electric storage device based on an accumulated amount of currents measured by the current measurement component is defined as a current accumulation method and estimation of state of charge of the electric storage device based on an open circuit voltage (OCV) of the electric storage device measured by the voltage measurement component is defined as an OCV method, define an estimated state of charge based on estimation based on results of estimation by the current accumulation method and the OCV method with heavier weight assigned to the OCV method when the state of charge estimated by the OCV method is within a specified range in which a variation in open circuit voltage relative to a variation in state of charge is larger than a reference value;
• and
• define an estimated state of charge based on estimation results of estimation by the current accumulation method and the OCV method with heavier weight assigned to the current accumulation method when the state of charge estimated by the OCV method is not within the specified range.