CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of the PCT International Application No. PCT/JP2018/048558 filed on Dec. 28, 2018, which claims the benefit of foreign priority of Japanese patent application 2018-031228 filed on Feb. 23, 2018, the contents all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a management device that manages a state of a plurality of series-connected cells, and relates to an electricity storage system.

BACKGROUND ART

In recent years, there has been an expanding demand for secondary batteries such as lithium-ion batteries and nickel-metal-hydride batteries. Secondary batteries are used for various use purposes such as in-vehicle use and stationary electricity storage use, for example, back up, peak shift, and frequency regulation (FR). Particularly in recent years, a volume of shipments of electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) have increased, and there have been more cases where an EV and/or PHEV is charged from a charger installed outside the vehicle.

Along with the increase, there have been more cases where an inexpensive and low-spec charger is used. A low-spec charger cannot sufficiently remove a ripple component generated when alternate-current (AC) power of a commercial power source system is rectified, and a current on which a large ripple component is superimposed flows into a secondary battery. Also in a stationary electricity storage use, downsizing and cost reduction of power conditioners are required; accordingly, there is a case where a current on which a large ripple component is superimposed flows into a secondary battery.

In a case of an electricity storage system including a plurality of series-connected cells, a voltage is measured for each cell to monitor whether each cell voltage is within an allowable voltage range (for example, see PTL 1). When the cells are charged from a low-spec charger, there is a concern that the cell voltages pulsate due to influence of a ripple current and surpass the allowable voltage range of cell.

CITATION LIST

Patent Literature

PTL 1; Unexamined Japanese Patent Publication No. 2008-112740

SUMMARY OF THE INVENTION

Because the ripple of cell voltage is a minute voltage fluctuation, a highly accurate voltage measurement circuit is necessary to highly accurately monitor the ripple of a cell voltage. It is further necessary to sample the cell voltage at a sampling frequency twice or more than a ripple frequency. To achieve this sampling, an expensive and large-sized voltage measurement circuit is necessary (for example, analog front-end IC). In particular, the circuit size needs to be larger for a larger number of series connection of the cells, and a system size and a cost will be increased.

The present invention has been conceived in view of the above circumferences, and an object of the present invention is to provide a technique that can measure a ripple of a voltage of each of a plurality of series-connected cells, with an inexpensive and small-scale circuit.

In order to solve the above issue, a management device of an aspect of the present invention includes: a cell voltage measurement unit that measures a voltage of each cell of a plurality of cells that are series-connected; a total voltage measurement unit that measures a total voltage of the plurality of cells; and a controller that manages an internal impedance of each cell of the plurality of cells. The controller detects a ripple of the total voltage measured by the total voltage measurement unit, estimates a ripple of each cell voltage by multiplying the ripple, which is detected, of the total voltage by a ratio of the internal impedance of each cell to a resultant internal impedance of the plurality of cells, and determines whether the ripple of each cell voltage is within an allowable voltage range.

The present invention enables to measure a ripple of a voltage of each of a plurality of series-connected cells with an inexpensive and small-scale circuit.

