A converter unit comprising: a first converter circuit; a voltage tracking unit configured to change an input voltage to the first converter circuit and to track the input voltage from the first converter circuit at which an amount of output power from the first converter circuit is maximized; and a voltage identification unit configured to identify the input voltage to the first converter circuit at which the amount of output power from the first converter circuit is maximized, when a change in the input power or the output power of the first converter circuit with respect to a period of time or a change in input power or output power of the first converter circuit with respect to the input voltage at the first converter circuit satisfies a predetermined condition, wherein, when the voltage identification unit identifies the input voltage to the first converter circuit at which the amount of the output power from the first converter circuit is maximized, the voltage tracking unit is adapted to track the input voltage at the first converter circuit at which the amount of the output power of the first converter circuit is maximized and to change the input voltage at the first converter circuit with the identified input voltage at the first converter circuit as a starting point, characterized in that: the first converter circuit is a boost circuit, the converter unit is a boost unit, and the voltage identification unit is adapted to Identify the input voltage at the first boost circuit at which the output power of the first boost circuit is maximized based on at least one of a first start clock time and a first end clock time when the first start clock time at which the input voltage at the first boost circuit reaches a first reference voltage is earlier than a reference start clock time and when the first end clock time at which the input voltage at the first boost circuit falls below a second reference voltage is later than a reference end clock time. a first converter circuit; a voltage tracking unit configured to change an input voltage to the first converter circuit and to track the input voltage from the first converter circuit at which an amount of output power from the first converter circuit is maximized; and a voltage identification unit configured to identify the input voltage to the first converter circuit at which the amount of output power from the first converter circuit is maximized, when a change in the input power or the output power of the first converter circuit with respect to a period of time or a change in input power or output power of the first converter circuit with respect to the input voltage at the first converter circuit satisfies a predetermined condition, the first converter circuit is a boost circuit, the converter unit is a boost unit, and the voltage identification unit is adapted to Identify the input voltage at the first boost circuit at which the output power of the first boost circuit is maximized based on at least one of a first start clock time and a first end clock time when the first start clock time at which the input voltage at the first boost circuit reaches a first reference voltage is earlier than a reference start clock time and when the first end clock time at which the input voltage at the first boost circuit falls below a second reference voltage is later than a reference end clock time.