Direct-current bus voltage detection circuit for three-level frequency converter

The DC bus voltage detection circuit comprises a voltage sampling circuit, a photoelectric isolation circuit and a voltage amplification circuit which are connected in sequence, and the voltage sampling circuit comprises a series resistance sampling circuit and a first voltage follower which are connected in sequence. Two input ends of the series resistance sampling circuit are respectively connected with two buses, and an output end of the series resistance sampling circuit is connected with an input end of the first voltage follower; the optoelectronic isolation circuit comprises an isolation input circuit, a linear optocoupler and an isolation output circuit which are connected in sequence, and the input end of the isolation input circuit is connected with the output end of the first voltage follower; the voltage amplification circuit comprises a second voltage follower and an operational amplifier proportion operation circuit which are connected in sequence, the input end of the second voltage follower is