A photovoltaic energy storage system , comprising one or more conversion circuits and a detection circuit , wherein the one or more conversion circuits are connected in parallel between a positive bus and a negative bus; the detection circuit comprises a signal source excitation branch , a first sampling circuit , and a control circuit ; one terminal of the signal source excitation branch is connected to a ground wire, and the other terminal of the signal source excitation branch is connected to the positive bus or the negative bus; the signal source excitation branch comprises an alternating current signal source and a sampling resistor that are connected in series; and the first sampling circuit is connected in parallel to the sampling resistor , and the control circuit is connected to both an input terminal of the alternating current signal source and an output terminal of the first sampling circuit ; the control circuit is configured to control the alternating current signal source to output harmonic signals of a first frequency and a second frequency, wherein the first frequency is different from the second frequency; the first sampling circuit is configured to: when the alternating current signal source outputs the harmonic signal of the first frequency, collect a voltage at both terminals of the sampling resistor to obtain a first voltage; when the alternating current signal source outputs the harmonic signal of the second frequency, collect a voltage at both terminals of the sampling resistor to obtain a second voltage; and send the first voltage and the second voltage to the control circuit ; and the control circuit is further configured to obtain, based on the harmonic signals of the first frequency and the second frequency, the first voltage, and the second voltage, a ground insulation impedance obtained after the one or more conversion circuits are connected in parallel. the detection circuit comprises a signal source excitation branch , a first sampling circuit , and a control circuit ; one terminal of the signal source excitation branch is connected to a ground wire, and the other terminal of the signal source excitation branch is connected to the positive bus or the negative bus; the signal source excitation branch comprises an alternating current signal source and a sampling resistor that are connected in series; and the first sampling circuit is connected in parallel to the sampling resistor , and the control circuit is connected to both an input terminal of the alternating current signal source and an output terminal of the first sampling circuit ; the control circuit is configured to control the alternating current signal source to output harmonic signals of a first frequency and a second frequency, wherein the first frequency is different from the second frequency; the first sampling circuit is configured to: when the alternating current signal source outputs the harmonic signal of the first frequency, collect a voltage at both terminals of the sampling resistor to obtain a first voltage; when the alternating current signal source outputs the harmonic signal of the second frequency, collect a voltage at both terminals of the sampling resistor to obtain a second voltage; and send the first voltage and the second voltage to the control circuit ; and the control circuit is further configured to obtain, based on the harmonic signals of the first frequency and the second frequency, the first voltage, and the second voltage, a ground insulation impedance obtained after the one or more conversion circuits are connected in parallel. <EOS>