A power conversion system comprising: a first power converter and a second power converter, which are connected by a DC bus; wherein the first power converter includes a DC-DC converter and a first controller, wherein the first controller includes a first bus voltage detector; wherein the second power converter includes an inverter and a second controller, wherein the second controller includes a second bus voltage detector; wherein the DC-DC converter is configured to convert a DC power supplied from a solar cell into a DC power of a different voltage and to output the DC power to the DC bus; wherein the inverter is configured to convert the DC power input from the DC bus into an AC power and to output the AC power to a system; wherein the first controller is configured to subject the DC-DC converter to maximum power point tracking, MPPT, control to perform a step-up operation when a voltage on the DC bus is lower than a first reference voltage and to control the DC-DC converter to suspend the step-up operation when the voltage is equal to or higher than the first reference voltage, wherein the voltage on the DC bus is detected by the first bus voltage detector; wherein the second controller configured to control the inverter to maintain the voltage on the DC bus constant when the voltage on the DC bus is lower than a second reference voltage and to subject the inverter to MPPT control to maximize an output power of the inverter when the voltage is equal to or higher than the second reference voltage, wherein the voltage on the DC bus is detected by the second bus voltage detector; and wherein the second reference voltage is set to be lower than the first reference voltage. a first power converter and a second power converter, which are connected by a DC bus; wherein the first power converter includes a DC-DC converter and a first controller, wherein the first controller includes a first bus voltage detector; wherein the second power converter includes an inverter and a second controller, wherein the second controller includes a second bus voltage detector; wherein the DC-DC converter is configured to convert a DC power supplied from a solar cell into a DC power of a different voltage and to output the DC power to the DC bus; wherein the inverter is configured to convert the DC power input from the DC bus into an AC power and to output the AC power to a system; wherein the first controller is configured to subject the DC-DC converter to maximum power point tracking, MPPT, control to perform a step-up operation when a voltage on the DC bus is lower than a first reference voltage and to control the DC-DC converter to suspend the step-up operation when the voltage is equal to or higher than the first reference voltage, wherein the voltage on the DC bus is detected by the first bus voltage detector; wherein the second controller configured to control the inverter to maintain the voltage on the DC bus constant when the voltage on the DC bus is lower than a second reference voltage and to subject the inverter to MPPT control to maximize an output power of the inverter when the voltage is equal to or higher than the second reference voltage, wherein the voltage on the DC bus is detected by the second bus voltage detector; and wherein the second reference voltage is set to be lower than the first reference voltage.