| 摘要 |
In a multilevel power conversion circuit using a flying capacitor (condenser), a capacity of the capacitor needs to be designed based on the three parameters of the permitted voltage variation range of the capacitor; the integrated current flowing in the capacitor; and a carrier period. Specifically, if the permitted voltage variation range of the capacitor is limited within a small value, the price of the capacitor goes higher and its size gets larger. In a process of changing an alternate current voltage from zero to +Ed (negative to positive) or from zero to -Ed (positive to negative), a control method according to the invention detects voltages across the capacitors and when the detected voltage is lower than a predetermined voltage value, a switching operation pattern capable of charging the capacitor is given to switching elements during a short period of time; when the detected voltage is higher than the predetermined voltage value, a switching operation pattern capable of discharging the capacitor is given to the switching elements during a short period of time. Therefore, the voltage variation value of the capacitors is limited within a specified variation range. [Reference numerals] (1) Positive voltage order?; (10,4) Condenser voltage detection; (11,5) Size comparison with an average voltage; (12,6) Forceful pattern output; (13) Ed output; (2) Positive voltage PWM; (3) Negative voltage order?; (7) -Ed output; (8) Negative voltage PWM; (9) Positive voltage order? |
