PWM CONTROL METHOD AND APPARATUS FOR KEEPING DIRECT CURRENT-SIDE CURRENT CONSTANT IN THREE-LEVEL CONVERTER

摘要

The present invention relates to a pulse width modulation (PWM) control method and apparatus for keeping a direct current-side current constant in a three-level converter, which can control, according to a PWM scheme, such that a direct current-side current is kept constant on average at every switching cycle in the three-level converter for converting alternating current into direct current or converting direct current into alternating current. To this end, a PWM control apparatus may comprise: a modulation function generator for receiving a three-phase reference wave signal corresponding to a command of an alternating current-side terminal voltage that a three-level converter desires to generate, and generating modulation functions (d_a, d_b, and d_c) of respective phases from the received three-phase reference wave signal; a d₀ generator for calculating ranges of duty ratios (d_a0, d_b0, and d_c0) of NP-switches of the respective phases, from the modulation functions (d_a, d_b, and d_c) of the respective phases generated by the modulation function generator, and determining a value of d₀ which satisfies d_a0=d_b0=d_c0=d₀, from a common intersection of the calculated ranges; a duty ratio generator for determining duty ratios (d_ap, d_an, d_bp, d_bn, d_cp, and d_cn) of the respective phases, the duty ratios (d_ap, d_an, d_bp, d_bn, d_cp, and d_cn) being uniquely determined, by using the modulation functions (d_a, d_b, and d_c) of the respective phases and the determined value of d₀; and a gating signal generator for generating gating signals for turning on and turning off IGBTs of the respective phases, from the duty ratios of the respective phases.