DC/AC power converter with DC side double frequency pulsation suppression caused by AC side faults
View Patent ↗A commanded negative-sequence current is added to a commanded current so as to suppress double-frequency pulsation on the DC side. The commanded negative-sequence current is found from three values (i.e., the detected value of positive-sequence voltage vector on the power-supply side, the detected value of negative-sequence voltage vector, and a commanded positive-sequence current). Thus, the pulsations which occur on the DC side of a semiconductor power converter and which have a frequency double the power-supply frequency are suppressed even when the AC power supply is at fault while assuring stability of the current control system, thus permitting stable and continuous operation.
1. A semiconductor power converter comprising:
a power converter including arms constituting three-phase bridge connections having AC-side terminals which are connected with a three-phase AC system via an inductance, said arms having self-extinguishing semiconductor devices connected thereto, said self-extinguishing semiconductor devices being IGBTs or combinations of MOSFETs and free-wheeling diodes;
a voltage-measuring device for measuring an AC voltage developed across the three-phase AC system;
a current-measuring device for measuring an AC current flowing through the power converter;
a phase detector for detecting phase θ of the AC voltage;
an AC current adjuster for outputting commanded pulses to the power converter based on a commanded active current value I qref and a commanded reactive current value I dref along two axes and on an output from the AC current-measuring device;
a two-phase voltage vector calculator for receiving a measured value of voltage developed across the three-phase AC system and calculating a positive-sequence voltage vector V p and a negative-sequence voltage vector V n ; and
a phase calculator for calculating and outputting a positive-sequence voltage phase θ p from a reference phase θ for the two-phase voltage vector calculator and from the positive-sequence voltage vector V p ;
wherein said AC current adjuster calculates a commanded positive-sequence current vector I pref from the commanded two-axis current values I qref and I dref , calculates a commanded negative-sequence current vector I nref using the relationship, I nref =−(V n /V p )×I pref , calculates commanded three-phase current vectors I aref , I bref , and I cref from the commanded positive-sequence current vector I pref and from the commanded negative-sequence current vector I nef , calculates commanded three-phase current values from the commanded three-phase current vectors and from the positive-sequence voltage phase θ p , and outputs commanded pulses to bring the commanded three-phase current values into agreement with the measured values of AC current.
2. The semiconductor power converter of claim 1 , wherein there are further provided a three-phase voltage vector calculator for receiving the measured value of voltage of the three-phase AC system and outputting three-phase voltage vectors (V a , V b , V c ) and a target voltage calculator for calculating a target voltage vector E 1 aref of a first phase from the AC voltage vector V a , the commanded current vector I aref , and the impedance value of the inductance, calculating a target voltage value e 1 aref from the target voltage vector E 1 aref and from the reference phase θ, and similarly calculating and outputting a target voltage value e 1 bref of a second phase and a target voltage value e 1 cref of a third phase, and wherein said AC current adjuster calculates and outputs correcting three-phase voltage values (e 2 aref , e 2 bref , e 2 cref ) to bring the commanded three-phase current values (i aref , i bref , i cref ) into agreement with the measured AC current values, adds the correcting three-phase voltage values (e 2 aref , e 2 bref , e 2 cref ) to the target three-phase voltage values (e 1 aref , e 1 bref , e 1 cref ), respectively, for each individual phase, takes the results as commanded three-phase voltage values, and outputs commanded pulses to bring the three-phase output voltages from the power converter into agreement with the commanded three-phase voltage values.
3. The semiconductor power converter of claim 1 , further comprising a DC voltage-measuring device for measuring the DC output voltage from the power converter, a DC voltage adjuster for outputting a commanded first-axis current I qref to bring the measured DC voltage value and the commanded DC voltage value into coincidence, a current vector calculator for receiving the measured value of AC current and calculating a positive-sequence current vector I p , and a power factor adjuster for calculating a positive-sequence reactive power output Q p from the positive-sequence current vector I p and from the positive-sequence voltage vector V p and outputting a commanded second-axis current value I dref to bring the positive-sequence reactive power output Q p and the commanded reactive power value into coincidence, and wherein said commanded positive-sequence current vector I pref is calculated from the commanded two-axis current values I qref and I dref .