Power conversion system

Claim 2

A power conversion system, comprising: a single-phase AC power source for generating an AC power; an AC/DC power converter connected to said single-phase AC power source for converting said AC power into a DC power; a main smoothing capacitor connected to DC terminals of said AC/DC power converter; a DC active filter connected in parallel with said main smoothing capacitor for controlling a compensation current (IF) flowing in said DC active filter such as to absorb an amount of fluctuation of said AC power supplied from said single-phase AC power source; and a load device connected to said main smoothing capacitor as a DC voltage source for receiving a first DC voltage (Vd) applied to said main smoothing capacitor.

Claim 3

The power conversion system according to claim 1, wherein said DC active filter includes: a DC constant voltage source for generating a second DC voltage; a voltage source PWM inverter connected to said DC constant voltage source for converting said second DC voltage into a variable-voltage AC voltage; a single-phase transformer connected to AC side output terminals of said voltage source PWM inverter; and a DC smoothing capacitor connected in series with a secondary winding of said single-phase transformer; said compensation current (IF) flowing through said DC smoothing capacitor.

Claim 4

The power conversion system according to claim 1, wherein said DC active filter includes: a DC constant voltage source for generating a second DC voltage; a voltage source PWM inverter connected to said DC constant voltage source for converting said second DC voltage into a variable-voltage AC voltage; and a series circuit of a DC smoothing capacitor and an inductor, said series circuit being connected in series with AC side output terminals of said voltage source PWM inverter; said compensation current (IF) flowing through said series circuit.

Claim 5

The power conversion system according to claim 1, wherein said DC active filter includes: a DC constant current source for generating a DC current; a current source PWM inverter connected to said DC constant current source for converting said DC current into a variable-current AC current; a high frequency capacitor connected to AC output terminals of said current source PWM inverter; and a DC smoothing capacitor connected in series with said high frequency capacitor; said compensation current (IF) flowing through said DC smoothing capacitor.

Claim 6

The power conversion system according to claim 1, wherein said DC active filter includes: a DC constant current source for generating a DC current; a current source PWM inverter connected to said DC constant current source for converting said DC current into a variable-current AC current; a high frequency capacitor connected to AC output terminals of said current source PWM inverter; a single-phase transformer connected in parallel with said high frequency capacitor; and a DC smoothing capacitor connected in series with a secondary winding of said single-phase transformer; said compensation current (IF) flowing through said DC smoothing capacitor.

Claim 7

The power conversion system according to claim 1, wherein said DC active filter includes: a high frequency voltage source for supplying a high frequency voltage; a circulating current type cycloconverter connected to receive said high frequency voltage as an input for generating a single-phase AC voltage; and a DC smoothing capacitor connected in series with output terminals of said circulating current type cycloconverter; said compensation current (IF) flowing through said DC smoothing capacitor.

Claim 8

The power conversion system according to one of claims 2 to 6: wherein a capacitance of said DC smoothing capacitor of said DC active filter is larger than a capacitance of said main smoothing capacitor.

Claim 9

The power conversion system according to claim 1: wherein said DC active filter controls said compensation current (IF) in response to a difference of a first DC current (Id1) outputted by said AC/DC power converter and a second DC current (Id2) fed into said load device.

Claim 10

The power conversion system according to claim 1: wherein said DC active filter controls said compensation current (IF) in response to a difference of a calculated value (Pc) of an AC instantaneous power of said AC/DC power converter and a calculated value (Pav) of a mean active power supplied from said single-phase AC power source.

Claim 11

The power conversion system according to claim 1: wherein said AC/DC power converter includes a PWM converter for controlling an input current (Is) supplied from said single-phase AC power source such that said first DC voltage (Vd) applied to said main smoothing capacitor is practically constant.

Claim 12

The power conversion system according to claim 10; wherein a command value (IF*) for said compensation current (IF) of said DC active filter is given as: IF*=(k1·ec*·Is*-k2·Vsm·Ism*)/Vd where a voltage command value of said PWM converter is ec*, an input current command value of said PWM converter is Is*, a peak value of said input current command value (Is*) of said PWM converter is Ism*, a peak value of an output voltage (Vs) of said single-phase AC power source is Vsm, a detection value of said first DC voltage of said main smoothing capacitor is Vd, and proportionality constants are k1 and k2.

Claim 13

The power conversion system according to claim 10: wherein, when said input current (Is) supplied from said single-phase AC power source and an output voltage (Vs) of said single-phase AC power source are controlled to be in-phase sine waves by said PWM converter, a command value (IF*) for said compensation current (IF) of said DC active filter is given as: IF*=-Ism·Vcm/(2·Vd)·cos (2ωt-θ) (during power running), and IF*=+Ism·Vcm/(2·Vd)·cos (2ωt-θ) (during regenerative operation) where VLsm=ω·Ls·Ism Vcm=(Vsm.sup.2 +VLsm.sup.2).sup.1/2 θ=tan.sup.-1 (VLsm/Vsm) and, where a peak value of said output voltage (Vs) of said single-phase AC power source is Vsm, a peak value of said input current (Is) of said PWM converter is Ism, and a detection value of said first DC voltage of said main smoothing capacitor is Vd.

Claim 14

The power conversion system according to claim 10: wherein, when said input current (Is) supplied from said single-phase AC power source is controlled to be a sine wave with lagging phase angle φ with respect to an output voltage (Vs) of said single-phase AC power source by said PWM converter, a command value (IF*) for said compensation current (IF) of said DC active filter is given as: IF*=-Ism·Vcm/(2·Vd)·cos (2ωt-θ-φ) (during power running), and IF*=+Ism·Vcm/(2·Vd)·cos (2ωt-θ-φ) (during regenerative operation) where Ism=(IPm.sup.2 +IQm.sup.2).sup.1/2 φ=tan.sup.-1 (IQm/IPm) VcP=Vsm-ω·Ls·IQm VcQ=-ω·Ls·IPm Vcm=(VcP.sup.2 +VcQ.sup.2).sup.1/2 θ=tan.sup.-1 (VcQ/VcP) and, where a peak value of said output voltage (Vs) of said single-phase AC power source is Vsm, a peak value of said input current (Is) of said PWM converter is Ism, an active component of said peak value (Ism) is IPm, a reactive component of said peak value (Ism) is IQm and a detection value of said first DC voltage of said main smoothing capacitor is Vd.

Claim 15

The power conversion system according to claim 1, wherein said load device includes: a PWM inverter connected to said main smoothing capacitor for converting said first DC voltage (Vd) into a three-phase AC voltage, and a three-phase induction motor driven by said PWM inverter.

Claim 16

A power conversion system, comprising: a single-phase AC power source for generating an AC power, wherein the frequency of fluctuation of said AC power is twice that of the frequency of said AC power source; an AC/DC power converter connected to said single-phase AC power source for converting said AC power into a DC power; a main smoothing capacitor connected to the DC terminals of said AC/DC power converter; a DC active filter connected in parallel with said main smoothing capacitor for controlling a compensation current (IF) flowing in said DC active filter such as to absorb an amount of fluctuation of said AC power supplied from said single-phase AC power source; a load device connected to said main smoothing capacitor as a DC voltage source for receiving said first DC voltage (Vd) applied to said main smoothing capacitor; and said AC/DC power converter further comprising a PWM converter for controlling an input current (Is) supplied from said single-phase AC power source such that said first DC voltage (Vd) applied to said main smoothing capacitor is practically constant.

Claim 17

A power conversion system, comprising: a single-phase AC power source for generating an AC power, wherein the frequency of fluctuation of said AC power is twice that of the frequency of said AC power source; an AC/DC power converter connected to said single-phase AC power source for converting said AC power into a DC power; a main smoothing capacitor connected to the DC terminals of said AC/DC power converter; a DC active filter connected in parallel with said main smoothing capacitor for controlling a compensation current (IF) flowing in said DC active filter such as to absorb an amount of fluctuation of said AC power supplied from said single-phase AC power source; a load device connected to said main smoothing capacitor as a DC voltage source for receiving said first DC voltage (Vd) applied to said main smoothing capacitor; and said AC/DC power converter further comprising a PWM converter for controlling an input current (Is) supplied from said single-phase AC power source such that said first DC voltage (Vd) applied to said main smoothing capacitor is practically constant.