Hybrid series active/parallel passive power line conditioner with controlled harmonic injection
First Claim
1. A power line conditioner, comprising:
- an active filter, said active filter being coupled, in series through a series transformer, to a three-phase power distribution network, said three-phase power distribution network including a voltage source inducing three-phase input currents at a first end of said three-phase power distribution network, a load at a second end of said three-phase power distribution network, said load circulating three-phase load currents;
a passive filter coupled, in parallel, to said three-phase power distribution network; and
an active filter controller coupled to said active filter, said active filter controller including means for generating control signals to force said active filter, with signals applied to said series transformer, to allow a predetermined amount of load harmonics into said voltage source, said load harmonics corresponding to selected harmonics of said three-phase load currents, and thereby reduce the voltage distortion at said passive filter.
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Abstract
A power line conditioner includes an active filter coupled, in series, and a passive filter coupled, in parallel, to a three-phase power distribution network. The three-phase power distribution network includes a voltage source that induces three-phase input currents at a first end of the three-phase power distribution network. A load, circulating three-phase load currents, is positioned at a second end of the three-phase power distribution network. The active filter controller of the invention uses synchronous transformations to identify selected harmonic reference components corresponding to individual harmonics of the three-phase load currents. The selected harmonic reference components are multiplied by a predetermined factor corresponding to a permissible percentage of the individual harmonics that may be injected into the supply voltage. This results in active filter reference signal components that are applied to the active filter. In response to the active filter reference signal components, the active filter injects a permissible percentage of harmonics into the supply voltage so as to reduce the voltage distortion at the passive filter. By reducing voltage distortion, the controlled injection of harmonics into the supply allows for a simplified passive filter design. Consequently, the passive filter may be implemented as a power factor correction capacitor.
93 Citations
21 Claims
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1. A power line conditioner, comprising:
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an active filter, said active filter being coupled, in series through a series transformer, to a three-phase power distribution network, said three-phase power distribution network including a voltage source inducing three-phase input currents at a first end of said three-phase power distribution network, a load at a second end of said three-phase power distribution network, said load circulating three-phase load currents; a passive filter coupled, in parallel, to said three-phase power distribution network; and an active filter controller coupled to said active filter, said active filter controller including means for generating control signals to force said active filter, with signals applied to said series transformer, to allow a predetermined amount of load harmonics into said voltage source, said load harmonics corresponding to selected harmonics of said three-phase load currents, and thereby reduce the voltage distortion at said passive filter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of operating a power line conditioner of the type including an active filter serially coupled, through a series transformer, to a three-phase power distribution network and a passive filter parallely coupled to said three-phase power distribution network, said three-phase power distribution network including a voltage source inducing three-phase input currents at a first end of said three-phase power distribution network and a load at a second end of said three-phase power distribution network, said load circulating three-phase load currents, said method comprising the steps of:
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identifying, with an active filter controller, selected harmonic signals corresponding to specific harmonic signals of said three-phase load currents; establishing, with said active filter controller, a controlled percentage of said selected harmonic signals; and forcing said active filter, with signals received from said active filter controller and applied to said series transformer, to allow said controlled percentage of said selected harmonic signals into said voltage source to reduce the voltage distortion at said passive filter. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification