US 5,625,545 AGranted

Medium voltage PWM drive and method

AssigneeHalmar Robicon Group

InventorPeter W. Hammond

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Abstract

An electric drive apparatus and method for controlling medium-voltage alternating current motors wherein a multi-phase power transformer having multiple secondary windings provides multi-phase power to multiple power cells, each of which have a single-phase output and are controllable by a modulation controller. The primary and secondary windings in the power transformer may be star- or mesh-connected; the secondary windings may be shifted in phase. Because the power cells are connected in series, the maximum output voltage for each cell may be less than the maximum line-to-line voltage. The power cells can have a tri-state output which can be controlled using pulse-width modulation techniques. AC input power is converted to DC output power for each output phase. Output power modulation can be produced by interdigitating a selected number of carrier signals so that harmonic components reflected back to the input are attenuated.

Claims48

Dependent claims

An electric drive for use with a multi-phase AC load comprising:

(a) a multi-phase power transformer, said power transformer having at least one primary winding circuit and a plurality of secondary winding circuits, said primary winding circuit being electrically connectable to a source of multi-phase AC power;
(b) a plurality of power cells, each of said plurality of power cells having an input connected with a respective one of said plurality of secondary winding circuits, each of said plurality of power cells having a single-phase controllable output to such multi-phase AC load, and said plurality of power cells being serially connected with respective others of said power cells in each phase output line to such multi-phase AC load;
(c) modulation control means connected to respective ones of said plurality of power cells, so that the output of said respective ones of said plurality of power cells is controlled;
(d) said plurality of power cells each having a rectifier electrically connected to a respective one of said plurality of secondary winding circuits and having an electrical output;
(e) said plurality of power cells includes a pre-selected number of power cells in series in each phase output line and said plurality of secondary winding circuits are spaced apart in electrical phase by a number of degrees equal to 60 divided by said pre-selected number thereby reducing harmonics in lines to said source;
and
(f) said modulation control means further having means for selectively controlling a switching event of each of said plurality of power cells so that said switching event of respective one of said plurality of power cells in each phase output line is spaced in time from said switching event of respective others of said plurality of power cells in the respective phase output line thereby reducing harmonic components in such output lines to such load.

4 more elements

An electric drive for use with a multi-phase AC load comprising:

(a) a multi-phase power transformer, said power transformer having at least one primary winding circuit and a plurality of secondary winding circuits, said primary winding circuit being electrically connectable to a source of multi-phase AC power;
(b) a plurality of power cells, each of:said plurality of power cells having an input connected with a respective one of said plurality of secondary winding circuits, each of said plurality of power cells having a single-phase controllable output to such multi-phase AC load, and said plurality of power cells being serially connected with respective others of said power cells in each phase output line to such multi-phase AC load;
(c) modulation control means connected to respective ones of said plurality of power cells, so that the output of said respective ones of said plurality of power cells is controlled;
(d) a bypass circuit connected between a first phase output line segment and a second phase output line segment for selecting bypassing at least one of said plurality of power cells;
said bypass circuit further having;
(i) a diode bridge connected between said first phase output line segment and said second phase output line, and said diode bridge having a gating control input line and a gating control output line;
(ii) bypass gating means, connected between said gating control input line and said gating control output line, for selectively providing a current path for said load current through said diode bridge;
(iii) voltage snubbing means for limiting a maximum voltage between said first phase output line segment and said second phase output line segment;
and
(iv) bypass means for selectively permitting said load current to pass through said bypass circuit.

7 more elements

An electric drive for use with a multi-phase AC load comprising:

(a) a multi-phase power transformer, said power transformer having at least one primary winding circuit and a plurality of secondary winding circuits, said primary winding circuit being electrically connectable to a source of multi-phase AC power;
(b) a plurality of power cells, each of said plurality of power cells having an input connected with a respective one of said plurality of secondary winding circuits, each of said plurality of power cells having a single-phase controllable output to such multi-phase AC load, and respective ones of said plurality of power cells being serially connected with respective others of said plurality of power cells in each phase output line to such multi-phase AC load;
(c) each of said plurality of power cells having
i. a rectifier electrically connected to a respective one of said plurality of secondary winding circuits and having an electrical output,
ii. a smoothing filter connected to said output of said rectifier,
iii. a converter connected to said smoothing filter, and the output of said converter connected to respective one of said phase output lines of such multi-phase load;
(d) modulation control means connected to each of said converter, so that the output of said converter is controlled, said control means having
i. a plurality of local modulator controllers connected to respective ones of said plurality of power cells,
ii. a master modulator controller operably connected to each of said plurality of local modulator controllers, and
iii. means for selectively controlling a switching event of each of said plurality of power cells so that said switching event of respective one of said plurality of power cells in each phase output line is spaced in time from said switching event of respective others of said plurality of power cells in the respective phase output line thereby reducing harmonic components in such output lines to such load.

7 more elements

An electric drive for use with a multi-phase AC load comprising:

(a) a multi-phase power transformer, said power transformer having at least one primary winding circuit and a plurality of secondary winding circuits, said primary winding circuit being electrically connectable to a source of multi-phase AC power;
(b) a plurality of power cells, each of said plurality of power cells having an input connected with are respective one of said plurality of secondary winding circuits, each of said plurality of power cells having a single-phase controllable output to such multi-phase AC load, and respective ones of said plurality of power cells being serially connected with respective others of said plurality of power cells in each phase output line to such multi-phase AC load;
(c) each of said plurality of power cells having
i. a rectifier electrically connected to a respective one of said plurality of secondary winding circuits and having an electrical output
ii. a smoothing filter connected to said output of said rectifier,
iii. a converter connected to said smoothing filter, and the output of said converter connected to respective one of said phase output lines such multi-phase load;
(d) modulation control means connected to each said converter, so that the output to said converter is controlled, said control means having
i. a plurality of local modulator controllers connected to respective ones of said plurality of power cells, and
ii. a master modulator controller operably connected to each of said plurality of local modulator controllers;
(e) a bypass circuit, connected between a first phase output line segment and a second phase output line segment, for selectively bypassing at least one of said plurality of power cells, said bypass circuit further having
a. a diode bridge connected between said first phase output line segment and said second phase output line segment, and said diode bridge having a gating control input line and a gating control output line;
b. gating means, connected between said gating control input line and said gating control output line, for selectively providing a current path for said load current through said diode bridge;
c. voltage snubbing means for limiting a maximum voltage between said first phase output line segment and said second phase output line segment;
and
d. bypass means for selectively permitting said load current to flow through said bypass circuit.

12 more elements

A method of controlling multi-phase AC power to a load comprising:

a. transforming an input voltage to a plurality of secondary voltage sources;
b. supplying power to each phase of said load from a plurality of power cells fed from said plurality of secondary voltage sources;
c. applying a multi-phase current to said load from a plurality of said power cells connected in series in each phase to said load;
d. selectively controlling the output of said power cells to one of a preselected positive voltage level, a preselected negative voltage level, and a generally zero voltage level;
(e) shifting in phase a plurality of said secondary power sources from said input voltage;
and
(f) selectively controlling a switching event of each of said power cells so that said switching event of respective one of said plurality of said power cells in phase output line is spaced in time from said switching event of respective others of said plurality of power cells in respective phase output line thereby reducing harmonic components in said phase output lines to said load;
(g) selectively applying at least one control signal to said plurality of said power cells so that each of said plurality of power cells conducts a current at a predetermined voltage, with a predetermined polarity, and for a predetermined duration;
and
h) interdigitating a preselected lumber of carrier signals to each of said plurality of said power cells so that harmonic components in a power frequency spectrum are generally attenuated.

7 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/203,803Filed 1 Mar 1994
Granted: 29 Apr 1997
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

H02M 7/49
Converters with outputs that each can have more than two voltages levels: combination of the output voltage waveforms of a plurality of converters
H02M 3/285
Using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC: single converters…
H02M 3/337
Using semiconductor devices only: in push-pull configuration
H02M 7/23
Using semiconductor devices only: arranged for operation in parallel