Enhanced conduction angle power factor correction topology

Details Enhanced conduction angle power factor correction topology Enhanced conduction angle power factor correction topology

2002-04-01

2003-05-20

Sterrett, Jeffrey (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C363S048000

Reexamination Certificate

active

06567283

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improved topology for single and multi-phase power factor correction and improved total harmonic distortion (THD).
BACKGROUND ART
Electric power distribution is a necessary element of systems that operate with electronic power or in the distribution of electronic power. Electronic devices are generally connected to some power source wherein the power arrives in one form and is transferred and transformed into a form more suitable for the operation of the equipment.
Power is more efficiently transferred in AC form with most utilities providing AC sources. For devices requiring DC input, rectification of the AC source to DC is required. AC-DC converters may also be used to “actively” rectify and boost the resulting DC output. Power converters, such as inverters, are necessary in modem power systems for converting AC or DC power to conditioned AC for feeding a power grid or for direct connection to loads. The AC input power may come from any of the energy generating devices such as photovoltaics, micro-turbines, fuel cells, superconducting storage, wave energy, etc. . . . Modern systems need to be able to interconnect a variety of sources and provide stable power.
An example of a common inverter device is a half bridge circuit configuration. An AC input source connects to a full-wave rectifier with a smoothing capacitor connected to a DC output. Across the smoothing capacitor, a series circuit of switching elements is connected while these switching elements are turned alternately ON and OFF at a high frequency by a pulse width modulator (PWM). Across one of the switching elements, a series resonance circuit of a resonating inductor and a resonating capacitor is connected through a DC component cutting capacitor, while a load is connected in parallel across the resonating capacitor.
A DC voltage is generated at the smoothing capacitor so that the switching elements are alternately turned ON and OFF, with a high frequency rectangular wave voltage V is applied through the DC component cutting capacitor to the load, and a high frequency voltage is supplied to the load due to a resonating action of the resonating inductor and capacitor.
The resulting switching has an inherent inefficiency. The switching elements can be power MOSFET or IGBT, with the switching controlled so that an inverter circuit current will be at a delayed phase with respect to the high frequency rectangular wave voltage V. The power factor of the inverter circuit current is, therefore not unity with respect to the high frequency rectangular wave voltage. A larger current than that to be supplied to the load causes a switching loss. There are further problems because an “actively” controlled switching element of a large current rating is required, and a high cost incurred.
Another example of a power source device is a full-wave rectifier that connects to an AC input source with one of the switching elements connected through an inductor to the DC output of the full-wave rectifier. A smoothing capacitor is connected through a diode across the switching element. An input current in accordance with the input voltage from the AC power source is supplied. In this case, a voltage boosting chopper circuit is established by means of the inductor, one switching element, diode and smoothing capacitor, while the one switching element is also employed as a switching element of the inverter circuit.
To the smoothing capacitor, a series circuit of a pair of switching elements is connected, and a diode is connected in inverse parallel across each of these switching elements. Across one of these switching elements, an inverter load circuit is connected through a DC component cutting capacitor, and the inverter load circuit includes a series resonance circuit of another resonating inductor and a resonating capacitor, while a load is connected in parallel across the resonating capacitor. The respective switching elements are caused to be alternately turned ON and OFF by a DC voltage from the smoothing capacitor, and a rectangular wave voltage is supplied to the inverter load circuit, whereby a high frequency is caused to flow to the resonating inductor. The switching element also acts as a chopper circuit, so that an input current will be caused to flow through one of the inductors, the input current distortion is improved, and the smoothing capacitor is charged by an energy accumulated in the inductor.
It should be understood that a current from the resonating inductor and a current from the other inductor are made to flow to the switching element as superposed on each other so as to be a large current. This results in a power loss or inefficiency as the switching element has to be larger in size to handle larger loads.
Another example is a capacitor that is connected in series with an inductor, whereby the charging energy to the smoothing capacitor is weakened, and the voltage of the smoothing capacitor is restrained. The chopper operation turns ‘ON’ the switching elements which causes an input current to flow from the AC power source through the full-wave rectifier, another capacitor, the inductor, a switching element and full-wave rectifier, and an energy is accumulated in these another capacitor and one inductor.
As the switching element turns ‘OFF’, a current flows through the inductor, the diode, smoothing capacitor, full-wave rectifier, another capacitor and inductor, and the smoothing capacitor and capacitor are charged by a voltage induced at the inductor. Further, when the other switching element is turned ‘ON’, a current flows through another capacitor, another diode, another switching element, an inductor and another capacitor so that the other capacitor will be a power source, and a current in a reverse direction to that in the previous period is caused to flow to the one inductor.
Pulse Width Modulated (PWM) power inverters are generally available in three-phase bridge, H-bridge, and half bridge configurations. The rectifier fed, electrolytic bus capacitor banks often consist of two or more capacitors connected in series to expand the maximum bus voltage capacity. For distributed power applications a neutral is typically connected to the center of the DC bus, between the two series caps. The capacitor charge path of the PWM inverter is through the series capacitors simultaneously, tending to keep the total bus voltage (upper and lower bus voltages) constant.
However, a diode rectifier circuit such as is typically used by a switching power supply requires a large input current value relative to the power consumption as represented by an input power factor of about 0.6 to 0.67. Thus, the reactive power in supplying and distributing power systems is generally inefficient, as well as very high THD.
There have been numerous attempts to alleviate the problems and inefficiencies noted in the prior art devices.
FIG. 1
shows a basic schematic of a three phase AC input with a single boost. The inductor L is connected in series after the rectifier section
10
so that it operates on the rectified three phase AC signal. When the gating switch SW is turned ‘ON’, the current builds up in L. When the switch SW is turned ‘OFF’, the inductor charge L is discharged into the capacitor C and forms the output DC signal. Typically the switch SW is pulse width modulated to control the energy transfer.
FIG. 2
illustrates a basic schematic of a three phase four wire scheme with dual boost. Once again, the inductors L
1
and L
2
are connected after the rectifier section
20
. The switches SW
1
and SW
2
control the current flow and charging of the inductors L
1
and L
2
that are discharged into C
1
and C
2
respectively with the DC output level formed from the output capacitors C
1
and C
2
.
The basic schematic of
FIG. 3
illustrates a three phase active converter. In this circuit, the AC inductors L
1
-L
3
are each connected to the switches SW
1
-SW
6
, wherein a complicated switching control operates to “actively” rectify and boost the resulting DC voltage that is stored

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