Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
2002-10-23
2004-09-14
Patel, Rajnikant B (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S098000, C363S132000
Reexamination Certificate
active
06791850
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a DC-to-AC power inverter and a method of operation for the DC-to-AC power inverter, and more particular to those applied to DC-to-AC power inverters.
BACKGROUND OF THE INVENTION
DC-to-AC power inverters are commonly used in equipment such as uninterruptible power supplies (UPSs), motor drives, and other applications. Conventional DC-to-AC power inverters use a pulse width modulated technique to stabilize the output voltage thereof. Please refer to
FIG. 1
which is a schematic diagram illustrating a DC-to-AC power inverter according to the prior art. As shown
FIG. 1
, the DC-to-AC power inverter
100
includes a switching circuit
101
, a RMS voltage calculation module
102
, a summing module
103
, a voltage control module
104
, a phase lock loop
105
, a multiplier module
106
, and a voltage mode control circuit
107
. Meanwhile, the voltage mode control circuit
107
operates the switching circuit
101
as a voltage controlled inverter. The voltage mode controller
108
is here shown as including a plurality of modules executing on a combination of a data processor (e.g., a microprocessor, digital signal processor (DSP), or combination thereof) and an associated memory. The modules include the RMS voltage calculation module
102
that computes an RMS voltage V
rms
from an output voltage V
out
sensed at the output port
109
. The RMS voltage V
rms
is subtracted from a first reference voltage signal V
ref1
at a summing module
103
to determine a second reference voltage signal V
ref2
. The second reference voltage signal V
ref2
is modulated by the voltage control module
104
to generate a third reference voltage signal V
ref3
. The reference signal &thgr; is processed by the phase lock loop
105
and multiplied by the third reference voltage signal V
ref3
in the multiplier module
106
to produce a computed reference voltage signal V
ref
. Hence the voltage mode control circuit
107
responsive to the reference voltage signal V
ref
and the output voltage V
out
operates the switching circuit
101
as a voltage controlled inverter.
Generally speaking, there are some drawbacks in the typical parallel operation of an uninterruptible power supply system to be described as follows:
(1) Computationally intensive operations, such as RMS voltage calculations, need a complex circuit or expensive circuit, such as the DSP chip to implement the calculation.
(2) On the other hand, the DC-to-AC power inverter needs a multiplier module to perform the voltage command signal calculation. It will exhaust a great amount of hardware resources to perform the voltage command signal calculation, whether it is implemented by digital signal processing architectures or corresponding analog signal processing architectures.
It is therefore attempted by the applicant to deal with the above situation encountered with the prior art.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to propose a DC-to-AC power inverter and a method of operation for the DC-to-AC power inverter to reduce computationally intensive operations, such as RMS voltage calculations and multiplication calculations.
According to an aspect of the present invention, a DC-to-AC power inverter includes an input port, an output port, a switching circuit electrically connected between the input port and the output port responsive to control signals to convert a DC voltage at the input port to an AC output voltage, and a system controller for sensing the AC output voltage at the output port and transforming the AC output voltage to generate a first reference current signal, for sensing an output current at the output port to generate an output current signal, for generating a reference current signal by adding the first reference current signal to the output current signal, and for generating the control signals responsive to the reference current signal and a sensed inverter current signal by sensing an inverter current at the switching circuit.
Preferably, the system controller includes a inverter current sensor coupled to the switching circuit for sensing the inverter current at the switching circuit to generate the inverter current signal, an output current sensor for sensing the output current at the output port to generate the output current signal, a voltage control circuit coupled to the output port and the output current sensor for generating the reference current signal responsive to the output current signal and the sensed output voltage signal, and a current mode control circuit coupled to the voltage control circuit to generate the control signals responsive to the first reference current signal.
Preferably, the voltage control circuit includes a voltage sensor coupled to the output port for sensing the AC output voltage to generate the output voltage signal, a subtractor received the output voltage signal and a reference voltage signal for generating an error voltage signal by subtracting the output voltage signal from the reference voltage signal, a voltage controller coupled to the subtractor for transforming the error voltage signal to the first reference current signal, and an adder coupled to the voltage controller and the output current sensor for generating the reference current signal responsive to the first reference current signal and the output current signal.
According to another aspect of the present invention, a control method for a DC-to-AC power inverter, wherein the DC-to-AC power inverter comprises an input port, an output port, a switching circuit electrically connected between the input port and the output port responsive to control signals to convert a DC voltage at the input port to an AC output voltage, includes the steps of sensing the AC output voltage at the output port and transforming the AC output voltage to generate a first reference current signal, sensing an output current at the output port to generate an output current signal, generating a reference current signal by adding the first reference current signal to the output current signal, and generating the control signals responsive to the reference current signal and a sensed inverter current signal by sensing an inverter current at the switching circuit.
Preferably, the control method further includes the steps of sensing the inverter current at the switching circuit to generate the inverter current signal, sensing the output current at the output port to generate the output current signal, generating the first reference current signal responsive to the output current signal and the sensed output voltage signal, and generating the control signals responsive to the first reference current signal.
Preferably, the control method further includes the steps of sensing the AC output voltage to generate the output voltage signal, generating an error voltage signal by subtracting the output voltage signal from the reference voltage signal, transforming the error voltage signal to the first reference current signal, and generating the reference current signal responsive to the first reference current signal and the output current signal.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which:
REFERENCES:
patent: 4947310 (1990-08-01), Kawabata et al.
patent: 5442538 (1995-08-01), Ikeda et al.
Pai Fu-Sheng
Tsai Ming-Tsung
Delta Electronics , Inc.
Patel Rajnikant B
Volpe and Koenig P.C.
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