Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2002-07-30
2003-12-16
Sherry, Michael (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S037000, C307S046000, C307S048000, C307S066000
Reexamination Certificate
active
06665198
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power supply apparatus and a method for an input harmonic current suppression, an input power factor compensation, and an output voltage regulation, and especially to those applied to an uninterruptible power supply system.
BACKGROUND OF THE INVENTION
Power supply circuits are commonly used in equipment such as uninterruptible power supply system, motor drives, and other applications. Conventional UPSs use a variety of different circuit topologies, including standby, line-interactive and on-line topologies. Generally, each of three topologies has advantages and disadvantages. The selection of an uninterruptible power supply is varied, which depends on the needs of the application.
The major difference between topologies is whether, under normal conditions, the load is supplied from a primary AC power source. A typical standby UPS topology includes a switch that directly connects the load to the primary AC power source under normal conditions and that transfers the load to a secondary AC source derived from a battery or other auxiliary source when the primary AC power source fails. Due to the time needed to operate the switch, such a standby UPS often exhibit a significant interruption in power delivered to the load. In addition, standby UPSs often do not compensate for the power quality, e.g., voltage sag, voltage dip, harmonic distortion and low power factor. Nevertheless, the standby topology is often used for low-cost UPSs, because it is more cheaper to produce than other topologies.
A typical on-line UPS includes a series train of an AC/DC converter and a DC/AC inverter. The AC/DC converter converts the primary AC power source to a DC voltage on a DC bus and the DC/AC inverter converts the DC voltage to an AC output voltage at a load from an AC input voltage provided by the primary AC power source such as the utility. For this reason, on-line UPSs are also sometimes called a ‘double-conversion’ UPS. Typically, the on-line UPS includes the DC bus link that is used to isolate the load from disturbance and other sag of the primary AC power source. Also, the DC bus is also coupled to an auxiliary source of power, such as a battery, which maintains the DC voltage on the DC bus as the primary AC power source fails. In addition, the AC output voltage of an on-line UPS is well regulated, and there's no interruption in the supply to the load when the primary AC power source fails. Other circuits, such as filters and regulators, may be included in the path with the rectifier and the inverter. An on-line UPS can also have a power factor correction (PFC) circuit built into the rectifier. However, an on-line UPS is less efficient than a standby UPS, but guarantees that the supply to the load is clean and well regulated inspite of the condition of the primary AC power source.
A line interactive UPS may use a switch arrangement similar to that of the standby topology, but may also include means for regulating and conditioning the AC power source to improve the power quality. The Line-interactive UPS is limited in capacity, which is impractical over 5 KVA.
Hence, the development of an UPS with the performance of high input power factor, low input current harmonic, high efficiency and compensation for voltage sags and dips is very important. UPS systems are, however, relatively very expensive. 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 power supply apparatus and a method with the performance of input harmonic currents suppression, input power factor compensation, and an output voltage regulation.
According to an aspect of the present invention, a power supply apparatus includes an input port, an output port, an energy storage device for providing a first voltage, a first power converter electrically connected to the energy storage device for providing a first compensating voltage from the first voltage, and electrically connected in parallel with the input port for controlling the first compensating voltage such that an input current at the input port is a substantial sinusoidal wave and in phase with an input voltage at the input port, a link inductor electrically connected between the input port and the first power converter for providing isolation between the input voltage and the first compensating voltage, and a second power converter electrically connected in series with the output port for providing a second compensating voltage from the first voltage to maintain an output voltage at the output port.
Preferably, the power supply apparatus further includes a backup power supply function, which the first power converter provides the first compensating voltage as a main power when an AC power source at the input port is interrupted.
Preferably, an input power factor at the input port is approaching to a unity power factor.
Preferably, the first compensating voltage is a vector addition of the input voltage and a second voltage where a voltage vector of the second voltage is substantially perpendicular to a voltage vector of the input voltage.
Preferably, the power supply apparatus includes an uninterruptible power supply (UPS).
Preferably, the first voltage is a DC bus voltage.
Preferably, the energy storage device includes a battery.
Preferably, the first power converter includes a first switching circuit electrically connected to the energy storage device for providing the first compensating voltage from the first voltage, a first filter inductor having one end electrically connected to an output end of the first switching circuit and the other end electrically connected to the link inductor for filtering the first compensating voltage, a first filter capacitor electrically connected in parallel with the first filter inductor for filtering the first compensating voltage, and a first control device electrically connected to the first switching circuit for controlling the first switching circuit to generate the first compensating voltage in response to a first control signal.
Preferably, the first control device includes a first subtractor for subtracting a feedback signal of the first voltage from a first command signal to determine a second command signal, a first compensator electrically connected to the first subtractor for generating a third command signal by compensating the second command signal, a sinusoidal signal generator electrically connected to the AC power source for capturing both phase and frequency of the input voltage to generate a first sinusoidal signal with unity amplitude, a first phase shift circuit electrically connected to the sinusoidal signal generator for processing a phase shift of the first sinusoidal signal to generate a second sinusoidal signal, a multiplier electrically connected to the first phase shift circuit and the first compensator to multiply the third command signal by the second sinusoidal signal to generate a fourth command signal, a second subtractor electrically connected to the AC power source and the multiplier for subtracting the fourth command signal from an input voltage signal and to generate a fifth command signal, a third subtractor for subtracting a feedback signal of the first compensating voltage from the fifth command signal to generate a sixth command signal, a first controller electrically connected to the third subtractor for processing a signal processing of the sixth command signal to generate a first modulation signal, and a first pulse width modulation generator electrically connected to the first controller for transforming the first modulation signal to generate a first pulse width modulation signal which operates the first switching circuit to provide the first compensating voltage.
Preferably, the first command signal is a DC bus reference voltage signal.
Preferably, the feedback signal of the first voltage is a feedback signal of the DC bus voltage.
Preferably, the first phase shift circuit processes a
Chou Hung-Liang
Tasi Wen-Yin
Wu Chin-Chang
Delta Electronics , Inc.
Laxton Gary L.
Sherry Michael
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