This application claims the benefit of Taiwan application Serial No. 97131340, filed Aug. 15, 2008, the subject matter of which is incorporated herein by reference.
1. Field of the Invention
The invention relates in general to a power conversion system and a power conversion method thereof, and more particularly to a power conversion system for respectively and independently supplying electric powers to a driving unit and a control unit, and a power conversion method thereof.
2. Description of the Related Art
However, the conventional power conversion system 10 includes the following drawbacks. First, the control unit 140 and the driving unit 130 share the same DC power VDC1, so the power ripple ΔV1 of the DC power VDC1 can reach as high as 7V, thereby seriously influencing the stability of the circuit operation of the control unit 140. Second, the size of the power ripple ΔV1 changes with the variations of the frequency of the AC power AC, the capacitor Cin1 and the load 20. Thus, if the power ripple ΔV1 is to be kept unchanged with the change of the load 20, the capacitance of the capacitor Cin1 has to be increased so that the system cost is increased. Third, if the frequency of the AC powerAC is too low, the capacitance of the capacitor Cin1 also has to be increased so that the system cost is increased. Fourth, when the power ripple ΔV1 is too large, the circuit design may become difficult.
The invention is directed to a power conversion system and a power conversion method thereof, wherein electric powers are respectively and independently supplied to a driving unit and a control unit. Thus, the following advantages can be obtained.
First, because the driving unit and the control unit are respectively and independently powered, the control unit has the better stability.
Second, the driving unit and the control unit are respectively and independently powered and the power consumption of the control unit is small. So, a capacitor with the lower capacitance can be selected to filter the DC power inputted to the control unit so that the system cost can be reduced.
Third, the power ripple of the DC power inputted to the control unit is greatly reduced. So, the difficulty of the circuit design can be reduced.
According to a first aspect of the present invention, a power conversion system is provided. The power conversion system includes a driving unit, a control unit, a first DC power supply circuit and a second DC power supply circuit. The control unit controls the driving unit to drive a load. The first DC power supply circuit converts an AC power into a first DC power outputted to the driving unit, while the second DC power supply circuit converts the AC power into a second DC power outputted to the control unit.
According to a second aspect of the present invention, a power conversion method is provided. The power conversion method includes the steps of: converting an AC power into a first DC power outputted to a driving unit; and converting the AC power into a second DC power outputted to a control unit to control the driving unit to drive a load.
The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.
The DC power supply circuit 310 and the DC power supply circuit 320 respectively and independently supply the powers to the driving unit 330 and the control unit 340. So, the stability of the control unit 340 cannot be influenced even if the DC power VDC2 has the very large power ripple and noise. In addition, as shown in
The DC power supply circuit 310 and the DC power supply circuit 320 respectively and independently supply the powers to the driving unit 330 and the control unit 340, and the control unit 340 has the low power consumption. So, the selected capacitor Cin2 may have the smaller capacitance to decrease the system cost.
The control unit 340 is, for example, a buck-boost converter, a buck converter or a boost converter. The driving unit 330 may be, for example, a pulse width modulation (PWM) controller or a pulse frequency modulation (PFM) controller. In order to make the invention be easily understood, the driving unit 330 and the control unit 340 of
The driving unit 330 and the control unit 340 are respectively a buck-boost converter and a PFM controller, for example. The PFM controller includes a switch terminal SW, a ground GND, a power supply source VCC, a feedback terminal FB and an output terminal Vo. The ground GND is coupled to the ground, and the power supply source VCC receives the DC power VDC3 outputted from the DC power supply circuit 320.
In detail, the driving unit 330 includes an inductor L, a diode D6, a capacitor Co and a resistor RFB. A first terminal of the inductor L is coupled to first terminals of the rectifying unit 312 and the capacitor Co, and a second terminal of the inductor L is coupled to a positive terminal of the diode D6 and the switch terminal SW of the control unit 340. A second terminal of the capacitor Co is coupled to a negative terminal of the diode D6, the output terminal Vo of the control unit 340 and a first terminal of the resistor RFB. A second terminal of the resistor RFB is coupled to the feedback terminal FB of the control unit 340 in order to adjust the output voltage Vo according to a level of a feedback signal of the resistor RFB. When the driving unit 330 is the buck-boost converter, the output voltage Vo may be lower than, higher than or equal to the DC power VDC2. The control unit 340 controls the driving unit 330 to output the output voltage Vo according to a duty cycle D of a PWM signal, wherein the output voltage is equal to:
In the power conversion system and the power conversion method thereof, the electric powers are respectively and independently supplied to a driving unit and a control unit. Thus, the following advantages can be obtained.
First, because the driving unit and the control unit are respectively and independently powered, the control unit has the better stability.
Second, the driving unit and the control unit are respectively and independently powered and the power consumption of the control unit is small. So, a capacitor with the lower capacitance can be selected to filter the DC power inputted to the control unit so that the system cost can be reduced.
Third, the power ripple of the DC power inputted to the control unit is greatly reduced. So, the difficulty of the circuit design can be reduced.
While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
Number | Date | Country | Kind |
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97131340 | Aug 2008 | TW | national |