# Patent

## Title
Dual-source converter with auxiliary circuit and controller

## Abstract

Disclosed is a dual-source converter for a hybrid power supply. The converter includes a first power circuit, a second power circuit, an auxiliary circuit, an output circuit and a closed loop circuit. The first power circuit is electrically connected to the second power circuit in series for receiving two varied voltage sources. The auxiliary circuit is configured to achieve soft switching of all switches. The closed loop circuit is configured to control the duty cycles of the first power circuit, the second power circuit and the auxiliary circuit so as to improve the efficiency of the dual-source converter.

## Background
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a converter and, more particularly, to a dual-source converter that can be switched between a single-source mode and a dual-source mode.
2. Related Prior Art
As the population of the world is growing, the consumption of energy is increasing while the reserve of non-renewable energy is declining. Hence, It is getting more important to use renewable energy. To use various types of the renewable energy, there are various types of devices such as fuel cells, solar cells and wind turbines. With help from power electronics and automation techniques, these devices can be used in vehicles, uninterruptible power supplies and independent generators for example. The fuel cells, solar cells and wind turbines however generate current at low voltage. Moreover, the voltage of the current fluctuates with load or the power production is limited by the natural environment. Generally speaking, the renewable energy cannot be sued in ordinary electric appliances directly. Therefore, DC/DC converters are necessary electric devices for using the renewable energy.
Conventionally, one set of electric devices for using the renewable energy is used together with one set of converters to convert the various types of the renewable energy. A conventional system includes many converters connected in parallel to a DC high-voltage bus, and is used as a power source in front of an inverter or used as a direct power source for an electric appliance. The conventional system is however bulky, complicated and expensive. Most of the DC/DC converters are conventional boost-type DC/DC converters. By adjusting the duty cycle of a switch, the boost ratio is controlled. There is however a problem with this process. Conventionally, the switching of the switch is hard switching, and there is a reverse recovery current in an output diode. In the transient on state of a power semiconductor switch, a huge current travels through the output diode to build a reverse-biased voltage. However, the large current, which travels through the semiconductor switch, incurs a serious loss in the switching and a low conversion efficiency.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.
SUMMARY OF INVENTION
It is an objective of the present invention to provide a dual-source converter for executing soft switching with a low loss in turning on.
It is another objective of the present invention to provide a dual-source converter that can be used in a hybrid generation system to effectively increase the total conversion efficiency but reduce the cost of building the hybrid generation system.
To achieve the foregoing objectives, the dual-source converter includes a first power source circuit, a second power source circuit, an auxiliary circuit, an output circuit and a closed-loop controller. The first power source circuit includes a first power-source switch and a first switch. The first power-source switch is electrically connected to a first power source. The first switch is coupled to the first power-source switch. The first power source circuit converts the first power source to a first current source. The second power source circuit is connected, in series, to the first power source circuit. The second power source circuit includes a second power-source switch and a second switch. The second power-source switch is electrically connected to a second power source. The second switch is coupled to the second power-source switch. The second power source circuit converts the second power source to a second current source. The auxiliary circuit includes an auxiliary switch, a first auxiliary diode, a second auxiliary diode, an auxiliary capacitor and an auxiliary inductor. The auxiliary switch includes first and second ends. The second end of the auxiliary switch is coupled to a first end of the first switch. The first auxiliary diode includes first and second ends. The first end of the first auxiliary diode is electrically connected to the second end of the auxiliary switch. The second auxiliary diode includes first and second ends. The first end of the second auxiliary diode is electrically connected to the second end of the first auxiliary diode. The second end of the second auxiliary diode is electrically connected to the first end of the auxiliary switch. The second auxiliary diode is used to suppress a voltage across the first auxiliary diode. The auxiliary capacitor includes first and second ends. The first end of the auxiliary capacitor is electrically connected to the first end of the auxiliary switch. The second end of the auxiliary capacitor is electrically connected to the second end of the second switch. The auxiliary capacitor is used to store energy of the first and second current sources. The auxiliary inductor includes first and second end. The first end of the auxiliary inductor is electrically connected to the second end of the first auxiliary diode. The auxiliary inductor is used to release the energy of the first and second current sources from the auxiliary capacitor. The auxiliary circuit stores or releases the energy of the first and second current sources by switching the auxiliary switch. The output circuit is electrically connected to the auxiliary circuit. The output circuit receives the energy of the first and second current sources from the auxiliary inductor. The closed-loop controller is electrically connected to the first and second power source circuits, the auxiliary circuit and the output circuit. Based on a feedback signal and a command signal, the closed-loop controller controls duty cycles of the first and second switches and the auxiliary switch so that the first and second switches and the auxiliary switch can be switched at zero voltage. The closed-loop controller controls the switching of the first and second power switches so that the first and second power sources are connected or cut off.
In another aspect, each of the first power source and the second power source is selected from the group consisting of a secondary cell, a super capacitor, a fuel cell, a solar cell, a DC wind turbine and a rectified AC wind turbine.
In another aspect, the first power source circuit further includes a first inductor between the first power-source switch and the first switch. The second power source circuit further includes a second inductor between the second power-source switch and the second switch. The first inductor and the second inductor respectively filter out current ripples from the first power source and the second power source and store the energy of the first and second power sources.
In another aspect, the first power source circuit further includes a first inductor connected, in parallel, to the first power source. The second power source circuit further includes a second inductor connected, in parallel, to the second power source. The first inductor and the second inductor respectively filter out current ripples from the first power source and the second power source and store the energy of the first and second power sources.
In another aspect, the closed-loop controller includes a controlling circuit and a driving circuit. The controlling circuit compares the feedback signal with the command signal and provides a controlling signal according to the comparison. The driving circuit provides a plurality of driving signals to the first switch, the second switch and the auxiliary switch according to the controlling signal. The driving circuit provides a plurality of switching signals to the first power-source switch and the second power-source switch.
In another aspect, the feedback signal is provided from the first power source circuit, the second power source circuit or the output circuit. The command signal is a nominal current or voltage corresponding to the feedback signal.
In another aspect, the driving signals include a first switch-driving signal, a second switch-driving signal and an auxiliary switch-driving signal. The auxiliary switch-driving signal is the sum of a signal complementary to the first switch-driving signal and another signal complementary to the second switch-driving signal.
In another aspect, the duty cycles of the first switch-driving signal and the second switch-driving signal get longer but the duty cycle of the auxiliary switch-driving signal gets shorter as the controlling signal gets larger. The duty cycles of the first switch-driving signal and the second switch-driving signal get shorter but the duty cycle of the auxiliary switch-driving signal gets longer as the controlling signal gets smaller.
In another aspect, the switching signals include a first power-source switch-switching signal and a second power source-switching signal to control the switching of the first power-source switch and the second power-source switch, respectively.
In another aspect, when the first auxiliary diode builds a reverse-biased voltage, while an auxiliary inductor current continues to travel through the auxiliary inductor, the second auxiliary diode provides a path with a reduced loss in turning on. The auxiliary inductor current travels to the auxiliary capacitor through the second auxiliary diode to reduce a current that travels through a parasitic diode of the auxiliary switch.
Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings.



BRIEF DESCRIPTION OF DRAWINGS
The present invention will be described via detailed illustration of the preferred embodiment referring to the drawings wherein:
FIG. 1 is a block diagram of a dual-source converter according to the preferred embodiment of the present invention;
FIG. 2 shows an equivalent circuit of the dual-source converter shown in FIG. 1;
FIGS. 3A-3G shows the dual-source converter shown in FIG. 1, in a single-source mode;
FIG. 4 shows the waveforms of various signals of the dual-source converter in the single-source mode shown in FIGS. 3A-3G versus time;
FIGS. 5A-5N shows the dual-source converter shown in FIG. 1, in a dual-source mode;
FIG. 6 shows the waveforms of various signals of the dual-source converter in the dual-source mode shown in FIGS. 5A-5N versus time;
FIG. 7 shows the waveforms of various signals of the dual-source converter shown in FIG. 1 in the single-source mode;
FIG. 8 shows the waveforms of various signals of the dual-source converter shown in FIG. 1 in the dual-source mode;
FIG. 9 shows the conversion efficiency of the dual-source converter shown in FIG. 1 in the single-source mode; and
FIG. 10 shows the conversion efficiency of the dual-source converter shown in FIG. 1 in the dual-source mode.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring to FIG. 1, a dual-source converter 1 includes a first power source circuit 101, a second power source circuit 103, an auxiliary circuit 105, an output circuit 107 and a closed-loop controller 109 according to the preferred embodiment of the present invention. The first power source circuit 101 is electrically connected to the second power source circuit 103 in series. The auxiliary circuit 105 is electrically connected to both of the first power source circuit 101 and the second power source circuit 103. The output circuit 107 is electrically connected to the auxiliary circuit 105. The closed-loop controller 109 is electrically connected to all of the first power source circuit 101, the second power source circuit 103, the auxiliary circuit 105 and the output circuit 107.
In the preferred embodiment, the first power source circuit 101 includes a first power switch Sp1, a first capacitor C1, a first inductor L1 and a first switch S1. The positive end of the first power switch Sp1 is electrically connected to the positive end of a first power source V1. The positive end of the first capacitor C1 is electrically connected to the negative end of the first power switch Sp1. The negative end of the first capacitor C1 is electrically connected to the negative end of the first power source V1. The first power source V1, the first power switch Sp1 and the first capacitor C1 together form a loop.
Moreover, the positive end of the first inductor L1 is electrically connected to the positive end of the first capacitor C1. The drain of the first switch S1 is electrically connected to the negative end of the first inductor L1. The source of the first switch S1 is electrically connected to the negative end of the first capacitor C1. The first capacitor C1, the first inductor L1 and the first switch S1 together form another loop.
In the preferred embodiment, the second power source circuit 103 includes a second power-source switch Sp2, a second capacitor C2, a second inductor L2 and a second switch S2. The positive end of the second power source Sp2 is electrically connected to the positive end of the second power source V2. The positive end of the second capacitor C2 is electrically connected to the negative end of the second power-source switch Sp2. The negative end of the second capacitor C2 is electrically connected to the negative end of the second power source V2. The second power source V2, the second power-source switch Sp2 and the second capacitor C2 together form a loop.
Moreover, the positive end of the second inductor L2 is electrically connected to the positive end of the second capacitor C2. The source of the second switch S2 is electrically connected to the negative end of the second capacitor C2. The drain of the second switch S2 is electrically connected to the negative end of the second inductor L2 and the source of the first switch S1. That is, the second power source circuit 103 is connected, in series, to the first power source circuit 101 by the connection of the second switch S2 to the first switch S1. The second inductor L2, the second capacitor C2 and the second switch S2 together form a loop.
The first switch S1 and the second switch S2 are power semiconductor switches. The first power source V1 and the second power source V2 can be secondary cells, super capacitors, fuel cells, solar cells, DC wind turbines or rectified AC wind turbines. The first power source V1 and the second power source V2 can be of a same type or two different types.
The dual-source converter 1 of the present invention is characterized by that the first and second power source circuits are used for different types of renewable energy, and that the two types of energy can be converted to a stable first current and a stable second current, and that the first and second power sources can be switched to one another flexibly. However, the elements included in the first power source circuit 101 and the second power source circuit 103 and their interconnection are not limited to those discussed above. Those skilled in the art can modify the preferred embodiment and achieve the same effects.
In the preferred embodiment, the auxiliary circuit 105 includes an auxiliary switch Sa, a first auxiliary diode Da1, a second auxiliary diode Da2, an auxiliary capacitor Ca and an auxiliary inductor La. The source of the auxiliary switch Sa is electrically connected to the drain of the first switch S1. The anode of the auxiliary diode Da1 is electrically connected to the source of the auxiliary switch Sa. The anode of the auxiliary diode Da2 is electrically connected to the cathode of the first auxiliary diode Da1. The cathode of the second auxiliary diode Da2 is electrically connected to the drain of the auxiliary switch Sa. The positive end of the auxiliary capacitor Ca is electrically connected to the drain of the auxiliary switch Sa. The negative end of the auxiliary capacitor Ca is electrically connected to the source of the second switch S2. The positive end of the auxiliary inductor La is electrically connected to the cathode of the auxiliary diode Da1.
The auxiliary circuit 105 is characterized by the connection to both of the first power source circuit 101 and the second power source circuit 103. By switching the auxiliary switch Sa, electricity of the first current source and electricity of the second current source are stored or released to protect the first switch S1 and the second switch S2. Therefore, the elements of the auxiliary circuit 105 and their interconnection are only given for exemplary purposes. Those skilled in the art can modify the preferred embodiment and achieve the same effects.
In the preferred embodiment, the output circuit 107 includes an output capacitor Co. The positive end of the capacitor Co is electrically connected to the negative end of the auxiliary inductor La. The negative end of the capacitor Co is electrically connected to the negative end of the auxiliary capacitor. The output circuit 107 is used to provide an output voltage to an output load Ro. The output load Ro is connected, in parallel, to the capacitor Co.
In the preferred embodiment, the closed-loop controller 109 includes a controlling circuit 1091 and a driving circuit 1093. The controlling circuit 1091 is coupled to the driving circuit 1093. The controlling circuit 1091 receives a feedback signal Sf from the first power source circuit 101, the second power source circuit 103 or the auxiliary circuit 105. Furthermore, the controlling circuit 1091 receives a command signal Sc corresponding to the feedback signal Sf. The command signal Sc is the nominal signal of the feedback signal Sf. A first switch-driving signal T1, a second switch-driving signal T2 and an auxiliary switch-driving signal Ta are provided from the driving circuit 1093 to adjust the duty cycles of the first switch S1, the second switch S2 and the auxiliary switch Sa. Moreover, the driving circuit 1093 can provide a first power-source switching signal Tp1 and a second power-source switching signal Tp2 to trigger the first power switch Sp1 and the second power-source switch Sp2. Thus, the closed-loop controller 109, the first power source circuit 101, the second power source circuit 103, the auxiliary circuit 105 and the output circuit 107 together form a control mechanism.
Referring to FIG. 2, there is shown a dual-source converter 1′ equivalent to the dual-source converter 1. In FIG. 2, the directions of the voltage and current in every element are marked up while the closed-loop controller 109 is omitted. Referring to FIGS. 1 and 2, the operation and functions of the dual-source converter 1′ will be described in detail.
Referring to FIG. 2, regarding the dual-source converter 1′, there are several assumptions. At first, all of the first capacitor C1, the second capacitor C2, the auxiliary capacitor Ca and the output capacitor Co include sufficient capacities, and are equivalent to constant voltage sources. The voltage across the auxiliary capacitor Ca is the auxiliary capacitor voltage Va, and the voltage across the output capacitor Co is the output voltage Vo. Secondly, the first switch S1, the second switch S2, the auxiliary switch Sa, the first auxiliary diode Da1 and the second auxiliary diode Da2 are ideal elements, and the voltages across the above-mentioned elements can be ignored when they are turned on. Thirdly, the first power-source switch Sp1 and the second power-source switch Sp2 can be ignored when they are turned on.
The operation of each of the circuits included in the dual-source converter 1′ will be described later. By switching the first power switch Sp1, the first power source circuit 101 converts the first power source V1 to a first inductor current iL1, electric energy in the form of a current. By switching the second power-source switch Sp2, the second power source circuit 103 converts the second power source V2 to a second inductor current iL2, electric energy in the form of a current. The auxiliary circuit 105 stores the electric energy of the first inductor current iL1 and the electric energy of the second inductor current iL2 through the auxiliary capacitor Ca. The auxiliary inductor La is used to release electric energy from the auxiliary capacitor Ca to the output circuit 107. In the storage and release of the electric energy, flexible switching and highly efficient conversion are achieved by switching the auxiliary switch Sa. The voltage across the second auxiliary diode Da2 is used to suppress the voltage across the first auxiliary diode Da1, i.e., to suppress the first auxiliary diode voltage vDa1. The output circuit 107 uses the output capacitor Co to receive electric energy from the auxiliary inductor La.
The closed-loop controller 109 uses the controlling circuit 1091 to receive a feedback signal Sf and a command signal Sc corresponding to the feedback signal Sf. The controlling circuit 1091 compares the feedback signal Sf with the command signal So and provides a controlling signal Sd based on the comparison. The feedback signal Sf is the first inductor current iL1 from the first power source circuit 101, the second inductor current iL2 from the second power source circuit 103, or the output voltage Vo from the output circuit 107. The command signal Sc is a nominal first inductor current i′L1 (not marked up), a nominal second inductor current i′L2 (not marked up) or a nominal output voltage V′o (not marked up).
Based on the amplitude of the controlling signal Sd, the driving circuit 1093 provides the first switch-driving signal T1 to the first switch S1, the second switch-driving signal T2 to the second switch S2, and the auxiliary switch-driving signal Ta to the auxiliary switch Sa. In the preferred embodiment, the duty cycles of the first switch-driving signal T1, the second switch-driving signal T2 and the auxiliary switch-driving signal Ta change according to the controlling signal Sd. The auxiliary switch-driving signal Ta is the sum of a signal complementary to the first switch-driving signal T1 and another signal complementary to the second switch-driving signal T2. That is, if the controlling signal Sd gets larger, the duty cycles of the first switch-driving signal T1 and the second switch-driving signal T2 while the duty cycle of the auxiliary switch-driving signal Ta gets smaller. On the contrary, if the controlling signal Sd gets smaller, the duty cycles of the first switch-driving signal T1 and second switch-driving signal T2 get shorter but the duty cycle of the auxiliary switch-driving signal Ta. Thus, by adjusting the boost ratio of the dual-source converter 1′, the boost ratios of the control first inductor current iL1, the second inductor current iL2 and the output voltage Vo are adjusted. The driving circuit indirectly controls the putout power of the first power source and the output power of the second power source, thus achieving the closed-loop control mechanism.
Furthermore, the driving circuit 1093 provides the first power switching signal Tp1 to the first power switch Sp1, and provides the second power-source switching signal Tp2 to the second power-source switch Sp2. Thus, by switching the control first power switch Sp1 and the second power-source switch Sp2, the dual-source converter 1′ is switched between a single-source mode and a dual-source mode.
As discussed above, the operation of the dual-source converter 1′ can be outlined as follows:
When the first switch S1 is turned off but the second switch S2 is turned on, the first inductor L1 recharges the auxiliary capacitor Ca, the auxiliary inductor La and the output capacitor Co, and provide energy to the output load Ro. Meanwhile, the auxiliary switch Sa is turned on. The auxiliary switch Sa can be turned on at zero voltage. Then, The first inductor current iL1 and the auxiliary capacitor voltage Va are provided to the output capacitor Co, and energy is provided to the output load Ro.
Similarly, when the first switch S1 is turned on but the second switch S2 is turned off, the second inductor L2 recharges the auxiliary capacitor Ca, the auxiliary inductor La and the capacitor Co, and provides energy to the output load Ro. Meanwhile, the auxiliary switch Sa is turned on. The auxiliary switch Sa can be turned on at zero voltage. Then, the second inductor current iL2 and the auxiliary capacitor voltage Va are provided to the output capacitor Co, and energy is provided to the output load Ro. The first inductor current iL1 and the second inductor current iL2 recharge the output circuit 107 sequentially.
Moreover, when both of the first switch S1 and the second switch S2 are turned on, the first power source V1 and the second power source V2 recharge the first inductor L1 and the second inductor L2, respectively. The auxiliary inductor current iLa recharges the output capacitor Co of the output circuit 107, and provides energy to the output load Ro continuously. The auxiliary inductor current iLa decreases to zero eventually.
According to the preferred embodiment of the present invention, the dual-source converter 1′ is switched between the single-source mode and the dual-source mode based on the type of an actual load and the state of the supply of energy. The operations of in the two modes will be described later.
Referring to FIGS. 3A-3G, the dual-source converter 1′ is operated in the single-source mode. Referring to FIG. 4, the waveforms of the signals versus time are shown.
Referring to FIGS. 3A-3G, when the second power source V2 fails, or for the purpose of responding to different output loads, or for the purpose of saving energy, it might be desired to stop the second power source V2 from providing power. To this end, the second power sources witch Sp2 is turned off to cut off the second power source V2, and to keep the second switch S2 on. Now, the dual-source converter 1′ is operated in the single-source mode for using the first power source V1 only.
At first, there are defined the switching cycle Ts of the switches, the duty cycle d1 of the first switch, the duty cycle da of the auxiliary switch, the duty cycle ddcm of the discontinuous mode and the duty cycle dd of the dead zone time.
Mode 1 [t0 ̃t1]
As t=t0, the auxiliary inductor current iLa is returned to zero. Now, the first switch S1 is turned on but the auxiliary switch Sa is turned off. The first power source V1 recharges the first inductor L1.
Mode 2 [t1 ̃t2]
As t=t1, the first switch S1 is turned off, and the first switch voltage vS1 is increased to the auxiliary capacitor voltage Va. Now, the auxiliary switch Sa is still on. The first inductor current iL1 continues to travel through the parasitic diode of the auxiliary switch Sa, and recharges the auxiliary capacitor Ca. Now, the auxiliary switch current iSa is negative, and the voltage vLa across the auxiliary inductor is Va−Vo, and the auxiliary inductor current iLa is increased from zero linearly. Then, the first auxiliary diode Da1 is turned on.
Mode 3 [t2 ̃t3]
As t=t2, the auxiliary switch current iSa is still negative. Now, the auxiliary switch Sa is turned on at zero voltage. After the auxiliary switch Sa is turned on, a positive-directional path is provided to the auxiliary switch current iSa. When the auxiliary inductor current iLa is increased to a value larger than the first inductor current iL1, the auxiliary switch current iLa is positive. Now, energy is released from the auxiliary capacitor voltage Va to the auxiliary inductor La and the output voltage Vo. In Modes 2 and 3, t=t1 ̃t3, the time can be represented by (dd+da)Ts. In these modes, the voltage vLa across the auxiliary inductor is Va−Vo, and the voltage vL1 across the first inductor is V1−Va. Hence, the auxiliary inductor current iLa and the first inductor current iL1 can be represented by Equations (1) and (2) as follows:

iLa(t)=(Va−Vo)(t−t1)/La  (1)

iL1(t)=(IL1+0.5ΔiL1)+(V1−Va)(t−t1)L1  (2)

wherein IL1 represents the average value of the first inductor current iL1, and ΔiL1 represents the ripple of the first inductor current iL1. As t=t3, the maximum value of the auxiliary inductor current iLa is represented by Equation (3) as follows

iLa(t3)=(Va−Vo)(dd+da)Ts/La  (3)

According to the voltage vL1 across the first inductor, ΔiL1 can be rewritten to be Equation (4) as follows:

ΔiL1=(Va−V1)(dd+da)Ts/L1  (4)

Mode 4 [t3 ̃t4]

As t=t3, the auxiliary switch Sa is turned off but the first switch S1 is kept on. Because the auxiliary inductor current iLa must continue to travel and the auxiliary inductor current iLa is larger than the first inductor current iL1, the first switch voltage vS1 is reduced to zero before the parasitic diode of the first switch S1 is turned on to receive the difference between the auxiliary inductor current iLa and the first inductor current iL1. The first diode current iDa1 is identical to the auxiliary inductor current iLa. The auxiliary inductor La begins to provide electricity to the output voltage Vo. Now, the voltage vLa across the auxiliary inductor is −Vo, the auxiliary inductor current iLa is decreased from the local maximum value linearly.
Mode 5 [t4 ̃t5]
As t=t4, the parasitic diode of the first switch S1 is turned on, and the first switch S1 is turned on at zero voltage. Now, the first power source V1 recharges the first inductor L1, and the first switch current iS1 is increased from a negative value to a positive value eventually, and the auxiliary inductor current iLa continues to provide electricity to the voltage Vo. In Modes 4 and 5, t=t3 ̃t5, time can be represented by (dd+ddcm)Ts. In these modes, the voltage vLa across the auxiliary inductor is −Vo, and the voltage vL1 across the first inductor is V1. Therefore, the auxiliary inductor current iLa can be represented by Equation (5) as follows:

iLa(t)=[(Va−Vo)(dd+da)Ts−Vo(t−t3)]/La  (5)

Mode 6 [t5 ̃t6]

As t=t5, the auxiliary inductor current iLa is reduced to zero, iLa(t5)=0 is substituted in Equation (5) to provide the relationship between the auxiliary capacitor voltage Va and the output voltage Vo represented by Equation (6) as follows:

(Va−Vo)(dd+da)=Vo(dd+ddcm)  (6)

Because auxiliary inductor current iLa provided from the auxiliary inductor La to the output voltage Vo is reduced to zero, there is reverse recovery current in the first auxiliary diode Da1, and the output voltage Vo recharges the parasitic capacitor of the first auxiliary diode Da1 through the auxiliary inductor La.
Mode 7 [t6 ̃t7]
As t=t6, the first auxiliary diode Da1 builds a reverse-biased voltage. Then, the auxiliary inductor current iLa must continue to travel to the auxiliary capacitor Ca through the second auxiliary diode Da2, to complete a cycle of the operation of the first power source V1 in the single-source mode.
It should be noted that the second auxiliary diode Da2 provides a path with little loss in turning on, to reduce the current that travels through the parasitic diode of the auxiliary switch Sa to protect the auxiliary switch Sa. Thus, a high-voltage surge that could be caused by the resonance of a parasitic capacitor of a power semiconductor element with a leak capacitor is avoided so that the power semiconductor is protected.
According to volt-second balance theory, in a cycle of the operation of the first power source V1 in the single-source mode, the average of the voltage vL1 across the first inductor is zero, and their relationship can be represented by Equations (7a) and (7b) as follows:

[V1(d1+dd)+(V1−Va)(da+dd)]Ts=0  (7a)

Va=V1/(da+dd)  (7b)

According to Equations (6) and (7b), and it is assumed that the duty cycle dd of the dead zone time is short, the sum of the duty cycle d1 of the first switch and the duty cycle da of the auxiliary switch is close to 1, and Equations (6) and (7b) can respectively be rewritten to be Equations (8a) and (8b) as follows:

Vo=Va(1−d1)/(1+ddcm−d1)  (8a)

Va=V1/(1−d1)  (8b)

In consideration that the average current of the output capacitor Co in all of the switch cycles is zero to retain the stability of the output voltage Vo, and the average current of the output capacitor Co is identical to the average current La of the auxiliary inductor, and with an assumption that reverse recovery current caused by the first auxiliary diode Da1 in Mode 7 is very small and can be ignored, this relationship can be represented by Equation (9) as follows:

(1−d1)(1−d1+ddcm)(Va−Vo)Ts/2La=Vo/Ro  (9)

The duty cycle ddcm of the non-continuous current mode and the output voltage Vo can respectively be derived from Equations (8) and (9) and represented by Equations (10a) and (10b) as follows:




  
    
      
        
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Similarly, when the first power source V1 fails, or when the first power source V1 is instructed not to provide power in response to a different output load Ro and for saving energy, the first power witch Sp1 is turned off to cut off the first power source V1, and the first switch S1 is kept on. Now, the dual-source converter 1′ can be switched to a mode wherein the second power source V2 alone provides electricity.
The mode wherein the second power source V2 alone provides electricity is identical to the mode wherein the first power source V1 alone provides electricity. Thus, based on the foregoing theory, the relationship between the voltages can be represented by Equations (11a) and (11b) as follows:




  
    
      
        
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wherein d2 represents the duty cycle of the second switch. As discussed above, the dual-source converter 1′ can achieve the goal of energy convention with highly efficient boost through the duty cycles d1, d2 and da of the first switch S1, the second switch S2 and the auxiliary switch Sa, respectively.

Subsequently, referring to FIGS. 5A-5N, the dual-source converter is in the dual-source mode wherein both of the first and second power sources are used. Referring to FIG. 6, the waveforms of various signals of the dual-source converter in the dual-source mode are shown.
It should be noted that FIGS. 5 and 6 are based on a condition that the first inductor current iL1 is larger than second inductor current iL2. At first, there are defined the first auxiliary switch duty cycle dal, the second auxiliary switch duty cycle da2, the first non-continuous current mode duty cycle ddcm1, the second non-continuous current mode duty cycle ddcm2, the switch cycle Ts, the first switch duty cycle d1, the second switch duty cycle d2, the auxiliary switch duty cycle da and the dead zone duty cycle dd.
Moreover, the dual-source converter 1′ is in the dual-source mode on a condition that the sum of the first switch duty cycle d1 and the second switch duty cycle d2 is greater than 1. That is, d1+d2≧1. This is to prevent a path of the first inductor current iL1 connected in series to the second inductor current iL2 when both of the first switch S1 and the second switch S2 are turned off.
Mode 1 [t0 ̃t1]
As t=t0, the auxiliary inductor current iLa is returned to zero. Now, both of the first switch S1 and the second switch S2 are turned on but the auxiliary switch Sa is turned off. The first power source V1 and the second power source V2 recharge the first inductor L1 and the second inductor L2, respectively.
Mode 2 [t1 ̃t2]
As t=t1, the second switch S2 is turn off, and the second switch voltage vS2 is increased to the auxiliary capacitor voltage Va. Now, the auxiliary switch Sa is still off. The second inductor current iL2 continues to travel to the first power source circuit 101 and the parasitic diode of the auxiliary switch Sa and recharges the auxiliary capacitor Ca. Now, the auxiliary switch current iSa is negative, and the voltage vLa across the auxiliary inductor is Va−Vo. The auxiliary inductor current iLa is increased from zero. The first auxiliary diode Da1 is turned on accordingly.
Mode 3 [t2 ̃t3]
As t=t2, the auxiliary switch current iSa is still negative. Now, the auxiliary switch Sa is turned on at zero voltage. Once turned on, the auxiliary switch Sa provides a path in a positive direction for the auxiliary switch current iSa When the auxiliary inductor current iLa is increased linearly so that it is larger than the second inductor current iL2, the auxiliary switch current iSa is positive. Now, energy of the auxiliary capacitor voltage Va is released from to the auxiliary inductor La and the output voltage Vo. In Modes 2 and 3, t=t1 ̃t3, time can be represented by (da+da2)Ts. In these modes, the voltage vLa across the auxiliary inductor is Va−Vo. The voltage across the second inductor is V2−Va. Hence, the auxiliary inductor current iLa and the second inductor current iL2 can respectively be represented by Equations (12) and (13) as follows:

iLa(t)=(Va−Vo)(t−t1)/La  (12)

iL2(t)=(IL2+0.5ΔiL2)+(V2−Va)(t−t1)/L2  (13)

wherein IL2 represents the average value of the second inductor current iL2, and ΔiL2 represents the ripple of the second inductor current iL2. As t=t3, the maximum value of the auxiliary inductor current iLa can be represented by Equation (14) as follows:

iLa(t3)=(Va−Vo)(dd+da2)Ts/La  (14)

Based on the voltage vL2 across the second inductor, ΔiL2 can be represented by Equation (15) as follows:

ΔiL2=(Va−V2)(dd+da2)Ts/L2  (15)

Moreover, in Modes 2 and 3, t=t1 ̃t3, the first switch current iS1 can be represented by iL1−iL2. Because the first inductor current iL1 is larger than the second inductor current iL2, the first switch current iS1 is positive. Because the loss of the switch in turning on is positively proportional to the square of the current that travels through it, the first switch S1 is connected, in series, to the second switch S2 to considerably reduce such loss in the present invention.
Mode 4 [t3 ̃t4]
As t=t3, the auxiliary switch Sa is turned off. Because the auxiliary inductor current iLa must continue to travel and the auxiliary inductor current iLa is larger than the second inductor current iL2, the second switch voltage vS2 is reduced to zero before the parasitic diode of the second switch S2 is turned on. The local maximum value of the auxiliary inductor current La beings to drop linearly.
Mode 5 [t4 ̃t5]
As t=t4, wherein the parasitic diode of the second switch S2 is turned on, the second switch S2 is turned on at zero voltage. Now, the second switch current iS2 is increased from zero to positive eventually. In Modes 4 and 5, t=t3 ̃t5, time can be represented by (dd+ddcm2)Ts. In these modes, the voltage vLa across the auxiliary inductor is −Vo. Hence, the auxiliary inductor current iLa can be represented by Equation (16) as follows:

iLa(t)=[(Va−Vo)(dd+da2)Ts−Vo(t−t3)]/La  (16)

Mode 6 [t5 ̃t6]

As t=t5, the auxiliary inductor current iLa is reduced to zero. The condition that iLa(t5)=0 is included in Equation (16) to provide the relationship between the auxiliary capacitor voltage Va and the output voltage Vo by Equation (17) as follows:

(Va−Vo)(dd+da2)=Vo(dd+ddcm2)  (17)

Because the auxiliary inductor current iLa provided from the auxiliary inductor La to the output voltage Vo is reduced to zero, there is reverse recovery current in the first auxiliary diode Da1. The output voltage Vo recharges the parasitic capacitor of the first auxiliary diode Da1 through the auxiliary inductor La.
Mode 7 [t6 ̃t7]
As t=t6, the first auxiliary diode Da1 builds a reverse-biased voltage. Then, the auxiliary inductor current iLa must continue to travel to the auxiliary capacitor Ca through the second auxiliary diode Da2.
Mode 8 [t7 ̃t8]
As t=t7, the auxiliary inductor current iLa is returned to zero. Now, the operation of the dual-source power source converter 1′ is identical to the operation in Mode 1.
Mode 9 [t8 ̃t9]
As t=t8, the first switch S1 is turned off. Now, the auxiliary switch Sa is still off. The first inductor current iL1 continues to travel through the second power source circuit 103 and the parasitic diode of the auxiliary switch Sa and recharges the auxiliary capacitor Ca. Now, the auxiliary switch current iSa is negative, and the voltage vLa across the auxiliary inductor is Va−Vo, and the auxiliary inductor current iLa is increased from zero linearly, and the first auxiliary diode Da1 is turned on accordingly.
Mode 10 [t9 ̃t10]
As t=t9, the auxiliary switch current iSa is still negative. Now, the auxiliary switch Sa is turned on at zero voltage. Once turned on, the auxiliary switch Sa provides a path in a positive direction for the auxiliary switch current iSa. When the auxiliary inductor current iLa is increased linearly so that it is larger than the first inductor current iL1, the auxiliary switch current iSa is positive. Now, the energy of the auxiliary capacitor voltage Va is released to the auxiliary inductor La and the voltage Vo. In Modes 9 and 10, t=t8 ̃t10, time can be represented by (da+da1)Ts. In these modes, the voltage vLa across the auxiliary inductor is Va−Vo, and the voltage across the first inductor is V1−Va. Hence, the auxiliary inductor current iLa and the first inductor current iL1 can respectively be represented by Equations (18) and (19) as follows:

iLa(t)=(Va−Vo)(t−t8)/La  (18)

iL1(t)=(IL1+0.5ΔiL1)+(V1−Va)(t−t8)/L1  (19)

As t=t10, the local maximum value of the auxiliary inductor current iLa can be represented by Equation (20):

iLa(t10)=(Va−Vo)(dd+da1)Ts/La  (20)

According to the voltage vL1 across the first inductor, ΔiL1 can be represented by Equation (21) as follows:

ΔiL1=(Va−V1)(dd+da1)Ts/L1  (21)

Mode 11 [t10 ̃t11]

As t=t10, the auxiliary switch Sa is turned off. Because the auxiliary inductor current iLa must continue to travel and the auxiliary inductor current iLa is larger than the first inductor current iL1, the first switch voltage vS1 is reduced to zero before the parasitic diode of the first switch S1 is turned on, and the local maximum value of the auxiliary inductor current iLa begins to drop linearly.
Mode 12 [t11 ̃t12]
As t=t11, when the parasitic diode of the first switch S1 is turned on, the first switch S1 is turned on at zero voltage. Now, the first switch current iS1 is increased from negative to positive eventually. In Modes 11 and 12, t=t10 ̃t12, time can be represented by (dd+ddcm1)Ts. In these modes, the voltage vLa across the auxiliary inductor is −Vo. Hence, the auxiliary inductor current iLa can be represented by Equation (22) as follows:

iLa(t)=[(Va−Vo)(dd+da1)Ts−Vo(t−t10)]/La  (22)

Mode 13 [t12 ̃t13]

As t=t12, the auxiliary inductor current iLa is reduced to zero. A condition that iLa(t12)=0 is included in Equation (22) to provided the relationship between the capacitor voltage Va and the output voltage Vo represented by Equation 23 as follows:

(Va−Vo)(dd+da1)=Vo(dd+ddcm1)  (23)

Because the auxiliary inductor current provided from the auxiliary inductor La to the output voltage Vo is reduced to zero, there is reverse recovery current in the first auxiliary diode Da1. The output voltage Vo recharges the parasitic capacitor of the first auxiliary diode Da1 through the auxiliary inductor La.
Mode 14 [t13 ̃t14]
As t=t13, the first auxiliary diode builds a reverse-biased voltage. Then, the auxiliary inductor current iLa must continue to travel to auxiliary capacitor Ca through the second auxiliary diode Da2 to complete a cycle of the operation of the dual-source converter in the dual-source mode.
According the volt-second balance theory, in the switch cycles of the first switch S1 and the second switch S2, the average of the voltage vL1 across the first inductor and the average of the voltage vL2 across the second inductor are zero. Their relationship can be represented by Equations (24a), (24b), (24c) and (24d) as follows:

[V1(d1+dd)+(V1−Va)(da1+dd)]Ts=0  (24a)

Va=V1/(da1+dd)  (24b)

[V2(d2+dd)+(V2−Va)(da2+dd)]Ts=0  (24c)

Va=V1/(da2+dd)  (24d)

According to Equations (17), (23), (24b) and (24d), with an assumption that the duty cycle dd of the dead zone time is very short, the sum of the first switch duty cycle d1 and the first auxiliary switch duty cycle da1 is close to 1, and the sum of the second switch duty cycle d2 and the second auxiliary switch duty cycle da1 is close to 1 so that Equations (23), (17), (24b) and (24d) can be rewritten to be Equations (25a), (25b), (25c) and (25d) as follows:

Vo=Va(1−d1)/(1+ddcm1−d1)  (25a)

Vo=Va(1−d2)/(1+ddcm2−d2)  (25b)

Va=V1/(1−d1)  (25c)

Va=V2/(1−d2)  (25d)

The average current of the output capacitor Co in all of the switch cycles is zero to retain the stability of the output voltage Vo. Moreover, the average current of the output capacitor Co is identical to the average current of the auxiliary inductor La. Furthermore, it is assumed that the reverse recovery current caused by the first auxiliary diode Da1 in the Modes 7 and 14 is small and can be ignored. Thus, their relationship can be represented by Equation (26) as follows:

[(1−d1)(1−d1+dcm1)+[(1−d2)(1−d2+dcm2)](Va−Vo)Ts/2La=Vo/Ro  (26)

Based on Equations (25) and (26), the first non-continuous current mode duty cycle ddcm1, the second non-continuous current mode duty cycle ddcm2 and the output voltage Vo can be represented by Equations (27a), (27b) and (27c).




  
    
      
        
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wherein the duty cycle dx can be simplified to be (1−d1)2+(1−d2)2. In addition, the first switch duty cycle d1 and the second switch duty cycle d2 can be derived from Equation (27c) and represented by Equation (28) as follows:

V1/(1−d1)=V2/(1−d2)  (28)

From Equations (27a) to (27c), it can be known that when the dual-source converter 1′ is in the dual-source mode, by controlling the duty cycles T1{grave over ( )}T2Ta of the first switch S1, the second switch S2 and the auxiliary switch Sa, respectively, energy conversion with highly efficient boost is achieved. Moreover, based on the ratio of the voltage of the first power source V1 over the voltage of the second power source V2, there is an optimal combination of the first switch duty cycle d1 with the second switch duty cycle d2.
To verify the effects of the dual-source converter 1′, some data obtained from the use thereof will be given later.
Referring to FIG. 7, the first power source V1 is a 120V DC power source, and the first power source V1 imitates an output voltage from a solar cell. The second power source V2 is a 160V DC power source, and the second power source V2 imitates an output voltage from a wind turbine. The output voltage Vo is a 360V high voltage DC bus voltage.
The specifications of the elements included in the dual-source converter 1′ are listed in Table 1 as follows:







TABLE 1







Specification of Dual-Source Converter 1′











Element
Symbol
Parameter







First inductor
L1
800uH



Second inductor
L2
800uH



First switch
S1
IRFP460



Second switch
S2
IRFP460



Auxiliary switch
Sa
IRFP460



First auxiliary diode
Da1
MUR8100



Second auxiliary diode
Da2
MUR8100



Auxiliary capacitor
Ca
 47uF



Auxiliary inductor
La
 35uH



Output capacitor
Co
 47uF










Referring to FIG. 7, in Part (a), there are shown the first switch-driving signal T1, the auxiliary capacitor voltage Va, the output voltage Vo and the first inductor current iL1. As shown in FIG. 7, Part (a), the first inductor current iL1 continues and would not easily cause damages to the first power source V1. The output voltage Vo is controlled to be 360V.
Referring to FIG. 7, Part (b), there are shown the first switch-driving signal T1, the auxiliary switch-driving signal Ta, the first switch voltage vS1 and the first switch current iS1. As shown in FIG. 7, Part (b), the first switch-driving signal T1 and the auxiliary switch-driving signal Ta are complementary to each other and provide brief dead zone time for each other to avoid short circuit of the auxiliary capacitor Ca due to synchronous turning on of the switches S1 and Sa. As shown in FIG. 7, Part (b), when the first switch S1 is turned on, the first switch current iS1 is negative, and the first switch S1 can be switched at zero voltage to effectively reduce the loss in the switching and increase the conversion efficiency.
Referring to FIG. 7, Part (c), there are shown the first switch-driving signal T1, the auxiliary switch-driving signal Ta, the auxiliary switch voltage vSa and the auxiliary switch current iSa. As shown in FIG. 7, Part (c), when the auxiliary switch Sa is turned on, the auxiliary switch current iSa is negative, and the auxiliary switch Sa can be switched at zero voltage.
Referring to FIG. 7, Part (d), there are shown the first switch-driving signal T1, the auxiliary switch-driving signal Ta, the vDa1 across the first auxiliary diode and the first auxiliary diode current iDa1. Because the first auxiliary diode Da1 is connected, in series, to the auxiliary inductor La, the waveform of the first auxiliary diode current iDa1 goes up and down linearly, and effectively avoid a surge due to the  current in the output diode as would be in a conventional boost circuit.
Referring to FIG. 7, Part (e), there are shown the first switch-driving signal T1, the auxiliary switch-driving signal Ta, the voltage vDa2 across the second auxiliary diode and the second auxiliary diode current iDa2. The second auxiliary diode Da2 is used to suppress the voltage across vDa1 the first auxiliary diode so that the voltage vDa1 across the first auxiliary diode is retained to be the auxiliary capacitor voltage Va.
Referring to FIG. 8, the dual-source converter uses both of the first power source V1 and the second power source V2. The power of the output load Ro is 5 kW.
Referring to FIG. 8, Part (a), there are shown first switch-driving signal T1, the second switch-driving signal T2, the auxiliary switch-driving signal Ta and the output voltage Vo. As shown in FIG. 8, Part (a), the first switch-driving signal T1 and the second switch-driving signal T2 are complementary to the auxiliary switch-driving signal Ta, and provide brief dead zone time for each other to avoid short circuit of the auxiliary capacitor Ca that would be caused by synchronous turning on of the first switch S1, the second switch S2 and the auxiliary switch Sa. The output voltage Vo is controlled to be 360V.
FIG. 8, Part (b) shows the first switch-driving signal T1, the first switch voltage vS1, the first inductor current iL1 and the first switch current iS1. As shown in FIG. 8, Part (b), when the first switch S1 is turned on, the first switch current iS1 is negative, and the first switch S1 can be switched at zero voltage to reduce the loss in the switching and increase the conversion efficiency. Moreover, when the second switch S2 is turned on, the first switch current iS1 is reduced to iL1−iL2 and the loss in the switching is reduced, and the conversion efficiency is further increased.
FIG. 8, Part (c) shows the second switch T2, the second switch voltage vS2, the second inductor current iL2 and the second switch current iS2. As shown in FIG. 8, Part (c), when the second switch S2 is turned on and the second switch current iS2 is negative, the second switch S2 can be switched at zero voltage. In addition, when the first switch S1 is turned on, the second switch current iS2 is reduced to iL2−iL1. Now, the second switch current iS2 is negative but much smaller than the original second inductor current iL2 so that the loss in the turning on is further reduced.
FIG. 8, Part (d) shows the auxiliary switch-driving signal Ta, the auxiliary switch voltage vSa, the auxiliary capacitor voltage Va and the auxiliary switch current iSa. As shown in FIG. 8, Part (d), when the auxiliary switch Sa is turned on, the auxiliary switch current iSa is negative, and the auxiliary switch Sa can be switched at zero voltage.
FIG. 8, Part (e) shows the first switch-driving signal T1, the second switch-driving signal T2, the voltage vDa1 across the first auxiliary diode and the first auxiliary diode current iDa1. Because the first auxiliary diode Da1 is connected, in series, to the auxiliary inductor La, the waveform of the first auxiliary diode current iDa1 goes up and down linearly.
FIG. 8, Part (f) shows first switch-driving signal T1, the second switch-driving signal T2, the voltage vDa2 across the second auxiliary diode and the second auxiliary diode current iDa2. The second auxiliary diode Da2 is used to suppress the voltage vDa1 across the first auxiliary diode so that the first auxiliary diode voltage vDa1 is controlled to be the auxiliary capacitor voltage Va.
Finally, referring to FIGS. 9 and 10, there is shown the conversion efficiency of the dual-source converter by simulation. FIG. 9 shows the conversion efficiency of the dual-source converter 1′ in the single-source mode wherein only the first power source V1 is used. There are two conditions for simulation. At first, the first power source V1 is 120V. Secondly, the output voltage Vo is 360V. As shown in FIG. 9, the conversion efficiency can be as high as 95.6%.
FIG. 10 shows the conversion efficiency of the dual-source converter 1′ is in the dual-source mode wherein both of the power source V1 and the second power source V2 are used. There are two conditions for simulation. At first, the first power source V1 is 120V. Secondly, the second power source V2 is 160V. The output voltage Vo is 360V. The conversion efficiency can be as high as 96.2%.
Based on the data obtained by simulation referring to FIGS. 9 and 10, it is verified that the dual-source converter of the present invention provides high conversion efficiency.
As discussed above, according to the present invention, the power sources at different voltages are connected, in series, to each other and converted to a stable power source, and the dual-source converter can be switched between the single-source mode and the dual-source mode. In the dual-source mode, the dual-source converter effectively reduces the loss in the turning on and increases the conversion efficiency. With the auxiliary circuit, all of the switches can be switched at zero voltage to achieve flexible switching. Furthermore, the inductor current in the dual-source converter continues to travel to effectively filter out current ripples to avoid damages of a device operated on the renewable energy.
The present invention has been described via the detailed illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.

## Claims

1. A dual-source converter including:
a first power source circuit including a first power-source switch and a first switch, wherein the first power-source switch is electrically connected to a first power source, wherein the first switch is coupled to the first power-source switch, wherein the first power source circuit converts the first power source to a first current source;
a second power source circuit connected, in series, to the first power source circuit, wherein the second power source circuit includes a second power-source switch and a second switch, wherein the second power-source switch is electrically connected to a second power source, wherein the second switch is coupled to the second power-source switch, wherein the second power source circuit converts the second power source to a second current source;
an auxiliary circuit including:
an auxiliary switch including first and second ends, wherein the second end of the auxiliary switch is coupled to a first end of the first switch;
a first auxiliary diode including first and second ends, wherein the first end of the first auxiliary diode is electrically connected to the second end of the auxiliary switch;
a second auxiliary diode including first and second ends, wherein the first end of the second auxiliary diode is electrically connected to the second end of the first auxiliary diode, wherein the second end of the second auxiliary diode is electrically connected to the first end of the auxiliary switch, wherein the second auxiliary diode is used to suppress a voltage across the first auxiliary diode;
an auxiliary capacitor including first and second ends, wherein the first end of the auxiliary capacitor is electrically connected to the first end of the auxiliary switch, wherein the second end of the auxiliary capacitor is electrically connected to the second end of the second switch, wherein the auxiliary capacitor is used to store energy of the first and second current sources; and
an auxiliary inductor including first and second end, wherein the first end of the auxiliary inductor is electrically connected to the second end of the first auxiliary diode, wherein the auxiliary inductor is used to release the energy of the first and second current sources from the auxiliary capacitor, wherein the auxiliary circuit stores or releases the energy of the first and second current sources by switching the auxiliary switch;

an output circuit electrically connected to the auxiliary circuit, wherein the output circuit receives the energy of the first and second current sources from the auxiliary inductor; and
a closed-loop controller electrically connected to the first and second power source circuits, the auxiliary circuit and the output circuit, wherein based on a feedback signal and a command signal, the closed-loop controller controls duty cycles of the first and second switches and the auxiliary switch so that the first and second switches and the auxiliary switch can be switched at zero voltage, wherein the closed-loop controller controls the switching of the first and second power switches so that the first and second power sources are connected or cut off.

2. The dual-source converter according to claim 1, wherein each of the first power source and the second power source is selected from the group consisting of a secondary cell, a super capacitor, a fuel cell, a solar cell, a DC wind turbine and a rectified AC wind turbine.

3. The dual-source converter according to claim 1, wherein the first power source circuit further includes a first inductor between the first power-source switch and the first switch, wherein the second power source circuit further includes a second inductor between the second power-source switch and the second switch, wherein the first inductor and the second inductor respectively filter out current ripples from the first power source and the second power source and store the energy of the first and second power sources.

4. The dual-source converter according to claim 1, wherein the first power source circuit further includes a first inductor connected, in parallel, to the first power source, wherein the second power source circuit further includes a second inductor connected, in parallel, to the second power source, wherein the first inductor and the second inductor respectively filter out current ripples from the first power source and the second power source and store the energy of the first and second power sources.

5. The dual-source converter according to claim 1, wherein the closed-loop controller includes:
a controlling circuit for comparing the feedback signal with the command signal and providing a controlling signal according to the comparison; and
a driving circuit for providing a plurality of driving signals to the first switch, the second switch and the auxiliary switch according to the controlling signal, wherein the driving circuit provides a plurality of switching signals to the first power-source switch and the second power-source switch.

6. The dual-source converter according to claim 5, wherein the feedback signal is provided from the first power source circuit, the second power source circuit or the output circuit, wherein the command signal is a nominal current or voltage corresponding to the feedback signal.

7. The dual-source converter according to claim 5, wherein the driving signals include a first switch-driving signal, a second switch-driving signal and an auxiliary switch-driving signal, wherein the auxiliary switch-driving signal is the sum of a signal complementary to the first switch-driving signal and another signal complementary to the second switch-driving signal.

8. The dual-source converter according to claim 7, wherein the duty cycles of the first switch-driving signal and the second switch-driving signal get longer but the duty cycle of the auxiliary switch-driving signal gets shorter as the controlling signal gets larger, wherein the duty cycles of the first switch-driving signal and the second switch-driving signal get shorter but the duty cycle of the auxiliary switch-driving signal gets longer as the controlling signal gets smaller.

9. The dual-source converter according to claim 5, wherein the switching signals include a first power-source switch-switching signal and a second power source-switching signal to control the switching of the first power-source switch and the second power-source switch, respectively.

10. The dual-source converter according to claim 1, wherein when the first auxiliary diode builds a reverse-biased voltage, while an auxiliary inductor current continues to travel through the auxiliary inductor, the second auxiliary diode provides a path with a reduced loss in turning on, wherein the auxiliary inductor current travels to the auxiliary capacitor through the second auxiliary diode to reduce a current that travels through a parasitic diode of the auxiliary switch.