Power conversion apparatus and controlling method thereof

A power conversion apparatus and a controlling method thereof are disclosed. The power conversion apparatus is applied with a power generation apparatus, which outputs a first signal. The power conversion apparatus includes a conversion-sensing circuit, a control signal generating circuit and a switching circuit. The conversion-sensing circuit converts the first signal into a second signal, and senses at least a voltage waveform change of the second signal to generate a time interval. The control signal generating circuit is electrically connected with the conversion-sensing circuit and outputs a control signal according to the time interval. The switching circuit is electrically connected with the power generation apparatus and the control signal generating circuit, and has a plurality switching elements. The switching circuit receives the first signal and conducts one of the switching elements according to the control signal so as to convert the first signal and output an output signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 101125018 filed in Taiwan, Republic of China on Jul. 12, 2012, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a conversion apparatus and a controlling method thereof, and in particular, to a power conversion apparatus and a controlling method thereof.

2. Related Art

Recently, due to the rise of the environmental awareness and the gradual depletion of the fossil energy (e.g., petroleum and coal), countries around the world become aware of the importance of the development of the new type energy. The wind power is the inexhaustible energy without the doubt of energy depletion and can also avoid the problem of the energy monopoly. Thus, the countries around the world also actively develop the wind power generation system to expect to reduce the dependence on the fossil energy by increasing the utilization of the wind power.

The wind power generation system needs to convert the electric power, generated from the wind power generator (hereinafter referred to as a wind generator) via an electric power conversion apparatus. In addition to saving or supplying the converted electric power to the load, the converted electric power may also be connected to the power supply grid in parallel. The architectures of the conventional electric power conversion apparatus may be substantially classified into a passive architecture and an active architecture.

In the passive architecture, a passive full-bridge rectifier converts the three-phase power, outputted from the wind generator, into the single-phase power, and then achieves the objects of energy conversion through the operations of an inductor and a switch. Because the use of only a single switch can achieve the energy conversion, the energy loss of the apparatus is extremely small. When being applied to the low wind speed or the low power wind generator, the conversion efficiency of the apparatus is relatively high. However, the passive architecture cannot actively control and adjust the power factor, and the loss thereof also proportionally rises with the increases of the power and the current. When being applied to the middle or high wind speed or the high power wind generator, the power loss of the apparatus upon conversion is relatively high.

In the active architecture, six active switches and three inductors are utilized, and the instantaneous rotating speed is obtained through a rotor position detector (e.g., an encoder) disposed on the generator to control the instantaneous rotating speed, so that the power conversion apparatus can complete the electric power conversion. Because the active architecture can be synchronously changed with the change of the three-phase AC power outputted form the wind generator and can achieve the full power energy conversion, the conversion efficiency thereof is relatively high and the energy loss thereof is relatively low when being applied to the high wind speed or the high power wind generator. However, the active architecture needs to drive six active switches to operate concurrently and needs to supply the power to the position detector disposed on the generator to have the long distance line loss, so that the power loss is much larger than that of the passive system. Thus, the active architecture is not advantageous to the wind energy conversion for the low wind speed or the low power wind generator.

Therefore, it is an important subject to provide a power conversion apparatus, having full power and high efficiency energy conversion and lower power loss, and a controlling method thereof.

SUMMARY OF THE INVENTION

In view of the foregoing subject, an objective of the invention is to provide a power conversion apparatus, having full power and high efficiency energy conversion and lower power loss, and a controlling method thereof.

To achieve the above objective, the present invention discloses a power conversion apparatus applied with a power generation apparatus, which outputs a first signal. The power conversion apparatus includes a conversion-sensing circuit, a control signal generating circuit, and a switching circuit. The conversion-sensing circuit converts the first signal into a second signal and senses at least one voltage waveform change of the second signal to generate a time interval. The control signal generating circuit is electrically connected with the conversion-sensing circuit and outputs a control signal according to the time interval. The switching circuit is electrically connected with the power generation apparatus and the control signal generating circuit, and has a plurality of switching elements. The switching circuit receives the first signal and turns on one of the switching elements according to the control signal so as to convert the first signal and output an output signal. In addition, the conversion-sensing circuit includes a Schmitt trigger or any other waveform shaping circuit. The time interval is equal to one third of a time difference between a rising edge and a falling edge of a voltage waveform of the second signal; otherwise, the time interval is equal to a time difference between a rising edge of one of the voltage waveforms of the second signal and a falling edge of the other of the voltage waveforms of the second signal.

In addition, the control signal generating circuit obtains a frequency of the first signal according to the time interval. Besides, the control signal generating circuit controls the switching circuit according to information of a corresponding voltage peak value of the first signal during a certain interval. Otherwise, the control signal generating circuit controls the switching circuit by way of space vector pulse width modulation.

The power conversion apparatus further includes a first energy storage unit and a second energy storage unit. The first energy storage unit is electrically connected with the power generation apparatus and the switching circuit. The first energy storage unit stores and releases electric power generated by the power generation apparatus according to turn-on and turn-off of the switching elements, respectively. The second energy storage unit is electrically connected with the switching circuit and stores electric power of the output signal.

The power conversion apparatus further includes a brake energy recovery circuit electrically connected with the switching circuit. The brake energy recovery circuit has a switch unit, a first energy storage element and a second energy storage element. The switch unit is electrically connected with a first terminal of the first energy storage element, and a second terminal of the first energy storage element is electrically connected with a first terminal of the second energy storage element. In addition, the switch unit has a first switch element electrically connected with the first terminal of the first energy storage element. The first energy storage element stores braking energy of the power generation apparatus when the first switch element turns on, and the second energy storage element stores energy released from the first energy storage element when the first switch element turns off. The switch unit further has a second switch element electrically connected with a first terminal of the first switch element and the first terminal of the first energy storage element. The first energy storage element stores energy released from the second energy storage element when the second switch element turns on, and the first energy storage element releases the stored energy to the power generation apparatus when the second switch element turns off.

To achieve the above objective, the present invention further discloses a controlling method applied with a power conversion apparatus. The power conversion apparatus comprises a conversion-sensing circuit, a control signal generating circuit and a switching circuit. A power generation apparatus outputs a first signal inputted to the power conversion apparatus. The controlling method comprising: sensing the first signal and converting the first signal into a second signal via the conversion-sensing circuit; sensing at least one voltage waveform change of the second signal and generating a time interval via the conversion-sensing circuit; outputting a control signal via the control signal generating circuit and according to the time interval; and turning on one of a plurality of switching elements of the switching circuit via the switching circuit and according to the control signal, and converting the first signal into an output signal and outputting the output signal. Herein, the time interval is equal to one third of a time difference between a rising edge and a falling edge of a voltage waveform of the second signal; otherwise, the time interval is equal to a time difference between a rising edge of one of the voltage waveforms of the second signal and a falling edge of the other of the voltage waveforms of the second signal.

In addition, the control signal generating circuit obtains a frequency of the first signal according to the time interval. Besides, the control signal generating circuit controls the switching circuit according to information of a corresponding voltage peak value of the first signal during a certain interval.

The power conversion apparatus further includes a brake energy recovery circuit electrically connected with the switching circuit. The brake energy recovery circuit has a switch unit, a first energy storage element and a second energy storage element.

The first energy storage element stores braking energy of the power generation apparatus when a first switch element of the switch unit turns on, and the second energy storage element stores energy released from the first energy storage element when the first switch element turns off.

In addition, the first energy storage element stores energy released from the second energy storage element when a second switch element of the switch unit turns on, and the first energy storage element releases the stored energy to the power generation apparatus when the second switch element turns off.

To achieve the above objective, the present invention further discloses a power conversion apparatus including a control signal generating circuit and a brake energy recovery circuit. The control signal generating circuit is electrically connected with the power generation apparatus and outputs a control signal according to a first signal generated by the power generation apparatus. The brake energy recovery circuit is electrically connected with the power generation apparatus and the control signal generating circuit. The control signal controls the brake energy recovery circuit to store energy generated when the power generation apparatus brakes, and controls the brake energy recovery circuit to release the stored electric power to the power generation apparatus.

As mentioned above, the power conversion apparatus of the invention utilizes the conversion-sensing circuit to convert the first signal into the second signal and to sense at least one voltage waveform change of the second signal to generate the time interval, so as to obtain the instantaneous rotating speed and the frequency of the power generation apparatus and achieve the control of the instantaneous rotating speed. Thus, the prior art position detector can be replaced, and it is unnecessary to provide the power for the position detector so that no long distance line loss occurs. In addition, the control signal generating circuit of the invention outputs the control signal according to the time interval so as to control one of the switching elements of the switching circuit to turn on and off, and the first signal is converted and outputted. Because only the switch operation of one switching element is switched in one duration, the power consumption of the switching element can be decreased, the current harmonic wave of the output signal can be minimized, and the power conversion apparatus has the full power and high efficiency energy conversion.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic illustration showing a power conversion apparatus1according to a preferred embodiment of the invention. Referring toFIG. 1, a power conversion apparatus1may be applied with a power generation apparatus G. The power generation apparatus G may output a first signal S1, which is a three-phases balanced sine wave voltage signal with the stable phase sequence. The power generation apparatus G may be, for example but without limitation to, a wind power generator of a wind power generation system, and may also be another power generation apparatus, such as a thermal power generation apparatus, a waterpower power generation apparatus, a solar power generation apparatus or any other power generation apparatus. In addition, the output, after the conversion of the power conversion apparatus1, can charge the battery module for storage, and may also be supplied to the load or may be connected to the power supply grid in parallel. However, the invention is not particularly restricted thereto.

The power conversion apparatus1includes a conversion-sensing circuit11, a control signal generating circuit12and a switching circuit13. In addition, the power conversion apparatus1may further include a first energy storage unit14and a second energy storage unit15.

The conversion-sensing circuit11can sense the first signal S1, and convert the first signal S1into a second signal S2. Please refer toFIGS. 1, 2A and 2B, whereinFIGS. 2A and 2Bare schematic illustrations showing waveforms of three-phase line voltages of the first signal S1and the second signal S2of the power conversion apparatus, respectively.

The first signal S1is a three-phase balanced sine wave voltage signal with the stable phase sequence. So, it is possible to sense the first signal S1via, for example, a potential transformer (PT, not shown), and to utilize the conversion-sensing circuit11to convert the first signal S1into the second signal S2. The conversion-sensing circuit11may include a Schmitt trigger or any other waveform shaping circuit. In this embodiment, the Schmitt trigger functions as the waveform shaping circuit, and can, for example, convert the voltage transition points of the three-phase sine wave first signal S1(line voltages Vab, Vbcand Vca) ofFIG. 2Ainto the square wave signals (i.e., the second signal S2) with the rising and falling edges, respectively. As shown inFIG. 2B, taking the line voltage Vabas an example, the sine wave changes from the negative polarity to the positive polarity at 0°, so that a rising edge of the second signal S2can be obtained. In addition, the sine wave changes from the positive polarity to the negative polarity at 180°, so that a falling edge of the second signal S2is obtained, and so on. Therefore, as shown inFIG. 2B, the line voltages Vab, Vbcand Vcaof the first signal S1may be respectively converted into the square waves of the second signal S2, and the three square waves of the second signal S2correspond to the line voltages Vab, Vbcand Vcaof the first signal S1.

In addition, the conversion-sensing circuit11can sense at least one voltage waveform change of the second signal S2to generate a time interval. Herein, the time interval is, for example, equal to one third of a time difference between a rising edge and a falling edge of a certain line voltage waveform of the second signal S2. Specifically, taking the line voltage Vabof the first signal S1ofFIG. 2Bas an example, the time difference between the rising edge and the falling edge of the line voltage waveform of the second signal S2is the time required for the waveform of the line voltage Vabto change from 0° to 180° (i.e., a half period of the line voltage Vab), so one time interval is equal to the time required for the phase of the first signal S1to change 60° (180/3).

In addition, in another implemented example, the time interval may also be equal to the time difference between the rising edge of one voltage waveform of the second signal S2and the falling edge of the other voltage waveform of the second signal S2. Herein, as shown inFIG. 2A, the time difference between the rising edge of one line voltage waveform of the second signal S2and the falling edge of the other line voltage waveform of the second signal S2is also the time required for the waveform of the first signal S1to change 60°.

After the time interval is obtained, the control signal generating circuit12can calculate to obtain the period of the first signal S1(the period is equal to 6 times of the time interval) and the frequency (the frequency is equal to 1/period) according to the time interval so as to obtain the instantaneous rotating speed and the frequency of the power generation apparatus G. Thus, the power conversion apparatus1can achieve the control of the instantaneous rotating speed. Not only the prior art position detector (the price of the position detector is high) is needed, but the power of the position detector needs not to be provided and, the long distance line loss is eliminated. More specifically, the invention does not intend to restrict the time interval to the time for the first signal S1to change 60°. In other aspects, the time interval may also be the time required for the change of 30° or any other angle. Alternatively, utilizing the first signal S1to perform the mathematical calculation can also obtain the instantaneous rotating speed and the frequency of the power generation apparatus G.

With reference toFIG. 1, the control signal generating circuit12is electrically connected with the conversion-sensing circuit11and can output a control signal CS according to the time interval. The control signal CS is a pulse width modulation (PWM) signal and can include the information of the instantaneous rotating speed and the frequency of the power generation apparatus G. The control signal generating circuit12can output the control signal CS to control the switching circuit13according to the information of a corresponding voltage peak value of the first signal S1during a certain interval. The control signal generating circuit12can control the switching circuit13via the space vector pulse width modulation (SVPWM) or the sinusoidal pulse width modulation (SPWM).

The switching circuit13is electrically connected with the power generation apparatus G and the control signal generating circuit12. In addition, the switching circuit13may also be electrically connected with the first energy storage unit14and the second energy storage unit15. The switching circuit13has a plurality of switching elements131ato131fand a plurality of diodes132ato132f. The diodes132ato132fare disposed respectively corresponding to the switching elements131ato131f. Herein, the switching elements131ato131fmay be power transistors, respectively, and the six diodes132ato132fare connected in parallel to the six switching elements131ato131fin one-to-one manners, respectively. In addition, the switching circuit13can receive the first signal S1and can turn on one of the switching elements131ato131faccording to the control signal CS so as to convert the first signal S1and output an output signal OS.

As shown inFIG. 1, the first energy storage unit14is electrically connected with the power generation apparatus G and the switching circuit13, and can turn on and off according to the switching elements131ato131fto store and release the electric power of the first signal S1, respectively. Herein, the first energy storage unit14has, from top to bottom, three inductors141a,141band141c, which are electrically connected with the three-phase circuit at the output of the power generation apparatus G and the switching circuit13. The inductor141ais electrically connected with the switching elements131aand131band the diodes132aand132b, the inductor141bis electrically connected with the switching elements131cand131dand the diodes132cand132d, and the inductor141cis electrically connected with the switching elements131eand131fand the diodes132eand132f. In addition, the second energy storage unit15is electrically connected with the switching circuit13and can store the electric power outputted from the power conversion apparatus1. Herein, the second energy storage unit15is a capacitor capable of storing the electric power of the output signal OS. Of course, in other aspects, the output signal OS outputted from the switching circuit13may also be supplied to other load apparatuses, or may be used in other applications. In addition, the power conversion apparatus1may further include a filter unit17, which is disposed between the first energy storage unit14and the power generation apparatus G and electrically connected with the first energy storage unit14and the power generation apparatus G. The filter unit17may include three capacitors electrically connected between the first energy storage unit14and the power generation apparatus G in a Y-shape connection manner. The filter unit17can filter out the noise to stabilize the voltage signals inputted to and outputted from the power generation apparatus G.

Hereinbelow, illustrations will be made with reference to the associated drawings to describe how the control signal CS controls one of the switching elements131ato131fso as to convert the first signal S1and generate the output signal OS to make the power conversion apparatus1have the high conversion efficiency.

Please refer toFIGS. 3A to 8C, which are schematic illustrations showing waveforms of the first signal S1of the power conversion apparatus1of the invention and operations of different switching elements, respectively. It is to be firstly specified that some elements are not shown inFIGS. 3A to 8C. For example, the power generation apparatus G, the conversion-sensing circuit11, the control signal generating circuit12and the inductor141aof the first energy storage unit14are not shown inFIGS. 3B and 3C. In addition, the switching elements131aand131band131dto131f, which do not operate, are not shown, either. In addition, no filter unit17is shown inFIGS. 3A to 8C.

As shown inFIGS. 3A and 3Bof this embodiment, when the first signal S1is in the duration from 0° to 60°, the line voltage Vbchas the voltage peak value (as shown in the zone A) higher than the line voltage Vaband the line voltage Vca. The control signal generating circuit12can output the control signal CS when the line voltage Vbchas the peak value and when the first signal S1is in the duration from 0° to 60°, so as to control the switching element131cto switch and make the power conversion apparatus1have the high conversion efficiency.

As shown inFIG. 3B, the control signal CS (not shown) only turns on the switching element131cand generates the loop of the current i via the inductor141c, the diode132e, the switching element131cand the inductor141baccording to the line voltage Vbc, so that the inductors141band141ccan store the electric power of the line voltage Vbc. In addition, as shown inFIG. 3C, the control signal CS (not shown) is again utilized to control the switching element131cto turn off, the electric power stored in the inductors141band141ccan be converted and outputted to the second energy storage unit15for storage through the loop of the current i via the inductor141c, the diode132e, the diode132dand the inductor141b.

In addition, as shown inFIGS. 4A and 4Bof this embodiment, when the first signal S1is in the duration from 60° to 120°, the line voltage Vabhas the voltage peak value (as shown in the zone B) higher than the line voltage Vbcand the line voltage Vca. The control signal generating circuit12can output the control signal CS when the line voltage Vabhas the peak value and when the first signal S1is in the duration from 60° to 120°, so as to control the switching element131bto switch and make the power conversion apparatus1have the high conversion efficiency.

As shown inFIG. 4B, the control signal CS (not shown) only turns on the switching element131band generates the loop of the current i via the inductor141a, the switching element131b, the diode132dand the inductor141baccording to the line voltage Vab, so that the inductors141aand141bcan store the electric power of the line voltage Vab. In addition, as shown inFIG. 4C, the control signal CS (not shown) is again utilized to control the switching element131bto turn off and the electric power stored in the inductors141aand141bcan be converted and outputted to the second energy storage unit15for storage through the loop of the current i via the inductor141a, the diode132a, the diode132dand the inductor141b.

In addition, as shown inFIGS. 5A and 5Bof this embodiment, when the first signal S1is in the duration from 120° to 180°, the line voltage Vcahas the voltage peak value (as shown in the zone C) higher than the line voltage Vbcand the line voltage Vab. The control signal generating circuit12can output the control signal CS when the line voltage Vcahas the peak value and when the first signal S1is in the duration from 120° to 180°, so as to control the switching element131eto switch and make the power conversion apparatus1have the high conversion efficiency.

As shown inFIG. 5B, the control signal CS (not shown) only turns on the switching element131eand generates the loop of the current i via the inductor141a, the diode132a, the switching element131eand the inductor141caccording to the line voltage Vca, so that the inductors141aand141ccan store the electric power of the line voltage Vca. In addition, as shown inFIG. 5C, the control signal CS (not shown) is again utilized to control the switching element131eto turn off, and the electric power stored in the inductors141aand141ccan be converted and outputted to the second energy storage unit15for storage through the loop of the current i via the inductor141a, the diode132a, the diode132fand the inductor141c.

In addition, as shown inFIGS. 6A and 6Bof this embodiment, when the first signal S1is in the duration from 180° to 240°, the line voltage Vbchas the voltage peak value (as shown in the zone D) higher than the line voltage Vaband the line voltage Vca. The control signal generating circuit12can output the control signal CS when the line voltage Vbchas the peak value and when the first signal S1is in the duration from 180° to 240°, so as to control the switching element131dto switch and make the power conversion apparatus1have the high conversion efficiency.

As shown inFIG. 6B, the control signal CS (not shown) only turns on the switching element131dand generates the loop of the current i via the inductor141b, the switching element131d, the diode132fand the inductor141caccording to the line voltage Vbc, so that the inductors141band141ccan store the electric power of the line voltage Vbc. In addition, as shown inFIG. 6C, the control signal CS (not shown) is again utilized to control the switching element131dto turn off and the electric power stored in the inductors141band141ccan be converted and outputted to the second energy storage unit15for storage through the loop of the current i via the inductor141b, the diode132c, the diode132fand the inductor141c.

In addition, as shown inFIGS. 7A and 7Bof this embodiment, when the first signal S1is in the duration from 240° to 300°, the line voltage Vabhas the voltage peak value (as shown in the zone E) higher than the line voltage Vbcand the line voltage Vca. The control signal generating circuit12can output the control signal CS when the line voltage Vabhas the peak value and when the first signal S1is in the duration from 240° to 300°, so as to control the switching element131ato switch and make the power conversion apparatus1have the high conversion efficiency.

As shown inFIG. 7B, the control signal CS (not shown) only turns on the switching element131aand generates the loop of the current i via the inductor141b, the diode132c, the switching element131aand the inductor141aaccording to the line voltage Vab, so that the inductors141aand141bcan store the electric power of the line voltage Vab. In addition, as shown inFIG. 7C, the control signal CS (not shown) is again utilized to control the switching element131ato turn off, and the electric power stored in the inductors141aand141bcan be converted and outputted to the second energy storage unit15for storage through the loop of the current i via the inductor141b, the diode132c, the diode132band the inductor141a.

In addition, as shown inFIGS. 8A and 8Bof this embodiment, when the first signal S1is in the duration from 300° to 360° (or 0°), the line voltage Vcahas the voltage peak value (as shown in the zone F) higher than the line voltage Vbcand the line voltage Vab. The control signal generating circuit12can output the control signal CS when the line voltage Vcahas the peak value and when the first signal S1is in the duration from 300° to 360°, so as to control the switching element131fto switch and make the power conversion apparatus1have the high conversion efficiency.

As shown inFIG. 8B, the control signal CS (not shown) only turns on the switching element131fand generates the loop of the current i via the inductor141c, the switching element131f, the diode132band the inductor141aaccording to the line voltage Vca, so that the inductors141aand141ccan store the electric power of the line voltage Vca. In addition, as shown inFIG. 8C, the control signal CS (not shown) is again utilized to control the switching element131fto turn off, and the electric power stored in the inductors141aand141ccan be converted and outputted to the second energy storage unit15for storage through the loop of the current i via the inductor141c, the diode132e, the diode132band the inductor141a.

As mentioned hereinabove, the power generation apparatus G of the invention can convert the first signal S1into the second signal S2via the conversion-sensing circuit11upon the low power output, and sense at least one voltage waveform change of the second signal S2to generate the time interval, so as to obtain the instantaneous rotating speed and the frequency of the power generation apparatus G and make the power conversion apparatus1achieve the control of the instantaneous rotating speed. Not only the prior art position detector (the price of the position detector is high) is needed, but the power of the position detector needs not to be provided and the long distance line loss is eliminated. In addition, the control signal generating circuit12is further utilized to output the control signal CS according to the time interval, so as to control one of the switching elements of the switching circuit13to turn on and off via the SVPWM or the SPWM. Because only the on/off operation of one switching element is switched in one duration, the switch power consumption of the power transistor can be reduced, and the current harmonic wave of the output signal OS can be minimized, so that the power conversion apparatus1has the high efficiency energy conversion upon the low power output of the power generation apparatus G. In addition, upon the high power output of the power generation apparatus G, the power conversion apparatus1can simultaneously switch the operations of six switching elements131ato131fvia the SVPWM or the SPWM, so that the output electric power of the power generation apparatus G can be converted. Similarly, the control signal CS of the SVPWM or the SPWM can also be generated by the conversion-sensing circuit11via the control signal generating circuit12. Therefore, the power conversion apparatus1of the invention has the advantages of the full power and high efficiency energy conversion as well as the lower power loss.

In addition, please refer toFIG. 9, which is a schematic illustration showing a power conversion apparatus1aaccording to another preferred embodiment of the invention.

What is mainly different from the power conversion apparatus1of theFIG. 1is that the power conversion apparatus1amay further include a brake energy recovery circuit16electrically connected with the switching circuit13and the second energy storage unit15. The brake energy recovery circuit16can recover the electric power generated when the power generation apparatus G is braking. When no wind or the breeze is present, the stored electric power controls the switching circuit13to operate through the control signal generating circuit12by way of the SVPWM or the SPWM, and the first energy storage unit14and the filter unit17filter out the noise signal and then release the energy to the power generation apparatus G to start the blades and to solve the problem of the starting inertia of the power generation apparatus G. Thus, it is possible to solve the problems, such as the overheating of the brake resistor, the too long starting time of the control device or the output module, the missed short energy receiving, the brake resistor loss caused by the incomplete starting of the output module, the long-term waste of the considerable energy and the like, encountered during the prior art electric power conversion processes.

The brake energy recovery circuit16has a switch unit, a first energy storage element162and a second energy storage element163. In this embodiment, the switch unit may have a first switch element161aand a second switch element161b. In addition, the switch unit may further have two diodes164aand164brespectively connected in parallel to the first switch element161aand the second switch element161b. Herein, the diode164ais connected in parallel to the first switch element161a, and the diode164bis connected in parallel to the second switch element161b. In addition, the first switch element161a, the diode164a, the second switch element161band the diode164bare electrically connected with the first terminal of the first energy storage element162, the second terminal of the first energy storage element162is electrically connected with the first terminal of the second energy storage element163, and the second terminal of the second energy storage element163is electrically connected with the second switch element161band the diode164b. In this embodiment, the first energy storage element162is an inductor, and the second energy storage element163is a capacitor, and may be a super capacitor or any other elements capable of storing energy.

Please refer toFIGS. 10A to 10D, which are schematic illustrations showing operations of the brake energy recovery circuit16ofFIG. 9, respectively, wherein the conversion-sensing circuit11and the control signal generating circuit12are not shown inFIGS. 10A to 10D. In addition, the switch elements of the switch unit, which do not operate, are also not shown. For example, the second switch element161bis not shown inFIGS. 10A and 10B.

In this embodiment, as shown inFIG. 10A, when the power generation apparatus G is braking, the brake energy recovery circuit16can recover the electric power generated when the power generation apparatus G is braking. Herein, the control signal generating circuit12(not shown inFIG. 10A) can be utilized to control the first switch element161aof the brake energy recovery circuit16to turn on by way of PWM, and the current1generated by the brake energy can be stored by the first energy storage element162(the inductor stores the energy) via the first switch element161a. In addition, as shown inFIG. 10B, the control signal generating circuit12(not shown inFIG. 10B) is again utilized to control the first switch element161aof the brake energy recovery circuit16to turn off by way of PWM, so that the energy stored in the first energy storage element162can be released and stored to the second energy storage element163(the inductor releases the energy).

In addition, as shown inFIG. 10C, when the power generation apparatus G is to be started at no wind or at the breeze, the second switch element161bcan be controlled to turn on, and the second energy storage element163can release the stored electric power, which is received by the first energy storage element162(the inductor stores the energy). In addition, as shown inFIG. 10D, by controlling the second switch element161bto turn off, the energy stored in the first energy storage element162can be released (the inductor releases the energy) to the second energy storage unit15, and the power generation apparatus G can convert the reverse first signal S1, generated by the second energy storage unit15, via the switching circuit13, so that the power generation apparatus G becomes a motor to start the blades and solve the problem of the starting inertia of the power generation apparatus G. When no wind is present, this energy may also be released to any load electrically connected with the second energy storage unit15. The signals for controlling the first switch element161aand the second switch element161bmay be PWM signals, and may be generated by the control signal generating circuit12or another control circuit. Herein, the invention is not particularly restricted thereto.

In addition, the technological characteristics of the power conversion apparatus1acan be obtained with reference to the power conversion apparatus1, so detailed descriptions thereof will be omitted.

In addition, please refer toFIGS. 1 and 11simultaneously, whereinFIG. 11is a schematic flow chart showing a controlling method of the power conversion apparatus of the invention.

The controlling method of the invention is applied with the power conversion apparatus1. The power conversion apparatus1includes a conversion-sensing circuit11, a control signal generating circuit12and a switching circuit13, wherein a power generation apparatus G outputs a first signal S1inputted to the power conversion apparatus1. The controlling method includes the following steps. In step S01, the conversion-sensing circuit11senses and converts the first signal S1into a second signal S2. In step S02, the conversion-sensing circuit11senses at least one voltage waveform change of the second signal S2and generates a time interval. In step S03, the control signal generating circuit12outputs a control signal CS according to the time interval. In step S04, the switching circuit13turns on one of a plurality of switching elements131ato131fof the switching circuit13according to the control signal CS, so as to convert the first signal S1and output an output signal OS.

In addition, please refer toFIGS. 9 and 12simultaneously, whereinFIG. 12is a schematic flow chart showing another controlling method of the power conversion apparatus of the invention.

The controlling method of the invention may further include the following steps S05and S06. In the step S05, a first switch element161aof the switch unit is controlled to turn on, so as to store the braking energy of the power generation apparatus G to the first energy storage element162. In the step S06, the first switch element161ais controlled to turn off to store the energy, released from the first energy storage element162, to the second energy storage element163. In addition, the controlling method may further include the following steps S07and S08. In the step S07, a second switch element161bof the switch unit is controlled to turn on to store the energy, released from the second energy storage element163, to the first energy storage element162. In the step S08, the second switch element161bis controlled to turn off to release the energy, released from the first energy storage element162, to the power generation apparatus G.

In addition, the technological characteristics of the power conversion apparatus and the controlling method thereof have been described hereinabove, so detailed descriptions thereof will be omitted.

In summary, the power conversion apparatus of the invention utilizes the conversion-sensing circuit to convert the first signal into the second signal and to sense at least one voltage waveform change of the second signal to generate the time interval, so as to obtain the instantaneous rotating speed and the frequency of the power generation apparatus and achieve the control of the instantaneous rotating speed. Thus, the prior art position detector can be replaced, and it is unnecessary to provide the power for the position detector so that no long distance line loss occurs. In addition, the control signal generating circuit of the invention outputs the control signal according to the time interval so as to control one of the switching elements of the switching circuit to turn on and off, and the first signal is converted and outputted. Because only the switch operation of one switching element is switched in one duration, the power consumption of the switching element can be decreased, the current harmonic wave of the output signal can be minimized, and the power conversion apparatus has the full power and high efficiency energy conversion.