High-efficiency high step-up ratio direct current converter with interleaved soft-switching mechanism

A high-efficiency high step-up ratio direct current converter with an interleaved soft-switching mechanism is provided. The direct current converter includes a voltage-multiplier circuit and an active clamping circuit. The voltage-multiplier circuit includes two isolating transformers, two main switches disposed on a primary side of the two isolating transformers, four diodes disposed on a secondary side of the two isolating transformers and four capacitors disposed on the secondary side of two isolating transformers, configured to boost a voltage of a direct-current power to a desired voltage value. The active clamping circuit, electrically connected to the voltage-multiplier circuit, includes two active clamp switches and a clamp capacitor to lower a voltage surge of the two main switches so that the two main switches and the two active clamp switches can be soft switched on.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a high-efficiency high step-up ratio direct current converter with an interleaved soft-switching mechanism.

2. Description of the Related Art

It can be said that modern high technology civilization is developed on a base of massive consumption of petrochemical energies. According to the researches and statistics, however, the petrochemical energy will be gradually consumed, and the storage amount of global petroleum fuel could afford us for use less than forty years. When the petrochemical energy is utilized to improve quality of life, a large amount of greenhouse gases are simultaneously produced, resulting in greenhouse effect and damages of nature ecological environment. In view of increasing price of petroleum every day, many countries in the world begin to promote energy saving and carbon reduction. Also, clean renewable energies such as solar energy, wind power and fuel cell are gradually valued, and thus energy technologies connected therewith are gradually applied and developed.

It is difficult to build a large renewable energy generation system on an island with small area but densely populated due to space limitation, and therefore a small distributed electric power system is gradually valued. A small renewable energy can be composed of electric power conversion circuits such as a solar photovoltaic module or fuel cell, a step-up DC/DC converter, a DC/AC converter, etc. In general, a solar or fuel cell supplies a low voltage DC power (20V-45V). However, a post-stage DC/AC converter requires a higher DC input voltage (350V-400V) for conversion into a commonly-used AC (110 Vrms, 220 Vrms), thereby supplying to a load or parallel operation with the utility. Therefore, it is essential to use a high step-up ratio DC/DC converter to attain a front-stage step-up purpose. However, due to a large current input of such a high step-up ratio DC/DC converter, larger current ripple and flip-flop switching loss are easily occurred therewith.

BRIEF SUMMARY OF THE INVENTION

In view of this, the invention provides a high step-up ratio direct current/direct current converter with an interleaved switching technique and a switch soft-switching technique, thereby promoting efficiency of the converter. Besides, the converter of the invention is characterized with wide-range input/output voltage and modularization, considerably suitable for applying to a future distributed renewable power system.

The invention provides a high-efficiency high step-up ratio direct current converter with an interleaved soft-switching mechanism. The direct current converter includes a voltage-multiplier circuit and an active clamping circuit. The voltage-multiplier circuit includes two isolating transformers, two main switches disposed on a primary side of the two isolating transformers, four diodes disposed on a secondary side of the two isolating transformers and four capacitors disposed on the secondary side of two isolating transformers, configured to boost a voltage of a direct-current power to a desired voltage value. The active clamping circuit, electrically connected to the voltage-multiplier circuit, includes two active clamp switches and a clamp capacitor to lower a voltage surge of the two main switches so that the two main switches and the two active clamp switches can be soft switched on.

In one aspect of the invention, the two main switches are configured to be in interleaved switching operation, the two active clamp switches are configured to be in interleaved switching operation, and the two main switches and the two active clamp switches are configured to be in complementary switching operation.

In another aspect of the invention, the two main switches and the two active clamp switches are soft switched with dead time provided therebetween.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a circuit diagram of a first embodiment of a high-efficiency high step-up ratio direct current converter30with an interleaved soft-switching mechanism of the invention, in which the direct current converter30comprises an active clamping circuit10and a voltage-multiplier circuit20. The voltage-multiplier circuit20comprises two isolating transformers220and221, two main switches210and211disposed on a primary side of the two isolating transformers220and221, four diodes231,232,233and234disposed on a secondary side of the two isolating transformers220and221, and four capacitors241,242,243and244. The isolating transformer220comprises an excitation inductance2201and a leakage inductance2202, and the isolating transformer221comprises an excitation inductance2211and a leakage inductance2212. The voltage-multiplier circuit20is characterized with high voltage conversion ratio, capable of reducing conduction loss and facilitating to increase efficiency. The active clamping circuit10electrically connected to the voltage-multiplier circuit20comprises two active clamp switches101and102and two clamp capacitors105and106. The active clamping circuit10is configured to attain main purposes, including to lower a voltage surge of the two main switches210and211so that the two main switches210and211and the two active clamp switches101and102are capable of attaining a soft-switching property of zero voltage switching (ZVS) when the two main switches210and211and the two active clamp switches101and102are switched on, and further to increase power conversion efficiency of integral circuit. An output terminal of the direct current converter30of the invention is capable of connecting to a load or post-stage converter.

FIG. 2shows a fundamental principle followed by a switching operation of the main switches210and211and the active clamp switches101and102. The interleaved switching operation of the main switches210and211(with difference of a half switching cycle, i.e., phase difference of 180 degrees) are illustrated inFIG. 2, in which V210and V211represent driving voltages of the main switches210and211, respectively. The complementary switching operation of the active clamp switches101and102are illustrated inFIG. 2, in which V101and V102represent driving voltages of the active clamp switches101and102, respectively. In order to prevent the occurrence of short on the primary-side clamp capacitors105and106, it is required to provide dead time between the operations of the main switches210and211and the active clamp switches101and102as shown inFIG. 3. With an operation cycle divided into twelve intervals, the working modes of the direct current converter30will be described in details hereinafter.

FIG. 4shows an equivalent circuit of the direct current converter30in a first working mode, in which the main switches210and211are switched on, the active clamp switches101and102are switched off, the diodes233and232are switched on, and the diodes231and234are switched off. Because the current advancedly flows through an equivalent body diode (not shown in FIGs.) of the main switch210in a previous working mode (a twelfth mode), the main switch210in the first working mode is able to be zero-voltage switched on. A primary-side input current of the isolating transformer220flows out from the dot, and a secondary-side current of the isolating transformer220flows in the dot for storing energy to the capacitor243when flowing through the diode233. The capacitor241releases energy from the load40. A primary-side input current of the isolating transformer221flows in the dot, and a secondary-side current of the isolating transformer221flows out from the dot for releasing energy from the capacitor242and the load40when flowing through the diode232and the capacitor242. With respect to current directions illustrated inFIG. 4, a dashed line represents a current direction when the first working mode is started, and a solid line represents a current direction when the first working mode is ended. InFIG. 4, it can be appreciated that the current iLk1flowing through the leakage inductance2202is changed from a negative current to a positive current in the first working mode. When the current iLk1flowing through the leakage inductance2202is equal to a current iLm1flowing through the excitation inductance2201, the primary-side current of the isolating transformers220begins to flow in the dot, and a second working mode is started.

FIG. 5shows an equivalent circuit of the direct current converter30in the second working mode, in which the main switches210and211are switched on, the active clamp switches101and102are switched off, the diodes231and232are switched on, and the diodes233and234are switched off. The primary-side current of each of the isolating transformers220and221flows in the dot, and the secondary-side current of each of the isolating transformers220and221flows out from the dot for releasing energy from the capacitor242and the load40when flowing through the diodes231and232and the capacitors243and244, respectively. As shown inFIG. 3, when the main switch211is switched off in the second working mode, a third working mode is started.

FIG. 6shows an equivalent circuit of the direct current converter30in the third working mode, in which the main switch210is switched on, the main switch211and the active clamp switches101and102are switched off, the diodes231and232are switched on, the diodes233and234are switched off, and at this moment the switches210,211,101, and102are situated at the dead time. The primary-side currents of each of the isolating transformers220and221flows in the dot, and a secondary-side current of the isolating transformers220and221flows out from the dot for releasing energy from the capacitor241and242and the load40when flowing through the diodes231and232and the capacitors243and244. Due to the continuous flow of the current iLk1of the leakage inductance2212, the equivalent body diode of the active clamp switch102is switched on, and the current advancedly flows through the equivalent body diode of the active clamp switch102. Thus, the active clamp switch102is able to be zero-voltage switched on at the beginning of the fourth working mode. As shown inFIG. 3, when the active clamp switch102is switched on in the third working mode, a fourth working mode is started.

FIG. 7shows an equivalent circuit of the direct current converter30in the fourth working mode, in which the main switch210and the active clamp switch102are switched on, the main switch211and the active clamp switch101are switched off, the diodes231and232are switched on, and the diodes233and234are switched off. As mentioned above, because the equivalent body diode of the active clamp switch102is already switched on in the previous working mode (the third working mode), the active clamp switch102is able to be zero-voltage switched on at the beginning of the fourth working mode. The primary-side current of each of the isolating transformers220and221flows in the dot, and the secondary-side current of each of the isolating transformers220and221flows out from the dot for releasing energy from the capacitors241and242and the load40when flowing through the diodes231and233and the capacitors243and244, respectively. When the current iLk2flowing through the leakage inductance2212is equal to a current iLm2flowing through the excitation inductance2211in the fourth working mode, the primary-side current of the isolating transformers221begins to flow out from the dot, and a fifth working mode is started.

FIG. 8shows an equivalent circuit of the direct current converter30in the fifth working mode, in which the main switch210and the active clamp switch102are switched on, the main switch211and the active clamp switch101are switched off, the diodes231and234are switched on, and the diodes233and232are switched off. The primary-side current of the isolating transformer220flows in the dot, and the secondary-side current of the isolating transformer220flows out from the dot for releasing energy from the capacitor241and the load40when flowing through the diode231and the capacitor243. The primary-side current of the isolating transformer221flows out from the dot, and the secondary-side current of the isolating transformer221flows in the dot for storing energy in the capacitor244when flowing through the diode234. The capacitor243releases energy from the load40. With respect to current directions illustrated inFIG. 8, a dashed line represents a current direction when the fifth working mode is started, and a solid line represents a current direction when the fifth working mode is ended. InFIG. 8, it can be appreciated that the current iLk2flowing through the leakage inductance2212is changed from a positive current to a negative current in the fifth working mode. As shown inFIG. 3, when the active clamp switch102is switched off in the fifth working mode, a sixth working mode is started.

FIG. 9shows an equivalent circuit of the direct current converter30in the sixth working mode, in which the main switch210is switched on, the main switch211and the active clamp switches101and102are switched off, the diodes231and234are switched on, the diodes233and232are switched off, and at this moment the switches210,211,101, and102are situated at the dead time. The primary-side current of the isolating transformer220flows in the dot, and the secondary-side current of the isolating transformer220flows out from the dot for releasing energy from the capacitor241and the load40when flowing through the diode231and the capacitor243. The primary-side current of the isolating transformer221flows out from the dot, and the secondary-side current of the isolating transformer221flows in the dot for storing energy in the capacitor244when flowing through the diode234. The capacitor242releases energy from the load40. Due to the continuous flow of the current iLk2of the leakage inductance2212, the equivalent body diode of the main switch211to be switched on, and the current of the main switch211advancedly flows through the equivalent body diode of the main switch211. Thus, the main switch211is able to be zero-voltage switched on at the beginning of the seventh working mode. As shown inFIG. 3, when the main switch211is switched on in the sixth working mode, the seventh working mode is started.

FIG. 10shows an equivalent circuit of the direct current converter30in the seventh working mode, in which the main switches210and211are switched on, the active clamp switches101and102are switched off, the diodes231and234are switched on, and the diodes233and232are switched off. As mentioned above, because the current of the main switch211already flows through the equivalent body diode of the main switch211in the previous working mode (the sixth working mode), the main switch211is able to be zero-voltage switched on at the beginning of the seventh working mode. The primary-side current of the isolating transformer220flows in the dot, and the secondary-side current of the isolating transformer220flows out from the dot for releasing energy from the capacitor241and the load40when flowing through the diode231and the capacitor243. The primary-side input current of the isolating transformer221flows out from the dot, and the secondary-side current of the isolating transformer221flows in the dot for storing energy in the capacitor244when flowing through the diode234. The capacitor242releases energy from the load40. With respect to current directions illustrated inFIG. 10, a dashed line represents a current direction when the seventh working mode is started, and a solid line represents a current direction when the seventh working mode is ended. InFIG. 10, it can be appreciated that the current iLk2flowing through the leakage inductance2212is changed from a negative current to a positive current in the seventh working mode. When the current iLk2flowing through the leakage inductance2212is equal to a current iLm2flowing through the excitation inductance2211, the primary-side current of the isolating transformers221begins to flow in the dot, and the eighth working mode is started.

FIG. 11shows an equivalent circuit of the direct current converter30in the eighth working mode, in which the main switches210and211are switched on, the active clamp switches101and102are switched off, the diodes231and232are switched on, and the diodes233and234are switched off. The primary-side current of each of the isolating transformers220and221flows in the dot, and the secondary-side current of each of the isolating transformers220and221flows out from the dot for releasing energy from the capacitors241and242and the load40when flowing through the diodes231and232and the capacitors243and244, respectively. As shown inFIG. 3, when the main switch210is switched off in the eighth working mode, the ninth working mode is started.

FIG. 12shows an equivalent circuit of the direct current converter30in the ninth working mode, in which the main switch211is switched on, the main switch210and the active clamp switches101and102are switched off, the diodes231and232are switched on, the diodes233and234are switched off, and at this moment the switches210,211,101, and102are situated at the dead time. The primary-side current of each of the isolating transformers220and221flows in the dot, and the secondary-side current of each of the isolating transformers220and221flows out from the dot for releasing energy from the capacitors241and242and the load40when flowing through the diodes231and232and the capacitors243and244, respectively. Due to the continuous flow of the current iLk1of the leakage inductance2202, the equivalent body diode of the active clamp switch101is switched on, and the current of the active clamp switch101advancedly flows through the equivalent body diode of the active clamp switch101. Thus, the active clamp switch101is able to be zero-voltage switched on at the beginning of the tenth working mode. As shown inFIG. 3, when the active clamp switch101is switched on in the ninth working mode, the tenth working mode is started.

FIG. 13shows an equivalent circuit of the direct current converter30in the tenth working mode, in which the main switch211and the active clamp switch101are switched on, the main switch210and the active clamp switch102are switched off, the diodes231and232are switched on, and the diodes233and234are switched off. As mentioned above, because the equivalent body diode of the active clamp switch101is already switched on in the previous working mode (the ninth working mode), the active clamp switch101is able to be zero-voltage switched on at the beginning of the tenth working mode. The primary-side current of each of the isolating transformers220and221flows in the dot, and the secondary-side current of each of the isolating transformers220and221flows out from the dot for releasing energy from the capacitors241and242and the load40when flowing through the diodes231and233and the capacitors243and244, respectively. When the current iLk1flowing through the leakage inductance2202is equal to a current iLm1flowing through the excitation inductance2201in the tenth working mode, the primary-side current of the isolating transformers220begins to flow out from the dot, and the eleventh working mode is started.

FIG. 14shows an equivalent circuit of the direct current converter30in the eleventh working mode, in which the main switch211and the active clamp switch101are switched on, the main switch210and the active clamp switch102are switched off, the diodes233and232are switched on, and the diodes231and234are switched off. The primary-side current of the isolating transformer220flows out from the dot, and the secondary-side current of the isolating transformer220flows in the dot for storing energy in the capacitor243when flowing through the diode233. The capacitor241releases energy from the load40. The primary-side current of the isolating transformer221flows in the dot, and the secondary-side current of the isolating transformer221flows out from the dot for releasing energy from the capacitor242and the load40when flowing through the diode232and the capacitor244. With respect to current directions illustrated inFIG. 14, a dashed line represents a current direction when the eleventh working mode is started, and a solid line represents a current direction when the eleventh working mode is ended. InFIG. 14, it can be appreciated that the current iLk1flowing through the leakage inductance2202is changed from a positive current to a negative current in the eleventh working mode. As shown inFIG. 3, when the active clamp switch102is switched off in the eleventh working mode, the twelfth working mode is started.

FIG. 15shows an equivalent circuit of the direct current converter30in the twelfth working mode, in which the main switch211is switched on, the main switch210and the active clamp switches101and102are switched off, the diodes233and232are switched on, the diodes231and234are switched off, and at this moment the switches210,211,101, and102are situated at the dead time. The primary-side current of the isolating transformer220flows out from the dot, and the secondary-side current of the isolating transformer220flows in the dot for storing energy in the capacitor243when flowing through the diode233. The capacitor241releases energy from the load40. The primary-side current of the isolating transformer221flows in the dot, and the secondary-side current of the isolating transformer221flows out from the dot for releasing energy from the capacitor242and the load40when flowing through the diode232and the capacitor244. Due to the continuous flow of the current iLk1of the leakage inductance2202, the equivalent body diode of the main switch210is switched on, and the current of the main switch210advancedly flows through the equivalent body diode of the main switch210. Thus, the main switch210is able to be zero-voltage switched on at the beginning of the first working mode. As shown inFIG. 3, when the main switch210is switched on in the twelfth working mode, the operation is returned to the first working mode to regularly perform the above-described modes.

By mathematical model derivation and simulation verification, an ideal step-up ratio of the direct current converter can be obtained as follows (when ratio of winding of each of the isolating transformers T1and T2is n)(n1=n2=n).

where Vorepresents the output voltage, Vsrepresents the input voltage, and D represents the duty cycle of the main switches210and211.

The invention can develop other embodiments of the circuit structure in accordance with placement and adaption of different active clamping circuits. Referring toFIGS. 16,17,18and19,FIG. 16represents a circuit diagram of a second embodiment of a direct current converter of the invention,FIG. 17represents a circuit diagram of a third embodiment of a direct current converter of the invention,FIG. 18represents a circuit diagram of a fourth embodiment of a direct current converter of the invention, andFIG. 19represents a circuit diagram of a fifth embodiment of a direct current converter of the invention. The second, third, fourth and fifth embodiments differ from the first embodiment in that the second, third, fourth and fifth embodiments provide different arrangements of the active clamp switches101and102and the clamp capacitors105and106, respectively. Moreover, only one clamp capacitor107, which is a combination of the two clamp capacitors105and106of the first embodiment, is provided in the fourth and fifth embodiments, and the clamp capacitor107has similar operation principle and efficacy and same step-up ratio to the clamp capacitors105and106of the first embodiment. Thus, the related description of the clamp capacitor107is omitted.

The invention provides advantages as follows.

Firstly, the direct current converter of the invention is provided with a circuit protection by electrically isolating the low-voltage side from the high-voltage side.

Secondly, with respect to increment of conversion efficiency, the input low-voltage side switches cooperated with an active clamp technique are capable of attaining a zero-voltage soft-switching operation and reducing the switching losses. Accordingly, the direct current converter of the invention is provided with a property of high conversion efficiency.

Thirdly, with the direct current converter of the invention cooperated with the active clamp technique, the working range of the switch of the converter is not limited. Further, with the circuit of the invention provided with an inherently extreme high step-up ratio, it is advantageous to voltage boosting of a solar energy battery module (e.g., in parallel operation with the utility) required by a post-stage converter. Accordingly, the direct current converter of the invention is particularly suitable for a medium-small solar photovoltaic module with large voltage fluctuation range.

Fourthly, the direct current converter of the invention is capable of being modulized and operated without additional inductance, thereby reducing costs and increasing productivity.

The direct current converter of the invention is capable of applying on a renewable energy system (e.g., solar photovoltaic generation system). However, it is to be understood that the application of the invention is not limited thereto, and the invention is suitable for a system which is required of boosting the voltage of a DC power.