FIELD OF INVENTION
[001] The present invention relates to the apparatus for a converter. More specifically, the present invention relates to a switched mode supply based converter with active rectification.
BACKGROUND
[002] Switched-mode power supplies (SMPSs) are being commonly employed and are increasingly replacing “classical” power supplies which are made of a transformer and a linear voltage regulator. Unlike a linear power supply, SMPS offers the advantage of short time involved in voltage corrections during high transitions, which minimizes wasted energy. This higher power conversion efficiency is an important advantage of a SMPS. SMPS are also substantially smaller and lighter than a linear supply due to the smaller transformer size and weight. Therefore, switching power converters are used for varied applications such as to charge batteries of mobile devices for example, mobile phones, portable computers, portable electric drills, etc.
[003] SMPS uses switching power converters to convert one voltage into another voltage which may be used as a supply voltage for an electric device or an electronic circuit. Many different switching power converter topologies have been employed such as buck converters, boost converters, Cuk converters, flyback converters, etc.
[004] Despite the advantages of SMPS, manufacturing SMPS with low voltage and high current is currently impossible without huge energy losses. Conventional SMPS employ diodes which have disadvantage of constant voltage drop thereby resulting in high power losses as heat and hence, poor efficiency levels.
[005] Therefore, a modified switching power converter which addresses the disadvantages offered by the existing systems is required to be devised.
SUMMARY
[006] A converter with active rectification is disclosed. The converter includes a transformer having a primary side and a secondary side. The primary side is equipped to receive a first voltage supply while the secondary side provides a second voltage supply. The converter includes at least one pair of first power switches. The first power switches are configured to make/break an electrical circuit to control the first voltage supply supplied to the primary side of the transformer. A SMPS controller is employed to regulate switching pattern of the first power switches. The converter further includes at least one pair of second power switches coupled to the secondary side of the transformer. The second power switches are configured to provide a continuous DC supply. An output voltage conditioner is coupled to the tappings of the secondary side of the transformer. The output voltage conditioner is configured to control switching pattern of the second power switches and a polarity reversal circuit is coupled to the output of the second power switches for providing an output voltage at a predefined polarity.
BRIEF DESCRIPTION OF DRAWINGS
[007] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale.
[008] FIG. 1 depicts an exemplary architecture of a converter in accordance with an embodiment of the present invention.
[009] FIG. 1a depicts an exemplary architecture of a converter without microcontroller in accordance with an embodiment of the present invention.
[0010] FIG. 1b depicts a polarity reversal circuit 120 in accordance with an embodiment of the present invention.
[0011] FIG. 2 illustrates the working of the converter 100 in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF DRAWINGS
[0012] Prior to describing the invention in detail, definitions of certain words or phrases used throughout this patent document will be defined: the terms "include" and "comprise", as well as derivatives thereof, mean inclusion without limitation; the term "or" is inclusive, meaning and/or; the phrases "coupled with" and "associated therewith", as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; Definitions of certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases.
[0013] Wherever possible, same reference numbers will be used throughout the drawings to refer to same or like parts. Moreover, references to various elements described herein are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice-versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claims.
[0014] Particular embodiments of the present disclosure are described herein below with reference to the accompanying drawings, however, it is to be understood that the disclosed embodiments are merely examples of the disclosure, which may be embodied in various forms. Well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure.
[0015] The present invention discloses a converter which receives an input voltage and subsequently generates an output voltage from the input voltage triggered by a switching signal. The converter of the present invention is a switched-mode power supply based converter (or a switching converter). In an embodiment, the converter is employed for generating an output of low voltage and high current without huge energy losses. Therefore, the converter as per the present invention has high efficiency levels.
[0016] The converter may include a plurality of components such as, without limitation, one or more of an alternating current (AC) input line, filters, rectifiers, control circuit, transformer, polarity reversal circuit, feedback circuit, a SMPS controller, a microcontroller, etc. The said components operate in a synchronized manner to produce a desired output which may be used as a supply voltage for an electric device or an electronic circuit, such as a water purification unit, air purifier or other purifying devices, charging device, device that requires high power such as portable welding machine, etc.
[0017] In an embodiment, the present invention includes an active rectification circuit in place of diodes. Also, the present invention involves H-Bridge polarity reversal circuit. The presence of active rectification with H-bridge generates an output voltage with minimized energy losses thereby increasing the efficiency of the converter as compared to conventional systems.
[0018] Referring to FIG. 1, an exemplary architecture of the converter 100 is illustrated. As shown in the figure, the converter 100 includes one or more input terminals 102, a filtering circuit 104, a rectifying circuit 106, a power factor correction circuitry 108, at least one pair of first power switches 110a and 110b, a transformer 112, an output voltage conditioner 114, at least one pair of second power switches 114a and 114b, a feedback loop 116, a SMPS controller 116a, a galvanic isolation means 116b, a microcontroller 118 and a polarity reversal circuit 120.
[0019] As shown in FIG. 1, the converter 100 includes two input terminals 102 to which an input AC voltage may be applied. The converter 100 as described in the following disclosure relates to an AC-DC converter 100, however, it must be noted that that other types of converters also lie within the scope of the present invention.
[0020] The filtering circuit 104 is an input line filter which consists of an electronic circuit connected between the input terminals 102 and the rectifying circuit 106 of the converter 100. The design and components of the filtering circuit 104 are so selected that they do not unnecessarily increase the volume and cost of the supply or compromise the power supply performance of the converter 100. Even though there are various filter designs with different characteristics and effects on power supply performance, the present invention employs for example, a ferrite core material to suppress electromagnetic or radio frequency interferences (EMI or RFI) while offering a balance between size, cost and performance.
[0021] The input voltage passes through the filtering circuit 104 before reaching the rectifying circuit 106. In an embodiment, the filtering circuit 104 attenuates all the higher frequencies and only allows frequencies in the range of 50Hz or 60 Hz to pass through the next stage.
[0022] The filtering circuit 104 is employed to reduce the interference from the electromagnetic signals (EMI signals) and other electrical noises present in the input terminal 102. The filtering circuit 104 prevents the EMI signals generated within the power supply to affect any other equipment(s) connected on the same line. Further, the filtering circuit 104 prevents high frequency voltage and EMI signals on the power line from passing through and reaching the supply’s output. The filtering circuit 104 is also used to ensure that the power supplies comply with government regulations and agency standards.
[0023] The rectifying circuit 106 is provided for transforming the input voltage (AC) into a DC voltage.
[0024] The rectifying circuit 106 is provided with at least four diodes in a bridge arrangement to provide the output voltage of one polarity for input voltage of both polarities. The rectifying circuit 104 may include one of, without limitation, vacuum tube diodes, mercury-arc valves, stacks of copper and selenium oxide plates, semiconductor diodes, silicon-controlled rectifiers, etc. The rectifying circuit 106 of the present invention may be single-phase or multi-phase circuit. The rectifying circuit 106 provides a DC output.
[0025] The present invention may include a power factor correction circuitry 108 in order to mitigate the amount of reactive power drawn by the converter 100.
[0026] The first power switches 110a and 110b help to make/break the electrical circuit of the converter 100 by removing/restoring a conducting path in the electrical circuit of the converter 100. The first power switches control a first voltage supply supplied to the transformer 112. In an embodiment, the operation of the first power switches 110a and/or 110b is controlled by specialized integrated circuits through/via galvanic isolation to protect these specialized integrated circuits. The first power switches 110a and 110b may be operated through signals of the SMPS controller 116a.
[0027] The first power switches 110a and/or 110b may include a power transistor such as a bipolar junction transistor (BJT), insulated-gate bipolar transistor (IGPT), a field effect (FET) such as a metal oxide semiconductor field effect transistor (MOSFET) or a suitable thyristor such as a gate turn-off thyristor, depending on the amount of power transformed by the converter 100. In an embodiment, the first power switches 110a and/or 110b include two MOSFETs in parallel configuration. The parallel connection of the MOSFETs result in decreased forward voltage drop. Further, the MOSFETs have low on-resistance and can withstand high currents.
[0028] In an embodiment, the first power switches 110a and 110b are of high voltage (300-500v) low current (20 -40A) type.
[0029] The transformer 112 may be a step-down transformer which is used to convert the high input voltage to a low output voltage. The coils of wire on each side of the transformer 112 have different numbers of turns, causing the input voltage to the transformer 112 to be different from the output voltage.
[0030] In an embodiment, the transformer 112 of the present invention may include, for example, a ferrite core for enabling efficient operation at switching frequencies between 20 - 60 kilohertz to several megahertz. Other readily known types of transformers, including core-less transformers, may be used. The transformer 112 is designed to provide low power loss, small physical size, low weight and little audible vibration. The operating frequencies of the transformer 112 lie beyond the audible range and can provide quiet operation.
[0031] The transformer 112 has a primary side and a secondary side. The primary side is equipped to receive a first voltage supply. The secondary side provides a second voltage supply. The primary and secondary sides include at least a primary and a secondary winding. In one embodiment, the transformer 112 with an auxiliary winding at the secondary side may be used to preserve galvanic isolation between the primary and the secondary winding and to avoid utilization of other electrically insulating devices, for example, electro-optical devices, in the feedback loop 116. Different embodiments of the present invention, however, may utilize different types of transformers, including transformers with a primary and a secondary winding only.
[0032] The primary winding of primary side is connected in series with the first power switches 110a and/or 110b of the transformer 112. The first power switches 110a and/or 110b on the primary side function to interrupt the flow of electrical current and thereby the provision of electrical energy to the primary side of the transformer 112.
[0033] The secondary side of the transformer 112 may include two secondary tappings ‘a’, ‘c’ and a center tap ‘b’. The center tap ‘b’ on the secondary side of the transformer 112 may serve as the positive terminal connected to the input of the polarity reversal circuit 120 and the output voltage conditioner 114. The other two secondary tappings ‘a’ and ‘c’ of the transformer 112 are connected to second power switches 114a and 114b respectively and the output voltage conditioner 114.
[0034] The output voltage conditioner 114 smoothens, filters, rectifies and stabilizes the voltage provided by the transformer 112 at the secondary winding and provides a suitable quality output voltage under operating conditions to a load connected to the output of the converter 100. The output voltage conditioner 114 is configured to control the switching pattern of the second power switches 114a and/or 114b. The output voltage conditioner 114 for use with the converter 100 according to one embodiment of the present invention may include a number of different devices including, diodes, capacitors, inductors and optional resistors, or other devices or components as would be readily understood by a person skilled in this art, for example, for smoothening, filtering, rectifying and stabilizing the output voltage. Other electronic devices such as integrated regulators, operational amplifiers and/or other parts as would be readily understood by a person skilled in the art may be employed in different output voltage conditioners.
[0035] In an embodiment, the output voltage conditioner 114 includes a synchronous rectifier/active rectifier. The output voltage conditioner 114 includes two second power switches 114a, 114b of low voltage (25-40v) and high current (200 – 550A) type. The gates of second power switches 114a and 114b may be controlled by the output voltage conditioner 114. In an embodiment, the output voltage conditioner 114 is programmed to control the switching pattern of the second power switches 114a, 114b on its own.
[0036] In an embodiment, the microcontroller 118 is remotely connected to the output voltage conditioner 114.
[0037] The feedback loop 116 is a wire linking which operatively couples the secondary side of the transformer 112 and the SMPS controller 116a. The feedback loop 116 helps to ensure that the output voltage delivered by the transformer 112 is equivalent (or nearly equivalent) to a desired value of output voltage. Therefore, the feedback loop 116 allows the output voltage to be constant, irrespective of changes in the input voltage or load current.
[0038] The SMPS controller 116a regulates the switching pattern of the first power switches 110a and/or 110b of the converter 100. In an embodiment, the SMPS controller 116a turns on/off the first power switches 110a and/or 110b based upon the instructions received by the microcontroller 118. The microcontroller 118 may direct the SMPS controller 116a to activate/deactivate the first power switches 110a and/or 110b based upon the associated electronic device or depending upon the inputs received from the feedback loop 116.
[0039] In an alternate embodiment, the SMPS controller 116a is programmed to activate/deactivate the first power switches 110a and/or 110b (as shown in FIG. 1a). The SMPS controller 116a may activate/deactivate the first power switches 110a and/or 110b depending upon the inputs received from the feedback loop 116.
[0040] In an embodiment, the SMPS controller 116a may compare the output voltage (as obtained from the transformer 112) with the desired value. The difference (or error) between output voltage and the desired voltage is used to adjust the switching pattern of the first power switches 110a and/or 110b, until the difference becomes zero or close enough to zero. The SMPS controller 116a may maintain a look up table which stores the desired value and error.
[0041] The galvanic isolation means 116b provides electrical or magnetic separation between the low and high voltage sections of the converter 100. The galvanic isolation means 116b provides a barrier across which dangerous voltages cannot pass in the event of a fault or component failure. In an exemplary embodiment as represented in FIG. 1, the galvanic isolation means 116b provides a barrier between the SMPS controller 116a and the first power switches 110a, 110b. The galvanic isolation means 116b may include, without limitation, one or more of, a transformer, an opto-isolator, a capacitor, a magnetocoupler, etc.
[0042] The microcontroller 118 activates/deactivates or controls the SMPS controller 116a and the polarity reversal circuit 120. Alternately, the microcontroller 118 may be absent as depicted in FIG. 1a.
[0043] In an embodiment, the polarity reversal circuit 120 of the present invention includes an H-bridge device as represented in FIG. 1b. The polarity reversal circuit 120 includes four solid state switching devices Q1, Q2, Q3, Q4 such as transistors like insulated-gate bipolar transistors (IGBT), power bipolar junction transistor (BJT), field-effect transistor (FET) like metal oxide semiconductor field effect transistor (MOSFET), etc. that switch the polarity of the output voltage applied to the electronic device. The function of the polarity reversal circuit 120 of the present invention is to provide a predefined polarity i.e. forward or reverse voltage to the electronic device at predefined phases as controlled by the microcontroller 118.
[0044] Alternately, as represented in FIG. 1a, microcontroller 118 may be absent and hence, the polarity reversal circuit 120 is self-programmed to reverse the polarity of the second voltage supply.
[0045] The process of operation of the converter 100 is represented in FIG. 2. The operation of the converter 100 commences when the converter is supplied with an input supply at step 201. As described earlier, the converter 100 is supplied with an AC supply.
[0046] At step 203, preconditioning of the input supply takes place. The preconditioning of the input supply includes attenuation of all the higher frequencies in the supply by the filtering circuit 104 to allow an input of 50Hz or 60 Hz to pass through the next stage.
[0047] At step 205, the input supply is converted to a DC supply with the help of the rectifying circuit 106.
[0048] At step 207, one of the first power switches 110a/110b is turned on. The first power switches 110a/110b are configured to make/break an electrical circuit to control the first voltage supply supplied to the primary side ‘a’ of the transformer 112.
[0049] The first power switches 110a and 110b act as a switch to provide an AC supply to the transformer 112. The first power switches 110a, 110b are turned on/off by the voltage applied on respective gate terminals of the first power switches 110a, 110b. This voltage is applied when the SMPS controller 116a emits a pulse, say square wave pulse when it receives an activation signal from the microcontroller 118. The SMPS controller 116a may receive the signal from the microcontroller 118 for the associated electronic device to perform a function like water purification, welding, battery charging, etc. In an embodiment, the SMPS controller 116a may generate a signal in the frequency range of 20khz to 200khz depending upon the ratings of the various components of the circuit.
[0050] The duty cycle of the pulse maybe decided by the output voltage sensed from the feedback loop 116 as described below. In an embodiment, the first power switches 110a and 110b are turned on and off alternatively in synchronization with the duty cycle and frequency of the pulse, say, a PWM square wave. This pulse passes through the galvanic isolation means 116b that trims and isolates high/low frequency to yield a signal to be provided to the gates of the first power switches 110a, 110b. For example, during the positive cycle of the square wave pulse by the SMPS controller 116a, the galvanic isolation means 116b sends an input to the gate of the first power switch 110a while in the negative cycle of the square wave pulse, the galvanic isolation means sends a signal to the gate of the first power switch 110b.
[0051] Depending upon the first power switch 110a/110b that is turned on, the polarities of the primary winding of the transformer 112 are configured at step 209. For example, if the first power switch 110a is switched on, the polarity of the corresponding terminal of the primary winding of the transformer 112 is positive while the polarity of the other terminal of the primary terminal is negative. Similarly, if the first power switch 110b is switched on, the polarity of the terminals of the primary winding are reversed. The transformer 112 thus receives a steady supply from the two first power switches 110a and 110b. The transformer 112 converts the high input supply voltage to a low output voltage.
[0052] At step 211, post-conditioning (or active rectification/synchronous rectification) of the low output voltage obtained from the transformer 112 takes place. The second power switches 114a/114b are configured to provide a continuous supply. The gate of the respective second power switches 114a or 114b is turned on when the output voltage conditioner 114 sends a signal to the gate of the respective switch 114a or 114b. For example, when the terminal ‘a’ of the secondary winding is at negative polarity, the output voltage conditioner 114 sends a signal to the gate of the second power switch 114a and turns it on. Similarly, when the terminal ‘c’ of the secondary winding is at negative polarity, the output voltage conditioner 114 sends a signal to the gate of the second power switch 114b and turns it on. The output of the arrangement of the two second power switches 114a/114b is a rectified low output voltage that can be directly applied to a polarity reversal circuit employed for varied applications like water purification, welding, charging of battery, etc.
[0053] A filter capacitor may also be connected to smooth out any ripples at the common output of the second power switches 114a and 114b with respect to the positive center tap of the transformer’s 112 secondary side ‘b’.
[0054] At step 213, the low output voltage from the secondary side ‘b’ of transformer 112 is fed to the SMPS controller 116a via the feedback loop 116. The SMPS controller 116a then compares the output voltage with the desired value and uses the error between them to adjust the switching pattern of the first power switches 110a and/or 110b, until the error becomes zero or close enough to zero. The first power switches 110a and 110b may be turned on and off alternatively by a pulse, for example of PWM signals, at a frequency fixed between 20khz to 200khz generated by SMPS controller 116a. The duty cycle of the fixed frequency PWM square wave may be decided by the output voltage sensed from the feedback loop 116.
[0055] At step 215, once the error between the output voltage and the desired value reaches zero, the polarity of the output voltage with zero error may be optionally reversed on directions by the microcontroller 118. In an embodiment, on receiving forward polarity signal from the microcontroller 118, the switches Q1 and Q4 are turned on, whereas Q2 and Q3 are turned off through appropriate device drivers. Hence, forward polarity at the output of polarity reversal circuit 120 is obtained which in turn powers the electronic device.
[0056] Alternately, on receiving reverse polarity signal from the microcontroller 118, the switches Q1 and Q4 are turned off, whereas Q2 and Q3 are turned on through appropriate device drivers. Hence, reverse polarity at the output of polarity reversal circuit 120 is obtained which in turn powers the electronic device.
[0057] The foregoing description of preferred embodiments of the present disclosure provides illustration and description, but is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. No element, act, or instruction used in the description of the present disclosure should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article "a" is intended to include one or more items. Where only one item is intended, the term "one" or similar language is used.

WE CLAIM:
1. A converter comprising:
a transformer having a primary side and a secondary side, the primary side being equipped to receive a first voltage supply, the secondary side for providing a second voltage supply;
at least one pair of first power switches, the first power switches being configured to make/break an electrical circuit to control the first voltage supply supplied to the primary side of the transformer;
a SMPS controller employed to regulate switching pattern of the first power switches 110a and/or 110b;
at least one pair of second power switches coupled to the secondary side of the transformer, the second power switches being configured to provide a continuous DC supply;
an output voltage conditioner coupled to the tappings of the secondary side of the transformer, the output voltage conditioner being configured to control switching pattern of the second power switches 114a and/or 114b; and
a polarity reversal circuit coupled to the second power switches for providing an output voltage at a predefined polarity.
2. The converter as claimed in claim 1 wherein the at least one pair of first power switches and at least one pair of second power switches include MOSFETs/FETs/IGBTs/Thyristors for active rectification.
3. The converter as claimed in claim 1 wherein the transformer is a step down transformer.
4. The converter as claimed in claim 1 wherein a galvanic isolation means is disposed between the SMPS controller and the first power switches.
5. The converter as claimed in claim 1 wherein the converter includes a feedback loop to ensure that the second voltage supply is equivalent (or nearly equivalent) to a desired value of output voltage.
6. The converter as claimed in claim 1 wherein the first voltage supply is a rectified DC supply.
7. The converter as claimed in claim 1 wherein the SMPS controller and the polarity reversal circuit receive directions from a microcontroller.
8. The converter as claimed in claim 1 wherein the polarity reversal circuit is an H-bridge device.