The present invention generally relates to flyback converters and associated systems and methods and, in particular, to flyback converters with dual alternating current (AC) and direct current (DC) output.
Traditional flyback converters are generally used for isolated power conversion and include a voltage input and a load output. Flyback converters generally include multiple secondary windings that can be used to construct multiple DC output ports. Some flyback converters can be used to support a DC load. Other flyback converters can be used to support an AC load.
Thus, rather than having the capability to support both DC and AC loads, the appropriate flyback converter must be used based on the desired output load at the output. Having multiple independent converters can be inefficient in a number of applications, e.g., in rural areas where both high voltage (for charging phones, batteries, light-emitting diode (LED) lighting, and the like) and high frequency (for fluorescent light) power applications are needed, in disaster or military zones, or the like.
Thus, a need exists for flyback converters that provide dual DC and AC output. These and other needs are addressed by the flyback converters and associated systems and methods of the present disclosure.
In accordance with embodiments of the present disclosure, exemplary flyback converters are provided. The flyback converters include a voltage input, a flyback transformer including a primary winding circuitry, and two secondary winding circuitries (e.g., first and second secondary winding circuitries). The flyback transformer can be electrically connected to the voltage input. The first secondary winding circuitry can be electrically connected to the flyback transformer. The second secondary winding circuitry can be electrically connected to the flyback transformer. The first secondary winding circuitry can be a direct current (DC) output circuit. The second secondary winding circuitry can be an alternating current (AC) output circuit.
The voltage input can be a direct current (DC) voltage input. The second secondary winding circuitry can include an inductor-capacitor low pass filter (LPF). The flyback converter can include a metal-oxide-semiconductor field-effect transistor (MOSFET) and/or other transistors electrically connected to the voltage input. The flyback converter can include a snubber circuit electrically connected across the primary winding circuitry of the flyback transformer. The snubber circuit can include a snubber capacitor, a snubber resistor, and an incoming duty signal.
A flyback turns ratio of the flyback transformer can be 1:N. The DC output circuit can include a rectifying diode, a capacitor, and a load (e.g., a resistor). The AC output circuit can include an inductor, a capacitor, and a load (e.g., a resistor). The first secondary winding circuitry can include a first secondary coil. The second secondary winding circuitry can include a second secondary coil. The flyback converter can include a gate driver and a pulse width modulator.
In accordance with embodiments of the present disclosure, exemplary systems for converting electrical power are provided that include a flyback converter as described herein. The systems can include a voltage input source providing the voltage input to the flyback converter.
In accordance with embodiments of the present disclosure, exemplary methods of converting electrical power are provided. The methods include receiving a voltage input at a flyback converter. The methods include converting the voltage input with the first secondary winding circuitry to a DC output voltage. The methods include converting the voltage input with the second secondary winding circuitry to an AC output voltage. The methods can include operating the flyback converter with a switching pulse.
Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.
To assist those of skill in the art in making and using the disclosed flyback converters and associated systems and methods, reference is made to the accompanying figures, wherein:
In accordance with embodiments of the present disclosure, exemplary flyback converters are provided that include a topology with dual DC and AC outputs. As will be discussed in greater detail below, the topology of the exemplary flyback converter elaborates the diversity of the DC and AC power forms in a single converter. In particular, the flyback converter takes advantage of one of the additional secondary windings of a flyback transformer to generate a continuous high-frequency AC output voltage, along with the conventional DC output voltage on a different output port, thereby providing a flyback converter for various applications.
The DC output can follow the substantially traditional configuration, while the AC output can be achieved by adding an inductor capacitor (L-C) LPF to an additional secondary winding. The dual output flyback converter integrates a standalone DC/DC converter with a DC/AC inverter, thereby saving space and switching devices, as well as improving the total energy conversion efficiency of the flyback converter, compared to conventional separated AC-DC, DC-DC and/or AC-DC-AC conversion. The AC output of the flyback converter can be used simultaneously to the DC output. Thus, rather than having only a DC output, both AC and DC outputs can be used simultaneously for a variety of applications. In some embodiments, the outputs can be correlated. In some embodiments, the range of the DC output and/or the AC output relative to the DC and/or AC input can vary depending on a turns ratio N of the transformer, the duty cycle of the MOSFET and/or transistor, or both.
The exemplary flyback converter offers various output power forms with enhanced power efficiency and low-cost electrical components in order to increase energy availability in daily use, eventually saving costs for the user. Specifically, it can be more economical to use a multi-winding flyback transformer even for a single-output application, as compared to traditional flyback converters, thereby adding the AC output port as an optional output with a minimal cost increase.
Flyback transformers used in single DC output flyback converters generally include more than one secondary output port. The flyback converters discussed herein can use one of the additional output ports as an AC output port at no extra cost (except the added filter), as compared to using a completely separate converter to generate the AC output. The flyback converter also provides AC and DC outputs that are electrically isolated from each other and from the input. Isolation of the AC and DC outputs can be critical in several applications and acts as a safety feature for the flyback converter.
The exemplary flyback converters can be used for a variety of applications, especially when both DC and AC power are necessary. However, it should be understood that the flyback converters can also be used for only DC or only AC output. For example, in rural, solar-powered, stand-alone systems, the flyback converter can be integrated with solar photovoltaics (PV) in rural energy systems providing energy to simple DC loads (such as batteries, phones, LED lighting, or the like), as well as high-frequency AC loads (such as fluorescent lights with a bypassed front end rectifier and high-frequency inverter). Thus, the flyback converters allow for distributed energy systems for rural areas along with conventional power supply.
Solar power systems may require inverters to convert the solar DC voltages to household AC outlets for use (e.g., 60 W). These are generally referred to as micro inverters since due to the small box size (as opposed to large transformers). The exemplary flyback converters can be used in these types of inverters, power converters, or the like. The flyback converters can also be used in, e.g., disaster zones, hospital applications, military applications, or the like, wherein both AC and DC power output is desired.
With reference to
The converter 100 includes a flyback transformer 122. The transformer 122 can have a 1:N flyback turns ratio. One side of the transformer 122 includes a primary coil 124 (e.g., a primary winding circuitry) with a voltage (Vp) 126. The opposing side of the transformer 122 includes a first secondary coil 128 and a second secondary coil 130 (e.g., first and second secondary winding circuitries). In some embodiments, the converter 100 can include multiple secondary coils. A voltage 132 (Vs1) can pass over the first secondary coil 128 and includes a current 134 (Is1). A voltage 136 (Vs2) can pass over the second secondary coil 130 and includes a current 138 (L2).
The converter 100 includes a DC output circuit 140 associated with the first secondary coil 128 and an AC output circuit 142 associated with the second secondary coil 130. The DC output circuit 140 can include a rectifying diode 144 (D1). The DC output circuit 140 further includes a capacitor 146 (C), a load resistor 148 (Rddc), and a current 150 (Idc) passing over the load resistor 148. The DC output circuit 140 includes a DC output port 152 having a DC output voltage 154 (Vdc).
The AC output circuit 142 includes an inductor 156 (Lf), a capacitor 158 (Cf), a resistive load 160 (Rac), and a current 162 (Iac) passing over the resistive load 160. The inductor 156 and the capacitor 158 can form a low-pass filter (LPF) 168 of the AC output circuit 142. The AC output circuit 142 further includes an AC output port 164 having an AC output voltage (Vac).
With reference to
The converter 200 includes a voltage input 102, a ground 202, and a MOSFET 116. The converter 200 further includes a snubber circuit 106, a gate driver 204 for sending a gate signal, and a gate driver power source 206. The converter 200 can include a pulse width modulation (PWM) input 208 and a flyback transformer 122. The converter 200 includes a DC output circuit 140 with a load 210 and an AC output circuit 142 with a load 212. The AC output circuit 142 can include a sensing resistor 214 and an LPF (Lf, Cf) 216.
Although the topology discussed herein is in reference to the converter 100, it should be understood that the description also applies to the converter 200, except for any distinctions noted herein. As discussed above, the converter 100 of
As shown in
The AC output port circuit 142 can include a second-order resonant circuit low-pass filter 168 to shape the voltage 136 from a zero-offset square wave to a substantially sinusoidal wave. The AC output voltage 166 can be substantially continuous since the voltage 136 is a substantially continuous square wave induced by the primary winding, e.g., coil 124, and MOSFET 116 switching. The AC terminal can provide a continuous output at the switching frequency. The real power transferred from the second secondary coil 130 to the load and the filter 168 can be ideally conserved since the filter 168 only contains an inductor 156 and a capacitor 158 that impact reactive power.
The exemplary prototype converter 200 of
The converter 200 was constructed with minimum leads, wires, and a two-layer prototype board, thereby reducing board parasitic effects. The dual-output flyback converter 200 was tested in the discontinuous conduction mode (DCM). Various resistive loads were tested at both AC and DC output ports. The results from these tests under various input voltages with open-loop control were recorded and are shown in
With reference to
With reference to
Various inputs with the converter load combination were tested, i.e., where the DC and AC resistance value Rdc=50.4Ω and Rac=31Ω. The results for the experimentation is shown below in Table 1.
Modeling assists in understanding the proposed topology including interaction between the input and output, and between the DC and AC output ports. Only an ideal converter is considered and compared to the non-ideal experimentation results provided. It can be assumed that both the DC and AC output powers are completely dissipated in the resistive loads where other resistive elements, e.g., capacitor ESR, or the like, are ignored. The snubber circuit can be neglected since under ideal conditions, all energy stored in the flyback transformer air gap would be released to the dual-output ports in the discontinuous conduction mode.
Through the average input voltage and current waveforms in
where Ipeak represents the peak value of the input current (e.g., the current value at the end of every switching “ON” period) and I0 represented the returning input current value at the end of every switching cycle. Since the flyback converter topology is operated in discontinuous conduction mode, the input current returns to approximately zero before the end of a switching cycle and, thus, I0 is always approximately zero. T represents one period time of a switching cycle (e.g., T=1/f). Don represents the duty ratio of the MOSFET switching signal where the input current Iin increases to the peak current Ipeak during DonT, and Doff represents the portion of T during which the input current Iin decays from the peak current Ipeak to approximately zero. Equation 1 can therefore be rewritten as Equation 2:
For modeling purposes, the sum of the DC and AC output port energy can be assumed to be equal to the input energy value because of energy conservation and assuming an ideal converter. Thus, the total output energy can be represented by Equation 3:
The LC low-pass filter can alter the continuous square wave at the transformer second secondary winding into a sinusoidal wave with zero-offset at the AC output port. In particular, the LC low-pass filter blocks high frequency components and keeps the fundamental component in the Fourier series of the square wave. With the Fourier series, the square wave can be represented by Equation 4:
Replacing Vac in Equation 4 with Equation 3 and rearranging the terms yields Vdc as shown in Equation 5:
Thus, as described herein, the exemplary flyback converters offer a topology with dual DC and AC outputs, thereby providing a flyback converter for various applications and improving the efficiency of traditional flyback converters.
While exemplary embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the invention.
The present application claims priority benefit to a provisional application entitled “Dual AC and DC Output Flyback Converter and Associated Systems and Methods,” which was filed on Apr. 28, 2015, and designated by Ser. No. 62/153,579. The entire content of the foregoing provisional patent application is incorporated herein by reference.
Number | Date | Country | |
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62153579 | Apr 2015 | US |