Reducing Input Harmonic Distortion in Power Supplies

Abstract

Embodiments of a system for reducing input harmonic distortion of a power supply are provided. The system includes a power source coupled to the power supply. The power supply includes an input stage configured to receive an input signal from the power supply, wherein the input signal is received at a known input frequency; and a conversion stage operated to convert the input signal to an output signal, wherein the output signal has an output frequency. The power supply also includes an output stage operated to generate an output power based on the output signal; and a controller configured to provide a control signal to the output stage of the power supply to modify the output signal. Embodiments of a power supply and method for reducing input harmonic distortion of a power supply are also provided.

Description

Background Art

[0001] The present invention generally relates to power supplies having three-phase input power and single-phase loads. The present disclosure relates to reducing input harmonic distortion in such power supplies.

[0002] Many power supplies utilize a rectifier as a front-end converter to transform a three-phase input into a substantially direct current (DC) output. The rectifier produces a 6-pulse harmonic current in its input while providing an output voltage harmonic of 6 times the input frequency. A capacitor bank is used at the rectifier output to filter out some of these voltage harmonics and to attenuate the resonance produced by the output alternating current (AC) inverter that transforms the DC voltage into a variable frequency output voltage. Depending on the requirements of the load, the AC inverter can have a three-phase output or a single-phase output. In some applications, the configuration of the rectifier, DC capacitors, and inverter constitutes the entire power supply that feeds the load. Individually, such a configuration is referred to as a power unit in the present disclosure.

[0003] In other applications such as those described in the exemplary embodiments, multiple power cells are used to form a medium voltage generation circuit at the output while utilizing multiple secondary winding transformers at the input to feed each rectifier. The inverter in each power cell has a single-phase output that is connected in series with the inverters from the other power cells to provide a medium voltage output in each phase. A three-phase output load can be connected, or in a simpler form, a single-phase load can be powered if only one output phase is used. The secondary winding of the transformer is phase shifted to cancel the 6-pulse harmonics generated by the individual rectifiers. Due to the harmonic cancellation, the input current or the primary winding current in the multi-winding transformer has greatly reduced harmonics.

[0004] When the load is a three-phase balanced load, the total output power delivered has a substantially DC value. The input source of the power supply is then required to provide substantially constant power, resulting in a balanced current. Due to the use of phase-shifted secondary windings, the harmonic distortion in the input current is also low. Problems arise when the load is a single-phase output load and the output power has large fluctuations at twice the output frequency. This fluctuation is not attenuated by the capacitor bank, because the main function of the capacitor bank is to filter out harmonics at 6 times the input frequency and those at the switching frequency of the inverter. The output power fluctuations are transferred to the input side of the power supply, causing undesirable frequencies to appear. These currents may cause undesirable effects such as flicker and harmonic losses in the power system feeding the power supply. Summary of the invention

[0005] Embodiments of the present disclosure relate to a system for reducing input harmonic distortion of a power supply. A non-limiting example of the system includes a power source coupled to the power supply. The power supply includes: an input stage configured to receive an input signal from the power supply, wherein the input signal is received at a known input frequency; and a conversion stage operated to convert the input signal to an output signal, wherein the output signal has an output frequency. The power supply also includes an output stage operated to generate an output power based on the output signal; and a controller configured to provide a control signal to the output stage of the power supply to modify the output signal.

[0006] In addition to or as an alternative to one or more of the features described herein, further embodiments include a controller having a control and a pulse width modulation (PWM) module that modifies an output signal. In one or more embodiments, the control modifies the output signal by injecting a different frequency component into the output signal.

[0007] In addition to or as an alternative to one or more features described herein, further embodiments include injecting a frequency component that is three times the output frequency of the output signal and has a phase shift that is dependent on the load power factor, which reduces distortion at the power supply input stage.

[0008] Embodiments of the present disclosure relate to a method for reducing input harmonic distortion in a power supply. A non-limiting example of the method includes receiving a signal representing an input voltage and estimating an input frequency of the signal; receiving an output frequency command and comparing the output frequency to the input frequency; and modifying the output frequency to maintain a difference between the input frequency and the output frequency based at least in part on the comparison. The method also includes receiving an output voltage and current signal and estimating an output current phase angle relative to the output voltage; generating an output voltage command based at least in part on the output frequency and the output current phase angle; and providing the output voltage command to a controller to generate a switching signal.

[0009] Embodiments of the present disclosure relate to a power supply for reducing input harmonic distortion. A non-limiting example of the power supply includes an input stage configured to receive an input signal from a power supply, wherein the input signal is received when the input signal has a known input frequency; and an output stage configured to provide output power at an output frequency. The power supply also includes a controller configured to provide a control signal to the output stage of the power supply, wherein the controller also includes a control and a pulse width modulation (PWM) module for generating a control that modifies the output signal by injecting a frequency component into the output signal, which has a phase shift that depends on the load power factor to drive a single-phase load.

[0010] Additional technical features and benefits are achieved through the technology of the present invention. Embodiments and aspects of the present invention are described in detail herein and are considered to be part of the claimed subject matter. For a better understanding, please refer to the detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The details of the exclusive rights described herein are particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the embodiments of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1A A diagram depicting a system and power supply for reducing input harmonic distortion according to one or more embodiments;

[0013] Figure 1B A diagram depicting a system and power supply for reducing input harmonic distortion according to one or more embodiments;

[0014] Figure 2 The three-phase input current waveforms without output frequency component injection are depicted;

[0015] Figure 3 Depicted Figure 2 Harmonic components of the three-phase input current;

[0016] Figure 4 depicts three-phase input current waveforms with output frequency component injection according to one or more embodiments;

[0017] Figure 5 Depicted Figure 4 The harmonic components of the three-phase input current; and

[0018] Figure 6 A flow chart of a method for reducing input harmonic distortion of a power supply is depicted.

[0019] The figures depicted herein are illustrative. Without departing from the spirit of the present invention, there may be many variations of the figures or operations described therein. For example, actions may be performed in different orders, or actions may be added, deleted or modified. In addition, the term "coupling" and its variations describe having a communication path between two elements, and do not mean a direct connection between elements without an intermediate element / connection between the elements. All of these variations are considered to be part of the specification.

[0020] In the drawings and the following detailed description of the disclosed embodiments, various elements shown in the drawings have two or three-digit reference numbers. With few exceptions, the leftmost digit of each reference number corresponds to the figure in which the element is first shown. DETAILED DESCRIPTION

[0021] The components and materials that make up the various embodiments described below are intended to be illustrative rather than limiting. Many suitable components and materials that will perform the same or similar functions as the materials described herein are contemplated within the scope of the embodiments of the present invention.

[0022] Various embodiments of the present invention are described herein with reference to the accompanying drawings. Without departing from the scope of the present invention, alternative embodiments of the present invention may be designed. Various connections and positional relationships (e.g., above, below, adjacent, etc.) are described below and are described between the elements in the accompanying drawings. Unless otherwise indicated, these connections and / or positional relationships may be direct or indirect, and the present invention is not intended to be limited in this respect. Therefore, the coupling of entities may refer to direct or indirect coupling, and the positional relationship between entities may be a direct or indirect positional relationship. In addition, the various tasks and process steps described herein may be incorporated into a more comprehensive program or process with additional steps or functions not described in detail herein.

[0023] The following definitions and abbreviations are used to interpret the claims and specification. As used herein, the terms "comprises," "including," "comprising," "containing," "having," "having," "containing," or "containing" or any other variation thereof are intended to cover a non-exclusive inclusion. For example, a composition, mixture, process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

[0024] Additionally, the term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" may be understood to include any integer greater than or equal to 1, i.e., one, two, three, four, etc. The term "plurality" may be understood to include any integer greater than or equal to 2, i.e., two, three, four, five, etc. The term "connected" may include both indirect "connected" and direct "connected."

[0025] The terms "about," "substantially," "approximately," and variations thereof are intended to include the degree of error associated with the measurement of a particular quantity, based on the equipment available at the time the application was filed. For example, "about" may include a range of 8% or 5% or 2% of a given value.

[0026] For the sake of brevity, conventional techniques related to making and using aspects of the present disclosure may or may not be described in detail herein. In particular, various aspects of computing systems and specific computer programs that implement the various technical features described herein are well known. Therefore, for the sake of brevity, many conventional implementation details are only briefly mentioned herein, or are omitted entirely without providing well-known system and / or process details.

[0027] Turning now to an overview of the technology more specifically related to aspects of the present disclosure, a power supply is provided with a three-phase input and a single-phase load on the output. The fluctuations in output power and the effect on input current can be shown by the following analysis.

[0028] Ignoring the switching harmonics of the inverter, if the output voltage v of the power supply is defined by the following equations 1 and 2 o and current i o :

[0029]

[0030] and

[0031]

[0032] where v o and i o are the RMS values ​​of the output voltage and current respectively; ω o is the angular frequency of the output and is equal to 2πf o , f o is the output frequency; and is the phase angle of the output current relative to the voltage.

[0033] Then, the output power p o Given by Equation 3:

[0034]

[0035] p o The first term is the DC component representing the average power of the load, p o The second term of is the fluctuation term at twice the output frequency.

[0036] This power pulsation causes the input AC current to have harmonic components as shown below. In the worst case, if the capacitor bank does very little filtering of the power fluctuations, then all the output power is provided by the input source, i.e., p i =p o , where p i is the input power. If the input voltage v is defined by the following equation 4 i :

[0037]

[0038] where ω i is the angular frequency of the output and is equal to 2πf i , and f i is the input frequency, then it can be seen that the input current has the form shown in Equation 5:

[0039]

[0040] Therefore, the input current (f i ±2f o ) have additional harmonic components at the power source. The magnitude of these components depends on the energy storage capabilities within the power source and may be high enough to cause harmonic related problems such as unbalance, flicker, and harmonics in the power system that provides power to the power source.

[0041] In a specific application, the power supply is used to generate heat throughout a passive resistive load, such as a pipe or pipeline used to transport fluids. In the field of oil exploration and production, the extraction of oil is performed below sea level where the temperature is very low. In a non-limiting example, the passive load does not use power from the power supply to power electrical components such as motors. Due to its viscosity-related properties, it may become difficult to transport oil or other fluids at such temperatures. In a non-limiting example, the power supply is used to heat the pipeline to the appropriate temperature to ensure that the extracted oil can flow through the pipeline to its destination.

[0042] In a non-limiting example, because the pipeline is a single-phase resistive load, the quality of the output power provided by a power supply for a heating application may include greater distortion than, for example, a power application providing power to an induction motor. An induction motor requires a high quality output power signal with minimal distortion, and the quality of the signal must be maintained to ensure proper operation of the motor.

[0043] The technology described herein is directed to addressing distortion at the input stage of a power supply as opposed to the output stage. In a non-limiting example, because the load is a pipe that needs to be heated to transfer a fluid, the amount of distortion in the output power provided by the power supply is not important. Therefore, operating the power supply to provide a constant output power can reduce distortion at the input of the power supply.

[0044] The power provided by the power supply is at the output frequency f of the power supply. opulsating at twice the power of the power supply. This pulsation must also be provided by the power source feeding the power supply, and the pulsation may cause distortion of the input phase current. Excessive input harmonic distortion on the phase current may have many adverse effects, and the imbalance between the input phase currents may cause unexpected heating and premature failure of the power supply components. In order to avoid or minimize the pulsating power fed back to the power source or utility feed, the output power can be modulated and the frequency components injected to approximate a constant, which effectively reduces the harmonics at the power supply input. This can reduce and / or eliminate the harmonics caused by power pulsation.

[0045] Turning now to an overview of aspects of the present disclosure, one or more embodiments of the present disclosure address the above-mentioned shortcomings of the prior art by injecting frequency components at the output stage of the power supply to compensate for and / or eliminate harmonics at the input of the power supply.

[0046] In an embodiment of the present disclosure, a system for a variable frequency drive operably coupled to a single-phase resistive load (e.g., a metal pipe) is provided. o ) to modulate the power supply output voltage (the output voltage of the variable frequency drive). As described below, this allows for a reduction in power ripples in the power supplied to the load and a reduction in harmonics generated on the input side of the power supply.

[0047] Output voltage o is now defined to include an additional component at the third harmonic and is now shown as Equation 6:

[0048]

[0049] And due to the load characteristics, the power supply current i o remains essentially the same and is defined by the following Equation 7:

[0050]

[0051] Where V 3o is the RMS value of the third harmonic component in the output voltage, It is the adjustable phase angle of the third harmonic component relative to the voltage fundamental component.

[0052] Output power o Defined as Equation 8:

[0053]

[0054] From equation 8 above, we can see that using 3*f o The output voltage will be modulated by 2*f o and 4*f o The additional power ripple at 2*fo The total component at can be obtained by choosing 3*f o The harmonic frequency at the output is reduced by correctly adjusting the phase of the components relative to the fundamental frequency component. i ±2*f o ) and (f i ±4*f o ). By introducing 3*f o The cancellation provided by the appropriate phase shift of the components makes (f i ±2*f o ) is reduced, and (f i ±4*f o ) is due to the energy storage component (such as a DC capacitor bank) filtering out the energy at 4*f o More higher frequency components at the

[0055] exist Figure 1A , an example of a power supply 100 that converts three-phase AC power from a power source and provides a single-phase output is shown. The input stage of the power supply 100 is a rectifier stage and includes a plurality of diodes 101A, 101B, 101C, 103A, 103B, and 103C to convert the input AC voltage into a substantially DC voltage with an AC ripple.

[0056] The capacitors 105A, 105B act as a smoothing filter and represent a configuration of a capacitor bank, wherein the value of the capacitors 105A, 105B depends on the power demand of the load.

[0057] Thus, conditionally, a single-phase H-bridge inverter may be used to convert the DC voltage into a variable frequency AC, which may include a plurality of semiconductor switches. In one or more embodiments, the switches may include power transistors, such as transistors 107 (Q1), 109 (Q2), 111 (Q3), and 113 (Q4) as shown. Transistors 107 to 113 may include MOSFETs or insulated gate bipolar transistors (IGBTs). Transistors 107 to 113 may be fully turned on or fully turned off during operation. Transistors 107 to 113 may receive control signals from controller 123. It should be understood that any type of gating controller may be used and is not limited to Figure 1A In addition, there are other configurations of single-phase output converters, such as neutral point clamped (NPC).

[0058] The single phase H-bridge output converter can reflect the ripple current at twice the frequency of the output.Capacitors 105A, 105B can be used to smooth the ripple caused by both the input rectifier and the output converter.

[0059] In the following discussion, Figure 1AThe power supply shown in refers to the power unit. When a higher load voltage is desired, such as Figure 1B As shown, the output voltage of several power cells A1 to A6 is increased by using a series connection of output stages. The control of each individual power cell A1-A6 is now performed by a central controller (e.g., central control system 159), which coordinates the switching moments to generate a nearly sinusoidal output voltage. The central controller can be coupled to each power cell A1-A6 using a fiber optic cable to provide signals for local control of the power cell.

[0060] Due to the three-phase rectification at the input of the power supply 100, the input current has 6-pulse harmonics, that is, there are components at the 5th, 7th, 11th, 13th, etc. harmonics. When multiple power cells A1-A6 are used, a multi-secondary winding transformer 151 can be used to mitigate the unwanted 6-pulse harmonic components, where each secondary winding 155 is phase shifted from its adjacent winding. Each power cell input is fed by a dedicated secondary winding 155, which allows for the cancellation of harmonics in the current of the primary winding 153 of the transformer 151. In one or more embodiments, three-phase AC power is provided to the primary winding 153 at a constant voltage and frequency. The results shown in this disclosure are with reference to Figure 1B It should be understood that the techniques described herein can be applied to any power supply having a single-phase output to drive a single-phase load 157. In one or more embodiments, single-phase AC power is used to drive a single-phase load 157 at a variable voltage and variable frequency.

[0061] exist Figure 2 In the example, the input phase current waveform is shown on the graph 200. The three-phase input current represents the current when the output voltage of the power supply is not 3*f o The component is modulated (at frequency f o =f i ), the current supplied from the power source to the power supply when the power is on. Each horizontal division represents approximately 2 milliseconds, and each vertical division represents 50 amps. Phase currents 210 and 230 have higher distortion and will be referred to below. Figure 3 In this example, the output voltage of the power supply 100 is provided at 50 Hz, so the output power will pulsate at 100 Hz, which is the output frequency f o The 100 Hz power ripple causes the line-side current of the power supply 100 to ripple with components of 50 Hz ± 100 Hz (i.e., 50 Hz and 150 Hz). i It is also 50Hz, so the main component will be directly affected by the pulsation in an unbalanced form.

[0062] Reference Figure 3As shown in the table, the line side currents have significant total harmonic distortion (THD), for example, 10.6% for phase A current, 9.2% for phase B current, and 10.4% for phase C current. The imbalance is illustrated by the changes in the amplitude of the phase currents 210 , 220 , and 230 .

[0063] Figure 3 A table 300 is depicted, which also shows the main harmonic frequency components and corresponding amplitudes of the input phase currents, where the fundamental frequency component is normalized to 100%. As expected, the most dominant harmonic component is at 150 Hz. The next most significant harmonic occurs at 250 Hz, which is a result of the uncancelled 6-pulse harmonics in the power cell current. However, the amplitude of the harmonics at 250 Hz is much smaller than the harmonics at 150 Hz.

[0064] Figure 4 An example of a graph 400 is depicted showing a graph having 3*f o The three-phase input current 410, 420 and 430 are represented as the input current waveform with 3*f during the operation of the power supply. o In the case of o In the case of modulation, the frequency f o With f i Each horizontal segment of the graph 400 represents approximately 2 milliseconds, and each vertical segment represents 40 amps. In this example, the output voltage of the power supply 100 is provided at 50.5 Hz, and the input frequency is 50 Hz. As previously described, the input current will have harmonic components at (50 Hz ± 2 * 50.5 Hz) and (150 Hz ± 2 * 50.5 Hz), that is, harmonic components at 51 Hz, 151 Hz, 152 Hz, and 252 Hz. Figure 4 As shown, the imbalance in the three-phase input currents 410, 420, and 430 is reduced, and when measured over a period of 1 second, the current imbalance is only 0.5%.

[0065] Figure 5 A table 500 is depicted showing the o The harmonic frequency components and corresponding THD values ​​of the three-phase input current of the power supply when the output voltage is modulated in the case of component injection. The harmonic components now appear at the above frequencies, but with lower individual amplitudes and lower THD.

[0066] Comparing Table 300 with Table 500, the THD values ​​of the frequency components shown in Table 500 have been reduced compared to the values ​​of the frequency components shown in Table 300. This can reduce voltage distortion and imbalance in the three-phase input current. The THD of the A phase current (La) is 7.7%, the THD of the B phase current (Lb) is 7.7%, and the THD of the C phase current (Lc) is 7.7%. Not only are the input currents 410, 420, and 430 balanced, but the distortion in the input currents 410, 420, and 430 is also reduced. This reduces power ripple at the power supply input.

[0067] Reference now Figure 6 , a flow chart of a method 600 for reducing input harmonic distortion in a power supply according to one or more embodiments is shown. The method 600 may be implemented in a system such as Figure 1A or Figure 1B The method 600 starts at block 602 and proceeds to block 604, which provides receiving an input signal and estimating an input frequency. In one or more embodiments, the input is a three-phase signal from a power source. Block 606 receives a command for an output frequency and compares the input to the output frequency.

[0068] If the difference between the input and output frequencies is below a predefined limit (e.g., 0.5 Hz), block 608 modifies the output frequency. If this is the case, the output frequency is adjusted to be less than or greater than the input frequency by the predefined limit. If the difference is greater than the predefined limit, the output frequency is not modified. Block 610 receives signals representing the output voltage and the output current and estimates the phase difference (or load power factor angle) between the voltage and the current. Block 612 generates an output voltage command based on a component at the updated output frequency, a component at three times the output frequency, and an appropriate phase shift based on the load power factor.

[0069] Block 614 provides an output voltage command to a controller that generates a PWM switching signal for the output switching stage of the power supply. The PWM circuit injects the desired voltage by controlling the modulation (changing the ON / OFF time) at the output stage of the power supply. In one or more embodiments of the present disclosure, in addition to the component at the switching frequency, the PWM circuit also injects a frequency component at three times the output frequency. The modified output signal provides a more constant power output from the power supply and reduces pulsation on the input side of the power supply. In turn, the distortion at the power supply input is reduced, which improves the operation of the power supply.

[0070] The load may include, but is not limited to, a single-phase passive resistive inductive load, such as a pipeline. The output power provided from the power supply is used to directly heat the load, the output power including the injected frequency component. In this embodiment, the output power is not used to drive the motor. The method 600 ends at block 616.

[0071] Technical effects and benefits include reducing voltage distortion and imbalance on the input side of the power supply. Benefits also include reducing flicker in components connected to the input side of the power supply. This can increase the life and reliability of the power supply while meeting flicker standards.

[0072] Although the present invention has described in detail the specific embodiments and methods for practicing, it will be appreciated by those skilled in the art that various modifications and substitutions may be made to these details according to the overall teaching of the present disclosure. Therefore, the specific arrangements disclosed are intended to be illustrative and not to limit the scope of the present invention, which is given in full by the following claims and any and all embodiments thereof.

[0073] Descriptions of various embodiments of the present invention have been presented for illustrative purposes, but these descriptions are not intended to be exhaustive or to limit the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terms used herein are selected to best explain the principles of the embodiments, practical applications or technical improvements over technologies found on the market, or to enable those of ordinary skill in the art to understand the embodiments described herein.

Claims

1. A system for reducing input harmonic distortion of a power supply, the system comprising: a power source coupled to the power supply; The power supply comprises: an input stage configured to receive an input signal from the power supply, wherein the input signal comprises an input frequency, wherein the input signal is a three-phase input signal, and wherein the power supply is a three-phase power supply; wherein the power supply is configured to convert the input signal into an output signal, wherein the output signal has an output frequency; an output stage operative to generate output power based on the output signal; and a controller configured to provide a control signal to an output stage of the power supply to modify the output signal, wherein the controller further comprises a control and pulse width modulation (PWM) module for modifying the output signal, wherein the control modifies the output signal by injecting a frequency component into the output signal, wherein the injected frequency component is a frequency component of three times the output frequency of the output signal and has a phase shift that is dependent on the load power factor to reduce distortion at the input stage of the power supply, and The system further includes a single-phase load that is insensitive to distortion in the modified output signal.

2. The system according to claim 1, wherein: The single-phase load is a passive load.

3. The system according to claim 2, wherein: The single-phase load is a pipeline for transmitting a fluid.

4. The system of claim 1, further comprising one or more direct current (DC) link capacitors, wherein the one or more DC link capacitors couple the input stage and the output stage of the power supply.

5. A method for reducing input harmonic distortion of a power supply, the method comprising: receiving an input signal representing an input voltage and estimating an input frequency of the input signal, wherein the input signal is a three-phase input signal from the power supply, and wherein the power supply is a three-phase power supply driving a single-phase load; receiving an output frequency command, and comparing the output frequency with the input frequency; based at least in part on the comparison, modifying the output frequency to maintain a difference between the input frequency and the output frequency; receiving output voltage and current signals and estimating an output current phase angle relative to the output voltage; generating an output voltage command based at least in part on the output frequency and the output current phase angle; and providing the output voltage command to a controller to generate a switching signal, wherein the output voltage command is a sum of a component at the output frequency and a component at three times the output frequency, the component at three times the output frequency having a phase delay based at least in part on the output current phase angle, wherein the single-phase load is insensitive to distortion in the modified output signal, and Wherein if the compared value is less than a predefined limit value, the output frequency is adjusted by adding or subtracting the predefined limit value from the output frequency.

6. The method according to claim 5, wherein: If the compared value is greater than the predefined limit, the output frequency is not adjusted.

7. The method according to claim 5, wherein: The output voltage is used to generate heat for the single-phase load.

8. The method according to claim 7, wherein: The single-phase load is a pipeline for transmitting a fluid.

9. A power supply comprising: an input stage configured to receive an input signal from a power source, wherein the input signal comprises an input frequency, wherein the input signal is a three-phase input signal, and wherein the power source is a three-phase power source; an output stage configured to provide an output power based on an output signal, wherein the output signal includes an output frequency; and a controller configured to provide a control signal to the output stage of the power supply, wherein the controller further comprises a control and pulse width modulation (PWM) module for generating and modifying the output signal, wherein the control modifies the output signal by injecting a frequency component into the output signal, the frequency component having a phase shift that depends on the load power factor to drive a single-phase load, wherein the injected frequency component is a frequency component of three times the output frequency of the output signal, wherein the power supply also includes a single-phase load, and Wherein the modified output signal drives a single-phase load that is insensitive to distortion in the modified output signal.

10. The power supply according to claim 9, wherein: The output stage includes an H-bridge configuration of switches.

11. The power supply of claim 9, further comprising one or more direct current (DC) link capacitors, wherein the one or more DC link capacitors are connected to a link between the input stage and the output stage of the power supply.

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