Patent Publication Number: US-2023155508-A1

Title: Multi-level power converter and control

Description:
BACKGROUND 
     Data centers such as operated by Google™, Facebook™, and other entities provide indispensable services for our society. The energy consumption for all data centers worldwide is around 2% of overall electric energy usage. Therefore, datacenter providers are constantly looking to improve the efficiency of power conversion in order to save energy or to be able to increase the CPU/GPU/ASIC, etc., power of servers in existing data centers. Machine learning and artificial intelligent architectures require very powerful GPUs or custom designed ASICs to meet the required calculation power. 
     Higher voltage distribution and efficient conversion systems are necessary to reduce losses and increase the overall power density of the conversion system. In the last few years, 48V DC at the rack level has been introduced by vendors enabling several different scenarios to provide high power to digital load, such as CPU/ASIC/GPU. These architectures are coordinated, e.g., by the Open compute consortium, currently OCP 3.0 is the most modern architecture supporting 48V DC distribution within the rack. 
     One type of power supply to convert an input voltage into an output voltage is a so-called a multi-level buck converter. A 3-level buck converter is a versatile topology to convert and regulate power from a higher input to a lower output voltage. Due to the intrinsic nature of the converter, it works specifically well at an input voltage to output voltage ratio of 2:1. 
     BRIEF DESCRIPTION 
     Implementation of clean energy (or green technology) is very important to reduce our impact as humans on the environment. In general, clean energy includes any evolving methods and materials to reduce an overall toxicity on the environment from energy consumption. 
     This disclosure includes the observation that raw energy, such as received from green energy sources or non-green energy sources, typically needs to be converted into an appropriate form (such as desired AC voltage, DC voltage, etc.) before it can be used to power end devices such as servers, computers, mobile communication devices, wireless base stations, etc. In certain instances, energy is stored in a respective one or more battery resource. Alternatively, energy is received from a voltage generator. Regardless of whether energy is received from green energy sources or non-green energy sources, it is desirable to make most efficient use of raw energy (such as storage and subsequent distribution) provided by such systems to reduce our impact on the environment. This disclosure contributes to reducing our carbon footprint and better use of energy via more efficient energy conversion. 
     This disclosure further includes the observation that power conversion efficiency of conventional power supplies can be improved. For example, to this end, embodiments herein include novel ways of providing improved performance of power conversion via implementation of novel control techniques. 
     More specifically, the novel power supply as described herein includes a controller. The controller receives a target ripple current value indicative of a ripple current associated with an output current of a power converter powering a load. In one embodiment, the output current of the power converter includes a DC output current component and an AC output current component (such as the ripple current). When generating the output voltage and corresponding output current of the power converter, the controller selects a switching frequency of operating the power converter as a function of a magnitude of the received target ripple current value. The controller then applies the selected switching frequency to switches in the power converter to produce the output current with a magnitude of the ripple current as indicated by the target ripple current value. 
     In further example embodiments, the power converter produces the output current (and corresponding output voltage) based on a received input voltage. In one embodiment, the target ripple current value is a constant ripple current value assigned to or associated with different magnitudes of the input voltage. In such an embodiment, the controller varies a magnitude of the switching frequency applied to the switches such that the ripple current associated with the output current of the power converter is equal to the constant ripple current value for the different magnitudes of the input voltage. Thus, in one embodiment, although a magnitude of the input voltage drops over time, the magnitude of the ripple current is constant or least controlled to a desired value as a function of the magnitude of the input voltage and/or one or more other parameters associated with the power supply. 
     In still further example embodiments, the magnitude of the target ripple current value varies based at least in part on a magnitude of an input voltage converted by the power converter into the output current. Thus, in one embodiment, as the magnitude of the input voltage supplied to the power converter changes over time, the controller adjusts the switching frequency applied to switches in the power converter. The magnitude of the ripple current of the output current varies depending on a magnitude of the input voltage and potentially one or more other parameters as discussed herein. 
     Further embodiments herein include, via the controller or other suitable entity, deriving the selected switching frequency in which to apply to the multi-level power converter and produce the output current based on the target ripple current value and a magnitude of an input voltage converted by the power converter into the output current. 
     In still further example embodiments, the output current supplied by the power converter to the load (dynamic or static) includes a DC current component and an AC peak-to-peak current component. In one embodiment, the ripple current as discussed herein represents the AC peak-to-peak current component. 
     The magnitude of the AC peak-to-peak current component can be any suitable value. In one embodiment, the magnitude of the AC peak-to-peak current component is less than 50% of a magnitude of the DC current component. 
     In yet further example embodiments, the controller or other suitable entity selects the switching frequency of operating the power converter to produce the output current based on the magnitude of the received target ripple current value and an inductance of the power converter. 
     In still further nonlimiting example embodiments, the power converter is a multi-level buck converter having more than 2 levels. The inductance of the power converter provides a way to store and/or control delivery of current during respective one or more switching cycles. 
     In further example embodiments, the magnitude of the ripple current value is selected based at least in part to reduce switching losses associated with the power converter. 
     As previously discussed, the controller can be configured to apply a varying switching frequency to the power converter depending on one or more parameters such as a magnitude of the input voltage, magnitude of the output voltage, magnitude of the output current, inductance of the power converter, number of voltage levels supported by the power converter, output voltage, input voltage, switching losses of the power converter, desired ripple current associated with the produced output current, etc. 
     Further embodiments herein include, via the controller, preventing the switching frequency applied to the power converter from dropping below a threshold level while generating the output current over a range of different magnitudes of the input voltage. 
     As previously discussed, power converter can be configured to convert an input voltage into the output voltage and corresponding output current supplied to the dynamic load. In further example embodiments, the controller switches between operating the power converter in a first mode and a second mode. For example, during conditions in which the magnitude of the input voltage is above a threshold level, the controller operates the power converter in a first mode of switching between use of a first voltage level and a second voltage level to produce the output current. During conditions in which the magnitude of the input voltage is below the threshold level, the controller operates in a second of switching between the second voltage level and a third voltage level to produce the output voltage and corresponding output current. 
     In still further example embodiments, the controller produces a first modulation index value, namely m_real, based on: i) a magnitude of the output voltage, and ii) a magnitude of an input voltage converted by the power converter into the output current; as previously discussed, the controller or other suitable entity derives the switching frequency based on the first modulation index value. 
     In still further example embodiments, the first modulation index value, m_real, equals Vout/Vin, where Vout is a magnitude of the output voltage of the power converter supplying the output current to the load, where Vin is a magnitude of the input voltage. The controller produces a second modulation index value, m_eff, equal to m_real MODULO (1/N_cells), where N_cells=n_levels−1, where the value n_levels equals a number of different voltages supported by the power converter to produce the output voltage; wherein the switching frequency is f_sw; and wherein: 
         f _ sw= Vin/(Δ i·L )· m _ eff ·(1/ N _cells− m _ eff ),
 
     where Δi=the target ripple current value, and 
     where L=a magnitude of an inductance implemented in the power converter to convert the input voltage into the output current. 
     In further example embodiments, the power supply as discussed herein includes a power converter having a multi-level converter structure. The number of levels is equal to or greater than 3; the power converter operates in at least one operation range of input to output voltage ratios with a variable switching frequency. In one embodiment, the variable frequency depends on one or more parameters such as a ratio of input voltage to output voltage. The controller as discussed herein adjusts the switching frequency in order to keep the ripple current of the output current constant or some target value as previously discussed. 
     In still further example embodiments, the target ripple current value may be a function of an efficiency of the power converter as well as one or more other parameters such as input voltage. In such an instance, the controller as discussed herein monitors a magnitude of the input voltage and the one or more operational settings of the power converter (such as DC output voltage setpoint, magnitude of DC output current, etc.) to determine an appropriate switching frequency in which to generate the output voltage and corresponding output current from the power converter. 
     Note that embodiments herein are useful over conventional techniques. For example, in contrast to conventional techniques, the novel controller as described herein provides unique control of generating an output voltage and corresponding output current. 
     These and other more specific embodiments are disclosed in more detail below. 
     Note that any of the resources as discussed herein can include one or more computerized devices, apparatus, hardware, etc., execute and/or support any or all of the method operations disclosed herein. In other words, one or more computerized devices or processors can be programmed and/or configured to operate as explained herein to carry out the different embodiments as described herein. 
     Yet other embodiments herein include software programs to perform the steps and/or operations summarized above and disclosed in detail below. One such embodiment comprises a computer program product including a non-transitory computer-readable storage medium (i.e., any computer readable hardware storage medium) on which software instructions are encoded for subsequent execution. The instructions, when executed in a computerized device (hardware) having a processor, program and/or cause the processor (hardware) to perform the operations disclosed herein. Such arrangements are typically provided as software, code, instructions, and/or other data (e.g., data structures) arranged or encoded on a non-transitory computer readable storage medium such as an optical medium (e.g., CD-ROM), floppy disk, hard disk, memory stick, memory device, etc., or other a medium such as firmware in one or more ROM, RAM, PROM, etc., or as an Application Specific Integrated Circuit (ASIC), etc. The software or firmware or other such configurations can be installed onto a computerized device to cause the computerized device to perform the techniques explained herein. 
     Accordingly, embodiments herein are directed to a method, system, computer program product, etc., that supports operations as discussed herein. 
     One embodiment herein includes a computer readable storage medium and/or system having instructions stored thereon to facilitate generation of an output voltage to power a load. The instructions, when executed by computer processor hardware, cause the computer processor hardware (such as one or more co-located or disparately located processor devices or hardware) to: receive a target ripple current value indicative of a ripple current associated with an output current of a power converter powering a load; select a switching frequency of operating the power converter as a function of a magnitude of the received target ripple current value; and apply the selected switching frequency to switches in the power converter to produce the output current with the ripple current as indicated by the target ripple current value. 
     The ordering of the steps above has been added for clarity sake. Note that any of the processing steps as discussed herein can be performed in any suitable order. 
     Other embodiments of the present disclosure include software programs and/or respective hardware to perform any of the method embodiment steps and operations summarized above and disclosed in detail below. 
     It is to be understood that the system, method, apparatus, instructions on computer readable storage media, etc., as discussed herein also can be embodied strictly as a software program, firmware, as a hybrid of software, hardware and/or firmware, or as hardware alone such as within a processor (hardware or software), or within an operating system or a within a software application. 
     Note further that although embodiments as discussed herein are applicable to controlling operation of a power supply including one or more regulated power converter stages and one or more switched-capacitor converters, the concepts disclosed herein may be advantageously applied to any other suitable voltage converter topologies. 
     Additionally, note that although each of the different features, techniques, configurations, etc., herein may be discussed in different places of this disclosure, it is intended, where suitable, that each of the concepts can optionally be executed independently of each other or in combination with each other. Accordingly, the one or more present inventions as described herein can be embodied and viewed in many different ways. 
     Also, note that this preliminary discussion of embodiments herein (BRIEF DESCRIPTION OF EMBODIMENTS) purposefully does not specify every embodiment and/or incrementally novel aspect of the present disclosure or claimed invention(s). Instead, this brief description only presents general embodiments and corresponding points of novelty over conventional techniques. For additional details and/or possible perspectives (permutations) of the invention(s), the reader is directed to the Detailed Description section (which is a summary of embodiments) and corresponding figures of the present disclosure as further discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an example diagram illustrating a power converter controller including a switching frequency selector and one or more flying capacitors according to embodiments herein. 
         FIG.  2    is an example detailed diagram illustrating an example controller and multi-level power converter according to embodiments herein. 
         FIG.  3    is an example graph illustrating duty cycle versus ripple current according to embodiments herein. 
         FIG.  4    is an example graph diagram illustrating variation of a switching frequency applied to a multi-level power converter to provide a constant output ripple current as a magnitude of an input voltage decays over time according to embodiments herein. 
         FIG.  5    is an example diagram illustrating control of a power converter and generation of an output current according to embodiments herein. 
         FIGS.  6 A,  6 B,  6 C, and  6 D  illustrate different control modes of operating a multi-level power converter via control signals in  FIG.  5    according to embodiments herein. 
         FIG.  7    is an example diagram illustrating control of a power converter and generation of an output current according to embodiments herein. 
         FIGS.  8 A,  8 B,  8 C, and  8 D  illustrate different control modes of operating a multi-level power converter via control signals in  FIG.  5    according to embodiments herein. 
         FIG.  9    is an example graph diagram illustrating variation of a magnitude of a switching frequency to provide a target output ripple current as a magnitude of an input voltage varies over time according to embodiments herein. 
         FIG.  10    is an example graph diagram illustrating variation of a magnitude of a switching frequency to provide a target output ripple current as a magnitude of an input voltage varies over time according to embodiments herein. 
         FIGS.  11 A and  11 B  are example diagrams illustrating implementations of a multi-level power converter and application of switching frequency control according to embodiments herein. 
         FIG.  12    is an example diagram illustrating computer architecture operable to execute one or more operations according to embodiments herein. 
         FIG.  13    is an example diagram illustrating a general method according to embodiments herein. 
         FIG.  14    is an example diagram illustrating fabrication of a multi-level power converter (such as a regulated voltage converter) on a circuit board according to embodiments herein. 
     
    
    
     The foregoing and other objects, features, and advantages of embodiments herein will be apparent from the following more particular description herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, with emphasis instead being placed upon illustrating the embodiments, principles, concepts, etc. 
     DETAILED DESCRIPTION 
     As previously discussed, embodiments herein are useful over conventional techniques. For example, in contrast to conventional techniques, the novel power supply as described herein includes a controller. The controller regulates generation of an output signal from the power converter based on a target ripple current value. For example, the controller receives a target ripple current value indicative of a ripple current associated with an output voltage and corresponding output current of a power converter powering a load. In one embodiment, the output current of the power converter includes a DC output current component and an AC output current component (such as the ripple current). When generating the output current of the power converter, the controller selects a switching frequency of operating the power converter as a function of a magnitude of the received target ripple current value (AC output current component). The controller then applies the selected switching frequency to switches in the power converter to produce the output current with a magnitude of the ripple current as indicated by the target ripple current value. 
     Now, more specifically,  FIG.  1    is an example diagram illustrating a power converter including a switching frequency selector and one or more flying capacitors according to embodiments herein. 
     As shown in this example embodiment, power supply  100  includes a controller  140 , power converter  111  (a.k.a., voltage converter), and load  118 . 
     In one embodiment, each of the components in power supply  100  represents an entity such as an apparatus, electronic device, electronic circuitry, etc., although they can be implemented in any suitable manner. 
     The controller  140  and corresponding switching frequency selector  141  can be instantiated as or include hardware (such as circuitry), software (executable instructions), or a combination of hardware and software resources where applicable. In other words, the controller  140  can be implemented as controller hardware, controller software, or a combination of controller hardware and controller software. 
     In accordance with further example embodiments, the power converter  111  includes one or more flying capacitors such as flying capacitor FC 1 , flying capacitor FC 2 , etc. The power converter  111  further includes a network of switches  125  (such as including one or more switches Qx), and inductor  144 . 
     During operation, via control signals  105  controlling switches  125 , the controller  140  controls conveyance of energy from the input voltage  120  and the one or more flying capacitors (such as FC 1 , FC 2 , etc.) to the inductor  144 . The flying capacitors are charged and discharged from one or more reference voltages such as input voltage  121  (as received from the input voltage source  120 - 1 ), ground, etc., via switching of the network of switches  125  controlled by controller  140 . The inductor  144  converts the received energy from the input voltage  121  and flying capacitors FC 1 , FC 2 , etc., into an output voltage  123  and corresponding output current  122  to power the dynamic load  118 . 
     In further example embodiments, the controller  140  receives a target ripple current value TRCV indicative of a ripple current associated with generation of the output current  122 . As previously discussed, in one embodiment, the output current  122  of the power converter includes a DC output current component and an AC output current component. (such as the ripple current as previously mentioned). The AC output current component can take any suitable from such as SINE wave, sawtooth wave, etc. 
     When generating the output current  122  of the power converter  111 , the controller  140  selects a switching frequency SF of operating the power converter  111  and corresponding switches  125  (a.k.a., Qx) as a function of a magnitude of the received target ripple current value TRCV. The controller  140  then applies the selected (appropriate) switching frequency SF to switches  125  in the power converter  111  to produce the output current  122  with a magnitude of the ripple current (AC component) as indicated by the target ripple current value TRCV. 
       FIG.  2    is an example detailed diagram illustrating an example controller and multi-level power converter according to embodiments herein. 
     In this example embodiment, the power converter  111 - 1  is implemented as multi-level power converter and includes input voltage source  120 - 1 , multiple switches Q 1 , Q 2 , Q 3 , and Q 4 , flying capacitor FC 1 , inductor  144 , and output capacitor C 1 . 
     In one embodiment, the switches  125  (such as Q 1 , Q 2 , Q 3 , and Q 4 ) are implemented as field effect transistors. However, note that the switches Q 1 , Q 2 , Q 3 , and Q 4  can be implemented via any suitable type of resource. 
     Further in this example embodiment, the multiple switches Q 1 , Q 2 , Q 3 , and Q 4  are connected in series between the input reference voltage and the ground reference. For example, the drain node (D) of switch Q 1  is connected to the input voltage source node  120 - 1  (such as a battery, voltage supplied by another power supply, etc.); the source node (S) of switch Q 1  is connected to the drain node (D) of switch Q 2  (a.k.a., node  293 ); the source node (S) of switch Q 2  is connected to the drain node (D) of switch Q 3  and node  292  of the inductor  144 ; the source node (S) of switch Q 3  is connected to the drain node (D) of switch Q 4 ; the source node (S) of switch Q 4  is connected to ground. 
     This example instance of the multi-level power converter  111 - 1  includes a flying capacitor FC 1 . The flying capacitor FC 1  is connected in parallel with the series combination of switches Q 2  and Q 3 . More specifically, a first node of the flying capacitor FC 1  is connected to the node  293 ; a second node of the flying capacitor FC 1  is connected to the node  294 . 
     Further in this example embodiment, the control signals  105  include control signal S 1 , control signal S 2 , control signal S 3 , and control signal S 4 . 
     As shown, the control signal S 1  is applied the gate node of the switch Q 1  to control its operation; the control signal S 2  is applied the gate node of the switch Q 2  to control its operation; the control signal S 3  is applied the gate node of the switch Q 3  to control its operation; the control signal S 4  is applied the gate node of the switch Q 4  to control its operation. 
     In still further example embodiments, the controller  140  can be configured to regulate a magnitude of the output voltage  123  (Vout) from the power converter  111 - 1  to power the dynamic load  118 . 
     For example, in one embodiment, the power converter  111 - 1  receives a setpoint reference voltage  215  (such as 24 VDC or other suitable value) indicating a magnitude at which to produce the output voltage  123 . During generation of the output voltage  123  and corresponding output current  122 , the controller  140  implements the comparator  241  to produce an error voltage  245  indicating a difference between the magnitude of the output voltage  123  and the setpoint reference voltage  215 . The controller  140  varies a duty cycle of the control signals  105  (namely, control signal S 1 , control signal S 2 , control signal S 3 , and control signal S 4 ) such that a DC component of the output voltage  123  is substantially equal to the setpoint reference voltage  215 . 
     Thus, switches Q 1 -Q 4  are controlled to convert the input voltage  121  into an output current  122 . The controller  140  controls a switching frequency SF of control signals  105  applied to the switches Q 1 , Q 2 , Q 3 , and Q 4  such that the AC (ripple) current associated with the output current  122  substantially matches (such as in 10%, 20%, or any suitable amount, etc.) a respective target ripple current value TRCV. Thus, the controller  140  as discussed herein simultaneously implements multiple types of control when producing the output voltage  123  and corresponding output current  122 . 
     For example, the controller  140  varies a duty cycle of controlling respective switches  125  (Q 1 , Q 2 , Q 3 , and Q 4 ) in a similar manner as previously discussed to maintain a magnitude of the output voltage  123  at a desired level. Additionally, the controller  140  selects an appropriate switching frequency SF such that the ripple current of output current  122  is approximately equal to the target reference current value TRCV. 
       FIG.  3    is an example graph illustrating duty cycle versus ripple current according to embodiments herein. 
     Graph  315  of  FIG.  3    illustrates a magnitude of ripple current versus duty cycle when implementing the power converter  111  as discussed herein. For example, the curve  315  illustrates a normalized magnitude of the ripple current with respect to the duty cycle for a standard buck converter. On the other hand, the curve  320  in graph  310  indicates a magnitude of the ripple current associated with the output current  122  via implementation of a multi-level power converter  111  (3 voltage levels 0, Vin/2, and Vin). As shown in graph  310 , when controlling the switches  125  in the power converter  111  with a 50% duty cycle control signals  105 , the ripple current is substantially zero. 
     In one embodiment, the voltage source  120 - 1  is a battery; a magnitude of the input voltage  121  decays over time. The power converter  111  is suitable for power conversion from, e.g., a battery ranging from a voltage of 60 VDC gradually degrading to 40 VDC. The 3-level buck power converter  111  in  FIG.  2    provides a regulated 24 VDC bus output voltage  123 , which is subsequently transferred into 12V by a capacitive divider such as a switch tank converter. Buck converters typically operate at a constant switching frequency, where the switching frequency is limited by the amount of switching losses. 
     Embodiments herein include producing a non-zero ripple current (such as indicated by the setpoint target ripple current value TRCV) on the output current  122  while also regulating a magnitude of a DC voltage component of the corresponding output voltage  123  to a desired setpoint reference voltage. 
       FIG.  4    is an example graph diagram illustrating variable control of a switching frequency under ideal conditions to provide a constant output ripple current as a magnitude of an input voltage decays over time according to embodiments herein. 
     Graph  400  illustrates operation of the power converter  111  over time based on a variable input voltage  121 . For example, assume that the controller  140  receives a target DC voltage value of 24 VDC as the setpoint reference voltage  215 . Additionally, assume that the controller  140  receives a target ripple current voltage setting of TRCV=4 Amperes AC. 
     At time T 80 , the input voltage  121  such as received from a battery or other suitable entity (source  120 - 1 ) starts at a magnitude of around 60 VDC. A magnitude of the input voltage  121  decreases over time as the energy in the battery is depleted from time T 80  to time T 85 . In a manner as previously discussed, the controller  140  regulates a magnitude of the output voltage  123  to be 24 VDC. 
     Additionally, over a range of different magnitudes of the input voltage  121 , the controller  140  implements switching frequency selector  141  to apply an appropriate switching frequency SF to switches  125  in the power converter  111  such that the magnitude of the ripple current associated with the output current  122  is equal to the target ripple current value TRCV=4 Amps for the range of different magnitudes of the input voltage  121 . More specifically, see envelope  410  indicating a range of the ripple current associated with the generated output current  122  over a range of different magnitudes of the input voltage  121 . In this example embodiment, the envelope  410  indicates that the ripple current of the output current is substantially constant. 
     Note further that the graph  400  also illustrates that the switching frequency selector  141  and controller  140  reduce a magnitude of the switching frequency SF between time T 80  and T 83  to accommodate the change in the input voltage  121 . As previously discussed, control of the switching frequency SF results in a substantially constant ripple current of around 4 amperes. Assume in this example embodiment that the dynamic load  118  consumes around 50 DC amperes at an output voltage of 24 VDC. In such an instance, the average output current  122  is 50 AMPS including the 4 AMP ripple current component. 
     Thus, between time T 80  and T 83 , the controller  140  and corresponding switching frequency selector  141  reduce a magnitude of the switching frequency SF, in which a duty cycle of operating switches is less than 50%. At or around time T 83 , the operation of the power converter  111  reaches an inflection point. After time T 83 , because the input voltage  121  is below a threshold level of around 48 VDC, the controller  140  and corresponding switching frequency selector  141  increase a magnitude of the switching frequency SF, in which a duty cycle of operating switches is greater than 50%. Examples are shown in  FIGS.  5 - 8   . 
     Referring again to  FIG.  4   , in still further example embodiments, to maintain a magnitude of the ripple current to around the target value of 4 Amperes, note that the controller  140  can be configured to produce a first modulation index value, namely m_real, based on: i) a magnitude of the output voltage  123 , and ii) a magnitude of an input voltage  121  converted by the power converter  111  into the output current  122 . As further discussed below, the controller  140  or other suitable entity derives the switching frequency SF based on the first modulation index value. 
     In one embodiment, the first modulation index value, 
         m _real=Vout/Vin,  (equation 1)
 
     where Vout is a magnitude of an output voltage  123  of the power converter  111  supplying the output current  122  to the load  118 , where Vin is a magnitude of the input voltage  121 . 
     The switching frequency selector  141  and controller  140  produce a second modulation index value, 
         m _ eff=m _real×MODULO×(1/ N _cells),  (equation 2)
 
       where  N _cells= n _levels−1,  (equation 3)
 
     where n_levels equals a number of different voltages (such as 3 levels for the power converter  111  in  FIG.  2   , in which N_cells=2) supported by the power converter  111  to produce the output voltage  123 ; wherein the switching frequency is f_sw (a.k.a., switching frequency SF signal); and wherein: 
         f _ sw =Vin/(Δ i·L )· m _ eff ·(1/ N _cells− m _ eff ),
 
     where Δi=the target ripple current value TRCV=4 amperes, and 
     where L=a magnitude of an inductance (inductor  144  such as 2 microhenries or other suitable value) implemented in the power converter  111  to convert the input voltage  121  into the output current  122 . 
       FIG.  5    is an example diagram illustrating control of a power converter and generation of an output current according to embodiments herein.  FIGS.  6 A,  6 B,  6 C, and  6 D  illustrate different control modes of operating a multi-level power converter via control signals in  FIG.  5    according to embodiments herein. The following description references related  FIGS.  5 ,  6 A,  6 B,  6 C, and  6 D . 
     When a magnitude of the input voltage  121  is greater than twice the magnitude of the output voltage setpoint value (such as 24 VDC), the controller  140  generates the control signals  105  in a manner as shown in graph  510  of  FIG.  5   . For example, the controller  140  implements multiple control phases or modes A 1 , A 2 , A 3 , and A 4  to produce the output voltage  123  and corresponding output current  122  via control signals having a duty cycle of less than 50% ( FIGS.  5 ,  6 A,  6 B,  6 C, and  6 D ) because the magnitude of the input voltage  121  is greater twice the output voltage setpoint of 24 VDC. 
     As shown in  FIG.  5   , during mode A 1 , between time T 51  and T 52 , the controller  140  activates switches Q 1  and Q 3  to an ON state and switches Q 2  and Q 4  to an OFF state. As shown in  FIG.  6 A , operation of mode A 1  causes current to flow from the input voltage source  120 - 1  through a circuit path including the switch Q 1 , flying capacitor FC 1 , switch Q 3 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode A 1  includes charging of the flying capacitor FC 1 . 
     As shown in  FIG.  5   , during mode A 2 , between time T 52  and T 53 , the controller  140  activates switches Q 3  and Q 4  to an ON state and switches Q 1  and Q 2  to an OFF state. As shown in  FIG.  6 B , operation of mode A 2  causes current to flow from the ground reference through a circuit path including the switch Q 4 , switch Q 3 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode A 2  includes coupling the inductor  144  to ground. 
     As shown in  FIG.  5   , during mode A 3 , between time T 53  and T 54 , the controller  140  activates switches Q 2  and Q 4  to an ON state and switches Q 1  and Q 3  to an OFF state. As shown in  FIG.  6 C , operation of mode A 3  causes current to flow from the ground reference through a circuit path including the switch Q 4 , flying capacitor FC 1 , switch Q 2 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode A 3  includes discharging of the flying capacitor FC 1 . 
     As shown in  FIG.  5   , during mode A 4 , between time T 54  and T 55 , the controller  140  activates switches Q 3  and Q 4  to an ON state and switches Q 1  and Q 2  to an OFF state. As shown in  FIG.  6 D , operation of mode A 4  causes current to flow from the ground reference through a circuit path including the switch Q 4 , switch Q 3 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode A 4  includes coupling the inductor  144  to ground. 
     As further shown in graph  510 , the controller  140  repeats this control cycle over time. 
     As previously discussed, switching of the switches  125  in this manner results in generation of an output current  122  having a desired magnitude of ripple current. 
       FIG.  7    is an example diagram illustrating control of a power converter and generation of an output current according to embodiments herein.  FIGS.  8 A,  8 B,  8 C, and  8 D  illustrate different control modes of operating a multi-level power converter via control signals in  FIG.  7    according to embodiments herein. 
     When a magnitude of the input voltage  121  is less than twice the magnitude of the output voltage setpoint value (such as 24 VDC), the controller  140  generates the control signals  105  in a manner as shown in graph  710  of  FIG.  7   . For example, the controller  140  implements multiple control phases or modes B 1 , B 2 , B 3 , and B 4  to produce the output voltage  123  and corresponding output current  122  via control signals having a duty cycle of greater than 50% ( FIGS.  7 ,  8 A,  8 B,  8 C, and  8 D ) because the magnitude of the input voltage  121  is greater twice the output voltage setpoint of 24 VDC. 
     As shown in  FIG.  7   , during mode B 1 , between time T 71  and T 72 , the controller  140  activates switches Q 1  and Q 2  to an ON state and switches Q 3  and Q 4  to an OFF state. As shown in  FIG.  8 A , operation of mode B 1  causes current to flow from the input voltage source  120 - 1  through a circuit path including the switch Q 1 , switch Q 2 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode B 1  includes connecting the inductor  144  to the input voltage source  120 - 1 . 
     As shown in  FIG.  7   , during mode B 2 , between time T 72  and T 73 , the controller  140  activates switches Q 1  and Q 3  to an ON state and switches Q 2  and Q 4  to an OFF state. As shown in  FIG.  8 B , operation of mode B 2  causes current to flow from the input voltage source  120 - 1  through a circuit path including the switch Q 1 , flying capacitor FC 1 , switch Q 3 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode B 2  includes charging the flying capacitor FC 1 . 
     As shown in  FIG.  7   , during mode B 3 , between time T 73  and T 74 , the controller  140  activates switches Q 1  and Q 2  to an ON state and switches Q 3  and Q 4  to an OFF state. As shown in  FIG.  8 C , operation of mode B 3  causes current to flow from the input voltage source  120 - 1  through a circuit path including the switch Q 1 , switch Q 2 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode B 3  includes connecting the inductor  144  to the input voltage source  120 - 1 . 
     As shown in  FIG.  7   , during mode B 4 , between time T 74  and T 75 , the controller  140  activates switches Q 2  and Q 4  to an ON state and switches Q 1  and Q 3  to an OFF state. As shown in  FIG.  8 D , operation of mode B 4  causes current to flow from the ground reference through a circuit path including the switch Q 4 , flying capacitor FC 1 , switch Q 2 , and the inductor  144  to produce the output voltage  123  and corresponding output current  122 . Thus, mode B 4  includes discharging the flying capacitor FC 1 . 
     As further shown in graph  710 , the controller  140  repeats this control cycle over time. 
     As previously discussed, switching of the switches  125  in this manner results in generation of an output current  122  having a desired magnitude of ripple current. 
       FIG.  9    is an example graph diagram illustrating variation of switching frequency to provide a target output ripple current as a magnitude of an input voltage varies over time according to embodiments herein. 
     Graph  900  illustrates operation of the power converter  111  over time based on a variable input voltage  121 . For example, assume that the controller  140  receives a target DC voltage value of 24 VDC as the setpoint reference voltage  215 . Additionally, assume that the controller  140  receives a variable target ripple current voltage setting of TRCV=2-4 Amperes AC (such as peak to peak ripple). 
     At time T 90 , the input voltage  121  such as received from a battery or other suitable entity (source  120 - 1 ) starts at a magnitude of around 60 VDC. A magnitude of the input voltage  121  decreases over time as the energy in the battery is depleted from time T 90  to time T 95 . In a manner as previously discussed, the controller  140  regulates a magnitude of the output voltage  123  to be 24 VDC. 
     Additionally, over a range of different magnitudes of the input voltage  121 , the controller  140  implements switching frequency selector  141  to apply an appropriate switching frequency SF to switches  125  in the power converter  111  such that the magnitude of the ripple current associated with the output current  122  is equal to the target ripple current value TRCV as shown by envelope  910  for the different magnitudes of the input voltage  121 . More specifically, see envelope  910  indicating a range of the ripple current associated with the generated output current  122  over a range of different magnitudes of the input voltage  121 . In this example embodiment, the envelope  910  indicates that the desired magnitude of the ripple current of the output current  122  varies over time such as based on the magnitude of the input voltage  121  or suitable parameters. In this example embodiment, varying a magnitude of the ripple current over time for different magnitudes of the input voltage  121  results in a more efficient conversion (such as lower switching losses) of the input voltage  121  into the output voltage  123  and corresponding output current  122 . 
     Note further that the graph  900  also illustrates that the switching frequency selector  141  and controller  140  reduce a magnitude of the switching frequency SF between time T 90  and T 93  to accommodate the change in the input voltage  121 . As previously discussed, control of the switching frequency SF results in a substantially variable ripple current between approximately 2-4 Amps. Note that embodiments herein include, if desired, implementation of a look-up table to determine an appropriate setting of the switching frequency SF. In other words, in a manner as previously discussed, the switching frequency selector  141  and corresponding controller  140  can be configured to implement equations to determine the appropriate switching frequency to apply to respective switches  125  to achieve a desired ripple current on the output current  122 . Alternatively, the controller  140  and corresponding switching frequency selector can be configured to include a look-up table of a predetermined mapping of input voltage (and/or one or more other monitored power supply parameters) to an appropriate switching frequency SF for those power supply conditions. 
     Assume in this example embodiment that the dynamic load  118  consumes around 50 DC amperes at an output voltage of 24 VDC. In such an instance, the average output current  122  is 50 AMPS including a variable amount of ripple current component. 
     Thus, between time T 90  and T 93 , the controller  140  and corresponding switching frequency selector  141  reduce a magnitude of the switching frequency SF, in which a duty cycle of operating switches is less than 50%. At or around time T 93 , the operation of the power converter  111  reaches an inflection point. After time T 93 , because the input voltage  121  is below a threshold level of around 48 VDC, the controller  140  and corresponding switching frequency selector  141  increase a magnitude of the switching frequency SF, in which a duty cycle of operating switches is greater than 50%. Examples were previously discussed in  FIGS.  5 - 8   . 
       FIG.  10    is an example graph diagram illustrating variation of switching frequency to provide a target output ripple current as a magnitude of an input voltage varies over time according to embodiments herein. 
     Graph  1000  illustrates operation of the power converter  111  over time based on a variable input voltage  121 . For example, assume that the controller  140  receives a target DC voltage value of 24 VDC as the setpoint reference voltage  215 . Additionally, assume that the controller  140  receives a variable target ripple current voltage setting of TRCV=1-4 Amperes AC (such as peak to peak ripple) for different power supply conditions. 
     At time T 10 , the input voltage  121  such as received from a battery or other suitable entity (source  120 - 1 ) starts at a magnitude of around 60 VDC. A magnitude of the input voltage  121  decreases over time as the energy in the battery is depleted from time T 10  to time T 15 . In a manner as previously discussed, the controller  140  regulates a magnitude of the output voltage  123  to be 24 VDC. 
     Additionally, over a range of different magnitudes of the input voltage  121 , the controller  140  implements switching frequency selector  141  to apply an appropriate switching frequency SF to switches  125  in the power converter  111  such that the magnitude of the ripple current associated with the output current  122  is equal to the target ripple current value TRCV as shown by envelope  1010  for the different magnitudes of the input voltage  121 . More specifically, see envelope  1010  indicating a range of the ripple current associated with the generated output current  122  over a range of different power supply conditions such as magnitudes of the input voltage  121 . In this example embodiment, the envelope  1010  indicates that the desired magnitude of the ripple current of the output current  122  varies over time such as based on the magnitude of the input voltage  121  or suitable parameters. In this example embodiment, varying a magnitude of the ripple current over time for different magnitudes of the input voltage  121  results in a more efficient conversion (such as lower switching losses) of the input voltage  121  into the output voltage  123  and corresponding output current  122 . 
     Note further that the graph  1000  also illustrates that the switching frequency selector  141  and controller  140  reduce a magnitude of the switching frequency SF between time T 10  and T 13  to accommodate the change in the input voltage  121 . As previously discussed, control of the switching frequency SF results in a substantially variable ripple current between approximately 1-4 Amps. Note that embodiments herein include, if desired, implementation of a look-up table to determine an appropriate setting of the switching frequency SF. In other words, in a manner as previously discussed, the switching frequency selector  141  and corresponding controller  140  can be configured to implement equations to determine the appropriate switching frequency to apply to respective switches  125  to achieve a desired ripple current on the output current  122 . Alternatively, the controller  140  and corresponding switching frequency selector  141  can be configured to include a look-up table of a predetermined mapping of input voltage (and/or one or more other monitored power supply parameters) to an appropriate switching frequency SF for those power supply conditions. 
     Assume in this example embodiment that the dynamic load  118  consumes around 50 DC amperes at an output voltage of 24 VDC. In such an instance, the average output current  122 -AVE is 50 AMPS (which may vary somewhat) including a variable amount of ripple current component. 
     Thus, between time T 10  and T 13 , the controller  140  and corresponding switching frequency selector  141  reduce a magnitude of the switching frequency SF, in which a duty cycle of operating switches is less than 50%. At or around time T 13 , the operation of the power converter  111  reaches an inflection point. After time T 13 , because the input voltage  121  is below a threshold level of around 48 VDC, the controller  140  and corresponding switching frequency selector  141  increase a magnitude of the switching frequency SF, in which a duty cycle of operating switches is greater than 50%. Examples were previously discussed in FIGS. 
     Between about time T 12  and T 14 , the switching frequency SF does not drop below a lower frequency threshold level of around 200 KHz. 
       FIG.  11 A  is an example diagram illustrating a 3-level Bipolar switched Neutral-point-clamp topology controlled according to embodiments herein. 
     In this example embodiment, the controller  140 - 1  controls a switching frequency of operating the power converter  111 - 11 A (such as a 3-level Bipolar switched Neutral-point-clamp topology) such that an output current  122 - 11 A of the respective power converter  111 - 11 A is set to a desired ripple current value over a range of different magnitudes of the input voltage  121 - 11 A. In other words, embodiments herein propose a power converter and a corresponding control method where the regulation of the power converter  111 - 11 A is adjusted in such a way that at least in one operation range of input to output voltages the current ripple is constant or varies. 
       FIG.  11 B  is an example diagram illustrating a 37-level Hybrid Active Neutral-point clamp topology controlled according to embodiments herein. 
     In this example embodiment, the controller  140 - 2  controls a switching frequency of operating the power converter  111 - 11 B (such as a 7-level Hybrid Active Neutral-point clamp topology) such that an output voltage of the respective power converter  111 - 11 B is constant over a range of different magnitudes of the input voltage. In other words, embodiments herein propose a power converter and a corresponding control method where the regulation of the power converter  111 - 11 B is adjusted in such a way that at least in one operation range of input to output voltages the current ripple stays constant or varies with respect to a desired ripple current value. Note that, for the 7-level inverter, this operation point exists for output voltages of ⅚ VDC; ⅔ VDC; ½ VDC; ⅓ VDC and ⅙ VDC with VDC being the input voltage. 
       FIG.  12    is an example block diagram of a computer system for implementing any of the operations as previously discussed according to embodiments herein. 
     Any of the resources (such as controller  140 , switching frequency selector  141 , etc.) as discussed herein can be configured to include computer processor hardware and/or corresponding executable instructions to carry out the different operations as discussed herein. 
     As shown, computer system  1250  of the present example includes an interconnect  1211  that couples computer readable storage media  1212  such as a non-transitory type of media (which can be any suitable type of hardware storage medium in which digital information can be stored and retrieved), a processor  1213  (computer processor hardware), I/O interface  1214 , and a communications interface  1217 . 
     I/O interface(s)  1214  supports connectivity to power converter  111 . 
     Computer readable storage medium  1212  can be any hardware storage device such as memory, optical storage, hard drive, floppy disk, etc. In one embodiment, the computer readable storage medium  1212  stores instructions and/or data. 
     As shown, computer readable storage media  1212  can be encoded with controller application  140 - 1  (e.g., including instructions) to carry out any of the operations as discussed herein. 
     During operation of one embodiment, processor  1213  accesses computer readable storage media  1212  via the use of interconnect  1211  in order to launch, run, execute, interpret or otherwise perform the instructions in controller application  140 - 1  stored on computer readable storage medium  1212 . Execution of the controller application  140 - 1  produces controller process  140 - 2  to carry out any of the operations and/or processes as discussed herein. 
     Those skilled in the art will understand that the computer system  1250  can include other processes and/or software and hardware components, such as an operating system that controls allocation and use of hardware resources to execute controller application  140 - 1 . 
     In accordance with different embodiments, note that computer system may reside in any of various types of devices, including, but not limited to, a power supply, switched-capacitor converter, power converter, a mobile computer, a personal computer system, a wireless device, a wireless access point, a base station, phone device, desktop computer, laptop, notebook, netbook computer, mainframe computer system, handheld computer, workstation, network computer, application server, storage device, a consumer electronics device such as a camera, camcorder, set top box, mobile device, video game console, handheld video game device, a peripheral device such as a switch, modem, router, set-top box, content management device, handheld remote control device, any type of computing or electronic device, etc. The computer system  1450  may reside at any location or can be included in any suitable resource in any network environment to implement functionality as discussed herein. 
     Functionality supported by the different resources will now be discussed via flowchart in  FIG.  13   . Note that the steps in the flowcharts below can be executed in any suitable order. 
       FIG.  13    is a flowchart  1300  illustrating an example method according to embodiments herein. Note that there will be some overlap with respect to concepts as discussed above. 
     In processing operation  1310 , the controller  140  receives a target ripple current value indicative of a ripple current associated with an output current  122  of a power converter  111  powering a load  118 . 
     In processing operation  1320 , the switching frequency selector of the controller  140  selects a switching frequency SF of operating the power converter  121  as a function of a magnitude of the received target ripple current value TRCV. 
     In processing operation  1330 , the controller applies the selected switching frequency SF to switches Qx in the power converter  121  to produce the output current  122  with the ripple current as indicated by the target ripple current value TRCV. 
       FIG.  14    is an example diagram illustrating fabrication of a power converter circuit on a circuit board according to embodiments herein. 
     In this example embodiment, fabricator  1540  receives a substrate  1510  (such as a circuit board). 
     The fabricator  1540  affixes the power supply  100  (and corresponding components such as controller  140 , switching frequency selector  141 , power converter  111 , one or more flying capacitors, switches  125 , power converter  111 , etc., as previously discussed) to the substrate  1510 . One or more circuit paths  1521  provide connectivity amongst the different components as discussed herein. Via circuit paths  1522  (such as one or more traces, cables, wires, etc.), the fabricator  1540  couples the power supply  100  to load  118 . In one embodiment, the circuit paths  1522  convey the output voltage  123  and corresponding generated output current  122  to the load  118 . 
     Accordingly, embodiments herein include a system comprising: a substrate  1510  (such as a circuit board, standalone board, mother board, standalone board destined to be coupled to a mother board, etc.); a power supply  100  including corresponding components (such as controller  140 , power converter  111 , and corresponding components) as described herein; and a load  118 . As previously discussed, the load  118  is powered based on conveyance of output voltage  123  and corresponding output current  122  over one or more circuit paths  1522  from the power supply  100  to the load  118 . 
     Note that further embodiments herein include a system (as shown in  FIG.  15   ) comprising: the circuit substrate  1510  and the load  118  disposed on the substrate  1510  or remotely located with respect to the substrate  1510 . The power supply  100  (apparatus) and corresponding components are affixed directly to the circuit substrate  1510  or sockets or sub-assemblies (such as sockets, etc.) of the substrate  1510 . The power supply  100  powers the load  118  via the output voltage  123  (such as via one or more circuit paths  1522 ). 
     Note that the load  118  can be any suitable circuit or hardware such as one or more CPUs (Central Processing Units), GPUs (Graphics Processing Unit) and ASICs (Application Specific Integrated Circuits such those including one or more Artificial Intelligence Accelerators), which can be located on the substrate  1510  or disposed at a remote location. 
     Note again that techniques herein are well suited for use in power supply applications. However, it should be noted that embodiments herein are not limited to use in such applications and that the techniques discussed herein are well suited for other applications as well. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present application as defined by the appended claims. Such variations are intended to be covered by the scope of this present application. As such, the foregoing description of embodiments of the present application is not intended to be limiting. Rather, any limitations to the invention are presented in the following claims.