Highly efficient parallel power conversion system using adaptive dynamic efficiency optimization

Abstract

A system (10) for controlling a plurality of power converters (12a-12n) to turn each of the plurality of power converters on or off as a function of sensed input power (22) and sensed output power (24), thereby operating one or more of the on-state power converters within an optimum power efficiency range.

Description

[Technical field]

[0001] Related patent applications This application claims priority to U.S. Provisional Patent Application No. 62 / 752,893, filed October 31, 2018, and U.S. Provisional Patent Application No. 62 / 817,651, filed March 13, 2019, the contents of which are incorporated herein by reference.

[0002] 2. Background of the Invention The present invention relates to power conversion systems, and more particularly to power conversion systems that optimize power usage of system components. [Background technology]

[0003] Conventional power conversion systems are known, typically using a magnetic power converter to convert a power parameter, such as current or voltage, from a first level to a second level. A typical magnetic power converter uses a transformer to convert the power between the first level and the second level. Thus, when the power increases from the first level to the second level, the power converter is called a step-up power converter. Similarly, when the power decreases from the first level to the second level, the power converter is called a step-down power converter.

[0004] The use of magnetic power converters has the disadvantage that they typically use windings arranged around a core, resulting in power losses. Furthermore, the efficiency curves of conventional magnetic transformers and inverters typically peak at about 50% of rated load and then begin to drop as the load approaches the maximum rated load. Conventional transformers also suffer from reduced efficiency at low loads. The primary cause of the reduced efficiency at low loads is power losses due to operating control circuits and device drivers configured to switch the high capacitance gates of large switching transistors, while the primary cause of the reduced efficiency at high loads is resistive losses at high currents. Summary of the Invention

[0005] Summary of the Invention The present invention relates to a power conversion system that uses a controller to control the operation of a power converter array. The controller controls the power converter array by operating an appropriate number of power converters within an optimal power efficiency range while supplying power to a load. The controller cooperates with a selection unit to optionally select a specific operating frequency for each of the power converters. The power conversion system may further include an optional comparison unit for comparing a measurement of the instantaneous power delivered by the system to a threshold value to determine if the system requires a bypass of the controller and to instruct the off-state power converters to discharge stored power directly to the load.

[0006] The present invention relates to a system for controlling a plurality of power converters of a power system comprising a plurality of power converters forming an array for converting power from a first level to a second level, the plurality of power converters being coupled at their input side to a common input power line for providing an input power of the first level and coupled at their output side to a common output power line for providing a power of the second level to a load. The system also includes a controller coupled to the plurality of power converters for controlling the power output of the plurality of power converters, an input sensing circuit for sensing an input power on the common input power line and sending an input power signal to the controller, and an output sensing circuit for sensing an output power on the common output power line and sending an output power signal to the controller. The controller is configured to control each of the plurality of power converters to switch each of the plurality of power converters to an on state or an off state as a function of the sensed input power and the sensed output power, thereby operating one or more of the plurality of power converters in an on state within an optimal power efficiency range.

[0007] According to the present invention, the power converter may include a switched-capacitor DC-DC step-down power converter for converting power from a first power level to a second power level, the second power level being lower than the first power level. Alternatively, the power converter may include a DC-DC power converter, a DC-AC power converter or an AC-DC power converter. In another embodiment, each power converter may include a plurality of capacitors in which power is stored. The capacitors may optionally be electrically connected in a parallel configuration, a series configuration, a parallel-series configuration or a series-parallel configuration.

[0008] According to another aspect of the invention, the control device may include a processor, a lookup table, and memory for storing instructions that, when received by the processor, instruct the processor to calculate a power for one or more of a plurality of power converters, access the lookup table based on the power of the one or more power converters, and determine from the lookup table which of the plurality of power converters the control device should place in an on and off state.

[0009] According to another aspect, the controller may include a memory unit for storing instructions for controlling the multiple power converters, a signal conditioner for conditioning the input power signal and the output power signal to generate a regulated output power signal, an AC-DC converter for converting the regulated output power signal to a DC regulated output power signal, and a processor for processing the DC regulated output power signal and generating a controller output signal for controlling one or more of the multiple power converters to ON and OFF states based on the stored instructions. The regulated output power signal may include a regulated output voltage component and a regulated output current component, and the processor may include a filter for averaging the regulated output power component and the regulated output current component of the regulated output power signal, a power calculation unit for calculating power of one or more of the multiple power converters based on the average of the regulated output power component and the regulated output current component to generate a power calculation output signal, a hysteresis unit for reducing noise in the power calculation output signal, and a look-up table for storing information related to multiple power levels of at least one power converter of the multiple power converters corresponding to the multiple power converters to be in an ON or OFF state. In this manner, the controller generates one or more output control signals for turning on and off one or more of the multiple power converters based on the look-up table, and the power level of the controller corresponds to the power requirements of the load.

[0010] The signal conditioner may include a voltage regulation unit for buffering the input and output voltage components to remove noise therefrom and scaling the input and output voltage components to selected voltage levels used by the controller, and a current regulation unit for filtering the input and output current components. The current regulation unit may include a low pass filter for filtering the input and output current components.

[0011] According to yet another aspect, a system may include a signal conditioner for conditioning an input power signal and an output power signal to generate a conditioned power signal, a clock selection unit coupled to the controller and the plurality of power converters for varying a frequency of one or more of the plurality of power converters, and a comparison unit coupled to the controller and the selection unit. The controller generates a first output control signal, and the comparison unit receives the conditioned output power signal and the first output control signal and responsively generates an output comparison signal. In particular, the comparison unit receives the conditioned output power signal and the first output control signal and responsively generates an output comparison signal when a value of the conditioned output power signal is greater than a value of the first output control signal.

[0012] Further, the output comparison signal is sent to a clock selection unit, which then sends an output signal to the multiple power converters, and in response to the output signal from the clock selection unit, the stored power of one or more capacitors of the power converters in the off state is sent to a common output power line. The clock selection unit includes one or more clock generators for generating frequencies and a selector for selecting a frequency.

[0013] The present invention also relates to a method for controlling a plurality of power converters in a power system, the method including providing a plurality of power converters forming an array for converting power from a first power level to a second power level; providing a controller coupled to the plurality of power converters for controlling a power output of the plurality of power converters; sensing an input power on the input power line by an input sensing circuit coupled to the controller and to the input power line and sending an input power signal to the controller; sensing an output power on the output power line by an output sensing circuit coupled to the controller and to the output power line and sending an output power signal to the controller; and controlling each of the plurality of power converters to switch to an on state or an off state as a function of the sensed input power and the sensed output power, thereby operating one or more of the plurality of power converters in an on state within an optimum power efficiency range.

[0014] The power converter preferably includes a switched capacitor type DC-DC step-down power converter for converting power from a first power level to a second power level, the second power level being lower than the first power level.

[0015] According to another aspect, the method includes calculating power of one or more of a plurality of power converters and, based on the power of the one or more power converters, accessing a lookup table and determining from the lookup table which of the plurality of power converters a controller should place in an on and off state.

[0016] The controller may include a memory unit for storing instructions for controlling the multiple power converters, a signal conditioner for conditioning the input power signal and the output power signal to generate a regulated output power signal, an AC-DC converter for converting the regulated output power signal to a DC regulated output power signal, and a processor for processing the DC regulated output power signal and generating a controller output signal for controlling one or more of the multiple power converters based on the stored instructions to place the multiple power converters in on and off states.

[0017] According to another aspect, the regulated output power signal includes a regulated output voltage component and a regulated output current component, and the processor includes a filter unit for averaging the regulated output power component and the regulated output current component of the regulated output power signal, a power calculation unit for calculating power of one or more of the multiple power converters based on the average of the regulated output power component and the regulated output current component to generate a power calculation output signal, a hysteresis unit for reducing noise in the power calculation output signal, and a look-up table for storing information related to multiple power levels of at least one power converter of the multiple power converters corresponding to a power converter to be in an on state or an off state. The controller generates one or more output control signals for placing one or more of the multiple power converters in an on state and an off state based on the look-up table.

[0018] According to another aspect of the method of the present invention, the system is configured to adjust the input power signal and the output power signal to generate a regulated output power signal, vary the frequency of one or more of the multiple power converters, compare a value of a control signal generated by the controller to a value of the regulated output power signal, generate a comparison signal if the value of the regulated output power signal is greater than the value of the control signal, and further configured to send stored power in capacitors of one or more of the off-state power converters to an output power line in response to the comparison signal.

[0019] The control device generates a first output control signal, and the method further includes adjusting the input power signal and the output power signal by a signal conditioner to generate a regulated output power signal, varying a frequency of one or more of the plurality of power converters by a clock selection unit, comparing the regulated output power signal with the first output control signal by a comparison unit, and generating an output comparison signal in response if a value of the regulated output power signal is greater than a value of the first output control signal.

[0020] The method further includes transmitting the output comparison signal to a clock selection unit which then transmits output signals to the plurality of power converters, and delivering stored power in the one or more capacitors of each of the plurality of power converters in the off state to an output power line in response to the output signal from the clock selection unit. The clock selection unit includes one or more clock generators for generating frequencies and a selector for selecting a frequency. [Brief description of the drawings]

[0021] These and other features and advantages of the present invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which like reference characters refer to like elements throughout the different drawings, the drawings illustrate the principles of the invention and, although not to scale, show relative dimensions. [Figure 1]FIG. 1 is a simplified circuit diagram of a power conversion system for supplying power to a load from an array of power converters in accordance with the teachings of the present invention. [Diagram 2] FIG. 2 is a simplified block diagram of the power converter of FIG. 1 in accordance with the teachings of the present invention. [Diagram 3] FIG. 3 is a simplified block diagram of the controller of FIG. 1 in accordance with the teachings of the present invention. [Figure 4] FIG. 4 is a simplified block diagram of the signal conditioner of FIG. 3 in accordance with the teachings of the present invention. [Diagram 5] FIG. 5 is a graphical illustration of a power efficiency curve for the power converter of FIG. 1 in accordance with the teachings of the present invention. [Figure 6] FIG. 6 is a second embodiment of the power conversion system of the present invention employing an optional comparison unit and an optional selection unit. [Figure 7] FIG. 7 is a simplified block diagram of the selection unit of FIG. 6 in accordance with the teachings of the present invention. [Figure 8] FIG. 8 is a graphical illustration of power efficiency curves for the power converter of FIG. 1 operating at various frequencies in accordance with the teachings of the present invention. [Figure 9] FIG. 9 is a simplified flow diagram illustrating steps in operating the power conversion system of FIGS. 1 and 6 in accordance with the teachings of the present invention. [Figure 10] FIG. 10 is a graphical illustration of power efficiency curves for the power converter of FIG. 1 with adaptive dynamic efficiency optimization (ADEO) techniques in accordance with the teachings of the present invention and for a system where ADEO is not employed, as well as a conventional magnetic power converter. [Figure 11] FIG. 11 is a simplified flow diagram illustrating steps in varying the operating frequency of one or more of the power converters of the power conversion systems of FIGS. 1 and 6 in accordance with the teachings of the present invention. [Figure 12] FIG. 12 is a simplified flow diagram illustrating the steps involved in employing the instantaneous limited reserve (ILR) feature of the power conversion system of FIGS. 1 and 6 in accordance with the teachings of the present invention. [Figure 13] FIG. 13 is an exemplary look-up table suitable for use in the power conversion system of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Detailed Description of the Invention The term "power converter" as used in this disclosure is intended to include any type of converter capable of converting power or related power components, including voltage and current, from one level to another. Power converters can include magnetic or inductive converters and non-magnetic converters, such as switched capacitor power converters. Additionally, power converters contemplated in this disclosure can include DC-DC converters, DC-AC converters, and AC-DC converters, and can also include step-up and step-down power converters. DC-DC converters can also include conventional inductor-based DC-DC converters, such as buck or boost converters, as are known in the art of DC-DC converters.

[0023] Switched capacitor power converters tend to reach the peak or near-peak efficiency of the load curve more quickly and maintain the efficiency closer to the peak of the load curve for a longer period of time than magnetic power converters. However, switched capacitor power converters tend to have a decrease in power efficiency before and after reaching the peak efficiency. That is, while switched capacitor power converters can maintain the efficiency close to the peak efficiency over a wider operating range, they have a clear efficiency curve with the efficiency peak at some point in the rated load range and the efficiency decreasing as the load moves away from the peak efficiency point. The inventors of the present invention have realized that there is an optimum efficiency and a power range within which the power converter should be operated.

[0024] The term "electrical power" as used in this disclosure may refer to voltage, current, or known electrical power, which corresponds to a current passed through an electrical potential (VI) and expressed in watts.

[0025] The present invention relates to a power conversion system 10 as shown in FIG. The illustrated power conversion system 10 includes a plurality of power converters, preferably switched capacitor type power converters 12a, 12b and 12n, which are coupled to a common input power line 14 and a common output power line 16 to form a power converter array 20. Those skilled in the art will readily appreciate that any number of power converters may form part of the power converter array 20 based on the overall power requirements of the system 10 and a load 26. The power converters 12a-12n are coupled to the common output power line 16 and are arranged in a parallel electrical configuration with one another. An input sense circuit 22 is coupled to the input power line 14 and an output sense circuit 24 is coupled to the output power line 16. An external load 26 is coupled to the output power line 16. A controller 30 is coupled to the input sense circuit 22, the output sense circuit 24 and the power converters 12a-12n.

[0026] The power converters are preferably step-down power converters, but may be step-up power converters if desired. The power converters 12a, 12b, and 12n are configured to convert a first input voltage Vin provided on the input power line 14 to a second, lower voltage Vout provided on the output power line 16. The input sense circuit 22 senses the input voltage and input current levels provided on the input power line 14 and provides these power measurements to the controller 30. Similarly, the output sense circuit 24 senses the output current and output voltage levels provided on the output power line 16 and also provides these power measurements to the controller 30. The input sense circuit 22 and the output sense circuit 24 thus include suitable and known voltage and current sensors or detectors for measuring or sensing the voltages and currents on the input power line 14 and the output power line 16. The controller 30 processes the input voltage and current data from the sense circuits 22, 24 to calculate the instantaneous power of the system and provides control signals to the power converters 12a, 12b, 12n to control or regulate the power converters. A load 26 is coupled to the output power line 16 and corresponds to any load in the system 10. A load may be, for example, any type of resource, hardware, or device that requires power to operate.

[0027] The illustrated power converters 12a, 12b, and 12n may be any type of power converter, preferably including switched-capacitor power converters. Furthermore, the power converters may be DC-DC, DC-AC, or AC-DC converters, preferably including DC-DC converters. An example of a type of switched-capacitor power converter suitable for use in the power conversion system 10 of the present invention includes the MxC200 DC-DC power converter manufactured by Helix Semiconductor, USA. FIG. 2 illustrates a simplified example of a power converter suitable for use as part of the power converter array 20. The illustrated power converter 12a may include selected power conversion circuitry (not shown) in addition to one or more capacitors. The capacitors may be integrated within the power converter or associated with the power converter, such as, for example, flying capacitors. In one embodiment, the power converter may include a series of capacitors 36a, 36b, and 36c arranged in any suitable electrical configuration based on the level or magnitude of the step-down voltage the converter is designed to achieve. In one embodiment, the capacitors may be capacitors having a MuxCapacitor® topology manufactured by Helix Semiconductor. Thus, the capacitors may be electrically connected in a parallel configuration, a series configuration, a parallel-series configuration, or preferably in the illustrated series-parallel configuration. In the present example, muxcapacitors 36a, 36b, 36c may each be designed to have a selected gain, such as a gain of 0.5, but may be designed to have any selected gain characteristic. The muxcapacitors are included in the MxC200 power converter sold by Helix Semiconductor. In the illustrated example, muxcapacitor 36a is coupled in series with muxcapacitors 36b and 36c, which are connected in parallel. Continuing with this example, for example, if the input voltage is 48V, the output of muxcapacitor 36a is 24V at branch 38, and this voltage level is provided to muxcapacitors 36b and 36c, which are connected in parallel.The muxcapacitors 36b, 36c further step down the voltage from the intermediate voltage of 24V to an output voltage of 12V. Those skilled in the art will readily appreciate that the voltage converter can be configured in any selected manner, and that FIG. 2 illustrates the step-down operating characteristics of the converter for simplicity. Additionally, the capacitors and / or muxcapacitors can be connected in any suitable configuration depending on the desired output voltage. A common input power line 14 may provide the necessary operating power to the power converter. The muxcapacitors are configured to store power therein.

[0028] The illustrated power conversion system 10 may have any suitable number of power converters depending on the type of load 26 to be powered. For example, a relatively large power conversion system may have as many as 1000 power converters, while a relatively small power conversion system may have only five power converters. In one embodiment, the present invention contemplates arranging a suitable array 20 of power converters to form a 1 kW or greater power system. In particular, a plurality of power converters may be connected as a power converter array 20 to generate 1000 W of power converted from 48 Vdc to 12 Vdc. For example, each of the power converters 12a, 12b, 12n in the illustrated array may be designed to reach peak efficiency at a selected power level, such as, for example, from about 2.0 W to about 6.0 W of power, with each converter having a power capacity of about 15 W.

[0029] The illustrated controller 30 is intended to control the power converters 12a-12n of the power converter array 20 to enable or turn on an appropriate number of power converters in response to the power requirements of the load 26. The controller 30 is adapted or configured to control and turn on or enable an appropriate number of power converters while maintaining or achieving near peak power efficiency of the power converters of the power conversion system 10.

[0030] 3 and 4 illustrate details of the controller 30 and associated system components. The controller 30 includes a signal conditioning unit 50 for conditioning the input power signal 42 generated by the input sense circuit 22 and the output power signal 44 generated by the output sense circuit 24. The sense circuits 22 and 24 sense the input and output voltages and currents on the power lines 14 and 16, respectively, and generate the output power signals in response thereto. In particular, the voltage components (e.g., sensed voltages) of the input power signal 42 and the output power signal 44 are provided to a voltage conditioning unit, which may include a voltage scaling and buffering unit 52, where the voltages are scaled and conditioned to remove any unwanted noise in the power signals and to scale the voltages to voltage levels suitable for use by the system components. A suitable voltage range may be within the range of about 0.0V to about 3.3V. Similarly, the current components (e.g., sensed currents) of the power signals of the input power signal 42 and the output power signal 44 are provided to a current conditioning unit, such as a current sense gain and filtering unit 54, where the current is sensed and filtered suitable for use by an analog-to-digital (AD) converter 60. The current sense gain and filtering unit 54 converts the input current signal using a suitable current sense resistor to output a signal that requires amplification (i.e., gain) and filtering suitable for use by the AD converter 60. The filtering portion of the current sense gain and filtering unit 54 removes signal noise before amplification using a suitable filter, such as, for example, a low pass filter. For example, the current sense gain and filtering unit 54 may use a Butterworth low pass filter to filter the current signal, although other types of filters may be used.

[0031] The controller 30 further includes an analog-to-digital converter 60 that receives output power signals 59 from the signal conditioner 50, including output signals 56, 58 from the voltage scaling and buffering unit 52 and the current sense gain and filtering unit 54, respectively, and converts these analog output signals to digital output signals 62. The converted output signals 62 are introduced to a processor or processing unit 70. The processor 70 is configured to communicate with one or more memory units 72 and a digital-to-analog (DA) converter 74. The processor 70 may include any suitable logic circuitry that is responsive to and processes instructions from the memory unit 72. In one embodiment, the processor 70 may be provided by a commercially available or custom designed microprocessor unit. The processor 70 may utilize instruction level parallelism, thread level parallelism, various cache levels, and / or multi-core processors. The memory unit 72 is configured to store data and enable access to any memory location by the processor 70. The memory unit 72 may store software, signal information, and other executable instructions used by the processor 70. The memory 72 may be a single memory module, or may be implemented as a series of memory modules located within the controller or throughout the system 10, or as part of a hardware or network in communication with the power conversion system 10.The memory 72 may be any suitable type of memory, including volatile and / or non-volatile memory, examples of which include dynamic random access memory (DRAM) or static random access memory (SRAM), burst SRAM or synchronous burst SRAM (BSRAM), fast page mode DRAM (FPM DRAM), enhanced DRAM (EDRAM), extended data output RAM (EDO RAM), extended data output DRAM (EDO DRAM), burst extended data output DRAM (BEDO DRAM), single data rate synchronous DRAM (SDR SDRAM), double data rate SDRAM (DDR SDRAM), direct Rambus DRAM (DRDRAM), or extreme data rate DRAM (XDR SDRAM). DRAM), non-volatile read access memory (NVRAM), flash memory non-volatile static RAM (nvSRAM), ferroelectric RAM (FeRAM), magnetoresistive RAM (MRAM), phase change memory (PRAM), conductive bridge RAM (CBRAM), Silicon-Oxide-Nitride-Oxide Silicon (SONOS), resistive memory (RRAM), racetrack, Nano-RAM (NRAM) or Millipede memory, including any variation. The memory unit 72 can also include, without limitation, RAM, ROM, EPROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage, or any other non-transmission medium usable to store information accessed by a computing device. In contrast, a communication medium may embody computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism. "Computer-readable storage media" as defined in this disclosure does not include communication media. Accordingly, computer storage or memory media should not be construed as propagating signals per se, nor should they be referred to as being transitory in nature.Although the propagated signals may reside in a computer storage medium, the propagated signals themselves are not an example of computer storage media that is intended to be non-transitory. Although the memory unit 72 is illustrated within the controller 30, it will be understood that the memory unit may be distributed or located remotely and accessed via a network or other communications link. The processor 70 may communicate with the memory unit 72 via any suitable bus system.

[0032] The illustrated processor 70 may include a filter unit 80 for averaging the power components (i.e., current and voltage) of the converted power signal 62 received from the A / D converter 60. The filtered output signal 82 is then conveyed to a power calculation unit 84 configured to calculate the power and, if desired, the power efficiency of the multiple power converters or of the power conversion system 10 based on the voltage and current components of the power signal. The power calculation unit 84 generates a power calculation output signal 86 that is introduced to a hysteresis unit 88. The hysteresis unit 88 reduces chatter or noise in the output signal 90 that may adversely affect any clock signaling occurring downstream in the system 10 by setting a switching or threshold level in a selected direction at a different level than the threshold level in the opposite direction. The hysteresis unit serves to prevent the controller from rapidly turning on and off the power converter (i.e., chattering) when the measured power level is at or near the converter switching level (e.g., 3.90 W in FIG. 13). The hysteresis unit 88 is applied after the power is calculated by the power calculation unit 84, and the hysteresis unit does not send an output signal 90 to a look-up table (LUT) 92 unless the calculated power has changed by more than the hysteresis amount compared to the previous power calculation. The controller uses the LUT 92 to quickly determine the correct power configuration for the power conversion system 10. In particular, the look-up table determines the appropriate number of power converters 12a-12n of the power converter array 20 to operate to meet the power requirements of the load 26 while operating the power converters 12a-12n within a selected optimum power efficiency range. The LUT 92 may be a multi-dimensional table that correlates various total power levels required by the load with a corresponding number of power converters to operate. An example of a simplified version of the look-up table 92 suitable for use in the present invention is shown in FIG. 13. The illustrated exemplary look-up table 92 is for a two-dimensional look-up table for a power converter system with a total power rating of approximately 20 W.The 20 W power converter system may be comprised of six power converters 12a-12n that may be mounted in any selected manner, such as across two separate circuit boards 194 and 196, with each circuit board 194, 196 containing three of the power converters. In the illustrated exemplary table, the input variable is the measured power 192 and the output is a control signal generated by the controller 30 and sent to each circuit board, which controls how many power converters to turn on and operate at the high speed clock frequency as determined by the selection unit 110 shown in Figures 6 and 7. The illustrated lookup table 92 contains a series of measured power metrics within the 20 W power range of the system. As shown, if a board has a setting of 0, all power converters associated with it will operate at the slow clock frequency and therefore be turned off or disabled, and if the setting is 1, at least one of the power converters will be turned on and operate at the fast clock frequency while the other two power converters operate at the slow clock frequency and are turned off. Lookup table 92 indicates that if the power system level is less than 3.9W, all six power converters will be turned off and operate at the slow clock frequency. As power increases, the power converters of the first circuit board are switched on one at a time. For example, if the power level is between 3.91 and 6.5W, the first power converter will be turned on, the second power converter will be turned on at a power level between 6.51 and 9.1W, and the third power converter will be turned on at a power level between 9.11 and 12.7W. During this time, all power converters of the second circuit board will be turned off and operate at the slow clock frequency. At power levels above 12.71, in addition to the power converters on the first circuit board, the power converters on the second circuit board are also turned on one at a time as the power increases. The power converters are preferably switched on while other power converters are turned on, operating within their respective optimum power efficiency ranges.That is, the controller 30 keeps the power converters on when operating within an optimal power efficiency range and turns on the additional power converters when the load requires additional power and the on power converters are operating outside of the optimal power efficiency range. Those skilled in the art will readily appreciate that the look-up table 92 may have any suitable format or configuration based on the total power of the system, the number of power converters used, and the number of circuit boards or blades used to electrically mount the power converters. The processor 70 may also include a universal asynchronous receiver-transmitter (UART) device 98 for receiving instructions from a user according to any suitable communication method, such as via a serial interface (e.g., Universal Serial Bus (USB)). Those skilled in the art will readily appreciate that the processor 70 may include or perform the functionality of any of the components of the controller 30 shown, and that the configuration shown in FIG. 3 is merely one example of a suitable configuration.

[0033] The controller generates a pair of output signals based on information stored in a look-up table (LUT) 92, of which output signal 94 is sent to a selection unit 110 for adjusting a frequency, such as a clock frequency, of one or more of the power converters 12a-12n, and output signal 96 is provided to a digital-to-analog (DA) converter 74 where it is converted from a digital signal to an analog signal and then sent to a comparison unit 120 for addressing load power conditions requiring a fast response time. Those skilled in the art will readily appreciate that the controller may generate a single output signal rather than multiple output signals, in series rather than in parallel as shown.

[0034] In this embodiment, the illustrated power converters 12a-12n have an operating power load range of about 0 W to about 15 W, and the power converters are configured to reach near a peak operating power efficiency of about 97% at a rated load power of about 2.6 W. As shown in FIG. 5, each of the power converters 12a-12n has a power efficiency characteristic versus load current of the converter turned on, which is plotted corresponding to the power required by the load. As shown in the graph 100, each power converter is capable of achieving a peak power efficiency when providing a relatively low load current to the load 26. The power converters can achieve a peak power efficiency of about 97% at a load current of about 0.25-0.30 amps, which is equivalent to a rated load power of about 2.6 W. It is also shown that each power converter is capable of maintaining a power efficiency of greater than 90% over substantially the entire rated power range of the converter. As used in this disclosure, an "optimum power efficiency range" is intended to mean a converter power efficiency and / or system power efficiency of greater than about 90%, preferably greater than about 95%. The above ranges also contemplate operating each of the power converters 12a-12n such that the power of each converter is within the range of about 2.0W to about 6.0W, preferably about 2.5W to about 5.0W. The power levels can be readily correlated to the load current levels shown in the graphs of Figures 5, 8 and 10 in accordance with known electrical conversion techniques. Those skilled in the art will readily appreciate that depending on the type of power converter used in the array 20, the power converter may be operated outside of its optimum power efficiency range. When so operated, the power converter sacrifices efficiency for density (e.g., more watts per cubic centimeter) and therefore higher power per power converter.

[0035] The power conversion system 10 of the present invention may include a clock selection unit 110 and an optional comparison unit 120, as shown in Figures 6 and 7. Like reference numerals refer to like elements throughout the various figures unless otherwise specified. The clock selection unit 110 is configured to receive the output signal 94 generated by the controller 30 and select one or more parameters of the power conversion system, such as an operating frequency of one or more of the power converters 12a-12n in the power converter array 20. The clock selection unit 110 allows a system or user to select or optimize the number of power converters 12a-12n that operate at a selected frequency. In one embodiment, the clock selection unit 110 may be configured to select an operating clock frequency of one or more of the power converters 12a-12n by selecting an initial or first clock frequency that enables or turns on the power converters and a second, lower clock frequency that disables or turns off the power converters. In this manner, the controller 30, via the clock selection unit 110, may turn on and off the selected power converters 12a-12n during use. Depending on the size of the initial load 26, the controller 30 determines an appropriate number of power converters to operate based on the information stored in the LUT 92 to accommodate the power requirements of the load 26 while operating the power converters 12a-12n within an optimal power efficiency range. The processor 70 of the controller 30 determines the number of power converters to turn on or enable by accessing the LUT 92. As shown in FIG. 7, the clock selection unit 110 may include a clock generator 112 and a selector 114. The clock generator 112 generates a clock frequency signal that is sent to the selector 114. The selector 114 also receives the output signal 94 from the controller 30. The illustrated clock generator 112 may be located in the clock selection unit or may be located elsewhere in the system, such as in the power converter array 20.The clock selection unit may use a single clock generator for generating a first or higher frequency (e.g., 200 kHz) that can be reduced by the clock selection unit to a second lower frequency (e.g., 100 kHz) if desired. Alternatively, the clock generator 112 may include multiple clock generators for generating separate clock signals at different frequencies (e.g., 100 kHz and 200 kHz). In one embodiment, the clock selection unit 110, in cooperation with the controller 30, may set the clock frequency of one or more power converters to an enabled or on clock frequency and set the clock frequency of the remaining power converters to a second lower disabled or off clock frequency (e.g., an off mode or a standby mode, etc.). Those skilled in the art will readily appreciate that the clock frequency can be set to any selected frequency range depending on the type of power converter used in the system, the configuration of the power conversion system 10, and the size of the load 26. In one embodiment, the clock frequency may be in the range of about 0 kHz to about 250 kHz. More specifically, the on-clock frequency may be about 100 kHz or about 200 kHz, and the off-clock frequency may be about 50 kHz. The off-clock frequency also allows the capacitors 36a-36c in the power converters 12a-12n to remain charged even when the power converters are turned off. Furthermore, the on-clock frequency is sufficient to effectively achieve optimal or maximum efficiency of the power converter for a given load 26. The selection unit 110 may use any suitable electronic circuitry to assist in receiving the output signal from the controller 30 and to perform the appropriate frequency selection, and may include one or more of a multiplexer, a comparator, an FPGA, and the like. The operational characteristics of these components are well known in the art.

[0036] FIG. 8 shows two exemplary clock frequencies suitable for turning on the power converters 12a-12n. Graph 130 shows power converter power efficiency curves versus load current per operating power converter required by load 26 for clock frequencies of 100 kHz and 200 kHz. Graph 132 for the 100 kHz frequency shows that the power converter operating at this frequency achieves peak or optimum power efficiency at a lower required load current. Graph 134 for the 200 kHz frequency shows that the power converter achieves peak or optimum power efficiency at a higher required load current, but maintains higher power efficiency over a wider range of load currents. Thus, the power conversion system 10 can select either the 100 kHz or 200 kHz frequency at which to turn on the power converters, both depending on the type of power converter used in the system and the size of the load 26. In one example of operation, the selection unit 110 may select the frequency of the power converters as 100 kHz when the load current per power converter is between about 0.0 A and about 0.5 A, and then switch the frequency to a higher 200 kHz when the load current per power converter is between about 0.5 A and about 1.5 A. In this example, the controller 30 controls or operates the power converters at the lower frequency of 100 kHz until all power converters are turned on and a required load current per power converter of about 0.5 A is reached. Once this is achieved, the controller 30 increases the frequency to 200 kHz via the selection unit 110 as the load current per power converter rises above the 0.5 A level. Thus, the controller 30 can dynamically vary the operating frequency of the power converters as a function of the load 26, using lower frequencies for relatively light loads and higher frequencies for relatively heavy loads, thereby operating the power converters within an optimum power efficiency range. The frequency ranges and selections may be stored in memory 72 of the system 10 or controller 30, and the controller 30 may implement the appropriate clock frequency based on instructions stored therein.

[0037] The power conversion system 10 of the present invention may also employ an optional comparison unit 120 that functions as an instantaneous response or limited reserve (ILR) circuit to temporarily and nearly instantaneously provide power to the load 26 when the load demands a relatively sudden increase in power such that the normal duty cycle of the controller is too slow or delayed to properly turn on the power converters to provide power to the load 26. As shown, the comparison unit 120 receives an instantaneous power signal 59 from the controller 30 that provides information regarding the instantaneous current and voltage demands of the load 26 and information regarding the input power. The comparison unit 120 also receives an output signal 96 from the controller 30 that serves as a power threshold signal for the comparison unit. The comparison unit 120 compares the instantaneous power signal 59 to the threshold output signal 96, and if the value of the power signal 59 is greater than the value of the output signal 96, the system 10 bypasses the controller 30 and transmits a signal via the selection unit 110 to the power converter array 20 to provide instantaneous power from the power converter array 20 to the load 26. As shown in Figures 3 and 6, the instantaneous power signal 59 is generated before being provided to the processor 70 of the controller 30. The signal 96 is therefore time delayed due to various processing occurring within the processor 70 and external to the processor, such as the filter 80, the power calculation unit 84, the hysteresis unit 88 and the LUT 92. If the instantaneous power signal 59 is greater than the threshold power level provided by the output signal 96 and determined by the controller 30, the power conversion system 10 requires that additional power be provided by the power converter array 20 to the load 26. However, in some cases, this power must be provided to the load 26 sooner than the controller 30 can provide instructions to the power converter array 20 to turn on the additional power converters to provide the required power to the load. Thus, the comparison unit 120 bypasses the controller 30 to generate an output signal 122, which is sent to the selection unit 110, which then sends the output signal 116 to the power converter array 20. When the output signal 116 is received by the power converter array 20, the power converters in the off state supply stored or reserve energy directly to the load 26 from their internal capacitors 36a-36c.While the quick response energy from the power converter array temporarily provides additional power to the load 26, the controller 30 processes the input information from the system 10 to determine the appropriate number of power converters to switch on to provide the load 26 with a sustained, more durable source of power that meets the current load power demands. In one embodiment, the controller 30 may switch on all of the power converters 12a-12n in the array 20 to provide power to the load 26 and then determine the appropriate number of power converters to switch off based on the real-time load power demands. The comparison unit 120 may use any suitable type of electronic components to perform the comparison operation, which may include, for example, comparators, multipliers, etc., and may be implemented using analog components, digital components, or a combination of both.

[0038] The power conversion system 10 of the present invention is scalable to high power and voltage levels (e.g., greater than 1 kW). The power converter array 20 converts the input power to relatively lower power levels with relatively high power efficiency (at or near 97%). The power conversion system 10 further employs a power converter array 20 that achieves high power density by eliminating inductive devices, including bulky and inefficient transformers.

[0039] In operation, input power is provided from a suitable power source (not shown) to the power line 14 and thus to the converter array 20 and the power converters 12a-12n forming the array. The power converters are preferably DC-DC converters which step down or reduce the voltage on the output power line 16 from an input level (e.g. 48V) to a suitable output level (e.g. 12V). Output power is provided to a load 26. An input sense circuit 22 measures, senses or detects the input voltage and current using known detectors, and an output sense circuit measures, senses or detects the output voltage and current using known detectors. The input and output power information generated by the sense circuits 22, 24 is provided to a controller 30.

[0040] When the power conversion system 10 transitions from a no load (0.0 W) state or condition and then begins to increase the power delivered to the load 26, the system first turns on or enables the power converter 12a. The first power converter 12a reaches a peak or optimum efficiency of about 97% at about 2.6 W and maintains power efficiency near this level up to about 6.0 W. Thus, the optimum efficiency power range for operating the power converters is about 2.5 W to about 6.0 W for each power converter. The first or initial power converter 12a can also accommodate powers greater than 6.0 W, but then the power converters will no longer operate within the optimum power efficiency range. When the power delivered by the power converters reaches a predetermined power level (e.g., about 5.0 W), the controller 30 turns on or enables the second power converter 12b to share the power load and deliver power to the load 26. Power conversion system 10 turns on an appropriate number of power converters 12a-12n so that each power converter operates within its optimum power range and therefore at peak or near-peak efficiency.

[0041] FIG. 9 is a schematic flow diagram illustrating at least a portion of the method of the present invention. The power conversion system 10 senses the input and output voltages and currents (e.g., power) using the input sense circuit 22 and the output sense circuit 24 at step 140. The current and voltage information is provided to the controller 30. The controller 30 then monitors and calculates the power requirements of the load 26 via the output current and voltage sensed by the output sense circuit 24 at step 142. The controller then enables or turns on one or more of the power converters 12a-12n of the power converter array 20 to provide the required power to the load 26 at step 144. The controller 30 also determines the operating frequency of the power converters via the controller 30 and the selection unit 110 as shown in FIG. 6. The controller 30 then determines whether the power converters 12a-12n are operating within an optimal power efficiency range at step 146 by monitoring the power of each power converter. If the power converters are not operating within the optimum power efficiency range, the controller controls the number of power converters to be operated at step 148. For example, if the power is above the optimum power efficiency range, the controller turns on a selected number of additional power converters. If the power of each power converter is below the optimum power efficiency range, the controller turns off a selected number of power converters. If the power converters are operating within the optimum power efficiency range, the controller 30 maintains the number of power converters operating at step 150. The illustrated process may be repeated one converter at a time until the maximum number of converters in the array 20 is in operation. Using the adaptive dynamic efficiency optimization (ADEO) technique of the present invention, all power converters after the second converter operate within the optimum power efficiency range. This approach eliminates the traditional efficiency curve of the power converter and allows the power conversion system 10 to operate at peak or very close to peak efficiency at any point within the rated load range above 2.6 W, which is approximately 0.26% of the rated load for a 1 kW design.

[0042] As shown in FIG. 10, the power efficiency curve of the system 10 of the present invention is compared with the power efficiency curve of a conventional magnetic or inductive power converter system and the power efficiency curve of the system 10 when the power converter is operated without the adaptive dynamic efficiency optimization of the present invention. The power efficiency curve 160 of the present invention when operated under the adaptive dynamic efficiency optimization method implemented and controlled by the controller 30 can reach a peak or near peak operating efficiency of about 97% at less than about 1% of the rated power load. When the power converters 12a-12n are switched off and on by the controller 30 to maintain them within their respective optimal power efficiency ranges, the power efficiency curve 160 is maintained within the optimal power efficiency range. In contrast, the power efficiency curve of the system 10 when operated without ADEO shows that the system 10 does not reach the peak efficiency level of the system 10 with ADEO, but does reach the peak power efficiency level at a higher load current level. Power efficiency curve 168, which represents a power conversion system using a magnetic power converter without the ADEO of the present invention, also shows that the system reaches a lower level of peak efficiency at higher load currents than the other systems.

[0043] Optionally, the power conversion system 10 of the present invention may select or vary the operating frequency of each power converter during use. As shown in FIG. 11, the system 10 may determine the size of the load by monitoring the power requirements of the load 26 using the output sense circuit 24 in a first step 170. The controller 30 may determine the power requirements of the power converter array 20 by referencing a power table stored in the LUT 92. The controller may select an appropriate clock frequency for operating the power converters in step 172 based on the stored instructions. The system may then monitor the current required by the load to ascertain its power requirements, and based on this information, the controller may determine in step 174 whether the load current is below a selected threshold level (e.g., 0.5 A). If the load current is below the threshold level, the system may maintain the current frequency of the power converters 12a-12n (e.g., 100 kHz). If the load current is above the threshold level, the controller 30 may adjust or change the frequency level of the power converter (eg, to 200 kHz) at step 176 .

[0044] The instantaneous limited reserve (ILR) characteristics of the power conversion system 10 of the present invention are shown, for example, in Figures 6 and 12. The system 10, via the input sense circuit 22, the output sense circuit 24, and the controller 30, calculates the instantaneous power of the input power line 14 and the output power line 16, in step 180. The controller 30 then calculates the power requirement of the load, in step 182, and sends a control signal to the power converter array 20 to supply power to the load. The comparison unit 120 may then compare the instantaneous power signal 59, and any value related thereto, if desired, to the power control signal 96 generated by the controller 30, in step 184. The power control signal 96 serves as a threshold for the comparison unit 120. The comparison unit 120 then determines, in step 186, whether the instantaneous power value of the signal 59 is greater than the threshold 96. If the instantaneous power value is less than or equal to the threshold, the system continues to monitor and determine the instantaneous power value. On the other hand, if the instantaneous power value 59 is greater than the threshold 96, then at step 188 the comparison unit 120 generates an output signal 122 which is sent to the selection unit 110 which sends a signal to the power converter array 20, bypassing the controller 30, instructing the power converters in the off state or off mode to release their stored power to the output power line 16. The instantaneous power is delivered to the load 126, providing an initial power boost while the controller determines the appropriate number of power converters 12a-12n to turn on.

[0045] It will therefore be apparent from these descriptions that the present invention effectively attains the objects set forth above. Although several modifications may be made in the above configuration without departing from the scope of the present invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

[0046] It is also understood that the following claims encompass all of the general and specific features of the invention described in this disclosure, and all language within the scope of the invention is intended to be included therein as a matter of language.

[0047] Having described the invention, what is believed to be new and what is claimed for protection by Letters Patent is as follows:

Claims

1. 1. A system for controlling a plurality of power converters in a power system, comprising: a plurality of switched capacitor power converters forming an array for converting power between a first power level and a second power level, the plurality of switched capacitor power converters being arranged in parallel with one another, each switched capacitor power converter including a plurality of capacitors for storing power; a common input power line input-side coupled to a plurality of said switched-capacitor power converters for providing input power at said first power level; a common output power line coupled at an output side to a plurality of said switched capacitor power converters for supplying output power to a load at said second power level; a controller coupled to a plurality of the switched capacitor power converters for controlling a power output of the switched capacitor power converters; an input sense circuit coupled to the common input power line and to the controller for sensing the input power on the common input power line and transmitting an input power signal to the controller; an output sense circuit coupled to the common output power line and to the controller for sensing the output power on the common output power line and transmitting an output power signal to the controller; a signal conditioner for conditioning the input power signal and the output power signal to generate a conditioned output power signal; a clock selection unit coupled to the controller and to a plurality of the switched capacitor power converters; a comparison unit coupled to the controller and the clock selection unit; The comparison unit is comparing a first output control signal generated by the controller with the regulated output power signal to generate an output comparison signal; configured to transmit the output comparison signal to the clock selection unit; the clock selection unit is configured to send an output signal to one or more of the plurality of switched capacitor power converters in response to the output comparison signal; the controller is configured to control each of the plurality of switched-capacitor power converters to switch each of the plurality of switched-capacitor power converters to an on state or an off state as a function of the sensed input power and the sensed output power, thereby operating one or more of the plurality of switched-capacitor power converters in the on state within an optimum power efficiency range; A system in which one or more of the switched capacitor power converters in the off state deliver power stored in one or more of the capacitors to the common output power line in response to the output signal from the clock selection unit.

2. 2. The system of claim 1, wherein each of the plurality of switched-capacitor power converters comprises a switched-capacitor DC-DC step-down power converter for converting the power from the first power level to the second power level, the second power level being lower than the first power level.

3. The system of claim 1 , wherein each of the plurality of switched-capacitor power converters comprises a DC-DC power converter, a DC-AC power converter, or an AC-DC power converter.

4. The system of claim 1 , wherein a plurality of the capacitors are electrically connected in a parallel configuration, a series configuration, a parallel-series configuration, or a series-parallel configuration.

5. The control device includes: A processor; A lookup table; When received by the processor, to the processor, Calculating the power of one or more of the plurality of switched capacitor power converters; accessing the lookup table based on the power of one or more of the switched capacitor power converters, and determining from the lookup table which of the plurality of switched capacitor power converters the controller should place in the on state and the off state; and a memory for storing instructions to instruct the system to:

6. The control device includes: a memory unit for storing instructions for controlling a plurality of said switched capacitor power converters; an analog-to-digital (A-D) converter for converting the regulated output power signal into a digital regulated output power signal; 2. The system of claim 1, further comprising: a processor for processing the digitally regulated output power signal and generating output control signals for controlling one or more of the switched capacitor power converters to the on and off states based on the stored instructions.

7. The digital regulated output power signal includes a regulated output voltage component and a regulated output current component, the processor: a filter for averaging the regulated output voltage component and the regulated output current component of the digital regulated output power signal; a power calculation unit for calculating power of one or more of the plurality of switched-capacitor power converters based on an average of the regulated output voltage component and the regulated output current component to generate a power calculation output signal; a hysteresis unit for reducing noise in the power calculation output signal; a look-up table for storing information relating to a plurality of power levels of at least one of the plurality of switched-capacitor power converters corresponding to the switched-capacitor power converter to be in the on state or the off state; 7. The system of claim 6, wherein the processor is configured to use the lookup table to determine which switched capacitor power converter should be in the on state or the off state that corresponds to the noise-reduced power calculation output signal.

8. 8. The system of claim 7, wherein the controller generates the one or more output control signals for placing one or more of the switched-capacitor power converters in the on and off states based on the look-up table.

9. The system of claim 8 , wherein the power level of the switched capacitor power converter corresponds to a power requirement of the load.

10. The input power signal has an input voltage component and an input current component, the output power signal has an output voltage component and an output current component, and the signal conditioner a voltage regulation unit for buffering the input voltage components and the output voltage components to remove noise therefrom and for scaling the input voltage components and the output voltage components to selected voltage levels for use by the controller; The system of claim 6 , further comprising: a current conditioning unit for filtering the input current component and the output current component.

11. The system of claim 10 , wherein the current regulation unit includes a low pass filter for filtering the input current component and the output current component.

12. 2. The system of claim 1, wherein the clock selection unit is configured to vary an operating frequency of each of the plurality of switched capacitor power converters by selecting a clock to supply to each of the plurality of switched capacitor power converters.

13. 1. A method for controlling a plurality of switched-capacitor power converters in a power system, comprising: providing a plurality of switched capacitor power converters forming an array for converting power between a first power level and a second power level, wherein inputs of the plurality of switched capacitor power converters are coupled to a common input power line and outputs of the plurality of switched capacitor power converters are coupled to a common output power line, the plurality of switched capacitor power converters being arranged in parallel with each other, each switched capacitor power converter including a plurality of capacitors for storing power; providing a controller coupled to a plurality of said switched capacitor power converters for controlling a power output of the plurality of said switched capacitor power converters; sensing, with an input sense circuit coupled to the controller and to the common input power line, input power on the common input power line and transmitting an input power signal to the controller; sensing, with an output sense circuit coupled to the controller and to the common output power line, an output power on the common output power line and transmitting an output power signal to the controller; adjusting the input power signal and the output power signal to generate a regulated output power signal; comparing a value of a control signal generated by the controller to a value of the regulated output power signal and generating a comparison signal if the value of the regulated output power signal is greater than the value of the control signal; controlling each of the plurality of switched-capacitor power converters to switch each of the plurality of switched-capacitor power converters to an on state or an off state as a function of the sensed input power and the sensed output power, thereby operating one or more of the plurality of switched-capacitor power converters in the on state within an optimum power efficiency range; and transmitting power stored in one or more of the capacitors in the switched-capacitor power converter in the off state to the common output power line in response to the comparison signal.

14. 14. The method of claim 13, wherein each of the plurality of switched-capacitor power converters comprises a switched-capacitor DC-DC step-down power converter for converting the power from the first power level to the second power level, the second power level being lower than the first power level.

15. determining the power of one or more of the switched capacitor power converters; 14. The method of claim 13, further comprising: accessing a lookup table based on the power of one or more of the switched capacitor power converters; and determining from the lookup table which of the switched capacitor power converters the controller should place in the on state and the off state.

16. The control device includes: a memory unit for storing instructions for controlling a plurality of said switched-capacitor power converters; a signal conditioner for conditioning the input power signal and the output power signal to generate the conditioned output power signal; an analog-to-digital (A-D) converter for converting the regulated output power signal into a digital regulated output power signal; and a processor for processing the digitally regulated output power signal and generating output control signals for controlling one or more of the switched capacitor power converters to place the switched capacitor power converters in the on and off states based on the stored instructions.

17. The digital regulated output power signal includes a regulated output voltage component and a regulated output current component, the processor: a filter unit for averaging the regulated output voltage component and the regulated output current component of the digital regulated output power signal; a power calculation unit for calculating power of one or more of the plurality of switched-capacitor power converters based on an average of the regulated output voltage component and the regulated output current component to generate a power calculation output signal; a hysteresis unit for reducing noise in the power calculation output signal; a look-up table for storing information relating to a plurality of power levels of at least one of the plurality of switched-capacitor power converters corresponding to the switched-capacitor power converter to be in the on state or the off state; 17. The method of claim 16, wherein the processor is configured to use the lookup table to determine which switched capacitor power converter should be in the on state or the off state that corresponds to the noise reduced power calculation output signal.

18. 20. The method of claim 17, wherein the controller generates one or more of the output control signals for placing one or more of the switched-capacitor power converters in the on and off states based on the look-up table.

19. The controller generates a first output control signal, and the method includes: conditioning, with a signal conditioner, the input power signal and the output power signal to generate the conditioned output power signal; comparing, with a comparison unit, the regulated output power signal and the first output control signal and generating an output comparison signal in response when a value of the regulated output power signal is greater than a value of the first output control signal; sending the output comparison signal to a clock selection unit, which then sends an output signal to a plurality of the switched capacitor power converters; 14. The method of claim 13, further comprising: delivering power stored in one or more of the capacitors of each of the switched-capacitor power converters in the off state to the common output power line in response to the output signal from the clock selection unit.

20. 20. The method of claim 19, wherein the clock selection unit is configured to vary an operating frequency of each of the plurality of switched capacitor power converters by selecting a clock to supply to each of the plurality of switched capacitor power converters.

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