Patent Publication Number: US-2020300037-A1

Title: Direct-current power distribution in a control system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/813,552, filed Mar. 4, 2019, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     A typical window treatment, such as a roller shade, a drapery, a roman shade, and/or a venetian blind, may be mounted in front of a window or opening to control an amount of light that may enter a user environment and/or to provide privacy. A covering material (e.g., a shade fabric) on the window treatment may be adjusted to control the amount of daylight from entering the user environment and/or to provide privacy. The covering material may be manually controlled and/or automatically controlled using a motorized drive system to provide energy savings and/or increased comfort for occupants. For example, the covering material may be raised to allow light to enter the user environment and allow for reduced use of lighting systems. The covering material may also be lowered to reduce the occurrence of sun glare. 
     SUMMARY 
     A control system may include a direct-current (DC) power bus for charging (e.g., trickle charging) internal energy storage elements in control devices of the control system. For example, the control devices may be motorized window treatments configured to adjust a position of a covering material to control the amount of daylight entering a space. The system may include a DC power supply that may generate a DC voltage on the DC power bus. For example, the DC power bus may extend from the DC power supply around the perimeter of a floor of the building and may be connected to all of the motorized window treatments on the floor (e.g., in a daisy-chain configuration). Wiring the DC power bus in such a manner may dramatically reduce the installation labor and wiring costs of an installation, as well as decreasing the chance of a miswire. 
     Each control device may be configured to control when the internal energy storage element charges from the DC bus voltage. For example, each control device may be configured to determine when to charge the internal energy storage element from the DC bus voltage in response to a message received via a communication circuit. Each control device may be configured to transmit a message including a storage level of the internal energy storage element. The storage level of the internal storage element may be a percentage of a maximum capacity (e.g., 60% of the maximum storage capacity) or a percentage of a maximum voltage, or a preset voltage level of the internal storage element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified block diagram of a load control system having load control devices and motorized window treatments. 
         FIGS. 2A-2C  are floorplan views of a direct-current (DC) power distribution system for a control system. 
         FIG. 3  is a block diagram of an example motor drive unit of a motorized window treatment. 
         FIG. 4  is a block diagram of an example supplemental energy storage element. 
         FIG. 5  is a flowchart of an example movement tracking control procedure that may be executed by a control circuit of a load control device. 
         FIG. 6  is a flowchart of an example internal storage charging control procedure that may be executed by a control circuit of a load control device. 
         FIG. 7  is a flowchart of an example low-power mode control procedure that may be executed by a control circuit of a load control device. 
         FIG. 8  is a flowchart of an example pre-charge control procedure that may be executed by a control circuit of a load control device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a simple diagram of an example load control system for controlling the amount of power delivered from an alternating-current (AC) power source (not shown) to one or more electrical loads. The load control system  100  may comprise a system controller  110  (e.g., a load controller or a central controller) operable to transmit and/or receive digital messages via a wired and/or a wireless communication link. For example, the system controller  110  may be coupled to one or more wired control devices via a wired digital communication link  104 . The system controller  110  may be configured to transmit and/or receive wireless signals, e.g., radio-frequency (RF) signals  106 , to communicate with one or more wireless control devices. The load control system  100  may comprise a number of control-source devices and/or a number of control-target devices for controlling an electrical load. The control-source devices may be input devices operable to transmit digital messages configured to control an electrical load via a control-target device. For example, control-source devices may transmit the digital messages in response to user input, occupancy/vacancy conditions, changes in measured light intensity, or other input information. The control-target devices may be load control devices operable to receive digital messages and control respective electrical loads in response to the received digital messages. A single control device of the load control system  100  may operate as both a control-source and a control-target device. The system controller  110  may be configured to receive digital messages from the control-source devices and transmit digital messages to the control-target devices in response to the digital messages received from the control-source devices. The control-source devices and the control-target devices may also, or alternatively, communicate directly. 
     The load control system  100  may comprise a load control device, such as a dimmer switch  120 , for controlling a lighting load  122 . The dimmer switch  120  may be adapted to be wall-mounted in a standard electrical wallbox. The dimmer switch  120  may comprise a tabletop or plug-in load control device. The dimmer switch  120  may comprise a toggle actuator  124  (e.g., a button) and/or an intensity adjustment actuator  126  (e.g., a rocker switch). Successive actuations of the toggle actuator  124  may toggle, e.g., turn off and on, the lighting load  122 . Actuations of an upper portion or a lower portion of the intensity adjustment actuator  126  may respectively increase or decrease the amount of power delivered to the lighting load  122  and increase or decrease the intensity of the lighting load from a minimum intensity (e.g., approximately 1%) to a maximum intensity (e.g., approximately 100%). The dimmer switch  120  may further comprise a plurality of visual indicators  128 , e.g., light-emitting diodes (LEDs), which may be arranged in a linear array and/or may be illuminated to provide feedback of the intensity of the lighting load  122 . The dimmer switch  120  may be configured to receive digital messages from the system controller  110  via the RF signals  106  and to control the lighting load  122  in response to the received digital messages. The dimmer switch  120  may also, or alternatively, be coupled to the wired digital communication link  104 . Examples of wall-mounted dimmer switches are described in greater detail in U.S. Pat. No. 5,248,919, issued Sep. 28, 1993, entitled LIGHTING CONTROL DEVICE, and U.S. Pat. No. 9,679,696, issued Jun. 13, 2017, entitled WIRELESS LOAD CONTROL DEVICE, the entire disclosures of which are hereby incorporated by reference. 
     The load control system  100  may further comprise one or more remotely-located load control devices, such as light-emitting diode (LED) drivers  130  for driving respective LED light sources  132  (e.g., LED light engines). The LED drivers  130  may be located remotely, for example, in the lighting fixtures of the respective LED light sources  132 . The LED drivers  130  may be configured to receive digital messages from the system controller  110  via the digital communication link  104  and to control the respective LED light sources  132  in response to the received digital messages. The LED drivers  130  may be coupled to a separate digital communication link, such as an Ecosystem® or digital addressable lighting interface (DALI) communication link, and the load control system  100  may include a digital lighting controller coupled between the digital communication link  104  and the separate communication link. The LED drivers  132  may include internal RF communication circuits or be coupled to external RF communication circuits (e.g., mounted external to the lighting fixtures, such as to a ceiling) for transmitting and/or receiving the RF signals  106 . The load control system  100  may further comprise other types of remotely-located load control devices, such as, for example, electronic dimming ballasts for driving fluorescent lamps. 
     The load control system  100  may further comprise a plurality of daylight control devices, e.g., motorized window treatments, such as motorized roller shades  140 , to control the amount of daylight entering the building in which the load control system may be installed. A motorized roller shades  140  may comprise a covering material (e.g., a window treatment fabric  142 ). The covering material may be wound around a roller tube for raising and/or lowering the window treatment fabric  142 . The motorized roller shades  140  may comprise motor drive units  144  (e.g., electronic drive units). The motor drive units  144  may be located inside the roller tube of the motorized roller shade. The motor drive units  144  may be coupled to the digital communication link  104  for transmitting and/or receiving digital messages. The motor drive units  144  may include a control circuit. The control circuit may be configured to adjust the position of the window treatment fabric  142 , for example, in response to digital messages received from the system controller  110  via the digital communication link  104 . Each of the motor drive units  144  may include memory for storing association information for associations with other devices and/or instructions for controlling the motorized roller shade  140 . The motor drive units  144  may comprise an internal RF communication circuit. The motor drive units  144  may also, or alternatively, be coupled to an external RF communication circuit (e.g., located outside of the roller tube) for transmitting and/or receiving the RF signals  106 . The load control system  100  may comprise other types of daylight control devices, such as, for example, a cellular shade, a drapery, a Roman shade, a Venetian blind, a Persian blind, a pleated blind, a tensioned roller shade systems, an electrochromic or smart window, and/or other suitable daylight control device. 
     The load control system  100  may comprise one or more other types of load control devices, such as, for example, a screw-in luminaire including a dimmer circuit and an incandescent or halogen lamp; a screw-in luminaire including a ballast and a compact fluorescent lamp; a screw-in luminaire including an LED driver and an LED light source; an electronic switch, a controllable circuit breaker, or other switching device for turning an appliance on and off; a plug-in load control device, a controllable electrical receptacle, or a controllable power strip for controlling one or more plug-in loads; a motor control unit for controlling a motor load, such as a ceiling fan or an exhaust fan; a drive unit for controlling a motorized window treatment or a projection screen; motorized interior or exterior shutters; a thermostat for a heating and/or cooling system; a temperature control device for controlling a setpoint temperature of a heating, ventilation, and air conditioning (HVAC) system; an air conditioner; a compressor; an electric baseboard heater controller; a controllable damper; a variable air volume controller; a fresh air intake controller; a ventilation controller; hydraulic valves for use in radiators and radiant heating systems; a humidity control unit; a humidifier; a dehumidifier; a water heater; a boiler controller; a pool pump; a refrigerator; a freezer; a television or computer monitor; a video camera; an audio system or amplifier; an elevator; a power supply; a generator; an electric charger, such as an electric vehicle charger; and/or an alternative energy controller. 
     The load control system  100  may comprise one or more input devices, e.g., such as a wired keypad device  150 , a battery-powered remote control device  152 , an occupancy sensor  154 , a daylight sensor  156 , and/or a shadow sensor  158 . The wired keypad device  150  may be configured to transmit digital messages to the system controller  110  via the digital communication link  104  in response to an actuation of one or more buttons of the wired keypad device. The battery-powered remote control device  152 , the occupancy sensor  154 , the daylight sensor  156 , and/or the shadow sensor  158  may be wireless control devices (e.g., RF transmitters) configured to transmit digital messages to the system controller  110  via the RF signals  106  (e.g., directly to the system controller). For example, the battery-powered remote control device  152  may be configured to transmit digital messages to the system controller  110  via the RF signals  106  in response to an actuation of one or more buttons of the battery-powered remote control device  152 . The occupancy sensor  154  may be configured to transmit digital messages to the system controller  110  via the RF signals  106  in response to detection of occupancy and/or vacancy conditions in the space in which the load control system  100  may be installed. The daylight sensor  156  may be configured to transmit digital messages to the system controller  110  via the RF signals  106  in response to detection of different amounts of natural light intensity. The shadow sensor  158  may be configured to transmit digital messages to the system controller  110  via the RF signals  106  in response to detection of an exterior light intensity coming from outside the space in which the load control system  100  may be installed. The system controller  110  may be configured to transmit one or more digital messages to the load control devices (e.g., the dimmer switch  120 , the LED drivers  130 , and/or the motorized roller shades  140 ) in response to the received digital messages, e.g., from the wired keypad device  150 , the battery-powered remote control device  152 , the occupancy sensor  154 , the daylight sensor  156 , and/or the shadow sensor  158 . While the system controller  110  may receive digital messages from the input devices and/or transmit digital messages to the load control devices for controlling an electrical load, the input devices may communicate directly with the load control devices for controlling the electrical load. 
     The load control system  100  may comprise a wireless adapter device  160  that may be coupled to the digital communication link  104 . The wireless adapter device  160  may be configured to receive the RF signals  106 . The wireless adapter device  160  may be configured to transmit a digital message to the system controller  110  via the digital communication link  104  in response to a digital message received from one of the wireless control devices via the RF signals  106 . For example, the wireless adapter device  160  may re-transmit the digital messages received from the wireless control devices on the digital communication link  104 . 
     The occupancy sensor  154  may be configured to detect occupancy and/or vacancy conditions in the space in which the load control system  100  may be installed. The occupancy sensor  154  may transmit digital messages to the system controller  110  via the RF signals  106  in response to detecting the occupancy and/or vacancy conditions. The system controller  110  may be configured to turn one or more of the lighting load  122  and/or the LED light sources  132  on and off in response to receiving an occupied command and a vacant command, respectively. The occupancy sensor  154  may operate as a vacancy sensor, such that the lighting loads are turned off in response to detecting a vacancy condition (e.g., not turned on in response to detecting an occupancy condition). Examples of RF load control systems having occupancy and vacancy sensors are described in greater detail in commonly-assigned U.S. Pat. No. 8,009,042, issued Aug. 30, 2011, entitled RADIO-FREQUENCY LIGHTING CONTROL SYSTEM WITH OCCUPANCY SENSING; U.S. Pat. No. 8,199,010, issued Jun. 12, 2012, entitled METHOD AND APPARATUS FOR CONFIGURING A WIRELESS SENSOR; and U.S. Pat. No. 8,228,184, issued Jul. 24, 2012, entitled BATTERY-POWERED OCCUPANCY SENSOR, the entire disclosures of which are hereby incorporated by reference. 
     The daylight sensor  156  may be configured to measure a total light intensity in the space in which the load control system is installed. The daylight sensor  156  may transmit digital messages including the measured light intensity to the system controller  110  via the RF signals  106 . The digital messages may be used to control an electrical load (e.g., the intensity of lighting load  122 , the motorized window shades  140  for controlling the level of the covering material, the intensity of the LED light sources  132 ) via one or more control load control devices (e.g., the dimmer switch  120 , the motor drive unit  144 , the LED driver  130 ). Examples of RF load control systems having daylight sensors are described in greater detail in commonly-assigned U.S. Pat. No. 8,410,706, issued Apr. 2, 2013, entitled METHOD OF CALIBRATING A DAYLIGHT SENSOR; and U.S. Pat. No. 8,451,116, issued May 28, 2013, entitled WIRELESS BATTERY-POWERED DAYLIGHT SENSOR, the entire disclosures of which are hereby incorporated by reference. 
     The shadow sensor  158  may be configured to measure an exterior light intensity coming from outside the space in which the load control system  100  may be installed. The shadow sensor  158  may be mounted on a façade of a building, such as the exterior or interior of a window, to measure the exterior natural light intensity depending upon the location of the sun in sky. The shadow sensor  158  may detect when direct sunlight is directly shining into the shadow sensor  158 , is reflected onto the shadow sensor  158 , or is blocked by external means, such as clouds or a building, and may send digital messages indicating the measured light intensity. The shadow sensor  158  may transmit digital messages including the measured light intensity to the system controller  110  via the RF signals  106 . The digital messages may be used to control an electrical load (e.g., the intensity of lighting load  122 , the motorized window shades  140  for controlling the level of the covering material, and/or the intensity of the LED light sources  132 ) via one or more control load control devices (e.g., the dimmer switch  120 , the motor drive unit  144 , and/or the LED driver  130 ). The shadow sensor  158  may also be referred to as a window sensor, a cloudy-day sensor, or a sun sensor. 
     The load control system  100  may comprise other types of input device, such as: temperature sensors; humidity sensors; radiometers; pressure sensors; smoke detectors; carbon monoxide detectors; air quality sensors; motion sensors; security sensors; proximity sensors; fixture sensors; partition sensors; keypads; kinetic- or solar-powered remote controls; key fobs; cell phones; smart phones; tablets; personal digital assistants; personal computers; laptops; timeclocks; audio-visual controls; safety devices; power monitoring devices (such as power meters, energy meters, utility submeters, utility rate meters); central control transmitters; residential, commercial, or industrial controllers; or any combination of these input devices. These input devices may transmit digital messages to the system controller  110  via the RF signals  106 . The digital messages may be used to control an electrical load (e.g., the intensity of lighting load  122 , the motorized window shades  140  for controlling the level of the covering material, and/or the intensity of the LED light sources  132 ) via one or more control load control devices (e.g., the dimmer switch  120 , the motor drive unit  144 , and/or the LED driver  130 ). 
     The system controller  110  may be configured to control the load control devices (e.g., the dimmer switch  120 , the LED drivers  130 , and/or the motorized roller shades  140 ) according to a timeclock schedule. The timeclock schedule may be stored in a memory in the system controller. The timeclock schedule may be defined by a user of the system controller (e.g., a system administrator using a programming mode of the system controller  110 ). The timeclock schedule may include a number of timeclock events. The timeclock events may have an event time and a corresponding command or preset. The system controller  110  may be configured to keep track of the present time and/or day. The system controller  110  may transmit the appropriate command or preset at the respective event time of each timeclock event. An example of a load control system for controlling one or more motorized window treatments according to a timeclock schedule is described in greater detail in commonly-assigned U.S. Pat. No. 8,288,981, issued Oct. 16, 2012, entitled METHOD OF AUTOMATICALLY CONTROLLING A MOTORIZED WINDOW TREATMENT WHILE MINIMIZING OCCUPANT DISTRACTIONS, the entire disclosure of which is hereby incorporated by reference. 
     The load control system  100  may be part of an automated window treatment control system. The system controller  110  may control the shades according to automated window treatment control information. For example, the automated window treatment control information may include the angle of the sun, sensor information, an amount of cloud cover, and/or weather data, such as historical weather data and real-time weather data. For example, throughout course of calendar day, the system controller  110  of the automated window treatment control system may adjust the position of the window treatment fabric multiple times, based on the calculated position of the sun or sensor information. The automated window treatment control system may determine the position of the window treatments in order to affect a performance metric. The automated window treatment system may command the system controller  110  to adjust the window treatments to the determined position in order to affect a performance metric. The automated window treatment control system may operate according to a timeclock schedule. Based on the timeclock schedule, the system controller may change the position of the window treatments throughout a calendar day. The timeclock schedule may be set to prevent the daylight penetration distance from exceeding a maximum distance into an interior space (e.g., work space, transitional space, or social space). The maximum daylight penetration distance may be set to a user&#39;s workspace. The system controller  110  may adjust the position of the window treatments according to collected sensor information. 
     The system controller  110  may be operable to be coupled to a network, such as a wireless or wired local area network (LAN) via a network communication bus  162  (e.g., an Ethernet communication link), e.g., for access to the Internet. The system controller  110  may be connected to a network switch  164  (e.g., a router or Ethernet switch) via the network communication bus  162  for allowing the system controller  110  to communicate with other system controllers for controlling other electrical loads. The system controller  110  may be wirelessly connected to the network, e.g., using Wi-Fi technology. The system controller  110  may be configured to communicate via the network with one or more network devices, such as a smart phone (e.g., an iPhone® smart phone, an Android® smart phone, a Windows® smart phone, or a Blackberry® smart phone), a personal computer  166 , a laptop, a tablet device, (e.g., an iPad® hand-held computing device), a Wi-Fi or wireless-communication-capable television, and/or any other suitable wireless communication device (e.g., an Internet-Protocol-enabled device). The network device may be operable to transmit digital messages to the system controller  110  in one or more Internet Protocol packets. Examples of load control systems operable to communicate with network devices on a network are described in greater detail in commonly-assigned U.S. Patent Application Publication No. 2013/0030589, published Jan. 31, 2013, entitled LOAD CONTROL DEVICE HAVING INTERNET CONNECTIVITY, the entire disclosure of which is hereby incorporated by reference. 
     The operation of the load control system  100  may be programmed and/or configured using the personal computer  166  or other network device. The personal computer  166  may execute a graphical user interface (GUI) configuration software for allowing a user to program how the load control system  100  may operate. The configuration software may generate load control information (e.g., a load control database) that defines the operation and/or performance of the load control system  100 . For example, the load control information may include information regarding the different load control devices of the load control system (e.g., the dimmer switch  120 , the LED drivers  130 , and/or the motorized roller shades  140 ). The load control information may include information regarding associations between the load control devices and the input devices (e.g., the wired keypad device  150 , the battery-powered remote control device  152 , the occupancy sensor  154 , the daylight sensor  156 , and/or the shadow sensor  158 ), and/or how the load control devices may respond to input received from the input devices. Examples of configuration procedures for load control systems are described in greater detail in commonly-assigned U.S. Pat. No. 7,391,297, issued Jun. 24, 2008, entitled HANDHELD PROGRAMMER FOR LIGHTING CONTROL SYSTEM; U.S. Patent Application Publication No. 2008/0092075, published Apr. 17, 2008, entitled METHOD OF BUILDING A DATABASE OF A LIGHTING CONTROL SYSTEM; and U.S. Patent Application Publication No. 2017/0123390, published May 4, 2017, entitled COMMISSIONING LOAD CONTROL SYSTEMS, the entire disclosure of which is hereby incorporated by reference. 
     The system controller  110  may be configured to automatically control the motorized window treatments (e.g., the motorized roller shades  140 ). The motorized window treatments may be controlled to save energy and/or improve the comfort of the occupants of the building in which the load control system  100  may be installed. For example, the system controller  110  may be configured to automatically control the motorized roller shades  140  in response to a timeclock schedule, the daylight sensor  156 , and/or the shadow sensor  158 . The roller shades  140  may be manually controlled by the wired keypad device  150  and/or the battery-powered remote control device  152 . 
       FIGS. 2A-2C  are floorplan views of a direct-current (DC) power distribution system  200  for a control system (e.g., the load control system  100  shown in  FIG. 1 ) that may be installed in a building  202 . The control system may comprise one or more motorized window treatments  240  (e.g., the motorized roller shades  140  shown in  FIG. 1 ) for controlling the amount of daylight entering the building  202  through respective windows  204 . Each motorized window treatment  240  may comprise a respective roller tube and a respective covering material (not shown), such as the window treatment fabric  142  of the motorized roller shades  140  shown in  FIG. 1 . The motorized window treatments  240  may also comprise respective motor drive units  244  (e.g., the motor drive units  144  shown in  FIG. 1 ) configured to adjust the positions of the respective covering materials. Each motor drive unit  244  may comprise an internal energy storage element, such as one or more rechargeable batteries and/or supercapacitors (e.g., as will be described in greater detail below). 
     The DC power distribution system  200  may comprise a DC power supply  290  (e.g., a Class 2 power supply), which may be electrically coupled to the motor drive units  244  of the motorized window treatments  240  via a DC power bus  292 . The DC power supply  290  may be electrically coupled to an alternating-current (AC) mains supply for receiving an AC mains line voltage. The DC power supply  290  may be configured to generate (e.g. from the AC mains line voltage) a DC bus voltage on the DC power supply  292  for charging (e.g., trickle charging) the energy storage elements of the motor drive units  244 . The DC power bus  292  may be electrically coupled to the motor drive units  244  in a daisy-chain configuration (e.g. in parallel). For example, each motor drive unit  244  may comprise two power connectors (e.g., a power-in connector and a power-out connector) to allow for each daisy-chaining of the motor drive units. The DC power supply  290  may be configured to adjust (e.g., temporarily adjust) the magnitude of the DC bus voltage under certain conditions (e.g., in response to the number of motor drive units  244  that presently need to charge their internal energy storage elements). The DC power supply  290  may be configured to perform the functions (e.g. any of the example functions of described herein) of a system controller (e.g. the system controller  110 ). Further, in some examples, the DC power supply  290  may comprise a system controller (e.g. the system controller  110 ). 
     As shown in  FIG. 2A , the DC power bus  292  may be a single cable (e.g., a single wire run) that may extend (e.g. in approximately a full loop) around the perimeter of an entire floor of the building  202  for charging the energy storage elements of all of the motor drive units  244  on the floor. The cable of the DC power bus  292  may comprise at least two or more electrical wires (e.g., electrical conductors) for distributing the DC bus voltage from the DC power supply  290  to the motor drive units  244  of the DC power distribution system  200 . For example, the building may comprise a plurality of floors and the DC power distribution system  200  may comprise a plurality of respective power buses  292 , with one of the power buses  292  on each of the floors of the building. The AC mains power source may be coupled to the DC power bus  292  on each floor of the building through a single circuit breaker  294  on each floor. 
     The energy storage elements of the motor drive units  244  may have a limited capacity for moving (e.g. capacity to power the movement of) the covering materials of the respective motorized window treatments  240 . For example, the energy storage elements of the motor drive unit  244  may have a capacity to power a predetermined number of movements (e.g., full movements) of the covering materiel, where a full movement of the covering material may be a movement from a fully-open position to a fully-closed position or a movement from the fully-closed position to the fully-open position. The motor drive units  244  may be configured to limit (e.g. prevent future movement at the limit or after the limit is exceeded) the number of movements (e.g. full movements) and/or the total amount (e.g. a number of rotations of the roller tube) of movement, for example, over a period of time (e.g., one day). For example, the motor drive units  244  may be configured to count the number of movements (e.g. full movements) during a day and prevent future movement of the covering material after the number (e.g. predetermined number) of movements exceeds a movement threshold (e.g., less than or equal to ten full movements, such as approximately five to ten full movements). In addition, the motor drive units  244  may be configured to store the total amount of movement (e.g., in units of rotation of the motor and/or linear distance of movement of a lower edge of the covering material) during a day and prevent future movement of the covering material after the total amount of movement exceeds a distance threshold (e.g. a predetermined amount of movement). For example, the distance threshold may be a value representing four full movements of the covering material between the fully-closed position and the fully-open position. The motor drive units  244  may also be configured to limit the frequency of movements. The motor drive units  244  may once again allow movement of the covering material at the end of the present day, at the end of a predetermined period of time after movement is stopped, and/or when the internal energy storage element has charged to an acceptable level. 
     The motor drive units  244  may be configured to communicate with each other via a communication link (not shown), such as a wired or wireless communication link. For example, if the motor drive units  244  are configured to transmit and receive wireless signals, such as radio-frequency (RF) signals, the DC power bus  292  may simply comprise two electrical conductors for suppling voltage and current to the motor drive units. In addition, the DC power bus  292  may be packaged together with a wired digital communication link (e.g., an RS-485 digital communication link) to allow the motor drive units  244  to communicate via the wired communication link. Further, the motor drive units  244  may be configured to communicate with each other by transmitting signals via the two electrical conductors of the DC power bus  292 , for example, using a power-line communication (PLC) technique. 
     The motor drive units  244  may be configured to learn the storage levels of the energy storage elements of the other motor drive units  244  in the DC power distribution system  200  (e.g. as a percentage of a maximum storage capacity of the energy storage elements and/or a voltage level of the energy storage elements). For example, the motor drive units  244  may each periodically transmit the storage level of its energy storage element. 
     The motor drive units  244  may each be configured to control when the internal energy storage element charges. Multiple motor drive units  244  may charge the internal energy storage elements at the same time. In addition, a limited number of motor drive units  244  (e.g., one at a time) may be configured to charge the internal energy storage elements at once. The motor drive units  244  may be configured to coordinate when each of the motor drive units  244  charges its internal energy storage element. The motor drive units  244  may be configured to arbitrate with each other by communicating via the communication link in order to determine which motor drive unit(s)  244  should presently be charging its internal energy storage element. The motor drive units  244  may be configured to prioritize which motor drive unit should charge its internal energy storage element based on power needs of the motor drive units. For example, the motor drive units  244  having the lowest storage level of all of the motor drive units in the DC power distribution system  200  may be configured to charge its energy storage element before the other motor drive units. 
     Another device, such as a system controller (e.g., the system controller  110 ) and/or the DC power supply  290 , may communicate with the motor drive units  244  to manage which of the motor drive unit(s)  244  is presently charging its internal energy storage element (e.g. based on the storage level(s) of the internal energy storage element(s)). The system controller may be configured to learn when multiple shades are required to move at the same time (e.g., to close all of the motorized window treatments at the end of a day as part of a timeclock schedule). For example, the system controller may store a history of movements of the motorized window treatments  240  and may be configured to determine which motor drive unit  244  should charge its internal energy storage element based on a determination of a motorized window treatment that is expected to move next (e.g., the most likely motorized window treatment to move). As such, the motor drive units  244  may be configured to control the charging of their internal energy storage element (e.g., to a particular storage level) based on past and/or expected usage of the motorized window treatment  240 . 
     The motor drive units  244  may be configured to operate in a normal power mode. In normal power mode, the motor drive units  244  may be configured rotate their motor at a normal speed. Further, in normal power mode, the motor drive units  244  may be configured to charge their internal energy storage element to maximum capacity, or in some examples, to less than the maximum capacity, such as 60% of the maximum capacity. The motor drive units  244  may be configured to operate in a low-power mode during a high power demand event and/or during an energy depletion event. A high-power demand event may be a period of high energy usage of a plurality of load control devices, for example, such as when many (e.g., more than one or a majority) of the motorized window treatments need to move at the same time and/or when many (e.g., more than one or a majority) of the internal energy storage elements of the motor drive units  244  are charging. An energy depletion event may be, for example, when the DC power distribution system  200  is operating in a condition in which many (e.g. a majority of) of the internal energy storage elements of the motor drive units  244  are depleted (e.g., below a threshold level of storage, such as 20%). When operating in the low-power mode, the motor drive units  244  may be configured to, for example, control the motor to rotate as a slower speed (e.g., to reduce power consumption of the motor) and/or delay movements or operation of the motor. 
     The system controller and/or the DC power supply  290  may cause the motor drive units  244  to enter the low-power mode by transmitting a message to the motor drive units  244  (e.g. to the control circuits of the motor drive units  244 ). For example, the system controller and/or the DC power supply  290  may be configured to transmit a digital message to the motor drive units  244  (e.g., via the RF signals  106 ) for causing the motor drive units to enter the low-power mode. Alternatively or additionally, the DC power supply  290  may be configured to detect the high-power demand event (e.g., by measuring a magnitude of an output current of the DC power supply) and signal to the motor drive units  244  by generating a pulse on the DC power bus  292 . For example, the DC power supply  290  may generate the pulse by temporarily increasing the magnitude of the DC bus voltage and/or may temporarily decreasing the magnitude of the DC bus voltage (e.g., to approximately zero volts). The motor drive units  244  may be configured to enter the low-power mode in response to detecting the pulse in the magnitude of the DC bus voltage. 
     In some cases, one motorized window treatment  240  may be required to move more often than another motorized window treatment. If one of the motor drive units  244  determines that its internal energy storage element has a large storage level (e.g., as compared to the storage level of one or more of the other motor drive units), the motor drive unit  244  may be configured to share charge from its internal energy storage element with one or more of the other motor drive units (e.g. the internal energy storage elements of other motor drive units). In addition, multiple motor drive units  244  may be configured to share charge with multiple other motor drive units. 
     As shown in  FIG. 2B , the DC power distribution system  200  may further comprise a supplemental energy storage element  296  (e.g., an external energy storage element) that may be coupled to the DC power bus  292  between two of the motor drive units  244 . The supplemental energy storage element  296  may be configured to charge from the DC power supply  292 , for example, at times when the internal energy storage elements of the motor drive units  244  are charged to suitable levels. For example, during an energy depletion event, the supplemental energy storage element  296  may be configured to charge the internal energy storage elements of the motor drive units  244  that are downstream (e.g. a subset of motor drive units electrically coupled to the DC power bus  292  after the supplemental energy storage element  296 ) from the supplemental energy storage element  296  on the DC power bus  292 . At this time, the supplemental energy storage element  296  may be configured to disconnect from the DC power supply  290  and the motor drive units  244  that are upstream (e.g. a subset of motor drive units electrically coupled to the DC power bus  292  between the supplemental energy storage element  296  and the DC power supply  290 ) from the supplemental energy storage element  296  on the DC power bus  292 . For example, the supplemental energy storage element may comprise an internal switching circuit, such as a relay, for disconnecting from the DC power supply  290 . The DC power distribution system  200  may comprise more than one supplemental energy storage element  296 . 
     The system controller may be configured to determine the existence of an energy depletion event (e.g., when the DC power distribution system  200  is operating in a condition in which most of the internal energy storage elements of the motor drive units  244  are depleted). For example, the supplemental energy storage element  296  may be configured to log in memory and/or report to the system controller when the supplemental energy storage element  296  is needed to charge the internal energy storage elements of the downstream motor drive units  244 . The system controller may be configured to optimize when the motor drive units  244  move and/or charge their internal energy storage elements to avoid further energy depletion events. For example, the personal computer  166  may be configured to send an alert to a building manager to indicate that the DC power distribution system  200  was operating in a condition in which most of the internal energy storage elements of the motor drive units  244  were depleted. 
     As shown in  FIG. 2C , the DC power supply  290  may comprise two outputs  298   a ,  298   b  that are connected to two DC power bus legs  292   a ,  292   b  (e.g. two cables electrically coupled to the motor drive units  244 ) that extend around the floor of the building  202 . For example, the DC power supply  290  may include a first output  298   a  that is electrically coupled, via a first cable of the DC power bus  292   a , to a first subset of the motor drive units of the plurality of motorized window treatments, and a second output  298   b  that is electrically coupled, via a first cable of the DC power bus  292   b , to a second subset of the motor drive units of the plurality of motorized window treatments. With the two DC power bus legs  292   a ,  292   b , the distance between the DC power supply  290  and the motor drive units  244  at the ends of the DC power bus legs  292   a ,  292   b  may be reduced. 
       FIG. 3  is a block diagram of an example motor drive unit  300  of a motorized window treatment (e.g., one of the motor drive units  144  of the motorized roller shades  140  of  FIG. 1  and/or one of the motor drive units  244  of the motorized window treatments  240  of  FIGS. 2A-2C ). The motor drive unit  300  may comprise a motor  310  (e.g., a DC motor) that may be coupled for raising and lowering a covering material. For example, the motor  310  may be coupled to a roller tube of the motorized window treatment for rotating the roller tube for raising and lowering a covering material (e.g., a flexible material, such as a shade fabric). The motor drive unit  300  may comprise a load control circuit, such as a motor drive circuit  320  (e.g., an H-bridge drive circuit) that may generate a pulse-width modulated (PWM) voltage V PWM  for driving the motor  310  (e.g. to move the covering material between a fully-open and fully-closed position). 
     The motor drive unit  300  may comprise a control circuit  330  for controlling the operation of the motor  310 . The control circuit  330  may comprise, for example, a microprocessor, a programmable logic device (PLD), a microcontroller, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or any suitable processing device or control circuit. The control circuit  330  may be configured to generate a drive signal VDRV for controlling the motor drive circuit  320  to control the rotational speed of the motor  310 . For example, the drive signal VDRV may comprise a pulse-width modulated signal, and the rotational speed of the motor  310  may be dependent upon a duty cycle of the pulse-width modulated signal. In addition, the control circuit  330  may be configured to generate a direction signal VDIR for controlling the motor drive circuit  320  to control the direction of rotation of the motor  310 . The control circuit  330  may be configured to control the motor  310  to adjust a present position P PRES  of the shade fabric of the motorized window treatment between a fully-open position P OPEN  and a fully-closed position P CLOSED . 
     The motor drive unit  300  may include a rotational position sensing circuit, e.g., a Hall effect sensor (HES) circuit  340 , which may be configured to generate two Hall effect sensor (HES) signals V HES1 , V HES2  that may indicate the rotational position and direction of rotation of the motor  310 . The HES circuit  340  may comprise two internal sensing circuits for generating the respective HES signals V HES1 , V HES2  in response to a magnet that may be attached to a drive shaft of the motor. The magnet may be a circular magnet having alternating north and south pole regions, for example. For example, the magnet may have two opposing north poles and two opposing south poles, such that each sensing circuit of the HES circuit  340  is passed by two north poles and two south poles during a full rotation of the drive shaft of the motor. Each sensing circuit of the HES circuit  340  may drive the respective HES signal V HES1 , V HES2  to a high state when the sensing circuit is near a north pole of the magnet and to a low state when the sensing circuit is near a south pole. The control circuit  330  may be configured to determine that the motor  310  is rotating in response to the HES signals V HES1 , V HES2  generated by the HES circuit  340 . In addition, the control circuit  330  may be configured to determine the rotational position and direction of rotation of the motor  310  in response to the HES signals V HES1 , V HES2 . 
     The motor drive unit  300  may include a communication circuit  342  that allows the control circuit  330  to transmit and receive communication signals, e.g., wired communication signals and/or wireless communication signals, such as radio-frequency (RF) signals. For example, the motor drive unit  300  may be configured to communicate signals with external control devices (e.g., the motor drive units  244  shown in  FIGS. 2A-2C ). The motor drive unit  300  may further comprise a user interface  344  having one or more buttons that allow a user to provide inputs to the control circuit  330  during setup and configuration of the motorized window treatment. The control circuit  330  may be configured to control the motor  310  to control the movement of the covering material in response to a shade movement command received from the communication signals received via the communication circuit  342  or the user inputs from the buttons of the user interface  344 . The user interface  344  may also comprise a visual display, e.g., one or more light-emitting diodes (LEDs), which may be illuminated by the control circuit  330  to provide feedback to the user of the motorized window treatment system. The motor drive unit  300  may comprise a memory (not shown) configured to store the present position P PRES  of the shade fabric and/or the limits (e.g., the fully-open position P OPEN  and the fully-closed position P CLOSED ). The memory may be implemented as an external integrated circuit (IC) or as an internal circuit of the control circuit  330 . 
     The motor drive unit  300  may comprise one or more power connectors, such as two power connectors  350   a ,  350   b  (e.g. each comprising two power terminals, such as a positive terminal and a negative terminal) for receiving an input voltage V IN  from, for example, an external power supply (e.g., the DC power supply  292 ) via a DC power bus (e.g., the DC power bus  292 ). For example, one of the two power connectors  350   a ,  350   b  may be a power-in connector that is connected to upstream motor drive units, and the other of the two power connectors  350   a ,  350   b  may be a power-out connector that is connected to downstream motor drive units, which may allow for easy wiring of the motor drive units (e.g., in the daisy-chain configuration). The motor drive unit  300  may also comprise a charging circuit  352  (e.g., that receives the input voltage V IN  through a diode D 354 ) and an energy storage element  355 . The energy storage element  355  may comprise one or more supercapacitors, rechargeable batteries, or other suitable energy storage devices. A supercapacitor of a motor drive unit may have an energy storage capability in the range of approximately 12-26 J/cm 3 . By contrast, an electrolytic capacitor may have an energy storage capability of approximately 1 J/cm 3  (e.g., in the range of about 1/10 th  to 1/30 th  of a supercapacitor), while a battery has an energy storage capability of greater than approximately 500 J/cm 3  (e.g., about 15 to 50 times (or more) the energy storage capability of a supercapacitor). 
     The charging circuit  352  may be configured to charge (e.g., trickle charge) the energy storage element  355  from the input voltage V IN  to produce a storage voltage V S  across the energy storage element. The storage voltage V S  may be coupled to the control circuit  330  through a scaling circuit  356 , which may generate a scaled storage voltage V SS . The control circuit  330  may be configured to determine the magnitude of the storage voltage V S  in response to the magnitude of the scaled storage voltage V SS . 
     The motor drive unit  300  may further comprise a power supply  358  that receives the storage voltage V S  and generates a first supply voltage V CC1  (e.g., approximately 40 volts) for powering the motor  310  and a second supply voltage V CC2  (e.g., approximately 3.3 V) for powering the control circuit  330  and other low-voltage circuitry of the motor drive unit  300 . When the control circuit  330  control the motor drive circuit  320  to rotate the motor  310 , the power supply  358  conducts current from the energy storage element  355 . The charging circuit  352  is configured to conduct an average current from the DC power bus that is much smaller than the peak current required by the motor drive circuit  320  to rotate the motor  310 . The storage level of the energy storage element  355  may decrease when the motor  310  is rotating and may slowly increase as the charging circuit  352  charges (e.g., trickle charges) the energy storage element. For example, the energy storage element  355  of the motor drive unit  300  may have a capacity to power a predetermined number of full movements (e.g., less than or equal to 10 full movements, such as approximately 5-10 full movements) of the covering materiel. 
     The control circuit  330  may be configured to periodically transmit messages including the storage level of the energy storage element  355  (e.g., the magnitude of the storage voltage V S ) via the communication circuit  342 . The control circuit  330  may be configured to learn the storage levels of energy storage elements of the other motor drive units coupled to the DC power bus in the DC power distribution system via messages received via the communication circuit  342 . The control circuit  330  may be configured to communicate with the other motor drive units to coordinate when each of the charging circuits  352  charges its energy storage element  355 . The control circuit  330  may generate a charging enable signal V CHRG  for enabling and disabling the charging circuit  352  (e.g. to charge the energy storage element  355  based on communication with the other motor drive units). 
     The motor drive unit  300  may also comprise a controllable switching circuit  360  coupled between the energy storage element  355  and the power connectors  350   a ,  350   b  through a diode D 362 . The control circuit  330  may generate a switch control signal V SW  for rendering the controllable switching circuit  360  conductive and non-conductive. The control circuit  330  may be configured to render the controllable switching circuit  360  conductive to bypass the charging circuit  352  and the diode D 354  and allow the energy storage element  335  to charge energy storage elements of other motor drive units coupled to the DC power bus. The control circuit  330  may allow the energy storage element  335  to charge energy storage elements of other motor drive units coupled to the DC power bus based on the storage levels of energy storage elements of the other motor drive units (e.g. if the storage levels of energy storage elements of the other motor drive units are low), based on a message received from the system controller, based on a message received from another motor drive unit, based on a determination that another motor drive unit is charging from the DC power bus, based on another motor drive unit in use/moving a motor, based on a determination that another motor drive unit has an upcoming energy usage event, and/or based on another motor drive unit having a high-power demand event. Further, in some examples, the motor drive unit  300  may include a boost converter (not shown) in series with or instead of the switch  360 . In such examples, the control circuit  330  may be configured to increase (e.g., boost) the voltage across the energy storage element  335  when connecting the energy storage element  335  to the DC power bus (e.g., when providing power from the energy storage element  335  to the DC power bus). The inclusion of a boost converter in the motor drive unit  300  may be beneficial when, for example, the internal storage element  335  has a low voltage rating. 
       FIG. 4  is a block diagram of an example supplemental energy storage element  400  (e.g., the supplemental energy storage element  296  of the DC power distribution system  200 ). The supplemental energy storage element  400  may comprise two power connectors  450   a ,  450   b  (e.g., a power-in connector and a power-out connector, respectively) for receiving an input voltage V IN  from, for example, an external power supply (e.g., the DC power supply  290 ) via a DC power bus (e.g., the DC power bus  292 ). The supplemental energy storage element may comprise a controllable switching circuit  460  coupled between the power connectors  450   a ,  450   b  through a diode. 
     The supplemental energy storage element  400  may comprise a charging circuit  452  and an energy storage element  455 . The energy storage element  455  may comprise one or more supercapacitors, rechargeable batteries, and/or other suitable energy storage devices. The charging circuit  452  may receive an input voltage V IN  through a diode D 454 . The charging circuit  452  may be configured to charge (e.g., trickle charge) the energy storage element  455  from the input voltage V IN  to produce a storage voltage V S  across the energy storage element. The supplemental energy storage element  400  may comprise a control circuit  430  for controlling the charging circuit  452 . The control circuit  430  may comprise, for example, a microprocessor, a programmable logic device (PLD), a microcontroller, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or any suitable processing device or control circuit. The storage voltage V S  may be coupled to the control circuit  430  through a scaling circuit  456 , which may generate a scaled storage voltage V SS . The control circuit  430  may be configured to determine the magnitude of the storage voltage V S  in response to the magnitude of the scaled storage voltage V SS . The supplemental energy storage element  400  may further comprise a power supply  458  that receives the storage voltage V S  and generates a supply voltage V CC  (e.g., approximately 3.3 V) for powering the control circuit  430  and other low-voltage circuitry of the supplemental energy storage element  400 . 
     The control circuit  430  may generate a switch control signal V SW1  for rendering the controllable switching circuit  460  conductive and non-conductive (e.g. in response to a message received from external devices such as the power supply, the system controller, and/or load control devices). The control circuit  430  may be configured to render the controllable switching circuit  460  conductive to bypass the charging circuit  452  and allow the energy storage element  455  to charge energy storage elements of drive circuits (e.g., motor drive units) coupled to the DC power bus. The supplemental energy storage element  400  may also comprise a controllable switching circuit  462 . The control circuit  430  may generate a switch control signal V SW2  for rendering the controllable switching circuit  462  conductive and non-conductive (e.g. in response to a message received from external devices such as the power supply, the system controller, and/or load control devices). The control circuit  430  may be configured to render the controllable switching circuit  462  conductive to allow the energy storage element  455  to charge from the input voltage V IN . 
     The supplemental energy storage element  400  may also comprise a controllable switching circuit  464 . The control circuit  430  may generate a switch control signal V SW3  for rendering the controllable switching circuit  464  conductive and non-conductive (e.g. in response to a message received from external devices such as the power supply, the system controller, and/or load control devices). The control circuit  430  may be configured to render the controllable switching circuits  462  and  460  non-conductive and the controllable switching circuit  464  conductive, for example, to charge the internal energy storage elements of one or more devices (e.g., motor drive units) connected to the DC power bus. 
     The supplemental energy storage element  400  may include a communication circuit  442  that allows the control circuit  430  to transmit and receive communication signals, e.g., wired communication signals and/or wireless communication signals, such as radio-frequency (RF) signals. For example, the supplemental energy storage element  400  may be configured to communicate signals with external control devices, such as those connected to the DC power bus. The supplemental energy storage element  400  may receive messages from other devices (e.g. those connected to the DC power bus, such as a power supply, a system controller, and/or load control devices) and may control one or more internal switches, such as the controllable switching circuit  460 ,  462 , and/or  464  in response to the received message. 
     Further, in some examples, the supplemental energy storage element  400  may include a boost converter (not shown) in series with or instead of the switch  464 . In such examples, the control circuit  430  may be configured to increase (e.g., boost) the voltage across the energy storage element  455  when connecting the energy storage element  455  to the DC power bus (e.g., when providing power from the energy storage element  455  to the DC power bus). The inclusion of a boost converter in the supplemental energy storage element  400  may be beneficial when, for example, the internal storage element  455  has a low voltage rating. 
       FIG. 5  is a flowchart of an example movement tracking control procedure  500  that may be executed by a control circuit of a load control device (e.g., the control circuit of the motor drive unit  144 , a control circuit of the motor drive units  244 , the control circuit  330  of the motor drive unit  300 , etc.). At  510 , the control circuit may receive a command (e.g. a command to move a covering material of a window treatment). At  512 , the control circuit may determine if a movement tracking limit has been reached. For example, the control circuit may store movement tracking data that indicates a number of movements of the covering material (e.g. a number of full movements between a fully-open and a fully-closed position) and/or an amount of movement of the covering material (e.g., in units of rotations of the motor and/or linear distance of movement of a lower edge of the covering material), for example, over a period of time. For example, the period of time may be a static period of time, such as one day, or the period of time may be a rolling period, such as 12 hours or 24 hours. The control circuit may reset the movement tracking data at the expiration of the period of time (e.g., at the end of the day). The control circuit may be preconfigured with the movement tracking limit and/or may receive the movement tracking limit from the system controller. At  512 , the control circuit may determine whether the movement tracking limit has been reached by comparing the movement tracking data to the movement tracking limit. 
     If the control circuit determines that the movement tracking limit has been reached at  512 , the control circuit may disregard the received command (e.g. by not moving the covering material in response to the received command) and exit the control procedure  500 . Accordingly, in some examples, in response to a determination that the movement tracking limit has been reached at  512 , the control circuit does not generate drive signals for controlling the motor drive circuit based on received commands after the limit is reached or exceeded, for example, for the remainder of a static period of time (e.g., for the remainder of the day) and/or for a part or the entirety of a rolling period of time. 
     If the control circuit determines that the movement tracking limit has not been reached at  512 , then at  514 , the control circuit may determine if a commanded position (e.g. a position that the covering material would be at after executing the received command) can be reached without exceeding the movement tracking limit. For example, the command may indicate a number of movements of the covering material and/or an amount movement of the covering material. The control circuit may compare the combination of the movement tracking data and the number and/or amount of movement(s) indicated by the command to the movement tracking limit. At  514 , if the control circuit determines that the movement tracking limit would be exceeded by moving to the commanded position, then the control circuit may disregard the received command (e.g. not move the covering material in response to the received command), and the control circuit may exit the control procedure  500 . If the control circuit determines that the commanded position can be reached without exceeding the movement tracking limit at  514 , then the control circuit may execute the received command (e.g. rotate the motor to move a covering material to the commanded position) at  516 . At  518 , the control circuit may update the movement tracking data based on the command, for example, by adding the number of movements or number of rotations to the movement tracking data, and exit the control procedure  500 . Though described as a control circuit executing control procedure  500 , the control procedure  500  may be performed by a system controller alone or in conjunction with a control circuit of a load control device. 
       FIG. 6  is a flowchart of an example internal storage charging control procedure  600  that may be executed by a control circuit of a load control device (e.g. the control circuit of the motor drive unit  144 , a control circuit of the motor drive units  244 , the control circuit  330  of the motor drive unit  300 , etc.). The control circuit may be configured to receive and/or store the storage level(s) of the internal energy storage element(s) of the other device(s) (e.g. load control devices such as motor drive units) in a DC power distribution system (e.g., the DC power distribution system  200 ). For example, the control circuit may execute the control procedure  600  periodically. In addition, the control circuit may start the control procedure  600 , for example, in response to a timeclock event/schedule and/or in response to the internal energy storage of the load control device or supplemental energy storage element reaching a preconfigured level. 
     At  612 , the control circuit may receive and/or store the storage level(s) of other device(s) (e.g. load control devices such as motor drive units). At  614 , the control circuit may determine the storage level of the internal energy storage element of the load control device, for example, by sampling a storage voltage level (e.g., the scaled storage voltage V SS ) of the internal energy storage element. At  616 , the control circuit may determine if the storage level of its internal energy storage element is the lowest of all internal energy storage elements of the devices within the DC power distribution system (e.g. based on a comparison of the received storage levels of the other devices in the DC power distribution system and the storage level of the load control device). If the control circuit determines that the storage level of its internal energy storage element is the lowest at  616 , then the control circuit may charge its internal energy storage element at  618 , and may render a controllable switching circuit (e.g., the controllable switching circuit  360 ) of the load control device non-conductive, at  620 . After rendering the controllable switching circuit non-conductive, the control circuit may exit the control procedure  600 . 
     If the control circuit determines that the storage level of its internal energy storage element is not the lowest at  616 , then the control circuit may not charge its internal energy storage element at  622 . At  624 , the control circuit may determine if the load control device should charge an energy storage element of another device in the DC power distribution system. When determining whether to charge another device in the DC power distribution system, the control circuit may, for example, consider the storage level of the other devices, which other device has the lowest storage level, a message received from the system controller, a message received from another device, whether another device is charging from the DC power bus, whether another device is in use (e.g., whether another device is experiencing a high-power demand event), a timeclock schedule, and/or a history of usage events of the other devices (e.g., whether another device has an upcoming energy usage event). 
     If the control circuit determines that the load control device should not charge an energy storage element of another device in the DC power distribution system at  624 , the control circuit may render controllable switching circuit non-conductive at  620  and exit the control procedure  600 . If the control circuit determines that the load control device should charge another device in the DC power distribution system at  624 , the control circuit may render the controllable switching circuit of the load control device conductive at  626  (e.g., for a predetermined amount of time). By rendering the controllable switching circuit conductive, the control circuit may bypass the charging circuit (e.g., the charging circuit  352  and the diode D 354 ) and allow its internal energy storage element to charge energy storage element(s) of other devices coupled to the DC power bus. After the control circuit renders the controllable switching circuit conductive at  626 , the control circuit may exit the control procedure  600 . 
     Although described as a control circuit of a load control device executing the control procedure  600 , the control procedure  600  may be performed by a control circuit of a supplemental energy storage element (e.g. a control circuit of the supplemental energy storage element  296 , the control circuit  430  of the supplemental energy storage element  400 , etc.). The supplemental energy storage element may have a first controllable switching circuit (e.g. controllable switching circuit  460 ), a second controllable switching circuit (e.g. controllable switching circuit  462 ), and a third controllable switching circuit (e.g. controllable switching circuit  464 ). The control circuit of the supplemental energy storage element may generate a switch control signal V SW1 , V SW2 , V SW3 , for rendering each of the controllable switching circuits conductive and non-conductive. If control procedure  600  is performed by the control circuit of a supplemental energy storage element, then instead of rendering a controllable switching circuit of the load control device non-conductive at  620 , the control circuit may render the third controllable switching circuit of the supplemental energy storage element non-conductive and the second controllable switching circuit of the supplemental energy storage element conductive (e.g. to allow the supplemental energy storage element to charge) at  620 . Further, instead of rendering a controllable switching circuit of the load control device conductive at  626 , the control circuit may render the third controllable switching circuit conductive, the first controllable switching circuit non-conductive, and the second controllable switching circuit  462  non-conductive (e.g. to allow the supplemental energy storage element to charge energy storage elements of motor drive units coupled to the DC power distribution system). 
       FIG. 7  is a flowchart of an example low-power mode control procedure  700  that may be executed by a control circuit of a load control device (e.g. the control circuit of the motor drive unit  144 , a control circuit of the motor drive units  244 , the control circuit  330  of the motor drive unit  300 , etc.). The control circuit may execute the control procedure  700  periodically or based on a timeclock schedule/event. At  712 , the load control device may operate in a normal power mode. In the normal power mode, the control circuit may be configured to control a drive circuit according to normal operating conditions. For example, if the load control device is a motorized window treatment, the control circuit may be configured to control a motor drive unit (e.g., the motor drive unit  244 ) to rotate a motor (e.g., the motor  310 ) at a normal speed. Further, in the normal power mode, the control circuit may be configured to charge its internal energy storage element to maximum capacity, or in some examples, to less than the maximum capacity, such as 60% of the maximum capacity. 
     At  714 , the control circuit may determine if a high-power demand event is occurring, for example, based on a received message (e.g. from the system controller, one or more other load control devices, and/or the DC power supply  290 ), the magnitude of a DC bus voltage, and/or a timeclock schedule/event. In some examples, the control circuit may receive the message based on a measurement of a magnitude of an output voltage of a DC power supply (e.g., the DC power supply  290 ). The control circuit may receive the message via wireless communication (e.g. RF signals) and/or via wired communication (e.g. a pulse on the DC bus voltage and/or power-line communication (PLC)). For example, a high-power demand event may be when many of the motorized window treatments need to move at the same time and/or when a DC power distribution system (e.g. the DC power distribution system  200 ) is operating in a condition in which many (e.g. a majority) of the internal energy storage elements of the motor drive units are depleted. If the control circuit determines that a high-power demand event is occurring at  714 , then the load control device may operate in the low-power mode at  718 . When operating in the low-power mode, the control circuit may be configured to control the drive circuit using operating conditions that require less power than the normal mode. For example, if the load control device is a motorized window treatment, then the control circuit may be configured to control the motor drive unit to rotate the motor at a slower speed (e.g., to reduce power consumption of the motor) than the speed used during normal-power mode and/or may delay the control of the motor drive unit when operating in the low-power mode. The load control device may operate in the low-power mode until the high-power demand event ends, for a predetermined amount of time, and/or until a message is received (e.g. from the system controller, power supply, and/or other load control devices). After operating in low-power mode at  718 , the control circuit may exit the control procedure  700  (e.g., based on a received message/command). 
     If the control circuit determines that a high-power demand event is not occurring at  714 , then the control circuit may determine if an energy depletion event is occurring at  716  (e.g., determine whether the internal energy storage elements of many (e.g. a majority of) load control devices of the DC power distribution system are depleted). The control circuit may determine the existence of an energy depletion event based on a received message/command (e.g. from the system controller, power supply, and/or other load control devices). For example, the control circuit may determine whether the internal energy storage elements of many load control devices are below a threshold power level (e.g., less than 20% of maximum capacity). If the control circuit determines that an energy depletion event is occurring at  716 , then the load control device may operate in a low-power mode at  718 . After operating in the low-power mode at  718 , the control circuit may exit the control procedure  700  (e.g. if the internal energy storage elements that were depleted now exceed the power threshold). If the control circuit determines that the internal energy storage elements of many load control devices are not depleted at  716 , then the control circuit may exit the control procedure  700 . 
       FIG. 8  is a flowchart of an example pre-charge control procedure  800  that may be executed by a control circuit of a load control device (e.g. the control circuit of the motor drive unit  144 , a control circuit of the motor drive units  244 , the control circuit  330  of the motor drive unit  300 , etc.). For example, the control circuit may execute the control procedure  800  periodically. In addition, the control circuit may execute the control procedure  800 , for example, in response to receiving a message from a system controller and/or based on a timeclock schedule/event. At  810 , the control circuit may identify an upcoming energy-usage event (e.g. based on a timeclock schedule and/or past usage). Examples of upcoming energy-usage event may be, for example, movements of a motor (e.g., the motor  310 ) (e.g., to move a covering material), turning on or adjusting an intensity of a lighting load, etc. 
     At  812 , the control circuit may charge its internal energy storage element (e.g. to an elevated level) in preparation for the upcoming energy-usage event. In some example, the load control device may maintain the internal energy storage element to a power level that is less than the maximum power level (e.g., at 60% of the maximum energy storage capacity of the internal energy storage element). In such examples, and in preparation for the upcoming energy-usage event, the control circuit may charge its internal energy storage element to the maximum power level in preparation for the upcoming energy-usage event (e.g., prior to driving a motor to rotate a roller tube of a motorized window treatment). Further, in some instances, the control circuit may not be charging its internal energy storage element because the control circuit is allowing other load control devices of the system to charge their respective internal energy storage elements. And as such, for example, the internal energy storage element of the load control device may be at a power level that is less than the maximum power level. In such instance, the control circuit may begin charging its internal energy storage element in response to receiving an indication of an upcoming energy-usage event, and for example, may stop charging the internal energy storage elements of the other load control devices. 
     At  814 , the control circuit may perform the energy-usage event. For example, if the load control device is a motorized window treatment, then the control circuit may control a motor drive unit (e.g., the motor drive unit  320 ) to drive the motor to move the covering material (e.g. consuming the charge that was stored in preparation for the energy-usage event). After the control circuit has performed the energy-usage event, the control circuit may exit the control procedure  800 .