Patent Publication Number: US-2023155397-A1

Title: Charging and discharging control of energy devices in a power system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority, under U.S.C. § 119, from U.S. Provisional Application No. 63/424,859, filed on Nov. 11, 2022, entitled “Apparatus and Method for Charging and Discharging Batteries in a Power System”, the contents of which is incorporated herein by referred in its entirety. The present application is also a continuation-in-part of application Ser. No. 17/884,984, filed on Aug. 10, 2022, entitled “Sequential Power Discharge for Batteries in a Power System”, the content of which is incorporated herein by referred in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to control switches applicable for concurrent switching, break-before-make or make-before-make power multiplexing, configurable for charging, discharging, or a combined charging and discharging use, and linkable into a charging or a discharging control chain for sequential and parallel operations, and into a charging and discharging combined control chain to control operation for a plurality of energy storage devices in a power system automatically. 
     BACKGROUND 
     In conventional power switches or power multiplexers, when several of such switches or multiplexers are cascaded into a chain configuration for power output control, a microcontroller is often used to control the order of their outputs. Commercially available power multiplexers may be linkable to control power sequencing without the use of an external microcontroller, such as the Texas Instrument® TPS22990 power sequencer or TPS25942x Power MUX. However, their power multiplexing requires to monitor the power output status of a prior control switch in order to switch over to a subsequent control switch when switching between two neighboring control switches. 
     For example, the TPS22900 power sequencer, which connects the Power Good (PG) output from a prior TPS22900 switch to enable the ON-input signal of a subsequent TPS22900 switch, where only after its open drain PG output signal is pulled to a logic high and is sensed by the ON-input pin at a subsequent TPS22900 device, then can the subsequent one be switched on for power output. There may be a voltage gap between the output of two TPS22900 switches during such a “break-before-make” power switching. 
     Similarly, the TPS25942x Power Mux may use a similar pull-up PGOOD to interface with the Over-Voltage Protection (OVP) input pin on a subsequent TPS25942x Power Mux, which is also a break-before-make switching. However, the Diode Mode control pin (DMODE) in the chip may be used for a “make-before-break” power multiplexing control. The make-before-break switching means the second switch is turned-on for power output before the first switch is turned off. The make-before-break switching is good for power switching between two power sources at same voltage. Regardless of a break-before-make or a make-before-break power switching, a drawback in most conventional switches is that a handshake is required for a successor switch to monitor the power status of a predecessor switch to determine when a control switchover may take place. 
     SUMMARY 
     In an embodiment, control switches applicable for concurrently switching, break-before-make or make-before-break power multiplexing, and configurable for charging, discharging, or charging and discharging use are disclosed. An embodiment linking a plurality of control switches into a charging, discharging, or charging and discharging control chain to perform sequential and parallel power operations for a plurality of energy devices, such as batteries or battery modules, is also disclosed. 
     Battery is a key component in an electric vehicle (EV). The battery installed in EV is typically a large battery pack to deliver high energy for EV use. It often takes a relatively long time to charge a large battery pack, unless a high-power charging system is available to reduce the charging time. However, the high-power charging system may not be available in most places. A method to address the battery charging issue for EV is also addressed when a high-intensity charging system is not available. 
     A plurality of energy devices can be grouped in a battery pack for EV use. To manage the charging and discharging of the plurality of energy devices, a plurality of control switches coupled to the plurality of energy devices can be chosen, where the control switch may be a charging control switch, a discharging control switch, a dual-operation control switch, or a charging and discharging combined control switch. The plurality of control switches may be linked in series to form a sequential charging control chain, a sequential discharging control chain, or a charging and discharging combined sequential control chain to control the charging and/or discharging of the plurality of energy devices. A control switch deposed in a front position of the control chain has a higher priority than the control switch deposed in a rear position of the control chain. 
     In an embodiment, both the charging control switch and the discharging control switch include a 1:2 de-multiplexer. The 1:2 demultiplexer is named as demultiplexer hereafter. The demultiplexer plays a pivot role in the control switch. The demultiplexer comprises a demultiplexer input connected to an enable input signal to the control switch. The demultiplexer is controlled by a select control signal derived from the output of a comparator, which is adapted to compare an attenuated voltage derived from an energy device coupled to the control switch with a reference voltage to generate the comparator output. The demultiplexer also comprises two outputs, where one of the outputs, namely a positivity output, is generated by ANDing the demultiplexer input with the select control signal, and the other one of the demultiplexer outputs, namely a negativity output, is generated by ANDing the demultiplexer input with an inverse or an inverting function of the select control signal. In an embodiment, the switching timing of two demultiplexer outputs can be adjusted, so that the deactivation of the transfer device in the control switch and the activation of the transfer device in a subsequent control switch in the linked control chain can be manipulated to take place in any order when the select control signal to demultiplexer changes state. 
     In an embodiment, a direct wiring interconnect, a buffer, an even number of inverters, a delay line, or a programmable delay line may be included between the select control signal input to the demultiplexer and the positivity output to delay the assertion of the positivity output. An open drain inverter, an inverting buffer, an odd number of inverters, an inverting delay line or an inverting programmable delay line may be used as the inverting function to delay the asserting of negativity output. By manipulating the delay timing in the assertion of the positivity output and the negativity output, various applications in concurrent, make-before-break or break-before-make power multiplexing are readily achievable. The concurrent switching minimizes power glitches in the power multiplexing. 
     In an embodiment, one of the two demultiplexer outputs is coupled to the transfer device in the control switch, and the other one of the demultiplexer outputs is coupled to an enable output signal to enable a subsequent control switch. Both the positivity output and the negativity output are negated when the enable input signal to the control switch, so is to the input of the demultiplexer, is disabled. When the enable input signal to the control switch is enabled, one of the two demultiplexer outputs is enabled. The demultiplexer controls the switching between the control switch and the subsequent control switch based on the energy status monitored by a comparator device in the control switch. There is no need for a subsequent control switch to monitor power status in a prior control switch, except that the prior control switch simply issues an enable signal to the subsequent control switch to proceed power multiplexing as well as to control timing for a concurrent, a break-before-make or a make-before-break switching. 
     In an embodiment, the select control signal to the demultiplexer may be generated by ANDing the derived comparator output with qualifiers on the abnormality detection status, such as insufficient energy or over-voltage being monitored at the power input port of the control switch, over-temperature, over-current, and short-circuit being detected by the control switch, and assertion of an external INHIBIT control signal to the control switch, and so on. Any abnormality being detected de-activates the transfer device in the control switch and asserts the enable output signal to the subsequent control switch. 
     In an embodiment, the control switch can be portioned into the control section and the transfer section, where the control section comprises the demultiplexer and its control logic and abnormality detection circuits for the generation of the select control signal to the demultiplexer. The transfer section comprises the power input port, the transfer device, the control signal to activate the transfer device and the power output port. By separating the transfer section from the control switch enables the selection of different transfer devices to meet different power requirements. 
     In an embodiment, the plurality of the control switches may be linked into a sequential control chain by coupling the enable output signal of a prior control switch to the enable input signal of a subsequent control switch. For the control switch in the sequential control chain, with a proper connection of the power input port to an external DC power source or to an energy store device, and the connection of power output port to an energy store device or for external use, the sequential control chain can be configured as a sequential charging control chain or as a sequential discharging control chain. 
     In an embodiment, the sequential control chain may be portioned into multiple sub-control chains, where an associated enable input signal is coupled to the first control switch for each sub-control chain to enable operation of the sub-control chains in parallel, when the associated enable input signal to the sub-control chain is asserted. Different DC power may be coupled to different sub-control chains, which is useful for a power system having multiple external power sources available for power charging operation. 
     In an embodiment, a parallel control signal may be ORed with the enable input signal of each control switch linked in a control chain to empower a parallel charging or a parallel discharging operation for the control switches in the sequential control chain. The selection of a sequential or a parallel charging operation may be determined by the availability DC power source and the energy status of the set of battery modules coupled to the control chain. The control chain proceeds charging and/or discharging control automatically without an external micro-controller to control the charging and discharging sequence once the control chain is activated. 
     In an embodiment, a protection switch may be coupled at the output of the energy store device or battery module, where the protection switch is normally-open when the control chain is disabled, which prevents energy leakage from the battery module. The protection switch is closed to enable both input and output of energy from the battery module. 
     In an embodiment, a sequential charging control chain and a sequential discharging control chain can be coupled to the same set of battery modules to conduct a sequential charging, a sequential discharging, or a sequential concurrent charging and discharging for a set of battery modules coupled to both control chains in a power system when enabled. 
     In an embodiment, the comparator output of the control switch may be XORed or XNORed with an external control signal CHARGE, which is input to the control switch to generate a select control signal. The control switch including an XOR gate in deriving the control for the select control signal is named as an XOR control switch hereafter. By inputting a high to the XOR gate, i.e. a high at the CHARGE signal, the XOR control switch can be configured to function as a charging control switch. In addition, by inputting a low to the XOR gate, the XOR control switch can be configured to function as a discharging control switch. The XOR signal can also be used to by-pass or to switch-off the enable of the transfer device in an XOR control switch and to assert an output enable signal to a subsequent control switch during power transfer, when the enable input signal to the XOR control switch is enabled. 
     If the inverse of the external control signal CHARGE, namely a DISCHARGE control signal, is chosen as input to the XOR control switch, then the XOR gate will be converted to an XNOR gate to form an XNOR control switch. The XOR control switch or the XNOR control switch can be configured as a charging or a discharging control switch by simply changing the polarity of the external control signal CHARGE or DISCHARGE. 
     In an embodiment, a charging control switch and a discharging control switch can be combined to form a combined charging and discharging control switch, where a single comparator is used to generate a comparison output to derive the select control signal for both charging and discharging operations. Two 2:1 demultiplexers are included in the combined control switch, where one is for controlling the charging operation and the other is for controlling the discharging operation. 
     In an embodiment, an OR function with a second enable input signal at its input may be coupled to the enable input signal to the charging demultiplexer to enable parallel charging for the combined control switch, so is an additional OR function with a separate enable input signal coupled to the enable input signal to the discharging demultiplexer to enable parallel discharging for the combined control switch. 
     In an embodiment, when a plurality of combined control switches are linked to form a combined control chain, it can concurrently proceed charging and discharging for a plurality of battery modules coupled to the control chain. The concurrent charging and discharging operations at the combined control chain proceed on different battery modules, with the discharging operation takes precedent over the charging operation if both operations collide. That is when a battery module coupled to combined control chain being discharged, it will not be charged at the same time. 
     In an embodiment, a single transfer device is adopted for the combined control switch. The transfer device may be separate from the control section as an external device to provide more flexibility in power transfer for both charging and discharging operations. The transfer device may be integrated in the combined control switch, where a separate 2:1 multiplexer is required to select the power input to the transfer device in the combined control switch either from an external DC power source or from an energy device coupled to the combined control switch, so is an additional  1 : 2  selector to select energy output from the transfer device either to output to the energy device during the charging operation or to output for external use the during discharging operation. 
     The power switching may take place between two control switches that are not next to each other in the control chain with a timing skew of about one AND gate per stage. The power multiplexing may skip multiple control switches in the control chain to activate a control switch which meets the switching condition. Some variations in the control switch and the control chain will be depicted in detail. 
     In an embodiment, the charging, discharging, dual charging or discharging, and the combined charging and discharging control switch may be implemented as integrated circuits, or using discrete devices. They can be embedded in a power system for power multiplexing control. The transfer device and the control section in the control switch may be implemented as two integrated circuits so that different transfer device can be chosen for use in different power rating. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1 A  is a basic configuration of a sequential charging control switch, in accordance with one embodiment of the present disclosure. 
         FIG.  1 B  illustrates an alternative configuration of a sequential charging control switch, in accordance with one embodiment of the present disclosure. 
         FIG.  2 A  is an exemplary control switch for parallel and sequential charging control, in accordance with one embodiment of the present disclosure. 
         FIG.  2 B  illustrates another exemplary control switch for parallel and sequential charging control, in accordance with one embodiment of the present disclosure. 
         FIG.  3 A  illustrates an exemplary sequential charging control chain for a set of battery modules, in accordance with one embodiment of the present disclosure. 
         FIG.  3 B  is an example to incorporate parallel charging function in a sequential charging control chain, in accordance with one embodiment of the present disclosure. 
         FIG.  4 A  is a basic configuration of a sequential discharging control switch, in accordance with one embodiment of the present disclosure. 
         FIG.  4 B  illustrates an alternative configuration of a sequential discharging control switch, in accordance with one embodiment of the present disclosure. 
         FIG.  5    illustrates an exemplary control switch for parallel and sequential discharging control, in accordance with one embodiment of the present disclosure. 
         FIG.  6    illustrates an exemplary sequential discharging control chain for a set of battery modules, in accordance with one embodiment of the present disclosure. 
         FIG.  7    illustrates an example of sequential charging and discharging control chains coupled to a set of battery modules, in accordance with one embodiment of the present disclosure. 
         FIG.  8 A  illustrates an exemplary control switch for charging or discharging control, in accordance with one embodiment of the present disclosure. 
         FIG.  8 B  illustrates another exemplary control switch for charging or discharging control, in accordance with one embodiment of the present disclosure. 
         FIG.  8 C  illustrates an exemplary control switch chipset for parallel and sequential charging or discharging control, in accordance with one embodiment of the present disclosure. 
         FIG.  9    illustrates various examples of using XOR/XNOR control switches for sequential charging or discharging control, in accordance with one embodiment of the present disclosure. 
         FIG.  10    illustrates an example of using various XOR control switches for sequential charging and discharging control chains coupled to a set of battery modules, in accordance with one embodiment of the present disclosure. 
         FIG.  11    illustrates an exemplary control chain configuration embedded with sub-control chains, in accordance with one embodiment of the present disclosure. 
         FIG.  12    illustrates an exemplary control switch chipset for parallel and sequential charging and discharging control, in accordance with one embodiment of the present disclosure. 
         FIG.  13 A  illustrates a basic configuration of a combined sequential charging and discharging control switch, in accordance with one embodiment of the present disclosure. 
         FIG.  13 B  illustrates an equivalent configuration of a combined sequential charging and discharging control switch, in accordance with one embodiment of the present disclosure. 
         FIG.  14    illustrates an exemplary parallel and sequential charging and discharging control chain, in accordance with one embodiment of the present disclosure. 
     
    
    
     DETAIL DESCRIPTIONS 
     There are advantages in partitioning the entire battery pack in an EV into a number of smaller removable batteries, referred to herein alternatively as battery modules or removable battery modules, to gain flexibility to control the charging and discharging of battery either on the battery pack as a whole or on the battery modules, depending upon the availability of power resources. 
     One advantage in partitioning the entire battery pack into a number of smaller removable battery modules is that the battery capacity in an EV becomes scalable. Depending upon the driving need, a suitable number of battery modules may be installed in the vehicle to optimize cost and energy use, rather than having a large battery pack in the vehicle all the time, which not only is more expensive to own, but also may not be energy efficient to carry a large pack of battery when driving around. A large battery pack may not be necessary for a short commuter. 
     Also, adapting the battery modules in an EV may provide drivers with another advantage, namely the flexibility to replace the depleted battery modules in a service station, or simply to charge a few depleted battery modules in a shorter time to get sufficient energy to reach destination, where the driver may then fully charge the entire battery pack. If a charging service is unavailable in a remote area, the EV driver may carry a few spare battery modules for replacement purpose. If spared battery modules are available, the spared battery modules may be charged at home station while the EV is being driven outside. The depleted battery modules may be replaced right away when the EV returns to the home station, so that the EV would be ready for driving again after replacing the depleted battery modules without a wait time to charge the battery pack. This may be useful for driving or delivery service companies. 
     Fast charging a relatively large battery pack, often requires a relatively more powerful charger which may not be available in most places, such as home. Using a level-1 or level-2 charger for charging a battery pack, takes longer time. For example, a 120V 20A AC level-1 charger may top out at about 2.4 KW and a 240V 40A AC level-2 charger may top out at about 9.6 KW. It would take hours or even a day to charge up a battery pack of 50 KWh capacity with such chargers. However, if a battery pack is partitioned into multiple removable battery modules, it would take a shorter time to charge up a certain number of battery modules that are sufficient for driving, compared with charging up an entire battery pack. 
     Energy harvesting is an emerging technology for EV. Although installing solar panel on EV surface may provide less power than a level-1 or level-2 charger, it may be suitable to charge a battery module having a smaller energy capacity. By observing the energy status of the battery modules, the EV driver could perceive to manage the EV battery charging with more flexibility. 
     When the battery pack in an EV is organized as a set of removable batteries, a method to manage the charging and discharging of the batteries in the battery pack automatically and without using an external microcontroller is desirable. A battery is alternatively referred to herein as a battery module or an energy device. There are many variations in control switches, which may be referred to as load switches, power multiplexers, power sequencers, or power switches, depending upon the applications. For example, some applications use power multiplexing to provide different voltages to power a single load under different cases for power saving or for legacy support concerns. Some power multiplexing is between a main power rail and a backup power rail at same voltage to provide a consistent power for use. 
     Partitioning a large battery pack in an EV into a set of smaller batteries or battery modules enables the charging and discharging of batteries in the battery pack to proceed on a per module basis.  FIG.  1 A  is an exemplary schematic diagram of a control switch  100  for power charging control, in accordance with one embodiment of the present disclosure. The control switch  100  may be linked to other control switches in a serial fashion to form a sequential control chain. An energy storage device, i.e., a battery or a battery module, could be coupled to a control switch in the sequential control chain. In an embodiment, the charging control switch  100  may comprise, in part, three basic elements, i.e., a voltage comparison device or comparator  110 , a 1:2 demultiplexer  120 , and a power transfer device  140 . The power transfer device may be composed of a set of MOS-FETS or bipolar transistors. The voltage comparator  110  compares an attenuated voltage VBATT, coupled to the battery module  145  derived by the voltage divider resistors R 1  and R 2 , with a reference voltage Vref to generate comparator  110 &#39;s output. The comparator output is saturated to a logic high when there is sufficient energy in the battery module  145 . Positive logic is selected for the comparator output in most of the examples described herein, unless specified otherwise. It is understood that by reversing the order of comparator inputs, the comparator output changes state, in which case inverter  115  may be eliminated. The 1:2 demultiplexer is referred to herein alternatively as a demultiplexer. The enable input signal PSCEN, namely a Prior Sequential Charging Enable signal, input to the control switch  100  is also an input to demultiplexer  120 . The enable output signal NXCEN, namely Next Charging Enable, which is an output from the control switch  100  and is also an output from the demultiplexer. The interface signal transferred through the control switch from the PSCEN input to the NXCEN output is only one AND gate delay. 
     The demultiplexer  120  has a select control signal  119 , which is derived from the output of comparator  110 . In the example shown in  FIG.  1   , the select control signal  119  of the demultiplexer  120  is the output of comparator  110  being inverted by inverter  115 . The demultiplexer  120  has two outputs. One output of demultiplexer  120  is derived by ANDing the select control signal  119  with the demultiplexer input via AND gate  125 , which is referred to as a “positivity output” hereinafter. The other output of demultiplexer  120  is derived by ANDing an inverse of the select control signal  119  by inverter  130  with the demultiplexer input via AND gate  135 , which is referred to as a “negativity” output hereinafter. Either the positivity output or the negativity output may be coupled to the transfer device  140  in control switch  100 . In the example shown in  FIG.  1   , the positivity output is coupled to the transfer device  140  and the negativity output is coupled to the enable output signal NXCEN. 
     In control switch  100 , when the enable input signal PSCEN is asserted and when energy in the battery module  145  is below a threshold voltage, the comparator  110 &#39;s output saturates to a logic low. The inversion of comparator output being a logic high value to the select control signal of demultiplexer  120  will assert the positivity output to enable the transfer device  140  to transfer energy from the external DC power source  105  to charge battery module  145 . In the meantime, the negativity output is negated to disable the NXCEN output from control switch  100 , which is also an enable input PSCEN to a subsequent control switch  101 . 
     If the delay from the select control signal  119  in control switch  100  through the negativity output to enable a transfer device  141  in a subsequent (also referred to herein as successor) control switch  101  is longer than the delay to negate the positivity output at control switch  100 , then a break-before-make power multiplexing takes place at the rise of the select control signal  119 , i.e., when the battery module  145  becomes fully charged. 
     The configuration of the demultiplexer is especially resilient in power multiplexing control. For example, if a delay device or delay buffer  123  is included between the select control signal  119  and the AND gate  125  in control switch  100  to adjust the timing to negate the positivity output so that the turn-off of transfer device  140  in control switch  100  matches the turn-on of the transfer device  141  in subsequent control switch  101  almost at the same time, then a concurrent switching is achieved. However, if the delay of the delay buffer  123  is further extended, then a break-before-make power switching can also be readily achievable at the rise of the select control signal  119 . The delay buffer  123  may be a wire connection, a buffer, an even number of inverters coupled in series, a delay line, a programmable delay line, and the like. The delay buffer  123  may be coupled along the timing path of the positivity output signal from the select control signal  119  to the input to transfer device  140 . 
     In an embodiment, the power multiplexing between the control switch  100  and a subsequent control switch  101  is completely under the control of a front control switch  100 , which means the subsequent control switch  101  does not need to query the voltage level or the power status at the front control switch  100  in order to switch the power control over. The front control switch  100  simply adopts a single enable output signal to control both switching and switching timing in a power multiplexing. 
     The negation of signal PSCEN negates the control switch  100  and all subsequent control switches linked to the control switch  100  in a control chain. When the signal PSCEN input is asserted, and when the battery module  145  has sufficient energy, the comparator  110  will saturate to a logic high level. The output of inverter  115  becomes a logic low to de-activate transfer device  140  in control switch  100 , thereby disconnecting DC power source  105  from charging the battery module  145 . In the meantime, the logic-low output at the inverter  115  will assert the NXCEN enable output signal, thereby activating the transfer device  141  in a subsequent control switch  101  to charge its associated battery module  146 . 
     If the battery module  145  does not have sufficient energy, the comparator  110 &#39;s output saturates to a logic low. The inverted output of comparator  110  to logic high by inverter  115  will activate the transfer device  140  in control switch  100  to transfer DC power source  105  to charge battery module  145 . In the meantime, the NXCEN output signal will be negated so that the transfer device  141  in any subsequent control switch  101  is inactivated and thus inhibited from charging its associated battery module  146 . 
     The transfer device  140  in  FIG.  1 A  uses a pair of PMOS-FET (PMOS)  142 ,  143  transfer gates to control power transfer. The body diodes in the pair of PMOS  142 ,  143  block the reverse current from power output pin VB and leakage current from the DC power source  105 . The body diode in PMOS  142  also provides a pull-up power for NMOS-FET (NMOS)  141 , which is pulled-down to drive the pair of active low PMOS  142 ,  143  when the output of AND  125  is asserted. The open drain STATUS output is pulled-up by an external resistor R 4  and is driven by NMOS  144 . The STATUS output is asserted when transfer device  140  is activated to charge battery module  145 . 
       FIG.  1 B  is another configuration of a sequential charging control switch  150 , in accordance with an embodiment of the present disclosure. The transfer device  190  in control switch  150  is coupled to the negativity output in the example. Instead of using an inverted comparator output as the select control signal as shown in  FIG.  1 A , the comparator  160  output is directly used as the select control signal  169  in control switch  150 . In  FIG.  1 B , the negativity output is coupled to the transfer device  190  in control switch  150 , and the positivity output controls the NXCEN signal. 
     If an inverse of the comparator  160 &#39;s output is used as the select control signal in control switch  150 , the positivity output shall be converted to the negativity output and the negativity output shall be converted to the positivity output without altering the functionality of the control switch, except that the characteristic of output timing is different. One advantage of demultiplexer  170  in control switch  150  is that by adjusting the device size of inverter  180 , it may balance the switching timing of the transfer devices in the control switch  150  and in a subsequent control switch. 
     In an embodiment, in the demultiplexer  170  when the inverter  180  coupled to the negativity output (at AND gate  175 ) is replaced by an inverse delay device, such as an inverting delay buffer, an odd number of inverters in series, a fixed or a programmable delay line with inverted output, to extend the assertion timing of negativity output at AND gate  175 , so that different types of switching, such as concurrently, break-before-make, or make-before-break power multiplexing is readily achievable by simply adjusting the delay timing at the negativity output, regardless of the transfer gate is being connected to the positivity output or to the negativity output. Similarly, a delay device may be incorporated at the positivity output path to adjust the positivity output timing for various power multiplexes. The inverse delay device or the delay device may be within the demultiplex or may be incorporated at the output path of the negativity output or the positivity output in the control switch respectively. 
       FIG.  2 A  illustrates an exemplary sequential charging control switch  200 , in accordance with another embodiment of the present disclosure. A parallel charging control is included in the control switch  200  as an optional feature. A parallel charging can charge more battery modules concurrently when a larger power source is available, such as a level-3 charger. Whereas sequential charging, which charges battery module one at a time, may be more suitable for connecting to a smaller power source. To support both parallel and sequential charging, an OR gate  231  receives a first enable input “Parallel Charging ON” (PACON), and a second enable input “Prior Sequential Charging Enable” PSCEN, to generate a new enable input “Prior Charging Enable” PRCEN, for control switch  200 . The PRCEN signal shown becomes an input to the 1:2 demultiplexer  220 . The OR gate  231  may be included in the control switch  200 , or an external add-on device to the control switch. 
     Either the assertion of PSCEN or the assertion of PACON could enable demultiplexer  220  in control switch  200  to activate transfer device  240  to transfer a DC power source  205  to charge battery module  245 , provided that the energy in the battery module  245  being detected by the comparator  210  is at a low level, and that the DC power source  205  being detected by the comparator  211  has sufficient energy in it. The comparator  210  monitors an attenuated voltage VBATT from battery module  245 , derived by voltage divider R 3 , R 4 , and the comparator  211  monitors an attenuated voltage VATT of DC power source  205 , derived by voltage divider R 1 , R 2 . 
     In control switch  200 , besides monitoring energy status of battery module  245  by comparator  210  output, the select control signal to demultiplexer  220  is derived by ANDing enable qualifiers with AND gate  219  which performs a Boolean AND of, in part, the energy status of DC power source  205  and the detected status on abnormalities, such as overvoltage and over current at power input, device junction over-temperature, short circuit, plus an optional inhibit control INHIBIT, which is useful for external device to temporarily disable control switch  200 . The assertion of abnormalities will cause the demultiplexer  220  to deactivate the transfer device  240  and assert the NXCEN signal to enable a subsequent control switch. 
     The transfer device  240  in control switch  200  uses a pair of NMOS field-effect transistors  242 ,  243  to control power transfer. The gate voltage of a NMOS transistor shall be higher than its source voltage for the transistor to operate in a conductive region. A charge pump  246  which sources VIN from the DC power source  205  boosts the output voltage of driver  241  to turn on NMOS transistors for power transfer when the transfer device  240  is activated. 
     It is flexible to couple the transfer device in the control switch to the positivity output or the negativity output as long as the polarity of the select control signal can be changed accordingly. The control switch  250  in  FIG.  2 B , which is otherwise similar to control switch  200  of  FIG.  2 A , shows such an example. When the negativity output is chosen to activate the transfer device  290  in demultiplexer  270 , the polarity of the select control signal is inverted from AND  219  to a NAND function. A Boolean equivalence shown in  FIG.  2 B  converts the NAND function into an OR  269 , where all inputs to OR  269  are inverted accordingly. The converted OR  269  output becomes the select control signal to demultiplexer  270 . 
       FIG.  3 A  illustrates an exemplary sequential charging control chain which links a set of charging control switches in series, in accordance with another embodiment. Although only three control switches  310 ,  320 ,  330  are shown in the example, it is understood that more control switches may be linked in a control chain. In the example shown in  FIG.  3 A , a key switch  301  controls the activation of the control chain  300 . When key switch  301  is open, the pull-down resistor R 1  disables the entire control chain  300 . When the key switch  301  is closed, a logic high V LOGIC  output from key switch  301  asserts an enable input signal PSCEN to the first control switch  310 , which also activates the control chain  300 . The control switch  310  monitors the energy status at DC power source  305  with comparator  311 , and the energy status in battery module  319  with comparator  312 . Both comparison results are coupled to AND gate  313  in the example to generate the select control signal for the demultiplexer  315 . Either the positivity output or the negativity output may be chosen to activate the transfer device. In control switch  310 , the positivity output is chosen. An inverter  314  is required to invert the comparator  312  output for the charging application. When energy in battery module  319  is below a threshold voltage, the comparator  312  output saturates to a logic low. As the transfer device  318  in the example of  FIG.  3    is coupled to positivity output, it requires a logic high at the select control signal to assert the positivity output, and inverter  314  inverts the comparator output in such conditions. 
     When the battery module  319  is charged to reach a threshold level, the comparator  312  output saturates to a logic high and the AND  313  output becomes a logic low. A low logic level signal at the select control signal of demultiplexer  315  asserts signal NXCEN at negativity output, and asserts signal PSCEN, thereby enabling a subsequent control switch  320  and de-activating the transfer device  316  coupled to the positivity output in control switch  310 . A similar process will proceed until all control switches  320 ,  330  in the charging control chain  300  are activated, thus causing all battery modules  319 ,  329 ,  339  to be sufficiently charged and disconnected from the DC power source  305 . 
     A linking sequence is formed as described below. The linking sequence as shown in  FIG.  3 A  starts from the PSCEN signal being supplied by key switch  301 ; the signal PSCEN, in turn is input to AND gate  317  in control switch  310  to generate signal NXCEN, which, in turn, is shown as being the signal PSCEN input to the second control switch  320  and applied to input to AND gate  327  in control switch  320 ; AND gate  327  generates signal NXCEN for control switch  330 , which, in turn, is shown as being the PSCEN input to a third control switch  330 , and the like. The linking sequence, as described herein, forms the sequential control chain  300 , where a common DC power source  305  charges a set of battery modules  319 ,  329 ,  339 . The first switch in the chain, namely control switch  310 , has a higher priority than control switch  320 , and control switch  320  has a higher priority than control switch  330 . 
     An asserted enable control output signal may skip multiple contiguous control switches in the control chain, if energy in the batteries coupled to these control switches happens to be full. The delay in search of a subsequent control switch to activate in a sequential control chain is one AND gate delay per stage. 
     In some embodiments, when an enable output signal from a higher priority control switch in a control chain is asserted, such as replacing a fully changed battery module with an empty battery module in a battery pack, all subsequent enable output signals starting from that higher priority control switch are negated to activate the higher priority control switch for battery charging, regardless of the number of stages in between. 
       FIG.  3 B  illustrates an example of an embodiment of a charging control switch  350  that implements parallel control. Embodiment  350  is similar to embodiment  300  except that embodiment  350  includes, in part, an OR gate to OR (i.e., perform a Boolean OR function) a parallel enable signal PACON applied to all control switches  360 ,  370  and  380 . For example, the OR gate  364  associated with charging control switch  360  performs a Boolean OR operation of signal PACON with the serial enables signal PSCEN associated with charging control switch  360  to generate a control signal PRCEN applied to AND gate  367 . The output signal of AND gate  367  is applied to an input terminal of OR gate  374  associated with charging control switch  370 , and similarly the output signal of AND gate  377  is applied to an input terminal of OR gate  384  associated with charging control switch  380 . Accordingly, all control switches in the control chain  350  can be enabled for parallel charging and for sequential charging for all battery modules coupled to the control chain  350 . Key switches  302 ,  303  are adapted to assert the enable signal for sequential charging and parallel charging respectively. Key switch  351  initiates sequential charging and key switch  352  initiates parallel charging. Similarly, when key switch  352  is open, the parallel charging control signal PACON is disabled by the pull-down resistor R 2  and the control chain  300  is enabled for sequential charging if the key  351  is closed to assert the signal PSCEN. However, when key switch  352  is closed, the assertion of PACON will cause all outputs at OR gates  364 ,  374 ,  384  to assert, thereby to enable all control switches  360 ,  370 ,  380 , alternatively referred to herein as charging control switches, in the control chain  350  to activate their respective transfer devices  366 ,  376 ,  386  to transfer energy from the DC power source  355  to charge their associated battery modules  369 ,  379 ,  389  concurrently. When battery modules in the parallel charging control chain are charged, AND gate  368 ,  378 ,  388  coupled to their respective negativity outputs to enable transfer device  366 ,  376 ,  386 , disposed respectively in control switch  360 ,  370 ,  380 , will be negated to cut off the DC power source  355  from further charging the respective battery module, while the respective enable output signals coupled to their respective positivity outputs generated by AND gate  367 ,  377 ,  387  are asserted. However, the assertions of the enable output signals have no impact on parallel charging operation. The ORed outputs from OR gates  364 ,  374 ,  384  suppress, respectively, the outputs of AND gates  367 ,  377 ,  387 , when the parallel charging operation is enabled. 
     A parallel charging is suitable to charge battery modules when there is a high-intensity power source available for fast charging, such as a level-3 charger. Other charging sources, such as a level-1 or a level-2 charger, may not be energetic enough to timely charge up an entire battery pack. Some emerging technology, such as installing solar panel on car surface or even disposing piezoelectric membranes on air flow path in EV to harvest moving energy could be an viable option, although may not be as intensive. A sequential charging chain is suitable for harvesting such green energy resources, if the battery pack in EV are partitioned into multiple smaller battery modules. 
     Depending upon the intensity of regenerated energy and the cost consideration, for example, solar panel may use a device that performs pulse width modulation (PWM) at the output of solar panel, which is switched on and off at a specific frequency to generate an output voltage compatible with the voltage rating of battery modules to charge the battery modules linked in a sequential charging control chain. However, when a large solar power system is available for battery charging, the solar panel output may be connected to a more efficient maximum power point tracking (MPPT) device adapted to output a relatively higher voltage and power to charge more batteries at once. Such a large-scale solar panel may activate parallel charging in a charging control chain with parallel charging support when a strong solar power output is available. When the solar panel output becomes relatively weaker, the charging may be automatically switched to sequential charging. 
       FIG.  4 A  is a basic schematic configuration of a sequential discharging control switch  400 , in accordance with one embodiment of the present disclosure. Switch  400  as shown includes, in part, a voltage comparator  410 , a 1:2 demultiplexer  420 , and a power transfer device  440 . The comparator  410  compares an attenuated voltage VATT derived from voltage divider R 1 , R 2  coupled to battery module  405  to a reference voltage Vref. The output of comparator  410  is used to generate select control signal for demultiplexer  420 . 
     A discharging control switch is similar to a charging control switch, where both monitor the energy status of a coupled battery. However, for a charging control switch, when energy in the coupled battery is detected to be a low level, a charging activity takes place until the battery is charged to a designated level (e.g., 80%, 90%, or 100% as determined by a user) at which point the charging stops. For a discharging control switch, when energy in the coupled battery is detected as a logic high indicating that the battery charge is sufficient, a discharging activity takes place. The discharging activity stops when the energy in the battery reaches a designated level (e.g., 5%, 10%, or 15% as determined by a user). The difference between the two control switches is at the comparator output being saturated to a logic high for the discharging operation, or saturated to a logic low for the charging operation. The transfer device in control switch is activated when charging or discharging takes place. 
     In control switch  400 , the transfer device  440  may be adapted to couple to the positivity output or to the negativity output, depending upon the choice of a proper polarity for the select control signal. Control switch  400  shown in  FIG.  4 A  may further include, in part, a delay buffer  425  coupled to the positivity output at AND gate  425 . The delay buffer  425  may be a wiring interconnect, a buffer, an even number of inverters, a delay line, a programmable delay line, and the like. The delay buffer  425  may be included along the timing path of the positivity output signal from the select control signal to the input to transfer device  420 . It also includes an inverter  430  at the input to the negativity output at AND gate  435 . The inverter  430  may be an odd number of inverters, an inverting buffer, a fixed or a programmable inverting delay line, and the like. Accordingly, the discharging control switch  400  is adapted to perform concurrent, break-before-make, or make-before-break power multiplexing. 
     Referring to  FIG.  4 A , when the battery module  405  has sufficient energy, the output of comparator  410  saturates to a logic high level. A high at the comparator  410 &#39;s output, which is also as the select control signal for demultiplexer  420 , asserts the positivity output, thereby to activate transfer device  440  to transfer energy from battery module  405  to VOUT in power discharging, if the enable input signal PSDEN is also asserted. 
     Conversely, if comparator  410 &#39;s output saturates to a logic low level, thereby indicating that battery module  405  does not have sufficient energy for output, then a logic low signal at the select control signal of demultiplexer  420  asserts the negativity output; this asserts the enable output signal for a subsequent control switch to activate its transfer device to discharge a coupled battery module to output energy for external use, provided that it has sufficient energy available. 
     A buffer  426  may be coupled at next to the enable input of transfer device  440  to indicate that power discharging is in progress at control switch  400 . If buffer  426  is reconnected to the comparator  410 &#39;s output, then it would indicate the power status of battery module  405 , regardless of any abnormality that may encounter in the control switch  400 . 
       FIG.  4 B  is another schematic configuration of a sequential discharging control switch  450 , in accordance with another embodiment of the present disclosure. In switch  450 , the positivity output and the negativity output, being the outputs of AND gates  485  and  480 , coupled to signal NXDEN and transfer device  490  are reversed relative to the negativity and the positivity outputs coupled to signal NXDEN and transfer device  440  in control switch  400 . The polarity of the select control signal for demultiplexer  470  of  FIG.  4 B  is inverted by inverter  465  relative to that of demultiplexer  420  of  FIG.  4 A . 
       FIG.  5    is a schematic diagram of a parallel and sequential discharging control switch  500 , in accordance with another embodiment of the preset disclosure. The parallel and sequential discharging control switch  500  includes qualifier logic to detect operational abnormalities, such as overvoltage and over current at input power, device junction over-temperature, short circuit, and the like. The inverse of detected abnormalities is logically ANDed, via NAND gate  515 , with the comparator  510  output to generate the select control signal for demultiplexer  520 , where the comparator  510 &#39;s output monitors the energy status in battery module  505 . An optional control signal INHIBIT may be included for an external device to disable the transfer device  540  in control switch  500 . 
     In  FIG.  5   , if battery module  505  has sufficient energy and no abnormalities come across, the AND function output will be at a logic high, which is implemented by NAND gate  515  so as to output a logic low to assert the negativity output to activate the transfer device  540 . In case encountering any abnormality, the select control signal will become a logic high for demultiplexer  520  to deactivate the transfer device  540  and to assert the NXCEN, which causes a subsequent control switch to be activated. 
     Similarly, a second enable input signal PADEN is included in the control switch  500  to OR with the sequential enable input signal PSDEN by OR gate  516  to generate an input signal PRDEN for input to the demultiplexer  520 . Either the assertion of PADEN or the assertion of PSDEN will assert the negativity output to activate transfer device  540  to transfer battery  505  energy for external use when the select control signal at output of NAND  515  is a logic low. The OR gate  516  may be an internal logic or an external add-on device to control switch  500 . 
     An output buffer  576  may be coupled at the negativity output next to the transfer device  540  for status observation. When the STATUS output is asserted, it indicates the control switch  500  is discharging battery energy through terminal VOUT under a satisfactory discharging condition. The output buffer may be re-positioned to the output of comparator  510  to indicate if the battery module  505  has sufficient energy, and thus for observing the energy status of respective battery module in a battery pack. 
       FIG.  6    is a schematic diagram of a sequential discharging control chain  600  linking a set of discharging control switches  610 ,  620 ,  630 ,  640  to control sequential discharging for a set of battery modules  650 ,  660 ,  670 ,  680  in a battery pack  605 , in accordance with one embodiment of the present disclosure. Although only four discharging control switches  610 ,  620 ,  630 ,  640  are shown, it is understood that any number of discharging control switches may be chained to form a link. 
     Key switch  606  is used to initiate the discharging operation in control chain  600 . Optional switches, BK i  and SW i , where is an index ranging from 1 to 4 in the example shown in  FIG.  6   , are connected in series for each discharging switch. For example, optional switches BK 1  and SW 1  are connected to the discharging switch  610  between battery module  650  and the input to the discharging switch  610 . Similarly, switches BK 2  and SW 2  are used in discharging switch  620  between battery module  660  and the input to the discharging switch  620 . Switch BK i  is normally open and the SW i  switch is normally closed. When control key switch  606  is open, its pull-down resistor R 1  ensures all BK i  switches remain open. When the key switch  606  is closed, a logic high voltage V LOGIC  is delivered to enable the sequential discharging control chain  600  and to close all BK i  switches so that battery modules are coupled to their respective discharging control switches in the sequential discharging control chain  600 . 
     Each switch SW i  becomes open when the energy in its respective battery module falls below a designated level. For example, when energy in battery module  650  is depleted to fall below a designated level, signal NSDEN 1  will be asserted to open switch SW i , which will disconnect battery module  650  from control switch  610  in order to prevent further depletion of energy in battery module  650 . The assertion of signal NSDEN 1  also enables a subsequent control switch  620  in control chain  600  to proceed power discharging, provided that its coupled battery module  660  has sufficient energy. Otherwise, a next control switch  630  will be enabled by asserting signal NSDEN 2 , which will also disconnect the SW 2  switch. The operation proceeds automatically and, in the manner described until all battery modules coupled to their associated discharging control switches in the control chain  600  are depleted, at which point all SW i  switches become open again. 
     A delay element also referred to herein as device  618  may be optionally included at the output of the first control switch  610 . Initially all switches BK i  switches are open via pull-down resistors R 1  when the control key switch  606  is open. In the exemplary control chain  600 , the positivity output at the output of AND gate  616  disposed in control switch  610  is initially at a logic low due to the negation of signal PSDEN 1 . But when the control key switch  606  is closed, signal PSDEN 1  is asserted to enable signal NSDEN 1  after an AND gate delay and may open switch SW 1  earlier than the assertion of the comparator  612 , thereby possibly causing a race condition with the rise of energy in control switch  610 , which may, in turn, prevent battery module  650  from sourcing power to control switch  610 . To prevent such a race condition, delay device  618  is used at the output of AND  616 . The delay associated with delay device  618  is selected to be long enough for the first control switch  610  in the control chain  600  to be fully initialized to prevent switch SW 1  from being switched off too early. The race, if not inhibited, may prevent a few battery modules from supplying power. In some embodiment, switches SW i , which are adapted to protect their coupled battery modules from deep depletion when the key switch  606  is kept on for a long time, may not be used in the discharging chain  600 . In such embodiments switches BK i  may be maintained to prevent battery modules from deep-depletion when battery pack  605  is keyed off. 
       FIG.  7    is a schematic diagram of a sequential charging and discharging control for a set of battery modules  719 ,  729 ,  739  in battery pack  705 , in accordance with one embodiment of the present disclosure. Battery pack  705  is shown as being coupled to a sequential charging control chain  700  adapted to perform sequential charging, and also coupled to a sequential discharging control chain  750  adapted to perform sequential discharging. The sequential charging and discharging may take place concurrently. Although only three charging control switches and three discharging control switches, i.e., only three stages, are shown, with each charging and discharging stage associated with one of the battery modules, it is understood that embodiments of the present application are not so limited and equally apply to any number of stages. As shown each stage includes a charging control switch in the charging control chain  700 , a battery module in battery pack  705 , an optional switch CK i  for battery charging protection and an optional switch BK i  for battery discharging protection, and a discharging control switch, where “i” is an index ranging from 1 to 3 in this example. Although the positivity output is chosen to activate the transfer device in the charging control switch and the negativity output is chosen to activate the transfer device in the discharging control switch, it is understood that different configurations may also be used. 
     In  FIG.  7   , a normally-open key switch  702  is chosen to initiate the operation of the sequential charging control chain  700 , which includes charging control switches  710 ,  720  and  730 . When a control switch in a charging control chain meets the activation conditions, such as a coupled battery module being in place, or the energy in a coupled battery module being below a predefined value, or no abnormalities in control switch being detected, and the loke, then the control switch is activated to charge its coupled battery module. Otherwise, the control switch will be skipped to search for another subsequent control switch in the control chain that meets the activation condition to activate. The search for a control switch in the control chain to be activated could be as fast as an AND gate delay per stage. A control switch and its subsequent switch to be activated are normally back-to-back in most cases. 
     In an embodiment, the demultiplexer in the control switch controls the switching from a control switch (e.g.,  710 ) to a subsequent control switch (e.g.,  720 ) without a handshake protocol. The switching time to de-activate a control switch (e.g.,  710 ) and to activate a subsequent control switch (e.g.,  720 ) in the control chain  700  is also controllable by the demultiplexer (e.g.,  716 ) in the control switch (e.g.,  710 ), where the assertion and the desertion of the positivity output and the negativity output, respectively, in the control switch (e.g.,  710 ) can be controlled by adjusting the internal delay in the demultiplexer (e.g.,  716 ). 
     A set of normally-open switches CK 1 , CK 2  and CK 3  are shown as being disposed between the charging control switches  710 ,  720 ,  730  and the battery modules  719 ,  729 ,  739  respectively. When the key switch  702  is open, the pull-down resistor R 1  connected to key switch  702  will keep all switches CK 1 , CK 2  and CK 3  open to prevent potential power leakage from battery modules, such as due to the presence of a current path in voltage divider connected to battery module. When the key switch  702  is closed, all CK 1 , CK 2 , and CK 3  switches are closed, thereby enabling the charging control switches  710 ,  720 ,  730  to connect to their respective battery modules  719 ,  729 ,  739  in the sequential charging chain  700 . 
     It is possible to divide the charging control chain into multiple sub-control chains. For example, the link connection between the negativity output of control switch  720  and the enable input PSCEN of control switch  730  is disconnected and a key switch  704  is connected to the PSCEN input to control switch  730 , then two sub-control chains, where one consists of control switches  710 ,  720  and the other consists of control switch  730 , are formed. When the same DC power source is applied to multiple sub-control chains, then power charging to the multiple sub-control chains proceeds in parallel. Different DC power sources may be connected to different sub-control chains to charge sub-control chains respectively when the DC power sources are available. A microcontroller may be used to activate the control chain or portions of the control chain, instead of using a key switch. 
     In the sequential discharging control chain  750  is shown as including the discharging control switches  760 ,  770 ,  780 , where a separate normally-open key switch  703  initiates the operation of the sequential discharging control chain  750 . The output timing of demultiplexer (e.g.,  766 ) in its associated discharging control switch (e.g.,  760 ) may be adjusted to enable concurrent switching to a subsequent discharging control switch (e.g.,  770 ) to minimize power glitch during the discharging power transition in control chain  750 . 
     A set of normally-open switches BK 1 , BK 2  and BK 3  are shown as being disposed between the battery modules  719 ,  729 ,  739  and the discharging control switches  760 ,  770 ,  780 , respectively. When, for example, key switch  703  is open, the pull-down resistor R 2  coupled to the output of key switch  703  will keep all switches BK 1 , BK 2 , BK 3  open to prevent power leakage from battery modules  719 ,  729 ,  739 . When switch  703  is closed, switches BK 1 , BK 2 , BK 3  will be closed to couple battery module  719 ,  729 ,  739  to their respective discharging control switches  760 ,  770 ,  770  to enable sequential power discharging for the set of battery modules in the control chain  750 . 
     Similarly, in some embodiments, the discharging control chain may be divided into multiple sub-control chains with each sub-control chain being enabled by an associated key switch. For example, when the link connection between the negativity output of control switch  770  and the PSDEN input to control switch  780  is disconnected and a key switch  705  is connected to the PSDEN input of the control switch  780 , then two discharging sub-control chains, where one consists of control switches  760 ,  770  and the other consists of switch  780 , are formed. When the outputs of both discharging sub-control chains are coupled together and both key switches  703 ,  705  are closed, then both sub-control chains will discharge power simultaneously to double the VOUT power output. When the discharging control chain is partitioned into multiple sub-control chains with outputs of all sub-control chains being coupled together, then the output current of the discharging control chain will be increased by multi-folds when all switch keys are closed to enable the sub-control chains. The output of discharging sub-control chain may be sourced for different applications. The highest power output from the discharging control chain  750  is achieved when all control switches are enabled to operate in parallel. 
     The sequential charging control chain  700  and the sequential discharging control chain  750  are adapted to perform sequential charging control and sequential discharging control concurrently. The control switches in both charging and discharging control chains are adapted to avoid collision when the same battery module is accessed for charging and discharging concurrently. Using the battery module  719  as an example, if the battery module  719  has sufficient energy, the comparator  711  in the charging control switch  710  will saturate to a logic high and its inverted output will negate the select control signal at AND  715  to disable the transfer device  718  in the charging control switch  710 . This causes the battery module  719  to be disconnected and thus prevents battery module  719  from being charged by the DC power source  701  when the battery module is enabled to be discharged, regardless of whether the control switch  710  is activated by the charging control chain  700  for charging. Thus, when a battery module has sufficient energy to undergo discharging, the battery module will be skipped by the charging control chain so as not to be charged. 
     Conversely, if a battery module does not have sufficient energy, the battery module&#39;s corresponding discharging control switch is prevented from activating its transfer device to source energy in the discharging control chain. Thus, when, for example, the charging control switch  710  in the control chain  700  has been enabled to charge its battery module  719 , the discharging of the battery module  719  is prevented automatically. 
     In an embodiment, the charging control chain and the discharging control chain coupled to same set of battery modules in a battery pack will not charge and discharge the same battery module at the same time, and thus are adapted to operate seamlessly for battery charging and discharging under the control of control switches linked in charging and discharging control chains. Preventing a DC power source  701  from supplying power to a battery module when the battery module is being discharging avoids voltage contention between the DC power input and the battery module&#39;s output at VBOUT. 
     The control chain configuration in  FIG.  7    may be used to harvest energy from various DC power sources. To simultaneously harvest energy from multiple DC power sources to charge a battery pack, a charging control chain may be divided into multiple sub-control chains to enable concurrent charging by various power sources, where a sub-control chain is coupled to a respective DC power source to power the charging control switches controlled by a charging sub-control chain. In EV applications, such multiple DC power sources may include, for example, the power charger, the energy harvested from solar panel installed on the EV&#39;s body surface, and the potential energy harvested from piezoelectric membranes affixed along the air flow path. The air flow induces bending and vibrations of the piezoelectric membranes from which energy may be harvested energy during driving. 
       FIG.  8 A  illustrates an exemplary switch adapted to control power charging or power discharging, in accordance with one embodiment of the present disclosure. The configuration of a charging control switch and a discharging control switch are different in that the comparison device in the charging control switch monitors if energy in a coupled battery module is below a predefined level to initiate the energy charging operation, while the comparison device in the discharging control switch monitors if energy in a coupled battery module is above a predefined level before initiating the energy discharging operation. The select control signal for the demultiplexer in both control switches differ in the polarity of comparator output. 
     Referring to  FIG.  8 A , a two-input exclusive OR gate  815  receives the output of comparator  810  at one of its input terminals, and receives control signal CHARGE at its other input terminal. Signal CHARGE is also an input to the control switch  800  which is adapted to function as a charging control switch, if the CHARGE control signal is set to a logic high or “1”, where XOR  815  acts as an inverter as is also shown in control switch  100  of  FIG.  1 A . 
     The XOR gate  815  operates as a pass-through buffer if signal CHARGE is at a logic low or “0”. When signal CHARGE is set to “0”, control switch  800  operates as a discharging control switch, as is also shown in the discharging control switch  400  of  FIG.  4 A . The second input to XOR  815  is the output of comparator  810 , which monitors an attenuated voltage at power input VIN. For charging operation, VIN of control switch  800  is coupled to an external DC energy source with VOUT output coupled to a battery module or to a load. While for discharging operation, VIN is coupled to a battery module with VOUT to be connected for external use. 
     The XOR  815  output is shown as being ANDed with other qualifiers, such as an inverted INHIBIT input via inverter  816  and the detected results of abnormalities, using AND function  819 , that in response generates the select control signal of 1:2 demultiplexer  820 , where an inverted Abnormality signal indicates no abnormalities being encountered by control switch  800 . The INHIBIT control is an optional feature for an external device to temporarily disable the power transfer function in control switch, if necessary. The 1:2 demultiplexer  820  controls the enabling of transfer device  830  and the switching to other control switch. The control switch  800  is applicable for charging or discharging operations by selecting the CHARGE control signal. The control switch  800  may be alternatively referred to herein as a “duality control switch”. 
       FIG.  8 B  illustrates another exemplary switch adapted to control power charging or power discharging, in accordance with another embodiment of the present disclosure. Referring to  FIGS.  8 A and  8 B , the positivity output which is adapted to activate the transfer device  830  in duality control switch  800  of  FIG.  8 A  may be converted to the negativity output to activate the transfer device  860  of  FIG.  8 B , shown as being coupled to the demultiplexer  870  in control switch  850  in  FIG.  8 B . For the reconfiguration, the select control signal at output of AND  819  should also be inverted into NAND accordingly. The Boolean equivalence shown in control switch  850  of  FIG.  8 B  includes the conversion of NAND into OR  869  in  FIG.  8 B , as well as the inversion of all its inputs in control switch  850 , which include the inversion of XOR  815  to XNOR  865  and the elimination of inverters at the INHITBIT input and the abnormality inputs. The buffer  879  is an optional feature for power transfer status observation. 
     Referring to  FIG.  8 B , having the negativity output signal of the demultiplexer to drive the transfer device in a control switch is advantageous in concurrent switching control. For example, in control switch  850 , by adjusting the device size of inverter  875 , or using an odd number of inverters linked in series to replace the single inverter  875 , or using a fixed or a programmable delay line with an inverted output, so that the total delay from select control signal at input to demultiplexer  870  through the inverter function  875  to negativity output to deactivate the transfer device  860  matches the total delay of positivity output through AND gate  878  to enable and to activate the transfer device in a subsequent control switch, then a concurrent switching in power multiplexing is achieved 
     However, if the delay of inverter function  875  in demultiplexer  870  is adjusted to further extend the delay so that the transfer device in a subsequent control switch is fully turned on, while the transfer device  860  in the control switch  850  is still not turned off during power switching, then this achieves a make-before-break power multiplexing, which is useful in the applications where a load is connected to multiple power sources but cannot afford to have any interruption in the power supply to the load. Such extended delays are useful for the persistent power application. 
     By referring to  FIG.  8 A , similarly, the switching timing for transfer device  830  in control switch  800  may be adjusted by including a delay buffer device  826  at the positivity output path of demultiplexer  820 , which may be a simple wire connection, a buffer, an even number of inverters in series, a delay line, or a programmable delay line with adjustable delay timing to achieve a concurrent switching or a break-before-make power multiplexing. In the break-before-make power multiplexing, the total delay from the assertion of select control signal, through the negativity output via AND gate  828  and the demultiplexer of a subsequent control switch to activate its transfer device is longer than the total delay to the positivity output to deactivate the transfer device  830  in control switch  800 . The break-before-make power multiplexing is useful in the applications where multiple DC power sources of different voltages are connected to power a load. The adjustment of delay timing at the two demultiplexer outputs in control switch is distinct and advantageous. 
     In an embodiment, the transfer device  830 ,  860  of  FIG.  8 A,  8 B  may be an external device to provide more flexibility for use by a heavier power load as shown in  FIG.  8 C . The transfer device in the transfer section  882  of control switch  880  in  FIG.  8 C  may be an off-the-shelf device, while the control section  881  may be implemented using discrete devices or as one or more integrated circuits. 
     The duality control switch  800  in  FIG.  8 A  may be re-configured to use an inversion of the CHARGE signal, i.e., DISCHARGE, as an external control for discharge operation. When the inversion of CHARGE is selected as a control input, the XOR  815  in  FIG.  8 A  is inverted and replaced by XNOR  885  as shown in  FIG.  8 C . In  FIG.  8 C , when the DISCHARGE input is a logic high or “1”, the XNOR  885  functions as a pass-through buffer and the control switch  880  becomes as a discharging control switch. When the DISCHARGE input is a logic low or “0”, the XNOR  885  functions as an inverter and the control switch  880  operates as a charging control switch. The output of NAND gate  889 , which is an inversion of the select control AND in control switch  800  shown in  FIG.  8 A , provides the select control signal of demultiplexer  890  in control switch  880 . Thus, the transfer device  895  in control switch  880  is changed to couple from the positivity output to the negativity output. 
     An optional parallel charging and discharging operations may be included in control switch  880 . This is achieved by incorporating a second control enable signal PAEN, i.e., a parallel enable or a pairing enable, at the input of control switch  880  to OR with the sequential enable signal PSEN by OR gate  888  to generate a new enable signal PREN to apply to the control section  881  in control switch  880 , which is also a new enable input to the demultiplexer  890 . 
       FIG.  9    shows a variety of examples using XOR/XNOR gates, in part, in the implementation of charging or discharging operations for the duality control switch, where four cases are illustrated for sequential charging control and four cases are also illustrated for sequential discharging control. Only the AND function is illustrated in the derivation of the select control signal for duality control switch. If the NAND function is also included in the derivation of the select control signal, then the number of configurations of a duality control switch in charging or discharging operation is doubled. Rather than using a specific CHARGE or DISCHARGE to name the control input of duality control switch, a neutral name “Function Select” is used instead. Regardless of the CHARGE or DISCHARGE signal being a “1” or “0”, the duality control switch can perform either as a charging control switch or as a discharging control switch. Using “function select” to name the input control signal avoids such a confusion. 
     In  FIG.  9   , all illustrations (i)-(viii) assume the enable input signal to the duality control switch is asserted. The illustration (i) is a sequential charging control switch of case  1 , where comparator  911  compares an attenuated voltage derived from energy device (or battery)  919  coupled to control switch  910 . When the attenuated voltage detected by comparator  911  causes the comparator output to saturate to a logic low or “0”, it means there is no sufficient energy in energy device  919 , where “battery empty” is used to represent such a situation hereinafter. When the function select is a positive input or “1”, the XOR gate  912  inverts the comparator output to have a high or “1” at the AND  915  output as select control signal to assert positivity output at control switch  910 . If transfer device  918  is selected to couple to positivity output, the assertion of positivity output will activate the external DC power source to charge energy device  919  or battery, a sequential charging control switch  910  is formed. 
     The illustration (ii) of  FIG.  9    shows a sequential charging control switch of case  2 . When battery is empty to cause comparator&#39;s  921  output to saturate to a logic low or “0”, and when function select is a negative input or “0”, the XOR gate  922  buffers comparator&#39;s  921  output to have a low or “0” at the AND  925  output as select control signal to assert the negativity output at control switch  920 . If transfer device  928  is selected to couple to the negativity output, the assertion of negativity output will activate the external DC power source to charge energy device  929  or battery, a sequential charging control switch  920  is thus formed. 
     The illustration (iii) shows a sequential charging control switch of case  3 . When battery is empty, the comparator  931  saturates to a logic low or “0”. And when the function select is a positive input or “1”, the XNOR gate  932  buffers the comparator  931  output to have a low or “0” at AND  935  output as select control signal to assert negativity output. If transfer device  938  is coupled to the negativity output of control switch  930 , the assertion of negativity output will activate transfer device  938  for external DC power source to charge energy device  939  or battery, a sequential charging control switch  930  is formed. 
     The illustration (iv) shows a sequential charging control switch of case  4 . When battery is empty, the comparator  941  saturates to a logic low or “0”. And when the function select is a negative input or “0”, the XNOR gate  942  inverts comparator&#39;s  941  output to have a high or “1” at the AND  945  output as select control signal to assert positivity output. If the transfer device  948  is coupled to the positivity output of control switch  940 , the assertion of positivity output will activate transfer device  948  for external DC power source to charge energy device  949  or battery coupled to control switch  940 , a sequential charging control switch  940  is thus formed. 
     Referring to (i) and (iii), or (ii) and (iv) in  FIG.  9   , when the function select input is kept unchanged, by changing XOR to XNOR in the pair of charging control switches  910  and  930 , or changing XNOR to XOR in the pair of charging control switches  920  and  940 , the coupling of transfer device to positivity output or to negativity output in each pair of control switches shall be exchanged accordingly to perform as charging control switch, except that the characteristic of output timing in each pair of control switches is altered. 
     The illustration (v) of  FIG.  9    shows a sequential discharging control switch of case  1 , where comparator  951  compares an attenuated voltage derived from energy device (or battery)  959  coupled to control switch  950 . When the attenuated voltage detected by comparator  951  causes the comparator output to saturate to a logic high or “1”, it means a sufficient energy in energy device  959  and “battery full” is used to represent such a situation hereinafter. When function select is a negative input or “0”, the XOR gate  952  buffers comparator output to have a high or “1” at the AND  955  output as select control signal to assert positivity output. If transfer device  958  is coupled to the positivity output of control switch  950 , the assertion of positivity output will activate transfer device  958  to output energy from energy device  959  for external use, a sequential discharging control switch  950  is thus formed. 
     The illustration (vi) of  FIG.  9    shows a sequential discharging control switch of case  2 . When energy device  969  or battery coupled to control switch  960  is full, comparator  961  saturates to a logic high or “1”. And when function select is a positive input or “1”, the XOR gate  962  inverts the comparator&#39;s  961  output to have a low or “0” at the AND  965  output as select control signal to assert negativity output. If transfer device  968  is coupled to the negativity output of control switch  960 , the assertion of negativity output will activate transfer device  968  to transfer energy from energy device  969  for external use, a sequential discharging control switch  960  is thus formed. 
     The illustration (vii) of  FIG.  9    shows a sequential discharging control switch of case  3 . When energy device  979  or battery coupled to control switch  970  is full, comparator  971  saturates to a logic high or “1”, and when the function select is a negative input or “0”, the XNOR gate  972  inverts the comparator&#39;s  961  output to be a low or “0” at the AND  975  output as select control signal to assert negativity output. If transfer device  978  is coupled to the negativity output of control switch  970 , the assertion of negativity output will activate transfer device  978  to transfer energy from energy device  979  for external use, a sequential discharging control switch  970  is thus formed. 
     Similarly, the illustration (viii) of  FIG.  9    shows a sequential discharging control switch of case  4 . When energy device  989  or battery coupled to control switch  980  is full, comparator  981  saturates to a logic high or “1”. And when function select is a positive input or “1”, the XNOR gate  982  buffers the comparator&#39;s  981  output to have a high or “1” at the AND  985  output as select control signal to assert the positivity output. If transfer device  988  is coupled to the positivity output of control switch  980 , the assertion of positivity output will activate transfer device  988  to transfer energy from energy device  989  for external use, a sequential discharging control switch  980  is also formed. 
     Referring to (i) and (v), (ii) and (vi), (iii) and (vii), or (iv) and (viii), both control switches  910  and  950 ,  920  and  960 ,  930  and  970 , or  940  and  980  have the same configuration. It simply to apply a proper function select input, a duality control switch can be used as a charging control switch or as a discharging control switch. For example, the XOR control switch  910  is a charging control switch when the function select is a positive input, and it becomes a discharging control switch when the function select is a negative input, as shown in control switch  950 . Similarly, for example, the XNOR control switch  930  is a charging control switch when the function select is a positive value, and it becomes a discharging control switch when the function select is a negative value, as shown in control switch  970 . 
     Referring to (v) and (vi), or (vii) and (viii) of  FIG.  9   , for a discharging control switch, when the function select is changed from  0  to  1 , and the transfer device is recoupled from negativity output to positivity output as shown in control switches  950  and  960 , or recoupled from positivity output to negativity output as shown in control switches  970  and  980 , the discharging functionality is unchanged, except that the output timing characteristic is altered. Similar conversion is applicable for charging control switches (i) and (ii), or (iii) and (iv), where when function select input is changed from 1 to 0, and the transfer device is reconnected from positivity output to negativity output as in control switches  910  and  920 , or from negativity output to positivity output as in control switches  930  and  940 , the charging functionality is unchanged, except that the output timing characteristic is altered. 
     Referring to (v) and (viii), or (vi) and (vii) of  FIG.  9   , if not to change the external coupling of the negativity output or the positivity output, i.e., not to change the output timing characteristic of discharging control switch, this can be achieved by changing the input to function select and exchanging XOR and XNOR in control switch. This is also applicable for charging control switch, which is obvious by observing (i) and (iv), or (ii) and (iii). 
       FIG.  10    is a schematic diagram of a control circuit adapted to perform sequential charging and discharging for a number of battery modules, in accordance with one embodiment of the present disclosure. The duality control switch, as described above, is used to implement the sequential charging control chain  1000  and the sequential discharging control chain  1050  for the exemplary battery modules  1019 ,  1029 ,  1039  in battery pack  1005 . Although only three battery module and control switches are shown in the example, it is understood that any number of battery modules and control switches may be used. The operation and functionality of sequential charging control chain  1000  and sequential discharging control chain  1050  are similar to those described with reference to the sequential charging control chain  700  and the sequential discharging control chain  750  shown in  FIG.  7   . 
     When the function select input to duality control switches  1010 ,  1020 ,  1030  in the charging control chain  1000  is tied to a logic high or V LOGIC , it enables XOR gates  1013 ,  1023 ,  1033  disposed in the duality control switches  1010 ,  1020 ,  1030  respectively, to function as an inverter for each of the duality control switches  1010 ,  1020 ,  1030  to be a charging control switch. Thus, the control chain  1000  is functioning as a sequential charging control chain. 
     Conversely, if the function select input is tied to the ground, or to a logic low state, then the XOR gates  1063 ,  1073 ,  1083  in the duality control switches  1060 ,  1070 ,  1080  respectively operate as passing-through buffers, and the duality control switches  1060 ,  1070 ,  1080  perform as discharging control switches. The control chain  1050  therefore functions as a sequential discharging control chain. By applying proper function select input to the duality control switches linked in a control chain, the control chain may function as a sequential charging control chain or as a sequential discharging control chain. 
     In an embodiment, a second enable input signal may be included in the control switch to enhance functionality of a linked control chain. For example, as shown in  FIG.  8 B , a PAEN signal, namely a parallel enable signal, may be ORed with a sequential enable input signal PSEN to generate a new enable input PREN for control switch  850 . 
       FIG.  11    is an exemplary control chain configured by control switch incorporating an external OR function, in accordance with one embodiment of the present disclosure. The control chain  1100  includes a set of batteries  1191 ,  1192 , . . . ,  1199  bundled in a battery pack  1190  coupled to a charging control chain, consisting of charging sub-chains  1110 ,  1120 , and  1130  for various charging operation, and a discharging control chain, consisting of discharging sub-control chains  1150 ,  1160  for various discharging operation. 
     The OR function coupled to each control switch receives two inputs, i.e., a sequential enable input and a parallel enable input. The sequential enable input signal may be an enable output from a prior control switch, or may be asserted by a key switch or by a microcontroller. For example, if key switch  1101 ,  1102 ,  1103 ,  1105 , or  1106  is used to enable sub-chain  1110 ,  1120 ,  1130 ,  1150 , or  1160 , by closing key switch  1101 ,  1102 ,  1103  to assert PSCEN1, PSCEN2, PSCEN3 signal as input to OR gate  1111 ,  1121 ,  1131  to enable the first control switch  1112 ,  1122 ,  1132  of respective sub-chain  1110 ,  1120 ,  1130 , it would enable the charging of all sequential sub-chains  1110 ,  1120 , and  1130  concurrently, where in each sub-chain its linked control switch would be charged sequentially. This is different from closing key switch  1104  to assert PACEN1 enable signal, being input to all OR gates  1111 ,  1113 ,  1121 ,  1123 , and  1125  to enable all control switches  1112 ,  1114 ,  1122 ,  1124  and  1126  in sub-chains  1110  and  1120  to receive DC power source  1181  to charge the set of batteries  1191 ,  1192 , . . . ,  1195  in parallel. Either conducting parallel charging for all control switches in sub-chains or conducting ‘parallel sequential’ charging for all sub-chains, it depends upon the availability and strength of DC power source for charging. 
     The two sub-chains  1110  and  1120  may be linked into a single extended sub-chain by coupling the enable output PSCEN2 from the control switch  1114  of sub-chain  1110  to the PSCEN2 enable input to control switch  1122  of sub-chain  1120 , where the key switch  1102  may be coupled to enable the sub-chain  1120  separately. The NXCEN1 may be ORed with PSCEN2 before input to OR gate  1121  coupled to control switch  1122 . Different DC power sources, such as DC power source  1181 ,  1182 , may be supplied to charge different sub-chains, such as sub-chains  1110 ,  1130 . More parallel charging to batteries or sub-chains of battery concurrently reduces charging time for battery pack  1190 . 
     Similarly, by the closing key switch  1105 ,  1106  to assert PSDEN 1 , PSDEN 2  as input to OR gate  1151 ,  1161  to enable the first control switch  1152 ,  1162  of respective sub-chain  1150 ,  1160  would enable concurrent sequential discharging of sub-chains  1150 ,  1160 . The VOUT1 of sub-chain  1150  and the VOUT2 of sub-chain  1160  may be two separate outputs for different application use. They may be coupled together to increase the output current from battery pack  1190 . When more sub-chains are enabled concurrently to discharge energy and have output coupled together, the output current increases. However, the highest output current from a discharging sub-chain, for example the sub-chain  1150 , is to assert the PADEN1 parallel enable signal to enable all control switches in the sub-chain  1150  to output their power concurrently. 
     Similarly, the sub-chain  1150  may be linked to the sub-chain  1160  to form an extended sequential discharging chain by coupling the enable output NXDEN1 from the control switch  1158  of sub-chain  1150  to the PSDEN 2  enable input of sub-chain  1160 , where the switch key  1106  may be coupled to enable the discharging of sub-chain  1160  separately. The NXDEN1 output may be ORed with the output from key switch  1106  to become the PSDEN 2  input to OR gate  1161  coupled to control switch  1162 . 
       FIG.  12    shows an example of a circuit, in accordance with one embodiment of the present disclosure that combines a charging control switch and a discharging control switch in a chipset to facilitate both charging and discharging control for a battery module, where the control sections of charging control switch and discharging control switch are combined, but the transfer device is separated from the control section to increase its flexibility to support different power rating in applications. Such a configuration may be alternatively referred to as a “combined control switch in chipset”. Single transfer device is sufficient if to charge and discharge to the same battery module. This is because when a battery has sufficient energy for discharge, it does not need to charge at the same time. 
     The exemplary combined charging and discharging control switch in chipset  1200  shown in  FIG.  12    includes a control section  1201  and a separate power transfer section  1202 , where the control section  1201  comprises, in part, a charging demultiplexer  1215  to generate charging control outputs NXCEN and CHARGE for charging operation, and a discharging demultiplexer  1225  to generate discharging control outputs NXDEN and DISCHARGE for discharging operation. Both demultiplexers  1215 ,  1225  use the same comparator  1210  to generate respective select control signal. 
     The comparator  1210 , which compares an attenuated voltage VBATT from voltage divider R 1 , R 2  coupled to battery module  1249 , with a reference voltage Vref, to generate a comparator output, where AND gate  1213  receives the inversion of comparator output, the inversion of abnormality input and the inversion of external INHIBIT control to generate select control signal for the charging demultiplexer  1215 , while the AND gate  1223  receives the comparator output, the inversion of abnormality input and the inversion of external INHIBIT control to generate select control signal for the discharging demultiplexer  1225 . 
     The charging demultiplexer  1215  receives PRCEN as its input, which ORs two external enable signals, including a sequential enable input PSCEN for linking to a front charging control switch and a second enable input PACON useful to enable parallel charging operation for control switches linked in a charging control chain. The charging demultiplexer  1215  generates two control outputs, including NXCEN signal, which is a negativity output from ANDing the PRCEN with the inversion of select control signal generated by AND function  1213  for linking and enabling a follower control switch, and a CHARGE signal, which is a positivity output from ANDing the PRCEN with the select control signal for activating the transfer device  1240  to charge a coupled battery  1249 . The external coupling of positivity output and negativity output can be exchanged when the AND  1213  output is inverted, where the inverted AND function  1213  may be Boolean converted to OR function with all its inputs also inverted. 
     The discharging demultiplexer  1225  receives PRDEN as its input, which ORs two external enable signals, including a sequential enable input PSDEN for linking to a front discharging control switch and a second enable input PADON useful to enable parallel discharging operation for control switches linked in a discharging control chain. The discharging demultiplexer  1225  generates two control outputs, including NXDEN signal, which is a negativity output from ANDing the PRDEN with the inversion of select control signal generated by AND function  1223  for linking and enabling a follower discharging control switch, and a DISCHARGE signal, which is a positivity output from ANDing the PRDEN with the select control signal to control the closing of a normally-open switch  1230  when energy in battery  1249  is output for external use. The external coupling of positivity output and negativity output can be exchanged when the AND  1223  output is inverted, where the inverted AND function  1223  may be Boolean converted to OR function with all its inputs also inverted. 
       FIG.  13 A  shows an example of a circuit that combines a charging control switch and a discharging control switch into a single control switch for charging and discharging a battery module, alternatively referred to as a “combined control switch” hereinafter, in accordance with one embodiment of the present disclosure. The combined control switch  1300  comprises, in part, a charging demultiplexer  1310 , a discharging demultiplexer  1320 , and a comparator  1320 , which compares an attenuated voltage VBATT derived from voltage divider R 1 , R 2  coupled to battery module  1349  to a reference voltage Vref, where the output of comparator saturates to a logic high or ‘1’ when the battery module  1349  has sufficient energy in it or is ‘energy full’. 
     The charging demultiplexer  1310  receives the comparator output to generate two outputs, where a positivity output, which ANDs an enable input signal PSCEN from a front charging control switch with comparator output by AND gate  1311  to generate NXCEN as link control and enable signal to a follower charging control switch, and a negativity output, which ANDs the enable input signal PSCEN with inversion of the comparator output by AND gate  1312  to generate an input for the OR function  1319 . 
     The discharging demultiplexer  1320  receives the comparator output to generate two outputs, where a negativity output, which ANDs enable input signal PSDEN from a front discharging control switch with the inversion of comparator output by AND gate  1318  to generate NXDEN as link control and enable signal to a follower discharging control switch, and a positivity output, which ANDs the enable input signal PSDEN with the comparator output by AND gate  1313  to generate an input for the OR gate  1319 . The output of OR gate  1319  activates transfer device  1335 , when the combined control switch  1300  is activated for charging or discharging operation. 
     The combined control switch  1300  also includes a 2:1 multiplexer  1330 , where its input is either selected from a DC power source  1301  when comparator output is a logic low or ‘0’, or selected from battery module  1349  when comparator output is a ‘1’. The multiplexer output  1330  is input to transfer device  1335 , where the output of transfer device  1335  is further coupled to a 1:2 selector  1340 , which routes output to charge battery module  1349  when the comparator output is a ‘0’, and outputs energy from battery module  1349  for external use when the comparator output is a ‘1’. The transfer device  1335  is in part of combined control switch  1300 . 
     At any given time, either the positivity output via AND gate  1312  of charging demultiplexer  1310  or the negativity output via AND gate  1317  of discharging demultiplexer  1020  is enabled, but not both, depending upon if the comparator  1315 &#39;s output being saturated to logic high or logic low. The discharging function takes a precedence over the charging function in the combined control switch  1300 . When battery module  1349  has sufficient energy for output, the comparator output will select 2:1 multiplexer  1330  and  1 : 2  selector  1340  to output energy from battery module  1349  for external use, and not to charge the battery module then. 
     In the charging and discharging combined control switch  1350  shown in  FIG.  13 B , the negativity output of the charging demultiplexer  1360  and the positivity output of the discharging demultiplexer  1370  are ORed by OR gate  1369  to form a 2:1 multiplexer  1375  to control the activation of transfer device  1385 , where the output of compactor  1365  is used as select control signal for multiplexer  1375 . 
       FIG.  14    is an exemplary charging and discharging control chain  1400  configurated by two combined control switches  1410 ,  1430 , in accordance with one embodiment of the present disclosure. Although only two stages are shown in the example, it is applicable to more than two stages. 
     The combined control switch  1410  includes a charging input OR gate  1411 , which receives a sequential enable input PSCEN plus a second enable input PACON for charging control, and a discharging input OR gate  1421 , which receives a sequential enable input PSDEN plus a second enable input PADON for discharging control. 
     The combined control switch  1410  also includes an output enable OR gate  1413 , which receives the positivity output from the combined demultiplexer  1415  and the abnormality detection result to generate NXCEN1 signal to enable the charging control for a subsequent combined control switch  1430 , and also includes an output enable OR gate  1423 , which receives the negativity output from the combined demultiplexer  1415  and the abnormality detection output to generate NXDEN1 signal to enable the discharging control for the subsequent combined control switch  1430 . An embedded transfer device  1417  is activated by the output of multiplexer  1414 , gated by the inversion of the abnormality detection result at AND  1415 . The detection of any abnormality will de-activate the transfer device  1417  and assert both NXCEN1 and NXDEN1 enable signals to enable the charging control section and the discharging control section of the subsequent combined control switch. 
     Similarly, the combined control switch  1430  includes OR gate  1431 ,  1441 , which receives the NXCEN1, NXDEN1 output from the front combined control switch  1410  for linking to the PSCEN2, PSDEN 2  input, plus receiving the PACON, PADON input respectively. 
     The PSCEN1, PSDEN 1 , PACON or PADON may be asserted by closing the key switches  1403 ,  1404 ,  1402  or  1405 , or by using an external micro-controller, to enable the sequential charging, sequential discharging, parallel charging, or parallel discharging of the combined control chain  1400 . When battery module does not have sufficient energy, the battery module  1419 ,  1439  will be charged by DC power source  1401  through multiplexer  1416 ,  1436 , transfer device  1417 ,  1437 , and selector  1418 ,  1438  according to the priority of combined control switch  1410 ,  1430  coupled to the battery module  1419 ,  1439 , if the PSCEN1 enable signal is asserted to charge battery module  1419 ,  1439  sequentially. All battery modules  1419 ,  1439  will be charged concurrently, if the PACON enable signal is asserted. 
     Similarly, when battery modules have sufficient energy, the battery modules  1419 ,  1439  will be discharged through multiplexer  1416 ,  1436 , transfer device  1417 ,  1437 , and selector  1418 ,  1438  to output energy for external use according to the priority of combined control switch  1410 ,  1430  coupled to the battery module  1419 ,  1439 , if the PSDEN 1  enable signal is asserted for energy in battery module  1419 ,  1439  to be discharged sequentially. All battery modules  1419 ,  1439  will be discharged concurrently, if the PACON enable signal is asserted. 
     By using the combined control switch to implement a charging and discharging control chain in a power system, the number of control switches can be reduced by half. 
     CONCLUSION 
     In summary, the embodiment to incorporate a 1:2 demultiplexer in control switch enables the linking of control switches into a control chain for charging, discharging or power multiplexing in a power system. The control switch can be configured as a charging control switch, a discharging control switch, a charging or discharging selectable control switch, or a charging and discharging combined control switch. The flexibility to control the delay at the demultiplexer output of control switch enables concurrent, make-before-break or break-before-make power multiplexing between the control switches linked in a control chain. 
     Partitioning a large energy storage device into multiple smaller energy storage units provides more flexibility in controlling the charging and discharging of the large energy storage device, such as a battery pack in an electric vehicle. If the battery pack in an EV is partitioned into smaller, removable and easily installable battery modules, it would be more feasible to recover regenerated energies, more friendly to manage the charging of EV battery, and may also lower the EV ownership cost. The control switch may be configured with discrete components, in integrated circuits, or partitioned into a chipset including a separate transfer device to meet various power application requirements.