The present disclosure relates to a switched-mode voltage converter system, and more particularly, to a switched-mode voltage converter system with energy recovery.
Switched mode voltage converters (or DC/DC converters) are generally configured to receive a source voltage and generate an output voltage as a transformed version of a control input voltage. Many configurations of DC/DC converters exist including Buck converters, boost converters, Buck/boost converters and flyback converters. These voltage converters typically receive energy from a power source and employ switches and energy storage elements to convert that energy to a desired output voltage using modulated switching frequencies and/or pulse widths to control the output voltage of the converter. Some portion of the energy that is drawn from the power supply may be wasted during the operation of the converter resulting in decreased efficiency and increased cost.
Features and advantages of the claimed subject matter will be apparent from the following detailed description of embodiments consistent therewith, which description should be considered with reference to the accompanying drawings, wherein:
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art.
Generally, the present disclosure provides a device, system and method for driving a load with energy recovery, wherein the load has a reactive component that is capacitive. The device may include a switched-mode voltage converter which provides an output voltage to the load that is based on a control signal. The output voltage may be, for example, an amplified version of the control signal. Energy released from the capacitive load, as part of a charge/discharge cycle, may be recovered and stored in a second capacitor, a boost capacitor which may be coupled to the converter. Energy losses in the converter and dissipation in the load may be replenished from an energy source, for example a battery, which further charges the boost capacitor through a second converter which may be a boost converter.
Switched mode converters generally receive energy from a power source and employ switches and energy storage elements to convert that energy to the desired output voltage using modulated switching frequencies and/or pulse widths to control the conversion ratio of the converter. Embodiments of the present disclosure, however, provide for the converter to receive at least a portion of its energy from an energy recovery process associated with the load. The reactive element of the load that is capacitive, CLOAD 114, may, for example, be a piezoelectric speaker or a transducer (including a transducer for tactile feedback). CLOAD 114 may alternately store and release energy as part of a charge/discharge cycle in response to variations in the output voltage 116, which varies in proportion to the control voltage. The released energy from CLOAD 114 may be recovered and stored in boost capacitor CBOOST 108 to provide energy to the converter 110 for subsequent operation. Energy losses in the converter 110 and power dissipation in the dissipative element of the load 120 may be replenished from energy source 118, for example a battery providing source voltage Vsource 104, which can augment the charge on the boost capacitor 108, for example when the voltage on the boost capacitor drops below a pre-defined threshold. A boost converter 106 may be used to convert the voltage from the energy source 118, i.e., Vsource 104, to a suitable voltage range VBOOST 112 for the converter 110. VBOOST 112 is typically larger than Vsource, and in some embodiments VBOOST may have a nominal value of 35 volts while Vsource may have a nominal value of 3.5 volts. Additionally, CBOOST 108 is typically larger than CLOAD 114, and in some embodiments CBOOST may have a nominal value of 10 μF while CLOAD may have a nominal value of 1 μF.
Advantageously, this two stage approach, employing a separate boost converter for energy replenishment, allows power transfers to and from the load to be performed at higher voltages (compared to the voltage supplied by the battery) and therefore lower currents. Additionally, the boost converter is called on to deliver only the power needed to replenish energy losses in the system and therefore may operate at lower power levels.
In some embodiments, the boost converter 106 and the switched-mode voltage converter 110 may be incorporated on an integrated circuit (IC) and the boost capacitor may be coupled to a boost port provided on the IC.
In operation the boost converter 106 may convert the voltage from the energy source 118 (e.g., a battery) from a first lower value, for example in the approximate range of 2 to 5 volts, to a second higher value, for example in the approximate range of 30 to 40 volts. This may be accomplished through the use of an energy storage inductor L1 and a switching network S1 and S2. The switching modulation of S1 and S2 may be adjusted to provide the desired voltage at the boost capacitor CBoost 108. In some embodiments, L1 may have an inductance with a nominal value of 1 μH.
In operation the four quadrant switched-mode voltage converter 202 may operate from the supply voltage provided at the boost capacitor CBoost 108 and may provide an output voltage VL 116 to the load that is based on an input control signal Vcontrol 102. The output voltage 116 may track the control signal 102. For example, the output voltage 116 may be an amplified or attenuated version of the control signal 102. This may be accomplished through the use of an energy storage inductor L2 and a switching network S3 through S8. The switching modulation of switches S3-S8 may be adjusted to provide the desired output voltage. In some embodiments, L2 may have an inductance with a nominal value of 2 μH. The modulation or pulse width of the switching network S3-S8, may be controlled by pulse width calculator 206. In some embodiments, the pulse width calculator 206 may be a quadratic pulse width calculator, the operations of which are described in greater detail in a previously filed provisional patent application Ser. No. 61/654,242, filed Jun. 1, 2012. Loop filter 204 amplifies the error signal, or difference between the output voltage 116 and the control signal voltage 102, and performs filtering operations that improve the stability of the control loop. In some embodiments, the loop filter may be modeled by the following transfer function:
which is a low pass filter with a cut-off frequency of ωp where nominal values for the parameters may be A=10 (20 dB) and, ωp=2π(10 kHz). The filtered error signal is then provided to the pulse width calculator 206 which modulates the switching network S3-S8 to adjust the gain of the converter 202.
Operation 300b illustrates two stages of an energy recovery cycle (second mode of operation) of the four quadrant switched-mode voltage converter 202. In the first stage 202c, switches S7 and S8 are closed while switches S3, S4, S5 and S6 are open. In this configuration current flows from the load back through the inductor. In the second stage 202d, switches S4 and S5 are closed while switches S3, S6, S7 and S8 are open permitting current to flow back from the inductor to the boost capacitor for storage until a subsequent delivery cycle.
The transition between energy delivery mode and energy recovery mode may be based on a comparison of the output voltage 116 to the control voltage 102. For example, if
VL<k Vcontrol,
where k is a pre-determined proportionality constant, then the converter may operate in energy delivery mode, otherwise the converter may operate in energy recovery mode.
The boost converter 106 may share a common inductor with the switched-mode voltage converter 402. Because inductors are typically the largest and most expensive components in the system there is an advantage to sharing a single inductor between the two converters 106 and 402. The shared common inductor may be used to deliver energy from the energy source to the boost capacitor, to delivery energy from the boost capacitor to the load, and to recover energy from the load to the boost capacitor. The duty cycle allocated to each of these 3 operations, however, will be shorter resulting in a larger inductor current and greater power loss. Additionally, when transitioning from one of the three operations in a first cycle to a different operation in a subsequent cycle, energy remaining in the inductor at the end of the first cycle may adversely affects performance in the following cycle.
In the buck-boost configuration shown in the embodiment of
Capacitors Ccmp and Ccmn are provided to increase stability at the common mode output. In some embodiments, these capacitors may have nominal values of 0.047 μF.
In the inverting buck-boost configuration shown in the embodiment of
As used herein, use of the term “nominal” or “nominally” when referring to an amount means a designated or theoretical amount that may vary from the actual amount.
The term “switches” may be embodied as MOSFET switches (e.g. individual NMOS and PMOS elements), BJT switches, diodes and/or other switching circuits known in the art. In addition, “circuitry” or “circuit”, as used in any embodiment herein, may include, for example, singly or in any combination, hardwired circuitry, programmable circuitry, state machine circuitry, and/or circuitry that is included in a larger system, for example, elements that may be included in an integrated circuit.
Embodiments of the methods described herein may be implemented in a system that includes one or more storage mediums having stored thereon, individually or in combination, instructions that when executed by one or more processors perform the methods. Here, the processor may include, for example, a system CPU (e.g., core processor) and/or programmable circuitry. Thus, it is intended that operations according to the methods described herein may be distributed across a plurality of physical devices, such as processing structures at several different physical locations. Also, it is intended that the method operations may be performed individually or in a subcombination, as would be understood by one skilled in the art. Thus, not all of the operations of each of the flow charts need to be performed, and the present disclosure expressly intends that all subcombinations of such operations are enabled as would be understood by one of ordinary skill in the art.
The storage medium may include any type of tangible medium, for example, any type of disk including floppy disks, optical disks, compact disk read-only memories (CD-ROMs), compact disk rewritables (CD-RWs), digital versatile disks (DVDs) and magneto-optical disks, semiconductor devices such as read-only memories (ROMs), random access memories (RAMs) such as dynamic and static RAMs, erasable programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs), flash memories, magnetic or optical cards, or any type of media suitable for storing electronic instructions.
Thus, the present disclosure provides devices, systems and methods for recovering energy from a load. According to one aspect there is provided a voltage converter device. The device may include a first voltage converter circuit including a boost voltage node and an output voltage port, the output voltage port coupled to a load, the first voltage converter circuit configured to deliver energy from the boost voltage node to the load in a first mode, the first voltage converter circuit configured to deliver energy from the load to the boost voltage node in a second mode. The device of this example may also include a second voltage converter circuit coupled to an energy source and to the boost voltage node, the second voltage converter circuit configured to convert a first voltage associated with the energy source to a second voltage associated with the boost voltage node. The device of this example may further include a boost capacitor coupled to the boost voltage node, the boost capacitor configured to store the energy delivered from the load.
According to another aspect there is provided a method. The method may include delivering energy, in a first mode of operation of a first voltage converter circuit, from a boost capacitor coupled to a boost voltage node of the first voltage converter circuit, to a load coupled to an output voltage port of the first voltage converter circuit. The method of this example may also include delivering energy from the load to the boost voltage node in a second mode of operation of the first voltage converter circuit. The method of this example may further include converting, by a second voltage converter circuit, a first voltage associated with an energy source, to a second voltage associated with the boost voltage node. The method of this example may further include storing energy delivered to the boost voltage node in the boost capacitor.
According to another aspect there is provided a power supply system. The system may include a switched-mode power supply circuit configured to generate a DC output voltage from a DC input voltage. The switched-mode power supply circuit of this example may include a first voltage converter circuit including a boost voltage node and an output voltage port, the output voltage port coupled to a load, the first voltage converter circuit configured to deliver energy from the boost voltage node to the load at the DC output voltage in a first mode, the first voltage converter circuit configured to deliver energy from the load to the boost voltage node in a second mode. The switched-mode power supply circuit of this example may also include a second voltage converter circuit coupled to an energy source and to the boost voltage node, the second voltage converter circuit configured to convert a first voltage associated with the energy source to a second voltage associated with the boost voltage node. The switched-mode power supply circuit of this example may further include a boost capacitor coupled to the boost voltage node, the boost capacitor configured to store the energy delivered from the load.
The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described (or portions thereof), and it is recognized that various modifications are possible within the scope of the claims. Accordingly, the claims are intended to cover all such equivalents. Various features, aspects, and embodiments have been described herein. The features, aspects, and embodiments are susceptible to combination with one another as well as to variation and modification, as will be understood by those having skill in the art. The present disclosure should, therefore, be considered to encompass such combinations, variations, and modifications.
This application claims the benefit of U.S. provisional application Ser. No. 61/654,223, filed Jun. 1, 2012, and U.S. provisional application Ser. No. 61/654,242 filed Jun. 1, 2012, which are incorporated fully herein by reference.
Number | Date | Country | |
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61654223 | Jun 2012 | US | |
61654242 | Jun 2012 | US |