WO2015003611A1

WO2015003611A1 - Adaptive ac and/or dc power supply

Info

Publication number: WO2015003611A1
Application number: PCT/CN2014/081820
Authority: WO
Inventors: Siew Chong Tan; Shu Yuen HUI; Chi Kwan Lee; Felix Fulih Wu
Original assignee: The University Of Hong Kong
Priority date: 2013-07-09
Filing date: 2014-07-08
Publication date: 2015-01-15
Also published as: EP3020111A1; CN105474496A; EP3020111A4; CN112103967A

Abstract

Embodiments of an adaptive power supply are disclosed for accommodating instances in which too much power is generated for a load demand and instances in which too little power is generated for a load demand.

Description

ADAPTIVE AC AND/OR DC POWER SUPPLY

FIELD

[001] This disclosure relates to power-generation circuitry for use in power systems with or without renewable energy sources, which may, on occasion, vary in availability.

BACKGROUND

[002] In traditional power systems, a power-generation company may produce electrical energy to supply load centers in a centralized and unidirectional manner. In general, basic "load-following" control methodology comprises an arrangement in which power generation follows energy demand. Thus, a balance among power generation and power demand (e.g., "load") may be employed to bring about a stable power-generation system. However, in view of an increasing use of distributed renewable energy sources, such as wind and solar energy, a less centralized and dynamic power generation system may emerge. For example, renewable energy sources may be installed in a distributed manner, in which actual locations of solar and/or wind generating capacity is unknown to a power company. Therefore, a power company may not be capable of precisely determining total power generation, especially in view of geographically varying wind speed, cloud cover, and so forth. While power-generation and load may be mitigated by temporary energy-storage facilities, such as water reservoirs for storage of potential energy and/or chemical energy storage facilities, such as batteries, these solutions may be problematic. Chemical storage, for example, may be cost prohibitive. In another example, water reservoirs for potential energy storage may be subject to geographical limitations. BRIEF DESCRIPTION OF THE DRAWINGS

[003] Claimed subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. Together with objects, features, and/or advantages thereof, claimed subject matter may be better understood by reference to the following detailed description if read with the accompanying drawings in which:

[004] FIG. 1 a shows a simplified control schematic of series reactive power compensator for output voltage support in transmission according to embodiments.

FIG. 1 b shows a simplified control schematic of series-reactive power compensator as a central dimming system based on a power inverter circuit according to embodiments.

FIG. 1 c shows a simplified control schematic of series reactive power compensator as an electric spring according to embodiments.

FIG. 2 shows a single-phase version of an electric spring based on a half-bridge power inverter and a low-pass inductor-capacitive filter and an Undeland snubber circuit according to embodiments.

FIG. 3a shows a schematic of a single-phase power system according to embodiments.

FIG. 3b shows a schematic of a single-phase power system including use of an electric spring circuit according to embodiments.

FIG. 4 shows a single-phase electric spring for a three-phase system according to embodiments.

FIG. 5 shows a three-phase electric spring according to embodiments.

FIG. 6 shows an adaptive power supply for a single-phase system according to an embodiment.

FIG. 7 shows an adaptive power supply for a three-phase system according to an embodiment.

FIG. 8 shows an electric spring installed on a high voltage side of a step-down transformer according to an embodiment.

FIG. 9 shows another adaptive power supply according to an embodiment.

FIG. 10 shows an adaptive DC power supply according to an embodiment.

FIG. 11 shows an adaptive DC power supply set up with a standard power outlet according to an embodiment.

FIG. 12 shows adaptive AC and/or DC power supplies forming part of the power supply infrastructure according to an embodiment.

FIG. 13 shows a DC bus power supply according to an embodiment.

FIG. 14 shows a setup of the future power supplies according to an embodiment.

FIG. 15 shows an accessible mechanism for changing input voltage reference by external bodies such as the power companies and authorities according to an embodiment.

[005] Reference is made in the following detailed description to the accompanying drawings, which form a part hereof, wherein like numerals may designate like parts throughout to indicate corresponding or analogous elements. For simplicity and/or clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, it is to be understood that other embodiments may be utilized and structural and/or logical changes may be made without departing from the scope of claimed subject matter. It should also be noted that directions and references such as, for example, up, down, top, bottom, over, above and so on, may be used to facilitate the discussion of the drawings and are not intended to restrict application of claimed subject matter. Therefore, the following detailed description is not to be taken in a limiting sense and the scope of claimed subject matter is intended to be defined by the appended claims and equivalents. DETAILED DESCRIPTION

[006] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, methods, apparatuses, or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter.

[007] Reference throughout this specification to one implementation, an implementation, one embodiment, an embodiment, or the like may mean that a particular feature, structure, or characteristic described in connection with a particular implementation or embodiment may be included in at least one implementation or embodiment of claimed subject matter. Thus, appearances of such phrases in various places throughout this specification are not necessarily intended to refer to the same implementation or to any one particular implementation described. Furthermore, it is to be understood that particular features, structures, or characteristics described may be combined in various ways in one or more implementations. In general, of course, these and other issues may vary with the particular context. Therefore, the particular context of the description or usage of these terms may provide helpful guidance regarding inferences to be drawn for that particular context.

[008] Likewise, the terms, "and," "and/or," and "or" as used herein may include a variety of meanings that will, again, depend at least in part upon the context in which these terms are used. Typically, "and/or" as well as "or" if used to associate a list, such as A, B or C, is intended to mean A, B, or C, here used in the exclusive sense, as well as A, B and C. In addition, the term "one or more" as used herein may be used to describe any feature, structure, or characteristic in the singular or may be used to describe some combination of features, structures, or characteristics.

[009] Embodiments may comprise various demand-side power management methods. Literature review for the period of 2005 to 2012 shows that demand-side (e.g., load) management (or sometimes known as demand response) [1 ],[2] can be broadly summarized as:

• Scheduling of delay-tolerant power demand tasks [3-5]

• Use of energy storage to alleviate peak demands [6]

• Real-time pricing [7-9]

• Direct load control or on-off control of smart loads [10-12]

[010] While above-identified methods may have particular advantages, at least some methods may be subject to certain limitations. For example, although it may be practical to schedule power demand in terms of days or even hours in advance, response to real-time power fluctuations may be more problematic. Additionally, although energy storage may represent one or more relatively advantageous solutions, use of batteries may be relatively expensive. Additionally, use of such as water reservoirs, in which water is impelled uphill for later conversion from potential into electrical energy, such a solution may be more practical in mountainous regions and less practical in low-lying regions. In other instances, for example, real-time pricing may be relatively effective for curbing power demand of price-conscious large customers, but may not be applicable to ordinary domestic consumers.

[011] Under certain circumstances, a power company may employ direct load control to shed power loads to avoid power system collapse. However, such centralized control strategies may not be effective for use with future power grids that may comprise relatively decentralized and intermittently available renewable energy sources providing electrical energy at an input side of a distribution network. Although on-off control of electric loads such as water heaters and air-conditioners has been proposed, such approaches may be overly intrusive and result in considerable inconvenience to consumers. Recent work based on wide-area measurements for real-time tracking of node voltage levels, for example, for use by a data center for central and regional control of a distribution area has been examined. Such real-time tracking of node voltage levels is usually based on information and communications technology (ITC), such as wireless communications, satellite synchronization and internet/intranet control. In some instances, this approach may be effective under normal operating conditions, but may be more difficult to implement if the wireless communications systems are disabled in weather emergencies or during unfavorable atmospheric conditions (such as strong solar storms). In other instances, use of the Internet infrastructure may also be undesirable due to hacking of servers involved in reporting node voltage levels, for example.

[012] A recent innovation in load response may relate to development of "Electric Springs" [13], [14]. Electric springs may comprise circuitry for power-electronics-based power controllers that adopt an "input-voltage control" for regulating supply voltage of a power system. In this particular context, it is to be understood that the term demand it meant to refer to an electronic load and use of the term demand throughout should be construed in a manner consistent with such an understanding. Likewise, the term control is meant to refer to at least partially control and/or being able to at least partially regulate. Again, use of the term control throughout should be construed in a manner consistent with such an understanding. Likewise, the term 'based on,' such as a description that X is 'based on Y or X may be 'based on' Y, is meant to indicate that X is or may be based at least partially on Y; however, there may be other factors or considerations as well that may not necessarily have been expressly articulated. Again, use of the term 'based on' throughout should be construed in a manner consistent with such an understanding.

[013] As power inverter circuits are commonly used in power system applications, it may be useful to determine a difference between the input and output control methods. For example, FIG. 1 a shows a simplified control schematic of series reactive power compensator for output voltage support in transmission (v₀ regulated), and FIG. 1 b shows a simplified control schematic of series-reactive power compensator as a central dimming system (v₀ regulated) based on a power inverter circuit. In FIGs. 1 and 2, directions of active power (e.g. , electric current) flow are highlighted. In FIGs. 1 and 2, an output port (Vo) is referred to an output direction of power flow.

[014] FIG. 1 c shows a simplified control schematic of series reactive power compensator as an electric spring (v_s regulated). Unlike the examples illustrated in FIG. 1 a and FIG. 1 b, an electric spring adopts an input-voltage control, in which an input port (v_s) refers to an input port of active power flow. For example, an input power port may refer to a power main (e.g. , busbar).

[015] In particular embodiments, an electric spring comprises a switched-mode power inverter, a low-pass filter, and an input-voltage control for regulating an input AC voltage (usually a node voltage of a local AC main). A single-phase version of an electric spring based on a half-bridge power inverter and a low-pass inductor-capacitive filter and an Undeland snubber circuit is shown in FIG. 2. In principle, a circuit, such as the circuit of FIG. 2 may be capable of accommodating both active and reactive power, therefore giving the circuits an ability to contribute, at least theoretically, to voltage and frequency stability in a power system. In some embodiments, half-bridge, full-bridge, and multi-level power inverters may be to form one or more electric spring circuits. In addition, it has been practically demonstrated that the use of electric springs can allow the load demand to follow intermittent power generation [14] and also to enable a reduction in energy storage requirements in a power system [15]. With an incorporation of a droop control [16], electric springs can be distributed over a power grid to provide distributed stability support for a power grid.

[016] In embodiments, use of one or more electric springs lies in a "demand side." For example, electric springs can be associated with non-critical loads, which may be characterized as electric loads capable of tolerating a certain variation of supply voltages. Electric springs may be embedded into electric appliances such as electric water heaters and/or refrigerators to form smart loads that may be adaptive to a fluctuating power supply. In embodiments, we describe a modified concept of an electric spring on a "power supply side" and extend and incorporate an electric spring concept to form a "Smart Power Supply." Unlike some implementations of electric springs that may adopt, for example, "input-voltage control" only, a modified smart power supply may employ an "input-voltage and/or output voltage" control. Additionally, electric springs may be considered as being associated with a power supply, as opposed to being associated with an electric load, for example.

[017] Embodiments may involve power system infrastructures for AC and/or DC power supplies that may incorporate an electric spring to form one and more adaptive power supplies. One or more implementations may be described in the form of an AC power supply. Subsequently, an adaptive DC power supply based on one or more similar principles is described.

[018] FIG. 3a shows a schematic of a single-phase power system. It should be noted, however, that while a symbol of a transformer used in FIG. 3a may indicate a single-phase system, in an embodiment, a multi-phase power system, such as a three-phase power system, for example, may be employed. For simplicity, a single-phase system is used for illustrative purposes only, and claimed subject matter is not limited in this regard. In FIG. 3a terminal "L" may refer to "live" terminal and N may refer to a neutral terminal. A standard AC mains, live-to-neutral voltage, which may be referred to as a phase voltage, may typically be in a range of 220.0 V-240.0 V for approximately 50.0 Hz power systems and 100.0 V to 110.0 V for approximately 60 Hz power systems. In many countries, power companies may regulate AC main voltage within a tight tolerance of a certain percentage (e.g. +/- 6% of a nominal AC main voltage in Hong Kong). A tolerance for a standard AC main is labeled as X% in FIG. 3.

[019] As shown in FIG. 3b, an embodiment may include use of an electric spring circuit, which may be based at least in part on an AC-to-AC power inverter, for an AC voltage output, and may be used to form an adaptive AC power supply. The "live" terminal of an adaptive AC power supply is termed

3S Ladapt- [020] For a single-phase system, an electric spring may comprise a half-bridge power inverter circuit shown in FIG. 4. In other embodiments, a full-bridge power inverter or other type of power inverter, such as a multilevel power inverter, for example, may be used. An output voltage of a power inverter may be a sinusoidal pulse-width-modulated (PWM) signal, which may be filtered using a low-pass filter to generate a controllable sinusoidal voltage as an electric spring voltage. A power inverter of an electric spring may accommodate reactive and/or real power. DC link capacitors of a power inverter may provide storage energy that may provide reactive power compensation for regulating node voltage at an AC main, for example. For reactive power control, the vector of current flowing into a load of an adaptive power supply may be at least approximately perpendicular to a voltage vector of an electric spring. An example of control methodology of an electric spring for voltage regulation using pure reactive power control may be described in [13]-[16].

[021] If real and reactive power controls are determined to be advantageous, a DC power source, such as a battery, can be connected in parallel with one or more capacitors, or may be used to replace the capacitors entirely, for example. Use of an active power source has been addressed in [13]. In this instance, for example, a current vector of a load in an adaptive power supply may not be approximately perpendicular to a voltage vector of an electric spring. Operating modes of such electric spring with both real and reactive power control have been reported by the inventors in [17].

[022] For a three-phase system, for example, a single-phase electric spring, such as shown in FIG. 4 may be used for one or more phases. In embodiments, a single-phase electric spring may be used for each phase of a three-phase system, for example. An embodiment of a three-phase electric spring circuit is shown in FIG. 5. A three phase power inverter with DC link capacitors and/or active DC voltage source (such as a battery), and a low-pass filter (comprising an inductor and capacitor) form a basic unit of a three-phase electric spring circuit. Through primary windings of a 3-phase transformer X-Y-Z with terminals X1 , Y1 and Z1 , filtered electric spring voltages may be coupled to three secondary windings with terminal X2, Y2, and Z2. Output terminals XX, YY and ZZ may thus form three-phase line voltage output terminals of a three-phase adaptive power supply. Both star-connected loads and delta-connected loads may be connected to a three-phase adaptive power supply, such as, for example, as shown in FIG. 5. It should be noted that a three-phase transformer may also be replaced by three single-phase transformers, for example, provided that connections of a three single-phase transformers are equivalent or at least similar to those shown in FIG. 5.

[023] An adaptive power supply based, at least in part, on an electric spring concept is not limited to low-voltage distribution power networks, for example, and may, at least in principle, be applied to medium-voltage and high-voltage power networks. For medium and high voltage applications, for example, multilevel power inverters, for use at higher voltages (e.g., higher voltage ratings) may replace at least portions of a two-level power inverter shown in FIG. 5, for example.

[024] FIG. 6 illustrates an adaptive power supply for a single-phase system, according to an embodiment. The electric spring and input and output control loops are implemented on a low-voltage side of a distribution line. A similar principle may be applied to a three-phase power system as shown in FIG. 7. If preferred, an electric spring may be installed on a high voltage side of a step-down transformer as shown in FIG. 8.

[025] Embodiments differ from previous concepts of electric springs reported in [13]-[16] in at least three ways.

• An electric spring circuit may be incorporated into a power supply side (as part of a power supply infrastructure) regardless of the type of loads. In previous reports, electric springs can be independent circuits external to power supplies and/or embedded in electric appliances.

• An adaptive power supply may employ both input-voltage and input-frequency control (for regulating a standard AC main voltage and reducing frequency instability in a traditional sense of electric springs reported in [13]-[16]). An output-voltage control (for limiting maximum and minimum voltage values of an adaptive AC main voltage and allowing an output AC voltage to vary within maximum and minimum voltage levels according to input-voltage and input frequency control) as illustrated in FIG. 3b.

• Use of an active DC power source, such as a battery, may enable both voltage and frequency control loops to be included in an adaptive power supply system as shown in FIG. 9.

[026] As shown in the embodiment of FIG. 9, there may be, for example, four main control blocks in a control scheme. Control block 1 may perform an adaptive voltage regulation function based on an input-frequency control. Control block 2 may perform an adaptive voltage regulation function based on an input-voltage control. Control block 3 may perform a reactive-power compensation function based, at least in part, on input power displacement angle control. Control block 4 may perform an overcurrent protection function based, at least in part, on output current detection.

[027] In embodiments, control block 1 may comprise a circuit or other means of implementing a method to detect a frequency, f_s, of an input voltage V_s. A detected frequency may be compared against a desired frequency fs(preset) for an input voltage. The difference of these two frequencies E_fs is scaled by a factor K_f and then passed through a limiter and input into the summer Sum. In control Block 2, a circuit or method to detect the RMS value of an input voltage, e.g.,, Vs,_rms is adopted. The detected RMS voltage is compared against a pre-set and/or a desired RMS voltage Vs,_rms(preset)- The difference of these two voltages Evs.rms may be scaled by a factor K_v and passed through a limiter and input into a summer labeled "Sum." At summer "Sum," a signal from control block 1 and control block 2 may be added with a desired reference value of an output voltage V₀(_Preset) to provide an adaptive output voltage reference value of Vo(_Preset₎±AV. The output of Sum may be passed through a limiter, for example, which may set one or more limits of an output voltage reference point |V_0ref| to be not less than V_min, for example, and not be more than V_max, such that V_min≤ |V_0ref|≤ V_max. Values of V_max and V_min can be set and/or may be programmable. The control blocks 1 and 2 may perform a function of automatic load shedding or load boosting, for example. When a detected f_s is higher than fs(preset), which may indicate, for example, that a power bus (e.g., a busbar) is under-loaded, an output voltage reference is adaptively adjusted to a higher value such that a regulated output voltage at Ladapt is higher. In some embodiments, for passive loads, a higher L_aciapt may result in a larger power drawn from a main. This may be conversely true for f_s lower than fs(preset)- Concurrently, when a detected Vs,_rms is higher than Vs,rms(preset), which may also signify that a power bus is under-loaded, an output voltage reference may be adaptively adjusted to a higher value such that a regulated output voltage at Ladapt is higher, and vice versa.

[028] By detecting, for example, a displacement angle between an input voltage V_S(LF) and an input current I_S(LF), reactive power compensation may be performed at control block 3. For example, an input voltage V_s and an input current l_s may be passed through a low pass filter to retain their fundamental frequency components, e.g., V_S(LF) and I_S(LF)- Signals may be passed through a phase angle detection circuit/method to obtain phase angle displacement +Θ. A positive angle for +Θ may signify that input current is leading an input voltage, which may be equivalent, or at least similar to behavior exhibited by a capacitive circuit. A negative angle (-Θ) may indicate, for example, that an input current may be lagging an input voltage, for example, which may exhibit behavior similar to that of an inductive circuit.

[029] Θ may subsequently be compared against a desired displacement angle e(_preset), of which a difference E_e may be passed through a compensator and/or a limiter before being fed into a phase delay circuit to alter a sinusoidal signal 5ίη2πίί into

By varying an angle e_COm, different reactive power compensation may be performed. For power factor correction, a desired phase angle is set as e(_preset) = 0. In the case of +Θ, e_COm will be a negative value, which should result in the electric spring generating a voltage that creates inductive power to compensate for a capacitive effect of a load. In the case of -Θ, e_COm may be a positive value, which should result in the electric spring generating a voltage that creates capacitive power to compensate for an inductive effect of a load.

[030] A sinusoidal signal varying at 5ίη2πίί corresponds an oscillating frequency of an input voltage V_s and it is obtained through a frequency synchronization circuit using V_S(LF)- An output of a phase delay circuit comprising a signal

may be modulated with an output from Sum/Limiter comprising, for example, a signal |V_0ref| - This may give an instantaneous output voltage reference of V_0ref which may be used for real-time control of an adaptive output voltage V₀ at L_aciapt- For a voltage feedback control, V₀ may be compared against V_0ref, of which their difference may be compensated and limited before passing into a gate pattern generator for controlling one or more switching actions of an electric spring.

[031] In control block 4, at least in some implementations, a load current l₀ may be sensed and compared against a value of an maximum allowable current l₀(iim) through a comparator, for example. In the event of overcurrent or short circuit at an output load such that l₀ > lo(Nm), for example, a comparator may, in response, trigger a output high signal to reset the flip-flop, thereby turning off the Gate Pattern Generator. A reset may restart an electric spring.

[032] There are at least three differences between standard AC mains and embodiments of an adaptive AC main:

• Conventional AC mains often employ a tight tolerance of X% for a voltage fluctuation. However, an adaptive AC main may exhibit an output voltage that may be regulated to within a wider tolerance with a maximum value (+n% of a nominal value) and a minimum value (-m% of a nominal value). • Standard AC mains may be regulated by a power company to fulfill commitments to maintain a well regulated power supply within a tight tolerance. However, when using an adaptive power supply output voltage may be regulated within a wider voltage to vary load power consumptions for loads for which power is being supplied.

• There is no longer a need to differentiate between critical and non-critical loads for embodiments of an electric spring. Adaptive power supply may be based on electric spring technology that is now part of a power supply infrastructure. Variable and/or constant power loads may be connected to an adaptive power supply provided that loads can accommodate a varying voltage within maximum and minimum voltage levels of an adaptive power supply.

[033] In essence, an intermittent nature of renewable power generation can be matched by a load demand variation through embodiments of an adaptive power supply. This may permit power generation to be balanced by a load demand. If such power balance is achieved, a voltage of a standard power supply may be regulated to a nominal value.

[034] If a total power generation at an instant is lower than a load demand, voltage of an adaptive power supply may be reduced dynamically so as to reduce power consumption of electric loads, except those of constant power type. If power generation is less than load demand, such that a voltage of an adaptive power supply reaches its minimum value, some load power may come from an energy storage (such as battery) of an adaptive power supply through a power inverter of an electric spring. By using an input voltage control to regulate AC mains voltage (e.g., voltage of a standard power supply), voltage of an adaptive power supply may vary in such a way that total power consumption of a load using an adaptive power supply may change in order to achieve a power balance between power supplied and power loading.

[035] If the power generation at any instant is larger than the load demand, the adaptive power supply may increase voltage in such way that total power consumption may increase to balance, or at least to reduce the imbalance of, the power generation. When a maximum value of a voltage level of an adaptive power supply is reached, extra power generation may be shunted into the battery for storage. In this manner, a balance between the power generation and load demand can still be maintained.

[036] Embodiments of an adaptive AC power supply can be extended to an adaptive DC power supply as shown in FIG. 10 for DC electric loads. Similar to the AC counterpart, the DC voltage output has a maximum and a minimum level that can be set or programmed. For example, for a nominal DC voltage of approximately 48.0 V, the maximum level may be n% higher and a minimum level may be m% lower than approximately 48.0 V. A DC voltage variation may be controlled in such a way that the DC load power consumption will balance, or reduce the imbalance of, the power generation and load demand. Adaptive DC power supply can be set up with a standard power outlet as shown in FIG. 11.

[037] Embodiments, such as adaptive AC and/or DC power supplies can form part of the power supply infrastructure as shown in FIG.12. Fed by the standard AC mains, AC and DC power sources may accommodate the intermittent nature of future power grids with high penetration of dynamically changing renewable energy sources. Embodiments offer an adaptive power supply infrastructure that may satisfy a control paradigm in which load demand follows power generation - which may be desirable for future smart grid. FIG. 13 illustrates a single-phase example of the standard and adaptive power supplies based at least in part on particular embodiments. An electric spring circuit with real power compensation typically requires installation of a DC energy storage system, such as a battery storage system. Using particular embodiments, a battery storage system may be optionally replaced by the DC bus power supply, as shown in FIG. 13.

[038] FIG.14 illustrates one embodiment of this invention about the setup of the future power supplies. It shows that the adaptive ac power supply can be derived from the standard ac mains supply. It also demonstrates that the adaptive high-voltage dc power supply and low-voltage power supply can also be derived from the same standard ac mains supply.

[039] Descriptions of adaptive power supplies based on the use of the electric springs so far, assume that electric springs are operating as individual units. It should be noted, however, these electric springs can also incorporate the droop control into the input voltage control loops so that these electric springs can help the adaptive voltage supplies to regulate the mains voltage in a coordinated manner - as described in patent application [16].

[040] Moreover, it is proposed that an accessible mechanism is provided so that the power companies or authorities can control the reference mains voltage in the control loops of the electric springs so as to provide a new mechanism to controlling the mains voltage levels in different parts of the power grids. This voltage control enables the power companies to control the mains voltage in different parts of the power grids for various purposes. An example is to vary the voltage level in order to reduce unnecessary current flows in the distribution network in order to reduce the conduction losses. This accessible mechanism for changing input voltage reference by external bodies such as the power companies and authorities is illustrated in FIG.15. The voltage references provided by the external bodies can be transmitted through a wired or a wireless mechanism.

[041] Additionally, it is also proposed that a load setting control mechanism with output signal is provided so that electricity consumers can use it for the automatic control on the amount of power used in their smart electrical appliances or smart load. This mechanism, which can be optionally adopted in the adaptive supplies for directly changing the load power, is illustrated in FIG.15. The control mechanism detects the input frequency and voltage level and determines if the power grid is overloaded or underloaded. It provides an output signal R_set, which contains information on the level of loading available in the power grids. Future smart electrical appliances can be designed to adjust its power consumption based on the information provided by R_set- As an example, the load setting control may be integrated with the adaptive power supply with earth to form a four-pin power socket outlet, as shown in FIG. 13. Such an integration is extendable to all adaptive power supplies.

[042] Similar to Fig.9, there are four main control blocks in the control scheme in FIG.15. Here, an optional Load Setting Control Block is introduced for performing load power control in smart appliances. The override control of the voltage reference is included in Control Block 1 and Control Block 2. Control Block 1 performs the adaptive voltage regulation function based on the input-frequency control. Control Block 2 performs the adaptive voltage regulation function based on the input-voltage level control. Control Block 3 performs the reactive-power compensation function based on input power displacement angle control. Control Block 4 performs the over current protection function based on output current detection.

[043] In Control Block 1 , a circuit or method to detect the frequency f_s of the input voltage V_s is adopted. The detected frequency is compared against the reference frequency f_Sref for the input voltage. The difference of these two frequencies E_fs is scaled by a factor K_f and then passed through a limiter and input into the summer Sum. Here, the reference frequency f_Sref is typically the internally pre-set desired frequency fs(preset), which is the default frequency of the power grid_. An override function is included so that in case the power authority would like to alter the frequency of the transmitted power, it can be done by feeding a "True" signal and the new desired frequency reference f_S(_ext) to the override block, which will then adopt f_Sref as fs(ext).

[044] In Control Block 2, a circuit or method to detect the RMS value of the input voltage, e.g., Vs,_rms is adopted. The detected RMS voltage is compared against the reference RMS voltage Vs,_ref- The difference of these two voltages Evs.rms is scaled by a factor K_v then passed through a limiter and input into the summer Sum. Here, the reference RMS voltage Vs,_ref is typically the internally pre-set desired RMS voltage V_S(preset), which is the default frequency of the power grid_. An override function is included so that in case the power authority would like to alter the voltage of the transmitted power, it can be done by feeding a "True" signal and the new desired RMS voltage reference V_S(_ext) to the override block, which will then adopt V_Sref as Vs(ext).

[045] In the Load Setting Control Block, both the frequency error E_fs and the RMS voltage error Evs.rms are respectively scaled by the factors K_y and K_x and then passed through limiters and input into a summer. The output is a signal +ΔΡ, of which a positive value corresponds to a surplus of grid power generation and a negative value corresponds to a shortfall of grid power generation. +ΔΡ is fed into a quantizer which converts it into an output signal Rset of discrete values (e.g. in the range of -2,-1 ,0, 1 ,2) that have implicit meaning to the smart appliances connected to the supply. For example, an R_set = -2 may suggest that the smart appliance operates at its lowest power since there is a shortfall of power generation. R_set = ^_1 means lower power operation of the smart appliance. R_set = 0 means normal operation. R_set = 1 means higher power operation and R_set = 2 means to operate the appliance at maximum power.

[046] In the preceding description, various aspects of claimed subject matter have been described. For purposes of explanation, specific numbers, systems or configurations are set forth to provide a thorough understanding of claimed subject matter. However, it should be apparent to one skilled in the art having the benefit of this disclosure that claimed subject matter may be practiced without the specific details. In other instances, well-known features are omitted or simplified so as not to obscure claimed subject matter. While certain features have been illustrated or described herein, many modifications, substitutions, changes, or equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications or changes that fall within the spirit of claimed subject matter.

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Claims

CLAIMS What is claimed is:

1. An adaptive power supply comprising an electric spring to employ an input voltage and/or output voltage control.

2. The adaptive power supply of claim 1 , wherein the electric spring comprises a power inverter.

3. The adaptive power supply of claim 2, wherein the power inverter is a half bridge power inverter, a full bridge power inverter or a multilevel power inverter.

4. The adaptive power supply of claim 2, wherein the power inverter is capable of generating a sinusoidal pulse-width-modulated signal.

5. The adaptive power supply of claim 1 , wherein the electric spring is a single phase electric spring used for one or more phases.

6. The adaptive power supply of claim 1 , wherein the electric spring is a three-phase electric spring.

7. The adaptive power supply of claim 6, wherein the three-phase electric spring comprises a three phase power inverter comprising:

one or more DC link capacitors;

an input port for receiving a DC voltage; and

a low pass filter.

8. The adaptive power supply of claim 6, wherein the three-phase electric spring is capable of accommodating one or more DC-connected loads or one or more AC-connected loads.

9. The adaptive power supply of claim 1 further comprising an adaptive voltage regulator, said adaptive voltage regulator comprising an input control means and an output control means, wherein the input control means can be used for adaptive voltage regulation and reactive power compensation, the output control means can be used for overcurrent protection.

10. The adaptive power supply of claim 9, wherein the input control means is accessible to control the mains voltage levels through external references, which is transmittable through a wired or a wireless means.

11 . The adaptive power supply of claim 9, wherein the input control means can detect a phase angle displacement between an input voltage and an input current.

12. The adaptive power supply of claim 11 , wherein if said phase angle displacement is a positive phase angle displacement, then the electric spring at least partially produces a voltage via inductive power to, at least in part, compensate for a capacitive effect of a load.

13. The adaptive power supply of claim 11 , wherein if said phase angle displacement is a positive phase angle displacement, then the electric spring at least partially produces a voltage via capacitive power to, at least in part, compensate for a inductive effect of a load.

14. The adaptive power supply of claim 9, wherein the input control means comprises a control block for performing an adaptive voltage regulation based, at least in part, on and input-frequency control.

15. The adaptive power supply of claim 9, wherein the input control means comprises a control block for performing an adaptive voltage regulation based on input-voltage control.

16. The adaptive power supply of claim 9, wherein the input control means comprises a control block for performing a reactive-power compensation based, at least in part, on input power displacement angle control.

17. The adaptive power supply of claim 9, wherein the input control means comprises a control block for performing a load setting control, at least in part, on load power consumption of electrical appliance.

18. The adaptive power supply of claim 9, wherein the output control means comprises a control block for performing an overcurrent protection based, at least in part, on output current detection.

19. The adaptive power supply of claim 1 , wherein if power generation at an instant is larger than load demand, voltage of the adaptive power supply is increased to reduce an imbalance between power generation and load.

20. The adaptive power supply of claim 1 , wherein if power generation at an instant is larger than load demand, then a part of generated power is shunted to one or more chemical storage devices.

21 . An apparatus comprising the adaptive power supply according to any one of claims 1 -20.

22. The apparatus of claim 21 , wherein the adaptive power supply is an adaptive AC power supply or an adaptive DC power supply.