US20190036449A1 - Switch network of a multilevel power converter architecture - Google Patents
Switch network of a multilevel power converter architecture Download PDFInfo
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- US20190036449A1 US20190036449A1 US15/660,319 US201715660319A US2019036449A1 US 20190036449 A1 US20190036449 A1 US 20190036449A1 US 201715660319 A US201715660319 A US 201715660319A US 2019036449 A1 US2019036449 A1 US 2019036449A1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4837—Flying capacitor converters
Definitions
- the present invention relates to electrical circuits for power conversion, for example, between different voltages and/or between AC and DC power, and in particular to a multilevel architecture for power converters that can provide improved power conversion of high voltages.
- Conventional power conversion for example, converting between different levels of AC power, may employ a transformer having inductively linked coils that transform input AC voltage to output AC voltage according to the turns ratio of coils.
- Windfarms and photovoltaic arrays may need to transform between low-voltage AC or DC to medium voltage grid power (2 kV to 35 kV) while recharging systems for electric vehicles may need to reduce medium voltage grid power to lower AC or DC voltages (200-400 volts) as needed for battery charging.
- the cost, weight and bulk of the transformer may be reduced through the use of solid-state switching devices.
- solid-state devices convert input AC power to DC and then synthesize a higher frequency AC waveform that may work with a smaller transformer. Output from the transformer is then reconverted by additional solid-state devices to DC and then to the desired level of AC.
- a transformer-less medium voltage power conversion system could be developed by directly converting input AC power to the desired AC or DC output using semiconductor devices.
- Wideband (WBG) devices such as silicon carbide (SiC) MOSFETs may provide sufficiently high-frequency operation for this application and may have sufficiently high breakdown voltages to allow them to operate with power from medium voltage grids by connecting multiple devices in series.
- Rapid switching of high voltages by solid-state devices can create problems of generating electromagnetic interference and high dv/dt (voltage change rate) such as can be damaging to electrical insulation on motors and the like. Placing solid-state devices in series can require careful coordination of the switching times of the devices to ensure that an individual device does not instantaneously experience excess voltages beyond their rated breakdown voltage.
- the present invention provides a power converter using a pyramid architecture that limits the voltage difference handled by each switch to reduce electromagnetic interference and high dv/dt.
- the pyramid design permits asynchronous operation of the switches eliminating the criticality of switch synchronization allowing the switching speed and duty cycle to be adjusted, for example, to reduce EMI and to improve power-sharing among semiconductor devices.
- the invention provides a power converter having a capacitive divider with one end providing a first converter terminal and a second end. providing a second converter terminal attachable to a ground reference.
- the capacitive divider presents a series of different nodes between series connected capacitances.
- a multilevel switch network with each level having at least one switch having an electrically controllable pole movable between throws, has a first level with multiple switches whose throws communicate with each of the different nodes of the capacitive divider.
- the switches of each next level of the multilevel switch network have their throws in electrical communication with poles of switches of a previous level so that the number of switches in each level decreases from the first level to a last level, the last level having a single switch associated with a single pole providing a third converter terminal.
- At least one switch signal generator controls a switching of the switches to provide a power transformation between the first converter terminal and the third converter terminal providing a reduction in voltage and increase in current at the third converter terminal with respect to the first converter terminal.
- the proportion of reduction in voltage and increase in current is determined by a duty cycle of switching of the switches.
- Each of the switches of each level may be isolated from switches of a next level by inductors.
- the power converter may further include energy storage capacitances distributed among the switches and positioned between the throws of each switch.
- the switches closest to the third converter terminal may have higher current capacity than the switches closest to the second converter terminal.
- Each of the switches may be a single-pole, double-throw switch and the number of switches in each successive level decreases by one with respect to the previous level.
- the switch signal generator may modulate the duty cycle of individual switches based on measurements of at least one of current and voltage at the individual switch, for example, the modulation of the duty cycle response to a voltage at the pole of the switch.
- the switch generator may switch the electric switches in excess of 100 kilohertz.
- the electric switches may be silicon carbide MOSFET transistors.
- the power converter may further include a second multilevel switch network, each level having at least one switch having an electrically controllable pole movable between throws, wherein a first level of the second multilevel switch network has multiple switches whose throws communicate with each of the different nodes of the capacitive divider to provide switchable connections from each of the different nodes to respective poles; and the switches of each next level of the multilevel switch network have their throws in electrical communication with the poles of switches of a previous level and the number of switches in which the level decreases from the first level to a last level having a single switch associated with a single pole providing a fourth converter terminal.
- a second multilevel switch network each level having at least one switch having an electrically controllable pole movable between throws
- the switches may switch asynchronously with respect to other switches.
- the switches may operate at different frequencies and/or duty cycles.
- the switches may be contained in mechanically and electrically interconnectable modules each module including two throw terminals and a pole terminal exposed for interconnection with other modules or circuitry; a semiconductor; a single-pole, double-throw switch having a pole and two throws connected to the respective throw terminals; an inductor connected between the pole and the pole terminal; and a capacitor connected between throw terminals.
- the invention may provide a power converter having input terminals for receiving three-phase AC electrical power and having a capacitive divider attached to each of the inputs providing a series of different amplitude electrical AC signals.
- First and second multilevel switch networks are associated with each capacitive divider, each level of each switch network having at least one switch having an electrically controllable pole movable between throws, wherein a first level of each switch network has multiple switches whose throws communicate with each of the different nodes of the capacitive divider to provide switchable connections from each of the different nodes to respective poles; and wherein the switches of each next level of the multilevel switch network have their throws connected to poles of switches of a previous level; and wherein the number of switches in which the level decreases from the first level to a last level have a single switch associated with a single pole providing a third converter terminal and fourth converter terminal for the first and second multilevel switch networks, respectively.
- An electronic commutating switch assembly may selectively connect one of the third converter terminals of the first multilevel switch networks to one side of a load output and one of the fourth converter terminals of the second multilevel switch assemblies to a second side of the load output to apply power to a load.
- At least one switch signal generator may control a switching of the switches and electronic commutating switch assembly to provide a power transformation between the three-phase AC electrical power and the load attached to the load output.
- FIG. 1 is a diagram showing a perspective view of an example charging station providing a transformer-less step-down of medium voltage grid voltage as implemented by a modular power converter (shown in fragmentary perspective view) assembled from a set of switching modules in a pyramid structure (shown schematically) each switching module including a series inductor and shunting capacitor (shown schematically) together with a single single-pole, double-throw switch implemented with solid-state semiconductor switches (shown schematically);
- a modular power converter shown in fragmentary perspective view
- each switching module including a series inductor and shunting capacitor (shown schematically) together with a single single-pole, double-throw switch implemented with solid-state semiconductor switches (shown schematically);
- FIG. 2 is a simplified schematic of the pyramid structure of the present invention showing voltage levels during an AC to AC voltage step-down operation
- FIG. 3 is an example waveform generated during the step-down operation of FIG. 2 under no load conditions
- FIG. 4 is a simplified schematic similar to FIG. 2 of the pyramid structure the present invention during a voltage step-up operation.
- FIG. 5 is a schematic representation of the pyramid structure of FIG. 3 implementing a three-phase circuit for AC/DC or AC/AC conversion;
- FIG. 6 is a set of waveforms showing the reduced ripple provided by the circuit of FIG. 5 in three-phase AC to DC conversion;
- FIG. 7 is a diagram of a control loop that may be implemented in each switching module providing for localized adjustment of duty cycle for voltage or current control or semiconductor matching and providing for randomization of frequency or phase for reduction of emitted electromagnetic interference;
- FIG. 8 is a figure similar to that of FIG. 3 showing an alternative embodiment of the pyramid structure without distributed capacitors and inductors using multiple ground-level voltages.
- a modular power converter 10 of the present invention may be used to provide for a step down of voltage from a medium voltage grid 12 , having voltages ranging from 2 kV to 35 kV, to AC or DC charging voltage 14 on the order of 200 to 400 volts for charging an electric automobile 16 .
- This example should not be considered limiting as the present application can also be used in a wide variety of other power conversion applications including those associated with motor control, photovoltaic arrays, wind farms, power distribution and the like.
- the modular power converter 10 may be constructed of multiple switching modules 18 , for example, assembled in multilevel stacks 20 with various levels 19 separated by insulating standoffs 22 or the like. Switching modules 18 within a stack 20 and between stacks may be interconnected electrically by jumpers 24 or functionally similar electrical connectors.
- the input voltage from the medium voltage grid 12 may be received at a first level 19 , (for example, the lowermost level) in the stack 20 and an output voltage may be extracted at the last level 19 (for example, the uppermost level) in the stack 20 providing a natural degree of voltage isolation as a result of the segregation of different voltage ranges into different levels 19 in the stacks 20 as will be discussed below.
- a particular physical ordering of the switching modules 18 in the stacks 20 and levels 19 is not required so long as the topology of the stack, as will be discussed below, is respected.
- sixteen switching modules 18 are configured in stacks 20 labeled I-IV and in levels 19 labeled A-D with a highest level A providing a single upper terminal 26 for providing a stepped-down voltage and the lowest level D receiving a high-voltage AC voltage at terminal 28 , each of the voltages at terminals 26 and 28 referenced to a ground terminal 30 at a ground potential.
- Level A provides an apex of current flow pattern conforming generally to a pyramid 29 with level D providing the base of the pyramid 29 .
- Extending along the base is a voltage divider 27 formed of series-connected capacitors 50 extending between terminal 28 and terminal 30 . Interconnections between the capacitors 50 or between the first capacitor 50 and terminal 28 or the last capacitor 50 and terminal 30 are node points which present different voltage levels as will be discussed below.
- the switching modules 18 alone or in combination implement different of a set of electronically controllable single throw double pole switches 31 .
- Each of four switching modules 18 of level D independently provide four corresponding single-pole, double-throw switches 31 .
- the poles of each switch 31 connect to nodes on opposite sides of a corresponding capacitor 50 of the voltage divider 27 thereby receiving different voltages per the voltage drop across each capacitor 50 .
- poles of adjacent switches 31 connect to common nodes and thus to each other.
- the configuration of the switching modules 18 at a level D will be termed “throw serial” to the extent that the adjacent switches 31 in the switching modules 18 in the level D are joined in series by pairs of interconnected throws of different adjacent switching modules 18 .
- the poles of the switches 31 of switching modules 18 of level D then pass voltages to the throws of three switches 31 of switching modules 18 in the next higher-level C being second the level of the pyramid 29 .
- These switches 31 of level C are also connected in “throw serial” fashion so that each throw of a given switch 31 connects to a different pole of adjacent switches 31 in level D.
- the poles of the switches 31 of switching modules 18 in level C then connect to the throws of two effective switches 31 ′ at level B beginning with the third level of the pyramid 29 .
- These effective switches 31 ′ by combining in parallel the switches 31 of two different switching modules 18 , handle approximately twice as much current as the switch 31 from a single switching module 18 .
- the poles 36 of each switch 31 of a pair of adjacent switching modules 18 are connected together, and the left throw terminals 48 a of each switch 31 of the pair of switching modules 18 are connected together and the right throw terminals 48 b of each switch 31 of the pair of switching modules 18 are connected together to form switch 31 ′.
- This configuration will be termed “throw-parallel.”
- Each throw of the two effective switches 31 ′ connects to a different pole of adjacent switches 31 in level C and thus are also connected in throw serial fashion.
- the pole's two effective switches 31 ′ then connect to the throws of a single effective switch 31 ′′ of level A firmed of the throw-parallel connection for four switches 31 of four switching modules 18 in level A.
- This parallel connection increases current carrying capacity of effective switch 31 ′′ to be four times that of an individual switching module 18 , for example, of level D. in this throw-parallel connection, the poles 36 of all four switches 31 of each switching module 18 in level A are connected together, and all of the left throw terminals 48 a are connected together and all of the right throw terminals 48 b are connected together for these four switches.
- the pole of effective switch 31 ′′ provides power to terminal 26
- the pyramid 29 so formed provides one less switch 31 (or effective switch 31 ′ or 31 ′′) in each succeeding level and generally boosts current as indicated by arrow 32 as one moves up the pyramid 29 (from level D to level A) which may be matched through conservation of energy by a reduction in voltage with respect to ground 33 as one moves down the pyramid 29 (from level A to level D). While the present example considers a voltage step-down from terminal 28 to terminal 26 , a voltage step-up may be obtained as will be discussed below by operating the pyramid 29 in the opposite direction from terminal 26 to terminal 28 . Corresponding current step-up or current step-down can similarly be obtained.
- each switching module 18 includes not only the above described electronically controllable single-throw, double-pole switch 31 but also a switch controller 34 which, for example, may be a discrete circuit or microcontroller executing a stored program 37 contained in computer memory.
- the switch controller 34 communicates control signals to the switch 31 to control connection of the pole 36 between different throw terminals 48 and will normally operate to provide a periodic switching of the switch 31 whose frequency and duty cycle may be flexibly modulated.
- Each of the switch controllers 34 may communicate (with or without wires) over control lines 40 with a central controller 42 as will be discussed below and may provide for control parameters to the switch controller 34 . It will be appreciated that the function of the central controller 42 and switch controllers 34 may be arbitrarily distributed among the central controller 42 and the switch controllers 34 .
- the pole 36 of the switch 31 of each switching module 18 communicates with an upper pole terminal 44 of the switching module 18 through an inductor 46 .
- the throws 38 of the switch 31 may communicate with corresponding lower throw terminals 48 a and 48 b.
- These lower throw terminals 48 a and 48 b are shunted with a capacitor 50 that may be rated in breakdown voltage only according to the voltage difference between the throw terminals 48 a and 48 b, which, as will be seen, will normally be a small fraction of the total voltage handled by the converter 10 .
- Each of the pole terminals 44 , and throw terminals 48 a, and 48 b may have provisions for receiving jumpers 24 interconnecting the switching modules 18 , for example, electrical connectors, screw terminals or the like.
- the upper pole terminal 44 may be connected to the lower throw terminals 48 a or 48 b of switching modules in a higher level or may be connected to external circuits for example as terminal 26 .
- the lower throw terminals 48 a or 48 b may connect to the upper terminals 44 of switching modules 18 in lower levels or to the terminals 28 and 30 to form the lower-level voltage divider 27 .
- the switch controller 34 may monitor voltage at throw terminals 48 a and 48 b as well as at the voltage at pole 36 . In addition, the switch controller 34 may monitor the current flow through the pole 36 and may adjust its control of the switch 31 according to those measurements as will be discussed below.
- each switching module 18 may be constructed of solid-state diodes and MOSFETs, the latter preferably being wideband gap MOSFETs, for example, silicon carbide although the invention also contemplates that other switching devices such as silicon IGBTs may be used in some embodiments.
- the switch 31 When it is desirable that the switch 31 operate with current flow in two directions from terminal 28 to terminal 26 , for example, as required for regenerative power conversion, the switch 31 may be formed of a parallel connection of two bidirectional switch elements 52 a and 52 b that are alternatively activated so that switch element 52 a provides current flow between the pole 36 and a first throw 38 a and switch element 52 b provides current flow between the pole 36 and a second throw 38 b.
- Each of switch elements 52 a and 52 b may be formed in turn of parallel connections of two transistor elements 59 a and 59 b, each of the latter providing a serially connected MOSFET 54 and Schottky diode 56 , where the orientation of the diodes 56 is in opposite directions in the two transistor elements 59 a and 59 b.
- Control leads 58 from the MOSFETs 54 are routed to the switch controller 34 so that only one of the switching elements 52 a or 52 b is activated at a time according to the state of the switch 31 .
- each of the switching elements 52 a and 52 b may incorporate only one of the serial connected MOSFETs 54 and corresponding diodes 56 so that the diodes face in opposite directions for the selected pair of MOSFETs and corresponding diodes 56 between the different elements 52 a and 52 b. That is, the switch 31 may use either transistor elements 59 a only when there is current flow from terminal 28 to terminal 26 or transistor elements 59 b only when there is current flow from terminal 26 to terminal 28 .
- FIG. 2 a simplified version of the pyramid 29 will be described as having only two levels 19 a and 19 b providing a voltage step-down from a high-voltage AC on terminal 28 to a lower voltage AC signal on terminal 26 or a lower voltage DC signal on terminal 26 .
- the pyramid 29 acts as a buck converter reducing voltage through control of the duty cycle of the constituent switches 31 .
- the reduction in voltage can provide a lower voltage, equal frequency AC waveform or an arbitrary voltage DC waveform, or by changing the DC voltage, a synthesized AC waveform of arbitrary frequency.
- switches 31 may be either actual or effective switches as needed for current handling capacity.
- the high-voltage voltage V is applied to terminal 28 which is then divided by the voltage divider 27 to provide three different voltages at three nodes of the voltage divider equal to V, V/2 and 0 volts respectively (for equal capacitors 50 ). Voltages at these different nodes are received by switches 31 a and 31 b of corresponding switching modules 18 in a first level 19 a. Specifically, the voltage at terminal 28 of V communicates with a first throw 38 a of first switch 31 a, and a node voltage of V/2 is received at the second throw 38 b of switch 31 a and at the first throw 38 c of switch 31 b. The voltage of 0 and is then received by throw 38 d of switch 31 b.
- Switches 31 a and 31 b may be modulated at a high frequency with respect to the voltage at terminal 28 (the latter typically being on the order of 60 hertz and the former, for example, being 200 kilohertz).
- the duty cycle of the switching waveform may be arbitrarily controlled but in this example will be considered to be 50 percent for the first level 19 a meaning that the switches spend equal time with the pole connected to each throw. This will produce a voltage at the pole 36 of switch 31 a of 3V/4 (50 percent of V plus 50 percent of V/2). This voltage is connected to throw 38 e of switch 31 c on level 19 b.
- the pole 36 of switch 31 b will have a voltage of V/4 as a result of its different voltage inputs. This pole 36 may be connected to second throw 38 f of switch 31 c of level 19 b.
- switch 31 c is operated with a 75 percent duty cycle (75 percent of the time being in the leftmost position communicating with throw 38 e and 25 percent of the time being in the rightmost position communicating with throw 38 f ).
- the pole 36 of switch 31 c attached to upper terminal 26 will then provide a (average) voltage of 5V/8.
- the filtering action and energy storage of the capacitors 50 and inductors 46 and the high switching speed of the switches 31 prevents any individual switch from instantaneously receiving the full voltage V across it such as may lead to switch damage.
- the voltage on the upper terminal 26 will be an AC waveform that has been reduced from an amplitude of V to an amplitude of 5V/8. Nevertheless, it will be appreciated that the modulation of the switches may be rapidly changed allowing the AC waveform on terminal 28 to be effectively rectified or even synthesized to a second AC waveform of arbitrary frequency and phase as part of a three-phase system or the like as will be discussed below.
- the operation of the switches 31 maybe asynchronous with respect to each other, and the phases and frequencies of switching of the switches 31 maybe randomized, both approaches reducing emitted electrical interference.
- High-frequency operation of the switches 31 permits effective filtration of the switch frequency with modest component sizes of the capacitors 50 and inductors 46 .
- the capacitors 50 and inductors 46 further reduce effects of parasitic energy transfer between the levels 19 such as may include high frequency and high-voltage components damaging to the switches and generating electromagnetic interference. It will be appreciated that the partitioning of the voltage transition into multiple levels 19 and the use of voltage divider 27 allows smaller voltage capacitors 50 , while distributing the capacitors 50 throughout the switches 31 allows the use of smaller capacity capacitors.
- Rectification may also be Obtained by using unidirectional switches 31 as discussed above.
- the values of the inductors 45 and capacitor 50 are set to according to a desired limitation on ripple current.
- the inductor values will be greater than one micro-Henry.
- the circuit of FIG. 3 may also be operated in a boost mode to provide a step-up in voltage from an AC or DC voltage (V a ) applied to the upper terminal 26 to provide an output AC voltage (V out ) on terminal 28 having a higher voltage.
- V a AC or DC voltage
- V out output AC voltage
- energy may be stored in the inductances 46 when they are switched to a throw 38 associated with a lower voltage and that energy used to boost the voltage on the other throw when the pole 36 switches to the alternate throw 38 release the inductive energy into that throw 38 .
- pyramids 29 a - 29 f may be combined in a three-phase system providing greater flexibility in power conversion.
- the bases of pyramid 29 a and 29 b may be joined to form a common voltage divider 27 (formed of parallel combinations of capacitors 50 in different switching modules 18 ) with pyramid 29 a directed upwardly (as depicted) to terminal 26 a and pyramid 29 b extending downwardly (as depicted) to terminal 26 b.
- pyramids 29 c and 29 d may be paired and pyramids 29 e and 29 f may be paired providing upper terminals 26 c and 26 e respectively and lower terminals 26 d and 26 f respectively.
- Each of the pyramid pairs may be fed with an AC source through terminals 28 providing waveforms that are each separated in phase by 120 degrees so that the output waveforms, for example, at terminals 26 a, 26 c, and 26 e represent a three-phase output of reduced voltage with respect to the voltages on terminals 28 as shown in FIG. 6 .
- each of the terminals 26 a, 26 c, and 26 e may be pairwise interconnected by capacitors 61 and may connect to corresponding throws of a three-throw, single pole commutation switch 60 , for example, implemented by semiconductor devices in a manner analogous to that described above with respect the switches 31 .
- the pole of this commutation switch 60 connects to one side of the load 62 .
- the other side of the load 62 may connect to a pole a second single pole, triple-throw commutation switch 64 whose throws connect respectively to terminals 26 b, 26 d, and 26 f.
- these terminals 26 b, 26 d, and 26 f are pairwise interconnected by capacitors 61 .
- the commutation switches 60 and 64 may sequence through the terminals 26 a, 26 b, or 26 c to select a particular terminal whose output voltage is sufficient to provide the desired output voltage V c . In this way, a more consistent DC voltage 68 may be generated. Where the level V c is sufficiently high, there is no overlap between the active regions 66 existing for the terminals 26 , and effectively continuous voltage can be obtained by energy stored in a low pass filter, for example, provided between the commutation switches 60 and 64 and the load 62 . The generated voltage may be constant when DC voltage is required or modulated to produce an AC waveform of arbitrary frequency.
- this structure of back-to-back pyramids 29 may also be used in boost configuration by placing commutation switches 60 and 64 so that their throws receive terminals 28 of each pair of back-to-back pyramids 29 and placing the three phases of electrical power across terminals 26 of the pyramid pair (e.g., terminals 26 a and 26 b for first phase, etc.)
- switch controller 34 may receive control signals, for example, describing control value 65 indicating desired output voltage or current to be produced by a particular switch module 18 from a central controller 42 .
- the switch controller 34 may be preprogrammed with a value indicating that desired control value 65 .
- the switch controller 34 may establish a local feedback control loop to control the duty cycle of the switches 31 to produce the desired current or voltage by comparing the control value 65 to a measured value of voltage or current at the switching modules 18 , for example, as monitored by the controller 34 as discussed with respect to FIG. 1 .
- the switch 31 may be monitored with respect to current passing through the pole 36 and this value compared at a summing junction 70 to the desired control value 65 indicating a desired current.
- the output from the summing junction 70 may control a waveform generator 72 to affect the duty cycle of that waveform generator 72 , for example, to change the current flow.
- a current source may be implemented, or switches 31 connected in parallel can be better controlled to share current load.
- the measurement of switch 31 may be, for example, the voltage at the pole 36 such as will affect the voltages on the capacitors 50 at the next higher or lower level, and the duty cycle of the switch 31 may be controlled to provide a certain desired step-down or step-up voltage.
- controller 34 may also implement a random perturbation signal 74 moderating the phase or frequency of the waveform generator 72 to reduce emissions of electromagnetic interference from the ensemble of switches 31 .
- switch levels 19 may provide one throw attached to one of several ground reference points 78 having voltages set to different levels between the voltage of the output terminal 26 and input terminal 28 thereby providing the gradation in voltage across different levels providing the benefits discussed above.
- a first low level 19 a in the pyramid 29 may have one throw tied to absolute ground 33
- a second level 19 b may have one throw tied to a second ground reference N1+ of slightly higher voltage
- a third level 19 c may have at least one throw tied to a third ground reference N0+ of even higher voltage where 0 ⁇ N1+ ⁇ N0+ ⁇ V out , and where V out is the voltage at output terminal 26 .
- references to “a controller” and “a processor” or “the microprocessor” and “the processor,” can be understood to include one or more microprocessors that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices.
- references to memory can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor-controlled device, external to the processor-controlled device, and can be accessed via a wired or wireless network.
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Abstract
Description
- The present invention relates to electrical circuits for power conversion, for example, between different voltages and/or between AC and DC power, and in particular to a multilevel architecture for power converters that can provide improved power conversion of high voltages.
- Conventional power conversion, for example, converting between different levels of AC power, may employ a transformer having inductively linked coils that transform input AC voltage to output AC voltage according to the turns ratio of coils.
- For many applications, and in particular applications related to renewable energy including windfarms, electric vehicles, and photovoltaic arrays, transformer systems are unacceptably bulky, expensive, and inflexible. Windfarms and photovoltaic arrays may need to transform between low-voltage AC or DC to medium voltage grid power (2 kV to 35 kV) while recharging systems for electric vehicles may need to reduce medium voltage grid power to lower AC or DC voltages (200-400 volts) as needed for battery charging.
- The cost, weight and bulk of the transformer may be reduced through the use of solid-state switching devices. In a “dual active bridge” design, solid-state devices convert input AC power to DC and then synthesize a higher frequency AC waveform that may work with a smaller transformer. Output from the transformer is then reconverted by additional solid-state devices to DC and then to the desired level of AC.
- Preferably, a transformer-less medium voltage power conversion system could be developed by directly converting input AC power to the desired AC or DC output using semiconductor devices. Wideband (WBG) devices such as silicon carbide (SiC) MOSFETs may provide sufficiently high-frequency operation for this application and may have sufficiently high breakdown voltages to allow them to operate with power from medium voltage grids by connecting multiple devices in series.
- Rapid switching of high voltages by solid-state devices can create problems of generating electromagnetic interference and high dv/dt (voltage change rate) such as can be damaging to electrical insulation on motors and the like. Placing solid-state devices in series can require careful coordination of the switching times of the devices to ensure that an individual device does not instantaneously experience excess voltages beyond their rated breakdown voltage.
- The present invention provides a power converter using a pyramid architecture that limits the voltage difference handled by each switch to reduce electromagnetic interference and high dv/dt. The pyramid design permits asynchronous operation of the switches eliminating the criticality of switch synchronization allowing the switching speed and duty cycle to be adjusted, for example, to reduce EMI and to improve power-sharing among semiconductor devices.
- Specifically, then, in one embodiment the invention provides a power converter having a capacitive divider with one end providing a first converter terminal and a second end. providing a second converter terminal attachable to a ground reference. The capacitive divider presents a series of different nodes between series connected capacitances. A multilevel switch network, with each level having at least one switch having an electrically controllable pole movable between throws, has a first level with multiple switches whose throws communicate with each of the different nodes of the capacitive divider. The switches of each next level of the multilevel switch network have their throws in electrical communication with poles of switches of a previous level so that the number of switches in each level decreases from the first level to a last level, the last level having a single switch associated with a single pole providing a third converter terminal. At least one switch signal generator controls a switching of the switches to provide a power transformation between the first converter terminal and the third converter terminal providing a reduction in voltage and increase in current at the third converter terminal with respect to the first converter terminal.
- It is thus a feature of at least one embodiment of the invention to provide an architecture that provides the voltage differences between input and output in a series of levels to limit the voltage difference handled by each switch and thus limiting the voltage rate of change to reduce electromagnetic interference and equipment wear.
- The proportion of reduction in voltage and increase in current is determined by a duty cycle of switching of the switches.
- It is thus a feature of at least one embodiment of the invention to provide an extremely flexible converter that can dynamically change the voltage and current conversion ratios.
- Each of the switches of each level may be isolated from switches of a next level by inductors.
- It is thus a feature of at least one embodiment of the invention to eliminate high-frequency coupling between the switches, for example, through parasitic elements.
- The power converter may further include energy storage capacitances distributed among the switches and positioned between the throws of each switch.
- It is thus a feature of at least one embodiment of the invention to provide distributed energy storage in the switching network such as preserves the voltage segregation between levels while eliminating the need for expensive high-voltage capacitors.
- The switches closest to the third converter terminal may have higher current capacity than the switches closest to the second converter terminal.
- It is thus a feature of at least one embodiment of the invention to provide a pyramid structure that reflects the transformation between current and voltage to allow tailoring of the switches at each level to the necessary current levels, for example, by tandem semiconductor devices.
- Each of the switches may be a single-pole, double-throw switch and the number of switches in each successive level decreases by one with respect to the previous level.
- It is thus a feature of at least one embodiment of the invention to provide a simple architecture that may be, for example, implemented modularly to suit a variety of different conversion applications.
- The switch signal generator may modulate the duty cycle of individual switches based on measurements of at least one of current and voltage at the individual switch, for example, the modulation of the duty cycle response to a voltage at the pole of the switch.
- It is thus a feature of at least one embodiment of the invention to allow ready accommodation of different component parameters associated with each switch through simple adjustment of the switching signal.
- The switch generator may switch the electric switches in excess of 100 kilohertz.
- It is thus a feature of at least one embodiment of the invention to provide a switching speed compatible with high-voltage conversion that minimizes harmonic content in the output waveform.
- The electric switches may be silicon carbide MOSFET transistors.
- It is thus a feature of at least one embodiment of the invention to provide an architecture suitable tier such high-speed transistors that moderates problems of high-speed switching as far as electrical interference, capacitive effects and dv/dt damage to insulation and the like.
- The power converter may further include a second multilevel switch network, each level having at least one switch having an electrically controllable pole movable between throws, wherein a first level of the second multilevel switch network has multiple switches whose throws communicate with each of the different nodes of the capacitive divider to provide switchable connections from each of the different nodes to respective poles; and the switches of each next level of the multilevel switch network have their throws in electrical communication with the poles of switches of a previous level and the number of switches in which the level decreases from the first level to a last level having a single switch associated with a single pole providing a fourth converter terminal.
- It is thus a feature of at least one embodiment of the invention to provide improved efficiency in rectification or AC conversion through a double-ended configuration.
- The switches may switch asynchronously with respect to other switches. Alternatively or in addition, the switches may operate at different frequencies and/or duty cycles.
- It is thus a feature of at least one embodiment of the invention to reduce electromagnetic interference generated by the power converter.
- The switches may be contained in mechanically and electrically interconnectable modules each module including two throw terminals and a pole terminal exposed for interconnection with other modules or circuitry; a semiconductor; a single-pole, double-throw switch having a pole and two throws connected to the respective throw terminals; an inductor connected between the pole and the pole terminal; and a capacitor connected between throw terminals.
- It is thus a feature of at least one embodiment of the invention to provide an architecture that can be readily expanded and reconfigured for different applications.
- In one embodiment, the invention may provide a power converter having input terminals for receiving three-phase AC electrical power and having a capacitive divider attached to each of the inputs providing a series of different amplitude electrical AC signals. First and second multilevel switch networks are associated with each capacitive divider, each level of each switch network having at least one switch having an electrically controllable pole movable between throws, wherein a first level of each switch network has multiple switches whose throws communicate with each of the different nodes of the capacitive divider to provide switchable connections from each of the different nodes to respective poles; and wherein the switches of each next level of the multilevel switch network have their throws connected to poles of switches of a previous level; and wherein the number of switches in which the level decreases from the first level to a last level have a single switch associated with a single pole providing a third converter terminal and fourth converter terminal for the first and second multilevel switch networks, respectively. An electronic commutating switch assembly may selectively connect one of the third converter terminals of the first multilevel switch networks to one side of a load output and one of the fourth converter terminals of the second multilevel switch assemblies to a second side of the load output to apply power to a load. At least one switch signal generator may control a switching of the switches and electronic commutating switch assembly to provide a power transformation between the three-phase AC electrical power and the load attached to the load output.
- It is thus a feature of at least one embodiment of the invention to provide a versatile three-phase power converter.
- These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.
-
FIG. 1 is a diagram showing a perspective view of an example charging station providing a transformer-less step-down of medium voltage grid voltage as implemented by a modular power converter (shown in fragmentary perspective view) assembled from a set of switching modules in a pyramid structure (shown schematically) each switching module including a series inductor and shunting capacitor (shown schematically) together with a single single-pole, double-throw switch implemented with solid-state semiconductor switches (shown schematically); -
FIG. 2 is a simplified schematic of the pyramid structure of the present invention showing voltage levels during an AC to AC voltage step-down operation; -
FIG. 3 is an example waveform generated during the step-down operation ofFIG. 2 under no load conditions; -
FIG. 4 is a simplified schematic similar toFIG. 2 of the pyramid structure the present invention during a voltage step-up operation. -
FIG. 5 is a schematic representation of the pyramid structure ofFIG. 3 implementing a three-phase circuit for AC/DC or AC/AC conversion; -
FIG. 6 is a set of waveforms showing the reduced ripple provided by the circuit ofFIG. 5 in three-phase AC to DC conversion; -
FIG. 7 is a diagram of a control loop that may be implemented in each switching module providing for localized adjustment of duty cycle for voltage or current control or semiconductor matching and providing for randomization of frequency or phase for reduction of emitted electromagnetic interference; and -
FIG. 8 is a figure similar to that ofFIG. 3 showing an alternative embodiment of the pyramid structure without distributed capacitors and inductors using multiple ground-level voltages. - Referring now to
FIG. 1 , in one exemplary application, amodular power converter 10 of the present invention may be used to provide for a step down of voltage from amedium voltage grid 12, having voltages ranging from 2 kV to 35 kV, to AC orDC charging voltage 14 on the order of 200 to 400 volts for charging anelectric automobile 16. This example should not be considered limiting as the present application can also be used in a wide variety of other power conversion applications including those associated with motor control, photovoltaic arrays, wind farms, power distribution and the like. - The
modular power converter 10 may be constructed ofmultiple switching modules 18, for example, assembled inmultilevel stacks 20 withvarious levels 19 separated by insulatingstandoffs 22 or the like. Switchingmodules 18 within astack 20 and between stacks may be interconnected electrically byjumpers 24 or functionally similar electrical connectors. - In this application, the input voltage from the
medium voltage grid 12 may be received at afirst level 19, (for example, the lowermost level) in thestack 20 and an output voltage may be extracted at the last level 19 (for example, the uppermost level) in thestack 20 providing a natural degree of voltage isolation as a result of the segregation of different voltage ranges intodifferent levels 19 in thestacks 20 as will be discussed below. A particular physical ordering of the switchingmodules 18 in thestacks 20 andlevels 19, however, is not required so long as the topology of the stack, as will be discussed below, is respected. - In an explanatory example shown in
FIG. 1 , sixteen switchingmodules 18 are configured instacks 20 labeled I-IV and inlevels 19 labeled A-D with a highest level A providing a singleupper terminal 26 for providing a stepped-down voltage and the lowest level D receiving a high-voltage AC voltage atterminal 28, each of the voltages atterminals ground terminal 30 at a ground potential. Level A provides an apex of current flow pattern conforming generally to apyramid 29 with level D providing the base of thepyramid 29. Extending along the base is avoltage divider 27 formed of series-connectedcapacitors 50 extending betweenterminal 28 andterminal 30. Interconnections between thecapacitors 50 or between thefirst capacitor 50 and terminal 28 or thelast capacitor 50 and terminal 30 are node points which present different voltage levels as will be discussed below. - The switching
modules 18 alone or in combination implement different of a set of electronically controllable single throw double pole switches 31. Each of four switchingmodules 18 of level D independently provide four corresponding single-pole, double-throw switches 31. The poles of eachswitch 31 connect to nodes on opposite sides of a correspondingcapacitor 50 of thevoltage divider 27 thereby receiving different voltages per the voltage drop across eachcapacitor 50. In this connection, poles ofadjacent switches 31 connect to common nodes and thus to each other. The configuration of the switchingmodules 18 at a level D will be termed “throw serial” to the extent that theadjacent switches 31 in the switchingmodules 18 in the level D are joined in series by pairs of interconnected throws of differentadjacent switching modules 18. - The poles of the
switches 31 of switchingmodules 18 of level D then pass voltages to the throws of threeswitches 31 of switchingmodules 18 in the next higher-level C being second the level of thepyramid 29. Theseswitches 31 of level C are also connected in “throw serial” fashion so that each throw of a givenswitch 31 connects to a different pole ofadjacent switches 31 in level D. - The poles of the
switches 31 of switchingmodules 18 in level C then connect to the throws of twoeffective switches 31′ at level B beginning with the third level of thepyramid 29. Theseeffective switches 31′, by combining in parallel theswitches 31 of twodifferent switching modules 18, handle approximately twice as much current as theswitch 31 from asingle switching module 18. Specifically, thepoles 36 of eachswitch 31 of a pair ofadjacent switching modules 18 are connected together, and the left throw terminals 48 a of eachswitch 31 of the pair of switchingmodules 18 are connected together and the right throw terminals 48 b of eachswitch 31 of the pair of switchingmodules 18 are connected together to formswitch 31′. This configuration will be termed “throw-parallel.” Each throw of the twoeffective switches 31′ connects to a different pole ofadjacent switches 31 in level C and thus are also connected in throw serial fashion. - The pole's two
effective switches 31′ then connect to the throws of a singleeffective switch 31″ of level A firmed of the throw-parallel connection for fourswitches 31 of four switchingmodules 18 in level A. This parallel connection increases current carrying capacity ofeffective switch 31″ to be four times that of anindividual switching module 18, for example, of level D. in this throw-parallel connection, thepoles 36 of all fourswitches 31 of each switchingmodule 18 in level A are connected together, and all of the left throw terminals 48 a are connected together and all of the right throw terminals 48 b are connected together for these four switches. The pole ofeffective switch 31″ provides power toterminal 26 - The
pyramid 29 so formed provides one less switch 31 (oreffective switch 31′ or 31″) in each succeeding level and generally boosts current as indicated byarrow 32 as one moves up the pyramid 29 (from level D to level A) which may be matched through conservation of energy by a reduction in voltage with respect toground 33 as one moves down the pyramid 29 (from level A to level D). While the present example considers a voltage step-down from terminal 28 toterminal 26, a voltage step-up may be obtained as will be discussed below by operating thepyramid 29 in the opposite direction from terminal 26 toterminal 28. Corresponding current step-up or current step-down can similarly be obtained. - Referring still to
FIG. 1 , in one embodiment, each switchingmodule 18 includes not only the above described electronically controllable single-throw, double-pole switch 31 but also aswitch controller 34 which, for example, may be a discrete circuit or microcontroller executing a storedprogram 37 contained in computer memory. Theswitch controller 34 communicates control signals to theswitch 31 to control connection of thepole 36 between different throw terminals 48 and will normally operate to provide a periodic switching of theswitch 31 whose frequency and duty cycle may be flexibly modulated. Each of theswitch controllers 34 may communicate (with or without wires) overcontrol lines 40 with acentral controller 42 as will be discussed below and may provide for control parameters to theswitch controller 34. It will be appreciated that the function of thecentral controller 42 andswitch controllers 34 may be arbitrarily distributed among thecentral controller 42 and theswitch controllers 34. - Referring still to
FIG. 1 , thepole 36 of theswitch 31 of each switchingmodule 18 communicates with anupper pole terminal 44 of theswitching module 18 through aninductor 46. Conversely thethrows 38 of theswitch 31 may communicate with corresponding lower throw terminals 48 a and 48 b. These lower throw terminals 48 a and 48 b are shunted with acapacitor 50 that may be rated in breakdown voltage only according to the voltage difference between the throw terminals 48 a and 48 b, which, as will be seen, will normally be a small fraction of the total voltage handled by theconverter 10. - Each of the
pole terminals 44, and throw terminals 48 a, and 48 b may have provisions for receivingjumpers 24 interconnecting the switchingmodules 18, for example, electrical connectors, screw terminals or the like. In this way, theupper pole terminal 44 may be connected to the lower throw terminals 48 a or 48 b of switching modules in a higher level or may be connected to external circuits for example asterminal 26. Similarly, the lower throw terminals 48 a or 48 b may connect to theupper terminals 44 of switchingmodules 18 in lower levels or to theterminals level voltage divider 27. - The
switch controller 34 may monitor voltage at throw terminals 48 a and 48 b as well as at the voltage atpole 36. In addition, theswitch controller 34 may monitor the current flow through thepole 36 and may adjust its control of theswitch 31 according to those measurements as will be discussed below. - The
switch 31 of each switchingmodule 18 may be constructed of solid-state diodes and MOSFETs, the latter preferably being wideband gap MOSFETs, for example, silicon carbide although the invention also contemplates that other switching devices such as silicon IGBTs may be used in some embodiments. - When it is desirable that the
switch 31 operate with current flow in two directions from terminal 28 toterminal 26, for example, as required for regenerative power conversion, theswitch 31 may be formed of a parallel connection of two bidirectional switch elements 52 a and 52 b that are alternatively activated so that switch element 52 a provides current flow between thepole 36 and a first throw 38 a and switch element 52 b provides current flow between thepole 36 and a second throw 38 b. - Each of switch elements 52 a and 52 b may be formed in turn of parallel connections of two transistor elements 59 a and 59 b, each of the latter providing a serially connected
MOSFET 54 andSchottky diode 56, where the orientation of thediodes 56 is in opposite directions in the two transistor elements 59 a and 59 b. Control leads 58 from theMOSFETs 54 are routed to theswitch controller 34 so that only one of the switching elements 52 a or 52 b is activated at a time according to the state of theswitch 31. - It will be appreciated that when only single directional current flow is required. through the
switch 31, each of the switching elements 52 a and 52 b may incorporate only one of the serial connectedMOSFETs 54 andcorresponding diodes 56 so that the diodes face in opposite directions for the selected pair of MOSFETs andcorresponding diodes 56 between the different elements 52 a and 52 b. That is, theswitch 31 may use either transistor elements 59 a only when there is current flow from terminal 28 toterminal 26 or transistor elements 59 b only when there is current flow from terminal 26 toterminal 28. - Referring now to
FIG. 2 , a simplified version of thepyramid 29 will be described as having only two levels 19 a and 19 b providing a voltage step-down from a high-voltage AC onterminal 28 to a lower voltage AC signal onterminal 26 or a lower voltage DC signal onterminal 26. - In this mode of operation, the
pyramid 29 acts as a buck converter reducing voltage through control of the duty cycle of the constituent switches 31. The reduction in voltage can provide a lower voltage, equal frequency AC waveform or an arbitrary voltage DC waveform, or by changing the DC voltage, a synthesized AC waveform of arbitrary frequency. These latter two conversions may preferably use thepyramid 29 in a three-phase mode as will be discussed below. In this discussion, it will be understood that switches 31 may be either actual or effective switches as needed for current handling capacity. - In this example, the high-voltage voltage V is applied to terminal 28 which is then divided by the
voltage divider 27 to provide three different voltages at three nodes of the voltage divider equal to V, V/2 and 0 volts respectively (for equal capacitors 50). Voltages at these different nodes are received by switches 31 a and 31 b of corresponding switchingmodules 18 in a first level 19 a. Specifically, the voltage atterminal 28 of V communicates with a first throw 38 a of first switch 31 a, and a node voltage of V/2 is received at the second throw 38 b of switch 31 a and at the first throw 38 c of switch 31 b. The voltage of 0 and is then received by throw 38 d of switch 31 b. - Switches 31 a and 31 b may be modulated at a high frequency with respect to the voltage at terminal 28 (the latter typically being on the order of 60 hertz and the former, for example, being 200 kilohertz). The duty cycle of the switching waveform may be arbitrarily controlled but in this example will be considered to be 50 percent for the first level 19 a meaning that the switches spend equal time with the pole connected to each throw. This will produce a voltage at the
pole 36 of switch 31 a of 3V/4 (50 percent of V plus 50 percent of V/2). This voltage is connected to throw 38 e of switch 31 c on level 19 b. Similarly, thepole 36 of switch 31 b will have a voltage of V/4 as a result of its different voltage inputs. Thispole 36 may be connected to second throw 38 f of switch 31 c of level 19 b. - Assume now in this example that switch 31 c is operated with a 75 percent duty cycle (75 percent of the time being in the leftmost position communicating with
throw 38 e and 25 percent of the time being in the rightmost position communicating with throw 38 f). Thepole 36 of switch 31 c attached toupper terminal 26 will then provide a (average) voltage of 5V/8. - Ignoring the filter effects of the
inductors 46, it will be appreciated that for 25 percent of the time the voltage varies between zero volts and V/2 in equal proportion, and for 75 percent of the time the voltage varies between V/2 and V in equal proportion. The present invention, by transforming a switching between zero and V volts to a set of sequential transitions between zero and V/2 volts and between V/2 volts and V volts, serves to decrease the dv/dt values of the resulting waveform in comparison to a direct switching between zero and V volts. In addition, the filtering action and energy storage of thecapacitors 50 andinductors 46 and the high switching speed of theswitches 31 prevents any individual switch from instantaneously receiving the full voltage V across it such as may lead to switch damage. - if the duty cycles of the
switches 31 are left constant as described above, the voltage on theupper terminal 26 will be an AC waveform that has been reduced from an amplitude of V to an amplitude of 5V/8. Nevertheless, it will be appreciated that the modulation of the switches may be rapidly changed allowing the AC waveform onterminal 28 to be effectively rectified or even synthesized to a second AC waveform of arbitrary frequency and phase as part of a three-phase system or the like as will be discussed below. - Generally, changing the duty cycle of the
switches 31 to favor the right-side throws will decrease this output voltage whereas changing the duty cycle of theswitches 31 to favor the left side throws will increase the output voltage. - Generally, the operation of the
switches 31 maybe asynchronous with respect to each other, and the phases and frequencies of switching of theswitches 31 maybe randomized, both approaches reducing emitted electrical interference. High-frequency operation of theswitches 31 permits effective filtration of the switch frequency with modest component sizes of thecapacitors 50 andinductors 46. Thecapacitors 50 andinductors 46 further reduce effects of parasitic energy transfer between thelevels 19 such as may include high frequency and high-voltage components damaging to the switches and generating electromagnetic interference. It will be appreciated that the partitioning of the voltage transition intomultiple levels 19 and the use ofvoltage divider 27 allowssmaller voltage capacitors 50, while distributing thecapacitors 50 throughout theswitches 31 allows the use of smaller capacity capacitors. - Rectification may also be Obtained by using
unidirectional switches 31 as discussed above. - The values of the inductors 45 and
capacitor 50 are set to according to a desired limitation on ripple current. In this regard the inductor values may be set according to the formula: Lmin=ΔV/(dnomFsΔImax), which ensures an inductance value large enough to maintain a small enough current ripple due to switching. For instance, an inductance Lmin=20 microhenry for a switch operating at a nominal frequency Fs=1 MHz, with dnom=50% nominal duty ratio, switching between levels that are ΔV=100V apart, will ensure that the current ripple will be 10 A. In many applications the inductor values will be greater than one micro-Henry. Similarly capacitor values may be set according to the formula: Cmin=ΔI/(dnomFsΔVmax), which would be large enough to maintain a small enough voltage ripple due to switching. For instance, an capacitance Cmin=20 microfarad for a switch operating at a nominal frequency Fs−1 MHz, with dnom=50% nominal duty ratio, switching between two current levels that are ΔI=100 A apart, will ensure that the voltage ripple will be 10V. In many applications, the capacitor values to be greater than one microfarad. - Referring now to
FIG. 4 , the circuit ofFIG. 3 may also be operated in a boost mode to provide a step-up in voltage from an AC or DC voltage (Va) applied to theupper terminal 26 to provide an output AC voltage (Vout) onterminal 28 having a higher voltage. Here, for a given instantaneous positive voltage oninput terminal 26, energy may be stored in theinductances 46 when they are switched to athrow 38 associated with a lower voltage and that energy used to boost the voltage on the other throw when thepole 36 switches to thealternate throw 38 release the inductive energy into thatthrow 38. Conversely, for a given negative voltage oninput terminal 28, energy stored in theinductances 46, when thepole 36 is switched to athrow 38 associated with a higher voltage, may be used to boost the voltage on the other throw when thepole 36 switches to that other throw. Through proper timing of the switching of eachswitch 31, arbitrary voltages may be imposed on thecapacitors 50 of the bottommost level to generate an arbitrary AC output voltage atterminal 28. Generally, this timing of the switching of theswitches 31 will consider the charge rate of theinductor 46, its saturation point if any, and the current draw fromterminal 28, for example, as monitored by monitoring the voltage on thecapacitors 50. Control of this timing may he through feedback control implemented by the switch controller 34 (shown inFIG. 1 ) as will be discussed below. When the voltage oninput terminal 26 is a direct current voltage or an AC voltage in a three-phase system as will be discussed below, this AC output voltage atterminal 28 may be of arbitrary frequency and phase. - Referring now to
FIG. 5 , the present invention contemplates thatmultiple pyramids 29 a-29 f may be combined in a three-phase system providing greater flexibility in power conversion. In the example ofFIG. 5 , the bases of pyramid 29 a and 29 b may be joined to form a common voltage divider 27 (formed of parallel combinations ofcapacitors 50 in different switching modules 18) with pyramid 29 a directed upwardly (as depicted) to terminal 26 a and pyramid 29 b extending downwardly (as depicted) to terminal 26 b. Likewise pyramids 29 c and 29 d may be paired and pyramids 29 e and 29 f may be paired providing upper terminals 26 c and 26 e respectively and lower terminals 26 d and 26 f respectively. - Each of the pyramid pairs may be fed with an AC source through
terminals 28 providing waveforms that are each separated in phase by 120 degrees so that the output waveforms, for example, at terminals 26 a, 26 c, and 26 e represent a three-phase output of reduced voltage with respect to the voltages onterminals 28 as shown inFIG. 6 . - Referring again to
FIG. 5 , each of the terminals 26 a, 26 c, and 26 e may be pairwise interconnected bycapacitors 61 and may connect to corresponding throws of a three-throw, singlepole commutation switch 60, for example, implemented by semiconductor devices in a manner analogous to that described above with respect theswitches 31. The pole of thiscommutation switch 60 connects to one side of theload 62. The other side of theload 62 may connect to a pole a second single pole, triple-throw commutation switch 64 whose throws connect respectively to terminals 26 b, 26 d, and 26 f. Again, these terminals 26 b, 26 d, and 26 f are pairwise interconnected bycapacitors 61. - Referring now to
FIGS. 5 and 6 it will be appreciated that depending on the desired output voltage Vc, there will be a limited duration ofactive regions 66 during which that voltage can be provided by a giventerminal 26 when terminal 28 (shown inFIG. 5 ) is provided with an AC waveform. By proper sequencing of the commutation switches 60 and 64, different of the output waveforms may be selected to extend the effectiveactive regions 66. So, for example, if it is desired to produce a DC output waveform of Vc less than the input voltage V using the buck converter process ofFIG. 3 , the commutation switches 60 and 64 may sequence through the terminals 26 a, 26 b, or 26 c to select a particular terminal whose output voltage is sufficient to provide the desired output voltage Vc. In this way, a moreconsistent DC voltage 68 may be generated. Where the level Vc is sufficiently high, there is no overlap between theactive regions 66 existing for theterminals 26, and effectively continuous voltage can be obtained by energy stored in a low pass filter, for example, provided between the commutation switches 60 and 64 and theload 62. The generated voltage may be constant when DC voltage is required or modulated to produce an AC waveform of arbitrary frequency. - Referring again to
FIG. 5 , it will be appreciated this structure of back-to-back pyramids 29 may also be used in boost configuration by placing commutation switches 60 and 64 so that their throws receiveterminals 28 of each pair of back-to-back pyramids 29 and placing the three phases of electrical power acrossterminals 26 of the pyramid pair (e.g., terminals 26 a and 26 b for first phase, etc.) - Referring now to
FIG. 7 ,switch controller 34 may receive control signals, for example, describingcontrol value 65 indicating desired output voltage or current to be produced by aparticular switch module 18 from acentral controller 42. Alternatively, theswitch controller 34 may be preprogrammed with a value indicating that desiredcontrol value 65. In either case, theswitch controller 34 may establish a local feedback control loop to control the duty cycle of theswitches 31 to produce the desired current or voltage by comparing thecontrol value 65 to a measured value of voltage or current at the switchingmodules 18, for example, as monitored by thecontroller 34 as discussed with respect toFIG. 1 . So, for example, theswitch 31 may be monitored with respect to current passing through thepole 36 and this value compared at a summingjunction 70 to the desiredcontrol value 65 indicating a desired current. The output from the summingjunction 70 may control awaveform generator 72 to affect the duty cycle of thatwaveform generator 72, for example, to change the current flow. By controlling current, a current source may be implemented, or switches 31 connected in parallel can be better controlled to share current load. - Alternatively, the measurement of
switch 31 may be, for example, the voltage at thepole 36 such as will affect the voltages on thecapacitors 50 at the next higher or lower level, and the duty cycle of theswitch 31 may be controlled to provide a certain desired step-down or step-up voltage. - In addition,
controller 34 may also implement arandom perturbation signal 74 moderating the phase or frequency of thewaveform generator 72 to reduce emissions of electromagnetic interference from the ensemble of switches 31. - These various functions of creating a
random perturbation signal 74 at summingjunction 70 and thewaveform generator 72 may be implemented in hardware or software as is generally understood in the art. - Referring now to
FIG. 8 , although the preferred embodiment of the invention provides for distributedcapacitances 50 andinductances 46 associated with eachmodule 18, many of the benefits of the invention may be obtained without distributedinductances 46 andcapacitances 50 and instead attach various switch levels to stabilizing ground references implemented by other means. For example, someswitch levels 19 may provide one throw attached to one of severalground reference points 78 having voltages set to different levels between the voltage of theoutput terminal 26 andinput terminal 28 thereby providing the gradation in voltage across different levels providing the benefits discussed above. In this example, a first low level 19 a in thepyramid 29 may have one throw tied toabsolute ground 33, a second level 19 b may have one throw tied to a second ground reference N1+ of slightly higher voltage, and a third level 19 c may have at least one throw tied to a third ground reference N0+ of even higher voltage where 0<N1+<N0+<Vout, and where Vout is the voltage atoutput terminal 26. - Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” “left” and “right” refer to directions in the drawings to which reference is made and are not limiting with respect to the inventions absolute orientation. Likewise, terms such as “front”, “back”, “rear”, “bottom”, and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.
- The terms “pyramid” and “pyramidal” are provided only for convenience of reference to the general form of the present invention and are not intended to limit the invention to an exact pyramid but rather are intended to include, for example, the embodiments of
FIG. 1 which is physically not a pyramidFIG. 8 electrically where successive rows may have identical numbers of switches. - When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
- References to “a controller” and “a processor” or “the microprocessor” and “the processor,” can be understood to include one or more microprocessors that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices. Furthermore, references to memory, unless otherwise specified, can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor-controlled device, external to the processor-controlled device, and can be accessed via a wired or wireless network.
- It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.
Claims (22)
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US20200350833A1 (en) * | 2019-05-03 | 2020-11-05 | The Regents Of The University Of California | Pyramid-type multilevel converter topology |
CN112241155A (en) * | 2019-07-16 | 2021-01-19 | 深圳市道通科技股份有限公司 | Interface converter and automobile diagnosis system |
CN112311271B (en) * | 2020-10-14 | 2021-11-02 | 燕山大学 | Three-level bidirectional buck-boost AC/DC converter and control method thereof |
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US8674757B2 (en) * | 2011-11-01 | 2014-03-18 | Neoenergy Microelectronic, Inc. | Switching system and method for control thereof |
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EP2946464B1 (en) * | 2013-01-21 | 2019-12-18 | ABB Schweiz AG | A multilevel converter with hybrid full-bridge cells |
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