US20200195133A1 - Flying capacitor balancing in a multi-level voltage converter - Google Patents
Flying capacitor balancing in a multi-level voltage converter Download PDFInfo
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- US20200195133A1 US20200195133A1 US16/219,147 US201816219147A US2020195133A1 US 20200195133 A1 US20200195133 A1 US 20200195133A1 US 201816219147 A US201816219147 A US 201816219147A US 2020195133 A1 US2020195133 A1 US 2020195133A1
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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
- 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
- H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
- H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
-
- 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
- H02M3/156—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 with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—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 with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
-
- 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
- H02M7/4833—Capacitor voltage balancing
-
- 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
-
- 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
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0009—Devices or circuits for detecting current in a converter
-
- 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
- H02M1/0095—Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
-
- 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
- H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
- H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
- H02M3/072—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps adapted to generate an output voltage whose value is lower than the input voltage
Definitions
- Multi-level step-down voltage converters have more than two switches and one or more flying capacitors as a switching stage, and an inductor-capacitor (LC) filter as an output stage.
- LC inductor-capacitor
- a drawback of these converters is an intrinsic instability of the flying-capacitor voltage under Peak Current Mode Control (PCMC).
- PCMC Peak Current Mode Control
- the instability associated with the flying-capacitor voltage in PCMC should not be confused with sub-harmonic oscillations, which is also found in step-down converters under PCMC, and can be suppressed using a compensation ramp.
- the flying-capacitor voltage instability is a separate phenomenon which naturally occurs under PCMC, and also under voltage-mode control, whenever there is a mismatch between switching groups or their driving signals. Flying capacitor voltage unbalance does not occur in a multi-level converter under Valley Current Mode Control (VCMC).
- VCMC Valley Current Mode Control
- FIG. 1 illustrates a schematic diagram of a voltage converter with control circuit in accordance with aspects of the disclosure.
- FIG. 2A illustrates a schematic diagram of a voltage converter with a control circuit, which includes an angle modulation circuit, in accordance with aspects of the disclosure.
- FIGS. 2B-2D illustrate graphs of simulation results of the voltage converter with control circuit of FIG. 2A .
- FIG. 3A illustrates a schematic diagram of a voltage converter with a control circuit, which includes a peak offset modulation circuit, in accordance with aspects of the disclosure.
- FIGS. 3B-3D illustrate graphs of simulation results of the voltage converter with control circuit of FIG. 3A .
- FIG. 4 illustrates a flowchart of a voltage converting method in accordance with aspects of the disclosure.
- aspects of the current disclosure are directed to sensorless control to overcome instability associated with flying capacitor voltage runaway in Peak Current Mode Controlled (PCMC) multi-level flying capacitor voltage converters.
- a controller of this disclosure balances the flying capacitor voltage by controlling an interleaved constant frequency modulator to generate first and second duty cycle commands of respective first and second switching circuits of the voltage converter such that the duty cycle error is compensated.
- “Sensorless” means that the control is based on information already available, in this case, the duty cycle difference; no additional measurements are required.
- the controller may use either of two different types of control to remove the unbalance: (1) modulation of a phase angle between duty cycle commands used to drive switching circuits; or (2) modulation of peak current offset of PCMC.
- FIG. 1 illustrates a schematic diagram of a voltage converter with control circuit 100 in accordance with aspects of the disclosure.
- the voltage converter in this example is a three-level Buck voltage converter.
- the voltage converter comprises an input voltage V g , a switching stage 10 , an output stage 20 , a peak current mode control stage 30 , and a control circuit 100 .
- the switching stage 10 comprises a first switching circuit and a second switching circuit.
- the first switching circuit includes a flying capacitor C fly coupled in parallel with first switches A 1 , B 1 coupled in series.
- the first switches A 1 , B 1 are configured to be driven by a first duty command D 1 having a first duty cycle.
- the second switching circuit includes the flying capacitor C fly and second switches A 2 , B 2 coupled in series between input voltage terminals of the input voltage V g .
- the second switches A 2 , B 2 are configured to be driven by a second duty command D 2 having a second duty cycle.
- the second switches A 2 , B 2 are driven by a same input Pulse Width Modulation (PWM) signal, while the first switches A 1 , B 1 are driven by a PWM signal which is shifted in phase by 180°.
- PWM Pulse Width Modulation
- the output stage 20 comprises an inductor L o , an output capacitor C o , and a load current I o .
- the PCMC stage 30 mode turns on the duty command D 1 /D 2 and starts the charging of the inductor L o at a fixed frequency, and turns off the inductor current i L when the inductor current i L crosses a peak reference current i ref .
- a comparator C determines that the sensed inductor current i L and the peak reference current i ref are equal, a PWM signal is reset to zero.
- the set is provided periodically by a clock frequency clk so the PWM signal goes high (to logic 1) at a fixed frequency.
- the PCMC stage 30 of a conventional three-level voltage converter under a flying capacitor voltage disturbance induces two different duty commands D 1 and D 2 fed to the respective first and second switching circuits (A 1 , B 1 ), (A 2 , B 2 ).
- the duty commands are the PWM signal.
- a difference between these duty commands D 1 , D 2 leads to flying capacitor voltage instability due to flying capacitor voltage runaway.
- the flying capacitor voltage runaway is induced by an inherent positive feedback action on the flying capacitor voltage V fly imposed by the PCMC.
- the control circuit 100 of this disclosure is configured to sense the duty cycle difference, which is induced by the PCMC.
- the control circuit 100 applies a control action based on the duty cycle difference in order to compensate for a variation in the charging and discharging times of the flying capacitor C fly leading to the flying capacitor voltage runaway.
- a goal of the controller 100 is to force the duty cycles of the duty commands D 1 , D 2 to be equal. Since the average of the flying capacitor current i fly is proportional to the duty cycle difference, such control forces the flying capacitor average current to zero at steady state.
- the controller 100 will not only eliminate the instability of the flying capacitor voltage V fly , but will also inherently achieve flying capacitor voltage balancing.
- the flying capacitor voltage V fly is balanced when equal to a voltage converter input voltage V g divided by (N ⁇ 1), where N is a number of voltage levels of the voltage converter.
- control circuit 100 as applied to a three-level Buck converter, that is, a voltage converter with one flying capacitor and four switches.
- the disclosed control circuit 100 is applicable to any type of multi-level voltage converter with any number of flying capacitors and switches. The greater the number of voltage levels, the greater the number of duty cycles. In general, an N-level converter has N ⁇ 1 duty cycles.
- FIGS. 2A-2D are directed to a control circuit 200 that is configured to control the duty cycle difference to be equal based on angle modulation.
- FIGS. 3A-3D are directed to a control circuit 300 that is configured to control the duty cycle difference to be equal based on peak offset modulation.
- FIG. 2A illustrates a schematic diagram of a voltage converter with details of the control circuit 200 , which includes an angle modulation circuit, in accordance with aspects of the disclosure.
- control circuit 200 having the angle modulation circuit is configured to control the interleaved constant frequency modulator 240 by adjusting, based on a duty cycle difference e d [n] between the first and second duty cycles DC 1 , DC 2 , a phase angle difference between the first and second duty commands D 1 , D 2 .
- the voltage converter which in this example is a three-level voltage converter, has three degrees of freedom that can be controlled.
- the first and the second degrees are the duty commands D 1 , D 2 of the respective switching circuits (A 1 , B 1 ), (A 2 , B 2 ), which are used for regulation of the output voltage V o .
- the phase angle modulation of control circuit 200 uses this third degree of freedom to eliminate the positive feedback behavior discussed above.
- the angle modulation circuit of the control circuit 200 comprises a duty cycle difference determination circuit 210 , a control loop 220 , and a synchronization signal generator 230 .
- the duty cycle difference determination circuit 210 comprises a duty cycle calculator 212 and an adder 214 .
- the duty cycle calculator 212 is configured to calculate the first and second duty cycles DC 1 , DC 2 of the respective first and second duty commands D 1 , D 2 .
- the adder 214 is configured to subtract the duty cycles (DC 2 ⁇ DC 1 ) and output a duty cycle difference e d [n].
- the control loop 220 is configured to generate a delay time d T s based on the duty cycle difference e d [n].
- the synchronization signal generator 230 is configured to generate first and second synchronization signals to control the interleaved constant frequency modulator 240 to generate the respective first and second duty commands D 1 , D 2 .
- the synchronization signal generator 230 comprises adder 232 , pulse generator 2341 , pulse generator 2342 , and OR gate 236 .
- first and second synchronization signal pulses are interleaved by 180°, that is, one of the generated signal pulses would have a 0° phase delay ⁇ delay , and the other would have a 180° ( ⁇ ) phase delay ⁇ delay .
- the adder 232 is configured to subtract the delay time d T s , which is based on a difference between the duty cycles (DC 2 ⁇ DC 1 ), from this normal 180° ( ⁇ ) phase delay ⁇ delay and thus introduce a change in the phase shift between the two signal pulses to be output by the two pulse generators 2341 , 2342 .
- the pulse generators 2341 , 2342 are configured to generate respective synchronization signals that will be statically interleaved by time
- the OR gate 236 then combines the synchronization signals in order to generate a clock pulse signal which is applied to a flip-flop set input (not shown) in the interleaved constant frequency modulator 240 .
- the interleaved constant frequency modulator 240 which is known, generates an interleaved version of gate signal pulses for the first switching circuit (A 1 , B 1 ) and the second switching circuit (A 2 , and B 2 ).
- the two gate signal pulses are for the two respective phases of the switching cycle.
- V ⁇ fly V g 2 ,
- the values of time correction d , duty cycle difference, and flying capacitor average current are zero at steady state.
- FIGS. 2B-2D illustrate simulation results of the voltage converter with the control circuit 200 of FIG. 2A .
- FIG. 2B illustrates a graph 200 B showing the duty cycle difference DC 2 ⁇ DC 1 and the delay d in the phase shift between the two phases.
- FIG. 2C illustrates a graph 200 C showing a flying capacitor voltage V fly and flying capacitor current i fly .
- FIG. 2D illustrates a graph 200 D showing steady state waveforms of the switching node voltage v sw , inductor current i L , output voltage v o , and flying capacitor voltage v fly .
- FIG. 3A illustrates a schematic diagram of a voltage converter with details of the control circuit 300 , which includes a peak offset modulation circuit, in accordance with aspects of the disclosure.
- the control circuit 300 of FIG. 3A differs from the control circuit 200 of FIG. 2A , as discussed above, in that rather than adjusting the phase shift between the two phases, the peak current of the Peak Current Mode Control (PCMC) is adjusted by a peak current offset. Again, the difference in the duty cycles e d [n] is used as input, and then there is a control loop 320 that is configured to output the peak current offset ⁇ I ref , which is used to adjust the peak current of the PCMC.
- PCMC Peak Current Mode Control
- the peak offset modulation circuit of the control circuit 300 comprises a duty cycle difference determination circuit 310 , a control loop 320 , and a peak offset selector circuit 330 .
- the control loop 320 in this example may alternatively be referred to as a peak offset generator circuit.
- the duty cycle difference determination circuit 310 , the control loop 320 , and the interleaved constant frequency modulator 340 are otherwise basically the same as the duty cycle difference determination circuit 210 , the control loop 220 , and the interleaved constant frequency modulator 240 , respectively, of FIG. 2A , and thus their detailed descriptions will not be repeated here.
- the peak offset selector circuit 330 comprises an inverter ⁇ 1 and a multiplexer M, and is configured to select the peak current offset ( ⁇ I ref or ⁇ I ref ) for asymmetric application to the peak reference current within a switching cycle. More specifically, the multiplexer M receives at one of it inputs the generated positive peak current offset ⁇ I ref , and at the other of its inputs the negative peak current offset ⁇ I ref from the inverter ⁇ 1, which inverts the generated peak current offset ⁇ I ref .
- the generated peak current offset ⁇ I ref is added asymmetrically in the positive (first) direction or negative (second) direction during a single switching cycle according to which switching circuit is on, the first switching circuit (A 1 , B 1 ) or the second switching circuit (A 2 , B 2 ). Which switching circuit (A 1 , B 1 ), (A 2 , B 2 ) is on depends on the phase and thus which of the respective duty commands D 1 , D 2 is active.
- the multiplexer M is configured to select either a positive peak current offset ⁇ I ref or a negative peak current offset ⁇ I ref depending on the phase.
- the second switching circuit (A 2 , B 2 ) is on, so the peak offset ⁇ I ref is subtracted from the peak reference current i ref [n]. Otherwise, if the switching cycle is between T s /2 and T s , the first switching circuit (A 1 , B 1 ) is on, so the peak offset ⁇ I ref is added to the peak reference current i ref [n].
- the output of the peak offset selector circuit 330 is coupled to an adder A, which introduces the peak current offset ⁇ I ref to the PCMC.
- the peak current offset application is performed according to which switching circuit, (A 1 , B 1 ) or (A 2 , B 2 ), is turned on as follows:
- V ⁇ fly V g 2
- a peak current offset value ⁇ I ref is provided by the control loop 320 which regulates the duty cycle difference e d [n].
- the duty commands D 1 , D 2 under such conditions are given by:
- the duty cycle difference e d [n] based control stabilizes and balances the flying capacitor voltage V fly using the sensorless peak offsetting modulation implementation under the condition:
- Equation ⁇ ⁇ 17 2 ⁇ ( 0.5 - M ) M ⁇ ⁇ when ⁇ ⁇ the ⁇ ⁇ operating ⁇ ⁇ mode ⁇ ⁇ M > 0.5 .
- FIGS. 3B-3D illustrate simulation results of the voltage converter with the control circuit 300 of FIG. 3A .
- FIG. 3B illustrates a graph 300 B showing a duty difference DC 2 ⁇ DC 1 and a peak current offset ⁇ I ref .
- FIG. 3C illustrates a graph 300 C showing flying capacitor voltage v fly and flying capacitor current i fly .
- FIG. 3D illustrates a graph 300 D showing steady state waveforms of switching node voltage v sw , inductor current i L , output voltage, and flying capacitor voltage v fly .
- the feedback sign is operating mode dependent, as shown in Equations 8 and 9.
- Apply the peak current offset ⁇ I ref to regulate the duty cycle difference e d [n] is verified, as shown in FIG. 3B .
- the reference current ⁇ I ref , duty difference e d [n], and flying capacitor average current tend to go to zero, and the flying capacitor voltage V fly converges to
- FIG. 3D The stable and balanced operating point is shown in FIG. 3D , where the inductor current i L and switching node voltage v sw waveforms are periodic with frequency 2f s , and the flying capacitor voltage V fly is balanced with a ripple having frequency f s .
- FIG. 4 illustrates a flowchart of a voltage converting method 400 in accordance with aspects of the disclosure.
- Step 410 driving, by a first duty command D 1 having a first duty cycle, first switches A 1 , B 1 of a first switching circuit having a flying capacitor C fly coupled in parallel with the first switches A 1 , B 1 coupled in series.
- Step 420 driving, by a second duty command D 2 having a second duty cycle, second switches A 2 , B 2 of a second switching circuit having the flying capacitor C fly coupled in parallel with the second switches A 2 , B 2 coupled in series between input voltage terminals of an input voltage V g .
- Step 430 balancing, by a control circuit 100 / 200 / 300 , a voltage V fly of the flying capacitor C fly by controlling a interleaved constant frequency modulator 240 / 340 to generate the first and second duty cycle commands D 1 , D 2 such that the first and second duty cycles are the same.
- aspects of this disclosure rely on replacing flying capacitor voltage sampling with detecting a difference between duty commands D 1 , D 2 induced by a PCMC.
- the simplified architecture eliminates the ADC, measurement devices, or signal conditioning circuitries required for the flying capacitor voltage measurement. In addition, there is increased reliability due to the input voltage independent operation.
- the disclosure is described as addressing flying capacitor voltage imbalance under PCMC. It is also envisioned that the concepts described herein are applicable to address such an imbalance due to a voltage control mode or voltage squared control mode.
- a multi-level voltage converter comprising: a first switching circuit including a flying capacitor coupled in parallel with first switches coupled in series, the first switches configured to be driven by a first duty command having a first duty cycle; a second switching circuit including the flying capacitor and second switches coupled in series between input voltage terminals of an input voltage, the second switches configured to be driven by a second duty command having a second duty cycle; and a control circuit configured to balance a voltage of the flying capacitor by controlling a interleaved constant frequency modulator to generate the first and second duty cycle commands such that the first and second duty cycles are the same.
- control circuit includes an angle modulation circuit configured to control the interleaved constant frequency modulator by adjusting, based on a duty cycle difference between the first and second duty cycles, a phase angle between the first and second duty commands.
- the angle modulation circuit comprises: a duty cycle difference determination circuit configured to determine the duty cycle difference; and a synchronization signal generator configured to generate first and second synchronization signals to control the interleaved constant frequency modulator to generate the respective first and second duty commands, and to delay the second synchronization signal by a delay time corresponding with the duty cycle difference.
- the angle modulation circuit comprises: a control loop configured to generate the delay time based on the duty cycle difference.
- control circuit includes a peak offset modulation circuit configured to control the interleaved constant frequency modulator by generating, based on a duty cycle difference between the first and second duty cycles, a peak current offset for a peak reference current of Peak Current Mode Control (PCMC).
- PCMC Peak Current Mode Control
- the peak offset modulation circuit comprises: a peak offset generator circuit configured to generate the peak current offset based on the duty cycle difference; and a peak offset selector circuit configured to select the generated peak current offset based on which of the first and second duty commands is active.
- the peak offset selector circuit is configured to select the peak current offset to adjust the peak reference current by the peak current offset in a first direction when the first duty command is active, and in a second direction opposing the first direction when the second duty command is active.
- a method of multi-level voltage converting comprising: driving, by a first duty command having a first duty cycle, first switches of a first switching circuit having a flying capacitor coupled in parallel with the first switches coupled in series; driving, by a second duty command having a second duty cycle, second switches of a second switching circuit having the flying capacitor and the second switches coupled in series between input voltage terminals of an input voltage; and balancing, by a control circuit, a voltage of the flying capacitor by controlling a interleaved constant frequency modulator to generate the first and second duty cycle commands such that the first and second duty cycles are the same.
- any combination of examples 11-13 further comprising: controlling, by the control circuit which includes an angle modulation circuit, the interleaved constant frequency modulator by adjusting, based on a duty cycle difference between the first and second duty cycles, a phase angle between the first and second duty commands.
- the method of example 14, further comprising: determining, by a duty cycle difference determination circuit within the angle modulation circuit, the duty cycle difference; generating, by a synchronization signal generator within the angle modulation circuit, first and second synchronization signals for controlling the interleaved constant frequency modulator to generate the respective first and second duty commands; and delaying, by the synchronization signal generator, the second synchronization signal by a delay time corresponding with the duty cycle difference.
- any combination of examples 11-16 further comprising: controlling, by the control circuit which includes a peak offset modulation circuit, the interleaved constant frequency modulator by generating, based on a duty cycle difference between the first and second duty cycles, a peak current offset for a peak reference current of Peak Current Mode Control (PCMC).
- PCMC Peak Current Mode Control
- any combination of examples 11-17 further comprising: generating, by a peak offset generator circuit within the peak offset modulation circuit, the peak current offset based on the duty cycle difference; and selecting, by a peak offset generator circuit within the peak offset modulation circuit, the generated peak current offset based on which of the first and second duty commands is active.
- any combination of examples 1-19 further comprising: selecting, by the peak offset selector circuit, the peak current offset to adjust the peak reference current by the peak current offset in a first direction when the first duty command is active, and in a second direction opposing the first direction when the second duty command is active.
- bipolar transistors e.g., PNP or NPN
- MOS transistors e.g., MOS transistors
- PNP may be used instead of NPN
- PMOS may be used instead of NMOS.
- This disclosure is intended to cover any adaptations or variations of the specific embodiments discussed herein.
Abstract
Description
- Multi-level step-down voltage converters have more than two switches and one or more flying capacitors as a switching stage, and an inductor-capacitor (LC) filter as an output stage.
- A drawback of these converters is an intrinsic instability of the flying-capacitor voltage under Peak Current Mode Control (PCMC). The instability associated with the flying-capacitor voltage in PCMC should not be confused with sub-harmonic oscillations, which is also found in step-down converters under PCMC, and can be suppressed using a compensation ramp. The flying-capacitor voltage instability is a separate phenomenon which naturally occurs under PCMC, and also under voltage-mode control, whenever there is a mismatch between switching groups or their driving signals. Flying capacitor voltage unbalance does not occur in a multi-level converter under Valley Current Mode Control (VCMC).
-
FIG. 1 illustrates a schematic diagram of a voltage converter with control circuit in accordance with aspects of the disclosure. -
FIG. 2A illustrates a schematic diagram of a voltage converter with a control circuit, which includes an angle modulation circuit, in accordance with aspects of the disclosure. -
FIGS. 2B-2D illustrate graphs of simulation results of the voltage converter with control circuit ofFIG. 2A . -
FIG. 3A illustrates a schematic diagram of a voltage converter with a control circuit, which includes a peak offset modulation circuit, in accordance with aspects of the disclosure. -
FIGS. 3B-3D illustrate graphs of simulation results of the voltage converter with control circuit ofFIG. 3A . -
FIG. 4 illustrates a flowchart of a voltage converting method in accordance with aspects of the disclosure. - Aspects of the current disclosure are directed to sensorless control to overcome instability associated with flying capacitor voltage runaway in Peak Current Mode Controlled (PCMC) multi-level flying capacitor voltage converters. A controller of this disclosure balances the flying capacitor voltage by controlling an interleaved constant frequency modulator to generate first and second duty cycle commands of respective first and second switching circuits of the voltage converter such that the duty cycle error is compensated. “Sensorless” means that the control is based on information already available, in this case, the duty cycle difference; no additional measurements are required. The controller may use either of two different types of control to remove the unbalance: (1) modulation of a phase angle between duty cycle commands used to drive switching circuits; or (2) modulation of peak current offset of PCMC.
-
FIG. 1 illustrates a schematic diagram of a voltage converter withcontrol circuit 100 in accordance with aspects of the disclosure. - The voltage converter in this example is a three-level Buck voltage converter. The voltage converter comprises an input voltage Vg, a
switching stage 10, anoutput stage 20, a peak currentmode control stage 30, and acontrol circuit 100. - The
switching stage 10 comprises a first switching circuit and a second switching circuit. The first switching circuit includes a flying capacitor Cfly coupled in parallel with first switches A1, B1 coupled in series. The first switches A1, B1 are configured to be driven by a first duty command D1 having a first duty cycle. The second switching circuit includes the flying capacitor Cfly and second switches A2, B2 coupled in series between input voltage terminals of the input voltage Vg. The second switches A2, B2 are configured to be driven by a second duty command D2 having a second duty cycle. The second switches A2, B2 are driven by a same input Pulse Width Modulation (PWM) signal, while the first switches A1, B1 are driven by a PWM signal which is shifted in phase by 180°. - The
output stage 20 comprises an inductor Lo, an output capacitor Co, and a load current Io. - The PCMC
stage 30 mode, as is known, turns on the duty command D1/D2 and starts the charging of the inductor Lo at a fixed frequency, and turns off the inductor current iL when the inductor current iL crosses a peak reference current iref. In other words, when a comparator C determines that the sensed inductor current iL and the peak reference current iref are equal, a PWM signal is reset to zero. The set is provided periodically by a clock frequency clk so the PWM signal goes high (to logic 1) at a fixed frequency. - Operations of the
switching stage 10,output stage 20, and PCMCstage 30 are known. For the sake of brevity, their detailed descriptions are omitted here. - The PCMC
stage 30 of a conventional three-level voltage converter under a flying capacitor voltage disturbance induces two different duty commands D1 and D2 fed to the respective first and second switching circuits (A1, B1), (A2, B2). The duty commands are the PWM signal. A difference between these duty commands D1, D2 leads to flying capacitor voltage instability due to flying capacitor voltage runaway. The flying capacitor voltage runaway is induced by an inherent positive feedback action on the flying capacitor voltage Vfly imposed by the PCMC. - The
control circuit 100 of this disclosure is configured to sense the duty cycle difference, which is induced by the PCMC. Thecontrol circuit 100 applies a control action based on the duty cycle difference in order to compensate for a variation in the charging and discharging times of the flying capacitor Cfly leading to the flying capacitor voltage runaway. Hence, a goal of thecontroller 100 is to force the duty cycles of the duty commands D1, D2 to be equal. Since the average of the flying capacitor current ifly is proportional to the duty cycle difference, such control forces the flying capacitor average current to zero at steady state. Thecontroller 100 will not only eliminate the instability of the flying capacitor voltage Vfly, but will also inherently achieve flying capacitor voltage balancing. The flying capacitor voltage Vfly is balanced when equal to a voltage converter input voltage Vg divided by (N−1), where N is a number of voltage levels of the voltage converter. - This disclosure describes the
control circuit 100 as applied to a three-level Buck converter, that is, a voltage converter with one flying capacitor and four switches. However, the disclosure is not limited in this respect. The disclosedcontrol circuit 100 is applicable to any type of multi-level voltage converter with any number of flying capacitors and switches. The greater the number of voltage levels, the greater the number of duty cycles. In general, an N-level converter has N−1 duty cycles. - The
control circuit 100 will be described in more detail below.FIGS. 2A-2D are directed to acontrol circuit 200 that is configured to control the duty cycle difference to be equal based on angle modulation.FIGS. 3A-3D are directed to acontrol circuit 300 that is configured to control the duty cycle difference to be equal based on peak offset modulation. -
FIG. 2A illustrates a schematic diagram of a voltage converter with details of thecontrol circuit 200, which includes an angle modulation circuit, in accordance with aspects of the disclosure. - By way of overview, the
control circuit 200 having the angle modulation circuit is configured to control the interleavedconstant frequency modulator 240 by adjusting, based on a duty cycle difference ed[n] between the first and second duty cycles DC1, DC2, a phase angle difference between the first and second duty commands D1, D2. - The voltage converter, which in this example is a three-level voltage converter, has three degrees of freedom that can be controlled. The first and the second degrees are the duty commands D1, D2 of the respective switching circuits (A1, B1), (A2, B2), which are used for regulation of the output voltage Vo. The phase angle difference between the switching circuits (A1, B1) and (A2, B2), which is nominally set to n to generate output ripple at a frequency equal to twice that of the switching frequency fs, is the third degree of freedom. The phase angle modulation of
control circuit 200 uses this third degree of freedom to eliminate the positive feedback behavior discussed above. - The angle modulation circuit of the
control circuit 200 comprises a duty cycledifference determination circuit 210, acontrol loop 220, and asynchronization signal generator 230. There is also a known interleavedconstant frequency modulator 240. - The duty cycle
difference determination circuit 210 comprises aduty cycle calculator 212 and anadder 214. Theduty cycle calculator 212 is configured to calculate the first and second duty cycles DC1, DC2 of the respective first and second duty commands D1, D2. Theadder 214 is configured to subtract the duty cycles (DC2−DC1) and output a duty cycle difference ed[n]. - The
control loop 220 is configured to generate a delay timed Ts based on the duty cycle difference ed[n]. - The
synchronization signal generator 230 is configured to generate first and second synchronization signals to control the interleavedconstant frequency modulator 240 to generate the respective first and second duty commands D1, D2. Thesynchronization signal generator 230 comprisesadder 232,pulse generator 2341,pulse generator 2342, andOR gate 236. - Normally first and second synchronization signal pulses are interleaved by 180°, that is, one of the generated signal pulses would have a 0° phase delay ϕdelay, and the other would have a 180° (π) phase delay ϕdelay. The
adder 232 is configured to subtract the delay timed Ts, which is based on a difference between the duty cycles (DC2−DC1), from this normal 180° (π) phase delay ϕdelay and thus introduce a change in the phase shift between the two signal pulses to be output by the twopulse generators - The
pulse generators -
- The OR
gate 236 then combines the synchronization signals in order to generate a clock pulse signal which is applied to a flip-flop set input (not shown) in the interleavedconstant frequency modulator 240. - The interleaved
constant frequency modulator 240, which is known, generates an interleaved version of gate signal pulses for the first switching circuit (A1, B1) and the second switching circuit (A2, and B2). The two gate signal pulses are for the two respective phases of the switching cycle. - To validate the control to compensate for the positive feedback action, the forced duty commands after considering a generic time shift
-
- are given by:
-
- which lead to the approximated flying capacitor average current given by:
-
- Accordingly, the angle modulation is inherently stable since
-
- At steady state operating point D2=D1=M, where M is the converter voltage conversion ratio, flying capacitor voltage
-
- flying capacitor average current Ifly=0, and interleaving time correction
d =0. The values of time correctiond , duty cycle difference, and flying capacitor average current are zero at steady state. -
FIGS. 2B-2D illustrate simulation results of the voltage converter with thecontrol circuit 200 ofFIG. 2A .FIG. 2B illustrates agraph 200B showing the duty cycle difference DC2−DC1 and the delayd in the phase shift between the two phases.FIG. 2C illustrates agraph 200C showing a flying capacitor voltage Vfly and flying capacitor current ifly.FIG. 2D illustrates agraph 200D showing steady state waveforms of the switching node voltage vsw, inductor current iL, output voltage vo, and flying capacitor voltage vfly. -
FIG. 3A illustrates a schematic diagram of a voltage converter with details of thecontrol circuit 300, which includes a peak offset modulation circuit, in accordance with aspects of the disclosure. - The
control circuit 300 ofFIG. 3A differs from thecontrol circuit 200 ofFIG. 2A , as discussed above, in that rather than adjusting the phase shift between the two phases, the peak current of the Peak Current Mode Control (PCMC) is adjusted by a peak current offset. Again, the difference in the duty cycles ed[n] is used as input, and then there is acontrol loop 320 that is configured to output the peak current offset δIref, which is used to adjust the peak current of the PCMC. - The peak offset modulation circuit of the
control circuit 300 comprises a duty cycledifference determination circuit 310, acontrol loop 320, and a peak offsetselector circuit 330. There is also a known interleavedconstant frequency modulator 340. Thecontrol loop 320 in this example may alternatively be referred to as a peak offset generator circuit. The duty cycledifference determination circuit 310, thecontrol loop 320, and the interleavedconstant frequency modulator 340 are otherwise basically the same as the duty cycledifference determination circuit 210, thecontrol loop 220, and the interleavedconstant frequency modulator 240, respectively, ofFIG. 2A , and thus their detailed descriptions will not be repeated here. - The peak offset
selector circuit 330 comprises an inverter −1 and a multiplexer M, and is configured to select the peak current offset (δIref or −δIref) for asymmetric application to the peak reference current within a switching cycle. More specifically, the multiplexer M receives at one of it inputs the generated positive peak current offset δIref, and at the other of its inputs the negative peak current offset −δIref from the inverter −1, which inverts the generated peak current offset δIref. The generated peak current offset δIref is added asymmetrically in the positive (first) direction or negative (second) direction during a single switching cycle according to which switching circuit is on, the first switching circuit (A1, B1) or the second switching circuit (A2, B2). Which switching circuit (A1, B1), (A2, B2) is on depends on the phase and thus which of the respective duty commands D1, D2 is active. The multiplexer M is configured to select either a positive peak current offset δIref or a negative peak current offset −δIref depending on the phase. If the switching cycle is between zero and Ts/2, the second switching circuit (A2, B2) is on, so the peak offset δIref is subtracted from the peak reference current iref[n]. Otherwise, if the switching cycle is between Ts/2 and Ts, the first switching circuit (A1, B1) is on, so the peak offset δIref is added to the peak reference current iref[n]. The output of the peak offsetselector circuit 330 is coupled to an adder A, which introduces the peak current offset δIref to the PCMC. - The peak current offset application is performed according to which switching circuit, (A1, B1) or (A2, B2), is turned on as follows:
-
i ref[n]|M<0.5 =i ref[n]−δI ref[n] when A 2 is ON, and i ref[n]+δI ref[n] when A 1 is ON. (Equation 8) -
i ref[n]|M<0.5 =i ref[n]+δI ref[n] when A 2 is ON, and i ref[n]−δI ref[n] when A 1 is ON. (Equation 9) - Hence, the inherent positive feedback is eliminated and the voltage controller is stabilized. In addition, forcing
-
- balances the flying capacitor voltage Vfly. The equal value and different sign of the peak current offset within a single switching cycle is to maintain the average of the peak reference current iref unchanged, which decreases the output voltage regulation degradation. The same technique is adopted here, but instead replacing the flying capacitor and input voltage measurements with determining the duty cycle difference ed[n], information which is already available inside the
controller 300 as shown inFIG. 3A . A peak current offset value δIref is provided by thecontrol loop 320 which regulates the duty cycle difference ed[n]. The duty commands D1, D2 under such conditions are given by: -
- The peak current reference modification as shown in Equations 8 and 9 leads to flying capacitor average currents shown below,
-
- As shown, the duty cycle difference ed[n] based control stabilizes and balances the flying capacitor voltage Vfly using the sensorless peak offsetting modulation implementation under the condition:
-
-
FIGS. 3B-3D illustrate simulation results of the voltage converter with thecontrol circuit 300 ofFIG. 3A .FIG. 3B illustrates agraph 300B showing a duty difference DC2−DC1 and a peak current offset δIref.FIG. 3C illustrates agraph 300C showing flying capacitor voltage vfly and flying capacitor current ifly.FIG. 3D illustrates agraph 300D showing steady state waveforms of switching node voltage vsw, inductor current iL, output voltage, and flying capacitor voltage vfly. - In order to stabilize the voltage controller, the feedback sign is operating mode dependent, as shown in Equations 8 and 9. Apply the peak current offset δIref to regulate the duty cycle difference ed[n] is verified, as shown in
FIG. 3B . At steady state the reference current δIref, duty difference ed[n], and flying capacitor average current tend to go to zero, and the flying capacitor voltage Vfly converges to -
- as shown in
FIG. 3B andFIG. 3C . The stable and balanced operating point is shown inFIG. 3D , where the inductor current iL and switching node voltage vsw waveforms are periodic with frequency 2fs, and the flying capacitor voltage Vfly is balanced with a ripple having frequency fs. -
FIG. 4 illustrates a flowchart of avoltage converting method 400 in accordance with aspects of the disclosure. - At
Step 410, driving, by a first duty command D1 having a first duty cycle, first switches A1, B1 of a first switching circuit having a flying capacitor Cfly coupled in parallel with the first switches A1, B1 coupled in series. - At
Step 420, driving, by a second duty command D2 having a second duty cycle, second switches A2, B2 of a second switching circuit having the flying capacitor Cfly coupled in parallel with the second switches A2, B2 coupled in series between input voltage terminals of an input voltage Vg. - At
Step 430, balancing, by acontrol circuit 100/200/300, a voltage Vfly of the flying capacitor Cfly by controlling a interleavedconstant frequency modulator 240/340 to generate the first and second duty cycle commands D1, D2 such that the first and second duty cycles are the same. - Aspects of this disclosure rely on replacing flying capacitor voltage sampling with detecting a difference between duty commands D1, D2 induced by a PCMC. The simplified architecture eliminates the ADC, measurement devices, or signal conditioning circuitries required for the flying capacitor voltage measurement. In addition, there is increased reliability due to the input voltage independent operation.
- The disclosure is described as addressing flying capacitor voltage imbalance under PCMC. It is also envisioned that the concepts described herein are applicable to address such an imbalance due to a voltage control mode or voltage squared control mode.
- The techniques of this disclosure may also be described in the following examples.
- A multi-level voltage converter, comprising: a first switching circuit including a flying capacitor coupled in parallel with first switches coupled in series, the first switches configured to be driven by a first duty command having a first duty cycle; a second switching circuit including the flying capacitor and second switches coupled in series between input voltage terminals of an input voltage, the second switches configured to be driven by a second duty command having a second duty cycle; and a control circuit configured to balance a voltage of the flying capacitor by controlling a interleaved constant frequency modulator to generate the first and second duty cycle commands such that the first and second duty cycles are the same.
- The multi-level voltage converter of example 1, wherein when the flying capacitor voltage is balanced, the flying capacitor voltage is equal to a voltage converter input voltage divided by (N−1), where N is a number of voltage levels of the voltage converter.
- The multi-level voltage converter of any combination of examples 1 and 2, wherein when the flying capacitor voltage is balanced, an average current of the flying capacitor is zero.
- The multi-level voltage converter of any combination of examples 1-3, wherein the control circuit includes an angle modulation circuit configured to control the interleaved constant frequency modulator by adjusting, based on a duty cycle difference between the first and second duty cycles, a phase angle between the first and second duty commands.
- The multi-level voltage converter of example 4, wherein the angle modulation circuit comprises: a duty cycle difference determination circuit configured to determine the duty cycle difference; and a synchronization signal generator configured to generate first and second synchronization signals to control the interleaved constant frequency modulator to generate the respective first and second duty commands, and to delay the second synchronization signal by a delay time corresponding with the duty cycle difference.
- The multi-level voltage converter of example 5, wherein the angle modulation circuit comprises: a control loop configured to generate the delay time based on the duty cycle difference.
- The multi-level voltage converter of any combination of examples 1-6, wherein the control circuit includes a peak offset modulation circuit configured to control the interleaved constant frequency modulator by generating, based on a duty cycle difference between the first and second duty cycles, a peak current offset for a peak reference current of Peak Current Mode Control (PCMC).
- The multi-level voltage converter of any combination of examples 1-7, wherein the peak offset modulation circuit comprises: a peak offset generator circuit configured to generate the peak current offset based on the duty cycle difference; and a peak offset selector circuit configured to select the generated peak current offset based on which of the first and second duty commands is active.
- The multi-level voltage converter of any combination of examples 1-8, wherein the peak offset selector circuit is configured to select the peak current offset for asymmetric application to the peak reference current within a switching cycle.
- The multi-level voltage converter of any combination of examples 1-9, wherein the peak offset selector circuit is configured to select the peak current offset to adjust the peak reference current by the peak current offset in a first direction when the first duty command is active, and in a second direction opposing the first direction when the second duty command is active.
- A method of multi-level voltage converting, comprising: driving, by a first duty command having a first duty cycle, first switches of a first switching circuit having a flying capacitor coupled in parallel with the first switches coupled in series; driving, by a second duty command having a second duty cycle, second switches of a second switching circuit having the flying capacitor and the second switches coupled in series between input voltage terminals of an input voltage; and balancing, by a control circuit, a voltage of the flying capacitor by controlling a interleaved constant frequency modulator to generate the first and second duty cycle commands such that the first and second duty cycles are the same.
- The method of example 11, wherein when the flying capacitor voltage is balanced, the flying capacitor voltage is equal to a voltage converter input voltage divided by (N−1), where N is a number of voltage levels of the voltage converter.
- The method of any combination of examples 11 and 12, wherein when the flying capacitor voltage is balanced, an average current of the flying capacitor is zero.
- The method of any combination of examples 11-13, further comprising: controlling, by the control circuit which includes an angle modulation circuit, the interleaved constant frequency modulator by adjusting, based on a duty cycle difference between the first and second duty cycles, a phase angle between the first and second duty commands.
- The method of example 14, further comprising: determining, by a duty cycle difference determination circuit within the angle modulation circuit, the duty cycle difference; generating, by a synchronization signal generator within the angle modulation circuit, first and second synchronization signals for controlling the interleaved constant frequency modulator to generate the respective first and second duty commands; and delaying, by the synchronization signal generator, the second synchronization signal by a delay time corresponding with the duty cycle difference.
- The method of example 15, further comprising: generating, by a control loop within the angle modulation circuit, the delay time based on the duty cycle difference.
- The method of any combination of examples 11-16, further comprising: controlling, by the control circuit which includes a peak offset modulation circuit, the interleaved constant frequency modulator by generating, based on a duty cycle difference between the first and second duty cycles, a peak current offset for a peak reference current of Peak Current Mode Control (PCMC).
- The method of any combination of examples 11-17, further comprising: generating, by a peak offset generator circuit within the peak offset modulation circuit, the peak current offset based on the duty cycle difference; and selecting, by a peak offset generator circuit within the peak offset modulation circuit, the generated peak current offset based on which of the first and second duty commands is active.
- The method of any combination of examples 11-18, further comprising: selecting, by the peak offset selector circuit, the peak current offset for asymmetric application to the peak reference current within a switching cycle.
- The method of any combination of examples 1-19, further comprising: selecting, by the peak offset selector circuit, the peak current offset to adjust the peak reference current by the peak current offset in a first direction when the first duty command is active, and in a second direction opposing the first direction when the second duty command is active.
- Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. For example the aspect of the disclosure may be implemented non-digitally, bipolar transistors (e.g., PNP or NPN) may be used instead of MOS transistors, a PNP may be used instead of NPN, and/or a PMOS may be used instead of NMOS. This disclosure is intended to cover any adaptations or variations of the specific embodiments discussed herein.
Claims (17)
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