RU2791909C1 - Method for controlling a pulsed power converter in medium current mode - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: in the control method pulse power converter is in the medium current mode, including the measurement of the current in the electrical circuit of the load current in the pulse power converter, the simultaneous formation of a current feedback signal to an additionally introduced second pulse-width modulator after subtracting a fixed voltage from the current feedback signal by means of an additionally introduced device voltage subtraction, at the output of which control pulses of increasing voltage of the required duty cycle are formed by means of the power circuit of increasing voltage formed by the inductor and additionally introduced second field-effect transistor, second power diode and smoothing capacitor, integration of current feedback signal, formation of average current feedback signal, control of average current mode of switching power converter by forced switching between current stabilization and step-down voltage modes by means of multiplexer formed by resistor, operational amplifier and a power diode, comparing the value of the step-down voltage signal proportional to the current in the inductor, which together with the switching device containing the field-effect transistor, forms the step-down electrical circuit of the pulse power converter, with the set reference voltage value obtained as a result of monitoring the average current mode of the pulse power converter, control of a pulse-width modulator using an average current signal and switching in a pulsed power converter from the output of a pulse-width modulator, forming control pulses of a step-down voltage of the required duty cycle, coming to the gate of the field-effect transistor through the driver.

EFFECT: increasing the stability of the battery charging process both in terms of voltage and current with increased efficiency in a wide range of voltages, conversion factors and power levels of a pulsed power converter while improving the transient response with a sharp change in the operating mode.

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Description

The alleged invention relates to the field of electrical engineering, namely: to the field of converter electrical engineering, in particular, to methods for controlling pulse power converters, namely: to methods for controlling a step-down and step-up voltage converter, and can be used in methods of organizing power supply for various devices in many areas of technology, for example, in methods of organizing a battery charge on board an aircraft with a hybrid power plant by means of powerful pulsed power converters of a step-down and step-up type for controlled voltage and current, as well as in methods of organizing a secondary power supply for equipment and functional equipment of aircraft with stabilized voltage and the limit value of the current in the load.

The solution to the problem of increasing levels of pollution and noise and vibration due to the increase in the number of air travel can be, by analogy with cars, the replacement of traditional internal combustion engine aircraft with all-electric or partially electric hybrid aircraft. Among other things, the problem of creating such aircraft is due to the development of power plants of low weight and dimensions with high efficiency and optimal distribution and use of energy on board the aircraft.

The energy required for flight can be stored in supercapacitors, fuel cells and lithium batteries, which are characterized by energy density, power density, lifetime and cost.

Supercapacitors have a high power density and provide a long service life with high efficiency, as well as fast charging/discharging [1, 2], and can operate over a wide temperature range. Their main disadvantage is the high cost and high weight with a lower specific energy compared to rechargeable batteries. Therefore, supercapacitors are used where multiple cycles are required or when there are no alternative technical solutions due to the need to operate at extreme operating temperatures.

Unlike a battery, a fuel cell continuously generates electricity. Fuel cells can achieve power densities in excess of 1000 W/kg [3]. The use of fuel cells makes it possible to redistribute thrust, which has a positive effect on the aerodynamic efficiency of aircraft. In addition, the multifunctional integration of a hydrogen fuel cell into an aircraft allows the use of by-products such as water, heat, or depleted oxygen to provide vital processes such as de-icing, air conditioning, and water supply [4]. However, the operation of fuel cells requires reservoirs for hydrogen, a system for controlling heat removal, which significantly affects the mass of this energy source, and also affects the efficiency of its use on board aircraft [5].

Lithium batteries have a high energy density, low weight, can be quite compact and ergonomic. Their main advantage over fuel cells is the ability to charge while in flight. In addition, they can be connected in series and in parallel to increase the operating voltage and/or current. However, it is very important to properly manage the operation of batteries and their state of charge on board an electric aircraft. Particular attention should be paid to the charge and discharge cycles of the battery. Batteries that are not working properly, overloaded, damaged, or short circuited can cause a fire. To ensure the correct charge modes for lithium batteries, an optimally operating power converter with accurate control of the current and voltage of the charge during the charging process is required [4-9].

A buck-boost converter is a type of DC/DC converter that has an output voltage greater than or less than the input voltage. In other words, a combined converter includes the functionality of a buck converter as well as the functionality of a boost converter.

A known method for controlling a voltage converter, comprising the steps of discretizing the input voltage, output voltage, input current and output current of the voltage converter, which includes a voltage reduction circuit, including a first set of switches, containing first switches, and a voltage increase circuit, including a second set of switches , containing the second switches, where the second set of switches is separate and can be controlled independently from the first set of switches, wherein, when the input voltage is greater than the sum of the output voltage and the first fixed voltage, which is greater than or equal to zero volts, the power supply from the voltage converter is controlled to load by controlling the switching operations of the first switches using appropriate pulse width modulation control signals, respectively, and by turning off the second set of switches, and when the input voltage is less than the output voltage on voltage, control the supply of power from the voltage converter to the load by controlling the switching operations of the second switches using appropriate pulse-width modulated control signals, respectively, and by turning off the first set of switches [10].

The disadvantages of the known method of controlling the converter include a large number of semiconductor elements, which create additional losses. In addition, such a circuit does not provide a fast measurement of the current in the inductor, which does not allow the use of modern effective methods of pulse width modulation control, such as peak current mode and average current mode.

Closest to the claimed method in its technical essence (prototype) is a method for controlling a pulse power converter in the average current mode, including measuring the current in the electrical circuit of the load current in the pulse power converter, generating a current feedback signal, integrating the current feedback signal, formation of an average current feedback signal, control of the average current mode of a switching power converter by forced switching between the modes of current stabilization and step-down voltage by means of a multiplexer formed by a resistor, an operational amplifier and a diode, comparison of the value of the step-down voltage signal proportional to the current in the inductor with the set reference value voltage obtained as a result of monitoring the average current mode of the pulse power converter, control of the pulse width modulator using the average current signal and switching in the pulse power converter generator from the output of the pulse-width modulator [11].

The known method for controlling a switching buck converter does not provide a voltage boost mode, which is required in a number of practically important applications, for example, including battery charging, maintaining a constant voltage on the inverter motor bus.

A new achieved technical result of the proposed invention is to increase the stability of the battery charging process both in terms of voltage and current, with increased efficiency in a wide range of voltages, conversion factors and power levels of a pulsed power converter while improving the transient response with a sharp change in operating mode.

The new technical result is achieved by the fact that in the method of controlling the pulse power converter in the medium current mode, including measuring the current in the electrical circuit of the load current in the pulse power converter, generating a current feedback signal, integrating the current feedback signal, generating a feedback signal by average current, control of the average current mode of the pulse power converter by forced switching between the modes of current stabilization and step-down voltage by means of a multiplexer formed by a resistor, an operational amplifier and a power diode, comparison of the value of the step-down voltage signal proportional to the current in the inductor, forming together with a switching device containing a field transistor, step-down voltage circuit of a switching power converter, with a set reference voltage value obtained as a result of monitoring the average current mode of a switching power converter converter, control of a pulse-width modulator using an average current signal and switching in a pulse power converter from the output of a pulse-width modulator that generates control pulses of a step-down voltage of the desired duty cycle, through a driver arriving at the gate of a field-effect transistor, unlike the prototype, the formation of a feedback signal current is simultaneously carried out on an additionally introduced second pulse-width modulator after subtracting a fixed voltage from the current feedback signal by means of an additionally introduced voltage subtraction device, at the output of which control pulses of increasing voltage of the desired duty cycle are formed by means of a power circuit of increasing voltage formed by an inductor and additionally introduced a second field effect transistor, a second power diode and a smoothing capacitor.

The voltage feedback output of the switching power converter can be further combined with an average current feedback signal.

It is possible to limit the distortion of the output signals in the voltage feedback loop and in the current feedback loop by limiting the change in the bandwidth of the signals in the voltage feedback loop and in the current feedback loop.

It is possible to generate pulses of a certain duration by means of a pulse-width modulator, depending on the level of the error signal at the input of the pulse-width modulator.

It is possible, when controlling a multiphase pulse power converter, to generate different current signals and measure them separately in each phase, and generate a voltage signal at the input of the first operational amplifier common to all phases.

The control method of the pulse power converter is implemented as follows.

The proposed method for controlling a pulse power converter is based on controlling a pulse power converter in the medium current mode by using two feedback loops: internal for average current and external for voltage, based on power electrical circuits of step-down and step-up voltage.

A constant voltage Vin is supplied to the input of the pulsed power converter. The control of the pulse power converter is implemented through voltage and current feedback. The current sensor 1 measures the current that flows through the inductor 2 (figure 1). The current signal is fed to the current error signal amplifier, which includes the first operational amplifier 3 and the first RC circuit 4, 5, 6 of the current feedback frequency correction to ensure stable operation of the system as a whole. Thus, the input of the first operational amplifier 3 receives a voltage signal Vis, which is proportional to the current in the inductor 2, and a reference voltage signal Vset. The value of the voltage signal Vset is formed depending on the value of the reference voltage Vref1, the value of the reference voltage Vref2 and the current value of the voltage Vout at the output of the switching power converter, which is formed on the load 7, which can be a storage battery. The voltage Vout after the voltage divider containing resistors 8 and 9 is fed to the voltage error amplifier containing the second operational amplifier 10 and the second frequency correction RC circuit 11, 12, where it is compared with the reference voltage value Vref1. The second operational amplifier 10 generates an error signal E, which, together with the set reference voltage Vref2, is input to the multiplexer for forced switching between current and voltage stabilization modes, containing a step-down resistor 13, a third operational amplifier 14 and a power diode 15. If the error signal E is greater than the value Vref1, then the power diode 15 is open, the forced switching multiplexer between the current and voltage stabilization modes works as a follower, and the voltage signal Vset is equal to the voltage signal Vref1. In this case, the pulse power converter works as a current stabilizer.

If the error signal E is less than the value of the reference voltage Vref1, then the power diode 15 is closed and the voltage signal Vset is equal to E, since the voltage drop across the pull-down resistor 13 can be neglected. In this case, the pulse power converter works as a voltage stabilizer.

That is, after the formation of the feedback signal on the average current, it is compared with the received set reference voltage value Vset, which can take on the value of both Vref1 and E, as a result of forced switching between the current and voltage stabilization modes, thereby controlling the average current mode.

The formation of the current feedback signal from the output of the first operational amplifier 3 Veca is simultaneously carried out to the additionally introduced second pulse-width modulator 16 after subtracting a fixed voltage Vd from the current feedback signal, commensurate with the difference between the maximum and minimum values of the sawtooth signal Vramp, by additionally the introduced voltage subtraction device 17, at the output of which control pulses of increasing voltage of the required duty cycle are formed by means of a power electric circuit of increasing voltage, formed by additionally introduced second driver 18, the second field-effect transistor 19 and the second power diode 20, identical to the power elements in the voltage reduction circuit and performing similar functions. In practice, the value of the voltage Vd is chosen in the range from 0.95 to 1.05 of the value of Vramp. The diode 21, the transistor 22, the inductor 2 and the capacitor 25 together form a step-up converter and, as part of the described converter, perform the function of boosting the voltage.

The signal from the output of the first operational amplifier 3 Veca is supplied to both the pulse-width modulator 21 and the second pulse-width modulator 16 after subtracting the fixed voltage Vd from it. At the input of the pulse-width modulator 21, the signal Veca is compared with the sawtooth voltage signal Vramp. At the output of the pulse-width modulator 21, control pulses of a step-down voltage of the required duty cycle are formed, which, after the driver 22, are fed to the gate of the field-effect transistor 23, which, together with the power diode 24, the inductor 2 and the smoothing capacitor 25, forms the power electrical circuit of the step-down converter (Fig.1) . At the output of the second pulse-width modulator 16, boost-voltage control pulses of the desired duty cycle are generated, which, after the second driver 18, are fed to the gate of the second field-effect transistor 19, which, together with the second power diode 20, the inductor 2, and the smoothing capacitor 25, forms the power circuit of the step-up voltage converter (figure 1).

Switching between buck and boost modes is automatic based on the signal levels Veca, Vd and the amplitude of the sawtooth signal Vramp. When designing, it is possible to include one of the cases: 1) when the saw blade span Vramp Vp is less than the voltage value Vd, and 2) when Vp > Vd.

In the first case (Vp is less than Vd figure 2), depending on the magnitude of the signals from the error amplifiers Veca and Veca - Vd, either the direct conversion mode is implemented (that is, when the permanently open transistor 23 passes the input voltage directly and the second field-effect transistor 19 is permanently closed, either a buck mode or a boost mode, as illustrated in FIG. 2, respectively.

In the second case ((Vp greater than Vd figure 3), it is possible to implement the two main modes of lowering and increasing the voltage described above. But there is still a mixed mode, when both power field effect transistors 19, 23 are in switching mode. From the point of view of losses, it is better to implement the first case and set Vd > Vp, since the switching losses in mixed mode are doubled.But the second case has the advantage of smoother adjustment of the mode control due to the absence of a dead zone, that is, a zone with a width equal to (Vd - Vp) (Fig.2), in which a change in the error signal Veca does not lead to a change in the duty cycle of the control pulses of the field effect transistor 23 and the second field effect transistor 19.

Due to the presence of feedback loops in the switching power converter: 1) by current, formed by the average current sensor 1 and the current error amplifier, including the first operational amplifier 3 and the first RC circuit 4, 5, 6 of the current feedback frequency correction, and 2 ) by voltage, formed by a voltage divider containing resistors 8,9, a voltage error amplifier containing a second operational amplifier 10 and a second RC circuit 11, 12 frequency correction, and a forced switching multiplexer between current and voltage stabilization modes, containing a step-down resistor 13 , the third operational amplifier 14 and the power diode 15, the proposed technical solution allows you to independently and with high accuracy set and control both the average current of the pulse power converter and the voltage at the output of the pulse power converter. To form the necessary transfer function of a closed-loop control system in the current feedback loop, the first RC chain 4, 5, 6 and the second frequency correction RC chain 11, 12 are introduced in the voltage feedback loop.

This control system can effectively work in switching power converters of voltage step-down and step-up type in the medium current mode used to charge lithium batteries on board aircraft with a hybrid power plant, due to the two-stage process of charging lithium-ion batteries (figure 4). At the initial stage I, the battery is charged at constant current and the voltage on the battery gradually increases. When the predetermined voltage is reached in stage II, charging continues at a constant voltage and is accompanied by a gradual decrease in the charging current.

If necessary, the voltage feedback output of the switching power converter can be further combined with the average current feedback signal.

If necessary, you can limit the distortion of the output signals in the voltage feedback loop and in the current feedback loop by limiting the change in the bandwidth of the signals in the voltage feedback loop and in the current feedback loop.

If necessary, it is possible to generate pulses of a certain duration by means of the second pulse-width modulator 16 and pulse-width modulator 21, depending on the level of the error signal at the input of the second pulse-width modulator 16 and pulse-width modulator 21.

The proposed method can be applied when controlling a multi-phase pulse power converter, when the pulse power converter serves as a phase of a more powerful buck-boost converter (Fig.5). In this case, the current signals Vis are different and are measured in each phase separately, and the voltage signal at the input of the first operational amplifier Vset is common for all phases, which provides an accurate balance of currents in different phases (channels) of the converter. All phases are connected to the output at one point.

Based on the foregoing, the new achievable technical result of the proposed invention is provided by the following technical advantages compared to the prototype.

1. An increase in the stability of the control of a step-down and step-up voltage switching power converter is achieved when the battery is charged at a current of at least 1000%, which ensures a normal battery charging process, for example, on board an aircraft, while ensuring a high ratio of converter power to its mass and its high efficiency due to the operation of transistors at a frequency of hundreds of kHz and the use of an average current mode in the control circuit of the converter with the possibility of stabilizing both voltage and current.

2. A higher (not less than 10%) efficiency of the operation of a step-down and step-up switching power converter is provided due to the operation of transistors at a frequency of hundreds of kHz and the use of an average current mode in the key control circuit with the possibility of stabilizing both voltage and current.

3. The service life of batteries is extended when charging from a pulsed power converter by means of the proposed control method by optimizing the charge current by at least 10%.

4. A higher (at least 5%) ratio of the power of a step-down and step-up type pulse power converter to its mass is provided by optimizing the operation of transistors at a frequency of hundreds of kHz and using an average current mode in the key control circuit with the possibility of stabilizing both voltage, so is the current.

5. The transient response is improved with a sharp change in the operating mode by at least 5% due to the use of the average current mode to control the buck-boost voltage converter.

Sources used

1. Zhang Y. et al. Model and control for supercapacitor-based energy storage system for metro vehicles, Electrical Machines and Systems, ICEMS 2008, p.2695-2697.

2. Lu Y., Hess H. L., Edwards D. B. Adaptive control of an ultracapacitor energy storage system for hybrid electric vehicles, IEMDC'07, vol. 1, p.129-133.

3. Bradley T. H. et al. Test results for a fuel cell-powered demonstration aircraft: SAE Technical Paper, 2006, 01-3092.

4. Sharpe J. E. et al.: Modeling the potential of adsorbed hydrogen for use in aviation, Microporous and Mesoporous Materials, vol. 209, p.135-140.

5. Verstraete D. Long range transport aircraft using hydrogen fuel, International Journal of Hydrogen Energy, vol. 38, no. 34, p.14824-14831.

6. Varyukhin A.N., Gordin M.V., Dutov A.V., Moshkunov S.I., Khomich V.Yu., Shershunova E.A. Powerful pulse DC converter based on silicon carbide transistors // Applied Physics. 2021. №1. pp.75-81.

7. Varyukhin A.N., Gordin M.V., Zakharchenko B.C., Malanichev V.E., Malashin M.V., Moshkunov S.I., Nebogatkin S.V., Khomich V.Yu., Shershunova E. A. Power multiphase pulse converter for hybrid aircraft // Izvestia of the Russian Academy of Sciences. Energy. 2019. No. 6. pp.121-129.

8. Varyukhin A.N., Zakharchenko B.C., Geliev A.V., Gordin M.V., Kiselev I.O., Zhuravlev D.I., Zagumenov F.A., Kazakov A.V., Vavilov V. E. Formation of the appearance of an electric power plant for an ultralight manned aircraft // Aviation engines. 2020. No. 3(8). C.5.

9. Shershunova E.A., Moshkunov S.I., Varyukhin A.N., Gordin M.V. Four-phase pulsed DC voltage converter for use in hybrid and electric power plants of aircraft. Abstracts of the 19th International Conference "Aviation and Cosmonautics". 2020. S.232-233.

10. Patent RU 2617991, 2017, MKI H02M 3/158, H02M 1/088, G05F 1/565.

11. Patent RU 2766320, 2022, MKI G05F 1/56.

Claims (5)

1. A method for controlling a pulse power converter in the medium current mode, including measuring the current in the electrical circuit of the load current in the pulse power converter, generating a current feedback signal, integrating the current feedback signal, generating an average current feedback signal, monitoring the average current mode current of the pulse power converter by forced switching between the modes of current stabilization and step-down voltage by means of a multiplexer formed by a resistor, an operational amplifier and a power diode, comparing the value of the step-down voltage signal proportional to the current in the inductor, which together with a switching device containing a field-effect transistor, an electric step-down voltage circuit switching power converter, with a set voltage reference obtained by monitoring the average current mode of the switching power converter, pulse width mode control using a medium current signal and switching in a pulse power converter from the output of a pulse-width modulator that generates control pulses of a step-down voltage of the required duty cycle, which are fed to the gate of a field-effect transistor by means of a driver, characterized in that the formation of a current feedback signal is simultaneously carried out on an additional input the second pulse-width modulator after subtracting a fixed voltage from the current feedback signal by means of an additionally introduced voltage subtraction device, at the output of which control pulses of increasing voltage of the required duty cycle are formed by means of a boosting voltage power circuit formed by an inductor and additionally introduced by a second field-effect transistor, a second power diode and a smoothing capacitor. 2. The method according to claim 1, characterized in that the voltage feedback output signal of the switching power converter is additionally combined with an average current feedback signal. 3. The method of claim. 1, characterized in that the distortion of the output signals in the voltage feedback loop and in the current feedback loop is limited by limiting the change in the bandwidth of the signals in the voltage feedback loop and in the current feedback loop. 4. The method according to claim 1, characterized in that pulses of a certain duration are generated by means of a pulse-width modulator depending on the level of the error input signal. 5. The method according to claim 1, characterized in that when controlling a multi-phase pulse power converter, the current signals are formed differently and measured in each phase separately, and the voltage signal at the input of the first operational amplifier is formed common to all phases.

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