RU2569679C1 - Method to control multiphase step-up dc converter with input current stabilisation and device for control multiphase step-up dc converter with input current stabilisation - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: based on pulse-width modulation of control signals the method to control multiphase step-up DC converter with input current stabilisation consists in generation of control signals by pulse-width modulation for high-frequency keys in each converter phase; to this end current values of current feedback signals in each phase are compared with their reference values, and on the basis of comparison results mismatch signals are generated, by means of these mismatch signals pulse-width modulated (PWM) signals of fixed frequency are generated. At that in each phase signals of input voltage are compared with threshold value in each phase additionally, and when input voltage has value less than the preset threshold value then by means of mismatch signal, against input voltage, the second PWM signal is generated with frequency of at least 4 times less than frequency of the first PWM signal, and the above second PWM signal is used to control keys of the respective converter phase till value of input voltage does not exceed the preset threshold value. The device for control multiphase step-up DC converter with input current stabilisation in each phase comprises input current sensor, comparison circuit for current sensor signals with reference signal and PWM-controller, to which input current mismatch signals are delivered and which outputs are coupled to key drivers in each phase of the converter. The device comprises additionally in each phase a voltage comparator that compares input voltage with threshold level, the second PWM-controller operating at frequency at least 4 times less than frequency of the first PWM-controller, and a selector coupled to the voltage comparator and switching the first or the second PWM-controller to key drivers in the respective controller phase depending on signal of the voltage comparator.

EFFECT: extended range of input voltage towards lower values with simultaneous stabilisation of input current by means of a simple and cost-effective circuit.

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Description

The invention relates to electrical engineering, and in particular to methods of controlling a pulsed multiphase constant-voltage converter of step-up type, and can be used in charge-discharge devices, in battery simulation devices, load simulation used for testing power supply systems, as well as in other devices, where It is required to obtain a stabilized current and a constant output voltage when the input voltage changes over a wide range.

A known method of controlling a pulsed voltage (current) stabilizer, involving the use of a control loop, the actuating element of which is an electronic switch controlled by signals obtained by pulse width modulation (PWM), as well as a device based on this principle. When the stabilized voltage or current is changed using feedback and PWM, a control signal is obtained in which the pulse width at a fixed frequency changes so that the voltage or current remains stable with a certain degree of accuracy (Power supplies of electronic equipment. Reference / G.S. Naivelt , K.B. Mazel, Ch.I. Khusainov, etc. Under the editorship of G.S. Naivelt. - M .: Radio and communications, 1986. - 576 p. (P. 32, Fig. 1.10).

, стремится к 1. На частоте синхронизации 50 кГц при длительности синхроимпульса 1,5 мкс невозможно обеспечить γ больше чем 0,925. Для выходного напряжения U_вых=180 B минимальное значение напряжения U_вx при максимальном γ U_вх=(1-γ)U_вых=(1-0,925)·180 В=13,5 В.The disadvantage of this control method is the small input voltage range at which voltage or current can be stabilized. To build wide-range multiphase systems based on a boost converter with stabilization of the input current and with a stable output voltage, it is necessary to synchronize the PWM controllers of each phase with an external synchronization pulse of 1.5 μs duration. A feature of the use of PWM controllers of the UCx846 series is that the duration of a dead time pause formed in it is determined by the duration of the synchronization pulse. With a decrease in the input voltage, the relative duration of the control pulses γ, defined as $$\gamma =\left(\mathrm{one}-\frac{U_{\mathrm{at}x}}{U_{\mathrm{at}sx}}\right)$$

, tends to 1. At a clock frequency of 50 kHz with a clock duration of 1.5 μs, it is impossible to provide γ greater than 0.925. For the output voltage U _out = 180 B _Bx minimum value of the voltage U at the maximum γ U _in = (1-γ) U = _O (1-0,925) · 180 V 13.5 V.

Known methods for controlling converters in which the PWM operates with a variable frequency depending on various operating conditions, for example, in the device according to US patent No. 5675479 achieve improved efficiency of the converter at low loads by reducing the PWM frequency, at high loads, on the contrary, increase the PWM frequency . Also known US patent No. 5390101, in which using a voltage-controlled generator increase the frequency of the PWM with increasing load. All these examples relate to improving the efficiency of PWM converters in the part of the load curve, where significant power is consumed from the converter and the frequency range on which they operate is relatively narrow, as well as a narrow input voltage range at which it is possible to stabilize the current or voltage ( the minimum value of the input voltage, indicated, for example, in US patent No. 5390101, is 90 V). However, in discharge devices, as well as in battery simulation devices used, for example, for ground tests of spacecraft power systems, the converter often needs to operate at relatively low input voltages (from 5 V), at constant output voltage levels , for example, 180 V, while ensuring stabilization of the input current. In this regard, the object of the invention is to expand the range of input voltages in the direction of low values, while ensuring stabilization of the input current using a simple and inexpensive circuit.

The problem is solved in that in the method of controlling a multiphase step-up DC-DC converter with stabilization of the input current, based on pulse-width modulation of the control signals, in the same way as in the prototype, control signals for high-frequency switches of each phase are generated by pulse-width modulation method, why the current values of the current feedback signals in each phase are compared with their reference values, based on the results of the comparison, mismatch signals are generated, with power error signals form PWM signals with a fixed frequency. Unlike the prototype, the control method in each phase additionally compares the input voltage signals with a threshold value and, when the input voltage has a value lower than the set threshold level, a second PWM signal is generated, the frequency of which is not less than 4 times lower than the frequency of the first PWM signal , and the specified second PWM signal is used to control the keys of the corresponding phase of the converter, until the value of the input voltage exceeds the set threshold level.

A control device for a multiphase step-up DC-DC converter with stabilization of the input current in each phase contains an input current sensor, a circuit for comparing the signals of the current sensor with the reference signal, and a PWM controller, the input of which receives current mismatch signals, the outputs of which are connected to the key drivers of each phase of the converter . Unlike the prototype, the device further comprises a voltage comparator comparing the input voltage with a threshold level, a second PWM controller operating at a frequency of at least 4 times lower than the frequency of the first PWM controller, and a sampling device connected to the voltage comparator and connecting the first or second PWM controllers for the key drivers of each phase of the converter, depending on the signal of the voltage comparator.

When switching to a lower frequency, the input voltage range can be expanded while maintaining the required synchronization pulse duration for multiphase systems. For example, at a synchronization frequency of the first PWM controller of 50 kHz, reducing the synchronization frequency of the second PWM controller to 10 kHz allows you to achieve a maximum value of γ equal to 0.985, at which the minimum possible input voltage U _in = 2.7 V at an output voltage of 180 V.

In each case, the frequency reduction ratio is determined on the basis of the minimum input voltage at a given input voltage. For normal operation of the converter, it is important that at a given frequency with a maximum γ, the time of a dead time pause is at least 1.5 μs. In this case, a large difference between the frequencies of the first and second PWM controllers can lead to an increase in the ripple amplitude in the inductor. When the frequency of the second PWM is 2–3 times lower than the frequency of the first PWM, it is impossible to achieve the required lower threshold of the input voltage, providing the necessary amount of dead time.

Further, the essence of the claimed invention is illustrated using the drawing, which schematically shows a control circuit for one of the phases 1 of a multiphase boost converter with current stabilization in accordance with the claimed invention, each phase of which is shifted by 360 / m el. degrees relative to each other, where m is the number of phases. The step-up converter control device in each phase contains a current sensor 2, a step-up converter cell 3, an output filter 4 common to all phases, a first PWM controller (high frequency) 5, a second PWM controller 6 (low frequency), a sampling device 7, and a comparator voltage 8, comparing the magnitude of the input voltage with a threshold level. The current sensor outputs are connected to the first and second PWM controllers. Each of the PWM controllers 5 and 6 contains a device for comparing current current values with a reference value, indicated in the drawing as Ust. I. Sampling device 7 is connected to a comparison device 8 and to the outputs of the first and second PWM controllers 5 and 6. From the output of the sampling device 7, control signals corresponding to the first or second PWM controller are supplied to the keys of boost converter 3.

During operation, boost converter 3 begins to convert the input DC voltage with stabilization of the input current, for example, to discharge the battery, which is fed through the filter 4 to the further circuit of the discharge device. In this case, the signals of the current values of the input current from the current sensor 2 enter the PWM controller 5 or 6, where they are compared with the incoming current reference value. I. As a part of each PWM controller 5 or 6, an internal sawtooth voltage generator, synchronized by an external synchronization pulse, is operating. As long as the input voltage remains in the range (15-180) V, the output of the comparison circuit 8 receives a signal to connect the first PWM controller 5, through which the PWM controller 5 generates high-frequency pulses with a frequency of 50 kHz, thereby generating power switch control signals Converter 3. The formation of the PWM signal occurs with a duty cycle γ, determined by the formula:

. $$\gamma =\left(\mathrm{one}-\frac{U_{\mathrm{at}x}}{U_{\mathrm{at}sx}}\right)$$

.

, составляет 0,972, т.е. стремится к 1, и на данной частоте невозможно обеспечить необходимую длительность бестоковой паузы из-за наличия необходимого импульса синхронизации ШИМ-контроллеров каждой из фаз. Т.е. при частоте ШИМ, равной 50 кГц, диапазон регулирования входного тока, например зарядно-разрядного устройства, при малых входных напряжениях ограничен длительностью импульса синхронизации. Поэтому расширение диапазона входных напряжений разрядного устройства обеспечивается при низких входных напряжениях от (5-15) В переходом к пониженной частоте работы ШИМ-контроллера, в приведенном примере, от 50 кГц к 10 кГц. Когда входное напряжение имеет величину в диапазоне от 5 В до 15 В, со схемы сравнения 8 приходит сигнал на устройство выборки 7 на переключение ко второму ШИМ-контроллеру 6, при этом его внутренний генератор пилообразного напряжения генерирует импульсы с пониженной в 5 раз частотой, формируя импульсы управления с увеличенной паузой между импульсами.If the input voltage is, for example, 5 V, and the output voltage is 180 V, then $$\gamma =\left(\mathrm{one}-\frac{5}{180}\right)$$

is 0.972, i.e. tends to 1, and at this frequency it is impossible to provide the necessary duration of a dead time pause due to the presence of the necessary synchronization pulse of the PWM controllers of each phase. Those. at a PWM frequency of 50 kHz, the range of regulation of the input current, for example, a charge-discharge device, at low input voltages is limited by the duration of the synchronization pulse. Therefore, the expansion of the input voltage range of the discharge device is provided at low input voltages from (5-15). In the transition to a reduced frequency of the PWM controller, in the above example, from 50 kHz to 10 kHz. When the input voltage has a value in the range from 5 V to 15 V, a signal arrives from the comparison circuit 8 to the sampling device 7 to switch to the second PWM controller 6, while its internal sawtooth voltage generator generates pulses with a frequency reduced by 5 times, forming control pulses with an increased pause between pulses.

, уменьшается, время открытого состояния ключа повышающего преобразователя Δt увеличивается при уменьшении γ, а амплитуда пульсаций тока в дросселе ΔI не превышает ее максимального значения на высокой частоте (при γ=0,5) из-за меньшей скорости нарастания тока в дросселе.With a decrease in the input voltage and a transition to a lower frequency of operation, the rate of current rise in the inductor of the boost converter, determined by the formula $$\frac{\Delta I}{\Delta t}=\frac{U_{\mathrm{at}x}}{L}$$

decreases, the open time of the key of the boost converter Δt increases with decreasing γ, and the amplitude of the current ripple in the inductor ΔI does not exceed its maximum value at a high frequency (at γ = 0.5) due to the lower slew rate of the current in the inductor.

Reducing the frequency of the PWM signal from 50 kHz to 10 kHz in the input voltage range from 5 V to 15 V allowed expanding the input voltage range of the boost converter, at which the input current is stabilized without increasing ripple at the required output voltage.

Claims (2)

1. A control method for a multiphase step-up DC-DC converter with stabilization of the input current, based on pulse-width modulation of control signals, in which control signals for high-frequency switches of each phase are generated by pulse-width modulation, for which the current values of current feedback signals are compared with their reference values, based on the results of the comparison generate the mismatch signals, using the mismatch signals form the PWM signals with a fixed frequency, characterized in that the input voltage signals are additionally compared with a threshold value, and when the input voltage has a value lower than the set threshold level, a second PWM signal is generated with a comparison signal for the input voltage in each phase, the frequency of which is lower than the frequency of the first PWM the signal at least 4 times, and the specified second PWM signal is used to control the keys of the corresponding phase of the Converter, until the magnitude of the input voltage exceeds the set threshold level. 2. A control device for a multiphase step-up converter with stabilization of the input current, containing an input current sensor in each phase, a circuit for comparing the signals of the current sensor with the reference signal, and a PWM controller, the input of which receives current mismatch signals, the outputs of which are connected to the key drivers of the corresponding phase converter, characterized in that it further comprises a voltage comparator comparing the input voltage with a threshold level, and in each phase a second PWM controller operating with a frequency of at least 4 times lower than the frequency of the first PWM controller, and a sampling device connected to the voltage comparator and connecting the first or second PWM controller to the key drivers of the corresponding converter phase, depending on the signal of the voltage comparator.