RU2573433C1 - Single-step dc voltage converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: to output of PWM-controller intended to control current level the signal is delivered, and the above signal is equal to difference in current values of the primary and secondary windings of transformer; thus inner current control loop is formed in addition to the main loop of output voltage stabilising.

EFFECT: improved stability and operation speed of single-step forward converter, wherein transistor switching takes place at zero value of current in process of quasi-resonant oscillation at load-bearing elements.

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Description

The invention relates to a conversion technique and can be used in power systems of radio devices, automation and computer technology.

It is known to use a current sensor connected in series with the transformer primary winding and transistor [1], [2], [3] as a part of a single-cycle direct-current converter of direct voltage. The presence of a current sensor in the primary circuit of the transformer eliminates the possibility of saturation of the transformer magnetic circuits and the output filter inductor. Each of the single-cycle converters - analogues [1], [2], [3] contains input terminals for supplying a constant supply voltage, between the input terminals the transformer primary winding, a transistor and a current sensor are connected in series, the control electrode of the transistor is connected to the output terminal of the control circuit, the secondary winding of the transformer through a rectifier and an output filter is connected to the output terminals of a single-phase converter, the output terminals of a single-phase converter are connected to a stabilization circuit of the output voltage, the stabilization circuit of the output voltage is part of the control circuit, the operation of the stabilization circuit of the output voltage occurs without taking into account the current value of the current sensor signal. Another part of the control circuit receives a signal from the current sensor that a predetermined current level has been exceeded and generates a switching control effect on the transistor, regardless of the operating mode of the output voltage stabilization circuit. The disadvantages of this single-cycle converter operation control scheme are:

- low resistance of the converter to external disturbing factors (a change in the supply voltage level at the input or a change in the output load), the transition to a new steady state is accompanied by fluctuations in the output voltage;

- low speed of the converter, for a transition to a new steady state (after completion of external disturbing factors), a relatively large period of time is required for the damping of the output voltage fluctuations.

The closest analogue selected as a prototype is a single-ended direct-current direct-voltage DC-DC converter with additional feedback on the output filter choke current [4], page 290. The prototype circuit is made using the so-called control of the converter operation in the peak (maximum) choke current mode output filter, in the foreign literature such a mode of controlling the operation of the converter is indicated by “current mode”, control in the peak current mode of the choke of the output filter is implemented I am using specialized PWM controller microcircuits [5]. A distinctive feature of controlling the operation of a single-cycle converter in the peak current mode of the output filter inductor is the presence of two types of control loops:

- internal (additional, slave) circuit for regulating the amplitude of the current of the output filter inductor;

- the main (external) output voltage stabilization circuit.

The operation of the current control loop is subordinate to the stabilization circuit of the output voltage, the interaction between the two types of control loops is carried out by a PWM controller. From [4] it is known that the presence of two types of control loops in the composition of a single-cycle forward-flow converter extremely favorably affects its stability and speed. To simplify and ease the construction of the circuit in single-ended linear converters, when forming the internal current control loop, the current is measured not of the output filter inductor, but the current in the primary circuit of the transformer (transistor current), i.e. the use of various current signal models is allowed. For normal operation of the PWM controller, the model of the current signal (form of the current signal) must be strictly monotonic from the time the transistor is turned on to the time the transistor turns off. The prototype circuit contains a first input terminal for supplying a positive potential of the supply voltage, a common wire, which is the second input terminal for supplying a supply voltage, between the input terminals of a single-phase converter, the primary winding of the transformer, a transistor and a current sensor are connected in series, the current sensor is resistive, therefore, the input terminals of the current sensor simultaneously are the output terminals of the current sensor, one of the terminals of the current sensor is connected to a common wire, the control electrode of the transistor is connected to the corresponding output of the PWM controller, the secondary winding of the transformer through the rectifier and the output filter is connected to the output terminals of the single-phase converter, the first output terminal of the single-phase converter is connected to the output terminal of the error amplifier of the PWM controller, the second output terminal of the single-phase converter is connected to a common wire. Just like the proposed device, the prototype circuit is made using a specialized PWM controller microcircuit, which allows forming additional feedback on the output filter inductor current (or current in the transformer primary winding circuit). In the prototype circuit, the internal (additional, subordinate) current regulation loop is implemented by connecting the output of the current sensor to the output of the PWM controller designed to control the current level, the external (main) output voltage stabilization loop is implemented by connecting the first output terminal of the converter with the output of the PWM error amplifier input -controller, moreover, the internal structure of the PWM controller is constructed in such a way that the output of the error amplifier of the PWM controller is connected to one of the inputs of the comparator, the second input d is the output of the comparator PWM controller designed to control the current level. The current trend in constructing converter circuits is that developers actively use resonant (quasi-resonant) oscillations of currents and voltages on power elements [6]. The disadvantage of the prototype, compared with the proposed device, is that in the prototype circuit an internal current control loop cannot be formed if the current shape in the transformer primary winding is caused by resonant processes on the power elements of the converter.

The technical result when using the proposed device is that the stability and speed of a single-stroke linear converter increases, in which the transistor switches at zero (minimum) current during a quasi-resonant oscillatory process on power elements.

The technical result is achieved by the fact that in a single-cycle DC-DC converter operating in quasi-resonant mode, an internal current control loop is formed in addition to the main output voltage stabilization loop, a current signal equal to the difference between the currents of the primary and secondary windings of the transformer is used to form the internal current control loop. The synthesis of the required current signal and its transmission to the output of the PWM controller, designed to control the current level, is performed in accordance with the distinctive part of the formula of the proposed device: the input terminals of the second current sensor are connected in series with the secondary winding of the transformer, the first output terminal of the first current sensor is connected to the first the output terminal of the second current sensor, the second output terminal of the second current sensor is connected to the output of the PWM controller, designed to control the current level.

In FIG. 1 shows a diagram of a single-cycle DC-DC converter with the following notation: first input terminal 1; second input terminal 2; transformer 3; primary winding of the transformer 3.1; secondary winding of the transformer 3.2; transistor 4; PWM controller 5; first current sensor 6; second current sensor 7; rectifier 8; output filter 9; the first output terminal of the converter 10; the second output terminal of the converter 11; wire 12 of the internal current control loop; wire 13 of the main circuit for stabilizing the output voltage.

In FIG. Figure 2 shows a diagram of a single-cycle DC-DC converter, the operation of which uses the positive effect of switching a transistor at zero (minimum) current during a quasi-resonant oscillatory process on power elements. The circuit of FIG. 2 differs from the circuit in FIG. 1 in that the design of the rectifier 8 is changed and the design of the output filter 9 is changed. The designations of the elements in FIG. 2 correspond to the notation in FIG. one.

In FIG. 3 shows a diagram of a single-cycle DC-DC converter, corresponding to paragraph 2 of the claims, the circuit of the converter is supplemented by an RC filter 14, the remaining designations of the elements in FIG. 3 coincide with the designations of the elements in FIG. one.

In FIG. 4 shows diagrams of currents and voltages explaining the operation of the circuits in FIG. 1, FIG. 2, FIG. 3.

In FIG. Figure 5 shows the waveforms of the signals recorded during operation of a device implemented in practice.

The single-ended DC-voltage converter (Fig. 1 and Fig. 2) contains the first input terminal for supplying a positive potential of the supply voltage 1, the common wire 2, which is the second input terminal for supplying the supply voltage, between the input terminals of the single-phase converter is connected in series: primary transformer winding 3.1 , the transistor 4 and the input terminals of the first current sensor 6. The first current sensor 6 and the second current sensor 7 have input terminals and output terminals, and the first output terminal of the current sensors is different from the second output terminal of the current sensors with a higher value of the potential of the output voltage of the current sensors, if a resistive type current sensor is used as the first current sensor 6 in the converter circuit, then the input terminals of the first current sensor are simultaneously the output terminals of the first current sensor. The second output terminal of the first current sensor 6 is connected to a common wire. The control electrode of the transistor 4 is connected to the corresponding output terminal of the PWM controller 5. One of the power terminals of the PWM controller 5 is connected to the common wire 2. The secondary winding of the transformer 3.2 is connected through the rectifier 8 and the output filter 9 to the output terminals of the single-ended converter 10 and 11. First the output terminal 10 of a single-phase converter is connected to the input terminal of the error amplifier of the PWM controller 5 using wire 13, i.e. wire 13 forms the main circuit for stabilizing the output voltage. The second output terminal 11 of the single-phase converter is connected to a common wire 2. Wire 12 forms an internal current control loop, and the distinctive part of the formula of the proposed device describes the synthesis of the current signal and feed it using wire 12 to the output of the PWM controller 5, designed to control the current level namely, in series with the secondary winding of the transformer 3.2, the input terminals of the second current sensor 7 are connected, the first output terminal of the first current sensor 6 is connected to the first output terminal the second current sensor 7, the second output terminal of the second current sensor 7 is connected to the output of the PWM controller 5, designed to control the current level.

The principle of operation of the proposed device is described using diagrams of voltages and currents in FIG. 4. The drawing of FIG. 4 is divided into two parts, the diagrams corresponding to the normal (different from the quasi-resonant) mode of a single-phase converter are shown on the left side, the diagrams corresponding to the single-phase converter operating mode in which the transistor switches at zero (minimum) current during quasi-resonant oscillatory process on power elements. It is known that the current in the primary circuit of the transformer of a single-phase converter is equal to the sum of the currents: magnetization current and secondary current of the transformer [7], p. 108. That part of the circuit of the proposed device in FIG. 1, which is described by the distinguishing part of the formula, performs the function of subtracting the signal of the second current sensor from the signal of the first current sensor, the subtraction result is the magnetization current of the transformer. On the left side of FIG. four:

- plot Uout. 5 shows the output pulses of the PWM controller 5 supplied to the control electrode of the transistor 4;

- Diagram i 3.1 shows the output signal of the first current sensor 6 (current in the circuit of the transformer primary winding), which is typical for a single-stroke linear converter operating in the normal (not in quasi-resonant) mode [4], p. 290;

- diagram i 3.2 shows the output signal of the second current sensor 7, i.e. current in the secondary circuit of the transformer;

- diagram i 5 shows the synthesized current signal equal to the difference between the currents of the primary and secondary windings of the transformer, i.e. the magnetization current of the transformer 3, supplied to the input of the PWM controller 5, designed to control the current level.

The function of subtracting the signal of the second current sensor 7 from the signal of the first current sensor 6 is due to the fact that the first output terminal of the first current sensor 6 is connected to the first output terminal of the second current sensor 7, and the second output terminal of the second current sensor 7 is the output for the synthesized current signal. As well as the output signal of the first current sensor 6 (plot i 3.1 in the left part of Fig. 4 in the form of a trapezoid laid on the side), the current signal obtained as a result of synthesis (plot i 5 in the left part of Fig. 4 in the form of a triangle) can be used to form an internal current control loop in addition to the main output voltage stabilization loop, because does not contain maxima and minima between the times of turning on and off the transistor. Thus, for a single-cycle direct-current DC-DC converter operating in the normal (not quasi-resonant) mode (Fig. 1), the proposed synthesis of the current signal solves the problem of expanding the arsenal of technical means aimed at forming an internal current control loop in addition to the main stabilization loop output voltage. In the proposed device, the transition to the quasi-resonant mode is carried out by changing the design of the rectifier 8 and changing the design of the output filter 9 compared to the prototype circuit (see Fig. 2). The introduction of the resonance inductance Lr and the resonance capacitance Cr into the output filter 9 makes it possible to obtain a quasi-resonant oscillatory process similar to the oscillatory process described in [6], moreover, the resonant inductance Lr may not be explicitly present in the circuit, under certain conditions, the properties of the resonant inductance Lr manifests transformer 3. For a single-cycle DC-DC converter in which the transistor switches at zero (minimum) current during quasi-resonance clear oscillatory process on the power elements (Fig. 2), the use of the output signal of the first current sensor 6 to form the internal current control loop is impossible, because this signal (plot i 3-1 on the right side of FIG. 4) has a maximum in the middle part of the pulse, between the on and off times of transistor 4. On the right side of FIG. four:

- plot Uout. 5 shows the output pulses of the PWM controller 5 supplied to the control electrode of the transistor 4;

- Diagram i 3.1 shows the output signal of the first current sensor 6 (current in the circuit of the transformer primary winding), which is typical for a single-stroke linear converter operating in quasi-resonant mode [6], p. 82;

- diagram i 3.2 shows the output signal of the second current sensor 7, i.e. current in the secondary circuit of the transformer;

- diagram i 5 shows the synthesized current signal equal to the difference between the currents of the primary and secondary windings of the transformer, i.e. the magnetization current of the transformer 3, supplied to the input of the PWM controller 5, designed to control the current level.

As in the circuit of FIG. 1, in the circuit of FIG. 2, the function of subtracting the signal of the second current sensor from the signal of the first current sensor is performed, the subtraction result is the magnetization current of the transformer 3, here it should be noted that diagram i 5 on the right side of FIG. 4 coincides in shape with plot i 5 on the left side of FIG. 4. The current signal obtained as a result of conversion (synthesis) (plot i 5 on the right side of Fig. 4) can be used to form an internal current control loop in addition to the main output voltage stabilization loop, because does not contain maxima and minima between the times of turning on and off of transistor 4. It should be noted that when using the magnetizing current of transformer 3 to form the internal current control loop, the protective functions characteristic of analog and prototype circuits are preserved:

- saturation of the magnetic circuit of the transformer 3 does not occur, because the amplitude of the magnetization current of the transformer is monitored in each switching cycle;

- saturation of the magnetic circuits of the output filter chokes does not occur, because the current in the load is limited by the maximum energy stored in the resonance capacitance Cr of the output filter 9.

The second claim describes the fact that the transmission of the current signal from the second output terminal of the second current sensor 7 to the output of the PWM controller 5, designed to control the current level, can be performed using an RC filter 14 (see Fig. 3). The inclusion in the circuit of the RC filter 14 with a small time constant allows you to suppress high-frequency switching noise in the composition of the current signal, this prevents malfunctions in the single-ended Converter.

The proposed device can be implemented on a serial element base. The interaction of the circuit elements described in the consideration of the principle of operation of a single-cycle DC-DC converter is confirmed by objective data. In a device implemented in practice, the transistor switches at a zero (minimum) current value, this is achieved due to the presence of a resonant inductance Lr and a resonant capacitance Cr in the output filter (see Fig. 2, Fig. 3). In FIG. Figure 5 shows the waveforms of the signals recorded during operation of a device implemented in practice. The first probe that records the voltage at the output of the PWM controller connected to the control electrode of the transistor in the oscillograms of FIG. 5 corresponds to the diagram Uout 5 in FIG. 4 (right side). The second probe, which registers the current in the primary circuit of the transformer, on the oscillograms of FIG. 5 corresponds to diagram i 3.1 in FIG. 4 (right side). The third probe, which records the current signal supplied to the output of the PWM controller, designed to control the current level, on the oscillograms of FIG. 5 corresponds to plot i 5 in FIG. 4 (right side). The fourth probe, which registers the current in the secondary circuit of the transformer in the oscillograms of FIG. 5 (lower part), corresponds to diagram i 3.2 in FIG. 4 (right side).

When considering the waveforms in FIG. 5, the following can be noted:

- pulse signals recorded during operation of a device implemented in practice mainly coincide in shape and phase with the diagrams in FIG. 4 (right side);

- a slight difference between real signals and idealized images does not affect the performance of the device;

- registration of the voltage signal at the output of the PWM controller connected to the control electrode of the transistor (probe 1), the current signal in the primary circuit of the transformer (probe 2) and the synthesized current signal supplied to the output of the PWM controller designed to control the current level (probe 3), was carried out simultaneously, because there are no obstacles to the simultaneous registration of these signals, the zero value for these signals is equal to the potential of the common wire, these signals are shown in the upper part of FIG. 5;

- the oscillogram recording the current in the secondary circuit of the transformer (probe 4) could not be displayed on the same field with other signals, because the potentials of the first output terminal and the second output terminal of the second current sensor differ from the potential of the common wire (the oscilloscope probes are connected to each other through the input terminals of the oscilloscope, this creates an invalid mode when trying to simultaneously register all four signals);

- the synthesized current signal supplied to the output of the PWM controller, designed to control the current level (probe 3), has a form that allows you to organize an internal current control loop as part of a single-cycle DC-DC converter.

Thus, in the device implemented in practice, the complex shape of the current in the primary circuit of the transformer, due to resonant processes on the elements of the output filter, is converted into a simpler (strictly monotonic) in order to be able to form an internal current control loop in addition to the main stabilization loop output voltage. The presence of two types of control loops in a single-cycle DC-DC converter is a sufficient condition for obtaining a technical result, which consists in increasing the stability and speed of the device when exposed to external disturbing factors, such as a change in the supply voltage at the input or a change in the load at the output.

BIBLIOGRAPHY

1. US No. 4330816, H02H 7/122, publ. 05/18/1982.

2. US No. 5465201, H02M 3/335, H02H 7/12, publ. 11/07/1995.

3. US No. 6631064 B2, H02H 3/08, H02H 9/02, publ. 10/07/2003.

4. Volovich G.I. Circuitry of analog and analog-to-digital electronic devices. - M.: Publishing House "Dodeca - XXI", 2005. - 528 p.

5. http://www.ti.com/ UCC38C43 BiCMOS Current Mode PWM Controller.

6. Eranosyan S., Lantsov V. Quasi-resonant secondary power sources: problems, a new look // Power Electronics, No. 3, 2007. - P. 78-84.

7. Goncharov A. Elementary school for the construction of pulsed DC / DC converters (first grade) // Electronic Components, No. 6, 2002. - P. 106-111.

Claims (2)

1. A single-ended DC-voltage converter containing a first input terminal for supplying a positive potential of a supply voltage, a common wire being a second input terminal for supplying a supply voltage, a transformer primary winding, a transistor and input terminals of a first current sensor are sequentially connected between input terminals of a single-phase converter the output terminal of the current sensors differs from the second output terminal of the current sensors by a higher value of the potential of the output voltage of the sensors current, the second output terminal of the first current sensor is connected to a common wire, the control electrode of the transistor is connected to the corresponding terminal of the PWM controller, one of the power terminals of the PWM controller is connected to the common wire, the secondary winding of the transformer through the rectifier and the output filter is connected to the output terminals of a single-ended the converter, the first output terminal of the single-ended converter is connected to the input terminal of the error amplifier of the PWM controller, the second output terminal of the single-ended converter is connected to bschim wire, characterized in that in series with the secondary winding of transformer input terminals includes a second current sensor, the first output of the first current sensor output is connected to the first output terminal of the second current sensor, the second output terminal of the second current sensor is connected to the output of PWM controller. 2. The single-ended DC-voltage converter according to claim 1, characterized in that the second output terminal of the second current sensor is connected to the output of the PWM controller via an RC filter.

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