RU2717232C1 - Two-cycle resonance dc-dc converter - Google Patents

Abstract

FIELD: physics; electricity.

SUBSTANCE: invention relates to power conversion equipment and is intended for conversion and control of energy consumed from DC source, and transmitting the converted energy to its receiver using a transformer link between the source and the energy receiver circuits. Invention is resonance type voltage converter. It contains: electric circuit in the form of the first and the second branches, each of which is connected between supply buses and is formed by two power keys connected in series with controlled direct conductivity and uncontrolled inverse conductivity, for example, field transistors. Besides, the converter contains the first and the second throttle. One output of the first throttle winding is connected to the connection point of power switches of the first branch, and one output of the second throttle winding is connected to the connection point of power switches of the second branch. Converter comprises first primary winding magnetically connected to secondary winding connected via appropriate rectifier to output filter capacitor, in parallel to which DC load is connected, and a second primary winding magnetically connected to the secondary winding connected through a corresponding rectifier to the output filter capacitor, in parallel to which the DC load is connected, besides, the capacitor and four diodes.

EFFECT: technical result is higher energy efficiency of electric power conversion.

3 cl, 12 dwg

Description

The proposed device relates to a power converting technique and is intended for converting and regulating the energy consumed from a direct current source, and transmitting the converted energy to its receiver using transformer coupling between the source and receiver power circuits.

A push-pull resonant voltage converter is known (RF patent No. 2455746 "Push-pull bridge converter" by application No. 201018703 dated 05/12/2010. Published on July 10, 2012. Author: B. Glebov. Patent holder: Svyazengineering CJSC (RU)). The known device contains:

- An electric circuit in the form of the first and second branches, each of which is connected between the power buses and is formed by two power switches connected in series with controlled direct conductivity and uncontrolled inverse conductivity (for example, field effect transistors). The electric circuit also contains the first and second chokes, and one terminal of the winding of the first of these chokes is connected to the connection point of the power switches of the first branch, and one terminal of the winding of the second of the chokes is connected to the connection point of the power switches of the second branch.

- The first primary winding magnetically connected to the secondary winding connected through an appropriate rectifier to the output filter capacitor in parallel with which the DC load is connected, and the second primary winding magnetically connected to the secondary winding connected through the corresponding rectifier to the output filter capacitor in parallel to which is connected DC load.

- Capacitor and four diodes: first, second, third and fourth.

In this case, the first primary winding, said capacitor and the second primary winding, form a three-link serial electrical circuit. In it, the first and second primary windings of the power transformer are included according to. The first output of the capacitor is connected to the first and second power lines, respectively, through the first and second diodes, and the second output of the capacitor is connected to the first and second power lines, respectively, through the third and fourth diodes.

The second terminal of the winding of the first inductor is connected to the first output of the three-link serial electric circuit, and the second terminal of the winding of the second inductor is connected to the second output of the three-link serial electric circuit.

In the first embodiment of the known device, the primary windings, magnetically connected to the secondary winding connected to the load, are combined by a common magnetic circuit on which this secondary winding is placed, and all of these windings together with the magnetic circuit form a single transformer.

In another embodiment of the known device, each primary winding and the secondary winding associated with it magnetically correspond to a separate magnetic circuit, which together with the windings placed on it form a separate transformer.

A disadvantage of the known device is that in each cycle of operation in the maximum power transmission mode, the capacitor of the resonant LC circuit is charged to a full supply voltage. This means transferring energy to this capacitor, which could be transferred to the load circuit. Thereby, the conversion efficiency of electric energy is reduced.

The aim of the proposed technical solutions is to increase the efficiency of conversion of electrical energy.

This goal is achieved by the fact that an additional transformer and an additional rectifier are introduced into the push-pull resonant DC / DC converter. In this case, the primary winding of the additional transformer is connected in parallel with the capacitor of the resonant LC circuit, and the secondary winding is connected to the output filter capacitor through an additional rectifier.

In a first embodiment of the device of FIG. 1, power supply 3 is connected to power buses 1 and 2 (positive and negative). Between these buses, the first electric circuit is connected in the form of two branches. One of them is formed by two power switches 4 and 5 connected in series, the other by power switches 6 and 7 connected in series. The first electric circuit contains two chokes 8 and 9 with the same winding inductance. The condition of strict equality is not mandatory. However, to simplify the description of physical processes, it is believed that the inductances are equal.

Power switches 4, 5, 6 and 7 have controlled direct conductivity and uncontrolled inverse conductivity. In the future, power switches with such properties in the drawings relating to different embodiments of the proposed device are shown in the form of field-effect transistors. This class of semiconductor devices is characterized by controlled conductivity for currents of forward direction and constantly present high conductivity for currents of inverse direction. Direct conductivity control is provided by signals specified in the input circuits of field-effect transistors.

Regardless of the actual type of power switches used in the proposed device, a prerequisite is the similarity of their properties to the above properties of field-effect transistors. Further in the description, for the purpose of abbreviation, the term "power switch with controlled direct conductivity and uncontrolled inverse conductivity" is replaced by the term "power transistor".

The power transformer 10 of the device of FIG. 1, is made with the first and second primary windings 11 and 12. The windings have the same number of turns and are galvanically separated from one another. We can assume that the primary winding of the power transformer 10 has a number of turns, which is equal to the sum of the number of turns of the windings 11 and 12.

In the device of FIG. 1, a three-link serial circuit is formed, which is formed by the first primary winding 11 of said power transformer 10 (first link), a capacitor 13 (second link), and the second primary winding 12 (third link). These elements are connected in series, and the primary windings 11 and 12 are included according. The primary windings 11 and 12 add up to the total primary winding of the power transformer 10.

The second output of the inductor winding 8 is directly connected to the first output of the indicated serial electric circuit (with the beginning of the first primary winding 11 of the power transformer 10), and the second output of the inductor winding 9 is directly connected to the second output of this circuit (with the end of the second primary winding 12 of the power transformer 10) .

The first output of the capacitor 13 is connected to the power buses 1 and 2 through the diodes 14 and 15, and the second output of this capacitor is through the diodes 16 and 17.

The secondary winding 18 of the power transformer 10 through a rectifier 19 is connected to the capacitor 20 of the output filter, in parallel with which a DC load 21 is connected.

The proposed device differs from the prototype device in that it includes an additional transformer 22 with primary and secondary windings 23 and 24, as well as an additional rectifier 25. The primary winding 23 is connected in parallel to the capacitor 13 of the resonant LC circuit, and the secondary winding 24 through an additional rectifier 25 is connected to the capacitor 20 of the output filter.

The principle of regulating the flow of energy transmitted from the power source 3 to the load 21 is based on the use of the oscillatory nature of the electrical processes that occur during operation of the device and due to the presence of LC circuit elements in it. Elements of an LC chain include:

- the inductance of the inductor winding 8, which is connected to the first output of the three-link serial electrical circuit (to the beginning of the first primary winding 11 of the first power transformer 10);

- capacitor 13;

the inductance of the inductor winding 9, which is connected to the second terminal of the three-link serial electrical circuit (to the end of the second primary winding 12 of the first power transformer 10).

A known method of controlling power transistors of a bridge circuit, called "phase control"("phase-shift pulse wight modulation" - "phase-shift PWM", Eng.). The method consists in the fact that the first and second transistors connected in series in a bridge circuit are controlled by paraphase pulse signals of their first sequence (U _A , U _B in Fig. 2). The third and fourth transistors, also connected in series in the bridge circuit, are controlled by paraphase pulse signals of their second sequence (U _C , U _D in Fig. 2). In this case, the second sequence of paraphase pulse signals is shifted relative to the first sequence by an adjustable time. By changing the shear time between pulse sequences, the output voltage is regulated. With respect to the bridge resonant circuit, the phase control method is described in RF patent No. 2572002.

The control device provides a “technological” delay in the appearance of signals generated in each given clock cycle, in relation to the completion of the control signals generated in the previous clock cycle.

The end of the signals provides locking power transistors, which in the previous clock cycle were in a state of high conductivity. Due to the “technological” delay in the appearance of signals generated in the next clock cycle, an interval is formed during which all the power transistors of the circuit are locked. Accordingly, at this interval, the connection between the midpoints of the power transistors connected in series to all branches of the circuit with power buses 1 and 2 is broken.

The current of the LC circuit, due to the energy stored at the end of the previous cycle in the magnetic storage devices (chokes) of the LC circuit, continues to flow for some time in the same direction as when the power transistors were locked that were in direct conduction at the moment immediately before the end of control signals in the previous measure. The capacitors of power transistors are recharged with this current.

In the interval of recharging the capacitors of power transistors for a short period of time, the potential of the midpoint of that branch of the electric circuit in FIG. 1, which during the previous cycle was “tied” to the high potential of bus 1. The specified binding was made through a power transistor connected to this bus, which was in a state of high conductivity in the previous cycle. For example, if the previous clock cycle was even, then a high potential value at the beginning of the recharge interval occurs at the midpoint of the branch that was connected to bus 1 via a power transistor 6. When the lowering potential of the midpoint reaches a small negative value, it will go into the state of inverse conductivity a power transistor whose output circuit is between the indicated midpoint and bus 1. If the previous clock cycle was even, then the power transistor 7 will go into the inverse conduction state.

Simultaneously with the considered process of recharging the capacitances of power transistors 6 and 7, a gradual increase in the potential of the midpoint of that branch of the electric circuit in FIG. 1, which was “tied” to the zero potential of bus 2 during the previous cycle. The specified connection was made through a power transistor connected to this bus, which was in a state of high conductivity in the previous cycle. For example, if the previous clock cycle was even, then a low potential value (close to zero) at the beginning of the recharge interval occurs at the midpoint of the branch that was connected to bus 2 via power transistor 5. When the rising midpoint potential slightly exceeds the positive potential of the bus 1, a power transistor will go into the state of inverse conductivity, the output circuit of which is between the indicated midpoint and bus 1. If the previous clock cycle was even, then the power will go into the state of inverse conductivity th transistor 4.

The process of recharging the capacities of power transistors takes such a short time in comparison with the period of operation that the duration of this process can be neglected. Therefore, without a significant error, we can assume that almost immediately after the locking of one pair of power transistors in each of the electrical circuits in FIG. 1, another pair goes into the state of inverse conduction.

На этой частоте работает предлагаемое устройство.With the values of the inductances of the windings of the chokes 8 and 9, which are equal to L _re j2, and the value of the capacitor 13 equal to C _res , the resonant frequency of the LC circuit is

At this frequency, the proposed device.

The duration of the voltage pulses at the output of the bridge circuit, i.e. between points 4 and 7 in the circuit of FIG. 1, depends on the value of the regulatory parameter D. The pulse duration is maximum and equal to half the period of operation of the device with a value of D = 1. The pulse duration decreases with decreasing D.

With a decrease in the pulse duration at the output of the transistor bridge circuit, the voltage amplitude at the capacitor of the resonant LC circuit decreases, as well as the amplitude of the current that is consumed from the bridge circuit and transferred to the primary winding of the power transformer. Accordingly, the power transmitted to the load circuit of the proposed device is reduced. The foregoing is illustrated by the timing diagrams shown in FIG. 3-6. The diagrams are based on the results of modeling electrical processes in the proposed circuit.

The voltage across the capacitor 13 of the resonant LC circuit is represented by an alternating function of time, increasing and decreasing smoothly. Accordingly, the voltage on the primary and secondary windings of the additional transformer 22 gradually increases. When the increasing voltage of the secondary winding 24 slightly exceeds the level to which the capacitor 20 of the output filter is charged (by the magnitude of the voltage drop across the valve elements of the rectifier 25), these elements go into a state of high conductivity. In this case, the voltage of the secondary winding 24 ceases to change and is fixed at a level that is almost equal to the voltage on the capacitor 20 of the output filter. The voltage on the primary winding 23 of the additional transformer 22 also ceases to change, i.e. the voltage across the capacitor 13 of the resonant LC circuit. The primary current of the power transformer 10, which until the voltage across the capacitor 13 was fixed, flows through the primary winding 23 of the additional transformer 22, and through this transformer power is supplied to the load circuit. It is additional in relation to the power transmitted to the load circuit by a power transformer 10.

With respect to the load circuit (elements 20 and 21 in Fig. 1), the DC / DC converter circuit acts as a source of unipolar current pulses that rise and fall smoothly. The amplitude of these current pulses and the average value of the current supplied to the load 21 depends on the magnitude of the control parameter D. FIG. 7 shows the family of characteristics of regulation of the average value of the output current of the proposed circuit, based on the results of its modeling. Family curves are given for a number of voltage values on the primary winding of the power transformer 10, presented in relative units (normalized) according to the expression U1n = U1 / Ue. In this expression: U1 is the voltage transmitted to the primary winding of the power transformer from its secondary winding, Ue is the supply voltage of the circuit.

As follows from the curves in FIG. 7, the characteristics of the regulation of the output current are presented in the form of monotonously increasing functions that change from zero and take a maximum value when the value of the control parameter D is equal to unity. Accordingly, the condition D = 1 for each value of U1n corresponds to the maximum output power of the device.

The voltage across the capacitor 13 of the resonant LC circuit is limited by a value that exceeds the supply voltage Ue by the magnitude of the forward voltage drops on the diodes 14, 17 (or 15, 16). Therefore, the maxima of the values of the output voltage, current, and power of the device turn out to be forcibly limited.

When you turn on the circuit in operation, energy accumulates in the elements of the resonant LC circuit gradually from step to step. The increment of this energy for each cycle depends on the ratio of the voltage on the primary winding and the supply voltage, i.e. from voltage U1n on the primary winding, expressed in relative units. The closer to unity this value is, the smaller the indicated increment of energy, and, therefore, the longer the rise time of the output power to the maximum steady-state value.

In FIG. 8 according to the simulation results of the proposed device, the dependences of the time it takes for its output power to reach the maximum steady-state value on the voltage that is transmitted to the primary winding of the power transformer 10 from its secondary winding are given. The time in FIG. 8 is given in relative units (relative to the length of the period of operation of the circuit).

As follows from FIG. 8, the transient time assumes acceptably low values when the inequality U1n≤0.9 is satisfied. It is further assumed that this inequality is realized in the scheme.

In FIG. 9, according to the simulation results of the proposed device and the prototype device, the dependences of the maximum output power of the proposed circuit and the prototype circuit on the voltage transmitted to the primary winding of the power transformer from its secondary winding are given. As follows from the curves in FIG. 9, both devices proposed and the prototype device have the property of parametric stabilization of the power transmitted to the load, subject to a limited range of variation of the parameter U1n. However, the proposed device transfers more power to the load and has a wider range of parametric power stabilization (accuracy of parametric stabilization, for example, ± 10%). Accordingly, the proposed device consumes a lower current value from the power source than the prototype device, as illustrated by the curves shown in FIG. 10, built on the basis of simulation results. Thus, the goal of the invention is achieved - increasing the efficiency of conversion of electrical energy.

The current values shown in FIG. 7 and FIG. 10 in relative units are assigned to the normalizing current In = (Pout_max / Ue), where the value Pout_max corresponds to the operating mode in which D = 1 and U1n → 1.

The curves in FIG. 11 illustrates the power transmitted to the load by an additional transformer with respect to the total output power of the device.

The device shown in FIG. 12, in terms of construction, principle of operation and achievement of the set goal, is similar to that discussed above, which is shown in FIG. 1. It differs from it only in that it transfers power to the DC load 21 with two identical power transformers 10-1 and 10-2. The primary winding 11 of the power transformer 10-1 forms the first link of a three-link serial electric circuit, the capacitor 13 forms the second link, and the primary winding 12 of the power transformer 10-2 forms the third link of this circuit. In a three-link serial electrical circuit, the primary windings 11 and 12 are included according to.

The secondary winding 18-1 of the transformer 10-1 is connected to the capacitor 20 of the output filter through the rectifier 19-1, and the secondary winding 18-2 of the transformer 10-2 is connected to this capacitor through the rectifier 19-2.

The type of secondary windings of transformers (single-phase or two-phase), as well as the design of rectifiers (bridge circuit or circuit with two valve elements and, in addition, the type of valve elements used) are not essential features of the proposed device. In all the drawings, the secondary windings are indicated as single-phase. Rectifier bridge circuits correspond to them.

Claims (3)

1. A push-pull resonant DC-DC converter containing an electric circuit in the form of the first and second branches, each of which is connected between the power buses and is formed by two power switches connected in series with controlled direct conductivity and uncontrolled inverse conductivity, for example, field effect transistors, as well as in the form of the first and second chokes, and one terminal of the winding of the first of these chokes is connected to the connection point of the power switches of the first branch, and one terminal of the winding of the second inductor is connected to the point connecting the power switches of the second branch, as well as containing the first primary winding, magnetically connected to the secondary winding connected through an appropriate rectifier to the output filter capacitor, in parallel with which a DC load is connected, the second primary winding, magnetically connected to the secondary winding connected through the corresponding rectifier to an output filter capacitor, in parallel with which a DC load is connected, a capacitor, first, second, third and fourth diodes, the first I primary winding, the aforementioned capacitor and the second primary winding form a three-link serial electric circuit, where the first and second primary windings are switched on according to, the capacitor leads are connected to the power buses through the aforementioned first, second, third and fourth diodes; the second terminal of the winding of the first inductor, and the second terminal of the winding of the second inductor, different t m, which device additional transformer and a rectifier introduced, the primary winding of the additional transformer is connected in parallel to said capacitor, and its secondary winding via a further rectifier is connected to output filter capacitor which is shunted by a direct current load. 2. A push-pull resonant DC-DC converter according to claim 1, characterized in that the primary windings magnetically connected to the secondary winding connected to the output filter capacitor, in parallel with which a DC load is connected, are combined by a common magnetic circuit on which this secondary winding is located, and all of these windings together with the magnetic circuit form a single transformer. 3. The push-pull resonant voltage converter according to claim 1, characterized in that each primary winding and the secondary winding connected magnetically have a separate magnetic circuit, which together with the windings placed on it, form a separate transformer.

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