RU2256283C1 - Method for limiting reverse current during diode recovery - Google Patents

Abstract

FIELD: converter engineering.

SUBSTANCE: proposed method involves connection of saturable reactor in series with diode, this reactor being shorted out by circuit set up of series-connected resistor and second diode cumulatively connected to main diode; additional; winding magnetized by dc current is placed on saturable reactor core; additional winding turn number, direction and magnitude of current are chosen so as to ensure that reactor core will be saturated for forward current through diode. In order to reduce overvoltage across components, use can be made of component having nonlinear current-voltage characteristic, such as voltage regulator diode, varistor, suppressor, to function as resistor. In this way, diode reverse current is maintained constant in magnitude and proportional to magnetizing current, magnetic reversal process starts immediately upon diode recovery, and maximal value of relative pulse duration in cutoff state is unlimited.

EFFECT: enhanced efficiency.

2 cl, 4 dwg

Description

The invention relates to the field of electrical engineering and can be used in converting technology.

There is a method of limiting the reverse current when restoring a diode by switching it in series with an inductance diode, shunted by an additional diode and a resistor (G.A. Belov, S.A. Kuzmin. Transformers of alternating voltage 380 V to stabilized constant. Electronic equipment in automation. Ed. Yu. . I. Koneva. M., Radio and communications, 1981, issue 12, p. 53-57) [1].

The disadvantages of this method of limiting the reverse current of the diode are the large amplitude of the linearly increasing reverse current and low efficiency due to energy dissipation in the resistor.

To eliminate the first drawback, it is known to use a saturation inductor connected in series with a diode (Amorphous soft magnetic alloys and their use in secondary power sources: Reference manual / V.I. Khandogin, A.V. Raikova, N.N. Ershov, etc. Ed. . V.I. Khandogina. M., 1990, pp. 136-137) [2].

The disadvantage of this method of limiting the reverse current during restoration of the diode is its low efficiency due to energy dissipation in the resistor and losses due to magnetization reversal of the core of the saturation inductor. Low efficiency is associated with a long recovery time of the diode, because losses in the core of the saturation inductor and in the resistor are proportional to the change in the induction of the core of the saturation inductor under the action of the voltage saturation applied to the winding of the inductor during restoration of the diode. The recovery time of the diode is 5-10 lifetimes of minority carriers in the diode base, because the reverse current of the diode is negligible (compared to direct current) due to the large inductance of the saturation inductor in an unsaturated state.

When a direct voltage is applied to the diode, the current flows through the resistor - additional diode - diode circuit during the entire time of magnetization reversal of the saturation inductor core, therefore, the loss power is allocated in the resistor, which can be estimated by the formula:

where P _R is the average power released in the resistor;

I _D - direct current through the diode;

U _R is the voltage drop across the resistor;

τ _R is the magnetization reversal time of the saturation inductor core under the action of voltage U _R ;

f is the frequency with which the diode is restored;

U _o is the voltage applied to the saturation inductor during restoration of the diode;

τ _o - recovery time of the diode.

The problem solved by the invention is the increase in efficiency during restoration of the diode.

The essence of the invention lies in the fact that in the known method of limiting the reverse current when restoring the diode by connecting in series with the diode a saturation inductor, shunted by a circuit from a series-connected resistor and a second diode connected according to the diode, an additional winding magnetized by direct current is introduced on the core of the saturation inductor moreover, the number of turns of the additional winding, the direction and magnitude of the current is chosen so that the core of the saturation inductor is saturated for direct current through the diode.

In order to reduce overvoltages on the elements included in the diode reverse current limitation circuit or connected to it, instead of a resistor, an element with a non-linear current-voltage characteristic (zener diode, varistor, suppressor) can be used.

Figure 1 presents a schematic diagram of the implementation of the proposed method of limiting the reverse current when restoring the diode, figure 2 - curves of currents and voltages of circuit elements, figure 3, figure 4 - examples of the implementation of the proposed method in pulse voltage regulators step-down and step-up types respectively.

The circuit in Fig. 1 contains a saturation inductor 2 connected in series with diode 1, shunted by a circuit from a series-connected resistor 3 and a second diode 4, connected according to diode 1, an additional winding 5 with a magnetizing current I, introduced on the core of the saturation inductor 2.

The limitation of the reverse current during restoration of the diode 1 is as follows.

Let a direct current flow through diode 1 at the initial moment t ₀ (Fig. 2), the core of saturation inductor 2 is in a saturated state, the current through resistor 3 and the second diode 4 is zero.

At time t ₁ , a voltage opposite to diode 1 is applied to the diode 1 - saturation inductor 2 serial circuit, the core of saturation inductor 2 goes out of saturation and saturation inductor 2 starts to work as a transformer. In this case, a voltage is applied to the winding of the saturation inductor 2, which leads to a change in the induction in the core of the saturation inductor 2, and a current flows equal to the bias current I divided by the ratio of the number of turns of the winding of the saturation inductor 2 to the number of turns of the additional winding 5. This current is regenerative for diode 1, therefore, by choosing the bias current I and the number of turns of the additional winding 5, one can choose the rate of removal of minority charge carriers from the base region of diode 1, i.e. change the recovery time of diode 1. During this time, the core of the saturable inductor 2 should not enter saturation in order to avoid a sharp increase in the reverse current of diode 1.

At time t _2, diode 1 is restored, the current induced in the winding of the saturation inductor 2 is closed through the resistor 3 and the second diode 4, the sum of the reverse voltage and the voltage across the resistor 3 is applied to diode 1. The voltage applied to the winding of the saturation inductor 2 is opposite to the opposite voltage sign, so the core of the saturation inductor 2 begins to magnetize in the opposite direction. At time t _{3, the} core of saturation inductor 2 is saturated, the current in the winding of saturation inductor 2, resistor 3, and second diode 4 becomes equal to zero, and the opposite voltage is applied to diode 1.

At time t _{4, a} direct voltage is applied to diode 1 and a direct current begins to flow through diode 1. Because saturation inductor 2, the core of which is in a saturated state, has some inductance, at time t _{4, the} current flows through resistor 3 and additional diode 4. In the period t ₄ -t ₅ , current will be redistributed through resistor 3 and the winding of saturation inductor 2 By time t _5, all current will flow through the winding of saturation inductor 2.

At time t _{6, a} voltage opposite to diode 1 is applied to the diode 1 - saturation inductor 2 in series and the recovery process of diode 1 is repeated similarly to time t ₁ .

The average power loss in resistor 3 can be estimated as:

where P _R3 is the average power released in the resistor 3;

I is the bias current of the additional winding 5;

N ₅ - the number of turns of the additional winding 5;

N ₂ - the number of turns of the winding of the inductor saturation 2;

U _R3 - voltage drop across the resistor 3;

t ₃ -t ₂ is the time of reverse magnetization reversal of the core of saturation inductor 2 under the action of voltage U _R3 ;

f is the frequency with which the diode is restored;

U _o is the voltage applied to the saturation inductor during diode recovery (reverse voltage);

t ₂ -t ₁ - recovery time of diode 1.

To compare the losses in the resistor 3 with similar losses in the resistor of the prototype, we divide equation (2) by equation (I):

If we take I = I _D , N ₅ / N ₂ = 1/5, i.e. the reverse current of diode 1 is five times less than the direct current through this diode, then the time (t ₂ -t ₁ ) of the recovery of diode 1 will be several times less than the time τ _o - recovery time of diode 1 in the absence of reverse current. Accordingly, the power loss in the resistor 3 will be an order of magnitude less than the power loss in the resistor of the prototype, and the loss of magnetization reversal of the core of saturation inductor 2 will be several times smaller than the loss of magnetization reversal of the core of the prototype saturation inductor.

To reduce the voltage surge on resistor 3 and saturable inductor 2 when applying direct voltage to diode 1, instead of resistor 3, an element with a non-linear current-voltage characteristic (zener diode, varistor, suppressor) can be used.

In many practically important cases, you can refuse to use a separate magnetizing current source of the additional winding 5, and include the additional winding 5 in the circuit of the circuit (device) where the direct current flows, for example, in the LC filter circuit (Fig. 3) or in the circuit inductive energy storage (figure 4).

In FIG. 3 shows an example of the application of the proposed method for limiting the reverse current when restoring a diode in a pulse voltage regulator of a step-down type.

The pulse voltage regulator of FIG. 3 contains input 6, common 7 and output 8 outputs for connecting a power source 9 and load 10, respectively, a power switch 11, a reverse diode 1, an LC filter containing a reactor 12 and a capacitor 13, a saturation reactor 2, an additional diode 4, a resistor 3 , as well as an additionally introduced winding 5 on the core of the saturation inductor 2.

Consider how the reverse current is limited when the reverse diode 1 is restored in steady state.

Let the power switch 11 be open, the current of the inductor 12 is closed through the load 10, the reverse diode 1, the winding of the saturation inductor 2 and the additionally introduced winding 5, while the core of the saturation inductor 2 is saturated, the current through the additional diode 4 and resistor 3 is zero.

When the power switch 11 is closed, the voltage of the power supply 9 is applied to the winding of the saturation inductor 2, which brings the core of the inductor 2 out of saturation, as a result, the saturation inductor 2. starts to work like a transformer. A reverse current begins to flow through the reverse diode 1, equal to the current of the inductor 12 divided by the ratio of the number of turns of the saturation inductor 2 to the number of turns of the additionally introduced winding 5. At this time, the sum of the current flows through the inductors of the recovery current of the reverse diode 1.

After the recovery of the reverse diode 1, the current flowing through the winding of the saturation inductor 2 is closed through an additional diode 4 and resistor 3, while under the action of voltage on these elements, the process of reverse magnetization reversal of the core of the saturation inductor 2 begins, which ends with the saturation of the core and the current flowing through the diode 4 and the resistor 3. The core of the saturation inductor 2 is held in a saturated state by the current of the inductor 12 flowing through an additionally introduced winding 5.

Thus, the reverse current during restoration of the reverse diode 1 in the step-down voltage regulator is limited by the value of the inductor current 12 divided by the ratio of the number of turns of the saturation inductor 2 to the number of turns of the additionally introduced winding 5. By choosing the number of turns of the saturable inductor 2 and additionally introduced winding 5, you can minimize losses in the resistor 3 and losses on the magnetization reversal of the core of the saturation inductor 2 when restoring the reverse diode 1.

The inclusion of additionally introduced winding 5 in series with the inductor 12 simplifies the circuit of the pulse voltage regulator step-down type and sets the proportionality of the forward and reverse current through the return diode 1.

The step-up voltage switching regulator shown in FIG. 4, contains input 6, common 7 and output 8 outputs for connecting a power source 9 and load 10, respectively, a choke 12, a power switch 11, a diode 1, a capacitor 13, a saturation choke 2, an additional diode 4, a resistor 3, and also additionally introduced winding 5 on the core of saturation inductor 2.

Consider how the reverse current is limited when diode 1 is restored in steady state.

Let the power switch 11 open, the current of the inductor 12 is closed through the additionally introduced winding 5, the winding of the saturation inductor 2, diode 1, load 10, power supply 9, while the core of saturation inductor 2 is saturated, the current through the additional diode 11 and resistor 3 is to zero.

When the power switch 11 is closed, a voltage equal to the voltage at load 10 is applied to the winding of the saturation inductor 2, because diode 1 is in a conductive state. This voltage takes the core of inductor 2 out of saturation, as a result, saturation inductor 2 starts working like a transformer and a reverse current starts to flow through diode 4, equal to the inductor current 12 divided by the ratio of the number of turns of the saturation inductor 2 to the number of turns of the additional winding 5. Through the power the key 11 at this time flows the sum of the current of the inductor 12 and the recovery current of the diode 1.

After restoration of diode 1, the current induced in the winding of the saturation inductor 2 is closed through an additional diode 4 and resistor 3, the current in the power switch 11 becomes equal to the current in the inductor 12. Under the action of voltage on the additional diode 4 and resistor 3, the process of reverse magnetization reversal of the core of saturation inductor 2 begins , which ends with the saturation of the core and the cessation of current through the diode 4 and resistor 3.

The reverse current during restoration of diode 1 in the boost voltage regulator is limited by the value of the inductor current 12 divided by the ratio of the number of turns of the saturation inductor 2 to the number of turns of the additional winding 5. By choosing the number of turns of the saturation inductor 2 and this ratio, the losses in resistor 3 can be minimized loss of magnetization reversal of the core of saturation inductor 2 during restoration of diode 1.

The inclusion of the additionally introduced winding 5 in series with the inductor 12 simplifies the circuit of the pulse voltage regulator of the boost type and establishes the proportionality of the forward and reverse current through the diode 1.

Thus, the proposed method for limiting the reverse current during restoration of the diode has the following positive qualities:

- the reverse current of the diode is constant and equal to the bias current of the additionally introduced winding, divided by the ratio of the number of turns of the winding of the saturation inductor to the number of turns of the additionally introduced winding, therefore, at a given maximum reverse current of the diode, the diode recovery time is minimal;

- the process of magnetization reversal of the core of the saturation inductor starts immediately after the restoration of the diode, therefore there is no limit on the maximum duty cycle of the locked state of the diode up to 100%;

- the loss of magnetization reversal of the core of the saturation inductor is reduced several times, and the loss in the resistor is more than an order of magnitude compared to the prototype.

The most appropriate use of this invention in switching voltage regulators, power factor correctors, rectifiers, frequency and voltage converters operating at high input voltages, for example, in an electric drive of railway transport.

Information Sources Used

1. G.A. Belov, S.A. Kuzmin. 380 V AC / DC Converters Electronic technology in automation. Ed. Yu.I. Koneva. M., Radio and communications, 1981, issue 12, p. 53-57.

2. Amorphous soft magnetic alloys and their use in secondary power sources: Reference manual / V.I. Khandogin, A.V. Raikova, N.N. Ershov and others. Ed. V.I. Khandogina, M., 1990, pp. 136-137.

Claims (2)

1. The method of limiting the reverse current when restoring the diode by connecting in series with the diode a saturation inductor, shunted by a circuit from a series-connected resistor and a second diode connected according to the diode, characterized in that an additional winding magnetized by a direct current is introduced on the core of the saturation inductor, and the number of turns additional winding, the direction and magnitude of the current is chosen so that the core of the saturation inductor is saturated for direct current through the diode. 2. The method of limiting the reverse current during restoration of the diode according to claim 1, characterized in that as a resistor an element with a non-linear current-voltage characteristic is used, for example, a zener diode, varistor, suppressor.

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