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INVENTION
Patent of the Russian Federation RU2291550

SINGLE-PHASE SEMI-INVERTER INVERTER

Inventor's name: The shopman Lev Teodorovich (RU); Shopman Grigory Gertsenovich
The name of the patent holder: State Educational Institution of Higher Professional Education "Ulyanovsk State Technical University"
Address for correspondence: 432027, Ulyanovsk, Severnyy Venets, 32, GOU VPO "Ulyanovsk State Technical University", Vice-rector for scientific work
Date of commencement of the patent: 2005.08.09

A single-phase half-bridge inverter containing a half-bridge in the form of two transistors and two reverse diodes connected in series in a conducting direction is proposed. The second half-bridge is formed by two series-connected capacitors. In the diagonal of an alternating current, the load is predominantly of the transformer type, and the diagonal of the direct current is connected to the corresponding poles of the power source shunted by the smoothing capacitor. The peculiarity is that the circuit is additionally equipped with a four-winding transformer with three identical primary windings and one secondary winding connected to the control system. Primary windings form a bifillar in the load circuit, and in the case of a through short-circuit, preventively limit the short-circuit current at the level of the magnetizing current of the transformer. The technical result is to increase the reliability of protection.

DESCRIPTION OF THE INVENTION

The invention relates to the field of electrical engineering, namely to single-phase half-bridge inverters, mainly with transformer load.

Single-phase half-bridge inverters have found wide application in various secondary power supplies, in particular, they are used in some modifications of welding transformers of inverter type [1-3].

The known circuits of such inverters [4] contain in the power part (Fig. 1) a half bridge in the form of two series-connected transistors 1, 2 and two reverse diodes 3, 4. The second half of the bridge is formed by two series-connected capacitors 5, 6, and into the diagonal of the variable Bridge 1, 2, 5, 6, the load 7 is switched on.

The diagonal of the direct current of the bridge is connected to the power supply U through a reactor 8 connected in series between one of the poles, for example, a positive one, of the power source U _n and the diagonal of the diagonal of the bridge bridge of the same name, 1, 2, 5, 6. The throttle 8 is shunted by a reverse diode 9, And a smoothing capacitor 10 is connected in parallel with the output of the power supply U _n . The inverter is controlled from a typical control system 11 (see Figs.33-10 and 33-12) [4]. The advantage of a half-bridge inverter is the simplicity of the circuit, and the absence of a constant component in the diagonal of the load, which makes it possible to effectively use a half bridge inverter for a transformer load. A throttle 8 with a reverse diode 9 is a typical node of known inverters and provides a decrease in the steepness of the current rise of transistors 1, 2, which is especially important for through short-circuits of the inverter, that is, with simultaneous unlocking of transistors 1 and 2.

This device is the closest device of the same designation to the claimed invention for a combination of features and is adopted as a prototype. The reasons preventing the achievement of the following technical result when using a prototype is that the throttle 8 (FIG. 1), while decreasing the steepness of the current rise, simultaneously reduces the frequency bandwidth of the inverter, and therefore its inductance should be small, which, in its Turn, reduces the reliability of protection of the inverter for through short circuits.

The technical result is an increase in the protection reliability and an increase in the range of use for the voltage and frequency of a single-phase half-bridge inverter.

Said technical result in the implementation of the invention is achieved in that in a known device comprising a single-phase half-bridge inverter having in the power part a half bridge in the form of two series-connected transistors and two reverse diodes and a second half of the bridge formed by two series-connected capacitors, the load included in the diagonal An alternating current bridge, a power source connected to the diagonal of the direct current of said bridge and shunted by a smoothing capacitor, and a typical control system, an additional four-winding transformer is connected to the power circuit with three identical primary windings and one secondary winding connected to one of the inputs of said typical system Wherein one primary winding of said transformer is connected between one of the poles of the power supply and the same pole of the diagonal of the direct current of the bridge, and the other two primary windings are interconnected according to and opposite to the first winding, their common point forms one of the terminals of the diagonal of the alternating current Bridge and is combined with the load, and the free ends are connected to the emitter of one and the collector of the second transistor, forming, together with these transistors and reverse diodes, half-bridge of the inverter.

This made it possible to limit the through-current short-circuit current, expand the frequency bandwidth of the inverter and use it for voltage, and increase the reliability of the inverter in general.

The essence of the invention is explained in FIG. 2, which shows a circuit of a single-phase half-bridge transistor inverter.

The device (FIG. 2) comprises a half-bridge in the power section of two transistors 1, 2 connected in series, two reverse diodes 3, 4. Two identical windings of the transformer 5 are connected between the emitter of the transistor 1 and the collector of the transistor 2: winding 6 and Winding 7, and the common point of these windings forms one of the terminals of the diagonal of the alternating current of the bridge, the second half-bridge of which is formed by capacitors 8 and 9, the common point of which is the second terminal of the diagonal of the bridge. The free terminals of the capacitors 8, 9 as free terminals of the transistors 1, 2 are connected to the diagonal of the direct current of the bridge. The load 10 is connected to the diagonal of the alternating current, and the power supply U _n through a series of poles connected in one of its poles (in FIG. 2 this is a positive pole), the third winding 11 of the transformer 5 is connected to the same poles of the diagonal of the DC bridge current. Moreover, the winding 11 is turned on opposite to the windings 6 and 7. The secondary winding 12 of the transformer 5 is connected to one of the inputs of a typical control system 13 by a half-bridge inverter whose two outputs are connected to the control inputs of transistors 1 and 2. Directly to the output of the power supply is connected a smoothing capacitor 14.

DEVICE FUNCTIONALIZES AS FOLLOWS

As in the known half-bridge single-phase inverters, the output of the control system 13 is a conventional pulse width modulator that provides antiphase pulses to transistors 1 and 2. The squareness of these pulses is determined by the reference signals (current, voltage), and the frequency in modern inverters feeding, for example, welding transformers, reaches 100 kHz.

Let the power supply U _n be switched on, and the capacitors 8, 9 are charged each to a voltage of about 0.5 U _p . Then, the first pulse from the output of the control system 13, for example, applied to the transistor 1, the transistor 1 is unlocked, and the capacitor 8 is discharged to the load 10. The same current flows through the winding 11 and the winding 6 of the transformer 5. Since the windings have the same number of turns and are turned on inverted, they form a bifillar and do not introduce a reactance into the load circuit. Condenser 9 is charging at this time. If the load is sufficient for a full discharge of the capacitor 8, then the capacitor 9 will be charged to the voltage U _n by the end of the inverter half-cycle. When the transistor 2 is unlocked, the bifilar is formed by the windings 11 and 7 of the transformer 5.

Thus, in the operating mode of the inverter, the transformer 5 does not introduce reactance into the load loop, and the maximum frequency of the inverter is limited only by the parameters of the transistors 1, 2. Since the magnetic flux of the transformer 5 is equal to zero in the operating mode of the inverter, the voltage on the winding 12 is also zero.

When the transistors 1 and 2 are simultaneously opened, due to a malfunction in the control system or, for example, due to an increase in the recovery time of the locking properties when the transistor is warmed up, or for some other reason, a short-circuit through occurs and the current passes bypassing the load Partially), through all three primary windings 6, 7, 11 of the transformer 5. An uncompensated magnetic flux arises, a voltage appears on the winding 12 of the transformer 5. In this case, the through-current, while the transformer 5 is not saturated, is equal to the magnetizing current, i.e. Is negligible and not dangerous for transistors.

Thus, the protection against through short-circuits acts proactively, i.e. Does not increase the current for the time of saturation of the transformer 5 to dangerous values. This time can be selected when calculating a transformer larger than the tripping time for the tripping by a signal from the winding 12. Moreover, there is no need to overestimate the time of restoring the locking properties of transistors, since during a short-term "overlap" the through-current is negligible, and short-term pulses at The output of winding 12 can be blocked by a selector of duration, without switching off the inverter. The relative installed power of the transformer 5 with respect to the power transformer, i.e. To the load can be estimated approximately from the following considerations: the time of switching off and restoring the blocking properties of modern power transistors, for example, of the type IGBT of the IRG4 series does not exceed 0.5-0.6 microseconds. Let's take the time of saturation of the transformer 5 with double reserve t ₁ = 1, 2 μs. In the operating mode of the inverter, the loss in the iron of the transformer 5 is generally absent, so its core can be made on a soft magnetic iron with induction in (3-5) times greater than the induction of the core of a power transformer, usually performed on a ferrite. Then for a frequency of 50 kHz

Where P ₁ * is the relative installed power of the transformer 5, P ₂ is the power of the power transformer, B ₁ is the induction of the power transformer core, t ₂ is the half-cycle at 50 kHz, t ₁ is the saturation time of the transformer core 5, B ₂ is the induction in the core Transformer 5.

By calculation according to (1) Р ₁ * / Р ₂ = 0,024-0,032. The weight of the power transformer at a frequency (50 ÷ 100) kHz (0,5 ÷ 0,7) kg / kW, from which it is obvious that the weight and size parameters of the transformer 5 additionally introduced into the device are negligible, the mass does not exceed 0.07 kg. We note that the mass of the throttle and the reverse diode removed from the device is much larger.

Thus, the above technical result is achieved by simple means.

BIBLIOGRAPHY

1. "Castolin G-mbH - Germany," Kraftzwerg ", 1994-1996 gg.

2. "DC200 AL - Technotron" - Russia (directory), 1997

3. "Invertec V-130 - S-Linkoln - USA (catalog), 1998.

4. VA Prianishnikov - "Electronics", St. Petersburg., "Crown print", 400 pp., 1998.

CLAIM

A single-phase half-bridge inverter having in the power part half-bridge in the form of two series-connected transistors and two reverse diodes and the second half of the bridge formed by two series-connected capacitors, the load included in the diagonal of the alternating current of the bridge, the power source connected to the diagonal of the direct current of the bridge and Shunted by a smoothing capacitor, and a typical control system, characterized in that an additional four-winding transformer with three identical primary windings and one secondary winding connected to one of the inputs of said typical control system is inserted into the power circuit of the device, one primary winding of said transformer being connected between One of the poles of the power supply and the same pole of the diagonal of the direct current of the bridge, and the other two primary windings are connected to each other in accordance with and opposite to the first winding, their common point forms one of the diagonal leads of the bridge AC and is combined with the load, and the free ends are connected With an emitter of one and a collector of the second transistors, forming, together with these transistors and return diodes, a half-bridge of the inverter.

print version
Publication date 17.02.2007gg

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