RU87586U1 - INVERTER WITH BRIDGE SWITCH WITH TRANSFORMER PROTECTION AGAINST SINGLE-SIDED SATURATION - Google Patents

Abstract

A bridge inverter is a DC-to-AC converter preventing one-sided saturation of the output transformer, comprising a bridge switch for converting the DC voltage of the power source to AC, made in the form of a four-arm bridge with controlled keys in the shoulders, in which the vertices of the first diagonal are connected to the terminals for the power source, and the primary winding of the output transformer is connected to the vertices of the second diagonal of the bridge; means for generating the first half-cycle of the output voltage with the specified parameters, the output of which is connected to the key switching control circuits of the first pair of opposite shoulders of the bridge; means for detecting and storing the average voltage value generated in the first half-cycle, and storing the stored voltage until completion of the formation of the second half-period; means for generating a second half-cycle of the output voltage with an average voltage value equal to the stored average voltage value generated in the first half-cycle, the input of which is connected to the output of the means for detecting and storing the average voltage value generated in the first half-cycle, and the output is connected to the key switching circuits of the second pair opposite shoulders of the bridge; a clock of rectangular pulses with a period equal to the period of the output voltage of the bridge inverter, connected by the outputs to the control circuits of the frequency of operation of the means of forming the first and second half-periods; means for short-circuiting the transformer primary winding in pauses between generated pulses

Description

This solution relates to the field of electrical engineering and is intended for use in DC-AC converters.

Known devices for converting DC voltage to AC by periodically switching the polarity of the voltage supplied to the primary windings of the output transformer, from the output of which the AC voltage is removed to connect the load. They have the disadvantage of one-sided saturation of the output transformer magnetic circuit with changes in input voltage, load asymmetry, or circuit elements.

Known devices for eliminating this drawback by using means for detecting magnetic saturation of the magnetic core of the output transformer with a voltage control at the output of the current transformer additionally introduced into the circuit. The control of the saturation start of the magnetic circuit is carried out by monitoring the voltage at the output of the current transformer and determining the second derivative of the outflow in the output transformer [1]. With the coming saturation, protective measures are taken. In a DC-AC converter, such a solution requires a separate transformer current sensor and complex high-speed means of monitoring the second derivative, which complicates the design.

Known protection schemes for asymmetric saturation of the magnetic core of a power transformer with saturation compensation in the opposite direction, with additional power supply to the transformer winding with a current of opposite polarity [2].

However, this complicates the design, and in powerful inverters leads to a deterioration in overall dimensions.

A device is also known to prevent saturation of the transformer in the inverter for operation with capacitive load [3]. The inverter contains control circuits for the constant and variable components when controlling transistor switches and means of protection against transformer saturation. The disadvantage is the unsatisfactory weight and size indicators and the complexity of the design.

It is also known the use of two saturation sensors to combat saturation of the transformer, however, this significantly complicates the design [4].

There is also known a solution to combat saturation of the transformer according to the patent of the Russian Federation [5].

This device restricts the one-sided saturation of the transformer of a pulse voltage converter using means for detecting a signal proportional to the magnetization current of the transformer, means for comparing it with a given reference signal proportional to the maximum permissible magnetization current, and means for generating a control signal that corrects the magnetization reversal mode of the transformer.

The disadvantage of such a device is the complexity of the practical implementation of such a solution in the design, since to perform measurements and control the magnetic field in the magnetic circuit, a complex construction of the transformer magnetic circuit is required, in which it is necessary to isolate a part of the magnetic circuit, to create a short-circuited coil covering this selected part of the transformer magnetic circuit, and connect current measuring instruments to it, which complicates the design of both the magnetic circuit itself and the transducer as a whole.

The closest known analogue is a patent of the Russian Federation [6].

The inverter [6] contains means providing at its output stabilization of the effective voltage value in a given range of permissible values. One-sided saturation is prevented by the use of means that ensure the equality of volt-second areas in the positive and negative half-periods of the generated voltage, and the equality of magnetic fluxes in the magnetic core of a power transformer made with two identical primary power windings connected in series, the connection point of which is connected to one pole of the power source, and the ends of the windings through controlled switches are connected to the second pole of the power source. In addition, to eliminate the residual magnetization of the transformer magnetic core parallel to the primary winding of the transformer, a controlled key is connected to short-circuit this winding when the power switches of the windings are open when they are disconnected from the power source. The use of a comprehensive solution in this patent provides reliable prevention of one-sided saturation, rather than eliminating the occurrence or occurrence of saturation, as in other known prior solutions. However, such an inverter has unsatisfactory weight and size indicators due to a bulky transformer with two powerful primary windings, which is a drawback. And the use of an additional key for short-circuiting this winding with simultaneously open switches of power supply to the windings complicates the control and protection circuits of the keys from through currents.

The problem to which the invention is directed is to prevent one-sided saturation of the inverter output transformer using a transformer winding without taps, instead of a bulky winding with a tap from the middle according to the RF patent [6]. The proposed solution simplifies the design and leads to improved overall dimensions of the inverter.

To solve this problem, the following technical solution is proposed.

An inverter with a bridge switch with transformer protection against one-sided saturation contains means for creating the required voltage at its output. In this case, one-sided saturation is prevented by means ensuring the equality of the average voltage values, i.e. volt-second areas in the positive and negative half-periods of the generated voltage, and, therefore, the equality of the generated magnetic fluxes in the magnetic circuit of the output transformer. And instead of a separate short-circuit key of the primary winding of the transformer, the keys are used that are present in the bridge switch. This simplifies the circuit protection of power switches from through-currents.

The proposed solution is characterized by the following features.

An inverter with a bridge switch with transformer protection against one-sided saturation - a DC-to-AC converter, preventing one-way saturation of the output transformer, contains the following well-known technical solutions.

A bridge switch for converting a constant voltage of a power source into an alternating current, made in the form of a four-armed bridge with controlled keys in the shoulders, in which the vertices of the first diagonal are connected to the terminals for the power source,

and the primary winding of the output transformer is connected to the vertices of the second diagonal of the bridge.

Means of forming the first half-cycle of the output voltage with the specified parameters, the output of which is connected to the key switching control circuits of the first pair of opposite shoulders of the bridge.

Means for detecting and storing the average value of the voltage generated in the first half-cycle, and storing the stored voltage until completion of the formation of the second half-period.

Means for generating a second half-cycle of the output voltage with an average voltage value equal to the stored average voltage value generated in the first half-cycle, the input of which is connected to the output of the means for detecting and storing the average voltage value generated in the first half-cycle, and the output is connected to the key switching circuits of the second pair opposite shoulders of the bridge.

A clock of rectangular pulses with a period equal to the period of the output voltage of the bridge inverter, connected by the outputs to the control circuits of the frequency of operation of the means of forming the first and second half-periods. Means of short circuit of the primary winding of the transformer in the pauses between the generated pulses of the first and second half-periods.

The signs that distinguish the proposed solution from the known, the following.

The means of short-circuiting the primary winding of the output transformer in the pauses between the generated pulses of the first and second half-periods are formed by the controlled keys of those two adjacent shoulders of the four-armed bridge, the ends of which are the vertices of the second diagonal of this bridge with the primary winding of the output transformer connected. Moreover, the keys of these adjacent arms have two-sided conductivity, and the input circuit of each of these keys is made in the form of a two-input OR circuit.

The first inputs of these OR circuits are connected to the key inputs of the opposite shoulders of the bridge, and connected to the outputs of the corresponding half-period formers.

And the second inputs of these OR circuits are interconnected and with the output of an additional two-input OR-NOT circuit connected by inputs to the outputs of the half-period formers.

Moreover, the primary winding of the output transformer is made of several switched windings, with the possibility of changing the number of turns depending on the rated constant voltage of the power source to which the bridge inverter is connected.

The proposed solution is illustrated in figure 1, which shows a diagram of a bridge inverter - a DC-to-AC converter with the prevention of one-sided saturation of the output transformer and shows the main functional units and elements.

The diagram explains the structure of the bridge inverter and its operation.

Figure 1 adopted the following notation.

1, 2 - input power pins;

3 - bridge switch for converting the input DC voltage to AC;

4 ... 7 - keys of the bridge switch;

8 - output transformer;

9 - primary winding of the output transformer, with taps;

10 - secondary winding of the output transformer;

11, 12 - output conclusions;

13 - clock generator;

14 - means for generating voltage of the first half-cycle;

15 is a tool that stores the average value of the voltage generated in the first half-cycle;

16 - means for generating voltage of the second half-cycle;

17 - a logical element OR-NOT.

18, 19 - logical elements OR. In the circuit of the inverter of figure 1, the input terminals 1, 2 are designed to supply a constant voltage to the inverter from a power source. A bridge switch 3 is connected to them to convert the input DC voltage to AC. The bridge switch 3 contains managed keys 4 ... 7, and the keys 5 and 6 have two-way conductivity.

The vertices of the first diagonal of the bridge (key connection points 5, 6 and key connection points 4, 7) are connected to terminals 1, 2 for the power source;

the output transformer 8 is connected to the vertices of the second diagonal of the bridge (the connection points of the keys 4, 5 and the connection points of the keys 6, 7) by the primary winding 9.

The secondary winding 10 of the transformer 8 is connected to the output terminals 11, 12 for connecting the load.

As a means of short circuiting the primary winding 9 in the pauses between the generated pulses of the first and second half-periods, the elements of the bridge switch 3 are used - keys 5, 6 with two-sided conductivity.

The clock generator 13, which sets the period of the output voltage, is designed as a rectangular pulse generator with a period equal to a given period of the output voltage of the bridge inverter. The clock generator 13 has two outputs, and the output pulses at the second output are offset by half the period relative to the output pulses at the first output. The first and second outputs of the clock generator 13 are designed to control the frequency of formation of the first and second half-cycles.

The first output of the clock generator 13 is connected to the control circuits of the frequency of operation of the means 14 for forming the first half-cycle of the output voltage. The output of the generated voltage means 14 is connected to those control circuits of the bridge switch 3, which are designed to create in the primary winding 9 of the transformer 8 voltage of the first half-cycle. To the means 14 for forming the first half-cycle, the input of the means 15 for detecting and storing the average voltage value generated in the first half-period is also connected.

The second output of the clock generator 13 is connected to the frequency control circuits of the means 16 for generating the second half-cycle of the output voltage with an average voltage value equal to the stored average voltage value of the first half-cycle.

To the output of the means 15 for detecting and storing the average value of the voltage generated in the first half-cycle, and storing the stored average value of the voltage generated in the first half-cycle, the input of the means for forming the second half-period is connected 16.

The output of the generated voltage of the means for forming the second half-cycle is connected to those control circuits of the bridge switch 3, which are designed to create the voltage of the second half-period in the primary winding 9 of the transformer 8. The control input of the key 4 of the bridge switch 3 is connected directly to the output of the generated voltage of the first half-cycle of the means 14 for forming the first half-cycle. The control input of the key 6 of the bridge switch 3 through the OR gate 18 is also connected to the output of the generated voltage of the first half-cycle of the means 14 for forming the first half-cycle.

The control input of the key 7 of the bridge switch 3 is connected directly to the output of the generated voltage of the second half-cycle of the means 16 for forming the second half-cycle. The control input of the key 5 of the bridge switch 3 through the OR gate 19 is also connected to the output of the generated voltage of the second half-period of the means 16 for forming the second half-period.

The control inputs of the keys 5 and 6 for short-circuiting the primary winding 9 of the transformer 8 in the pauses between the generated pulses of the first and second half-periods are connected to the outputs of both means 14 and 16 of the formation of the first and second half-periods through a two-input logic circuit 17 - an OR-NOT circuit, and two-input logic circuits 18, 19 - OR circuits; in the closed state, the keys 5 and 6 are only with the simultaneous absence of generated pulses at the outputs of both means 14 and 16 of the formation of the first and second half-periods.

The inverter of figure 1 works as follows.

A constant voltage is supplied from the power source to the input terminals 1, 2 and is supplied to the bridge switch 3, which converts the constant voltage into alternating voltage.

With periodic switching of the keys 4, 6 and 5, 7 of the opposite shoulders of the bridge, the constant supply voltage is converted to alternating, and in this case, the first and second half-periods of the output alternating voltage are created, which enter the primary winding 9 of the transformer 8. From the secondary winding 10 of the transformer 8 connected to the output terminals 11, 12, an alternating voltage is applied to the connected load. In the pauses between the generated pulses of the first and second half-periods, the keys 5 and 6 in the adjacent shoulders of the bridge are closed. The clock generator 13 generates rectangular pulses to control the period of the generated voltage; rectangular pulses with a given period are taken from the first and second outputs, and the output pulses of the second output are offset by half the period relative to the output pulses at the first output.

The first output of the clock generator 13 is used in the formation of the first half-cycle, and the second output in the formation of the second half-cycle.

Each formation of the first half-cycle begins with the arrival of a pulse from the first output of the clock generator 13 to the voltage generating means 14 of the first half-cycle. The generated voltage from the output of the voltage generation means 14 of the first half-cycle is supplied to the control input of the key 4 of the bridge switch 3, as well as through the logic element OR 18 to the control input of the key 6 of the bridge switch 3, the keys 4 and 6 of the bridge are closed simultaneously, and the first half-periods of the output alternating voltage enter the primary winding 9 of the transformer 8.

When the desired predetermined voltage of the first half-cycle is reached, the formation of the first half-cycle is completed. At the same time, the keys 4, 6 of the bridge switch 3 open. Then, the inputs of the logical elements OR 18 and 19 from the output of the logical element OR-NOT 17 receive a signal that closes the keys 5 and 6, and they remain closed for the whole time, until there are no generated pulses at the outputs of the means 14, 16 of the formation of the first and second half-periods. The tool 15, which stores the average value of the voltage generated in the first half-cycle, stores the stored average value of the voltage until the completion of the formation of the second half-cycle, after which it is automatically set to the initial state of readiness for the next storage. Each formation of the second half-cycle begins with the arrival of a pulse from the second output of the clock generator 13 to the input of the voltage generating means 16 of the second half-cycle. The generated voltage from the output of the means for generating voltage of the second half-cycle is supplied to the bridge switch 3, the keys 5 and 7 of the bridge are closed at the same time, and the second half-periods of the output alternating voltage are supplied to the primary winding 9 of the transformer 8. When the average voltage value of the second half-cycle with the stored voltage is equal the first half-cycle means 16 completes the formation of the second half-cycle. At the same time, the keys 5, 7 of the bridge switch 3 open.

After that, in the same way as after the first half-cycle, the keys 5 and 6 are closed, and remain in a closed state for the entire time until there are no generated pulses at the outputs of the means 14, 16 for forming the first and second half-periods.

Various well-known solutions can be used to protect against pass-through currents through bridge keys, for example, with the generation of pulses by a clock generator not of a meander pattern, but with pauses between each half-cycle, or with the use of delay and protection means built into the bridge switch module.

Further, the processes of voltage formation of the first and second half-periods are periodically repeated similarly to the above.

After the measurements and calculations are completed, the circuits are set to the initial state of readiness for the next measurements and calculations by known means, for example, built-in means of automatic reset to the initial state.

The proposed solution with separate formation of stresses in the first and second half-periods solves various problems of generating the required stresses in such a way that the output voltage for the period is within the specified tolerances. For each pair of pulses in one period, the parameters of the first pulse correspond to a set value at which the required value of the output voltage for the first and second half-periods is provided with an acceptable error, within the required tolerances. And at the same time, one-sided saturation is prevented.

Depending on the specific applications, the formation of the first half-cycle can be carried out according to different laws, for example, with the required effective or average voltage value, or according to other laws, but when the second half-cycle is formed, the average voltage values of the first and second half-periods are always equal at the output, which prevents one-sided saturation.

The separate key of the winding short circuit in pauses is excluded, which simplifies the solution of problems of protection against through currents.

At the same time, the inverter can be powered from sources with different nominal voltages, for example, 24 V, or 36 V, or 48 V. For this, it is enough to switch the primary windings. Unification expands the functional capabilities of the operational power supply of different consumers; smaller reserves are required for backup, repair and new consumers.

The proposed solution allows to simplify the use of the inverter. Thanks to the proposed solution, the inverter's consumer performance improves, the level of unification increases.

Information sources.

1. US patent No. 6617839, Method for detecting current transformer saturation.

2. US Patent No. 4017786, Transformer saturation control circuit for a high frequency switching power supply.

3. US Patent No. 5317497, Internally excited, controlled transformer saturation, inverter circuitry.

4. RF patent No. 2027297, IPC Н02М 7/539, DC / AC converter of a given shape.

5. RF patent No. 2035833, IPC Н02М 7/538, Method for limiting one-sided saturation of a transformer of a pulse voltage converter.

6. RF patent №2282934, IPC Н02М 7/42, Voltage inverter with transformer protection from one-sided saturation.

Claims (1)

A bridge inverter is a DC-to-AC converter preventing one-sided saturation of the output transformer, comprising a bridge switch for converting the DC voltage of the power source to AC, made in the form of a four-arm bridge with controlled keys in the shoulders, in which the vertices of the first diagonal are connected to the terminals for the power source, and the primary winding of the output transformer is connected to the vertices of the second diagonal of the bridge; means for generating the first half-cycle of the output voltage with the specified parameters, the output of which is connected to the key switching control circuits of the first pair of opposite shoulders of the bridge; means for detecting and storing the average voltage value generated in the first half-cycle, and storing the stored voltage until completion of the formation of the second half-period; means for generating a second half-cycle of the output voltage with an average voltage value equal to the stored average voltage value generated in the first half-cycle, the input of which is connected to the output of the means for detecting and storing the average voltage value generated in the first half-cycle, and the output is connected to the key switching circuits of the second pair opposite shoulders of the bridge; a clock of rectangular pulses with a period equal to the period of the output voltage of the bridge inverter, connected by the outputs to the control circuits of the frequency of operation of the means of forming the first and second half-periods; means for short-circuiting the primary winding of the transformer in pauses between the generated pulses of the first and second half-periods, characterized in that the means for short-circuiting the primary winding of the transformer in the pauses between the generated pulses of the first and second half-periods are formed by controlled keys of those two adjacent shoulders of the four-armed bridge, the ends of which are vertices the second diagonal of this bridge with the connected primary winding of the output transformer, and the keys of these adjacent shoulders have two-sided conductivity, the input circuits of each of these keys are made in the form of a two-input OR circuit, and the first inputs of these OR circuits are connected to the inputs of the keys of the opposite shoulders of the bridge, and connected to the outputs of the corresponding formers of half-periods, and the second inputs of these OR circuits are connected to each other and to the output an additional two-input OR-NOT circuit connected by inputs to the outputs of the half-period former; moreover, the primary winding of the output transformer is made of several switched windings with the possibility of changing the number of turns depending on the rated constant voltage of the power source to which the bridge inverter is connected.