RU2280313C1 - Method for protecting voltage-inverter transformer from single-ended saturation - Google Patents

Abstract

FIELD: dc-to-ac voltage converters.

SUBSTANCE: novelty is that center-tapped primary power winding leads are alternately connected to power supply. First half-cycle is formed when first winding carries current while second winding is used for measuring current value of voltage. Second half-cycle is formed when second winding carries current and first winding is used as metering one. RMS value of this voltage is calculated during formation of first half-cycle, compared with desired reference value, and formation of first half-cycle is completed as soon as these values are equalized. In addition, mean value of voltage generated during first half-cycle is measured and stored in memory. Formation of second half-cycle involves only calculation of mean voltage which is compared with that stored during first half-cycle. Formation of second half-cycle is completed as soon as these voltages are equalized.

EFFECT: simplified design, ability of preventing single-ended saturation of inverter power transformer.

1 cl, 1 dwg

Description

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

Known devices for converting direct voltage to alternating by periodically switching the polarity of the voltage supplied to the primary windings of the power transformer, the output of which remove the alternating voltage to connect the load. They have a drawback - the occurrence of one-sided saturation of the magnetic core of a power transformer with changes in input voltage, load asymmetry, or circuit elements.

Known methods and devices for eliminating this drawback with the detection of magnetic saturation of the magnetic core of a power transformer by monitoring the output voltage of an additional current transformer introduced into the circuit. In particular, the control of the beginning of saturation 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 current in the power transformer [1]. However, in a DC / AC converter, such a solution requires a separate transformer current sensor and sophisticated high-speed means of monitoring the second derivative.

Known schemes to prevent asymmetric saturation of the magnetic core of a power transformer by compensating for the saturation current 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.

There is a method of preventing saturation of a transformer, implemented in an inverter for operation with a capacitive load - a fluorescent lamp [3]. The inverter contains control circuits for the constant and variable components when controlling transistor switches and means to prevent saturation of the transformer. 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].

The closest known analogue is a patent of the Russian Federation [5]. This known method of limiting the one-way saturation of a transformer of a pulse voltage converter consists in detecting a signal proportional to the magnetizing current of the transformer, comparing it with a predetermined reference signal proportional to the maximum permissible magnetizing current, and generating a control signal correcting the magnetization reversal mode of the transformer.

The disadvantage of this method is the complexity of the practical implementation of this method in the design, since this requires the detection of a signal proportional to the magnetization current of the transformer. In this case, it is necessary to measure the current in a short-circuited coil, covering part of the transformer magnetic circuit, which complicates the design of both the magnetic circuit itself and the converter as a whole, requiring an additional current transformer.

The problem to which the claimed invention is directed is to prevent one-sided saturation of the power transformer of the inverter-voltage converter when operating conditions arise that lead to asymmetries of current and voltage, as well as simplifying designs by eliminating functional units that use either Rogowski belt or modeling current transformer, or other structurally complex solutions.

For this, a solution was used in which the output of the converter was stabilized with the effective voltage value with predetermined limit values. In this case, one-sided saturation is prevented by ensuring the equality of volt-second areas in the positive and negative half-cycles and magnetic fluxes in the magnetic circuit of the inverter power transformer, made with two identical primary connected power windings in series.

The method of protection against one-sided saturation of the transformer in the inverter-converter of DC to AC with stabilization of the current value of the output voltage is as follows.

The power transformer of the inverter is performed with two identical in series connected primary power windings. A tap from the connection point of these windings is connected to one of the poles of the power source. And for the formation of alternating current, the conclusions from the ends of the first and second windings are alternately connected to the other pole of the power source.

When current flows from the power source through the first winding in the inverter, the first half-cycle of the alternating voltage is formed.

When current flows through the second winding in the inverter, a second alternating voltage half-cycle is formed.

This solution has the following set of features that distinguish the proposed method from the known.

The effective value of the voltage generated in the first half-cycle is made equal to a given reference value as follows.

The first winding of the power transformer is connected to the power source during the formation of the first half-cycle. The current voltage is proportional to the EMF of the magnetization of the transformer core, which is removed from the second winding of the power transformer disconnected from the power source at this time. During this measurement, the second winding of the power transformer is loaded on the active resistance and used as a measuring winding. The effective value of the current voltage is calculated, which is removed from the second winding of the power transformer. Compare the current value of the current voltage with a given reference value.

Upon reaching the equality of the calculated effective value of the current voltage with a given reference value, the formation of the first half-cycle is completed and the first winding of the power transformer is disconnected from the power source. In addition, they also measure the average value of the voltage generated in the first half-cycle, and remember it for the time required for the formation of the second half-cycle.

To form a second half-cycle, a second winding of the power transformer is connected to the power source. The current voltage is proportional to the EMF of the magnetization of the transformer core, which is removed from the first winding of the power transformer disconnected from the power source at that time.

During this measurement, the first winding of the power transformer is loaded on the active resistance and used as a measuring winding.

The average voltage value of the second half-cycle is made equal to the average value of the voltage generated in the first half-cycle.

To do this, measure the current voltage proportional to the EMF of the magnetization of the transformer core, which is removed from the first winding of the power transformer disconnected from the power source at that time.

The average value of the current voltage is calculated, compared with the stored value of the average value of the voltage generated in the first half-cycle.

Upon reaching the equality of the calculated average value of the current voltage with the stored value of the average voltage value of the first half-cycle, the formation of the second half-cycle is completed and the second winding of the power transformer is disconnected from the power source.

Further, these cycles of the formation of the first and second half-cycles are repeated.

This prevents one-sided saturation of the transformer due to the equality of the volt-second areas of the first and second half-cycles and, accordingly, the magnetic fluxes in the magnetic circuit of the transformer.

An output voltage is formed with the required effective value, the value of which is within the specified tolerances.

For this, according to the invention, a reference signal is created proportional to the value of the effective voltage value, which is required to be provided at the inverter output during the first half-cycle.

The first winding of the power transformer is connected to the power source.

The current voltage is proportional to the EMF of the magnetization of the transformer core, which is removed from the second winding of the power transformer disconnected from the power source at this time. During this measurement, the second winding of the power transformer is loaded on the active resistance and used as a measuring winding. On the resistance connected to the second winding of the power transformer of the inverter, performing the functions of the measuring winding during this half-cycle, measure the current voltage proportional to the magnetizing EMF of the transformer core, and form a voltage pulse of the first half-cycle with the first polarity.

In the process of generating the voltage of the first half-cycle, the current voltage proportional to the EMF of the magnetization of the transformer core is measured, its effective value is calculated, the result is compared with the aforementioned set value of the reference signal, and when the current value is equal to the reference, the voltage generation of the first half-cycle with the first polarity is completed.

In addition, the average voltage value for the first half-cycle is calculated and the result is stored for use in the process of generating a voltage pulse of the second half-cycle with a different, opposite polarity.

In the second half-cycle, a second voltage pulse is formed having a different, opposite polarity. When forming the voltage of the second half-cycle, the current voltage proportional to the EMF of the magnetization of the transformer core is measured, its average value is calculated, the result is compared with the stored value of the calculated average voltage value generated for the previous first half-cycle, and upon reaching the equality, the second pulse is completed.

In the formation of pulses of subsequent periods, all operations are repeated.

As a result of this, the average values of the voltages and volt-second areas of the generated pulses of the first and second polarity are equal during the first and second half-periods, and therefore the magnetic fluxes in the magnetic circuit, which eliminates the danger of one-sided saturation of the transformer magnetic circuit.

In this case, the value determined in accordance with the well-known formula is taken as the effective voltage value E _dT1 for the first half-period T1

where e ₁ is the current voltage of the first half-cycle,

and the average voltage value E _s1 of the first half-period T1 is expressed by the formula

For measurements over the second half-cycle, instead of T1 and e ₁ , T2 and e ₂ are used in the formulas.

To calculate these values, both known analog and known digital means can be used.

In the first half-cycle, a voltage is formed that satisfies the condition for the effective voltage value E _dT1 for the first half-period T1, in accordance with formula (1), and in addition, the average voltage value E _s1 of the first half-period T1 is calculated in accordance with formula (2) and the result is stored .

And in the second half-cycle they form a voltage

satisfying the condition for the average value, so that it is equal to the previously stored value E _{s1 of the} average voltage value of the first half-cycle, i.e.,

In subsequent periods, the operation is repeated.

The circuit of the inverter-Converter DC to AC according to this method is presented in figure 1, where the following notation.

1, 2 - input pins;

3, 4 - output conclusions;

5 - power transformer;

6 - the first winding;

7 - second winding;

8 - output winding;

9, 10 - power circuit and measurement switches;

11 - shaper;

12 - generator;

13 - channel for measuring and controlling the voltage of the first half-cycle;

14 - channel for measuring and controlling the voltage of the second half-cycle;

15 is a reference voltage source proportional to the required effective voltage value of the first half-cycle;

16 - calculator of the effective value of the current voltage of the first half-cycle;

17 - comparator comparing the current value of the current voltage of the first half-cycle with the reference;

18 - calculator of the average voltage value of the first half-cycle;

19 - calculator of the average value of the current voltage of the second half-cycle;

20 - storage device;

21 is a comparator comparing the average current voltage of the second half-cycle with the stored average voltage value of the first half-cycle.

In the inverter circuit according to the method, the input terminals 1, 2 are designed to supply a constant voltage to the inverter from a power source.

The output terminals 3, 4 of the inverter are designed to supply an external load with an alternating voltage stabilized by the value of the effective value with a given error and lying in the range from minimum to maximum value.

The power transformer 5 includes a series-connected first winding 6 and a second winding 7; a tap from their connection point is connected to pin 1.

The output winding 8 is connected to the output terminals 3, 4. The outputs of the ends of the windings 6 and 7 are connected to the managed switches 9 and 10, which are connected to the input terminal 2. The input control circuits of the switches 9 and 10 are connected to the outputs of the shaper 11, which serves to control the beginning and the end of the formation of stresses of the first and second half-periods.

The generator 12 sets the frequency of the generated alternating voltage; the output of this generator is connected to the input of the shaper 11.

The input of the channel 13 for measuring and controlling the voltage of the first half-cycle and the input of the channel 14 for measuring and controlling the voltage of the second half-cycle through the switches 9, 10 are connected to the managed switches 9 and 10 with the possibility of alternately connecting the channel 13 or 14 to the corresponding windings 6 or 7 of the transformer 5. The outputs of the channels 13 and 14 are connected to the inputs of the shaper 11.

The voltage measurement and control channel of the first half-cycle 13 contains the following circuits. The reference voltage source 15 is proportional to the required value of the effective voltage value of the first half-cycle.

The calculator 16 of the current value of the voltage of the first half-cycle.

Comparator 17 comparing the current effective voltage of the first half-cycle with the reference.

Calculator 18 of the average value of the generated voltage of the first half-cycle.

The inputs of the calculator of the effective value of the current voltage of the first half-cycle 16 and the average voltage calculator of the first half-cycle 18 are connected to the switch 9, and the output of the comparator 17 is connected to the input of the shaper 11.

The voltage measurement and control channel of the second half-cycle 13 contains the following circuits. The calculator of the average voltage value of the second half-cycle 19.

Storage device 20.

The comparator 21 compares the current average voltage of the second half-cycle with the stored average voltage value of the first half-cycle.

The input of the circuit of the average voltage calculator of the second half-cycle 19 is connected to the switch 10, and the output of the comparator 21 is connected to the input of the former 11. The input of the storage device 20 is connected to the output of the average voltage calculator 18 formed in the first half-period.

The inverter operates as follows.

A constant voltage is supplied from the power source to the input terminals 1, 2 and is supplied to the connection point of the windings 6, 7 of the transformer 5 and to the power inputs of the switches 9 and 10. The switches 9 and 10, controlled by the former 11, alternately connect the outputs of the windings 6 to terminal 2 7, converting a constant voltage into an alternating voltage, the frequency of which is set by the generator 12.

The output alternating voltage stabilized by the value of the effective value with a given error, i.e. lying in the range from minimum to maximum values, is removed from the output winding 8 of the transformer 5 connected to the output terminals 3, 4.

The first half-cycle of the output voltage is formed on the winding 7. The formation of the first half-cycle begins with a signal from the output of the generator 12 to the input of the shaper 11, then from the output of the shaper 11 to the input of the switch 10; current begins to flow through the winding 7, connected through the switch 10 to terminal 2. The winding 7 during the first half-cycle serves as the input power winding of the transformer 5 of the inverter.

The winding 6 during the first half-cycle is loaded with active resistance and performs the functions of a measuring winding, from which the current voltage is proportional to the EMF of the magnetization of the transformer core. The winding 6 of the switch 9 is connected to the input of the calculator 16 of the current value of the current voltage of the first half-cycle and to the input of the calculator of the average voltage value of the first half-cycle 18.

The calculator 16 performs the calculation of the effective value of the current voltage of the first half-cycle, which is removed from the winding 6 of the power transformer. From the output of the calculator 16 of the effective voltage value, the current measurement results are supplied to the first input of the comparator comparator circuit 17, and a voltage proportional to the required value of the effective voltage value of the first half-cycle is supplied to the second input of the comparator 17 from the reference voltage source 15. The comparator 17 compares the effective value of the current voltage with a given reference value.

Upon reaching the equality of the calculated effective value of the current voltage with a given reference value from the output of the comparator 17, a signal is sent to the input of the shaper 11 to complete the formation of the first half-cycle, after which a signal is received from the output of the shaper 11 to the input of the switch 10, by which the winding 7 of the power transformer 5 is disconnected from the source power output 2.

In addition, the calculator 18 calculates the average value of the voltage generated in the first half-cycle. From the output of the calculator 18, the result of calculating the average value of the voltage generated in the first half-cycle is fed to the input of the storage device 20 of the channel 14 for measuring and controlling the voltage of the second half-cycle, where this result is stored for the time required to form the second half-cycle.

The second half-cycle of the output voltage is formed on the winding 6. The formation of the second half-cycle begins with a signal from the output of the generator 12 to the input of the shaper 11, then from the output of the shaper 11 to the input of the switch 9; current begins to flow through the winding 6, connected through the switch 9 to terminal 2. The winding 6 during the second half-cycle serves as the input power winding of the transformer 5 of the inverter.

And the winding 7 during the second half-cycle is loaded with active resistance and performs the functions of a measuring winding, from which the current voltage is proportional to the EMF of the magnetization of the transformer core. The winding 7 of the switch 10 is connected to the input of the calculator 19 of the average value of the current voltage of the second half-cycle.

The calculator 19 performs the calculation of the average value of the current voltage of the second half-cycle, which is removed from the winding 7 of the power transformer. From the output of the calculator 16 of the average voltage value, the current measurement results are fed to the first input of the comparator comparator circuit 21, and a voltage proportional to the average voltage value of the first half-cycle is supplied to the second input of the comparator 21 from the storage device 20. The comparator 21 compares the average value of the current voltage with a stored value. When the calculated average value of the current voltage is reached with the stored value from the output of the comparator 21, a signal is issued to the input of the shaper 11 to complete the formation of the second half-cycle, after which a signal is received from the output of the shaper 11 to the input of the switch 9, by which the winding 6 of the power transformer 5 is disconnected from the power source Conclusion 2.

The frequency of the output voltage of the inverter is set by the generator of periodic pulses 12, the output of which controls the shaper 11. The formation of voltages of the first and second half-cycles begins when the pulses 11 receive pulses from the output of the generator 12, and ends with control signals from the outputs of channels 13 and 14.

With the beginning of the formation of the voltage of the first half-cycle, the current from the power source begins to flow through the winding 7 of the transformer 5, and the winding 6 becomes measuring.

With the beginning of the formation of the voltage of the second half-cycle, the current from the power source begins to flow through the winding 6 of the transformer 5, and the winding 7 becomes measuring.

The measuring signals of the first half-cycle from the measuring output of the switch 9 are fed to the input of the channel 13 for measuring and controlling the voltage of the first half-period, containing two means of measuring the current voltage generated in the first half-period:

- at the input of the meter of the actual voltage value 16,

- at the input of the meter average voltage 18.

The measuring signals of the second half-cycle from the measuring output of the switch 10 are fed to the input of the channel 14 for measuring and controlling the voltage of the second half-cycle, containing only one means of measuring the current voltage generated in the second half-period - to the input of the average voltage meter 19.

The meters 16, 18, 19 begin to measure almost from the moment the signal starts at the output of the driver 11.

The inverter contains a reference voltage source 15, which sets the value of the effective voltage value generated in the first half-cycle; its output is connected to the first input of the comparator 17, and the second input of the comparator 17 receives a signal from the meter of the actual value 16, and the measured effective value of the voltage at the output of the meter 16 is compared with the reference. When the equality of the effective voltage value with the reference voltage from the output of the comparator 17 to the first control input of the shaper 11, a signal is received to stop the formation of voltage; measurements are completed and reset.

The processes of voltage measurements by the meter 18 of the average voltage value and the meter 16 of the effective voltage value begin and end at the same time.

The measured average voltage value from the output of the meter 16 is fed to channel 14 — to the signal input of the means for storing the average voltage value — memory 20, where this value is stored until the completion of the voltage generation process of the second half-cycle.

When the measuring signals of the second half-cycle from the measuring output of the switch 10 are fed to the input of the average voltage meter 19, the latter starts to measure from the moment the signal starts. From the output of the meter 19, a voltage proportional to the average voltage value is supplied to the first input of the comparator 21, and a voltage proportional to the average voltage value generated in the first half-cycle is supplied to its second input of the output of the storage device 20. If these voltages are equal, an impulse is formed at the output of the comparator 19, which is supplied to the second input of the former 11, and the voltage generation of the second half-cycle is completed.

Simultaneously with the output of the comparator 19, the signal is also supplied to the second input of the storage device, setting it in the initial state of readiness for the next storage.

Measuring devices 14, 15, 16 after each completion of measurements for the corresponding half-cycle are automatically set to the initial state of readiness for the next measurements.

The average values of stresses generated in the first and second half-periods are equal.

The described measurements and operations can be performed by means of analog or digital technology.

Possible options for resetting and initializing the measuring devices 16-20 either by internal or external means, for example, by signals of circuits 12, 11, etc .; it does not matter.

The proposed method of alternately using the same transformer windings as power and measuring windings makes it possible to simplify designs using this method, to optimize the size, weight of transformer magnetic cores.

Known methods usually solve the problem of stabilizing the voltage so that the output voltage is equal to a certain predetermined value with some tolerances, usually symmetrical with respect to the required rating.

The proposed solution with separate formation of voltages in the first and second half-periods solves the stabilization problem so that the output voltage for the period is within the specified tolerances. In this case, the output voltage may have asymmetric tolerances with respect to the specified reference voltage, when the output transformer has an asymmetry of the voltages of the first and second half-periods, caused either by a power source and circuit elements, or by a non-linear load.

According to this method of switching the voltage of the power source, the magnitude of the effective voltage value of the second half-cycle in the general case is not equal to the required specified reference value of the effective voltage of the first half-cycle at the inverter output due to the inequality of mathematical functions describing the processes of formation of voltages of the first and second half-periods.

However, for most practical applications, the values of the effective voltage at the inverter output by the proposed method are within acceptable limits. For each pair of pulses in one period, the parameters of the first pulse correspond to a given value at which the effective value required by the tolerances is provided. The output voltage is within acceptable limits for practice.

For example, if the average value of the input voltage deviates by 20 percent during the formation of the second pulse, relative to the average value of the input voltage during the formation of the first pulse, the effective value of the output voltage differs from the set value by no more than 5 percent.

Thus, the proposed method eliminates the bulky and complex means of control and management used in known inverter circuits in order to prevent one-sided saturation of the transformer.

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 N 02 M 7/539, DC / AC Converter of a given shape.

5. RF patent No. 2035833, IPC N 02 M 7/538, Method for limiting one-sided saturation of a transformer for a pulse voltage converter.

Claims (1)

A method of protection against one-sided saturation of a transformer in an inverter-converter of direct voltage to alternating current with the stabilization of the effective value of the output voltage, in which the transformer is made with two identical primary power windings connected in series, the tap from their connection point is connected to one pole of the power source, and the conclusions from the ends the first and second windings are alternately connected to the other pole of the power source and when current flows through the first winding in the inverter, t is the first half-period of the alternating voltage, and when current flows through the second winding at the inverter output, a second alternating voltage half-cycle is formed, characterized in that the effective value of the generated voltage of the first half-period is made equal to a given reference value, for which the current voltage is proportional to the magnetization EMF of the transformer core, which is removed from the second winding of the power transformer disconnected from the power source at this time, which is loaded on a during this measurement tive resistance and is used as the measuring coil is calculated rms value of the current tension is compared with a predetermined reference value and on reaching equality computed rms current voltage with a predetermined reference value complete formation of the first half-period and off a first winding of the power transformer from the power source; in addition, the average value of the voltage generated in the first half-cycle is also measured and stored for the time necessary for the formation of the second half-period, and when the second half-period is formed, the average voltage of the second half-period is made equal to the average value of the voltage generated in the first half-period, for which current voltage proportional to the EMF of the magnetization of the core of the transformer, which is removed from the first winding of the power transformer disconnected from the power source at that time the atom, which is loaded on the active resistance during this measurement and used as a measuring winding, the average value of the current voltage is calculated, compared with the stored value of the average value of the voltage generated in the first half-cycle, and when the calculated average value of the current voltage is equal to the stored value of the average voltage values of the first half-cycle complete the formation of the second half-cycle; then these cycles are repeated; this prevents the one-sided saturation of the transformer due to the equality of the volt-second areas of the first and second half-cycles and magnetic fluxes in the magnetic circuit and generates an output voltage with the required effective value, the value of which is within the specified tolerances.